METROLOGY SYSTEM AND COHERENCE ADJUSTERS

A metrology system (400) includes a multi-source radiation system. The multi-source radiation system includes a waveguide device (502) and the multi-source radiation system is configured to generate one or more beams of radiation. The metrology system (400) further includes a coherence adjuster (500) including a multimode waveguide device (504). The multimode waveguide device (504) includes an input configured to receive the one or more beams of radiation from the multi-source radiation system (514) and an output (518) configured to output a coherence adjusted beam of radiation for irradiating a target (418). The metrology system (400) further includes an actuator (506) coupled to the waveguide device (502) and configured to actuate the waveguide device (502) so as to change an impingement characteristic of the one or more beams of radiation at the input of the multimode waveguide device (504).

FIELD

The present disclosure relates to illumination systems, for example, a coherence adjuster for metrology systems used in conjunction with lithographic processes.

BACKGROUND

During lithographic operation, different processing steps may require different layers to be sequentially formed on the substrate. Accordingly, it can be necessary to position the substrate relative to prior patterns formed thereon with a high degree of accuracy. Generally, alignment marks are placed on the substrate to be aligned and are located with reference to a second object. A lithographic apparatus may use an alignment apparatus for detecting positions of the alignment marks and for aligning the substrate using the alignment marks to ensure accurate exposure from a mask. Misalignment between the alignment marks at two different layers is measured as overlay error.

In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters may include, for example, the overlay error between successive layers formed in or on the patterned substrate and critical linewidth of developed photosensitive resist. This measurement can be performed on a product substrate and/or on a dedicated metrology target. There are various techniques for making measurements of the microscopic structures formed in lithographic processes, including the use of scanning electron microscopes and various specialized tools. A fast and non-invasive form of a specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Spectroscopic scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a function of wavelength) of the radiation scattered into a particular narrow angular range. By contrast, angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

Such optical scatterometers can be used to measure parameters, such as critical dimensions of developed photosensitive resist or overlay error (OV) between two layers formed in or on the patterned substrate. Properties of the substrate can be determined by comparing the properties of an illumination beam before and after the beam has been reflected or scattered by the substrate.

Production speed and throughput is of great importance in lithographic fabrication of ICs and electronic devices. It is desirable for metrology systems used in fabrication to acquire measurements quickly for increasing wafer throughput. To increase measurement speed, the amount of radiation detected by the metrology system can be increased (e.g., use a brighter source) to shorten measurement time intervals while maintaining high accuracy.

SUMMARY

Accordingly, it is desirable to improve illumination systems of metrology apparatuses for improving accuracy in measurements performed in conjunction with lithographic processes.

In some embodiments, a metrology system comprises a radiation source, a coherence adjuster, a detector, and a processor. The coherence adjuster comprises a waveguide device having an input and an output, a multimode waveguide device having an input and an output, and an actuator. The radiation source is configured to generate spatially coherent radiation. The input of the waveguide device is configured to receive the coherent radiation. The input of the multimode waveguide device is configured to receive radiation from the waveguide device. The output of the multimode waveguide device is configured to output a coherence adjusted beam of radiation for irradiating a target. The actuator is coupled to the waveguide device and is configured to actuate the waveguide device so as to change an impingement characteristic of the received radiation at the input of the multimode waveguide device. An interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic. The detector is configured to receive radiation scattered by the target based on the irradiating and to generate a measurement signal based on the received radiation at the detector. The processor is configured to analyze the measurement signal to determine a characteristic of the target.

In some embodiments, a coherence adjuster comprises a waveguide device having an input and an output, a multimode waveguide device having an input and an output, and an actuator. The input of the waveguide device is configured to receive coherent radiation. The input of the multimode waveguide device is configured to receive radiation from the waveguide device. The output of the multimode waveguide device is configured to output a coherence adjusted beam of radiation for irradiating a target. The actuator is coupled to the waveguide device and is configured to actuate the waveguide device so as to change an impingement characteristic of the received radiation at the input of the multimode waveguide device. An interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic.

In some embodiments, a coherence adjuster comprises a multimode waveguide device having an input and an output, and an adjusting device. The input of the multimode waveguide device is configured to receive spatially coherent radiation. The output of the multimode waveguide device is configured to output a coherence adjusted beam of radiation for irradiating a target. The adjusting device is coupled to a portion of the coherence adjuster and is configured to adjust the portion so as to change an impingement characteristic of the received radiation at the input of the multimode waveguide device. An interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic. The impingement characteristic comprises a distribution of incidence angles. The coherence adjuster is configured to adjust a beam diameter of the coherence adjusted beam based on a change of the distribution of incidence angles.

In some embodiments, a coherence adjuster comprises a multimode waveguide device having an input and an output, and a diffuser device. The input of the multimode waveguide device is configured to receive spatially coherent radiation. The output of the multimode waveguide device is configured to output a coherence adjusted beam of radiation for irradiating a target. The diffuser device is disposed upstream of the multimode waveguide device. The diffuser device is configured to change an impingement characteristic of the received radiation at the input of the multimode waveguide device. An interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic. The impingement characteristic comprises a distribution of angles of incidence. The diffuser device is further configured to adjust a beam diameter of the coherence adjusted beam based on a change of the distribution of incidence angles.

In some embodiments, a coherence adjuster comprises a multimode waveguide device having an input and an output, an adjusting device, and an adjustable beam expander. The input of the multimode waveguide device is configured to receive spatially coherent radiation. The output of the multimode waveguide device is configured to output a coherence adjusted beam of radiation for irradiating a target. The adjusting device is coupled to a portion of the coherence adjuster and is configured to adjust the portion so as to change an impingement characteristic of the received radiation at the input of the multimode waveguide device. An interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic. The impingement characteristic comprises a distribution of incidence angles. The adjustable beam expander is configured to adjust a beam diameter of the coherence adjusted beam.

In some embodiments, a metrology system includes a radiation source configured to generate spatially coherent radiation and a coherence adjuster. The coherence adjuster includes a multimode waveguide device including an input configured to receive the spatially coherent radiation and an output configured to output a coherence adjusted beam of radiation. The metrology system further includes a detector configured to measure a distribution of the coherence adjusted beam of radiation. The metrology system further includes a processor configured to compare the measured distribution with a desired distribution and determine a value of a parameter associated with the coherence adjuster based on the comparison. The processor is further configured to communicate the determined value of the parameter associated with the coherence adjuster to the coherence adjuster. The coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.

In some embodiments, a metrology system includes a radiation source configured to generate spatially coherent radiation and a coherence adjuster. The coherence adjuster includes a multimode waveguide device including an input configured to receive the spatially coherent radiation and an output configured to output a coherence adjusted beam of radiation for irradiating a target. The metrology system further includes a detector configured to receive radiation scattered by the target based on the irradiation and to generate a measurement signal based on the received radiation. The metrology system further includes a processor configured to determine a parameter associated with the target based on the measurement signal and compare the determined parameter with a desired parameter associated with the target. The processor is further configured to determine a value of a parameter associated with the coherence adjuster based on the comparison. The processor is further configured to communicate the determined value of the parameter associated with the coherence adjuster to the coherence adjuster. The coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.

In some embodiments, a method includes receiving a measurement signal, where the measurement signal is generated based on a measured distribution of a coherence adjusted beam of radiation output from a coherence adjuster. The method further includes comparing the measured distribution with a desired distribution and determining a value of a parameter associated with the coherence adjuster based on the comparison. The method also includes communicating the determined value of the parameter associated with the coherence adjuster to the coherence adjuster. The coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.

In some embodiments, a method includes receiving a measurement signal, where the measurement signal is generated based on radiation scattered by a target irradiated by a coherence adjusted beam of radiation from a coherence adjuster. The method further includes determining a parameter associated with the target based on the measurement signal and comparing the determined parameter with a desired parameter associated with the target. The method also includes determining a value of a parameter associated with the coherence adjuster based on the comparison. The method further includes communicating the determined value of the parameter associated with the coherence adjuster to the coherence adjuster. The coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.

In some embodiments, a non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform operations. The operations include receiving a measurement signal, where the measurement signal is generated based on a measured distribution of a coherence adjusted beam of radiation output from a coherence adjuster. The operations further include comparing the measured distribution with a desired distribution and determining a value of a parameter associated with the coherence adjuster based on the comparison. The operations also include communicating the determined value of the parameter associated with the coherence adjuster to the coherence adjuster. The coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.

In some embodiments, a non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform operations. The operations include receiving a measurement signal, where the measurement signal is generated based on radiation scattered by a target irradiated by a coherence adjusted beam of radiation from a coherence adjuster. The operations further include determining a parameter associated with the target based on the measurement signal and comparing the determined parameter with a desired parameter associated with the target. The operations also include determining a value of a parameter associated with the coherence adjuster. The operations further include communicating the determined value of the parameter associated with the coherence adjuster to the coherence adjuster. The coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.

In some embodiments, a metrology system includes a multi-source radiation system. The multi-source radiation system includes a combined waveguide device and the multi-source radiation system is configured to generate one or more beams of radiation. The metrology system further includes a coherence adjuster including a multimode waveguide device. The multimode waveguide device includes an input configured to receive the one or more beams of radiation from the multi-source radiation system and an output configured to output a coherence adjusted beam of radiation for irradiating a target. The metrology system further includes an actuator coupled to the combined waveguide device and configured to actuate the combined waveguide device so as to change an impingement characteristic of the one or more beams of radiation at the input of the multimode waveguide device.

In some embodiments, a metrology system includes a multi-source radiation system. The multi-source radiation system includes a combined waveguide device and the multi-source radiation system is configured to generate one or more beams of radiation. The metrology system further includes a coherence adjuster including a multimode waveguide device. The multimode waveguide device includes an input configured to receive the one or more beams of radiation and an output configured to output a coherence adjusted beam of radiation. The metrology system further includes an adjusting device coupled to a portion of the coherence adjuster and configured to adjust the portion so as to change an impingement characteristic of the one or more beams of radiation at the input of the multimode waveguide device.

In some embodiments, a metrology system includes a multi-source radiation system. The multi-source radiation system includes a first radiation source configured to generate a first radiation with a first polarization state, a second radiations source configured to generate a second radiation with a second polarization state orthogonal to the first polarization state, and combining element configured to generate the spatially coherent radiation by combining the first radiation and the second radiation. The metrology system further includes a coherence adjuster including a multimode waveguide device. The multimode waveguide device includes an input configured to receive the spatially coherent radiation from the multi-source radiation system and an output configured to output a coherence adjusted beam of radiation for irradiating a target.

Further features of the present disclosure, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.

The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.

DETAILED DESCRIPTION

This specification discloses one or more embodiments that incorporate the features of the present disclosure. The disclosed embodiment(s) are provided as examples. The scope of the present disclosure is not limited to the disclosed embodiment(s). Claimed features are defined by the claims appended hereto.

The term “about” as used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the term “about” can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present disclosure can be implemented.

Example Lithographic Systems

FIGS.1A and1Bshow schematic illustrations of a lithographic apparatus100and lithographic apparatus100′, respectively, in which embodiments of the present disclosure can be implemented. Lithographic apparatus100and lithographic apparatus100′ each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus100and100′ also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus100′, the patterning device MA and the projection system PS are transmissive.

The illumination system IL can include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatus100and100′, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable, as required. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

The terms “inspection apparatus,” “metrology apparatus,” or the like can be used herein to refer to, e.g., a device or system used for measuring a property of a structure (e.g., overlay error, critical dimension parameters) or used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment apparatus).

The term “projection system” PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

Lithographic apparatus100and/or lithographic apparatus100′ can be of a type having two (dual stage) or more substrate tables WT (and/or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT.

Referring toFIGS.1A and1B, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus100,100′ can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus100or100′, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (inFIG.1B) including, for example, suitable directing mirrors and/or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus100,100′, for example, when the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, can be referred to as a radiation system.

The illuminator IL can include an adjuster AD (inFIG.1B) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as “σ-outer” and “σ-inner,” respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can comprise various other components (inFIG.1B), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

Referring toFIG.1A, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2(for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W can be aligned using mask alignment marks M1, M2and substrate alignment marks P1, P2.

Referring toFIG.1B, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

The projection system PS projects an image of the mask pattern MP, where the image is formed by diffracted beams produced from the mark pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W. For example, the mask pattern MP can include an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction generates diverted diffracted beams with a change of direction in a direction perpendicular to the lines. Undiffracted beams (i.e., so-called zeroth order diffracted beams) traverse the pattern without any change in propagation direction. The zeroth order diffracted beams traverse an upper lens or upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zeroth order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD, for example, is disposed at or substantially at a plane that includes the pupil conjugate PPU of the projection system PS.

The projection system PS is arranged to capture, by means of a lens or lens group L, not only the zeroth order diffracted beams, but also first-order or first- and higher-order diffracted beams (not shown). In some embodiments, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can be used to utilize the resolution enhancement effect of dipole illumination. For example, first-order diffracted beams interfere with corresponding zeroth-order diffracted beams at the level of the wafer W to create an image of the line pattern MP at highest possible resolution and process window (i.e., usable depth of focus in combination with tolerable exposure dose deviations). In some embodiments, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some embodiments, astigmatism aberration can be reduced by blocking the zeroth order beams in the pupil conjugate PPU of the projection system associated with radiation poles in opposite quadrants. This is described in more detail in U.S. Pat. No. 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

With the aid of the second positioner PW and position sensor IF (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown inFIG.1B) can be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

In general, movement of the mask table MT can be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to a short-stroke actuator only or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks M1, M2, and substrate alignment marks P1, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

Mask table MT and patterning device MA can be in a vacuum chamber V, where an in-vacuum robot IVR can be used to move patterning devices such as a mask in and out of vacuum chamber. Alternatively, when mask table MT and patterning device MA are outside of the vacuum chamber, an out-of-vacuum robot can be used for various transportation operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

The lithographic apparatus100and100′ can be used in at least one of the following modes:1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed.2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

Combinations and/or variations on the described modes of use or entirely different modes of use can also be employed.

In a further embodiment, lithographic apparatus100includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

Subsequently the radiation traverses the illumination system IL, which can include a faceted field mirror device222and a faceted pupil mirror device224arranged to provide a desired angular distribution of the radiation beam221, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation221at the patterning device MA, held by the support structure MT, a patterned beam226is formed and the patterned beam226is imaged by the projection system PS via reflective elements228,229onto a substrate W held by the wafer stage or substrate table WT.

More elements than shown can generally be present in illumination optics unit IL and projection system PS. The grating spectral filter240can optionally be present, depending upon the type of lithographic apparatus. Further, there can be more mirrors present than those shown in theFIG.2, for example there can be one to six additional reflective elements present in the projection system PS than shown inFIG.2.

Collector optic CO, as illustrated inFIG.2, is depicted as a nested collector with grazing incidence reflectors253,254, and255, just as an example of a collector (or collector mirror). The grazing incidence reflectors253,254, and255are disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

Exemplary Lithographic Cell

FIG.3shows a lithographic cell300, also sometimes referred to a lithocell or cluster, according to some embodiments. Lithographic apparatus100or100′ can form part of lithographic cell300. Lithographic cell300can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input/output ports I/O1, I/O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus100or100′. These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

Exemplary Metrology System

In order to control the lithographic process to place device features accurately on the substrate, alignment marks are generally provided on the substrate, and the lithographic apparatus includes one or more for accurate positioning of marks on a substrate. These alignment apparatuses are effectively position measuring apparatuses. Different types of marks and different types of alignment apparatuses and/or systems are known from different times and different manufacturers. A type of system widely used in current lithographic apparatus is based on a self-referencing interferometer as described in U.S. Pat. No. 6,961,116 (den Boef et al.). Generally marks are measured separately to obtain X- and Y-positions. A combined X- and Y-measurement can be performed using the techniques described in U.S. Publication No. 2009/195768 A (Bijnen et al.), however. The full contents of both of these disclosures are incorporated herein by reference.

FIG.4Ashows a schematic of a cross-sectional view of an metrology system400that can be implemented as a part of lithographic apparatus100or100′, according to some embodiments. In some embodiments, metrology system400can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Metrology system400can be further configured to detect positions of alignment marks on the substrate and to align the substrate with respect to the patterning device or other components of lithographic apparatus100or100′ using the detected positions of the alignment marks. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

In some embodiments, metrology system400can include an illumination system412, a beam splitter414, an interferometer426, a detector428, a beam analyzer430, and an overlay calculation processor432. Illumination system412can be configured to provide an electromagnetic narrow band radiation beam413having one or more passbands. In an example, the one or more passbands can be within a spectrum of wavelengths between about 500 nm to about 900 nm. In another example, the one or more passbands can be discrete narrow passbands within a spectrum of wavelengths between about 500 nm to about 900 nm. Illumination system412can be further configured to provide one or more passbands having substantially constant center wavelength (CWL) values over a long period of time (e.g., over a lifetime of illumination system412). Such configuration of illumination system412can help to prevent the shift of the actual CWL values from the desired CWL values, as discussed above, in current alignment systems. And, as a result, the use of constant CWL values can improve long-term stability and accuracy of alignment systems (e.g., metrology system400) compared to the current alignment apparatuses.

In some embodiments, beam splitter414can be configured to receive radiation beam413and split radiation beam413into at least two radiation sub-beams. For example, radiation beam413can be split into radiation sub-beams415and417, as shown inFIG.4A. Beam splitter414can be further configured to direct radiation sub-beam415onto a substrate420placed on a stage422. In one example, the stage422is movable along direction424. Radiation sub-beam415can be configured to illuminate an alignment mark or a target418located on substrate420. Alignment mark or target418can be coated with a radiation sensitive film. In some embodiments, alignment mark or target418can have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when alignment mark or target418is rotated 180° about an axis of symmetry perpendicular to a plane of alignment mark or target418, rotated alignment mark or target418can be substantially identical to an unrotated alignment mark or target418. The target418on substrate420can be (a) a resist layer grating comprising bars that are formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interleaved on a product layer grating. The bars can alternatively be etched into the substrate. This pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, particularly the projection system PL, and illumination symmetry and the presence of such aberrations will manifest themselves in a variation in the printed grating. One in-line method used in device manufacturing for measurements of line width, pitch, and critical dimension makes use of a technique known as “scatterometry”. Methods of scatterometry are described in Raymond et al., “Multiparameter Grating Metrology Using Optical Scatterometry”, J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography”, SPIE, Vol. 3677 (1999), which are both incorporated by reference herein in their entireties. In scatterometry, light is reflected by periodic structures in the target, and the resulting reflection spectrum at a given angle is detected. The structure giving rise to the reflection spectrum is reconstructed, e.g. using Rigorous Coupled-Wave Analysis (RCWA) or by comparison to a library of patterns derived by simulation. Accordingly, the scatterometry data of the printed gratings is used to reconstruct the gratings. The parameters of the grating, such as line widths and shapes, can be input to the reconstruction process, performed by processing unit PU, from knowledge of the printing step and/or other scatterometry processes.

In some embodiments, beam splitter414can be further configured to receive diffraction radiation beam419and split diffraction radiation beam419into at least two radiation sub-beams, according to an embodiment. Diffraction radiation beam419can be split into diffraction radiation sub-beams429and439, as shown inFIG.4A.

It should be noted that even though beam splitter414is shown to direct radiation sub-beam415towards alignment mark or target418and to direct diffracted radiation sub-beam429towards interferometer426, the disclosure is not so limiting. It would be apparent to a person skilled in the relevant art that other optical arrangements can be used to obtain the similar result of illuminating alignment mark or target418on substrate420and detecting an image of alignment mark or target418.

As illustrated inFIG.4A, interferometer426can be configured to receive radiation sub-beam417and diffracted radiation sub-beam429through beam splitter414. In an example embodiment, diffracted radiation sub-beam429can be at least a portion of radiation sub-beam415that can be reflected from alignment mark or target418. In an example of this embodiment, interferometer426comprises any appropriate set of optical-elements, for example, a combination of prisms that can be configured to form two images of alignment mark or target418based on the received diffracted radiation sub-beam429. It should be appreciated that a good quality image need not be formed, but that the features of alignment mark418should be resolved. Interferometer426can be further configured to rotate one of the two images with respect to the other of the two images1800and recombine the rotated and unrotated images interferometrically.

In some embodiments, detector428can be configured to receive the recombined image via interferometer signal427and detect interference as a result of the recombined image when alignment axis421of metrology system400passes through a center of symmetry (not shown) of alignment mark or target418. Such interference can be due to alignment mark or target418being 180° symmetrical, and the recombined image interfering constructively or destructively, according to an example embodiment. Based on the detected interference, detector428can be further configured to determine a position of the center of symmetry of alignment mark or target418and consequently, detect a position of substrate420. According to an example, alignment axis421can be aligned with an optical beam perpendicular to substrate420and passing through a center of image rotation interferometer426. Detector428can be further configured to estimate the positions of alignment mark or target418by implementing sensor characteristics and interacting with wafer mark process variations.

In a further embodiment, detector428determines the position of the center of symmetry of alignment mark or target418by performing one or more of the following measurements:1. measuring position variations for various wavelengths (position shift between colors);2. measuring position variations for various orders (position shift between diffraction orders); and3. measuring position variations for various polarizations (position shift between polarizations).

This data can for example be obtained with any type of alignment sensor, for example a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Pat. No. 6,961,116 that employs a self-referencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software, or Athena (Advanced Technology using High order ENhancement of Alignment), as described in U.S. Pat. No. 6,297,876, which directs each of seven diffraction orders to a dedicated detector, which are both incorporated by reference herein in their entireties.

In some embodiments, beam analyzer430can be configured to receive and determine an optical state of diffracted radiation sub-beam439. The optical state can be a measure of beam wavelength, polarization, or beam profile. Beam analyzer430can be further configured to determine a position of stage422and correlate the position of stage422with the position of the center of symmetry of alignment mark or target418. As such, the position of alignment mark or target418and, consequently, the position of substrate420can be accurately known with reference to stage422. Alternatively, beam analyzer430can be configured to determine a position of metrology system400or any other reference element such that the center of symmetry of alignment mark or target418can be known with reference to metrology system400or any other reference element. Beam analyzer430can be a point or an imaging polarimeter with some form of wavelength-band selectivity. In some embodiments, beam analyzer430can be directly integrated into metrology system400, or connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other embodiments.

In some embodiments, beam analyzer430can be further configured to determine the overlay data between two patterns on substrate420. One of these patterns can be a reference pattern on a reference layer. The other pattern can be an exposed pattern on an exposed layer. The reference layer can be an etched layer already present on substrate420. The reference layer can be generated by a reference pattern exposed on the substrate by lithographic apparatus100and/or100′. The exposed layer can be a resist layer exposed adjacent to the reference layer. The exposed layer can be generated by an exposure pattern exposed on substrate420by lithographic apparatus100or100′. The exposed pattern on substrate420can correspond to a movement of substrate420by stage422. In some embodiments, the measured overlay data can also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data can be used as calibration data to calibrate the exposure pattern exposed by lithographic apparatus100or100′, such that after the calibration, the offset between the exposed layer and the reference layer can be minimized.

In some embodiments, beam analyzer430can be further configured to determine a model of the product stack profile of substrate420, and can be configured to measure overlay, critical dimension, and focus of target418in a single measurement. The product stack profile contains information on the stacked product such as alignment mark, target418, or substrate420, and can include mark process variation-induced optical signature metrology that is a function of illumination variation. The product stack profile can also include product grating profile, mark stack profile, and mark asymmetry information. An example of beam analyzer430is Yieldstar™, manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Pat. No. 8,706,442, which is incorporated by reference herein in its entirety. Beam analyzer430can be further configured to process information related to a particular property of an exposed pattern in that layer. For example, beam analyzer430can process an overlay parameter (an indication of the positioning accuracy of the layer with respect to a previous layer on the substrate or the positioning accuracy of the first layer with respective to marks on the substrate), a focus parameter, and/or a critical dimension parameter (e.g., line width and its variations) of the depicted image in the layer. Other parameters are image parameters relating to the quality of the depicted image of the exposed pattern.

In some embodiments, an array of detectors (not shown) can be connected to beam analyzer430, and allows the possibility of accurate stack profile detection as discussed below. For example, detector428can be an array of detectors. For the detector array, a number of options are possible: a bundle of multimode fibers, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. The use of a bundle of multimode fibers enables any dissipating elements to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range. In some embodiments, each PIN detector can have a separate pre-amp. The number of elements is therefore limited. CCD linear arrays offer many elements that can be read-out at high speed and are especially of interest if phase-stepping detection is used.

In some embodiments, a second beam analyzer430′ can be configured to receive and determine an optical state of diffracted radiation sub-beam429, as shown inFIG.4B. The optical state can be a measure of beam wavelength, polarization, or beam profile. Second beam analyzer430′ can be identical to beam analyzer430. Alternatively, second beam analyzer430′ can be configured to perform at least all the functions of beam analyzer430, such as determining a position of stage422and correlating the position of stage422with the position of the center of symmetry of alignment mark or target418. As such, the position of alignment mark or target418and, consequently, the position of substrate420, can be accurately known with reference to stage422. Second beam analyzer430′ can also be configured to determine a position of metrology system400, or any other reference element, such that the center of symmetry of alignment mark or target418can be known with reference to metrology system400, or any other reference element. Second beam analyzer430′ can be further configured to determine the overlay data between two patterns and a model of the product stack profile of substrate420. Second beam analyzer430′ can also be configured to measure overlay, critical dimension, and focus of target418in a single measurement.

In some embodiments, second beam analyzer430′ can be directly integrated into metrology system400, or it can be connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other embodiments. Alternatively, second beam analyzer430′ and beam analyzer430can be combined to form a single analyzer (not shown) configured to receive and determine the optical states of both diffracted radiation sub-beams429and439.

In some embodiments, processor432receives information from detector428and beam analyzer430. For example, processor432can be an overlay calculation processor. The information can comprise a model of the product stack profile constructed by beam analyzer430. Alternatively, processor432can construct a model of the product mark profile using the received information about the product mark. In either case, processor432constructs a model of the stacked product and overlay mark profile using or incorporating a model of the product mark profile. The stack model is then used to determine the overlay offset and minimizes the spectral effect on the overlay offset measurement. Processor432can create a basic correction algorithm based on the information received from detector428and beam analyzer430, including but not limited to the optical state of the illumination beam, the alignment signals, associated position estimates, and the optical state in the pupil, image, and additional planes. The pupil plane is the plane in which the radial position of radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor432can utilize the basic correction algorithm to characterize the metrology system400with reference to wafer marks and/or alignment marks418.

In some embodiments, processor432can be further configured to determine printed pattern position offset error with respect to the sensor estimate for each mark based on the information received from detector428and beam analyzer430. The information includes but is not limited to the product stack profile, measurements of overlay, critical dimension, and focus of each alignment marks or target418on substrate420. Processor432can utilize a clustering algorithm to group the marks into sets of similar constant offset error, and create an alignment error offset correction table based on the information. The clustering algorithm can be based on overlay measurement, the position estimates, and additional optical stack process information associated with each set of offset errors. The overlay is calculated for a number of different marks, for example, overlay targets having a positive and a negative bias around a programmed overlay offset. The target that measures the smallest overlay is taken as reference (as it is measured with the best accuracy). From this measured small overlay, and the known programmed overlay of its corresponding target, the overlay error can be deduced. Table 1 illustrates how this can be performed. The smallest measured overlay in the example shown is −1 nm. However this is in relation to a target with a programmed overlay of −30 nm. The process may have introduced an overlay error of 29 nm.

TABLE 1Programmed overlay−70−50−30−10103050Measured overlay−38−19−121436690Difference between32312931333640measured andprogrammed overlayOverlay error32—24711
The smallest value can be taken to be the reference point and, relative to this, the offset can be calculated between measured overlay and that expected due to the programmed overlay. This offset determines the overlay error for each mark or the sets of marks with similar offsets. Therefore, in the Table 1 example, the smallest measured overlay was −1 nm, at the target position with programmed overlay of 30 nm. The difference between the expected and measured overlay at the other targets is compared to this reference. A table such as Table 1 can also be obtained from marks and target418under different illumination settings, the illumination setting, which results in the smallest overlay error, and its corresponding calibration factor, can be determined and selected. Following this, processor432can group marks into sets of similar overlay error. The criteria for grouping marks can be adjusted based on different process controls, for example, different error tolerances for different processes.

In some embodiments, processor432can confirm that all or most members of the group have similar offset errors, and apply an individual offset correction from the clustering algorithm to each mark, based on its additional optical stack metrology. Processor432can determine corrections for each mark and feed the corrections back to lithographic apparatus100or100′ for correcting errors in the overlay, for example, by feeding corrections into the metrology system400.

Exemplary Apparatuses for Coherence Scrambling

As ICs continue to shrink, demand is increasing for lithographic tools capable of processing smaller and more densely packed metrology targets (e.g., alignment marks). A single wafer can include numerous targets for measurements (e.g., alignment, overlay, or the like). In turn, the large number of targets on the wafer can introduce delays in production due to the additional measurements, reducing production throughput. Therefore, it is desirable for metrology systems to measure targets faster for increasing wafer throughput.

A solution can be to reduce the time spent measuring each target. However, such an implementation can be challenging. For example, in an attempt to quickly move from target to target, a detection time (e.g., photon collection time or integration time) of a metrology system can be reduced. But in this scenario, the measurements can suffer signal-to-noise issues that degrade the reliability of the measurements. It is analogous to setting a very high shutter speed on a camera used in photography (e.g., a few milliseconds of exposure), resulting in the capture of a poorly resolved image due to the lack of sufficient illumination.

To address this issue, the amount of radiation detected by the metrology system can be increased (e.g., use a brighter source). Radiation sources may come in coherent and incoherent varieties. For metrology, a homogenous beam spot is desirable since inhomogeneity in the beam spot, such as a speckle pattern, can introduce errors in a measurement. The effect of a speckle pattern is analogous to a photograph image having uneven brightness-bright and dark areas.

Bright-source solutions are further constrained depending on the tool they are implemented in. For example, in typical microscopy applications, a light bulb can suffice for a number of reasons. Spatially incoherent radiation sources (e.g., lamps (light bulbs), LEDs, plasma sources (laser pumped plasma light source), or the like), can output bright and homogeneous light. The etendue of a light bulb (e.g., spread out in all directions) is not a problem for many microscopy applications. The term “etendue” can be used herein to refer to a property of light of an optical system that characterizes a spread of radiation intensity in area and angle. On the other hand, high-precision metrology systems, such as ones used in conjunction with lithographic processes, can have highly constraining etendue requirements, which can hinder light-bulb implementation. In the process of conditioning the etendue of a light bulb to conform to a high precision metrology system (e.g., via mirrors, lenses, apertures, and other optical hardware), much radiation can be lost. And lost radiation is counter to the goal of providing a high-brightness source.

In some embodiments, the terms “spatial coherence,” “spatially coherent,” “spatial incoherence,” or the like may be used to refer to coherence phenomena, or lack thereof, in which a portion of radiation (e.g., wavefronts) can interfere with a spatially shifted version of itself. Furthermore, the terms “temporal coherence,” temporally coherent,” “temporal incoherence,” or the like, may be used to refer to coherence phenomena, or lack thereof, in which a portion of radiation can interfere with a time-delayed version of itself. It should be appreciated that, depending on the radiation source, radiation can be spatially coherent, temporally coherent, or both.

For high-precision metrology systems, spatially coherent radiation sources, such as a laser, are desirable for their high brightness and tight etendue (e.g., a highly directional beam). Spatially coherent radiation sources can also be more energy efficient than traditional incoherent sources. However, speckle phenomena—an interference effect—can reduce their desirability. In embodiments described herein, the terms “interference pattern,” “speckle,” “speckling,” “speckling pattern,” or the like can be used to refer to coherent radiation having a cross section that exhibits inhomogeneous intensity.

In some embodiments, radiation from a spatially coherent source can be adjusted so as to reduce undesirable effects of speckles. The terms “scrambled,” “coherence scrambling,” or the like, can be used herein to refer to the phenomena where coherent radiation is converted into incoherent or partially-coherent radiation (either in part or in full) by, e.g., increasing incoherence of the radiation or changing a spatial intensity distribution of wavefronts of the radiation over time (e.g., varying the speckle pattern over time). The term “coherence adjustment” or the like can be used herein to refer to the process of adjusting a state of coherence of radiation—for example, adjusting a speckle pattern. It should be appreciated that, in the process of varying or scrambling a speckle pattern of coherent radiation, the instantaneous speckle pattern is an interference pattern of spatially coherent radiation, but the coherent radiation can appear to be scrambled or incoherent from the perspective of a detector that integrates the variation of the speckle pattern over a given time frame (e.g., averaging). The terms “coherence scrambler,” “coherence adjuster,” or the like can be used herein to refer to devices that implement adjustment of coherence to achieve coherence scrambling.

One method includes using a mechanical coherence adjuster, such as a diffuser plate. In some embodiments, a mechanical coherence adjuster can comprise a source of spatially coherent radiation and an actuatable diffuser plate. Coherent radiation can be incident on the actuatable diffuser plate. The radiation can scatter with unpredictable phases (e.g., randomized). The phases can be varied by moving the diffuser plate such that the incidence of the radiation on a rough surface changes over time. The radiation scattered (and coherence scrambled) by the diffuser plate can be collected to be sent to a target. The beam of scrambled radiation can have a speckle pattern that continually changes at a rate based on the roughness profile of the diffuser plate and rate of actuation.

In some embodiments, a metrology system can comprise the mechanical coherence adjuster to generate a beam of scrambled radiation to send to a target. As the radiation scattered from the target is received at a detector, the varying speckle pattern is integrated over a finite detection period (e.g., averaged out).

Certain mechanical coherence adjusters, such as a diffuser plate, can suffer a variety of issues. In some embodiments, diffuser plates can cause inefficient use of photons (e.g., some stray photons can be lost). Regarding speed of measurement, demands of the industry are gravitating toward metrology systems that can measure a target in milliseconds or less. It is desirable that a coherence adjuster be able to vary a speckle pattern over numerous distinct patterns in a detection period (e.g., 1000 variations in a millisecond) to attain a suitable averaging (a non-limiting example). However, a typical diffuser plate may be designed for pattern adjustment speeds in the range of kHz. Thus, some diffuser plate implementations can fall short of providing a satisfactory variation speed of a speckle pattern. Another problem of a diffuser plate is that it can produce random speckle patterns, and therefore might not produce enough variants of the pattern to scramble coherence within a given integration time-difficult to achieve optimal coherence scrambling. Additionally, having fast moving mechanical components in a clean environment (e.g., in a lithographic apparatus) can present problems, such as vibrations, release of contaminants, and catastrophic failures. Furthermore, some diffuser plates can be undesirably large and bulky for certain applications. However, if circumstances allow, some diffuser implementations can be used (e.g., as described with respect toFIG.12).

Embodiments of the present disclosure provide structures and functions to more quickly and efficiently perform inspection of structures on a substrate, for example, using a coherence adjuster to convert a powerful coherent source into a powerful coherence scrambled source for irradiating a target. Furthermore, the structures and functions of embodiments described herein allow for compact coherence scrambler modules that can be roughly pen-sized or fit on the palm of a user's hand. In some embodiments, structures and functions of coherence adjusters can be implemented using, e.g., a multi-mode fiber, a diffuser device, an actuatable fiber, or the like.

FIG.5shows a schematic of a coherence adjuster500, according to some embodiments. In some embodiments, coherence adjuster500can comprise a waveguide device502, a multimode waveguide device504, and an actuator506. Coherence adjuster500can further comprise a restoring device508.

In some embodiments, waveguide device502can comprise a single-mode fiber. Multimode waveguide device504can comprise a multimode fiber. The term “waveguide device” or the like can be used herein to refer to a device that can propagate radiation by directing the radiation along a guide and/or medium. An example of a waveguide device is an optical fiber. Another example of a waveguide device is a microwave cavity. Yet another example of a waveguide device is a strip of light-transmissive material affixed on a substrate (e.g., as can be found in photonic circuits).

In some embodiments, multimode waveguide device504can comprise an input facet510. The dimensions of input facet510, and the body of multimode waveguide device504, are capable of supporting multiple modes of propagation of radiation, as opposed to only a single mode.

In some embodiments, actuator506can comprise one or more actuator elements (e.g., one for each direction of motion). The actuator elements can comprise piezo devices. Actuator506can be coupled to waveguide device502. Restoring device508can comprise one or more restoring elements (e.g., one for each direction of motion). Restoring device508can be coupled to waveguide device502.

In some embodiments, waveguide device502can comprise an input for receiving a beam of coherent radiation512. Coherent radiation512can be at least spatially coherent radiation (e.g., can also include temporally coherent radiation) and can be generated by a radiation source514(e.g., a laser). Waveguide device502can further comprise an output from which a beam of radiation516can exit. Radiation516is coherent radiation512that has been adjusted before being received at input facet510.

In some embodiments, input facet510can receive radiation516from waveguide device502. Multimode waveguide device504can further comprise an output for outputting a beam of radiation518(also “coherence adjusted beam of radiation”). Beam of radiation518is radiation516that has been guided by multimode waveguide device504. Beam of radiation518can comprise an interference pattern (e.g., speckles) as a result of constructive and destructive interference. The form of the interference pattern depends on an impingement characteristic of radiation516at input facet510. The impingement characteristic can include, for example, a position and/or size of the beam spot of radiation516at input facet510(which influences which modes are used for propagation). Additionally or alternatively, the impingement characteristic can include angle(s) of incidence of radiation516at input facet510. In other words, the form of the interference pattern depends on the etendue of radiation516at input facet510.

Consequently, in some embodiments, an adjustment of the interference pattern can be achieved by changing the impingement characteristic (or changing the etendue of radiation516). Or in other words, the change of the impingement characteristic comprises a change of etendue of the received radiation at input facet510of multimode waveguide device504.

In some embodiments, an apparent coherence of beam of radiation518, over an integrated time frame, is reduced based on an adjustment of the interference pattern in response to the change of the impingement characteristic. The reference to the ‘integrated time frame’ relates to how a detector can integrate (e.g., average) the changing speckle pattern over a given time frame such that the detected radiation is indistinguishable from homogeneous, incoherent radiation. In other words, homogeneity of beam of radiation518, over an integrated time frame, is increased based on an adjustment of the interference pattern in response to the change of the impingement characteristic.

In some embodiments, actuating waveguide device502can change the impingement characteristic of beam of radiation516at input facet510.FIG.5illustrates an example of changing a position of a focus spot of radiation516at input facet510. In this non-limiting example, the change of the impingement characteristic comprises a change of a position of the focus spot of radiation516at input facet510of multimode waveguide device504. Further, in this non-limiting example, the change of position of the focus spot is illustrated as a raster scan pattern520. Other patterns can also be used, such as spiral scan pattern, Lissajous scan pattern, or the like. The modes of propagation used by radiation launched into multimode waveguide device504is changed over time as the focus spot of radiation516is moved across input facet510. The modes of propagation influence the configuration of rays of beam of radiation518(which superimpose and interfere to form the speckle pattern). Consequently, the speckle pattern also changes and evolves over time as input facet510is scanned. In contrast with the traditional diffuser plate described earlier, scanning a single mode fiber (or scanning galvanic mirrors) can sample the complete mode space of the multimode fiber equally within a given integration time which results in optimally scrambled coherence.

Referring back to the actuation mechanism, actuator506can deflect and/or translate waveguide device502so as to change the impingement characteristic of radiation516at input facet510. As mentioned, actuator506can comprise one or more piezo devices. The piezo device(s) can exhibit a mechanical response (e.g., movement) in response to a received electrical signal. It should be appreciated that actuator506can comprise, not only piezos, but other types and/or combinations of suitable motors (e.g., magnet-driven). Optionally, restoring device508can be used to restore waveguide device502to a resting position. For example, restoring device can comprise a spring(s), a flexure(s), a piston device(s), or the like, or combinations thereof. Restoring device508can restore a position of waveguide device502along an axis of motion of actuator506. For multiple actuator elements and restoring elements, sets can be arranged such that waveguide device502is translated/deflected and restored along more than one axis (e.g., X and Y axes, with Z being a direction of propagation of radiation516).

In some embodiments, coherence adjuster500can be used in a metrology system. Beam of radiation518can be directed to a target on a wafer. The metrology system can be used in conjunction with lithographic apparatuses and processes.

In some embodiments, parts of coherence adjuster500can be modular. For example, the output of waveguide device502can be fashioned as a fiber connector. Input facet510can also be part of a fiber connector. Waveguide device502and actuator506(and restoring device508, if present) can be housed in a module that connects to multimode waveguide device504. In other words, waveguide device502and actuator506can modularly decouple from multimode waveguide device504. Furthermore, it is desirable that the general dimensions of coherence adjuster500be fairly compact. For example, considering the typical sizes of off-the-shelf actuators and optical fiber connectors, coherence adjuster500can be envisaged as pen-sized device (e.g., approximately tens of centimeters in length and few centimeters in width).

FIG.6shows a schematic of a coherence adjuster600, according to some embodiments. In some embodiments, coherence adjuster600can also represent a more detailed view of coherence adjuster500(FIG.5). For example,FIG.6illustrates a more detailed view the coupling between two waveguide devices. Unless otherwise noted, elements ofFIG.6that have similar reference numbers as elements ofFIG.5(e.g., reference numbers sharing the two right-most numeric digits) can have similar structures and functions. For simplicity, the similar structures, as well as structures that have been omitted from view (for drawing clarity), will not be reintroduced in detail.

In some embodiments, waveguide device602can be in contact, or near-contact, with multimode waveguide device604. To reduce coupling loss, a coupling material622can be disposed between waveguide device602and multimode waveguide device604(e.g., disposed on multimode waveguide device604with waveguide device602being in contact with coupling material622). Coupling material622can comprise an index matching medium, for example, gel, oil, or the like. When waveguide device602is actuated (example vertical motion shown by double-sided arrows), coupling material622allows waveguide device602to move across an input facet of multimode waveguide device604while reducing friction to prevent damage of sensitive optical parts. Performing scan patterns at the input face of multimode waveguide device604is facilitated by coupling material622. However, in some embodiments, certain functionalities are allowed if waveguide device602and multimode waveguide device604are physically apart, as will be described in reference toFIG.7.

In some embodiments, size and modularity aspects of coherence adjuster600can be as described in reference toFIG.5.

FIG.7shows a schematic of a coherence adjuster700, according to some embodiments. In some embodiments, coherence adjuster700can also represent a more detailed view of coherence adjuster500(FIG.5). For example,FIG.7illustrates a more detailed view the coupling between two waveguide devices. Unless otherwise noted, elements ofFIG.7that have similar reference numbers as elements ofFIGS.5and6(e.g., reference numbers sharing the two right-most numeric digits) can have similar structures and functions. For simplicity, the similar structures, as well as structures that have been omitted from view (for drawing clarity), will not be reintroduced in detail.

In some embodiments, coherence adjuster700can comprise a waveguide device702, a multimode waveguide device704, and optical elements724and726(e.g., a lens or a system of lenses). Coherence adjuster700can also comprise a beam splitter device730, an optical element732(e.g., a lens or a system of lenses), and a detector728.

In some embodiments, radiation716, which is output from waveguide device702, is incident on an input facet710of multimode waveguide device704. Optical arrangements can be disposed between waveguide device702and multimode waveguide device704. For example, optical elements724and726can be disposed in the path of radiation716. Optical element724can collimate radiation716(e.g., make its propagation substantially parallel). Optical element726can focus radiation716so as to form a beam spot of radiation716that is focused at input facet710. Beam splitter device730can direct a portion of radiation716toward detector728. Detector728can generate a detection signal based on the received portion of radiation716. The detection signal can be analyzed (e.g., by a processor) to determine an impingement characteristic of radiation716at input facet710. In this manner, one or more aspects of the impingement characteristic can be observed or monitored (e.g., a position of a focus spot at input facet710) to ensure that beam of radiation718has desired scrambling characteristics (also “coherence adjusted beam of radiation”).

In some embodiments, optical element726can be removed such that the beam spot of radiation716is not focused at input facet710(or alternative/additional arrangements of optical elements can be used to achieve the same effect). In this scenario, with the beam spot filling a larger part, or nearly all, of input facet710, the impingement characteristic can still be changed (e.g., angle(s) of incidence). It should be appreciated that the beam diameter of radiation716at its widest has been exaggerated for a clearer drawing (e.g., it can be just wide enough to fill input facet710when unfocused). Embodiments that can use an unfocused beam at an input facet of a multimode waveguide device will be described in reference toFIG.11.

In some embodiments, parts of coherence adjuster700can be modular. For example, the output of waveguide device702can be fashioned as a fiber connector. Input facet710can also be part of a fiber connector. Waveguide device702and actuator706(and restoring device708, if present) can be housed in a first module. Detector728, beam splitter device730, and optical elements724,726, and732can be housed in a second module. The second module can decouple from multimode waveguide device704. The first module (e.g., waveguide device702and actuator706) can modularly decouple from the second module. It should be appreciated that decoupling the second module from multimode waveguide device704has the effect of decoupling waveguide device702and actuator706from multimode waveguide device704. Furthermore, it is desirable that the general dimensions of coherence adjuster700be fairly compact. For example, considering the typical sizes of off-the-shelf camera detectors, lenses, and optical fiber connectors, coherence adjuster700can be envisaged as fitting approximately on the palm of a user's hand (e.g., approximately tens of centimeters in breadth).

FIG.8shows a coherence adjuster800, according to some embodiments. In some embodiments, coherence adjuster800can also represent a more detailed view of coherence adjuster500(FIG.5). For example,FIG.8illustrates a more detailed view the coupling between two waveguide devices. Unless otherwise noted, elements ofFIG.8that have similar reference numbers as elements ofFIGS.5-7(e.g., reference numbers sharing the two right-most numeric digits) can have similar structures and functions. For simplicity, the similar structures, as well as structures that have been omitted from view (for drawing clarity), will not be reintroduced in detail.

In some embodiments, coherence adjuster800can comprise a waveguide device802, a multimode waveguide device804, an actuator806, and optical elements824and826(e.g., a lens or a system of lenses). Actuator806can comprise a piezo tube. The piezo tube can be disposed around waveguide device802, while leaving a flexible portion of waveguide device802to protrude toward multimode waveguide device804.

In some embodiments, waveguide device802can be a fiber (a non-limiting example). The angular range of radiation output by waveguide device802is denoted by NAfiber. Actuator806can be provided a signal (e.g., a current or voltage) to actuate waveguide device802. The actuation can cause waveguide device802to translate and/or deflect by an amount denoted by θ.

In some embodiments, actuating waveguide device802can change the impingement characteristic of radiation816at an input facet810of multimode waveguide device804. Similar toFIG.5,FIG.8illustrates an example of changing a position of a focus spot of radiation816at input facet810, but this is a non-limiting example and other impingement characteristics can be changed (e.g., as described in reference toFIG.11). The change of the impingement characteristic comprises a change of a position of the focus spot of radiation816at input facet810of multimode waveguide device804. Further, in this non-limiting example, the change of position of the focus spot can be performed as described earlier in reference to raster scan pattern520(FIG.5) (e.g., raster, spiral scan pattern, Lissajous, or the like). The modes of propagation used by radiation launched into multimode waveguide device804is changed over time as the focus spot of radiation816is moved across input facet810. Consequently, the speckle pattern also changes and evolves over time as input facet810is scanned.

In some embodiments, an apparent coherence of a beam of radiation that is output by multimode waveguide device804is reduced based on an adjustment of the speckle pattern in response to the change of the impingement characteristic. In other words, homogeneity of the beam of radiation output by multimode waveguide device804, over an integrated time frame, is increased based on an adjustment of the interference pattern in response to the change of the impingement characteristic.

In some embodiments, size and modularity aspects of coherence adjuster800can be as described in reference toFIG.7.

In some embodiments, optical elements824and826can be removed and waveguide device802and multimode waveguide device804can be disposed closer together, which will be described in reference toFIG.9.

FIG.9shows a coherence adjuster900, according to some embodiments. In some embodiments, coherence adjuster900can also represent a more detailed view of coherence adjuster500(FIG.5). For example,FIG.9illustrates a more detailed view the coupling between two waveguide devices. Unless otherwise noted, elements ofFIG.9that have similar reference numbers as elements ofFIGS.5-8(e.g., reference numbers sharing the two right-most numeric digits) can have similar structures and functions. For simplicity, the similar structures, as well as structures that have been omitted from view (for drawing clarity), will not be reintroduced in detail.

In some embodiments, coherence adjuster900can comprise a waveguide device902, a multimode waveguide device904, and an actuator906. Actuator906can comprise a piezo tube.

In some embodiments, actuator906can be provided a signal (e.g., a current or voltage) to actuate waveguide device902. The actuation can cause waveguide device902to translate and/or deflect by an amount denoted by θ. In some embodiments, actuating waveguide device902can change the impingement characteristic of radiation at an input facet910of multimode waveguide device904. Similar toFIG.5,FIG.9illustrates a non-limiting example of changing a position of a beam spot of the radiation at input facet910. The change of the impingement characteristic comprises a change of a position of the focus spot the radiation at input facet910. Further, in this non-limiting example, the change of position of the focus spot can be performed as described earlier in reference to raster scan pattern520(FIG.5) (e.g., raster, spiral scan pattern, Lissajous, or the like). The modes of propagation used by radiation launched into multimode waveguide device904is changed over time as the focus spot of the radiation at input facet910is moved across input facet910. Consequently, the speckle pattern also changes and evolves over time as input facet910is scanned.

In some embodiments, an apparent coherence of a beam of radiation that is output by multimode waveguide device904is reduced based on an adjustment of the speckle pattern in response to the change of the impingement characteristic. In other words, homogeneity of the beam of radiation output by multimode waveguide device904, over an integrated time frame, is increased based on an adjustment of the interference pattern in response to the change of the impingement characteristic.

In some embodiments, size and modularity aspects of coherence adjuster900can be as described in reference toFIG.5.

In some embodiments, a characteristic of the beam of radiation output by a multimode waveguide device (e.g., beam of radiation518(FIG.5)) can be further adjusted as described in reference toFIGS.10-13. The characteristic can be, for example, a beam diameter. Beam diameter adjustability (or spot size selector) can be useful for, e.g., allowing users of lithographic tools to implement their own, customized metrology targets rather than being constrained to factory-specified targets for the metrology system being used. For example, in the interest of miniaturization, smaller targets can be preferred in order to place more densely packed IC structures on a wafer. A consequence can be that a metrology system designed for larger targets may suffer inaccuracies when used on smaller targets since the beam diameter of the illuminator may be too large. For example, the radiation may fall on surrounding IC structures and introduce errors in the measurement. In another example, larger spots might not efficiently use all of the radiation when delivered to a small target (radiation falling outside of the target is unused radiation). Losslessly reducing the beam diameter conserves the energy in the beam and makes sure that all or most of it is sent to the target, preventing the ‘waste’ of the radiation that would otherwise fall outside of the target.

FIG.10shows a coherence adjuster1000, according to some embodiments. In some embodiments, coherence adjuster1000can also represent a system that is similar to coherence adjuster500(FIG.5), but with some parts rearranged or replaced. Unless otherwise noted, elements ofFIG.10that have similar reference numbers as elements ofFIGS.5-9(e.g., reference numbers sharing the two right-most numeric digits) can have similar structures and functions. For simplicity, the similar structures, as well as structures that have been omitted from view (for drawing clarity), will not be reintroduced in detail.

In some embodiments, coherence adjuster1000can comprise a waveguide device1002, a multimode waveguide device1004, an actuator1006, a reflective element1036, and an adjustable beam expander1038. Coherence adjuster1000can comprise additional optics, such as optical elements1024,1026, and/or1040(e.g., a lens or system of lenses).

In some embodiments, waveguide device1002has an input and an output. Multimode waveguide device1004has an input (e.g., input facet1010) and an output. Actuator1006can comprise one or more galvanometer elements. Actuator1006can be coupled to reflective element1036as a galvo mirror arrangement. It should be appreciated that, in some embodiments, waveguide device1002can be optional. For example, coherent radiation1012can be incident on reflective element1036without having to interact with waveguide device1002.

In some embodiments, the input of waveguide device1002can receive a beam of coherent radiation1012. Waveguide device1002can guide coherent radiation1012such that coherent radiation1012is directed to reflective element1036. Coherent radiation exits at the output of waveguide device1002. Coherent radiation1012can be at least spatially coherent radiation (e.g., can also include temporally coherent radiation) and can be generated by a radiation source1014(e.g., a laser). Optical element1024, disposed in the path of coherent radiation1012, can collimate coherent radiation1012(e.g., make its propagation substantially parallel).

In some embodiments, reflective element1036directs radiation1016toward input facet1010. Radiation1016is coherent radiation1012that has been adjusted before being received at input facet1010. Multimode waveguide device1004can output a beam of radiation1018(also “coherence adjusted beam of radiation”).

In some embodiments, adjustable beam expander1038can be disposed in the path of radiation1016. Adjustable beam expander1038can allow size adjustments of a beam diameter1042of radiation1016in a lossless manner. The dashed lines around the beams of radiation denote a different beam diameter. This can be accomplished, for example, using transparent optical elements (a system of lenses), as opposed to a lossy method like using an aperture stop that clips a beam of radiation. Lossless methods are desirable for maximizing brightness and efficiency of coherence adjusters. To a metrology system used in conjunction with lithographic processes, lost photons results in potentially longer exposure times (longer measurements), which in turn reduces throughput in wafer production. The adjustments to beam diameter1042are performed in a manner that also controls the focus angles (or beam spread, or etendue) of radiation1016at input facet1010. In turn, since multimode waveguide device1004can preserve the etendue of the received radiation, the etendue of beam of radiation1018can also be adjusted by adjustable beam expander1038. In other words, a beam diameter1042of beam of radiation1018can be adjusted by adjustable beam expander1038. Optical element1040can be disposed in the path of beam of radiation1018to collimate beam of radiation1018so as to make beam diameter1042constant or nearly constant. Here, an impingement characteristic of radiation1016at input facet1010comprises a distribution of incidence angles. In this manner, coherence adjuster1000can adjust beam diameter1042based on a change of the distribution of incidence angles.

In some embodiments, beam of radiation1018is radiation1016that has been guided by multimode waveguide device1004. Beam of radiation1018can comprise an interference pattern (e.g., speckles) as a result of constructive and destructive interference. The form of the interference pattern depends on an impingement characteristic of radiation1016at input facet1010. The impingement characteristic can further comprise a position of a focus spot of radiation1016at input facet1010(which influences which modes are used for propagation).

Consequently, in some embodiments, an adjustment of the interference pattern can be achieved by changing the impingement characteristic (or changing the etendue of radiation1016). Or in other words, the change of the impingement characteristic comprises a change of etendue of the received radiation at input facet1010of multimode waveguide device1004. The change of the impingement characteristic can comprise a change of a position of the focus spot of radiation1016at input facet1010of multimode waveguide device1004. The change of position of the focus spot is illustrated as a raster scan pattern1020(or can be other patterns as described herein). The scanning can be achieved by actuating a portion of the coherence adjuster (e.g., actuating reflective element1036). It should be appreciated that the distribution of angles of incidence is still controllable when moving the focus spot at input facet1010, and therefore the beam diameter control is simultaneously achievable with coherence scrambling effects. Other examples of using a galvo mirror arrangement with a multimode fiber can be found in NL Published Application 2024394, filed on Dec. 5, 2019, which is incorporated by reference herein in its entirety.

It should also be appreciated that, in some embodiments, the galvo mirror arrangement can be replaced with any of the other actuation solutions described in reference toFIGS.5-9and still achieve the interference pattern adjustments as well as the beam diameter adjustments. In this context, it can be said that actuator1006can actuate a portion of coherence adjuster1000so as to change the impingement characteristic, wherein the actuated portion is waveguide device1002(whereas in the galvo mirror arrangement, the actuated portion would be reflective element1036).

In some embodiments, actuator1006can be considered a specific example of a more general “adjusting device.” For example, instead of an actuator, the adjusting device can comprise electronics (e.g., non-mechanical). In some embodiments, reflective element1036can be replaced with an optical adjuster that does not rely on mechanical parts (e.g., a liquid crystal device). In this example arrangement, the adjusting device and the liquid crystal device can be arranged as a liquid crystal spatial light modulator. The liquid crystal spatial light modulator can be of a reflective or transmissive type. And instead of actuating a portion of coherence adjuster1000, the adjusting device can adjust a portion of coherence adjuster1000(e.g., the liquid crystal device), to achieve the change of the impingement characteristic.

In some embodiments, the adjusting device can be a plurality of actuators and reflective element1036can be a plurality of reflectors. In this example, the actuators and reflectors can be arranged as a digital micromirror device. And the adjusting device can adjust a portion of coherence adjuster1000(e.g., the reflectors), to achieve the change of the impingement characteristic.

In some embodiments, parts of coherence adjuster1000can be modular. For example, the output of waveguide device1002can be fashioned as a fiber connector. Input facet1010can also be part of a fiber connector. The arrangement involving the galvo mirror arrangement and adjustable beam expander can be housed in a module that waveguide device1002and multimode waveguide device1004connect to. It is desirable that the general dimensions of coherence adjuster1000be fairly compact. For example, considering the typical sizes of off-the-shelf galvo mirrors and beam expanders, coherence adjuster1000can be envisaged as fitting approximately on the palm of a user's hand (e.g., approximately tens of centimeters in breadth).

FIG.11shows a coherence adjuster1100, according to some embodiments. In some embodiments, coherence adjuster1100can also represent a system that is similar to coherence adjuster500(FIG.5), but with some parts rearranged or replaced. Unless otherwise noted, elements ofFIG.11that have similar reference numbers as elements ofFIGS.5-10(e.g., reference numbers sharing the two right-most numeric digits) can have similar structures and functions. For simplicity, the similar structures, as well as structures that have been omitted from view (for drawing clarity), will not be reintroduced in detail.

In some embodiments, coherence adjuster1100can comprise a waveguide device1102, a multimode waveguide device1104, an actuator1106, a reflective element1136, and optical elements1124,1126,1140and/or1144(e.g., a lens or system of lenses).

In some embodiments, waveguide device1102has an input and an output. Multimode waveguide device1104has an input (e.g., input facet1110) and an output. Actuator1106can comprise one or more galvanometer elements. Actuator1106can be coupled to reflective element1136as a galvo mirror arrangement. A difference betweenFIGS.10and11is that adjustments of beam diameter1142of a beam of radiation1118is handled by the galvo mirror arrangement rather than a beam expander. Beam of radiation1118exits the output of multimode waveguide device1104.

In some embodiments, coherent radiation1112generated by radiation source1114is directed to reflective element1136. Optical elements1124,1126and1144are arranged in the path of coherent radiation1112and1116. Radiation1116is coherent radiation1112that has been adjusted before being received at input facet1110. Optical element1124can collimate coherent radiation1112. The arrangement of optical elements1126and1144have the effect of collimating radiation1116at input facet1110rather than focusing the beam at input facet1110. The focus of radiation1116occurs at a far field of input facet1110. When scanning is performed using the galvo mirror arrangement, a scan pattern1120is used at the focus of radiation1116(e.g., at a plane that is a Fourier conjugate of the plane at input facet1110). The result is that radiation1116can form a larger beam spot at input facet1110. The beam spot of radiation1116can fill or nearly fill input facet1110. However, even when the beam spot at input facet1110is stationary during the scanning, by Fourier conjugate considerations, a distribution of incidence angles of radiation1116at input facet1110can change in response to the scanning. In other words, a change of an impingement characteristic of radiation1116can comprise a change of a focus spot at a conjugate plane of input facet1110. In this manner, an interference pattern of beam of radiation1118can be adjusted based on the change of the impingement characteristic.

In some embodiments, size and modularity aspects can be similar to those described in reference toFIG.10.

Similar to embodiments referencingFIG.10, in some embodiments, coherence adjuster1100can also adjust beam diameter1142by changing the distribution of incidence angles of radiation1116at input facet1110(e.g., by scanning focus spot at the conjugate plane of input facet1110). The dashed lines around beam of radiation1118denotes a different beam diameter. This method of scanning the conjugate plane of input facet1110can be implemented in embodiments referencing, e.g.,FIGS.5-13, with appropriate arrangement of the optics.

Furthermore, in some embodiments, the arrangements regarding liquid crystal spatial light modulators and digital micromirror devices can be implemented as described in reference toFIG.10.

FIG.12shows a coherence adjuster1200based on a diffuser implementation, according to some embodiments. In some embodiments, coherence adjuster1200can also represent a system that is similar to coherence adjuster500(FIG.5), but with some parts rearranged or replaced. Unless otherwise noted, elements ofFIG.12that have similar reference numbers as elements ofFIGS.5-11(e.g., reference numbers sharing the two right-most numeric digits) can have similar structures and functions. For simplicity, the similar structures, as well as structures that have been omitted from view (for drawing clarity), will not be reintroduced in detail.

In some embodiments, coherence adjuster1200can comprise a waveguide device1202, a multimode waveguide device1204, a diffuser device1246, and optical elements1224,1240,1243and/or1244(e.g., a lens or system of lenses). Diffuser device1246can comprise two or more selectable diffuser elements, e.g., diffuser elements1246aand1246bare labeled as non-limiting examples. Each diffuser element can comprise a diffuse materials that provide different scattering patterns (e.g., different spreads of incidence angles or different etendues). Though the diffuser elements are illustrated as separate circles on a wheel, it should be appreciated that such an arrangement of diffuser elements is not limiting. For example, other arrangements are possible, such as circle segments (e.g., pie-chart style), concentric rings, a combination of circle segments and concentric rings, or the like.

In some embodiments, waveguide device1202has an input and an output. Multimode waveguide device1204has an input and an output. A difference betweenFIG.12and previous figures is that adjustments of beam diameter1242, and interference pattern, of a beam of radiation1218is handled by diffuser device1246. Beam of radiation1218exits at the output of multimode waveguide device1204.

In some embodiments, diffuser device1246can be disposed at a conjugate plane of the input of multimode waveguide device1204. Diffuser device1246can be disposed downstream of waveguide device1202and upstream of multimode waveguide device1204. Optical elements1243and1243are used to collimate radiation1216onto the input of multimode waveguide device1204(as opposed to narrowly focusing to a small spot). Therefore, it should be appreciated that coherence adjuster1200implements changing a distribution of incidence angles at the input of multimode waveguide device1204similar to embodiments referencingFIG.11.

In some embodiments, diffuser element1246acan comprise diffuse material that provides a particular spread of radiation1216, which determines the spread of incidence angles at the input of multimode waveguide device1204. Diffuser element1246bcan comprise diffuse material that provides a spread of radiation1216that is different from the one provided by diffuser element1246a. Any suitable diffuse materials can be used as long as the spread of radiation1216is defined and different for each diffuser element. One example of such a diffuser element is an engineered diffuser (non-limiting example). Furthermore, it is desirable that the diffuse material spread the radiation in a lossless manner-again, engineered diffusers are an example of diffusers capable of lossless or nearly lossless diffusion. As discussed previously with respect to other figures, the distribution of incidence angles can determine the size of beam diameter1242. Therefore, by selecting adjusting the appropriate diffuser element1246aor1246bto be in the path of radiation1246, the size of beam diameter1242can be selected (a different beam diameter is shown by dashed lines). Furthermore, while diffuser device1246can provide coherence scrambling on its own, when used in conjunction with multimode waveguide device1204, coherence scrambling effects can be further enhanced.

In some embodiments, in the absence of diffuser device1246, rays of radiation1216can have a particular distribution of impingement positions at the input of multimode waveguide device1204. Therefore, a particular set of modes of propagation of multimode waveguide device1204are coupled into. Furthermore, a particular distribution of incidence angles impinge on at the input of multimode waveguide device1204. Consequently, rays of beam of radiation1218emerge from a particular locations of the output of multimode waveguide1208and with a particular distribution of exit angles. The exiting rays superimpose and interfere to form a speckle pattern of beam of radiation1218. In other words, an interference pattern of beam of radiation1218is based on the particular distribution of impingement positions and incidence angles at the input of multimode waveguide device1204.

However, in some embodiments, when radiation1216is allowed to interact with diffuser device1246, the rays of radiation1216can become scattered such that the distribution of impingement positions and angles of incidence is now vastly different from the scenario where no diffuser device is used. Consequently, the modes of propagation of multimode waveguide device1204are coupled into differently. In turn, the rays of beam of radiation1218emerge from altered locations of the output of multimode waveguide device1204and at altered exit angles. The result is that an interference pattern of beam of radiation1218can be vastly different from when no diffuser device is used.

In some embodiments, in the absence of multimode waveguide device1204, a translation/rotation of diffuser device1246can result in a mere translation/rotation of the interference pattern of beam of radiation1218(or other actuating motions can also be used, e.g., vibrating, moved back and forth, or the like). Depending on the diffuse material, a slow translation/rotation may not produce an adequate number of pattern variations within short integration times (e.g., short enough for a metrology system to perform fast measurements). Therefore, it may be desired to actuate diffuser device1246at faster speeds at the risk of undesirable vibrations and catastrophic failure.

However, in some embodiments that include both multimode waveguide device1204and diffuser device1246, even a small translation/rotation of diffuser device1246can cause a distinguishable change to the impingement of radiation1216at the input of multimode waveguide device1204. That small difference can cause a change in how radiation1216couples into modes of propagation of multimode waveguide device1204. The configuration of the emerging rays of beam of radiation1218from multimode waveguide device1204can be vastly altered in response to the small movement of diffuser device1246. In this manner, diffuser device1246can be used for fast coherence scrambling without resorting to actuate diffuser device1246at unsafe speeds.

In some embodiments, coherence adjuster1200works well using small movements of diffuser device1246, the size of diffuser device1246can be substantially smaller than traditional diffusers plates. Therefore, the size and modularity of coherence adjuster1200can be similar to what has been described above regarding galvo mirror arrangements (e.g., palm sized and coupled via detachable fiber connectors).

FIG.13shows graphs for describing spot size of a beam of radiation1318, according to some embodiments. In some embodiments, some of the structures shown inFIG.13can be similar to those of coherence adjuster500(FIG.5), but with some parts rearranged or replaced. Unless otherwise noted, elements ofFIG.13that have similar reference numbers as elements ofFIGS.5-12(e.g., reference numbers sharing the two right-most numeric digits) can have similar structures and functions. For simplicity, the similar structures, as well as structures that have been omitted from view (for drawing clarity), will not be reintroduced in detail.

In some embodiments, graphs1348and1350show intensity vs. beam diameter plot of beam of radiation1318(simulated). The horizontal axes represent a radial position with respect to an optical axis of beam of radiation1318, in arbitrary units (a.u.). The vertical axis represents radiation intensity in arbitrary units (a.u.). In graph1348, a beam diameter1342of beam of radiation1318is approximately 2 distance units. However, when using one of the methods described herein to shrink beam diameter1342to the values in graph1350, “intensity tails”1352can form. The formation of intensity tails is a known issue in applications that require small beam diameters. In the non-limiting example illustrated in graph1350, the intended beam diameter1342can be approximately 1 distance unit while the tails1352extend further out to a diameter of 2 distance units. Intensity tails1352cause problems by illuminating features outside of the intended beam diameter (e.g., when coherence adjuster is used in a metrology system for a lithographic process, while the main central beam is used to illuminate a target, intensity tails can unintendedly illuminate other structures). The illumination of extra features can introduce errors in metrology applications.

Therefore, in some embodiments, an aperture device1354can be used to block intensity tails1352. While the use of apertures was earlier described as less than ideal for their potential to reduce intensity (higher intensity is desirable), in the case of intensity tails, the use of aperture device1354can provide an acceptable trade-off between minimal intensity loss and prevention of metrology errors. After all, intensity tails1352make up only a small, negligible fraction of the total energy in beam of radiation1318. The radiation energy lost by blocking intensity tails1352can be marginal.

In some embodiments, radiation with a spectrum of wavelengths (e.g., non-zero bandwidth) can be used with a long multimode waveguide device1304(e.g., a long multimode fiber). Since propagation constants of waveguide modes are wavelength dependent and refractive index of multimode waveguide can be wavelength dependent, the radiation propagating within waveguide device1304can be delayed differently for different wavelengths. For a long enough fiber with suitable core material, the relative modes differ as a function of wavelength. The result is that an interference pattern of beam of radiation1318can be further adjusted using this mechanism. This can add another layer of faster scrambling to, e.g., the diffuser device implementation ofFIG.12(but embodiments referencing any of the other figures can also use the long fiber and multi-wavelength features). It should be appreciated that, for long enough fibers and/or large enough bandwidths that provide adequate a desired amount of scrambling, certain actuation or adjustment features of a coherence adjuster can be omitted. As a non-limiting example, in the diffuser example ofFIG.12, a 2-meter long multimode fiber can provide adequate scrambling such that the diffuser need not be actuated.

In some embodiments, multimode waveguide device1304can have a length of greater than approximately 2 meters, greater than approximately 5 meters, greater than approximately 10 meters, or greater than approximately 100 meters. In some embodiments, the length of multimode waveguide device1304can be determined based on the wavelength (and also based on a given amount of coherence scrambling). For example, multimode waveguide device1304can have a length of greater than approximately 106times an input wavelength, greater than approximately 107times an input wavelength, or greater than approximately 108times an input wavelength.

Furthermore, regarding embodiments referencingFIGS.5-13, the impingement characteristic of radiation at an input of a multimode waveguide can be changed deterministically, randomly, pseudo-randomly, or using a combination of deterministic and random changes. The goal is to provide a changing speckle pattern that disappears (e.g., appears homogeneous) in a short integration time.

In some embodiments, structures and functions of coherence adjusters ofFIGS.5-13can be implemented in metrology systems (e.g., metrology system400(FIGS.4A and4B)). Coherence adjusters can be implemented, for example, as part of illumination system412(FIGS.4A and4B).

Exemplary Systems and Methods for Controlling Beam Homogeneity

For incoherent (or partially coherent) sensors, the efficiency of coupling light into the sensor can be a trade-off between the amount of light available on a measurement target and the beam quality of the light at, for example, the measurement target. In some examples, the beam quality can include, but is not limited to, the homogeneity of the light. In some examples, for incoherent light, the efficiency of light coupling can be related to the etendue associated to a light source, the etendue associated to the sensor, or both. In one example, the etendue associated with an optical system can be proportional to the product of the area of the spread of the radiation intensity at the optical system (e.g., D2, where D is a diameter associated with the area associated with the optical system) and the square of the angle (e.g., a solid angle associated with the optical system—NA2) in an small-angle limit. In other words, the etendue of the light beam can be proportional to D2NA2in the small-angle limit. In a non-limiting example, D2can be the area of a cross-section of a fiber and NA can be the numerical aperture associated with the fiber.

According to some examples, a multimode waveguide device (a multimode fiber as a non-limiting example) can be used to transport the light from the light source to the incoherent (or partially coherent) sensor. In some examples, the multimode waveguide device can be configured to provide the light with desirable properties to the sensor. The desirable properties can include, but are not limited to, one or more of good mode mixing, a homogeneous illumination in the near field (e.g., the output of the multimode waveguide device), and a homogeneous illumination in the far field. In some examples, the desirable properties of the light provided to the sensor can be achieved by using a multimode waveguide device with a larger diameter at the input of the multimode waveguide device and/or higher NA. However, the embodiments of this disclosure are not limited to these examples.

For incoherent (or partially coherent) sensors, the etendue associated with the light source is to be matched with the etendue associated with the sensor. Using a multimode waveguide device with a small diameter and/or low NA can result in the inhomogeneity of the light outputted from the sensor. On the other hand, using a multimode waveguide device with a large diameter and/or high NA can result in the mismatch between the etendue associated with the light source and the etendue associated with the sensor.

According to some examples, when a radiation source generates a coherent radiation (e.g., spatially coherent and/or temporally coherent), the coherent radiation can have a very small etendue (e.g., the etendue associated with the radiation source is very small). Additionally, or alternatively, the coherent radiation can have a very high brightness. For the incoherent (or partially coherent) sensors, the coherent radiation from the light source can be scrambled into incoherent or quasi-incoherent light. The scrambling can be done using, for example, one or more coherence adjusters500,600,700,800,900,1000,1100, and1200discussed above. In some examples, using the coherence adjuster can result in an increase in the etendue of the light that the sensor receives. If the etendue of the light of the coherence adjuster is larger than the etendue associated with the sensor, a net light loss can occur, which can negate the advantages of using the radiation source that generated the coherent radiation.

Some embodiments of this disclosure are directed to system, method and/or computer program product aspects, and/or combinations and sub-combinations thereof to mitigate the homogeneity effects in both near field and far field by pre-adjusting and/or dynamically adjusting the light distribution at the output of a coherence adjuster and/or an input of a waveguide device coupled to a detector. In some embodiments (e.g., for partially coherent illumination), where the light distribution can be non-uniform in both area and NA, the light distribution in one or both of area and NA can be controlled and can be made to conform to predetermined distributions.

FIG.14shows a schematic of a system1401for adjusting light distribution, according to some embodiments. System1401can be a metrology system. System1401can be implemented as part of metrology system400ofFIG.4Aand/orFIG.4B. Additionally, or alternatively, system1401can be implemented in addition to metrology system400ofFIG.4Aand/orFIG.4B. According to some embodiments, system1401can include radiation source1414, coherence adjuster1400, optional waveguide device1406, detector1402, processor1404, storage device1410, and target1418.

In some embodiments, radiation source1414can include a radiation source configured to generate coherent radiation1412. As a non-limiting example, radiation source1414can include a white light laser. Coherent radiation1412can be at least spatially coherent radiation (e.g., can also include temporally coherent radiation) generated by radiation source1414. According to some embodiments, radiation source1414can include or be part of radiation source412ofFIG.4A or4B, radiation source514ofFIG.5, radiation source1014ofFIG.10, radiation source1114ofFIG.11, and/or radiation source1214ofFIG.12.

According some embodiments, radiation source1414can be coupled to coherence adjuster1400. Alternatively, radiation source1414can be part of coherence adjuster1400. In some embodiments, coherence adjuster1400can include one or more coherence adjusters500,600,700,800,900,1000,1100, and1200discussed above. Coherence adjuster1400is configured to receive coherent radiation1412from radiation source1414and generate and output a beam of radiation1428(also “coherence adjusted beam of radiation”). Beam of radiation1428can include an interference pattern (e.g., speckles) as a result of constructive and destructive interference. The form of the interference pattern can depends on an impingement characteristic of radiation within coherence adjuster1400as discussed above with respect to, for example,FIGS.5-13.

Although radiation source1414and coherence adjuster1400are illustrated as separate systems/devices, the embodiments of this disclosure are not limited to these examples. Radiation source1414and coherence adjuster1400can be part of one system/device. According to some embodiments, coherence adjuster1400can include a multimode waveguide device as illustrated inFIGS.5-13. In some embodiments, the multimode waveguide device can include a radially symmetric multimode fiber that can generate various radially symmetric field and angular illumination distributions including top-hat and annular patterns with sharp or smooth edge transitions. The multimode waveguide device can include other multimode waveguide devices of other symmetries that can generate a variety of other illumination distributions including, but not limited to, square patterns. In some examples, the distribution and edge control can minimize error associated to mark edges.

According to some embodiments, beam of radiation1428can be input to detector1402. For example, coherence adjuster1400and detector1402are coupled such that beam of radiation1428output by coherence adjuster1400is input to detector1402to be used by detector1402for measurement. In some embodiments, coherence adjuster1400can be coupled to detector1402using one or more optical elements (e.g., lenses, systems of lenses), one or more beam splitters, and the like. Additionally, or alternatively, coherence adjuster1400can be coupled to detector1402using one or more additional waveguide devices. As one example, optional waveguide1406is illustrated inFIG.14that couples coherence adjuster1400to detector1402. In a non-limiting example, optional waveguide1406can include a fiber. In another example, optional waveguide device1406can include a multimode waveguide device. In the example that optional waveguide device1406is used, waveguide device1406can include an input configured to receive beam of radiation1418. Optional waveguide device1406can include an output configured to output beam of radiation1429to detector1402. Beam of radiation1429is also a coherence adjusted beam of radiation. In some embodiments, target1418can be the same as or similar to target418ofFIGS.4A and4B. Target1418can include other suitable targets.

In some embodiments, coherence adjuster1400(with or without waveguide device1406) can direct beam of radiation1428(or1429) to target1418without first going through detector1402. For example, beam of radiation1430, which can irradiate target1418, can be (and/or include) beam of radiation1428(or1429) (or part of beam of radiation1428(or1429)).

In some embodiments, coherent radiation1412is from radiation source1414is delivered to coherence adjuster1400using a fiber (e.g., a single-mode fiber).

According to some embodiments, detector1402can be configured to measure one or more parameters associated with beam of radiation1428and/or one or more parameters associated with beam of radiation1429. In some embodiments, the one or more parameters associated with beam of radiation1428(and/or beam of radiation1429) can include a field distribution of beam of radiation1428(and/or beam of radiation1429). The field distribution as used herein includes intensity distribution in a field. For example, detector1402can be configured to measure a near field distribution of beam of radiation1428(and/or beam of radiation1429). In some embodiments, the near field distribution can include an intensity distribution (e.g., a spatial distribution—the image of the intensity) of the beam of radiation (e.g., beam of radiation1428and/or beam of radiation1429) measured/determined at a field plane. In other words, the near field distribution includes measuring the intensity distribution of the light at the field plane. Additionally, or alternatively, detector1402can measure a far field distribution of beam of radiation1428(and/or beam of radiation1429). In some embodiments, the far field distribution can include an intensity distribution (e.g., a spatial distribution—the image of the intensity) of the beam of radiation (e.g., beam of radiation1428and/or beam of radiation1429) measured/determined at a pupil plane. In other words, the far field distribution includes measuring the intensity distribution of the light at the pupil plane. Although field distribution is provided as one example for one or more parameters associated with beam of radiation1428(and/or beam of radiation1429), the embodiments of this disclosure are not limited to these examples and detector1402can be configured to measure other parameters of beam of radiation1428(and/or beam of radiation1429).

According to some embodiments, detector1402can include one or more optical detectors (e.g., one or more field cameras) to measure the near field distribution (intensity distribution at the near field) of beam of radiation1428(and/or beam of radiation1429). In some embodiments, the optical detector can be a detector positioned at a field plane. In some embodiments, the field plane can include an optical plane where an image of a target is focused. Although the optical detector is not explicitly illustrated inFIG.14, the optical detector can include, for example, beam analyzer430′ ofFIG.4B. In some embodiments, the optical detector (e.g., beam analyzer430′ ofFIG.4B) can be configured to receive beam of radiation1431(or part of beam of radiation1431) diffracted and/or scattered from target1418and determine an optical state of beam of radiation1431. The optical state can be a measure of beam wavelength, polarization, beam profile, or field distribution. According to some embodiments, by measuring the field distribution of beam of radiation1431(or part of beam of radiation1431), the optical detector can be configured to determine the near field distribution (intensity distribution at the near field) of beam of radiation1428(and/or beam of radiation1429). According to some embodiments, target1418includes a suitably chosen target used by the field camera to measure the near field distribution of beam of radiation1428(and/or beam of radiation1429). According to some aspects, the suitably chosen target can be a target of interest, which is being used in a particular metrology application (e.g., one of the alignment or overlay targets). Additionally, or alternatively, the suitably chosen target can include a calibration target that, for example, provides a detectable signal on a field camera, has a spatial extent for at least the size of the beam area to be qualified, and/or is homogeneous in (reflection or diffraction) properties across a measurement area.

Although one example of the optical detector is provided, the embodiments of this disclosure are not limited to this example and detector1402can include one or more other detectors configured to measure the near field distribution (intensity distribution at the near field) of beam of radiation1428(and/or beam of radiation1429). For example, the optical detector can include a detector located at a field plane of system1401that receives beam of radiation1428(and/or beam of radiation1429) or part of beam of radiation1428(and/or part of beam of radiation1429) without the beam of radiation being diffracted from target1418. In a non-limiting example, the optical detector can include a detector located at the position of interferometer426ofFIGS.4A and4Bthat is configured to receive beam of radiation1428(and/or beam of radiation1429) or part of beam of radiation1428(and/or part of beam of radiation1429) without the beam of radiation being diffracted from target1418.

In some embodiments, the near field distribution (intensity distribution at the near field) can refer to the field distribution of beam of radiation1429at output of waveguide device1406(or input of detector1402), when waveguide device1406is used. Additionally, or alternatively, the near field distribution (intensity distribution at the near field) can refer to the field distribution of beam of radiation1428at the output of coherence adjuster1400(or input of detector1402), when waveguide device1406is not used.

According to some embodiments, detector1402can include one or more optical detectors (e.g., one or more pupil cameras) to measure the far field distribution (intensity distribution at the far field) of beam of radiation1428(and/or beam of radiation1429). Detector1402can include the pupil camera in addition to, or in alternative to, the optical detector discussed above. In some embodiments, the pupil camera can be a detector positioned at a pupil plane. In some embodiments, the pupil camera can include an optical plane where a radiation source is focused. Although the pupil camera is not explicitly illustrated inFIG.14, the pupil camera can include, for example, beam analyzer430ofFIGS.4A and4B. In some embodiments, the pupil camera (e.g., beam analyzer430ofFIGS.4A and4B) can be configured to receive beam of radiation1431(or part of beam of radiation1431) diffracted and/or scattered from target1418and determine an optical state of beam of radiation1431. The optical state can be a measure of beam wavelength, polarization, beam profile, or field distribution. According to some embodiments, by measuring the field distribution of beam of radiation1431(or part of beam of radiation1431), the pupil camera can be configured to determine the far field distribution (intensity distribution at the far field) of beam of radiation1428(and/or beam of radiation1429).

Although one example of the pupil camera is provided, the embodiments of this disclosure are not limited to this example and detector1402can include one or more other detectors configured to measure the far field distribution (intensity distribution at the far field) of beam of radiation1428(and/or beam of radiation1429). For example, the pupil camera can include a detector located at a pupil plane of system1401that receives beam of radiation1428(and/or beam of radiation1429) or part of beam of radiation1428(and/or part of beam of radiation1429) without the beam of radiation being diffracted from target1418.

In addition to, or in alternate to, measuring one or more parameters associated with beam of radiation1428and/or one or more parameters associated with beam of radiation1429(e.g., the field distribution), detector1402(alone or in combination with processor1404) can be configured to measure one or more parameters associated with target1418. For example, detector1402can include one or more of detector428, beam analyzer430, and beam analyzer430′ ofFIGS.4A and4B. The one or more parameters associated with target1418can include, but are not limited to, a position of target1418, a position of the center of symmetry of an alignment mark or target1418, an overlay of target1418, a critical dimension of target1418, a focus of target1418, and the like.

Detector1402can be configured to receive beam of radiation1431diffracted and/or scattered by target1408and generate a measurement signal based on the received radiation. For example, detector1402(alone or in combination with processor1404) can be configured to determine a position of a state (e.g., stage422ofFIGS.4A and4B) and correlate the position of stage with the position of the center of symmetry of an alignment mark or target1418. As such, the position of alignment mark or target1418and, consequently, the position of a substrate (e.g., substrate420ofFIGS.4A and4B) can be accurately known with reference to the stage. Alternatively, detector1402can be configured to determine a position of system1401or any other reference element such that the center of symmetry of alignment mark or target1418can be known with reference to system1400or any other reference element. Detector1402(alone or in combination with processor1404) can be further configured to determine the overlay data between two patterns and a model of the product stack profile of a substrate including target1418. Detector1402(alone or in combination with processor1404) can also be configured to measure overlay, critical dimension, and focus of target1418.

According to some embodiments, system1401can be configured to adjust one or more parameters of coherence adjuster1400and/or adjust one or more parameters of radiation source1414using the determined/measured one or more parameters associated with beam of radiation1428(and/or one or more parameters associated with beam of radiation1429). Additionally, or alternatively, system1401can be configured to adjust one or more parameters of coherence adjuster1400and/or adjust one or more parameters of radiation source1414using the determined/measured one or more parameters associated with target1418. Therefore, system1401can be configured to dynamically adjust the light distribution at the output of a coherence adjuster and/or an input of a waveguide device coupled to a detector so that mitigate the homogeneity effects in both near field and far field.

Although some embodiments are discussed with respect to coherence adjuster1400and/or radiation source1414adjusting their parameter(s) based on the measured parameter(s) of the coherence adjusted beam of radiation1428(or1429) and/or measured parameter(s) of target1418, this disclosure is not limited to these embodiments. Some embodiments of this disclosure (as discussed in more detail below) can include coherence adjuster1400and/or radiation source1414being pre-adjusted (e.g., being calibrated) based on one or more models.

According to some embodiments, detector1402can be configured to send the measured one or more parameters associated with beam of radiation1428and/or the measured one or more parameters associated with beam of radiation1429to processor1404. As discussed above, the one or more parameters associated with beam of radiation1428(and/or beam of radiation1429) can include a field distribution of beam of radiation1428(and/or beam of radiation1429). The field distribution can include one or more of a near field distribution and the far field distribution. Although field distribution is provided as one example for the measured one or more parameters, the embodiments of this disclosure are not limited to these examples and detector1402can be configured to send other measured parameters of beam of radiation1428(and/or beam of radiation1429) to processor1404. In some embodiments, processor1404can include processor432ofFIGS.4A and4B.

Additionally, or alternatively, processor1404can be configured to determine one or more parameters associated with target1418. For example, as discussed above, detector1402can be configured to receive beam of radiation1431diffracted and/or scattered by target1408and generate a measurement signal based on the received radiation. Detector1402can send the measurement signal to processor1404for further processing. Processor1404can determine the one or more parameters associated with target1418using the measurement signal received from detector1402. The one or more parameters associated with target1418can include, but are not limited to, a position of target1418, a position of the center of symmetry of an alignment mark or target1418, an overlay of target1418, a critical dimension of target1418, a focus of target1418, and the like.

According to some embodiments, processor1404can use the parameter(s) of the coherence adjusted beam of radiation (beam of radiation1428and/or1429), the determined parameters of target1418, or any combination of them to determine one or more parameters for coherence adjuster1400. Additionally, or alternatively, processor1404can use the parameter(s) of the coherence adjusted beam of radiation (beam of radiation1428and/or1429), the determined parameters of target1418, or any combination of them to determine one or more parameters for radiation source1414.

For example, processor1404can use the measured near field distribution of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) alone to determine one or more parameters for coherence adjuster1400(and/or to determine one or more parameters for radiation source1414). In one embodiment, processor1404can use the measured near field distribution of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) with the determined parameter(s) of target1418to determine one or more parameters for coherence adjuster1400(and/or to determine one or more parameters for radiation source1414).

In one embodiment, processor1404can use the measured far field distribution of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) alone to determine the one or more parameters for coherence adjuster1400(and/or to determine one or more parameters for radiation source1414). In one embodiment, processor1404can use the measured far field distribution of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) with the determined parameter(s) of target1418to determine the one or more parameters for coherence adjuster1400(and/or to determine one or more parameters for radiation source1414).

In one embodiment, processor1404can use the measured near field distribution and the measured far field distribution of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) to determine the one or more parameters for coherence adjuster1400(and/or to determine one or more parameters for radiation source1414). In one example, processor1404can use the measured near field distribution and the measured far field distribution of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) with the determined parameter(s) of target1418to determine the one or more parameters for coherence adjuster1400(and/or to determine one or more parameters for radiation source1414).

In one embodiment, processor1404can use the determined parameter(s) of target1418alone to determine the one or more parameters for coherence adjuster1400with the determined parameters of target1418(and/or to determine one or more parameters for radiation source1414).

According to some embodiments, a desired value for each one of the one or more parameters of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) can be stored in storage device1410accessible by processor1404. For example, storage device1410can store a desired distribution for the coherence adjusted beam of radiation (beam of radiation1428and/or1429). The desired distribution can include a desired far field distribution, a desired near field distribution, and the like. In some embodiments, the desired value(s) for the parameter(s) of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) can be determined based on the structure of system1401, the requirements for system1401, the requirements for one or more devices in system1401, and the like. In some embodiments, the desired values for the parameter(s) of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) can be set by a user/operator of system1401and/or of a lithographic apparatus (e.g., lithographic apparatus100or100′) associated with system1401.

According to some embodiments, to determine one or more parameters for coherence adjuster1400and/or one or more parameters for radiation source1414, processor1404compares the measured parameter(s) of the coherence adjusted beam of radiation (beam of radiation1428and/or1429) with their associated desired values. In some examples, processor1404can further use a model (e.g., a mathematical model) to apply to the difference between the measured value(s) and the desired value(s) to determine one or more parameters for coherence adjuster1400and/or one or more parameters for radiation source1414.

In an embodiment, the model can include a model between parameter(s) of coherence adjuster1400and a distribution (e.g., near field distribution, far field distribution) of the coherence adjusted beam of radiation (beam of radiation1428and/or1429). Additionally, or alternatively, the model can include a model between parameter(s) of radiation source1414and a distribution (e.g., near field distribution, far field distribution) of the coherence adjusted beam of radiation (beam of radiation1428and/or1429). In a non-limiting example, the model can include predetermined inverse correction coefficients. In some embodiments, processor1404can use artificial intelligence and machine learning techniques and technologies such as, but not limited to, logistic regression, random forest regression models, decision tree based algorithms, and the like to determine the inverse correction coefficients for the model.

According to some embodiments, a desired value for each one of the one or more parameters of target1418can be stored in storage device1410accessible by processor1404. For example, storage device1410can store a desired value for, but not limited to, a position of target1418, a position of the center of symmetry of an alignment mark or target1418, an overlay of target1418, a critical dimension of target1418, a focus of target1418, and the like. In some embodiments, the desired value(s) for the parameter(s) of target1418can be determined based on the structure of system1401, the requirements for system1401, the requirements for one or more devices in system1401, the requirement for a corresponding lithographic apparatus and the like. In some embodiments, the desired values for the parameter(s) of target1418can be set by a user/operator of system1401and/or of a lithographic apparatus (e.g., lithographic apparatus100or100′) associated with system1401.

According to some embodiments, to determine one or more parameters for coherence adjuster1400and/or one or more parameters for radiation source1414, processor1404compares the measured parameter(s) of target1418with their associated desired values. In some examples, processor1404can further use a model (e.g., a mathematical model) to apply to the difference between the measured value(s) and the desired value(s) to determine one or more parameters for coherence adjuster1400and/or one or more parameters for radiation source1414.

In an example, the model can include a model between parameter(s) of coherence adjuster1400and parameter(s) of target1418. Additionally, or alternatively, the model can include a model between parameter(s) of radiation source1414and parameter(s) of target1418. In a non-limiting example, the model can include predetermined inverse correction coefficients. In some embodiments, processor1404can use artificial intelligence and machine learning techniques and technologies such as, but not limited to, logistic regression, random forest regression models, decision tree based algorithms, and the like to determine the inverse correction coefficients for the model.

In some embodiments, processor1404can use the model between parameter(s) of coherence adjuster1400and the distribution of the coherence adjusted beam of radiation, the model between parameter(s) of coherence adjuster1400and parameter(s) of target1418, or a combination of both to determine the one or more parameters for coherence adjuster1400. Additionally, or alternatively, processor1404can use the model between parameter(s) of radiation source1414and the distribution of the coherence adjusted beam of radiation, the model between parameter(s) of radiation source1414and parameter(s) of target1418, or a combination of both to determine the one or more parameters for radiation source1414.

According to some embodiments, after determining the one or more parameters for coherence adjuster1400and/or the one or more parameters for radiation source1414, processor1404can communicate these parameter(s) to coherence adjuster1400and/or radiation source1414, respectively, to adjust the coherence adjuster1400and/or radiation source1414.

According to some embodiments, coherence adjuster1400can include coherence adjuster500ofFIG.5or coherence adjuster700ofFIG.7. In these embodiments, the determined parameter(s) for coherence adjuster1400can include determined parameter(s) for coherence adjuster500or700. Processor1404can communicate the determined parameter(s) for coherence adjuster500or700to coherence adjuster500or700, respectively, to adjust coherence adjuster500or700based on the determined parameter(s). Additionally, or alternatively, processor1404can adjust or control coherence adjuster500or700based on the determined parameter(s). Adjusting coherence adjuster500or700can include changing the impingement characteristic of radiation516(or716) at input facet510(or910). The impingement characteristic can include, for example, a position the beam spot of radiation516(or716) at input facet510(or710) (which influences which modes are used for propagation). Additionally or alternatively, the impingement characteristic can include angle(s) of incidence of radiation516(or716) at input facet510(or710) using, for example, small lens modifications.

In some embodiments, adjusting coherence adjuster500or700based on the determined parameter(s) can include using a variable dwell time for applying radiation516(or716) at different locations at input facet510(or710) of multimode waveguide device504(or704). Additionally, or alternatively, adjusting coherence adjuster500or700based on the determined parameter(s) can include modulating an intensity of beam of radiation518(or718) (the coherence adjusted beam of radiation) as a function of a position of the beam spot of radiation516(or716) at input facet510(or710) of multimode waveguide device504(or704).

In some embodiments, processor1404can communicate the determined parameter(s) for coherence adjuster500to coherence adjuster500to control or adjust parameter(s) of actuator506and/or restoring device508so as to change the impingement characteristic of radiation516at input facet510. For example, determined parameter(s) for coherence adjuster500can include parameter(s) associated with actuator506and/or restoring device508. In some embodiments, actuator506, and/or restoring device508can be provided a signal (e.g., a current or voltage) by processor1404to change the states/parameter(s) of actuator506, and/or restoring device508. Additionally, or alternatively, actuator506, and/or restoring device508can be provided a signal (e.g., a current or voltage) by processor1404to actuate their corresponding waveguide device (502) based on the determined parameter(s).

In some embodiments, processor1404can communicate the determined parameter(s) for coherence adjuster700to coherence adjuster700to control or adjust parameter(s) of actuator706and/or restoring device708so as to change the impingement characteristic of radiation716at input facet710. For example, determined parameter(s) for coherence adjuster700can include parameter(s) associated with actuator706and/or restoring device708. In some embodiments, actuator706and/or restoring device708can be provided a signal (e.g., a current or voltage) by processor1404to change the states/parameter(s) of actuator706and/or restoring device708. Additionally, or alternatively, actuator706and/or restoring device708can be provided a signal (e.g., a current or voltage) by processor1404to actuate waveguide device702based on the determined parameter(s). In some embodiments, processor1404can communicate the determined parameter(s) for coherence adjuster700to coherence adjuster700to control or adjust parameter(s) of optical elements724and726(e.g., a lens or a system of lenses), beam splitter device730, and/or optical element732(e.g., a lens or a system of lenses).

According to some embodiments, coherence adjuster1400can include coherence adjuster800ofFIG.8and/or coherence adjuster900ofFIG.9. In these embodiments, the determined parameter(s) for coherence adjuster1400can include determined parameter(s) for coherence adjuster800(or900). Processor1404can communicate the determined parameter(s) for coherence adjuster800(or900) to coherence adjuster800(or900) to adjust coherence adjuster800(or900) based on the determined parameter(s). Additionally, or alternatively, processor1404can adjust or control coherence adjuster800(or900) based on the determined parameter(s). Adjusting coherence adjuster800(or900) can include changing the impingement characteristic of radiation816at the input facet (e.g.,910). The impingement characteristic can include, for example, a position and/or size of the beam spot of radiation816at the input facet (e.g.,910) (which influences which modes are used for propagation). Additionally or alternatively, the impingement characteristic can include angle(s) of incidence of radiation816at the input facet (e.g.,910) using, for example, small lens modifications.

In some embodiments, adjusting coherence adjuster800(or900) based on the determined parameter(s) can include using a variable dwell time for applying radiation816at different locations at the input facet (e.g.,910) of multimode waveguide device804(or904). Additionally, or alternatively, adjusting coherence adjuster800(or900) based on the determined parameter(s) can include modulating an intensity of beam of radiation (the coherence adjusted beam of radiation) as a function of a position of the beam spot of radiation816at the input facet (e.g.,910) of multimode waveguide device804(or904). Additionally, or alternatively, adjusting coherence adjuster800(or900) based on the determined parameter(s) can include modulating an intensity of beam of radiation (the coherence adjusted beam of radiation) as a function of angle(s) of incidence of radiation816at the input facet (e.g.,910) of multimode waveguide device804(or904) using, for example, small lens modifications.

In some embodiments, processor1404can communicate the determined parameter(s) for coherence adjuster800(or900) to coherence adjuster800(or900) to control or adjust parameter(s) of actuator806and/or actuator906so as to change the impingement characteristic of radiation816at the input facet (e.g.,910). For example, determined parameter(s) for coherence adjuster800(or900) can include parameter(s) associated with actuator806and/or actuator906. In some embodiments, actuator806and/or actuator906can be provided a signal (e.g., a current or voltage) by processor1404to change the states/parameter(s) of actuator806and/or actuator906. Additionally, or alternatively, actuator806and/or actuator906can be provided a signal (e.g., a current or voltage) by processor1404to actuate their corresponding waveguide device (802or902) based on the determined parameter(s).

In some embodiments, processor1404can communicate the determined parameter(s) for coherence adjuster800to coherence adjuster800to control or adjust parameter(s) of optical elements824and826(e.g., a lens or a system of lenses).

According to some embodiments, coherence adjuster1400can include coherence adjuster1000ofFIG.10, coherence adjuster1100ofFIG.11, and/or coherence adjuster1200ofFIG.12. In these embodiments, the determined parameter(s) for coherence adjuster1400can include determined parameter(s) for coherence adjuster1000(1100, or1200). Processor1404can communicate the determined parameter(s) for coherence adjuster1000(1100, or1200) to coherence adjuster1000(1100, or1200, respectively) to adjust coherence adjuster1000(1100, or1200) based on the determined parameter(s). Additionally, or alternatively, processor1404can adjust or control coherence adjuster1000(1100, or1200) based on the determined parameter(s). Adjusting coherence adjuster1000(1100, or1200) can include changing the impingement characteristic of radiation1016(1116, or1216) at input facet1010(or1110).

For example, considering coherence adjuster1000ofFIG.10, processor1404can communicate the determined parameter(s) for coherence adjuster1000to coherence adjuster1000to control or adjust parameter(s) of adjustable beam expander1038ofFIG.10. For example, determined parameter(s) for coherence adjuster1000can include parameter(s) associated with adjustable beam expander1038. In some embodiments, adjustable beam expander1038can be provided a signal (e.g., a current or voltage) by processor1404to change the states/parameter(s) of adjustable beam expander1038. As discussed with respect toFIG.10, adjustable beam expander1038can allow size adjustments of a beam diameter1042of radiation1016in a lossless manner, according to some embodiments. The adjustments to beam diameter1042are performed in a manner that also controls the focus angles (or beam spread, or etendue) of radiation1016at input facet1010. In turn, since multimode waveguide device1004can preserve the etendue of the received radiation, the etendue of beam of radiation1018can also be adjusted by adjustable beam expander1038. Here, an impingement characteristic of radiation1016at input facet1010can include a distribution of incidence angles.

As another example, considering coherence adjuster1000ofFIG.10, processor1404can communicate the determined parameter(s) for coherence adjuster1000to coherence adjuster1000to control or adjust parameter(s) of actuator1006and/or reflective element1036ofFIG.10(or the adjusting device discussed with respect toFIG.10). For example, determined parameter(s) for coherence adjuster1000can include parameter(s) associated with actuator1006and/or reflective element1036. In some embodiments, actuator1006can be provided a signal (e.g., a current or voltage) by processor1404to change the states/parameter(s) of actuator1006and/or reflective element1036. As discussed with respect toFIG.10, the change of the impingement characteristic can include a change of a position of the focus spot of radiation1016at input facet1010of multimode waveguide device1004.

In some embodiments, processor1404can communicate the determined parameter(s) for coherence adjuster1000to coherence adjuster1000to control or adjust parameter(s) of optical elements1024,1026, and/or1040(e.g., a lens or a system of lenses).

In some embodiments, considering coherence adjuster1100ofFIG.11, processor1404can communicate the determined parameter(s) for coherence adjuster1100to coherence adjuster1100to control or adjust parameter(s) of actuator1106and/or reflective element1136ofFIG.11(or the adjusting device discussed with respect toFIG.11). For example, determined parameter(s) for coherence adjuster1100can include parameter(s) associated with actuator1106and/or reflective element1136. In some embodiments, actuator1106can be provided a signal (e.g., a current or voltage) by processor1404to change the states/parameter(s) of actuator1106and/or reflective element1136. As discussed with respect toFIG.11, a change of an impingement characteristic of radiation1116can include a change of a focus spot at a conjugate plane of input facet1110. In this manner, an interference pattern of beam of radiation1118can be adjusted based on the change of the impingement characteristic.

In some embodiments, processor1404can communicate the determined parameter(s) for coherence adjuster1100to coherence adjuster1100to control or adjust parameter(s) of optical elements1126and/or1140(e.g., a lens or a system of lenses).

In some embodiments, considering coherence adjuster1200ofFIG.12, processor1404can communicate the determined parameter(s) for coherence adjuster1200to coherence adjuster1200to control or adjust parameter(s) of diffuser device1246ofFIG.12. For example, the determined parameter(s) for coherence adjuster1200can include parameter(s) associated with diffuser device1246. In some embodiments, actuator1206can be provided a signal (e.g., a current or voltage) by processor1404to change the states/parameter(s) of diffuser device1246. As discussed with respect toFIG.12, by selecting and/or adjusting the appropriate diffuser element1246aor1246bof diffuser device1246to be in the path of radiation, the size of beam diameter1242can be selected (a different beam diameter is shown by dashed lines). In some embodiments, the determined parameter(s) for diffuser device1246sent by processor1404to coherence adjuster1200can include which diffuser element to use. Additionally, or alternatively, the determined parameter(s) for diffuser device1246sent by processor1404to coherence adjuster1200can include a rotation, a vibration, and/or a speed of rotation for diffuser device1246.

In some embodiments, processor1404can communicate the determined parameter(s) for coherence adjuster1200to coherence adjuster1200to control or adjust parameter(s) of optical elements1224,1240,1243, and/or1244(e.g., a lens or a system of lenses).

It is noted that although some exemplary parameters of coherence adjuster1400are discussed above that can be controlled and adjusted by processor1404, the embodiments of this disclosure are not limited to these parameters. Processor1404can control and adjust other parameters of coherence adjuster1400based on information processor1404receives from detector1402and/or based on information stored in, for example, storage device1410.

In addition to, or in alternate to, controlling and adjusting coherence adjuster1400discussed above, processor1404can control and adjust radiation source1414based, at least, on determining the one or more parameters for radiation source1414. In some embodiments, the one or more parameters for radiation source1414can include, but are not limited to, a wavelength of the radiation (e.g., radiation1412) generated by radiation source1414and/or a frequency band of the radiation (e.g., radiation1412) generated by radiation source1414. In some embodiments, the one or more parameters for radiation source1414can include, but are not limited to, an angle of incidence of the radiation (e.g., radiation1412) generated by radiation source1414at coherence adjuster1400. In some embodiments, the one or more parameters for radiation source1414can include, but are not limited to, an intensity of the radiation (e.g., radiation1412) generated by radiation source1414as a function of the position of a focus point of the radiation (e.g., radiation1412) at coherence adjuster1400. In some embodiments, the one or more parameters for radiation source1414can include, but are not limited to, dwell time of the spot of the radiation (e.g., radiation1412) generated by radiation source1414at different locations in coherence adjuster1400.

FIG.15Aillustrates an example method1500for determining parameter(s) for a coherence adjuster and/or a radiation source and adjusting the coherence adjuster and/or the radiation source using the determined parameter(s), according to some embodiments of the disclosure. As a convenience and not a limitation,FIG.15Amay be described with regard to elements ofFIG.14. Method1500may represent the operation of a system (e.g., system1401) implementing operations for determining parameter(s) for a coherence adjuster and/or a radiation source and adjusting the coherence adjuster and/or the radiation source using the determined parameter(s). Method1500may also be performed by computer system2100ofFIG.21. But method1500is not limited to the specific embodiments depicted in those figures, and other systems may be used to perform the method as will be understood by those skilled in the art. It is to be appreciated that not all operations may be needed, and the operations may not be performed in the same order as shown inFIG.15A.

At1502, a measurement signal is received. For example, processor1404ofFIG.14can receive the measurement signal from detector1402ofFIG.14. In some embodiments, the measurement signal can be generated by, for example, detector1402based on a measured distribution (intensity distribution in a field) of a coherence adjusted beam of radiation output from the coherence adjuster. In some embodiments, the measured distribution can include measured near field distribution (measured intensity distribution of the coherence adjusted beam of radiation in the near field). Additionally, or alternatively, the measured distribution can include measured far field distribution (measured intensity distribution of the coherence adjusted beam of radiation in the far field).

At1504, the measured distribution is compared with a desired distribution. For example, processor1404can compare the measured distribution with the desired distribution. In some embodiments, processor1404is configured to determine (e.g., extract) the measured distribution from the received measurement signal. In some examples, the desired distribution can desired near field distribution (desired intensity distribution of the coherence adjusted beam of radiation in the near field). Additionally, or alternatively, the desired distribution can include desired far field distribution (desired intensity distribution of the coherence adjusted beam of radiation in the far field).

At1506, one or more parameters associated with the coherence adjuster or one or more parameters associated with a radiation source are determined based on the comparison. For example, processor1404can determine one or more parameters associated with the coherence adjuster based on the comparison1504and/or a difference between the measured distribution and the desired distribution. Additionally, or alternatively, processor1404can determine one or more parameters associated with the radiation source based on the comparison1504and/or a difference between the measured distribution and the desired distribution.

According to some embodiments, determining the one or more parameters associated with the coherence adjuster can include using a model between parameters of the coherence adjuster and a distribution of the coherence adjusted beam of radiation. In some embodiments, the model can include one or more inverse correction coefficients. In some embodiments, determining the one or more parameters associated with the coherence adjuster and/or using the one or more inverse correction coefficients can include using a machine learning model. In some embodiments, the model can be stored in, for example, storage device1410accessible by processor1404. In some embodiments, determining the one or more parameters associated with the coherence adjuster can include using an iteratively optimization method optimizing the one or more parameters associated with the coherence adjuster based on the comparison1504.

According to some embodiments, determining the one or more parameters associated with the radiation source can include using a model between parameters of the radiation source and a distribution of the coherence adjusted beam of radiation. In some embodiments, the model can include one or more inverse correction coefficients. In some embodiments, determining the one or more parameters associated with the radiation source and/or using the one or more inverse correction coefficients can include using a machine learning model. In some embodiments, the model can be stored in, for example, storage device1410accessible by processor1404. In some embodiments, determining the one or more parameters associated with the radiation source can include using an iteratively optimization method optimizing the one or more parameters associated with the radiation source based on the comparison1504.

At1508, the determined one or more parameters associated with the coherence adjuster is communicated to the coherence adjuster and/or the determined one or more parameters associated with the radiation source are communicated to the radiation source. For example, processor1404can communicate the determined one or more parameters associated with the coherence adjuster to coherence adjuster1400. Additionally, or alternatively, processor1404can communicate the determined one or more parameters associated with the radiation source to radiation source1414.

Instead of (or in addition to) communicating the determined parameter(s), operation1508can include adjusting or controlling (for example, using processor1404) coherence adjuster1400using the determined one or more parameters associated with the coherence adjuster. Additionally, or alternatively, operation1508can include adjusting or controlling (for example, using processor1404) radiation source1414using the determined one or more parameters associated with radiation source.

In some embodiments, at1506, processor1404determines a value of a parameter of coherence adjuster1400. And at1508, processor1404communicates the determined value of the parameter to coherence adjuster1400. Coherence adjuster1400adjusts the parameter associated with coherence adjuster1400based at least on the determined value of the parameter. In some embodiments, coherence adjuster1400can adjust the parameter associated with coherence adjuster1400using other values in addition to the determined value of the parameter. In some embodiments, adjusting the parameter associated with coherence adjuster1400based at least on the determined value of the parameter can include using a variable dwell time for the received spatially coherent radiation at different locations at an input of the multimode waveguide device of the coherence adjuster. Additionally, or alternatively, adjusting the parameter associated with coherence adjuster1400based at least on the determined value of the parameter can include modulating an intensity of the coherence adjusted beam of radiation as a function of position of a spatially coherent radiation (received from, for example, radiation source1414) at the input of the multimode waveguide device of the coherence adjuster. Additionally, or alternatively, adjusting the parameter associated with coherence adjuster1400based at least on the determined value of the parameter can include modulating an intensity of the coherence adjusted beam of radiation as a function of an angle of incidence of the spatially coherent radiation (received from, for example, radiation source1414) at the input of the multimode waveguide device of the coherence adjuster.

In some embodiments, at1506, processor1404determines a value of a parameter of radiation source1414. And at1508, processor1404communicates the determined value of the parameter to radiation source1414. Radiation source1414adjusts the parameter associated with radiation source1414based at least on the determined value of the parameter. In some embodiments, radiation source1414can adjusts the parameter associated with radiation source1414using other values in addition to the determined value of the parameter. In some embodiments, adjusting the parameter associated with radiation source1414based at least on the determined value of the parameter can include adjusting wavelength associated with the radiation beam generated by the radiation source. In some embodiments, adjusting the parameter associated with radiation source1414based at least on the determined value of the parameter can include using a variable dwell time for the spot of the radiation beam generated by the radiation source at different locations at an input of the coherence adjuster. Additionally, or alternatively, adjusting the parameter associated with radiation source1414based at least on the determined value of the parameter can include modulating an intensity of the radiation beam generated by the radiation source as a function of the position of the radiation beam generated by the radiation source at the input of the coherence adjuster.

FIG.15Billustrates an example method1520for determining parameter(s) for a coherence adjuster and/or a radiation source and adjusting the coherence adjuster and/or the radiation source using the determined parameter(s), according to some embodiments of the disclosure. As a convenience and not a limitation,FIG.15Bmay be described with regard to elements ofFIG.14. Method1520may represent the operation of a system (e.g., system1401) implementing operations for determining parameter(s) for a coherence adjuster and/or a radiation source and adjusting the coherence adjuster and/or the radiation source using the determined parameter(s). Method1520may also be performed by computer system2100ofFIG.21. But method1520is not limited to the specific embodiments depicted in those figures, and other systems may be used to perform the method as will be understood by those skilled in the art. It is to be appreciated that not all operations may be needed, and the operations may not be performed in the same order as shown inFIG.15B.

At1522, a measurement signal is received. For example, processor1404ofFIG.14can receive the measurement signal from detector1402ofFIG.14. In some embodiments, the measurement signal can be generated by, for example, detector1402based on radiation scattered by a target (e.g., target1418) irradiated by a coherence adjusted beam of radiation from a coherence adjuster (e.g., coherence adjuster1400).

At1524, one or more parameters associated with the target is determined based on the measurement signal. The parameter(s) associated with the target can include, but is not limited to, overlay, alignment, critical dimension, focus, and the like.

At1526, the determined parameter(s) is compared with a desired parameter associated with the target. For example, processor1404can compare the determined parameter(s) with a desired parameter(s) associated with the target. In some embodiments, processor1404is configured to determine (e.g., extract) the parameter(s) from the received measurement signal. In some embodiments, the desired parameter(s) associated with the target can include, but is not limited to, overlay, alignment, critical dimension, focus, and the like.

At1528, one or more parameters associated with the coherence adjuster or one or more parameters associated with a radiation source are determined based on the comparison. For example, processor1404can determine one or more parameters associated with the coherence adjuster based on the comparison1504and/or a difference between the determined parameter(s) and the desired parameter(s). Additionally, or alternatively, processor1404can determine one or more parameters associated with the radiation source based on the comparison1504and/or a difference between the determined parameter(s) and the desired parameter(s).

According to some embodiments, determining the one or more parameters associated with the coherence adjuster can include using a model between parameters of the coherence adjuster and parameters of the target. In some embodiments, the model can include one or more inverse correction coefficients. In some embodiments, determining the one or more parameters associated with the coherence adjuster and/or using the one or more inverse correction coefficients can include using a machine learning model. In some embodiments, the model can be stored in, for example, storage device1410accessible by processor1404. In some embodiments, determining the one or more parameters associated with the coherence adjuster can include using an iteratively optimization method optimizing the one or more parameters associated with the coherence adjuster based on the comparison1504.

According to some embodiments, determining the one or more parameters associated with the radiation source can include using a model between parameters of the radiation source and parameters of the target. In some embodiments, the model can include one or more inverse correction coefficients. In some embodiments, determining the one or more parameters associated with the radiation source and/or using the one or more inverse correction coefficients can include using a machine learning model. In some embodiments, the model can be stored in, for example, storage device1410accessible by processor1404. In some embodiments, determining the one or more parameters associated with the radiation source can include using an iteratively optimization method optimizing the one or more parameters associated with the radiation source based on the comparison1504.

At1530, the determined one or more parameters associated with the coherence adjuster is communicated to the coherence adjuster and/or the determined one or more parameters associated with the radiation source are communicated to the radiation source. For example, processor1404can communicate the determined one or more parameters associated with the coherence adjuster to coherence adjuster1400. Additionally, or alternatively, processor1404can communicate the determined one or more parameters associated with the radiation source to radiation source1414.

Instead of (or in addition to) communicating the determined parameter(s), operation1530can include adjusting or controlling (for example, using processor1404) coherence adjuster1400using the determined one or more parameters associated with the coherence adjuster. Additionally, or alternatively, operation1530can include adjusting or controlling (for example, using processor1404) radiation source1414using the determined one or more parameters associated with radiation source.

In some embodiments, at1528, processor1404determines a value of a parameter of coherence adjuster1400. And at1530, processor1404communicates the determined value of the parameter to coherence adjuster1400. Coherence adjuster1400adjusts the parameter associated with coherence adjuster1400based at least on the determined value of the parameter. In some embodiments, coherence adjuster1400can adjust the parameter associated with coherence adjuster1400using other values in addition to the determined value of the parameter. In some embodiments, adjusting the parameter associated with coherence adjuster1400based at least on the determined value of the parameter can include using a variable dwell time for the received spatially coherent radiation at different locations at an input of the multimode waveguide device of the coherence adjuster. Additionally, or alternatively, adjusting the parameter associated with coherence adjuster1400based at least on the determined value of the parameter can include modulating an intensity of the coherence adjusted beam of radiation as a function of position of a spatially coherent radiation (received from, for example, radiation source1414) at the input of the multimode waveguide device of the coherence adjuster. Additionally, or alternatively, adjusting the parameter associated with coherence adjuster1400based at least on the determined value of the parameter can include modulating an intensity of the coherence adjusted beam of radiation as a function of an angle of incidence of the spatially coherent radiation (received from, for example, radiation source1414) at the input of the multimode waveguide device of the coherence adjuster.

In some embodiments, at1528, processor1404determines a value of a parameter of radiation source1414. And at1530, processor1404communicates the determined value of the parameter to radiation source1414. Radiation source1414adjusts the parameter associated with radiation source1414based at least on the determined value of the parameter. In some embodiments, radiation source1414can adjust the parameter associated with radiation source1414using other values in addition to the determined value of the parameter. In some embodiments, adjusting the parameter associated with radiation source1414based at least on the determined value of the parameter can include adjusting wavelength associated with the radiation beam generated by the radiation source. In some embodiments, adjusting the parameter associated with radiation source1414based at least on the determined value of the parameter can include using a variable dwell time for the spot of the radiation beam generated by the radiation source at different locations at an input of the coherence adjuster. Additionally, or alternatively, adjusting the parameter associated with radiation source1414based at least on the determined value of the parameter can include modulating an intensity of the radiation beam generated by the radiation source as a function of the position of the radiation beam generated by the radiation source at the input of the coherence adjuster.

Although methods1500and1520are discussed as separate methods, the embodiments of this disclosure can include a combination of methods1500and1520or a combination of one or more steps of methods1500and1520. For example, processor1404can control or adjust coherence adjuster1400using measured distribution of the coherence adjusted beam of radiation and the determined parameter(s) of the target. Similarly, processor1404can control or adjust radiation source1414using measured distribution of the coherence adjusted beam of radiation and the determined parameter(s) of the target.

FIG.16Aillustrates an example feedforward (e.g., open loop) method1600for determining parameter(s) for a coherence adjuster and adjusting the coherence adjuster based on the determined parameter(s), according to some embodiments of the disclosure. As a convenience and not a limitation,FIG.16Amay be described with regard to elements ofFIG.14. Method1600may represent the operation of a system (e.g., system1401) implementing operations for determining parameter(s) for a coherence adjuster and adjusting the coherence adjuster based on the determined parameter(s). Method1600may also be performed by computer system2100ofFIG.21. But method1600is not limited to the specific embodiments depicted in those figures, and other systems may be used to perform the method as will be understood by those skilled in the art. It is to be appreciated that not all operations may be needed, and the operations may not be performed in the same order as shown inFIG.16A.

In addition to, or in alternate to, methods1500and1520that can operate based on feedback information provided by detector1402, method1600can be performed by processor1404without the feedback information. In some embodiments, method1600can be performed as a calibration (e.g., open loop) method for calibrating system1401before and/or during operation of system1401.

At1602, one or more parameters associated with the coherence adjuster is determined using a desired distribution of the coherence adjusted beam of radiation and a model between parameters of the coherence adjuster and a distribution of the coherence adjusted beam of radiation. For example, processor1404can determine one or more parameters associated with coherence adjuster1400using a desired distribution of the coherence adjusted beam of radiation (e.g., beam of radiation1428or1429) and a model between parameters of the coherence adjuster and a distribution of the coherence adjusted beam of radiation.

In some embodiments, the model can stored in storage device1410accessible by processor1404. In some embodiments, the model can include one or more inverse correction coefficient.

At1604, the determined one or more parameters associated with the coherence adjuster are communicated to the coherence adjuster. For example, processor1404communicates the determined one or more parameters to coherence adjuster1400. Operation1604can be similar to operation1508ofFIG.15A.

Although method1600is discussed with respect to a model between parameters of the coherence adjuster and a distribution of the coherence adjusted beam of radiation, similar operations can be performed using a model between parameters of the coherence adjuster and parameter(s) of a target (e.g., target1418).

FIG.16Billustrates an example feedforward (e.g., open loop) method1620for determining parameter(s) for a radiation source and adjusting the radiation source based on the determined parameter(s), according to some embodiments of the disclosure. As a convenience and not a limitation,FIG.16Bmay be described with regard to elements ofFIG.14. Method1620may represent the operation of a system (e.g., system1401) implementing operations for determining parameter(s) for a radiation source and adjusting the radiation source based on the determined parameter(s). Method1620may also be performed by computer system2100ofFIG.21. But method1620is not limited to the specific embodiments depicted in those figures, and other systems may be used to perform the method as will be understood by those skilled in the art. It is to be appreciated that not all operations may be needed, and the operations may not be performed in the same order as shown inFIG.16B.

In addition to, or in alternate to, methods1500and1520that can operated based on feedback information provided by detector1402, method1620can be performed by processor1404without the feedback information. In some embodiments, method1620can be performed as a calibration (e.g., open loop) method for calibrating system1401before and/or during operation of system1401.

At1622, one or more parameters associated with the radiation source is determined using a desired distribution of the coherence adjusted beam of radiation and a model between parameters of the radiation source and a distribution of the coherence adjusted beam of radiation. For example, processor1404can determine one or more parameters associated with radiation source1414using a desired distribution of the coherence adjusted beam of radiation (e.g., beam of radiation1428or1429) and a model between parameters of the radiation source and a distribution of the coherence adjusted beam of radiation.

In some embodiments, the model can stored in storage device1410accessible by processor1404. In some embodiments, the model can include one or more inverse correction coefficient.

At1624, the determined one or more parameters associated with the radiation source are communicated to the radiation source. For example, processor1404communicates the determined one or more parameters to radiation source1414. Operation1624can be similar to operation1508ofFIG.15A.

Although method1620is discussed with respect to a model between parameters of the radiation source and a distribution of the coherence adjusted beam of radiation, similar operations can be performed using a model between parameters of the radiation source and parameter(s) of a target (e.g., target14180).

Exemplary Multi-Source Radiation Systems for Coherence Scrambling

Some embodiments of this disclosure are directed to using multi-source radiation systems with the coherence adjusters discussed above. In some embodiments, the multi-source radiation system includes two or more radiation sources (e.g., spatially coherent radiation sources). Each of the two or more radiation sources of the multi-source radiation system can generate coherent radiation. The generated coherent radiations from the radiation sources of the multi-source radiation system can be at least spatially coherent radiations. Additionally, or alternatively, the generated coherent radiations from the radiation sources of the multi-source radiation system can include temporally coherent radiations.

According to some embodiments, the multi-source radiation system can parallelize the generated radiations from the two or more radiation sources and combine the power of the generated radiations to increase the power of the radiation that is input to the coherence adjuster. Therefore, the multi-source radiation system of this disclosure can increase the power of coherence adjusted beam of radiation generated by the coherence adjuster. For example, the multi-source radiation system combines spatially coherent radiation sources and scan the radiation sources simultaneously or substantially simultaneously over a facet of a multimode waveguide device. Doing so can enable the multi-source radiation system to combine the power or the beam of radiations from multiple radiation sources to increase the power of the coherence adjusted beam of radiation at the output of the multimode waveguide device.

Additionally, or alternatively, the multi-source radiation system can include two or more radiation sources with orthogonal polarization states. For example, the multi-source radiation system can include two radiation sources with orthogonal polarization states. The multi-source radiation system combines the radiations from the two radiation sources to a combined radiation to increase the power of the combined radiation.

According to some embodiments, and as discussed in more detail below, the multi-source radiation system can be used with one or more of coherence adjusters500,600,700,800,900,1000,1100,1200, and1400ofFIGS.5-12and14.

FIG.17illustrates a schematic of multi-source radiation system1700, according to some embodiments. Multi-source radiation system1700can include plurality of radiation sources1701, plurality of waveguide devices1703, waveguide combining element1705, and combined waveguide device1707, according to some embodiments.

Plurality of radiation sources1701a-1701n(herein referred to as radiation sources1701) can include coherent radiation sources. For example, one or more of radiation sources1701can include spatially coherent radiation sources. Additionally, or alternatively, one or more of radiation sources1701can include temporally coherent radiation sources. In some examples, one or more of radiation sources1701can include a laser source (for example, but not limited to, a vertical-cavity surface-emitting laser (VCSEL)).

In some embodiments, each radiation source1701(e.g., radiation sources1701a-1701n) can be coupled to waveguide combining element1705using a corresponding waveguide device1703(e.g., waveguide devices1703a-1703n). In some examples, waveguide device1703can include a single-mode fiber. However, the embodiments of this disclosure are not limited to this example, and waveguide device1703can include other devices/fibers. Each of waveguide devices1703can include an input that receives a beam of radiation (e.g., a coherent beam of radiation) from its corresponding radiation source. Each of waveguide devices1703can also include an output from which a beam of radiation (e.g., an adjusted coherent beam of radiation) exits.

Waveguide combining element1705can receive the coherent beams of radiation from radiation sources1701through corresponding waveguide devices1703. Waveguide combining element1705can include an input that receives the beams of radiation (e.g., the adjusted coherent beams of radiation) from waveguide devices1703. Waveguide combining element1705can combine the coherent beams of radiation from radiation sources1701and output the combined coherent beams of radiation to combined waveguide device1707. Waveguide combining element1705can include an output from which the combined coherent beams of radiation exit.

Combined waveguide device1707includes an input that receives the combined coherent beams of radiation from waveguide combining element1705. According to some embodiments, waveguide combining element1705can have different structures resulting in different multi-source fiber facets1709-1713at the output of combined waveguide device1707. Although some exemplary multi-source fiber facets1709-1713are provided inFIG.17, the embodiments of this disclosure are not limited to these examples and the multi-source fiber facets can include other arrangements.

In some embodiments, waveguide combining element1705can include a bundled single-mode fiber with thinned or adiabatically tapered cladding. Additionally, or alternatively, waveguide combining element1705can include bundled single-mode fibers fused into a multimode fiber. Additionally, or alternatively, waveguide combining element1705can include a Photonic Integrated Circuit (PIC) configured to combine single-mode waveguide devices (e.g., fibers) into a multimode waveguide device (e.g., a fiber). PIC can also be configured to combine radiation into a multi-core waveguide device. However, the embodiments of this disclosure are not limited to these examples and waveguide combining element1705can include other devices configured to combine a plurality of radiation source into a multi-source fiber facet.

According to some embodiments, the output of multi-source radiation system1700(e.g., the multi-source fiber facet) can include different arrangements. In some embodiments, the different arrangements for the output of multi-source radiation system1700can depend on, for example, waveguide combining element1705. The output of multi-source radiation system1700combines the power of radiation sources1701to provide a combined power to the coherence adjusters discussed above. According to some embodiments, the output of multi-source radiation system1700can include a bundle of single-mode waveguide devices (e.g., fibers). For example, the output of multi-source radiation system1700can include a fiber bundle with coarsely or densely spaced cores. Single-mode fiber bundle1709illustrates one example of the fiber bundle with coarsely or densely spaced cores. In this example, four radiation sources1701and/or four waveguide devices1703are combined into single-mode fiber bundle1709(e.g., a bundle of 4 fibers). In a non-limiting example, the centers of the waveguide devices (e.g., fibers) in single-mode fiber bundle1709can be separated from each other by approximately 100 μm. However, the embodiments of this disclosure can include single-mode fiber bundle1709generated based on the combination of any number of radiations sources and/or waveguide devices. Also, the embodiments of this disclosure can include single-mode fiber bundle1709having different measurements between the centers of the waveguide devices in single-mode fiber bundle1709.

In some embodiments, the output of multi-source radiation system1700can include multi-core fiber (MCF)1711. In this example, three radiation sources1701and/or three waveguide devices1703are combined into MCF1711(e.g., 3-cores). In a non-limiting example, the centers of the waveguide devices in MCF1711can be separated from each other by approximately 10 μm. However, the embodiments of this disclosure can include MCF1711generated based on the combination of any number of radiations sources and/or waveguide devices. Additionally, the embodiments of this disclosure can include MCF1711having different measurements between the centers of the waveguide devices in MCF1711.

In some embodiments, the output of multi-source radiation system1700can include small core multimode fiber1713, which combines waveguide devices1703(e.g., a plurality of single-mode fibers) into a multimode waveguide device.

As discussed above, multi-source radiation system1700can be used at least with one or more of coherence adjusters500,600,700,800,900,1000,1100,1200, and1400ofFIGS.5-12and14.

In one embodiment, multi-source radiation system1700can be used as radiation source514and waveguide device502ofFIG.5. For example, radiation source514ofFIG.5can include radiation sources1701, waveguide devices1703, and waveguide combining element1705ofFIG.17. And waveguide device502ofFIG.5can include combined waveguide device1707ofFIG.17. In other words, the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be input to input facet510of multimode waveguide device504ofFIG.5. In this example, beam of radiation516ofFIG.5can include one or more beams of radiation exiting multi-source radiation system1700.

According to some embodiments, actuator506and/or restoring device508ofFIG.5can be applied to combined waveguide device1707. Therefore, the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be scanned over input facet510of multimode waveguide device504ofFIG.5. For example, actuator506and/or restoring device508ofFIG.5can be configured to change impingement characteristic of the one or more beams of radiation exiting multi-source radiation system1700at input510of multimode waveguide device504.

In some embodiments, actuator506and/or restoring device508can be configured to change impingement characteristic of each one of the one or more beams of radiation exiting multi-source radiation system1700at the input of multimode waveguide device1204. For example, actuator506and/or restoring device508can be configured to change a impingement characteristic of a first one of the one or more beams of radiation exiting multi-source radiation system1700at input510of multimode waveguide device504and can be configured to change the impingement characteristic of a second one of the one or more beams of radiation exiting multi-source radiation system1700at input510of multimode waveguide device504.

In one embodiment, multi-source radiation system1700can be used as a radiation source (not shown inFIG.7) and waveguide device702ofFIG.7. For example, waveguide device702ofFIG.7can include combined waveguide device1707ofFIG.17. In other words, the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be input to input facet710of multimode waveguide device704ofFIG.7. In this example, beam of radiation716ofFIG.7can include one or more beams of radiation exiting multi-source radiation system1700. According to some embodiments, actuator706and/or restoring device708ofFIG.7can be applied to combined waveguide device1707. Therefore, the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be scanned over input facet710of multimode waveguide device704ofFIG.7.

For example, actuator706and/or restoring device708ofFIG.7can be configured to change impingement characteristic of the one or more beams of radiation exiting multi-source radiation system1700at input710of multimode waveguide device704. In some embodiments, actuator706and/or restoring device708can be configured to change impingement characteristic of each one of the one or more beams of radiation exiting multi-source radiation system1700at the input of multimode waveguide device1204. For example, actuator706and/or restoring device708can be configured to change a first impingement characteristic of a first one of the one or more beams of radiation exiting multi-source radiation system1700at input710of multimode waveguide device704. Actuator706and/or restoring device708can also be configured to change a second impingement characteristic of a second one of the one or more beams of radiation exiting multi-source radiation system1700at input710of multimode waveguide device704.

Similarly, multi-source radiation system1700can be used as a radiation source (not shown inFIG.8) and waveguide device802ofFIG.8. For example, waveguide device802ofFIG.8can include combined waveguide device1707ofFIG.17. In some embodiments,834can be the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713). In this example, beam of radiation816ofFIG.8can include one or more beams of radiation exiting multi-source radiation system1700. According to some embodiments, actuator806ofFIG.8can be applied to combined waveguide device1707.

Multi-source radiation system1700can be used as a radiation source (not shown inFIG.9) and waveguide device902ofFIG.9. For example, waveguide device902ofFIG.9can include combined waveguide device1707ofFIG.17. In this example, actuator906ofFIG.9can be applied to combined waveguide device1707. The output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be scanned over input facet910of multimode waveguide device904ofFIG.9.

In one embodiment, multi-source radiation system1700can be used as radiation source1014and waveguide device1002ofFIG.10. For example, radiation source1014ofFIG.10can include radiation sources1701, waveguide devices1703, and waveguide combining element1705ofFIG.17. And waveguide device1002ofFIG.10can include combined waveguide device1707ofFIG.17. In other words, the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be input to input facet1010of multimode waveguide device1004ofFIG.10. In this example, beam of radiation1012ofFIG.10can include one or more beams of radiation exiting multi-source radiation system1700. According to some embodiments, the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be scanned over input facet1010of multimode waveguide device1004ofFIG.10. In this example, multiple radiation source (in multi-source radiation system1700) can be scanned simultaneously or substantially simultaneously over the input facet of the multimode waveguide device.

For example, the impingement characteristic of the one or more beams of radiation exiting multi-source radiation system1700can be changed at input1010of multimode waveguide device1004ofFIG.10. In some embodiments, impingement characteristic of each one of the one or more beams of radiation exiting multi-source radiation system1700can be changed at input1010of multimode waveguide device1004. For example, a first impingement characteristic of a first one of the one or more beams of radiation exiting multi-source radiation system1700can be changed at input1010of multimode waveguide device1004. And a second impingement characteristic of a second one of the one or more beams of radiation exiting multi-source radiation system1700can be changed at input1010of multimode waveguide device1004.

In one embodiment, multi-source radiation system1700can be used as radiation source1114and waveguide device1102ofFIG.11. For example, radiation source1114ofFIG.11can include radiation sources1701, waveguide devices1703, and waveguide combining element1705ofFIG.17. And waveguide device1102ofFIG.11can include combined waveguide device1707ofFIG.17. In other words, the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be input to input facet1110of multimode waveguide device1104ofFIG.11. In this example, beam of radiation1112ofFIG.11can include one or more beams of radiation exiting multi-source radiation system1700. According to some embodiments, the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be scanned over a far field plane of input facet1110of multimode waveguide device1104ofFIG.11. In this example, multiple radiation source (in multi-source radiation system1700) can be scanned simultaneously or substantially simultaneously over the far-field plane of the input facet of the multimode waveguide device.

For example, the impingement characteristic of the one or more beams of radiation exiting multi-source radiation system1700can be changed at the far field plane of input1110of multimode waveguide device1104ofFIG.11. In some embodiments, impingement characteristic of each one of the one or more beams of radiation exiting multi-source radiation system1700can be changed at input1110of multimode waveguide device1104. For example, a first impingement characteristic of a first one of the one or more beams of radiation exiting multi-source radiation system1700can be changed at the far field plane of input1110of multimode waveguide device1104. Additionally, a second impingement characteristic of a second one of the one or more beams of radiation exiting multi-source radiation system1700can be changed at the far field plane of input1110of multimode waveguide device1104.

In one embodiment, multi-source radiation system1700can be used as radiation source1214and waveguide device1202ofFIG.12. For example, radiation source1214ofFIG.12can include radiation sources1701, waveguide devices1703, and waveguide combining element1705ofFIG.17. And waveguide device1202ofFIG.12can include combined waveguide device1707ofFIG.17. In other words, the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) can be input to input facet of multimode waveguide device1204ofFIG.12. Diffuser device1246ofFIG.12can be disposed downstream of multi-source radiation system1700and upstream of multimode waveguide device1204ofFIG.12.

According to some embodiments, diffuser device1246ofFIG.12can be configured to change an impingement characteristic associated with the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713) at the input facet of multimode waveguide device1204ofFIG.12. For example, diffuser device1246ofFIG.12can be configured to change an impingement characteristic of the one or more beams of radiation exiting multi-source radiation system1700at the input of multimode waveguide device1246.

In some embodiments, diffuser device1246can be configured to change impingement characteristic of each one of the one or more beams of radiation exiting multi-source radiation system1700at the input of multimode waveguide device1204. For example, diffuser device1246can be configured to change a first impingement characteristic of a first one of the one or more beams of radiation exiting multi-source radiation system1700at the input of multimode waveguide device1204. Additionally, diffuser device1246can be configured to change a second impingement characteristic of a second one of the one or more beams of radiation exiting multi-source radiation system1700at the input of multimode waveguide device1204.

In one embodiment, multi-source radiation system1700can be used as radiation source1414ofFIG.14. In other words, the output of radiation source1414ofFIG.14is can be the same as the output of multi-source radiation system1700(e.g., single-mode fiber bundle1709, MCF1711, and/or small core multimode fiber1713).

FIGS.18A-18Cshow example schematics of scan pattern of multi-source fiber facets of multi-source radiation system1700, according to some embodiments. For example,FIG.18Aillustrates scan pattern1820afor single-mode fiber bundle1709ofFIG.17, according to some embodiments.FIG.18Billustrates scan pattern1820bfor MCF1711ofFIG.17, according to some embodiments.FIG.18Cillustrates scan pattern1820cfor small core multimode fiber1713ofFIG.17, according to some embodiments.

Scan patterns1820a-1820ccan include one or more of scan patterns520,720,920,1020, and1120(e.g., raster, spiral scan pattern, Lissajous, or the like) ofFIGS.5,7, and9-11.

According to some embodiments, the scan patterns ofFIGS.18A-18Ccan depend on the multi-source fiber facets of multi-source radiation system1700. For example, scan pattern1820aofFIG.18Acan be used for a fiber bundle with coarsely or densely spaced cores as illustrated in single-mode fiber bundle1709ofFIG.17.FIG.18Aillustrates a non-limiting example including four fibers associated with four radiation sources. In this example, each fiber (e.g., each corresponding beam of radiation) can be scanned over a part of the input facet of the multimode waveguide device of the coherence adjuster of this disclosure. For example, scan pattern1820acan include four scan pattern1820aa,1820ab,1820ac, and1820ad, each corresponding to one of the fibers (e.g., corresponding beams of radiation).

In some embodiments, by scanning each fiber (e.g., each corresponding beam of radiation) over a part of the input facet of the multimode waveguide device of the coherence adjuster, the whole input facet of the multimode waveguide device can be covered. Alternatively, scanning each fiber over a part of the input facet of the multimode waveguide device of the coherence adjuster can result scanning part of (e.g., not the whole of) the input facet of the multimode waveguide device. In some embodiments, the fibers (e.g., their corresponding beams of radiation) can be scanned simultaneously or substantially simultaneously.

According to some embodiments, scan pattern1820bofFIG.18Bcan be used for a multi-core fiber (e.g., densely spaced fiber/radiation sources) as illustrated in MCF1711ofFIG.17.FIG.18Billustrates a non-limiting example including three fibers associated with three radiation sources. In this example, all the fibers (e.g., all the corresponding beams of radiation) can be scanned together over the input facet of the multimode waveguide device of the coherence adjuster of this disclosure. For example, scan pattern1820bcan include the scan pattern for scanning all the fibers together over the input facet of the multimode waveguide device of the coherence adjuster. In some embodiments, all the fibers can be scanned together over a part of the input facet of the multimode waveguide device of the coherence adjuster. In some embodiments, a first subset of the fibers can be scanned together over the input facet of the multimode waveguide device of the coherence adjuster and then other subset(s) of the fibers can be scanned.

In a non-limiting example, a Photonic Integrated Circuit (PIC) can be used to achieve one or more of multi-source fiber facets1709-1713. However, the embodiments of this disclosure are not limited to this example and other techniques can be used for achieving one or more of multi-source fiber facets1709-1713.FIG.18Cillustrates a non-limiting example including multiple modes (e.g., N modes, where N is greater than or equal to a number of fibers/radiation sources). In some embodiments, scan pattern1820cis a scan pattern for a small specked pattern. In the example ofFIG.18C, speckle pattern from a small core multimode fiber can be scanned over the input facet of the multimode waveguide device of the coherence adjuster of this disclosure. For example, scan pattern1820ccan include the scan pattern for scanning the speckle pattern from the small core multimode fiber over the input facet of the multimode waveguide device of the coherence adjuster. In some embodiments, the speckle pattern from the small core multimode fiber can be scanned over a part of the input facet of the multimode waveguide device of the coherence adjuster.

FIGS.19A and19Billustrate an exemplary system1900for changing a coarsely spaced source array to a densely spaced source array, according to some embodiments. As discussed above, according to some embodiments, the output of multi-source radiation system1700can include MCF1711and/or small core multimode fiber1713. In some embodiments, MCF-like source can be generated based on a fiber bundle with coarsely spaced cores (e.g., a fiber bundle with coarsely spaced cores used in single-mode fiber bundle1709). In the MCF-like source, the images of coarsely spaced cores from fiber bundle will be spaced denser.FIGS.19A and19Billustrate one exemplary system that can be used to generate MCF1711based on the fiber bundle with coarsely spaced cores.

As illustrated inFIGS.19A and19B, source array1901can include a coarsely spaced array of radiation sources (and/or fibers/cores). As a non-limiting example, the coarsely spaced array of radiation sources of source array1901can be spaced about 100 μm, which then can become densely spaced about 20 μm. However, the embodiments of this disclosure are not limited to this example and the coarsely spaced array of radiation sources of source array1901can be spaced using different measurements and can become densely spaced at different measurement. In some examples, source array1901can include a plurality of radiation sources1701ofFIG.17that are arranged coarsely spaced with respect to each other. For example, source array1901can include a plurality of radiation sources with small spot size and large spacing. Additionally, or alternatively, source array1901can include a plurality of waveguide devices1703ofFIG.17(e.g., the outputs of waveguide devices1703), according to some embodiments.

System1900includes optical elements1903(e.g., microlens arrays) and optical elements1905(e.g., free-space optics), according to some embodiments. Optical elements1903acan be configured to collimate the beams of radiation from their corresponding source in radiation source1901. Optical elements1903bcan receive the collimated beams of radiation and generate intermediate source image array1907. In some embodiments, intermediate source image array1907can include sources images with large spot size and large spacing. For example, source array1901and intermediate source image array1907can have similar (e.g., the same or substantially the same) spacing. However, each source image on intermediate source image array1907can have larger spot size than its corresponding source on source array1901.

According to some embodiments, optical elements1905aand1905b(collectively referred to as optical elements1905) are configured to convert intermediate source image array1907to source array1909. Each source on source array1909can have similar (e.g., the same or substantially the same) spot size than its corresponding source on source array1901. However, source array1909has smaller spacing between its sources compare to source array1901. Therefore, system1900can be configured to change a coarsely spaced source array (e.g., source array1901) to a densely spaced source array (e.g., source array1909).

In some embodiments, the NA remains the same or substantially the same in system1900although a coarsely spaced source array is changed to a densely spaced source array. In other words, NA associated with optical elements1903is the same or substantially the same as the NA associated with optical elements1905. For example, the width of the radiation between optical elements1903aand1930b(e.g., width1904) is the same or substantially the same as the width of the radiation between optical elements1905aand1905b(e.g., width1906). In some examples, width1904is measured at pupil plane1920of optical elements1903aand width1906is measured at pupil plane1930of optical element1905a.

It is noted that althoughFIGS.19A and19Bare discussed with respect to optical elements1903and1905, other optical elements and/or arrangements can be used to a coarsely spaced source array (e.g., source array1901) to a densely spaced source array (e.g., source array1909). For example, reflective optical elements can be used in addition to, or in place of, optical elements1903and/or1905.

Additionally, or alternatively, system1900ofFIG.19Acan be used as waveguide combining element1705ofFIG.17to, for example, couple a plurality of single-mode sources (e.g., single-mode waveguide devices1703) into a multimode multi-core fiber (MCF—e.g., MCF1711).

FIG.20shows a schematic of a multi-source radiation system2000, according to some embodiments. Multi-source radiation system2000can be configured to generate coherent radiation (e.g., spatially coherent radiation). Multi-source radiation system2000can include a first radiation source2001aconfigured to generate a first radiation with a first polarization state. Multi-source radiation system2000can include a second radiation source2001bconfigured to generate a second radiation with a second polarization state. According to some embodiments, the second polarization state is orthogonal to the first polarization state. Multi-source radiation system2000can also include a combining element2003configured to generate the coherent radiation by combining the first radiation and the second radiation.

According to some embodiments, combining element2003can include a polarizing beam splitter (PBS). However, the embodiments of this disclosure are not limited to this example, and combining element2003can include other optical elements configured to combine two radiations from two radiation sources. For example, combining element2003can be configured to combine two radiations with orthogonal polarization states. Combining element2003can receive a first radiation2006awith a first polarization state (e.g., a vertical polarization state or a s polarization state) from radiation source2001a. Combining element2003can receive the first radiation2006ausing optional waveguide device2005aand/or optional collimator2007a. However, the embodiments of this disclosure are not limited to optional collimator2007aand/or optional waveguide device2005a, and other optical elements can be used to carry radiation2006ato combining element2003. First radiation2006acan include a coherent radiation (e.g., a spatially coherent radiation).

Combining element2003can also receive a second radiation2006bwith a second polarization state (e.g., a horizontal polarization state or a p polarization state) from radiation source2001b. According to some embodiments, the second polarization state is orthogonal to the first polarization state. Combining element2003can receive the second radiation2006busing optional waveguide device2005band/or optional collimator2007b. However, the embodiments of this disclosure are not limited to optional collimator2007band/or optional waveguide device2005b, and other optical elements can be used to carry radiation2006bto combining element2003. According to some embodiments, the second polarization state is orthogonal to the first polarization state. Second radiation2006bcan include a coherent radiation (e.g., a spatially coherent radiation).

Combining element2003can combine first radiation2006aand second radiation2006bto generate coherent radiation2008(e.g., spatially coherent radiation). In some examples, coherent radiation2008can have the first and second polarization sates of first and second radiations2005aand2005b. Coherent radiation2008is output from multi-source radiation system2000to the coherent adjusters of this disclosure. Coherent radiation2008can have a radiation power as the combination of the radiation power of radiation2006aand the radiation power of radiation2006b. For example, coherent radiation2008can have a radiation twice the radiation power of radiation2006a(or radiation2006b). In some embodiments, optional collimator2009aand/or optional waveguide device2011can be used to connect multi-source radiation system2000with the coherent adjusters of this disclosure. However, the embodiments of this disclosure are not limited to optional collimator2009aand/or optional waveguide device2011and other optical elements can be used to carry coherent radiation2008to the coherent adjusters of this disclosure.

Multi-source radiation system2000can be used with one or more of coherence adjusters500,600,700,800,900,1000,1100,1200, and1400ofFIGS.5-12and14.

In one embodiment, multi-source radiation system2000can be used as radiation source514(and/or radiation source514and waveguide device502) ofFIG.5. For example, coherent radiation2008can include radiation512or radiation516ofFIG.5. According to some embodiments, if coherent radiation2008includes radiation516ofFIG.5, actuator506and/or restoring device508ofFIG.5can be applied to waveguide device2011. Coherent radiation2008can be scanned over input facet510of multimode waveguide device504ofFIG.5. For example, actuator506and/or restoring device508ofFIG.5can be configured to change impingement characteristic of coherent radiation2008at input510of multimode waveguide device504.

In one embodiment, multi-source radiation system2000can be used as a radiation source (not shown inFIG.7) with (or instead of) waveguide device702ofFIG.7. For example, coherent radiation2008can include radiation to waveguide device702or radiation716ofFIG.7. According to some embodiments, if coherent radiation2008includes radiation716ofFIG.7, actuator706and/or restoring device708ofFIG.7can be applied to waveguide device2011. Coherent radiation2008can be scanned over input facet710of multimode waveguide device704ofFIG.7. For example, actuator706and/or restoring device708can be configured to change impingement characteristic of coherent radiation2008at input710of multimode waveguide device704. Similarly, multi-source radiation system2000can be used with waveguide device602ofFIG.6.

Similarly, multi-source radiation system2000can be used as a radiation source with (or instead of) waveguide device802ofFIG.8. For example, coherent radiation2008can include radiation to waveguide device802or radiation816ofFIG.8. According to some embodiments, if coherent radiation2008includes radiation816ofFIG.8, actuator806ofFIG.8can be applied to waveguide device2011. Multi-source radiation system2000can be used as a radiation source with (or instead of) waveguide device902ofFIG.9. In some embodiments, actuator906ofFIG.9can be applied to waveguide device2011. Coherent radiation2008can be scanned over input facet910of multimode waveguide device904ofFIG.9.

In one embodiment, multi-source radiation system2000can be used as radiation source1014(and/or radiation source1014and waveguide device1002) ofFIG.10. For example, coherent radiation2008can include radiation1012ofFIG.10. According to some embodiments, coherent radiation2008can be scanned over input facet1010of multimode waveguide device1004ofFIG.10. For example, the impingement characteristic of coherent radiation2008can be changed at input1010of multimode waveguide device1004ofFIG.10.

In one embodiment, multi-source radiation system2000can be used as radiation source1114(and/or radiation source1114and waveguide device1102) ofFIG.11. For example, coherent radiation2008can include radiation1112ofFIG.10. According to some embodiments, coherent radiation2008can be scanned over a far field plane of input facet1110of multimode waveguide device1104ofFIG.11. For example, the impingement characteristic of coherent radiation2008can be changed at the far field plane of input1110of multimode waveguide device1104.

In one embodiment, multi-source radiation system2000can be used as radiation source1214(and/or radiation source1214and waveguide device1202) ofFIG.12. For example, coherent radiation2008can include radiation1212ofFIG.12. In another example, coherent radiation2008can include radiation out of waveguide1202ofFIG.12. Coherent radiation2008can be input to input facet of multimode waveguide device1204ofFIG.12. Diffuser device1246ofFIG.12can be disposed downstream of multi-source radiation system2000and upstream of multimode waveguide device1204. According to some embodiments, diffuser device1246ofFIG.12can be configured to change an impingement characteristic associated with coherent radiation2008at the input facet of multimode waveguide device1204. For example, diffuser device1246ofFIG.12can be configured to change an impingement characteristic of coherent radiation2008at the input of multimode waveguide device1246.

In one embodiment, multi-source radiation system2000can be used as radiation source1414ofFIG.14. In other words, the output of radiation source1414ofFIG.14is can be the same as the output of multi-source radiation system2000(e.g., coherent radiation1412can be the same as coherent radiation2008.

Various embodiments may be implemented, for example, using one or more well-known computer systems, such as computer system2100shown inFIG.21. One or more computer systems2100may be used, for example, to implement any aspect of the disclosure discussed herein, as well as combinations and sub-combinations thereof.

Computer system2100may include one or more processors (also called central processing units, or CPUs), such as a processor2104. Processor2104may be connected to a communication infrastructure or bus2106.

Computer system2100may also include customer input/output device(s)2103, such as monitors, keyboards, pointing devices, etc., which may communicate with communication infrastructure2106through customer input/output interface(s)2102.

Computer system2100may also include a main or primary memory2108, such as random access memory (RAM). Main memory2108may include one or more levels of cache. Main memory2108may have stored therein control logic (i.e., computer software) and/or data.

Computer system2100may also include one or more secondary storage devices or memory2110. Secondary memory2110may include, for example, a hard disk drive2112and/or a removable storage device or drive2114. Removable storage drive2114may be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, tape backup device, and/or any other storage device/drive.

Removable storage drive2114may interact with a removable storage unit2118. Removable storage unit2118may include a computer usable or readable storage device having stored thereon computer software (control logic) and/or data. Removable storage unit2118may be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and/any other computer data storage device. Removable storage drive2114may read from and/or write to removable storage unit2118.

Secondary memory2110may include other means, devices, components, instrumentalities or other approaches for allowing computer programs and/or other instructions and/or data to be accessed by computer system2100. Such means, devices, components, instrumentalities or other approaches may include, for example, a removable storage unit2122and an interface2120. Examples of the removable storage unit2122and the interface2120may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and/or any other removable storage unit and associated interface.

Computer system2100may further include a communication or network interface2124. Communication interface2124may enable computer system2100to communicate and interact with any combination of external devices, external networks, external entities, etc. (individually and collectively referenced by reference number2128). For example, communication interface2124may allow computer system2100to communicate with external or remote devices2128over communications path2126, which may be wired and/or wireless (or a combination thereof), and which may include any combination of LANs, WANs, the Internet, etc. Control logic and/or data may be transmitted to and from computer system2100via communication path2126.

In some embodiments, a tangible, non-transitory apparatus or article of manufacture comprising a tangible, non-transitory computer useable or readable medium having control logic (software) stored thereon may also be referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system2100, main memory2108, secondary memory2110, and removable storage units2118and2122, as well as tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system2100), may cause such data processing devices to operate as described herein.

The embodiments may further be described using the following clauses:1. A metrology system comprising:a radiation source configured to generate spatially coherent radiation;a coherence adjuster comprising:a waveguide device comprising:an input configured to receive the spatially coherent radiation; andan output;a multimode waveguide device comprising:an input configured to receive radiation from the waveguide device; andan output configured to output a coherence adjusted beam of radiation for irradiating a target; andan actuator coupled to the waveguide device and configured to actuate the waveguide device so as to change an impingement characteristic of the received radiation at the input of the multimode waveguide device, wherein an interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic;a detector configured to receive radiation scattered by the target based on the irradiating and to generate a measurement signal based on the received radiation at the detector; anda processor configured to analyze the measurement signal to determine a characteristic of the target.2. The metrology system of clause 1, wherein a homogeneity of the coherence adjusted beam, over an integrated time frame, is increased based on an adjustment of the interference pattern in response to the change of the impingement characteristic.3. A coherence adjuster comprising:a waveguide device comprising:an input configured to receive spatially coherent radiation; andan output;a multimode waveguide device comprising:an input configured to receive radiation from the waveguide device; andan output configured to output a coherence adjusted beam of radiation; andan actuator coupled to the waveguide device and configured to actuate the waveguide device so as to change an impingement characteristic of the received radiation at the input of the multimode waveguide device, wherein an interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic.4. The coherence adjuster of clause 3, wherein an apparent coherence of the coherence adjusted beam, over an integrated time frame, is reduced based on an adjustment of the interference pattern in response to the change of the impingement characteristic.5. The coherence adjuster of clause 3, wherein the change of the impingement characteristic comprises a change of etendue of the received radiation at the input of the multimode waveguide device.6. The coherence adjuster of clause 3, further comprising one or more lenses configured to focus radiation from the waveguide device at the input of the multimode waveguide device.7. The coherence adjuster of clause 6, wherein the change of the impingement characteristic comprises a change of position of a focus spot of radiation at the input of the multimode waveguide device.8. The coherence adjuster of clause 3, further comprising one or more lenses configured to focus radiation from the waveguide device at a conjugate plane of the input of the multimode waveguide device.9. The coherence adjuster of clause 8, wherein the change of the impingement characteristic comprises a change of position of a focus spot of radiation at the conjugate plane of the input of the multimode waveguide device.10. The coherence adjuster of clause 3, wherein:the actuator comprises one or more piezo devices; andthe actuating comprises deflecting and/or translating the waveguide device using the one or more piezo devices.11. The coherence adjuster of clause 3, wherein the waveguide device and the actuator are configured to modularly detach from the multimode waveguide device.12. The coherence adjuster of clause 3, the multimode waveguide device comprises a multimode fiber.13. The coherence adjuster of clause 3, wherein the waveguide device comprises a single-mode fiber.14. The coherence adjuster of clause 3, further comprising an oil or a gel disposed on the multimode waveguide device, wherein the waveguide device is in contact with the oil or gel.15. The coherence adjuster of clause 3, further comprising:a detector configured to generate a detection signal based on received radiation; anda beam splitter configured to direct a portion radiation from the waveguide device to the detector, wherein the coherence adjuster is configured to determine the impingement characteristic based on the detection signal.16. A coherence adjuster comprising:a multimode waveguide device comprising:an input configured to receive spatially coherent radiation; andan output configured to output a coherence adjusted beam of radiation; andan adjusting device coupled to a portion of the coherence adjuster and configured to adjust the portion so as to change an impingement characteristic of the received radiation at the input of the multimode waveguide device, whereinan interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic,the impingement characteristic comprises a distribution of incidence angles, andthe coherence adjuster is configured to adjust a beam diameter of the coherence adjusted beam based on a change of the distribution of incidence angles.17. The coherence adjuster of clause 16, further comprising a reflective element configured to direct the spatially coherent radiation to the multimode waveguide device, whereinthe adjusting device comprises an actuator,the reflective element and actuator are arranged as a galvo mirror, andthe reflective element is the adjusted portion.18. The coherence adjuster of clause 16, further comprising a liquid crystal device configured to direct the spatially coherent radiation to the multimode waveguide device, whereinthe adjusting device and the liquid crystal device are arranged as a liquid crystal spatial light modulator, andthe liquid crystal device is the adjusted portion.19. The coherence adjuster of clause 16, further comprising reflectors configured to direct the spatially coherent radiation to the multimode waveguide device, whereinthe adjusting device comprises actuators,the actuators and the reflectors are arranged as a digital micromirror device, andthe reflectors are the adjusted portion.20. The coherence adjuster of clause 16, further comprising a waveguide device disposed upstream of the multimode waveguide device, wherein the actuated portion is the waveguide device and the waveguide device comprises:an input configured to receive the spatially coherent radiation; andan output configured to output the spatially coherent radiation before being received at the multimode waveguide device.21. A coherence adjuster comprising:a multimode waveguide device comprising:an input configured to receive spatially coherent radiation; andan output configured to output a coherence adjusted beam of radiation; anda diffuser device disposed upstream of the multimode waveguide device and configured to change an impingement characteristic of the received radiation at the input of the multimode waveguide device, whereinan interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic,the impingement characteristic comprises a distribution of angles of incidence, andthe diffuser device is further configured to adjust a beam diameter of the coherence adjusted beam based on a change of the distribution of incidence angles.22. The coherence adjuster of clause 21, whereinthe diffuser device comprises first and second selectable diffuser elements corresponding to first and second different etendues of the radiation received at the input of the multimode waveguide device; andthe system is further configured to select the beam diameter based on a selection from the first and second selectable diffuser structures.23. The coherence adjuster of clause 21, wherein the diffuser devices is further configured to be rotated, translated, and/or vibrated to change the impingement characteristic.24. The coherence adjuster of clause 21, wherein:the coherent radiation comprises a non-zero wavelength bandwidth;the multimode waveguide device is configured to change relative modes of radiation having different wavelengths; andthe adjusting of the interference pattern is further based on the change of the relative modes.25. The coherence adjuster of clause 21, wherein the multimode waveguide device has a length greater than approximately 2 meters.26. A coherence adjuster comprising:a multimode waveguide device comprising:an input configured to receive spatially coherent radiation; andan output configured to output a coherence adjusted beam of radiation;an adjusting device coupled to a portion of the coherence adjuster and configured to adjust the portion so as to change an impingement characteristic of the received radiation at the input of the multimode waveguide device, whereinan interference pattern of the coherence adjusted beam is adjusted based on the change of the impingement characteristic, andthe impingement characteristic comprises a distribution of incidence angles; andan adjustable beam expander configured to adjust a beam diameter of the coherence adjusted beam.27. A metrology system, comprising:a radiation source configured to generate spatially coherent radiation;a coherence adjuster comprising:a multimode waveguide device comprising:an input configured to receive the spatially coherent radiation; andan output configured to output a coherence adjusted beam of radiation;a detector configured to measure a distribution of the coherence adjusted beam of radiation; anda processor configured to:compare the measured distribution with a desired distribution;determine a value for a parameter associated with the coherence adjuster based on the comparison; andcommunicate the determined value of the parameter associated with the coherence adjuster to the coherence adjuster,wherein the coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.28. The metrology system of clause 27, wherein the detector comprises a field camera configured to measure a near field distribution of the coherence adjusted beam of radiation.29. The metrology system of clause 27, wherein the detector comprises a pupil camera configured to measure a far field distribution of the coherence adjusted beam of radiation.30. The metrology system of clause 27, wherein the detector comprises a pupil camera configured to measure a far field distribution of the coherence adjusted beam of radiation and a field camera configured to measure a near field distribution of the coherence adjusted beam of radiation.31. The metrology system of clause 27, wherein:the detector is further configured to receive radiation scattered by the target based on the irradiating and to generate a measurement signal based on the received radiation at the detector, andthe processor is further configured to:determine a parameter associated with the target based on the measurement signal;compare the determined parameter with a desired parameter associated with the target; anddetermine the value for the parameter associated with the coherence adjuster or a value for a parameter associated with the radiation source based on the comparing the measured distribution with the desired distribution and the comparing the determined parameter with the desired parameter.32. The metrology system of clause 27, wherein to determine the value of the parameter associated with the coherence adjuster, the processor is further configured to use a model between parameters of the coherence adjuster and a distribution of the coherence adjusted beam of radiation.33. The metrology system of clause 32, wherein the model comprises one or more inverse correction coefficients.34. The metrology system of clause 32, wherein to determine the one or more parameters associated with the coherence adjuster, the processor is further configured to use a machine learning model.35. The metrology system of clause 27, wherein:the processor is further configured to:determine a value for a parameter associated with the radiation source based on the comparison; andcommunicate the determined value for the parameter associated with the radiation source to the radiation source, andthe radiation source is configured to adjust the parameter associated with the radiation source based on the determined value.36. The metrology system of clause 35, wherein to determine the value of the parameter associated with the radiation source, the processor is further configured to use a model between parameters of the radiation source and a distribution of the coherence adjusted beam of radiation.37. The metrology system of clause 36, wherein the model comprises one or more inverse correction coefficients.38. The metrology system of clause 36, wherein to determine the value of the parameter associated with the radiation source, the processor is further configured to use a machine learning model.39. The metrology system of clause 27, wherein to adjust the parameter associated with the coherence adjuster based on the determined value, the coherence adjuster is configured to use a variable dwell time for the received spatially coherent radiation at different locations at the input of the multimode waveguide device.40. The metrology system of clause 27, wherein to adjust the parameter associated with the coherence adjuster based on the determined value, the coherence adjuster is configured to modulate an intensity of the coherence adjusted beam of radiation as a function of position of the received spatially coherent radiation at the input of the multimode waveguide device.41. The metrology system of clause 27, wherein to adjust the parameter associated with the coherence adjuster based on the determined value, the coherence adjuster is configured to modulate an intensity of the coherence adjusted beam of radiation as a function of an angle of incidence of the received spatially coherent radiation at the input of the multimode waveguide device.42. The metrology system of clause 27, wherein the processor is further configured to determine the value of the parameter associated with the coherence adjuster using the desired distribution of the coherence adjusted beam of radiation and a model between parameters of the coherence adjuster and a distribution of the coherence adjusted beam of radiation.43. The metrology system of clause 42, wherein the model comprises one or more inverse correction coefficients.44. The metrology system of clause 27, wherein the processor is further configured to determine the value of the parameter associated with the radiation source using the desired distribution of the coherence adjusted beam of radiation and a model between parameters of the radiation source and a distribution of the coherence adjusted beam of radiation.45. The metrology system of clause 44, wherein the model comprises one or more inverse correction coefficients.46. The metrology system of clause 27, wherein the coherence adjuster further comprises:a waveguide device comprising an input configured to receive the spatially coherent radiation and an output.47. The metrology system of clause 27, further comprising a waveguide device configured to carry the coherence adjusted beam of radiation from the coherence adjuster to the detector.48. The metrology system of clause 27, wherein the coherence adjuster further comprises:an adjusting device coupled to a portion of the coherence adjuster and configured to adjust the portion so as to change an impingement characteristic of the received spatially coherent radiation at the input of the multimode waveguide device in response to the determined value of the parameter.49. The metrology system of clause 27, wherein the radiation source comprises a multi-source radiation system.50. A metrology system comprising:a radiation source configured to generate spatially coherent radiation;a coherence adjuster comprising:a multimode waveguide device comprising:an input configured to receive the spatially coherent radiation; andan output configured to output a coherence adjusted beam of radiation for irradiating a target;a detector configured to receive radiation scattered by the target based on the irradiating and to generate a measurement signal based on the received radiation;a processor configured to:determine a parameter associated with the target based on the measurement signal;compare the determined parameter with a desired parameter associated with the target;determine a value of a parameter associated with the coherence adjuster based on the comparison; andcommunicate the determined value of the parameter associated with the coherence adjuster to the coherence adjuster,wherein the coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.51. The metrology system of clause 50, wherein:the detector is further configured to measure a distribution of the coherence adjusted beam of radiation, andthe processor is further configured to:compare the measured distribution with a desired distribution; anddetermine the value of the parameter associated with the coherence adjuster or a value of a parameter associated with the radiation source based on the comparing the measured distribution with the desired distribution and the comparing the determined parameter with the desired parameter.52. The metrology system of clause 50, wherein to determine the value of the parameter associated with the coherence adjuster, the processor is further configured to use a model between parameters of the coherence adjuster and parameters of the target.53. The metrology system of clause 52, wherein the model comprises one or more inverse correction coefficients.54. The metrology system of clause 52, wherein to determine the value of the parameter associated with the coherence adjuster, the processor is further configured to use a machine learning model.55. The metrology system of clause 50, wherein:the processor is further configured to:determine a value for a parameter associated with the radiation source based on the comparison; andcommunicate the determined value for the parameter associated with the radiation source to the radiation source, andthe radiation source is configured to adjust the parameter associated with the radiation source based on the determined value.56. The metrology system of clause 55, wherein to determine the value of the parameter associated with the radiation source, the processor is further configured to use a model between parameters of the radiation source and parameters of the target.57. The metrology system of clause 56, wherein the model comprises one or more inverse correction coefficients.58. The metrology system of clause 56, wherein to determine the value of the parameter associated with the radiation source, the processor is further configured to use a machine learning model.59. The metrology system of clause 50, wherein to adjust the parameter associated with the coherence adjuster based on the determined value, the coherence adjuster is configured to use a variable dwell time for the received spatially coherent radiation at different locations at the input of the multimode waveguide device.60. The metrology system of clause 50, wherein to adjust the parameter associated with the coherence adjuster based on the determined value, the coherence adjuster is configured to modulate an intensity of the coherence adjusted beam of radiation as a function of position of the received spatially coherent radiation at the input of the multimode waveguide device.61. The metrology system of clause 50, wherein to adjust the parameter associated with the coherence adjuster based on the determined value, the coherence adjuster is configured to modulate an intensity of the coherence adjusted beam of radiation as a function of an angle of incidence of the received spatially coherent radiation at the input of the multimode waveguide device.62. The metrology system of clause 50, wherein the processor is further configured to determine the value of the parameter associated with the coherence adjuster using the desired parameter of the target and a model between parameters of the coherence adjuster and parameters of the target.63. The metrology system of clause 62, wherein the model comprises one or more inverse correction coefficients.64. The metrology system of clause 50, wherein the processor is further configured to determine the value of the parameter associated with the radiation source using the desired parameter of the target and a model between parameters of the radiation source and parameters of the target.65. The metrology system of clause 64, wherein the model comprises one or more inverse correction coefficients.66. The metrology system of clause 50, wherein the coherence adjuster further comprises:a waveguide device comprising an input configured to receive the spatially coherent radiation and an output.67. The metrology system of clause 50, further comprising:a waveguide device configured to carry the coherence adjusted beam of radiation from the coherence adjuster to the detector.68. The metrology system of clause 50, wherein the coherence adjuster further comprises:an adjusting device coupled to a portion of the coherence adjuster and configured to adjust the portion so as to change an impingement characteristic of the received spatially coherent radiation at the input of the multimode waveguide device in response to the determined value of the parameter.69. The metrology system of clause 50, wherein the radiation source comprises a multi-source radiation system.70. A method, comprising:receiving a measurement signal, wherein the measurement signal is generated based on a measured distribution of a coherence adjusted beam of radiation output from a coherence adjuster;comparing the measured distribution with a desired distribution;determining a value of a parameter associated with the coherence adjuster based on the comparison; andcommunicating the determined value of the parameter associated with the coherence adjuster to the coherence adjuster,wherein the coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.71. A method, comprising:receiving a measurement signal, wherein the measurement signal is generated based on radiation scattered by a target irradiated by a coherence adjusted beam of radiation from a coherence adjuster;determining a parameter associated with the target based on the measurement signal;comparing the determined parameter with a desired parameter associated with the target;determining a value of a parameter associated with the coherence adjuster based on the comparison; andcommunicating the determined value of the parameter associated with the coherence adjuster to the coherence adjuster,wherein the coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.72. A non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform operations, the operations comprising:receiving a measurement signal, wherein the measurement signal is generated based on a measured distribution of a coherence adjusted beam of radiation output from a coherence adjuster;comparing the measured distribution with a desired distribution;determining a value of a parameter associated with the coherence adjuster based on the comparison; andcommunicating the determined value of the parameter associated with the coherence adjuster to the coherence adjuster,wherein the coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.73. A non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform operations, the operations comprising:receiving a measurement signal, wherein the measurement signal is generated based on radiation scattered by a target irradiated by a coherence adjusted beam of radiation from a coherence adjuster;determining a parameter associated with the target based on the measurement signal;comparing the determined parameter with a desired parameter associated with the target;determining a value of a parameter associated with the coherence adjuster; andcommunicating the determined value of the parameter associated with the coherence adjuster to the coherence adjuster, wherein the coherence adjuster is configured to adjust the parameter associated with the coherence adjuster based at least on the determined value.74. A metrology system comprising:a multi-source radiation system comprising a combined waveguide device, wherein the multi-source radiation system is configured to generate one or more beams of radiation;a coherence adjuster comprising a multimode waveguide device, the multimode waveguide device comprising:an input configured to receive the one or more beams of radiation from the multi-source radiation system; andan output configured to output a coherence adjusted beam of radiation for irradiating a target; andan actuator coupled to the combined waveguide device and configured to actuate the combined waveguide device so as to change an impingement characteristic of the one or more beams of radiation at the input of the multimode waveguide device.75. The metrology system of clause 74, wherein the multi-source radiation system further comprises:a plurality of radiation sources configured to generate a plurality of spatially coherent beams of radiation; anda plurality of waveguide devices coupled to the plurality of radiation sources and configured to receive the plurality of spatially coherent beams of radiation.76. The metrology system of clause 75, wherein:the multi-source radiation system further comprises a waveguide combining element coupled between the plurality of waveguide devices and the combined waveguide device, andthe waveguide combining element is configured to receive a plurality of beams of radiation from the plurality of waveguide devices and generate the one or more beams of radiation.77. The metrology system of clause 74, wherein the waveguide combining element comprises at least one of a bundled single-mode fiber with thinned or adiabatically tapered cladding, a bundled single-mode fiber fused into a multimode fiber, or a Photonic Integrated Circuit (PIC) configured to combine single-mode waveguide devices into a multimode waveguide device.78. The metrology system of clause 74, wherein the actuator is configured to actuate the combined waveguide device so as to change a first impingement characteristic of a first one of the one or more beams of radiation at the input of the multimode waveguide device and to change a second impingement characteristic of a second one of the one or more beams of radiation at the input of the multimode waveguide device.79. The metrology system of clause 74, wherein:the actuator comprises one or more motors, andthe actuating comprises deflecting and/or translating the combined waveguide device using the one or more motors.80. A metrology system comprising:a multi-source radiation system comprising a combined waveguide device, wherein the multi-source radiation system is configured to generate one or more beams of radiation;a coherence adjuster comprising a multimode waveguide device, the multimode device comprising:an input configured to receive the one or more beams of radiation; andan output configured to output a coherence adjusted beam of radiation; andan adjusting device coupled to a portion of the coherence adjuster and configured to adjust the portion so as to change an impingement characteristic of the one or more beams of radiation at the input of the multimode waveguide device.81. The metrology system of clause 80, further comprising a reflective element configured to direct the one or more beams of radiation to the multimode waveguide device, wherein:the adjusting device comprises an actuator,the reflective element and actuator are arranged as a galvo mirror, andthe reflective element is the adjusted portion.82. The metrology system of clause 80, further comprising reflectors configured to direct the one or more beams of radiation to the multimode waveguide device, wherein:the adjusting device comprises actuators,the actuators and the reflectors are arranged as a digital micromirror device, andthe reflectors are the adjusted portion.83. The metrology system of clause 80, wherein the multi-source radiation system further comprises:a plurality of radiation sources configure to generate a plurality of spatially coherent beams of radiation;a plurality of waveguide devices coupled to the plurality of radiation sources and configured to receive plurality of spatially coherent beams of radiation; anda waveguide combining element coupled between the plurality of waveguide devices and the combined waveguide device, wherein the waveguide combining element is configured to receive a plurality of beams of radiation from the plurality of waveguide devices and generate the one or more beams of radiation.84. The metrology system of clause 80, wherein the waveguide combining element comprises at least one of a bundled single-mode fiber with thinned or adiabatically tapered cladding, a bundled single-mode fiber fused into a multimode fiber, a multi-core fiber (MFC), or a Photonic Integrated Circuit (PIC) configured to combine waveguide devices into a multimode waveguide device or to combine radiation into a multi-core waveguide device.85. The metrology system of clause 80, wherein the actuator is configured to actuate the portion of the coherence adjuster so as to change a first impingement characteristic of a first one of the one or more beams of radiation at the input of the multimode waveguide device and to change a second impingement characteristic of a second one of the one or more beams of radiation at the input of the multimode waveguide device.86. A metrology system comprising:a multi-source radiation system configured to generate spatially coherent radiation, the multi-source radiation source comprising:a first radiation source configured to generate a first radiation with a first polarization state;a second radiations source configured to generate a second radiation with a second polarization state orthogonal to the first polarization state; anda combining element configured to generate the spatially coherent radiation by combining the first radiation and the second radiation; anda coherence adjuster comprising a multimode waveguide device, the multimode waveguide device comprising:an input configured to receive the spatially coherent radiation from the multi-source radiation system; andan output configured to output a coherence adjusted beam of radiation for irradiating a target.87. The metrology system of clause 86, wherein the combining element comprises a polarizing beam splitter.88. The metrology system of clause 86, further comprising:an actuator coupled to the multi-source radiation system and configured to actuate a waveguide device of the coherence adjuster or a waveguide device of the multi-source radiation system so as to change an impingement characteristic of the spatially coherent radiation at the input of the multimode waveguide device.89. The metrology system of clause 86, further comprising:an adjusting device coupled to a portion of the coherence adjuster and configured to adjust the portion so as to change an impingement characteristic of the spatially coherent radiation at the input of the multimode waveguide device.90. The metrology system of clause 86, further comprising:a diffuser device disposed upstream of the multi-source radiation system and configured to change an impingement characteristic of the spatially coherent radiation at the input of the multimode waveguide device.

Although specific reference can be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein can be processed, before or after exposure, in for example a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology unit and/or an inspection unit. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present disclosure is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

The terms “radiation,” “beam,” “light,” “illumination,” or the like as used herein may encompass all types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength λ of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-20 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm; and/or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some embodiments, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.

The term “substrate” as used herein describes a material onto which material layers are added. In some embodiments, the substrate itself can be patterned and materials added on top of it may also be patterned, or may remain without patterning.

Although specific reference can be made in this text to the use of the apparatus and/or system according to the present disclosure in the manufacture of ICs, it should be explicitly understood that such an apparatus and/or system has many other possible applications. For example, it can be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, LCD panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle,” “wafer,” or “die” in this text should be considered as being replaced by the more general terms “mask,” “substrate,” and “target portion,” respectively.

While specific embodiments of the disclosure have been described above, it will be appreciated that embodiments of the present disclosure may be practiced otherwise than as described. The descriptions are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the disclosure as described without departing from the scope of the claims set out below.

The foregoing description of the specific embodiments will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

The breadth and scope of the protected subject matter should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.