Patent ID: 12216409

DESCRIPTION OF EMBODIMENTS

<Contents>

1. Terms

2. Overview of exposure system according to comparative example

2.1 Configuration

2.2 Operation

2.3 Exemplary exposure operation on wafer

2.4 Relation between scanning field and static exposure area

2.5 Typical process of OPE correction

2.6 Problem

3. Embodiment 1

3.1 Overview of lithography system3.1.1 Configuration3.1.2 Operation

3.2 Exemplary laser apparatus3.2.1 Configuration3.2.2 Operation3.2.3 Other

3.4 Exemplary contents of processing by lithography control unit

3.5 Exemplary contents of processing by exposure control unit

3.6 Exemplary contents of processing by laser control unit

3.7 Effect

3.8 Other

4. Embodiment 2

4.1 Configuration

4.2 Operation

4.3 Effect

4.4 Other

5. Embodiment 3

5.1 Configuration

5.2 Operation

5.3 Exemplary contents of processing by laser control unit

5.4 Exemplary data of file B

5.5 Effect

5.6 Other

6. Exemplary excimer laser apparatus that uses solid-state laser device as oscillator

6.1 Configuration

6.2 Operation

6.3 Description of semiconductor laser system6.3.1 Configuration6.3.2 Operation6.3.3 Other

6.4 Effect

6.5 Other

7. Hardware configurations of various control units

8. Electronic device manufacturing method

9. Other

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings. The embodiments described below are examples of the present disclosure, and do not limit the contents of the present disclosure. Not all configurations and operations described in each embodiment are necessarily essential as configurations and operations of the present disclosure. Components identical to each other are denoted by an identical reference sign, and duplicate description thereof will be omitted.

1. Terms

Terms used in the present disclosure are defined as described below.

A critical dimension (CD) is the dimension of a minute pattern formed on a wafer such as a semiconductor. In lithography, a CD value of a pattern changes under influence of the dimension of the pattern as well as surrounding patterns. Thus, the CD after exposure is different between, for example, a case in which a pattern is disposed in isolation on a reticle and a case in which the pattern is disposed adjacent to any other pattern. The degree of the difference changes with not only the distance between the other adjacent pattern, density, kind, and the like but also settings of an optical system of an exposure device used for exposure. Such an optical proximity effect is referred to as an OPE. Note that a proximity effect other than the optical proximity effect is obtained with an image development process or any other process at image development.

An OPE curve is a graph in which the kind of a pattern is plotted on the horizontal axis and the CD value or the difference between the CD value and a target CD value is plotted on the vertical axis. The OPE curve is also referred to as an OPE characteristic curve.FIG.1illustrates an exemplary OPE curve. InFIG.1, the horizontal axis represents a through pitch, and the vertical axis represents the CD value. The through pitch is an exemplary pattern.

Optical proximity correction (OPC) is to provide bias and an auxiliary pattern to a reticle pattern based on exposure experiment data in advance so that the CD on a wafer after exposure becomes equal to a target value, since it is known that the CD value changes due to the OPE in some cases. The OPC is typically performed at the stage of process development by a device manufacturer.

OPE correction is correction different from the OPC. The OPE is also affected by settings of an optical system used for exposure, such as the numerical aperture (NA), illumination σ, and ring belt ratio of each lens, and thus the CD value can be adjusted to a target value by adjusting optical system parameters of an exposure apparatus. This adjustment is referred to as OPE correction. The CD value can be controlled by the OPC and the OPE correction. The OPC is often performed at the stage of process development including reticle production, and the OPE correction is often performed at (right before) or halfway through mass production after reticle production. In addition, a proximity effect such as micro loading effect other than the optical proximity effect is obtained with image development or the like, and the CD may be adjusted through optical system adjustment for such a proximity effect together with the optical proximity effect in some cases.

Overlay is overlay of a minute pattern formed on a wafer such as a semiconductor.

A spectrum line width Δλ is an index value of a spectrum line width that affects exposure performance. The spectrum line width Δλ may be, for example, a bandwidth with which the integral energy of a laser spectrum is 95%.

2. Overview of Exposure System According to Comparative Example

2.1 Configuration

FIG.2schematically illustrates the configuration of an exposure system10according to a comparative example. The comparative example of the present disclosure is an example that the applicant recognizes as known only by the applicant, but is not a publicly known example that is recognized by the applicant. The exposure system10includes a laser apparatus12and an exposure apparatus14. The laser apparatus12is a variable-wavelength narrow-band oscillation ArF laser apparatus including a laser control unit20, a non-illustrated laser chamber, and a non-illustrated line narrow module.

The exposure apparatus14includes an exposure control unit40, a beam delivery unit (BDU)42, a high reflective mirror43, an illumination optical system44, a reticle46, a reticle stage48, a projection optical system50, a wafer holder52, a wafer stage54, and a focus sensor58.

The wafer holder52holds a wafer WF. The illumination optical system44is an optical system through which a pulse laser beam is guided to the reticle46. The illumination optical system44shapes the laser beam into a scanning beam having a substantially rectangular shape and uniform light intensity distribution. In addition, the illumination optical system44controls the incident angle of the laser beam on the reticle46. The projection optical system50images a reticle pattern on the wafer WF. The focus sensor58measures the height of a wafer surface.

The exposure control unit40is connected to the reticle stage48, the wafer stage54, and the focus sensor58. The exposure control unit40is also connected to the laser control unit20. Each of the exposure control unit40and the laser control unit20is configured as a non-illustrated processor and includes a storage device such as a memory. The storage device may be mounted on the processor.

2.2 Operation

The exposure control unit40controls movement of the wafer stage54in a Z axial direction to correct a focus position in a wafer height direction (the Z axial direction) based on the height of the wafer WF, which is measured by the focus sensor58.

By a step-and-scan scheme, the exposure control unit40transmits control parameters of a target laser beam to the laser control unit20and controls the reticle stage48and the wafer stage54while transmitting a light emission trigger signal Tr to perform scanning exposure of an image of the reticle46to the wafer WF. The control parameters of a target laser beam include, for example, a target wavelength λt and a target pulse energy Et. Note that the phrase “target laser beam” means “target pulse laser beam”. “Pulse laser beam” is simply written as “laser beam” in some cases.

The laser control unit20controls a selection wavelength of the line narrow module so that the wavelength λ of a pulse laser beam emitted from the laser apparatus12becomes equal to the target wavelength λt. The laser control unit20also controls excitation intensity so that the pulse energy E of the pulse laser beam becomes equal to the target pulse energy Et. Accordingly, the laser control unit20causes emission of the pulse laser beam in accordance with the light emission trigger signal Tr. In addition, the laser control unit20transmits, to the exposure control unit40, various kinds of measurement data of the pulse laser beam emitted in accordance with the light emission trigger signal Tr. The various kinds of measurement data include, for example, the wavelength λ and the pulse energy E.

2.3 Exemplary Exposure Operation on Wafer

FIG.3illustrates an exemplary output pattern of the light emission trigger signal Tr transmitted from the exposure control unit40to the laser control unit20. In the example illustrated inFIG.3, an actual exposure pattern starts, after adjustment oscillation is performed for each wafer WF. Specifically, the laser apparatus12first performs the adjustment oscillation and then performs burst operation for first wafer exposure (Wafer #1) after a predetermined time interval.

The adjustment oscillation is oscillation with emission of an adjustment pulse laser beam but no irradiation of the wafer WF with the pulse laser beam. The adjustment oscillation is performed under a predetermined condition until the laser is stabilized in a state in which exposure is possible, and is performed before lot of wafer production. A pulse laser beam Lp is emitted at a predetermined frequency of, for example, several hundreds Hz to several kHz approximately. In wafer exposure, it is typical to perform burst operation that repeats a burst duration and an oscillation stop duration. The burst operation is performed in the adjustment oscillation as well.

InFIG.3, each interval in which pulses are closely spaced is the burst duration in which the pulse laser beam is continuously emitted for a predetermined duration. InFIG.3, each interval in which no pulse exists is the oscillation stop duration. Note that, in the adjustment oscillation, the length of each continuous emission duration of pulses does not need to be constant, but continuous emission operation may be performed in continuous emission durations with different lengths for adjustment. After the adjustment oscillation is performed, followed by a relatively large time interval, the first wafer exposure (Wafer #1) is performed at the exposure apparatus14.

The laser apparatus12stops oscillation during a step in exposure by the step-and-scan scheme and emits a pulse laser beam in accordance with the interval of the light emission trigger signal Tr during scanning. Such a pattern of laser oscillation is referred to as a burst oscillation pattern.

FIG.4illustrates an exemplary exposure pattern of step-and-scan exposure on the wafer WF. Each of a plurality of rectangular regions illustrated in the wafer WF inFIG.4is a scanning field SF. The scanning field SF is an exposure region of one scanning exposure and also referred to as a scanning region. As illustrated inFIG.4, wafer exposure is performed by dividing the wafer WF into a plurality of exposure regions (scanning fields) of a predetermined size and performing scanning exposure in each exposure region in a duration between start (Wafer START) and end (Wafer END) of the wafer exposure.

Specifically, the wafer exposure repeats steps such as the first scanning exposure (Scan #1) in a first predetermined exposure region of the wafer WF and the second scanning exposure (Scan #2) in a second predetermined exposure region. During one scanning exposure, a plurality of pulse laser beams Lp (Pulse #1, Pulse #2, . . . ) can be continuously emitted from the laser apparatus12. After the scanning exposure (Scan #1) ends in the first predetermined exposure region, followed by a predetermined time interval, the scanning exposure (Scan #2) is performed in the second predetermined exposure region. When such scanning exposure is sequentially repeated and completed for all exposure regions of the first wafer WF, the adjustment oscillation is performed again and then wafer exposure (Wafer #2) of the second wafer WF is performed.

The step-and-scan exposure is performed in an order illustrated with dashed line arrows inFIG.4, namely, Wafer START→Scan #1→Scan #2→ . . . →Scan #126→Wafer END. Each wafer WF is an example of a “semiconductor substrate” or a “photosensitive substrate” in the present disclosure.

2.4 Relation Between Scanning Field and Static Exposure Area

FIG.5illustrates the relation between one scanning field SF on the wafer WF and a static exposure area SEA. The static exposure area SEA is a beam irradiation region having a substantially rectangular shape and substantially uniform light intensity distribution and used for scanning exposure in the scanning field SF. Exposure is performed as the reticle46is irradiated with a substantially rectangular and substantially uniform scanning beam shaped through the illumination optical system44while the reticle46and the wafer WF are moved in mutually different directions along a short axial direction of the scanning beam (in this example, a Y axial direction) in accordance with a scaling-down ratio of the projection optical system50. Accordingly, each scanning field SF on the wafer WF is subjected to scanning exposure to a reticle pattern. The static exposure area SEA can be understood as an area in which collective exposure by a scanning beam is possible.

InFIG.5, a direction toward the negative Y axial direction side in the upward longitudinal direction is a scanning direction, and a direction toward the positive Y axial direction side is a wafer moving direction. A direction (X axial direction) parallel to the sheet ofFIG.5and orthogonal to the Y axial direction is referred to as a scanning width direction. The size of each scanning field SF on the wafer WF is, for example, 33 mm in the Y axial direction and 26 mm in the X axial direction.

FIG.6is an explanatory diagram of the static exposure area SEA. When Bx represents the length of the static exposure area SEA in the X axial direction and By represents the width of the static exposure area SEA in the Y axial direction, Bx corresponds to the size of each scanning field SF in the X axial direction and By is sufficiently smaller than the size of each scanning field SF in the Y axial direction. The width By of the static exposure area SEA in the Y axial direction is referred to as an N slit. The number NSLof pulses to which resist on the wafer WF is exposed is given by an expression below.
NSL=(By/Vy)·f

Vy: scanning speed of the wafer in the Y axial direction

f: laser repetition frequency (Hz)

Note that a scanning beam with which the reticle46is illuminated has, on the wafer WF, a size in accordance with magnification of the projection optical system50of the exposure apparatus14. For example, when the magnification of the projection optical system50is ¼, the scanning beam with which the reticle46is illuminated has a size ¼ times larger on the wafer WF. A scanning field area on the reticle46is a scanning field SF having a size ¼ times larger on the wafer WF. The beam width (By width) of the scanning beam with which the reticle46is illuminated in the Y axial direction leads to the width By of the static exposure area SEA on the wafer WF in the Y axial direction.

2.5 Typical Process of OPE Correction

The OPE correction is processing that is performed after acquisition of the OPE curve (reference OPE curve) of a particular exposure apparatus as a reference and includes adjusting exposure conditions and the like of another exposure apparatus so that the OPE curve of the other exposure apparatus becomes closer to the reference OPE curve. The OPE correction is performed to correct a machine difference (individual difference) of an exposure apparatus. The particular exposure apparatus as a reference is referred to as a “reference exposure apparatus”. The reference exposure apparatus is, for example, an exposure apparatus used in device development. The target exposure apparatus is, for example, an exposure apparatus used in mass production, and is an exposure apparatus for which matching adjustment is performed so that the OPE curve of the exposure apparatus becomes close to the reference OPE curve. The “other exposure apparatus” is referred to as a “matching exposure apparatus” in some cases.

FIG.7is a plan view schematically illustrating each scanning field SF on the wafer WF and a pattern region in the scanning field SF. The wafer WF includes a plurality of scanning fields SF, and the CD of every target pattern in each scanning field SF is typically measured when the OPE correction is performed. In many cases, for the plurality of scanning fields SF in the wafer WF, the CD of every target pattern existing in a pattern region PA of each scanning field SF is measured and an OPE curve representing the relation (OPE characteristic) between the pattern and the CD is obtained. Then, an average OPE curve is obtained by averaging the OPE curves obtained for the scanning fields SF. Settings of the exposure apparatus14and the like are adjusted so that the average OPE curve thus obtained becomes closer to the reference OPE curve.

FIG.8is a flowchart illustrating an exemplary procedure of the OPE correction. Some or all steps illustrated inFIG.8are implemented, for example, as a processor of a non-illustrated information processing device configured to manage parameters of the exposure apparatus14executes a program.

At step S1, the information processing device measures the CD of every target pattern in a scanning field SF, which is subjected to exposure under a reference exposure condition by using the reference exposure apparatus. In addition, the information processing device measures the CD in a plurality of scanning fields SF as necessary and calculates the average of the CDs. Note that a non-illustrated wafer examination device may be used for the CD measurement. The reference OPE curve is obtained as the processing at step S1is performed.

Then at step S2, the information processing device sets an exposure condition same as the reference exposure condition to the matching exposure apparatus14.

Then at step S3, the matching exposure apparatus14subjects the wafer WF to exposure under the set exposure condition.

Then at step S4, the information processing device measures the CD of every target pattern in the scanning region, which is obtained through the exposure at step S3. In addition, the information processing device measures the CDs in a plurality of scanning fields SF as necessary and calculates the average of the CDs. The OPE curve of the matching exposure apparatus14is obtained as the processing at step S4is performed.

At step S5, the information processing device determines whether the difference between the OPE curves of the two exposure apparatuses is in an allowable range. The “two exposure apparatuses” are the reference exposure apparatus and the matching exposure apparatus14. Thus, the information processing device determines whether the difference between the reference OPE curve obtained at step S1and the OPE curve obtained at step S4is in the allowable range. When the result of the determination at step S5is “No”, the information processing device proceeds to step S6.

At step S6, the information processing device obtains an exposure condition with which the OPE curve difference is smallest based on a simulation or based on a result of exposure actually performed under a changed exposure condition. The “exposure condition” includes optical system settings of the exposure apparatus14, the spectrum line width of exposure light, an exposure amount, and focus. The optical system settings of the exposure apparatus14largely change with illumination system shapes such as the NA of each lens of the projection optical system50and the NA, illumination a, and ring belt ratio of each lens of the illumination optical system44.

At step S7, the information processing device sets the exposure condition obtained at step S6to the matching exposure apparatus14. After step S7, the information processing device returns to step S3. When the result of the determination at step S5is “Yes”, the information processing device ends the flowchart inFIG.8.

In this manner, the exposure condition of the matching exposure apparatus14is determined so that the difference between the OPE curve of the matching exposure apparatus14and the reference OPE curve of the reference exposure apparatus is in the allowable range. Note that step S1inFIG.8may be performed by a processor that functions as an exposure control unit in the reference exposure apparatus. Steps S2to S7inFIG.8may be performed by a processor that functions as an exposure control unit in the matching exposure apparatus14.

FIG.9is a graph illustrating an exemplary reference OPE curve obtained by measuring an exposure result of the reference exposure apparatus and an exemplary OPE curve obtained by measuring an exposure result of the matching exposure apparatus14. InFIG.9, the horizontal axis represents the kind of a pattern, and the vertical axis represents the CD. InFIG.9, the graph OPE_ref is the reference OPE curve of the reference exposure apparatus, and the graph OPE_mtc is the OPE curve of the matching exposure apparatus14.

2.6 Problem

FIG.10is a schematic diagram schematically illustrating an exemplary pattern in each scanning field SF of the wafer WF. Exposure in various patterns is performed in each scanning field SF, and the scanning field SF is divided into a plurality of partial areas in accordance with the kinds of the patterns.FIG.10illustrates an example in which a first partial area (Area1), a second partial area (Area2), and a third partial area (Area3) are provided in the scanning field SF. The form of pattern is different among the partial areas, and the OPE characteristic is different among the partial areas. Note that, the number, shapes, array form, and the like of partial areas in the scanning field SF are not limited to those in the example illustrated inFIG.10.

FIG.11illustrates exemplary OPE curves of the first partial area Area1 and the second partial area Area2 in a scanning field SF having a scanning number Scan #A. Since the OPE is different among patterns in exposure, it is desirable to obtain an optimum OPE characteristic for each partial area in the scanning field SF.

However, the typical OPE correction adjusts settings of the illumination optical system44and the projection optical system50of the exposure apparatus14as described with reference toFIGS.7to9, and thus cannot adjust the illumination optical system44and the projection optical system50of the exposure apparatus14at high speed for a layer of an exposure process. As a result, it has been difficult to adjust the OPE characteristic halfway through scanning exposure.

3. Embodiment 1

3.1 Overview of Lithography System

3.1.1 Configuration

FIG.12illustrates an exemplary configuration of a lithography system100according to Embodiment 1. Description will be made on the difference of the configuration illustrated inFIG.12from the configuration illustrated inFIG.2. The lithography system100illustrated inFIG.12includes a lithography control unit110in addition to the configuration illustrated inFIG.2, and data transmission-reception lines are additionally provided between the lithography control unit110and the exposure control unit40and between the lithography control unit110and the laser control unit20, respectively.

The lithography system100includes the laser apparatus12, the exposure apparatus14, and the lithography control unit110. The lithography system100is an example of an “exposure system” in the present disclosure. In the lithography system100, a target spectrum line width Δλt is added as a control parameter of a target laser beam. Data of the target spectrum line width Δλt is transmitted from the exposure control unit40to the laser control unit20.

The lithography control unit110is configured as a non-illustrated processor. The lithography control unit110includes a storage device such as a memory. The processor may include the storage device.

A reticle pattern of the reticle46used in the lithography system100includes, for example, a plurality of partial areas corresponding to the plurality of partial areas (Area1 to Area3), respectively, described with reference toFIG.10. The partial areas may be obtained, for example, through region division into strip-shaped regions that are continuous in a direction orthogonal to the scanning direction. Note that the shapes and number of partial areas are not limited to those in the example illustrated inFIG.10.

A partial area of each scanning field SF is referred to as “Area(k)”. The index k indicates an area number of the partial area. When the scanning field SF includes n partial areas, k is an integer of 1 to n. The partial areas of the scanning field SF correspond to partial areas of the reticle46on a one-to-one basis, and thus the partial area Area(k) can be understood as a partial area of the reticle46. A large number of patterns are disposed in each partial area Area(k).

The lithography control unit110has a calculation program that calculates optimum laser-beam control parameters of each partial area Area(k). The calculation program includes a program that calculates line widths (in other words, the OPE) of a plurality of patterns based on a pure Fourier imaging optical theory by changing the settings of the exposure apparatus14and the laser-beam control parameters and calculates optimum settings of the exposure apparatus14and optimum laser-beam control parameters by using a mathematical method such as linear or non-linear optimization. Examples of parameters related to the settings of the exposure apparatus14include the NA of each lens of the projection optical system50and the illumination a and ring belt ratio of the illumination optical system44.

3.1.2 Operation

The lithography control unit110calculates, by using the calculation program, optimum laser-beam control parameter values with which the OPE corresponding to each partial area Area(k) becomes closer to a reference OPE, and stores a result of the calculation in a file A. The laser-beam control parameter values stored in the file A include the value of a central wavelength, the value of a spectrum line width, and the value of pulse energy. The description “optimum control parameter values” means laser-beam control parameter values for the OPE curve corresponding to the partial area Area(k), the difference of which from the reference OPE curve is in an allowable range. An OPE curve, the difference of which from the reference OPE curve is in an allowable range, is referred to as an “optimum OPE curve” in some cases.

The lithography control unit110may receive data related to the laser apparatus12and including the laser-beam control parameters from the laser control unit20and may store the data. For example, the lithography control unit110receives data of the wavelength λ, the spectrum line width Δλ, and the pulse energy E from the laser control unit20and stores the data.

The exposure control unit40reads the laser-beam control parameter values corresponding to each partial area Area(k) of the scanning field SF of the wafer WF from the file A in the lithography control unit110.

The exposure control unit40transmits the laser-beam control parameter values of each pulse at exposure in each partial area Area(k) to the laser apparatus12. The following exposure operation may be the same as that of the exposure system10inFIG.2. In addition, the spectrum line width Δλ of each pulse can be varied by, for example, controlling a delay time Δt between synchronization timings of an oscillator22and an amplifier24of the laser apparatus12, which will be described later, for the pulse.

3.2 Exemplary laser apparatus

3.2.1 Configuration

FIG.13illustrates an exemplary configuration of the laser apparatus12. The laser apparatus12illustrated inFIG.13is a line narrowing ArF laser apparatus including the laser control unit20, the oscillator22, the amplifier24, a monitor module26, and a shutter28. The oscillator22includes a chamber60, an output coupling mirror62, a pulse power module (PPM)64, a charger66, and a line narrow module (LNM)68.

The chamber60includes windows71and72, a pair of electrodes73and74, and an electrically insulating member75. The PPM64includes a switch65and a non-illustrated charging capacitor and is connected to the electrode74via feed-through of the electrically insulating member75. The electrode73is connected to the chamber60that is grounded. The charger66charges the charging capacitor of the PPM64in accordance with a command from the laser control unit20.

The line narrow module68and the output coupling mirror62constitute an optical resonator. The chamber60is disposed so that a discharge region of the pair of electrodes73and74is disposed on the optical path of the resonator. The output coupling mirror62is coated with a multi-layered film that reflects part of a laser beam generated in the chamber60and transmits another part of the laser beam.

The line narrow module68includes two prisms81and82, a grating83, and a rotation stage84that rotates the prism82. The line narrow module68changes the incident angle of a pulse laser beam on the grating83by rotating the prism82by using the rotation stage84, and accordingly, controls the oscillation wavelength of the pulse laser beam. The rotation stage84may include a piezoelectric element capable of performing high-speed response so that response to each pulse is possible.

The amplifier24includes an optical resonator90, a chamber160, a PPM164, and a charger166. The configurations of the chamber160, the PPM164, and the charger166are the same as the configurations of the corresponding elements of the oscillator22. The chamber160includes windows171and172, a pair of electrodes173and174, and an electrically insulating member175. The PPM164includes a switch165and a non-illustrated charging capacitor.

The optical resonator90is a Fabry-Perot optical resonator constituted by a rear mirror91and an output coupling mirror92. The rear mirror91partially reflects part of a laser beam and transmits another part of the laser beam. The output coupling mirror92partially reflects part of a laser beam and transmits another part of the laser beam. The reflectance of the rear mirror91is, for example, 80% to 90%. The reflectance of the output coupling mirror92is, for example, 10% to 30%.

The monitor module26includes beam splitters181and182, a spectrum detector183, and a photosensor184configured to detect pulse energy of a laser beam. The spectrum detector183may be, for example, an etalon spectrometer. The photosensor184may be, for example, a photodiode.

3.2.2 Operation

When having received data of the target wavelength λt, the spectrum line width Δλt, and the target pulse energy Et from the exposure control unit40, the laser control unit20controls the rotation stage84of the LNM68so that an emission wavelength becomes equal to the target wavelength λt, controls a scheme to be described later so that the target spectrum line width Δλt is obtained, and controls at least the charger166of the amplifier24so that the target pulse energy Et is obtained.

When having received the light emission trigger signal Tr from the exposure control unit40, the laser control unit20provides a trigger signal to each of the switch165of the PPM164and the switch65of the PPM64so that a pulse laser beam emitted from the oscillator22discharges when entering a discharge space of the chamber160of the amplifier24. As a result, the pulse laser beam emitted from the oscillator22is subjected to amplified oscillation at the amplifier24. The amplified pulse laser beam is sampled by the beam splitter181of the monitor module26to measure the pulse energy E, the wavelength λ, and the spectrum line width Δλ.

The laser control unit20acquires data of the pulse energy E, the wavelength λ, and the spectrum line width Δλ measured by using the monitor module26. Then, the laser control unit20controls the charging voltage of the charger166, the oscillation wavelength of the oscillator22, and the discharge timings of the oscillator22and the amplifier24so that the difference between the pulse energy E and the target pulse energy Et, the difference between the wavelength λ and the target wavelength λt, and the difference between the spectrum line width Δλ and the target spectrum line width Δλt each become closer to zero.

The laser control unit20can control the pulse energy E, the wavelength λ, and the spectrum line width Δλ for each pulse. The spectrum line width Δλ of the pulse laser beam emitted from the laser apparatus12can be controlled by controlling the delay time Δt between the discharge timings of the chamber60of the oscillator22and the chamber160of the amplifier24.

The pulse laser beam having transmitted through the beam splitter181of the monitor module26enters the exposure apparatus14through the shutter28.

3.2.3 Other

Although the optical resonator90is a Fabry-Perot resonator in the example illustrated inFIG.13, the amplifier may include a ring resonator.

3.4 Exemplary Contents of Processing by Lithography Control Unit

FIG.14is a flowchart illustrating exemplary processing performed by the lithography control unit110of Embodiment 1. Steps illustrated inFIG.14are implemented through execution of a program by the processor that functions as the lithography control unit110.

At step S10, the lithography control unit110receives input of data of parameters including parameters of the illumination optical system44, parameters of the projection optical system50, and parameters of resist.

Examples of the parameters of the illumination optical system44include the value of σ and an illumination shape. Examples of the parameters of the projection optical system50include lens data and lens NA. Examples of the parameters of resist include sensitivity.

At step S11, the lithography control unit110initializes the index k, which indicates the area number of a partial area, to one. Note that k is an integer of 1 to 3 in the example illustrated inFIG.10.

At step S12, the lithography control unit110receives input of pattern information on the reticle pattern of the partial area Area(k).

At step S13, the lithography control unit110sets initial values of the laser-beam control parameters. The laser-beam control parameters may be, for example, the wavelength λ, the spectrum line width Δλ, and an exposure amount (dose) D. Note that the pulse energy E may be used in place of or in addition to the exposure amount D.

The relation between the exposure amount D and the pulse energy E on the wafer surface is expressed by an expression below.
D=T·E·NSL/(Bx·By)

In the expression, T represents transmittance from the laser apparatus12to the wafer WF.

At step S14, the lithography control unit110calculates an OPE curve based on the input data. Specifically, the lithography control unit110calculates the OPE curve of the partial area Area(k) with given conditions in accordance with the calculation program.

At step S15, the lithography control unit110determines whether the absolute value of the difference between the OPE curve calculated at step S14and the reference OPE curve is in an allowable range. Data of the reference OPE curve is acquired by using the reference exposure apparatus in advance and held at the lithography control unit110. An indicator for evaluating the allowable range may be, for example, the sum of the absolute value of the difference between the CD values on the OPE curve and the reference OPE curve at each pattern, and the allowable range may be a predetermined range.

When the result of the determination at step S15is “No”, the lithography control unit110proceeds to step S16. At step S16, the lithography control unit110sets new values of the laser-beam control parameters and returns to step S14. Steps S14to S16are performed a plurality of times with different values of the laser-beam control parameters until the OPE curve, the difference of which from the reference OPE curve is in the allowable range, is obtained. The loop through steps S14to S16corresponds to processing of searching for a combination of laser-beam control parameter values with which an optimum OPE curve that is close to the reference OPE curve is obtained.

When the result of the determination at step S15is “Yes”, the lithography control unit110proceeds to step S17. At step S17, the lithography control unit110writes data of the laser-beam control parameters with which the OPE curve, the difference of which from the reference OPE curve is in the allowable range, is obtained to the file A as the OPE (k) indicating the OPE characteristic of the partial area Area(k). The data of the laser-beam control parameter written to the file A may be, for example, a combination of parameter values of the wavelength λ(k), the spectrum line width Δλ(k), the exposure amount D(k), and the pulse energy E(k) (refer toFIG.15). The wavelength λ(k), the spectrum line width Δλ(k), the exposure amount D(k), and the pulse energy E(k) are each an example of a “laser control parameter” in the present disclosure. The exposure amount D(k) may be calculated from the product of pulse energy density on a non-illustrated wafer in the exposure apparatus14and the number NSLof pulses. The data may be received from the exposure control unit40by the lithography control unit110.

At step S18, the lithography control unit110determines whether the value of the index k is equal to n. The number n is the number of partial areas in the scanning field SF and is an upper limit value (maximum value) that the index k takes. The number n is three in the example illustrated inFIG.10.

When the result of the determination at step S18is “No”, the lithography control unit110increments the value of the index k (step S19) and returns to step S12.

When the result of the determination at step S18is “Yes”, the lithography control unit110ends the flowchart inFIG.14. The method of calculating the laser control parameter in accordance with the flowchart inFIG.14is an example of a “laser control parameter production method” in the present disclosure.

FIG.15is a table listing exemplary data written to the file A. As illustrated inFIG.15, the file A stores, for each of the partial areas Area(1) to Area(n), data of parameters such as the exposure amount D, the wavelength λ, the spectrum line width Δλ, and the pulse energy E with which an optimum OPE characteristic is obtained. For example, a method of calculating an optimum laser-beam control parameter of the OPE (k) of each partial area Area(k) calculates line widths (in other words, the OPE) of a plurality of patterns based on a pure Fourier imaging optical theory by changing the settings of the exposure apparatus14and/or the laser-beam control parameters and calculates optimum settings of the exposure apparatus14and optimum laser-beam control parameters by using a mathematical method such as linear or non-linear optimization. Examples of setting parameters of the exposure apparatus14include the NA of each lens and the illumination σ and ring belt ratio of the illumination optical system44.

A reticle region corresponding to the partial area Area(1) is an example of a “first region” in the present disclosure, and a reticle region corresponding to the partial area Area(2) is an example of a “second region” in the present disclosure. Each of the partial area Area(1) and the partial area Area(2) is an example of “each of the regions” in the present disclosure. Among a plurality of partial areas, one partial area may correspond to the “first region” of the present disclosure, and another partial area may correspond to the “second region” of the present disclosure. The OPE curve is an example of a “proximity effect characteristic” in the present disclosure, and the reference OPE curve is an example of a “reference proximity effect characteristic” in the present disclosure. The file A is an example of a “first file” and a “file” in the present disclosure. An optimum OPE curve obtained for the partial area Area(1) is an example of a “first proximity effect characteristic” in the present disclosure. An optimum OPE curve obtained for the partial area Area(2) is an example of a “second proximity effect characteristic” in the present disclosure.

Control of the laser-beam control parameters so that an optimum OPE curve is obtained for each partial area Area(k) corresponds to correction of the OPE of each partial area in the scanning field SF with the laser-beam control parameters and is understood as a form of the OPE correction.

3.5 Exemplary Contents of Processing by Exposure Control Unit

FIG.16is a flowchart illustrating exemplary processing performed by the exposure control unit40of Embodiment 1. Steps illustrated inFIG.16are implemented through execution of a program by the processor that functions as the exposure control unit40.

At step S20, the exposure control unit40reads data of the file A stored in the lithography control unit110.

At step S21, the exposure control unit40calculates the laser-beam control parameters for the OPE correction of each partial area based on reticle pattern information and the data of the file A.

At step S22, the exposure control unit40calculates target values (λt, Δλt, and Et) of the laser-beam control parameters of each pulse in each scanning field SF based on the position of each partial area.

At step S23, the exposure control unit40performs exposure in each scanning field SF by moving the reticle46and the wafer WF while transmitting the target values (λt, Δλt, and Et) of the laser-beam control parameters of each pulse and the light emission trigger signal Tr to the laser control unit20.

At step S24, the exposure control unit40determines whether exposure has been performed in all scanning fields SF in the wafer WF. When the result of the determination at step S24is “No”, the exposure control unit40returns to step S23. When the result of the determination at step S24is “Yes”, the exposure control unit40ends the flowchart inFIG.16.

3.6 Exemplary Contents of Processing by Laser Control Unit

FIG.17is a flowchart illustrating exemplary processing performed by the laser control unit20of Embodiment 1. Steps illustrated inFIG.17are implemented through execution of a program by the processor that functions as the laser control unit20.

At step S31, the laser control unit20reads data of the target laser-beam control parameters (λt, Δλt, and Et) transmitted from the exposure control unit40.

At step S32, the laser control unit20sets the rotation stage84of the line narrow module68of the oscillator22so that the wavelength λ of a pulse laser beam emitted from the laser apparatus12becomes closer to the target wavelength λt.

At step S33, the laser control unit20sets the synchronization timings of the oscillator22and the amplifier24so that the spectrum line width Δλ of the pulse laser beam emitted from the laser apparatus12becomes closer to the target spectrum line width Δλt.

At step S34, the laser control unit20sets the charging voltage of the amplifier24so that the pulse energy E becomes closer to the target pulse energy Et.

At step S35, the laser control unit20waits for input of the light emission trigger signal Tr and determines whether the light emission trigger signal Tr is input. When the light emission trigger signal Tr is not input, the laser control unit20repeats step S35. When the light emission trigger signal Tr is input, the laser control unit20proceeds to step S36.

At step S36, the laser control unit20measures data of the laser-beam control parameters by using the monitor module26. The laser control unit20acquires data of the wavelength λ, the spectrum line width Δλ, and the pulse energy E through the measurement at step S36.

At step S37, the laser control unit20transmits the data of the laser-beam control parameters measured at step S36to the exposure control unit40and the lithography control unit110.

At step S38, the laser control unit20determines whether to stop laser control. When the result of the determination at step S38is “No”, the laser control unit20returns to step S31. When the result of the determination at step S38is “Yes”, the laser control unit20ends the flowchart inFIG.17.

The target wavelength λt, the target spectrum line width Δλt, and the target pulse energy Et that are set for a pulse laser beam with which the partial area Area(1) is to be irradiated are examples of a “first target wavelength”, a “first target spectrum line width”, and a “first target pulse energy” in the present disclosure. The pulse laser beam with which the partial area Area(1) is irradiated is an example of a “first pulse laser beam” in the present disclosure. Similarly, the target wavelength λt, the target spectrum line width Δλt, and the target pulse energy Et that are set for a pulse laser beam with which the partial area Area(2) is to be irradiated are examples of a “second target wavelength”, a “second target spectrum line width”, and a “second target pulse energy” in the present disclosure. The pulse laser beam with which the partial area Area(2) is to be irradiated is an example of a “second pulse laser beam” in the present disclosure. Transmission of data of the target wavelength λt, the target spectrum line width Δλt, and the target pulse energy Et from the exposure control unit40to the laser control unit20is an example of “instruction of the values of pulse-laser-beam control parameters to the laser apparatus” in the present disclosure.

3.7 Effect

The lithography system100according to Embodiment 1 adjusts the optical systems of the exposure apparatus14by performing the typical OPE correction described with reference toFIG.8and then additionally adjusts the laser-beam control parameters for the position of each partial area Area(k) in scanning exposure. With the lithography system100according to Embodiment 1, the laser-beam control parameters corresponding to an optimum OPE are determined for the pattern of each partial area Area(k) in each scanning field SF and exposure is performed with each pulse. Accordingly, the OPE characteristic, which is dependent on the position of scanning, can be adjusted at high speed.

Note that although the OPE characteristic is described in Embodiment 1, the description is also applicable to any other proximity effect characteristic and to correction performed so that an overall proximity effect characteristic including the OPE and the other proximity effect becomes closer to a reference characteristic.

3.8 Other

Embodiment 1 is described with an example in which functions of the lithography control unit110and the exposure control unit40are divided, but the present invention is not limited to this example and the exposure control unit40may have the function of the lithography control unit110.

The calculation process as illustrated inFIG.14may be performed in advance by a computer on which the calculation program is installed, and the file A as illustrated inFIG.15may be stored in a storage unit of the lithography control unit110or the exposure control unit40. The lithography control unit110may be a server configured to manage various parameters used for scanning exposure. The server may be connected to a plurality of exposure systems through a network. For example, the server is configured to perform the calculation process as illustrated inFIG.14and write calculated values of the control parameters to the file A in association with the corresponding partial area Area(k).

In Embodiment 1, calculation of the calculation process as illustrated inFIG.14is ended when the value of ΔCD has reached the allowable range, but the present invention is not limited to this example and further calculation may be performed to obtain the laser-beam control parameters with which the value of ΔCD is minimum.

Note that, in Embodiment 1, the value of ΔCD illustrated inFIG.14is the sum of the absolute value of the CD difference of each pattern, but the present invention is not limited to this example and the value of ΔCD may be, for example, a calculation value expressed by an expression below.
ΔCD=SQRT{(w1·ΔCD1+w2·ΔCD2+ . . . +wnΔCDn)/n}

where wk represents a weight of a pattern k, ΔCDk represents the difference of the CD value of the pattern k from a reference value, and n represents the number of patterns.

4. Embodiment 2

4.1 Configuration

FIG.18illustrates an exemplary configuration of a lithography system102according to Embodiment 2. The lithography system102according to Embodiment 2 includes a wafer examination device310in addition to the configuration inFIG.12. The other configuration may be the same as that of Embodiment 1. The wafer examination device310can measure the CD, the height of the wafer WF, and overlay by irradiating the wafer WF with a laser beam and measuring its reflected light or diffracted light. The wafer examination device310may be a high-resolution scanning electron microscope (SEM). The wafer examination device310includes a wafer examination control unit320, a wafer holder352, and a wafer stage354. The wafer examination device310is an example of an “examination device” in the present disclosure.

The lithography control unit110is connected to a line through which data and the like are transmitted to and received from the wafer examination control unit320.

4.2 Operation

The wafer WF having completed exposure using the exposure apparatus14is held by the wafer holder352of the wafer examination device310and subjected to various kinds of measurement by the wafer examination device310. The lithography control unit110associates a pattern and a CD value at each position on the wafer WF, which are measured by the wafer examination device310, with the laser-beam control parameters of exposure at the position.

The lithography control unit110calculates data of the laser-beam control parameters for optimum OPE correction at each partial area based on a result (pattern and CD) of actual exposure of the wafer WF and stores the data as the file A. The other operation is the same as that in Embodiment 1. The exposure-completed wafer WF as a target of examination by the wafer examination device310is an example of an “exposure-completed semiconductor substrate” in the present disclosure.

FIG.19is a flowchart illustrating exemplary processing at the lithography control unit110of Embodiment 2.

At step S40, the lithography control unit110transmits a measurement signal for the wafer WF to the wafer examination device310. The wafer examination device310performs measurement based on the measurement signal from the lithography control unit110.

At step S41, the lithography control unit110determines whether examination of the wafer WF is completed. When having completed examination of the wafer WF, for example, the wafer examination device310transmits an examination completion signal indicating the examination completion to the lithography control unit110. The lithography control unit110determines whether the examination is completed based on whether the examination completion signal is received.

When the result of the determination at step S41is “No”, the lithography control unit110waits at this step. When the result of the determination at step S41is “Yes”, the lithography control unit110proceeds to step S42.

At step S42, the lithography control unit110receives a pattern and a CD value at each position on the exposure-completed wafer WF from the wafer examination device310. Data of a reticle pattern may be stored in advance when it is difficult to acquire pattern information from a result of measurement by the wafer examination device310.

At step S43, the lithography control unit110sets one to the value of the index k.

Then at step S44, the lithography control unit110sets the value of ΔCDmax as an initial value of ΔCDmin. The value of ΔCDmin is the minimum value of the difference between a CD curve and a target CD curve. The value of ΔCDmax is the maximum value of the difference between the CD curve and the target CD curve.

Then at step S45, the lithography control unit110sets one to the value of an index i. The index i is a set number for identifying a set of laser-beam control parameters. The value of the index i indicates a data set (data combination) of the laser-beam control parameters.

At step S46, the lithography control unit110calculates a set (i) of laser-beam control parameters in the partial area Area(k). The lithography control unit110produces data of control parameters for each pulse of a laser beam in each scanning based on the number of the wafer WF, the scan number of the wafer WF, and the like from the exposure apparatus14and the laser apparatus12and stores the data in the file A. The set (i) of laser-beam control parameters in the partial area Area(k) can be obtained from the stored data.

At step S47, the lithography control unit110measures an OPE curve (k, i) related to each partial area Area(k, i) under an exposure condition of the set (i) of laser-beam control parameters.

At step S48, the lithography control unit110calculates the difference ΔCD between a reference OPE curve (k) of the partial area Area(k) and the measured OPE curve (k, i). The difference ΔCD may be, for example, the sum of the absolute value of the CD value difference of each pattern.

At step S49, the lithography control unit110determines whether ΔCDmin>ΔCD is satisfied. When the result of the determination at step S49is “Yes”, the lithography control unit110proceeds to step S50and performs processing of replacing the value of ΔCDmin with ΔCD.

Then, at step S51, the lithography control unit110stores a data set of the partial area Area(k) and the set (i) of laser-beam control parameters in the file A as correction data of the OPE (k).

After step S51, the lithography control unit110proceeds to step S52. When the result of the determination at step S49is “No”, the lithography control unit110skips steps S50to S51and proceeds to step S52.

At step S52, the lithography control unit110determines whether the value of the index i is equal to a predetermined upper limit value imax. When the result of the determination at step S52is “No”, the lithography control unit110increments the value of the index i (step S53) and returns to step S46. When the result of the determination at step S52is “Yes”, the lithography control unit110proceeds to step S54.

At step S54, the lithography control unit110determines whether the value of the index k is equal to a predetermined value n. When the result of the determination at step S54is “No”, the lithography control unit110increments the value of the index k (step S55) and returns to step S44. When the result of the determination at step S54is “Yes”, the lithography control unit110ends the flowchart inFIG.19.

FIG.20illustrates an exemplary OPE curve for each set (i) of laser-beam control parameters in the partial area Area(k). InFIG.20, Area(k) denotes the reference OPE curve, and Area(k, i) denotes the OPE curve with which the value of ΔCD is minimum.

4.3 Effect

With the lithography system102according to Embodiment 2, the laser control parameters corresponding to an optimum OPE can be determined for the pattern of each partial area in each scanning field SF based on a result of actual exposure of the wafer WF, and exposure can be performed for each pulse.

As a result, error in the CD due to the individual difference (machine difference) of the exposure apparatus14can be corrected for an optimum OPE by adjusting the laser-beam control parameters. Thus, with the same reticle pattern, a desired resist pattern can be formed despite the individual difference of the exposure apparatus14.

According to Embodiment 2, data of the file A can be constantly updated based on a result of actual exposure, and thus exposure can be performed with optimum laser-beam control parameters for each partial area, which are optimum for a current exposure process. As a result, stability of the CD value of a resist pattern improves.

4.4 Other

In Embodiment 2, data of the file A may be produced first by performing test exposure. Data of the file A is produced by performing test exposure through, for example, a procedure as follows.

[Procedure “a”] At each scanning of the wafer WF, scanning exposure is performed with a set of target laser-beam control parameters (λt, Δλt, and Et) set to constant target values. Then, the values of the set of target laser-beam control parameters (λt, Δλt, and Et) at the next scanning exposure are changed, and the scanning exposure is performed with constant target values. This change is repeated through scanning exposure.

[Procedure “b”] The first file A may be produced based on an examination result of the wafer WF subjected to exposure through Procedure “a” and the set (i) of laser-beam control parameters for the exposure.

5. Embodiment 3

5.1 Configuration

FIG.21illustrates an exemplary configuration of a lithography system103according to Embodiment 3. Description will be made on the difference of the configuration illustrated inFIG.21from the configuration illustrated inFIG.18. In the lithography system103illustrated inFIG.21, moving integrated values are used in place of the target laser-beam control parameters. Specifically, a moving integrated value λmvt of a target wavelength, a moving integrated value Δλmvt of a target spectrum line width, and a moving integrated value Dmvt of target pulse energy are used in place of the target wavelength λt, the target spectrum line width Δλt, and the target pulse energy Et as the target laser-beam control parameters transmitted from the exposure control unit40to the laser control unit20. The exposure control unit40transmits the moving integrated values of the target laser-beam control parameters as well as information of the number NSLof pulses, which corresponds to the number of samples of moving integration, to the laser control unit20. The other configuration is the same as that inFIG.18.

In the present specification, moving integrated values of the laser-beam control parameters are defined as described below.

Regarding spectrum parameters, a wavelength and a spectrum line width that are calculated from a spectrum waveform obtained through moving integration with the number NSLof samples as described later are represented by λmv and Δλmv.

Regarding pulse energy parameters, the integrated value of pulse energy, which is obtained through moving integration with the number NSLof samples, is represented by Dmv.

Target values of these parameters are represented by λmvt, Δλmvt, and Dmvt, respectively.

5.2 Operation

The lithography control unit110inFIG.21associates a pattern and a CD value at each position on the wafer WF, which are measured by the wafer examination device310, with the laser-beam control parameters (moving integrated values) of exposure at the position.

The lithography control unit110calculates data of the laser-beam control parameters (moving integrated values) for optimum OPE correction at each partial area based on a result (pattern and CD) of actual exposure of the wafer WF and stores data of a result of the calculation as a file A2. In the data stored in the file A2, the laser-beam control parameters are moving integrated values.

The laser control unit20receives target laser-beam control parameters (moving integrated values), calculates a target spectrum waveform F(λ)t and a target pulse energy Et of the next pulse, and controls the laser apparatus12so that these target values are achieved.

5.3 Exemplary Contents of Processing by Laser Control Unit

FIG.22is a flowchart illustrating exemplary processing performed by the laser control unit20of Embodiment 3. Description will be made on the difference of the flowchart illustrated inFIG.22from the flowchart illustrated inFIG.17. The flowchart illustrated inFIG.22includes steps S30and S31ain place of step S31inFIG.17. The flowchart illustrated inFIG.22also includes steps S37aand S37bin place of step S37inFIG.17.

At step S30, the laser control unit20reads data of the moving integrated values of the target laser-beam control parameters, which is transmitted from the exposure control unit40. The data acquired by the laser control unit20includes data of λmvt, Δλmvt, Dmvt, and NSL.

At step S31a, the laser control unit20calculates target laser-beam parameter values (λt, Δλt, and Et) of the next pulse. Exemplary processing contents applied to step S31awill be described later with reference toFIGS.23and24. Steps S32to S36, following step S31a, are the same as those inFIG.17.

At step S37aafter step S36, the laser control unit20writes the moving integrated values (λmv, Δλmv, and Dmv) of the laser-beam control parameters and spectrum waveform data to a file B. Exemplary data stored in the file B will be described later with reference toFIG.25.

Then at step S37b, the laser control unit20transmits measured moving integrated values of the laser-beam control parameters to the exposure control unit40and the lithography control unit110. After step S37b, the process proceeds to step S38. The subsequent steps are the same as those inFIG.17.

FIG.23is a flowchart illustrating the exemplary processing contents applied at step S31ainFIG.22.FIG.24illustrates exemplary spectrum waveforms obtained at calculation steps illustrated inFIG.23.

At step S61inFIG.23, the laser control unit20performs conversion into a target normalized spectrum waveform Iaumv(λ)t with the target values λmvt and Δλmvt. The target normalized spectrum waveform Iaumv(λ)t is calculated through approximation based on the moving integrated value λmvt of the target wavelength and the moving integrated value λmvt of the target spectrum line width. Note that the spectrum line width may be a spectrum width in which 95% of energy is included.

A waveform diagram illustrated at the top ofFIG.24illustrates the target normalized spectrum waveform Iaumv(λ)t calculated at step S61. The spectrum waveform of a normal excimer laser can be approximate to a spectrum waveform of the Lorentz distribution, the Gaussian distribution, or an intermediate distribution between the Lorentz distribution and the Gaussian distribution.

Then, the laser control unit20calculates a target moving-integration spectrum waveform Smv(λ)t. The target moving-integration spectrum waveform Smv(λ)t is expressed by an expression below.
Smv(λ)t=Iaumv(λ)t·NSL

A waveform diagram illustrated second from the top ofFIG.24illustrates an example of the target moving-integration spectrum waveform Smv(λ)t calculated at step S61.

At step S63, the laser control unit20calculates a spectrum waveform Spp(λ) from data of the file B by integrating spectrum waveform data of a pulse NSL−1 before to the previous pulse. A waveform diagram illustrated third from the top ofFIG.24illustrates an example of the spectrum waveform Spp(λ) calculated at step S63. A waveform illustrated with a dashed line in a graph of the spectrum waveform Spp(λ) inFIG.24is a measured spectrum waveform of the previous pulse.

Then at step S64, the target spectrum waveform F(λ)t of the next pulse is calculated from the difference between the target moving-integration spectrum waveform Smv(λ)t and Spp(λ). The target spectrum waveform F(λ)t is expressed by an expression below.
F(λ)t=Smv(λ)t−Spp(λ)

A waveform diagram illustrated at the bottom ofFIG.24illustrates an example of the target spectrum waveform F(λ)t of the next pulse, which is calculated at step S64.

Then at step S66, the laser control unit20calculates the target wavelength λt and the target spectrum line width Δλt from the target spectrum waveform F(λ)t of the next pulse.

The laser control unit20performs processing at steps S72to S73in parallel to or concurrently with the processing at steps S61to S66.

At step S72, the laser control unit20calculates Esump from data of the file B by integrating energy of a pulse NSL−1 before to the previous pulse.

At step S73, the laser control unit20calculates the target pulse energy Et from the difference between Dmvt and Esump.
Et=Dmvt−Esump

After steps S66and S73, the laser control unit20ends the flowchart inFIG.23and returns to the main flow inFIG.22.

5.4 Exemplary Data of File B

FIG.25is a table listing exemplary data written to the file B. As illustrated inFIG.25, the file B records, in association with time-point data TIME for each pulse, a record including data of the pulse energy E, the integrated value Dmv of moving-integration pulse energy, the wavelength λ, the wavelength λmv of a moving-integration spectrum waveform, the spectrum line width Δλ, the spectrum line width Δλmv of the moving-integration spectrum waveform, and a spectrum waveform F(λ).

The wavelength λmv(z−NSL+1) of the moving-integration spectrum waveform and the spectrum line width Δλmv(z−NSL+1) of the moving-integration spectrum waveform are values calculated from a spectrum waveform Smv(λ) obtained by integrating light intensity at each wavelength based on data of the spectrum waveform F(λ) of a pulse (z−NSL+1) to a pulse z. The file B is an example of a “second file” in the present disclosure. The values of the pulse energy E, the wavelength λ, and the spectrum line width Δλ illustrated inFIG.25are each an example of a “measured value of a pulse-laser-beam control parameter” in the present disclosure.

5.5 Effect

In the lithography system103according to Embodiment 3, the laser-beam control parameter values of exposure in each scanning field SF are moving integrated values in a precise sense.

A laser beam emitted from the laser apparatus is controlled by calculating target values of the laser-beam control parameters of the next pulse so that the laser-beam control parameters become equal to target moving integrated values.

As a result, exposure can be performed with the laser-beam control parameters (moving integrated values) for optimum OPE correction at each partial area.

5.6 Other

In Embodiment 3, the wavelength λmv(z−NSL+1) of the moving-integration spectrum waveform and the spectrum line width Δλmv(z−NSL+1) of the moving-integration spectrum waveform are calculated based on an actually measured spectrum waveform, but the present invention is not limited to this example. For example, an approximate expression may be calculated from a measured wavelength λ and a measured spectrum line width Δλ and stored as data of the file A.

In Embodiment 3, the laser apparatus12receives the moving integrated values (λmvt, Δλmvt, and Dmvt) and the number NSLof pulses of moving integration as the laser-beam control parameters, and the laser control unit20calculates target laser-beam control parameters (λt, Δλt, and Et) of the next pulse and controls the laser apparatus12, but the present invention is not limited to this example. For example, such calculation may be performed at the lithography control unit110, and target laser-beam control parameters (λt, Δλt, and Et) for each pulse may be transmitted to the laser control unit20directly or through the exposure control unit40. Alternatively, the calculation may be performed at the exposure control unit40, and target laser-beam control parameters (λt, Δλt, and Et) for each pulse may be directly transmitted to the laser control unit20.

In Embodiment 3, the moving-integration wavelength λmv and the moving-integration spectrum line width Δλmv are calculated from the moving-integration spectrum waveform Smv(λ) over the number NSLof samples, but the present invention is not limited to this example. The same wavelength λmv and the same spectrum line width Δλmv can be calculated from a moving average spectrum Fmv(λ)=Smv (λ)/NSL.

In addition, the integrated value Dmv of moving-integration pulse energy over the number NSLof samples is calculated, but the present invention is not limited to this example. Moving average pulse energy Emv=Dmv/NSLmay be obtained from Dmv and used as a pulse-laser-beam control parameter.

Thus, in the present specification, the moving integrated value of a pulse-laser-beam control parameter is synonymous with the moving average value of the pulse-laser-beam control parameter. Specifically, a wavelength λmv, a spectrum line width Δλmv, and moving average pulse energy Emv obtained from a moving-average spectrum waveform may be used as the moving average values of pulse-laser-beam control parameters.

6. Exemplary Excimer Laser Apparatus that Uses Solid-State Laser Device as Oscillator

6.1 Configuration

The laser apparatus12of the configuration exemplarily described with reference toFIG.13includes a line narrowing gas laser apparatus as the oscillator22, but the configuration of a laser apparatus is not limited to the example inFIG.13.

FIG.26illustrates another exemplary configuration of a laser apparatus. A laser apparatus212illustrated inFIG.26may be used in place of the laser apparatus12illustrated inFIG.13. In the configuration illustrated inFIG.26, an element common or similar to that inFIG.13is denoted by the same reference sign, and thus description is omitted.

The laser apparatus212illustrated inFIG.26is an excimer laser apparatus that uses a solid-state laser device as an oscillator, and includes a solid-state laser system222, an excimer amplifier224, and a laser control unit220.

The solid-state laser system222includes a semiconductor laser system230, a titanium sapphire amplifier232, a pumping pulse laser234, a wavelength conversion system236, and a solid-state laser control unit238.

The semiconductor laser system230includes a distributed-feedback (DFB) semiconductor laser configured to emit a CW laser beam having a wavelength of 773.6 nm approximately and a semiconductor optical amplifier (SOA) configured to generate pulses of the CW laser beam. An exemplary configuration of the semiconductor laser system230will be described later with reference toFIG.27.

The titanium sapphire amplifier232includes titanium sapphire crystal. The titanium sapphire crystal is disposed on the optical path of a pulse laser beam subjected to pulse amplification at the SOA of the semiconductor laser system230. The pumping pulse laser234may be a laser apparatus configured to emit second-order harmonic light of a YLF laser. Yttrium lithium fluoride (YLF) is solid-state laser crystal expressed by the chemical formula LiYF4.

The wavelength conversion system236includes a plurality of non-linear optical crystals, performs wavelength conversion of an incident pulse laser beam, and emits a fourth-order harmonic pulse laser beam. The wavelength conversion system236includes, for example, LBO crystal and KBBF crystal. The LBO crystal is non-linear optical crystal expressed by the chemical formula LiB3O5. The KBBF crystal is non-linear optical crystal expressed by the chemical formula KBe2BO3F2. Each crystal is disposed on a non-illustrated rotation stage so that the incident angle on the crystal can be changed.

The solid-state laser control unit238controls the semiconductor laser system230, the pumping pulse laser234, and the wavelength conversion system236in accordance with a command from the laser control unit220.

The excimer amplifier224includes the chamber160, the PPM164, the charger166, a convex mirror241, and a concave mirror242. The chamber160includes the windows171and172, the pair of electrodes173and174, and the electrically insulating member175. ArF laser gas is introduced into the chamber160. The PPM164includes the switch165and the charging capacitor.

The excimer amplifier224has a configuration in which seed light having a wavelength of 193.4 nm is amplified by passing through a discharge space between the pair of electrodes173and174three times. The seed light having a wavelength of 193.4 nm is a pulse laser beam emitted from the solid-state laser system222.

The convex mirror241and the concave mirror242are disposed outside the chamber160so that the pulse laser beam emitted from the solid-state laser system222is expanded by passing three times.

The seed light having a wavelength of 193.4 nm approximately and having entered the excimer amplifier224passes through a discharge space between a pair of discharge electrodes412and413three times by being reflected at the convex mirror241and the concave mirror242. Accordingly, the beam of the seed light is enlarged and amplified.

6.2 Operation

When having received the target wavelength λt, the target spectrum line width Δλt, and the target pulse energy Et from the exposure control unit40, the laser control unit220calculates, from table data, an approximate expression, or the like, a target wavelength λ1ctand a target spectrum line width Δλ1chtof a pulse laser beam from the semiconductor laser system230with which the target values are achieved.

The laser control unit220transmits the target wavelength λ1ctand the target spectrum line width Δλ1chtto the solid-state laser control unit238and sets charging voltage to the charger166so that a pulse laser beam output from the excimer amplifier224has the target pulse energy Et.

The solid-state laser control unit238controls the semiconductor laser system230so that the wavelength and spectrum line width of a pulse laser beam emitted from the semiconductor laser system230become closer to the target wavelength λ1ctand the target spectrum line width Δλ1cht. The scheme of the control performed by the solid-state laser control unit238will be described later with reference toFIGS.27to30.

In addition, the solid-state laser control unit238controls two non-illustrated rotation stages to achieve such an incident angle that wavelength conversion efficiency of the LBO crystal and the KBBF crystal of the wavelength conversion system236is maximum.

When the light emission trigger signal Tr is transmitted from the exposure control unit40to the laser control unit220, a trigger signal is input to the semiconductor laser system230, the pumping pulse laser234, and the switch165of the PPM164of the excimer amplifier224in synchronization with the light emission trigger signal Tr. As a result, pulse current is input to the SOA of the semiconductor laser system230, and a pulse-amplified pulse laser beam is emitted from the SOA.

The pulse laser beam is emitted from the semiconductor laser system230and further pulse-amplified at the titanium sapphire amplifier232. The pulse laser beam then enters the wavelength conversion system236. As a result, the pulse laser beam of the target wavelength λt is output from the wavelength conversion system236.

When having received the light emission trigger signal Tr from the exposure control unit40, the laser control unit220transmits a trigger signal to each of a SOA260of the semiconductor laser system230to be described later, the switch165of the PPM164, and the pumping pulse laser234so that a pulse laser beam emitted from the solid-state laser system222discharges when entering the discharge space of the chamber160of the excimer amplifier224.

As a result, the pulse laser beam emitted from the solid-state laser system222is amplified at the excimer amplifier224through three-time passing. The pulse laser beam amplified by the excimer amplifier224is sampled by the beam splitter181of the monitor module26, the pulse energy E is measured by using the photosensor184, and the wavelength λ and the spectrum line width Δλ are measured by using the spectrum detector183.

The laser control unit220may correct and control the charging voltage of the charger166and the wavelength λ1ctand the spectrum line width Δλ1chtof the pulse laser beam emitted from the semiconductor laser system230based on the pulse energy E, the wavelength λ, and the spectrum line width Δλ measured by using the monitor module26so that the difference between the pulse energy E and the target pulse energy Et, the difference between the wavelength λ and the target wavelength λt, and the difference between the spectrum line width Δλ and the target spectrum line width Δλt each become closer to zero.

6.3 Description of Semiconductor Laser System

6.3.1 Configuration

FIG.27illustrates an exemplary configuration of the semiconductor laser system230. The semiconductor laser system230includes a distributed-feedback semiconductor laser250of a single longitudinal mode, a semiconductor optical amplifier (SOA)260, a function generator (FG)261, a beam splitter264, a spectrum monitor266, and a semiconductor laser control unit268. The distributed-feedback semiconductor laser is referred to as a “DFB laser”.

The DFB laser250emits a continuous wave (CW) laser beam having a wavelength of 773.6 nm approximately. The DFB laser250can change its oscillation wavelength by current control and/or temperature control.

The DFB laser250includes a semiconductor laser element251, a Peltier element252, a temperature sensor253, a temperature control unit254, a current control unit256, and a function generator257. The semiconductor laser element251includes a first clad layer271, an active layer272, and a second clad layer273and includes a grating274at the boundary between the active layer272and the second clad layer273.

6.3.2 Operation

The DFB laser250has an oscillation central wavelength that can be changed by changing a setting temperature T and/or a current value A of the semiconductor laser element251.

When a spectrum line width is controlled by chirping the oscillation wavelength of the DFB laser250at high speed, the control of the spectrum line width can be performed by changing the current value A of current flowing through the semiconductor laser element251at high speed.

Specifically, a central wavelength λ1chcand a spectrum line width Δλ1chof the pulse laser beam emitted from the semiconductor laser system230can be controlled at high speed by transmitting values of parameters of a DC component value A1dc, a variation width A1acof an AC component, and a period A1Tof the AC component as current control parameters from the semiconductor laser control unit268to the function generator257.

The spectrum monitor266may measure wavelength by using, for example, a spectrometer or a heterodyne interferometer.

The function generator257outputs, to the current control unit256, an electric signal having a waveform in accordance with a current control parameter designated by the semiconductor laser control unit268. The current control unit256performs current control so that current in accordance with the electric signal from the function generator257flows through the semiconductor laser element251. Note that the function generator257may be provided outside the DFB laser250. For example, the function generator257may be included in the semiconductor laser control unit268.

FIG.28is a conceptual diagram of a spectrum line width achieved by chirping. The spectrum line width Δλ1chis measured as the difference between a maximum wavelength and a minimum wavelength generated by chirping.

FIG.29is a schematic diagram illustrating the relation among current flowing through the semiconductor laser, wavelength change by chirping, a spectrum waveform, and light intensity. A graph GA displayed at a lower-left part ofFIG.29is a graph illustrating change of the current value A of current flowing through the semiconductor laser element251. A graph GB displayed at a lower-central part ofFIG.29is a graph illustrating chirping caused by the current of the graph GA. A graph GC displayed at an upper part ofFIG.29is a schematic diagram of a spectrum waveform obtained by the chirping of the graph GB. A graph GD displayed at a lower-right part ofFIG.29is a graph illustrating change of the light intensity of a laser beam emitted from the semiconductor laser system230due to the current of the graph GA.

Current control parameters of the semiconductor laser system230include the following values as illustrated in the graph GA.

A1dc: DC component value of current flowing through the semiconductor laser element

A1ac: variation width of the AC component of current flowing through the semiconductor laser element (the difference between a maximal value and a minimal value of the current)

A1T: period of the AC component of current flowing through the semiconductor laser element

In the example illustrated inFIG.29, triangular wave is illustrated as an exemplary AC component of a current control parameter, and variation of light intensity of the CW laser beam emitted from the DFB laser250due to variation of triangular-wave current is small.

The relation between a time width DTWof an amplification pulse of the SOA260and the period A1Tof the AC component preferably satisfies Expression (1) below.
DTW=n·A1T(1)

where n is an integer equal to or larger than one.

When the relation of Expression (1) is satisfied, change of the spectrum waveform of an amplified pulse laser beam can be suppressed irrespective of the timing of pulse amplification at the SOA260.

Even when Expression (1) is not satisfied, a pulse width range at the SOA260is, for example, 10 ns to 50 ns. The period A1Tof the AC component of current flowing through the semiconductor laser element251is sufficiently shorter than the pulse width of the SOA260(the time width DTWof an amplification pulse). For example, the period A1Tis preferably 1/1000 to 1/10 of the pulse width of the semiconductor optical amplifier260. More preferably, the period A1Tmay be 1/1000 to 1/100 of the pulse width.

The SOA260preferably has a rising time that is, for example, equal to or smaller than 2 ns, more preferably equal to or smaller than 1 ns. The rising time is a time Rt required when the amplitude of the waveform of pulse current increases from 10% to 90% of a maximum amplitude as illustrated inFIG.30.

6.3.3 Other

In the example illustrated inFIG.29, triangular wave is illustrated as an exemplary waveform of the AC component of current, but the present invention is not limited to this example and the waveform may be any waveform that changes in a constant period, for example. Examples of the waveform of the AC component other than triangular wave include sine wave and square wave. Various target spectrum waveforms can be generated by controlling the waveform of the AC component.

6.4 Effect

The laser apparatus212, which uses the solid-state laser system222as an oscillator, has the following advantages over a case in which an excimer laser is used as an oscillator.

[1] The solid-state laser system222can control the wavelength λ and the spectrum line width Δλ at high speed and high accuracy by controlling the current value A of the DFB laser250. Specifically, the laser apparatus212can control the oscillation wavelength and the spectrum line width Δλ at high speed by controlling the current value A of the DFB laser250immediately after receiving data of the target wavelength λt and the target spectrum line width Δλt. Thus, the wavelength λ and the spectrum line width Δλ of a pulse laser beam emitted from the laser apparatus212can be changed and controlled at high speed and high accuracy for each pulse.

[2] Moreover, spectrum waveforms of various functions, which are different from a normal spectrum waveform, can be generated through chirping by controlling the current value A of the DFB laser250.

[3] Thus, a laser apparatus that includes an oscillator using a solid-state laser system including a DFB laser and includes an excimer amplifier is preferable for controlling the wavelength λmv or line width Δλmv of a moving-integration spectrum obtained from a spectrum waveform of the moving integrated value of a spectrum waveform as a laser control parameter.

6.5 Other

An embodiment of a solid-state laser device is not limited to the example illustrated inFIGS.26to30and may be, for example, a solid-state laser system including a DFB laser having a wavelength of 1547.2 nm approximately and an SOA, and a wavelength conversion system may be a laser apparatus configured to emit eighth-order harmonic light of 193.4 nm. Another solid-state laser device may be a system including a CW oscillation DFB laser and an SOA and configured to pulse-amplify wavelength by controlling the current value of current flowing through the DFB laser and causing pulse current to flow through the SOA.

In the example illustrated inFIG.26, a multi-pass amplifier is illustrated as an exemplary excimer amplifier, but the present invention is not limited to this embodiment, and the excimer amplifier may be, for example, an amplifier including an optical resonator such as a Fabry-Perot resonator or a ring resonator.

7. Hardware Configurations of Various Control Units

A control device that functions as the laser control unit20, the exposure control unit40, the lithography control unit110, the solid-state laser control unit238, the semiconductor laser control unit268, and any other control unit can be achieved by hardware and software combination of one or a plurality of computers. The software is synonymous with a program. The computers conceptually include a programmable controller. Each computer may include a central processing unit (CPU) and a memory. The CPU included in the computer is an example of a processor.

Some or all of processing functions of the control device may be implemented by using an integrated circuit such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC).

Functions of a plurality of control devices can be implemented by a single control device. Moreover, in the present disclosure, the control device may be connected with each other through a communication network such as a local area network or the Internet. In a distributed computing environment, a program unit may be stored in local and remote memory storage devices.

8. Electronic Device Manufacturing Method

FIG.31schematically illustrates an exemplary configuration of the exposure apparatus14. The exposure apparatus14includes the illumination optical system44and the projection optical system50. The illumination optical system44illuminates, with a laser beam incident from the laser apparatus12, the reticle pattern of the reticle46disposed on the non-illustrated reticle stage48. The laser beam having transmitted through the reticle46is subjected to reduced projection through the projection optical system50and imaged on a non-illustrated workpiece disposed on a workpiece table WT. The workpiece may be a photosensitive substrate such as a semiconductor wafer to which resist is applied. The workpiece table WT may be the wafer stage54.

The exposure apparatus14translates the reticle stage48and the workpiece table WT in synchronization so that the workpiece is exposed to the laser beam on which the reticle pattern is reflected. A semiconductor device can be manufactured through a plurality of processes after the reticle pattern is transferred onto the semiconductor wafer through the exposure process as described above. The semiconductor device is an example of an “electronic device” in the present disclosure.

The laser apparatus12inFIG.31may be, for example, the laser apparatus212including the solid-state laser system222, which is described with reference toFIG.26.

9. Other

The description above is intended to be illustrative and the present disclosure is not limited thereto. Therefore, it would be obvious to those skilled in the art that various modifications to the embodiments of the present disclosure would be possible without departing from the spirit and the scope of the appended claims. Further, it would be also obvious for those skilled in the art that embodiments of the present disclosure would be appropriately combined.

The terms used throughout the present specification and the appended claims should be interpreted as non-limiting terms. For example, terms such as “comprise”, “include”, “have”, and “contain” should not be interpreted to be exclusive of other structural elements. Further, indefinite articles “a/an” described in the present specification and the appended claims should be interpreted to mean “at least one” or “one or more”. Further, “at least one of A, B, and C” should be interpreted to mean any of A, B, C, A+B, A+C, B+C, and A+B+C as well as to include combinations of the any thereof and any other than A, B, and C.