Abstract:
A pellicle for integrated circuit equipment operating in an EUV range includes a multi-layered structure of alternating layers. The pellicle is constructed and arranged to reflect or absorb undesired radiation and to intercept debris to enhance the spectral purity of a radiation beam.

Description:
FIELD 
     The present invention relates to a pellicle, a lithographic apparatus and a method for manufacturing a device. 
     BACKGROUND 
     A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. 
     In a lithographic apparatus, the size of features that can be imaged on the substrate is limited by wavelength of the projection radiation. To produce integrated circuits with a higher density of devices, and hence higher operating speeds, it is desirable to be able to image smaller features. While most current lithographic projection apparatus employ ultraviolet light generated by mercury lamps or excimer lasers, it has been proposed to use shorter wavelength radiation in the range of about 5 nm to about 20 nm, especially around 13 nm. Such radiation is termed extreme ultraviolet (EUV) or soft X-ray and suitable sources include, for example, laser-produced plasma sources, discharge plasma sources or synchrotron radiation from electron storage rings. 
     In conventional ultra-violet lithography, a patterning device is typically protected from a debris with a suitable pellicle arranged in a direct vicinity of the patterning device. 
     EUV radiation sources, such as discharge plasma radiation sources referred to above, may operate with a relatively high partial pressure of a gas or vapor to emit EUV radiation. In a discharge plasma source, for example, a discharge is created in between electrodes, and a resulting partially ionized plasma may subsequently be caused to collapse to yield a very hot plasma that emits radiation in the EUV range. The very hot plasma Xe is used as gas in the plasma. since a Xe plasma radiates in the extreme UV (EUV) range around 13.5 nm. For an efficient EUV production, a typical pressure of 0.1 mbar is used near the electrodes to the radiation source. A drawback of having such a rather high Xe pressure is that Xe gas absorbs EUV radiation. For example, 0.1 mbar Xe transmits over 1 m only 0.3% EUV radiation having a wavelength of 13.5 nm. It is therefore desirable to confine the rather high Xe pressure to a limited region around the source. To achieve this, the source can be contained in its own vacuum chamber in which the collector mirror and illumination optics may also be contained. 
     The known pellicle used for ultraviolet applications may not be suitable for EUV range. 
     SUMMARY OF THE INVENTION 
     It is an aspect of the invention to provide a lithographic apparatus operating in EUV range with a pellicle having a substantial transmission for wavelengths lying in EUV range. 
     According to an aspect of the invention there is provided a pellicle for integrated circuit equipment operating in an EUV range includes a multi-layered structure of alternating layers. The pellicle is constructed and arranged to reflect or absorb undesired radiation and to intercept debris to enhance the spectral purity of a radiation beam. 
     According to an aspect of the invention, there is provided an assembly comprising a patterning device and a pellicle for integrated circuit equipment operating in an EUV range includes a multi-layered structure of alternating layers. The pellicle is constructed and arranged to reflect or absorb undesired radiation and to intercept debris to enhance the spectral purity of a radiation beam. 
     According to an aspect of the invention there is provided a lithographic apparatus for maskless EUV applications. The apparatus comprises an illumination system constructed and arranged to condition a radiation beam emanating from a source of radiation and to supply the conditioned radiation beam to a spatial light modulator for patterning the radiation beam, a substrate table constructed and arranged to hold a substrate, a projection system constructed and arranged to project the conditioned radiation beam onto a target portion of the substrate, and a pellicle constructed and arranged between the illumination module and the spatial light modulator. The pellicle comprises a multi-layered structure of alternating layers. The pellicle is constructed and arranged to reflect or absorb undesired radiation and to intercept debris to enhance the spectral purity of the radiation beam. 
     According to an aspect of the invention, there is provided a lithographic apparatus comprising an illumination system constructed and arranged to condition a radiation beam, and a support constructed and arranged to support a patterning device. The patterning device is capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam, and the support is displaceably arranged. The apparatus also includes a substrate table constructed and arranged to hold a substrate, a projection system constructed and arranged to project the patterned radiation beam onto a target portion of the substrate, and a pellicle. The pellicle comprises a multi-layered structure of alternating layers, and is constructed and arranged to reflect or absorb undesired radiation and to intercept debris to enhance the spectral purity of the radiation beam. 
     According to an aspect of the invention, there is provided a device manufacturing method comprising intercepting a beam of EUV radiation with a pellicle, enhancing the spectral purity of the beam of EUV radiation with the pellicle by reflecting or absorbing undesired radiation and intercepting debris, patterning the beam of EUV radiation with a patterning device, and projecting the patterned beam of EUV radiation onto a substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: 
         FIG. 1  depicts a lithographic apparatus according to an embodiment of the invention; 
         FIG. 2  schematically depicts a pellicle according to an embodiment of the present invention; 
         FIG. 3  schematically depicts a cross-section of part of the pellicle shown in  FIG. 2 ; 
         FIG. 4  schematically depicts a pellicle according to another embodiment of the present invention; 
         FIG. 5  schematically depicts a cross-section of part of the pellicle shown in  FIG. 4 ; and 
         FIG. 6  schematically depicts an assembly according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B, notably Extreme Ultra Violet (EUV) radiation; a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. 
     The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. 
     The support structure supports, i.e. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” 
     The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. 
     The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. 
     The term “projection system” used herein should be broadly interpreted as encompassing 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 or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”. 
     As here depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask). 
     The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. 
     Referring to  FIG. 1 , the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases, the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if desired, may be referred to as a radiation system. 
     The illuminator IL may comprise an adjuster AD 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 may comprise various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. 
     The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the support structure (e.g., 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. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear-encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. 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 (which is not explicitly depicted in  FIG. 1 ) can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may 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 may 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 may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M 1 , M 2  and substrate alignment marks P 1 , P 2 . Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are 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 may be located between the dies. 
     The depicted apparatus could be used in at least one of the following modes: 
     1. In step mode, the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam 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. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 
     2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam 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 mask table MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. 
     3. In another mode, the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is 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 programmable patterning device, such as a programmable mirror array of a type as referred to above. 
     Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. 
       FIG. 2  schematically depicts a pellicle  100  according to an embodiment of the present invention. The pellicle  100  has a multi-layered structure formed by a plurality, for example about 50, alternating Zr/Si layers  102 . Alternative embodiments may have between about 2 and about 200 alternating Zr—Si layers  102 . 
     The pellicle  100  may also include a mesh  104 . The mesh  104  may be made from a suitable metal, for example Cu, and may form a honeycomb structure that includes substantially hexagonal shaped apertures, each having a size of about 1-1.5 mm 2 . The mesh  104  penetrates from one side to the other side of the alternating Zr/Si layers  102 . In alternative embodiments, meshes  104  may be placed adjacent to one side only or on both sides of the Zr/Si layers  102 , or may partially penetrate into the Zr/Si layers  102 . 
     The mesh  104  enhances the integral strength of the Zr/Si layers  102 . The Zr/Si layers  102  are mounted in a substantially circular shaped base  106 . The shape of the base  106  may facilitate the incorporation of the pellicle  100  into a lithographic apparatus, notably by forming an assembly with a patterning device (not shown). The pellicle  100  is therefore easy to handle. Alternatively, the base may have a rectangular shape. The illustrated embodiment is not intended to be limiting in any way. The pellicle may be mounted to a reticle having the same circular or rectangular shape. 
     The Zr/Si layers  102  are designed to be substantially robust. For example, Zr/Si layers  102  are shown in  FIG. 2  with a mesh and with a total thickness of about 200 nm and a surface area of about 10 cm can withstand pressure differences up to about 0.5-1 bar. 
       FIG. 3  schematically depicts a cross-section of a part of the pellicle  100  shown in  FIG. 2 . In  FIG. 3  the thickness of the Zr layers  108  is about 1 nm and the thickness of the Si layers  110  is about 3 nm.  FIG. 3  shows the mesh  104  extending through the Zr/Si layers  102 . In alternative embodiments, although not shown, the thickness of the Zr/Si layers  102  may be variable. Although not fully shown in  FIG. 3 , there may be about 50 or more alternating layers of Zr and Si. 
       FIG. 4  schematically depicts a pellicle  200  according to another embodiment of the present invention. A multi-layer structure formed by alternating Zr/Si layers  202  are not as strong as the Zr/Si layers  102 . For example, Zr/Si layers  202  with a total thickness of about 200 nm and a surface area of about 10 cm can withstand pressure differences of only about 0.1 mbar. The multi-layer structure may be mounted in a base  206 , as shown in  FIG. 4 . 
       FIG. 5  schematically depicts a cross-section of part of the pellicle  200  shown in  FIG. 4 . In  FIG. 5 , the thickness of the Zr layers  208  is about 1 nm and the thickness of the Si layers  10  is about 3 nm. In alternative embodiments, although not shown, the thickness of the Zr/Si layers  202  may be variable. Although not fully shown on  FIG. 5 , there may be 5 about 0 or more alternating layers of Zr and Si. 
     It is noted, that the pellicle  100 ,  200  may be easily mountable to a lithographic patterning device and may also be easily removed. Additionally, although not shown, the pellicle  100 ,  200  may be made in a modular form and may therefore form any desirable surface area. For example, may have a surface area of about 12 cm by about 15 cm (i.e., about 12×15 cm 2 ). 
     Using the pellicle  100 ,  200  as is described with reference to the foregoing, effective filtering of DUV is obtainable. The pellicle can thus act as a spectral purity filter, having only about 20% light loss with up to about 100×10 5  gain in EUV to DUV ratio. In addition, the pellicles  100 ,  200  may mitigate debris such as atomic particles, micro-particles and ions emitted produced from a suitable radiation source. 
       FIG. 6  schematically depicts an assembly  10  according to the invention. In particular a mask MA which may comprise a transparent, for example quartz, substrate  11  on one face of which is provided a chrome pattern  12  representing the pattern which is to be printed on a substrate. A frame  13  surrounds the chrome pattern and supports the pellicle  14  in spaced relation to the mask MA. The pellicle  14  may comprise any embodiment as is discussed with reference to the foregoing. The pellicle  14  is therefore a thin, substantially EUV transparent membrane that is configured to protect the chrome pattern and in particular is configured to prevent dust particles from settling on the chrome pattern. As is discussed with reference to the foregoing, the pellicle  14  may also act as a spectral purity filter and/or mitigate debris propagating from an EUV source in a suitable lithographic apparatus. Therefore, the multi-layered pellicle according to embodiment of the invention provide a synergistic solution for mask protection, debris mitigation, and spectral purity. 
     Frame  13  is sized so that the pellicle is spaced from the plane of the chrome pattern  12  by a distance d, for example, about 5 mm, so that any dust particle adhering to the pellicle is out of focus during exposure and does not print in the resist on the substrate. The pellicle  14  may have a height of about 6.3±0.3 mm, an outer width of about 122±0.3 mm, an inner width of about 118±0.3 mm, an outer length of about 150±0.3 mm, and an inner length of about 146±0.3 mm. In an embodiment of the assembly, the pellicle comprises a surface  14   a  facing the patterning device or mask MA and a particle-trapping surface  14   b . The particle-trapping surface  14   b  is located at a distance of the reflective surface of the mask MA. The distance may have a value between about 5 mm and about 7 mm. A venting hole  15  may be incorporated in the frame  13  to allow equalization of pressure between the pellicle  14  and mask MA and outside. The venting hole  15  may comprise a filter  16  to prevent debris from entering the space between the mask MA and the pellicle  14 . 
     Preferably, the pellicle  14  has a total thickness of the multi-layered structure of alternating layers ranging from about 10 nm to about 700 nm. More preferably, the alternating layers forming the multi-layered structure are formed from a combination of any of the following: Zr and Si layers; Zr and B 4 C layers; Mo and Si layers; Cr and Sc layers; Mo and C layers; and Nb and Si layers. 
     The pellicle, as is set forth anywhere in the foregoing, is also applicable for maskless EUV applications. In this case the pellicle is preferably positioned between the illumination module of the lithography apparatus and the spatial light modulator at an off-focus position. In this embodiment the pellicle also serves as a spectral purity filter. Due to the fact that the pellicle in the maskless EUV lithography apparatus is arranged at an off-focus position, any precipitations on a pellicle surface are not imaged into a substrate. 
     Although specific reference may 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, liquid-crystal 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 may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may 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. 
     Although specific reference may have been made above to the use of embodiments of the invention in the context of lithography, it will be appreciated that the invention may be used in other applications. 
     The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including electromagnetic radiation, such as ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and especially extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm). 
     The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components. 
     While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. 
     The descriptions above 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 invention as described without departing from the scope of the claims set out below.