Abstract:
A high resolution and high data rate spot grid array printer system is provided, wherein an image representative of patterns to be recorded on a reticle or on a layer of a semiconductor die is formed by scanning a substrate with electron beams. Embodiments include a printer comprising an optical radiation source for irradiating a photon-electron converter with a plurality of substantially parallel optical beams, the optical beams being individually modulated to correspond to an image to be recorded on the substrate. The photon-electron converter produces an intermediate image composed of an array of electron beams corresponding to the modulated optical beams. A de-magnifier is interposed between the photon-electron converter and the substrate, for reducing the size of the intermediate image. A movable stage introduces a relative movement between the substrate and the photon-electron converter, such that the substrate is scanned by the electron beams.

Description:
CLAIM OF PRIORITY FROM PROVISIONAL APPLICATION  
       [0001]    This application claims priority from U.S. the provisional application Serial No. 60/331,035. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a maskless photon-electron spot-grid array lithography system. The present invention has particular applicability to lithography for imaging semiconductor substrates.  
         BACKGROUND ART  
         [0003]    Photolithography is a technique for producing images on semiconductor devices. Typically, an image formed on a mask or “reticle” is transferred to a semiconductor substrate, or wafer, where it exposes a resist layered on the substrate. It is desired to pattern smaller and smaller features on semiconductor substrates, which requires the use of shorter and shorter wavelengths of the light that is used to image the patterns. Optical lithography systems using light in the deep ultraviolet (UV) wavelengths create patterns with resolutions of about 0.25 microns. Further decreases in wavelength to 193 nm enable the imaging of patterns with resolutions of 0.18 microns and 0.13 microns. For further improvements in resolution even;shorter wavelengths are necessary, and a number of systems using the shorter wavelengths of electron beams have been proposed to image patterns with resolutions of 0.1 microns and below.  
           [0004]    Electron beam mask projection, such as in SCALPEL, (L. R. Harriott, S. D. Berger, J. A. Liddle, G. P. Watson, and M. M. Mkrtchyan, J. Vac. Sci. Technology, B12, 3533 (1994)) use a scattering mask illuminated by electrons to pattern a substrate. While such systems are capable of high resolution, they are limited by the requirement of making multiple specialty masks, the requirement of including multiple electron lenses, and the ultimate limitation of stochastic Coulomb interactions between individual particles in the beam.  
           [0005]    A hybrid photon-electron array printer based on a traditional deep-ultraviolet demagnification scanner-steppers and using a 4× mask is described in High throughput electron lithography with multiple aperture pixel by pixel enhancement of resolution concept, Journal of Vacuum Science and Technology B 16(6), November/December 1998, page 3177. In this proposal a 4× mask is illuminated by 106-108 optical subbeams formed by a microlens array. After demagnification these subbeams are focused on a photon-electron converter plate. Each photon subbeam triggers the emission of a narrow beam of electrons. The electron beams are focused individually on a wafer. The mask and wafer are both scanned through the many beams, exposing the entire wafer. The use of the optical imaging system simplifies the image formation and the use of the final electron patterning provides improved resolution. Further, this concept overcomes the inherent problem of Coulomb interaction present in the SCALPEL system.  
           [0006]    Unfortunately, due to decreasing design rules and the wide use of RET (Resolution Enhancement Techniques) such as OPC (Optical Proximity Correction) and PSM (Phase Shift Masks), the masks used in image-projection systems have become increasingly difficult and expensive to make. Masks fro electron-projection systems are also extremely difficult and expensive to make. Since many masks are needed to form the multiple patterns required to manufacture an integrated circuit, the time delay in making the masks and the expense of the masks themselves is a significant cost in the manufacture of semiconductors. This is especially so in the case of smaller volume devices, where the cost of the masks cannot be amortized over a large number of devices. Thus, it is desirable to provide a fast apparatus for making semiconductor chips while eliminating the need for expensive masks. It is also desirable to improve the obtainable resolution of optical lithography. Further, such a device may be useful for directly patterning a small number of substrates, such as runs of prototype devices, and for making masks.  
           [0007]    Accordingly, it is desirable to develop a hybrid photon-electron system having the high resolution of an electron imaging system, the simplicity and speed of optical systems, and the high throughput of a mask or massively parallel writing system, but do so without the requirement of a mask.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a maskless photon-electron spot-grid array lithography system. According to the present invention, patterns are produced by a massive array of optical beams modulated by a spatial light modulator (SLM) array. The optical beams are focused on a photon-electron converter, which forms corresponding arrays of electron beams. The electron beams are focused on the substrate to expose a desired pattern on a substrate layered with electron-sensitive resist.  
           [0009]    According to the present invention, the foregoing and other advantages are achieved in part by a method for printing, comprising the steps of generating an array of substantially parallel light beams; modulating individual light beams to form a spot-grid pattern corresponding to a sampling of an image to be recorded on a substrate; converting the modulated light beams to electron beams to provide a corresponding spot-grid pattern of electron beams; and scanning the substrate relative to the electron beams while the generating, modulating, converting and scanning steps are being performed, such that the image is recorded on the substrate.  
           [0010]    Another advantage of the present invention is a step of compensating for mechanical inaccuracies in the movable stage.  
           [0011]    Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout, and wherein:  
         [0013]    [0013]FIG. 1 illustrates a printer according to an embodiment of the present invention.  
         [0014]    [0014]FIG. 1A illustrates one embodiment of electron optics  155  of FIG. 1.  
         [0015]    [0015]FIG. 1B illustrates an alternative embodiment of photon-electron converter  145 .  
         [0016]    [0016]FIG. 1C illustrates another embodiment of electron optics  155 .  
         [0017]    [0017]FIG. 1D illustrates another embodiment of electron optics  155 .  
         [0018]    [0018]FIG. 1E illustrates the electron deflector array of FIG. 1D.  
         [0019]    [0019]FIG. 2 is a cross section of a printer according to another embodiment of the present invention.  
         [0020]    [0020]FIG. 3 illustrates an example of a slanted scan pattern.  
         [0021]    [0021]FIG. 4 is a cross section of a printer according to another embodiment of the present invention.  
         [0022]    [0022]FIG. 5A illustrates a pinhole array limiter.  
         [0023]    [0023]FIG. 5B illustrates an array of apertures. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0024]    The present invention provides a printer that includes a maskless direct-write hybrid optical/electron imaging system. A programmable optical system forms a massive array of optical beams which are individually focused on a photon-electron converter. The spot-grid pattern formed by the focused optical beams is converted to a corresponding spot-grid pattern of electron beams which are focused on a semiconductor substrate layered with an electron-sensitive resist so as to expose the resist with the spot-grid array pattern. The substrate is then translated relative to the electron beam array by a movable stage as subsequent patterns are focused on the substrate so as to build up a final complete image on the substrate.  
         [0025]    In certain embodiments of the present invention, the optical radiation source of the inventive printer includes a light source for generating an array of substantially parallel light beams, and a programmable spatial light modulator selectively modulates optical beams from the array of optical beams. An array of microlenses is provided for focusing light from the light source into the photon-electron converter. Relay optics, such as an optical demagnifier, may be employed between the spatial light modulator and the microlens array to decrease the size of the optical image so as to map the individual pixels from the spatial light modulator onto corresponding elements in the microlens array. The microlenses can be a two-dimensional array of diffractive or refractive micro-lenses. The photon-electron converter produces a spot-grid array electron image corresponding to the optical image incident on it, but with significantly reduced spot sizes. This electron image is then focused on the substrate with an appropriate electron lens.  
         [0026]    A movable stage moves the substrate relative to the electron beam array in a substantially linear scanning direction that is slanted slightly relative to one axis of the electron beam array such the surface of the substrate is completely exposed as the substrate is scanned across the slanted array of electron beams. In various embodiments of the present invention, the movable stage and the array configuration provide for alternative scan patterns including patterns which overlap, patterns which do not overlap, patterns which provide redundancy, and patterns that provide for various degrees of interleaving. As the substrate is scanned relative to the electron beam array, the pattern generated by the optical and electron systems are programmed so as to build up the desired final and complete image on the substrate.  
         [0027]    [0027]FIG. 1 illustrates a printer according to an embodiment of the present invention. Referring to FIG. 1, a light source  105 , which may be a continuous wave laser or a pulsed laser, provides optical radiation which is collimated by collimating lens  110  and reflected by beam splitter  115  onto a two-dimensional spatial light modulator (SLM)  120 .  
         [0028]    Spatial light modulator  120  modulates the light so as to produce a parallel array of modulated light beams corresponding to a desired pattern. In one embodiment of the present invention, SLM  120  comprises an array of micromirrors, such as the Model DMD available from Texas Instruments of Dallas, Tex. The individual micromirrors of SLM  120  are responsive to an input pattern data signal  100  such that light is selectively reflected from each SLM element (also called a pixel) to produce the desired pattern of parallel light beams. The parallel light beams pass back through beam splitter  115  to relay optics  125 .  
         [0029]    Relay optics  125  image each of the SLM elements onto a corresponding microlens in microlens array (MLA)  130 . Relay optics  125  preferably provide for a reduction in the overall size of the optical pattern to correspond to the preferred smaller size of microlens array  130  relative to SLM  120 . However, in general the function of relay optics  125  is to map the optical spot-grid pattern produced by SLM  120  (referred to as the “first intermediate pattern”) onto microlens array  135 . Accordingly, as will be described in more detail below, the relay optics may provide a magnification of 1× or greater as required by the relative sizes of SLM  120  and microlens array  135 .  
         [0030]    Microlens array  130  comprises an array of microlenses, with one microlens corresponding to each element of SLM  120 . Each microlens focuses the optical beam incident on it to an optical spot  140  on the surface of photon-electron converter  145 . Thus the optical spot-grid pattern formed on the surface of photon-electron converted  145  (referred to as the “second intermediate pattern) corresponds to the first intermediate pattern except that its overall size may be magnified (or demagnified) by relay optics  125  and the size of the individual beams have been reduced to smaller spots by the focusing effect of microlens array  130 .  
         [0031]    Spots  140  focused on photon-electron converter  145  are well separated from one-another to prevent cross-talk or interference between the beams. In the preferred embodiment, photon-electron converter  145  comprises a photocathode which generates an array of electron sources  150  in response to incident light beams. The spot-grid pattern of electron sources produced by photon-electron converter  145  (referred to as the third intermediate pattern) thus corresponds to the second intermediate pattern focused on the surface of photon-electron converter  145 .  
         [0032]    Electron optics  155  focuses electrons emerging from the individual electron sources of photon-electron converter  145  to points on substrate  160 . As a result a spot-grid pattern is imaged on substrate  160  (referred to as the fourth intermediate pattern). Different alternatives of electron optics  155  are provided in the embodiments described below, which provide various degrees of demagnification in between the image size of the third intermediate pattern and the fourth intermediate pattern. (See FIGS.  1 A- 1 D and the corresponding discussion.) However, in all cases the spots of the fourth intermediate pattern are significantly reduced in size relative to the spots of the first intermediate pattern generated by SLM  120 . In the preferred embodiment, the size of spots  165  imaged by electrons onto substrate  160  have typical dimensions of 25 nanometers. This significant reduction is spot size results in the improved resolution of the present invention.  
         [0033]    An alternative embodiment of electron optics  155  is illustrated in FIG. 1A. In the alternative embodiment illustrated in FIG. 1A, electron optics  155  comprises an array of apertures  170  and an array of Einzel lenses  172 . Einzel lenses are well known as electrostatic lens for focusing electron beams. As illustrated in FIG. 1A, Einzel lenses consist of three parallel plates, wherein the top and bottom plates ( 172 A and  172 C) have the same potential. An electron beam passes through holes in each of the three plates, and is focused to a spot on substrate  160 . In this embodiment the spacing between adjacent spots on substrate  160  is equal to the corresponding spacing between the optical spots incident on photon-electron converter  145 , but the size of the individual spots is significantly reduced, resulting in a significant improvement in resolution.  
         [0034]    An alternative embodiment of photon-electron converter  145  is illustrated in FIG. 1B. In this alternative embodiment, wherein the second intermediate pattern generated by microlens array  130  are focused onto a corresponding array of microtips  174 . Optically activated microtips, such as those used as electron sources in electron microscopes, are physically small, sharply pointed sources of electrons. Each microtip generates electrons in response to incident optical illumination, and the electron source size is determined by the physical size of the microtip. The “tip of the tip” of these sources is microscopically small, and the physical size of the electron emitting tip of a microtip is significantly smaller than the size of the optical spot incident on the microtip. Thus the spot size of the third intermediate pattern is significantly smaller than that of the second intermediate pattern. Therefore, in this embodiment, the microtip provides for a significant reduction in spot size and a corresponding improvement in resolution. Electrons from the array of microtip sources  174  are focused into an array of electron beams  176  by electron optics  156 , which forms the fourth intermediate pattern on substrate  160 . Electron optics  156  must focus the electrons emerging from the individual microtips and accelerate them towards substrate  160 . Such electron optics are well known, and may comprise, for example, a uniform magnetic field combined with an electrostatic field, both aligned along the z-axis (normal to the surface of the substrate.)  
         [0035]    Another embodiment of the electron optics  155  is shown in FIG. 1C. In this embodiment, electron optics  155  comprises a demagnifying lens  180 , such as is known in the field of electron microscopy. In this embodiment, the demagnification reduces the overall size of the fourth intermediate pattern, the distance between adjacent spots, and the size of individual spots. The reduction of the individual spot size improves resolution. However, this embodiment requires a design of a wide field optics objective, which may suffer from distortions.  
         [0036]    Another embodiment of the electron optics  155  is shown in FIG. 1D. The embodiment of FIG. 1D uses an electron deflector array  190  in combination with a micro-electron lens array  192 . Electron deflector array  190  is further illustrated in FIG. 1E and comprises an array of quadrapole deflectors for deflecting each of the electron beams to a point “f.” As illustrated, electron deflector array  190  comprises an array of apertures for passing individual electron beams, and four electrostatic plates  193   a,    193   b,    193   c,  and  193   d  placed about each aperture. A voltage signal is applied to each plate for deflecting the electron beams through point f. Each Micro electron lens array is  192  similar in construction to the array of Einzel lenses  172  illustrated in FIG. 1A is positioned to re-collimate the electron beams forming a demagnified image. That is, the fourth intermediate pattern is smaller in overall size and has smaller individual spot sizes relative to the third intermediate image. Thus, the use of a deflector array results in the reduction of both spot size and distance between spots (overall image size) without the need to design a wide-field objective, as in FIG. 1C.  
         [0037]    Mechanical stage  167 , which supports substrate  160 , is illustrated in FIG. 1. Mechanical stage  167  translates substrate  160  in the y direction, which is substantially parallel to one of the axes y′ of the electron beam array of the fourth intermediate pattern. The deviation from parallel is chosen such that as substrate  160  is translated relative to the beam array, and as the beam array is modulated to form sequential spot-grid patterns, the spot-grid patterns interlace or interleave so as to leave no gaps in the mechanical cross-scan direction (the x direction). In this way a complete image is scanned onto substrate  160 . There are a number of ways in which this slanted scan can be implemented. For example, the beams may track paths with centers spaced on pixel width apart; or they may track paths spaced one-half pixel width apart and spots on adjoining tracks could be offset one-half pixel width (or less) along the y-axis, resulting in a more tightly packed array of spots on the substrate. Further, scanning patterns with a pitch of less than one pixel between scan lines can be interleaved.  
         [0038]    Another embodiment of the present invention will now be described with reference to FIG. 2. The printer of FIG. 2 comprises the above-described components of the printer of FIG. 1, including light source  105  and collimating lens  110 . In this embodiment, SLM  220  is a selectively transmissive spatial light modulator, which modulates a parallel array of beams similar to those of SLM  120  in response to a pattern data signal  100 . That is, light incident on each element, or pixel, is selectively transmitted or blocked, corresponding to an on or off state for that pixel. An array of microshutters suitable for this function is described in “A proposal for maskless, zoneplate-array nanolithography,” Smith, Henry I., J. Vac. Sci Techno. B 14(6), November/December 1996 and in “Maskless Lithography Using a Multiplexed Array of Fresnel Zone Plates,” U.S. Pat. No. 5,900,637, issued to Henry I. Smith, May 4, 1999.  
         [0039]    Referring still to FIG. 2, light beams  225  from SLM  220  are shaped by beam shaper  230 , which narrows the beams prior to their transmission to focusing optics  235 . Focusing optics  235  comprises a microlens for focusing each of the beams onto an optical demagnifier  240 . Focusing optics  235  focus modulated light beams  225  into an image substantially equal in size to the original image produced by SLM  220 , however the individual spot sizes are greatly reduced.  
         [0040]    Optical demagnifier  240  reduces the overall image size of the pattern produced by SLM  220  and further reduces the individual spot sizes. Optical demagnifier  240  focuses the demagnified image onto the surface of photon-electron converter  145 .  
         [0041]    The configuration of FIG. 2 allows the use of relatively low cost focusing optics  235 , such as microlenses with a relatively small numerical aperture (NA). Several types of lenses can be used in focusing optics  235 , such as standard lenses or microlenses of either the refractive or diffractive type. For relatively low NAs and large fields of view (FOVs), plastic diffractive elements can be used. This allows for FOVs of many tens of centimeters across or even more. For high NA applications microlens arrays (typically tens of microns across) can be used. If diffractive lens elements are used, the lens array can further contain an aperture array (i.e., a pinhole array) to truncate the higher scattering orders created by the diffractive elements. Diffractive lenses are particularly suitable when used in conjunction with short wavelengths of light, such as extreme ultraviolet (EUV) of about 13 nm, to practice the invention.  
         [0042]    Examples of microlens arrays are abundant in the literature, and include “Microlens array with spatial variations of the optical functions,” Hessler et al, Pure Appl. Opt. 6(1997) 673-681, and “A Microlens Direct-Write Concept for Lithography,” Davidson, SPIE 3048, p346.  
         [0043]    Moreover, the micro-lens arrays referred to herein, such as microlens array  130  and focusing optics  235 , can be a single array of lenses, or multiple arrays arranged in series, as per conventional optical techniques, so the optical paths of the individual lens elements from the separate arrays form a compound lens. Such an arrangement results in arrays of compound lenses having a higher numerical aperture than can be obtained with arrays of single lenses. Such compound micro-lens arrays can be mechanically assembled by stacking individual lens arrays, or manufactured by, for example, well-known MEMS (micro-electro mechanical systems) manufacturing techniques.  
         [0044]    Examples of arrays of diffractive optical elements are Fresnel zone plates. They can be designed to work at any wavelength, and arrays of Fresnel zone plates have been used in lithography in a process referred to as zone-plate-array lithography (ZPAL). These arrays and there use are described in “Lithographic patterning and confocal imaging with zone plates,” Gil et al, J. Vac. Sci. Technol. B 18(6), November/December 2000, and “Maskless, parallel patterning with zone-plate array lithography, Carter et al, J. Vac. Sci. Technol. B 17(6), November/December 1999. In general, these diffractive zone plate arrays are suitable substitutes for refractive optical microlens arrays.  
         [0045]    In an alternative embodiment of the present invention, illustrated in FIG. 4, an array of individually controlled lasers are used as light source  400  to create array of beams incident on SLM  405 . In this embodiment of the present invention, the individual lasers can be modulated to a desired intensity (i.e., gray level) to more finely control the image writing. Light source  400  can comprise an array of vertical cavity surface emitting lasers (VCSELs), available from Band Gap Engineering of Colorado. VCSELs are semiconductor lasers that emit light from the top of the chip, straight up.  
         [0046]    An example of a scanning pattern is illustrated in FIG. 3. As illustrated, an array of spots (the fourth intermediate pattern) is incident on substrate  160 . For simplicity, FIG. 3 shows an eight wide (a-h) by six deep (1-6) array of spots. When practicing the present invention, the spot array will typically consist of hundreds, thousands or more electron beams. The shift in the mechanical cross-scan x direction between the centers of spots in consecutive lines determines the pixel size in the x direction (i.e., the projection px on the x-axis of the distance between the e&#39;th spot in the first line e1 and the e&#39;th spot in the 2nd line e2). To obtain continuous coverage of substrate  160 , the last spot in column d6 must trace a path no more than one pixel away in the cross-scan x direction from the tangent of the first spot in an adjacent column (c1). The pixel size in the mechanical scan y direction py (not shown) is determined by the distance traversed between the spot center of a given spot between two consecutive irradiations of substrate  160 ; that is, the distance between the center of a spot f4 at time 0 (“f4t0”) and the same spot one irradiation interval later (“f4t1”). This distance is determined by multiplying the stage velocity and irradiation interval.  
         [0047]    In a further embodiment of the present invention, substrate  160  is translated relative to the beam array to form an interlacing pattern, as each spot is moved a distance that is greater than the pitch between two successive spots, during successive irradiations of substrate  160 , when a pulsed laser source (such as an Excimer laser or Q laser) for light source  105 .  
         [0048]    Motion of substrate  160  can be achieved by any means ensuring accurate and linear motion, such as can be obtained from a conventional interferometer-controlled stage with linear motors and air-bearings, commercially available from Anorad Corporation of New York. Further, in an alternative embodiment of the invention, the substrate can be held stationary and the optics generating the beam array can be translated relative to the substrate is translated relative to the wafer.  
         [0049]    To correct for any residual inaccuracy such as that created by mechanical vibrations of the stage, a compensator for compensating for inaccuracies in the stage&#39;s movement. Referring to FIG. 2, an two-dimension interferometer device  235 , which is either part of the stage or an additional component, is coupled to stage to detect its position and to allow for the generation of a position error signal. These errors can be compensated by a number of alternatives. First, a compensator  250  can be coupled to beam shaper  230  and focusing optics  235  to move them by an amount sufficient to compensate for the error in the stage position. Second, a compensator  260  can be coupled to demagnifier  240  to move it by an amount to compensate for the stage position error. Third, a compensator could be coupled to a mirror movable on two axes for varying the angle of incidence of the light source onto one of the optical elements of the printer, so as to compensate for the stage position error. For example, if the optical path was folded by 90 degrees between beam shaper  230  and focusing optics  235 , and a movable mirror was positioned to direct light from beam shaper  230  to focusing optics  235 , changing the angle of the mirror would vary the angle of incidence of the light on focusing optics  235 , resulting in a translation of the focused image.  
         [0050]    In further embodiments of the present invention, the inventive printer comprises a limiter preceding photon-electron converter  145 . The limiter prevents or significantly reduces writing errors to photon-electron converter  145  resulting from an interaction with reflected optical beams, non parallel optical beams, side-lobes and the like. Referring to FIG. 5 a,  a limiter  500  comprises a pinhole array, wherein pin holes  501  correspond to the light beams of the light beam array generated to impinge on photon-electron converter  145 . In another embodiment of the present invention illustrated in FIG. 5 b,  limiter  510  comprises an array of apertures  511  corresponding to the light beams of the light beam array, each aperture  511  having a width w at least half a wavelength of each of the light beams.  
         [0051]    One advantage of the present invention is that it eliminates the requirement of a high-order reduction lens. More specifically, mask-based lithography systems typically utilize masks that are four or five times (4× or 5×) the size of the desired final pattern. This requires the use of a demagnification lens, commonly referred to as a “stepper lens,” which are typically quite expensive. This has been the case even in current mask-based hybrid photon-electron systems such as described in “High throughput electron lithography with multiple aperture pixel by pixel enhancement of resolution concept,” Kruit, P., J. Vac. Sci. Technol. B 16(6), November/December 1998. In contrast, when a programmable maskless source is used, as in the various embodiments of the present invention, the magnification between the source patterns and the substrate is not subject to the same restrictions, and may be one for both the optical and electron optics. Low-distortion optics are more easily designed with low magnifications. Accordingly, the optics may be designed for low distortion, and the input data signal patterns may be loaded accordingly. That is, since the resolution in the present system is determined by the spot size, not the image demagnification, the pattern data to be mapped to the substrate needs simply to be loaded into the programmable source array at the appropriate time and in the appropriate position in accordance with the configuration selected for the photon optics, electron optics, and writing strategy.  
         [0052]    The writing strategy and other design considerations affect the design choice for the magnification. For example, if a simple linear scan of a slightly rotated scan is used, where the grid comprises N×N Pixels with a pitch of D, and the address unit size on the wafer is d, then the required de-magnificaiton M will be M=D/(d*N). In some cases this might lead to a slight magnification. For example, if D=15 microns, N=1000 and d=25 nm, then M=0.6. (A slight demagnification. However, the cost and distortion corresponding to this slight demagnification would be significantly less than that of current 4× and 5× stepper lens.  
         [0053]    This results in simpler and more distortion-free optics. In fact, the best optics would result from the use of an SLM image having the same size as the final image. i.e., a 1× magnification. Such a reduction element is required in mask systems, where the mask is significantly larger than the desired final image and such reduction elements, or “stepper lenses” are typically quite expensive. However, in the preferred embodiment of the present invention, this element may be advantageously  
         [0054]    The following calculations illustrate the throughput of a printer according to an embodiment of the invention.  
         [0055]    Definitions:  
         [0056]    FOV—Field-of-view in microns on substrate (assume square)  
         [0057]    D—Pitch between spots on substrate in microns  
         [0058]    p—Pixel size on substrate in microns  
         [0059]    ny and nx—number of rows and columns in array respectively  
         [0060]    N—total number of spots in array  
         [0061]    DR—Data-rate requirement (pixels/second/array)  
         [0062]    FR—Frame-rate requirement (array-read/second)  
         [0063]    V—stage velocity in y direction in microns/sec  
         [0064]    Since FOV=D*nx and, without interleaving, ny=D/p, the total number of spots N is:  
           N=nx*ny =( FOV/D )*( D/p )= FOV/p    
         [0065]    For a given data-rate requirement (DR) the frame rate (FR) and hence stage velocity required are:  
         
       FR=DR/N=DR*p/FOV  
     
         [0066]    and  
           V=FR*p=DR*p 2 /FOV    
         [0067]    Example:  
         FOV=10 mm=10000 micron  
           DR= 10 Tera-pix/sec=1012 pix/sec  
         P=10 nm=0.01 micron  
           N= 10000/0.01=1,000,000=106=&gt;an 100 by 100 array;  
           FR= 1010/104=106=1 mega-frames/second  
           V= 106*0.01 micron=10 mm/sec  
         [0068]    The present invention is applicable to the manufacture of various types of semiconductor devices, particularly high-density semiconductor devices having a design rule of about 0.18□ and under.  
         [0069]    The present invention can be practiced by employing conventional materials, methodology and equipment. Accordingly, the details of such materials, equipment and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention can be practiced without resorting to the details specifically set forth. In other instances, well known processing structures have not been described in detail, in order not to unnecessarily obscure the present invention.  
         [0070]    Only exemplary embodiments of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. Further, the description is intended to be descriptive and not limiting. For example, the description of the present invention refers to light sources and discusses optical sources and optical radiation in terms of light and light images. However, the inventor includes all wavelengths of electromagnetic radiation when he references “light,” and not to limit it to visible wavelengths. For example, shorter wavelengths of light, referred to as ultra-violet, deep ultraviolet, extreme ultra-violet, X-rays etc all are considered within the scope of “light” as they all refer to photons and electromagnetic radiation, and are distinguished only by the wavelength of the radiation.