Abstract:
A maskless pattern generating system for use in lithographic processing includes a liquid crystal pixel array. The system generates a light beam and applies a voltage level to each pixel of the pixel array to modulate a polarization state of the light beam so as to create a pattern image. The voltage levels correspond to greyscale levels assigned to the pixels. The system can receive a control signal input based on pattern information that defines the pattern image. The setting of the individual voltage levels can allow the liquid crystal pixel array to act as a phase shift mask, can allow the pattern image to be shifted, and can allow the manipulation of a pattern image edge. This maskless pattern writing system acts as a light valve to control pattern imagery, on a pixel by pixel basis, for the purposes of direct writing patterns.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. patent application Ser. No. 10/755,470, filed Jan. 13, 2004, the contents of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates generally to lithographic processing. More particularly, this invention relates to a maskless optical writer for direct writing high resolution patterns to substrates such as integrated circuit wafers.  
         [0004]     2. Background Art  
         [0005]     Lithography is a process used to create features on the surface of substrates. Such substrates can include those used in the manufacture of flat panel displays, circuit boards, various integrated circuits, and the like. A frequently used substrate for such applications is a semiconductor wafer. During lithography, a wafer is disposed on a wafer stage and held in place by a chuck.  
         [0006]     The chuck is typically a vacuum or electrostatic chuck capable of securely holding the wafer in place. The wafer is exposed to an image projected onto its surface by exposure optics located within a lithography apparatus. While exposure optics are used in the case of photolithography, a different type of exposure apparatus can be used depending on the particular application. For example, x-ray, ion, electron, or photon lithographies each may require a different exposure apparatus, as is known to those skilled in the relevant art. The particular example of photolithography is discussed here for illustrative purposes only.  
         [0007]     The projected image produces changes in the characteristics of a layer, for example photoresist, deposited on the surface of the wafer. These changes correspond to the features projected onto the wafer during exposure. Subsequent to exposure, the layer can be etched to produce a patterned layer. The pattern corresponds to those features projected onto the wafer during exposure. This patterned layer is then used to remove, dope, or otherwise affect exposed portions of underlying structural layers within the wafer, such as conductive, semiconductive, or insulative layers. This process is then repeated, together with other steps, until the desired features have been formed on the surface, or in various layers, of the wafer.  
         [0008]     Step-and-scan technology works in conjunction with a projection optics system that has a narrow imaging slot. Rather than expose the entire wafer at one time, individual fields are scanned onto the wafer one at a time. This is done by moving the wafer and the reticle or light valve that defines the pattern simultaneously such that the imaging slot is moved across the field during the scan. The wafer stage must then be stepped between field exposures to allow multiple copies of a pattern to be exposed over the wafer surface. In this manner, the sharpness of the image projected onto the wafer is maximized.  
         [0009]     Reticles (also known as masks or photomasks) are used to block photoresist exposure in selected areas, defining the pattern to be exposed. Reticles, and the use of reticles, can be expensive, especially for small wafer runs.  
         [0010]     An alternative to using reticles is to use a maskless light valve called a spatial light modulator (SLM), such as a grating light valve (GLV) or a digital micromirror device (DMD) (also known as a digital micromirror array or a tilt-mirror array). A DMD is an array of a multitude of tiny mirrors, each mirror representing one pixel of a pattern. Each micromirror can be individually programmed to be turned on or off, thereby allowing the micromirror array to be programmed to represent a desired pattern. When an individual micromirror is turned on, an illumination is reflected by that mirror toward exposure optics and ultimately to a photoresist or substrate (e.g., a wafer). When an individual micromirror is turned off, the illumination is not reflected toward the exposure optics and therefore is not then reflected toward the photoresist or substrate. In this way, the DMD becomes a maskless light valve.  
         [0011]     One disadvantage of using a DMD is that micromirrors generally can only be on or off. In other words, a DMD does not easily allow greyscaling. In order to change greyscaling using a DMD, the micromirror needs to be precisely tilted to an exact angle. However, the customized tilting of the micromirror can have negative effects. For example, telecentricity may change due the image plane no longer being orthogonal to the optics as a result of a mirror tilt. In addition, with a DMD, one does not have control of the phase of the light for individual pixels. Therefore, a DMD cannot easily be used as a phase shift mask.  
         [0012]     What is needed is a maskless optical writer for direct writing patterns to substrates, without the disadvantages associated with reticle systems and known light valve systems described above.  
       BRIEF SUMMARY OF THE INVENTION  
       [0013]     A maskless pattern generating system for use in lithographic processing includes a liquid crystal pixel array. The system generates a light beam and applies a voltage level to each pixel of the pixel array to modulate a polarization state of the light beam so as to create a pattern image. The voltage levels correspond to greyscale levels assigned to the pixels. The system can receive a control signal input based on pattern information that defines the pattern image. This maskless pattern writing system acts as a light valve to control pattern imagery, on a pixel by pixel basis, for the purposes of direct writing patterns.  
         [0014]     One advantage of the invention is that the programmable pattern generator can be used as a phase shift mask. The pattern image can become phase-shifted when the individual voltage levels applied to the pixels of the pixel array are set past one cycle of light. Another advantage is that placement of the pattern image can be shifted when the individual voltage levels set for the pixels corresponding to the pattern image are shifted in one direction by the same number of pixel rows. A further advantage of this invention is that an edge of the pattern image can be manipulated by setting the individual voltage levels corresponding to the pixels that are either part of the pattern image edge or a pixel row beyond the pixels of the pattern image edge, for example.  
         [0015]     Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. The above features and advantages are not each required for all disclosed embodiments of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0016]     The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.  
         [0017]      FIG. 1  is an exemplary illustration of a maskless optical writing system as is currently known by those skilled in the art.  
         [0018]      FIG. 2  is an exemplary illustration of a maskless optical writing system, according to an embodiment of the present invention.  
         [0019]      FIG. 3  is an exemplary illustration of a maskless optical writing system using polarized illumination, according to an embodiment of the present invention.  
         [0020]      FIG. 4A  illustrates the workings of a liquid crystal display, according to an embodiment of the present invention.  
         [0021]      FIG. 4B  illustrates the workings of a reflective liquid crystal display, according to an embodiment of the present invention.  
         [0022]      FIG. 5  is an exemplary illustration of a pattern generator controller data manipulator, according to an embodiment of the present invention.  
         [0023]      FIG. 6  is a flowchart illustrating a method of generating a maskless pattern, according to an embodiment of the present invention.  
         [0024]      FIGS. 7A and 7B  are flowcharts illustrating step  682  of the method illustrated in  FIG. 6 , according to embodiments of the present invention.  
         [0025]      FIG. 8  is a flowchart illustrating a method of generating a maskless pattern, according to an embodiment of the present invention.  
         [0026]      FIG. 9  is a flowchart illustrating step  808  of the method illustrated in  FIG. 8 , according to an embodiment of the present invention.  
         [0027]      FIG. 10  is a flowchart illustrating a method of performing maskless lithography, according to an embodiment of the present invention.  
         [0028]      FIGS. 11A and 11B  are flowcharts illustrating step  1022  of the method illustrated in  FIG. 10 , according to embodiments of the present invention.  
         [0029]      FIG. 12  is a flowchart illustrating a method of performing maskless lithography, according to an embodiment of the present invention.  
         [0030]      FIG. 13  is a flowchart illustrating step  1252  of the method illustrated in  FIG. 12 , according to an embodiment of the present invention.  
         [0031]      FIG. 14  is a flowchart illustrating step  1256  of the method illustrated in  FIG. 12 , according to an embodiment of the present invention.  
         [0032]      FIGS. 15 and 16  are flowcharts illustrating methods of performing maskless lithography, according to embodiments of the present invention.  
         [0033]      FIG. 17  is a chart illustrating the shifting of an exposed edge through the use of greyscaling, according to an embodiment of the present invention.  
         [0034]      FIGS. 18 and 19  illustrate the shifting of an exposed edge through the use of greyscaling, according to an embodiment of the present invention. 
     
    
       [0035]     The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0036]     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those skilled in the art with access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.  
         [0037]     It should be noted that the terms “light,” “light beam,” and “illumination” are used interchangeably throughout this specification.  
         [0038]     A conventional maskless optical writing system  100  is depicted in  FIG. 1 .  
         [0039]     An illumination source  102  directs an illumination beam  104  toward a conventional pattern generator  106 . The pattern generator  106  may be a DMD form of an SLM, or some type of tilt-mirror device, for example. Pattern instructions are provided to the pattern generator  106  via a control signal  108  by a controller  110 . Controller  110  receives pattern information via a data stream  112  from a pattern information source  114 .  
         [0040]     In the conventional maskless optical writing system  100 , pattern generator  106  turns pixels (e.g., micromirrors of a DMD) on or off according to instructions received via control signal  108 . When illumination beam  104  is reflected by the “on” pixels within pattern generator  106 , a generated light beam  116  results. Generated light beam  116  is reflected toward a reduction optics  118 . Reduction optics  118  comprises a plurality of lenses that minimize light beam  116 , thereby minimizing the pattern image. The minimized pattern image is then projected as light beam  120  onto a substrate  124  (e.g., a semiconductor wafer, flat panel display, or the like workpiece) disposed on a substrate stage  122 . Substrate stage  122  may be a stepping and scanning stage, for example.  
         [0041]     The conventional maskless pattern generator, such as a DMD, does not easily allow greyscaling. In order to change greyscaling using a DMD, each micromirror must be tilted to an exact angle. However, the customized tilting of the micromirror can have negative effects. For example, telecentricity may change due to the image plane no longer being orthogonal to the optics as a result of a mirror tilt. In addition, with a DMD, one does not have control of the phase of the light for individual pixels. Therefore, a DMD cannot easily be used as a phase shift mask.  
         [0042]     A maskless optical writing system  200 , according to an embodiment of the present invention, is depicted in  FIG. 2 . A polarized illumination source  203  outputs a polarized beam  204 A. Polarized illumination source  203  is depicted as illumination source  202 , which provides an illumination beam  204  to a polarizer  205 A. Polarizer  205 A polarizes illumination beam  204 , resulting in a polarized illumination beam  204 A. It is to be appreciated by those skilled in the art that other types of polarized illumination sources can be used. Polarized illumination beam  204 A is then directed toward a non-conventional pattern generator  206 .  
         [0043]     In one embodiment of the present invention, the pattern generator  206  comprises a liquid crystal display (LCD) array. A pattern information source  114  provides a data stream  112  containing pattern information to a controller  210 . Controller  210  outputs a control signal  208  that contains pattern instructions for pattern generator  206 . Controller  210  can comprise hardware, software, or a combination of hardware and software.  
         [0044]     Controller  210  comprises a pattern information manipulator  230 . Pattern information manipulator  230  decodes pattern information received from data stream  112 , and assigns the pattern information data on a pixel-by-pixel basis. According to an embodiment of the present invention, the pattern information manipulator  230  assigns greyscale values for each pixel. Embodiments of pattern information manipulator  230  can comprise hardware, software, or a combination of hardware and software. Pattern information manipulator  230  will be described in more detail below.  
         [0045]     In maskless optical writing system  200 , the LCD array of pattern generator  206  comprises a plurality of LCD chips. Each pixel of each LCD chip is provided with a voltage corresponding to the instructions supplied by control signal  208 . The intensity of the resulting exposure on substrate  124  depends indirectly on the voltage supplied to each pixel and the resulting polarization modulation of the output light beams. It is this polarization modulation that creates the light valve, as described below.  
         [0046]     The general operation of an LCD array will now be discussed. As stated previously, in one embodiment of the present invention, pattern generator  206  is an LCD array, which comprises a plurality of LCD chips. Each LCD chip operates as is depicted in  FIG. 4A . The type of liquid crystal (LC) employed and how that LC material behaves in the presence of an electric field will determine its polarization and whether incident light is transmitted or not (in the case of a transmissive array), as is conventionally known in the LCD art. For example, the LC material in an LCD chip may have properties such that if no voltage is applied to LCD chip  432 A, the polarity of an incident polarized light beam wave  434 A changes (i.e., “rotates”) ninety degrees ( 900 ). Thus, transmitted polarized light beam wave  436 A is ninety degrees out of phase with respect to incident polarized light beam wave  434 A. This occurs because of the refractive properties of the LC material of LCD chip  432 A. Alternatively, application of a voltage to LCD chip  432 A may not cause the polarity of polarized light beam wave  434 A to rotate ninety degrees, thereby allowing light beam wave  434 A to simply pass through with the same polarity. At voltages in-between, however, the polarization of the light is partly rotated and elliptically polarized. Alternatively, the LC material may have opposite properties such that if no voltage is applied, the polarity does not change, and if a voltage is applied, the polarity changes ninety degrees.  
         [0047]     In one embodiment of the present invention, the liquid crystal material of the LCD array has properties such that when no voltage is supplied to a pixel, the polarity of the resulting light beam  216  from that pixel is rotated by ninety degrees. In this embodiment, when a certain voltage (a “no-polarity-change” voltage) is supplied to a pixel, the polarity of the resulting light beam  216  from that pixel does not change. If the desired result is for the pixels with no voltage supplied thereto to produce no light at all, then the light resulting from pixels with no voltage supplied thereto needs to be blocked. For this embodiment, a polarizer  205 B with the same polarity as the polarity of polarized illumination beam  204 A is employed. In this configuration, light beams  216  incident on pixels of LCD array  206  with no voltage supplied thereto will be at the opposite polarity as polarizer  205 B and will be blocked, producing no exposure in the corresponding areas of substrate  124 .  
         [0048]     Alternatively, light beams  216  incident on pixels of LCD array  206  with the “no-polarity-change” voltage supplied will be at the same polarity as polarizer  205 B and will be transmitted through as light beams  216 A. Light beams  216 A will then pass through reduction optics  118  as minimized light beams  220 , and will expose substrate  124  at the highest intensity. At voltages supplied to the pixels that are between zero and the “no-polarity-change” voltage, the polarization of the light is partly rotated and elliptically polarized, allowing some light to pass through polarizer  205 B, and therefore allowing greyscale levels to occur in light beams  216 A.  
         [0049]     In another embodiment of the present invention, the liquid crystal material of the LCD array has properties such that when a certain voltage is supplied to a pixel (e.g., a “90-degree-polarity-change” voltage), the polarity of the resulting light beam  216  from that pixel is rotated by ninety degrees. In this embodiment, when no voltage is supplied to a pixel, the polarity of the resulting light beam  216  from that pixel does not change. If the desired result is for the pixels with no voltage supplied thereto to produce no light at all, then the light resulting from pixels with no voltage supplied needs to be blocked. For this embodiment, a polarizer with a polarity opposite of the polarity of polarized illumination beam  204 A is employed. In this configuration, light beams  216  incident on pixels of LCD array  206  with no voltage supplied thereto will be at the opposite polarity as polarizer  205 B and will be blocked, producing no exposure in the corresponding areas of substrate  124 .  
         [0050]     Alternatively, light beams  216  incident on pixels of LCD array  206  with the “ 90 -degree-polarity-change” voltage supplied will be at the same polarity as polarizer  205 B and will be transmitted through as light beams  216 A. Light beams  216 A will then pass through reduction optics  118  as minimized light beams  220 , and will expose substrate  124  at the highest intensity. At voltages supplied to the pixels that are between zero and the “ 90 -degree-polarity-change” voltage, the polarization of the light is partly rotated and elliptically polarized, allowing some light to pass through polarizer  205 B, and therefore allowing greyscale levels to occur in light beams  216 A.  
         [0051]     In maskless optical writing system  200 , light beam  216 A is minimized by reduction optics  118 . Reduction optics  118  comprises a plurality of lenses.  
         [0052]     Reduction optics  118  can encompass any suitable reduction optics for this purpose, as is to be appreciated by those skilled in the art. Minimized light beam  220  is then projected onto substrate  124  held by substrate stage  122 . The intensity of the exposure on substrate  124  depends indirectly on the amount of voltage applied to each corresponding pixel of pattern generator  206 , as previously described.  
         [0053]     Another embodiment of the present invention is shown in  FIG. 3 . In maskless optical writing system  300  of  FIG. 3 , the function of polarizers  205 A/B of  FIG. 2  is performed by a single polarizing beam splitter  326 . In this embodiment, pattern generator  306  is a reflective LCD (RLCD) array. A significant difference between an LCD array and an RLCD array is that the incident light beam(s) for imaging the substrate is reflected off the RLCD, rather than being transmitted through. The polarization modulation occurs similarly in both LCD and RLCD arrays.  
         [0054]     An RLCD chip works as is depicted in  FIG. 4B . For example, the LC material in an RLCD chip may have properties such that if no voltage is applied to RLCD chip  432 B, the polarity of an incident polarized light beam wave  434 B changes (i.e., “rotates”) ninety degrees (90°). Thus, transmitted polarized light beam wave  436 B is ninety degrees out of phase with respect to incident polarized light beam wave  434 B. Alternatively, application of a voltage to RLCD chip  432 B may not cause the polarity of polarized light beam wave  434 A to rotate ninety degrees, thereby allowing light beam wave  434 A to simply reflect from the RLCD with the same polarity. At voltages in-between, however, the polarization of the light is partly rotated and elliptically polarized. Alternatively, the LC material may have opposite properties such that if no voltage is applied, the polarity does not change, and if a voltage is applied, the polarity changes  90  degrees.  
         [0055]     Referring again to  FIG. 3 , in maskless optical writing system  300 , a light source  302  outputs a light beam  304 . Light beam  304  is directed toward polarizing beam splitter  326 . Polarizing beam splitter  326  reflects a polarized beam  328  toward pattern generator  306 . Polarizing beam splitter  326  can be any polarizing dichroic mirror as known in the art. It will be appreciated by those skilled in the art that a polarized beam  305  will pass through polarizing beam splitter  326  with the opposite polarity as polarized beam  328  and be lost from the system.  
         [0056]     The RLCD array of pattern generator  306  comprises a plurality of RLCD chips. Each pixel of each RLCD chip is provided with a voltage corresponding to instructions supplied by control signal  208 . Pattern generator  306  reflects resulting light beams  316  back toward polarizing beam splitter  326 . As with maskless optical writing system  200 , the intensity of the resulting exposure on substrate  124  depends indirectly on the voltage supplied to each pixel and the resulting polarization modulation of the output light beams.  
         [0057]     In one embodiment of the present invention, the liquid crystal material of the RLCD array has properties such that when no voltage is supplied to a pixel, the polarity of resulting reflected light beam  316  from that pixel is rotated by ninety degrees. Reflected light beam  316  will then be at the correct polarity to pass directly through polarizing beam splitter  326 . In this embodiment, when a voltage is supplied to a pixel (e.g., a “no-polarity-change” voltage), the polarity of resulting reflected light beam  316  from that pixel does not change and will again reflect from polarizing beam splitter  326  as beam  317  and be lost from the system. At voltages supplied to pixels that are between zero and the “no-polarity-change” voltage, the polarization of resulting reflected beams  316  from those pixels is partly rotated and elliptically polarized, allowing some light to pass through polarizing beam splitter  326 , and therefore allowing greyscale levels to occur in reflected light beams  316 .  
         [0058]     In another embodiment of the present invention, the liquid crystal material of the RLCD array has properties such that when a certain voltage is supplied to a pixel (e.g., a “90-degree-polarity-change” voltage), the polarity of the resulting reflected light beam  316  from that pixel is rotated by ninety degrees. Reflected light beam  316  will then be at the correct polarity to pass directly through polarizing beam splitter  326 . In this embodiment, when no voltage is supplied to a pixel, the polarity of resulting reflected light beam  316  from that pixel does not change and will again reflect from polarizing beam splitter  326  as beam  317  and be lost from the system. At voltages supplied to pixels that are between zero and the “ 90 -degree-polarity-change” voltage, the polarization of resulting reflected beams  316  from those pixels is partly rotated and elliptically polarized, allowing some light to pass through polarizing beam splitter  326 , and therefore allowing greyscale levels to occur in light beams  316 .  
         [0059]     In maskless optical writing system  300 , resulting reflected light beam  316  is minimized by reduction optics  118 . Reduction optics  118  comprises a plurality of lenses. Reduction optics  118  can encompass any suitable reduction optics for this purpose, as is to be appreciated by those skilled in the art. Minimized light beam  320  is then projected onto substrate  124  held by substrate stage  122 . The intensity of the exposure on substrate  124  depends indirectly on the amount of voltage applied to each corresponding pixel of pattern generator  306 , as previously described.  
         [0060]     In embodiments of the present invention, pattern generators  206 / 306  are compatible with 157 nm illumination to 248 nm illumination, with 193 nm illumination preferred.  
         [0061]     A “slit” area defines the area of projection onto a substrate. The size of a slit area is related to magnification, chip size, and the number of chips arrayed.  
         [0062]     According to embodiments of the present invention, multiple chips are laid out in an array. For a high resolution wafer application, according to embodiments of the present invention, a slit area of approximately 8 mm by 22 mm is preferably used, which involves an array of chips. For wafer applications, this area can be as small as 4 mm by 12 mm or as large as 16 mm by 48 mm, depending on the optics design. However, this area can be smaller or larger than this range, depending on the application in which the invention is used. For example, the slit area for pattern generators used in a flat panel application could be as large as 8 cm by 22 cm or larger. Pattern generators used for projection televisions or cinema screens can cover even larger slit areas, used for screens of 50 feet or larger, for example. For large applications such as these, however, the pixel size will be large.  
         [0063]     In embodiments of the present invention, maskless optical writing systems  200 / 300  can generate pixel sizes on a substrate from 20 nm to 1.5 mm, with a preferred size of approximately 50 nm. According to embodiments of the present invention, reduction optics  118  can minimize a pattern image by a magnification range of 0.005× to 350×, with a magnification of 200× preferred.  
         [0064]     In embodiments of the present invention, light source  202 / 302  is a pulsed excimer laser. Using this laser, individual voltage levels of individual pixels are changed between laser pulses. In embodiments of the present invention, the light source  202 / 302  provides polarized light.  
         [0065]     As previously stated, controller  210  comprises a pattern information manipulator  230 . Pattern information manipulator  230  decodes pattern information received from data stream  112 , and assigns the pattern information data on a pixel-by-pixel basis. According to an embodiment of the present invention, the pattern information manipulator  230  assigns greyscale values for each pixel. Embodiments of pattern information manipulator  230  can comprise hardware, software, or a combination of hardware and software.  
         [0066]      FIG. 5  illustrates pattern information manipulator  230  in more detail.  
         [0067]     Data stream  112 , containing pattern information enters pattern information manipulator  230  and is decoded at a decoder  540 . Pixel addresses are generated at an address generator  542 . Instructions for each pixel are stored in a memory  544  as a pixel “matrix” in a row-by-column manner. For example, a pixel can correspond with an instruction to apply a “maximum” voltage, as depicted by pixel address  546 . Alternatively, a pixel can correspond with an instruction to apply no voltage, as depicted by pixel address  548 . A greyscale level of exposure can alternatively be assigned to a pixel by assigning a voltage that is in-between these two levels. For example, exposure at  75 % is assigned to pixel address  550 . It will be appreciated by those skilled in the art that some linearity correction is needed within the pattern information manipulator  230  of controller  210  to ensure that the greyscale effect is linear as compared to the voltages applied.  
         [0068]     A method  600  of generating a maskless pattern, according to an embodiment of the present invention, is illustrated in  FIG. 6 . The method starts at step  680  and immediately continues at step  682 . In step  682 , a light beam is generated. In step  684 , a control signal input is received from a controller based on pattern information provided to the controller. In step  686 , a pattern image is generated from the light beam based on the control signal input. In an embodiment, the pattern image is generated by setting individual voltage levels (i.e., greyscale levels) corresponding to individual pixels in a pixel array. Method  600  ends at step  688 .  
         [0069]     In one embodiment of the present invention, step  682  of method  600  is carried out as depicted in  FIG. 7A . Step  682  starts at step  790  and immediately continues to step  792 . In step  792 , a light beam is generated. In step  794 , the light beam is reflected toward a pattern generator. The reflection can be accomplished by any beam splitter. In an embodiment, a polarized beam splitter is used. In step  796 , the method returns to step  684  of method  600 .  
         [0070]     In another embodiment of the present invention, step  682  of method  600  is carried out as depicted in  FIG. 7B . Step  682  starts at step  790  and immediately continues to step  792 . In step  792 , a light beam is generated. In step  795 , the light beam is polarized. Polarization of the light beam can be accomplished using any polarizer as is recognized by those skilled in the art. In step  796 , the method returns to step  684  of method  600 .  
         [0071]     A method  800  of generating a maskless pattern, according to an embodiment of the present invention, is illustrated in  FIG. 8 . The method starts at step  802  and immediately continues at step  804 . In step  804 , a polarized illumination is generated. In step  806 , a control signal input is received from a controller based on pattern information provided to the controller. In step  808 , a polarization state of the polarized illumination is modulated. In step  810 , a pattern image is generated from the modulated polarized illumination based on the control signal input. Method  800  ends at step  812 .  
         [0072]     In one embodiment of the present invention, step  808  of method  800  is carried out as depicted in  FIG. 9 . Step  808  starts at step  914  and immediately continues to step  916 . In step  916 , a voltage level corresponding to a greyscale level (including black and white) is set for each individual pixel in a pixel array. In step  918 , the method returns to step  810  of method  800 .  
         [0073]     A method  1000  of performing maskless lithography, according to an embodiment of the present invention, is illustrated in  FIG. 10 . The method starts at step  1020  and immediately continues at step  1022 . In step  1022 , a light beam is generated. In step  1024 , a control signal input is received from a controller based on pattern information provided to the controller. In step  1026 , a pattern image is generated from the light beam based on the control signal input. In an embodiment, the pattern image is generated by setting individual voltage levels (i.e., greyscale levels) corresponding to individual pixels in a pixel array. In step  1028 , the pattern image is minimized by reduction optics for projection onto a substrate. In step  1030 , the substrate is positioned relative to the reduction optics. In step  1032 , the pattern image is received on the substrate. Method  1000  ends at step  1034 .  
         [0074]     In one embodiment of the present invention, step  1022  of method  1000  is carried out as depicted in  FIG. 11A . Step  1022  starts at step  1136  and immediately continues to step  1138 . In step  1138 , a light beam is generated. In step  1140 , the light beam is reflected toward a pattern generator. The reflection can be accomplished by any beam splitter, as is recognized by those skilled in the art. In an embodiment, a polarized beam splitter is used. In step  1142 , the method returns to step  1024  of method  1000 .  
         [0075]     In another embodiment of the present invention, step  1022  of method  1000  is carried out as depicted in  FIG. 11B . Step  1022  starts at step  1136  and immediately continues to step  1138 . In step  1138 , a light beam is generated. In step  1141 , the light beam is polarized. Polarization of the light beam can be accomplished using any polarizer, as is recognized by those skilled in the art. In step  1142 , the method returns to step  1024  of method  1000 .  
         [0076]     A method  1200  of performing maskless lithography, according to an embodiment of the present invention, is illustrated in  FIG. 12 . The method starts at step  1250  and immediately continues at step  1252 . In step  1252 , a polarized illumination is generated. In step  1254 , a control signal input is received from a controller based on pattern information provided to the controller. In step  1256 , a polarization state of the polarized illumination is modulated. In step  1258 , a pattern image is generated from the modulated polarized illumination based on the control signal input. In step  1260 , the pattern image is minimized by reduction optics for projection onto a substrate. In step  1262 , the substrate is positioned relative to the reduction optics. In step  1268 , the pattern image is received on the substrate. Method  1200  ends at step  1270 .  
         [0077]     In one embodiment of the present invention, step  1252  of method  1200  is carried out as depicted in  FIG. 13 . Step  1252  starts at step  1372  and immediately continues to step  1374 . In step  1374 , a polarized illumination is generated. In step  1376 , the polarized illumination is reflected toward a pattern generator. The reflection can be accomplished by any beam splitter. In an embodiment, a polarized beam splitter is used. In step  1378 , the method returns to step  1254  of method  1200 .  
         [0078]     In one embodiment of the present invention, step  1256  of method  1200  is carried out as depicted in  FIG. 14 . Step  1256  starts at step  1480  and immediately continues to step  1482 . In step  1482 , a voltage level corresponding to a greyscale level (including black and white) is set for each individual pixel in a pixel array. In step  1484 , the method returns to step  1258  of method  1200 .  
         [0079]     A method  1500  of performing maskless lithography, according to an embodiment of the present invention, is illustrated in  FIG. 15 . The method starts at step  1502  and immediately continues at step  1504 . Instep  1504 , a light beam is generated. In step  1506 , the light beam is polarized. In step  1508 , a control signal input is received from a controller based on pattern information provided to the controller. In step  1510 , a polarization state of the polarized light beam is modulated. In step  1512 , a pattern image is generated from the modulated polarized light beam based on the control signal input. In an embodiment, the pattern image is generated by setting individual voltage levels (i.e., greyscale levels) corresponding to individual pixels in a pixel array. In step  1514 , the pattern image is polarized. In step  1516 , the pattern image is minimized by reduction optics for projection onto a substrate. In step  1518 , the substrate is positioned relative to the reduction optics. In step  1520 , the pattern image is received on the substrate. Method  1500  ends at step  1522 .  
         [0080]     A method  1600  of performing maskless lithography, according to an embodiment of the present invention, is illustrated in  FIG. 16 . The method starts at step  1602  and immediately continues at step  1604 . In step  1604 , a light beam is generated. In step  1606 , the light beam is polarized. In step  1608 , the polarized light beam is reflected toward a pattern generator. In step  1610 , a control signal input is received from a controller based on pattern information provided to the controller. In step  1612 , a polarization state of the polarized light beam is modulated. In step  1614 , a pattern image is generated from the modulated polarized light beam based on the control signal input. In an embodiment, the pattern image is generated by setting individual voltage levels (i.e., greyscale levels) corresponding to individual pixels in a pixel array. In step  1616 , the pattern image is reflected toward reduction optics. In step  1618 , the pattern image is polarized. In step  1620 , the pattern image is minimized by reduction optics for projection onto a substrate. In step  1622 , the substrate is positioned relative to the reduction optics. In step  1624 , the pattern image is received on the substrate. Method  1600  ends at step  1626 .  
         [0081]     One advantage of the present invention is that it can be used as a phase shift mask. By applying a voltage over more than one cycle of light, a phase shift occurs that imparts useful characteristics similar to a phase shift mask as understood by those skilled in the art. To use the present invention as a phase shift mask, one changes the voltage past the point where the polarization has rotated 90 degrees. This pixel-by-pixel phase interference has the same effect as a phase shift mask, improving the resolution of the system.  
         [0082]     Another advantage of the present invention is that a pattern image can be easily moved by shifting the voltage levels applied to each pixel depending on exactly where the pattern needs to be placed. The placement of the pattern image is shifted when the individual voltage levels set for corresponding pixels are shifted in one direction by the same number of pixel rows or columns.  
         [0083]     A further advantage of the present invention is that greyscaling in the manner described allows the pattern to be easily moved relative to the definition grid. On a substrate, the light from each pixel merges into the light from other pixels. At the edges of a pattern, the light from the edge row of pixels “spills” over and gradually changes from light to dark in a graduated effect. How quickly the transition from light to dark occurs can be controlled by partly turning on the pixels in the transition region. In this way, the light levels of the pixels are manipulated by applying the appropriate voltage levels to “move” an edge of the pattern. This feature of the invention may be used to allow a transition (the gradual change from light to dark) to occur at a boundary that does not correspond to a basic grid boundary. For example, if the pixels are on a b  40  nm grid, and it is desired to position the edge of the pattern on a 5 nm grid, the result may be a transition that is not occurring at a location where one of the basic grid boundaries occurs. In order to move a pattern edge away from the basic grid boundary, the light levels of the pixels on either side of that boundary can be manipulated by applying the appropriate voltage levels to those pixels.  
         [0084]     The chart of  FIG. 17  shows the shifting of an exposed edge through the use of greyscaling as described in connection with the present invention. Chart  1760  shows the plotting of light intensity variation across an exposure edge. At a certain voltage applied to a pixel, the pixel is considered completely “off,” as shown by plot  1765 . At a different voltage applied to the pixel, the pixel is considered completely “on,” as shown by plot  1770 . At the same specific level of intensity (shown by dashed line  1775 ), the distance between the pattern edges when completely “off” (plot  1765 ) versus completely “on” (plot  1770 ) is 40 nm, which in this example is the width of the pixel. Varying the voltage level applied to the pixel to a voltage between the two voltage levels for “on” and “off” allow the pattern edge to be located at intermediate positions, as shown by the data plots in-between plot  1765  and  1770 .  
         [0085]      FIGS. 18 and 19  also illustrate the shifting of an exposed edge through the use of greyscaling as described in accordance with embodiments of the present invention. In  FIG. 18 , pixel rows  1882  of pixel grid  1880  are shown as completely “off.” Pixel rows  1884  are shown as completely “on.” Plot  1888  (shown above pixel grid  1880 ) shows a sharp transition between light and dark.  FIG. 19  shows the movement of the exposed pattern edge. Pixel rows  1982  of pixel grid  1980  are shown as completely “off.” Pixel rows  1984  are shown as completely “on.” Pixel row  1986  is shown at an intermediate state of “on,” in this case at 25% “on.” Setting pixel row  1986  to an intermediate state of on, in effect, has moved the edge of the pattern slightly to the left. Plot  1988  (shown above pixel grid  1980 ) shows the transition between light and dark as a more graduated transition than that of  FIG. 18 .  
       CONCLUSION  
       [0086]     This disclosure presents a maskless pattern writing system that acts as a light valve to control pattern imagery, on a pixel by pixel basis, for the purpose of direct writing patterns. While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the invention as defined in the appended claims. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.