Abstract:
A photolithography system and method for providing a pattern to a subject such as a wafer is provided. The system includes a pixel panel, such as a digital mirror device or a liquid crystal display, for generating for creating a plurality of pixel elements of the pattern. The pixel elements are simultaneously directed to a first site of the subject by a lense system. The system also includes a manipulator for moving the pixel elements, relative to the subject, to a second site of the subject so that a portion of the second site overlaps a portion of the first site.

Description:
BACKGROUND 
     The present invention relates generally to photographic exposure equipment, and more particularly, to a photolithography system and method, such as can be used in the manufacture of semiconductor integrated circuit devices. 
     In conventional photolithography systems, the photographic equipment requires a mask for printing a pattern onto a photo resist coated subject. The subject may include, for example, a semiconductor substrate for manufacture of integrated circuits, metal substrate for etched lead frame manufacture, conductive plate for printed circuit board manufacture, or the like. A patterned mask or photomask may include, for example, a plurality of lines, structures, or images. During a photolithographic exposure, the photo resist coated subject must be aligned to the mask very accurately using some form of mechanical control and sophisticated alignment mechanism. 
     U.S. patent Ser. No. 09/480,796, filed Jan. 10, 2000 and hereby incorporated by reference, discloses a novel system and method for photolithography which provides a moving pixel image onto specific sites on a subject. A “site” may represent a single pixel, or a group of pixels, depending on the embodiment. In one embodiment, the method projects a pixel-mask pattern onto a subject such as a wafer. The method provides a sub-pattern to a pixel panel pattern generator such as a deformable mirror device or a liquid crystal display. The pixel panel provides a plurality of pixel elements corresponding to the sub-pattern that may be projected onto the subject. 
     Each of the plurality of pixel elements is then simultaneously focused to discrete, non-contiguous portions of the subject. The subject and pixel elements are then moved (e.g., by vibrating one or both of the subject and pixel elements) and the sub-pattern is changed responsive to the movement and responsive to the pixel-mask pattern. As a result, light can be projected into the sub-pattern to create the plurality of pixel elements on the subject, and the pixel elements can be moved and altered, according to the pixel-mask pattern, to create a contiguous image on the subject. 
     Certain improvements are desired for maskless photolithograph systems in general, such as the above-described system and method. These improvements increase exposure area, increase exposure intensity, and/or handle errors in the pixel panel. 
     SUMMARY 
     A technical advance is achieved by a novel system and method for photolithography which provides a digital image from a pixel panel onto one or more specific sites on a subject. In one embodiment, the system includes a panel for generating the pattern and for creating a plurality of pixel elements. The pixel elements are simultaneously directed to a first site of the subject by one or more lenses. The system also includes a manipulator for moving the pixel elements, relative to the subject, to a second site of the subject so that a portion of the second site overlaps a portion of the first site. In some embodiments, the first and second sites are pixel-sites created by a single pixel of the panel. 
     In some embodiments, the panel is a micro mirror array for selectively reflecting light on and off to create the respective pixel elements. In other embodiments, the panel is a liquid crystal display for selectively allowing light to pass, thereby creating an on/off effect with the respective pixel elements. 
     In some embodiments, the manipulator further moves the pixel elements, relative to the subject, to a third site of the subject, so that a portion of the third site overlaps a portion of the first site. In some of these embodiments, the portion of the first site overlapped by the second site is the same as the portion of the first site overlapped by the third site. 
     In some embodiments, the manipulator is a mechanical device for physically moving the panel, relative to the subject. In some embodiments, the manipulator is a rotating prism with a first portion for moving a light path for the pixel elements to a first offset, and a second portion for moving the light path for the pixel elements to a second offset. 
     In some embodiments, the manipulator is an optical device for optically moving a light path for the pixel elements, relative to the subject. The manipulator may be a rotating optical device for selectively moving a light path for the pixel elements, relative to the subject. Alternatively or in addition, the manipulator may include multiple optical devices for moving a light path for the pixel elements in two dimensions, relative to the subject. 
     In some embodiments, the panel includes a first and second portion, each for creating corresponding portions of the plurality of pixel elements. In these embodiments, the system also includes an optical element, such as a beam splitter, for combining the pixel elements from the first portion of the panel with the pixel elements from the second portion of the panel so that both portions of pixel elements are directed to the substrate. In some embodiments, the first and second portions of pixel elements are adjacently provided to the substrate. Alternatively or in addition, the first and second portions of pixel elements may overlap each other. 
     In another embodiment, the system includes first and second panels for creating a first and second plurality of pixel elements, respectively. An optical element combines the first and second elements so that they are simultaneously projected onto a first site of the subject. 
     As a result, certain improvements are obtained. For one, errors or faulty pixels in the pixel panel are compensated. Also, in some embodiments the exposure area is increased, while in other embodiments the exposure intensity is increased. Furthermore, diagonal projections are better accommodated. Additional benefits can be readily seen from the attached drawings and the foregoing description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a photolithography system according to presently incorporated U.S. patent Ser. No. 09/480,796; 
     FIG. 2 illustrates a wafer and a plurality of sites exposed thereon. 
     FIGS. 3 a - 3   c  illustrate various overlapping configurations of sites. 
     FIGS. 4 a - 4   b  illustrate various overlapping configurations of sites for creating a diagonal circuit element. 
     FIG. 5 is a side view of a photolithography system for implementing one or more embodiments of the present invention. 
     FIG. 6 is a cross sectional view of a prism of the system of FIG.  5 . 
     FIG. 7 is a side view of a photolithography system for implementing other embodiments of the present invention. 
     FIG. 8 is a side view of a beam splitter for implementing even more embodiments of the present invention. 
     FIG. 9 is a diagram of several embodiments of a panel alignment stage for implementing features of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to exposure systems, such as can be used in semiconductor photolithographic processing. It is understood, however, that the following disclosure provides many different embodiments, or examples, for implementing different features of one or more inventions. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to limit the invention from that described in the claims. 
     With reference now to FIG. 1, a maskless photolithography system  30 , as described in presently incorporated U.S. patent Ser. No. 09/480,796, includes a light source  32 , a first lenses system  34 , a computer aided pattern design system  36 , a pixel panel  38 , a panel alignment stage  39 , a second lenses system  40 , a subject  42 , and a subject stage  44 . A resist layer or coating  46  may be disposed on the subject  42 . The light source  32  provides a collimated beam of light  48  which is projected upon the first lenses system  34  and onto the pixel panel  38 . The pixel panel  38  is provided with digital data via suitable signal line(s)  37  from the computer aided pattern design system  36  to create a desired pixel pattern (the pixel-mask pattern). The pixel-mask pattern may be available and resident at the pixel panel  38  for a desired, specific duration. Light emanating from (or through) the pixel-mask pattern of the pixel panel  38  then passes through the second lenses system  40  and onto the subject  42 . In this manner, the pixel-mask pattern is projected onto the resist coating  46  of the subject  42 . Any modifications and/or changes required in the pixel-mask pattern can be made using the computer aided pattern design system  36 . As a result, the need for fabrication of a new patterned printed mask, as would be required in conventional photolithography systems, is eliminated by the photolithography system  30  of the present disclosure. 
     Referring now to FIG. 2, the subject  42  may be a wafer, such as is used in conventional fabrication of semiconductor integrated circuits. It is understood, however, that many different substrates can benefit from the present invention, including for further example, a spherical shaped substrate. It is desired to project a plurality of images on the wafer  42  using the maskless photolithography system  30  of FIG.  1 . It is understood that the illustration of FIG. 2 is not to scale, and the images are positioned and sized, and the number of images are reduced, to better clarify the present discussion. 
     In the present embodiments, the photolithography system  30  is drawing a plurality of images at sites  50 ,  52 ,  54 ,  56 ,  58 ,  60 ,  62 , and  64 . The image sites  50 - 64  may be similar in some respects to the sites  90   a ,  90   b ,  90   c , and  90   d , as shown in FIG. 6 of presently incorporated U.S. patent Ser. No. 09/480,796. In another implementation, the image sites  50 - 64  may be similar in some respects to micro-sites  90 . 1   a ,  90 . 2   a ,  90 . 3   a  and  90 . 4   a , also shown in FIG. 6 of U.S. patent Ser. No. 09/480,796. Still other types of sites are contemplated. It is understood that the implementation of micro-sites in general is not a necessity for the present disclosure, but can be used in some embodiments. Other implementations, such as those discussed in U.S. Pat. No. 5,691,541, may also benefit from the present invention. 
     Continuing with the present embodiments, the image sites  50 - 56  are all adjacent to each other, and the image sites  58 - 64  are all adjacent to each other. However, various ones of the sites  50 - 64  overlap at certain portions. The overlapping is performed by offsetting the sites  58 - 64  by an increment less than the size of one image site. For example, the site  64  is offset from the site  56  by the value (x 1 , y 1 ), where x 1  is half the width of the site  56 , and y 1  is half the height of the site  56 , as shown on the attached FIG.  1 . By overlapping, errors in the pixel panel  38  can be accommodated. 
     In the embodiment of FIG. 2, the photolithography system  30  projects twice onto every portion of the wafer  42  (excluding, in some embodiments, the most peripheral portions of the wafer). For example, a portion P 1  is covered by the image site  56  and the image site  62 . Therefore, if one of the pixels of the pixel panel  38  is not working, the portion P 1  is still covered by one of the sites. However, in this scenario the portion P 1  is only exposed with half the intensity of other portions covered by two sites. 
     In addition, the intersection between two adjacent sites is facilitated by the overlapping site. For example, a line segment S 1  may be drawn to span the sites  54  and  56 . Since the line segment S 1  is contiguous, it is important that the adjacent sites  54 ,  56  intersect with precision. With conventional systems, such precision may not always be achievable, and a small gap may appear in the segment S 1  at the point of intersection between the two sites. 
     To accommodate for the gap and any other problems or inconsistencies, the site  60  also includes the segment S 1 . Since the portion of segment S 1  at the intersection between the two sites  54 ,  56  is completely inside the site  60  (the segment S 1  may actually be very long, and cover more sites), the overlapping of the site  60  fills in any gaps and alleviates many problems or inconsistencies that may occur. 
     Referring now to FIGS. 3 a ,  3   b , and  3   c , in another embodiment, a site  80  may be overlapped several times. For example, an area A 1  of site  80  may be overlapped once by a site  82 , a second time by a site  84 , and a third time by a site  86 . As a result, this extra redundancy allows for more faulty pixels and/or resolves more problems and inconsistencies. In addition, if only one of the pixels is not working, the intensity of the corresponding portion of the site  80  is reduced by only a fourth (instead of a half, as discussed with reference to FIG.  2 ). 
     Overlapping can be performed by physically moving one or both of the subject  42  or the pixel panel  38 . Alternatively or in addition, the overlapping can be facilitated by moving the pixel pattern in the pixel panel  38  by the computer aided pattern design system  36 . It is understood that the relative movement and hence the overlapping between the image and the subject can be performed in various manners. Furthermore, the relative movement can be a part of a normal line-scanning or image-scanning lithographic operation. 
     Referring to FIG. 4 a , in addition, the overlapped sites better support non-linear structures. For example, the sites  90 - 98  are diagonally situated to create a diagonal circuit structure such as a metal line or a poly region. The sites  90 - 98  may also represent subsets of one or more pixels from the pixel panel  38 . A diagonal line  99  is thereby created. 
     Referring also to FIG. 4 b , when the diagonal line  99  is developed, a slight “blurring” occurs at the corners of the sites  90 - 98 . This blurring helps to better create a developed diagonal line, now designated with the numeral  99 ′. 
     In some embodiments, the diagonally situated sites  90 - 98  may be exposed at a different intensity to the sites that are horizontal or vertical in nature. For example, a line may be created with a series of fully exposed horizontal sites. When the line moves in a diagonal direction, the corresponding sites can be partially exposed (e.g., at 50%). The overlapping of the diagonal sites causes only a portion of the sites to be more fully exposed (e.g., 50% times two). As a result, the diagonal line  99 ′ is better shaped after the blurring, than if all the diagonal sites  90 - 98  are fully exposed. 
     Referring now to FIG. 5, one embodiment of the maskless photolithography system  30  is shown with more mechanical detail. In this embodiment, the light source  32  (which may have one or more lenses  34  included therewith) projects light onto the pixel panel  38 . The pixel panel  38  and the lense system  40  are mounted together on a moving structure  100 . The moving structure  100  is also connected to a stage mover  102  for moving the structure, and thus all the components mounted to the structure, according to the desired overlapping process. It is noted that the light source  32  is connected to the pixel panel  38  through a flexible light conductor  104 . In an alternate embodiment, the light source  32  may be affixed to the moving structure  100 . The moving structure  100  is further connected to a stationary structure  106  for securing and facilitating the movement of the system  30  in a controlled manner. 
     The light from the source  32  reflects off the pixel panel  38  (according to the pixel pattern), through the lense system  40  and onto the wafer  42 , thus exposing one or more sites. The stage mover  102  moves the moving structure  100 , and thus the pixel panel  38  and the lense system  40 , to expose the offset sites. 
     In one embodiment, a parallel prism  110  is positioned in the light path between the pixel panel  38  and the wafer  42 . In one embodiment, the parallel prism  110  is a half disc. The prism  110  also includes a pivot point  112  that is connected to a rotating motor  114 . The motor  114  rotates the prism  110  so that the prism is in the light path half of the time, and is outside of the light path the other half of the time. In other embodiments, the parallel prism  110  may have several portions of different thicknesses, thereby producing varying degrees of offset. In still other embodiments, multiple parallel prisms may be used to provide offsets in multiple directions, or to combine to provide offsets in even more directions, such as is described in FIGS. 3 a - 3   c.    
     By using the prism(s)  110 , the amount of movement of the subject  42  and/or the moving structure  100  is reduced. This not only reduces mechanical errors, but also provides a better site location. 
     Referring also to FIG. 6, the light path is illustrated by light waves  120 . As the light  120  passes through the prism  110 , it is refracted so that as it leaves the prism, it is offset by a predetermined amount. For the sake of reference, the offset light waves are designated with the numeral  120   a  and the amount of the offset is designated by the numeral  122 . It is understood that properties of the prism  110  can be chosen to produce the desire offset. 
     In some embodiments, it may be desired to either increase the size of the site being exposed, or to increase the resolution of the site (or both). If the pixel panel  38  is a digital light processor (DLP) or digital mirror device (DMD) such as is illustrated in U.S. Pat. No. 5,079,544 and patents referenced therein, current technology provides a 600×800 array of mirrors. Therefore, for a resolution limit of 1 micron, each site will be about 0.6 mm×0.8 mm. However, the 1 micron resolution limit cannot be provided for diagonal lines. Therefore, an even smaller site (or a larger resolution limit) is required. 
     Because the resolution limit is often very important, it is sometimes desirable to combine several pixel panels for a single exposure. However, it is difficult to combine pixel panels in a production-worthy manner. For one reason, the edges of the pixel panels cannot abut to each other. That is, there will always be some amount of space between two adjacent pixel panels. 
     Referring now to FIG. 7, another embodiment of a maskless photolithography system is designated with the reference numeral  150 . The system  150  includes two pixel panels  38   a ,  38   b , two lense systems  40   a ,  40   b , and potentially two substrates  42   a ,  42   b . Interposed between the two pixel panels  38   a ,  38   b  and the substrates  42   a ,  42   b  is a beam splitter  152 . The beam splitter  152  may be a simple piece of transparent material that allows a portion of light from each panel to either pass through, or to reflect. 
     In the present embodiment, the pixel panel  38   a  includes five DMDs and the pixel panel  38   b  includes four DMDs, each labeled with the reference numeral  160 . To individually distinguish between each of the DMDs  160  in the attached drawings, a numeral “1”, “2”, “3”, “4”, “5”, “6”, “7”, and “8” is written inside the DMDs. These numerals  1 - 8  are provided to simplify the discussion and support ray-tracing techniques between the DMDs and the substrate(s). 
     The DMDs  160  of the pixel panel  38   a  (with the numerals  1 ,  3 ,  5 ,  7 , and  9 ) project their corresponding image through the lense section  40   a  and onto a first side  152   a  of the beam splitter  152 . Likewise, the DMDs  160  of the pixel panel  38   b  (with the numerals  2 ,  4 ,  6 , and  8 ) project their corresponding image through the lense section  40   b  and onto a second side  152   b  of the beam splitter  152 . 
     For the sake of example, light from the DMDs  160  designated with the numerals  5  and  8  can be ray traced (hereinafter DMD # 5  and DMD # 8 , respectively). A light ray  162  is projected from DMD # 5  through the lense  40   a  and onto the surface  152   a  of the beam splitter  152 . A portion of the light  162 , designated  162   b , passes straight through the beam splitter  152  and onto a site of the substrate  42   b  (the site designated with the numeral  5 ). A second portion of the light  162 , designated  162   a , reflects off of the beam splitter  152  and onto a site of the substrate  42   a  (also the site designated with the numeral  5 ). It is understood that the sum of the intensity of the light rays  162   a  and  162   b  should equal the intensity of the light ray  162 . 
     Likewise, a light ray  164  is projected from DMD # 8  through the lense  40   b  and onto the surface  152   b  of the beam splitter  152 . A portion of the light  164 , designated  164   a , passes straight through the beam splitter  152  and onto a site of the substrate  42   b  (the site designated with the numeral  8 ). A second portion of the light  164 , designated  164   b , reflects off of the beam splitter  152  and onto a site of the substrate  42   b  (also the site designated with the numeral  8 ). As above, the sum of the intensity of the light rays  164   a  and  164   b  should equal the intensity of the light ray  164 . 
     As a result, multiple DMDs can be combined to form a single site  180   a  and/or  180   b . The sites  180   a ,  180   b  may be relatively large and/or may have better resolution than the sites discussed in FIGS. 2-4 b  above. Referring also to FIG. 8, the DMDs can also be configured in different arrangements, such as illustrated, to accommodate the spacing requirements between adjacent DMDs. 
     Referring now to FIG. 9, in some embodiments, the pixel panel  38  of FIG. 1 is aligned with the panel alignment stage  39 . In most cases, alignment of the pixel pattern can be accomplished by adjusting the individual coordinates of the pattern by the computer aided design system  36 . This operation is more fully described in presently incorporated U.S. patent Ser. No. 09/480,796. However, it may be desirable to further align the pixel pattern using mechanical means. 
     In one embodiment, the panel alignment stage  39  includes two piezo electric mechanical devices (PZT)  200 ,  202 . The PZTs  200 ,  202  are individually controlled by a controller  204  to provide mechanical alignment of the pixel panel  38 . The pixel panel  38  (e.g., a DMD) is also loosely secured at a point  206  so that it can be moved or twisted in a desired way. 
     In another embodiment, instead of using the two PZTs  200 ,  202 , only a single PZT  208  is used. The PZT  208  may be used in combination with other mechanical devices, such as a spring  210  and one or more coils  212 , as well as the controller  204 . 
     In operation, the pixel panel  38  can perform adjustments of the pixel pattern in one plane (e.g., the plane that is parallel with FIG. 9) and the panel alignment stage  39  can perform various adjustments outside of the plane. As a result, the sites formed by the pixel panel  38  are relatively in focus across the entire site. 
     While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing form the spirit and scope of the invention, as set forth in the following claims.