Abstract:
A system for performing digital lithography onto a subject is provided. The system utilizes pixel panels to generate pixel patterns. Mirrors are utilized to divert and align the pixel elements forming the patterns onto a subject. A gradient lens system positioned between the panels and the subject simultaneously directs the pixel elements to the subject. The pixel elements may overlapping, adjacent, or spaced as desired. The pixel elements may be directed to multiple surfaces simultaneously. One or more point array units may be utilized in the system to achieve higher resolution.

Description:
CROSS REFERENCE 
     This invention relies on a provisional patent application U.S. Ser. No. 60/207,038 filed on May 25, 2000. 
    
    
     BACKGROUND 
     The present invention relates generally to lithographic 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 subject. The subject may include, for example, a photo resist coated 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 subject must be aligned to the mask very accurately using some form of mechanical control and sophisticated alignment mechanism. 
     U.S. Pat. No. 5,691,541, which is hereby incorporated by reference, describes a maskless, reticle-free lithography system. The system employs a pulsed or strobed eximer laser to reflect light off a programmable digital mirror device (DMD) for projecting a line image onto a substrate. The substrate is mounted on a stage that is projected during the sequence of pulses. 
     U.S. Pat. No. 4,925,279, which is hereby incorporated by reference, describes a telecentric F-θ lens system that employs a coherent light source (laser) to direct a beam of light through an F-θ lens system and onto a subject. The beam of light scans a line across the subject to produce a resulting image. 
     The above-two described systems suffer from a very small exposure area with relatively poor resolution. Being line scanning systems, each system requires a relatively large amount of time for the entire surface of the substrate to be exposed. In addition, the coherent light sources (used for lasers) are not only very expensive, but are unreliable. Further still, F-θ lenses are extremely expensive. 
     U.S. Pat. Ser./No. 09/480,796, filed Jan. 10, 2000 and hereby incorporated by reference, discloses a novel system and method for photolithography which projects a moving pixel image onto specific sites of 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 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 systems and methods. For example, it is desirable to have a relatively large exposure area, to provide good image resolution, to provide good redundancy, to use a relatively inexpensive incoherent light source, to provide high light energy efficiency, to provide high productivity and resolution, and to be more flexible and reliable. 
     SUMMARY 
     A technical advance is provided by a novel method and system for performing digital lithography onto a subject. In one embodiment, the system comprises first and second panels for generating first and second patterns, each pattern comprising a plurality of pixel elements, a first mirror for diverting the pixel elements of the first pattern to align with the pixel elements of the second pattern, a first gradient lens system positioned between the first and second panels and the subject for simultaneously directing the pixel elements to the subject, and means for providing relative movement between the first and second panels and the subject to scan the pixel elements across the subject. 
     In another embodiment, the system comprises third and fourth panels for generating third and fourth patterns, a second mirror for diverting the pixel elements of the third pattern to align with the pixel elements of the fourth pattern, and a second gradient lens system positioned between the third and fourth panels and the subject for simultaneously directing the pixel elements to the subject. The system is operable to scan the pixel elements from the first and second panels across a first surface of the subject, and to scan the pixel elements from the third and fourth panels across a second surface of the subject. In yet another embodiment, the first and second surfaces are on opposite sides of the subject. 
     In still another embodiment, the system comprises a point array unit and means for providing relative movement between the unit and a subject to scan the pixel elements across the subject. The point array unit includes a panel for generating the pattern, a first lens system positioned between the panel and the subject for directing the pixel elements to the subject, and a second lens system for focusing the pixel elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a photolithography system for implementing various embodiments of the present invention. 
     FIG. 2 illustrates one possible arrangement of pixel panels for use in the photolithography system of FIG.  1 . 
     FIGS. 3,  4   a,    4   b  illustrates another possible arrangement of pixel panels and reflecting surfaces for use in the photolithography system of FIG.  1 . 
     FIG. 5 illustrates a subject being image scanned by the pixel panels and reflecting surfaces of FIG.  2 . 
     FIG. 6 illustrates a pixel pattern moving across one of the pixel panels of FIG.  3 . 
     FIG. 7 illustrates a pattern reducer for shrinking an image size for one of the pixel panels of FIG.  3 . 
     FIGS. 8-9 illustrate another embodiment of a photolithography system for exposing multiple surfaces of a substrate. 
     FIG. 10 illustrates still another arrangement for use in the system of FIG. 1, the arrangement utilizing a hyper spatial light modulator and a lens system. 
     FIG. 11 illustrates using multiple panels and reflecting surfaces to expand the system of FIG.  3 . 
     FIG. 12 illustrates a subject being scanned by the pixel panels and reflecting surfaces of FIG.  11 . 
     FIG. 13 illustrates the system of FIG. 3 with the addition of a lens. 
     FIG. 14 illustrates the system of FIG. 13 with additional panels and reflecting surfaces. 
     FIG. 15 illustrates an exemplary point array unit. 
     FIG. 16 illustrates the system of FIG. 1 using a plurality of the point array units of FIG. 15 to scan a subject. 
    
    
     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 the invention. 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. 
     In the following description of various embodiments of the present invention, the same numerals and/or letters may be used in the various embodiments. This repetition is for the purpose of clarity and does not in itself indicate a relationship between the various embodiments and/or configurations discussed. 
     Referring now to FIG. 1, a maskless photolithography system  30 , such as is described in U.S. Pat. Ser./No. 09/480,796 and hereby incorporated as if reproduced in its entirety, is one example of a system that can benefit from the present invention. In the present example, the maskless photolithography system  30  includes a light source  32 , a first lens system  34 , a computer aided pattern design system  36 , a pixel panel  38 , a panel alignment stage  39 , a second lens 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  may be an incoherent light source (e.g., a Mercury lamp) that provides a collimated beam of light  48  which is projected through the first lens 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 lens 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 . 
     The computer aided mask design system  36  can be used for the creation of the digital data for the pixel-mask pattern. The computer aided pattern design system  36  may include computer aided design (CAD) software similar to that which is currently used for the creation of mask data for use in the manufacture of a conventional printed mask. Any modifications and/or changes required in the pixel-mask pattern can be made using the computer aided pattern design system  36 . Therefore, any given pixel-mask pattern can be changed, as needed, almost instantly with the use of an appropriate instruction from the computer aided pattern design system  36 . The computer aided mask design system  36  can also be used for adjusting a scale of the pattern or for correcting image distortion in the pattern. 
     In some embodiments, it may be desirable to increase the size of the site being exposed and/or to increase the resolution of the site. 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 for a set of potential pixel elements. For the sake of simplicity and clarity, the pixel panel  38  will be further illustrated as one or more DMDs. 
     Referring now to FIG. 2, in one embodiment, three DMDs  38  can be aligned side by side to produce four pixel mask patterns  50 . Each pixel mask pattern  50  is of a specific width d 1  and specific height h 1 . It is noted that even when the three DMDs  38  are pressed against each other, the corresponding pixel mask patterns  50  are always separated by a minimum distance d 2 . It may be desirable to make the separation distance d 2  to be equal to or less that zero because, if the separation distance d 2  is less than zero, then some overlap can occur between adjacent pixel mask patterns  50 . This overlap provides for greater reliability and redundancy. 
     Referring now to FIGS. 3,  4   a,  and  4   b,  in a preferred embodiment, the DMDs  38  are separated from each other, rotated, and spatially arranged. For the sake of reference, the three DMDs are designated  38   a,    38   b,    38   c  and their corresponding pixel mask patterns and/or projection images are designated  50   a,    50   b,    50   c,  respectively. The DMDs  38   a  and  38   c  are each associated with a reflection device  52 ,  54 , respectively. The reflection devices  52 ,  54  may be mirrors, prisms, or any other suitable reflection device. Furthermore, the reflection devices  52 ,  54  may be separate or may be formed from a single monolithic substrate. For the sake of simplicity and clarity, the devices  52 ,  54  are illustrated as mirrors. Also for the sake of simplicity and clarity, any intervening lenses have been left out of these figures and the following description. 
     The DMD  38   a  projects the image  50   a  onto the mirror  52 , which further directs the image  50   a  onto the subject  42  at a site  56   a.  The DMD  38   b  projects the image  50   b  directly onto the subject  42  at a site  56   b  adjacent to, or overlapping with, the site  56   a.  The DMD  38   c  projects the image  50   c  onto the mirror  54 , which further directs the image  50   c  onto the subject  42  at a site  56   c  adjacent to, or overlapping with, the site  56   b.  Referring specifically to FIG. 4 b,  in this arrangement, a distance d 3  between the images  50   a  and  50   c  is less than or equal to the width d 1 . 
     Referring now to FIG. 5, in some embodiments, a gradient lens  60  can form a portion or all of the lens system  40 . Examples of a gradient lens include a lens plate, a lens array, and a planar microlens array, which are all sold under the brand name SELFOC by Nippon Sheet Glass Company, Limited, of Osaka, Japan. In the present embodiment, the gradient lens system  60  is an array of lenses that provide a 1:1 image transfer without inverting the image. These types of lenses are often used in copy machines, facsimile machines, and the like. 
     In operation, the images from the DMDs  38   a,    38   c  reflect off of the mirrors  52 ,  54 , respectively, and through the lens system  60 . The lens system  60  further directs the images to the subject  42 , e.g., a wafer, and exposes the photo resist  46  thereon. The present system can be used for image scanning, whereby the images from the DMDs  38   a,    38   c  are scanned and moved across the subject  42  responsive to the relative scanning movement between the two (represented by an arrow  70 ). 
     Referring also to FIG. 6, corresponding to the image scanning described above, the pixel-mask pattern being projected by the DMDs  38  changes accordingly. This correspondence can be provided, in one embodiment, by having the computer system  36  of FIG. 1 control both the scanning movement  70  and the data provided to the DMDs  38 . The illustrations of FIG.  6  and the following discussion describe how the data can be timely provided to the DMDs  38 . 
     FIG. 6 shows three intermediate images of one of the DMDs  38  and the corresponding signal lines  37 , each with a suffix “0.1”, “0.2”, or “0.3”. The signals  37 . 1 ,  37 . 2 ,  37 . 3  and DMDs  38 . 1 ,  38 . 2 ,  38 . 3  correspond to portions  42 . 1 ,  42 . 2 ,  42 . 3 , respectively, of the subject  42 . Each portion may include a plurality of sites, such as the sites  56   a,    56   b,    56   c  of FIG.  3 . It is understood that the illustrated spacing between the portions  42 . 1 ,  42 . 2 ,  42 . 3  is exaggerated for the sake of clarity, and since the pattern is image scanned, overlapping between portions may actually occur. 
     In the first intermediate image, the pattern of DMD  38 . 1  is created responsive to receiving data D 0  provided through the signal lines  37 . 1 . In the present example, the pattern is created as a matrix of pixel elements in the DMD  38 . 1 . After a predetermined period of time (e.g., due to exposure considerations being met), the pattern is shifted. The shifted pattern, shown as DMD  38 . 2 , includes additional data D 1  provided through the signal lines  38 . 2 . The shifting between patterns may also utilize a strobing or shuttering of the light source  32 . In the second intermediate image of FIG. 6, D 1  represents the left-most column of pixel elements in the pattern of DMD  38 . 2 . After another predetermined period of time, the pattern (now shown as DMD  38 . 3 ) is shifted again. The twice-shifted pattern includes additional data D 2  provided through the signal lines  38 . 2 . In the third intermediate image of FIG. 6, D 2  now represents the left-most column of pixel elements in the pattern of the DMD 38 . 3 . Thus, the pattern moves across the DMD  38  in a direction  72 . It is noted that the pattern direction  72 , as it is being provided to the DMD  38  from the signal lines  37 , is moving opposite to the scanning direction  70 . 
     Referring now to FIG. 7, in some embodiments, it may be desirable to provide a higher resolution of the images from the pixel mask pattern onto the subject  42 . This may be accomplished, for example, by inserting a pattern reducer  78  in line between the DMD  38  and the subject  42 . In one embodiment, the pattern reducer  78  may be a Schott fiber optic taper, such as sold by Edmund Industrial Optics of Barrington, N.J. A fiber optic taper is a coherent fiber optic plate that transmits a reduced image from its input surface to its output surface. Thus, in the embodiment of FIG. 7, an image  80  produced by the DMD  38  appears as a reduced image  82  on the subject  42  because of the pattern reducer  78 . The pattern reducer  78  may, in some embodiments, be positioned adjacent to the gradient lens system  60 . 
     Referring now to FIGS. 8 and 9, in another embodiment, the system can be used to perform multiple surface exposures. A plurality of DMDs  38   a,    38   b  are positioned accordingly with the mirrors  52 ,  54  on each side of the subject  42 . Two gradient lens systems  60  are also positioned on each side of the subject  42 . The stage  44  for the subject  42  is configured to support and move the subject, but to also allow both sides of the subject to be exposed. In the present embodiment, the stage  44  consists of rollers on either side of the subject  42 , it being understood that other embodiments may also be used. 
     The light source  32  (e.g., a Mercury lamp  100  and associated mirror  102 ) projects the light  48  through the lens system  34  and onto a Hepa filter  104 . The Hepa filter  104  directs the light  48 , using a diverter  106 , to the pixel panels  38   a,    38   b.  The pixel panels  38   a,    38   b  project the light through the mirrors  52 ,  54 , through the gradient lens system  60 , and onto one side of the subject  42 . This process occurs on both sides of the subject. The subject  42  is scanned in the direction  70  so that the images from the pixel panels  38  are image scanned onto both sides of the subject. 
     Referring now to FIG. 10, in an alternative embodiment, a hyper spatial light modulator  110  is positioned above a subject  42  and a stage  44 . The modulator  110  may receive data signals through the signal lines  37  from the design system  36  of FIG.  1 . The modulator uses these signals to redirect light  48  into an image pattern, illustrated by exemplary pixels  50   a,    50   b.  The modulator  110  projects the pattern through a gradient lens  60 , which in the present embodiment is a lens array. The lens  60  focuses the image onto a site  56  on the subject  42 . 
     Referring now to FIGS. 11 and 12, in another embodiment, a plurality of DMDs  38   a-k  and mirrors  114 - 126  are utilized to project a plurality of images  50   a-k  (each illustrated by a single line in FIG. 11 for clarity) onto a plurality of sites  56   a-k  on a subject  42  of FIG. 12 in a manner similar to that illustrated in FIG.  3 . The DMDs  38   a-k  are separated from each other, rotated, and spatially arranged as shown. The DMDs  38   a,    38   c,    38   d,    38   f,    38   g,    38   i,  and  38   j  are associated with the mirrors  114 - 126 , respectively. 
     As in FIG. 3, the DMD  38   a  projects the image  50   a  onto the mirror  114 , which further directs the image  50   a  onto the subject  42  at the site  56   a  of FIG.  12 . The DMD  38   b  projects the image  50   b  directly onto the subject  42  at the site  56   b  adjacent to, or overlapping with, the site  56   a.  The DMD  38   c  projects the image  50   c  onto the mirror  116 , which further directs the image  50   c  onto the subject  42  at the site  56   c  adjacent to, or overlapping with, the site  56   b.    
     The DMD  38   d  projects the image  50   d  onto the mirror  118 , which further directs the image  50   d  onto the subject  42  at the site  56   d  adjacent to, or overlapping with, the site  56   c.  The DMD  38   e  projects the image  50   e  directly onto the subject  42  at the site  56   e  adjacent to, or overlapping with, the site  56   d.  The DMD  38   f  projects the image  50   f  onto the mirror  120 , which further directs the image  50   f  onto the subject  42  at the site  56   f  adjacent to, or overlapping with, the site  56   e.  This arrangement may be continued as desired, with each exposed site adjacent to or overlapping the preceding site. Additional DMDs  38   g-k,  which operate in the same manner in conjunction with the mirrors  122 - 126  to expose sites  56   g-k,  are shown for purposes of illustration but are not described. 
     Referring now specifically to FIG. 12, exemplary adjacent sites  56   a-k,  such as may be projected by the DMDs  38   a-k  of FIG. 11, are illustrated on a portion of a subject  42 . The sites  56   a-k  may be adjacent or overlapping, depending on the desired behavior of the DMDs  38   a-k  of FIG.  11 . 
     Referring now to FIG. 13, in another embodiment, three DMDs  38   a-c  and two mirrors  114 ,  116  are arranged similarly to those illustrated in FIGS. 3,  4   a,  and  4   b,  except that a lens system  40  is positioned between the DMDs  38   a-c /mirrors  114 ,  116  and the subject  42 . The lens system  40  may comprise a gradient lens or any other type of lens, and may be a single lens or multiple lenses. The lens system  40  may be designed to focus, redirect, or otherwise project light which is directed to the lens system  40 . 
     The DMD  38   a  projects an image  50   a  (illustrated by a single line for clarity) onto the mirror  114 , which further directs the image  50   a  onto the lens system  40 . The lens system  40  projects the image  50   a  onto the subject  42  at the site  56   a.  The DMD  38   b  projects the image  50   b  directly onto the lens system  40 , which projects the image  50   b  onto the subject  42  at the site  56   b  adjacent to, or overlapping with, the site  56   a.  The DMD  38   c  projects the image  50   c  onto the mirror  116 , which further directs the image  50   c  onto the lens system  40 . The lens system  40  projects the image  50   c  onto the subject  42  at the site  56   c  adjacent to, or overlapping with, the site  56   b.    
     Referring now to FIG. 14, in another embodiment, a plurality of DMDs  38   a-g,  a plurality of mirrors  114 - 124 , and a lens system  40  are arranged similarly to those illustrated in FIG.  13 . The DMDs  38   a-g  are separated from each other, rotated, and spatially arranged as shown. The DMDs  38   a,    38   b,    38   c,    38   e,    38   f,  and  38   g  are associated with the mirrors  114 - 124 , respectively. 
     The DMDs  38   a-c  project an image  50   a-c,  respectively (illustrated by a single line for clarity) onto the mirrors  114 - 118 . The mirrors  114 - 118  direct their associated images  50   a-c  onto the lens system  40 . The lens system  40  projects the images  50   a-c  onto a subject  42  at sites  56   a-c.  Each site  56   b,    56   c  is adjacent to, or overlapping with, the preceding site  56   a,    56   b,  respectively. The DMD  38   d  projects an image  50   d  directly onto the lens system  40 , which projects the image  50   d  onto the subject  42  at the site  56   d  adjacent to, or overlapping with, the site  56   c.  The DMDs  38   e-g  project an image  50   e-g,  respectively (illustrated by a single line for clarity) onto the mirrors  120 - 124 . The mirrors  120 - 124  direct their associated images  50   e-g  onto the lens system  40 . The lens system  40  projects the images  50   e-g  onto a subject  42  at sites  56   e-g.  Each site  56   e-g  is adjacent to, or overlapping with, the preceding site  56   d-f,  respectively. 
     Referring now to FIG. 15, a point array unit  130  may include a DMD  38 , a lens system  40 , a microlens array  132 , and a grating  134 . The unit  130  may be used in place of a DMD to achieve a higher resolution for an exposure site. In operation, the DMD  38  receives data signals through the signal lines  37  (not shown) from the design system  36  of FIG.  1 . The DMD  38  uses these signals to reflect light  48  as an image pattern  50 . The pattern  50  is projected through the lens system  40 , which may serve to focus or redirect the image  50  onto the microlens array  132 . The microlens array  132  may be a compilation of individual microlenses that correspond to one or more of a plurality of individual pixels of the DMD  38 . In the present embodiments, there are as many individual microlenses as there are pixel elements DMD  38 . For example, if the DMD  38  has 600×800 pixels, then the microlens array  132  may have 600×800 microlenses. In other embodiments, the number of lenses may be different from the number of pixel elements in the DMD  38 . In these embodiments, a single microlens may accommodate multiple pixels elements of the DMD, or the pixel elements can be modified to account for alignment. 
     The microlens array  132  projects the image  50  onto the grating  134 . The grating may be a conventional shadow mask device that is used to eliminate and/or reduce certain bandwidths of light and/or diffractions between individual pixels of the DMD  38  and/or the microlens array  132 . The grating  134  may take on various forms, and in some embodiments, may be replaced with another device or not used at all. The light passes through the grating  134  and exposes a site  56  on a subject  42 . 
     Referring now to FIG. 16, a plurality of the point array units  130  of FIG. 15 are illustrated. In addition, a second lens system  40   b  has been added to the units  130  between the grating  134  and the subject  42 . The lens systems  40   b  may be used to focus or redirect the images  50  onto the sites  56 . The plurality of units  130  enable the simultaneous exposure of the plurality of sites  56  on the subject  42  through a stage scanning process in the direction  136 . It is noted that all units may be operating simultaneously, selected units may be operating, or no units may be operating at any given time, depending on the desired results. It is also noted that other scanning methods may be utilized to achieve the results of the stage scanning of FIG.  16 . 
     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 from the spirit and scope of the invention. For example, it is within the scope of the present invention that alternate types and/or arrangements of microlenses, pixel panels and/or lenses may be used. Furthermore, the order of components such as the microlens array  132 , the lenses  40 , and/or the grating  134  may be altered in ways apparent to those skilled in the art. Additionally, the type and number of components may be supplemented, reduced or otherwise altered. Therefore, the claims should be interpreted in a broad manner, consistent with the present invention.