Abstract:
A system for image-scanning a pixel-mask pattern onto a subject, such as a subject in digital photolithography, is provided. The system includes a pixel panel for generating a pixel pattern formed of pixel elements. A lens system positioned between the panel and the subject simultaneously directs the pixel elements to the subject. A mirror positioned between the panel and the subject enables the system to direct the pixel elements to a portion of the subject at any one time. A computing system may be used to generate the pixel elements and provide the pixel elements to the panel in a predetermined sequence.

Description:
CROSS REFERENCE 
     This invention relies on a provisional patent application U.S. Ser. No. 60/207,039 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. 
     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 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 image-scanning a pixel-mask pattern onto a subject. The system comprises a panel for generating a pattern comprising a plurality of pixel elements and a lens system positioned between the panel and the subject for simultaneously directing the pixel elements to the subject. The system includes a mirror positioned between the panel and the subject for directing the pixel elements to a portion of the subject at any one time and means for moving the mirror to scan the pixel elements across the subject. 
     In another embodiment, the system includes means for moving the subject to further scan the pattern across the subject. In yet another embodiment, the system includes means for sequentially providing the pixel elements to the panel so that the pixel elements of the pattern can move in conjunction with the movement of the mirror. In still another embodiment, the lens system includes at least one F-θ lens. 
    
    
     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 embodiment of a pixel panel and a lens system for use in the photolithography system of FIG.  1 . 
     FIG. 3 illustrates a pixel pattern moving across the pixel panel of FIG.  2 . 
     FIG. 4 illustrates a subject being image scanned by the pixel panel and lens system of FIG.  2 . 
    
    
     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. 
     With reference now to FIG. 1, a maskless photolithography system  30 , as described in presently incorporated U.S. Pat. Ser. No. 09/480,796, 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  is an incoherent light source (e.g., a Mercury lamp) that provides a collimated beam of light  48  which is projected upon 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 . 
     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 for a set of potential pixel elements. Each mirror provides a pixel that is about 17 microns in size. 
     Referring now to FIG. 2, in one embodiment, the second lens system  40  includes a pair of F-θ lenses  50  and  52 . An F-θ lens is one that satisfies the equation: 
     
       
         
           y=f·θ, 
         
       
     
     where y represents the distance from an optical axis of the lens to a beam spot on a image formation surface to be scanned, f represents the focal length of the F-θ lens, and θ represents the angle of incidence of the beam upon the lens. 
     Positioned between the two F-θ lenses  50 ,  52  is a multi-faceted mirror  54 . The mirror  54  is rotatable (e.g., by a motor  55 ), as indicated by a direction arrow  56 , so that each facet of the mirror sequentially aligns with a first axis  58  with a second axis  60 . In the present embodiment, the first axis  58  perpendicularly extends from a central point of the DMD  38  and the second axis perpendicularly extends from a central point 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. For example, the pattern can be modified as it is provided to the DMD  38 , discussed in greater detail below, to account for any distortion at the edges of the subject  42 . 
     In operation, the DMD  38  projects the pixel-mask pattern through the first F-θ lens system  50  and onto the faceted mirror  54 . The pattern reflects off one of the facets of the mirror  54 , through the second F-θ lens system  52 , and onto the subject  42 . Since the mirror  54  is rotating, the reflected pattern actually moves to different portions of the subject  42 . For example, when the mirror  54  is at a position as illustrated in FIG. 2, the pattern is projected to an upper portion  42   a  of the subject  42 . But as the mirror  54  rotates in the direction  56 , the pattern moves along the subject  42  in a direction  70 . Eventually, the pattern is “image scanned” to include a central portion  42   b  and a lower portion  42   c  of the subject. 
     Referring also to FIG. 3, corresponding to the image scanning described above, the pixel-mask pattern being projected by the DMD  38  changes accordingly. This correspondence can be provided, in one embodiment, by having the computer system  36  control both the motor  55  and the data provided to the DMD  38 . The illustrations of FIG.  3  and following discussions describe how the data can be timely provided to the DMD  38 . 
     FIG. 3 shows three intermediate images of the DMD  38  and the signal lines  37 , each with a suffix “a”, “b”, or “c”. The signals  37   a ,  37   b ,  37   c  and DMDs  38   a ,  38   b ,  38   c  correspond to the portions  42   a ,  42   b ,  42   c , respectively. The portions  42   a ,  42   b ,  42   c  are identified by precise movement of the motor  55 , and hence the mirror  54 . It is understood that the illustrated spacing between the portions  42   a ,  42   b ,  42   c  is exaggerated for the sake of clarity, and since the pattern is image scanned, some overlapping between portions will actually occur. 
     In the first intermediate image, the pattern of DMD  38   a  is created responsive to receiving data D 0  provided through the signal lines  37   a . In the present example, the pattern is created as a matrix of pixel elements in the DMD  38   a . After a predetermined period of time (e.g., due to exposure considerations being met), the pattern is shifted. The shifted pattern (now shown as DMD  38   b ) includes additional data D 1  provided through the signal lines  38   b . In the second intermediate image of FIG. 3, D 1  represents the left-most column of pixel elements in the pattern of DMD 38   b . After another predetermined period of time, the pattern (now shown as DMD  38   c ) is shifted again. The twice-shifted pattern includes additional data D 2  provided through the signal lines  38   b . In the third intermediate image of FIG. 3, D 2  now represents the left-most column of pixel elements in the pattern of the DMD 38   c . 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 also to FIG. 4, the subject  42  and the alignment stage  44  are illustrated as rectangular in shape to better describe the following aspects of the present embodiment. It is understood, however, that many different shaped subjects, including flat wafers or three-dimensional non-planar substrates, may benefit from the present invention. In FIG. 4, a first image scan  74 . 1  is produced on the subject  42 . Additional image scans  74 . 2 - 74 . 12  can be produced by moving the subject  42  (e.g., by movement of the stage  44 ) in a direction  76 . This movement  76  can be performed as a step function, or as a linear function. 
     FIG. 4 illustrates an example of linear movement  76 . Since the movement is linear, the subject  42  is constantly moving in the direction  76 . As a result, the image scans  74 . 1 - 74 . 12  appear slanted, when compared to the stage  44 . To offset this slanting, the subject  42  may be rotated at an angle a on the stage  44 . This produces straight image scans  74 . 1 - 74 . 12 , as seen by the subject  42 . 
     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.