Abstract:
An “image writing” and “image reading” system and method for providing a pattern to a subject such as a wafer is provided or an image to an image sensor such as CCD. The system includes a pixel panel, such as a digital mirror device or a liquid crystal display or other SLM, for generating for creating a plurality of sub-image array of the pattern in image writing? case. The pixel elements are simultaneously divided to a sub-image array on the subject by a lens system. The system also includes a manipulator for moving, stepping or scanning the pixel panel, relative to the subject so that it can create a contiguous whole image on the subject

Description:
BACKGROUND OF INVENTION 
       [0001]    The invention relates to two fields that can be broadly categorized as “image writing” and “image reading”. The invention&#39;s primary intended application for image writing would be as a microlithography printer for semiconductor manufacture, PCB and LCD manufacture; however this field may also include applications such as document printing, photographic reproduction, etc. Its primary intended application in the image reading field would be as a high-resolution document scanner, although it could also potentially be used for other applications, for example as a scanning microscope with camera, or as a reader for optical mass storage media, etc. The following description will focus on the photographic exposure equipment and scanning system, and more particularly, to a photolithography system and method, such as can be used in the manufacture of semiconductor integrated circuit devices, although the specification can be applied by obvious extension to other applications as well. 
         [0002]    The present invention relates generally to in conventional photolithography systems, the photographic equipment requires a mask for imaging 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 photo mask may include, for example, a plurality of lines, structures, or images. With conventional photolithography, the patterned masks are typically very expensive. In addition, the photomasks are characterized as requiring a very long mask purchase lead time. The long mask purchase lead time is not very helpful when a short product development cycle is desired. Further, if a particular mask design is found to require a design change in the pattern, no matter how small of a then mask modification cost and a respective lead time to implement the required change can cause serious problems in the manufacture of the desired product. 
         [0003]    In current maskless system, there are two method which are using in actual system. One is to use a directly reduced image of a spatial light modulator (SLM) or other device on substrate surface, another is point array method which uses a microlens or multi-microlens to get a focus point array of microlens focus plane on the substrate. 
         [0004]    Direct reduced image method is simple but the image size on the substrate is very small and cause very slow productivity. 
         [0005]    In point array approach, 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. It uses a very small micolens. There are advantages to using very small microlenses for such applications. For example, the microlenses&#39; focusing resolution may be limited by chromatic dispersion and by the size of the illumination source (if an extended source such as an arc lamp is used), but the effect of these factors can be mitigated by using small microlenses. If the microlenses are sufficiently small these factors become insignificant and focusing resolution is dominated by diffraction. If the microlens material has significant optical absorption over the operating wavelength range, it would also be advantageous to use small microlenses in order to minimize the absorption loss. However, very small microlenses cannot easily be formed without incurring significant fill factor losses. The microfabrication processes may not be able to produce accurately profiled lens surfaces if the microlens apertures are closely juxtaposed. The structure supporting the microlenses can also take up some of space between microlenses (particularly if the structural material is not optically transparent and has open light transmission channels). Furthermore, if the microlens array is integrated with electronic or micromechanical components (e.g., surface proximity sensors or microlens focus actuators), the space required to accommodate these elements can also significantly limit the lens fill factor. Point array method need to align microlens with each pixel. Any error will cause significant cross talk and noise and lower the energy efficiency. Another disadvantage is depth of focus (DOF) which affects actual system performance. The DOF of point array method is depended on microlens numerical aperture (N.A.) rather than image itself, such as an image with very rough feature size has same DOF of microlens. 
       SUMMARY 
       [0006]    The present invention has been devised in order to solve problems with the current technology described above, and an object of the present invention is to provide an optical system which can accurately project a divided sub-image array of a spatial light modulation on the substrate. 
         [0007]    The invention provides imaging systems and techniques that circumvent the tradeoff between image resolution and field size which is the source of much of the complexity and expense of conventional microlithography systems. A technical advance is achieved by a novel system and method for photolithography which provides a digital image from a pixel panel onto 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. An image divider and reduction lenses are included in the system. It may be microlenses or other device such as fiber taper, Fresnel lens or magnetic lens. The function of image divider and reduction lenses is to form a divided sub-image array. 
         [0008]    In order to achieve the object described above, an exposure device of a first aspect of the present invention includes: a light source which emits a light beam for exposure; a spatial light modulation device at which a plurality of modulation elements, which respectively change light modulation states thereof in accordance with control signals, are one or two-dimensionally arranged, the spatial light modulation device being for modulating the light beam, which is incident at the plurality of modulation elements from the light source, at each of the modulation elements; the microlens array set at which a plurality of microlenses are one or two-dimensionally arranged with a pitch corresponding to the plurality of sub-image size, The microlens set has at least two microlens arrays. The first microlens array set is for condensing light beams and the second microlens array is for shrinking sub-image size on the substrate, which have been modulated by the modulation elements, at the respective microlens; 
         [0009]    Each of the plurality of sub-image is then simultaneously focused to discrete, non-contiguous portions of the subject. The subject and sub-images are then moved relatively and the pattern on SLM is changed by computer data generating system responsive to the movement and responsive to the pixel-mask pattern. As a result, light can be projected into the pattern to create the plurality of sub-images on the subject, and the sub-images can be moved and altered, according to the pixel-mask pattern, to create a contiguous whole image on the subject. 
         [0010]    In some embodiments, the method also removes noise light from each of the sub-image by passing through an aperture array on the field microlens array focus plane. 
         [0011]    In some embodiments, the method also removes noise light from each of the sub-image by passing through a shadow mask on the image microlens array. 
         [0012]    In some embodiments, the method also removes noise light from each of the sub-image by passing through a shadow mask on image plane of image microlens array. 
         [0013]    In some embodiments, the step of focusing simultaneously creates a plurality of coplanar sub-image array on the subject. This can be accomplished, for example, through a microlense array or a fiber taper. 
         [0014]    In some embodiments, the step of changing the pixels is accomplished by sequentially providing a plurality of bit maps. Each of the bit maps is used to create the patterns on SLM. 
         [0015]    Therefore, an advantage of the present invention is that it eliminates or reduces the problems in the art associated with conventional masks. 
         [0016]    Another advantage of the present invention is that it provides a lithographic system and method with increased resolution. 
         [0017]    Still another advantage of the present invention is that it provides an improved photolithography system, such improvement being in DOF, SLM alignment requirement. 
         [0018]    A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  illustrates the divided sub-image array optical system; 
           [0020]      FIG. 2  illustrates a sub-image from an image; 
           [0021]      FIG. 3  illustrate various divided sub-images; 
           [0022]      FIGS. 4˜5  illustrate a fiber taper as the function of a divided sub-image array optical system; 
           [0023]      FIG. 6  is a sample view of a divided sub-image array and field lens position related with sub-image; 
           [0024]      FIG. 7  is a sub-image array after shrinking microlens array; 
           [0025]      FIGS. 8˜9  illustrate another embodiment of the present invention; 
           [0026]      FIG. 10  is an embodiment of scanning exposure system of  FIGS. 6˜7 ; 
           [0027]      FIG. 11  illustrates a maskless photolithography system including a pattern generator and mask pattern design system according to one embodiment of the present invention; 
           [0028]      FIGS. 12˜13  illustrate cross-sectional views of more embodiments of the divided sub-image array maskless photolithography system; 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    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. 
         [0030]    With reference now to  FIG. 1 , a divide sub-image array optical system includes a light source  101 , a spatial light modulator (SLM)  102 , a field microlens array  104 , an aperture array  113 , a shrinking image microlens array  105 , a subject  107 . A resist layer or coating may be disposed on the subject  107 . The light source  101  provides a uniform light beam onto the SLM  102 . The SLM  102  creates a desired pixel pattern (the pixel-mask pattern). The pixel-mask pattern may be available and resident at the SLM  102  for a desired, specific duration. Light emanating from (or through) the pixel-mask pattern of the SLM  102  then passes through the field microlenses array  104  and focus onto the aperture array  113 . The aperture function is to reduce any noise light. It may not use in the actual system to reduce system cost. The light will pass through the second microlens array which shrinks each of sub-images on the substrate. In this manner, the pixel-mask pattern is projected onto the substrate of the subject  107 . SLM  102 , field microlens  104 , aperture array  113 , image microlens array  105  could be aligned each other with each optical axis. The subject  107  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 nonflat substrate. It is desired to project a plurality of sub-images on the wafer  107  using the maskless photolithography system 
         [0031]    Referring now to  FIG. 2 , is to indicate a sub-images  102  from an image  102 . A sub-image  106  is a portion of whole image  102 . The area shape  103  may be square circle, triangle or any other shape which is decided by actual system design. In this sample, it is a square shape  103 .  FIG. 3  shows an image  102  is divided to several sub-images  103  in different shape. Each of sub-image should include at least four pixels. 
         [0032]      FIG. 4  and  FIG. 5  show another approach to get a sub-image. It uses a fiber taper  201  which can directly reduce a image  103  to small size of image  106 . The function is same as field microlens array plus image microlens array. A fiber taper  201  consists of a bundle of optical fibers which has a different size in both of ends. If an object is input on the big size end, an image will be on the small size end. The end of a fiber taper may be a round, square or other shape. A fiber taper array can be used to get a divided sub-image array which is same as microlens array case but the cost may be much higher than microlens array. 
         [0033]    In the embodiment of  FIG. 1 , the image may like  FIG. 6  after the light  101  passes through SLM  102  and the field microlens array  104 . To reduce image aberrations, SLM  102  is close to field microlens array as much as possible.  102   a   1 ,  102   a   2 ,  102   a   3 ,  102   a   4 , and  102   b   1  are sub-images before shrinking. The microlens  104  totally covers 5×5 pixels in  FIG. 6 . The edge pixels may dummy for reducing cross-talk and noise. In the case, the microlens  104  is aligned within dummy pixel center rather than pixel edge. It will significantly lower the SLM and microlens alignment accuracy requirement and noise light but it reduces light efficiency in the system. When a sub-image  104  is a rectangle shape and considering that each sub-image has a length of l elements and a width of w elements, then the light loss can be determined as 
         [0000]      Loss=( w+l− 1)/( w×l )  (1) 
         [0034]    From this equation, bigger w and l will reduce the light energy loss. 
         [0035]    Referring now to  FIG. 7 , the example of  FIG. 6  can shrink to 4×4 effective pixels in a sub-image array. The edge pixels of the sub-image are dark for reducing noise light and alignment. It is obvious that the pixel size in  FIG. 7  is much smaller than original size in  FIG. 6 . simultaneously moving, stepping or scanning the sub-image array relative to the subject so that a sub-image array can make a whole pattern on the subject. 
         [0036]      FIG. 8  and  FIG. 9  shows another embodiment to do scanning exposure without tilting sub-image  106  because each sub-image are not aligned within a line. For example,  106   a   2  is shifted two elements in right direction if assuming the shrinking ratio is the half of original size  102   a   1 . Due to sub-image  106   a   1 ,  106   a   2 ,  106   a   3  and  106   a   4  are shifted two elements relatively in right direction and if scanning is in vertical direction, the sub-image array is not necessary to tilt like  FIG. 10  case. Because the sub-image is not tilted, the computing of image data may be easier than  FIG. 10  case.  FIG. 10  shows a scanning case of  FIG. 7 . In  FIG. 10 , there is a tilt angle  203 . each element will make a line in scanning direction  202 . 
         [0037]    With reference now to  FIG. 11 , the maskless photolithography system of the present disclosure includes a light source  101 , a computer pattern generating and system control unit  115 , a SLM  102 , a lens system  103 , a field microlens array  104 , a aperture array  113 , a image microlens array  105 , a subject  106  and stage  107 . A resist layer or coating may be disposed on the subject  106 . The light source  101  is a uniform beam of light which is projected onto the SLM  102 . The SLM  102  is provided with digital data via suitable signal line(s) from the computer pattern generating and control system  115  to create a desired pixel pattern (the pixel-mask pattern). The pixel-mask pattern may be available and resident at the SLM  102  for a desired, specific duration. Light emanating from (or through) the pixel-mask pattern of the SLM  102  then passes through the lenses system  103  and onto the field microlens array surface  104 . The field microlens focuses the light to the focus plane  113 . An aperture array may be put on the focus plane  113  to remove some of noise light. Then the light reaches image microlens array which shrinks the sub-image. A subject  106  is on the image microlens array&#39;s image plane so the pixel images of SLM  102  are on the subject  106 . The subject may be stepped, scanned or rotated by the stage  107  which is controlled by computer system  115 . In this manner, the pixel-mask pattern is projected onto the resist coating of the subject  106 . Any modifications and/or changes required in the pixel-mask pattern can be made using the computer data generating and control system  115 . 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 of the present disclosure. 
         [0038]    Referring now to  FIG. 12 , in an embodiment of the  FIG. 11 , the photolithography system in  FIG. 11  utilizes an optical system  103  to image SLM  102  on the surface  102 ′ of the field microlens  104  according to reduce optical aberrations. It is understood that the lens system  103  is adaptable to various components and requirements of the photolithography system, and one of ordinary skill in the art can select and position lenses appropriately. For the sake of example, a group of lenses  103   a  and an additional lens  103   b  are configured with the optic system  103 . The optical system  103  is a telecentric optical system in general speaking. 
         [0039]      FIG. 13  illustrates a similar optic system  114  is placed between the image microlens array  105  and the stage  107 . This optical system images the sub-image array  106  to surface  106 ′ on stage  107 . It increases system working distance which is the distance between last lens and stage because generally the distance of the sub-image  106  to image microlens array is too short for some of applications. Meantime it is possible to put a shadow mask  116  on the sub-image array surface  106  to reduce noise light because there are a lot of empty area between sub-images. 
         [0040]    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.