Abstract:
A distortion compensation system for use in an imaging device such as a photolithography system is described. The system projects a plurality of image portions onto a plurality of portions of a subject. The system includes a plurality of light-distance modulators corresponding to the plurality of image portions and a mechanical manipulator for individually manipulating each of the light-distance modulators. In this way, any distortion in the subject is compensated by the individual manipulation of the light-distance modulators.

Description:
BACKGROUND  
         [0001]    The present application is a continuation-in-part of U.S. patent application Ser. No. 09/918,732 filed Jul. 31, 2001, which is hereby incorporated by reference.  
           [0002]    The present invention relates generally to optical systems, and more particularly, to optical display systems such as photolithography systems.  
           [0003]    It is often a goal of optical display systems to project an image onto a subject that is properly focused across the entire surface of the subject. Such a goal becomes difficult to achieve when the subject&#39;s surface is not flat. For example, a printed circuit board may be relatively flat, but have some variable distortions in its surface. In another example, a curved film may not have any variable distortions, but because it is not flat, it is still difficult to focus an image over the entire surface. In a third example, a semiconductor may be spherical in shape and may also have some variable distortions, both of which make it difficult to focus an image over the entire surface of the subject. What is desired is an advance in optical display systems to accommodate surface distortion of various kinds.  
         SUMMARY  
         [0004]    A technical advance is achieved by a distortion compensation system for use in an imaging device such as a photolithography system. In one embodiment, the system projects a plurality of image portions onto a corresponding plurality of surface portions of a subject. The system includes a plurality of light-distance modulators corresponding to the plurality of image portions and a mechanical manipulator for individually manipulating each of the light-distance modulators. In this way, any distortion in the subject is compensated by the individual manipulation of the light-distance modulators.  
           [0005]    In another embodiment, an optical system is provided for use with an image source for projecting an image onto a surface having a surface plane. The optical system includes a first optical device corresponding to the surface plane and spaced from the surface plane at a predetermined distance. The first optical device includes a plurality of individual distance modulators each for receiving a portion of the image and reflecting the portion to a portion of the surface. Each modulator individually adjusts to modify the distance between it and the surface plane. The optical system also includes a second optical device for receiving the image and directing the image towards the first optical device.  
           [0006]    In another embodiment, a system is provided for projecting an image onto a surface, the surface having first and second portions that are not planar with each other. The system includes a light source for projecting a light onto a mask having first and second mask portions for converting the light to first and second images, respectively. The system also includes first and second lens subsystems corresponding to the first and second images and the first and second surface portions, respectively. The system further includes first and second support structures for individually positioning the first and second lens subsystems and mask portions, respectively, so that a depth of focus for the first and second images can be individually adjusted for the corresponding surface portion.  
           [0007]    In another embodiment, a digital photolithography system is provided for projecting an image onto a surface having first and second portions. The system includes a light source for projecting a light and first and second digital pixel panels for converting the light into first and second images, respectively. The system also includes first and second lens subsystems corresponding to the first and second images and the first and second surface portions, respectively. The system further includes a micro-manipulator for individually positioning the first lens subsystem so that a depth of focus for the first image can be individually adjusted for the first surface portion.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIGS. 1 a - 1   b  are simplified block diagrams of photolithography systems that will benefit from various embodiments of the present invention.  
         [0009]    FIGS.  2 - 4  and  7  are diagrammatic view of a distortion compensation system for use in either of the systems of FIGS. 1 a  or  1   b.    
         [0010]    FIGS.  5 - 6  are operational views of a portion of the distortion compensation system shown in FIG. 4. 
     
    
     DETAILED DESCRIPTION  
       [0011]    The present disclosure relates to optical devices and optical systems, such as can be used in 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 addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.  
         [0012]    Referring now to FIG. 1 a , a digital photolithography system  100  is one example of a system that can benefit from the present invention. In the present example, the digital photolithography system  100  includes a light source  102 , a first lens system  104 , a computer aided pattern design system  106 , one or more digital masks  108 , a panel alignment stage  110 , a distortion compensation system  112 , a subject  114 , and a subject stage  116 . A resist layer or coating  118  may be disposed on the subject  114 . The light source  102  may be an incoherent light source (e.g., a Mercury lamp) that provides a collimated beam of light  120  which is projected through the first lens system  104  and onto the pixel panel  108 . The light  120  is of a type (e.g., wavelength and intensity) that can expose the resist layer  118 , as is well known in the art.  
         [0013]    In one embodiment, the digital masks  108  include one or more pixel panels, such as a digital/deformable mirror device (“DMD”) or liquid crystal display (“LCD”). The pixel panels are provided with digital data via suitable signal line(s)  128  from the computer aided pattern design system  106  to create a desired pixel pattern (the pixel-mask pattern). The pixel-mask pattern may be available and resident at each pixel panel  108  for a desired, specific duration. Light emanating from (or through) the pixel-mask pattern of the pixel panel  108  then passes through the distortion compensation system  112  (discussed in greater detail below) and onto the subject  114 . In this manner, the pixel-mask pattern is projected onto the resist coating  118  of the subject  114 .  
         [0014]    The computer aided mask design system  106  can be used for the creation of the digital data for the pixel-mask pattern. The computer aided pattern design system  106  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  106 . 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  106 . The computer aided mask design system  106  can also be used for adjusting a scale of the image or for correcting image distortion.  
         [0015]    In some embodiments, the computer aided mask design system  106  is connected to a first motor  122  for moving the stage  116 , and a driver  124  for providing digital data to the pixel panels  108 . In some embodiments, an additional motor  126  may be included for moving the pixel panel. The system  106  can thereby control the data provided to the pixel panel  108  in conjunction with the relative movement between the pixel panels  108  and the subject  114 .  
         [0016]    Referring now to FIG. 1 b , an analog photolithography system  150  is another example of a system that can benefit from the present invention. In the present example, the analog photolithography system  150  includes a light source  152 , one or more analog masks  158 , a mask alignment stage  160 , the distortion compensation system  112 , and the subject  114 . The analog system  150  may include many of the same components as the digital system  100  (FIG. 1 a ), which have been omitted from FIG. 1 b  for the sake of clarity.  
         [0017]    To illustrate the diversity of the present invention, the subject  114  of FIG. 1 b  is illustrated as a sphere while the subject  114  of FIG. 1 a  is illustrated as a relatively flat printed circuit board. It is understood, however, that the present invention applies to any shaped subject. For the following discussion, many different shaped subjects will be used interchangeable for the sake of example.  
         [0018]    Referring now to FIG. 2, using the digital photolithography system of FIG. 1 a  as an example, one embodiment of the distortion compensation system  112  includes a phase shift device  202  to adjust the projection of light onto the subject  114 . The phase shift device  202 , one embodiment of which is discussed in greater detail in presently incorporated U.S. patent application Ser. No. 09/918,732, is operable to project light in such a way as to account for surface irregularities on the subject  114 . In the present embodiment, the phase shift device  202  includes a plurality of actuators  204  which control the displacement of a surface  206 . The surface  206  is reflective and so operable as a mirror.  
         [0019]    In operation, light  208  is reflected from one of the masks  108  and into a beam splitter  210 . The beam splitter  210  is operable to reflect a portion of the light and allow a portion of the light to pass through. The portion of the light reflected by the beam splitter  204  enters a lens  214 . The light passes from the lens  214  into a lens  216 , which projects the light onto the phase shift device  202 .  
         [0020]    The mirror  206  of the phase shift device  202  may initially be at a neutral position, which is defined for purposes of illustration to correspond to an image plane  218 . The light is reflected from the mirror  206  through the lenses  216 ,  214  and into the beam splitter  210 . The beam splitter  210  passes a portion of the light through in the direction of the subject  114 . The light which passes through the beam splitter  210  is focused on an image plane  220  as follows.  
         [0021]    The lenses  214 ,  216  will ordinarily focus an image located at the image plane  218  onto the image plane  220 , assuming the lenses remain in a constant location. Moving the image plane  218  closer to the lenses will move the location of the image plane  220  away from the lenses. Moving the image plane  218  away from the lenses will move the location of the image plane  220  closer to the lenses. Therefore, the distance of the image plane  218  from the lenses determines the distance of the image plane  220  from the lenses.  
         [0022]    If the focal length of the distortion compensation system formed by lenses  214 ,  216  remains constant, then displacing a portion of the image plane  218  will move the corresponding portion of the image plane  220  the same distance. Likewise, by displacing multiple portions of the image plane  218  by different amounts, each corresponding portion of the image plane  220  will be similarly displaced. Therefore, by controlling portions of the image plane  218 , the location of various portions of the image plane  220  can be controlled.  
         [0023]    The actuators  204  of the phase shift device  202  are operable to displace the mirror  206  so as to displace the original image plane  218  to a displaced image plane  222 . By controlling the displacement of the mirror  206 , the phase of portions of the light may be altered in a controllable manner. The light, after being reflected by the displaced mirror  206  of the phase shift device  202 , is focused on a displaced image plane  224  instead of the original image plane  220 . The displaced image plane  224  is similar to the image plane  222  formed by the mirror  206 . The amount of similarity may depend on the resolution of the distortion compensation system, the properties of the beam splitter, and similar issues. In this manner, the image projected by the mask  108  maybe distorted in a controllable manner and projected onto the subject  114 .  
         [0024]    Referring now to FIG. 3, another embodiment of the distortion compensation system  112  is illustrated with the addition of a sensor  302 , which in the present embodiment is a Shack-Hartmann wavefront sensor, to correct for surface irregularities in the subject  114 . The sensor  302  may detect irregularities in the nanometer range on the surface of the subject  114  by receiving a wavefront which embodies the surface of the subject  114 . The wavefront may then be analyzed to determine information such as the location and magnitude of irregularities. The resulting wavefront analysis information may be used to adjust the displacement of the mirror  206  of the phase shift device  202  so as to account for the irregularities.  
         [0025]    In operation, as in FIG. 2, light  208  travels from the mask  108  into the beam splitter  210 . A portion of the light  208  is reflected by the beam splitter  204  into the lens  214 . Another portion of the light  208  passes through the beam splitter  204 . The light passes from the lens  214  into the lens  216 , which projects the light onto the phase shift device  202 .  
         [0026]    As in FIG. 2, the mirror  206  of the phase shift device  202  may ordinarily be at a neutral position, which is defined for purposes of illustration to correspond to an image plane  218 . The light is reflected from the mirror  206  through the lenses  216 ,  214  and into the beam splitter  210 . The beam splitter  210  passes a portion of the light through in the direction of the subject  114 . If the mirror  206  is in the neutral position (forming the image plane  118 ), the light will be focused on a similar image plane  220  on the subject  114 . If irregularities exist on the surface of the subject  114 , the light will not be properly focused at those points. Assuming that the surface of the subject does not conform to the image plane  220 , the light which is reflected by the subject  114  will be reflected from an image plane  224  which is formed by the surface of the subject  114 . The light will be reflected back into the beamsplitter  210 , which in turn reflects a portion of the light into a second beamsplitter  304 . A portion of the light passes through the beamsplitter  304  and into a filter  306 , such as a rotating filter. Light exiting from the rotating filter  306  enters the sensor  302 .  
         [0027]    The sensor  302  is operable to detect the light reflected from the surface of the subject  114  as wavefront information, which is passed to a computer system (e.g., computer  106  of FIG. 1). The computer system  106  may analyze the information to identify irregularities, calculate the magnitude and/or location of the irregularities, and perform similar operations. In addition, the computer system may be connected to the phase shift device  202  by one or more signal lines  308 . The computer system  106  utilizes the information obtained about surface irregularities of the subject  114  to send signals to the phase shift device  202 . The signals serve to control the actuators  204  and the displacement of the mirror  206  (and, therefore, form a new image plane  222 ) in such a way as to make corrections for the irregularities on the surface of the subject  114 .  
         [0028]    Following this displacement of the mirror  206 , the light projected from the mask  108 , off the beam splitter  210 , and through the lenses  214 ,  216  will reflect from the image plane  222  formed by the displaced mirror  206 , rather than the original image plane  218 . The light will be reflected through the lenses  216 ,  214  and the beam splitter  210 . The reflected light, which includes phase shifted light caused by the displacement of the mirror  206 , will be properly focused onto the image plane  224  formed by the surface of the subject  114 .  
         [0029]    Therefore, the mirror  206  is deformed by the actuators  204  in such a manner as to “mirror” the deformations on the surface of the subject  114  and thus cause the light projected onto the surface to be uniformly in focus. Further refinements of the image plane  224  may occur by repeating the operation through the sensor  302  and correcting the image plane  222  formed by the mirror  206 . It is noted that the distortion compensation system may act as a multiplier for the measured substrate surface irregularities, thus allowing very small changes of position of the mirror  206  to be optically magnified to adjust for larger subject surface defects.  
         [0030]    In another embodiment, a second light source  308  can be used to provide a light  310  for producing the image for the sensor  302 . The light  310  is reflected by the beam splitters  304  and  210  towards the subject  114 , and then is reflected back towards the sensor  302 . In some embodiments, the light  310  may have unique properties that do not interfere with the light  208 . For example, the light  310  may not be visible light, or may be of a wavelength that is different from the light  208 .  
         [0031]    Referring now to FIG. 4, in other embodiments, the distortion compensation system  112  includes three different lens subsystems  402   a ,  402   b ,  402   c , each of the lens subsystems being similarly constructed. For the sake of clarity, further reference will be made to individual subsystems by using suffixes “a,” “b,” and “c” corresponding to the subsystems  402   a ,  402   b ,  402   c , respectively, and generically to the subsystems without using any suffixes.  
         [0032]    Each subsystem  402  includes a housing  404  for securing and positioning one or more lenses  406 . Each housing  404  further connects to a body portion  408  through a piezo-electric (PZT) device  410 . Each PZT device  410  can move its corresponding body portion  408 , relative to the subject  114 , in a direction indicated by arrows  412 . Although not shown, in some embodiments, additional PZT devices may be connected to each housing  404  for tilting the corresponding subsystems  402 , as indicated by angles θ. Each subsystem  402  is directed towards, and responsible for exposing, a portion of the surface of the subject  114  identified as zones  412 .  
         [0033]    In one embodiment, three different mask images  420   a ,  420   b ,  420   c  are produced by three different portions of the mask(s)  108 ,  158 . For example, three different analog masks (or three portions of a single mask) can produce the images  420 . The subsystem  402   a  focuses the image  420   a  onto the surface zone  412   a  of the subject  114 ; the subsystem  402   b  focuses the image  420   b  onto the surface zone  412   b ; the subsystem  402   c  focuses the image  420   c  onto the surface zone  412   c . Some embodiments may further utilize a scanning system for exposing the entire zone with the corresponding image, while other embodiments may use different technologies, such as step and scan. There are many embodiments of the distortion compensation system  112  that can incorporate one or more of the following functionalities.  
         [0034]    Referring also to FIG. 5, in some embodiments, each of the subsystems  402  are maintained in a parallel relationship to each other. To accommodate for non-planar variations in the surface of the subject  114 , one or more of the PZTs  410  can move the distortion compensation system in a direction indicated by the arrows  412 . As illustrated in the example of FIG. 5, the PZT  410   a  has moved the body portion  408   a  downward in the direction  412   a , and the PZT  410   b  has moved the body portion  408   b  upward in the direction  412   b.    
         [0035]    Referring also to FIG. 6, in some embodiments, each of the subsystems  402  do not have to be maintained in a parallel relationship to each other. For example, the subsystem  412   a  may be moved in an angular manner, represented by the angle θA, away from a “normal” position (such as is illustrated in FIG. 5). It is understood that the term normal normally means perpendicular to the subject  114 , but in the present example, the angle θA actually helps to align the subsystem  402   a  closer to a perpendicular relationship with the specific surface zone  412   a . As illustrated in the example of FIG. 6, the surface zone  412   a  is angled to the left, and the subsystem  402   a  is tilted to the left to help compensate for this surface distortion.  
         [0036]    In some embodiments, each of the different mask portions that correspond to the different mask images  420   a ,  420   b ,  420   c  are moved and/or rotated in accordance with the movement and rotation of the subsystems. Furthermore, additional light sources  102  and/or first lens systems  104  (if used) may also need to be moved and/or rotated accordingly.  
         [0037]    In the present embodiment, the angular movement of the subsystems  412  is accomplished by the PZTs  410 . It is understood that in some embodiments, there may be multiple PZTs for each subsystem, with some performing the parallel movement described in FIG. 5, and/or some doing the angular movement described in FIG. 6. Furthermore, it is understood that the drawings of the present patent are two dimensional, and that additional PZTs can be employed to provide additional movement to compensate for surface distortion.  
         [0038]    Referring now to FIG. 7, with reference to the embodiments discussed above with respect to FIGS.  4 - 6 , the movement of the subsystems  412  by the PZTs  410  can be accomplished by a distortion detection system  700 . The distortion detection system  700  includes two beam splitters  702 ,  704 , an imaging system  706  connected to a computer (such as the computer  106  of FIG. 1), and a secondary light source  708 . It is understood that there are many possible combinations of devices that can perform distortion compensation, such as having a different numbers of beam splitters.  
         [0039]    In the present embodiment, the secondary light source  708  produces an ultraviolet (UV) light  710  which does not adversely react with the photo resist  118  on the subject  114 . The UV light  710  reflects off the beam splitters  704 ,  702  and towards the subject  114 . The UV light  710  then reflects off of the subject  114 , back through the beam splitters  702 ,  704 , and onto the imaging system  706 . The imaging system  706  provides corresponding data to the computer  106 , which determines a depth of focus for the UV light  710 . It is known that in the present embodiment, there is an offset  712  between the depth of focus for the UV light  710  and the depth of focus for the imaging light  120 . With consideration of the offset  712 , the computer  106  can control the PZTs  410  to properly move and/or orient the subsystems  412  (FIG. 5 and/or FIG. 6). As a result, the PZTs  410  (which are actually part of the distortion compensation system  112  in the present embodiment) can maintain a proper depth of focus in near real-time. It is further understood that by comparing the depth of focus for the different subsystems  412   a ,  412   b ,  412   c , the computer can map the surface of the subject  114 , and can predict future adjustments to the PZTs  410  to provide a real-time focus.  
         [0040]    Referring to all of the FIGS. , with the embodiments discussed above, it is often known what the surface distortion will be. For example, in manufacturing spherical-shaped semiconductors, such as is disclosed in U.S. Pat. No. 5,955,776 (which is hereby incorporated by reference), it is known that the subject is spherical, and the surface distortion can be predetermined. In these embodiments, the position of the subsystems  412  (FIG. 4) and/or the phase shift device  202  can be relatively fixed.  
         [0041]    In other embodiments, the surface distortion may be an unknown variant. For example, a printed circuit board or a wafer may be relatively flat, but with a wavy surface due to various process irregularities. Or, a spherical device may have a known amount of distortion, but the surface may still have some irregularities that need to be addressed. In these embodiments, the positions of the subsystems  412  and/or the phase shift device  202  can be variable, as discussed above.  
         [0042]    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. Furthermore, the order of components 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.