Patent Publication Number: US-2023144586-A1

Title: Methods and apparatus for correcting lithography systems

Description:
BACKGROUND 
     Field 
     Aspects of the present disclosure relate to methods and apparatus for correcting lithography systems. In one example, a tilt correction, a tip correction, and a vertical correction are determined for an optical module of a lithography system. 
     Description of the Related Art 
     Operational issues can arise when an image plane projected by a lithography system is not parallel to a substrate and/or is not in focus. For example, a non-parallel and/or an out-of-focus image plane can cause incorrect patterning and/or mura on the substrate. Defects in the lithography system can also cause incorrect patterning and/or mura on the substrate. 
     Additionally, it can be difficult, time-consuming, and resource-consuming to cause the image plane to be in focus and/or to be parallel to the substrate. 
     Therefore, there is a need for methods and apparatus that facilitate placing image planes projected by lithography systems to be parallel to substrates and to be in focus. 
     SUMMARY 
     Aspects of the present disclosure relate to methods and apparatus for correcting lithography systems. In one example, a tilt correction, a tip correction, and a vertical correction are determined for an optical module of a lithography system. 
     In one implementation, a method of operating a lithography system includes directing first light beams toward a reflective surface of a first substrate using a spatial light modulator of an optical module. The method includes collecting the first light beams that reflect off of the reflective surface through at least an objective lens of the optical module. The method includes directing the first light beams collected through at least the objective lens toward a camera of the optical module using a beam splitter of the optical module. The method includes taking a plurality of first images, using the camera, of the first light beams directed toward the camera. The method includes directing second light beams at an oblique angle toward a patterned surface of a second substrate using an illumination source disposed below the objective lens. The method includes collecting the second light beams that scatter off of the patterned surface through at least the objective lens, and directing the second light beams collected through at least the objective lens toward the camera using the beam splitter. The method includes taking a plurality of second images, using the camera, of the second light beams directed toward the camera. The method includes determining a tip correction, a tilt correction, and an optimal vertical position for the optical module. 
     In one implementation, a non-transitory computer-readable medium includes instructions that, when executed, cause a lithography system to direct first light beams toward a reflective surface of a first substrate using a spatial light modulator of an optical module. The instructions also cause the lithography system to collect the first light beams that reflect off of the reflective surface through at least an objective lens of the optical module. The instructions also cause the lithography system to direct the first light beams collected through at least the objective lens toward a camera of the optical module using a beam splitter of the optical module. The instructions also cause the lithography system to take a plurality of first images, using the camera, of the first light beams directed toward the camera. The instructions also cause the lithography system to direct second light beams at an oblique angle toward a patterned surface of a second substrate using an illumination source disposed below the objective lens. The instructions also cause the lithography system to collect the second light beams that scatter off of the patterned surface through at least the objective lens. The instructions also cause the lithography system to direct the second light beams collected through at least the objective lens toward the camera using the beam splitter. The instructions also cause the lithography system to take a plurality of second images, using the camera, of the second light beams directed toward the camera. The instructions also cause the lithography system to determine a tip correction, a tilt correction, and an optimal vertical position for the optical module. 
     In one implementation, a non-transitory computer-readable medium includes instructions that, when executed, cause a lithography system to direct brightfield light beams toward a reflective surface of a first substrate using a spatial light modulator of an optical module. The instructions also cause the lithography system to take a plurality of brightfield images, using a camera of the optical module, of reflected brightfield light beams that reflect off of the reflective surface. The instructions also cause the lithography system to direct darkfield light beams toward a patterned surface of a second substrate. The instructions also cause the lithography system to take a plurality of darkfield images, using the camera, of scattered darkfield light beams that scatter off of the patterned surface. The instructions also cause the lithography system to determine a tip correction, a tilt correction, and an optimal vertical position for the optical module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features of the disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to implementations, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only common implementations of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective implementations. 
         FIG.  1    is a schematic partial perspective view of a lithography system, according to one implementation. 
         FIG.  2    is a perspective schematic view of an image projection apparatus used in the lithography system illustrated in  FIG.  1    during a brightfield illumination operation, according to one implementation. 
         FIG.  3    is a perspective schematic view of the image projection apparatus used in the lithography system illustrated in  FIG.  1    during a darkfield illumination operation, according to one implementation. 
         FIG.  4 A  is a schematic partial view of an image taken by the camera illustrated in  FIGS.  2  and  3   , according to one implementation. 
         FIG.  4 B  is a schematic illustration of a graph of the analyzed resolutions of the respective first images or second images, according to one implementation. 
         FIG.  5    is a schematic illustration of a graph of analyzed resolutions of images taken using the camera after correcting the optical module, according to one implementation. 
         FIG.  6    is a schematic illustration of a method of operating a lithography system, according to one implementation. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one implementation may be beneficially utilized on other implementations without specific recitation. 
     DETAILED DESCRIPTION 
     Aspects of the present disclosure relate to methods and apparatus for correcting lithography systems. In one example, a tilt correction, a tip correction, and a vertical correction are determined for an optical module of a lithography system. 
       FIG.  1    is a schematic partial perspective view of a lithography system  100 , according to one implementation. The lithography system  100  includes a base frame  110 , a slab  120 , a stage  130 , and a processing apparatus  160 . The base frame  110  rests on the floor of a fabrication facility and supports the slab  120 . Passive air isolators  112  are positioned between the base frame  110  and the slab  120 . In one embodiment, which can be combined with other embodiments, the slab  120  is a monolithic piece of granite, and the stage  130  is disposed on the slab  120 . A substrate  140  is supported by the stage  130 . A plurality of openings are formed in the stage  130  to allow a plurality of lift pins to extend therethrough. The lift pins raise to an extended position to receive the substrate  140 , such as from one or more transfer robots. The one or more transfer robots are used to load and unload substrates, such as the substrate  140 , to and from the stage  130 . 
     The substrate  140  includes any suitable material, for example, quartz used as part of a flat panel display. The substrate  140  can be made of other materials. The substrate  140  has a photoresist layer formed thereon. The photoresist layer is sensitive to radiation. A positive photoresist includes portions of the photoresist, which when exposed to radiation, will be respectively soluble to photoresist developer applied to the photoresist after the pattern is written into the photoresist. A negative photoresist includes portions of the photoresist, which when exposed to radiation, will be respectively insoluble to photoresist developer applied to the photoresist after the pattern is written into the photoresist. The chemical composition of the photoresist determines whether the photoresist will be a positive photoresist or negative photoresist. Examples of photoresists include, but are not limited to, one or more of diazonaphthoquinone, a phenol formaldehyde resin, poly(methyl methacrylate), poly(methyl glutarimide), and/or SU-8. During processing using the lithography system  100 , a pattern is formed on a process surface  141  of the substrate  140  to form the electronic circuitry, such as electronic circuitry for use on a large-area flat panel display screen. 
     The lithography system  100  includes a pair of supports  122  and a pair of tracks  124 . The pair of supports  122  are disposed on the slab  120 , and the slab  120  and the pair of supports  122  are a single piece of material. The pair of tracks  124  are supported by the pair of the supports  122 , and the stage  130  moves along the tracks  124  in the X-direction. The lithography system  100  can include one or more additional stages, in addition to the stage  130  illustrates. In one embodiment, which can be combined with other embodiments, the pair of tracks  124  is a pair of parallel magnetic channels. Each track  124  of the pair of tracks  124  is linear. In one embodiments, which can be combined with other embodiments, one or more of the tracks  124  is non-linear. An encoder  126  is coupled to the stage  130  in order to provide location information to a controller  101 . 
     The processing apparatus  160  includes a support  162  and a processing unit  164 . The support  162  is disposed on the slab  120  and includes an opening  166  for the stage  130  to pass under the processing unit  164 . The processing unit  164  is supported by the support  162 . In one embodiment, the processing unit  164  is a pattern generator configured to expose a photoresist in a photolithography process. In one embodiment, which can be combined with other embodiments, the pattern generator is configured to conduct a maskless lithography process. The processing unit  164  includes a plurality of image projection apparatus  200  (shown in  FIGS.  2  and  3   ). In one embodiment, which can be combined with other embodiments, the processing unit  164  includes as many as 84 or more image projection apparatus. Each image projection apparatus is disposed in a case  165 . The processing apparatus  160  can be used to conduct maskless direct patterning. 
     During operation of the lithography system  100 , the stage  130  moves in an X-direction from a loading position, as shown in  FIG.  1   , to a processing position. The processing position includes one or more positions of the stage  130  as the stage  130  passes under the processing unit  164 . During operation, the stage  130  is lifted by a plurality of air bearings and moves along the pair of tracks  124  from the loading position to the processing position. A plurality of vertical guide air bearings are coupled to the stage  130  and positioned adjacent an inner wall  128  of each support  122  to stabilize the movement of the stage  130 . The stage  130  also moves in a Y-direction by moving along a track  150  for processing and/or indexing the substrate  140 . The stage  130  is capable of independent operation and can scan a substrate  140  in one direction and step in the other direction. 
     A metrology system measures the X and Y lateral position coordinates of each of the stage  130  in real time so that each of the plurality of image projection apparatus can accurately locate the patterns being written in a photoresist covered substrate. The metrology system also provides a real-time measurement of the angular position of each of the stage  130  about a vertical or Z-axis. The angular position measurement can be used to hold the angular position constant during scanning using a servo mechanism. The angular position measurement can be used to apply corrections to the positions of the patterns being written on the substrate  140  by the image projection apparatus  200 , shown in  FIGS.  2  and  3   . In one embodiment, which can be combined with other embodiments, these techniques are used in combination. 
       FIG.  2    is a perspective schematic view of an image projection apparatus  200  used in the lithography system  100  illustrated in  FIG.  1    during a brightfield illumination operation, according to one implementation. The image projection apparatus  200  is used as each of the plurality of image projection apparatus corresponding to each of the cases  165  used in the lithography system  100  illustrated in  FIG.  1   . The image projection apparatus  200  includes an optical module  201 . The optical module  201  includes a housing  202 . 
     The image projection apparatus  200  directs a plurality of first light beams  222  toward a reflective surface  204  of a first substrate  240 . The first substrate  240  may move in the X-direction and the Y-direction, as the first light beams  222  are directed toward the reflective surface  204 . The first substrate  240  includes a mirror. In one embodiment, which can be combined with other embodiments, the reflective surface  204  is a continuous and planar surface. 
     The substrate  140  illustrated in  FIG.  1    is patterned using the lithography system  100 . The first substrate  240  illustrated in  FIG.  2    is used to calibrate the lithography system  100 , such as by adjusting the optical modules  201  of the image projection apparatus  200 . Each of the image projection apparatus  200  includes a respective motor to control a tilt position, a tip position, and a vertical position of the respective optical module  201 . The number of image projection apparatus  200  can vary based on the size of the substrate  140  and/or the speed of stage  130  (shown in  FIG.  1   ). 
     The optical module  201  includes a light source  206 , an aperture  208 , a lens  210 , a mirror  212 , a digital mirror device (DMD)  214 , a light dump  216 , a camera  218 , and a projection lens  220 . The light source  206  includes light emitting diodes (LED&#39;s) or lasers. In one example, the light source  206  includes a broadband LED. The light source  206  is capable of producing light beams having a predetermined wavelength. In one embodiment, which can be combined with other embodiments, the predetermined wavelength is in the blue or near ultraviolet (UV) range, such as 450 nm or less. The mirror  212  includes a spherical mirror. The camera  218  may include for example, a CCD camera and/or a CMOS camera. 
     The projection lens  220  includes an objective lens, such as a 10× objective lens. The DMD  214  includes a plurality of mirrors, and the number of mirrors of the DMD  214  may correspond to the resolution of the projected image. 
     During operation, first light beams  222  having a predetermined wavelength, such as a wavelength in the blue range, are emitted by the light source  206 . The first light beams  222  are reflected to the DMD  214  using the mirror  212 . The mirrors of the DMD  214  may be controlled individually, and each mirror of the plurality of mirrors of the DMD  214  may be set at an “on” position or an “off” position, based on pattern data. The pattern data may be provided to the DMD  214  using the controller  101 . When the first light beams  222  reach the mirrors of the DMD  214 , the mirrors that are at the “on” position reflect the first light beams  222  to direct the first light beams  222  through a beam splitter  230  and toward the projection lens  220  to be projected onto the reflective surface  204 . The projection lens  220  directs the first light beams  222  to the reflective surface  204  of the first substrate  240 . The mirrors that are at the “off” position reflect the first light beams  222  to direct the first light beams  222  to the light dump  216  instead of the reflective surface  204  of the first substrate  240 . 
     The first light beams  222  reflect off of the reflective surface  204  and are directed back toward the projection lens  220  as reflected first light beams  223 . The reflected first light beams  223  are collected using at least the projection lens  220 , and are directed toward the beam splitter  230 . The reflected first light beams  223  reflect off of the beam splitter  230  and are directed toward the camera  218 . The beam splitter  230  is oriented such that at least a portion of the light beams projecting toward the beam splitter  230  from the DMD  214  pass through the beam splitter  230  and project toward the projection lens  220 . The beam splitter  230  is oriented such that at least a portion of the light beams projecting toward the beam splitter  230  from the projection lens  220  are reflected toward the camera  218 . 
     The camera  218  takes a plurality of first images of the image plane projected onto the reflective surface  204 . The first images taken by the camera  218  include the reflected first light beams  223  that reflect off of the reflective surface  204 . The camera  218  transmits the plurality of first images including the reflected first light beams  223  to the controller  101 . 
     The optical module  201  is moved vertically while the first light beams  222  are projected onto the reflective surface  204  and the camera  218  takes the first images that include the reflected first light beams  223 . In one embodiment, which can be combined with other embodiments, the optical module  201  is moved vertically upward and/or downward along the Z-axis and relative to the first substrate  240 . In one example, the optical module  201  moves across a plurality of vertical positions. In one embodiment, which can be combined with other embodiments, the first images taken using the camera  218  correspond to a plurality of vertical positions of the optical module  201 . In one embodiment, which can be combined with other embodiments, the optical module  201  is disposed at a tip position and a tilt position while the optical module  201  moves vertically and the camera  218  takes the first images. 
     The projection lens  220  is part of a first illumination source that is a brightfield illumination source. The brightfield illumination source projects the first light beams  223  toward the reflective surface  204  within a field of view of the projection lens  220 . 
     During calibration of the lithography system  100  using the first substrate  240 , the first substrate  240  is not patterned by the first light beams  222 . In one embodiment, which can be combined with other embodiments, the first substrate  240  does not include a photoresist layer formed thereon. 
     In the implementation shown in  FIG.  2   , the optical module  201  includes a spatial light modulator (SLM) that is a part of the brightfield illumination source. In the implementation shown, the SLM includes the DMD  214 . The present disclosure contemplates that other SLM&#39;s and associated aspects thereof may be used in place of one or more aspects of the optical module  201  (such as in place of the DMD  214  and/or the light source  206 ). In one embodiment, which can be combined with other embodiments, the optical module  201  includes microLED arrays, VCSEL arrays, and/or LCD arrays as part of the first illumination source that is a brightfield illumination source. In one example, the microLED arrays, the VCSEL arrays, and/or the LCD arrays are used and one or more of the DMD  214 , the light source  206 , the aperture  208 , the lens  210 , the mirror  212 , and/or the light dump  216  are omitted. 
       FIG.  3    is a perspective schematic view of the image projection apparatus  200  used in the lithography system  100  illustrated in  FIG.  1    during a darkfield illumination operation, according to one implementation. 
     The optical module  201  includes an illumination source  250  disposed below the projection lens  220 . In one embodiment, which can be combined with other embodiments, the illumination source  250  is coupled to the projection lens  220 , and is disposed circumferentially about the projection lens  220 . 
     The illumination source  250  directs a plurality of second light beams  322  toward a patterned surface  304  of a second substrate  340 . The second light beams  322  are directed toward the patterned surface  304  at an oblique angle A 1  relative to the patterned surface  304 . The second substrate  340  is different than the first substrate  240  described above. The patterned surface  304 , is patterned for example, using lithography operations, deposition operations, and/or etching operations. The patterned surface  304  includes a plurality of structures  305  formed thereon to scatter the second light beams  322 . The illumination source  250  is a second illumination source. The illumination source  250  includes a darkfield illumination source that projects the second light beams  322  toward the patterned surface  304  from locations disposed outside of the field of view of the projection lens  220 . 
     The second substrate  340  illustrated in  FIG.  3    is used to calibrate the lithography system  100 , such as by adjusting the optical modules  201  of the image projection apparatus  200 . 
     In one example, the illumination source  250  includes a ring and a plurality of light emitters, such as LED&#39;s and/or laser emitters, that emit the second light beams  322 . In one example, the illumination source  250  includes broadband LED&#39;s. The illumination source  250  is capable of producing light beams having a predetermined wavelength. In one embodiment, which can be combined with other embodiments, the predetermined wavelength is in the blue or near ultraviolet (UV) range, such as 450 nm or less. 
     In one embodiment, which can be combined with other embodiments, the illumination source  250  includes a spatial light modulator (SLM). In one example, the illumination source  250  includes one or more of a digital mirror device (DMD), microLED arrays, VCSEL arrays, and/or LCD arrays. 
     During operation, second light beams  322  having a predetermined wavelength, such as a wavelength in the blue range, are emitted by the illumination source  250 . The second light beams  322  are directed to the patterned surface  304 . The second light beams  322  are scattered using the structures  305 , and are directed toward the projection lens  220  as scattered second light beams  323 . The scattered second light beams  323  are collected using at least the projection lens  220 , and are directed toward the beam splitter  230 . The scattered second light beams  323  reflect off of the beam splitter  230  and are directed toward the camera  218 . In one embodiment, which can be combined with other embodiments, the wavelength of the second light beams  322  projected using the darkfield illumination source is about the same as the wavelength of the first light beams  222  projected using the brightfield illumination source. In one example, the wavelength of the second light beams  322  is within a 50 nm difference of the wavelength of the first light beams  222 . 
     The camera  218  takes a plurality of second images of the image plane projected onto the patterned surface  304 . The second images taken by the camera  218  include the scattered second light beams  323  that scatter off of the patterned surface  304 . The camera  218  transmits the plurality of second images including the scattered second light beams  323  to the controller  101 . 
     In one embodiment, which can be combined with other embodiments, the reflected first light beams  223  are reflected brightfield light beams and the scattered second light beams  323  are scattered darkfield light beams. 
     The optical module  201  is moved vertically while the second light beams  322  are projected onto the patterned surface  304  and the camera  218  takes the second images that include the scattered second light beams  323 . In one embodiment, which can be combined with other embodiments, the optical module  201  is moved vertically upward and/or downward along the Z-axis and relative to the second substrate  340 . In one example, the optical module  201  moves across a plurality of vertical positions. In one embodiment, which can be combined with other embodiments, the second images taken using the camera  218  correspond to a plurality of vertical positions of the optical module  201 . In one embodiment, which can be combined with other embodiments, the optical module  201  is disposed at a tip position and a tilt position while the optical module  201  moves vertically and the camera  218  takes the second images. 
     During calibration of the lithography system  100  using the second substrate  340 , the second substrate  340  is not patterned by the second light beams  322 . 
     The controller  101  is in communication with aspects of the lithography system  100  and is configured to control aspects of the lithography system  100 . In one example, the controller  101  is in communication with, and configured to control, the optical modules  201  and corresponding motors, cameras  218 , DMD&#39;s  214 , light sources  206 , and/or illumination sources  250 . In one example, the controller  101  is configured to adjust the tilt position, the tip position, and the vertical position of the optical modules  205 . The tilt position is an angular position of the optical module  205  about the X-axis. The tip position is an angular position of the optical module  205  about the Y-axis. The vertical position is a lateral position of the optical module  205  along the Z-axis. In one embodiment, which can be combined with other embodiments, each of the X-axis, the Y-axis, and the Z-axis extends through a center of the respective optical module  205 . 
     The controller  101  receives the plurality of first images from the camera  218  that include the reflected first light beams  223 . The first images correspond to a plurality of vertical positions of the optical module  205 . For each of the first images, the controller  101  processes outer areas (e.g., corner areas) of the respective image and analyzes a resolution of each outer area. In one example, the corner areas of the first images that are analyzed include a top-left corner area, a top-right corner area, a bottom-left corner area, and a bottom-right corner area. The resolution indicates a number of pixels within the respective corner area, a focus level, and/or an amount of lighted area of the respective corner area that is recognized by the controller  101  or the camera  218 . In one embodiment, which can be combined with other embodiments, the pixels correspond to the reflected first light beams  223  appearing in the respective corner area of the respective first image. In one embodiment, which can be combined with other embodiments, the resolution indicates a measured light intensity of light within the respective corner area. The resolution for each outer area is analyzed for each of the first images (e.g., for each of the vertical positions), and an optimal first image is determined for each of the outer areas. For each outer area, the optimal first image is the first image, and the corresponding vertical position, at which the respective corner area has the highest resolution. In one example, the highest resolution is an optimal focus level having an optimal clarity, the largest measured light intensity, the largest amount of lighted area recognized by the controller  101  and/or the camera  218 , and/or the largest number of pixels. An optimal first image is determined for each of the top-left corner area, the top-right corner area, the bottom-left corner area, and the bottom-right corner area. 
     Using the optimal first image for each of the outer areas, the controller  101  determines an optimal brightfield tilt, an optimal brightfield tip, and an optimal brightfield vertical position. The optimal brightfield vertical position is determined by using the corresponding vertical positions of the optimal first images for the corner areas, and calculating an average of the corresponding vertical positions. The first images and the second images each include a first image length extending along the left and right sides and a second image length extending along the top and bottom sides in the image plane. 
     As shown in Equation 1 below, the optimal brightfield tilt (Tilt BF ) is determined by calculating a sine of a first brightfield difference D 1  divided by the first image length L 1 . 
       Tilt BF =sin( D 1/ L 1)  (Equation 1)
 
     In one example, the first brightfield difference D 1  is determined by subtracting the corresponding vertical position of the optimal first image for the bottom-left corner from the corresponding vertical position of the optimal first image for the top-left corner. In one example, the first brightfield difference D 1  is determined by subtracting the corresponding vertical position of the optimal first image for the bottom-right corner from the corresponding vertical position of the optimal first image for the top-right corner. 
     As shown in Equation 2 below, the optimal brightfield tip (Tip BF ) is determined by calculating a sine of a second brightfield difference D 2  divided by the second image length L 2 . 
         Tip   BF =sin( D 2/ L 2)  (Equation 2)
 
     In one example, the second brightfield difference D 2  is determined by subtracting the corresponding vertical position of the optimal first image for the top-right corner from the corresponding vertical position of the optimal first image for the top-left corner. In one example, the second brightfield difference D 2  is determined by subtracting the corresponding vertical position of the optimal first image for the bottom-right corner from the corresponding vertical position of the optimal first image for the bottom-left corner. 
     The controller  101  receives the plurality of second images from the camera  218  that include the scattered second light beams  323 . The second images correspond to a plurality of vertical positions of the optical module  205 . For each of the second images, the controller  101  processes outer areas (e.g., corner areas) of the respective image and analyzes a resolution of each corner area. In one example, the corner areas of the second images that are analyzed include a top-left corner area, a top-right corner area, a bottom-left corner area, and a bottom-right corner area. The resolution indicates a number of pixels within the respective corner area, a focus level, and/or an amount of lighted area of the respective corner area that is recognized by the controller  101  or the camera  218 . In one embodiment, which can be combined with other embodiments, the pixels correspond to the scattered second light beams  323  appearing in the respective outer area of the respective second image. In one embodiment, which can be combined with other embodiments, the resolution indicates a measured light intensity of light within the respective corner area. The resolution for each outer area is analyzed for each of the second images (e.g., for each of the vertical positions), and an optimal second image is determined for each of the outer areas. For each outer area, the optimal second image is the second image, and the corresponding vertical position, at which the respective outer area has the highest resolution. In one example, the highest resolution is an optimal focus level having an optimal clarity, the largest measured light intensity, the largest amount lighted area recognized by the controller  101  and/or the camera  218 , and/or the largest number of pixels. An optimal second image is determined for each of the top-left corner area, the top-right corner area, the bottom-left corner area, and the bottom-right corner area. 
     Using the optimal second image for each of the outer areas, the controller  101  determines an optimal darkfield tilt, an optimal darkfield tip, and an optimal darkfield vertical position. The optimal darkfield vertical position is determined by using the corresponding vertical positions of the optimal second images for the corner areas, and calculating an average of the corresponding vertical positions. 
     As shown in Equation 3 below, the optimal darkfield tilt (Tilt DF ) is determined by calculating a sine of a first darkfield difference D 3  divided by the first image length L 1 . 
       Tilt DF =sin( D 3/ L 1)  (Equation 3)
 
     In one example, the first darkfield difference D 3  is determined by subtracting the corresponding vertical position of the optimal second image for the bottom-left corner from the corresponding vertical position of the optimal second image for the top-left corner. In one example, the first darkfield difference D 3  is determined by subtracting the corresponding vertical position of the optimal second image for the bottom-right corner from the corresponding vertical position of the optimal second image for the top-right corner. 
     As shown in Equation 4 below, the optimal darkfield tip (Tip DF ) is determined by calculating a sine of a second darkfield difference D 4  divided by the second image length L 2 . 
         Tip   DF =sin( D 4/ L 2)  (Equation 4)
 
     In one example, the second darkfield difference D 4  is determined by subtracting the corresponding vertical position of the optimal second image for the top-right corner from the corresponding vertical position of the optimal second image for the top-left corner. In one example, the second darkfield difference D 4  is determined by subtracting the corresponding vertical position of the optimal second image for the bottom-right corner from the corresponding vertical position of the optimal second image for the bottom-left corner. 
     In one embodiment, which can be combined with other embodiments, the optimal first image is an optimal brightfield image and the optimal second image is an optimal darkfield image. 
     The controller  101  then determines a tip correction, a tilt correction, and an optimal vertical position for the optical module  205 . As shown in Equation 5 (below), the tilt correction (X) is determined by multiplying the optimal brightfield tilt (Tilt BF ) by a factor of 2.0 to determine a tilt value, and subtracting the tilt value from the optimal darkfield tilt (Tilt DF ): 
         X =Tilt DF −(2*Tilt BF )  (Equation 5)
 
     As shown in Equation 6 (below), the tip correction (Y) is determined by multiplying the optimal brightfield tip (Tip BF ) by a factor of 2.0 to determine a tip value, and subtracting the tip value from the optimal darkfield tip (Tip DF ): 
         Y=Tip   DF −(2* Tip   BF )  (Equation 6)
 
     As shown in Equation 7 (below), the optimal vertical position (Z L ) is determined by multiplying the optimal brightfield vertical position (Z BF ) by a factor of 2.0 to determine a vertical value, and subtracting the optimal darkfield vertical position (Z DF ) from the vertical value: 
         Z   L =(2* Z   BF )− Z   DF   (Equation 7)
 
     The controller  101  instructs the motor to adjust the tilt position (which was used during the taking of the first images and the second images) of the optical module  205  to a corrected tilt position using the tilt correction (X). The corrected tilt position is a corrected angular position of the optical module  205  about the X-axis after the tilt correction is applied to the tilt position. 
     In one embodiment, which can be combined with other embodiments, each of the tilt correction (X) and the tip correction (Y) includes an angular value, and the optimal vertical position (Z L ) includes a translational value. 
     The controller  101  instructs the motor to adjust the tip position (which was used during the taking of the first images and the second images) of the optical module  205  to a corrected tip position using the tip correction (Y). The corrected tip position is a corrected angular position of the optical module  205  about the Y-axis after the tip correction is applied to the tip position. 
     The controller  101  instructs the motor to adjust the vertical position of the optical module  205  to a corrected vertical position using the optimal vertical position (Z L ). The corrected vertical position is approximately equal to the optimal vertical position (Z L ) along the Z-axis. 
     After adjusting to the corrected tilt position, the corrected tip position, and the corrected vertical position, the optical module  205  is used to pattern substrates (such as the substrate  140  illustrated in  FIG.  1   ) using lithography operations. 
     The controller  101  includes a processor  181 , such as a central processing unit (CPU), a memory  182 , and a support circuit  183  for the processor  181 . The controller  180  may be one of any form of general-purpose computers that can be used in an industrial setting for controlling various lithography system components and sub-processors. The memory  182  stores software (source or object code), such as a computer program, that may be executed or invoked to control the overall operations of the lithography system  100  and/or optical modules  205  in manners described herein. 
     The controller  101  includes a non-transitory computer-readable medium (such as the memory  182 ) including instructions (such as the software) that when executed (such as by the processor  181 ) causes one or more of the operations described herein to be conducted. In one embodiment, which can be combined with other embodiments, the instructions, when executed, cause one or more of the operations described in relation to  FIGS.  1 - 6    to be conducted. In one embodiment, which can be combined other embodiments, the instructions of the non-transitory computer-readable medium of the controller  101 , when executed, cause one or more operations of the method  600  to be conducted. In one example, the instructions cause one or more of operations  601 - 621  to be conducted in relation to the lithography system  100  and/or the optical modules  205  and/or the aspects and/or components thereof. 
     Aspects described herein facilitate projecting light toward substrates (to pattern the substrates during lithography operations) at an image plane that is substantially parallel with substrates surfaces that are to be patterned. Aspects described herein also facilitate projecting light toward substrates at an image plane that is within focus across substantially the entirety of the image plane. As an example, adjusting optical modules to the corrected tip positions, the corrected tilt positions, and the corrected vertical positions facilitates adjusting the optical modules  205  such that the optical modules  205  image planes that are in focus and parallel to substrates that the projected image planes are patterning. Aspects described herein facilitate simply, quickly, and effectively calibrating the tilt, tip, and vertical positions of optical modules  205 . As an example, aspects described herein facilitate simply calibrating the optical modules  205  of the lithography system  105  using the same optical modules  205  that are used to pattern substrates. The calibration can be conducted quickly, for example, in a time period of 10 minutes or less. 
     Calibrating optical modules  205  using the tip correction, the tilt correction, and the optimal vertical position can also account for structural defects in the optical modules  205 , such as mura on lenses of the optical modules. Calibrating optical modules  205  also can account for positions defects in the optical modules  205 , such as certain components being misaligned. Calibrating the optical modules  205  using aspects described herein also facilitates effective and accurate patterning of substrates with reduced mura on the substrates, facilitating increased throughput, reduced machine downtime, reduced production time, and reduced operational costs. 
       FIG.  4 A  is a schematic partial view of an image  400  taken by the camera  218  illustrated in  FIGS.  2  and  3   , according to one implementation. The image  400  includes the first image length L 1  and the second image length L 2  in the image plane. The image  400  may be an example of one of the plurality of first images that include the reflected first light beams  223 . The image  400  may be an example of one of the plurality of second images that include the scattered second light beams  323 . The image  400  includes a plurality of image features  410  (e.g., pixels). In one example, when analyzing the first images, the image features  410  correspond to the reflected first light beams  223  appearing within the respective image  400 . In one example, when analyzing the second images, the image features  410  correspond to the scattered second light beams  323  appearing within the respective image  400 . 
     The image  400  includes corner areas  412 A- 412 D (a top-left corner area  412 A, a top-right corner area  412 B, a bottom-left corner area  412 C, and a bottom-right corner area  412 D) that are processed and analyzed. A resolution for each of the corner areas  412 A- 412 D is analyzed. In one example, the resolution of each corner area  412 A- 412 D includes the number of image features  410 A- 410 D (e.g., pixels) appearing within the respective corner area  412 A- 412 D. In one example, the resolution of each corner area  412 A- 412 D includes the measured light intensity of light appearing within the respective corner area  412 A- 412 D. 
       FIG.  4 B  is a schematic illustration of a graph  450  of the analyzed resolutions of the respective first images or second images, according to one implementation. The Y-axis of the graph  450  represents the resolution of the respective corner area  412 A- 412 D of the respective first images or second images. In one example, the resolution is the number of image features (e.g., pixels) appearing within the respective corner area  412 A- 412 D. In one example, the resolution is the measured light intensity of light within the respective corner area  412 A- 412 D. The X-axis of the graph  450  represents the image number of the respective first image or second image. The image number of the X-axis corresponds to the corresponding vertical position of the optical module  205  at which the image was taken by the camera  218 . The resolutions across the respective first images or the second images are mapped for each of the corner areas  412 A- 412 D and displayed in the graph  450 . A peak  460 A- 460 D is shown in the graph  450  for each of the corner areas  412 A- 412 D. The peak  460 A- 460 D for each respective corner area  412 A- 412 D corresponds to the image number (and corresponding vertical position) at which the respective corner area  412 A- 412 D has the highest resolution. The image number (and corresponding vertical position) indicates an optimal first image (if the first images are analyzed) or an optimal second image (if the second images are analyzed) for each respective corner area  412 A- 412 D. 
       FIG.  5    is a schematic illustration of a graph  550  of analyzed resolutions of images taken using the camera  218  after correcting the optical module  205 , according to one implementation. The images mapped in the graph  550  are taken after the tilt position of the optical module  205  is corrected to the corrected tilt position using the tilt correction, and the tip position is corrected to the corrected tip position using the tip correction. The resolutions of respective corner areas  512 A- 512 D are mapped in the graph  550 . The resolutions of the corner areas  512 A- 512 D are more aligned across image numbers (and corresponding vertical positions) as compared to the corner areas  412 A- 412 D illustrated in  FIG.  4 B . Peaks  560 A- 560 D of resolutions for the respective corners areas  412 A  412 D are aligned and occurring at the same image number (and corresponding vertical position to facilitate accurate patterning and a parallel image plane that is in focus. The peaks  560 A- 560 D of resolutions are also higher, after tip and tilt corrections, than the peaks  460 A- 460 D illustrated in  FIG.  4 B . The graph  550  is exemplary. 
       FIG.  6    is a schematic illustration of a method  600  of operating a lithography system, according to one implementation. At operation  601 , the method  600  includes directing first light beams toward a reflective surface of a first substrate using a digital mirror device of an optical module. Operation  603  includes collecting the first light beams that reflect off of the reflective surface of the first substrate through at least an objective lens of the optical module. Operation  605  includes directing the first light beams collected through at least the objective lens toward a camera of the optical module using a beam splitter of the optical module. Operation  607  includes taking a plurality of first images, using the camera, of the first light beams directed toward the camera. Operation  609  includes directing second light beams at an oblique angle toward a patterned surface of a second substrate using an illumination source disposed below the objective lens. Operation  611  includes collecting the second light beams that scatter off of the patterned surface through at least the objective lens. Operation  613  includes directing the second light beams collected through at least the objective lens toward the camera using a beam splitter. Operation  615  includes taking a plurality of second images, using the camera, of the second light beams directed toward the camera. 
     Operation  617  includes determining a tip correction, a tilt correction, and an optimal vertical position for the optical module. Operation  619  includes adjusting a tip position of the optical module to a corrected tip position using the tip correction, and adjusting a tilt position of the optical module to a corrected tilt position using the tilt correction. Operation  619  also includes adjusting a vertical position of the optical module to a corrected vertical position using the optimal vertical position. 
     In one embodiment, which can be combined with other embodiments, the first light beams are brightfield light beams and the second light beams are darkfield light beams. In one embodiment, which can be combined with other embodiments, the first images are brightfield images and the second images are darkfield images. In one embodiment, which can be combined with other embodiments, the objective lens is at least a part of a brightfield illumination source and the illumination source is at least a part of a darkfield illumination source. In one embodiment, which can be combined with other embodiments, the first substrate and the second substrate are test substrates. 
     Operation  621  includes patterning one or more production substrates using the lithography system with the optical module corrected to the corrected tip position, the corrected tilt position, and the corrected vertical position. 
     Benefits of the present disclosure include quickly and effective correcting tip positions, tilt positions, and vertical positions of optical modules; simply correcting optical modules with reduced expenditure of resources; correcting for defects in optical modules; projecting light at image planes that are parallel to substrates; projecting light at image planes that are in focus; accurately patterning substrates; reduced mura on patterned substrates; increased throughput; reduced production time; reduced machine downtime; and reduced operational costs. 
     Aspects of the present disclosure include a lithography system  100 ; optical modules  205 ; camera  218 ; first substrate  240 ; second substrate  340 ; first light beams  223 ; reflected first light beams  223 ; second light beams  322 ; scattered second light beams  323 ; controller  101 ; first images; second images; corner areas  412 A- 412 D of images  400 ; and method  600 . It is contemplated that one or more aspects disclosed herein may be combined. Moreover, it is contemplated that one or more aspects disclosed herein may include some or all of the aforementioned benefits. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The present disclosure also contemplates that one or more aspects of the embodiments described herein may be substituted in for one or more of the other aspects described. The scope of the disclosure is determined by the claims that follow.