Roll printer with decomposed raster scan and X-Y distortion correction

Abstract

A reflecting Offner-like optical system is described which is suitable for use in a photolithographic system in which the magnification is approximately 1 to 1, and where the format is flexible. The primary mirror is split into two halves, which are movable with respect to each other. Magnification is slightly changeable by moving the two halves of the split primary mirror forward and backward by slight amounts. The reflecting optical system is moved in a reciprocating manner across a nominally stationary photomask and an intermittently stationary flexible format, which includes a segment of a roll-to-roll web. The arctuate object and image are rotated 90 degrees by flat mirrors to enable efficient scan coverage as the entire mirror system shuttles back and forth across the mask and the web. Center to center distance between the object and the image fields is increased by the use of an aspheric secondary mirror.

1 ) An optical machine for creating an image of a master object on a format plane, including: 
 a first assembly defining a master object plane and a format plane in spaced apart positions;    a second assembly comprising a reflecting optical system wherein a concave mirror, a convex mirror and a concave mirror follow each other in series, the concave mirrors being spherical, of the same curvature, sharing approximately the same centers and being controllably movable with respect to each other for the purpose of introducing a slight change in magnification, for transferring successive parts of the image of the master object from the plane of the master object to the format plane at nearly unit magnification;    a third assembly which moves the second assembly in a reciprocating motion in a first direction to provide a first dimension of an areal scan pattern;    a fourth assembly coupled to the first and second assemblies for moving the first assembly incrementally in a second direction different from the first between movements of the second assembly to provide a second dimension of the areal scan pattern.    
   
   
       2 ) An optical machine according to  claim 1  including three air/vacuum bearings supporting the reciprocating motion of the second assembly, one bearing located generally under the object plane, one bearing located generally under the image plane, and the third bearing located under the centerline of the convex mirror, removed from the first two bearings to form a triangular support.  
   
   
       3 ) An optical machine according to  claim 2  further including two autofocus gages, each generating an error signal, one gage located close to the object plane, monitoring the distance of the object plane from the photomask plane and the other gage located close to the image plane, monitoring the distance of the image plane from the format plane.  
   
   
       4 ) An optical machine according to  claim 3  wherein there are three servoed lifters, one above each of the air/vacuum bearings under the object and image planes, wherein each lifter's movement is responsive to the error signal of the autofocus gage under its respective plane, and the third servo lifter above the rear air/vacuum bearing, its drive signal being generated as the average of the signals driving the other two lifters.  
   
   
       5 ) An optical machine according to  claim 1  including a mounting frame movably supporting the photomask and comprising drivers to permit slight controlled movement in two orthogonal directions, both directions lying within the object plane.  
   
   
       6 ) An optical machine according to  claim 1  for creating an image of a master object which is superimposed in registry upon another pre-existing image located in the format plane.  
   
   
       7 ) An optical machine according to  claim 6 , also comprising position sensitive gages carried on the second assembly which read fiducial marks on the photomask and on a preexisting format image.  
   
   
       8 ) A method of transferring images wherein an optical machine includes fiducial marks on a photomask and on a preexisting image and the optical machine undergoes successive raster passes comprising the steps of reading some fiducial marks on the photomask and fiducial marks on a pre-existing format image at the start of each raster pass, and reading additional fiducial marks on the photomask and on the format image at the end of each pass, and deriving from the readings knowledge of the distortion existing between selected positions on the photomask in X and Y relative to corresponding positions on the pre-existing format image, and from this knowledge developing driver control signals to progressively move the photomask within its frame during each reciprocating pass of the second assembly.  
   
   
       9 ) A method in accordance with  claim 8 , wherein the photomask undergoes slight movement in both X and Y within its frame during a raster pass, in response to driver signals to minimize positional mismatch during the pass between the centers of successive object fields on the master photomask object and the centers of corresponding successive image fields on the preexisting distorted format image.  
   
   
       10 ) A method in accordance with  claim 8  wherein fiducial marks on the photomask and fiducial marks on a pre-existing format image are read at the start of each raster pass, and additional fiducial marks on the photomask and on the pre-existing format image are read at the end of each pass, from the readings knowledge is derived of the magnification error existing between selected positions on the photomask in X and Y at the start of successive raster passes relative to corresponding positions on the pre-existing format image, and from this knowledge driver control signals are developed to adjust the magnification of the optical transfer assembly at the start of each raster pass.  
   
   
       11 ) A method in accordance with  claim 10  in which the optical transfer assembly comprises two concave mirrors and a convex mirror, and the method includes the steps of moving the concave mirrors incrementally in opposite directions aligned to the axis of the convex mirror at the start of each raster pass to adjust the magnification to compensate the extremes of the instantaneous field for measured Δx and Δy magnification errors.  
   
   
       12 ) A system for recording images on a recording web disposed in a substantially planar disposition between a take-up side and a supply side and comprising: 
 an areal platen disposed along the web and engageable to a substantial portion of the surface thereof;    an imaging system disposed between a master object plane and a format plane along the width of the web, the imaging system including an illuminating source and optics providing a controllable beam for illuminating an object plane with a portion of an image of the master object;    an optical transfer assembly for projecting an image of the master object across the web toward the format plane;    a first drive for reciprocating the optical transfer assembly along a first direction substantially equal to the width of the web such that a first direction of raster scan is provided at the format plane;    a second drive system engaging the vacuum platen for moving the web laterally relative to the first direction to provide a two dimensional raster action at the format plane, and    a third drive means for the recording web for repetitively delineating images of the complete master object on successive segments of the web.    
   
   
       13 ) A system for providing precision images of the object on a photomask comprising: 
 a web transport system for moving an image web substantially without twisting in a path between a supply region and a take-up region;    a web handling device along the web transport system comprising a vacuum platen engaged against a region of the web and controllably movable along the direction of movement of the web;    an imaging assembly disposed adjacent the web and including a light source, an optical magnification system, and focusing optics disposed in a multi-reflective path extending across the web path, the imaging assembly being disposed to project an image of a portion of the photomask at an objective position on the web;    a control system for scanning the imaging assembly across a portion of the photomask in the direction across the web, and a control system for shifting the web incrementally longitudinally relative to the direction of movement of the optical imaging assembly so as to provide a two-dimensional raster image of the photomask image.    
   
   
       14 ) An optical projection system for recording images on a photomask serially on a recording web, wherein the recording web is advanced substantially without twisting between supply and takeup sides, comprising: 
 a web transport system for advancing the web between supply and takeup locations;    an imaging assembly disposed adjacent the web path, the assembly including a radiation source for illuminating a portion of the photomask, and optics defining a multiply refolded light path, and including magnification and focusing controls varying the path length of the fields, the light path leading to a format position on the web;    a first raster scanning drive moving the imaging assembly along a first axis across the web to provide a first raster scan direction;    a second raster scanning drive moving the web laterally to the first raster scan direction in timed relation to the first raster scan movement, and    a control system for advancing the web an incremental distance when a complete raster has been provided.