Area based optical proximity correction in raster scan printing

Abstract

Methods and apparatus for correcting defects, such as rounded corners and line end shortening, in patterns formed via lithography are provided. Such defects are compensated for “post-rasterization” by manipulating the grayscale values of pixel maps.

1 . A method for adjusting corners of a pattern to be written into a sensitive recording surface, comprising:
 generating sub-pixel data for use in creating grayscale values for pixels by sampling sub-pixel locations of pixels that are covered by the pattern;   detecting corner pixels in the array, in which corners of the pattern lie, by examining the sub-pixel data; and   adjusting grayscale values of at least one of: one or more detected corner pixels and one or more pixels neighboring one or more detected corner pixels.   
     
     
         2 . The method of  claim 1 , wherein detecting corner pixels comprises examining the sub-pixel data to detect convex and concave corners of differing orientations. 
     
     
         3 . The method of  claim 2 , wherein examining the sub-pixel data to detect convex and concave corners of differing orientations comprises:
 constructing an array of pixels and corresponding sub-pixel data; and   comparing a set of corner detection overlays to the sub-pixel data of the array.   
     
     
         4 . The method of  claim 3 , wherein:
 each corner detection overlay is smaller in at least one dimension than the array of pixels; and   comparing the set of corner detection overlays to the sub-pixel data of the array comprises comparing the set of corner detection overlays to sub-arrays of sub-pixel data to detect corners at different pixel locations within the array.   
     
     
         5 . The method of  claim 4 , wherein at least two of the sub-arrays are offset from each other in at least one direction by less than one pixel. 
     
     
         6 . The method of  claim 5 , wherein at least two of the sub-arrays are offset from each other in at least one direction by a quarter pixel. 
     
     
         7 . The method of  claim 1 , wherein:
 detecting corner pixels in the array, in which corners of the pattern lie, by examining the sub-pixel data comprises detecting the same corner in adjacent pixels; and   selecting only one of the adjacent pixels as a corner pixel.   
     
     
         8 . The method of  claim 7 , wherein selecting only one of the adjacent pixels as a corner pixel comprises:
 selecting an inner-most adjacent pixel if the detected corner pixels are concave corner pixels; and   selecting an outer-most adjacent pixel if the detected corner pixels are convex corner pixels.   
     
     
         9 . The method of  claim 1 , further comprising:
 identifying a position within a detected corner pixel in which a corner lies; and   wherein adjusting the grayscale values comprises adjusting at least one grayscale value based on a corner correction factor retrieved, at least in part, using the identified position.   
     
     
         10 . The method of  claim 8 , wherein the corner correction factor is retrieved, at least in part, using a type and orientation of the detected corner. 
     
     
         11 . The method of  claim 1 , wherein adjusting the grayscale values comprises:
 increasing grayscale values of at least one of a convex corner pixel containing a convex corner and one or more pixels neighboring the convex corner pixel; and   decreasing grayscale values of at least one of a concave corner pixel containing a concave corner and one or more pixels neighboring the concave corner pixel.   
     
     
         12 . A method for adjusting corners of a pattern to be written into a sensitive recording surface, comprising:
 generating sub-pixel data by sampling sub-pixel locations of pixels that are covered by the pattern;   constructing an array of the pixels with corresponding sub-pixel data;   detecting corner pixels in the array by comparing a set of sub-pixel data in the array with one or more corner detection overlays; and   adjusting grayscale values of at least one of: one or more detected corner pixels and one or more pixels neighboring one or more detected corner pixels.   
     
     
         13 . The method of  claim 12 , wherein each corner detection overlay defines a first region in which all sub-pixel data must be of a first value, a second region in which all sub-pixel data must be of a second value, and a third region in which at least some of the sub-pixel data must not be of the second value 
     
     
         14 . The method of  claim 13 , wherein the one or more corner detection overlays comprise one or more convex corner detection overlays defining the first region in which all sub-pixel data must be a one and the second region in which all sub-pixel data must be a zero. 
     
     
         15 . The method of  claim 13 , wherein the one or more corner detection overlays comprise one or more concave corner detection overlays defining the first region in which all sub-pixel data must be a zero and the second region in which all sub-pixel data must be a zero. 
     
     
         16 . The method of  claim 13 , wherein:
 the first and third regions of each corner detection overlay are adjacent; and   the combined length of the first and third regions is greater than or equal to a length of one and one quarter pixel.   
     
     
         17 . The method of  claim 12 , wherein:
 constructing the array of the pixels with corresponding sub-pixel data comprises constructing an array of pixels greater in dimension than the corner detection overlays; and   comparing a set of sub-pixel data in the array with one or more corner detection overlays comprises comparing multiple sets of sub-pixel data with the one or more corner detection overlays in parallel.   
     
     
         18 . The method of  claim 12 , further comprising, for each detected corner pixel, identifying a position within the detected corner pixel containing a corresponding corner. 
     
     
         19 . The method of  claim 18 , wherein adjusting grayscale values of at least one of: one or more detected corner pixels and one or more pixels neighboring the corner pixels comprises:
 retrieving one or more correction factors based on an identified position within a detected corner pixel containing a corresponding corner; and   adjusting one or more grayscale values based on the retrieved correction factors.   
     
     
         20 . The method of  claim 19 , wherein retrieving one or more correction factors based on an identified position within a detected corner pixel containing a corresponding corner comprises retrieving the one or more correction factors based on the identified position and a corner type associated with the detected corner pixel. 
     
     
         21 . The method of  claim 20 , wherein the one or more correction factors comprise:
 a first correction factor for use in adjusting the grayscale value of the detected corner pixel; and   at least a second correction factor for use in adjusting the grayscale values of one or more pixels neighboring the detected corner pixel   
     
     
         22 . The method of  claim 18 , wherein identifying a position within the detected corner pixel comprises generating an N-bit corner tag, wherein N is an integer. 
     
     
         23 . The method of  claim 22 , wherein N=4. 
     
     
         24 . A system for writing a pattern in a resistive surface, comprising:
 a rasterizer for generating sub-pixel data by sampling sub-pixel locations of pixels that are covered by the pattern;   a corner detection unit for detecting corner pixels in an array of pixels by examining sub-pixel data corresponding to the pixels in the array; and   a corner correction unit for adjusting grayscale values of at least one of: one or more detected corner pixels and one or more pixels neighboring the corner pixels.   
     
     
         25 . The system of  claim 24 , wherein the corner detection unit is configured to generate corner tags identifying positions within corner pixels that contain corners. 
     
     
         26 . The system of  claim 25 , wherein the corner correction unit is configured to adjust grayscale values of at least one of: a detected corner pixel and one or more pixels neighboring the detected corner pixel using one or more correction factors retrieved based on a corresponding corner tag. 
     
     
         27 . The system of  claim 26 , wherein the one or more correction factors are retrieved based on the corresponding corner tag and a corner type associated with the detected corner pixel. 
     
     
         28 . The system of  claim 26 , wherein the one or more correction factors are retrieved based on the corresponding corner tag, the corner type associated with the detected corner pixel, and an orientation of the corner contained in the detected corner pixel. 
     
     
         29 . The system of  claim 26 , wherein the one or more correction factors comprise at least a first correction factor for use in adjusting the grayscale value of the detected corner pixel and at least a second correction factor for use in adjusting the grayscale value of one or more pixels neighboring the detected corner pixel. 
     
     
         30 . The system of  claim 29 , wherein the first and second correction factors are independently adjustable by a user.