Methods and apparatus to control grayscale photolithography

Abstract

A die includes a resist layer located over a semiconductor substrate, and a pattern developed in the resist layer. The pattern includes a plurality of locations of developed photoresist, each location of developed photoresist separated from a neighboring location of developed photoresist by a portion of undeveloped photoresist, and the developed photoresist at each location having a corresponding different thickness.

What is claimed is: 
     
         1 . A die comprising:
 a resist layer over a semiconductor substrate; and   a pattern developed in the resist layer, the pattern including a plurality of locations of developed photoresist, each location of developed photoresist separated from a neighboring location of developed photoresist by a portion of undeveloped photoresist, and the developed photoresist at each location having a corresponding different thickness.   
     
     
         2 . The die as claimed in  claim 1 , wherein the locations are arranged in the pattern such that each of the locations is immediately adjacent another of the locations. 
     
     
         3 . The die as claimed in  claim 2 , wherein the locations of developed photoresist are arranged in a linear array. 
     
     
         4 . The die as claimed in  claim 3 , wherein the photoresist thickness of the developed pads increases from one location to a neighboring location in the linear array. 
     
     
         5 . The die as claimed in  claim 2 , wherein the locations of developed photoresist are positioned in a square, rectangular, or triangular arrangement. 
     
     
         6 . The die as claimed in  claim 2 , wherein the locations of developed photoresist are positioned apart from each other on the die. 
     
     
         7 . The die as claimed in  claim 1 , wherein each location is configured as a developed pad suitable for an optical metrology measurement. 
     
     
         8 . The die as claimed in  claim 7 , wherein the developed pads have a length and a width of about 30 μm. 
     
     
         9 . The die as claimed in  claim 7 , wherein the developed pads include gray scale pads. 
     
     
         10 . The die as claimed in  claim 7 , wherein each developed pad includes a photoresist transition region, the transition region including an annular portion of photo resist with a thickness less than a full thickness of the photoresist and greater than a thickness of the photoresist at a center of the developed pad. 
     
     
         11 . The die as claimed in  claim 7 , wherein the developed pad has a circular shape. 
     
     
         12 . The die as claimed in  claim 1 , wherein the photoresist at each location has a thickness in a range from about 0.01 μm to about 0.50 μm. 
     
     
         13 . The die as claimed in  claim 1 , wherein the die is one instance of a plurality of die on a semiconductor wafer, each die of the plurality of die being coincident with a corresponding one of a plurality of the pattern. 
     
     
         14 . The die as claimed in  claim 1 , wherein the die is one of a plurality of die on a semiconductor wafer, each die of the plurality of die including an instance of the pattern. 
     
     
         15 . The die as claimed in  claim 1 , wherein the pattern includes four locations, a first location being undeveloped, a second location being completely developed, a third location having a depth representative of a surface develop rate of the photoresist, and a fourth location having a depth representative of a bulk develop rate of the photoresist. 
     
     
         16 . A die comprising:
 semiconductor devices arranged as an array;   a resist layer; and   a developed pattern defined on the resist layer by an exposure system and an optical mask, the developed pattern including portions of different depths to be optically measured by an optical thickness measurement device to control a grayscale lithography process of the die.   
     
     
         17 . The die as defined in  claim 16 , wherein the portions include pads. 
     
     
         18 . The die as defined in  claim 17 , wherein the pads include gray scale pads of sufficient size to be optically measured. 
     
     
         19 . The die as defined in  claim 18 , wherein the grayscale pads are generated by locally modulated transmittances that are defined by subresolution features of the optical mask. 
     
     
         20 . The die as defined in  claim 18 , wherein the grayscale pads are each located in multiple positions across a reticle or die.