Model-based scanner tuning systems and methods

Abstract

Systems and methods for tuning photolithographic processes are described. A model of a target scanner is maintained defining sensitivity of the target scanner with reference to a set of tunable parameters. A differential model represents deviations of the target scanner from the reference. The target scanner may be tuned based on the settings of the reference scanner and the differential model. Performance of a family of related scanners may be characterized relative to the performance of a reference scanner. Differential models may include information such as parametric offsets and other differences that may be used to simulate the difference in imaging behavior.

What is claimed is: 
     
         1 . A method for tuning a lithographic apparatus using a corresponding model, the method comprising:
 maintaining a lithographic process model characterizing the imaging behavior of the lithographic process for a given layer of a substrate using the lithographic apparatus, subject to changes in a set of tunable parameters on the lithographic apparatus;   generating simulated substrate contour in the given layer using a design layout and the lithographic process model;   identifying discrepancies in the simulated substrate contour against a reference;   quantifying the discrepancies with a cost function; and   performing iterations of the generating and identifying steps to minimize the cost function and obtain a desired degree of convergence of the simulated substrate contour with the reference, wherein at least one tunable parameter of the lithographic apparatus is adjusted prior to performing each iteration.   
     
     
         2 . The method of  claim 1 , wherein the lithographic process model is a sensitivity model. 
     
     
         3 . The method of  claim 1 , wherein the reference is a measured substrate contour from a reference lithographic process dissimilar to the lithographic process, for a set of patterns in the design layout. 
     
     
         4 . The method of  claim 3 , wherein the difference between an untuned substrate contour and the reference is obtained via a differential process model. 
     
     
         5 . The method of  claim 1 , wherein the reference is a simulated substrate contour from a reference lithographic process model dissimilar to the lithographic process model, for a set of patterns in the design layout. 
     
     
         6 . The method of  claim 1 , wherein the reference comprises design target polygons for a set of patterns in the design layout. 
     
     
         7 . The method of  claim 1 , wherein the discrepancies in the simulated substrate contour against the reference are obtained via an OPC verification tool. 
     
     
         8 . The method of  claim 7 , wherein the identifying discrepancies includes identifying hotspots. 
     
     
         9 . The method of  claim 8 , wherein the hotspots include yield-limiting defects occurring under process variations. 
     
     
         10 . The method of  claim 8 , wherein the hotspots include patterns in the design layout that are adversely affected by characteristics specific to the lithographic apparatus. 
     
     
         11 . The method of  claim 1 , wherein the cost function comprises imaging metric terms associated with every pattern in a tuning target pattern set. 
     
     
         12 . The method of  claim 1 , wherein the discrepancies in substrate contours result from one or more selected from: optics, mechanics, control and/or device-specific laser differences of the lithographic apparatus. 
     
     
         13 . The method of  claim 1 , wherein the discrepancies in substrate contours result from one or more selected from: mask, resist, track, and/or etch differences of the lithographic process. 
     
     
         14 . The method of  claim 1 , further comprising determining tuning offsets to bring critical dimensions for certain patterns in the design layout within predefined tolerances. 
     
     
         15 . The method of  claim 14 , wherein the generating, identifying and determining are repeated until a plurality of hotspots are eliminated. 
     
     
         16 . A non-transitory computer readable storage medium having instructions therein, the instructions, when executed by a computer system, configured to cause the computer system to perform the method of  claim 1 .