Optimized photomasks for photolithography
View Patent ↗Photomask patterns are represented using contours defined by level-set functions. Given target pattern, contours are optimized such that defined photomask, when used in photolithographic process, prints wafer pattern faithful to target pattern. Optimization utilizes “merit function” for encoding aspects of photolithographic process, preferences relating to resulting pattern (e.g. restriction to rectilinear patterns), robustness against process variations, as well as restrictions imposed relating to practical and economic manufacturability of photomasks.
1. A network-accessible computing apparatus, comprising:
a processor to execute instructions which include:
receiving a target pattern;
receiving a first file describing a first mask to produce a wafer pattern, which corresponds to the target pattern, in a photolithography process; and
generating a second file describing a second mask to produce another wafer pattern, which corresponds to the target pattern, in the photolithography process, wherein the second mask is based on the first mask and a difference of the wafer pattern and the target pattern;
wherein the generating involves using a level-set function to represent the first mask, and the other wafer pattern provides a design element in an integrated circuit.
2. A computer-program product for use in conjunction with a computer system, the computer-program product comprising a computer-readable storage device and a computer-program mechanism embedded therein, the computer-program mechanism comprising:
instructions for receiving a target pattern;
instructions for receiving a first file describing a first mask to produce a wafer pattern, which corresponds to the target pattern, in a photolithography process; and
instructions for generating a second file describing a second mask to produce another wafer pattern, which corresponds to the target pattern, in the photolithography process, wherein the second mask is based on the first mask and a difference of the wafer pattern and the target pattern;
wherein the generating involves using a level-set function to represent the first mask, and the other wafer pattern provides a design element in an integrated circuit.
3. The computer-program product of claim 2 , wherein the level-set function includes an initial level-set function corresponding to the first file describing the first mask.
4. The computer-program product of claim 2 , wherein the generating involves:
selecting an initial level-set function representing the first mask; and
evolving the initial level-set function in a series of iterations to generate a modified level-set function representing the second mask wherein:
each iteration has an input level-set function and an output level-set function modified from the input level-set function;
the initial level-set function is used as the input level-set function for the initial iteration;
the input level-set function for each iteration after the initial iteration is the output level-set function of the previous iteration; and
the output level-set function for each iteration is determined based, at least in part, upon the input-level set function and a merit function, wherein the merit function corresponds to a difference between an estimated wafer pattern associated with the input level-set function and the target pattern.
5. The computer-program product of claim 4 , wherein the initial level-set function is a distance function.
6. The computer-program product of claim 4 , wherein the output values from the initial level-set function represent the distance to a boundary of a pattern on the first mask.
7. The computer-program product of claim 4 , wherein iteratively evolving the initial level-set function further comprises adding a change function to the initial level-set function over the same domain as the initial level-set function.
8. The computer-program product of claim 7 , wherein the generating further comprises creating a rectilinear projection of the sum of the change function and the initial level-set function.
9. The computer-program product of claim 4 , wherein iteratively evolving the initial level-set function further comprises modifying the initial level-set function based at least in part upon the gradient of the merit function.
10. The computer-program product of claim 4 , wherein iteratively evolving the initial level-set function further comprises modifying the initial level-set function based at least in part upon a derivative of the merit function.
11. The computer-program product of claim 4 , wherein iteratively evolving the initial level-set function further comprises modifying the initial level-set function based at least in part upon the Frechet derivative of the merit function.