System and method for calibrating a lithography model
The present invention provides a method for calibrating a computational model of a lithography process by calculating a demerit function using an intensity measurement at a location of a wafer; and calibrating the lithography model or a mask making model by determining values of parameters of the computational model using the calculated demerit function. The method may also use a second demerit function that is defined by the sum of squares of differences between a simulated and measured critical dimensions of a feature on the wafer.
1. A method for calibrating a model of a photolithography process, comprising:
providing a computational model of a photolithography process, the computational model having an adjustable parameter;
printing a first pattern with the photolithography process as a printed pattern;
measuring an aspect of the printed pattern;
using the computational model to calculate an image intensity at a location determined according to the measured aspect;
minimizing a first cost function that comprises a first difference between the calculated image intensity and an intensity threshold;
calculating a second cost function comprising a second difference between a measured critical dimension of the printed pattern and a critical dimension simulated by the computational model;
minimizing the first cost function with respect to a model parameter;
determining if the computational model predicts that a portion of a first pattern will not print;
removing from a definition of the second cost function, the critical dimension of the portion of the first pattern that will not print; and
minimizing the second cost function with respect to the model parameter.
2. The method of claim 1 , wherein the photolithography process comprises projecting an optical image onto a semiconductor wafer.
3. The method of claim 1 , wherein the photolithography process comprises projecting an electron-beam image exposing a resist on a semiconductor wafer.
4. The method of claim 1 , wherein the photolithography process comprises scanning a switched electron beam exposing a resist on a semiconductor wafer.
5. The method of claim 1 , wherein the photolithography process comprises an electron beam exposing a resist on a photomask.
6. A computer program product having instructions embedded in a non-transitory computer useable medium, the instructions configured to cause a processor to perform the operations of:
providing a computational model of a photolithography process, the computational model having an adjustable parameter;
printing a first pattern with the photolithography process as a printed pattern;
measuring an aspect of the printed pattern;
using the computational model to calculate an image intensity at a location determined according to the measured aspect;
minimizing a first cost function that comprises a first difference between the calculated image intensity and an intensity threshold;
calculating a second cost function comprising a second difference between a measured critical dimension of the printed pattern and a critical dimension simulated by the computational model;
minimizing the first cost function with respect to a model parameter;
determining if the computational model predicts that a portion of a first pattern will not print;
removing from a definition of the second cost function, the critical dimension of the portion of the first pattern that will not print; and
minimizing the second cost function with respect to the model parameter.
7. The computer program product of claim 6 , wherein the photolithography process comprises projecting an optical image onto a semiconductor wafer.
8. The computer program product of claim 6 , wherein the photolithography process comprises projecting an electron-beam image exposing a resist on a semiconductor wafer.
9. The computer program product of claim 6 , wherein the photolithography process comprises scanning a switched electron beam exposing a resist on a semiconductor wafer.
10. The computer program product of claim 6 , wherein the photolithography process comprises an electron beam exposing a resist on a photomask.
11. A computer-aided design tool configured to calibrate a model of photolithography process, comprising:
a processor;
a memory connected to the processor; and
a non-transitory computer readable medium having instructions embedded therein, the instructions configured to cause the processor to perform the operations of:
providing a computational model of a photolithography process, the computational model having an adjustable parameter;
printing a first pattern with the photolithography process as a printed pattern;
measuring an aspect of the printed pattern;
using the computational model to calculate an image intensity at a location determined according to the measured aspect;
minimizing a first cost function that comprises a first difference between the calculated image intensity and an intensity threshold;
calculating a second cost function comprising a second difference between a measured critical dimension of the printed pattern and a critical dimension simulated by the computational model;
minimizing the first cost function with respect to a model parameter;
determining if the computational model predicts that a portion of a first pattern will not print;
removing from a definition of the second cost function, the critical dimension of the portion of the first pattern that will not print; and
minimizing the second cost function with respect to the model parameter.
12. The computer-aided design tool of claim 11 , wherein the photolithography process comprises projecting an optical image onto a semiconductor wafer.
13. The computer-aided design tool of claim 11 wherein the photolithography process comprises projecting an electron-beam image exposing a resist on a semiconductor wafer.
14. The computer-aided design tool of claim 11 , wherein the photolithography process comprises scanning a switched electron beam exposing a resist on a semiconductor wafer.
15. The computer-aided design tool of claim 11 , wherein the photolithography process comprises an electron beam exposing a resist on a photomask.