Patent ID: 8181128

Claim:
A method for determining a process model for a photolithography process, wherein the photolithography process uses a first layout to subject a wafer to a first exposure-and-development process, and later uses a second layout to subject the wafer to a second exposure-and-development process, wherein when the wafer is subjected to the second exposure-and-development process, the wafer's surface includes topography variations which are created at least partly due to the first exposure-and-development process, the method comprising: receiving process data, wherein the process data includes critical dimension measurements of patterns after the wafer is subjected to the second exposure-and-development process; determining an uncalibrated process model, wherein the uncalibrated process model includes a topography term which models the topography variations' influence on the second exposure-and-development process, wherein the topography term includes a first term and a second term, wherein the first term is convolved with a sum of a first layout function and a second layout function, wherein the second term is convolved with the second layout function, and wherein the first layout function represents the first layout and the second layout function represents the second layout; and determining, by computer, the process model by fitting the uncalibrated process model to the process data.