US Patent 8200468 Methods and system for lithography process window simulation

A method of efficient simulating imaging performance of a lithographic process utilized to image a target design having a plurality of features. The method includes the steps of determining a function for generating a simulated image, where the function accounts for process variations associated with the lithographic process; and generating the simulated image utilizing the function, where the simulated image represents the imaging result of the target design for the lithographic process. In one given embodiment, the function for simulating the aerial images with focus and dose (exposure) variation is defined as:I(x,f,1+ε)=I0(x)+└ε·I0(x)+(1+ε)·a(x)·(f−f0)+(1+ε)·b(x)·(f−f0)2┘where IO represents image intensity at nominal focus and exposure, fO represents nominal focus, f and ε represent an actual focus-exposure level at which the simulated image is calculated, and parameters “a” and “b” represent first order and second order derivative images with respect to focus change.