Patent ID: 8285030

Claim:
A computer-implemented method for determining a set of calibration parameters for use in a model of a photo-lithographic process, comprising: receiving images of a test pattern, wherein the test pattern was produced using the photo-lithographic process, wherein the images include a first image at a first focal plane in an optical system, a second image at a second focal plane in the optical system, and a third image at a third focal plane in the optical system, and wherein the first focal plane, the second focal plane and the third focal plane are different; calculating, by a computer, a first set of calibration parameters associated with the first image, a second set of calibration parameters associated with the second image, and a third set of calibration parameters associated with the third image; and determining an interpolation function based on the first set of calibration parameters, the second set of calibration parameters, and the third set of calibration parameters, wherein the interpolation function provides the set of calibration parameters corresponding to an arbitrary focal plane in a photo-lithographic system that implements the photo-lithographic process; and wherein the set of calibration parameters are used in a set of transmission cross coefficients in the model of the photo-lithographic process.