Patent ID: 8142965

Claim:
A method for use in controlling at least one parameter of a patterned structure characterizing a patterning process applied to the structure, the method comprising: (i) providing calibration data indicative of a merit function characterizing optical measurements in a patterned structure as a function of values of a certain parameter of the pattern including at least one value of the merit function below a certain threshold and at least one value of the merit function above said certain threshold; (ii) applying the optical measurements to at least one test patterned structure and determining a merit function, wherein the test patterned structure is characterized by a value of said certain parameter of the pattern intentionally increased by a predetermined value above a natural value of said certain parameter induced by a patterning process by which said pattern is produced on the test patterned structure; (iii) analyzing the determined merit function and the calibration data and determining said natural parameter value.