Patent ID: 8250497

Claim:
A method for measuring an overlay error using a system having an angular scatterometer, a data processing module, a matching unit and a database, and using a computer system, the method comprising the steps of: providing a two-dimensional array overlay target set to be measured, wherein the step of providing the two-dimensional array comprises: simulating diffraction spectra for a plurality of two-dimensional array overlay target sets, each of said plurality of two-dimensional array overlay target sets having at least one of a different first-dimensional overlay error and a different second-dimensional overlay error using the computer system, wherein each two-dimensional array overlay target set has a first two-dimensional array overlay target and a second two-dimensional array overlay target, a fixed offset existing between the first-dimensional overlay errors and between the second-dimensional overlay errors of the first two-dimensional array overlay target and the second two-dimensional array overlay target; calculating a root mean square error of the simulated diffraction spectra for each two-dimensional array overlay target set using the computer system and storing the calculated root mean square error-in the database; generating a curve of root mean square error as a function of first-dimensional overlay error for each second-dimensional overlay error using the computer system; selecting a sensitive overlay target set by taking slopes of the curves into consideration using the computer system; and designing the two-dimensional array overlay target set to be measured based on structural parameters of the sensitive overlay target set; measuring diffraction spectra of the two-dimensional array overlay target set to be measured using the angular scatterometer; calculating a root mean square error of the measured diffraction spectra of the two-dimensional array overlay target set to be measured using the data processing module; performing a matching process to find a root mean square error in the database matched with the root mean square error of the measured diffraction spectra of the two-dimensional array overlay target set to be measured using the matching unit; and determining a first-dimensional overlay error and a second-dimensional overlay error of the two-dimensional array overlay target set to be measured in accordance with the matched root mean square error using the matching unit.