Patent ID: 7460237

Claim:
A method of determining a structure parameter of a target pattern in a lithographic process used to manufacture a device layer on a substrate, the method comprising: calculating a series of calibration spectra from a reference pattern, each spectra being calculated using a different known value of a structure parameter of the reference pattern; performing spectral analysis on each calculated calibration spectra, for a selected number of points of the spectra, to obtain a common set of spectral components and a plurality of first sets of weighting factors, each first set of weighting factors representing one calculated spectrum; measuring a target spectrum produced by directing a beam of radiation onto the target pattern; performing spectral analysis on the measured target spectrum using the common set of spectral components obtained from the spectral analysis of the calculated calibration spectra to obtain a second set of weighting factors representing the measured target spectrum; comparing a representation of the first set of weighting factors and a representation of the second set of weighting factors; and using the comparison to derive a value for the structure parameter of the target pattern.