Patent ID: 9360768
Filing Date: 2016-06-07
CPC Classification: G01N,G03F

Claim Text:
1. A method of operating a metrology apparatus comprising: defining one or more first target profiles of one or more targets; storing initial calibration data of the metrology apparatus; compiling a library of modeled spectra that would be observed from inspection of the one or more targets using the metrology apparatus calibrated according to the initial calibration data; obtaining current calibration data of the metrology apparatus; modeling one or more second target profiles of the one or more targets at least partially based on the current calibration data and the library of spectra; determining any differences between one or more parameters of the one or more first target profiles and the one or more second target profiles; and using any of the determined differences between the one or more parameters to determine a drift in the one or more parameters, such that subsequent measurement stability of the metrology apparatus is improved when subsequently taking measurements of a physical target with the metrology apparatus.