Patent ID: 6236459
Filing Date: 2001-05-22
Classification: A61B,G01B

Abstract:
An interferometric method of determining a thin-film thickness, comprising:selecting a plurality of calibration thin films, each having a predetermined film thickness;illuminating each of said plurality of calibration thin films with light having substantially predetermined intensity and spectral characteristics and a coherence length approximately equal to or longer than each corresponding predetermined film thickness;filtering light reflected from each of said plurality of calibration thin films with a plurality of wavelength filters;detecting light in a plurality of image channels, wherein each image channel of said plurality of image channels contains light output from a respective one of said wavelength filters;determining a plurality of calibration weight vectors for each of a plurality of look-up thicknesses within a range of look-up thicknesses that includes at least some of said predetermined film thicknesses of said plurality of calibration thin films, said calibration weight vectors collectively containing both frequency and intensity information of said light reflected from said plurality of calibration thin films;generating a calibrated look-up table comprising said calibration weight vectors;illuminating a subject thin film with light having said substantially predetermined intensity and spectral characteristics and said coherence length;filtering light reflected from said subject thin film with each of said plurality of wavelength filters;detecting light in a plurality of image channels, wherein each image channel of said plurality of image channels contains light output from a respective one of said wavelength filters after said filtering light reflected from said subject thin film;determining a subject weight vector from light detected from said plurality of image channels of said subject thin film;selecting a calibration weight vector from said look-up table that is substantially the most equivalent calibration weight vector to said subject weight vector; anddetermining said subject thin-film thickness from said selected calibration weight vector.