Patent ID: 9587930
Date: 2017-03-07
CPC Classifications: G01B,G01N

Claim:
1. A method for determining the thickness of a layer in a sample stack of at least two layers with an assembly comprising a light source for illuminating a stack of layers with light and a detector for detecting light reflected by said sample stack of layers in a defined first wavelength range, the method comprising the steps of (a) obtaining a calibration curve by the calibrating steps of (b) illuminating said sample stack of layers with light from said light source; (c) detecting the intensity of said light reflected by said sample stack of layers with said detector in said defined first wavelength range; and (d) determining the thickness of said layer in said sample stack of layers from the intensity detected by said detector by means of said calibration curve, and wherein (e) further calibration curves are obtained of reference stacks, where the thickness of another, different layer is known also, thereby providing a first series of calibration curves in said defined first wavelength range; (f) a second plurality of calibration curves is obtained in the same way as the first series of calibration curves for a further wavelength range; (g) the thickness of said layer of said sample stack is determined from the intensity detected by said detector by means of said first and second series of calibration curves.