Patent ID: 6028669
Filing Date: 2000-02-22
Classification: G01B

Abstract:
A method of in situ monitoring of a process of modifying a thickness of an optically transparent layer, comprising:directing optical radiation against said layer in a manner that a first portion of said radiation is reflected from a surface of said transparent layer that is affected by the thickness modification and a second portion of said radiation is reflected from another surface that is not affected by the thickness modification,detecting a signal resulting from an interference between said first and second reflected portions of said optical radiation, said signal having a magnitude that varies over time according to an approximation of a sinusoidal function as the thickness of the layer is modified,forming from said signal an auxiliary function that is shifted in phase with respect to the signal by one-quarter of a period of said signal,determining values of time and magnitude of the signal at occurrences of peaks and valleys of said signal and said auxiliary function,ascertaining, from the determined values of the signal at the occurrence of at least one peak or valley of each of the signal and auxiliary function, quantities related to a period of magnitude variation of the signal, a d.c. offset of the signal and amplitude of the varying signal, andcalculating, from said quantities and an index of refraction of the material of said layer, at least one number related to the transparent layer thickness.