Patent ID: 6397680
Filing Date: 2002-06-04
Classification: G01B,G01N

Abstract:
A method for determining layer thickness or other parameters of a multilayer structure, comprising the steps of:producing an ultrasonic pulse in the multilayer structure for interaction therewith over a range of frequencies to obtain a time-dependent interaction signal characteristic of the multilayer structure; detecting the interaction signal from said multilayer structure; transforming said time-dependent interaction signal from the time domain to the frequency domain to obtain the frequency response of said multilayer structure; determining locations of peak or dip values over the range of frequencies from said frequency response of said multilayer structure to obtain a set of measured resonance frequencies; using a mathematical model describing the behaviour of said multilayer structure and containing at least one variable parameter to predict resonance frequencies for said multilayer structure, said mathematical model being in the form of a characteristic equation whose roots provide said predicted resonance frequencies; and adjusting said at least one variable parameter in said mathematical model to obtain a best fit of said predicted resonance frequencies with said measured resonance frequencies to thereby obtain said at least one variable parameter.