Laser interferometry for measuring the thickness of two-layers films.

We present the results of investigations of the technique based on the principles of laser interferometry for measuring the thickness of two-layers films. The actuality of this kind of measurements is a result of necessity to control the geometric parameters of such films in scientific research and industry. The method of measurement is based on the analyses of the dependence of reflection coefficient as a function of the incidence angle of the laser beam due to the interference. To measure such dependencies we had designed experimental setups, described in our articles. This apparatus gives an ability to make the measurements of dependence of reflection coefficient as a function of the incidence angle in the range of angles from 30 degrees to 60 degrees. The temporal duration of a single measurement is less than 0.2 ms, the diameter of probing spot is 30 mu m and illuminance is less than 1 mW/mm(2). Fast measurement of angle dependence allows to get many data points that give an ability to determinate the parameters of two-layers films with high fidelity and precision. The possibility to determinate film's parameters follows from the analysis of the character of theoretical dependencies of the reflection coefficient R as a function of thicknesses of two layers with the different incidence angle of the laser beam theta. It can be seen that the reflection coefficients considerable depend on the layers thicknesses and the incidence angle. It gives an ability to design a technique to ascertain the simple correspondence among the dependence R=f(theta) and the parameters of the film layers. An efficiency of this method was experimentally tested. We performed a series of measurements using the semiconductor structures Si3N4/SiO2/Si having different thicknesses of the films Si3N4 and SiO2, produced by the concern "Integral" (Minsk). The analysis of experimental and theoretical results shows that the described techniques can be applied for measuring the parameters of the multi-layers structures.