Residual stress estimation in SiC wafer using IR polariscope

Abstract

Relation between optical retardation and transmitted light intensityThe light intensity, I, that comes through the analyzer can be expressed as a Fourier's expansion as follows:Silicon carbide (SiC) single crystals have got into the spotlight as a material for power devices [1]. For quality control of SiC wafers, it is important that the estimation of the optical retardation in the wafers corresponds to the residual stress. For this estimation, photoelastic stress-strain measurement is suitable. Because, photoelasticity has the distinct advantages of being non-destructive, convenient, real time, precise, and quantitative compared with other stress-strain measurement techniques. Thus, an optical birefringence measurement system is made with a photoelastic modulator and polarized laser. A helium-neon (He-Ne) infrared laser is utilized as the light source for measuring the birefringence in SiC wafers. In this paper we will explain the principles behind the system and the process of estimation the stress in SiC wafers. The magnitudes of the retardations correspond to principal strain differences as well as the orientations of them are obtained simultaneously and quantitatively by using the system. We compared the distribution of the magnitudes and orientations in two different finishing wafers of SiC.