Polarized laser scattering detection of low-density and micron-scale subsurface cracks in silicon wafer

Abstract

Subsurface cracks (SSCs) of silicon wafers is inevitably generated during grinding due to the hard and brittle characteristics of the material. This paper studied a polarized laser scattering (PLS) detection method for low-density and micro-scale SSCs in silicon wafer. Samples with specific depths and densities of SSCs were prepared by using micro-indentation method. A PLS system was established to detect SSCs on the prepared samples. A numerical model of laser depolarization at SSCs was developed by using finite difference time-domain (FDTD) method. The depolarization mechanism at different inclination angles of SSCs is revealed. The correlation between the depth and density of SSCs and PLS detection signal is investigated experimentally. The results show that the PLS system could detect the SSCs in a low-density level and micron-scale depth. The developed PLS method could provide guidance to determination of the material removal amount in the subsequent ultra-grinding or polishing processes.