Depolarization of surface scattering in polarized laser scattering detection for machined silicon wafers

Monocrystalline silicon is currently one of the most used materials in the semiconductor industry. However, being hard and brittle, a silicon wafer commonly suffers from machining-induced subsurface damage (SSD). Detecting SSD is important for optimizing the machining process in order to improve the surface integrity of a machined wafer. Among the various detection methods, the polarized laser scattering (PLS) method has a huge potential in highly efficient detection. However, the surface scattering mechanism is not fully understood so far, which impedes the optimization of the PLS detection processes. This study resolves surface scattering based on the electromagnetic scattering theory. It is found that the depolarization caused by surface scattering increases with the surface roughness and the incident angle. With the consideration of the subsurface scattering characteristics and the distribution of the SSD, this study provides a solution for the PLS detection that comprises of the use of a horizontally polarized laser with vertical incidence to minimize the influence of surface scattering. This study provides a theoretical analysis of both surface and subsurface scattering to facilitate an optimized PLS detection.