Subsurface Damage Detection on Ground Silicon Wafers Using Polarized Laser Scattering

A silicon wafer is important for the electronic and computer industries. However, subsurface damage (SSD), which is detrimental to the performance and lifetime of a silicon chip, is easily induced in a silicon wafer during a grinding process since silicon is typically a hard and brittle material. Therefore, it is necessary to detect and remove SSD in the subsequent processes. In this study, a polarized laser scattering (PLS) system is installed to detect the SSD in a ground wafer. It is found that not only the subsurface crack but also the residual stress leads to depolarization of an incident light. The effects of residual stress on depolarization are studied. The residual stress results in the photoelasticity, which causes the depolarization of the incident light in the PLS system. The depolarization caused by the residual stress is determined by the directions and the difference of the principal stresses. When the polarization direction of the incident light is aligned with one of the principal stresses, the effects of the residual stress can be minimized; therefore, the subsurface crack can be quantitatively estimated by PLS.