An experimental investigation of silicon wafer thinning by sequentially using constant-pressure diamond grinding and fixed-abrasive chemical mechanical polishing

Abstract

Three-dimensional integration using through-silicon via (TSV) can significantly improve the performance and power consumption of microelectronic devices. In order to connect more chips vertically using TSV, the silicon wafer should be as thin as possible. As the most widely used method for wafer thinning, constant-feed grinding inevitably introduces serious mechanical damage and stress within a wafer, while common stress-relief processes such as chemical mechanical polishing (CMP) and etching cannot effectively balance the material removal rate and surface quality. To address these issues, in the present research, a novel thinning method was proposed that sequentially used constant-pressure diamond grinding and fixed-abrasive CMP to thin a wafer. It was found that by selecting the proper abrasive size and pressure, the constant-pressure diamond grinding can achieve both high-efficiency thinning and low-damage ductile removal of silicon. However, this method always generated processing stresses of 500–2000 MPa on the surface and produced a stress propagation layer with a depth of several tens of microns. The fixed-abrasive CMP utilized the tribochemical reaction between the CeO2 abrasive and silicon under friction to achieve effective material removal. The results demonstrated that this approach could provide an ultra-smooth surface with a roughness less than Ra 2 nm while the processing stress was no more than 150 MPa, making it ideal for the removal of grinding damage layers. By conducting sequential thinning with constant-pressure diamond grinding and fixed-abrasive CMP, this method proved to be an effective technique for the preparation of ultra-thin silicon wafers, exhibiting superior application prospects.