Study on CMP process of glass wafers with SiO2 based slurry for trench-glass-via interposer

This paper aims to study the chemical mechanical polishing (CMP) of glass wafer with effect of colloidal silica (SiO ₂ ) abrasive in different CMP process parameters. Conventional glass polishing usually adopts ceria (CeO ₂ ) abrasive due to its high material removal rate (MRR). However, with the development of 3D stacking integrated circuits (3DS-IC), the demand of glass wafer for trench-glass-via (TGV) instead of trench-silicon-via (TSV) has very tight specification of surface roughness and near-free-defects by CMP for next step of lithography process. Thus the ceria abrasive may not satisfy the surface quality as required in applications of glass wafer or TGV. The colloidal silica of SiO ₂ abrasive is considered because of its uniform particle size and familiar application in CMP for silicon wafer and thin film devices. In this study, viscosity and pH value of SiO ₂ slurry have been tested to characterize slurry properties. Some 40 × 40mm sliced substrates from 200mm (8") glass wafers have been used for polishing characteristics and evaluation of CMP process. Relationship between the process parameters, including down pressure, platen speed and slurry flow rate have been investigated. Performance of CMP tests including MRR, surface roughness and non-uniformity have been obtained for concluding the slurry performance for CMP of glass wafers.