Effects of Hydrolysis Reaction and Abrasive Drag Force Accelerator on Enhancing Si-Wafer Polishing Rate and Improving Si-Wafer Surface Roughness

Abstract

To satisfy the superior surface quality requirements in the fabrication of HBM (High-Bandwidth Memory) and 3D NAND Flash Memory, high-efficiency Si chemical mechanical planarization (CMP) is essential. In this study, a colloidal silica abrasive-based Si-wafer CMP slurry was developed to simultaneously achieve a high polishing rate (>= 10 nm/min) and low surface roughness (<= 0.2 nm) without inducing CMP-induced scratches. The proposed Si-wafer CMP slurry incorporates two functional components: triammonium phosphate (TAP) as a hydrolysis reaction accelerator and hydroxyethyl cellulose (HEC) as an abrasive drag force accelerator. The polishing rate enhancement mechanism of TAP was analyzed by monitoring the OH- mol concentration, surface adsorption behavior, and XPS spectra. The results showed that increasing the TAP concentration raised the OH- mol concentration and converted Si-Si and Si-O-Si bonds to Si-OH via a hydrolysis reaction, thereby increasing the polishing rate. However, excessive hydrolysis also led to increased surface roughness. On the other hand, HEC influenced slurry viscosity, abrasive dispersibility, and drag force. At low HEC concentrations, increased abrasive drag force improved the polishing rate. At high concentrations, however, HEC formed a hindrance layer on the Si surface via hydrogen bonding and condensation reactions, reducing the effective contact area of abrasives and thus decreasing the polishing rate. By optimizing the concentrations of TAP (0.0037 wt%) and HEC (<= 0.0024 wt%), the proposed slurry formulation achieved high-performance Si-wafer CMP, satisfying both surface roughness and polishing rate targets required for advanced memory packaging applications.