Composition design and optimization of electrochemical mechanical polishing slurry for single crystal SiC

Abstract

Objectives: Single crystal silicon carbide (SiC) is known for its high hardness and high chemical inertness, making it chanllenging to process effectively using traditional chemical mechanical polishing (CMP) methods. CMP often struggles to balance processing efficiency and surface quality for SiC. Electrochemical mechanical polishing (ECMP) is an effective method to achieve high material removal rates (MRR) and excellent surface quality when processing SiC. This study explores the main components and optimal ratios of SiC ECMP slurry through process testing.Methods: Using MRR and surface roughness as evaluation indicators, the types of conductive medium and abrasive particles in the ECMP slurry are first determined through single-factor experiments. Then, the influences of the conductive medium types, abrasive particle concentration, and the pH value of the polishing slurry, on both MRR and surface roughness, are analyzed to identify the optimal slurry parameters. Results: The results of the experiments indicate that when NaCl is used as the conductive medium and SiO2 as the polishing abrasive, SiC achieves both good polishing efficiency and surface quality. The increase in NaCl concentration enhances the electrochemical oxidation of SiC, leading to an increase in MRR and surface roughness. As the concentration of abrasives increases, the surface conductivity of SiC improves, boosting both material removal efficiency and surface roughness. However, after reaching a certain abrasive concentration, the oxidation state of SiC stabilizes, and both MRR and surface roughness tend to reach a constant value. When the polishing slurry is acidic, electrochemical oxidation of SiC is inhibited, leading to a reduced MRR. Conversely, when the slurry is alkaline, abrasive particles undergo chemical reactions, resulting in poor polishing surface quality. A neutral slurry effectively balances both MRR and surface quality. The optimal slurry paramaters for achieving this balance are a NaCl concentration of 0.6 mol/L, a SiO2 mass fraction of 6%, and a pH value of 7. Under these conditions, the MRR and surface roughness of SiC polishing were found to be 2.388 μm/h and 0.514 nm, respectively. Conclusions: The low oxidation rate of SiC, due to its high chemical inertness, is a key factor limiting the polishing efficiency in traditional CMP methods. ECMP overcomes this limitation by replacing chemical oxidation with electrochemical oxidation, allowing for both high polishing efficiency and superior surface quality of SiC.

Keywords

• single crystal sic
• electrochemical oxidation
• polishing slurry compositions
• surface roughness
• material removal rate