Interaction mechanism of Al2O3 abrasive in tantalum chemical mechanical polishing

Abstract

Al₂O₃ abrasive is expected to enhance chemical mechanical polishing (CMP) efficiency compared to the SiO₂ abrasive. However, Al₂O₃ powder has dispersion issues and the material removal mechanism by Al₂O₃ remains unclear. This study investigated the role of Al₂O₃ abrasive in the tantalum CMP. It is revealed that (NaPO₃)₆ can effectively disperse Al₂O₃ powder in water. PO₃⁻ improves the stability while Na⁺ deteriorates it. The total Na⁺ concentration should be lower than the turning point to attain high stability. With stable Al₂O₃-containing slurries, a relatively high material removal rate of tantalum can be obtained at an alkaline pH. The characterization results indicate that the Ta element can be adsorbed on Al₂O₃ probably due to the chemical interaction between Al₂O₃ and the tantalum surface. Moreover, the Al₂O₃ microsphere tip starts to remove tantalum at 0.48 GPa, which is much lower than the yield strength of the tantalum surface film. For the mechanism, tantalum can be oxidized by H₂O₂ at alkaline pH. When Al₂O₃ presses and slides on the tantalum surface, tribochemical reactions occur, forming a chemical bond of Al–O–Ta at the interface. As Al₂O₃ moves, the bond is stretched and tantalum is detached. The findings provide mechanistic insight into Al₂O₃ abrasive in CMP.