The role of interactions between abrasive particles and the substrate surface in chemical-mechanical planarization of Si-face 6H-SiC

Abstract

The interactions between abrasive particles and the wafer surface play a significant role in the chemical-mechanical planarization (CMP) process. The influence of interactions between silica or ceria nanoparticles and the substrate surface on the CMP of Si-face (0001) 6H-SiC in different slurries with varied pH values was investigated using zeta potential measurements, SEM observations, friction tests, polishing experiments and XPS analysis. Meanwhile, the interaction forces between the substrate surfaces and the abrasive nanoparticles were also estimated using the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Silica particles are prone to adhere to the Si-face 6H-SiC surface below pH 5 and are repelled above pH 5, while ceria particles tend to adhere to the similarly charged and oppositely charged 6H-SiC surfaces. This can be attributed to the fact that the ceria particle possesses a chemical tooth and Si–O–Ce bonds are formed between ceria particles and the 6H-SiC surface. The friction coefficient and material removal rate during the CMP of 6H-SiC could be reduced significantly by the adhesion of silica particles on the 6H-SiC surface resulting from the electrostatic interaction at pH 2 and 4, while this phenomenon was not observed when ceria particles were adsorbed. The XPS analysis indicated that more oxidized species (e.g. Si–C–O, Si–O_x–C_y, Si–O₂, Si₄–C_4−x–O₂, Si₄–C₄–O₄ and C–O) were formed during immersion in aq. KMnO₄ solution. Finally, an ideal electrostatic interaction between the abrasive particles and the 6H-SiC substrate surface during the CMP process was proposed.