Improvement in chemical mechanical polishing of 4H-SiC wafer by activating persulfate through the synergistic effect of UV and TiO2

Abstract

Chemical mechanical polishing (CMP) has revolutionized the processing of semiconductor material such as silicon carbide (SiC). However, the strong chemical bond between silicon atoms and carbon atoms gives SiC materials a very high mechanical hardness and chemical stability. Therefore, SiC wafers may suffer from a low material removal rate (MRR) and serious subsurface damage when traditional CMP methods are used. In this study, to improve the CMP properties of Si-face of the 4H-SiC wafers, the synergistic effect of UV and TiO 2 on the activation of persulfate (PS) was investigated for the first time. The response surface method was employed to study the effect of pH, PS concentration, and TiO 2 dosage on CMP in-depth, and to ultimately optimize the polishing process. The analysis demonstrated that an MRR of 608 nm/h can be obtained with the average surface roughness ( Sq ) of 0.521 nm when the pH is 6, in which the TiO 2 dosage is 0.015 wt% and the PS concentration is 3 wt%. Polarization curves, AC impedance spectra and X-ray photoelectron spectroscopy tests were performed to further analyze the chemical action of the slurry, which showed that the introduction of UV-TiO 2 strongly enhances the chemical action of slurry and results in the formation of a passivated layer on the SiC surface. Finally, based on the radical quenching experiments and the results mentioned above, a model that relates to the removal of 4H-SiC by UV-TiO 2 synergistic activation of PS is proposed.