Mechanism of polishing of SiO2 films by CeO2 particles

To examine the polishing mechanism in chemical mechanical polishing of a thermally grown SiO2 film by CeO2 particles, the surface structure of the film and the polishing waste were investigated by various analytical means. Fourier-transformed-infrared-attenuated-total-reflection (FT-IR-ATR) spectra indicated that the film surface structure was strained as a result of a reaction with CeO2. A small amount of Si was found by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) in the waste supernatant and it was detected as particles by optical interference measurement. The scanning electronic microscopy (SEM) image of the particles showed a not-well-defined shape like cotton scraps, but their IR transmission spectrum resembled that of the SiO2 film. From these results we concluded that the SiO2 film surface is first reacted with CeO2 particles and a multiple number of chemical bondings of Si–O–Ce are formed on the surface. Then mechanical tearing of Si–O–Si bonds leads to the SiO2 removal as a lump instead of Si(OH)4 monomer, and the lump is released from the CeO2 particles downstream.