XPS and AFM study of chemical mechanical polishing of silicon nitride

In this paper, the effect of chemical–mechanical polishing (CMP) of silicon nitride films was investigated using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Silicon nitride films with different deposition methods (PECVD and LPCVD) and two different silica-based slurries were studied. The surface chemical structure of as-deposited LPCVD film is slightly better than that of as-deposited PECVD film, and the surface morphologies (RMS roughness ∽0.3 nm for LPCVD film, and 1.9 nm for PECVD film) are much different. After CMP, the LPCVD film was more dramatically oxidized, and the surface became rougher for the process conditions used. The PECVD film was less dramatically oxidized, a subsilicon nitride (SiN x) appeared on the surface, and the surface became smoother. These results suggest that the quality of as-deposited nitride film, as well as the CMP process conditions, impact significantly on the quality of the polished surface.