Evolution of Fluorine Content with Precipitate Formation in Fluorine-Doped Silicon Oxide

Abstract

Precipitates appear on fluorine-doped silicon oxide (SiOF) film when the film surface is exposed to atmospheric air. They are flake-type and hexagonal-shaped and show up rapidly after initiation, clustered at wafer center. It was found that the onset of precipitation is closely related to fluorine concentration of SiOF films, those with higher fluorine content exhibit high propensity of precipitation, along with more significant fluorine loss. In this study, the microstructural changes of SiOF films in the course of precipitation were examined. The Fourier transform infrared spectra of SiOF films showed the declined intensities of Si–Fn (n = 1,2) bonding peaks at time after the formation of precipitates. In the surface analysis by X-ray photoelectron spectroscopy, the binding energy of F 1s reduced ∼0.5 eV after precipitation, indicating also decreased Si–Fn bonding on the surface layer of SiOF films. Meanwhile, analysis by thermal desorption spectroscopy indicated that the unstable fluorine content in the SiOF film is significantly reduced after precipitation.