X-ray reflectivity and FTIR measurements of N2 plasma effects on the density profile of hydrogen silsesquioxane thin films

The density depth profile and chemical bond structure of hydrogen silsesquioxane (HSQ) thin films treated with an N-2 plasma with varying power and exposure time were measured using specular X-ray reflectivity (SXR) and Fourier transform infrared (FTIR) spectroscopy. The SXR data indicated that the density profile of an untreated HSQ film is not uniform. At least four layers with different electron densities were required to fit the SXR data. For HSQ films treated with either increasing plasma power or plasma exposure time, the film roughness increased and a densified layer was observed at the film/air interface. The thickness of the densified layer increased with both plasma power and plasma exposure time. In the FTIR spectra of the plasma-treated films, the intensities of the Si-O peaks due to the network structure and the Si-OH peak due to water absorption increased and the intensities of the Si-H peaks decreased. The FTIR data show that the plasma converts the HSQ structure into a SiO2-like structure and are consistent with the densification observed in the SXR measurements. In general, the HSQ film is more sensitive to increasing plasma power than to increasing plasma exposure time. (C) 2001 The Electrochemical Society.