Mass and bond density measurements for PECVD a-SiCx:H thin films using Fourier transform-infrared spectroscopy

The absolute concentration of chemical bonds in Plasma Enhanced Chemically Vapor Deposited (PECVD) a-SiCx:H thin films have been determined via combining transmission Fourier-Transform Infra-red (FTIR) spectroscopy with X-ray Reflectivity (XRR) and Rutherford Backscattering (RBS) mass density and composition measurements. Specifically, we demonstrate in this paper that the integrated absorbance for the Si–C stretch in FTIR is linearly proportional to the mass density of PECVD a-SiCx:H films as determined by XRR and RBS. This linear relationship allows us to accurately determine the IR absorption cross section for the Si–C stretch. Using these cross sections in combination with IR proportionality constants/cross sections published by other researchers, we demonstrate that mass densities in agreement with XRR and RBS can be calculated from the integrated absorbances of the Si–C, Si–H, and C–H stretches in FTIR spectra. From additional mass balance relationships, we further demonstrate that the full elemental and bond concentrations can be determined. This analysis reveals the presence of significant Si–Si and C–C bonding in the a-SiCx:H films that was not clearly identified in previous FTIR investigations due to the low IR activity for these homopolar bonds. The bond and mass density calculations are demonstrated for both 3C-SiC and a-SiCx:H thin films with mass density values ranging from 1 to 3.2 g/cm3.

► Demonstration of mass density measurements utilizing FTIR. ► Determination of full chemical bond density in a-SiC:H utilizing FTIR. ► Determination of IR absorption cross section for Si-C stretch. ► Detection of significant Si-Si and C-C homopolar bonding in low-k a-SiC:H.