Influence of Different Carbon Precursors on Optical and Electrical Properties of Silicon Carbonitride Thin Films

Silicon carbonitride (SiCN) thin films are widely used for protective hard coatings due to their superior mechanical and chemical properties such as high wear resistance, chemical and thermal stability at high temperatures, and hardness. Another scope of study of SiCN thin films is as the low dielectric constant (LKC) materials, which are desired for replacing silicon oxide (SiO2) in integrated circuits (IC). SiCN owes the interest shown to being an intermediate compound between silicon nitride (Si3N4) which is a highly transparent, wide band gap (5 eV) dielectric, and silicon carbide (SiC) with excellent mechanical performance. In this study we present the optical and electrical properties of SiCN:H thin films fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR PECVD) by using a mixture of acetylene (C2H2) or methane (CH4), silane (SiH4), argon (Ar), and nitrogen (N2) gas precursors. Samples fabricated with two different carbon sources were analyzed and compared regarding their chemical composition as well as their electrical and optical properties. The atomic composition of Si, C, N, O, and H were determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analysis and the chemical bonds formed in SiCN:H were analyzed through Fourier transform infrared spectroscopy (FTIR). Optical bandgap, index of refraction and extinction coefficient were analyzed by variable angle spectroscopic ellipsometry (VASE) and will be presented for different deposition conditions. The dielectric constants and dielectric breakdown voltages of the thin films were determined through current-voltage (I-V) and capacitance-voltage (C-V) measurements. Lastly, the hardness properties are explained due to varying C and H concentrations.