Optical properties of plasma-enhanced chemical vapor deposited SiCxNy films by using silazane precursors

Abstract

In this study, amorphous silicon carbonitride (SiCxNy) films were fabricated by radio frequency (RF) chemical vapor deposition (PECVD) using a single silazane precursor and a low power density (0.15W/cm3) for better compositional control. The effects of the precursor chemical structure (C/Si ratio, CSiN structure, and vinyl groups) and deposition temperature (Ts) on the chemical structure and optical properties of SiCxNy films were examined using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Specifically, two new single precursors; namely, n-methyl-aza-2,2,4-trimethylsilacyclopentane (MTSCP) and 1,3-divinyl-1,1,3,3-tetramethyl-disilazane (DVTMDS) were studied and compared.SiCxNy films deposited using MTSCP involving SiC3N rings formed SiN and Si(CH2)3 crosslinked structures at Ts≤100°C, and were then changed to predominantly SiCH2NSi crosslinked structures at Ts>300°C, leading to a wide range of optical band gap from 5.2 to 3.7eV. Compared to DVTMDS-deposited SiCxNy films, their relatively higher percentage of SiCN structure accounted for the lower optical band gap and reduced transmission. DVTMDS with di-vinyl groups readily formed a Si(CH2)2 bridge in SiCxNy films Ts≤200°C, resulting in excellent optical transmittance. The transmittance in the visible wavelengths of 400°C-deposited SiCxNy film using DVTMDS still showed 85%. Also, tunable refractive index between 1.44 and 2.10 were obtained for SiCxNy films deposited at Ts≤400°C.