Characterization study of silicon nitride (SiN) thin-film hydrogen bonding for waveguide applications

Silicon nitride (SiN) and silicon dioxide (SiO₂) are high-index and low-index refraction materials that qualify them for waveguide applications. Here, we present the SiN thin film by studying hydrogen content on the surface of the fabricated thin films. The SiN thin films were deposited via plasma-enhanced chemical vapor deposition (PECVD) on a P-type (111) Silicon wafer with a silicon dioxide layer of 1 micron and resistivity of ~ 100 ohm-cm. Hydrogen bonds are formed on the thin-film surface which causes high propagation loss as both N-H bonds and Si-H bonds lead to absorption in the telecom spectrum. Ammonia-free deposition was utilized using only silane (SiH₄) and nitrogen (N₂) as precursors gases in PECVD run to reduce the hydrogen content. Process pressure was kept constant at 650 mTorr, varying the (SiH₄) concentration, RF power and temperature. The thicknesses of the deposited thin films were kept ~300 nm determined by scanning electron microscopy (SEM). while surface roughness was examined using atomic force microscopy (AFM). The hydrogen bonding content was studied using Raman, Fourier-transform infrared spectroscopy (FTIR) and Photoluminescence.