Growth of silicon nitride by nitridation of amorphous silicon at low temperature in hot-wire CVD

Silicon nitride (SiNx) layers of varying thickness were fabricated in a a-Si/SiNx/a-Si heterostructure via nitridation of the bottom a-Si layer, using ammonia (NH3) gas, in the hot-wire chemical vapor deposition (HWCVD) chamber at 250 °C. The thickness of the SiNx in the film was varied by changing the nitridation time (tN) in range of 1-30 min. Raman analysis showed that the a-Si and SiNx layers formed in the films were amorphous. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results indicated Si3N4 was formed in the nitrided a-Si. Presence of strong SiH2 (2086 cm−1) peaks in the FTIR spectrum suggested the hydrogen in a-Si effused at 250 °C. XPS Si2p spectra and high resolution transmission electron microscopy images showed thin SiNx layer of thickness 1.8-7.6 nm was formed. Formation of SiNx thicker than 7.6 nm even at a low temperature (250 °C) is suggestive of the H effusion promoting both the reaction and the diffusion of the nitridants in a-Si. The kinetics of the growth of SiNx during nitridation of the a-Si layer closely matches the growth process described by diffusion model, wherein the reaction of nitridants and a-Si is controlled by diffusion in the SiNx layer formed.