Phase stabilization by rapid thermal annealing in amorphous hydrogenated silicon nitride film

We have studied the effect of rapid thermal annealing (RTA) in the context of phase evolution and stabilization in hydrogenated amorphous silicon nitride (a-SiNx:H) thin films having different stoichiometries, deposited by an Hg-sensitized photo-CVD ( chemical vapor deposition) technique. RTA-treated films showed substantial densification and increase in refractive index. Our studies indicate that a mere increase in flow of silicon (Si)-containing gas would not result in silicon-rich a-SiNx : H films. We found that out-diffusion of hydrogen, upon RTA treatment, plays a vital role in the overall structural evolution of the host matrix. It is speculated that less incorporation of hydrogen in as-deposited films with moderate Si content helps in the stabilization of the silicon nitride (Si3N4) phase and may also enable unreacted Si atoms to cluster after RTA. These studies are of great interest in silicon photonics where the post-treatment of silicon-rich devices is essential.