Characterization of MOCVD-grown non-stoichiometric SiNx

The surface morphologies and X-ray photoelectron spectra of MOCVD-grown SiNx were investigated. Highly Si-rich SiNx nanoislands not fully covering the sapphire surface were observed for SiNx deposition at low temperature (545 °C) with NH3/SiH4 flow rate of 2500/40 sccm. The surface roughness decreased from 0.91 nm to 0.23 nm with the reduction of SiH4 flow rate from 40 sccm to 3 sccm. The reduction of the SiH4 flow rate did not cause a linear decrease of Si/N ratio, which indicated that the SiH4 supply was saturated when the NH3 supply was 2500 sccm and deposition temperature was fixed at 545 °C. Relatively “thick” SiNx layers with stoichiometry close to 1 were formed for SiNx deposition at high temperature due to high decomposition rate of ammonia and high reaction rate between silane and ammonia. The SiNx layers almost fully covered the sapphire surface and showed surface structures of both nanoislands and nanoholes. By employing the same NH3/SiH4 flow rate of 2500/40 sccm the surface roughness of SiNx layers decreased from 0.91 nm to 0.17 nm with the increase of deposition temperature from 545 °C to 1035 °C. Saturated pre-nitridation would likely cause surface roughening.