Characterization of silicon nitride thin films deposited by hot-wire CVD at low gas flow rates

Abstract

We examined the chemical, structural, mechanical and optical properties of amorphous hydrogenatedsilicon nitride thin films deposited by hot-wire chemical vapour deposition using SiH4, NH3and H2gases at total flow rates below 33 sccm. Time of flight secondary ion mass spectroscopy reveal that thefilm surfaces consist of predominantly Si with hydrogenated SixNyOzspecies. Energy dispersive X-rayspectroscopy and X-ray photoelectron spectroscopy corroborate on the N/Si ratio. Electron energy lossspectroscopy discloses that the thickness of the nitrogen rich oxidized interface between the SiNxfilmsand the c-Si substrate decrease with an enhancing NH3flow rate. By varying the NH3flow rate, denseSiNxfilms can be realized with hydrogen content between 16 and 9 at.%, a refractive index between 3.5and 1.9 and optical band gap ranging from 2 to 4.5 eV. The SiNxfilm stress is compressive for N/Si < 0.4and tensile for higher N/Si > 0.55. Mechanisms relating the HWCVD conditions and the film structure andproperties are proposed.