Residual stress in low pressure chemical vapor deposition $SiNx$ films deposited from silane and ammonia

Varied $SiNx$ films have been deposited by low pressure chemical vapor deposition from silane $SiH4$ and ammonia $NH3$ and the influences of the deposition parameters (temperature, total pressure and $NH3/SiH4$ gaseous ratio) on the film deposition rate, refractive index (assessed at a 830 nm wavelength), stoichiometry and thermomechanical stress are investigated and correlated. Low stress $(≈600 MPa)$ $Si3N4$ films are obtained for the highest deposition temperature and the lowest total pressure but the gaseous ratio is shown to be the dominant parameter. According to the $SiNx$ stoichiometry, silicon-rich silicon nitride and nitrogen-doped silicon (called NIDOS) depositions are obtained and compressive to tensile stresses are reported. A maximum in compressive stress is put into evidence for N/Si ratio roughly equal to 0.7 and is related to the cumulated effects of silicon nitridation and crystallization, characterizing the transition between nitrogen-doped silicon and silicon-rich silicon nitride. Finally, by considering stress, deposition rate, nonuniformity along the load and resistance to alkaline solutions, optimal (silicon-rich) silicon nitride deposition conditions are proposed for microelectromechanical applications.