Plasma-enhanced deposition of hard silicon nitride-like coatings from hexamethyldisiloxane and ammonia

Hard silicon nitride-like coatings have been grown in a high-density microwave electron cyclotron resonance discharge, using hexamethyldisiloxane (HMDSO) as the deposition precursor and ammonia as the reactive gas. Statistical experiment design methodology was used to investigate the effects of microwave power and NH3/HMDSO flow-rate ratio on the growth rate, elastic modulus and hardness of the plasma-grown coatings. The films deposited are hard, colorless and transparent, with growth rates of up to 0.5 μm/min. Films lasted 745–840 h in an ASTM B117 salt-fog corrosion test. X-Ray photoelectron spectroscopic analyses showed the coating composition to be SiCxOyNz, with significant carbon and up to 13.7 at.% nitrogen concentration. While not stoichiometric Si3N4, coatings grown at high microwave power and high NH3/HMDSO flow ratios had an elastic modulus of 176 GPa and hardness of 12.2 GPa, comparable to values reported for thermally grown silicon nitride.