SiCN coatings prepared by PACVD from TMS-NH₃-Ar system on steel

Abstract
SiCN coatings with continuous composition between Si₃N₄ and Sic (rich in Si) have been prepared by acting on the tetramethylsilane (TMS)/ammonia ratio in the gas phase. The deposit compositions (10 μm thick films) have been investigated by different means which stress the difficulties encountered. Nevertheless the trends are in fair agreement. An increase in ammonia partial pressure favors the incorporation of N in the deposits. XPS studies of the samples lead to the conclusion that the chemical environments of Si, C, N are more complicated than in a mixture situation ; there would be various bonding States. Deposition rates range from 12 μm h^-1 up to 30 μm h^-1 and are largely increased when dilution is reduced. Hardness and Young's modulus are driven by the C/N ratio : H_V lies between 22.6 GPa (Si₃N₄) to 26.2 GPa (SiC) with respectively apparent Young's modulus from 250-295 up to 357-431. All the films exhibit an adhesion of same order though N tends to increase the critical loads.