Thermal plasma chemical vapor deposition of Si-C-N coatings

A thermal plasma chemical vapor deposition process was used to synthesize Si-C-N films in a triple torch plasma reactor. In this system, three dc plasma jets converge at the substrate to create a chemically reactive region. Nitrogen or hydrogen was added to the argon plasma, while hexamethyldisilazane (HMDSN) was injected through a central injection probe above the converging jets. The dependence of the HMDSN to nitrogen or hydrogen ratio on the film quality and performance were studied. Micro X-ray diffraction was used to identify the presence of both α- and β-Si₃N₄ in the films deposited with nitrogen, while α- and β-SiC were detected in the depositions grown with hydrogen. Scanning electron microscope images indicated that film porosity decreased with lower reactant flow rates. Indentation tests conducted on the polished film cross-sections determined that the less porous films tended to exhibit higher hardness and elastic modulus. Surface wear tests of these films also showed reduced wear. For the deposition of Si-C-N films, an optimization must be made between high growth rates, which produce columnar films, on one side, and low porosity and high hardness at lower deposition rates on the other.