Annealing effects on a-SiC:H and a-SiCN:H films deposited by plasma CVD methods

Hydrogenated amorphous silicon carbide (a-SiC:H) and carbonitride (a-SiCN:H) films were deposited in RF and mid-frequency (MF) discharges and electron cyclotron resonance (ECR) plasma. Annealing was performed in high vacuum up to 1000 °C and the temperature-dependent gas effusion from the films was investigated in situ by mass spectrometry. Changes of mechanical film properties, i.e. thickness, stress and Young's modulus, were determined ex situ by profilometry and nanoindentation, respectively. Using elastic recoil detection analysis, Rutherford backscattering and X-ray photoelectron spectroscopy, effects of annealing on elemental composition and chemical bonding were investigated. Annealing the a-SiC:H films significantly increased their Young's modulus and decreased their thickness by up to 25% in the case of ECR plasma deposition. The a-SiCN:H films deposited by MF and RF discharge practically retained their Young's modulus and the film thickness shrinkage was below 3%. At intermediate temperatures, these films showed a small thickness increase. For ECR-deposited a-SiCN:H, the expansion was larger and accompanied by a distinct reduction of Young's modulus. Hydrogen effusion and plastic flow under both compressive and tensile stress have a pronounced impact on the mechanical film properties. Annealing effects on film structure and properties are discussed and fundamental processes are derived.