Surface oxidation behavior in air and O2-H2O-Ar atmospheres of continuous freestanding SiC films derived from polycarbosilane

In this contribution, thermodynamic computational calculations firstly carried out on Ar-Si-C-O/Ar-Si-C-O-H database demonstrate that passive oxidation is main reaction of continuous freestanding SiC films in both air and 14%H2O/8%O-2/78%Ar atmospheres. SiC films were subsequently annealed at 1300 degrees C, 1400 degrees C and 1500 degrees C for 1 h in air and O-2-H2O-Ar atmospheres. Results suggest that modulus, hardness and resistivity decrease whereas crystallite size of beta-SiC and a-cristobalite increase with elevated annealing temperature. In particular, hardness of wet oxidized samples is lower than that of air oxidized ones. Additionally, their oxidation kinetics models were also established and verified by annealing at 1200 degrees C in air and wet oxygen for different time from 1 h to 100 h. Oxidation of continuous freestanding SiC films is identified to follow parabolic oxidation kinetics, and water could effectively enhance the oxidation rates. It is revealed that SiO2 layer can protect SiC films from further oxidation, and their thickness increases with prolonged annealing time. In this study, a dense and uniform SiO2 layer with a thickness of 1.1-1.6 mu m was produced for sacrificial and passivation layer based on suitable thermal oxidation process (annealing at 1000 degrees C for 5 h in O-2-H2O-Ar environment). Interestingly, fast diffusion paths in this oxide layer could effectively accelerate oxidation process of SiC films. These obtained achievements would promote further applications of SiC films on microelectromechanical systems (MEMS) devices in harsh environments.