Long-term thermal mechanical stability of PECVD amorphous silicon carbide films for harsh environment microelectromechanical systems

Amorphous silicon carbide (a-SiC) thin films were deposited at 450°C by Plasma-Enhanced Chemical Vapor Deposition (PECVD) using silane and methane precursor gases. Films were deposited to a nominal 300nm thickness using a range of precursor gas flow rates, chamber pressures, and RF powers. For the conditions investigated, all films were deposited with high compressive stress (≥ -1,000MPa). Films were then annealed for 10 hours at 550°C residual stress measured periodically, with most films transforming to 300MPa-1,000MPa tensile stress. Films were then subjected to thermal treatment for 50 hours at 500°C to simulate prolonged microelectromechanical device operation at elevated temperatures. After an initial period, all film stresses stabilized to within 5% over 10 hours, with final stresses ranging from 170MPa compressive to 1,200MPa. Young´s modulus was determined via nano-indentation and was found to be a consistent 211.4 002B;/- 20.37GPa for each recipe. This, combined with an observed distributed range of stabilized stresses, indicate a potential new application of a-SiC with constant modulus and stable residual stress for high temperature sensors.