Pulsed-radio frequency plasma enhanced chemical vapour deposition of low temperature silicon nitride for thin film transistors

The growth of low temperature silicon nitride using radio frequency (RF) plasma enhanced chemical vapour deposition (PECVD) is associated with high porosity and surface roughness due to the short surface diffusion length of adsorbed radicals during the deposition. In this work we present pulsed-RF PECVD as a means of achieving a film with smoother surface and reduced density of voids. The growth process and the longer surface diffusion length are discussed as the main reason behind improvement of film density while maintaining the substrate temperatures. The deposited films exhibit improved electrical performance with 72% reduction in breakdown probability compared with conventional continuous-wave RF PECVD films. A low interfacial defect density with a field effect mobility of 1.1cm2/V.s and subthreshold slope of 0.3V/dec, was achieved when used as a gate dielectric in thin film transistors.