Chemical structure of low-temperature plasma deposited silicon nitride thin films

The infrared transmission (400-4000cm(-1)) was measured for a series of approximately 0.5mum thick NH3/SiH4 and plasma deposited silicon nitride thin film alloys prepared at temperatures between 80 and 300degreesC using fixed process parameters. It is demonstrated from a detailed analysis of the infrared spectra that the 'condensation' mechanism is not thermally activated as previously reported, but is an entropic process required to stabilise the film structure. Modelling of the various absorption bands in the infrared transmission spectrum using a multiple Lorentzian oscillator parametric model leads to the proposition that thermally activated 'condensation' (networking) is really the formation of N(-Sidrop)(3) bonds from the reaction between amine branches. Evidence that the absorption feature around 640cm(-1), usually attributed to Si-H (bending), is N-H related is also discussed.