Advanced Process Equipment for PECVD Silicon Nitride Deposition – an Experimental Study

Abstract

Originally developed Plasma Enhanced Chemical Vapor Deposition (PECVD) device is explored to produce the silicon nitride films to be used as a material for surface micromachined capacitive ultrasound transducers. Silicon nitride is deposited from silane and ammonia gas mixture diluted in argon in the 13.56 MHz RF plasma with adjustable power. The conditions of deposition experiments were modified alternating the silane to ammonia flow ratio and the RF power, while other process parameters were supposed to be constant. The process responses measured were the deposition rate, film thickness, refractive index, surface morphology and film composition. It was found a strong influence of silane to ammonia flow ratio to the deposition rate, the refractive index and the composition of the film. Greater ratios, causing higher deposition rates, tend to give the lower refractive index, poorer surface and lower nitrogen content in resulting film. The RF power was also found to non-linearly influence the deposition rate and resulting film properties. Although the performance of the new apparatus was found to be reliable enough, the X-ray photoelectron spectrometry discovered elevated oxygen content, which is to be reduced by reducing the quantity of residual gases in deposition chamber.