Equilibration in Amorphous Silicon Nitride Alloys

Abstract

Several series of amorphous silicon nitride thin films have been grown by plasma-enhanced chemical vapour deposition, where the ratio of ammonia and silane feed gases was held constant for each series while the deposition temperature was varied from 160 °C to 550 °C, and all other deposition conditions were held constant. Photothermal Deflection Spectroscopy measurements were used to determine the Urbach slope E₀ and the defect density N_D. It is found that N_D is determined by E₀ for most of these samples, suggesting that defect equilibration occurs in a-SiN_x:H for x up to at least 0.6. The growth temperature at which the disorder is minimised increases to higher values with increasing x, which is explained in terms of a hydrogen-mediated bond equilibration reaction. Fourier Transform Infra Red spectroscopy measurements were performed to determine the changes in hydrogen bonding with growth temperature. The results suggest that a second bond equilibration reaction also occurs at the growing surface, but that equilibrium cannot be reached at higher temperatures because of hydrogen evolution from Si-H bonds.