Plasma-enhanced chemical vapour-deposited silicon nitride films; The effect of annealing on optical properties and etch rates

The optical properties and etch rates of silicon nitride (SiNx:H) deposited by plasma-enhanced chemical vapour deposition (PECVD) and their correlation with bond concentrations have been studied. By varying the silane-to-total gas ratio, films with refractive index (n) between 1.92 and 3.00 were deposited. Higher n films had increased absorption and decreased etch rates. Annealing the samples at different temperatures revealed that all films were thermally stable up to 750 °C, above which all experienced a rise in n, attributed mainly to mass densification. The etch rate correlated well the N–H bond concentration for both annealed and as-deposited films.