Surface roughness of silicon oxynitride etching in C 2F 6 inductively coupled plasma

Abstract

Surface roughness of silicon oxynitride film was examined as a function of process parameters. Etching was conducted in a C 2F 6 inductively coupled plasma and surface roughness was measured by atomic force microscopy. The parameters involved include radio frequency source power, bias power, pressure, and C 2F 6 flow rate. For optimization, parameter effects on the deviations of etch rate, surface roughness and DC bias were related. The source power-induced DC bias was strongly correlated to the surface roughness. This was similarly observed for the bias power variations. Complex effects of pressure or C 2F 6 flow rate were reasonably explained by combining DC bias and reported [F] and [CF x ] variations. It is noticeable that the dominance of [F] or [CF x ] was similar for both variations in pressure and C 2F 6 flow rate. In other words, surface roughness seemed to be initially dominated by [F]-driven chemical etching and then by [CF x ]-driven polymer deposition. A useful clue identified for optimization is that for all parameter variations the smallest deviation of surface roughness occurred at the largest DC bias deviation.