ETCH MECHANISM IN THE LOW REFRACTIVE-INDEX SILICON-NITRIDE PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION PROCESS

In this letter the author reports a generalized mechanism for the plasma-enhanced chemical vapor deposition silicon nitride process which includes simultaneous surface deposition and etching reactions. The etching mechanism is caused by the hydrogen plasma in combination with the high plasma potential. For each deposition versus power or refractive index versus power curve there is a critical point which is determined by the critical power W(critical). When the power is lower than W(critical), the process can be explained by conventional deposition mechanisms. When the power is higher than W(critical), the hydrogen etching mechanisms becomes important. W(critical) depends on other process parameters such as the composition of the feeding stream. Experimental results confirmed the hydrogen etching mechanism, which is selective.