Etching of CVD Si3 N 4 in Acidic Fluoride Media

The process whereby CVD Si 3 N 4 films are etched in acidic fluoride solutions has been investigated at 25° and 60°C by use of a series of well‐characterized etchants. The rate law for the dissolution process has been identified and is found to be linear in both [ HF ] and [ HF 2 − ] , but independent of [F − ]. Although the exact magnitude of the etch rates of CVD Si 3 N 4 is known to depend on the deposition conditions used, it is thought that the general form of the rate law will remain constant. Comparison between the rate constants for Si 3 N 4 and those previously reported for SiO 2 suggests that the etch rate of Si 3 N 4 can be increased relative to that of SiO 2 by use of elevated temperatures and very low p H solutions, and by adjustment of the nitride deposition parameters so as to increase the NH 3 / Si ratio in the reaction mixture.