Etching Mechanism of Silicon Nitride in HF-Based Solutions

A reaction mechanism for the etching of silicon nitride layers in aqueous hydrofluoric acid solutions is proposed. The surface of consists of groups that are etched from the solid matrix via three possible routes. Depending on the pH, these groups are protonated to At the rate-limiting step consists of an elimination of and a subsequent addition of or HF to the vacant surface site to form Si-F. At the elimination of is assisted by followed by a transfer of one of the fluorides of to the vacant site. All subsequent reaction steps to remove the SiF unit are nucleophilic substitution reactions with low activation energies. The etch rates and mechanism of different types of silicon nitride films are compared with that of etching. Therefore, etch selectivity between these two materials can be explained. The theory is also applicable for silicon hydrogen passivation. © 2001 The Electrochemical Society. All rights reserved.