Electrochemical Studies of the Film Formation on Lithium in Propylene Carbonate Solutions under Open‐Circuit Conditions

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Abstract
A reaction mechanism for the etching of silicon nitride layers in aqueous hydrofluoric acid solutions is proposed. The surface of Si3N4Si3N4 consists of SiNH2SiNH2 groups that are etched from the solid matrix via three possible routes. Depending on the pH, these SiNH2SiNH2 groups are protonated (pKa=1.4)(pKa=1.4) to SiNH3+.SiNH3+. At pH 3,>pH 3, the elimination of NH2−NH2− is assisted by HF2−,HF2−, followed by a transfer of one of the fluorides of HF2−HF2− 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 SiO2SiO2 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.

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