Selective Si3N4 Etching in Si3N4/SiO2 Pair-Layer Stack Using Non-H3PO4-Based Superheated Water

Abstract

The selective etching of Si3N4 and SiO2 is a crucial step in the semiconductor process. In general, hot phosphoric acid is used to selectively etch Si3N4 to SiO2. In this study, superheated water was used for selective etching of Si3N4 to SiO2. The Si3N4 and SiO2 etching rates depend on the OH- concentration of superheated water. In addition, the etching rate of Si3N4 and Si3N4-to-SiO2 etch selectivity were improved by adding proper additives to superheated water. In particular, using HCl-, HF- and H2SiO3-added superheated water, a horizontal SiO2 trench structure was successfully achieved on a patterned Si3N4/SiO2 structure through selective etching of Si3N4 without thinning of the SiO2 layers.