Silica Formation during Etching of Silicon Nitride in Phosphoric Acid

Abstract

The etching of silicon nitride using phosphoric acid with silicon dioxide as a mask is an important process step used in the production of 3D NAND devices. This paper examines the theory of formation of a silica film onto the silicon dioxide surface during this etching step by performing a shell balance analysis of silica species in the etched out liquid volume of the 3D NAND structures. The method of moments is used to solve for the moments of the distribution of particle sizes, and this is used to solve for the potential energy barrier for silica particles to adhere to the silicon dioxide surface.