Effect of SiO2 Etching Inhibitor to H3PO4 for the Selective Si3N4 Wet Etching of 3D NAND

Abstract

3D NAND has a vertically stacked semiconductor structure to increase the memory density of semiconductor devices. 3D NAND devices are based on the multiply stacked silicon nitride (Si3N4) and silicon dioxide (SiO2) structure, and it is essential to high selectively etch Si3N4-to-SiO2 in the fabrication process. Hot phosphoric acid (H3PO4) has been typically used in the Si3N4-to-SiO2 selective etching process and the etch selectivity can increase by adding SiO2 etching inhibitors in H3PO4. In order to increase etching rate of Si3N4 and Si3N4-to-SiO2 etch selectivity, additives can be added in H3PO4. However, SiO2 etching inhibitors to increase Si3N4-to-SiO2 etch selectivity may occur by-product redeposition issue around the SiO2-layered trenches of Si3N4/SiO2 multi-stack structure. In this study, the etching behavior of the Si3N4/SiO2 multi-stack structures in SiO2 etching inhibitor-added H3PO4 was investigated. In addition, high selective Si3N4 etching with the control of redeposition was performed on the Si3N4/SiO2 multi-stack structure by adding proper SiO2 etching inhibitor in H3PO4.