Highly selective etching of SiN_x over SiO₂ using ClF₃/Cl₂ remote plasma

Abstract

Highly selective etching of silicon nitride over silicon oxide is one of the most important processes especially for the fabrication of vertical semiconductor devices including 3D NAND (Not And) devices. In this study, isotropic dry etching characteristics of SiNx and SiO2 using ClF3/Cl2 remote plasmas have been investigated. The increase of Cl2 percent in ClF3/Cl2 gas mixture increased etch selectivity of SiNx over SiO2 while decreasing SiNx etch rate. By addition of 15% Cl2 to ClF3/Cl2, the etch selectivity higher than 500 could be obtained with the SiNx etch rate of ~ 8 nm/min, and the increase of Cl percent to 20% further increased the etch selectivity to higher than 1000. It was found that SiNx can be etched through the reaction from Si-N to Si-F and Si-Cl (also from Si-Cl to Si-F) while SiO2 can be etched only through the reaction from Si-O to Si-F, and which is also in extremely low reaction at room temperature. When SiNx/SiO2 layer stack was etched using ClF3/Cl2(15%), extremely selective removal of SiNx layer in the SiNx/SiO2 layer stack could be obtained without noticeable etching of SiO2 layer in the stack and without etch loading effect.