Highly selective etching of SiNxover SiO2using ClF3/Cl2remote 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 SiN_xand SiO₂using ClF₃/Cl₂remote plasmas have been investigated. The increase of Cl₂percent in ClF₃/Cl₂gas mixture increased etch selectivity of SiN_xover SiO₂while decreasing SiN_xetch rate. By addition of 15% Cl to ClF₃/Cl₂, the etch selectivity higher than 500 could be obtained with the SiN_xetch rate of ∼8 nm min^-1, and the increase of Cl percent to 20% further increased the etch selectivity to higher than 1000. It was found that SiN_xcan be etched through the reaction from Si-N to Si-F and Si-Cl (also from Si-Cl to Si-F) while SiO₂can be etched only through the reaction from Si-O to Si-F, and which is also in extremely low reaction at room temperature. When SiN_x/SiO₂layer stack was etched using ClF₃/Cl₂(15%), extremely selective removal of SiN_xlayer in the SiN_x/SiO₂layer stack could be obtained without noticeable etching of SiO₂layer in the stack and without etch loading effect.

Keywords: 3D NAND; Cl2; chlorine monofluoride (ClF3); remote plasma etching; selective etching; silicon nitride (SiN x ); silicon oxide (SiO2).