Highly selective etching of SiN x over SiO 2 using ClF 3 /Cl 2 remote plasma

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 and SiO using ClF /Cl remote plasmas have been investigated. The increase of Cl percent in ClF /Cl gas mixture increased etch selectivity of SiN over SiO while decreasing SiN etch rate. By addition of 15% Cl to ClF /Cl , the etch selectivity higher than 500 could be obtained with the SiN 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 SiN can be etched through the reaction from Si-N to Si-F and Si-Cl (also from Si-Cl to Si-F) while SiO 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 SiN /SiO layer stack was etched using ClF /Cl (15%), extremely selective removal of SiN layer in the SiN /SiO layer stack could be obtained without noticeable etching of SiO layer in the stack and without etch loading effect.&#xD.