Mechanism of selective Si 3N 4 etching over SiO 2 in hydrogen-containing fluorocarbon plasma

Abstract

This paper describes the mechanism of selective Si 3N 4 etching over SiO 2 in capacitively-coupled plasmas of hydrogen-containing fluorocarbon gas, including CHF 3, CH 2F 2 and CH 3F. The etch rate of Si 3N 4 and SiO 2 is investigated as a function of O 2 percentage in all plasma gases. Addition of O 2 in feed gases causes plasma gas phase change especially H density. The SiO 2 etch rate decreases with increase of O 2 percentage due to the decline of CF x etchant. The Si 3N 4 etch rate is found to be strong correlated to the H density in plasma gas phase. H can react with CN by forming HCN to reduce polymer thickness on Si 3N 4 surface and promote the removal of N atoms from the substrate. Thus the Si 3N 4 etch rate increases with H intensity. As a result, a relative high selectivity of Si 3N 4 over SiO 2 can be achieved with addition of suitable amount of O 2 which corresponds to the maximum of H density.