Comparative study of CF₄ + X + He (X = C₄F₈ or C₄H₂F₆) plasmas for high aspect ratio etching of SiO₂ with ACL mask

Abstract

This work compared C4F8 and C4H2F6 gases (as third components in CF4 + He gas mixture) for the high aspect ratio etching of SiO2 through the amorphous carbon layer (ACL) mask. The research scheme included the study of gas‐phase plasma characteristics, etching kinetics, and etching profiles. It was found that CF4 + C4F8 + He and CF4 + C4H2F6 + He gas mixtures are featured by quite close plasma parameters, the kinetics of electron‐impact processes, and ion bombardment intensities. At the same, the use of C4H2F6 provides a bit lower F atom density together with a bit higher polymerizing ability. All these factors cause lower absolute etching rates for both SiO2 and ACL but provide better SiO2/ACL/ACL selectivity and profile features.