MEMS Industry-Worth Etching to Fabricate Tapered Structures in SiO2

This paper presents the results for developing SiO
₂
plasma etching with tapered sidewalls for microelectromechanical systems (MEMS). The experiment was designed in an industrial inductively-coupled plasma reactive ion etching tool, wherein a two-step etching process was developed for opening vias in the SiO
₂
with a sidewall angle of 68°-70°. The first step modified the photoresist profile from a vertical to a tapered profile using Ar/O
₂
/CF
₄
plasma with a high wafer platen power. The second step of SiO
₂
etching was performed in C
₄
F
₈
/H
₂
-based plasma with added inert gases and used a dual mechanism of photoresist pattern transfer and etch by-product redeposition on the sidewalls. The introduction of the photoresist profile tapering as the first step of the etching process not only facilitated fabrication of tapered sidewalls, but also helped to avoid etch-stop in structures with a critical dimension (CD) down to 1.5 μm and minimize the etch CD shrink. [2017-0089]