V. Bliznetsov, B. Li, J. W. Lee and H. Lin, "MEMS Industry-Worth Etching to Fabricate Tapered Structures in SiO2," in Journal of Microelectromechanical Systems, vol. 26, no. 6, pp. 1400-1407, Dec. 2017. doi: 10.1109/JMEMS.2017.2755046
Abstract:
This paper presents the results for developing SiO2 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 SiO2 with a sidewall angle of 68°–70°. The first step modified the photoresist profile from a vertical to a tapered
profile using Ar/O2/CF4 plasma with a high wafer platen power. The second step of SiO2 etching was performed in C4F8/H2-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 etchstop in structures with a critical dimension (CD) down to 1.5 μm and minimize the etch CD shrink.