Tunable Etch Profile for Scandium Doped Aluminum Nitride Piezoelectric Film

Abstract

Scandium-doped Aluminum Nitride ($\text{Sc}_{\mathrm{x}}\text{Al}_{1-\mathrm{x}}\mathrm{N}$) is reported to have attractive piezoelectric, pyroelectric and electro-optic properties with increased Sc concentration. However, high Sc concentration poses challenges, such as, lower etching rate, sidewall redeposition, and severe mask erosion during etching process. A Design of Experiments (DOE) was conducted to explore the etch sidewall tunability of the $\text{SC}_{0.2}\text{Al}_{0.8}\mathrm{N}$ film using an ICP plasma etch system. Key process parameters include chlorine/argon ratio, platen bias power and process pressure. For isolated patterns, generally required for MEMS devices such as PMUT, sidewall angle could be tuned from ~20° (super tapered) to 65° (relatively vertical). The tunability of the etch profile is attributed to the plasma constituents and sidewall byproduct redeposition.