The black silicon method. VI. High aspect ratio trench etching for MEMS applications

Etching high aspect ratio trenches (HARTs) in silicon is becoming increasingly important for MEMS applications. Currently, the most important technique is dry reactive ion etching (RIE). This paper presents solutions for the most notorious problems during etching HARTs: tilting and the aspect ratio dependent etching effects such as bowing, RIE lag, bottling, and micrograss or black silicon. To handle these problems submicron HARTs are etched and the black silicon method is used to direct the pressure, power, ion energy, or flows of a fluorine-based RIE into the preferred settings. The influence of ion energy and trajectory is found to be most critical. The behaviour of the HART process is explained with the help of a set of variables and used to optimise the final profile. After this optimisation the RIE setting found is used for etching supermicron HART's which are characteristic for MEMS applications.