Deep silicon etching in inductively coupled plasma reactor for MEMS

We have used an inductively coupled plasma (ICP) reactor to etch deep features with SF6/C4F8 pulsed processes. Microelectromechanical system (MEMS) applications require 10-500 mu m deep structures to be etched into silicon. The etch rate has to be carefully defined: in plasma etching the etch rate is a function of feature size (RIE lag), of etch time (ARDE,aspect ratio dependent etching) and loading (pattern density). Three processes have been characterized with respect to etch rate, loading, RIP-lag, ARDE and sidewall profile. The high rate process has 5 mu m/min maximum etch rate but it exhibits severe RIE-lag and ARDE. Two other processes with maximum etch rates of 3.5 mu m/min and 1.6 mu m/min are much less prone to RIE-lag and ARDE. Etch profiles and their non-idealities have been studied. Vertical, positively sloped, negatively sloped and barrel-like profiles result depending on process and feature size.