Open and filled DRIE trenches with high aspect ratio used for micro-mirror scanners

Abstract

In this paper, we report on results of an intensive study, which has been performed to understand and tune deep reactive ion etch (DRIE) processes for optimized aspect ratio, trench profile and etch mask selectivity. The development of the DRIE process was mainly driven by the increase of the etch depth. Trenches, made with these DRIE processes, are used for the fabrication of micro-scanner mirrors. Filled trenches are integrated for electrical isolation, open trenches for the etching of mechanical separated structures, e.g. mirror spring and comb electrodes. Especially for micro-scanners with high frequencies, the mirror thickness is of great importance due to the dependence on the dynamic mirror deformation. We investigated the influence of the passivation process by lowering the waferchuck temperature und by adding oxygen plasma as inhibitor. After an etch tool upgrade, we analyzed also the influence of a low-frequency (LF) generator and a new control software on the etch results. Goal of these developments of the DRIE process was a higher aspect ratio, an improved filling of isolation trenches and a higher selectivity to the etch mask.