Analysis of sidewall quality in through-wafer deep reactive-ion etching

The quality of channel sidewalls resulting from through-wafer deep reactive-ion etching is analysed using scanning electron microscopy, atomic-force microscopy and interferometry. Sidewall quality and profile are highly dependent on the width of the etched channel. Channels narrower than 100 lm show generally good sidewall smoothness, though with a bowed profile. This profile leads to ion-induced damage towards the bottom of the channel sidewall. Wider channels, in contrast, exhibit overpassivation of the sidewalls with a region of thick polymer build-up followed by vertical striations and a very rough surface, but with an overall vertical profile. Redeposition of the passivation from the trench bottom to the sidewalls as suggested by other researchers is supported by our observations. 2004 Elsevier B.V. All rights reserved.