Alternated process for the deep etching of titanium

Titanium is increasingly used as a platform material in microdevices dedicated to biological and bio medical applications. Existing processes for titanium deep etching use a chlorine based chemistry. This paper reports on a low reproducibility for such chemistries when titanium samples are glued onto a silicon carrier wafer. In this case, a SiOCl layer redeposits on the chamber walls as well as on the sample surface. This leads to a decrease of the etch rate and the formation of a very high roughness with a similar morphology as black silicon. The alternated process for the deep etching of titanium (APETi) described in this paper has been designed to improve the overall reproducibility by preventing high roughness formation. It is a time-multiplexed process where Cl-2/Ar plasma steps are alternated with SF6 plasma steps. The first step aims at etching with vertical walls (anisotropy) while the second aims at reducing the roughness by removing SiOCl from the sample surface.