“Etching under the corner” - inclined macropores by reactive ion etching

Abstract

Deep reactive ion etching at cryogenic temperatures has been used for a macropore formation in silicon. A double-mask set-up was applied. The first mask of a patterned thin aluminum or silicon oxide layer determined the pore size and density, and thicker patterns of silicon, glass, or SU-8 acted as a secondary mask changing the angle of the etched pores. Up to 45° inclined macropores have been obtained at the edges of a secondary mask. The inclination dependencies on the shape and structure of the secondary mask and on the etching parameters have been investigated. The effect is explained by the non-uniformity of etching ion direction at the sidewall of a thick secondary mask.