Effects of the etchmask properties on the anisotropy ratio in anisotropic etching of silicon in aqueous KOH

Abstract

The objective of the present study is to investigate the influence of the etchmask properties on anisotropic etching of silicon in a KOH/H 2 O solution. The mechanical stress induced in the silicon substrate by an LPCVD-Si 3 N 4 etchmask has been analysed by 3D finite element analysis. It is shown that the rise of the mechanical stress at the edges of etchmask openings is mainly affected by the thickness of the LPCVD-Si 3 N 4 etchmask. The effect of the mechanical stress on the anisotropy ratio was experimentally determined. It has been found that the anisotropy ratio decreases with increasing LPCVD-Si 3 N 4 etchmask thickness. Furthermore the use of SiO 2 /LPCVD-Si 3 N 4 double-layer etchmasks resulted in rough {111} side wall surfaces and a lower anisotropy ratio.

Surface termination and hydrogen bubble adhesion on Si(100) surfaces during anisotropic dissolution in aqueous KOH

“…The stability of the pyramidal hillocks is probably related to the presence of slow etching Si(1 1 1) planes limiting the pyramid sides [7,[48][49][50][51]. In what follows the etching surface is modelled considering a (1 0 0) surface exposing (1 1 1) planes [52] (see Fig.…”

Anisotropic Etching of Three-Dimensional Shapes in Silicon

“…[1][2][3] For ͑100͒-oriented wafers, widely used in MEMS technology, the ratio of the etch rates of ͑111͒ and ͑100͒ faces, referred to here as the anisotropic ratio, is of vital importance for making high-resolution micromechanical structures. Although in the most favorable case the anisotropic ratio can exceed 100, 4 control and reproducibility at this level are poor. The composition of the etchant and the etching conditions as well as the ͑mis͒orientation of both the wafer surface and the mask edge are clearly important.…”

“…Other factors which may play a role are dislocations in the silicon, defects at the silicon-mask interface, and impurities ͑even at very low concentrations͒ in the etchant. 4 Because of the practical importance of etching anisotropy, extensive studies have been devoted to mapping the etch rates of the various crystallographic faces of silicon in different alkaline etchants. Two experimental approaches have been used.…”

“…The system acts as a galvanic cell, as has been shown previously for electroless etching of GaAs. 23 The importance of such galvanic effects in silicon etching has been pointed out by Allongue and coworkers; 24,25 they showed that cathodic protection of a polished ͑111͒ surface by a roughened back surface in oxygen-free NH 4 F solution helps to obtain ideally flat hydride-terminated ͑111͒ surfaces. Considering the discussion above one might expect the anisotropic etching characteristics ͑e.g., the anisotropic ratio͒ to depend on the particular ''facet geometry'' which, of course, should be timedependent.…”

Convex corner undercutting of {100} silicon in anisotropic KOH etching: the new step-flow model of 3-D structuring and first simulation results

“…3). The actual instability has geometric reasons, but it can be enhanced by the mechanical stresses, which are induced into the silicon substrate by the possibly stressed etch mask materials [42]. This is the starting point of the "peeling" of the first (111) plane at the beginning of the etch attack.…”