Preparation of silicon thin diapharagms free from micropyramids using anisotropic etching in KOH solutions.

Abstract

Etch rates of (100) silicon wafers in KOH solutions were measured and correlated in a wide range of KOH concentration and solution temperature where etching proceeded anisotropically. The operating conditions to provide surfaces free from micropyramids (MPs) were empirically determined for the case of preparing silicon thin diaphragms from 4-in. wafers for use as pressure sensors. The relations between operating conditions and the presence of NIPS were shown diagrammatically in terms of KOH concentrations and temperatures, such as the findings that etched surfaces were smooth and free from MPs primarily at higher KOH concentrations and secondarily at higher temperatures. MP formation was assumed to be caused by silicon oxide precipitates existing in the wafers which dissolved in KOH solutions at rates much lower than the etch rates of silicon crystals under the operating conditions examined. In addition to these precipitates some silicon complexes and/or contaminants in the KOH solutions were also suggested to participate in NIP formation.