Assessment of silicon wafer material for the fabrication of integrated circuit sensors

The influence of process induced defects on the surface quality of wet anis otropically etched cavities in silicon wafers is investigated. Localized th inning of silicon substrates using cavities of this kind is a common method for fabricating, e.g., diaphragms for silicon pressure sensors. Wafers wit h four different concentrations of interstitial oxygen varying from 6.0 X 1 0(17) cm(-3) to 9.3 X 10(17) cm(-3) were exposed to a thermally simulated c omplementary metal oxide semiconductor process and subsequently anisotropic ally etched with potassium hydroxide or tetramethylammonium hydroxide solut ion. Crystal defects caused by oxygen precipitation, such as stacking fault s, punching systems, and dislocations, were found to be the origin of large craterlike defects in the sidewalls of the cavities. Wafer material with a n initial concentration of interstitial oxygen between 6.0 x 10(17) cm(-3) and 6.9 x 10(17) cm(-3) exhibits a very low density of small precipitate-di slocation complexes and, thus, etched cavities of good surface quality are obtained. In wafers with interstitial oxygen concentrations higher than 7.8 x 1017 cm-3 bulk stacking faults were observed and the surface quality of the cavity sidewalls diminishes. The microscopic morphology of the craterli ke defects in the {111} sidewalls of the etched cavities is explained using a computer simulation of the etching process. An influence of process indu ced defects on the surface quality of wet anisotropically etched {100) surf aces was not found. (C) 2000 The Electrochemical Society. S0013-4651(99) 10 -026-0. All rights reserved.