Variation of etch profile and surface properties during patterning of silicon substrates

Patterned silicon substrates form the basis for various microfluidic and mi cromechanical devices. Recent developments in microfluidic and micromechani cal systems for biomedical applications demand complex three-dimensional st ructure profiles and a well-defined surface quality of the etched patterns. The object of our investigations was to realize complex contours with diff erent sidewall angles in silicon. The technology includes the combination o f several etching steps of different character, possibly in combination wit h suitable coatings or oxidation. The investigations into plasma etching of silicon substrates were carried out using an Advanced Silicon Etch System from Surface Technology Systems Ltd. (STS), UK. Our experiments were based on three different silicon-etching processes: the Advanced Silicon Etch pro cess (ASE (TM)) introduced by STS; continuous anisotropic silicon etching; and silicon etching in pure SF,. Variation in the ratio of etching to passi vation causes drastic changes in the etch rate, tilt angle and quality of t he etched silicon surfaces. Positive and negative edge profiles with tilt a ngles between 60 and 100 degrees were realized by variation of the surface passivation and the intensity of etching. The roughness of the etched silic on surface can be varied by process modifications, within limits. A well-de fined surface topology can be realized using different procedures and compl ex three-dimensional patterns can be created in silicon substrates. The mai n steps of the technology were the anisotropic patterning of silicon with t he aid of sidewall passivation, deposition of an additional passivating lay er, and subsequent isotropic silicon etching. (C) 2001 Elsevier Science B.V . All rights reserved.