Deep Reactive Ion Etching (DRIE) is virtually shaping the MEMS-field. The basic technology originally developed at Bosch is free from the design restrictions and compatibility problems related to the old wet-etching technology which was based on potassium hydroxide (KOH-) solution. The technology has enabled a wide range of new devices like the inertial sensors for acceleration and yaw rate detection, pressure sensors for mid-to high-pressure applications, MEMS microphones, micro-mirrors and quite recently also timing devices fabricated in silicon. These products conquered both the automotive application area, and later on also the consumer field. From the surface-near micromachining of the early development stages, DRIE is nowadays heading towards a true 3D-microstructuring. Pressure sensors, microphones and micromirrors represent first examples of this trend, but also packaging applications like DRIE-structured silicon caps, functionalized silicon carrier substrates for intelligent systems-inpackage, and through-silicon vias (TSV's) for chip-stacking and new chip-integration concepts are receiving increasing attention.This paper leads from the early development phase targeting first high-volume products, to the development of advanced highrate etching solutions targeting today's new and challenging product families.

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A novel process for the preparation of thick porous silicon layers having very high porosities is proposed. Starting with thick layers of intermediate porosity the porosity is further increased in an additional step. This is done by means of controlled partial oxidation of the silicon skeleton followed by selective removal of the oxide film in an HF vapor phase etching process. Due to this, porosities beyond 90% are accessible since any further liquid phase contact is avoided and therefore no additional drying steps are necessary.