16 years after the registration of the method of anisotropically etching silicon, it is unconceivable to think about low-cost production of MEMS products without using the Bosch process. After presenting which brains lie behind the Bosch process, this article describes briefly what the patent presents.

Who is behind the "Bosch process" ?

On November 27^th 1993, Franz Lärmer and Andrea Urban (born Schilp) published the patent while working at Robert Bosch GmbH. Hereafter is a list of the full text patent in different versions:

• the original patent: EP0625285A1 (in German)
• the revised patent: EP0625282B1 (in German, English and French)
• the US version: US5501893 (in American English)

Method of anisotropically etching silicon

At the time, etching silicon was mainly realised with steady-state processes. However these processes are not well suited for deep silicon etching. Indeed, compared with the time-multiplexed gas-multiplexed process invented by Lärmer and Urban, these processes have low selectivity to mask, low max aspect ratio and create a huge notching whilst reaching an oxide stop layer.

The patent describes how to obtain vertical walls.