Micro and Nano Fabrication by Hans H. Gatzen Volker Saile & Jürg Leuthold

Author:Hans H. Gatzen, Volker Saile & Jürg Leuthold
Language: eng
Format: epub
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

4.3.4.3 Deep Reactive Ion Etching (DRIE)

Deep reactive ion etching (DRIE ) are processes for etching deep channels with vertical sidewalls into silicon, independently of crystal orientation (like location of {111} planes). One version is a room temperature vacuum process called “Bosch process ” (alternative names are “pulsed process” or “time multiplexed process”) [79]. It was invented by Lärmer and Urban (née Schilp) in 1994 working at Robert Bosch Corporate Research [80]. It was further refined in 1999 by the inventors [81], who were honored by receiving the European Inventor Award of the year 2007 in the category “Industry” [82]. The process is the basis for a multitude of sensors.

An even older alternative is called “Cryogenic DRIE ”, due to its low process temperatures [79, 83]. Both DRIE processes depend on inductively coupled fluorine plasmas for etching and sidewall passivation to enhance directionality. While the Bosch process alters between passivation steps and etching steps, during the cryostatic process passivation and etching occur simultaneously.

Bosch process: Fig. 4.43 depicts the Bosch process sequence. It starts with a microchannel already etched to a certain depth by previous etch cycles. The microchannel location is defined by a photoresist mask.

Fig. 4.43Schematic representation of the DRIE Bosch process. a Deposition process: dissociated C4F8 creates CF2 polymer film. b First etch process: removal of the polymer layer at the bottom of the microchannel due to ion bombardment. c Second etch process: isotropic etching of Si by F radicals at the microchannel’s bottom

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