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Bonding and Deep RIE - A powerful combination for high aspect ratio sensors and actuators

: Hiller, K.; Küchler, M.; Billep, D.; Schröter, B.; Dienel, M.; Scheibner, D.; Gessner, T.


Maher, M.-A. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Micromachining and Microfabrication Process Technology X : 25 - 27 January 2005, San Jose, California, USA
Bellingham, Wash.: SPIE, 2005 (SPIE Proceedings Series 5715)
ISBN: 0-8194-5689-6
Conference on Micromachining and Microfabrication Process Technology <10, 2005, San Jose/Calif.>
Fraunhofer IZM ()
Fraunhofer ENAS ()

In this paper we present the very promising results for two methods of the so-called Bonding and Deep RIE (BDRIE) technology, characterised by bonding of two wafers with pre-patterned vertical gaps and subsequent RIE trench etching of the active layer. In case of the anodically bonded silicon-glass compound detection electrodes for vertical movement are integrated. The silicon layer contains the movable structure as well as drive and detection electrodes for lateral movement. It is advantageous that finally the mechanical active elements consist of single crystalline silicon without any additional layers. The BDRIE approach allows a great variation of parameters. The active layer thickness can be defined due to application issues. Our examples show active layers thickness ranging from 30 up to 200 m, patterned by dry etching steps with maximum aspect ratio between 20:1 and 30:1. Structures with trench width variations of more than 50 (widest/smallest trench) have been f abricated successfully. Methods and results of preventing notching and backside etching of the active layer are presented as well. The size of the vertical gap can be as small as 1.5 m for a very sensitive detection or several tens or hundreds of microns in order to reduce damping and parasitic capacitance. Holes for release in the movable structure are not necessary and will therefore not restrict the design. However, restrictions are given by the minimum size of bond area and the relation between layer thickness, free standing area above the groove and bond pressure, which are discussed within the paper. Applications of BDRIE are inertial sensors like gyroscopes, step-by-step switchgears as well as micro mirrors.