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Fabrication of large-scale mono-crystalline silicon micro-mirror arrays using adhesive wafer transfer bonding

: Zimmer, F.; Niklaus, F.; Lapisa, M.; Ludewig, T.; Bring, M.; Friedrichs, M.; Bakke, T.; Schenk, H.; Wijngaart, W. van der


Dickensheets, D.L. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
MOEMS and miniaturized systems VIII : 27 - 28 January 2009, San Jose, California, USA
Bellingham, WA: SPIE, 2009 (SPIE Proceedings Series 7208)
ISBN: 978-0-8194-7454-4
ISSN: 0277-786X
Paper 720807
Conference "MOEMS and Miniaturized Systems" <8, 2009, San Jose/Calif.>
Fraunhofer IPMS ()
optical MEMS; micro mirror; spatial light modulator

Today, spatial light modulators (SLMs) based on individually addressable micro-mirrors play an important role for use in DUV lithography and adaptive optics. Especially the mirror planarity and stability are important issues for these applications. Mono-crystalline silicon as mirror material offers a great possibility to combine the perfect surface with the good mechanical properties of the crystalline material. Nevertheless, the challenge is the integration of mono-crystalline silicon in a CMOS process with low temperature budget (below 450°C) and restricted material options. Thus, standard processes like epitaxial growth or re-crystallization of poly-silicon cannot be used. We will present a CMOS-compatible approach, using adhesive wafer transfer bonding with Benzocyclobutene (BCB) of a 300nm thin silicon membrane, located on a SOI-donor wafer. After the bond process, the SOI-donor wafer is grinded and spin etched to remove the handle silicon and the buried oxide layer, which results in a transfer of the mono-crystalline silicon membrane to the CMOS wafer. This technology is fully compatible for integration in a CMOS process, in order to fabricate SLMs, consisting of one million individually addressable mono-crystalline silicon micro-mirrors. The mirrors, presented here, have a size of 16 x 16 ?m². Deflection is achieved by applying a voltage between the mirrors and the underlying electrodes of the CMOS electronics. In this paper, we will present the fabrication process as well as first investigations of the mirror properties.