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Selective adhesive bonding with SU-8 for zero-level-packaging

: Reuter, D.; Bertz, A.; Schwenzer, G.; Gessner, T.


Chiao, J.-C.; Jamieson, D.N.; Faraone, L.; Dzurak, A.S.:
Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems II : Monday 13 December 2004, Sydney
Bellingham, WA: SPIE, 2005 (Proceedings of SPIE 5650)
ISBN: 0-8194-5610-1
International Symposium on Smart Materials, Nano-, and Micro-Smart Systems <2004, Sydney>
Fraunhofer IZM ()
Fraunhofer ENAS ()

An adhesive bonding technique for wafer-level encapsulation of high aspect ratio microstructures (HARMS) is presented. The adhesive material is spin coated on a cap wafer and structured prior to bonding. Thus sealed cavities of variable height are created in the bonding layer. SU-8 negative photoresist is used as the adhesive material in combination with miscellaneous surface materials: silicon, silicon dioxide and aluminum. The influences of the bonding process parameters - bonding pressure, bonding temperature and process time - as well as the SU-8 layer properties on the bond strength and the homogeneity of the bond have been investigated. To evaluate the process conditions the shear strength of the bond has been measured according to the ASTM standard D 1002 for adhesive bonds. Each bond interface was tested by 32 test specimens of 10 by 10 mm2 side length. With optimal process conditions shear strength of 19.2, 23.3 and 21.3 MPa have been obtained for silicon, sili con dioxide and aluminium respectively. The application of the selective adhesive bonding technique has been successfully demonstrated by encapsulating different types of single crystal silicon inertial sensors.