Low temperature transfer bonding for MEMS. Utilizing and characterizing oxygen plasma assisted direct wafer bonding

Licentiatavhandling, 2006

Transfer bonding enables the integration of devices, e.g. integrated circuits (ICs) and transducers, fabricated using processes and/or designs that are not compatible with each other as well as double sided micromachining of thin films. This thesis presents a low temperature transfer process capable of transferring single crystalline silicon structures of a few μm2 using oxygen plasma assisted bonding. The transfer process can for example be used to integrate microelectromechanical systems with electronics fabricated on separate substrates. Further a test method for adhesion quantification of very small bonded areas is presented. Adhesion quantification samples using the presented transfer process have been fabricated and the fracture toughness of the bond interfaces have been successfully measured with high spatial resolution using an ordinary surface profiler. The average fracture toughness of the measured samples is in close accordance with values measured using the double cantilever beam method. The presented method enables investigations of very small bonded interfaces creating the possibility to gather information of the bond quality with high spatial resolution.