In this paper, we have presented the novel method of fabricating multiplayer-stacked SOI (MultiBond). Tight thickness and TTV control was achieved, which allowed the bonding of multiple layers of SOI of up to 4-layer stacks. Investigation of the stress showed that having the handle wafer oxidized at the back significantly reduced the stress by compensating for the buried oxide layers. Study was also made on the effect of incorporating different buried layers on the minority carrier lifetime in the SOI layer. Here, a thermally grown buried oxide layer gave the highest carrier lifetime. We have also investigated the surface defect density with different buried layer materials, and found that samples with tungsten silicide as a buried layer had the highest defect density, while an LPCVD TEOS oxide buried layer showed the lowest level.

In this work we have used a range of, electrical and physical characterisation techniques to assess the joined interface for hydrophobic direct silicon to silicon fusion bonding and its suitability for a range of applications. The physical characteristics of the bonded interface were analysed using spreading resistance profiling (SRP) measurements, transmission electron microscopy (TEM), and secondary ion mass spectroscopy (SIMS). Simple pn and PIN diode structures were manufactured and forward and reverse bias diode characteristics analysed. Different cleaning regimes used for silicon direct bonding were compared and related to the proposed applications in terms of electrical quality, oxygen gettering, and interface defects. Samples were prepared by joining polished silicon device wafers to polished silicon handles. The joined pairs were annealed at temperatures between 600degreesC and 1200degreesC, and the device wafers thinned by grinding and polishing. The results showed that a high quality bonded interface with good electrical quality and low leakage current at the interface can be obtained with hydrophobic cleaning. Hydrophilic cleaning is easier to implement but limits the electrical quality of the interface due to large oxide islands and thermal donors from interface oxygen. Applications of discrete power, photo-detectors and MEMS devices are discussed. MEMS processing requires the formation of released structures for operation and wafer bonding can provide an alternative to surface micro machining. Cavity bonding and novel structures formed by heavily doped buried layers and different orientations are demonstrated.