Mechanistic studies of hydrophilic wafer bonding and Si exfoliation for SOI fabrication

We have undertaken extensive mechanistic studies of both hydrophilic bonding and the hydrogen-induced exfoliation of silicon. We have combined a wide variety of spectroscopic techniques such as IR and Raman spectroscopies, Atomic Force and Transmission Electron Microscopies, as well as mass spectrometry, in order to definitively characterize these systems. We have studied the joining and bonding of oxidized wafers as a function of oxide type/thickness, wet chemical precleaning and annealing temperature. By studying thin chemical oxide layers (~4 Å thick), we have found that the 3-4 monolayers of molecular water trapped at the interface at room temperature, diffuse through the oxide layer and decompose at the Si/SiO₂ interface, resulting in the formation of a highly inhomogeneous, non-stoichiometric ~6-7 Å of additional oxide below 400"C