SOI material by wafer bonding: an overview

In wafer bonding work directed toward SOI (silicon-on-insulator) technology, an insulating material, usually SiO₂, present on one or both silicon wafers is sandwiched between the wafers upon bonding. Subsequent thinning of one of the wafers produces a monocrystalline film of desirable thickness separated from the substrate by the insulator. A method based on the theory of crack propagation has been devised to quantitatively study the bonded interface. In the particular case of oxidized silicon wafers, the bonding exhibits three different phases: a hydrogen-bond process dominates low temperature bonding; Si-O-Si bond formation accompanied by elastic wafer deformation occurs at the intermediate temperatures; and Si-O-Si bond formation is supported by plastic flow of the oxide at the highest temperatures. For most of the wafer bonding applications a controlled thinning of one of the wafers in the pair is required for the formation of a device film