Heterogeneous silicon integration by ultra-high vacuum wafer bonding

Heterogeneous integration of technologically important materials, such as SiC/Si, GaN/Si, Ge/Si, Si/nano-Si/Si, SiC-on-insulator (SiCOI), and ZrO₂/SiO₂/Si, was successfully made by ultra-high vacuum (UHV) wafer bonding. A unique, UHV bonding unit, especially designed to control interface structure, chemistry, and crystallographic orientation within narrow limits, was used to produce homophase and heterophase planar interfaces. In-situ thin-film-deposition capability in conjunction with the wafer bonding offered even more flexibility for producing integrated artificial structures. Prebonding surface preparation was critically important for the formation of strong bonded interfaces. The substrate-surface morphology was examined by atomic-force microscopy (AFM) prior to bonding. In-situ Auger spectroscopy measurements of surface chemistry were invaluable predictors of bonding behaviors. Plasma processing very effectively cleaned the substrates, achieving a near-perfect interfacial bond at the atomic scale. The integrity of the bonded interfaces was studied in the light of their structural and chemical characteristics analyzed by high-resolution, analytical electron microscopy.