Microscopy and Electrical Properties of Ge/Ge Interfaces Bonded by Surface-Activated Wafer Bonding Technology

We have performed microscopy and electric measurements of the Ge/Ge interfaces bonded by surface-activated wafer bonding (SAB) technology. Similarly to the case of Si wafer bonding, two Ge wafers of 50 mm in diameter, both doped by Ga with a concentration of $2.2\times 10^{14}$ cm -3 , were bonded by SAB at room temperature. The SAB process was performed in a high-vacuum chamber ($10^{-4}$ Pa) at room temperature. The bonding was achieved by attaching and pressing the two wafers, the contact surfaces of which were activated by argon ion beam irradiation. The cross-sectional scanning electron microscopy (SEM) image of the Ge/Ge bonded sample apparently shows an interface that seems to be caused by crystallographic discontinuity. The measurement by transmission electron microscope (TEM) reveals an atomic-disordered layer structure of about 3 nm in thickness at the interface of the bonded Ge/Ge. The resistivity of bonded Ge/Ge samples across the interfaces was measured at 300 and 77 K. As compared with the result of similar measurements for non bonded bulk Ge samples, we find no significant difference in resistivity between the bulk Ge and bonded Ge/Ge samples.