Effects of trace levels of Ge transferred to Si surfaces during thermal processing of SiGe wafers are presented here. Si wafers were coprocessed in an oxidation furnace with SiGe relaxed graded buffer layers grown on Si. Total X-ray fluorescence measurements on Si wafers showed Ge concentrations in varying degrees depending on oxidation temperature, time, and the number of coprocessed SiGe wafers. The Ge concentration level increases with increase of oxidation time, temperature, and SiGe wafer quantity. It was also observed that the furnace shows "memory" of the process during subsequent process runs. A chlorine-based purge of the oxidation tube after processing SiGe wafers helps reduce the Ge concentration remarkably. Metal oxide semiconductor capacitance and gate leakage characterization were used to evaluate the effects of transferred Ge on the gate oxide. The interface state density is marginally higher on Si wafers with transferred Ge. © 2003 The Electrochemical Society. All rights reserved.
The technical potential of room temperature bonding of wafers in vacuum using amorphous Si (a-Si) and Ge (a-Ge) films was studied. Transmission electron microscopy images revealed no interface corresponding to the original films surfaces for bonded a–Ge–a–Ge films. Analyses of film structure and the surface free energy at the bonded interface revealed higher bonding potential at the connected a–Ge–a–Ge interface than that of a–Si films. The electrical resistivity of a-Ge films is 0.62 Ωm, which is lower than that of a-Si film (4.7 Ωm), but 7–8 order higher than that of representative material films used for bonding in vacuum. Our results indicate that room temperature bonding using a–Ge films is useful to bond wafers without any marked influence on the electrical properties of devices on wafer surfaces caused by the electrical conductivity of films used for bonding.
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