SILICON-WAFER DIRECT BONDING WITHOUT HYDROPHILIC NATIVE OXIDES

Silicon wafer direct bonding was accomplished between two surfaces which had no hydrophilic native oxide layers. Prior to bonding, two wafers were dipped in conc-HF solution (similar to 49% aq.) to remove the native oxide layers and then immersed in deionized water. The level of bonding was evaluated by X-ray topography, high resolution transmission electron microscopy (HRTEM) and tensile strength measurement. It was found that the bonded wafer pairs were void-free and had good bonding strength. HRTEM observation showed that the crystal lattice was continuous and had only small distortions and precipitates. Spreading resistance (SR) measurement across the interface showed that the electric resistance did not increase at the bonding interface. It is suggested that the OH groups which substitute the F atoms terminated on the small portion of the surface play an important role in this conc-HF-treated bonding.