Modification of Si(100)-surfaces by SF6 plasma etching - Application to wafer direct bonding

The effect of plasma pretreatments (reactive ion etching in SF6 and SF6/O-2 ) on Si/Si wafer direct bonding was investigated. Etching in SF6 caused a b onding behaviour generally known from hydrophobic (HF etched) samples, wher eas adding O-2 to the feed gas caused the Si(100) surfaces to become hydrop hilic and spontaneous bonding was achieved. The structure of the bonded int erfaces were analysed by high-resolution electron microscopy, ellipsometry, multiple internal reflection spectroscopy, and secondary ion mass spectros copy. All the plasma treatments result in an interface structure analogous to that known from bonded hydrophobic wafer pairs. The interface does not i nvolve an additional layer such as an SiO2 or an amorphous Si layer but sma ll one-dimensional defects forming a disturbed layer about 1 to 2 nm thick.