Low‐temperature wafer direct bonding is considered a key tool for the fabrication of bulk micromechanic devices. The possibility of enhancing the bonding energy by applying an O2 plasma treatment before bonding has been the focus of recent studies. Here, the effect of storage following the plasma treatment, as well as the duration of the latter on the attainable activation of the surface, the bonding strength, and bubble generation, have been investigated. Immediately after the plasma treatment bond energies up to 1.6J/m2 are achieved. However, 50 h after the treatment bonded wafer pairs show bonding energies up to only 1.3J/m2 . The duration of the plasma treatment strongly affects the number, size, and distribution of interface bubbles. © 2000 The Electrochemical Society. All rights reserved.

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The effect of plasma pretreatments (reactive ion etching in SF6 and SF6/O2) on Si/Si wafer direct bonding was investigated. Etching in SF6 caused a bonding behaviour generally known from hydrophobic (HF etched) samples, whereas adding O2 to the feed gas caused the Si(100) surfaces to become hydrophilic and spontaneous bonding was achieved. The structure of the bonded interfaces were analysed by high‐resolution electron microscopy, ellipsometry, multiple internal reflection spectroscopy, and secondary ion mass spectroscopy. All the plasma treatments result in an interface structure analogous to that known from bonded hydrophobic wafer pairs. The interface does not involve an additional layer such as an SiO2 or an amorphous Si layer but small one‐dimensional defects forming a disturbed layer about 1 to 2 nm thick.

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