Time-dependent surface properties and wafer bonding of O2-plasma-treated sillicon (100) surfaces

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 O-2 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 1.6 J/m(2) are achieved. However, 50 h after the treatment bonded wafer pairs show bonding energies up to only 1.3 J/m(2). The duration of the plasma treatment strongly affects the number, size, and distribution of interface bubbles. (C) 2000 The Electrochemical Society. S0013-4651(99)08-103-3. All rights reserved.