Oxidation and induced damage in oxygen plasma in situ wafer bonding

In this paper we present our in silt, oxygen plasma-activated wafer bonding process. By keeping one wafer on the anode and the other on the cathode, w e have an asymmetric plasma load on the wafers, making our bonding process interesting for low-temperature applications where damage or defect-sensiti ve active layers are bonded to less sensitive carrier wafers. As a step in optimizing the discharge parameters for plasma bonding applications, the ef fect of the self-bias voltage on surface energy, oxidation rates, and damag e is investigated. An optimum in surface energy was found at moderate self- bias voltages, both at room temperature bonding and after low-temperature a nnealing at 200 degrees C. This is explained by the fact that at these volt ages there is a minimum oxide thickness, which promotes the diffusion of wa ter from the bond interface, and also by the fact that at these voltages we have the best surface cleaning conditions. Also, the surface oxide generat ed by the oxygen plasma seems to be reactive. With our in situ oxygen-plasm a-activated wafer bonding process there was a major increase in surface ene rgy for wafers bonded at moderate self-bias voltages compared to convention al wafer bonding performed in ambient air. (C) 2000 The Electrochemical Soc iety.