Oxidation and Induced Damage in Oxygen Plasma In Situ Wafer Bonding

Abstract

In this paper we present our in situ, oxygen plasma‐activated wafer bonding process. By keeping one wafer on the anode and the other on the cathode, we have an asymmetric plasma load on the wafers, making our bonding process interesting for low‐temperature applications where damage or defect‐sensitive active layers are bonded to less sensitive carrier wafers. As a step in optimizing the discharge parameters for plasma bonding applications, the effect of the self‐bias voltage on surface energy, oxidation rates, and damage is investigated. An optimum in surface energy was found at moderate self‐bias voltages, both at room temperature bonding and after low‐temperature annealing at 200°C. This is explained by the fact that at these voltages there is a minimum oxide thickness, which promotes the diffusion of water from the bond interface, and also by the fact that at these voltages we have the best surface cleaning conditions. Also, the surface oxide generated by the oxygen plasma seems to be reactive. With our in situ oxygen‐plasma‐activated wafer bonding process there was a major increase in surface energy for wafers bonded at moderate self‐bias volt‐ages compared to conventional wafer bonding performed in ambient air. © 2000 The Electrochemical Society. All rights reserved.