Spreading and interlayer formation at the copper-copper oxide/polycrystalline alumina interface

Abstract

Spreadability and reaction layer growth rates of copper-oxygen alloys on polycrystalline alumina were measured above the melting point of copper to better understand the direct bonding process. Spreading was measured as a function of composition and temperature by monitoring the diameter of molten droplets as a function of time. As the oxygen content of the melt increased from 0 to 3 wt pct, the spreading diameter increased linearly, at fixed time and temperature. Constant diameters were observed for oxygen compositions between approximately 3 and 6 wt pct. The diameters again increased linearly for oxygen concentrations greater than 7 wt pct. This behavior was explained by reference to the copper-oxygen binary phase equilibrium. An interfacial product was identified to be the complex oxide, CuA102. A detailed investigation of the interlayer growth kinetics was performed to understand the fundamental phenomena controlling the spreading rates. The growth rate of the CuAlO2 phase and the spreading rate were simultaneously measured for alumina in contact with a copper-2 wt pct oxygen alloy drop as a function of temperature. The reaction layer thickening was found to be diffusion controlled, with an apparent activation energy of 309 kJ/mol, and the spreading rate did not correlate with the thickening rate.