Direct bonding of Cu to oxidized silicon nitride by wetting of molten Cu and Cu(O) |
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Authors: | Shun-Ichiro Tanaka |
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Affiliation: | (1) Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan |
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Abstract: | When pressureless sintered silicon nitride with the main additives Y2O3 and Al2O3, having a thermal conductivity K = 20 W/m K, was oxidized at 1240–1360 °C in still air, the resulting surface oxide layer easily bonded to a copper plate
in the temperature region between 1065 and 1083 °C, and in the oxygen concentration range of 0.008–0.39 wt%, as shown in a
Cu–O phase diagram. The oxide on the silicon nitride was characterized as Y2O3·2SiO2 and mixed silicate glass with additives and impurities that diffused through the grain boundary. The bonding strength of
Cu/Si3N4 depends on the amount or layer thickness of silicate glass and reaches as high as 100 MPa by shear at room temperature. Detailed
analysis of the oxidation layer and the peeled-off surfaces of directly bonded Si3N4/Cu reveal that the main mechanism of bonding is wetting to glassy silicate phase by mixtures of molten Cu and α-solid solution
Cu(O), which solidify to α + Cu2O below 1065 °C by a eutectic reaction. The direct reactive wetting of molten Cu, supplied from the grain boundary of a Cu
plate, on the glassy phase enables very tight chemical bonding via oxygen atoms. |
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