Abstract: Eutectic Au-12Ge solder was employed to bond the SiC power devices to a Si₃N₄/Cu/Ni(P)/Au multi-layered substrate. The high-temperature reliability of the bond was investigated in detail at 200, 250, 300 and 330 °C, respectively. NiGe and Ni₅Ge₃ intermetallic compounds (IMCs) were identified at the Au-12Ge/Ni(P) interface by micro X-ray diffraction (μXRD) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDX). The growth of the Ni-Ge IMCs was dominated by Ni₅Ge₃ layer, which formed at the Ni₅Ge₃/NiGe interface by outward diffusion of Ni from the Ni(P) layer. The activation energy of the total Ni-Ge IMCs growth was 66 kJ/mol. The shear strength of the bond was tested at both 25 °C and the aging temperatures, respectively. The shear strength decreased slightly after aging at 200 and 250 °C. The shear strength tested at 250 °C was 46 MPa after aging at 250 °C for 3000 h. The shear strength aged at 300 and 330 °C rapidly decreased with aging time due to the rapid growth of the Ni₅Ge₃ IMC. To slow down the interfacial reaction between the high temperature solder and the Ni(P) layer, an approximately 200 nm-thick Ta/TaN/Ta new diffusion barrier (DB) was deposited on the substrate. Analysis by transmission electron microscopy (TEM) equipped with EDX, reveals that the Ta/TaN/Ta DB was bonded well to the Ni(P) layer and the solder. High temperature storage test at 330 °C for 1500 h reveals that the bond of the SiC devices maintained its high shear strength of approximately 56 MPa without decrease. The new DB effectively suppressed the interfacial reaction between the Au-12Ge solder and the Ni(P) layer of the substrate.

Key words: High-temperature solder, Interfacial reaction, Activation energy, Kinetics, Diffusion barrier, Reliability