Eutectic Au-12 Ge solder was employed to bond the SiC power devices to a Si_3N_4/Cu/Ni(P)/Au multilayered substrate.The high-temperature reliability of the bond was investigated in detail at 200,250,300 and 330 ℃,respectively.NiGe and Ni_5Ge_3 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 Ni_5Ge_3 layer,which formed at the Ni_5Ge_3/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 ℃ and the aging temperatures,respectively.The shear strength decreased slightly after aging at 200 and 250 ℃.The shear strength tested at 250 ℃ was 46 MPa after aging at 250 ℃ for 3000 h.The shear strength aged at 300 and 330 ℃ rapidly decreased with aging time due to the rapid growth of the Ni_5Ge_3 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 ℃ for1500 h reveals that the bond of the SiC devices maintained its high shear strength of approximately56 MPa without decrease.The new DB effectively suppressed the interfacial reaction between the Au-12 Ge solder and the Ni(P) layer of the substrate.
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