Solid-State Interfacial Reaction between Eutectic Au−Ge Solder and Cu/Ni(P)/Au Metalized Ceramic Substrate and Its Suppression

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.