Improvement in Joint Reliability of SiC Power Devices by a Diffusion Barrier Between Au-Ge Solder and Cu/Ni(P)-Metalized Ceramic Substrates

The long-term joint reliability of SiC power devices bonded on a ceramic substrate metalized with copper (Cu) and electroless nickel-phosphorus [Ni(P)] using a gold-germanium (Au-Ge) eutectic solder was investigated at 330°C in air. Rapid growth of Ni-Ge intermetallic compounds (IMCs) at the solder/Ni(P) interface and subsequent oxidation of the conductive Cu layer at the IMCs/Cu interface led to a dramatic decrease in bond strength and an increase in the electrical resistance of the joint. To improve the joint reliability, a 250-nm-thick tungsten (W) diffusion barrier (DB) was prepared on the surface of the substrate using a sputtering process. SiC Schottky barrier diode (SBD) power devices were then die-bonded to the W-DB-modified substrate with the Au-Ge eutectic solder using a vacuum reflow system. The bonded samples were aged at 330°C in air. After 1600 h, the joint strength was two times higher than that on the W-DB-free substrate, and no change was observed in the electrical resistance.