Improving the reliability of eutectic bonding vertical power light-emitting diodes by a Mo buffer layer

Abstract

As a major step in the conduction of heat dissipation, wafer bonding significantly contributes to device reliability. This work presents the Cu–Sn eutectic bonding with a Mo buffer layer for light emitting diodes to increase its reliability. The conventional Ag-paste bonding and Cu–Sn bonding (without Mo top layer) are also studied for comparison. Their reliability is measured using thermal shock treatments ranging from −40 to 120°C (200cycles). Experimental results indicate that the eutectic bonding with a Mo buffer layer demonstrates a better device performance than the other two counterparts. Following thermal shock treatment, the light droops for the Ag-paste, Cu–Sn, and Mo/Cu–Sn bonding samples are 15, 11 and 7%, respectively. Additionally, the increasing ratios of thermal resistance are 26, 33 and 19%, respectively. Moreover, adding the Mo buffer layer can relieve the thermal stress problem, owing to the thermal expansion mismatch in Gallium–Nitride/Cu–Sn/submount wafer bonding structures.