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

• Eutectic bonding with a Mo buffer layer is investigated in Cu–Sn eutectic bonding.
• Thermal shock treatments (− 40–120 °C, 200 cycles) were used to test reliability.
• Light droop for the Ag-paste, Cu–Sn, and Mo/Cu–Sn bonding was ~ 15, 11 and 7%.
• A Mo buffer layer can effectively relieve thermal stress.

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 (200 cycles). 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.