Cu-Cu direct bonding in air by in-situ reduction of copper oxide with glycerol

With the maximum operating temperature of semiconductor devices becomes higher, novel die attach methods for high temperature application are required. Cu-Cu direct bonding provides a simple solution that eliminates the use of die attach materials and the related reliability issues. However, the easy oxidation of copper is the main obstacle for Cu-Cu direct bonding. In this study, a simple and efficient method for Cu-Cu direct bonding in minutes at low pressure and low temperature in air without complex pre-treatment was developed. The problem of copper oxidation was solved by rapid in-situ reduction and temporary passivation of glycerol. The bonded samples show very high shear strength. The surface leveling effect of the glycerol reduction was verified, which is beneficial for bonding. The bonded samples showed little change in shear strength after 1000 h of aging at 250 degrees C in air, demonstrating a long-term high temperature service capability. This new bonding method has great potential in power devices packaging and flip chip bonding.