The method of pre-bonding and second bonding based on Mo/Au metal adhesion layers for the application of chips bonding

In order to improve bonding quality, a method of pre-bonding and second bonding based on Mo/Au metal adhesion layers was implemented to bond two semiconductor chips. After sputtering Mo/Au thin film on the substrates, two chips taken out from magnetron sputtering were first brought into contact with each other and applied to a pressure of 20 N, which is called pre-bonding. Then a pressure of 2000 N was applied to complete second bonding by using a wafer bonding machine. Pre-bonding and second bonding were both carried out at room temperature and atmospheric environment. The results indicate this method can significantly reduce void density, and a Mo/Au (10 nm/30 nm) nano-adhesion layer can achieve extremely low void density (0.3 %) after this bonding process, also, the original grain boundaries at Au/Au bonding interface have disappeared. While without pre-bonding, more bonding voids were found in the interface, with a minimum size of approximately 40 nm. And a nano-gap (∼2 nm) was clearly observed between the two bonding voids with transmission electron microscope, indicating that Au and Au bonding surfaces were not completely bonded together.