Influence Of Applied Load On Wafer Bonding In Vacuum

Low temperature direct wafer bonding was performed in vacuum. Different loads were applied during bonding processes. In all cases, the bond strength is above 19 MPa, which is high enough for practical applications. More interestingly, in contrast to the findings by others, we found that the applied load does play a very important role in wafer bonding, the higher the applied load, the lower the bond strength. The bonded wafers were examined by means of scanning acoustic microscope (SAM). It was found that both the bubble size and bubble number increase with an increase in applied load. This phenomenon is contributed to the applied load. High applied force keeps two wafer surfaces in tight contact. If there is any gas trapped during bonding process, such as hydrogen and water molecules, the tight contact prevents them from escaping out of the bonding interfaces, which results in the low bond strength. It also can be explained by one low temperature direct wafer bonding model.