(Invited) Surface Activated Wafer Bonding; Principle and Current Status

The surface activated bonding (SAB) is a method which achieves strong bonding at room temperature. It is assumed that at the bonding interface prepared by SAB atoms bind to each other by the same interatomic bonds with those in bulk materials, such as covalent bond, metallic bond, etc. SAB well matches the wafer direct bonding, because intimate contact at the bonding interface is spontaneously achieved by the attractive force between very smooth wafer surfaces. In SAB, the surfaces of bonded materials are sputter-etched, in other word “cleaned”, before bonding. Various materials, such as semiconductor wafers, single crystal oxide wafers, metal films on wafers, etc. has been successfully bonded. Recently, other surface treatments have been proposed to apply SAB to wide variety of materials. SAB has been used to fabricate integrated substrates for RF-filters for more than 10 years, and has been already applied in MEMS packaging in industry. Other applications, such as power semiconductors, solar cells, etc. are now extensively developed.