Wafer Level Hermetic Bonding Using Sn/In and Cu/Ti/Au Metallization

A low temperature hermetic wafer bonding using In/Sn interlayer and Cu/Ti/Au metallization was investigated for MEMS and sensor packaging application. Bonding was performed in a vacuum wafer bonder at 180°C and 150°C for 20 min under 5.5 MPa. It is found that bonding at 180°C, voids free joints composed of high temperature intermetallic compounds (IMCs) were obtained with good hermeticity and reliability. However, bonding at 150°C, voids were generated along the seal joint which caused poor hermeticity comparing with that bonded at 180°C. After four kinds of reliability tests, i. e., Pressure cooker test, high humidity storage, high temperature storage, temperature cycling test, dies bonded at 180°C showed good reliability properties by hermeticity test and shear tests. Present results proved that high yield and low temperature hermetic bonding can be achieved by using Sn/In/Cu metallization with thin Ti as a buffer layer.