부산대학교 도서관

Low-temperature hermetic wafer bonding using In/Sn interlayer and Cu/Ti/Au metallization was investigated for microelectromechanical systems packaging application. In this case, the thin Ti layer was used as a buffer layer to prevent the diffusion between solder interlayer and Cu after deposition and to save more solders for diffusion bonding process. Bonding was performed in a wafer bonder at 180 and 150$\; ^{\circ}$C for 20 min with a pressure of 5.5 MPa. It was found that bonding at 180$\; ^{\circ}$ C voids free seal joints composed of high-temperature intermetallic compounds were obtained with good hermeticity. However, with bonding at 150$\; ^{\circ}$C, voids were generated along the seal joint, which caused poor hermeticity compared with that bonded at 180$\; ^{\circ}$C. After four types of reliability tests—pressure cooker test, high humidity storage, high-temperature storage, and temperature cycling test—dies bonded at 180$\; ^{\circ}$C showed good reliability properties evidenced by hermeticity test and shear tests. Results presented here prove that high-yield and low-temperature hermetic bonding using Sn/In/Cu metallization with thin Ti buffer layer can be achieved.