Low temperature direct bonding for hermetic wafer level packaging

A novel hermetic wafer level packaging technology is presented in this paper, which was realized by the aid of low temperature direct bonding. One silicon wafer with etched cavities and the other bare wafer, which acted as cover and substrate respectively, were bonded to demonstrate the feasibility of this technology. The bonding surfaces of both wafers were activated hydrophilically by a series of wet chemical treatments and the data of contact angle measurement showed the activating process was efficient. After prebonding and annealing in 350deg for 5 hours, the hermeticity and bonding strength of the cavities in bonded wafers were evaluated. The average hermetic performance was 1.175times10^-8Paldrm³/s and strength was 7.8Mpa.