Low temperature glass-to-glass wafer bonding

In this paper, results of successful anodic bonding between glass wafers at low temperature are reported. Prior to bonding, a special technique was used, i.e., an amorphous and hydrogen free silicon film was deposited on one of the glass wafers using a sputtering technique. The effects of bonding temperature and voltage were investigated. The bonding temperature and the voltage applied ranged from 200°C to 300°C and 200 V to 1000 V, respectively. As the bonding temperature and bonding voltage increased, both the unbonded area and the size of voids decreased. Scanning electron microscope (SEM) observations show that the two glass wafers are tightly bonded. The bond strength is higher than 10 MPa for all the bonding conditions. Furthermore, the bond strength increases with increasing bonding temperature and voltage. The study indicates that high temperature and voltage cause more Na⁺ ions to neutralize at the negative electrode, which leads to higher charge density inside the glass wafer. Furthermore, the transition period to the equilibrium state also becomes shorter. It is concluded that the anodic bonding mechanisms involve both oxidation of silicon film and the hydrogen bonding between hydroxyl groups.