Ammonium Hydroxide Effect on Low-Temperature Wafer Bonding Energy Enhancement

A wafer prebonding treatment by ammonium hydroxide (NH 4 OH) leading to a high bonding strength at low temperatures is presented in three material systems. After 200°C annealing, a surface energy of about 700 mJ/m 2 for thermal silicon-oxide bonding and of 1300 mJ/m 2 for plasma-enhanced chemical vapor deposition oxide bonding is realized. It is suggested that the lower ability of ammonia, the by-product of a polymerization reaction, to break the siloxane (Si-O-Si) bridging bonds appears to be responsible for the increase in surface energy in both silicon oxide bonding cases. NH 4 OH treatment is also effective on bare germanium/ silicon-oxide bonding with a surface energy of 800 mJ/m 2 . A highly hydrophilic germanium surface obtained by this treatment accounts for the high bonding energy.