Pulse-Field-Assisted Wafer Bonding for Silicon on Insulator

We have developed a pulse-field-assisted bonding technique to give void-free, low-temperature wafer bonding for SOI (silicon on insulator). We bonded a pair of oxided wafers by applying pulses of a few hundred volts across the wafers at 800°C in a 0.1 Pa nitrogen ambient. To reduce the volatile materials on the surfaces of wafers, which cause voids at low temperature, we heated the wafers at reduced pressure. The impulsive electrostatic force deforms the insulating oxide and allows bonding despite surface roughness and wafer warpage. Our pulse-field-assisted bonding reduces both the bonding temperature and time. We obtained a bond strength of over 1700 kgf/cm2after thermal treatment at 800°C for 1 min. This paper also discusses surface roughness, voids, and bond strength.