Low-temperature titanium-based wafer bonding Ti/Si, Ti/SiO2, and Ti/Ti

Low-temperature Ti-based wafer bonding and its mechanisms have been investigated, namely, Ti/Si, Ti/SiO2, and Ti/Ti bonding. The bonding is carried out at 400 deg C with 10 kN down-force for 2 h in vacuum. Nearly void-free bonding and strong mechanical integrity were obtained in all three cases. Interfacial characterization by Auger electron spectroscopy and transmission electron microscopy indicates that Ti/Si bonding is based on a solid-state amorphization at 400 deg C, whereas Ti/SiO2 bonding is attributed to an interfacial reduction reaction. In Ti/Ti bonding, migration of Ti leads to significant grain extrusion across the bonding interface. A double bonding/thinning process, including both Ti/Si- and Ti/SiO2-based wafer bonding at back-end-of-the-line conditions, has been demonstrated on patterned wafers.