Low-Temperature Titanium-Based Wafer Bonding

Low-temperature Ti-based wafer bonding and its mechanisms have been investigated, namely, , , and bonding. The bonding is carried out at with down-force for 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 bonding is based on a solid-state amorphization at , whereas bonding is attributed to an interfacial reduction reaction. In bonding, migration of Ti leads to significant grain extrusion across the bonding interface. A double bonding/thinning process, including both - and -based wafer bonding at back-end-of-the-line conditions, has been demonstrated on patterned wafers.