Evaluation of Titanium Direct Bonding Mechanism

Direct metal bonding represents an advanced joining technology that allows vertical stacking with electrical conduction and even heat dissipation. For most metals used as bonding layers, direct bonding when operating at ambient air involves metal oxides. The bonding interface saddles with a trapped oxide layer that might affect electrical conduction and even complete sealing of bonding interface. Titanium especially, because of its high affinity with oxygen, makes oxide free direct bonding very difficult. In the mean time, the remarkable getter effect of Ti matrix allows the dissolution of oxygen during post bonding annealing. In this paper, the bonding limits with regards to the titanium thickness have been investigated. The key role of layer roughness on the bonding quality and energy has been pointed out. A titanium thickness below 10nm appears as a limit for an oxide free bonding.