Formation of passivation and adhesion layers for Cu via nitridation of Cu-Ti in an ammonia ambient

Passivation and adhesion layers for Cu have been formed by nitridation of Cu(90 nm)/Ti(20 nm)/SiO₂(90 nm) bilayers and 163 nm thick Cu(Ti 27 at.%) alloys at 400-700 °C for 30 min in an ammonia ambient. In both systems Ti segregated during annealing to the free surface to react with the NH₃ and formed an oxygen-rich Ti nitride passivation layer. The thickness of these layers was ∼ 12 nm for the bilayers and ∼ 20 nm for the alloys. Evaluation of the Ti nitride surface layers as diffusion barriers for Al and Cu showed stability up to 500 °C. The interfacial reaction between Ti and SiO₂ substrate resulted in the formation of a Ti₅Si₃/TiO_w structure. Adhesion results obtained from a scratch test showed that the bilayers exhibited good adhesion in the as-deposited state and were stable up to 400 °C, but displayed only fair adhesion above that temperature. The alloys exhibited poor to fair adhesion in the as-deposited condition and at 400 °C, but adhesion improved considerably after a 500 °C anneal. The behavior of the adhesion properties of both the bilayer and alloy system were related to the interfacial reaction.