Titanium-nitride self-encapsulation of Cu and Ag films on silicon dioxide

Encapsulation of Ag and Cu films via Ti nitridation of Ag(Ti) and Cu(Ti) alloy systems in an ammonia ambient has been investigated. Silver- and copper-titanium alloys on silicon dioxide of compositions varying from 4 to 27 at.% Ti were annealed at temperatures between 350°C and 700°C, for durations of 10-120 min in a flowing NH₃ ambient. Annealing of the Ag(Ti) and Cu(Ti) alloys at temperatures ≥400°C, resulted in segregation of Ti to the surface to form a TiN(O) encapsulation layer and to the alloy/SiO₂ interface. At the interface, Ti reacted with the SiO₂ to form a TiO/Ti₅Si₃ bilayer structure. Kinetic studies showed that Ti reactions take place within the first 10 min. This self-limiting behavior occurs for all annealing temperatures, but the encapsulation reaction increases with temperature. Four-point probe analysis of the alloy films suggests that the resistivity is controlled by the residual Ti concentration. Comparable resistivity values were obtained for Ag and Cu in the composition range considered. Resistivity values of ∼2.6 μΩ-cm were measured in encapsulated Ag films with initial low Ti concentrations after nitridation at 600°C.