Formation of titanium nitride by annealing Ag/Ti structures in ammonia ambient

Titanium nitride thin films have been formed in the temperature range of 400-600 °C by annealing Ag/Ti bilayer films on oxidized Si substrates in an ammonia ambient. Rutherford backscattering spectrometry and Auger depth profiling have shown the segregation of Ti at the surface and at interface. Ti diffused out through the silver layer and reacted with ammonia to form a TiN layer that self-encapsulated the silver film. A near-bamboo structure in the encapsulated Ag films was observed using cross-sectional transmission electron microscopy. Such a structure is expected to improve the electromigration resistance of the silver metallization. The kinetics of the Ti-nitride growth was studied by investigating its dependence on time, temperature, and Ag/Ti bilayer thicknesses. We also found that two processes govern the nitridation reaction. A dominant nitridation process takes place initially at fast growth rates. After 15 min anneals the nitride growth can be described by x² = B t, where B is a parabolic rate constant for the growing nitride phase. The parabolic rate constants follow an Arrhenius behavior with an apparent activation energy of ∼0.4 eV. These observations led to further discussion regarding the diffusion mechanism as well as the rate-limiting step.