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 degrees C by annealing Ag/Ti bilayer films on oxidized Si s ubstrates in an ammonia ambient. Rutherford backscattering spectrometr y and Auger depth profiling have shown the segregation of Ti at the su rface and at interface. Ti diffused out through the silver layer and r eacted with ammonia to form a TiN layer that self-encapsulated the sil ver film. A near-bamboo structure in the encapsulated Ag films was obs erved using cross-sectional transmission electron microscopy. Such a s tructure is expected to improve the electromigration resistance of the silver metallization. The kinetics of the Ti-nitride growth was studi ed by investigating its dependence on time, temperature, and Ag/Ti bil ayer thicknesses. We also found that two processes govern the nitridat ion reaction. A dominant nitridation process takes place initially at fast growth rates. After 15 min anneals the nitride growth can be desc ribed by x(2) = B t, where B is a parabolic rate constant for the grow ing nitride phase. The parabolic rate constants follow an Arrhenius be havior with an apparent activation energy of similar to 0.4 eV. These observations led to further discussion regarding the diffusion mechani sm as well as the rate-limiting step. (C) 1997 American Institute of P hysics.