Room temperature oxidation behavior of TiN thin films

The room temperature oxidation process of thin TiNx films, grown by DC reac tive magnetron sputtering, was studied by in-situ and real time spectroscop ic ellipsometry, X-ray reflectivity, Auger electron spectroscopy, X-ray pho toelectron spectroscopy and stress measurements. The films were deposited a t various negative bias voltages (V-b) in order to vary the TiNx stoichiome try and then exposed to several gases and to air at room temperature. The o xidation rate was found to depend strongly on V-b and thus on film stoichio metry. Fast oxidation was observed in films deposited at low \V-b\, that co ntain nitrogen which is weakly bonded to Ti and can be easily replaced by o xygen. At high \V-b\ values (aboue - 80 V) stoichiometric TiN films were de veloped, that were stable and not prone to oxidation. The results showed th at oxidation takes place in the bulk of thr: film and can proceed up to abo ut 10% transformation of titanium nitride into titanium oxide. The fastest step in the him oxidation mechanism is diffusion of oxygen along the column ar grain boundary structure, followed by the reaction of oxygen with the we akly bonded TiN. The results suggest that the oxidation process proceeds wi th different stages involving formation of TiON, followed by a slow stage o f TiO2 formation. These microstructural changes are consistent with the evo lution of compressive stresses in the films surd the increase in film densi ty and thickness and the: decrease in surface roughness as determined by X- ray reflectivity. (C) 1999 Elsevier Science S.A. All rights reserved.