X-ray photoelectron spectroscopy (XPS) has been used to investigate the thermal annealing of TIN films in the controlled atmosphere. The films were prepared by a cathodic are plasma deposition technique on Cu substrates. The flowing gases used in the annealing are air, N-2, Ar, and CO2/N-2/H-2 gas mixtures, which possess extremely different nitrogen and oxygen partial pressures. Annealing the samples in air at 300, 400, and 500 degrees C causes the gradual transformation from amorphous TiO2 to crystalline TiO2 on the TiN surface. Annealing in N-2 and Ar at slightly different temperatures results in various adsorbed nitrogen states. After annealing in CO2/N-2/H-2 = 10 : 81 : 9 and N-2/H-2 = 9 gas mixtures from 400 degrees C to 700 degrees C, the relative intensity of crystalline TiO2 increases with temperature and that of titanium oxynitride decreases. The adsorbed nitrogen associated with the oxidation of TiN is discussed. The TiN oxidation chemistry under these controlled oxygen and nitrogen partial pressures is also discussed.