Cobalt nitride thin films could be prepared by employing a direct current reactive sputtering deposition on (100) silicon substrates in mixtures of fixed Ar (4 X 10(-1) Pa) and N-2 at various partial pressures. The CoxN thin films could be tailored by appropriately controlling the partial pressure of the reactive nitrogen. With adequately increasing nitrogen to argon partial pressure, a series of sequence phase formation from alpha-Co, Co4N, Co3N, Co2N, and CON could be observed. The phase transition sequence was accompanied by a substantial refinement and improvement of the films' grain structure. Rapid thermal annealing of cobalt nitride thin films exhibited a stepwise decomposition via the dissociating Of Co4N-->Co3N+beta-Co(N), Co3N- Co2N+beta-Co(N), and Co2N-->CoN+beta-Co(N) with increasing the elevated temperature. Phase formation, thermal decomposition, electrical resistivity, and microstructure of reactive sputtered cobalt nitride films were discussed in this study. (C) 2004 American Vacuum Society.