Phase transition behavior of reactive sputtering deposited Co–N thin films using transmission electron microscopy

Abstract

Cobalt nitride thin films could be prepared by employing a direct current reactive sputtering deposition on (100) silicon substrates in mixtures of fixed Ar (4×10−1 Pa) and N2 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 α-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+β-Co(N), Co3N→Co2N+β-Co(N), and Co2N→CoN+β-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.