Deposition of cobalt oxide films by reactive pulsed magnetron sputtering

Abstract Cobalt oxide films were deposited with the help of reactive high power impulse magnetron sputtering (HiPIMS) and mid-frequency pulsed magnetron sputtering (PMS) in argon gas at an argon gas pressure of 1 Pa and with different oxygen admixtures. The HiPIMS discharge was operated at a repetition frequency f=100 Hz with a duty cycle of 1%. Deposition rate and ion fraction were measured. The intensity of plasma ions, in particular Co+ and O+, is enhanced during HiPIMS compared to PMS and extends to larger ion energies. Films deposited on glass substrates were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. Crystal structure and electrical resistivity of as-deposited films were found to depend on the deposition conditions. Deposited films are compatible with a non-stoichiometric Co3O4 spinel type crystal structure with unoccupied cobalt sites. PMS produces films with a preferred lattice orientation. HiPIMS show a large internal stress which relaxes during annealing. Electrical resistivity is several orders of magnitude smaller for films deposited by HiPIMS compared to PMS.