N-rich Zr–N films deposited by unbalanced magnetron sputtering enhanced with a highly reactive MW-ECR plasma

Zirconium nitride thin films were synthesized by a microwave electron cyclotron resonance (MW-ECR) plasma enhanced unbalanced magnetron sputtering (PE-UMS) technique. The results of plasma diagnostics by an electrostatic probe indicate that the electron temperature decreases with increasing nitrogen flow rate. The substrate ion current initially increases as the nitrogen flow rate increases at a low flow and then decreases with increasing nitrogen flow. The nitrogen concentration in the films increases and the grain size decreases while the N2+ ion density increases. The metastable Zr3N4 phase occurs as the N/Zr atomic ratio reaches 1.4. The films become amorphous as the N/Zr atomic ratio is higher. The corresponding microhardness of the deposited films increases from 22.5 GPa to the maximum of 26.8 GPa, and then decreases linearly to 19.8 GPa as the N2 flow rate increases from 8 to 14 sccm. The mechanism of the influence of the plasma characteristics on the microstructure and mechanical properties of the deposited films were discussed.