SiNx Coatings Deposited by Reactive High Power Impulse Magnetron Sputtering: Process Parameters Influencing the Nitrogen Content

Reactive high power impulse magnetron sputtering (rHiPIMS) was used to deposit silicon nitride (SiNx) coatings for biomedical applications. The SiNx growth and plasma characterization were conducted in an industrial coater, using Si targets and N2 as reactive gas. The effects of different N2-to-Ar flow ratios between 0 and 0.3, pulse frequencies, target power settings, and substrate temperatures on the discharge and the N content of SiNx coatings were investigated. Plasma ion mass spectrometry shows high amounts of ionized isotopes during the initial part of the pulse for discharges with low N2-to-Ar flow ratios of <0.16, while signals from ionized molecules rise with the N2-to-Ar flow ratio at the pulse end and during pulse-off times. Langmuir probe measurements show electron temperatures of 2–3 eV for nonreactive discharges and 5.0–6.6 eV for discharges in transition mode. The SiNx coatings were characterized with respect to their composition, chemical bond structure, density, and mechanical properties ...