title: SiNx Coatings Deposited by Reactive High Power Impulse Magnetron Sputtering: Process Parameters Influencing the Nitrogen Content.
abstract: 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 by X-ray photoelectron spectroscopy, X-ray reflectivity, X-ray diffraction, and nanoindentation, respectively. The SiNx deposition processes and coating properties are mainly influenced by the N2-to-Ar flow ratio and thus by the N content in the SiNx films and to a lower extent by the HiPIMS frequencies and power settings as well as substrate temperatures. Increasing N2-to-Ar flow ratios lead to decreasing growth rates, while the N content, coating densities, residual stresses, and the hardness increase. These experimental findings were corroborated by density functional theory calculations of precursor species present during rHiPIMS.
authors.affiliation: Thin Film Physics Division, Department of Physics (IFM), Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Susann
authors.initials: S
authors.lastname: Schmidt
authors.affiliation: Thin Film Physics Division, Department of Physics (IFM), Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Tuomas
authors.initials: T
authors.lastname: Hänninen
authors.affiliation: Thin Film Physics Division, Department of Physics (IFM), Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Goyenola
authors.affiliation: Thin Film Physics Division, Department of Physics (IFM), Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Jonas
authors.initials: J
authors.lastname: Wissting
authors.affiliation: Thin Film Physics Division, Department of Physics (IFM), Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Jens
authors.initials: J
authors.lastname: Jensen
authors.affiliation: Thin Film Physics Division, Department of Physics (IFM), Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Hultman
authors.affiliation: IHI Ionbond AG , Industriestraße 211, CH-4600 Olten, Switzerland.
authors.forename: Nico
authors.initials: N
authors.lastname: Goebbels
authors.affiliation: IHI Ionbond AG , Industriestraße 211, CH-4600 Olten, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Tobler
authors.affiliation: Thin Film Physics Division, Department of Physics (IFM), Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Hans
authors.initials: H
authors.lastname: Högberg
keywords: HiPIMS; Langmuir probe measurements; SiNx; XPS; positive ion plasma mass spectrometry; residual film stress