Structure, phase evolution and mechanical properties of HiPIMS, pulsed DC and DC sputtered Ta-N films

Heribert Marihart

Research output: ThesisDiploma Thesis

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Abstract

The microstructural development of reactively sputtered tantalum nitride thin films is investigated as a function of the N2-to-total pressure ratio (pN2/pT) and the operating mode of the metallic tantalum cathode by high power impulse magnetron sputtering (HiPIMS), pulsed direct current (DC) and DC sputtering. For all sputtering modes investigated, the phase evolution of the Ta-N films strongly depends on the nitrogen partial pressure, pN2, used when keeping the total pressure, pT, constant at 0.3 or 0.6 Pa. The major crystalline phases identified, with increasing the N2-to-total pressure ratio, are α- and β-Ta, orthorhombic o-Ta4N, hexagonal closed packed (hcp) γ-Ta2N, cubic δ-TaN, and hcp ε-TaN, respectively. The minimum pN2/pT-ratio needed for the formation of the individual nitride phases, decreases from DC to HiPIMS. For example, when using a pN2/pT-ratio of 13.4 %, the nitrogen content within the HiPIMS film is ~38.5 at.%, but only ~26.5 at.% within the pulsed DC and DC sputtered films. Therefore, the HiPIMS film is mainly composed of γ-Ta2N (with traces of ε-TaN) whereas the pulsed DC and DC sputtered films also contain o-Ta4N next to γ-Ta2N. These coatings—with a majority of γ-Ta2N—exhibit the highest hardness values with 38.2±4.6, 38±2.3, and 40±3.8 GPa among all samples studied, respectively. Further increasing pN2/pT leads to the formation of δ- and ε-TaN, which are the dominating phases for pN2/pT-values above 38.1 %. For higher N2-to-total pressure ratios, the phase fraction of ε-TaN increases on the expanse of δ-TaN and a significant reduction in hardness, even down to ~20 GPa, is observed. Based on our results we can conclude that the highest hardness is obtained for γ-Ta2N dominated films. Consequently, with respect to mechanical properties, the most important pN2/pT range is between 13.4 and 38.1 %, where the films undergo a transformation from γ-Ta2N (plus o-Ta4N) to δ- and ε-TaN. Generally, this phase transformation is shifted to lower pN2/pT-values when using HiPIMS instead of pulsed DC or DC sputtering.
Translated title of the contributionStruktur-, Phasenentwicklung und mechanische Eigenschaften von HiPIMS, gepulst DC und DC gesputterten Ta-N Schichten
Original languageEnglish
QualificationDipl.-Ing.
Supervisors/Advisors
  • Mayrhofer, Paul Heinz, Supervisor (internal)
Award date26 Jun 2015
Publication statusPublished - 2015

Bibliographical note

embargoed until 18-02-2020

Keywords

  • TaN
  • HiPIMS
  • pulsed DC
  • magnetron sputtering
  • DC
  • hard ceramic coatings

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