Oblique angle deposition of nickel thin films by high-power impulse magnetron sputtering

Publisher's version (útgefin grein)Background: Oblique angle deposition is known for yielding the growth of columnar grains that are tilted in the direction of the deposition flux. Using this technique combined with high-power impulse magnetron sputtering (HiPIMS) can induce unique properties in ferromagnetic thin films. Earlier we have explored the properties of polycrystalline and epitaxially deposited permalloy thin films deposited under 35° tilt using HiPIMS and compared it with films deposited by dc magnetron sputtering (dcMS). The films prepared by HiPIMS present lower anisotropy and coercivity fields than films deposited with dcMS. For the epitaxial films dcMS deposition gives biaxial anisotropy while HiPIMS deposition gives a well-defined uniaxial anisotropy. Results: We report on the deposition of 50 nm polycrystalline nickel thin films by dcMS and HiPIMS while the tilt angle with respect to the substrate normal is varied from 0° to 70°. The HiPIMS-deposited films are always denser, with a smoother surface and are magnetically softer than the dcMS-deposited films under the same deposition conditions. The obliquely deposited HiPIMS films are significantly more uniform in terms of thickness. Cross-sectional SEM images reveal that the dcMS-deposited film under 70° tilt angle consists of well-defined inclined nanocolumnar grains while grains of HiPIMS-deposited films are smaller and less tilted. Both deposition methods result in in-plane isotropic magnetic behavior at small tilt angles while larger tilt angles result in uniaxial magnetic anisotropy. The transition tilt angle varies with deposition method and is measured around 35° for dcMS and 60° for HiPIMS. Conclusion: Due to the high discharge current and high ionized flux fraction, the HiPIMS process can suppress the inclined columnar growth induced by oblique angle deposition. Thus, the ferromagnetic thin films obliquely deposited by HiPIMS deposition exhibit different magnetic properties than dcMS-deposited films. The results demonstrate the potential of the HiPIMS process to tailor the material properties for some important technological applications in addition to the ability to fill high aspect ratio trenches and coating on cutting tools with complex geometries.The authors would like to thank Dr. Fridrik Magnus for his helpful advice on interpretation of MOKE results. This work was partially supported by the University of Iceland Research Fund for Doctoral students, the Icelandic Research Fund Grant Nos. 130029 and 196141.Peer Reviewe

Strained interface layer contributions to the structural and electronic properties of epitaxial V2O3 films

We report on the transport properties of epitaxial vanadium sesquioxide (V2O3) thin films with thicknesses in the range of 1 to 120 nm. Films with thickness down to nanometer values reveal clear resistivity curves with temperature illustrating that even at these thicknesses the films are above the percolation threshold and continuous over large distances. The results reveal that with reducing thickness the resistivity of the films increases sharply for thicknesses below 4 nm and the metal-insulator transition (MIT) is quenched. We attribute this increase to a strained interface layer of thickness ∼ 4 nm with in-plane lattice parameters corresponding to the Al2O3 substrate. The interface layer displays a suppressed MIT shifted to higher temperatures and has a room temperature resistivity 6 orders of magnitude higher than the thicker V2O3 films.This work was supported by the University of Iceland Research Fund for Doctoral Students, the University of Iceland Research Fund, the Icelandic Student Innovation Fund, and the Icelandic Research Fund (Grant Nos. 207111 and 174271)

Optimization of HiPIMS discharges: The selection of pulse power, pulse length, gas pressure, and magnetic field strength

International audienc

On how to measure the probabilities of target atom ionization and target ion back-attraction in high-power impulse magnetron sputtering

High-power impulse magnetron sputtering (HiPIMS) is an ionized physical vapor deposition technique that provides a high flux of ionized target species for thin film growth. Optimization of HiPIMS processes is, however, often difficult, since the influence of external process parameters, such as working gas pressure, magnetic field strength, and pulse configuration, on the deposition process characteristics is not well understood. The reason is that these external parameters are only indirectly connected to the two key flux parameters, the deposition rate and ionized flux fraction, via two internal discharge parameters: the target atom ionization probability αt and the target ion back-attraction probability βt. Until now, it has been difficult to assess αt and βt without resorting to computational modeling, which has hampered knowledge-based optimization. Here, we present a simple method to deduce αt and βt based on measured deposition rates of neutrals and ions. The core of the method is a refined analytical model, which is described in detail. This approach is furthermore validated by independent calculations of αt and βt using the considerably more complex ionization region model, which is a plasma-chemical global discharge model