Preparation and characterization of high purity Ti thin films by high power impulse magnetron sputtering deposition


Preparation and characterization of high purity Ti thin films by high power impulse magnetron sputtering deposition

Meško, M.; Munnik, F.; Heller, R.; Grenzer, J.; Hübner, R.; Krause, M.

The increased ion-to-atom ratio in high power impulse magnetron sputtering (HiPIMS) allows directional deposition and film densification by the bombarding ions [1]. Recently, Andersson et al. showed HiPIMS gasless self-sputtering operation and proposed this method for the synthesis of ultraclean metal coatings through self-ion-assisted deposition [2]. In the present work we investigated Ti thin films prepared by direct current magnetron sputtering (dcMS) and HiPIMS with respect to their element composition, surface roughness, and microstructure. Ti films were deposited on Si/SiO2 substrates at room temperature. The base pressure prior to the two hours depositions was 5x10-5 Pa. The film thicknesses were determined by profilometry after the deposition and are 800 nm and 200 nm for dcMS and HiPIMS respectively. It is shown that Ti thin films prepared by HiPIMS do not suffer from bulk contamination like dcMS films (Fig. 1). In particular, the impurity levels for O, N and C are below the detection limit (0.3 – 0.5 at.%) of elastic recoil detection analysis (ERDA) and the hydrogen content was measured to 0.5 at.% for the HiPIMS case. Compared to the dcMS films, we observed an element specific reduction of impurities by a factor 3- 4 for N and H; and a factor of 20 for O. This suggests the presence of at least two sources of impurities. Unlike in [2], the HiPIMS self-sputtering regime was sustained in Ar gas. The high purity of Ti films can be partly explained by gas rarefaction and the cleaning effect of the bombarding ions. Moreover, densification effects presumably suppress post-deposition oxidation. The compositional effects are correlated with differences in the film microstructure revealed by SEM, XRD and TEM analysis. A more sensitive analytical method is needed to evaluate the actual impurity levels of O, N, and C in the deposited HiPIMS films.
[1] U. Helmersson, M. Lattemann, J. Bohlmark, A. P. Ehiasarian, J. T. Gudmundsson “Ionized physical vapor deposition (IPVD): A review of technology and applications” (2006) Thin Solid Films 513, 1–24
[2] J. Andersson and A. Anders “Gasless sputtering: Opportunities for ultraclean metallization, coatings in space, and propulsion” (2008) Appl. Phys. Lett. 92, 221503

Keywords: HiPIMS; self-sputtering; impurity level; Ti thin films

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