Abstract :
[en] High Power Impulse Magnetron Sputtering (HiPIMS) is known for its high ionization rate of the sputtered particles compared to conventional DC Magnetron Sputtering processes [1]. This feature renders HiPIMS very powerful to tailor film properties such as density, microstructure, etc. due to the energetic bombardment during the film growth [2-4]. In this work, the plasma chemical composition and the time evolution of the ion energy distributions were studied during reactive HiPIMS discharges for titanium oxide deposition.
The discharges were operated with a titanium target (100 mm Ø) in argon-oxygen mixtures using a 5 mTorr working pressure. The orifice of the mass spectrometer is located 80 mm in front of the target, i.e. at the substrate position. The oxygen flow rate ratio was varied between 0 and 40 %. For these conditions, the discharge evolved from the metallic to the poisoned regime. Three target voltages (Vt) were also considered namely 700, 800 and 900 V; the average power was kept constant by modifying the pulse frequency (5µs-pulse width). On the other hand, two pulse widths (5 and 20 µs) have been considered in order to study the amplitude of the target peak current (Ip).
As Ip increases by increasing Vt, the amount of oxygen needed to reach the transition is reduced. Mass spectrometry scans performed on Ar+, Ti+, O+, O2+ and TiO+ ion populations reveal an increase of the oxygen-based species (O+, O2+ and TiO+) before the transition while signals related to Ti+ and Ti2+ slowly decrease. As Vt increases, the signal related to the TiO+ ions, which are sputtered from the oxidized target, completely disappears. This might be attributed to a combination of i) the reduction of the erosion rate of the oxidized target surface when Vt is increased and ii) to the increased thickness of the oxide layer covering the target surface. Indeed, SRIM [4] simulations show that O+ ions can penetrate deeper in the Ti target as Vt increases. As O+ ions are thought to be produced to a large extent in the HiPIMS plasma, this would lead to a more efficient oxidation mechanism of the target. Moreover, the few TiO+ ions sputtered might be dissociated inside the dense HiPIMS plasma as Vt is increased. These considerations are supported by time-resolved mass spectrometry and deposition rate measurements.
References
[1] S. Konstantinidis, M. Ganciu, A. Ricard, J.P. Dauchot, M. Hecq, J. Appl. Phys. 99 - 1 (2006) 13307.
[2] J. Alami, K. Sarakinos, F. Uslu, M. Wuttig, J. Phys. D : Appl. Phys. 42 (2009) 015304.
[3] M. Samuelsson, D. Lundin, J. Jensen, M. A. Raadu, J. T. Gudmundsson, U. Helmersson, Surf. Coat. Technol. 205 (2010) 591-596.
[4] http://www.srim.org/.
