AVS 63rd International Symposium & Exhibition
    Thin Film Thursday Sessions
       Session TF-ThP

Paper TF-ThP45
Reactive RF Magnetron Sputtering of Vanadium Oxides: Substrate Bias Issues

Thursday, November 10, 2016, 6:00 pm, Room Hall D

Session: Thin Films Poster Session
Presenter: Sergey Jr. Maklakov, Institute for Theoretical and Applied Electromagnetics RAS, Russian Federation
Authors: S.A. Maklakov, Institute for Theoretical and Applied Electromagnetics RAS, Russian Federation
V.I. Polozov, Institute for Theoretical and Applied Electromagnetics RAS, Russian Federation
I.A. Ryzhikov, Institute for Theoretical and Applied Electromagnetics RAS, Russian Federation
V.N. Kisel, Institute for Theoretical and Applied Electromagnetics RAS, Russian Federation
Correspondent: Click to Email
Thin films of vanadium oxides are widely applied functional coatings for electronics. Non-stoichiometric nanocrystalline VOx films possess low thermal activation energy (~ 0.1 eV). These films serve as infrared detectors in uncooled bolometers. Under certain annealing conditions, VOx films undergo recrystallization, and stoichiometric VO2 oxide may be formed. Crystalline VO2 films possess metal-insulator transition at 68C. These VO2 films works as switches for transmission lines for terahertz and microwave range. All these VOx coatings are frequently deposited through magnetron sputtering.

Although reactive sputtering of vanadium in oxygen-containing atmosphere has been studied since 1960's, there are several points that still not clear. It is well known, that when a negative DC bias are applied to substrate, it provides additional energetic treatment of a growing film. It causes re-sputtering of a surface layer and increases effective surface temperature of a growing coating. As a result, films, grown under the bias conditions, are depleted with light elements and show decreased concentration of admixtures. These effects are studied well for biases more than -20 V (J. Phys. D: Appl. Phys. 39 (2006) 2220–2223). We present experiment which shows that substrate bias of low value may influence chemical reactivity of reactive components, giving similar results to large biases.

Series of VOx thin films was deposited by means of unbalanced RF magnetron source in Ar + O2 gas mixture. Oxygen-depleted films appear as black coatings with metal conductivity. Oxygen-rich films are yellow dielectrics. Oxygen content may be easily controlled through gas composition, which is a common knowledge. Gas mixture (13.6 % O2 for a vacuum facility applied) which gives transient VOx films between oxygen depleted and oxygen rich compositions, was applied for the experiment. Negative bias of a few volts (starting from -1 V), which is comparable to a floating potential, reduces vanadium oxidation state from V+5 down to V+2. No biased substrate, under designated conditions, results in VOx films, substantially consisting of V+5. Observed effect cannot be explained by resputtering process. Resistivity of VOx films in the series varies by 5 orders in magnitude. Reduction of vanadium oxidation state also changes the Meyer-Neldel rule type from conventional to inverse. This phenomenon may be caused by changes in oxygen reactivity associated with variations in RF discharge characteristics.

The study was financially supported by the Russian Foundation for Basic Research under grant No. 16-33-01089.