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Growth of thin TiOx films by high power pulsed magnetron sputtering from a compound TiO1.8 target.

Kostas Sarakinos ,  Jones Alami ,  Christian Klever ,  Matthias Wuttig 

Institute of Physics IA, RWTH Aachen Univesrity, Sommerfeldstraße 14, Aachen 52074, Germany

Abstract

We present a study on the growth of TiOx films by high power pulsed magnetron sputtering (HPPMS). High power unipolar pulses with a low duty cycle (<20%) are applied to a TiO1.8 target resulting in a high ionization of the sputtered material and consequenty an increased energetic bombardment of the growing film. We investigate the effect of pulse duty cycle on the deposition rate, the structure, the surface morphology and the optical properties of the TiOx films. Samples are sputtered at a constant average current mode on grounded, floated, and negatively biased substrates for different duty cycles (1.5%-20%). X-ray diffraction shows that in all cases nanocrystalline films are obtained. It is found that the peak target current (ITp) and the target voltage increase with decreasing pulse duty cycle, which has implication on the film properties. X-Ray Reflectometry (XRR) measurements show that the deposition rate for films sputtered at ITp<14 A increases with ITp and it is up to 60% higher with respect to the rate achieved by DC sputtering. The HPPMS rate decreases at ITp>14 A but remains slightly hihger than the DC rate. The existence of the two ITp regimes is discussed in the light of the change of the plasma characteristics upon increasing the peak current and the self-sputtering effect. Moreover, the XRR analysis shows that the HPPMS films exhibit surface roughness of ~0.5 nm, which is 70% lower than the corresponding DC values. Finally, spectroscopic ellipsometry measurements reveal that transparent films with band gap of ~3.2 eV are obtained in all cases. In addition, refractive indices up to 2.52 are obtained for HPPMS deposited films. These values are higher than the correspoding values for DC films (~2.46) grown at otherwise identical conditions.

 

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Presentation: Oral at E-MRS Fall Meeting 2006, Symposium A, by Kostas Sarakinos
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-15 08:16
Revised:   2009-06-07 00:44