High-rate sputtering deposition of high- and low-refractive index films from conductive composites
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esearch Letter
High-rate sputtering deposition of high- and low-refractive index films from conductive composites Li Qin Zhou, Department of Mechanical Engineering, Centre for Mechanical Technology and Automation, University of Aveiro, 3810-193 Aveiro, Portugal; Aveiro Nanotechnology Institute, University of Aveiro, 3810-193 Aveiro, Portugal Qi Hua Fan, Department of Electrical Engineering and Computer Science, South Dakota State University, Brookings, South Dakota Raul Simões, Department of Mechanical Engineering, Centre for Mechanical Technology and Automation, University of Aveiro, 3810-193 Aveiro, Portugal; Aveiro Nanotechnology Institute, University of Aveiro, 3810-193 Aveiro, Portugal Victor Neto, Department of Mechanical Engineering, Centre for Mechanical Technology and Automation, University of Aveiro, 3810-193 Aveiro, Portugal; Aveiro Nanotechnology Institute, University of Aveiro, 3810-193 Aveiro, Portugal Address all correspondence to Qi Hua Fan, Victor Neto at [email protected]; [email protected] (Received 22 February 2015; accepted 1 May 2015)
Abstract Dielectric thin films of high- and low-refractive index are the essential components for optical coatings. To achieve high sputtering rates and superior film quality, the authors have developed novel conductive SiO2:Si and ZnO:Zn composites that become conductive once the doped silicon and metal Zn reach a critical ratio. The sputtering characteristics of the composite targets in direct current and radio-frequency (RF) plasma discharge are quite different from the corresponding element targets. The optical properties of the RF sputtered SiO2 and ZnO films from the composite targets is comparable with the films obtained from RF sputtering of pure oxide targets.
Introduction Dielectric thin films of high- and low-refractive index are the essential building blocks for optical coatings.[1] Common low-refractive-index films are silicon oxide (SiO2, n ∼ 1.54) and magnesium fluoride (MgF, n ∼ 1.27); and high-refractive-index films include titanium oxide, zinc oxide, and silicon nitride (n ∼ 2.0). Two sputtering techniques are widely used to deposit dielectric thin films.[2] For the highest density films, radiofrequency (RF) sputtering of pure oxide ceramic targets is normally preferred.[3–9] For large area coating at high rates, reactive sputtering using element or alloy targets via direct current (DC) power supplies is the most common method.[10–12] Although RF sputtering results in high-quality films, it has the limitation of relatively low deposition rates. DC reactive sputtering from metallic targets has higher deposition rates but typically results in lower-quality films. In addition, there is a fundamental process stability problem due to oxide poisoning of the target surface when planar targets are used in DC reactive sputtering.[13–17] The ideal sputtering process of dielectric thin films would combine the high rates of reactive sputtering with the film quality and process stability of RF sputtered films. Toward this goal, the authors have developed novel conductive ZnO
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