Session WF2: Magnetron Sputter Deposition

Self-Assembled Multi-Layer a-C:H/Me Coatings by Reactive Sputter Deposition

The growth and characteristics of metal containing amorphous hydrogenated carbon thin films (a-C:H/Me) were studied in this research. The formation of self-assembled, alternating nano-layered structures are addressed. a-C:H/Me thin films were synthesized using one single target, a rotating but not revolving substrate, and constant feed gas compositions in a conventional reactive sputter deposition chamber. The metals used include Al, Si, Cu, Pt, Fe and Ni. Various mixtures of methane and argon having fixed total flow rates were used as the feed stocks. A number of growth parameters, including methane concentration, working pressure, electrode distance, dc power, substrate bias, and substrate temperature were used. The resulting a-C:H/Me thin films were found to exhibit three different structures. Among them, self-assembled, alternating nano-layered structures were observed in a-C:H/Cu, a-C:H/Pt, a-C:H/Fe, and a-C:H/Ni thin films. It was found that such self-assembled, alternating nano-layered structures can be obtained under controlled growth parameters for selected metals. A growth mechanism based on the considerations of clustering of carbon and metal, segregation of carbon, catalytic effects of metal, formation of carbide, energy of adatoms, and surface diffusion of metal and carbon, has been developed. Further data analysis was also performed to verify the validity of the mechanism.   

Applying Composition Control to Enhance the Mechanical and Thermal Properties of Zr-Cu-Ni-Al-N Thin Film Metallic Glass

This study focuses on the correlations among the compositions of Zr-Cu-Ni-Al-N thin film metallic glass (TFMG) and their properties. The TFMG was prepared by DC magnetron co-sputtering technique with Zr-Cu and Ni-Al targets. By adjusting working power, pressure and nitrogen flow rate, thin films with various constituents were fabricated. Also, the effect of Zr/Cu ratio on the physical properties will be explored. With the increasing nitrogen content in the system, the hardness was improved up to 100{\%} as compared to Zr-Cu TFMG. The strengthening mainly results from the atomic radii difference, and the enthalpy of mixing among mutual atomic bonding. In pursuit of high hardness, whether the coating still belongs to a metallic glass is critical. Differential scanning calorimetry (DSC) analysis further identifies the metallic glass characteristics of films with the formation of super-cooling regions. Finally, a Zr-Cu-Ni-Al-N TFMG with appropriate composition to exhibit improved hardness, thermal stability, and antimicrobial ability was revealed and discussed.   

Fabrication of spin valve junctions based on Fe/Fe$_{3}$Si/FeSi$_{2}$/Fe$_{3}$Si quadrilayered films by facing targets direct-current sputtering

In order to prepare magnetic multilayered films applicable to spin devices, the film preparation method is an important key that determines the quality of the spin devices, such as interfaces between layers and crystalline orientations. A facing targets direct-current sputtering (FTDCS) method, in which a couple of targets are positioned in parallel and a substrate is set in the direction perpendicular to the two targets, has the following features: (i) less plasma damage, (ii) fewer rises in the substrate temperature, and (iii) small stoichiometric differences between the target and film, owing to a substrate is free of the plasma. These features should be beneficial to Fe$_{3}$Si/FeSi$_{2}$ multilayered films at low substrate temperatures, with Fe$_{3}$Si and FeSi$_{2}$ sintered targets. In this study, Fe/Fe$_{3}$Si/FeSi$_{2}$/Fe$_{3}$Si multilayered films were prepared by employing the FTDCS method. The bottom Fe$_{3}$Si layers were epitaxially grown on Si(111) substrates, and they exhibited small coercive forces of less than 10 Oe. Posterior to FeSi$_{2}$ layers being deposited on the bottom Fe$_{3}$Si layers, polycrystalline Fe$_{3}$Si and Fe were successively deposited on the FeSi$_{2}$ layers. The resultant multilayered films showed sharp signals due to magnetoresistance as spin valves.   

Surface Roughness Control of DC Sputter Film Deposition by Superposition of VHF Power

Magnetron plasmas are one of the most important tools for sputter deposition of thin films. However, energetic particles from the sputtered target such as backscattered rare gas atoms or oxygen negative ions (O$^{-})$ from oxide targets sometimes induce physical and chemical damages as well as surface roughening to the deposited film surface during the sputtering processes. In our previous work, we have investigated spatial and energy distributions of O$^{-}$ ion in a RF plasma. We also have shown suppression of O$^{-}$ energy with VHF-superimposition and that O$^{-}$ energy can be controlled by a parameter $R$, which is a ratio of the VHF power to the total input power (VHF power $+$ DC power). In this study, influence of the VHF superposition on the deposition properties of ITO films such as deposition rate, RMS roughness or electrical resistivity is investigated. Deposition rate is strongly influenced by the VHF superposition although the DC current is the same, suggesting variation of sputter yield and positive ion current due to lowering of the target voltage. By superposition of the VHF power up to $R \sim$ 90{\%}, improved RMS roughness and the electrical resistivity is observed.   

Study of the mechanical properties and the microstructure of magnetron sputtered MoBC coatings

The aim of the present work was to prepare Mo$_{2}$BC films using magnetron sputtering. The studied films were deposited using a sputtering device equipped by four confocally arranged magnetrons accommodating 3 inch sputtering targets. All magnetron heads were aimed at a rotatable and biasable substrate holder that can be heated up to 750$^{\circ}$ C. Molybdenum, carbon and B$_{4}$C targets were co-sputtered simultaneously. Mo and B$_{4}$C targets were DC powered, while carbon target was connected to pulsed DC generator capable of pulsing up to frequency of 350 kHz. The pulsing frequency, bias and substrate temperatures were varied. The mechanical properties of layers were characterized by means of nanoindentation experiments using a Hysitron dual head TI950 triboindenter in both static and dynamic loading regime. The results of mechanical testing and XRD studies were correlated with microstructure observations by means of electron microscopy using a Tescan LYRA 3XMU SEM $\times$ FIB scanning electron microscope (SEM), a Philips CM12 STEM transmission electron microscope (TEM) and a JEOL 2010F high resolution TEM. Thin lamellar cross sections for TEM observations were prepared using a focused ion beam (FIB) in SEM.   

Scalable Plasma Engineering For Transparent-Conductive Performance Improvment in Al-Doped ZnO Thin Films

ZnO has been widely investigated for applications in opto-and nanoelectronics; such as automobile devices (e.g. panel lighting), traffic lights, optical recording media, scanning readers, video game consoles and LEDs. When it is doped, the special characteristics of ZnO-based compounds allow them to be used as a transparent conductor. Here, we present a scalable plasma engineering process based on DC magnetron sputtering for improving the transparent conductive- characterestics in Al doped ZnO thin films. Using a highly confined magnetron system, plasma densities and electron temprature were engineered systematically and its effect on transparent-conductive characeristics of films has been studied using plasma diagnostic tools (using Langmuir probe, optical essision spectraoscopy, current density) and films characterizations. Here, using DC power in similar range of conventional DC magnetron sputtering, present process produces plasma density one order greater and remarkably higher electron temperature. Such plasma conditions lead to good crystalline films with adequate oxygen vacancies, which in turn leads highly repitible resistivities in order of 10-4 $\Omega $ cm with average transmittance more than 85{\%} in entire visible region in 200 nm thick films.