Inverted Cylindrical Magnetron Research Articles

Comparative study of discharge characteristics and associated film growth for post-cathode and inverted cylindrical magnetron sputtering

In this study, an experimental investigation of a DC cylindrical magnetron discharge for argon gas in post-cathode (i.e. direct) and hollow-cathode (i.e. inverted) configurations was carried out. The discharge properties at different externally applied magnetic fields and operating pressures were measured and compared for both the configurations. The discharge current (I)–voltage (V) characteristics obey $${I\propto V^n}$$ , where the value of n is in the range of 3–8. The discharge current increases linearly with the magnetic field in the post-cathode configuration, whereas it saturates at higher magnetic fields in the case of inverted configuration. Measurement of plasma potential indicated a considerable anode fall in the inverted magnetron configuration, whereas a negligible anode fall and strong cathode fall were observed in the case of post-cathode configuration. The plasma density and electron temperature, measured using a double Langmuir probe, were observed to be higher in the inverted magnetron configuration. The plasma density was found to be maximum at around 3–4 cm away from the respective inner electrode in both the configurations. A clear change in surface morphology of copper thin film was observed in the case of inverted magnetron configuration, which might be due to the extra ionisation near the anode owing to the anode fall.

Titanium and titanium nitride thin films grown by dc reactive magnetron sputtering Physical Vapor Deposition in a continuous mode on stainless steel wires: Chemical, morphological and structural investigations

Ti and TiN thin films (50–140nm thick) are grown by dc reactive magnetron sputtering PVD in an inverted cylindrical magnetron (ICM) thanks to an original industrial process corresponding to a continuous reactive deposition on moving stainless steel wires. Thin films are fully characterized by X-ray Photoelectron Spectroscopy, Transmission Electron Microscopy coupled with Energy Dispersive Spectroscopy and Orientation Phase Mapping. The stoichiometry of TiN is adjusted thanks to N2 flow. At the beginning of poisoned mode, golden stoichiometric TiN thin films are obtained. In the metallic mode, greyish TiNx films are grown whereas at higher N2 flow, TiNxOy films are synthetized with preferential O incorporation instead of N enrichment. Grain orientation maps reveal that Ti and TiN thin films are highly polycrystalline: Ti films have an equiaxis morphology whereas TiN thin films have a tendency to present 〈111〉 columnar grains with 〈001〉 oriented grains at the nucleation step. Finally, a low temperature of growth (of about 350°C and <650°C) is needed in order to prevent chemical diffusion from the stainless steel substrate into the rich-titanium films.

Control of particle flux and energy on substrate in an inverted cylindrical magnetron for plasma PVD

Inverted cylindrical magnetrons (ICMs) are often used in dc, pulsed dc or mid-frequency ac mode for coating complex objects with thin films deposited by plasma PVD. Since in such a configuration the substrate is inherently surrounded by the target and hence by the plasma, the energy flux of the impinging particles represents the main contribution to the substrate heating. This can readily constitute a limiting factor in the deposition process, especially when it is not possible to cool and bias the substrate. This work concerns a dc-driven ICM configuration subjected to several constraints: not only is the substrate surface area small by comparison to the cathode surface area, but its imposed potential is the ground one, thus itself constituting the anode surface of the considered setup. Several important substrate heating factors are highlighted and, in order to reduce the most prominent of them, a means to raise the plasma potential is proposed. This is achieved by positively polarizing two additional electrodes with respect to the ground. This additional surface generates a redistribution of the current and consequently regulates the electron flux on the substrate. The results are shown as a function of bias applied on the auxiliary electrodes and discussed in terms of the impact on the substrate heating.

AFM Nano-Plough Planar YBCO Micro-Bridges: Critical Currents and Magnetic Field Effects

The critical current (Ic) of YBa2Cu3O7-x (YBCO) AFM plough micro-constrictions is measured as a function of temperature, width and the magnetic flux density (B), which was applied perpendicular to the YBCO ab-plane and surface of the bridges. C-axis oriented thin films of YBa2Cu3O7-x were deposited on MgO substrates using an inverted cylindrical magnetron (ICM) sputtering technique. The films were then patterned into 8-10 micron size strips, using standard photolithography and dry etching processes. Micro-bridges with widths between 1.9 microm to 4.1 microm were fabricated by using atomic force microscope (AFM) nanolithography techniques. Critical current versus temperature data shows a straight-line behavior, which is typical of constriction type Josephson junctions. The Ic versus B characteristics exhibited a modulation, and a suppression of the critical current of up to 84%. It was also found that the critical current increases with increasing constriction width.

High substrate temperature induced anomalous phase transition temperature shift in sputtered VO 2 thin films

Vanadium dioxide (VO 2) thin films were deposited onto Corning glass substrates by rf reactive inverted cylindrical magnetron sputtering at different substrate temperatures ( T s) ranging from 450 to 600 °C. The influence of substrate temperature on the structural and optical properties was systematically investigated. It revealed that the crystallinity of the VO 2 films improved significantly with T s. The substrate temperature to obtain films with transition temperature ( T c ∼ 70 °C) similar to VO 2 bulk single crystal was 450–500 °C, while high substrate temperatures from 550 to 600 °C tend to shift T c towards higher temperatures from 75 to 80 °C keeping the sharpness of the transition unaltered. Even if the variation of the T c of VO 2 is not dramatic “variation from 70 to 80 °C” with increasing T s is substantial for undoped VO 2 thin films. This sizeable variation of ∼10 °C confirms the tunability of the T c of VO 2 through T s.

Effects of substrate positioning for TiAlN films deposited by an inverted cylindrical magnetron sputtering system

TiAlN films up to 500 nm thick were deposited on glass substrates at three different positions inside an unbalanced inverted cylindrical magnetron sputtering system. The system used two 75 mm tall cylindrical targets (one titanium and one aluminum) separated by about 80 mm. One substrate was located near the titanium target, another near the aluminum target, and a third centered between the targets. In addition, at each location substrates were oriented at three different angles (0, 45, and 60°, measured relative to a horizontal platform). The sputtering power during deposition was maintained at 2 kW with constant argon and nitrogen gas flow rates. The films' elemental compositions at the different locations and orientations were analyzed using energy dispersive X-ray spectroscopy. The X-ray diffraction results showed the presence of a (200) NaCl crystal structure in some of the deposited films; however, the peak intensity varied with the substrate orientation indicating a competition between atom surface diffusion and amorphization. Scanning electron microscope images indicated a grained morphology for all samples.

Observation of Shapiro-Steps in AFM-Plough Micron-Size YBCO Planar Constrictions

Using an atomic force microscope (AFM), we successfully ploughed micron size planar constriction type junctions on YBa2Cu3O7-x thin films. The 100 nanometer (nm) thin films are deposited on MgO substrates by an inverted cylindrical magnetron (ICM) sputtering technique. The films are then patterned into 8-10 micron size strips, using photolithography and dry etching. A diamond coated tip was used with the AFM in this process. We were able to observe well defined current-voltage (I-V) characteristics and Shapiro-steps, successfully demonstrating a possible Josephson effect in these constrictions.

Study of the fluctuation conductivity in YBCO thin film with low transition temperatures

An insulating YBa 2 Cu 3 O 7 - δ (YBCO) thin film was grown by inverted cylindrical magnetron (ICM) sputtering and under nitrogen cooling instead of oxygen in situ annealing. This insulating film went through different annealing processes in flowing oxygen, each time with increasing annealing temperature. The resistivity as a function of temperature was measured after each annealing. The fluctuation conductivity σ ′ ( T ) is determined from the resistivity data and an analysis of the possible mechanisms for scattering of the fluctuating pairs is presented in this work. The crystal structure of the film through these different steps is also reported.

Thermochromic VO 2 thin films synthesized by rf-inverted cylindrical magnetron sputtering

The novel physical vapor deposition called inverted cylindrical magnetron sputtering (also known as hollow cathode sputtering) is commonly used to coat wires, fibers, ribbons as well as all sides of three-dimensional substrates. It is a reproducible method for the production of nano-structured systems onto complex shapes substrates. This paper reports the first synthesis and feasibility of reliably reproduced stoichiometric pure textured VO 2 nano-structures by the rf-inverted cylindrical magnetron sputtering. Morphological, structural, elemental analysis and optical properties of synthesized VO 2 under optimized conditions are reported.

Cr N x and Cr1−xAlxN as template films for the growth of α-alumina using ac reactive magnetron sputtering

Crystalline alumina thin films were deposited on WC–Co substrates using a reactive inverted cylindrical ac magnetron sputtering technique with a chromium oxide prelayer. The interfacial prelayer of chromium oxide was prepared by controlled oxidation of CrNx and Cr1−xAlxN films deposited previously using the same ac reactive magnetron configured with one Cr and Al target. The oxidation was carried out by annealing CrNx and Cr1−xAlxN films in air at 973 and 1373K, respectively. Scanning electron microscopy and energy dispersive x-ray microanalysis were carried out to investigate the thin film surface morphology and composition. The alumina coatings obtained on oxidized CrNx films (templates) were smooth and consisted primarily of κ and α phases. The diffraction peaks from the γ phase were not observed in any of the alumina coatings. The morphology and phase composition of the alumina coatings on the oxidized Cr1−xAlxN films (templates) were strongly dependent on the aluminum content in the films.

Structure-property correlations in aluminum oxide thin films grown by reactive AC magnetron sputtering

Crystalline alumina thin films were deposited on glass, silicon and WC-Co substrates by reactive inverted cylindrical AC magnetron sputtering technique both with and without aluminum precoating at two working pressures. Coatings prepared on Si wafers with Al precoating were found to be γ-phase of aluminum oxide. However alumina coatings prepared on Si wafer without Al precoating showed evidence for the presence of δ and θ-phases besides the γ-phase. Two coating samples grown on Si substrates with Al prelayer were annealed at 400 and 900 °C for 8 h under flowing oxygen conditions. Annealing at 400 °C increased the grain size for γ-alumina phase while annealing to 900 °C formed δ and κ-phases in the coatings. Scanning electron microscopy and energy dispersive X-ray microanalysis were carried out to investigate the thin film surface morphology and composition. While γ-alumina coatings were ultrafine grained, coatings containing δ- and κ-phases showed large size grains. Nanoindentation and nanoscratch tests were performed on all samples to determine the thin film hardness and scratch resistant properties. Higher working pressure during film deposition seemed to lower film hardness values. Significant differences were observed in the mechanical properties of alumina thin films grown with Al precoating on silicon substrates. While the Al precoating improves thin film adhesion and leads to less severe failure, it significantly decreased the thin film hardness as measured by nanoindentation technique.

Optical emission spectroscopy in an inverted cylindrical magnetron plasma

Optical emission spectroscopy was performed on a novel inverted cylindrical magnetron (ICM) sputtering system. This ICM technique offers the advantage of depositing insulating films such as alumina. Initial data were acquired for two conditions: titanium targets with argon (85 sccm) at 0.27 Pa and 6.5 kW; aluminum targets with argon (85 sccm) also at 0.27 Pa and 6.5 kW. For both plasma conditions, emission scans were acquired from 400 to 825 nm. After calibrating our spectroscopy system's optical response, we generated electronic Boltzmann plots using argon lines to evaluate the relative population of five specific excited states. From the Boltzmann plots, we calculated a Boltzmann temperature for each condition. Results indicate a higher temperature (5200 K) for the Ti conditions than for the Al conditions (2100 K), though the population of the argon excited states was higher for the Al conditions. These results are generally consistent with a two-temperature electron energy distribution function where the high energy electrons (responsible for the initial excitation of argon ground state atoms) have more energy for the Al plasma (producing more excited states) but where the low energy electrons and/or neutrals and ions (responsible for the relative distribution of excited states which are close in energy) have lower energy (producing a lower Boltzmann temperature).

Reactive deposition of nitrides and oxides using a twin-cathode inverted cylindrical magnetron

Nitrides and oxides of aluminum and other metals were reactively sputtered in a twin-cathode inverted cylindrical magnetron run with mid-frequency power. This geometry is particularly suited for coating three-dimensional objects of complex shape. However, high rate reactive sputtering in such an enclosed cathode has not been reported and presents unknown processing conditions. High rate deposition requires operation at a point that is normally unstable. For aluminum nitride films, high pumping speed was sufficient to ensure stable operation. Reactive deposition of oxides required feedback from the discharge current to control the flow of oxygen. This was successful for the relatively simple case of aluminum oxide, and the much more complicated case of titanium oxide. Films were deposited onto glass substrates under conditions of different pressure, power, and reactive gas flow. Reactive gas flows were found where good films of aluminum nitride and aluminum oxide could be deposited at high rates. Rates (relative to pure aluminum) were 32% for aluminum nitride and 26–40% for aluminum oxide. Both aluminum nitride and aluminum oxide films were insulating, non-absorbing, and adherent to the glass substrates.

Investigation of the electrical dissipation properties of in-plane aligned a-axis YBCO films grown on (100) LaSrGaO 4 substrates

a-axis YBa 2Cu 3O 7− δ (YBCO) films have been grown on tetragonal (100) LaSrGaO 4 (LSGO) substrates over a PrBa 2Cu 3O 7− δ (PBCO) template layer, using inverted cylindrical magnetron (ICM) sputtering. Detailed X-ray diffraction studies showed that more than 98% of the grains are in-plane aligned with the substrate axes. We have studied the vortex-related phase-transition-like behaviour in these films from dc electrical measurements made with the transport current along the b- and c-axes, and in magnetic fields up to 1 T. Good scaling collapse of the current–voltage isotherms for a wide range of temperatures about the transition is observed when using an algorithm based upon a continuous thermodynamic phase transition such as that between a vortex–liquid and a vortex–glass. We note that the critical scaling exponents are by no means “universal” as expected by some authors and that the exponent z is far higher than expected from analogies with spin–glass systems. The wide range of temperature over which collapse occurs and the very high values of z make the usual association of z and zν with a length and a time scale implausible. Importantly, the observed “transition” temperature, T t, differs appreciably between the two transport current directions for the same magnetic field and field angle. These observations cast doubt on an interpretation for the vortex-related behaviour based on a continuous thermodynamic phase transition such as that between a vortex–liquid and a vortex–glass and alternative possibilities must be explored.

Simultaneous double-sided deposition of HTS films on 3-inch wafers by ICM-sputtering

The construction of a system which allows simultaneous deposition of HTS films on both sides of 3-inch wafers is described. The wafers are placed in a heating cavity which can be heated to 1000/spl deg/C. Deposition is accomplished through two opposite holes in the cavity by inverted cylindrical magnetron (ICM) sputtering guns. YBaCuO films deposited on 3 inch CeO/sub 2/ buffered sapphire substrates revealed a growth quality and T/sub c/ and j/sub c/ values comparable to standard films with sufficient uniformity on both sides of the wafer. The surface resistance of the films measured in the frequency range of 2.68 to 145 GHz is 20 m/spl Omega/ at the highest frequency.

HTS quasiparticle injection devices with large current gain at 77 K

Recent progress on the development of planar QP-injection devices using YBCO and STO as an epitaxial injection barrier will be discussed. The main problem for HTS injection devices is to grow reliably a well defined, ultra-thin tunneling barrier suitable for QP tunneling. For this purpose, we used inverted cylindrical magnetron sputtering to first optimize the smoothness of our YBCO films by controlling tightly an relevant sputtering conditions. We are able to prepare smooth [001] YBCO films on [001] STO substrates on a routine basis with an average roughness varying between 1 and 2 nm. With these flat YBCO films both planar as well as grain boundary junctions were fabricated using epitaxial STO barriers between 2 and 8 nm thick and a 50 nm of Au counter electrode. Planar junctions with 6 nm STO barriers were in most cases fully insulating, in some cases, a current gain of up to 7.4 at 77 K was obtained. For 3 nm STO barriers, the highest current gain was 15 at 81 K. The injection results also show a scaling behavior with junction size. Based on the present materials development and device understanding, we consider a current gain of up to 20 at 77 K possible.

Influence of the process parameters on the growth of YSZ-layers prepared by Ion Beam Assisted Deposition (IBAD)

Cubic yttria stabilized zirconia (YSZ) thin films were grown on amorphous quartz, r-plane sapphire and stainless steel substrates by ion beam sputtering from a planar target under simultaneous ion bombardment (IBAD) during film growth and sputtering employing the inverted cylindrical magnetron (ICM) gun. The formation and modification of preferred orientations was studied by X-ray diffraction and TEM investigations as a function of different deposition parameters like substrate temperature, total pressure, deposition rate, ion beam energy and current. A preferred (100)-orientation could be achieved on untextured substrates by ICM-deposition at substrate temperatures above 800°C and by IBAD without external heating of the substrates. In-plane orientation of YSZ films on untextured substrates was only achieved with IBAD for an ion impact angle α s between 30° and 70°. For α s = 55° the best mosaic spread was observed. The observation of significantly smaller texture distribution widths for epitaxially post-deposited material than measured at the basic YSZ buffer layer was found to be due to a gradual improvement of YSZ growth under ion bombardment with increasing layer thickness.

Development of Na+-sensitive membranes based on sputtered Na-Al-Si glasses

Na+-sensitive microdevices are of increasing interest for integration in microanalytical systems e.g. for biomedical applications or for industrial process control. In order to produce ultra thin Na+-sensitive layers with fixed and reproducible composition and, in particular, defined Na concentration by means of RF sputtering, an off-axis geometry of a magnetron with cylindrical target was chosen for minimizing back-sputtering effects from the already deposited material. With this inverted cylindrical magnetron (ICM) it was possible to obtain reproducible and controllable sodium aluminosilicate glass layers on semiconductor substrates. Several surface and thin layer analytical techniques were applied for characterization of the membranes and for stoichiometry control. Especially by the non-destructive nuclear reaction analysis method a constant Na profile throughout the glass layer and — together with AES depth profiles — the diffusion barrier effect of an Si3N4 interface layer could be verified. Electrochemical measurements proved Nernstian sensitivity down to 10−4 M Na+ in solutions of pH 7, supporting sufficient stability and reproducibility of the sputtered Na+-sensitive layers.

Structural investigation of YBCO films and bicrystal grain boundary junctions

We present a structural analysis of YBCO superconducting thin films fabricatedin situ by Inverted Cylindrical Magnetron (ICM) sputtering on commercial SrTiO3 single-crystal and bicrystal substrates. A detailed structural characterization of the superconductor films was performed by using single-crystal X-ray diffractometry confirming that YBCO films have a strongc-axis orientation of the grains with a small mosaic spread. In the films grown on bicrystal substrates we observed a strong correlation with the lattice structure of the substrate. In addition, a surface analysis of the region across the grain boundary edge has been performed by using scanning electron microscopy.