Circular Magnetron Research Articles

Ion current optimization in a magnetron with tunable magnetic field configuration

The response of the ion current in the substrate region to the magnetic system configuration of a circular magnetron was studied during direct current sputtering of aluminum target. The unbalancing degree induced by changing of magnets’ positions was modelled with finite element methods. The ion saturation current in the substrate region showed more than twofold variation with unbalancing degree in the range 0.6–1.2. The dependence was non-monotonic, and the system was optimized to maximize the substrate ion current. The Langmuir probe diagnostics showed plasma density ~ 1016 m−3 in the optimized magnetic configuration.

Axisymmetric magnetically enhanced discharges described in terms of flux coordinates

Magnetically enhanced glow discharges and arcs are widely used in materials processing and other branches of plasma technology. An important class—including, for example, circular magnetrons, Hall thrusters, and certain ion sources—is axisymmetric devices with a poloidal magnetic field. This paper discusses the representation of such fields using the so-called flux coordinates (ψ,θ,s), a system of field aligned spatial coordinates which include the flux label ψ of a magnetic field line, the azimuth angle θ, and the arc length s. After reviewing the formalism—which finds widespread use in fusion research and plasma astrophysics—a number of special amendments are introduced to make it suitable for technological plasmas. Focus is put on the description of internal and external domain boundaries (separatrices and walls). The flux coordinates are numerically constructed for the confinement region of a circular magnetron using an analytical field model that was obtained in earlier investigations by fitting a physically plausible ansatz to Hall probe measurements. As a first application, the dynamics of the energetic electron component in a high power impulse magnetron sputtering discharge is investigated on the basis of a linear kinetic model and the corresponding confinement is calculated by solving an eigenvalue problem.

Tuning the size, composition and structure of Au and Co50Au50 nanoparticles by high-power impulse magnetron sputtering in gas-phase synthesis

Gas-phase synthesis of nanoparticles with different structural and chemical distribution is reported using a circular magnetron sputtering in an ion cluster source by applying high-power impulses. The influence of the pulse characteristics on the final deposit was evaluated on Au nanoparticles. The results have been compared with the more common direct current approach. In addition, it is shown for the first time that high-power impulses in magnetron based gas aggregation sources allows the growth of binary nanoparticles, CoAu in this case, with a variety of crystalline and chemical arrangements which are analyzed at the atomic level.

Influence of modulation frequency on the synthesis of thin films in pulsed magnetron sputtering processes

Abstract The research on the influence of modulation frequency on the properties of films synthesized using a unique pulsed power supply combined with a standard unbalanced circular magnetron was conducted in the process of pulsed magnetron sputtering (PMS). It was shown that by using different levels of modulation, the composition of plasma (measured by optical emission spectroscopy, OES) as well as film growth rate and morphology (observed with scanning electron microscope, SEM), can be changed. The impact of modulation is related to the used materials and gases and can vary significantly. It was concluded that modulation frequency can greatly influence the synthesis of materials and can be used as an additional parameter in PMS. Specific relations between modulation frequency and synthesized material require further investigation.

Reconstruction of the static magnetic field of a magnetron

The simulation of magnetron discharges requires a quantitatively correct mathematical model of the magnetic field structure. This study presents a method to construct such a model on the basis of a spatially restricted set of experimental data and a plausible a priori assumption on the magnetic field configuration. The example in focus is that of a planar circular magnetron. The experimental data are Hall probe measurements of the magnetic flux density in an accessible region above the magnetron plane [P. D. Machura et al., Plasma Sources Sci. Technol. 23, 065043 (2014)]. The a priori assumption reflects the actual design of the device, and it takes the magnetic field emerging from a center magnet of strength mC and vertical position dC and a ring magnet of strength mR, vertical position dR, and radius R. An analytical representation of the assumed field configuration can be formulated in terms of generalized hypergeometric functions. Fitting the ansatz to the experimental data with a least square method results in a fully specified analytical field model that agrees well with the data inside the accessible region and, moreover, is physically plausible in the regions outside of it. The outcome proves superior to the result of an alternative approach which starts from a multimode solution of the vacuum field problem formulated in terms of polar Bessel functions and vertical exponentials. As a first application of the obtained field model, typical electron and ion Larmor radii and the gradient and curvature drift velocities of the electron guiding center are calculated.

Design of circular composite sputtering cathode and simulation of its discharge characteristics

Based on the two-dimensional finite element method, the magnetic field of circular composite magnetron sputtering cathode is calculated by COMSOL software. The genetic algorithm and simulated annealing algorithm combined with Matlab optimization toolbox are used to optimize the structure of circular composite magnetron sputtering cathode, and the structural parameters with the largest utilization rate of target are obtained. For the resulting optimized magnetron cathode, based on the self-consistent particle simulation method, the discharge characteristics under different working conditions are simulated by VSim software. It is found that with the increase of non-equilibrium degree of magnetic field, the cathode surface potential drops to the maximum position and the location of the plasma aggregation, moving from the outer surface of the cathode to the center, the intensity of the magnetic field on the cathode surface decreases When the two coils have no currents flowing, the density of the plasma is largest and the thickness of the sheath is smallest In the two coils there flow reverse 5 A currents, the non-equilibrium magnetic field reaches a maximum value and the thickness of sheath is largest, the corresponding electric field strength is weak, which is not conducive to the impact ionization, so the plasma density is smallest However, in the two coils there flow positive 5 A currents, and the non-equilibrium magnetic field is smallest, the plasma density and the sheath thickness are not only related to the non-equilibrium magnetic field, but also to the magnetic field strength. Finally, according to the results of particle simulation, the target erosion depth of the magnetron cathode is studied. Combined with the sputtering yield curve, the curve of etching depth of the cathode target surface is obtained. It is found that the erosion range of the target extends from 60 mm to 76.2 mm (target radius) before and after optimization. By adjusting the magnitudes and directions of currents in the two coils, all the target surfaces can be etched, which greatly improves the target utilization.

Расчет движения подложки для повышения равномерности покрытий в установках с планарными цилиндрическими магнетронами

Расчет движения подложки для повышения равномерности покрытий в установках с планарными цилиндрическими магнетронами

Design and test of HTS magnet for circular planar magnetron cathode

The HTS magnet with half-closure iron yoke is investigated for circular planar magnetron cathode application. The design optimization of the magnet is performed with two optimization objectives: the maximum value of the horizontal component of magnetic field (Br) on the target surface Br1max, and the maximum value of Br where the magnetic field is parallel to the target surface Br2max. Aimed at the magnetron cathode with 3 inch target, the HTS coils are fabricated with YBCO tapes, and the iron yoke is fabricated with 1J22 alloy. The critical current and magnetic field of HTS magnet are simulated and tested at 77 K, the results show that the critical current of HTS magnet is about 50 A, and the designed HTS circular magnetron could generate the magnetic field higher than 0.13 T on the target surface, which could meet the requirement of high-field magnetron sputtering.

Focus on materials, semiconductors, vacuum, and cryogenics

Focus on materials, semiconductors, vacuum, and cryogenics

Spoke rotation reversal in magnetron discharges of aluminium, chromium and titanium

The rotation of localised ionisation zones, i.e. spokes, in magnetron discharge are frequently observed. The spokes are investigated by measuring floating potential oscillations with 12 flat probes placed azimuthally around a planar circular magnetron. The 12-probe setup provides sufficient temporal and spatial resolution to observe the properties of various spokes, such as rotation direction, mode number and angular velocity. The spokes are investigated as a function of discharge current, ranging from 10 mA (current density 0.5 mA cm−2) to 140 A (7 A cm−2). In the range from 10 mA to 600 mA the plasma was sustained in DC mode, and in the range from 1 A to 140 A the plasma was pulsed in high-power impulse magnetron sputtering mode. The presence of spokes throughout the complete discharge current range indicates that the spokes are an intrinsic property of a magnetron sputtering plasma discharge. The spokes may disappear at discharge currents above 80 A for Cr, as the plasma becomes homogeneously distributed over the racetrack. Up to discharge currents of several amperes (the exact value depends on the target material), the spokes rotate in a retrograde direction with angular velocity in the range of 0.2–4 km s−1. Beyond a discharge current of several amperes, the spokes rotate in a direction with angular velocity in the range of 5–15 km s−1. The spoke rotation reversal is explained by a transition from Ar-dominated to metal-dominated sputtering that shifts the plasma emission zone closer to the target. The spoke itself corresponds to a region of high electron density and therefore to a hump in the electrical potential. The electric field around the spoke dominates the spoke rotation direction. At low power, the plasma is further away from the target and it is dominated by the electric field to the anode, thus retrograde rotation. At high power, the plasma is closer to the target and it is dominated by the electric field pointing to the target, thus rotation.

The effect of changing the magnetic field strength on HiPIMS deposition rates

The marked difference in behaviour between HiPIMS and conventional dc or pulsed-dc magnetron sputtering discharges with changing magnetic field strengths is demonstrated through measurements of deposition rate. To provide a comparison between techniques the same circular magnetron was operated in the three excitation modes at a fixed average power of 680 W and a pressure of 0.54 Pa in the non-reactive sputtering of titanium. The total magnetic field strength B at the cathode surface in the middle of the racetrack was varied from 195 to 380 G. DC and pulsed-dc discharges show the expected behaviour that deposition rates fall with decreasing B (here by ~25–40%), however the opposite trend is observed in HiPIMS with deposition rates rising by a factor of 2 over the same decrease in B.These observations are understood from the stand point of the different composition and transport processes of the depositing metal flux between the techniques. In HiPIMS, this flux is largely ionic and slow post-ionized sputtered particles are subject to strong back attraction to the target by a retarding plasma potential structure ahead of them. The height of this potential barrier is known to increase with increasing B.From a simple phenomenological model of the sputtered particles fluxes, and using the measured deposition rates from the different techniques as inputs, the combined probabilities of ionization, α, and back attraction, β, of the metal species in HiPIMS has been calculated. There is a clear fall in αβ (from ~0.9 to ~0.7) with decreasing B-field strengths, we argue primarily due to a weakening of electrostatic ion back attraction, so leading to higher deposition rates. The results indicate that careful design of magnetron field strengths should be considered to optimise HiPIMS deposition rates.

High rate deposition of thin film cadmium sulphide by pulsed direct current magnetron sputtering

Cadmium Sulphide (CdS) is an important n-type semiconductor widely used as a window layer in thin film photovoltaics Copper Indium Selenide, Copper Indium Gallium (di)Selenide, Copper Zinc Tin Sulphide and Cadmium Telluride (CdTe). Cadmium Sulphide has been deposited using a number of techniques but these techniques can be slow (chemical bath deposition and Radio Frequency sputtering) or the uniformity and the control of thickness can be relatively difficult (close space sublimation). In this paper we report on the development of a process using pulsed Direct Current magnetron sputtering which allows nanometre control of thin film thickness using time only. The CdS thin films deposited in this process are highly uniform and smooth. They exhibit the preferred hexagonal structure at room temperature deposition and they have excellent optical properties. Importantly, the process is highly stable despite the use of a semi-insulating magnetron target. Moreover, the process is very fast. The deposition rate using 1.5kW of power to a 6-inch circular magnetron was measured to be greater than 8nm/s. This makes the process suitable for industrial deployment.

In situ synthesis of α-alumina layer at top yttrium-stabilized zirconia thermal barrier coatings for oxygen barrier

The thermally grown oxide (TGO) at the interface of a ceramic-bond coating plays an important role in the failure of the thermal barrier coating (TBC). Therefore, it is important to control the growth of TGO to improve its service lifetime. In this paper an aluminum film was first deposited on the surface of atmospheric plasma sprayed TBC by direct current circular magnetron sputtering. Then the TBC samples with the aluminum film received a vacuum heat treatment. In situ synthesis of α-Al2O3 layer was observed at the top of the ceramic coating through the reaction of Al and ZrO2. The schematic diagram and thermodynamic mechanism of in situ synthesis of α-Al2O3 layer were presented. The cross sections of as-sprayed and treated TBCs were characterized by field emission-scanning electron microscopy (FE-SEM). Both phase structures were analyzed by X-ray diffraction (XRD) and transmission electron microscope (TEM) assisted with energy dispersive spectroscopy (EDS) and focused ion beam (FIB). Finally, oxidation resistance was compared between as-sprayed TBCs and vacuum treated TBCs and the average thickness of TGO was 4.89±0.53 and 2.52±0.47μm correspondingly.

Numerical Simulation of Film Thickness Uniformity Deposited by Planar Circular Magnetron Sputtering System

There exist angular offset and eccentricity between target and substrate in most practical multi-target magnetron sputtering systems, which should be seriously considered when we calculate the film distribution. This simulation results suggested that excellent thickness uniformity can be obtained when increased the substrate-target distance, angular offset, and eccentricity, but decreased the film thickness simultaneously. However, superior uniformity films without reducing the thickness remarkably can also obtained when the geometry configuration are proper configured.

Installation and commissioning of the new Fermi National Accelerator Laboratory H- Magnetron

The Fermi National Accelerator Laboratory (FNAL) 40 year old Cockcroft-Walton 750 keV injectors with slit aperture magnetron ion sources have been replaced with a circular aperture magnetron, Low Energy Beam Transport, Radio Frequency Quadrupole Accelerator, and Medium Energy Beam Transport, as part of the FNAL Proton Improvement Plan. The injector design is based on a similar system at Brookhaven National Laboratory. The installation, commissioning efforts, and source operations to date will be covered in this paper along with plans for additional changes to the original design to improve reliability by reducing extractor spark rates and arc current duty factor.

Space-resolved velocity and flux distributions of sputtered Ti atoms in a planar circular magnetron discharge

The tuneable diode-laser-induced fluorescence (TD-LIF) technique was used to investigate both velocity and flux distributions of ground-state titanium atoms sputtered from a planar circular magnetron target working at a low pressure (0.4 Pa) and a high pressure (4 Pa). TD-LIF Doppler profiles were measured in front of the racetrack: (i) normal (vz) and parallel (vr) to the target at several distances (z), and (ii) for different angles (α) at 10 mm from the target, addressing the same local volume. The space variation of the velocity and flux distribution functions was deduced with high accuracy from the Doppler shift. Thus it was possible to determine the energetic over thermalized relative atom flux ratio going away from the cathode. The energy distribution function of Ti sputtered atoms in the normal direction is in good agreement with the extended Thompson's formula only for the collisionless sputtering regime, namely in the vicinity of the target and at low gas pressures. Moreover, TD-LIF measurements into the plasma but close to the racetrack centre with different angles of the laser beam show that the angular dependence of the energetic particles is well described by the projection of the normal velocity on each investigated direction. Hence, in this particular plasma region (10 mm in front of the racetrack), the actual angular velocity distribution is mainly governed by the component perpendicular to the target.

Influence of the magnetic field configuration on the reactive sputter deposition of TiN

AbstractA conventional 2 inch planar, circular magnetron has been designed allowing an in situ variation of the magnetic field configuration, i.e. the distance of the peripheral magnet ring and central magnet cylinder to the target could be varied independently from each other. The development of this kind of magnetron allows us to investigate the influence of the strength and shape of the magnetic field on the growth of TiN films. Such TiN films were deposited on grounded stainless steel substrates by sputtering a pure Ti target in a mixture of Ar and N2. The influence of the N2 flow and the magnetic field configuration on the crystallographic orientation of the deposited films has been investigated. At similar conditions, the influence of the magnetic field configuration and N2 flow on the discharge voltage, deposition rate and the ion flux towards the substrate has been investigated. No clear relationship between the ion‐to‐atom ratio and the crystallographic orientation has been observed.

Numerical Simulation of Inductive Phase Shift Due a Brain Hematoma

We show a theoretically electromagnetic induction method to detect the changes of ∞uid volume into an organic tissue. This method is technique to detect a phase shift through measurements of induced electrical currents due a RF signal. This method was designed for volumetric brain edema monitoring. Circular and planar magnetron coils were evaluated and compared for their ability to detect edema in the brain through volumetric inductive phase shift spectroscopy. The circular coil was considered as a single turn wire and the magnetron surface coil conflguration was based on the principle of the cavity magnetron with successive slots. The brain cavity was modeled as an idealized sphere transversely centered with respect to the coils. The volumetric sensitivity to changes in the brain was examined by inserting in the brain cavity a spherical edema/haematoma. Spectra of inductive phase shift induced in a second circular or magnetron receiver coils were estimated between frequencies from 100kHz to 50MHz. Phase shift shows sensitivity to the presence of the edema/haematoma increased with frequency. The use of a planar magnetron as the receiver coil produced a substantial increase in sensitivity, in particular at higher frequency of 50MHz. Trauma to the head may results in the accumulation of liquids or blood in certain region of the brain. Edema is a medical condition in which the relative amount of liquid in tissue or organs increases. Haematoma is a pathological condition in which accumulation of blood occurs in a speciflc region. The characteristic of brain edema/haematoma is that it develops in a delayed and gradually progressive fashion after a head trauma or event has occurred, over a period of hours or days, and is a cause of substantial mortality (1). Detection of edema/haematoma in the brain is essential for assessment of the medical condition and treatment. Because the complex electrical properties of edema/haematoma are substantially difierent from a hose of normal tissue, various measurements of electrical properties of the brain where proposed to non-invasive detect the changes in there (2{6). In order to optimize the detection technology we have explored, in a recent study, the possible use of a magnetron coil (7) on the inductive volumetric phase shift of the brain in the presence of a edema/haematoma. We have compared the sensitivity of a magnetron coil with that of a circular coil. The results have shown that the magnetron coil has a somewhat greater sensitivity to the detection of a edema/haematoma than the circular coil. This study reveals that the location of the edema/haematoma has a substantial efiect on the sensitivity of the magnetron and circu- lar coils. Furthermore, we flnd that at certain difierent frequencies the various locations of the edema/haematoma produce no volumetric phase shift.

Monte Carlo Simulation of Electrons' and Ions' Trajectories in Magnetron Sputtering Systems

AbstractA 3D simulation system has been developed to study electron and ion densities and other plasma parameters in circular and rectangular magnetron sputtering systems. Typically, 105 particles of each species are tracked simultaneously for a time period when the plasma parameters' distributions get stabilised. During this period, the particles undergo Lorentz force and different kinds of collisions. The collisions are generated by Monte Carlo method using null‐collision technique.

High Temporal Resolution Ion Energy Distribution Functions in HIPIMS Discharges

AbstractA technique for obtaining high time resolution ion energy distribution functions (IEDFs) at the substrate in depositing plasma has been demonstrated, and applied to a high power impulse magnetron sputtering (HIPIMS) discharge. Key to this technique is the electrostatic gating of ions inside the instrument end cap. To demonstrate the performance of this technique, IEDF measurements with a 2 µs time‐resolution have been made with the following HIPIMS operating conditions: a repetition rate of 100 Hz, a pulse width of 100 µs, a pressure of 0.26 Pa and a peak power density of 2.5 kW cm−2. The orifice of the mass spectrometer was positioned facing the racetrack region of the circular magnetron cathode. The Ar+ ions were detected 8 µs after initiation of the discharge voltage pulse, exhibiting a narrow distribution of energies, while Ti+ ions were detected 14 µs after the initiation, showing a high‐energy tail extending up to 100 eV. The time‐evolution of Ti+ ions show that the metal flux starts to be built up at the substrate position at times 20 µs after the pulse initiation.