Direct Current Magnetron Discharge Research Articles

Coherent High-Frequency Axial Oscillations in a Partially Magnetized Direct Current Magnetron Discharge.

High-frequency oscillations are observed in a neon plasma of a direct current magnetron discharge. At low discharge currents, we see highly coherent 60MHz fluctuations. Above a distinct current threshold, secondary 5-10MHz fluctuations emerge in addition to turbulent fluctuations in the 60-100MHz range. The oscillations in the total discharge current suggest axial wave propagation. A lower-hybrid wave theory is invoked to model the high-frequency oscillations. We attribute the low-frequency modes to a turbulence-driven inverse cascade process, as suggested by recent simulations.

Spoke formation in low temperature E×B plasmas: Transition from gradient-drift instability to ionization wave

Long wavelength plasma non-uniformities rotating in the azimuthal direction (“rotating spokes”) have been observed in a number of experiments on Hall thrusters or magnetron discharges. We use a two-dimensional (2D), axial-azimuthal particle-in-cell Monte Carlo collisions model to study the formation of instabilities in a direct current magnetron discharge under conditions close to recent experiments. Despite the simplified 2D geometry of the model, the simulations can reproduce the main features of the experimental results. At a given position above the cathode, corresponding to the spoke location, the simulations show large amplitude oscillations of the plasma density and a very sharp increase in the plasma potential and electron temperature at the leading edge of the spoke, as in time resolved probe measurements. Moreover, the simulations show that the instability evolves in time from a gradient-drift type of instability in the linear phase, to an ionization wave in the non-linear phase, with rotation in the +E×B direction in the first phase and in the −E×B direction in the second phase. The number of spokes is found to increase with pressure, as in experiments. The mechanisms of electron heating and the role of the B×∇B drift in electron heating and in the coherence and direction of spoke rotation are discussed.

On the correlation between the TiN thin film properties and the energy flux of neutral sputtered atoms in direct current magnetron discharge

In this study, the energy flux of sputtered atoms on a substrate was correlated to the properties of titanium nitride (TiN) films deposited using direct current magnetron sputtering (dcMS) under mixed Ar and N2 atmospheres. The neutral titanium sputtered atoms velocity distribution functions (AVDFs) were measured by tunable diode-laser induced fluorescence (TD-LIF), and the flux of particles and their energy were derived. Mass spectrometry was used to characterize the energy-resolved flux of the ions. It was found that the neutral sputtered atoms flux and deposition rate were in good agreement, indicating that the flux of the neutral titanium ground state represents the number of deposited atoms. Moreover, TiN films were deposited at different gas pressures and at various Ar/N2 gas mixtures close to the conditions where stoichiometric TiN was formed, without bias voltage and heating of the substrates. The energy flux of the sputtered neutral Ti into the substrate was calculated from TD-LIF measurements. At a relatively low magnetron discharge pressure of 0.4 Pa, we demonstrated that the energy of sputtered neutral Ti impinging on the substrate is higher than the energy flux of ionized particles corresponding mainly to Ar+. Thus, the influence of the energy flux of the sputtered atoms on the texture and microstructure of the films is revealed. The (200) texture was obtained at 0.4 Pa when the energy flux of the sputtered atoms was higher than the ion energy flux. At 1.3 Pa where the sputtered atoms energy flux is one order lower compared to 0.4 Pa the (111) texture was obtained. The high-energy flux of the ground state of Ti sputtered atoms seems to allow stress removal in the films.

Additive Production of a Material Based on an Acrylic Polymer with a Nanoscale Layer of Zno Nanorods Deposited Using a Direct Current Magnetron Discharge: Morphology, Photoconversion Properties, and Biosafety.

On the basis of a direct current magnetron, a technology has been developed for producing nanoscale-oriented nanorods from zinc oxide on an acrylic polymer. The technology makes it possible to achieve different filling of the surface with zinc oxide nanorods. The nanorods is partially fused into the polymer; the cross section of the nanorods is rather close to an elongated ellipse. It is shown that, with intense abrasion, no delamination of the nanorods from the acrylic polymer is observed. The zinc oxide nanorods abrades together with the acrylic polymer. Zinc oxide nanorods luminesces with the wavelength most preferable for the process of photosynthesis in higher plants. It was shown that plants grown under the obtained material grow faster and gain biomass faster than the control group. In addition, it was found that on surfaces containing zinc oxide nanorods, a more intense formation of such reactive oxygen species as hydrogen peroxide and hydroxyl radical is observed. Intensive formation of long-lived, active forms of the protein is observed on the zinc oxide coating. The formation of 8-oxoguanine in DNA in vitro on a zinc oxide coating was shown using ELISA method. It was found that the multiplication of microorganisms on the developed material is significantly hampered. At the same time, eukaryotic cells of animals grow and develop without hindrance. Thus, the material we have obtained can be used in photonics (photoconversion material for greenhouses, housings for LEDs), and it is also an affordable and non-toxic nanomaterial for creating antibacterial coatings.

Diagnostics of a high-pressure DC magnetron argon discharge with an aluminium cathode

In this article, the plasma parameters of a direct current magnetron discharge in argon at moderate pressure (10 to 40 Pa) using an aluminium cathode are explored. The density of argon excited states, the sputtered aluminium atom density and the electron temperature are estimated using a collisional–radiative model. The electron temperature obtained using optical emission spectroscopic data agrees well with measurements taken using a Langmuir probe. The influence of the discharge parameters, namely the background argon pressure and the discharge current, are discussed.

Operating modes of a magnetized direct-current discharge in helium at pressures ∼10 Pa

A high-pressure direct current magnetron discharge is analyzed using a self-consistent two-dimensional fluid model. This discharge has potential interest in plasma switching applications due to its ability to generate rather dense (plasma density of ∼1019 m−3) stable nonequilibrium plasmas at pressures of ∼13.3 Pa (100 mTorr). This discharge has several advantages over nanosecond pulsed high pressure discharges used in conventional plasma switchers since it operates at much lower voltages and lower gas pressures, with the advantage of much longer cathode lifetime. In the present paper, we analyze the operating modes of this magnetron discharge for conditions close to that of Sommerer et al. [J. Phys. D: Appl. Phys. 52, 435202 (2019)]. We observe the subnormal and normal modes of the magnetron operation whose physics differs from that typical for unmagnetized plasmas.

High Deposition Rate Symmetric Magnet Pack for High Power Pulsed Magnetron Sputtering

Abstract High power pulsed magnetron sputtering is a promising physical vapor deposition technique with two minor challenges that obstruct its broader implementation in industry and its use by researchers. The first challenge is the availability of low cost HPPMS power supplies with output power under 2 kW. Such power supplies are suited for circular planar magnetrons with target diameters between 50 mm to 150 mm. The second challenge is the overall lower deposition rates of HPPMS when compared with direct current magnetron discharges. The “e” magnet pack designed for a 100 mm sputter magnetron which was developed by the Center for Plasma Material Interactions at the University of Illinois at Urbana Champaign in collaboration with Kurt J. Lesker Company was capable of producing twice higher deposition rates in HPPMS compared to a conventional magnet pack. The cylindrically symmetric “TriPack” magnet pack presented here was developed based on magnetic field design solutions from the “e” magnet pack in order to keep the high deposition rates, but improve deposition uniformity, without the need for substrate rotation. The new cylindrically symmetric magnet pack for 100 mm diameter targets, along with a specially designed cooling well provides stable operation at 2 kW average power, even with low-temperature melting-point target materials. The deposition rates from the TriPack magnet pack is compared with a commercial conventional magnet pack for DC and HPPMS power supplies.

High-current impulse magnetron discharge with liquid target

Abstract Impulse magnetron with a liquid cathode operated in copper vapour without the working gas has been experimentally investigated. Stable discharge regimes were obtained through applying the high-current pulses over a 1.5 kW direct current magnetron discharge operated on a liquid copper target. The current–voltage characteristic of the discharge as well as the temporal evolution of the impulse current–voltage relations have been acquired for a constant magnetic field value on the target's surface. The pulsed Langmuir probe diagnostics has been utilized to measure the plasma parameters along the symmetry axis. The pulsed probe diagnostics revealed strong dependences of electron temperature and plasma density on the distance to the target's surface. Electron temperature measured 5 cm away from the target did not exceed 2 eV, and reduced down to 1 eV at longer distances. The maximum value of plasma density along the target's centerline was 2 × 1013 cm− 3, as measured at a distance of 5 cm.

Characterization of energetic and thermalized sputtered tungsten atoms using tuneable diode-laser induced fluorescence in direct current magnetron discharge

In this study a tuneable diode-laser induced fluorescence (TD-LIF) technique (λ0 = 407.4358 nm) is used to determine the atoms' velocity distribution function (AVDF) of energetic and thermalized sputtered tungsten (W) atoms in direct current magnetron discharge. The AVDF is characterized by probing the plasma above the centre of the target racetrack along the magnetron cathode axis in an argon–helium (Ar–He) mixture. Quantitative absorption measurements corroborated by deposition on silicon substrates are used to calibrate the TD-LIF relative measurements. Density, flux, temperature, AVDF and the flux velocity distribution function are derived from fitting the TD-LIF signals with four Gaussians (thermalized atoms) and four (energetic atom) functions (Stepanova and Dew 2004 Nucl. Instrum. Methods Phys. Res. B 215 357) taking into account the natural abundance and resonance wavelength shifts of the four main isotopes. Measurements show transport improvement for W atoms and an increase of the ratio of Ar ions to Ar neutrals with the increase of the percentage of He. All measurements are performed at 0.4 Pa and 100 W. The mean velocity of energetic W atoms typically ranges from 1900 to 2200 m s−1. The densities of thermalized and energetic atoms are in the same order of magnitude (∼109 cm−3) and their corresponding fluxes are several tens of times higher for energetic atoms (∼1015 cm−2 s−1).

Process monitoring during AlNxOy deposition by reactive magnetron sputtering and correlation with the film's properties

In this work, AlNxOy thin films were deposited by reactive magnetron sputtering, using an aluminum target and an Ar/(N2+O2) atmosphere. The direct current magnetron discharge parameters during the deposition process were investigated by optical emission spectroscopy and a plasma floating probe was used. The discharge voltage, the electron temperature, the ion flux, and the optical emission lines were recorded for different reactive gas flows, near the target and close to the substrate. This information was correlated with the structural features of the deposits as a first step in the development of a system to control the structure and properties of the films during reactive magnetron sputtering. As the target becomes poisoned, the discharge voltage suffers an important variation, due to the modification of the secondary electron emission coefficient of the target, which is also supported by the evolution of the electron temperature and ion flux to the target. The sputtering yield of the target was also affected, leading to a reduction of the amount of Al atoms arriving to the substrate, according to optical emission spectroscopy results for Al emission line intensity. This behavior, together with the increase of nonmetallic elements in the films, allowed obtaining different microstructures, over a wide range of compositions, which induced different electrical and optical responses of films.

Development of protective metal coatings on aluminum by magnetron sputtering

Depositions of copper and titanium coatings on aluminum foils and polished aluminum plates for thier protection against corrosion in alkaline media were performed. The coatings were deposited in three different types of magnetron sputtering systems: a direct current (DC) magnetron discharge, a high current impulse magnetron discharge, and a DC magnetron discharge with melted cathode. Only aluminum foils coated with copper films obtained by combined ion-plasma technology, which included preliminarily sputtering of the aluminum surface with an ion beam, deposition of a dense interlayer in the DC magnetron discharge with ion assistance of initial stage of deposition, and deposition of additional layer in the magnetron discharge with melted cathode, were resistant against 30 wt % NaOH solution.

Effect of process parameters on properties of argon–nitrogen plasma for titanium nitride film deposition

In this study, the effect of working pressure and input power on the physical properties and sputtering efficiencies of argon–nitrogen (Ar/N2) plasma in direct current magnetron discharge is investigated. The discharge in Ar/N2 is used to deposit TiN films on high speed steel substrate. The physical plasma parameters are determined by using Langmuir probe and optical emission spectroscopy. On the basis of the different reactions in the gas phase, the variation of plasma parameters and sputtering rate are explained. A prominent change of electron temperature, electron density, ion density, and degree of ionization of Ar is found as a function of working pressure and input power. The results also show that increasing working pressure exerts a negative effect on film deposition rate while increasing input power has a positive impact on the same. To confirm the observed physical properties and evaluate the texture growth as a function of deposition parameters, x-ray diffraction study of deposited TiN films is also done.

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High power pulsed magnetron sputtering is a promising physical vapor deposition technique with two minor challenges that obstruct its broader implementation in industry and its use by researchers. The first challenge is the availability of low cost HPPMS power supplies with output power under 2 kW. Such power supplies are suited for circular planar magnetrons with target diameters between 50 mm to 150 mm. The second challenge is the overall lower deposition rates of HPPMS when compared with direct current magnetron discharges. The “ε” magnet pack designed for a 100 mm sputter magnetron which was developed by the Center for Plasma Material Interactions at the University of Illinois at Urbana Champaign in collaboration with Kurt J. Lesker Company was capable of producing twice higher deposition rates in HPPMS compared to a conventional magnet pack. The cylindrically symmetric “TriPack” magnet pack presented here was developed based on magnetic field design solutions from the “ε” magnet pack in order to keep the high deposition rates, but improve deposition uniformity, without the need for substrate rotation. The new cylindrically symmetric magnet pack for 100 mm diameter targets, along with a specially designed cooling well provides stable operation at 2 kW average power, even with low-temperature melting-point target materials. The deposition rates from the TriPack magnet pack is compared with a commercial conventional magnet pack for DC and HPPMS power supplies.

Structure of the direct-current magnetron discharge in neon at different polarities of the electrode system

A dc magnetron discharge in neon is studied at different polarities of the electrode system. It is found that the electron energy distribution function is composed of three groups of electrons: fast electrons accelerated by the strong field of a cathode sheath, slow electrons confined in a potential well due to the space-charge field, and intermediate-energy electrons. It is shown that the energy distribution of the confined electrons is a Maxwell-Boltzmann distribution function, whereas the energy distribution of the intermediate electrons is typical of electron diffusion at a constant total energy. The measured values of the cathode sheath thickness depend on the source polarity.

Qualitative model of the magnetron discharge

A simple model of the direct current magnetron discharge is introduced, relating the discharge current I, voltage V, sheath thickness d, plasma density, pressure P, magnetic field and material constants. The model is based on microscopic physics, balancing the generation and loss of ions. After deriving the balance equation m ( d ) c ( P ) V W = 1 / γ , with m( d) a multiplication factor, c( P) a confinement factor, W the effective ionization potential of the sputter gas and γ the ion induced secondary electron emission coefficient, a generic description of the discharge is made. The model is shown to reproduce many experimental results reported in literature, including a minimum voltage and steep I–V characteristics.

Time-Resolved Ionisation Studies of the High Power Impulse Magnetron Discharge in Mixed Argon and Nitrogen Atmosphere

Magnetron sputtering technology is widely used to grow thin films on a range of substrate materials. High power impulse magnetron sputtering (HIPIMS) technology differentiates itself from other types of magnetron sputtering by the high degree of ionisation of the sputtered material achieved by applying high peak powers of 3 kW · cm−2 (4 A · cm−2) at duty cycles of <1%. The current paper discusses HIPIMS of Ti in mixed argon and nitrogen atmosphere, commonly used for hard coatings deposition. Estimation of the composition of the ion deposition flux arriving at the substrate position is extracted from energy-resolved mass spectrometry data. The measured time-resolved ion mass and ion energy distribution functions were compared for the HIPIMS discharge and industry-standard direct current (DC) and medium frequency pulsed DC magnetron discharges operated at the same average power of 2 W · cm−2. In inert Ar atmosphere, HIPIMS produced a metal-dominated ion flux with Ti1+ concentration of 46%, compared to 10% in DC operation. In reactive atmosphere of Ar and 10% N2 the HIPIMS discharge produced an ion flux with significantly increased content of ionised film-forming species such as Ti1+, Ti2+ and N1+. The atomic ion N1+ was the most abundant species representing 40% of the total flux with Ti1+ 19% and Ar1+ 19%. In contrast, the ion flux in DC and pulsed DC discharges was dominated by Ar1+ and molecular ion N.

Guiding the deposition flux in an ionized magnetron discharge

A study of the ability to control the deposition flux in a high power impulse magnetron sputtering discharge using an external magnetic field is presented in this article. Pulses with peak power of 1.4 kW cm−2 were applied to a conventional planar magnetron equipped with an Al target. The high power creates a high degree of ionization of the sputtered material, which opens an opportunity to control the energy and direction of the deposition species. An external magnetic field was created with a current carrying coil placed in front of the target. To measure the distribution of deposition material samples were placed in an array surrounding the target and the depositions were made with and without the external magnetic field. The distribution is significantly changed when the magnetic field is present. An increase of 80% in deposition rate is observed for the sample placed in the central position (right in front of the target center) and the deposition rate is strongly decreased on samples placed to the side of the target. The measurements were also performed on a conventional direct current magnetron discharge, but no major effect of the magnetic field was observed in that case.

Diagnostics of a N2/Ar direct current magnetron discharge for reactive sputter deposition of fullerene-like carbon nitride thin films

Plasma probe measurements and energy selective mass spectrometry were used to characterize the composition and energetic conditions of the ion flux of a direct current, N2/Ar, unbalanced magnetron sputtering plasma in front of a graphite target, depending on the total pressure and gas composition. It is shown that the flux of ionized film-forming species consist predominantly of CxNy (x,y⩽2) species. The total number of C-containing ions strongly depends on the N2 fraction in the discharge and can be increased by almost one order of magnitude scaling with the availability of N2 as the discharge gas. This finding suggests that besides C and N atoms and ions, other species, like preformed CxNy particles, play an important role during growth of fullerene-like (FL) carbon nitride (CNx) thin films. It is proposed that such clusters have a direct effect as growth templates or nucleation sites on the evolution of curved and cross-linked FL structures. The carbon target was identified as the main source of preformed C-containing species, following from the pressure dependence of the ion energy distributions of the most abundant CxNy (x,y⩽2) ions.

Transverse electric field and density gradient induced instabilities in a cylindrical magnetron discharge

Recent one-dimensional particle-in-cell simulations of a cylindrical postcathode direct current magnetron discharge have shown a transition from the usual positive space charge mode, dominated by a strong cathode fall, to a higher impedance negative space charge mode, characterized by a broad anode fall, as either the pressure is decreased or the magnetic field is increased. Such behavior is consistent with a steady decrease in the cross-field electron transport coefficients as calculated from classical fluid theory. However, experimental measurements of the distribution of electric potential between the electrodes do not exhibit any systematic variation with changes in magnetic field or pressure. This suggests that anomalous transport mechanisms increase the electron transport above the level predicted by classical transport theory, so maintaining the positive space charge mode at low pressures. It is shown using a fluid model that electrostatic oscillations with ω≳νi, where νi is the ion-neutral collision frequency, propagating in the E×B direction are unstable with growth rates comparable to the charged particle transit times. Such oscillations, which cannot be modeled in a one-dimensional particle-in-cell model, may contribute to the anomalous transport observed in experiments.

Prediction of the evolution of the erosion profile in a direct current magnetron discharge

We have performed a simulation of ion and fast neutral transport in the sheath region of a direct current magnetron discharge under different pressures by using the Boltzmann equation and the database from the two-dimensional (2D) results of a plasma structure, which was given by a hybrid model. Evolution of the erosion profile on the target surface has been predicted by using the 2D energy distributions of ions and fast neutrals incident on the target (cathode) surface. We confirmed that an accurate prediction of the erosion profile can be obtained by assuming that the constant sputtering yield corresponds to the cathode voltage under conditions of low pressures that make use of the film deposition processes.