Radio Frequency Magnetron Discharge Research Articles

Rotating spokes, potential hump and modulated ionization in radio frequency magnetron discharges

In this work, the transition from the gradient drift instability (GDI) into an m = 1 rotating spoke in the radio frequency magnetron discharge was studied by means of the two-dimensional axial-azimuthal (z − y) particle-in-cell/Monte Carlo collision method. The kinetic model combined with the linear analysis of the perturbation revealed that the cathode sheath (axial) electric field E z triggers the GDI, deforming the local potential until the instability condition is not fulfilled and the fluctuation growth stops in which moment the instability becomes saturated. The potential deformation consequently leads to the formation of the potential hump, surrounding which the azimuthal electric field E y is present. The saturation level of E y was found to be synchronized with and proportional to the time-changing voltage applied at the cathode, resulting in the RF-modulation of the electron heating in the E y due to drift. In the saturated stage of the instability, it was shown that the rotation velocity and direction of the spoke present in the simulations agree well with the experimental observation (Panjan 2019 J. Appl. Phys. 125 203303). In the instability linear stage, the instability mode wavelength and the growth rate were also found to be in good agreement with the prediction of the GDI linear fluid theory.

Sputter deposition of Titanium and Nickel thin films in radio frequency magnetron discharge characterized by optical emission spectroscopy and by Rutherford backscattering spectrometry

By using a homemade dual magnetron sputtering system, two combined investigations by Optical emission spectroscopy and by Rutherford backscattering spectrometry were performed on a Radio-Frequency discharge for Titanium and Nickel deposited in pure Argon gas. Line intensities of various species present in the plasma were compared to the Argon emission line I of 696.5nm for different gas pressure and power density values. The electron temperature was also determined from the collisional radiative model and then correlated to the gas pressure and the power density. It was found that the sputtering pressure alters the spectrum intensity of Nickel, but has no obvious effect on that of Titanium during sputtering. The variation of average deposition rate as a function of gas pressure was experimentally determined via the Rutherford backscattering technique and then correlated to the variation of electron temperature of (Titanium-Argon) and (Nickel-Argon) discharges versus gas pressure.

Modification of polylactic acid surface using RF plasma discharge with sputter deposition of a hydroxyapatite target for increased biocompatibility

Surface modification of polylactic acid (PLLA) by plasma of radio-frequency magnetron discharge with hydroxyapatite target sputtering was investigated. Increased biocompatibility was demonstrated using studies with bone marrow multipotent mesenchymal stromal cells. Atomic force microscopy demonstrates that the plasma treatment modifies the surface morphology of PLLA to produce rougher surface. Infrared spectroscopy and X-ray diffraction revealed that changes in the surface morphology are caused by the processes of PLLA crystallization. Fluorescent X-ray spectroscopy showed that the plasma treatment also changes the chemical composition of PLLA, enriching it with ions of the sputtered target: calcium, phosphorus and oxygen. It is hypothesized that these surface modifications increase biocompatibility of PLLA without increasing toxicity.

Effects of Increasing Magnetic Field and Decreasing Pressure on Asymmetric Magnetron Radio Frequency ${\rm Ar}/{\rm O}_{2}$ Discharges

The aim of this paper is to define the optimal couple of the total pressure and the magnetization of the permanent magnets for self-maintaining under optimal conditions an asymmetric magnetron radio frequency (RF) discharge. Electro-dynamics discharge simulations are based on a self-consistent particle model using Monte Carlo method for the treatment of collisions between charged particle and background gas. The simulations are performed at a fixed mixture of 90% Ar/10% O2 by simultaneously decreasing the total pressure P and increasing the magnetization σ. In the case of a sinusoidal RF power supply with 200 V for peak voltage and 13.56 MHz for frequency, the magnetization of the permanent magnets varies between 500 Gauss at 25 mTorr to 1400 Gauss at 5 mTorr. We use a semianalytical method for calculating the applied magnetic field generated by two permanent magnets that are composed of concentric rings. This enables generating, in a specific region of the interelectrode gap near the cathode, an optimal magnetic field crossing the RF electric field for application to magnetron discharges. The simulation results of RF magnetron discharge shown that, in the case of the lowest considered pressure (5 mTorr), a high magnetization of 1400 Gauss is the most favorable for self-maintaining the discharge and generating a quasi-ion beam energy distribution near the cathode that is interesting for cathode sputtering processes.

Energy fluxes in a radio-frequency magnetron discharge for the deposition of superhard cubic boron nitride coatings

Energy flux measurements by a calorimetric probe in a rf-magnetron plasma used for the deposition of super-hard c-BN coatings are presented and discussed. Argon as working gas is used for sputtering a h-BN target. Adding a certain amount of N2 is essential for the formation of stoichiometric BN films, since a lack of nitrogen will lead to boron rich films. Subsequently, the contributions of different plasma species, surface reactions, and film growth to the resulting variation of the substrate temperature in dependence on nitrogen admixture are estimated and discussed. In addition, SRIM simulations are performed to estimate the energy influx by sputtered neutral atoms. The influence of magnetron target power and oxygen admixture (for comparison with nitrogen) to the process gas on the total energy flux is determined and discussed qualitatively, too. The results indicate that variation of the energy influx due to additional nitrogen flow, which causes a decrease of electron and ion densities, electron temperature and plasma potential, is negligible, while the admixture of oxygen leads to a drastic increase of the energy influx. The typical hysteresis effect which can be observed during magnetron sputtering in oxygen containing gas mixtures has also been confirmed in the energy influx measurements for the investigated system. However, the underlying mechanism is not understood yet, and will be addressed in further investigations.

Investigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H2 radio frequency magnetron discharge

The plasma parameters and ion energy distributions (IED) of the dominant species in an Ar-H2 discharge are investigated with an energy resolved mass spectrometer and a Langmuir probe. The plasmas are generated in a conventional magnetron chamber powered at 150 W, 13.56 MHz at hydrogen flow rates ranging from 0 to 25 sccm with a fixed argon gas flow rate of 15 sccm. Various Hn+, SiHn+, SiHn fragments (with n = 1, 2, 3) together with Ar+ and ArH+ species are detected in the discharge. The most important species for the film deposition is SiHn (with n = 0, 1, 2). H fragments affect the hydrogen content in the material. The flux of Ar+ decreases and the flux of ArH+ increases when the hydrogen flow rate is increased; however, both fluxes saturate at hydrogen flow rates above 15 sccm. Electron density, ne, electron energy, Te, and ion density, ni, are estimated from the Langmuir probe data. Te is below 1.2 eV at hydrogen flow rates below 8 sccm, and about 2 eV at flow rates above 8 sccm. ne and ni decrease with increased hydrogen flow but the ratio of ni to ne increases. The formation of H+ ions with energies above 36 eV and electrons with energies greater than 2 eV contributes to the decrease in hydrogen content at hydrogen flow rates above 8 sccm. Analysis of the IEDs indicates an inter-dependence of the species and their contribution to the thin film growth and properties.

Hollow target magnetron-sputter-type solid material ion source

A thin-walled aluminum (Al) hollow electrode has been inserted into an ion source to serve as an electrode for a radio frequency magnetron discharge. The produced plasma stabilized by argon (Ar) gas sputters the Al electrode to form a beam of Al(+) and Ar(+) ions. The total beam current extracted through a 3 mm diameter extraction hole has been 50 μA, with the Al(+) ion beam occupying 30% of the total beam current.

Photocatalytic chemisorption of water on titanium dioxide thin films obtained by radio frequency magnetron deposition

The photocatalytic chemisorption of water on titanium dioxide (TiO 2) thin films was studied by photocurrent decay experiments on the films exposed to water vapour. The TiO 2 films were deposited on quartz substrates by sputtering of a high purity TiO 2 target in a radio frequency magnetron discharge in argon–oxygen gas. In vacuum (10 −2 Torr), the films with good photocatalytic activity had large induced photocurrent intensity and long electrical charge carrier lifetime, when compared to the films with low photocatalytic activity. The photocurrent decay in good photocatalytic films exposed to water–argon gas mixture at atmospheric pressure depended strongly on the gas humidity, larger decay rates being observed at larger humidity values. Because of the oxygen chemisorption, the photocurrent decay rates were larger in air than in the same humidity water–argon gas.

Diagnostics of the radio frequency magnetron discharge plasma used for TiO 2 thin film sputtering deposition

The density, temperature and energy distribution function of the electrons of the plasma nearby the deposition substrate of a radio frequency magnetron discharge used for sputtering deposition of TiO 2 thin films were measured by a cylindrical Langmuir probe. In the low-energy domain (0–15 eV), the electron energy distributions resembled a Maxwell distribution with a temperature value that decreased from 5 to 3 eV by the increase of the argon pressure from 1 to 20 mTorr. In the high-energy domain the electron energy distribution showed a depletion. At low values (approx. 0.5 sccm) the flow rate of argon affected the plasma density. This effect was attributed to the gas composition change induced by the atoms sputtered from the cathode titanium dioxide target, change that was proved by optical emission spectroscopy measurements.

Control of plasma parameters and wall sheath voltage in radio frequency magnetron discharge by grid bias

The plasma of a radio frequency (rf) magnetron discharge used for deposition of TiOx thin films was separated by a mesh grid into source (negative glow) and diffusion (deposition) plasmas. Langmuir probes were used to measure the potential, electron density, and electron temperature of both plasmas. While the change of the grid bias affected the diffusion plasma parameters, it did not change the source plasma parameters (except the potential). The use of the biased grid resulted in a decrease of temperature and an increase of density of plasma electrons in the film deposition region. With an increase of the grid biasing potential, the plasma potential increased in order to maintain a negative bias voltage across the grid sheath, the electron temperature increased, and the electron density decreased. The biased-grid-induced change of the plasma potential and the bias voltage across the wall sheath is explained based on the model of the asymmetric double probe, which is formed by the discharge chamber wall and the grid. The effect of the biased grid on the diffusion plasma parameters is discussed accounting for the particle transport phenomena in the system.

A new sputtering device of radio-frequency magnetron discharge using a rectangular hollow-shaped electrode

A new sputtering device using a radio-frequency magnetron discharge with a rectangular hollow-shaped electrode has been developed for a low-pressure discharge (∼ a few mTorr). The spatial structures of the electron density, the etching rate of the target material (copper), and the deposition rate were measured in uniform and convex profiles of the externally applied magnetic field. The device realized the uniform use of the target material under the arrangement of the magnetic-field configuration. The resistivity of the deposited copper thin film was also obtained, which was found to be similar to that of conventional copper (∼10−8 Ω m).