Magnetron Discharge Plasma Research Articles

Observation of instability in presence of E×B flow in a direct current cylindrical magnetron discharge plasma

An electrostatic instability with an intermediate frequency range (50–100 MHz) between the electron collision frequency and electron cyclotron frequency has been observed in presence of crossed electric and magnetic fields in a dc cylindrical magnetron plasma. The amplitude of the instability becomes maximum at particular values of the magnetic field and the discharge voltage. It is seen that when the magnetic field is increased the instability peaks at lower discharge voltages. The different modes of instability are prominent only when the neutral gas pressure is sufficiently low (∼4×10−3 mbar). The instability becomes suppressed when the magnetic field is high (>200 G). A constant amplitude test signal applied to the plasma through the cathode grows when its frequency matches with the frequency of the instability. The current-voltage characteristics form hysteresis loop in the instability excitation region.

The YASHMA-2 Plasma Facility for the Deposition of Coatings on Solid Surfaces

A laboratory facility for the deposition of coatings on solid surfaces using a magnetron-discharge plasma and ion beams is described. Its main performance characteristics and functional capabilities are presented.

Optical properties of Ta2O5 films obtained by reactive magnetron sputtering

This paper discusses how the optical properties of Ta2O5 films are affected by the conditions under which they are produced by reactive magnetron sputtering of a Ta target with either direct current or ultrasound-frequency alternating current. The dispersion dependences of the refractive and absorption indices, as well as the growth rate of the films, are computed. The effect of currents in the magnetron-discharge plasma on the optical properties of the films is investigated.

Two-dimensional nonlocal model of axially and radially inhomogeneous plasma of cylindrical magnetron discharge.

A cylindrical magnetron discharge (CMD) with two coaxial electrodes, a uniform axially directed magnetic field, and discharge ends closed by the shields biased at the cathode potential is considered. The presence of the shields creates axial inhomogeneity of plasma, which is taken into account in this study. At low pressures and small magnetic fields the pronounced nonlocal regime of the electron distribution function (EDF) formation is realized. The electron component is analyzed on the basis of radially and axially inhomogeneous Boltzmann kinetic equation. Unmagnetized electrons that move in axial direction are trapped in the axial potential well, their energy relaxation length exceeds the discharge vessel length, and the kinetic equation can be averaged over axial flights of electrons. Using a model two-dimensional potential profile, the EDFs at the different axial positions are obtained and two-dimensional distributions of the electron density, ionization rate, and current on cathode are calculated. The results of the modeling and experiments are compared for the dc CMD in Ar at a pressure of 3 Pa, magnetic field strength of 10 mT, and current of 150 mA.

Model of the Anode Layer of a Magnetron Discharge

The anode layer of the magnetron discharge plasma is considered within the framework of a hydrodynamic approximation with the electron mobility and collision frequency assumed to be constant. A rigorous solution of the system of equations has been obtained. The solutions of this problem known so far have been shown to be particular cases of the one found in this work. The range of applicability of the anode layer model to the calculation of the main parameters of dc magnetron sputtering systems is discussed.

Ion-assisted pulsed magnetron sputtering deposition of ta-C films

The process of ion-assisted deposition of ta-C films by pulsed magnetron sputtering of a graphite target has been investigated. Probe measurements of the magnetron discharge plasma have been performed and its space- and time-dependent characteristics have been obtained as functions of the sputtering parameters and the bias voltage applied to the substrate. It has been shown that the density of the pulsed magnetron discharge plasma approaches values typical of pulsed laser or vacuum arc cathode sputtering of graphite (10 17−10 18 m −3). Raman scattering was used to examine the ta-C films produced at both low and high pulsed bias voltages applied to the substrate ( U sub<1 kV, τ=160 s and 1 kV< U sub<6 kV, τ=40 μs, respectively). It has been shown that in the first case the maximum content of diamond-like carbon in the coating (50–60%) is achieved at a lower energy per deposited carbon atom ( E C=100–300 eV) than in the second one (40–50% at E C=1100–1200 eV). Despite the lower diamond-like phase content in the coatings produced at a high bias voltage, they show better adhesion to the substrate due to the ion mixing between the film and the substrate and between the film layers. The use of shorter bias pulses is also important to prevent breakdowns of the deposited dielectric ta-C film.

Anode effects in magnetron sputtering

Experimental examination of anode phenomena in a magnetron plasma is performed and qualitative analysis of the phenomena observed is given. Anode size effects and potential distribution in the magnetron discharge plasma are investigated. The observed effects are discussed in the context of the well-established theory for magnetized glow discharges. When a power supply is floating and only connected to chamber ground through a sufficiently large resistor, the chamber wall is taken out of the anode circuit. In the experiments, varying the resistance between 200 to 20 000 Ω kept the anodes designated “activated” and did not substantially change the anode size effects investigated. When the random electron impingement current, integrated over the anode area, becomes smaller than the external current imposed by the power supply, the anode assumes a positive potential with respect to the plasma. For a small anode, the positive potential reaches values high enough for an anode plasma to appear. Localized anode plasmas act as ion sources. The ions drift to the magnetron along the electric field lines and change the erosion rate of elongated targets locally. Positive control over the deposition rate distribution can be obtained, for example, by applying additional voltage between multiple small anodes.

Influence of working gas pressure on the properties of thin films of high-temperature superconductors obtained by magnetron sputtering

The surface morphology, composition, microstructure, and electrical properties of thin films of YBa2Cu3O7−x high-temperature superconductors, obtained by inverted magnetron sputtering, have been studied as a function of the pressure of the working gas mixture and results are presented. The main parameters of the magnetron discharge plasma near the substrate were determined by analyzing the characteristics of Langmuir probes. Changes in the properties of the films are considered to be caused by bombardment of the growing film with plasma ions accelerated in the floating potential field of the substrate. Films obtained at a pressure of 28 Pa and substrate temperature of 630 °C had a superconducting transition end temperature Tc,off=89 K and a critical current density jc=2 MA/cm2 (at 77 K) and were free from secondary phase particles larger than 10 nm.

Langmuir Probe Diagnostics of a Low Temperature Non‐Isothermal Plasma in a Weak Magnetic Field

AbstractThis article presents measurements by a cylindrical Langmuir probe in the plasma of a DC cylindrical magnetron discharge át the pressure 1.5 Pa that aim at the experimental assessment of the influence of a weak magnetic field to the estimation of the electron density when using conventional methods of probe data interpretation. The probe data was obtained under the presence of a weak magnetic field in the range 1.10−2−5.10−2 T. The influence of the magnetic field on the electron probe current is experimentally assessed for two cylindrical probes with different radii, 50 μm and 21 μm. This assessment is based on comparison of the values of the electron density estimated from the electron current part with the values of the positive ion density estimated from the positive ion current part of the probe characteristic respectively by assuming that at the magnetic field strengths used in the present study the probe positive ion currents are possible to be assumed as uninfluenced by the magnetic field. For interpretation of the probe positive ion current two theories are used and compared to each other: the radial motion model by Allen, Boyd and Reynolds [10] and Chen [11] and the model that accounts for the collisions of positive ions with neutrals in the probe space charge sheath that we call Chen‐Talbot model [8]. At lower magnetic field 3 · 10−2 T the positive ion density values interpreted by using the Chen‐Talbot model [8] are in better agreement with the values of electron density compared to those obtained by using the theory [10,11]; therefore the model [8] is used for calculation of the positive ion density from the probe data at higher magnetic fields. The comparison of the positive ion and electron density values calculated from the same probe data at higher magnetic fields shows that up to the magnetic field strength 4 . 10−2 T with the probe 100 μm and up to 5 . 10−2 T with the probe 42 μm in diameter respectively the decrease of the magnitude of the electron current at the space potential due to the magnetic field does not exceed the error limits that are usual for Langmuir probe measurements (absolute error ±20%).

Control of Ion Energy for Low-Damage Plasma Processing in RF Discharge

A new control technique for ion energy is based on the external electron injection into the capacitively coupled rf plasma using an auxiliary plasma source. The externally injected electrons replace the plasma electrons carrying the rf current and then reconstruct the rf sheath in which ions are accelerated. The experiment is carried out by using a parallel-plate rf plasma device with a magnetron discharge plasma source mounted behind the mesh grounded electrode. The experimental results show that the energies of ions are continuously controlled by varying the amount of injected electrons in a wide range from ≃(1/2)eV rf to ≃T e, and this result agrees with that derived from our simple model.