Petr Vašina

Experimental study of a pre-ionized high power pulsed magnetron discharge

This paper is focused on experimental studies of a high power pulsed magnetron discharge stabilized by low current pre-ionization. Time resolved studies were performed for a Cu target by optical emission spectroscopy and electrical measurements for different pressures of Ar buffer gas. Due to the elimination of the statistical delay time and a fast discharge current rise the quasi-stationary state was reached in 6 µs. The quasi-stationary state is characterized by an extremely high and pressure independent discharge current density of ~10 A cm−2 and stable Cu+ and Cu++ emissions. Such fast discharge dynamics permits the magnetron cathode current to be driven with a pulse of duration of the order of a few µs, significantly shorter than in other devices. During this short time, the plasma does not have time to undergo the transition from the glow to the arc discharge even at the extremely high cathode loads met in our case. Different stages of the fast discharge development are identified and the composition of the magnetized plasma as a function of the pressure is discussed in detail.

Characterization of a periodic instability in filamentary surface wave discharge at atmospheric pressure in argon

This study reports on a periodic instability in a microwave atmospheric pressure surface wave plasma. Time-resolved observation by means of a high-speed camera reveals that the discharge can operate in two different regimes. The discharge operates either in a static mode of a controlled number of filaments propagating alongside the wall of the fused silica tube or in a dynamic mode of one or more straight filaments together with one revolving filament. Microwave power and argon flow rate are interpreted as the scaling parameters that govern the self-organization in the discharge. The operating diagram is formed by alternating stripes of static and dynamic mode with well-defined borders.

On the oxygen addition into nitrogen post-discharges

It is well known that the dissociation degree of nitrogen can be substantially increased if a small amount of oxygen is added into an active discharge. In this work it is experimentally shown that a very similar phenomenon occurs also when oxygen is added into the nitrogen late post-discharge. A detailed kinetic model, valid for the oxygen addition into the active discharge, fails to interpret these new experimental observations, and, consequently, its completeness has to be questioned.

Simultaneous measurement of N and O densities in plasma afterglow by means of NO titration

In this work we describe a method based on NO titration that permits us to measure at the same time the absolute concentrations of N and O atoms in the gas phase. This method is suitable for low concentrations of oxygen atoms. We also discuss the validity of the titration method, especially the influence of the reaction time. It was used to study the influence of O2 admixture on the degree of dissociation of nitrogen in the afterglow. The results of the NO titration technique were compared with those obtained by means of electron paramagnetic resonance and with the relative values determined from emission of .

Laser desorption ionisation quadrupole ion trap time‐of‐flight mass spectrometry of titanium‐carbon thin films

RATIONALE Titanium-carbon (Ti-C) ceramic thin films (abbreviated as n-TiC/a-C:H) are very important for industrial applications. However, their chemical structure is still not completely resolved. The aim of this study was to determine the chemical composition of such n-TiC/a-C:H layers prepared by balanced magnetron sputtering under various experimental conditions. METHODS Mass spectrometric analysis of Ti-C thin films was carried out via laser desorption ionisation (LDI) using a quadrupole ion trap and reflectron time-of-flight analyser. The stoichiometry of clusters formed via laser ablation was determined, and the relative abundances of species for which the isotopic patterns overlaps were estimated using a least-squares program. RESULTS Ti-C films were found to be composites of (i) pure and hydrogenated TiC, (ii) titanium oxycarbides, and (iii) titanium oxides of various degrees of hydrogenation (all embedded in an amorphous and/or diamond-like carbon matrix). Hydrogenated titanium oxycarbide was the main component of the surface layer, whereas deeper layers were composed primarily of TiC and titanium oxides (also embedded in the carbon matrix). CONCLUSIONS Mass spectrometry proved useful for elucidating the chemical structure of the hard ceramic-like Ti-C layers produced by magnetron sputtering. The Ti-C layers were found to be complex composites of various chemical entities. Knowledge of the resolved structure could accelerate further development of these kinds of materials.

Study of a fast high power pulsed magnetron discharge: role of plasma deconfinement on the charged particle transport

In this paper, we report the influence of the various stages of the preionized high power pulsed magnetron discharge on the saturated ion substrate holder current. Our system allows superposition of a preionization low current dc discharge with high voltage pulses applied directly on the magnetron cathode. This system is characterized by a very fast and perfectly reproducible discharge current rise. For a 33?mm copper target, Ar pressure of ~1?Pa, voltage applied in a pulse of ~1?kV, the maximum cathode current of ~40?A is reached in 6??s. The dependence of the saturated ion substrate holder current was analyzed for varying time duration of the high power pulse from 2 up to 8??s by 0.5??s steps. It allows the discrimination of the contribution of elemental temporal intervals to the overall saturated ion substrate holder current. This analysis led to the conclusion that the transport of ballistic ions during the current pulse and in the afterglow is independent of time. We concluded that space charge effects are negligible for both discharge and post-discharge conditions and that electrons act as a neutralizing background. Finally, on the basis of a phenomenological kinetic model for the electron transport, physical explanations of these results are proposed which involve the transverse diffusion of low energy electrons out of the magnetized glow region through electron?ion Coulomb collisions.

Spatial characterization of an IPVD reactor : neutral gas temperature and interpretation of optical spectroscopy measurements

This paper deals with the characterization of an ionized physical vapour deposition (IPVD) reactor using an additional microwave plasma. The IPVD reactor was spatially characterized using optical emission spectroscopy, optical absorption spectroscopy and Langmuir probe measurements. A rectangular titanium target was used, the buffer gas was argon and the pressure was fixed at 4 Pa. The influence of the microwave power (between 0 and 900 W) and the magnetron discharge current (0.5 and 2 A) on the densities of the titanium species (neutral and ionic), argon emission line intensity and titanium and argon temperature variations was investigated. The titanium temperature and densities were measured using the pulsed resonant absorption spectroscopy technique. The neutral and ion fluxes on the substrate were deduced from these measurements. It was found that the ratio (Ti+)/(Tin) increases by a factor of 30 when additional microwave plasma is used. Moreover, we point out the temperature as a key parameter in plasma diagnostic interpretations.

Electron density measurements in afterglow of high power pulsed microwave discharge

In the paper we study, be means of microwave interferometry, the evolution of electron density in afterglow of pulsed driven nitrogen discharge. Recombination coeffients are derived, too.

Modelling of the reactive sputtering process with non-uniform discharge current density and different temperature conditions

The majority of current models of the reactive magnetron sputtering assume a uniform shape of the discharge current density and the same temperature near the target and the substrate. However, in the real experimental set-up, the presence of the magnetic field causes high density plasma to form in front of the cathode in the shape of a toroid. Consequently, the discharge current density is laterally non-uniform. In addition to this, the heating of the background gas by sputtered particles, which is usually referred to as the gas rarefaction, plays an important role. This paper presents an extended model of the reactive magnetron sputtering that assumes the non-uniform discharge current density and which accommodates the gas rarefaction effect. It is devoted mainly to the study of the behaviour of the reactive sputtering rather that to the prediction of the coating properties. Outputs of this model are compared with those that assume uniform discharge current density and uniform temperature profile in the deposition chamber. Particular attention is paid to the modelling of the radial variation of the target composition near transitions from the metallic to the compound mode and vice versa. A study of the target utilization in the metallic and compound mode is performed for two different discharge current density profiles corresponding to typical two pole and multipole magnetics available on the market now. Different shapes of the discharge current density were tested. Finally, hysteresis curves are plotted for various temperature conditions in the reactor.

Plasma diagnostics using electron paramagnetic resonance

Methods giving absolute concentrations of various species in the plasma are of utmost importance to plasma research. Besides currently prevalent laser methods, a method based on microwave absorption—electron paramagnetic resonance—can be successfully used for plasma diagnostics. It is able to detect many atoms, molecules and radicals in the ground or excited states. In this paper we give an overview of the method and several practical examples. (Some figures in this article are in colour only in the electronic version)