Jean Bretagne

Electron energy distribution functions in electron-beam-sustained discharges: application to magnetic multicusp hydrogen discharges

Electron energy distribution functions (EDF) in magnetic multicusp H2 discharges have been calculated by numerically solving the Boltzmann equation. Results for a 90 V, 1-10 A discharge at 40 m Torr are presented and discussed in connection with the importance of e-e Coulomb collisions, of wall losses and of the degree of dissociation affecting the EDF. Scaling laws with the discharge current, the pressure and the applied discharge voltage are presented. A satisfactory agreement is found between the calculated electron temperatures of low energy electrons ( epsilon <5 eV) and the corresponding experimental values obtained by probe techniques.

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.

Study of the transport of titanium neutrals and ions in the post-discharge of a high power pulsed magnetron sputtering device

This paper deals with the diagnostics of a high power pulsed magnetron sputtering device (HPPMS). The HPPMS plasma was spatially and temporally characterized in the post-discharge using optical absorption spectroscopy and Langmuir probe time resolved measurements. A circular titanium target was used, the buffer gas was argon and the pressure was fixed at 4 Pa. The titanium densities (neutrals and ions) were measured by a pulsed resonant absorption spectroscopy technique. We found an ionization degree higher than 0.5. Comparison beetween the experimental results and a simple one-dimensional model of diffusion shows that in these conditions, the transport of neutral and ionized sputtered atoms is mainly controlled by diffusion (ambipolar diffusion for ions).

New type of plasma reactor for thin film deposition: magnetron plasma process assisted by microwaves to ionise sputtered vapour

Abstract A new type of plasma reactor for thin film deposition has been designed: a magnetron-sputtering device assisted by microwave applicators to ionise the sputtered vapour of the magnetron. Ionizing the vapour has several advantages: improvement of the film quality, deposition on substrates with complex shapes, enhancement and control of the reactivity. The reactor consists of a planar rectangular magnetron cathode (22 cm×9 cm) and of two coaxial-type microwave applicators located perpendicularly to the substrate–magnetron axis, on both sides of the sputtered vapour flow. This reactor can operate on a wide pressure range: from 0.2 to 60 Pa. Several in-situ diagnostics have been performed to characterise the process in argon gas with chromium and titanium targets. Electron density of the order of 10 11 –10 12 cm −3 and electron temperature of 1.5–2 eV were measured in the microwave plasma by a cylindrical Langmuir probe; emission of metallic ions (Cr + , Ti + ) was clearly identified when the microwave plasma is turned on; concentration of Cr or Ti atoms was measured by absorption spectroscopy, a decrease of this concentration is observed when the microwave power is increased. Characterisation of thin titanium films was performed ex-situ by Rutherford backscattering spectroscopy (RBS) for Ti content and nuclear reaction analysis (NRA) for oxygen contamination. Film density was deduced from RBS and NRA measurements and X-ray reflectometry. Oxygen contamination in the film is clearly decreased when microwave plasma is turned on and with a bias applied to the substrate.

Study of a HPPMS discharge in Ar/O2 mixture: I. Discharge characteristics with Ru cathode

High power pulsed magnetron sputtering discharges have been actively studied during the last ten years in order to achieve high ionization fraction of sputtered species. These sputtering discharges begin to be well understood in non-reactive mode. However, very few works have been devoted to studying reactive conditions. We report results obtained for these discharges working in an Ar/O2 mixture, with a preionization system to accelerate the current pulse rising. A Ru target was used for deposition of RuO2 conductive oxide. This paper discusses the role played by the presence of oxygen on both the preionization phase and the high current discharge characteristics. A comparison is made of results obtained in an Ar/O2 mixture with those obtained in pure argon. Emphasis is laid on the influence of the O2 flow rate and of the total Ar/O2 mixture pressure. It is observed that the O2 content in the inlet gas mixture strongly affects the preionization phase by the electron attachment to O2 as well as the high current discharge development.

Tunable diode-laser induced fluorescence on Al and Ti atoms in low pressure magnetron discharges

Two different blue light laser diodes were used to investigate two types of atoms, namely Ti with resonance transition centred at λ0(Ti) = 398.289 nm and Al with λ0(Al) = 394.512 nm. Tunable diode-laser induced fluorescence offers local information on two groups of sputtered particles—non-thermalized and thermalized. The anisotropic velocity distribution functions (vdfs) are characterized probing the plasma along two directions: parallel to the target, vr, and perpendicular to it, vz. Measurements were performed in two plasma reactors both having planar magnetron cathodes with circular symmetry but with Ti and Al targets of different magnet strengths and diameters. The similar results of the vdf space dependence for these magnetron systems confirm the general behaviour of sputtered species transport. These similarities are related to the circular geometry and fundamentals of sputtering whereas differences are due to each specific sputtered element. The experimental results also show the effect of current density on the shape of vdf for Ti and Al. An increase in the current intensity implies a linear increase in the relative density of energetic sputtered atoms while the group of thermalized ones appears unaffected in the high current density regime.

Study of a HPPMS discharge in Ar/O2 mixture: II. Plasma optical emission and deposited RuOx film properties

A high power pulsed magnetron sputtering discharge was used in reactive gas conditions for the deposition of conductive ruthenium oxide. In a previous paper (paper I), the physical characterization of the discharge in the case of Ar/O2 mixtures was studied. This companion paper is devoted to the study of the transition from a metallic working regime to an oxide one. The plasma phase was analyzed with time resolved optical emission spectroscopy. Characteristic Ar?I, Ar?II and O?I emission lines of buffer gas atoms together with Ru?I and Ru?II ones of sputtered species were followed during the discharge pulse for different pressure values and flow rate composition of Ar/O2 gas mixture. Conjectures on specific kinetic processes such as Penning ionization and excitation and charge transfer are emphasized in order to interpret the temporal behavior of line emissions. The transition from metallic to oxide regimes, as observed by optical emission, is well correlated with the film stoichiometry and it is rather sharp. This transition was found to be intrinsically free of the hysteresis effect. However, the important modifications of the current and voltage discharge pulses at this transition region makes it difficult to precisely control deposited film stoichiometry.

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.

Non-equilibrium vibrational, dissociation and dissociative attachment kinetics of HCl under high electron density conditions typical of XeCl laser discharges

The non-equilibrium vibrational kinetics of pure HCl is studied for typical conditions of a discharge sustained xenon-chloride laser, namely: HCl partial pressure range 1 to 15 Torr, electron density from 1014 to 1016 cm-3 and reduced electric field from 2*10-17 to 5*10-17 V cm2. This work emphasizes the role of processes which are not usually included in the kinetic models for this laser. Particular attention is devoted to V-V (vibration-vibration) energy exchanges, direct dissociation by electron impact and deactivation of vibrational quanta by V-T (vibration-vibration) collisions. The role of the various vibrational levels on the formation of Cl- is also considered.