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Neutral gas temperature (Tg) is measured in an industrial high-density inductively coupled etch reactor operating in CF4, SF6, O2, Cl2, or HBr plasmas. Two laser diodes are used to deduce Tg from the Doppler widths of 772.38 and 811.5nm lines absorbed by Ar*(P23) metastable atoms, when a small amount of argon (5%) is added to the gas flow. With the 811.5nm beam passing parallel to the wafer, Tg near the wafer surface is obtained by laser absorption technique. With the 772.38nm beam entering the top of the reactor perpendicular to the wafer surface, the volume averaged temperature is deduced by laser induced fluorescence technique. The volume averaged Tg increases with radio frequency power and with pressure, although the temperature near the walls is only weakly dependent on gas pressure. The main effect of increasing the pressure is an enhancement of the temperature gradient between the discharge center and the wall boundary. Due to the thermal accommodation, the authors always observe a significant temp...

This paper deals with the diagnostics of an IPVD process called Highly Ionized Sputter Deposition Process (HISDP) using a high power pulsed magnetron plasma. The HISDP 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 and the buffer gas was argon. The titanium densities (neutrals and ions) were measured by pulsed resonant absorption spectroscopy technique. The comparison between the experimental results and a simple one-dimensional (1D) model of diffusion shows that the transport of neutral and ionized sputtered atoms is mainly controlled by diffusion for a pressure of 4 Pa (classical for neutrals and ambipolar for ions). Moreover, the limits of the optical absorption spectroscopy technique are investigated at lower pressures.

The Optical Emission Spectroscopy technique was used to monitor a magnetron discharge working in an Ar/O 2 mixture and in air. Hysteresis effects and instability, which are frequently observed when working with reactive gases, were clearly seen in the optical spectra. When the discharge power was increased, the atomic oxygen line intensity increased, saturated and then disappeared whilst, at the transition, sputtered material line intensities suddenly increased. In air, nitrogen lines were found to be less sensitive to this transition. The transition between the two regimes of the discharge is due to a change in the composition of surfaces from oxidised to metallic, as confirmed by the analysis of deposited films. In parallel with the experiment, a plasma model was developed for the magnetised region of the discharge which predicts the variations of the various plasma species in the Ar/O 2 mixture. This model explains the behaviour of line intensities on the two sides of the transition.

International audience; Silicon etching in Cl2-based plasmas is an important step for the fabrication of IC circuits but the plasma surface interactions involved in this process remain poorly understood. Based on the developments in plasma and reactor wall diagnostics, this paper reviews the recent progress in the understanding of radicals' interactions with surfaces during silicon etching processes. X-ray photoelectron spectroscopy analysis of the reactor walls shows that during Si etching in Cl2/O2 plasmas, the initial Al2O3 chamber walls are coated with a thin SiOCl layer. Broadband absorption spectroscopy with UV light emitting diodes is used to measure the densities of SiClX radicals (X = 0-2) and Cl2 molecules in steady state plasmas running with the chamber walls coated with different materials. To estimate the surface sticking/recombination probability of these radicals on different surfaces, we have performed time-resolved absorption measurements in the afterglow of pulsed discharges. Our work, in agreement with previous results, shows that the Cl2/Cl density ratio in the discharge is driven mainly by the chemical nature of the chamber walls explaining why process drifts are often observed in Cl2/O2 plasmas. The recombination coefficient of Cl atoms on SiOCl surfaces is about 0.007, while it is about 0.1 on clean walls (AlF3). Based on these results, we discuss the best strategy leading to reproducible process control, the present strategy being a systematic reactor cleaning/conditioning between wafers. The SiOCl layer deposition mechanism is then discussed in detail. The sticking coefficient of SiCl on this surface is near unity, while SiCl2 appears to be weakly reactive toward it. Therefore, SiCl (and SiCl+ ions) are the main vectors of Si deposition on the reactor walls, where their subsequent oxidization by O atoms leads to the formation of a SiOCl deposit. Furthermore, we show that SiCl reaction in the plasma volume with Cl2, through the exchange reaction SiCl + Cl2 → SiCl2 + Cl, is very important for the control of radical densities. Finally, time-resolved measurements of the gas temperature by laser-absorption Doppler spectroscopy show that in the afterglow of pulsed discharges the transport of particles is affected by the convection phenomenon. The very fast electron temperature cooling in the early afterglow generates a pressure gradient in the reactor which induces a rapid gas movement from the cold regions of the reactor toward the reactor center, where the plasma was generated. This leads to an increase in the density of stable molecules in the volume previously occupied by the plasma.

This paper discusses the possibility of producing high concentrations of O 2 (a 1 Δ g ) states at pressures up to atmospheric in rare-gas/oxygen/NO mixtures by using micro-plasmas. Micro-plasmas refer to electric discharges created in very small geometries which have been proven able to operate in DC mode at high pressure and high power loading without undergoing any glow to arc transition. The so-called Micro Cathode Sustained Discharge (MCSD), which is a three-electrode configuration using a Micro Hollow Cathode Discharge (MHCD) as a plasma cathode, can be operated as a non-self-sustained discharge with low values of the reduced electric field and of the gas temperature. As a result, these MCSDs can efficiently generate large amounts of singlet delta oxygen. In Ar/O 2 /NO mixtures, at an oxygen partial pressure of 10 mbar, high values of O 2 (a 1 Δ g ) number density (1.5 10 16 cm -3 ) and of the production yield (6.7 %) can be simultaneously obtained. For lower O 2 partial pressure, yields higher than 10 % have been measured. In He/O 2 /NO mixtures, O 2 (a 1 Δ g ) number densities around 10 16 cm -3 were achieved at atmospheric pressure for flow rates in the range 5-30 ln/mn, which could give rise to new applications.

International audience; Broad band absorption spectroscopy is widely used to measure the concentration of radicals, which is important to understand the physical chemistry of many plasmas. It is possible to increase the sensitivity of this technique and to perform time-resolved measurement by using light emitting diodes (LEDs) as a light source. The method is applied to detect CF2 radicals and Cl2 molecules in high density plasmas. The detection limit over 10ms integration time is as low as 3mTorr of Cl2. We conclude that the absorption spectroscopy with LEDs opens possibilities for precise process control and fundamental analysis of reactive media.

In rare gas/oxygen mixtures, the generation of O2(a∆g) states by microplasmas has been studied experimentally and theoretically. Microplasmas refer to electric discharges created in very small geometries able to operate in DC mode at high pressure without glow to arc transition. A microplasma configuration which has proven to be stable at atmospheric pressure and up to a power density of some 100 kW/cm is the Micro Hollow Cathode Discharge (MHCD) developed by Schoenbach and coworkers. MHCDs are created by applying a voltage between two closely spaced hollow electrodes separated by a dielectric layer. The thickness of the dielectric and the diameter of the hole are both on the order of some 100's microns. These MHCDs can be used as plasma cathodes for generating a diffuse discharge between the MHCD cathode and a third positively-biased electrode placed some distance away. This is the so-called Micro Cathode Sustained Discharge (MCSD) configuration. It is shown in the present paper that these MCSDs can be operated as nonself-sustained discharges with low values of the reduced electric field and of the gas temperature. As a result, these MCSDs can efficiently generate large amounts of singlet delta oxygen. In argon-oxygen mixtures, O2(a∆g) relative yields of 13 % were measured 23 cm downstream in the afterglow of the MCSD discharge, while in helium-oxygen mixtures, O2(a∆g) number densities above 10 cm were achieved at atmospheric pressure for flow rates in the range 5-30 ln/mn. Moreover, it has been demonstrated that MCSDs can be operated in parallel in this non-self-sustained discharge mode. Such arrays of MCSDs offer a new possibility to produce large amounts of O2(a∆g) states, which could give rise to a large spectrum of applications

Specific features of Hall thrusters, which are advanced electric propulsion devices for space applications, in terms of thrust, specific impulse, efficiency and lifetime make them suitable candidates for missions like geo-stationary satellite orbit correction and station keeping. A large research program devoted to the investigation of physical processes connected to the working of Hall thrusters has been carried out in France for many years. One of the current research topic concerns the erosion phenomena induced by the created plasma. Indeed, erosion of the ceramic insulators of a Hall thruster is always considered as a critical point as the main limiting factor for the thruster lifetime. It is clear that a better understanding as well as a better monitoring of wear processes of the insulators is necessary in order to employ Hall thrusters for long term missions like interplanetary journeys. By comparing experiments and numerical outcomes, it appears that present models describing erosion mechanisms, solely based on ion bombardment, do not explain the overall losses of insulator material and the periodic pattern observed at the channel outlet. The peculiar wear of the insulators could find its origin in the so-called "anomalous erosion" phenomenon. It is most likely that electrons play a major role in such an erosion process, however, the way they act and the deep reason for the formation of a network of longitudinal streaks are still to be clarified. In terms of erosion monitoring, to observe the light emitted by atoms sputtered from insulators appears to be a promising way of real-time controlling the wear of the ceramic walls.

A high speed electronic switch of discharge current has been used as a diagnostic tool of closed electron drift thrusters. Analysis of transients in discharge current and plasma spectral emissions leads to an evaluation of electron energy and density losses. Low energy excitation processes populating excited states from ion and neutral metastables are evidenced. Measurements of mean electron axial velocity are compared with neutral collision transport across magnetic field. Finally a strong correlation is evidenced between angular distribution of ejected ions and localization of the ionization zone in the thruster channel.

We report experimental results showing that singlet oxygen O2(aΔ1g) can be efficiently produced at atmospheric pressure in a three-electrode microcathode sustained discharge (MCSD) configuration. This configuration consists of a microhollow cathode discharge (MHCD) acting as a plasma cathode to sustain a stable glow discharge between the MHCD and a third planar electrode placed at a distance of 8 mm. Experiments were performed in He/O2/NO mixtures. O2(aΔ1g) number densities higher than 1016 cm−3 were measured in the MCSD afterglow at total flow rates up to 30 ln/mn, resulting in O2(aΔ1g) fluxes above 10 millimole per hour (mmol/h).

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.

A technique is described for the measurement of metastable-state densities by self-absorption in a plasma. The absorption parameter k 0 l is determined from the ratio of the total intensities of two partially self-absorbed lines ending on the level for which one wishes to determine the population. We develop this method for the case of a homogeneous medium for which the emission and absorption lines have Doppler, Lorentz or Voigt profiles. We study the error inherent in this model when the medium is spatially inhomogeneous. We apply this method to the measurement of atomic and ionic metastable concentrations in a highly ionized argon plasma.

The results of measurements made on an ATON-class Hall thruster in the French PIVOINE facility are presented. Diagnostics consist in optical emission spectroscopy, fast imaging, Langmuir probes arid ion energy analyser. The aim of this work was to compare the characteristics of the plasma in the channel and in the plume between two modes, called "swallow tail" and "spike" modes.