On the Secondary Electron Emission in DC Magnetron Discharge (original) (raw)

Recapture of secondary electrons by the target in a DC planar magnetron discharge

Vacuum, 2003

In this paper we describe a simple two-dimensional model that allows the study of the individual secondary electron orbits in a DC planar magnetron discharge. Emphasis is on the recapture of secondary electrons by the target, which is enabled by their small initial energy, because this reduces the effective secondary electron yield as seen by the discharge. This reduction depends strongly on both the position along the race track and the gas pressure and it can be substantial for typical planar magnetron operating conditions. Our simple model allows to conclude that because of the sensitivity of the discharge on the secondary electron yield, the current-voltage characteristic, the spatial distribution as well as the pressure dependence of the planar magnetron discharge will be influenced by recapture.

Influence of electron recapture by the cathode upon the discharge characteristics in dc planar magnetrons

Physical Review E, 2005

In dc magnetrons the electrons emitted from the cathode may return there due to the applied magnetic field. When that happens, they can be recaptured or reflected back into the discharge, depending on the value of the reflection coefficient ͑RC͒. A 2d3v ͑two-dimensional in coordinate and three-dimensional in velocity space͒ particle-in-cell-Monte Carlo model, including an external circuit, is developed to determine the role of the electron recapture in the discharge processes. The detailed discharge structure as a function of RC for two pressures ͑4 and 25 mtorr͒ is studied. The importance of electron recapture is clearly manifested, especially at low pressures. The results indicate that the discharge characteristics are dramatically changed with varying RC between 0 and 1. Thus, the electron recapture at the cathode appears to be a significant mechanism in magnetron discharges and RC a very important parameter in their correct quantitative description that should be dealt with cautiously.

A study of the DC discharge in a cylindrical magnetron comparison of experiment and a pic model

Czechoslovak Journal of Physics, 2000

We studied the DC discharge in a cylindrical magnetron experimentally and via numerical simulation. Presented experimental results have been obtained by probe measurements. Numerical results have been obtained using a one-dimensional PIC-MCC (XPDC1) code available at http://langmuir.eecs.berkeley.edu. We present a comparison of the experimentally obtained radial profiles of the floating and plasma potentials, the radial electric field, plasma density, the electron mean energy and the electron energy distribution function in the discharge plasma with the results obtained from the numerical model. While for most plasma parameters studied, a reasonable agreement is obtained, the calculated electric field is higher than that observed experimentally. This discrepancy is suggested to be due to the end effects of the discharge vessel.

Anomalous secondary electron emission of metallic surfaces exposed to a Glow Discharge plasma

Journal of Nuclear Materials, 2013

Article history: Available online xxxx a b s t r a c t Secondary electron emission (SEE) yields, c, of Li, stainless steel (SS) and W surfaces immersed in a He Direct Current Glow Discharge (dc-GD) Plasma have been calculated from the experimental I-V curves as a function of electron mean energy. The data obtained showed that c Li > c SS > c W . Line emission ratios 728/706 of excited He and Langmuir probe measurements provide a clear evidence of the presence of a suprathermal electron tail responsible for the observed SEE. The results show that SEE is well correlated with the anomalous extra current component found in the I-V curves. The resulting value of c Li is significantly higher than its theoretical value suggesting a possible synergetic effect of the ion bombardment in the SEE of lithium. The effect of Li surface oxidation has also been addressed, leading to a substantial decrease of both, sputtering yield and SEE yield of Li with higher oxygen content.

Two-dimensional fluid approach to the dc magnetron discharge

Plasma Sources Science & Technology, 2005

A two-dimensional (r, z) time-dependent fluid model was developed and used to describe a dc planar magnetron discharge with cylindrical symmetry. The transport description of the charged species uses the corresponding first three moments of the Boltzmann equation: continuity, momentum transfer and mean energy transfer (the last one only for electrons), coupled with the Poisson equation. An original method is proposed to treat the transport equations. Electron and ion momentum transport equations are reduced to the classical drift-diffusion expression for the fluxes since the presence of the magnetic field is introduced as an additional part in the electron flux, while for ions an effective electric field was considered. Thus, both continuity and mean energy transfer equations are solved in a classical manner. Numerical simulations were performed considering argon as a buffer gas, with a neutral pressure varying between 5 and 30 mTorr, for different voltages applied on the cathode. Results obtained for densities of the charged particle, fluxes and plasma potential are in good agreement with those obtained in previous studies.

Apparent secondary-electron emission coefficient and the voltage-current characteristics of argon glow discharges

Physical Review E, 2001

The accuracy of secondary-electron emission coefficients, that are used as input data of discharge models, seriously influences the calculated discharge characteristics. As it is very difficult to consider all possible electron emission processes of a cold cathode separately, in most of the recent models an apparent secondary coefficient ␥ is applied, which is often assumed to be constant, even for a wide range of discharge conditions. In contrast with this common assumption, the present calculations-based on a heavy-particle hybrid modelshow that in abnormal glow discharges ␥ varies considerably with changing discharge conditions: a factor of 3 change of ␥ has been found in the range of reduced current densities (0.04 mA cm Ϫ2 Torr Ϫ2 р j/p 2 р4 mA cm Ϫ2 Torr Ϫ2 ) covered in this study. The present simulations also confirm that ionization by heavy particles plays a significant role in the ion production at the abnormal cathode fall. Moreover, it is shown, that the fast heavy particles reflected from the cathode surface play the dominant role in the gas heating.

Modeling and Diagnostic of the Plasma of Magnetic Field Supported Discharges

Contributions to Plasma Physics, 2005

In this paper we present an experimental study of the variations of plasma parameters in both the axial as well as in radial directions in a 30 cm long cylindrical magnetron with outer cylindrically-shaped anode (diameter 58 mm) and coaxially placed cathode with a diameter of 1.8 cm. The measurements were made using three radially movable cylindrical Langmuir probes placed at three different axial positions between the magnetic coils. From the measurements there were evaluated electron density, electron mean energy, plasma potential and floating potential in dependence of the magnetic field (10-40 mT) and the argon pressure (2-7 Pa). In order to measure the axial variations of the discharge current, one half of the cathode length is segmented into 14 isolated segments with length of about 10 mm. The physical processes occurring in electrode regions and the positive column of a cylindrical magnetron discharge in crossed electric and magnetic fields are investigated basing on the solution of the Boltzmann kinetic equation by a multiterm decomposition of the electron phase space distribution function in terms of the spherical tensors. The influence of the distribution function anisotropy on the absolute values and radial profiles of the electron density and rates of various transport and collision processes is analyzed. The spiral lines for the directed particle and energy transport are obtained to illustrate the anisotropy effects in dependence on magnetic field. The electron equipressure surfaces are constructed in the form of ellipsoids of pressure and their transformation in the cathode and anode regions is studied. A strong anisotropy of the energy flux tensor in contrast to a weak anisotropy of the momentum flux density tensor is found. Particular results are obtained for the cylindrical magnetron discharge in argon at pressure 3 Pa, current 200 mA and magnetic fields ranging within 10 − 40 mT.

Simplified model for the DC planar magnetron discharge

Vacuum, 2004

This deposition technique is based on the generation of a magnetically enhanced gas discharge at reduced pressure, which will further be referred to as magnetron discharge. Note the distinction between the magnetron sputter deposition process and the magnetron discharge (MD) itself. Although MD research is stimulated (financially) by its industrial relevance, the MD on itself is also scientifically attractive. Here a plasma interacting with a magnetic field is concerned. This can lead to very complex behaviour, as also shown by the problems encountered in the plasma confinement needed for nuclear fusion. Objective The aim of the presented work is to obtain a fundamental understanding of the MD, i.e. the identification and modelling of the processes crucial for the generic MD behaviour. A first reaction might be to investigate the MD experimentally to reach this goal. However, a wealth of experimental data already exists. Moreover, most of these experimental measurements are accompanied by models and possible theories for their explanation. Unfortunately, the vast majority of these seem only valid for the accompanying experimental results, i.e. they lack general validity. Hence, at second thoughts, a better strategy seems to be the analysis of the already existing wealth of experimental measurements and proposed theories and to distil the generic magnetron discharge behaviour from them. If the different processes are identified, they can be modelled, i.e. they are described in mathematical terms. The collection of these models should lead to a self-consistent model for the MD that is able to reproduce the MD behaviour. When this reproducing is so calculation intensive that it requires a computer, it is usually referred to as a simulating. Through simulation one can study the response of the model to stimuli. This is not the same as an experiment where the response of the physical device to stimuli is investigated. As a result there will always be a difference between the simulation results and the experiments. Consequently, an important aspect of each model is its accuracy. One should also take into account that a model is only valid within certain boundaries: it never includes "all the physics" but only the physics relevant for the investigated process or technique. This implies that for each model one should consider its applicability. A wide variety of processes occurs in a MD: as well typical plasma processes, particle-particle interactions as solid-particle interactions occur. Moreover, the range of as well the energy as the time scale of the different processes is large. This effect is enhanced by the large range of operating conditions: as well current density, as gas pressure and even the magnetic field strength can vary over an order of magnitude. This turns the modelling of the MD into an interesting but challenging effort. Even when using what is considered now a powerful personal computer, the range of length and time scales increases the required computation time of very accurate MD Throughout the text, several acronyms are used, e.g. SE (Secondary Electron). HEE (High Energy Electron), ... All these acronyms are used for both the singular and plural form, e.g. "A SE is emitted from the target ... " but also "The SE are recaptured because ... ". The reason is that some of these acronyms are used with sub-or superscripts, e.g. HEE 51 , which

Determination of cathode fall thickness in magnetized dc plasma for argon gas discharge Determination of cathode fall thickness in magnetized dc plasma for argon gas discharge

The thickness of the cathode fall region (d c) in magnetized dc argon plasma has been investigated using two different methods, namely the axial potential distribution and the current density distribution along the glow discharge regions. The measurements have been carried out at the edge and center of the cathode surface. Dc (cold cathode) magnetron sputtering unit has been used. The radial and axial distributions of the magnetic field B, the I a –V a characteristic curves of the glow discharge and the axial potential distribution and the current density distribution have been investigated. The thickness of the cathode fall region was between 2 and 3.3 mm for the two methods in pressure (P) range of 0.53–4 mbar. It is concluded that a noticeable reduction of the cathode fall thickness (about 33%) has been found in the presence of a magnetic field and at the center of the cathode and stronger electric field at the edge of the cathode fall, and hence high rates of sputtering are expected.

Fundamental studies on a planar-cathode direct current glow discharge. Part II: numerical modeling and comparison with laser scattering experiments

Spectrochimica Acta Part B-atomic Spectroscopy, 2004

We have calculated the gas temperature, electron density, electron energy distribution function, and average electron energy, as a function of distance from the cathode, with a two-dimensional model for an argon direct-current glow discharge. The calculated results are compared with measured values from Rayleigh-and Thomson-scattering experiments, for different values of voltage, pressure and electrical current. The gas-temperature distribution and electron-density profile were found to be in reasonable agreement with experiment. For the electron energy, model and experiment give complementary information, since the experiment is able to detect only the thermal and low-energy electrons, whereas the model focuses mainly on the high-energy electrons. ᮊ