Low-density Argon Plasma Research Articles

Plasma and BIAS Modeling: Self‐Consistent Electrostatic Particle‐in‐Cell with Low‐Density Argon Plasma for TiC

We motivate our study by simulating the particle transport of a thin film deposition process done by PVD (physical vapor deposition) processes. In this paper we present a new model taken into account a self‐consistent electrostatic‐particle in cell model with low density Argon plasma. The collision model are based of Monte Carlo simulations is discussed for DC sputtering in lower pressure regimes. In order to simulate transport phenomena within sputtering processes realistically, a spatial and temporal knowledge of the plasma density and electrostatic field configuration is needed. Due to relatively low plasma densities, continuum fluid equations are not applicable. We propose instead a Particle‐in‐cell (PIC) method, which allows the study of plasma behavior by computing the trajectories of finite‐size particles under the action of an external and self‐consistent electric field defined in a grid of points.

A particle-in-cell plus Monte Carlo study of plasma-induced damage of normal incidence collector optics used in extreme ultraviolet lithography

We present a kinetic simulation of the plasma formed by photoionization in the intense flux of an extreme ultraviolet lithography (EUVL) light source. The model is based on the particle-in-cell plus Monte Carlo approach. The photoelectric effect and ionization by electron collisions are included. The time evolution of the low density argon plasma is simulated during and after the EUV pulse and the ion-induced sputtering of the coating material of a normal incidence collector mirror is computed. The relation between the time and position at which the ions are created and their final energy is studied, revealing how the evolution and the properties of the sheath influence the amount of sputtered material. The influence of the gas pressure and the source intensity is studied, evaluating the behavior of Ar+ and Ar2+ ions. A way to reduce the damage to the collector mirror is presented.

Electrical breakdown of anodized coatings in low-density plasmas

A comprehensive set of investigations has been performed involving arcing on a negatively biased anodized aluminum plate immersed in a low-density argon plasma at low pressures (Po w 7.5X 10~ torr). These arcing experiments were designed to simulate electrical breakdown of anodized coatings in a low-Earth orbital environment. When electrical breakdown of an anodized layer occurs, an arc strikes, and there is a sudden flux of electrons accelerated into the ambient plasma. This event is directly followed by ejection of a quasineutral plasma cloud consisting of ejected material blown out of the anodized layer. Statistical analysis of plasma cloud expansion velocities has yielded a mean propagation velocity, v 19.4 ± 3.5 km/s. As the plasma cloud expands into the ambient plasma, energy in the form of electrical noise is generated. The radiated electromagnetic noise is detected by means of an insulated antenna immersed in the ambient plasma. The purpose of the investigations is 1) to observe and record the electromagnetic radiation spectrum resulting from the arcing process, 2) to make estimates of the travel time of the quasineutral plasma cloud based on fluctuations to several Langmuir probes mounted in the ambient plasma, and 3) to study induced arcing between two anodized aluminum structures in close proximity.

Metastable level density and temperature measurement in a low-density argon plasma

Temperature and density measurements of the argon metastable atom level in a weakly diffusion ionized argon plasma are presented and discussed. The steady state collisionless unmagnetized plasma is generated at a gas pressure of 50 mPa, extruded by hot filament DC discharges and diffused in a chamber of about 40 l volume. The temperature is measured from the absorption linewidth and the density from the spectral absorption coefficient of a low-cost single-mode diode laser (801 479 nm) by scanning its frequency around the ArI transition.

Far-forward and forward CW. CO2 laser scattering measurements of ion-acoustic waves in a quiescent plasma

Far-forward and forward collective light scattering measurements of externally launched ion-acoustic waves in a low density argon plasma column have been performed with a c.w. CO2 laser. The scattering processes taking place are described theoretically by the same general formalism. Wave dispersive and damping properties are studied consistently from 2 to 200 cm-1. Plasma parameters are deduced and compared to electrostatic probe and antenna measurements. It is found that high frequency wave properties are erroneously measured with a grid antenna.

Ion heating by non-monochromatic RF above the lower hybrid frequency

Ion heating effects by a non-monochromatic r.f. near the lower hybrid frequency with slowly varying amplitude are investigated experimentally in a low density argon plasma. Temporal measurements of the ion velocity distribution function show different time evolution of ion energy, depending on the frequency spectra of the r.f. signal. When the r.f. is (balanced-) amplitude-modulated with noise, the heating effect on ions is more dominant than the cases of the monochromatic r.f. and the frequency-modulated r.f. For the sinusoidal amplitude modulation, maximum broadening of the ion velocity distribution function is observed when envelope of the amplitude varies near the ion cyclotron frequency, which qualitatively agrees with the theoretically expected behaviour. From simple analysis of single particle motion, it is suggested that ion heating may be caused by a low frequency oscillation driven by an oscillating collective ponderomotive force which is originally produced by the non-uniform r.f. electric field with slowly varying amplitude.

Measurements of turbulent waves by means of microwave scattering and correlation techniques

The turbulence induced by a current drawn in a low-density argon plasma is investigated by microwave scattering and correlation techniques. The azimuthal 30-GHz scattering system uses a newly designed variable waveguide in order to detect the scattered signal at any angle between 0° and 90°. Both diagnostic methods show that the turbulence is dominated by low-frequency waves propagating perpendicular with respect to the current. A comparison of these two important diagnostic methods for turbulent plasma is presented.

Optical Emission from a Low-Density Argon Plasma

In many laboratory experiments, the plasma parameters do not satisfy the requirements of the various theoretical radiation models that are needed for spectral plasma diagnostics. We report here a coaxial system from which we determine the empirical relationship between the electron number density of a low-pressure argon plasma and the intensity of atomic line emission. This system is unique in that it allows the concurrent determination of electron number density and line emission intensity at various locations in the plasma. Dependence of emission intensity on the neutral background pressure and the strength of the microwave pulse, which generates the plasma, suggests that the steady-state corona model is relevant for this system.

Physical and dynamical characteristics of a plasma flow in an electric T tube

Low density argon plasma is studied in an electric discharge T tube. In the experimental conditions the shock wave and the contact surface merge. The wave trajectory determined from measurements obtained by a rotating-mirror camera, is described by a similarity solution of blast waves; it enables the authors to calculate the fraction of energy transferred to the gas. The temperature and the electron density are deduced from spectroscopic measurements.

Comparison of Langmuir probe and spectroscopic electron temperature measurements

Deals with an experimental confirmation of the deviation from LTE in a low density argon plasma and of the applicability of the theory on the deviation from LTE developed by Griem. The excitation temperature determined spectroscopically using relative intensities of the resonance lines 4000-7000 AA of argon atoms was compared with the electron temperature measured by a conventional Langmuir probe. As a result it was found that the excitation temperature was 1000- 1500 degrees C higher than the electron temperature and that the difference between them increased along the radius of the plasma stream. It implies that the plasma was not in LTE. In fact the excitation temperature determined from relative populations of the 5p states of the argon atoms was found to agree quite well with electron temperature across the plasma stream.