A one-dimensional fluid model of a pulsed (square-wave power modulated) chlorine discharge was developed in order to study the spatiotemporal evolution of species densities and electron temperatures for various pressures, powers, pulsing frequencies and duty ratios. Simulation results show spontaneous separation of the plasma into an ion-ion core and an electron-ion edge during the power 'on' (active glow) fraction of the cycle. A transition from an electron-dominated plasma to an ion-ion plasma occurs during the power 'off' (afterglow) fraction of the cycle, under the conditions examined. The formation of an ion-ion plasma is favoured at lower power levels, higher pressures, and lower duty ratios. A minimum afterglow time is required for an ion-ion plasma to form and the negative ions to reach the walls. Increasing the afterglow period increases the fraction of time an ion-ion plasma is sustained in the reactor. The evolution of negative ion density profiles is especially complex due to the formation of self-sharpening fronts during power 'on' and subsequent back-propagation of the fronts during the power 'off' stage of the pulse. When possible, simulation results are compared to reported experimental data. In general, good agreement is obtained, except that the measured dependence of electron density on pulse period and duty ratio is more complex than predicted.

A three-dimensional finite element fluid model and a corresponding simulation tool have been developed for studying azimuthal asymmetries and their effect on etch uniformity in inductively coupled plasma ͑ICP͒ reactors. For silicon etching with chlorine in an ICP reactor with a planar coil, four different cases were examined: ͑a͒ uniform power deposition without a focus ring, ͑b͒ uniform power deposition with a focus ring, ͑c͒ nonuniform power deposition without a focus ring, and ͑d͒ nonuniform power deposition with a focus ring. When etching is ion driven, the power deposition profile is most important for etch uniformity, because azimuthal nonuniformities in the ion production rate can persist even down to the wafer level. For uniform power deposition, the effect of asymmetric pumping becomes more important. A focus ring can play an important role in alleviating azimuthal nonuniformities, especially in the nonuniform power deposition cases. Gas inlets pointing parallel to the wafer plane introduce only local disturbances in the species profiles.

Relatively electron-free positive- and negative-ion plasmas (ion–ion plasmas) have been achieved in the afterglow of pulsed-power Cl2 discharges. The application of a low-frequency (20 kHz) bias voltage phase locked to the source power modulation and synchronous with the ion–ion plasma, resulted in alternating fluxes of positive (Cl2+) and negative (Cl−) ions on a substrate. These results qualitatively agree with a one-dimensional fluid model. This technique to produce alternate irradiations could be used to reduce differential charging-induced damage in high-aspect-ratio etching processes.

Negative ion density fronts have been shown to occur in electronegative steady-state plasmas with hot electrons. In this Letter, we report theoretical and numerical results on the spatiotemporal evolution of negative ion density fronts during plasma ignition and extinction (afterglow). During plasma ignition, the negative ion fronts are analogous to hydrodynamic shocks. This is not the case during plasma extinction where, although negative ions diffuse freely in the plasma core, the negative ion front propagates towards the chamber walls with a nearly constant velocity.

A self-consistent global model of solenoidal-type inductively coupled plasma discharges including the effects of radio-frequency bias power

A comprehensive, two-dimensional, self-consistent model was developed and used to simulate chemical vapor infiltration of fiber-reinforced composite materials with radio frequency heating. The model included equations for energy transport, multicomponent mass transport, and pore structure evolution, coupled to Maxwell's equations to determine self-consistently the power absorbed by the preform from a radio frequency induction coil. The model equations were solved by a finite element method to study carbon chemical vapor infiltration in a cylindrical carbon preform. Simulations for a constant absorbed power showed that densification of the preform proceeds in an "inside out" manner, first in the radial direction and subsequently in the axial direction, for the aspect ratio studied. The power density distribution in the preform evolves in a complex manner as densified regions absorb more energy with increased densification. This may result in thermal runaway during the infiltration process and entrapment of porosity in the interior of the preform. Comparison of simulated results with reported experimental data showed semiquantitative agreement of important trends. A more accurate description of material properties is required for a quantitative match with the data.

Electric-discharge plasmas in gallium-iodide vapours are experimentally found to convert 40% of input electric power into ultraviolet and visible radiation (200–800 nm). The conditions are a weakly ionized positive column consisting of 5–10 Torr argon, and the gallium-iodide vapour is formed by heating condensed gallium-iodide to 100–120 °C. The input power density is 50–100 mW cm−3. The plasma is contained in a sealed silica tube and excited by an external radiofrequency antenna. Computational analysis and plasma diagnostics lead to a quantitative understanding that gallium atoms are formed by electron-impact dissociation of gallium-iodide compounds that evaporate into the plasma volume, and that further electron collisions excite the gallium atoms, which then decay by photon emission. High efficiency is possible only because several photons are emitted per dissociation event, and because nonradiative power channels such as electron-impact elastic heating and vibrational excitation are not dominant. The dissociated species recombine on the wall to reform the species that evaporates. The plasma properties change discontinuously as the molar ratio of iodine to gallium (I/Ga) in the system crosses the values I/Ga = 3 and I/Ga = 2, consistent with the thermodynamic properties of condensed gallium-iodide compounds.

The steady-state behavior of a ceramic slab under microwave heating by transverse magnetic illumination is analyzed. Local bifurcation techniques are applied to a one-dimensional model to classify the region of parametric sensitivity (or thermal runaway). It is observed that for a certain set of parameters, there are periodically recurring ranges of slab thickness for which thermal runaway may be avoided. The runaway dependence on other parameters critical to the operation of the process is also studied. The results presented here may be used to prevent thermal runaway in microwave heating of ceramics.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.129.102.12 Downloaded on 2015-05-25 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.129.102.12 Downloaded on 2015-05-25 to IP