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We investigated chemical sputtering of silicon films by Hy+ ions (with y being 2 and 3) in an asymmetric VHF Plasma Enhanced Chemical Vapor Deposition (PECVD) discharge in detail. In experiments with discharges created with pure H2 inlet flows, we observed that more Si was etched from the powered than from the grounded electrode, and this resulted in a net deposition on the grounded electrode. With experimental input data from a power density series of discharges with pure H2 inlet flows, we were able to model this process with a chemical sputtering mechanism. The obtained chemical sputtering yields were (0.3-0.4) ± 0.1 Si atom per bombarding Hy+ ion at the grounded electrode and at the powered electrode the yield ranged from (0.4 to 0.65) ± 0.1. Subsequently, we investigated the role of chemical sputtering during PECVD deposition with a series of silane fractions SF (SF(%)=[SiH4]/[H2]*100) ranging from SF=0% to 20%. We experimentally observed that the SiHy+ flux is not proportional to SF but decreasing from SF=3.4% to 20%. This counterintuitive SiHy+ flux trend was partly explained by an increasing chemical sputtering rate with decreasing SF and partly by the reaction between H3+ and SiH4 that forms SiH3+. [ABSTRACT FROM AUTHOR]

The direct simulation Monte Carlo (DSMC) method was used to investigate the efficiency of differential pumping in linear plasma generators operating at high gas flows. Skimmers are used to separate the neutrals from the plasma beam, which is guided from the source to the target by a strong axial magnetic field. In this way, the neutrals are prevented to reach the target region. The neutral flux to the target must be lower than the plasma flux to enable ITER relevant plasma-surface interaction (PSI) studies. It is therefore essential to control the neutral gas dynamics. The DSMC method was used to model the expansion of a hot gas in a low pressure vessel where a small discrepancy in shock position was found between the simulations and a well-established empirical formula. Two stage differential pumping was modeled and applied in the linear plasma devices Pilot-PSI and PLEXIS. In Pilot-PSI a factor of 4.5 pressure reduction for H2 has been demonstrated. Both simulations and experiments showed that the optimum skimmer position depends on the position of the shock and therefore shifts for different gas parameters. The shape of the skimmer has to be designed such that it has a minimum impact on the shock structure. A too large angle between the skimmer and the forward direction of the gas flow leads to an influence on the expansion structure. A pressure increase in front of the skimmer is formed and the flow of the plasma beam becomes obstructed. It has been shown that a skimmer with an angle around 53° gives the best performance. The use of skimmers is implemented in the design of the large linear plasma generator Magnum-PSI. Here, a three stage differentially pumped vacuum system is used to reach low enough neutral pressures near the target, opening a door to PSI research in the ITER relevant regime. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A dusty radio-frequency silane/hydrogen discharge is simulated, with the use of a one-dimensional fluid model. In the model, discharge quantities like the fluxes, densities, and electric field are calculated self consistently. A radius and an initial density profile for the spherical dust particles are given and the charge and the density of the dust are calculated with an iterative method. During the transport of the dust, its charge is kept constant in time. The dust influences the electric field distribution through its charge and the density of the plasma through recombination of positive ions and electrons at its surface. In the model this process gives an extra production of silane radicals, since the growth of dust is not included. Results are presented for situations in which the dust significantly changes the discharge characteristics, both by a strong reduction of the electron density and by altering the electric field by its charge. Simulations for dust with a radius of 2 µm show that the stationary solution of the dust density and the average electric field depend on the total amount of the dust. The presence of dust enhances the deposition rate of amorphous silicon at the electrodes because of the rise in the average electron energy associated with the decrease of the electron density and the constraint of a constant power input. [ABSTRACT FROM AUTHOR]

Presents a study which described a fluid model for an argon radio frequency discharge in a cylindrical discharge chamber. Values of the transport coefficients; Use of the Sharfetter-Gummel exponential scheme for the spatial discretization; Simulation results.

Deals with a study which considered the response of a radio-frequency discharge in an electronegative gas to laser-induced photodetachment. Background to the study; Theoretical model; Numerical technique; Conclusions.

Presents a numerical study on the ion and neutral angular impact energy distribution at the radio frequency-driven electrode of a reactive ion etcher. Contribution of the collision processes to the angular ion impact energy distribution; Derivation of expressions that can be used to predict average impact energies and angles; Calculation of the sputter yield.

Examines a self-consistent hybrid Monte Carlo-fluid model for a direct current glow discharge. Inclusion of collision rates of the fast electrons; Influence of the negative glow on the calculation in the cathode dark space; Overview of the fluid model for the ions and slow electrons.

Presents a study which used the high-power density of a frequency quadrupled pulsed neodymium-yttrium aluminum garnet laser to photodetach electrons from negative ions in radio frequency plasmas generated within a microwave cavity. Determination of negative ion densities; Measurement of the shape of the resonance curve; Pressure and power dependence of the electron density and of the negative ion density.