Volume 94, Issue 6, 15 September 2003
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
94(2003); http://dx.doi.org/10.1063/1.1598300View Description Hide Description
We demonstrate that corona discharges in xenon gas can be an efficient source of excimer vacuum ultraviolet (VUV)radiation. Conversion efficiencies of electrical power into VUV light greater than 50% have been observed. A model describing the light production mechanism in the discharge region including the influence of water vapor content in the 10 ppm region is presented. A prototype large area lamp consisting of 21 corona discharges operating in parallel has been built with VUV output power per area at the lamps surface. Based on the model and experimental results achieved, a continuous wave large area 172 nm excimer light source with output and a possible wall plug efficiency close to 48% is proposed.
94(2003); http://dx.doi.org/10.1063/1.1600526View Description Hide Description
A theoretical study is presented on a type of Penning trap configuration referred to as an electron plasma ion trap/source. Ions in the configuration are confined within a three-dimensional electric potential well, which is produced by a combination of the electric field generated by the trap electrodes and the electric field generated by a trapped electron plasma. The ion density is not limited by the Brillouin ion density limit. Instead, the ion charge density must be smaller than the electron charge density. Various mechanisms that may limit the electron charge density are identified. Example calculations are used to find that the most restrictive limit on the electron charge density is likely to be the voltage difference that must be applied to trap the electron plasma parallel to a magnetic field. For confinement of low-charge-state ions, the ion temperature must be smaller than the electron temperature. Relatively long ion confinement times are found to be possible, however, because the equilibration of the ion temperature and the electron temperature is a slow collisional process due to the disparate masses involved. The ions can be easily extracted before the ion temperature reaches a value such that ion loss to the electrode walls becomes a significant source of impurities. Thus, since ion–wall interactions can be minimal, high purity ion plasmas may be generated. A self-consistent finite-differences computation is used to predict a possible plasma equilibrium.
94(2003); http://dx.doi.org/10.1063/1.1602573View Description Hide Description
A fluid/Monte Carlo simulation model was developed to study plasma molding over an axisymmetric feature (a ring) resting on an otherwise planar surface in contact with a high-density rf plasma. The two-dimensional (r,z) time-dependent sheath potential, and ion density and flux profiles were predicted with a self-consistent fluid simulation. The trajectories of ions and energetic neutrals (resulting mainly by ion neutralization on the cylindrical sidewalls of the ring) were then followed with a Monte Carlo simulation, in an effort to obtain their energy and angular distributions on the substrate surface. When the sheath thickness was comparable to the size of the ring, strong radial electric fields deflected oncoming ions toward the sidewalls of the ring. The ion density was lower in the cylindrical well formed by the ring, compared to outside, resulting in a locally thicker sheath and a smaller spread in the double-peaked ion energy distributions at the bottom of the well. The ion impact angle increased progressively as the sidewalls were approached. The angular distribution of energetic (fast) neutrals at the bottom of the well was bimodal. The energy distribution of fast neutrals at the bottom of the well was broader compared to the parent ion energy distributions.
94(2003); http://dx.doi.org/10.1063/1.1603348View Description Hide Description
A one-dimensional particle-in-cell/Monte Carlo model is developed to study capacitively coupled (cc) radio-frequency discharges in a gas mixture of Ar, and The charged species, which are followed in the model, are: Electrons and and ions. The simulation considers electron – neutral (Ar, and collisions, various kinds of collisions of ions with neutrals, positive–negative ion recombination, and electron–ion recombination. The model yields results for electron and ion densities, fluxes and energy distributions, collision rates and electric field, and potential distributions. The simulations are performed for a ratio of mixture at a pressure of 30 mTorr in single (13.56 MHz) and dual frequency cc reactors and a comparison between the two frequency regimes is made. Results show that the structure of the discharges is electronegative in both cases. and ions are the main negative charge carriers in the single and dual frequency regime, respectively. In the presence of low-frequency (2 MHz) and a strong electric field, the light ions are no longer confined in the bulk plasma and they partially respond to the instantaneous electric field. The calculated electron energy probability function profiles can be approximated to a Druyvesteyn and bi-Maxwellian distribution with high-energy tails in the single- and dual-frequency regime, respectively. The ion energy distribution is narrow with one outstanding peak in the single-frequency scheme, whereas it is wide and bimodal in the dual-frequency scheme.