| AVS 57th International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS2-TuA |
| Session: | Plasma Sources |
| Presenter: | Z. Xiong, University of Michigan, Ann Arbor |
| Authors: | Z. Xiong, University of Michigan, Ann Arbor M.J. Kushner, University of Michigan, Ann Arbor |
| Correspondent: | Click to Email |
In electric discharge-pumped excimer lasers as used for photolithography sources in microelectronics fabrication, corona discharges are often used to provide UV photons to preionize the gas mixture. The preionization source, often called a corona bar, typically consists of a cylindrical metal rod surrounded by a dielectric. A discharge initiated by a high voltage pulse propagates around the surface of the corona bar, producing a surface-hugging avalanche wave similar to a gas phase streamer. The high electron temperature in the avalanche front produces radiating excited states that in turn produce the desired UV photons. We present results from a numerical study of an idealized corona bar discharge sustained in a multi-atmosphere Ne/Ar/F2/Xe gas mixture as used in ArF excimer lasers. The corona bar consists of a grounded metal cylinder surrounded by an annular dielectric layer of a few cm diameter. A point electrode (cathode) is located on the surface of the dielectric layer and is subject to a stepwise initial voltage change. The ensuing corona surface discharge was investigated using a 2-dimensional plasma hydrodynamics model with radiation photon transport. Continuity equations for charged and neutral species, and Poisson's equation are solved coincident with the electron energy equation with transport coefficients obtained from solutions of Boltzmann's equation. The ionization front, initiated from the point electrode, propagates along the cylinder surface (with speeds up to 3 x 108 cm/s that depend on the dielectric constant) charging the surface as it propagates. The ionization front usually stops before completing a full circle as the corona bar becomes progressively charged. The strength and propagation speed of the ionization wave are characterized by the electron density and temperature distributions along the cylinder circumference. The photon fluxes are collected on a surrounding circular surface. With radiation from short lived states such as Ne2*, the UV emission sweeps around the corona bar coincident with the ionization wave. The effects of dielectric constants, gas mixture and voltage on the corona discharge dynamics will be presented.
* Work supported by Cymer, Inc. and the Department of Energy Office of Fusion Energy Sciences.