Negative ion behavior in single- and dual-frequency plasma etching reactors: particle-in-cell/Monte Carlo collision study.
Particle-in-cell/Monte Carlo simulations are used to simulate the trajectories and energies of randomly sampled F- and CF-(3) ions in capacitively coupled radio-frequency discharges, in order to clarify the movement of the negative ions in the sheaths and plasma in both single- and dual-frequency regimes, as well as in symmetric and asymmetric discharges. In the single-frequency reactor both types of negative ions are confined in the plasma and the main loss mechanism is recombination with positive ions. In the dual-frequency reactor under certain operating conditions when the sheaths are wide and the bulk plasma is narrow the light F- ions move across from one sheath to the other, and they can even be lost at the electrodes. The main loss mechanisms are then electron detachment and absorption at the electrodes. The much heavier CF-(3) ions are still confined in the bulk and represent the major negative charge. In an asymmetric discharge the electric field in the sheath to the smaller (powered) electrode is much stronger than that in the sheath to the grounded electrode. Consequently, the F- ions reach mainly the grounded electrode.
Georgieva
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PLASMANT Research Group, Department of Chemistry, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk-Antwerp, Belgium. violeta.georgieva@ua.ac.be
Bogaerts
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