AVS 52nd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThA

Paper PS-ThA7
Extraction of a Directional, Nearly Mono-energetic Ion Beam Using an Inductively Coupled Pulsed Plasma with an Internal Coil

Thursday, November 3, 2005, 4:00 pm, Room 304

Session: Plasma Sources and Equipment
Presenter: L. Xu, University of Houston
Authors: L. Xu, University of Houston
D.J. Economou, University of Houston
V.M. Donnelly, University of Houston
P. Ruchhoeft, University of Houston
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Ion beams with narrow energy and angular distributions are important for large-area sub-10 nm feature etching and deposition. In this work, a 13.56 MHz pulsed (typically 100µs ON/100µs OFF) inductively coupled plasma reactor with a two-turn nickel coil immersed in the plasma was developed to generate a nearly mono-energetic, directional ion beam. This beam may be used for etching (Ar@super +@ ions on silicon exposed to chlorine) or deposition (low energy Ni@super +@ ions on silicon). The plasma chamber was separated from the differentially pumped processing chamber by an ion drift region. A three-grid ion energy analyzer located in the processing chamber, 75 cm from the ion source, was employed to measure the ion energy distribution (IED) and ion current density. A positive voltage pulse synchronized with the power-OFF (afterglow) period of the pulsed discharge was applied to an extraction ring electrode surrounding the plasma, raising the plasma potential (V@sub p@) and "pushing" positive ions out of the plasma through a grounded grid. With 100 V applied to the extraction ring electrode during the afterglow, the energy of the extracted ion beam peaked at 100.5 eV, and the FWHM of the IED was 3.0 eV. The corresponding ion current (measured by the analyzer with 1 degree acceptance angle) was 20 times higher than the ion current extracted during the power-ON (active glow, no acceleration voltage) period. This is because ions exiting the plasma during the afterglow have a lower divergence angle, due to the vertical acceleration and low T@sub e@. The ion drift tube downstream of the plasma was found to be a "natural filter" to effectively screen out ions in the wings of the energy and angular distributions, allowing a directional and nearly mono-energetic ion beam to reach the sample. This work was supported by the National Science Foundation (NSF-NIRT-0303790).