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Negative ion behavior in single- and dual-frequency plasma etching reactors: particle-in-cell/Monte Carlo collision
1PLASMANT Research Group, Department of Chemistry, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk-Antwerp, Belgium. violeta.georgieva@ua.ac.be
Summary
Particle-in-cell/Monte Carlo simulations reveal distinct negative ion behaviors in radio-frequency discharges. In dual-frequency systems, F- ions can be lost at electrodes, unlike heavier CF3- ions confined to the plasma bulk.
Area of Science:
- Plasma Physics
- Ion Transport
- Discharge Engineering
Background:
- Capacitively coupled radio-frequency (CCRF) discharges are crucial in semiconductor manufacturing.
- Understanding negative ion dynamics within plasma sheaths and bulk is essential for process control.
- Previous models often simplified ion behavior, necessitating detailed simulation.
Purpose of the Study:
- To elucidate the movement and loss mechanisms of F- and CF3- ions in CCRF discharges.
- To compare ion behavior across single-frequency, dual-frequency, symmetric, and asymmetric discharge configurations.
- To investigate the influence of sheath width and electric field strength on ion trajectories.
Main Methods:
- Particle-in-cell (PIC) simulations coupled with Monte Carlo collision models were employed.
- Trajectories and energies of randomly sampled F- and CF3- ions were tracked.
- Simulations covered single- and dual-frequency regimes, as well as symmetric and asymmetric electrode arrangements.
Main Results:
- In single-frequency discharges, both F- and CF3- ions are primarily confined to the plasma bulk, with recombination being the main loss.
- In dual-frequency discharges, under specific conditions (wide sheaths, narrow bulk), F- ions can traverse sheaths and be lost via electron detachment or electrode absorption.
- Heavier CF3- ions remain confined in the bulk, constituting the dominant negative charge carrier.
- In asymmetric discharges, F- ions preferentially migrate towards the grounded electrode due to stronger electric fields in the powered electrode sheath.
Conclusions:
- Negative ion transport and loss mechanisms are highly dependent on discharge frequency and configuration.
- Dual-frequency operation offers pathways for F- ion loss at electrodes, distinct from bulk recombination.
- CF3- ions serve as stable negative charge carriers in the plasma bulk.
- Asymmetric electrode configurations significantly influence ion flux distribution, directing F- ions towards the grounded electrode.
