Comparison of measurements and particle-in-cell simulations of ion energy distribution functions in a capacitively coupled radio-frequency discharge

TY - JOUR

T1 - Comparison of measurements and particle-in-cell simulations of ion energy distribution functions in a capacitively coupled radio-frequency discharge

AU - O'Connell, D.

AU - Zorat, R.

AU - Ellingboe, A. R.

AU - Turner, M. M.

PY - 2007/10

Y1 - 2007/10

N2 - The ion dynamics in the high-voltage sheath of a capacitively coupled radio-frequency plasma has been investigated using mass-resolved ion energy analysis in combination with a two-dimensional particle-in-cell (PIC) code. A symmetric confined discharge is designed allowing highly accurate comparisons of measured ion energy distribution functions in high-voltage sheaths with simulation results. Under the conditions investigated, the sheaths are not only collisional, but also chemically complex. This situation is common in applications but rare in laboratory experiments. Excellent agreement has been found for a hydrogen discharge benchmarking the code. Hydrogen is of particular interest since its light mass gives detailed insight into sheath dynamics, and an extensive database of collisional cross sections is available. The H-3(+) ion was found to be the dominant ion in the sheaths and the plasma bulk under most conditions investigated. H-3(+) exhibits the typical saddle-shaped ion energy distribution function indicative of ions created in the plasma bulk and traversing the entire sheath potential. H+ and H-2(+) are predominantly formed through collisions in the high-voltage sheath. H-2(+) ion energy distribution functions show structures resulting from symmetric charge exchange collisions with the background gas. Minor discrepancies between the experimental results and PIC simulations indicate slightly lower plasma densities in the simulation, resulting in larger sheath width. (C) 2007 American Institute of Physics.

AB - The ion dynamics in the high-voltage sheath of a capacitively coupled radio-frequency plasma has been investigated using mass-resolved ion energy analysis in combination with a two-dimensional particle-in-cell (PIC) code. A symmetric confined discharge is designed allowing highly accurate comparisons of measured ion energy distribution functions in high-voltage sheaths with simulation results. Under the conditions investigated, the sheaths are not only collisional, but also chemically complex. This situation is common in applications but rare in laboratory experiments. Excellent agreement has been found for a hydrogen discharge benchmarking the code. Hydrogen is of particular interest since its light mass gives detailed insight into sheath dynamics, and an extensive database of collisional cross sections is available. The H-3(+) ion was found to be the dominant ion in the sheaths and the plasma bulk under most conditions investigated. H-3(+) exhibits the typical saddle-shaped ion energy distribution function indicative of ions created in the plasma bulk and traversing the entire sheath potential. H+ and H-2(+) are predominantly formed through collisions in the high-voltage sheath. H-2(+) ion energy distribution functions show structures resulting from symmetric charge exchange collisions with the background gas. Minor discrepancies between the experimental results and PIC simulations indicate slightly lower plasma densities in the simulation, resulting in larger sheath width. (C) 2007 American Institute of Physics.

KW - SPECTROSCOPIC MEASUREMENTS

KW - GLOW-DISCHARGES

KW - RF DISCHARGES

KW - POSITIVE-IONS

KW - PLASMA

KW - BOMBARDMENT

KW - PRESSURE

KW - TRANSPORT

KW - SHEATHS

KW - OXYGEN

U2 - 10.1063/1.2795634

DO - 10.1063/1.2795634

M3 - Article

SN - 1070-664X

VL - 14

SP - -

JO - Physics of Plasmas

JF - Physics of Plasmas

IS - 10

M1 - 103510

ER -