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Title: Electron density modulation in a pulsed dual-frequency (2/13.56 MHz) dual-antenna inductively coupled plasma discharge

Abstract

The electron density, n{sub e}, modulation is measured experimentally using a resonance hairpin probe in a pulsed, dual-frequency (2/13.56 MHz), dual-antenna, inductively coupled plasma discharge produced in argon-C{sub 4}F{sub 8} (90–10) gas mixtures. The 2 MHz power is pulsed at a frequency of 1 kHz, whereas 13.56 MHz power is applied in continuous wave mode. The discharge is operated at a range of conditions covering 3–50 mTorr, 100–600 W 13.56 MHz power level, 300–600 W 2 MHz peak power level, and duty ratio of 10%–90%. The experimental results reveal that the quasisteady state n{sub e} is greatly affected by the 2 MHz power levels and slightly affected by 13.56 MHz power levels. It is observed that the electron density increases by a factor of 2–2.5 on increasing 2 MHz power level from 300 to 600 W, whereas n{sub e} increases by only ∼20% for 13.56 MHz power levels of 100–600 W. The rise time and decay time constant of n{sub e} monotonically decrease with an increase in either 2 or 13.56 MHz power level. This effect is stronger at low values of 2 MHz power level. For all the operating conditions, it is observed that the n{sub e} overshoots at the beginning of the on-phase before relaxing to a quasisteady state value. The relative overshoot densitymore » (in percent) depends on 2 and 13.56 MHz power levels. On increasing gas pressure, the n{sub e} at first increases, reaching to a maximum value, and then decreases with a further increase in gas pressure. The decay time constant of n{sub e} increases monotonically with pressure, increasing rapidly up to 10 mTorr gas pressure and at a slower rate of rise to 50 mTorr. At a fixed 2/13.56 MHz power level and 10 mTorr gas pressure, the quasisteady state n{sub e} shows maximum for 30%–40% duty ratio and decreases with a further increase in duty ratio.« less

Authors:
 [1];  [2];  [3];  [4]
  1. Plasma Research Laboratory, School of Physical Sciences, Dublin City University, Dublin 9 (Ireland)
  2. Department of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746 (Korea, Republic of)
  3. Department of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746, South Korea and SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, Gyeunggi-do 440-746 (Korea, Republic of)
  4. Plasma Research Laboratory, School of Physical Sciences, Dublin City University, Dublin 9, Ireland and Department of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746 (Korea, Republic of)
Publication Date:
OSTI Identifier:
22592850
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films; Journal Volume: 34; Journal Issue: 5; Other Information: (c) 2016 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; ANTENNAS; ARGON; AUGMENTATION; ELECTRON DENSITY; KHZ RANGE 01-100; MHZ RANGE; MIXTURES; MODULATION; PEAK LOAD; PLASMA; PULSE RISE TIME; PULSES

Citation Formats

Sirse, Nishant, E-mail: nishant.sirse@dcu.ie, Mishra, Anurag, Yeom, Geun Y., and Ellingboe, Albert R.. Electron density modulation in a pulsed dual-frequency (2/13.56 MHz) dual-antenna inductively coupled plasma discharge. United States: N. p., 2016. Web. doi:10.1116/1.4959844.
Sirse, Nishant, E-mail: nishant.sirse@dcu.ie, Mishra, Anurag, Yeom, Geun Y., & Ellingboe, Albert R.. Electron density modulation in a pulsed dual-frequency (2/13.56 MHz) dual-antenna inductively coupled plasma discharge. United States. doi:10.1116/1.4959844.
Sirse, Nishant, E-mail: nishant.sirse@dcu.ie, Mishra, Anurag, Yeom, Geun Y., and Ellingboe, Albert R.. Thu . "Electron density modulation in a pulsed dual-frequency (2/13.56 MHz) dual-antenna inductively coupled plasma discharge". United States. doi:10.1116/1.4959844.
@article{osti_22592850,
title = {Electron density modulation in a pulsed dual-frequency (2/13.56 MHz) dual-antenna inductively coupled plasma discharge},
author = {Sirse, Nishant, E-mail: nishant.sirse@dcu.ie and Mishra, Anurag and Yeom, Geun Y. and Ellingboe, Albert R.},
abstractNote = {The electron density, n{sub e}, modulation is measured experimentally using a resonance hairpin probe in a pulsed, dual-frequency (2/13.56 MHz), dual-antenna, inductively coupled plasma discharge produced in argon-C{sub 4}F{sub 8} (90–10) gas mixtures. The 2 MHz power is pulsed at a frequency of 1 kHz, whereas 13.56 MHz power is applied in continuous wave mode. The discharge is operated at a range of conditions covering 3–50 mTorr, 100–600 W 13.56 MHz power level, 300–600 W 2 MHz peak power level, and duty ratio of 10%–90%. The experimental results reveal that the quasisteady state n{sub e} is greatly affected by the 2 MHz power levels and slightly affected by 13.56 MHz power levels. It is observed that the electron density increases by a factor of 2–2.5 on increasing 2 MHz power level from 300 to 600 W, whereas n{sub e} increases by only ∼20% for 13.56 MHz power levels of 100–600 W. The rise time and decay time constant of n{sub e} monotonically decrease with an increase in either 2 or 13.56 MHz power level. This effect is stronger at low values of 2 MHz power level. For all the operating conditions, it is observed that the n{sub e} overshoots at the beginning of the on-phase before relaxing to a quasisteady state value. The relative overshoot density (in percent) depends on 2 and 13.56 MHz power levels. On increasing gas pressure, the n{sub e} at first increases, reaching to a maximum value, and then decreases with a further increase in gas pressure. The decay time constant of n{sub e} increases monotonically with pressure, increasing rapidly up to 10 mTorr gas pressure and at a slower rate of rise to 50 mTorr. At a fixed 2/13.56 MHz power level and 10 mTorr gas pressure, the quasisteady state n{sub e} shows maximum for 30%–40% duty ratio and decreases with a further increase in duty ratio.},
doi = {10.1116/1.4959844},
journal = {Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films},
number = 5,
volume = 34,
place = {United States},
year = {Thu Sep 15 00:00:00 EDT 2016},
month = {Thu Sep 15 00:00:00 EDT 2016}
}
  • Using a Langmuir probe, time resolved measurements of plasma parameters were carried out in a discharge produced by a pulsed dual frequency inductively coupled plasma source. The discharge was sustained in an argon gas environment at a pressure of 10 mTorr. The low frequency (P{sub 2} {sub MHz}) was pulsed at 1 kHz and a duty ratio of 50%, while high frequency (P{sub 13.56} {sub MHz}) was maintained in the CW mode. All measurements were carried out at the center of the discharge and 20 mm above the substrate. The results show that, at a particular condition (P{sub 2} {sub MHz} = 200more » W and P{sub 13.56} {sub MHz }= 600 W), plasma density increases with time and stabilizes at up to ∼200 μs after the initiation of P{sub 2} {sub MHz} pulse at a plasma density of (2 × 10{sup 17} m{sup −3}) for the remaining duration of pulse “on.” This stabilization time for plasma density increases with increasing P{sub 2} {sub MHz} and becomes ∼300 μs when P{sub 2} {sub MHz} is 600 W; however, the growth rate of plasma density is almost independent of P{sub 2} {sub MHz}. Interestingly, the plasma density sharply increases as the pulse is switched off and reaches a peak value in ∼10 μs, then decreases for the remaining pulse “off-time.” This phenomenon is thought to be due to the sheath modulation during the transition from “pulse on” to “pulse off” and partly due to RF noise during the transition period. The magnitude of peak plasma density in off time increases with increasing P{sub 2} {sub MHz}. The plasma potential and electron temperature decrease as the pulse develops and shows similar behavior to that of the plasma density when the pulse is switched off.« less
  • The axial and radial magnetic field profiles in a 13.56 MHz (radio frequency) laboratory 6 turn planar coil inductively coupled plasma reactor are simulated with the consideration of the effect of neutral gas heating. Spatially resolved electron densities, electron temperatures, and neutral gas temperatures were obtained for simulation using empirically fitted electron density and electron temperature and heuristically determined neutral gas temperature. Comparison between simulated results and measured fields indicates that neutral gas heating plays an important role in determining the skin depth of the magnetic fields.
  • Hysteresis in a 13.56 MHz planar coil, inductively coupled plasma (ICP) reactor is modeled using the methods prescribed in El-Fayoumiet al. and Turneret al. The stable working points of the reactor are identified by determining the intersections between simulated absorbed electron power and electron loss power curves. From the plots, transition currents between stable working points are identified and compared with experimentally measured values. Study of hysteresis in ICPs provides better understanding of ICP formation which would be useful for reactor pressure and current optimization.
  • The H mode transition and maintenance currents in a 13.56 MHz laboratory 6 turn planar coil inductively coupled plasma (ICP) reactor are simulated for low pressure argon discharge range of 0.02-0.3 mbar with neutral gas heating and at ambient temperature. An experimentally fitted 3D power evolution plot for 0.02 mbar argon pressure is also shown to visualize the effects of hysteresis in the system. Comparisons between simulation and experimental measurements show good agreement in the pressure range of 0.02-0.3 mbar for transition currents and 0.02-0.1 mbar for maintenance currents only when neutral gas heating is considered. This suggests that neutralmore » gas heating plays a non-negligible role in determining the mode transition points of a rf ICP system.« less