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Title: Transient plasma potential in pulsed dual frequency inductively coupled plasmas and effect of substrate biasing

Abstract

An electron emitting probe in saturated floating potential mode has been used to investigate the temporal evolution of plasma potential and the effect of substrate RF biasing on it for pulsed dual frequency (2 MHz/13.56 MHz) inductively coupled plasma (ICP) source. The low frequency power (P{sub 2MHz}) has been pulsed at 1 KHz and a duty ratio of 50%, while high frequency power (P{sub 13.56MHz}) has been used in continuous mode. The substrate has been biased with a separate bias power at (P{sub 12.56MHz}) Argon has been used as a discharge gas. During the ICP power pulsing, three distinct regions in a typical plasma potential profile, have been identified as ‘initial overshoot’, pulse ‘on-phase’ and pulse ‘off-phase’. It has been found out that the RF biasing of the substrate significantly modulates the temporal evolution of the plasma potential. During the initial overshoot, plasma potential decreases with increasing RF biasing of the substrate, however it increases with increasing substrate biasing for pulse ‘on-phase’ and ‘off-phase’. An interesting structure in plasma potential profile has also been observed when the substrate bias is applied and its evolution depends upon the magnitude of bias power. The reason of the evolution of this structure maymore » be the ambipolar diffusion of electron and its dependence on bias power.« less

Authors:
 [1];  [1];  [2]
  1. Department of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do, 440-746 (Korea, Republic of)
  2. (SAINT), Sungkyunkwan University, Suwon, Gyeonggi-do, 440-746 (Korea, Republic of)
Publication Date:
OSTI Identifier:
22611366
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 6; Journal Issue: 9; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AMBIPOLAR DIFFUSION; ARGON; ELECTRONS; EVOLUTION; MHZ RANGE; PLASMA POTENTIAL; PULSES; SUBSTRATES; TRANSIENTS

Citation Formats

Mishra, Anurag, Yeom, Geun Young, E-mail: gyyeom@skku.edu, and SKKU Advanced Institute of Nanotechnology. Transient plasma potential in pulsed dual frequency inductively coupled plasmas and effect of substrate biasing. United States: N. p., 2016. Web. doi:10.1063/1.4961940.
Mishra, Anurag, Yeom, Geun Young, E-mail: gyyeom@skku.edu, & SKKU Advanced Institute of Nanotechnology. Transient plasma potential in pulsed dual frequency inductively coupled plasmas and effect of substrate biasing. United States. doi:10.1063/1.4961940.
Mishra, Anurag, Yeom, Geun Young, E-mail: gyyeom@skku.edu, and SKKU Advanced Institute of Nanotechnology. 2016. "Transient plasma potential in pulsed dual frequency inductively coupled plasmas and effect of substrate biasing". United States. doi:10.1063/1.4961940.
@article{osti_22611366,
title = {Transient plasma potential in pulsed dual frequency inductively coupled plasmas and effect of substrate biasing},
author = {Mishra, Anurag and Yeom, Geun Young, E-mail: gyyeom@skku.edu and SKKU Advanced Institute of Nanotechnology},
abstractNote = {An electron emitting probe in saturated floating potential mode has been used to investigate the temporal evolution of plasma potential and the effect of substrate RF biasing on it for pulsed dual frequency (2 MHz/13.56 MHz) inductively coupled plasma (ICP) source. The low frequency power (P{sub 2MHz}) has been pulsed at 1 KHz and a duty ratio of 50%, while high frequency power (P{sub 13.56MHz}) has been used in continuous mode. The substrate has been biased with a separate bias power at (P{sub 12.56MHz}) Argon has been used as a discharge gas. During the ICP power pulsing, three distinct regions in a typical plasma potential profile, have been identified as ‘initial overshoot’, pulse ‘on-phase’ and pulse ‘off-phase’. It has been found out that the RF biasing of the substrate significantly modulates the temporal evolution of the plasma potential. During the initial overshoot, plasma potential decreases with increasing RF biasing of the substrate, however it increases with increasing substrate biasing for pulse ‘on-phase’ and ‘off-phase’. An interesting structure in plasma potential profile has also been observed when the substrate bias is applied and its evolution depends upon the magnitude of bias power. The reason of the evolution of this structure may be the ambipolar diffusion of electron and its dependence on bias power.},
doi = {10.1063/1.4961940},
journal = {AIP Advances},
number = 9,
volume = 6,
place = {United States},
year = 2016,
month = 9
}
  • 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 MHzmore » 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.« less
  • 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
  • Controlling time averaged ion energy distribution (IED) is becoming increasingly important in many plasma material processing applications for plasma etching and deposition. The present study reports the evolution of ion energy distributions with radio frequency (RF) powers in a pulsed dual frequency inductively discharge and also investigates the effect of duty ratio. The discharge has been sustained using two radio frequency, low (P{sub 2 MHz} = 2 MHz) and high (P{sub 13.56 MHz} = 13.56 MHz) at a pressure of 10 mTorr in argon (90%) and CF{sub 4} (10%) environment. The low frequency RF powers have been varied from 100 to 600 W, whereas the high frequency powers frommore » 200 to 1200 W. Typically, IEDs show bimodal structure and energy width (energy separation between the high and low energy peaks) increases with increasing P{sub 13.56 MHz}; however, it shows opposite trends with P{sub 2 MHz}. It has been observed that IEDs bimodal structure tends to mono-modal structure and energy peaks shift towards low energy side as duty ratio increases, keeping pulse power owing to mode transition (capacitive to inductive) constant.« less
  • An internal-type linear inductive antenna, referred to as a ''double comb-type antenna,'' was used as a large area plasma source with a substrate size of 880x660 mm{sup 2} (fourth generation glass size). The effects of the dual frequency (2 and 13.56 MHz) radio frequency (rf) power to the antenna as well as the power ratio on the plasma characteristics were investigated. High-density plasma on the order of 1.7x10{sup 11} cm{sup -3} could be obtained with a dual frequency power of 5 kW (13.56 MHz) and 1 kW (2 MHz) at a pressure of 15 mTorr Ar. This plasma density wasmore » lower than that obtained for the double comb-type antenna using a single frequency alone (5 kW, 13.56 MHz). However, the use of the dual frequency with a rf power ratio of approximately 1(2 MHz):5(13.56 MHz) showed better plasma uniformity than that obtained using the single frequency. Plasma uniformity of 6.1% could be obtained over the substrate area. Simulations using FL2L code confirmed the improvement in the plasma uniformity using the dual frequency to the double comb-type antenna.« less
  • No abstract prepared.