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Title: The radio-frequency fluctuation effect on the floating harmonic method

Abstract

The radio-frequency (RF) plasma diagnostics with an electrical probe facing a challenge, because the RF fluctuation oscillates the plasma potential and distorts the current-voltage (I-V) curve. As Langmuir probe is widely used in plasma diagnostics, many researchers have been studying the effect of RF fluctuation on probe and compensation methods. On the other hand, there have not been enough studies on the fluctuation effect on the floating harmonic method. Therefore, we investigated the impact of RF fluctuation on the floating harmonic method theoretically and experimentally. When the electrons are in ideal Maxwellian distribution, the floating potential is negatively shifted by the RF fluctuation, but the fluctuation does not distort I-V curve around the floating potential. However, in practical plasmas, the I-V curve and their harmonic components are distorted. This RF fluctuation effect becomes more significant in a low density plasma with a high impedance sheath. The second harmonic current decreases with the RF fluctuation while the first harmonic current is merely affected. Therefore, the electron temperatures measured with the floating harmonic method under low density plasma with uncompensated probe are overestimated than the results obtained with the compensated probe.

Authors:
;  [1];  [2];  [1];  [3]
  1. Department of Electrical Engineering, Hanyang University, Wangsimni-ro 222, Seongdong-gu, Seoul 04763 (Korea, Republic of)
  2. Department of Nanoscale Semiconductor Engineering, Hanyang University, Wangsimni-ro 222, Seongdong-gu, Seoul 04763 (Korea, Republic of)
  3. (Korea, Republic of)
Publication Date:
OSTI Identifier:
22599924
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 8; 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; DIAGRAMS; ELECTRON TEMPERATURE; ELECTRONS; FLUCTUATIONS; IMPEDANCE; LANGMUIR PROBE; PLASMA DENSITY; PLASMA DIAGNOSTICS; PLASMA POTENTIAL; RADIOWAVE RADIATION

Citation Formats

Lee, Jaewon, Kim, Kyung-Hyun, Kim, Dong-Hwan, Chung, Chin-Wook, E-mail: joykang@hanyang.ac.kr, and Department of Nanoscale Semiconductor Engineering, Hanyang University, Wangsimni-ro 222, Seongdong-gu, Seoul 04763. The radio-frequency fluctuation effect on the floating harmonic method. United States: N. p., 2016. Web. doi:10.1063/1.4960559.
Lee, Jaewon, Kim, Kyung-Hyun, Kim, Dong-Hwan, Chung, Chin-Wook, E-mail: joykang@hanyang.ac.kr, & Department of Nanoscale Semiconductor Engineering, Hanyang University, Wangsimni-ro 222, Seongdong-gu, Seoul 04763. The radio-frequency fluctuation effect on the floating harmonic method. United States. doi:10.1063/1.4960559.
Lee, Jaewon, Kim, Kyung-Hyun, Kim, Dong-Hwan, Chung, Chin-Wook, E-mail: joykang@hanyang.ac.kr, and Department of Nanoscale Semiconductor Engineering, Hanyang University, Wangsimni-ro 222, Seongdong-gu, Seoul 04763. 2016. "The radio-frequency fluctuation effect on the floating harmonic method". United States. doi:10.1063/1.4960559.
@article{osti_22599924,
title = {The radio-frequency fluctuation effect on the floating harmonic method},
author = {Lee, Jaewon and Kim, Kyung-Hyun and Kim, Dong-Hwan and Chung, Chin-Wook, E-mail: joykang@hanyang.ac.kr and Department of Nanoscale Semiconductor Engineering, Hanyang University, Wangsimni-ro 222, Seongdong-gu, Seoul 04763},
abstractNote = {The radio-frequency (RF) plasma diagnostics with an electrical probe facing a challenge, because the RF fluctuation oscillates the plasma potential and distorts the current-voltage (I-V) curve. As Langmuir probe is widely used in plasma diagnostics, many researchers have been studying the effect of RF fluctuation on probe and compensation methods. On the other hand, there have not been enough studies on the fluctuation effect on the floating harmonic method. Therefore, we investigated the impact of RF fluctuation on the floating harmonic method theoretically and experimentally. When the electrons are in ideal Maxwellian distribution, the floating potential is negatively shifted by the RF fluctuation, but the fluctuation does not distort I-V curve around the floating potential. However, in practical plasmas, the I-V curve and their harmonic components are distorted. This RF fluctuation effect becomes more significant in a low density plasma with a high impedance sheath. The second harmonic current decreases with the RF fluctuation while the first harmonic current is merely affected. Therefore, the electron temperatures measured with the floating harmonic method under low density plasma with uncompensated probe are overestimated than the results obtained with the compensated probe.},
doi = {10.1063/1.4960559},
journal = {Physics of Plasmas},
number = 8,
volume = 23,
place = {United States},
year = 2016,
month = 8
}
  • The floating harmonic method biases sinusoidal voltage to a probe sheath, and as its response, harmonic currents can be obtained. These currents can be used to determine the plasma parameters. However, different shapes of probes have different shapes of sheaths that can affect the diagnostic results. However, no research has been done on the sheath effect on the floating harmonic method. Therefore, we investigate the effect of the sheath during floating harmonic diagnostics by comparing cylindrical and planar probes. While the sinusoidal voltages were applied to a probe, because the sheath oscillated, the time variant ion current and their harmonicmore » currents were added to the electron harmonic currents. In the floating harmonic method, the harmonic currents are composed of only the electron harmonic currents. Therefore, the ion harmonic currents affect the diagnostic results. In particular, the electron temperature obtained by the small probe tip was higher than that of the large probe tip. This effect was exacerbated when the ratio of the probe tip radius to the sheath length was smaller.« less
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