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Title: “Virtual IED sensor” at an rf-biased electrode in low-pressure plasma

Abstract

Energy distribution and the flux of the ions coming on a surface are considered as the key-parameters in anisotropic plasma etching. Since direct ion energy distribution (IED) measurements at the treated surface during plasma processing are often hardly possible, there is an opportunity for virtual ones. This work is devoted to the possibility of such indirect IED and ion flux measurements at an rf-biased electrode in low-pressure rf plasma by using a “virtual IED sensor” which represents “in-situ” IED calculations on the absolute scale in accordance with a plasma sheath model containing a set of measurable external parameters. The “virtual IED sensor” should also involve some external calibration procedure. Applicability and accuracy of the “virtual IED sensor” are validated for a dual-frequency reactive ion etching (RIE) inductively coupled plasma (ICP) reactor with a capacitively coupled rf-biased electrode. The validation is carried out for heavy (Ar) and light (H{sub 2}) gases under different discharge conditions (different ICP powers, rf-bias frequencies, and voltages). An EQP mass-spectrometer and an rf-compensated Langmuir probe (LP) are used to characterize plasma, while an rf-compensated retarded field energy analyzer (RFEA) is applied to measure IED and ion flux at the rf-biased electrode. Besides, the pulsed selfbias methodmore » is used as an external calibration procedure for ion flux estimating at the rf-biased electrode. It is shown that pulsed selfbias method allows calibrating the IED absolute scale quite accurately. It is also shown that the “virtual IED sensor” based on the simplest collisionless sheath model allows reproducing well enough the experimental IEDs at the pressures when the sheath thickness s is less than the ion mean free path λ{sub i} (s < λ{sub i}). At higher pressure (when s > λ{sub i}), the difference between calculated and experimental IEDs due to ion collisions in the sheath is observed in the low energy range. The effect of electron impact ionization in the sheath on the origin and intensity of low-energy peaks in IED is discussed compared to ion charge-exchange collisions. Obviously, the extrapolation of the “virtual IED sensor” approach to higher pressures requires developing some other sheath models, taking into account both ion and electron collisions and probably including even a model of the whole plasma volume instead of plasma sheath one.« less

Authors:
;  [1]; ;  [1]
  1. Skobeltsyn Institute of Nuclear Physics, Moscow State University, SINP MSU, Moscow (Russian Federation)
Publication Date:
OSTI Identifier:
22600030
Resource Type:
Journal Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 7; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1070-664X
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CALIBRATION; CHARGE EXCHANGE; COMPARATIVE EVALUATIONS; ELECTRODES; ELECTRON COLLISIONS; ELECTRONS; ENERGY SPECTRA; ETCHING; EXTRAPOLATION; HYDROGEN; ION COLLISIONS; IONS; LANGMUIR PROBE; MASS SPECTROMETERS; MEAN FREE PATH; PLASMA PRESSURE; PLASMA SHEATH; SENSORS

Citation Formats

Bogdanova, M. A., Zyryanov, S. M., Faculty of Physics, Moscow State University, MSU, Moscow, Lopaev, D. V., and Rakhimov, A. T. “Virtual IED sensor” at an rf-biased electrode in low-pressure plasma. United States: N. p., 2016. Web. doi:10.1063/1.4956455.
Bogdanova, M. A., Zyryanov, S. M., Faculty of Physics, Moscow State University, MSU, Moscow, Lopaev, D. V., & Rakhimov, A. T. “Virtual IED sensor” at an rf-biased electrode in low-pressure plasma. United States. doi:10.1063/1.4956455.
Bogdanova, M. A., Zyryanov, S. M., Faculty of Physics, Moscow State University, MSU, Moscow, Lopaev, D. V., and Rakhimov, A. T. Fri . "“Virtual IED sensor” at an rf-biased electrode in low-pressure plasma". United States. doi:10.1063/1.4956455.
@article{osti_22600030,
title = {“Virtual IED sensor” at an rf-biased electrode in low-pressure plasma},
author = {Bogdanova, M. A. and Zyryanov, S. M. and Faculty of Physics, Moscow State University, MSU, Moscow and Lopaev, D. V. and Rakhimov, A. T.},
abstractNote = {Energy distribution and the flux of the ions coming on a surface are considered as the key-parameters in anisotropic plasma etching. Since direct ion energy distribution (IED) measurements at the treated surface during plasma processing are often hardly possible, there is an opportunity for virtual ones. This work is devoted to the possibility of such indirect IED and ion flux measurements at an rf-biased electrode in low-pressure rf plasma by using a “virtual IED sensor” which represents “in-situ” IED calculations on the absolute scale in accordance with a plasma sheath model containing a set of measurable external parameters. The “virtual IED sensor” should also involve some external calibration procedure. Applicability and accuracy of the “virtual IED sensor” are validated for a dual-frequency reactive ion etching (RIE) inductively coupled plasma (ICP) reactor with a capacitively coupled rf-biased electrode. The validation is carried out for heavy (Ar) and light (H{sub 2}) gases under different discharge conditions (different ICP powers, rf-bias frequencies, and voltages). An EQP mass-spectrometer and an rf-compensated Langmuir probe (LP) are used to characterize plasma, while an rf-compensated retarded field energy analyzer (RFEA) is applied to measure IED and ion flux at the rf-biased electrode. Besides, the pulsed selfbias method is used as an external calibration procedure for ion flux estimating at the rf-biased electrode. It is shown that pulsed selfbias method allows calibrating the IED absolute scale quite accurately. It is also shown that the “virtual IED sensor” based on the simplest collisionless sheath model allows reproducing well enough the experimental IEDs at the pressures when the sheath thickness s is less than the ion mean free path λ{sub i} (s < λ{sub i}). At higher pressure (when s > λ{sub i}), the difference between calculated and experimental IEDs due to ion collisions in the sheath is observed in the low energy range. The effect of electron impact ionization in the sheath on the origin and intensity of low-energy peaks in IED is discussed compared to ion charge-exchange collisions. Obviously, the extrapolation of the “virtual IED sensor” approach to higher pressures requires developing some other sheath models, taking into account both ion and electron collisions and probably including even a model of the whole plasma volume instead of plasma sheath one.},
doi = {10.1063/1.4956455},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 7,
volume = 23,
place = {United States},
year = {2016},
month = {7}
}