Numerical Simulation of Electron Transport in Electric and Magnetic Fields for Analysis of Electron Temperature and Number Density Profiles Measured in Argon Magnetic Neutral Loop Discharge Plasma

Sugawara, Hirotake; Osaga, Tsuyoshi; Tsuboi, Hideo; Kuwahara, Kazuhiro; Ogata, Seiji

doi:10.1143/jjap.49.086001

Cited by 14 publications

(17 citation statements)

References 18 publications

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“…A similar off-separatrix peak of the electron distribution is seen in an experimental result of Sugawara et al (2010) as well. Figure 4 shows the distribution of the mean electron energyε(r, z).…”

Section: Electron Distributionsupporting

confidence: 82%

Structure and dynamics of a magnetic neutral loop discharge plasma described using electron motion in a quadrupole magnetic field

Osaga¹,

Sugawara²,

Sakurai³

2011

Plasma Sources Sci. Technol.

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Abstract. Electron motion in a CF 4 magnetic neutral loop discharge (NLD) plasma was simulated using a Monte Carlo method. The spatial distribution of electrons illustrated the fundamental structure of the NLD plasma, and its dynamics were depicted from the distributions of the mean electron energy, the electron energy gain and the azimuthal electron flux. The peak of mean electron energy appeared at the neutral loop (NL), which confirmed that electrons gain energy near this loop.High mean electron energy was observed not only near the NL but also along the separatrices of the quadrupole magnetic field. Energetic electrons were transported along the separatrices and induced ionization at those locations. However, the electron distribution had valleys along the separatrices, because electrons accelerated near the NL were likely to leave this region where the binding of the magnetic field is weak. The azimuthal electron flux representing the loop plasma current showed that the electron conduction path around the NL, which has conventionally been modelled as a ring conductor, has a particular directionality due to the rectification effect of antiparallel magnetic fields composing the quadrupole magnetic field. The directionality in the upper and lower regions of the quadrupole magnetic field was opposite to that in the inner and outer regions.

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Section: Electron Distributionsupporting

confidence: 82%

Structure and dynamics of a magnetic neutral loop discharge plasma described using electron motion in a quadrupole magnetic field

Osaga¹,

Sugawara²,

Sakurai³

2011

Plasma Sources Sci. Technol.

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“…It was reported that the space charge field had the function of maintaining a high number of electrons [12]. In another report, the electron reflectivity at the vessel wall was set high as an alternative effect of the space charge field [5]. In the present simulation, the electron reflectivity was set at 100%.…”

Section: Trace Of Electronsmentioning

confidence: 87%

“…On the basis of this understanding, it has been reported that the etching rate profile on the substrate can be made uniform by varying the NL radius dynamically [3,4]. Recently, a computational analysis by the authors revealed that the electrons gain energy near the NL and are transported along the separatrix, which is the boundary dividing the plasma space into four regions according to the direction of the magnetic field lines [5]. The etchant production, as a result, is distributed not only in the vicinity of the NL but also along the separatrix [5].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, a computational analysis by the authors revealed that the electrons gain energy near the NL and are transported along the separatrix, which is the boundary dividing the plasma space into four regions according to the direction of the magnetic field lines [5]. The etchant production, as a result, is distributed not only in the vicinity of the NL but also along the separatrix [5]. This result indicates that it is not the NL radius itself but the foot of the separatrix that should be focused on when the position of the high etching rate on the substrate is discussed.…”

Section: Introductionmentioning

confidence: 99%

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Control of Magnetic Field for Sustainment of Ion Production and Uniform Ion Flux to Substrate in Neutral Loop Discharge Plasma

Yoshida

Sakurai

Sugawara

et al. 2013

Electrical Engineering Japan

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SUMMARYWe simulated electron and ion motions in a neutral loop discharge plasma under the control of the foot of the separatrix sweeping over the substrate and the neutral loop moving within a short distance from the RF antenna by a Monte Carlo method. We analyzed the distributions of ion production and ion flux to the substrate. We found that ion production is sensitive to the magnetic field gradient rather than to the electric field strength. Moreover, by superposing the flux distributions weighted by the residence time of the foot of the separatrix on the substrate, we obtained a uniform time-averaged distribution of the ion flux to the substrate in a radius range of r = 4.0 to 14.0 cm with σ/m = 0.25% (m: mean, σ: standard deviation).

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“…The electrons were traced for 200 RF periods and sampled in the last 50 to obtain the time-averaged electron distribution after the initial relaxation process. We assumed a high electron reflectivity of 0.99 at the sidewall, ceiling, and bottom of the vessel, regarding it as the sum of the surface reactions such as electron absorption and emission of the secondary electrons [6]. Fig.…”

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confidence: 99%

Electron Distribution in a Quadrupole Magnetic Field to Drive Magnetic Neutral Loop Discharge Plasma

Osaga

Sakurai

Sugawara

2011

IEEE Trans. Plasma Sci.

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-We simulated the electron motion in a quadrupole magnetic field that drives a neutral loop discharge (NLD) plasma, using a Monte Carlo method. The structure of the electron distribution in the NLD plasma was observed. Electrons underwent reciprocating motion between reflecting boundaries as they gyrated along magnetic field lines. During this motion, they deviated from the neutral loop and concentrated beside the separatrices of the quadrupole magnetic field.Index Terms -Electron number density, Monte Carlo method, neutral loop (NL) discharge (NLD) plasma, quadrupole magnetic field, separatrix.AGNETIC neutral loop (NL) discharge (NLD) plasma, used for dry etching, is a type of inductively coupled plasma. It can operate at low gas pressures (~ 1 mTorr) and high plasma densities (10 . The magnetic field induced by the coil currents is quadrupole, and a ring of zero magnetic field, i.e., the socalled NL, is formed in the vessel. A ring-shaped plasma, i.e., the NLD plasma, is generated along the NL by the electric power from an RF antenna [3]. The radius and position of the NLD plasma are controllable via the coil currents. A dynamic control utilizing this feature for uniform wide-area etching has been proposed [4]. To understand the structure of the NLD plasma, the electron motion in the quadrupole magnetic field was simulated by a Monte Carlo method. In this work, we observed the three-dimensional structure of the electron distribution in the NLD plasma. The diameter and height of the vessel were both 40 cm. Currents I 1 , I 2 , and I 3 of the top, middle, and bottom coils (60-turn coils) were set at +47.8, −55.75, and +47.8 A, respectively. The radius of the NL formed was 11 cm, and the gradient of the magnetic field was approximately 0.17 mT/cm near the NL. An RF (13.56 MHz) electric field with a sinusoidal waveform was induced by the oneturn RF antenna. Its amplitude at the NL was approximately 4.0 V/cm.The gas medium was assumed to be CF 4 at 5 mTorr.The electron collision cross sections of CF 4 were taken from [5]. The initial electrons were released in the NL region, which is the region where the magnetic field is weaker than the 0.48-mT strength of the RF-resonant magnetic field and the electric power is deposited into the plasma. The electrons were traced for 200 RF periods and sampled in the last 50 to obtain the time-averaged electron distribution after the initial relaxation process. We assumed a high electron reflectivity of 0.99 at the sidewall, ceiling, and bottom of the vessel, regarding it as the sum of the surface reactions such as electron absorption and emission of the secondary electrons [6]. Fig. 2 shows the electron number density n e . The highdensity region in which n e is higher than 20% of its peak value is extracted. n e is low near the separatrices of the quadrupole magnetic field, and electrons concentrate beside the separatrices. Electrons deviate from the separatrices, but further diffusion hardly proceeds. This is explained in the following manner. In the NL region, electr...

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Numerical Simulation of Electron Transport in Electric and Magnetic Fields for Analysis of Electron Temperature and Number Density Profiles Measured in Argon Magnetic Neutral Loop Discharge Plasma

Cited by 14 publications

References 18 publications

Structure and dynamics of a magnetic neutral loop discharge plasma described using electron motion in a quadrupole magnetic field

Structure and dynamics of a magnetic neutral loop discharge plasma described using electron motion in a quadrupole magnetic field

Control of Magnetic Field for Sustainment of Ion Production and Uniform Ion Flux to Substrate in Neutral Loop Discharge Plasma

Electron Distribution in a Quadrupole Magnetic Field to Drive Magnetic Neutral Loop Discharge Plasma

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