• Journal of the Korean institute of surface engineering
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• v.32 no.4
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• pp.513-520
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• 1999

In this study, we investigated the effects of variously configured magnets on the characteristics of the plasmas to enhance plasma uniformity and density of an inductively coupled plasma source. As the magnets, Helmholtz type axial electromagnets and various multi-dipole magnets types around the chamber wall were used. To characterize the plasma as a function of the combination of the magnets and magnetic field strengths, ion density, electron temperature, and plasma potential were measured using an electrostatic probe along the chamber diameter for Ar plasmas. The measured maximum ion densities were $8$\times$10^{ 11}$$cm^{-3}$ with 600W inductive power and at 5mTorr of operational pressure and the uniformity of ion density was less than 5.9% at 2mTorr of operational pressure. The combination of an optimized multi-dipole magnet type and an axial electromagnet showed the lowest electron temperature (3eV) and plasma potential ($34V{p}$ )

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.77-77
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• 2011

These days, a growing demand for memory device is filled up with the flash memory and the dynamic random access memory (DRAM). Although DRAM is a reasonable solution for current demand, the universal novel memory with high density, high speed and nonvolatility, needs to be developed. Among various new memories, the magnetic random access memory (MRAM) device is considered as one of good candidate memories because of excellent features including high density, high speed, low operating power and nonvolatility. The etching of MTJ stack which is composed of magnetic materials and insulator such as MgO is one of the vital process for MRAM. Recently, MgO has attracted great interest in the MTJ stack as tunneling barrier layer for its high tunneling magnetoresistance values. For the successful realization of high density MRAM, the etching process of MgO thin films should be investigated. Until now, there were some works devoted to the investigations on etch characteristics of MgO thin films. Initially, ion milling was applied to the etching of MgO thin films. However, ion milling has many disadvantages such as sidewall redeposition and etching damage. High density plasma etching containing the magnetically enhanced reactive ion etching and high density reactive ion etching have been employed for the improvement of etching process. In this work, inductively coupled plasma reactive ion etching (ICPRIE) system was adopted for the improvement of etching process using MgO thin films and etching gas mixes of $CH_4$/Ar and $CH_4$/$O_2$/Ar have been employed. The etch rates are measured by a surface profilometer and etch profiles are observed using field emission scanning emission microscopy (FESEM). The effects of gas concentration and etch parameters such as coil rf power, dc-bias voltage to substrate, and gas pressure on etch characteristics will be systematically explored.

• Journal of the Semiconductor & Display Technology
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• v.4 no.2 s.11
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• pp.11-14
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• 2005

In plasma processing reactors, it is common practice to control plasma density and ion bombardment energy by manipulating excitation voltage and frequency. In this paper, a dually excited capacitively coupled rf plasma reactor is self-consistently simulated with a three moment model. Effects of phase differences between primary and secondary voltage waves, simultaneously modulated at various combinations of commensurate frequencies, on plasma properties are investigated. The simulation results show that plasma potential and density as well as primary self-dc bias are nearly unaffected by the phase lag between the primary and the secondary voltage waves. The results also show that, with the secondary frequency substantially lower than the primary frequency, secondary self·do bias remains constant regardless of the phase lag. As the secondary frequency approaches to the primary frequency, however, the secondary self-dc bias becomes greatly altered by the phase lag, and so does the ion bombardment energy at the secondary electrode. These results demonstrate that ion bombardment energy can be more carefully controlled through plasma simulation.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.161-166
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• 2005

The plasma ion density in AC-PDP has shown to be increased from $5.6{\times}10^{11}cm^{-3}$ to $9.0{\times}10^{11)cm^{-3}$ as the Xe mixture ratio to neon increase from 1 % to 10 %, respectively, at fixed pressure of 400 Torr, by using the micro-Langmuir probe. It is noted that the plasma ion density is density increases as the gas pressure increases in this experiment. The electron temperature decreases from 2.3 to 1.2 eV as the Xe mole fraction increases from 1 % to 10 % at fixed pressure of 400 Torr, which is measured by the micro Langmuir probe and high-speed ICCD camera in this experiment. It is noted that the electron temperature decreases as the gas pressure increases from 150 to 400 Torr in this experiment. It is also observed that the exited Xe atom density and the plasma ion density are in strong correlation sharp between each other in this experiment. It is noted that $5.2{\times}10^{12}cm^{-3}$ in the $1s_5$ metastable state and $1.2{\times}10^{12}cm^{-3}$ in the $1s_4$ resonance state for the PDP cell with gap of 50 um distances under the fixed gas pressure of 400 Torr and Xe content ratio of 10 %.

• Journal of the Korean institute of surface engineering
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• v.37 no.4
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• pp.220-225
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• 2004

A new ion beam extraction system is designed using a simple ion mass filter and a micro mass balance and a QMS based detecting system. A quadrupole Mass Filter is used for selective ion beam formation from inductively coupled high density plasma sources with appropriate electrostatic lens and final analyzing QMS. Also a quartz crystal microbalance is set between a QMF and a QMS to measure the etching and polymerization rate of the mass selected ion beam. An inductively coupled plasma was used as a ion/radical source which had an electron temperature of 4-8 eV and electron density of $4${\times}$10^{11}$＃/㎤. A computer interfaced system through 12bit AD-DA board can control the pass ion mass of the qmf by setting RF/DC voltage ratio applied to the quadrupoles so that time modulation of pass ion's mass is possible. So the direct measurements of ion - surface chemistry can be possible in a resolution of $1\AA$/sec based on the qcm's sensitivity. A full set of driving software and hardware setting is successfully carried out to get fundamental plasma information of the ICP source and analysed $Ar^{+}$ beam was detected at the $2^{nd}$ QMS.

• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.289-295
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• 2015

By adopting a 2D time-dependent wave code, we investigate how mode-converted waves at the Ion-Ion Hybrid (IIH) resonance and compressional waves propagate in 2D density structures with a wide range of field-aligned wavenumbers to background magnetic fields. The simulation results show that the mode-converted waves have continuous bands across the field line consistent with previous numerical studies. These waves also have harmonic structures in frequency domain and are localized in the field-aligned heavy ion density well. Our results thus emphasize the importance of a field-aligned heavy ion density structure for ultra-low frequency wave propagation, and suggest that IIH waves can be localized in different locations along the field line.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.513-514
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• 2005

In plasma processing reactors, it is common practice to control plasma density and ion bombardment energy by manipulating excitation voltage and frequency. In this paper, a dually excited capacitively coupled rf plasma reactor is self-consistently simulated with a three moment model. Effects of phase differences between primary and secondary voltage waves, simultaneously modulated at various combination of commensurate frequencies, on plasma properties are investigated. The simulation results show that plasma potential and density as well as primary self-dc bias are nearly unaffected by the phase lag between the primary and the secondary voltage waves. The results also show that, with the secondary frequency substantially lower than the primary frequency, secondary self-dc bias remains constant regardless of the phase lag. As the secondary frequency approaches to the primary frequency, however, the secondary self-dc bias becomes greatly altered by the phase lag, and so does the ion bombardment energy at the secondary electrode. These results demonstrate that ion bombardment energy can be more carefully controlled through plasma simulation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.12
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• pp.2173-2178
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• 2007

Dynamics of plasma sheath was analyzed using simple ion fluid model with poison equation. Incident ion current, energy, potential distribution and space charge density profile were calculated as a function of time. The effects of initial floating sheath on the evolution of biased sheath were compared with ideal matrix sheath. The effects of finite rising time of pulse bias voltage on the ion current and energy was studied. The influence of surface charging on the evolution of sheath was also investigated

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1999.11a
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• pp.40-45
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• 1999

The effect of the addition of helium, neon, argon and xenon on the production of negative hydrogen ions has been studied in a magnetically confined dc filament discharge. The addition of helium and neon produced effects similar to an equivalent increase in hydrogen pressure. However, the addition of argon and low fractions of xenon produced significant increases in the negative ion density for hydrogen at pressures around 1 mTorr. The addition of argon and xenon, by increasing electron density and decreasing electron temperature, achieved conditions closer to optimum for negative ion production. The largest enhancement of negative hydrogen ion density occurred with the addition of argon; it is suggested that this is due to a resonant energy exchange between excited argon atoms and hydrogen molecules.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.310-311
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• 2011

Dual-frequency (DF) capacitively coupled plasmas (CCP) are used to separately control the mean ion energy and flux at the electrodes [1]. This separate control in capacitively coupled radio frequency discharges is one of the most important issues for various applications of plasma processing. For instance, in the Plasma Enhanced Chemical Vapor Deposition processes such as used for solar cell manufacturing, this separate control is most relevant. It principally allows to increase the ion flux for high deposition rates, while the mean ion energy is kept constant at low values to prevent highly energetic ion bombardment of the substrate to avoid unwanted damage of the surface structure. DF CCP can be analyzed in a fashion similar to single-frequency (SF) driven with effective parameters [2]. It means that DF CCP can be converted into SF CCP with effective parameters such as effective frequency and effective current density. In this study, comparison of DF CCP and its converted effective SF CCP is carried out through particle-in-cell/Monte Carlo (PIC-MCC) simulations. The PIC-MCC simulation shows that DF CCP and its converted effective SF CCP have almost the same plasma characteristics. In DF CCP, the negative resistance arises from the competition of the effective current and the effective frequency [2]. As the high-frequency current increases, the square of the effective frequency increases more than the effective current does. As a result, the effective voltage decreases with the effective current and it leads to an increase of the ion flux and a decrease of the mean ion energy. Because of that, the negative resistance regime can be called the preferable regime for solar cell manufacturing. In this preferable regime, comparison of DF (13.56+100 or 200 MHz) CCP and SF (60 MHz) CCP with the same effective current density is carried out. At the lower effective current density (or at the lower plasma density), the mean ion energy of SF CCP is lower than that of DF CCP. At the higher effective current density (or at the higher plasma density), however, the mean ion energy is lower than that of SF CCP. In this case, using DF CCP is better than SF CCP for solar cell manufacturing processes.