Temporal evolution of electron energy distribution function and plasma parameters in the afterglow of drifting magnetron plasma

Seo, Sang-Hun,In, Jung-Hwan,Chang, Hong-Young IOP Pub ; American Institute of Physics 2005 PLASMA SOURCES SCIENCE AND TECHNOLOGY Vol.14 No.3

<P>The temporal behaviour of the electron energy distribution function (EEDF) and the plasma parameters such as electron density, electron temperature and plasma and floating potentials in a mid-frequency pulsed dc magnetron plasma are investigated using time-resolved probe measurements. A negative-voltage dc pulse with an average power of 160 W during the pulse-on period, a repetition frequency of 20 kHz and a duty cycle of 50% is applied to the cathode of a planar unbalanced magnetron discharge with a grounded substrate. The measured electron energy distribution is found to exhibit a bi-Maxwellian distribution, which can be resolved with the low-energy electron group and the high-energy tail part during the pulse-on period, and a Maxwellian distribution only with low-energy electrons as a consequence of initially rapid decay of the high-energy tail part during the pulse-off period. This characteristic evolution of the EEDF is reflected in the decay characteristics of the electron density and temperature in the afterglow. These parameters exhibit twofold decay represented by two characteristic decay times of an initial fast decay time τ<SUB>1</SUB>, and a subsequent slower decay time τ<SUB>2</SUB> in the afterglow when approximated with a bi-exponential function. While the initial fast decay times are of the order of 1 µs (τ<SUB>T1</SUB> ∼ 0.99 µs and τ<SUB>N1</SUB> ∼ 1.5 µs), the slower decay times are of the order of a few tens of microseconds (τ<SUB>T2</SUB> ∼ 7 µs and τ<SUB>N2</SUB> ∼ 40 µs). The temporal evolution of the plasma parameters are qualitatively explained by considering the formation mechanism of the bi-Maxwellian electron distribution function and the electron transports of these electron groups in bulk plasma.</P>

Three-step decay of the plasma density near the substrate in pulsed-dc magnetron sputtering discharge

In, J H,Na, B K,Seo, S H,Chang, H Y,Han, J G IOP Pub ; American Institute of Physics 2009 Plasma sources science & technology Vol.18 No.4

<P>The plasma density near the substrate in a pulsed-dc magnetron sputtering source was measured using a time-resolved, wave-cutoff probe method. The decay of the plasma density during the off-phase had three periods with different decay times. In this paper, this type of decay is referred to as ‘three-step decay’. The three-step decay characteristics were examined under various conditions. From deduction using a number of references and the experimental results of tests done as part of this study, the spatial reversal of the plasma potential is assumed to cause three-step decay of the plasma density. In addition, the density decay time varied with the change in the magnetic field. This result indicates the existence of the magnetic field confinement effect on the plasma near the substrate during the off-phase.</P><P>The average electron density and the average substrate ion current increased with the pulse frequency and decreased with the duty cycle. This can be explained in terms of the changes in the overall plasma loss according to the pulse conditions. In particular, in a pulsed-dc magnetron sputtering source, magnetic field confinement and plasma potential reversal are thought to be two important factors changing the plasma loss.</P>

Control of ion energy distribution in low-pressure and triple-frequency capacitive discharge

Lee, S H,Tiwari, Pawan K,Lee, J K IOP Pub ; American Institute of Physics 2009 Plasma sources science & technology Vol.18 No.2

<P>One-dimensional particle-in-cell Monte Carlo collision (PIC-MCC) simulations of low-pressure (10 mTorr) argon plasmas sustained by a triple-frequency (1, 30 and 120 MHz) source in symmetrical current-driven and voltage-driven capacitively coupled plasma reactors are carried out. We concluded that the effective current, the effective voltage and the effective frequency are helpful in explaining the physics of triple-frequency capacitively coupled plasma sources (CCPs) alike single-frequency CCPs. The rf discharge parameters such as the ion energy distribution function (IEDF), the sheath length, the plasma potential and the powers dissipated by electrons and ions can be expressed as the effective frequency and the effective current density (or effective voltage). The analytical model of the IEDF for triple-frequency CCPs in the high-frequency regime is developed. The analytical calculations of the IEDF in the high-frequency regime through the effective frequency visualized in this paper are compared with the simulation results of the IEDF calculated from the 1D PIC-MCC model. The ion energy width and the average ion energy of the IEDF are controlled by the effective frequency, which is expressed as a function of the current density (or voltage) and frequency ratios of the triple-frequency source. The evolution of the effective frequency with the current density or voltage ratio of three frequency sources is different depending on the mode of operating source, which is either voltage or current. The effective frequency in voltage-driven CCPs is 2–10 times higher than that of current-driven CCPs at the same ratio of current density and voltage. As a result, the current-driven CCPs is more desirable than the voltage-driven CCPs from the aspect of independent control of ion flux and ion bombardment energy because the ion energy width increases with decreasing effective frequency.</P>

Investigation of the transition between glow and streamer discharges in atmospheric air

Choi, Jai Hyuk,Lee, Tae Il,Han, Inho,Baik, Hong Koo,Song, Kie Moon,Lim, Yong Sik,Lee, Eung Suok IOP Pub ; American Institute of Physics 2006 Plasma sources science & technology Vol.15 No.3

<P>Generally, the parameter <I>p</I> · <I>d</I> (pressure × gap distance) in dielectric barrier discharge (DBD) controls the electrical breakdown and also the plasma characteristics. We investigated the optimum plasma transition <I>p</I> · <I>d</I> by controlling the pressure. To find the transition <I>p</I> · <I>d</I> (<I>p</I> · <I>d</I><SUB>tr</SUB>) condition, optical emission spectroscopy (OES) was used to measure emission spectra from the DBD. All <I>p</I> · <I>d</I> data were normalized by the second positive system of nitrogen molecules, the wavelength of which was 337.1 nm. Then we compared the relative intensities of species generated during the discharge by OES analysis. Species selected for comparison were the first negative system (FNS) of nitrogen molecules (391.4 nm) and atomic oxygen spectra (777.1 nm). Experimental results showed that relative intensities were almost constant as <I>p</I> · <I>d</I> decreased, but at specific <I>p</I> · <I>d</I> data, the intensity started to increase. The increase in FNS of nitrogen molecules means not only an increase in electron energy but also a change in the plasma mode, streamer to glow transition. In the case of DBD using alumina with 1 mm thickness applied ac power, the plasma transition occurred at the 1 Torr cm condition.</P>

Microwave-excited atmospheric-pressure microplasmas based on a coaxial transmission line resonator

Choi, J,Iza, F,Do, H J,Lee, J K,Cho, M H IOP Pub ; American Institute of Physics 2009 PLASMA SOURCES SCIENCE AND TECHNOLOGY Vol.18 No.2

<P>We report the design, fabrication and characterization of two microwave-excited microplasma sources based on coaxial transmission line resonators (CTLR). The sources are capable of generating electric fields of ∼10<SUP>6</SUP> V m<SUP>−1</SUP> at 900 MHz and 2.45 GHz. These devices can self-ignite helium or argon discharges in a wide pressure range including atmospheric pressure. The gas temperature in an argon discharge open to atmospheric air is ∼400 K. Using air as a dielectric, the working gases can be passed through the CTLR, resulting in the formation of plasma jets suitable for surface treatments. The device efficiency on transferring the input power into the plasma is 50–85% depending on the gas used. No thermal damage or electrode erosion has been observed in the devices.</P>

Observation of inverse hysteresis in the E to H mode transitions in inductively coupled plasmas

Lee, Min-Hyong,Chung, Chin-Wook IOP Pub ; American Institute of Physics 2010 PLASMA SOURCES SCIENCE AND TECHNOLOGY Vol.19 No.1

<P>An inverse hysteresis is observed during the E mode to H mode transition in low pressure argon inductively coupled plasmas. The transition is accompanied by an evolution of electron energy distribution from the bi-Maxwellian to the Maxwellian distribution. The mechanism of this inversion is not clear. However, we think that the bi-Maxwellian electron energy distribution in E mode, where the proportion of high energy electron is much higher than the Maxwellian distribution, would be one of the reasons for the observed inverse hysteresis. As the gas pressure increases, the inverse hysteresis disappears and the E to H mode transition follows the scenario of usual hysteresis.</P>

Transient effects caused by pulsed gas and liquid injections into low pressure plasmas

Ogawa, D,Chung, C W,Goeckner, M,Overzet, L IOP Pub ; American Institute of Physics 2010 PLASMA SOURCES SCIENCE AND TECHNOLOGY Vol.19 No.3

<P>The fast injection of liquid droplets into a glow discharge causes significant time variations in the pressure, the chemical composition of the gas and the phases present (liquid and/or solid along with gas). While the variations can be large and important, very few studies, especially kinetic studies, have been published. In this paper we examine the changes brought about in argon plasma by injecting Ar (gas), N<SUB>2</SUB> (gas) hexane (gas) and hexane (liquid droplets). The changes in the RF capacitively coupled power (forward and reflected), electron and ion density (<I>n</I><SUB>e</SUB>, <I>n</I><SUB>i</SUB>), electron temperature (<I>T</I><SUB>e</SUB>) and optical emissions were monitored during the injections. It was found that the Ar injection (pressure change only) caused expected variations. The electron temperature reduced, the plasma density increased and the optical emission intensity remained nearly constant. The N<SUB>2</SUB> and hexane gas injections (chemical composition and pressure changes) also followed expected trends. The plasma densities increased and electron temperature decreased while the optical emissions changed from argon to the injected gas. These all serve to highlight the fact that the injection of evaporating hexane droplets in the plasma caused very little change. This is because the number of injected droplets is too small to noticeably affect the plasma, even though the shift in the chemical composition of the gas caused by evaporation from those same droplets can be very significant. The net conclusion is that using liquid droplets to inject precursors for low pressure plasmas is both feasible and controllable.</P>

Analysis of polymer surface treated by dielectric barrier discharge

Choi, Jai Hyuk,Lee, Eung Suok,Baik, Hong Koo,Lee, Se-Jong,Song, Kie Moon,Lim, Yong Sik IOP Pub ; American Institute of Physics 2005 Plasma sources science & technology Vol.14 No.2

<P>We investigate polymer surfaces after exposing them to dielectric barrier discharges with different flowing gases (He, CF<SUB>4</SUB>) in air. The relationship between the gas characteristics and the surface properties of polypropylene (PP) is determined by contact angle measurement, optical emission spectroscopy and x-ray photoelectron spectroscopy. Experimental results reveal that there is a definite relationship between the surface energy and the surface chemical composition of PP and also indicate that the hydrophilicity of PP in an atmospheric pressure (AP) discharge is more dependent on ionic bombardment than on the atomic oxygen composition at the surface and its hydrophobicity depends on the fluorine composition at the PP surface. In addition, it turns out that in a CF<SUB>4</SUB> discharge at AP, the CF<SUB>3</SUB> molecular band exhibits a continuum band at the orange line in the visible range.</P>

Characterization of a side-type ferrite inductively coupled plasma source for large-scale processing

Lee, Kyeonghyo,Lee, Youngkwang,Jo, Sungwon,Chung, Chin-Wook,Godyak, Valery IOP Pub ; American Institute of Physics 2008 PLASMA SOURCES SCIENCE AND TECHNOLOGY Vol.17 No.1

<P>A new type of inductively coupled plasma (ICP) utilizing an array of auxiliary discharges enhanced with ferromagnetic cores and placed at the chamber side is developed and characterized over a wide range of discharge conditions. The ICP electrical and plasma characteristics are measured over a wide range of discharge powers and argon gas pressures. It is shown that at 400 kHz driving frequency the antenna power factor of this ICP is close to 1, so the antenna voltage and current are much lower than those in a conventional ICP at similar rf power. Due to low driving frequency and low antenna voltage, the capacitive coupling in the ICP mode is practically eliminated, while due to enhanced ferromagnetic core coupling, the power transfer efficiency is higher than 95% at an rf power larger than 0.5 kW. Langmuir probe measurements show that the radial plasma non-uniformity over 300 mm can be less than 3%. This plasma source is expected to be suitable for large-scale plasma processing.</P>

A study on double hollow electrode discharge and the enhanced performance for electric discharge lamps

Lee, Tae Il,Park, Ki Wan,Hwang, Hyeon Seok,Choi, Jai Hyuk,Baik, Hong Koo IOP Pub ; American Institute of Physics 2006 PLASMA SOURCES SCIENCE AND TECHNOLOGY Vol.15 No.3

<P>We invented a double hollow electrode lamp (DHEL), applied an electron oscillation effect and measured its <I>I</I>–<I>V</I> curve in dc driving to evaluate the electrical characteristics. The volume discharge of this lamp showed an abnormal glow characteristic. Based on these results, we made a 9-channel flat panel lamp and confirmed the possibility of a parallel operation. In order to evaluate the enhanced performance of the DHEL, we compared it with a single hollow triode lamp and a diode lamp (DL). We measured the breakdown voltage, tube current and IR intensity of these three types of lamps. The DHEL showed the lowest breakdown voltage among the three lamps and a higher tube current than that of the DL. The IR intensity of the DHEL was more efficient than that of the DL; the enhanced quantity of efficiency was 11.8% at 0.922 W.</P>