Bulletin of the American Physical Society
2006 59th Annual Gaseous Electronics Conference
Tuesday–Friday, October 10–13, 2006; Columbus, Ohio
Session SRP1: Poster IIA |
Hide Abstracts |
Room: Holiday Inn Salon A, 4:00pm - 5:30pm |
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SRP1.00001: INDUCTIVELY COUPLED PLASMAS |
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SRP1.00002: Real time closed loop control of an Ar and Ar/O$_2$ plasma in an ICP R. Faulkner, F. Sober\'on, A. McCarter, D. Gahan, S. Karkari, V. Milosavljevic, C. Hayden, A. Islyaikin, V.J. Law, M.B. Hopkins, B. Keville, P. Iordanov, S. Doherty, J.V. Ringwood Real time closed loop control for plasma assisted semiconductor manufacturing has been the subject of academic research for over a decade. However, due to process complexity and the lack of suitable real time metrology, progress has been elusive and genuine real time, multi-input, multi-output (MIMO) control of a plasma assisted process has yet to be successfully implemented in an industrial setting. A ~Splasma parameter control strategy~T is required to be adopted whereby process recipes which are defined in terms of plasma properties such as critical species densities as opposed to input variables such as rf power and gas flow rates may be transferable between different chamber types. While PIC simulations and multidimensional fluid models have contributed considerably to the basic understanding of plasmas and the design of process equipment, such models require a large amount of processing time and are hence unsuitable for testing control algorithms. In contrast, linear dynamical empirical models, obtained through system identification techniques are ideal in some respects for control design since their computational requirements are comparatively small and their structure facilitates the application of classical control design techniques. However, such models provide little process insight and are specific to an operating point of a particular machine. An ideal first principles-based, control-oriented model would exhibit the simplicity and computational requirements of an empirical model and, in addition, despite sacrificing first principles detail, capture enough of the essential physics and chemistry of the process in order to provide reasonably accurate qualitative predictions. This paper will discuss the development of such a first-principles based, control-oriented model of a laboratory inductively coupled plasma chamber. The model consists of a global model of the chemical kinetics coupled to an analytical model of power deposition. Dynamics of actuators including mass flow controllers and exhaust throttle are included and sensor characteristics are also modelled. The application of this control-oriented model to achieve multivariable closed loop control of specific species e.g. atomic Oxygen and ion density using the actuators rf power, Oxygen and Argon flow rates, and pressure/exhaust flow rate in an Ar/O$_2$ ICP plasma will be presented. [Preview Abstract] |
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SRP1.00003: Electrical and plasma parameters of side type ferromagnetic ICP Kyeong Hyo Lee, Young Kwang Lee, Sung Won Cho, Chin Wook Chung A new class of plasma source for uniform processing of large surfaces, ferromagnetic ICP is developed in this presentation as an alternative to existing plasmas. This source has eight half square quartz tubes at side wall and each tube has two toroidal ferromagnetic cores. Electrical parameters are measured by an MKS impedance probe and plasma parameters are obtained from single langmuir probe data. Operating pressure is in the range of 2 mtorr to 50 mtorr and input power driven at 400 kHz is delivered up to 2 kW. Antenna voltage and current are less than 800 V and 6 A with high power factor and plasma density profile over 300 mm wafer is uniform at various pressure. [Preview Abstract] |
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SRP1.00004: On the E to H and H to E transition mechanisms in inductively coupled plasmas MinHyong Lee, KyeongHyo Lee, ChinWook Chung Inductively coupled plasmas (ICP) exhibit two mode operations of capacitive coupling (E mode) and inductive coupling (H mode), and the density jump and hysteresis have been reported during the transition between these modes. In this study, the total power transferred to the plasma by capacitive and inductive coupling is calculated from Maxwell’s equations and global model, and from this, conditions required for stable E and H mode operations are obtained. The E to H and the H to E transitions occur when the system reaches critical electron densities. Analytical criterion for stable H mode operation that the skin depth should be smaller than $\sqrt{\frac{2}{3}}R$ at low pressure, and $\frac{2}{\sqrt{3}}(\omega/\nu )R$ at high pressure is derived from the calculation. The dependence of transition electron densities and powers of E to H and H to E transitions on the pressure and discharge dimension is also discussed. [Preview Abstract] |
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SRP1.00005: On the multistep ionizations in argon inductively coupled plasms MinHyong Lee, SungHo Jang, ChinWook Chung The effect of the multistep ionizations on the plasma parameters in the inductively coupled plasma (ICP) has been investigated by experiments and theory. To obtain electron density and electron temperature precisely at various powers and pressures in the ICP, the electron energy distribution functions (EEDFs) are measured. It is found that at high pressures, the electron temperature from the EEDFs decreases and the electron density increases rapidly with the absorbed power while, at low pressures, the electron temperature is hardly changed and the electron density is almost linearly proportional to the absorbed power. The comparison between the experiment and our model including the multistep ionizations [M. H. Lee and C. W. Chung, Phys. Plasmas 12, 73501 2005] was done and the experiment was in close agreement with the model. This shows that the changes in the electron density and the electron temperature in the ICP are mainly due to the multistep ionizations. [Preview Abstract] |
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SRP1.00006: Diagnostics for an inductively coupled plasma in highly Ar-diluted oxygen Zhang Yong, Satoshi Hirao, Takeshi Ohmori, Takeshi Kitajima, Toshiaki Makabe Oxygen plasma has been widely used in microelectronics fabrications. It is known that the growth rate of SiO$_{2}$ in Si-wafer is enhanced in Ar-diluted O$_{2}$ plasma. One of the key reactions in the surface is caused by the oxygen metastable atom O($^{1}$D$_{2})$, which has the potential for the surface activation. The work [1] shows that Ar metastable Ar(1s$_{5})$ contributes greatly to the production of O($^{1}$D$_{2})$ in a CCP in highly Ar-diluted oxygen. In this paper, we have studied the influence of the Ar metastables on the production of O($^{1}$D$_{2})$ in an inductively coupled plasma (ICP) in O$_{2}$(0-20{\%})/Ar. ICP was sustained by a single turn current coil driven at 13.56 MHz. Space-resolved 3D density profiles of O($^{3}$p), Ar(2p$_{1})$, and Ar(2p$_{9})$ were observed by Radon inversion of the line integrated optical emissions. And Ar metastable density was measured by laser absorption spectroscopy. The experimental result would be useful for the understanding of the mechanism of the production of O($^{1}$D$_{2})$. \newline [1] T. Kitajima, T. Nakano, T. Makabe, Appl. Phys. Lett. 88, 091501 (2006). [Preview Abstract] |
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SRP1.00007: Dynamics of an E-H transition in ICP in Ar Satoshi Hirao, Yong Zhang, Toshiaki Makabe Inductively coupled plasma (ICP) has been widely used as a high density plasma source in various applications. ICP has two proper modes. One is a low density capacitively coupled mode sustained by the static electric field caused by the local potential difference of the induction coil (E-mode), and the other is a high-density inductively coupled mode sustained by the induced electromagnetic field (H-mode)[1]. There is a transition between both modes in ICP, and the space and time change between the modes will be still interesting for us. In the present study, we will investigate the spatiotemporal 2D-t change of the optical emission in ICP in Ar by using ICCD camera located on the top of the reactor. We mainly focus on the emission from Ar(2P$_1$) as a probe of high energy electrons, and discuss the dynamic characteristics of the E-H transition by way of ionization of high energy electrons. \newline \newline [1] Y. Miyoshi, T. Makabe {\it et al.}, IEEE Trans. Plasma Sci., 30(1), 130 (2002), and 33(2), 360(2005). [Preview Abstract] |
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SRP1.00008: Experimental Study on Radio Frequency Inductively Coupled Ar/NF$_3$ Discharges Katsuyuki Hanaki, Takashi Kimura We investigated the plasma parameters in radio frequency inductive Ar/NF$_3$ plasmas with the probe method and optical emission spectroscopy combined with actinometry. Plasma was produced in the cylindrical stainless steel chamber with 160 mm in inner diameter and 100 mm in length, and the power injected into the plasma was kept at 120W. Experiment was performed at three total pressures of 8m, 15m and 30 mTorr, changing the NF$_3$ content from 0$\%$ to 30$\%$. The structure of the measured electron energy probability functions (EEPFs) did not change at any NF$_3$ content, resulting in the same effective electron temperature. The measured EEPFs deviated from the Maxwellian distribution due to the large depletion of the electrons with the energy higher than 11-13 eV. On the other hand, the electron density markedly decreased even in small NF$_3$ addition lower than 5$\%$. The atomic fluorine density estimated by actinometry was approximately proportional to the NF$_3$ content. We investigated the effect of O$_2$ addition on the plasma parameters as well. The atomic fluorine density in Ar/NF$_3$/O$_2$ discharges depended on only NF$_3$ content. This fact may indicate that the reaction rate to produce the atomic fluorine by the collisions between the atomic oxygen and NF$_ {\rm x (x=1,2)}$ is much lower than that by the collisions between the atomic oxygen and CF$_{\rm x (x=2,3)}$. The atomic oxygen density was approximately proportional to O$_2$ content. [Preview Abstract] |
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SRP1.00009: Probe Measurements and Optical Emission Spectroscopy in RF Inductively Coupled Ar/SF$_6$ Discharges Takashi Kimura, Michio Mabuchi With the probe method and optical emission spectroscopy combined with actinometry, we investigated the dependence of the plasma parameters on the SF$_6$ content in radio frequency inductively coupled Ar/SF$_6$ discharges. Plasma was produced in the cylindrical stainless steel chamber with 160 mm in inner diameter and 75 mm in length, and the power injected into the plasma was kept at 140W. Experiment was performed in the total pressure range from 5 mTorr to 25 mTorr, changing the SF$_6$ content from 0$\%$ to 30$\%$. Under our experimental condition, the electron density and its effective temperature were independent of the SF$_6$ content. The electron density was on the order of 10$^{16}$ m$^{-3}$ and its effective temperature was about 4 eV. The atomic fluorine density estimated by actinometry, which was on order of 10$^{19}$ m$^{-3}$, was approximately proportional to the SF$_6$ content. We investigated the effect of dilution gas addition (H$_2$ and O$_2 $) on the plasma parameters as well. The measured electron energy probability functions (EEPFs) did not depend on the dilution gas content for the SF$_6$ content higher than 10$\%$, resulting in the constant effective electron temperature and the constant electron density. The atomic fluorine density gradually increased with increasing O$_2$ content whereas it markedly decreased with increasing H$_2$ content. [Preview Abstract] |
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SRP1.00010: Studies of Mode Transitions in Inductively Coupled Plasma Reactors Andre Daltrini, Stanislav Moshkalev, Thomas Morgan, William Graham Optical emission spectroscopy and Langmuir probe measurements have been used to study mode transitions and hysterisis in a GEC Inductively Coupled Plasma reactor operating in both Ar and Ar/O$_{2}$ mixtures over a range of pressures. Ar emission line ratios have been used to monitor the variations of the electron temperature and the influence of the metastable Ar atoms in both discharge modes [1]. The first results show a smooth decrease of the electron temperature with power, followed by an abrupt transition when the plasma jumps to the H mode, with a clear reduction in electron temperature. Similar results are obtained with a Langmuir probe. Also, a strong variation of the metastable density with the transition was observed. Its influence on the transition and associated hysteresis will be discussed. \newline \newline [1] S. A. Moshkalyov, P. G. Steen, S. Gomez, and W. G. Graham, Appl. Phys. Lett., \textbf{75}, 328 (1999). [Preview Abstract] |
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SRP1.00011: Measurements of Nonlocal Electron Energy Distribution Functions in the Afterglow of an RF ICP Discharge Jon Blessington, Charles DeJoseph, Jr., Vladimir Demidov, Mark Koepke, Jason Wynne In previous work [1], it was shown that even a small number of nonlocal fast electron, which do not significantly affect the overall mean electron energy, can dramatically change the plasma and near-wall sheath properties. In this work, Langmuir probe measurements of electron density, temperature and energy distribution functions (EEDF) in the afterglow of low-pressure (30-50 mTorr) noble-gas rf ICP discharges have been carried out. The experimental setup is described in [2]. The primary focus of this work was the investigation of the high energy portion of the EEDF which shows peaks corresponding to electrons with energies 5-20 eV, depending on the gas mixture. These peaks arise from electrons produced in Penning ionization with metastable noble gas atoms. ~This fast component of the EEDF can be controlled independently on the slow electrons, a direct consequence of the nonlocality. \newline \newline [1] V. Demidov et al. \textit{PRL} \textbf{95}, 215002 (2005). \newline [2] W. Guo et al., \textit{PSST} \textbf{10}, 43 (2002). [Preview Abstract] |
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SRP1.00012: CAPACITIVELY COUPLED PLASMAS II |
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SRP1.00013: Radio-frequency phase-modulation of spatial electron density in a two-frequency confined capacitive coupled discharge S.K. Karkari, C. Gaman, A.R. Ellingboe The effects of oscillating sheath, hence the dynamics of electron flow in the bulk plasma can be of significant importance in modeling a two or multi frequency capacitive coupled system. Most of the modeling results deal with bounded plasma sheath boundary, defined by the point of separation of maximum electron displacement from the positive space charge sheath. However in practical applications, the discharge gap is narrow ($\sim $ 1 cm) as is the case in a standard plasma processing tool (Exelan$^{\mbox{{\texttrademark}}}$, Lam Research Inc.) routinely used in semi-conductor manufacturing industries. The rf-sheaths can be a substantial fraction of the separation between the electrodes, leading to significant amount of electric field perturbing the bulk plasma density. We report on an experimental investigation of space and phase-resolve electron density using a floating hairpin resonance probe in a modified plasma tool (Exelan); the discharge is powered with the sum of voltages at 27.12 MHz and 1.937 MHz drive frequencies in Ar/O2/C$_{4}$F$_{8}$ gas mixtures. The results show that the electron density is modulated in the bulk of the discharge at both driving frequencies (1.937~MHz + 27.12 MHz). At the centre of the discharge the modulation frequency is twice the low frequency cycle due to the exclusion of electrons from the opposite sheath at alternate phase of the low-frequency cycle. [Preview Abstract] |
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SRP1.00014: ABSTRACT WITHDRAWN |
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SRP1.00015: ABSTRACT WITHDRAWN |
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SRP1.00016: Investigation of the Spatial Distribution Evolution of Electron Temperature in Capacitive Coupled Single- and Dual-Frequency RF Plasmas in Ar/O$_{2}$ mixture over the RF Period. S.G. Belostotsky, O.V. Braginsky, A.S. Kovalev, D.V. Lopaev, T.V. Rakhimova, A.N. Vasilieva The emission spectroscopy was applied for studying the temporal-spatial behavior of capacitive coupled single- and dual-frequency (1.76 MHz + 81 MHz) rf plasmas. As observed in the low-pressure ($<$ 100 mTorr) rf discharges, the intensity oxygen atom emission line O(3p$^{5}$P$\to $3p$^{5}$S) 777 nm is fully determined by the dissociative excitation of O$_{2}$ molecules with the ratio of O line to line Ar(2p$_{1}-$1s$_{2})$ 750 nm being a linear function of electron temperature. It allowed us to investigate evolution of the axial distributions of electron temperature over the rf period by using the temporally and spatially resolved actinometry technique. It was experimentally realized by the ns-gated ICCD camera equipped objective with narrow-band interference filters and synchronized with the LF voltage. It is shown that the high-frequency (HF) rf discharge provides uniform spatial distribution of electron temperature in the inter-electrode gap. With adding LF power, the strong electron heating near the electrode sheaths occurs synchronously with the LF period. With increasing LF power the electron heating becomes stronger and penetrates more deeply inside the bulk of plasma. At r pressures $\le $ 50 mTorr the electron temperature in the discharge center doesn't changes with applying LF power, but it isn't already so at the higher pressure that directly shows coupling two rf plasmas with increasing pressure. [Preview Abstract] |
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SRP1.00017: Capacitive Coupled Single- and Dual-Frequency RF Plasma in Argon Olga Proshina, Oleg Braginsky, Vladimir Ivanov, Alexander Kovalev, Dmitry Lopaev, Tatyana Rakhimova, Anna Vasilieva Capacitively coupled radio-frequency Ar plasma operated both in the Single Frequency (SF) and Dual Frequency (DF) regimes at high specific input powers has been studied both experimentally and theoretically in a pressure range of 20 mTorr - 100 mTorr. In the SF regime the discharge was operated at 1.76, 13.56 and 81 MHz. In the DF regime two frequencies combinations were used: \textbf{i} 13.56 -- 81 MHz; \textbf{ii} 1.76 -- 81 MHz. The measurements of the plasma density and the electron temperature by a Langmuir probe in the center between the electrodes as a function of the dissipated RF power were carried out. It was revealed that the low frequency (LF) power affects the electron density in a pressure range of 45 -- 100 mTorr. The decrease of the pressure to 20 mTorr results in an absence of the LF power influence on the electron density and consequently leads to the frequency decoupling. The PIC MC simulation was carried out to analyze the experimental data. It was shown that in SF discharge at 1.76 and 13.56 MHz the role of the secondary electron emission (SEE) is significant. The HF discharge at 80 MHz is operated in $\alpha $-mode at the same powers. The role of SEE on the DF discharge operation is significant at the studied conditions. The frequency decoupling takes place for the conditions when the sheaths are almost collisionless for $\gamma $-electrons. [Preview Abstract] |
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SRP1.00018: Experimental and Theoretical Study of Ion Energy Distribution in SF and DF CCP discharges Olga Proshina, Oleg Braginsky, Alexander Kovalev, Dmitry Lopaev, Yury Mankelevich, Mike Olevanov, Tatyana Rakhimova, Anna Vasilieva, Dmitry Voloshin The theoretical and experimental study of ion energy distribution function (IEDF) in single and dual frequency capacitive coupled RF discharge in Ar was carried out. Parameters of plasma source were taken in the widely used range for research purposes as well as for the microelectronics industrial processing devices: single frequency discharge (SF) at 80 MHz and dual frequency (DF) discharge at 1.76/80 MHz, specific input powers of 0.02--2 W/cm$^{2}$, pressures of 20--100 mTorr. The ion energy analyzer was used to measure IEDF on the grounded electrode. It was shown that the applied low frequency voltage governs energy width in the dual frequency regime. IEDF in SF and DF discharges was studied analytically and using Monte-Carlo (MC) simulations. Analytical expressions for IEDF and IEDF peaks location were derived. In MC simulations, ions trajectories were traced in a given electric field (from the global model and parametric expressions). Elastic and charge exchange collisions were taken into account. The MC calculations provide explanation of IEDF peaks height ratio in DF collisionless discharge. Theoretical estimations of IEDF shape in SF and DF cases are in good agreement with experimental data. [Preview Abstract] |
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SRP1.00019: Optical emission CT of etching plasmas for an effect of the anode phase of LF-bias voltage in a 2f-CCP in Ar and CF$_{4}$/Ar Mikio Ishimaru, Takeshi Ohmori, Takeshi Kitajima, Toshiaki Makabe It is essential to control and optimize 2-dimensional ion flux distribution modulated by strong sheath dynamics in front of an oxide wafer deeply biased by a low frequency source in a 2f-CCP etcher. In our previous work, we have estimated the effect of the secondary electron from the wafer at the cathodic phase of the low frequency bias voltage on the functional separation in the 2f-CCP. In the present work, we discuss a temporal profile of low energy electrons of the anodic phase of the bias by using 2D-t OES system. The profile of the net excitation rate of Ar(2p$_{9})$ is still observed in the sheath region at the anodic phase of the wafer, although the net rate of Ar(2p$_{1})$ as a probe of high energy electrons is very weak. These results may be supposed that the majority part of the signal of Ar(2p$_{9})$ will be caused by the reaction between the low energy electron and Ar metastable atom. We will perform a measurement of the absolute density of Ar metastables by using LAS to identify the effect of low energy electrons in the 2f-CCP. \newline [1] T. Akaike, T. Ohmori, T. Makabe, et al, 58$^{\rm th}$-GEC (San Jose; 2005). [Preview Abstract] |
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SRP1.00020: Low-pressure gas breakdown in dual-frequency (27/2 MHz) RF electric fields in nitrogen Valeriy Lisovskiy, Jean-Paul Booth, Karine Landry, David Douai, Valerick Cassagne, Vladimir Yegorenkov We present measured breakdown curves for dual-frequency (27.12 /2 MHz) discharges in nitrogen. RF voltages at frequencies of 27.12 MHz (HF) and 2 MHz (LF) were fed to the same powered electrode whereas another one was grounded. The inter-electrode gap was 20.4 mm. The 27 MHz breakdown curve is shifted to higher voltages and gas pressures when a 2 MHz voltage ($<$300 V) is added, due to the increased loss of electrons due to the drift in the LF field. At LF voltages above 300 V the LF field contributes to gas ionization. Positive ions oscillating in the enhanced LF field can collide with the electrode surface and produce secondary electrons. Therefore the HF breakdown voltage is decreased and approaches zero (a self-sustained LF discharge is ignited). Adding an HF voltage always leads to a decrease in the LF breakdown voltage because of the reduction of electron losses due to oscillations in the HF field. [Preview Abstract] |
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SRP1.00021: Optical Emission Measurements of Dual Frequency Capacitively Coupled Plasmas Eric Benck, Kristen Steffens Dual frequency capacitively coupled plasma sources are becoming increasingly important in semiconductor manufacturing processes. An imaging spectrometer combined with a high speed intensified CCD camera was used to obtain spatially and temporally resolved measurements of the optical emission from dual frequency (2 MHz / 13.56 MHz or 2 MHz / 27.12 MHz) plasmas created in a Gaseous Electronics Conference (GEC) reference reactor. The vertical distribution of the argon 750.4 nm transition was measured at the radial center of the discharge. For a single powered electrode the temporal distributions of the Ar excitation rate were also calculated. Significant changes in the temporal and vertical optical emission distributions were observed with changing feed gas (Ar, CF$_{4}$, and O$_{2})$ and gas pressure (100 mTorr to 1000 mTorr). The temporal distributions were insensitive to the amplitude of the lower frequency bias voltage. Changing from a single powered electrode to two separate powered electrodes also had a significant impact on the time resolved optical emission. [Preview Abstract] |
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SRP1.00022: COLLISION PROCESSES IN DISCHARGES AND PLASMAS |
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SRP1.00023: Excitation of the near-uv continuum of H$_2$ by fast H atoms A.V. Phelps We model the production of the near-uv continuum of H$_2$ by collisions of fast atoms, fast ions, and electrons with H$_2$ in a uniform-electric-field drift tube.\footnote{Z. Lj. Petrovi\'c and A. V. Phelps, Int'l. Seminar on Reactive Plasmas, Nagoya, June 17-19, (1991).} Relative intensities versus position at 300 Td $< E/N <$ 20 kTd (1 Td $= 10^{-21}$ V m$^2$), at 0.95 to 0.12 Torr, and 4 cm electrode separation are normalized to electron excitation coefficients at low $E/N$. Electron and heavy-particle induced excitation are separated by their growth toward the anode or the cathode, respectively. The excitation attributed to heavy-particles increases approximately as the cube of the distance from the anode. This growth is consistent with a three-step reaction sequence starting with a roughly uniform density of H$_2^+$ produced by electrons. A multi-beam model for the electrons, H$^+$, H$_2^+$, H$_3^+$, fast H$_2$, and fast H confirms this dependence. The principal excitation step is fast H + H$_2$ $\rightarrow$ H$_2(a^3\Sigma_ g^+)$ + H with a cross section roughly twice that for H$\alpha$ excitation. [Preview Abstract] |
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SRP1.00024: Possible Mechanism of ``Additional'' Production of H$^{-}$ in a Glow Discharge S. Belostotskiy, D. Economou, D. Lopaev, T. Rakhimova Based on measurements of H$^{-}$ and H densities a DC glow discharge in H$_{2}$ (P=0.1-3 Torr) the rate coefficient of H$^{-}$ production as a function of $E/N$ was determined. To analyze the mechanisms of H$^{-}$ production, a simple model of H$_{2}$ vibrational excitation was developed. Estimations of vibrational level densities ($v$=3-5) obtained from VUV absorption measurements were in reasonable agreement with the calculated data. The analysis revealed that standard mechanisms of H$^{- }$production (dissociative attachment to vibrationally excited molecules H$_{2}(v)$ and molecules in Rydberg states H$_{2}$(\textit{Ry})) were not enough to explain the experimental results. In order to describe both the shape (vs $E/N)$ and the magnitude of the measured H$^{-}$ production rate coefficient, an ``additional'' source of H$^{-}$, having a strong resonant electron attachment CS in the range of $\sim $5-9 eV, should be invoked. Although H$_{2}$ has no resonances in the 5-9 eV range, water is known to strongly dissociatively attach in this range. Thus, even small amounts (0.1-1{\%}) of water vapor in the apparatus can explain the origin of the ``additional'' H$^{-}$ production. This result is corroborated by the work of Cadez \textit{et. al.} in Proc. of XXVII ICPIG, 2005. This work was supported by the RFBR (No.05-02-17649a), Scientific School - 171113.2003.2 and NATO Collaborative Linkage Grant (No.980097). [Preview Abstract] |
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SRP1.00025: Model calculations of the ``flame'' in flowing-afterglow plasmas Rainer Johnsen, Richard Rosati, Michael Golde Our recent experience in analyzing optical emission from flowing-afterglow plasmas has led us to re-examine some of the simplifying assumptions that are often made in such experiments. One is often forced to carry out observations in the first few centimeters downstream from the reagent inlet, a region in which the reagent gas distribution is highly non-uniform. In this region, the ``flame'', i.e., optical emission that arise from reactions of active particles (ions, metastables etc) with reagent molecules, actually is hollow, roughly cone-shaped region, the center of which is essentially dark, while a cursory visual inspection gives the appearance of a solid luminous cone. This occurs for both ring-shaped and point-like gas inlets. If one were to measure the electron density immediately downstream from the reagent inlet, one would find a minimum on the flow tube axis, rather than a maximum. One would also find that a simple ``bulk-flow'' model seriously overestimates the rates at which some chemical reactions occur, because the reactions are limited by diffusion rather than by the chemical rates. We will present the results of model calculations and compare them to experimental observations of emission flames produced either by electron-ion recombination or metastable excitation. [Preview Abstract] |
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SRP1.00026: Dissociation, recombination and detachment in oxygen discharges diluted with argon Jon T. Gudmundsson, Eythor G. Thorsteinsson We use a global (volume averaged) model to study the presence of negative ions and metastable species in low pressure high density O$_2$/Ar discharge. In particular the role of argon dilution in the dissociation of oxygen is investigated and the increase in the metastable O($^2$D) density with argon dilution. Furthermore, the electronegativity of the discharge is explored as a function of argon dilution. We find the negative oxygen ion O$^-$ to be the dominant negative ion in the discharge in the pressure range of interest, 1 -- 100 mTorr. Dissociative attachment of the oxygen molecule in the ground state O$_2(^3 \Sigma_g^-)$ and the metastable oxygen molecule O$_2(a^1\Delta_g)$ are the dominating channels for creation of the negative oxygen ion O$^-$. At low pressure ($<$ 5 mTorr) electron impact detachement dominates the loss of negative ions but recombination involving O$^-$ and O$^+$ ions is an important loss channel. At higher pressure detachment on O($^3$P) becomes the main loss channel for the O$^-$ ion. [Preview Abstract] |
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SRP1.00027: Pump/Probe measurement of V-V transfer in O$_{2}$ and H$_{2}$ Tai Ahn, Igor Adamovich, Walter Lempert We present new sets of V-V rate coefficients for vibrational levels 0 -- 5 in O$_{2}$ and H$_{2}$ at 300 K, using a stimulated Raman -- spontaneous Raman pump/probe apparatus. For O$_{2}$ it is found that previously reported semi-classical trajectory calculations of Coleti and Billing underestimate the V-V rate coefficients by approximately one order of magnitude, in agreement with recent measurements by of Kalogerakis and the earlier observations of Diskin. For H$_{2}$ non-resonant processes, comparison with recalculated semi-classical predictions using the identical potential to that given by Cacciatori and Billing results in predicted rates which are too fast, by a factor of $\sim $2.5, consistent with the previously reported value of Kreutz. However for the ``resonant'' V-V process, H$_{2}$ (v=1) + H$_{2}$ (v=1) --$>$ H$_{2}$ (v=2) + H$_{2}$ (v=0), predictions are found to be too slow, by a factor of approximately two, consistent with previous reported data of Farrow and Chandler. This suggests that semi-classical calculation methods that treat the rotational motion classically may be unsuitable for H$_{2}$, due to rotational energy level spacings which are comparable to k$_{B}$T. [Preview Abstract] |
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SRP1.00028: Alignment relaxation and disorientation of Ne*(2p$_{i}$) atoms induced by collisions with He(1s$^{2}$) Cristian Bahrim, Vaibhav Khadilkar In order to explain experimental results in discharge cells at temperatures (T) between 17K and 600K obtained at Kyoto University (Seo \textit{et al. Journal of Physics B}\textbf{ 36}, 1885 (2003)), we report quantum calculations for the disalignment and the disorientation of Ne$^{\ast }$(2p$_{i})$ atoms on the 2p$^{5}$3p electronic configuration induced by collisions with He(1s$^{2})$. The excellent agreement theory-experiment for 77K $<$ T $<$ 600K indicates that the electrostatic interaction between atoms is accurately described by our model potential at internuclear distances below 12 a$_{o}$. However, significant discrepancies are revealed for 17K $<$ T $<$ 77K. The experiment predicts that both the disalignment and the disorientation cross sections vanish near zero collision energy, while our quantum calculations indicate a resonant structure in this region. Therefore, the long-range interaction between atoms is re-analyzed. This study requires an important computational effort for the calculation of the rate coefficients for disalignment and disorientation of the Ne$^{\ast }$(2p$_{i})$ atoms in isotropic collisions, with the inclusion of the statististical distribution of atoms. Agreement between theory and experiment is found when a slightly more repulsive long-range potential for the e(3p) + He interaction is included in our model. [Preview Abstract] |
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SRP1.00029: The sensitivity of calculated ion transport coefficients for testing ion-neutral interaction potentials Mark Hogan Several commonly measured ion transport coefficients were investigated in order to determine their sensitivity when used for testing the accuracy of proposed ion-neutral interaction potentials. The level of sensitivity was taken to be the average percentage difference between values of an ion transport coefficient calculated from two interaction potentials. 93 sets of comparisons were carried out. A variety of positive ions, negative ions, neutrals and temperatures were included in the comparisons done in order to draw as general a conclusion as possible. The sensitivity was determined to be 5.2{\%} for mobility, 10{\%} for the ratio of the transverse diffusion coefficient to mobility, 16{\%} for the ratio of the longitudinal diffusion coefficient to mobility, 17{\%} for the transverse diffusion coefficient, and 23{\%} for the longitudinal diffusion coefficient. In particular, it was found that the longitudinal diffusion coefficient is the most sensitive test and that the mobility is the least sensitive test. [Preview Abstract] |
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SRP1.00030: Mobility of O$^{+}$ in He, Ne and Ar and Interaction Potentials of HeO$^{+}$, NeO$^{+}$ and ArO$^{+}$ Daniel Danailov, Larry Viehland, Rainer Johnsen, Timothy Wright, Edmond Lee New experimental measurements are reported for the mobility of O$^{+}$ ions in He, Ne and Ar gases at 300 K. \ The accuracy of these new values is estimated as $\pm $% 2.5\%, which allows them to serve as a stringent test of new \textit{ab initio} potentials that we have calculated using the RCCSD(T) method. \ We employied the aug-cc-pV5Z basis set with counterpoise corrections and took spin-orbit coupling into account. \ The present expeimental values for O$^{+}$ in He lie below the calculated ones, but the difference becomes statistically significant only at moderate and high values of the ratio of the electric field strength to the gas number density; even there they are only marginally signficant. For O$^{+}$ in Ne the experimental values lie clearly below the theoretical curve and for O$^{+}$ in Ar the ion mobility dependence has clear minima in addition to the maximum shown in the other rare gases. [Preview Abstract] |
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SRP1.00031: Temperature dependence of argon excimer emission from pulsed discharge excited argon clusters Mark Masters, Hans Suedhoff, Mike De Armond, Clint Reynolds Argon second continuum excimer emission is observed from a pulsed discharge excited pulsed supersonic argon expansion. The expansion nozzle consists of a temperature controlled, 15 cm long slit with a variable width (35 $\mu $m to 250 $\mu $m). The intensity of the argon excimer emission near 126 nm is investigated as a function of the width of the expansion nozzle slit, temperature of the expansion nozzle and position within the cathode-anode gap. The pressure within the nozzle has been measured as 2--4 bar and the excitation consists of a 50 ns negative current pulse of about 15kV and 700A. The observation of the emission depends directly on the size and quantity of clusters formed in the expansion. To determine the dependence of the emission upon clusters and the cluster size distribution, the mean cluster size is diminished by increasing the expansion nozzle and gas temperature. The temporal evolution of the second continuum emission and the observed spectra are presented as a function of nozzle temperature and slit width. [Preview Abstract] |
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SRP1.00032: Effects of Electron Exchange in Fully Differential Cross Sections for Charged Particle Ionization A.L. Harris, M. Foster, J.L. Peacher, D.H. Madison, H.P. Saha, K. Bartschat Three dimensional fully differential cross sections (FDCS) for charged particle impact ionization of helium are examined. Previously, for heavy particle impact, the Three Distorted Wave (3DW) model had yielded good agreement with experiment in the scattering plane, but poor agreement outside the scattering plane. In particular, 3DW calculations for the perpendicular plane predicted a small flux of electrons with almost no structure, while experiment showed a much higher flux of electrons with structure. To better treat the ejected electron, the 3DW-Hartree Fock (3DW-HF) and 3DW-R Matrix (3DW-RM) theories are introduced. The primary improvement of these two calculations over a standard distorted wave treatment is that exchange between the continuum and bound electrons is treated properly. Results for ionization of helium by impact of both electrons and C$^{6+}$ ions will be presented. [Preview Abstract] |
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SRP1.00033: Low-Energy Electron Impact Ionization of Molecular Hydrogen J.G. Childers, Kelly Kuper, Murtadha A. Khakoo Relative doubly-differential cross sections for the electron impact ionization of molecular hydrogen have been measured at incident energies of 25~eV and 40~eV and scattering angles of $20^{\circ}$ to $130^{\circ}$. The calibration of the electron analyzer during these measurements employed the recent doubly-differential cross section measurements of atomic hydrogen.\footnote{J.G.Childers, K.\ E.\ James, Jr., Igor Bray, M.\ Baertschy, and M.A.Khakoo, {\em Phys.\ Rev.\ A} {\bf 69}, 022709 (2004).} These measurements represent a new calibration standard useful in the determination of the transmission function of electron analyzers. This work is funded by the National Science Foundation under grant \# NSF-RUI-PHY-9731890. [Preview Abstract] |
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SRP1.00034: Laser optogalvanic spectroscopy of neon and krypton in a discharge plasma Naveed Piracha, Kurt Nesbett, Sohala Moten, Phil Moeller We report studies on the temporal evolution of the optogalvanic signal in neon and krypton using commercial hollow cathode lamps in conjunction with Nd: YAG pumped dye laser system. Transitions resulting from the excitation of 3s[3/2]2 and 5s[3/2]2 metastable states have been selected to study the discharge mechanism. [Preview Abstract] |
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SRP1.00035: Importance of Relativistic effects and Exchange between Bound and Continuum Electrons on Electron Impact Ionization of Xenon. Z. Stegen, D.H. Madison, H.P. Saha, K. Bartschat, S. Bellm, J. Lower, R.P. McEachran, E. Weigold Exchange between bound and continuum electrons, known as exchange distortion, can have a significant effect in electron impact ionization, especially for the case of spin-polarized projectiles. A proper treatment of this effect can be done by using an R-matrix or Hartree-Fock calculation for the continuum electrons. Due to the computational demands of these methods, the Furness-McCarthy local potential approximation is often used. The validity of the Furness-McCarthy approximation will be determined by comparing individual partial waves from each approach. In addition to this, the importance of using relativistic wavefunctions and potentials will be examined. The theoretical results will be compared to experimental asymmetries and branching ratios from Australia National University. [Preview Abstract] |
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SRP1.00036: The role of chemi-ionization in fluorescent lamp discharges Abdur Rahman, Graeme Lister, Valery Sheverev Chemi-ionization processes resulting from the interaction of two excited Hg atoms have been widely used in numerical models of fluorescent lamp discharges. In particular, the Penning process Hg(6p$^{3}$P$_{2})$ + Hg(6p$^{3}$P$_{2}) \quad \to $ Hg$^{+}$ + Hg(6p$^{3}$S$_{0})$ has been invoked as an important contribution to ionization and to the maintenance electric filed. There is no experimental measurement of the cross section for this process and experiments to measure cross sections of other chemi-ionization rections have been shown to be unreliable [1]. Numerical calculations of cross sections for these processes [2] indicate that they are much smaller than those previously assumed. We present a series of computations showing the influence of the calculated cross sections on the ionization balance over a range of discharge parameters. For discharge parameters appropriate to fluorescent lamps under standard operating conditions, it is necessary to invoke alternative ionization mechanisms, such as ``ladder like'' ionization via higher Rhydberg states, in order to reproduce the experimental results. \newline \newline [1] V.A. Sheverev, G.G. Lister and V. Stepaniuk, 2005,\textit{Phys. Rev. E } \textbf{71}, 056404 \newline [2] J.S. Cohen, R. L. Martin, and L. A. Collins, 2002, Phys. Rev. A \textbf{66}, 012717. [Preview Abstract] |
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