Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session QW2: Inductively Coupled Plasmas |
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Chair: T. Makabe, Keiou University Room: Doubletree Hotel Cedar |
Wednesday, October 19, 2005 10:00AM - 10:15AM |
QW2.00001: 2D Fluid Simulation of VHF{\_}ICP Source with Parallel Resonance Antenna for Next Generation Etch Processing Sung Hee Lee, Jae Koo Lee Inductively coupled plasma is known for high-density material processing at low pressure. In addition to high density and low pressure, a next generation of plasma sources are needed to control the ion flux and ion-bombarding energy for wafer of over 300mm diameter. However the conventional ICP source with a spiral antenna have a problem of non-uniformity due to large inductance. To overcome the non-uniformity problem, the antenna is segmented and three segments are connected in parallel. The antenna with three segments connected in parallel also causes the non-uniformity problem due to the difference of inductance for each segments. The current in outer segment is larger than that of other segments and it causes the non-uniformity of plasma in radial direction. To reduce the problem, the variable capacitor is connected in series with outer segment. After all, we can overcome the problem of non- uniformity by the proper distribution of current among three segments with variable capacitor. To investigate the discharge phenomenon in the VHF(Very High Frequency){\_}ICP source that consists of the parallel resonance antenna, we have used a two-dimensional fluid simulation and the results from our simulation are compared with experimental data. * Jusung Engineering Co, Gwangju-Gun, Gyeonggi, S.Korea [Preview Abstract] |
Wednesday, October 19, 2005 10:15AM - 10:30AM |
QW2.00002: Numerical Study of Hysteresis Phenomenon in an Inductively Coupled Plasma in Ar Toshikazu Sato, Toshiaki Makabe As is well known, there exist two sustaining mechanisms in inductively coupled plasmas (ICPs), capacitive coupling mode (E mode) and inductive coupling mode (H mode)[1][2]. Especially in H mode, ICP in Ar is sustained by direct ionization and stepwise ionization of metastables. The ratio of these two processes significantly depends on the external conditions. A large amount of metastables in an ICP reactor gives a strong hysteresis of the plasma density as a function of input power, because high density plasma can be sustained by way of the stepwise ionization even at low power supply. In this paper, we numerically investigate the role of Ar metastables in the sustaining mechanism and the hysteresis characteristics in an Ar-ICP. The contribution of the stepwise ionization of Ar metastable to the total plasma production considerably depends on the gas pressure. The plasma density shows a strong hysteresis under the presence of metastables at 50 mTorr. We will also discuss the dependence of the hysteresis characteristics on gas pressure. \newline [1] Y. Miyoshi et al, IEEE Trans. Plasma Sci., 30, 130 (2002) \newline [2] Y. Miyoshi et al, J. Phys. D: Appl. Phys., 35, 454 (2002) [Preview Abstract] |
Wednesday, October 19, 2005 10:30AM - 10:45AM |
QW2.00003: Investigations on an inductively coupled magnetic neutral loop discharge Deborah O'Connell, Dragos Crintea, Martin Brennscheidt, Timo Gans, Uwe Czarnetzki An inductively coupled magnetic neutral loop discharge (NLD) was designed and has been investigated using various diagnostic techniques. Coaxial coils produce a magnetic field vanishing along a ring in the discharge - the so called neutral loop (NL). An oscillating rf electric field along the NL is induced through a planar four turn ICP antenna operated at 13.56 MHz. Stochastic electron heating in the NL allows for plasma operation at extremely low pressure, down to $10^{-2}$ Pa. These conditions are ideal for anisotropic etching, while uniform plasma surface treatment can be achieved by varying the NL diameter. Langmuir probe measurements, revealing electron densities up to $10^{12} cm^{-3}$ and electron temperatures up to 10 eV, are in good agreement with global model predictions. Phase resolved optical emission spectroscopy (PROES) allows us to distinguish the different power coupling mechanisms in the discharge. PROES is used to probe the high energy tail of the electron energy distribution function (EEDF), while the low energy part of the EEDF can be measured using phase resolved Thomson scattering. [Preview Abstract] |
Wednesday, October 19, 2005 10:45AM - 11:00AM |
QW2.00004: Electrical and Plasma Parameters of Distributed ICP Driven by Ferromagnetic Core Array WonKi Lee, ChinWook Chung, V.A. Godyak Two distributed plasma sources were explored and results were compared with corresponding data obtained in a conventional ICP with flat coil driven at 13.56 MHz. The first source was driven with six toroidal ferromagnetic cores at 400 kHz. This source was able to operate in a wide range of the input rf power. In reported experiments, the rf power delivered to plasma was up to 4 kW at the input rf voltage less than 300 V and high power factor and power transfer efficiency. The second source driven with eighteen toroidal inductors at fixed rf power has demonstrated an exceptional plasma uniformity measured near the discharge chamber bottom. Due to mainly resistive input impedance, the power factor of both ICP sources was close to 1 and the input voltage and current are order of magnitude less than in the similar wattage conventional ICP system operating at 13.56 MHz. Plasma parameters, the plasma density and electron temperature were obtained as appropriate integrals of the measured electron energy distribution functions. A twice less the plasma potential (15 V) was found in ICP driven with ferromagnetic cores at 400 kHz than that in the conventional ICP driven at 13.56 MHz. It seems that ICP with ferromagnetic cores has a great potential as a plasma sources for next generation plasma processing. [Preview Abstract] |
Wednesday, October 19, 2005 11:00AM - 11:15AM |
QW2.00005: Investigations of the E-H transition in an inductively coupled plasma using phase resolved optical emission spectroscopy Deborah O'Connell, Timo Gans, Uwe Czarnetzki Inductively coupled plasmas (ICPs) can be operated in capacitive mode (E-mode) or inductive mode (H-mode) depending on the RF power. At relatively low powers the electron density is not sufficient to sustain H-mode operation and the RF antenna acts as an electrode, therefore the discharge operates in E-mode. Phase resolved optical emission spectroscopy (PROES) can be used to distinguish between E- and H-mode. In pure H-mode the emission is modulated sinusoidally with twice the RF frequency while in E-mode the various excitation mechanisms are non- sinusoidal with one emission maximum per RF cycle. A Fourier analysis of the phase resolved emission, therefore, allows us to distinguish different power coupling mechanisms. Measurements in a pulsed ICP show that the discharge ignites in E-mode before turning to stable H-mode. In the transition from E- to H-mode instabilities can occur. In this instability regime strong plasma inhomogeneities, so called plasmoids, are also investigated. [Preview Abstract] |
Wednesday, October 19, 2005 11:15AM - 11:30AM |
QW2.00006: Comparison of Model and Experiment for Ar/O$_{2}$ Inductively Coupled Plasmas C.C. Hsu, M.A. Nierode, J.W. Coburn, D.B. Graves A detailed comparison has been made between measurements and a fluid model of an inductively coupled plasma in mixtures of argon and O$_{2}$. Measurements include electron density, electron energy distribution function, positive ion wall flux and composition, and O, Ar and O$_{2}$ densities measured at the chamber wall. The inductively coupled power ranged from 150 to 500W, the pressure from 5mT to 80mT, and the O$_{2}$/(Ar+O$_{2})$ inlet flow rate ratio varied from 0 to 1. The overall gas flow was kept at 33.5sccm. Model equations are solved with a commercial finite element package (FemLab$^{TM})$. The fluid model is shown to capture all trends in mean electron energy, neutral densities and the positive ion flux to the wall, as well as the electron density radial profile over the conditions investigated. The model predicts that the O$_{2}$-containing plasmas are weakly electronegative over the conditions studied. The measured eepf is nearly Maxwellian at high O$_{2}$ concentrations, and under these conditions the model prediction for T$_{e}$ are in good quantitative agreement with measurements. The stainless steel chamber walls are effective for O recombination, resulting in relatively low degrees of dissociation and strong gradients in O atom concentration, even at the lowest pressure. Model limitations will be discussed. [Preview Abstract] |
Wednesday, October 19, 2005 11:30AM - 11:45AM |
QW2.00007: Plasma Characteristics of Industrial Transformer Coupled Plasma L. Oksuz, A.R. Ellingboe Langmuir probes, double probes and capacitive probes are used to characterize an industrial transformer coupled plasma (TCP). Process gasses are mixtures of Ar/O$_2$/C$_4$F$_8$, such chemistry is similar to used in the etching of ULK materials. The obtained results are valuable for optimizing conditions for plasma processing for TCP. The plasma characteristics are investigated for varying gas mixtures, TCP power, substrate bias power and pressures for SiO$_2$ etching. Optimum etching process is strongly dependent on main power, O$_2$ flow rate or partial pressure of O$_2$, and pressure. The plasma density is found to drop with increasing partial-flow of either molecular gas up to 10{\%} flow of the molecular gas. Further addition of molecular gas has almost no affect on plasma density and electron temperature. The results are understood by a global model. [Preview Abstract] |
Wednesday, October 19, 2005 11:45AM - 12:00PM |
QW2.00008: Comparison of ICP with and without ferromagnetic core Valery Godyak, Benjamen Alexandrovich In spite of common operational principles, there are fundamental differences in electrical properties of a conventional transformer and a conventional inductively coupled plasma, ICP. Due to a strong coupling between primary and secondary circuits provided by a ferromagnetic core with high permeability, a conventional transformer behaves very closely to an ideal transformer, where the primary impedance is merely the load impedance times square of the primary winding turns. Experimental results of comparative study of ICP operated with and without ferromagnetic core are reported here. Electrical characteristics and power transfer efficiency of ICP with air core and different kinds of ferromagnetic cores have been measured in ICP of Kr/Hg mixture operating at 0.4 and 2.5 MHz in the discharge power range between 2 and 200 W. The comparison was made for discharges having the same geometry, gas fill and discharge power. It has been shown that ICPs enhanced with ferromagnetic core have significantly larger primary power factor and power transfer efficiency that those operated without ferromagnetic core. An extremely high power transfer efficiency (99{\%}) has been demonstrated for ICP with ferromagnetic core that corresponds to 1{\%} power loss in antenna with ferromagnetic core. This number is an order of magnitude better than that in the best helicon plasma sources having reputation of the most efficient plasma source. [Preview Abstract] |
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