Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session SR1: Inductively and Capacitively Coupled Plasmas |
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Chair: Greg Hebner, Sandia National Laboratories, Albuquerque, NM Room: Salon E |
Thursday, October 16, 2008 4:00PM - 4:15PM |
SR1.00001: 3-Dimensional Modeling of Capacitively-Coupled Plasmas with Asymmetric Reactor Elements Jason Kenney, Shahid Rauf, Ken Collins As plasma processing uniformity requirements grow more stringent, there is an increasing emphasis on the characterization of asymmetric reactor elements which may give rise to azimuthal non-uniformities. Experimental analysis of isolated components is difficult, however, providing impetus for the development of a three-dimensional fluid plasma model. In this model, charged species densities are computed by solving continuity equations for all species (using the drift-diffusion approximation) implicitly in time, in combination with the Poisson equation governing the electrostatic fields. The model also includes the full set of Maxwell equations in their potential formulation, Kirchhoff equations for the external circuit, electron temperature from the electron energy equation, and continuity equations for neutral species, along with non-uniform mesh generation. Using this model, we have investigated azimuthally asymmetric components (e.g., slit valve, off-axis plates, misaligned electrodes) with the potential to perturb the plasma density, ion flux, and electric fields and quantified the perturbations using Fourier analysis. [Preview Abstract] |
Thursday, October 16, 2008 4:15PM - 4:30PM |
SR1.00002: Comparison between fluid simulations and experiments in inductively-coupled Ar/Cl$_{2}$ plasmas Emilie Despiau-Pujo, Cormac S. Corr, Pascal Chabert, William G. Graham, Fernando G. Marro, David B. Graves Comparisons of 2D fluid simulations with experimental measurements of Ar/Cl$_{2}$ plasmas in a low pressure ICP reactor are reported. The electron density, negative ion fraction and Cl atom density are investigated for various conditions of Ar/Cl$_{2}$ ratio, gas pressure and applied RF power. Simulations show that the wall recombination coefficient of Cl atom ($\gamma )$ is a key parameter of the model and that neutral densities are very sensitive to its variations. The best agreement between model and experiment is obtained for $\gamma $=0.02, which is much lower than the value predicted for stainless steel walls ($\gamma $=0.6). This is consistent with reactor wall contaminations classically observed in such discharges. The plasma electronegativity decreases with RF power and increases with Cl$_{2}$ content. At high pressure, the power absorption and distribution of charged particles become more localized below the quartz window. Although the experimental trends are well reproduced by the model, the calculated charged particle densities are systematically overestimated by a factor of 3-5. The reasons for this discrepancy are discussed in the paper. [Preview Abstract] |
Thursday, October 16, 2008 4:30PM - 4:45PM |
SR1.00003: Electron series resonance in an inductive ion etching reactor Hyo-Chang Lee, Jin-Young Bang, Chin-Wook Chung The electron series resonance at an RF bias substrate was observed in a 13.56 MHz inductively coupled plasma (ICP). As ICP coil power increases, the impedance of the RF bias transits from a capacitive load to an inductive load. When bias voltages and discharge impedances reach minimum values, bias voltages and currents are in-phase at the transition. The transition can be understood as a series LC resonance between sheaths (capacitor) and plasma bulks (inductance due to electron inertia). This corresponds to the electron series resonance (ESR) observed in very high-frequency capacitive discharges, and a new ESR frequency is presented when sheath resistances are considered. [Preview Abstract] |
Thursday, October 16, 2008 4:45PM - 5:00PM |
SR1.00004: Electron and Ion Energy Distributions in Dual Frequency Capacitively Coupled Plasmas Considering Wave Effects Yang Yang, Mark J. Kushner Dual frequency, capacitively coupled plasma (DF-CCP) tools typically use a high frequency (tens to hundreds of MHz) to sustain the plasma and a low frequency (a few to 10 MHz) for ion acceleration onto the wafers. Achieving uniform, selective and anisotropic etching depends on one's ability to tailor electron energy distributions (EEDs) in the plasma and ion energy and angular distributions (IEADs) incident on wafers. With an increase in both the high frequency and the wafer size, electromagnetic wave effects must be considered that may produce radial variations in electron heating, effecting the spatial variations in EEDs; and in sheath voltages, that could effect the radial distribution of IEADs. To address these spatial variations, a generalized full Maxwell equation solver has been implemented in a 2-dimensional plasma hydrodynamics model. Using a variation of the Finite-Difference Time-Domain method, multiple frequencies can be resolved. Results will be discussed for the spatial dependence of IEADs and EEDs in DF-CCPs for low frequencies of $\le $10 MHz and high frequencies up to 200 MHz; and gas pressure of $<$ 10s mTorr in electropositive and electronegative gas mixtures. [Preview Abstract] |
Thursday, October 16, 2008 5:00PM - 5:15PM |
SR1.00005: Separate control of ion flux and energy in capacitively coupled RF discharges via the Electrical Asymmetry Effect Julian Schulze, Zoltan Donko, Brian Heil, Uwe Czarnetzki Recently a novel approach towards achieving separate control of ion flux and energy in capacitively coupled RF discharges based on the Electrical Asymmetry Effect (EAE) was proposed using fluid models. If the applied voltage waveform contains an even harmonic of its fundamental frequency, the sheaths will not be electrically symmetric. In order to balance electron and ion fluxes at each electrode a DC self bias develops. The self bias and, consequently, the ion energy can be controlled by tuning the phase between the two applied voltages. This technique works in geometrically symmetric and asymmetric discharges. Here the EAE is verified using a PIC simulation of a geometrically symmetric discharge. The self bias is found to be a nearly linear function of the phase angle. If the phase is changed, the ion flux stays constant within 5{\%}, while the self bias reaches values of up to 80{\%} of the applied voltage amplitude and the ion energy is changed by a factor of three. The EAE is investigated at different pressures and electrode gaps with focus on separate control of ion flux and energy. [Preview Abstract] |
Thursday, October 16, 2008 5:15PM - 5:30PM |
SR1.00006: The 2nd Harmonic ECR Microplasma in Narrow Closed Space for Low Pressure Conditions Hiroshi Fujiyama, Akihiro Yukishige, Ke Yan, Masanori Shinohara, Tatsuyuki Nakatani Plasma generation in narrow closed space has been succeeded for the pressure of 0.01Torr and gap length of 500$\mu $m in xenon gas for the 2$^{nd}$ harmonic Electron Cyclotron Resonance (2$^{nd}$ harmonic ECR). Resonant confinement of electrons at the 2$^{nd}$ harmonic ECR leads to interesting micro plasma characteristics: the higher electron density, the lower plasma potential, the lower electron temperature and the effective power absorption against with the well-known ECR plasma. PIC-MC simulation of low pressure micro plasma supported such interesting plasma characteristics obtained by the experiments and simulations. In the experiments, it was found that the typical micro plasma characteristics: the higher electron density, the lower plasma potential, the lower electron temperature became remarkable. The ionization degree for the 2$^{nd}$ harmonic ECR plasma in the present research, showed about 10$^{-3}$ by 2 order higher than that of PDP micro plasma. [Preview Abstract] |
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