Bulletin of the American Physical Society
62nd Annual Gaseous Electronics Conference
Volume 54, Number 12
Tuesday–Friday, October 20–23, 2009; Saratoga Springs, New York
Session XF2: Capacitively-Coupled Plasmas II |
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Chair: Pascal Chabert, CNRS - Ecole Polytechnique Room: Saratoga Hilton Ballroom 2 |
Friday, October 23, 2009 10:00AM - 10:15AM |
XF2.00001: High Frequency Capacitively Coupled Plasmas: Implicit Electron Momentum Transport with a Full-wave Maxwell Solver Yang Yang, Mark Kushner Excitation frequencies for capacitively coupled plasmas (CCPs) are increasing to hundreds of MHz. At these high frequencies electrons may not be in equilibrium with the local electric field. Modeling electron transport in high frequency CCP tools requires solving the electron momentum equation to address inertia; and the full set of Maxwell's equations to address wave effects. In this talk, we discuss results from a 2-dimensional modeling study of the plasma properties in 300 mm and 450 mm dual frequency CCP (DF-CCPs) tools. Algorithms for electron transport are improved by integrating the electron momentum equation into the full-wave Maxwell equation solver. To capture the high frequency heating, excitation rates are provided by spatially dependent electron energy distributions generated by a Monte Carlo simulation. Results will be discussed for plasma properties in DF-CCPs for low frequencies of $\le $ 10 MHz and high frequencies up to 200 MHz, and gas pressure of $<$10s mTorr in argon. Comparisons of plasma properties will be made to those obtained using drift-diffusion formulations. [Preview Abstract] |
Friday, October 23, 2009 10:15AM - 10:30AM |
XF2.00002: Space- and Time-dependent electron velocity distribution in VHF-CCP in CF$_{4}$/Ar Takashi Yagisawa, Toshiaki Makabe The electron velocity distribution (EVD) is fundamentally important for all aspects in plasma electronics. EVD given as a solution of the Boltzmann equation provides the swarm parameter as functions of external E/N and B/N utilized for a plasma simulation. Two-term expansion was traditionally employed for solving the Boltzmann equation. This method, however, cannot give EVD in a large E/N appearing in the ion sheath region in front of a wall surface. Particle simulation (PIC/MC) was also used to estimate EVD, but heavy computational load prohibits the sample of a large number of particles in order to eliminate the statistical fluctuation. A solution of the Boltzmann equation in phase space (velocity, position-space, and time) intrinsically involves numerical diffusion resulting from the differenciation of the advection terms. In this study, we develop the numerical procedure for predicting space- and time-dependent EVD. That is, the Boltzmann equation is solved in velocity space by using our direct numerical procedure (DNP) under the presence of 2D-t electric field distribution in VHF-CCP, calculated by the RCT model. Nonlinear behavior of EVD in the bulk plasma during one cycle of VHF (100 MHz) is discussed depending on the collisional relaxation time for energy and momentum of electrons. Also, we will investigate the temporal change of EVD in the sheath region under a large E/N. [Preview Abstract] |
Friday, October 23, 2009 10:30AM - 10:45AM |
XF2.00003: A scalable, VHF/UHF, capacitively coupled plasma source for large-area applications at high frequencies Bert Ellingboe, David O'Farrell, Cezar Gaman, Fiachra Green, Neal O'Hara, Tomasz Michna Process results are driving both plasma etch and CVD to higher frequencies; This is incompatible with increases in wafer size to 450mm and beyond. No where is the evidence more clear than in PECVD of amorphous and microcrystalline Silicon for the photo-active layer in thin-film photovoltaic devices. Growth rates for these layers, while maintaining the necessary mechanical and electrical properties, can increase with increasing rf frequency, and in some cases yield superior film properties at the higher deposition rates (P.G. Hugger, etal, MRS 2008). However, in this industry substrate sizes are very large, exceeding 1m characteristic lengths, which puts substantial limits for a conventional plasma diode topology on using frequency as a control vector to increase deposition rate, thus increasing factory through-put and decreasing cost. In this talk we will introduce a novel plasma source topology that enables increased rf frequencies on arbitrary size plasma source without causing wavelength effects. The concept is to segment the powered electrode into discrete tiles; For example as a checkerboard. Adjacent tiles can be powered out of phase with each other. In this way the displacement current coupled by one electrode is balance by and equal and opposite current of the adjacent electrode. Thus zero net current is coupled into the plasma, zero net current is coupled through the sheath above the substrate, and no wavelength effects occur even for substrates large in comparison to the rf wavelength. Highlights of recent results in the operation and application of the plasma source to PECVD of silicon will be presented. [Preview Abstract] |
Friday, October 23, 2009 10:45AM - 11:00AM |
XF2.00004: Selective Influence of Magnetic Field Direction on Plasma Uniformity Wenli Collison, Vladimir Kudriavtsev, Michael Barnes, Mark Kushner In this study we have investigated computationally hybrid ICP/CCP plasma reactor, with static magnets located under RF electrode. Plasma system is designed for discrete track recording magnetic disk etch applications. Effect of the orientation of magnetic field direction (radial or axial) is studied for Ar plasma using HPEM model [1]. Results show that for both radial and axial magnetic field orientations there is optimal magnet strength which provides maximum uniformity. Axial magnetic field orientation allows simultaneous reversal of both ion flux and plasma density radial distributions (when compared to similar plasma conditions without magnetic field present). Radial magnetic field orientation allows selective reversal of radial distribution of the ion flux, but without affecting radial distribution of plasma density Ne. This can be utilized as an independent knob for selective plasma control. Above described effects are explained by the changes in radial distributions of axial E field and of ion velocity. Finding optimal magnetic strength for both considered field orientations allowed reducing radial uniformity of the ion flux and plasma density across the disk from 7 to 3{\%} (axial) and from 10 to 2.5{\%} (radial). ~The effects of inclined magnetic field on the ion flux and plasma density have also been investigated.\\[0pt] [1] Y. Yang and M. J. Kushner , J. Vac. Sci. Technol. A \textbf{25}, 1420 (2007). [Preview Abstract] |
Friday, October 23, 2009 11:00AM - 11:15AM |
XF2.00005: Experimental and theoretical studies of the electrode impedance effect in capacitive discharges Dennis Ziegler, Thomas Mussenbrock, Ralf Peter Brinkmann, Yohei Yamazawa It is widely acknowledged that one can observe a strong harmonics content in the current of an asymmetric capacitive discharge, even in case of a strongly sinusoidal driving voltage. This particular phenomenon is directly connected to the heating of electrons.\footnote{T. Mussenbrock et al., Phys. Rev. Lett {\bf 101}, 085004 (2008).} It has been shown by means of careful measurements that the increase of certain harmonics indicates an increase of the electron density.\footnote{Y. Yamazawa et al., Jpn. J. Appl. Phys. {\bf 46}, 7453 (2007).} In this paper we revisit these experiments. We also propose a model to study the possibility of controlling the excitation of current harmonics using an external circuit and its effect on the electron density (which is often referred to as the electrode impedance effect). [Preview Abstract] |
Friday, October 23, 2009 11:15AM - 11:30AM |
XF2.00006: Influence of collisions on spatial damping of electrostatic electron waves in a low-pressure plasma Jens Oberrath, Ralf Peter Brinkmann Electrostatic electron waves in a plasma can be excited in several ways. One possibility is a resonance effect, if any rf frequency is locally equal to the electron plasma frequency. In this region the energy of the electric field increases and has to disperse into the plasma. Therefore, a transport mechanism is needed which is given by electrostatic waves. These waves can be damped in time and space domain. After a short time period waves with temporal damping do not exist in the plasma anymore. Thus, we are interested in waves with spatial damping to describe the resonance effect for any length of time. This damping depends on collisions between the electrons and the neutral background gas. To investigate the influence of collisions on the damping we formulate a kinetic model for the electron behavior in the high frequency range of weakly ionized low-pressure plasmas with elastic collisions. We assume an isotropic collision term with a constant collision frequency because of the huge mass difference between electrons and neutrals. This allows the derivation of a dispersion relation from the linearized Boltzmann-Poisson system for homogeneous longitudinal waves, which is able to describe the influence of collisions on the wave propagation of electrons. In addition we find the relation for a Vlasov plasma as a special case which shows the spatial Landau damping. [Preview Abstract] |
Friday, October 23, 2009 11:30AM - 11:45AM |
XF2.00007: Intermediate frequency breakdown Derek Monahan, Miles Turner The mechanisms underlying low-frequency/dc and high-frequency breakdown differ greatly due to the contrasting nature of the charged particle trajectories. At low-frequencies charged particle trajectories are open, terminating at the electrodes, and secondary electron producion at the cathode plays a central role in the breakdown process. At high-frequencies, and typical discharge dimensions, charged particle oscillations are closed. In this limit trajectories have a diffusive nature and ionization via field heated bulk electrons plays a central role in breakdown. Between these two frequency extremes one may envisage a regime in which electron trajectories are open and ion trajectories are closed. While experiments confirm breakdown may be achieved in such a regime, a plausible breakdown mechanism does not appear to have been identified. In this paper we investigate breakdown in this regime using a kinetic simulation and propose a breakdown mechanism in which secondary electron production via fast neutral bombardment of the electrodes plays a significant role. [Preview Abstract] |
Friday, October 23, 2009 11:45AM - 12:00PM |
XF2.00008: Atmospheric Pressure RF Plasma Electrical and Optical Characteristics Ali Gulec, Lutfi Oksuz, Noah Hershkowitz An atmospheric pressure 13.56 MHz RF source is used for plasma polymerization, nanocomposite deposition and for sterilization purposes. The air discharge electrical and optical characteristics are measured using monochromator and electrical probes. The addition of helium flow to the RF discharge system allows production of stable glow plasma discharge. The electron temperature and plasma densities are estimated using the emission lines of HeI and double probes. Emission of the He+air atmospheric pressure plasma is observed from the OH radical, several lines of the N$_{2}$, N$_{2}^{+}$ and atomic O, H and He lines. He flow rate and applied rf voltage affect on these emission spectra are investigated and the spectral lines are used for calculation of plasma parameters. Plasma electron temperature is calculated using HeI lines and compared with double probe data. The OI 777 and H$_{\alpha }$ 656 lines are also investigated by varying the applied voltage and He flow rate. The calculated electron temperature was approximately 0.2 eV and dependent on the He flow rate and applied power. [Preview Abstract] |
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