Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session VF1: Capacitively-Coupled Plasmas |
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Chair: Miles Turner, Dublin City University Room: 151 |
Friday, October 8, 2010 4:00PM - 4:30PM |
VF1.00001: Progress on simulations of multiple-frequency capacitively coupled discharges Invited Speaker: While routinely serving in industry for several decades, some details of the physics of capacitively coupled discharges are still to be clarified. This is particularly true for sources driven simultaneously by multiple frequencies, which have been used to realize an independent control of ion properties. Particle simulation studies aid understanding the characteristic phenomena taking place in these plasma sources. We investigate here the time and space resolved dynamics of charged particles in multi-frequency discharges. Our results for ``classical'' dual-frequency discharges (operated at substantially different frequencies) show a coupling between both frequencies, which finally limits the separate control of ion properties. We find that the separate control is also influenced by secondary electrons to considerable extent. The limitations of classical dual-frequency discharges can be overcome by driving the discharge by consecutive harmonics of a fundamental frequency - in this case the phase shifts between the harmonics act as control parameters of the ion energy. [Preview Abstract] |
Friday, October 8, 2010 4:30PM - 4:45PM |
VF1.00002: Two-dimensional hybrid simulation of capacitively coupled plasmas with two rf sources Yuan-Hong Song, Xiang Xu, Zhen-Hua Bi, Yu-Ru Zhang, You-Nian Wang From 1990s, to improve the performance of the traditional CCP reactors which are widely applied in microelectronic device fabrications, a dual-frequency (DF) source was introduced for the purpose of controlling the plasma density and ion bombardment energy separately. Moreover, in order to improve the radial uniformity of plasma density, a new technique was put forward in which two VHF voltages are applied to the top and bottom electrodes separately with a controlled phase shift between them. In this work, we employ a two-dimensional (2D) fluid model coupled with Monte-Carlo method to investigate the properties of CCP discharges driven by DF or two VHF sources. The ion energy distribution function (IEDF) and electron energy distribution function (EEDF) are calculated based on the discharge parameters resulting from the fluid model. In virtue of the full set of Maxwell equations, the electromagnetic effect induced by VHF sources has been also discussed. [Preview Abstract] |
Friday, October 8, 2010 4:45PM - 5:00PM |
VF1.00003: The Electrical Asymmetry Effect in multi-frequency capacitively coupled radio frequency discharges Julian Schulze, Zoltan Donko, Edmund Schuengel, Uwe Czarnetzki In capacitively coupled radio frequency discharges the Electrical Asymmetry Effect (EAE) provides the opportunity to generate a DC self bias $\eta $ electrically. In dual-frequency (df) discharges operated at two consecutive harmonics with adjustable phase shift $\theta $ between the driving voltages $\eta $ is generated as a function of $\theta $. The ion energy can be controlled separately from the ion flux at the electrodes by tuning $\theta $ in df discharges. Here, the EAE in geom. symmetric argon discharges driven at multiple consecutive harmonics is investigated by a PIC simulation: Compared to df discharges a significantly stronger self bias can be generated electrically. The mean ion energy at the electrodes can be controlled separately from the ion flux over a broader range. An analytical model demonstrates that df discharges represent only one particular - with respect to ion energy control less effective - scenario in the frame of a more abstract understanding of the EAE. A recipe how to customize the applied voltage waveform to generate the strongest possible DC self bias and to obtain maximum control of the ion energy will be presented. [Preview Abstract] |
Friday, October 8, 2010 5:00PM - 5:30PM |
VF1.00004: Electrode Impedance Effect in a CCP reactor Invited Speaker: The generation of harmonics of drive frequency is of great technological importance in CCP reactors. It is commonly observed that a minor change in an external circuit, such as changing the cable length between the RF power supply and the matcher, brings about a significant difference both in the amplitude of harmonics and in process results. Recently, Mussenbrock and Brinkmann proposed a nonlinear electron resonance heating (NERH) model that predicts the enhanced dissipation caused by the harmonics originating from the series resonance between plasma bulk and sheath [1]. This theory gives a good explanation of the change in the amplitude of harmonics and in plasma property. However, there is a discrepancy between the simplified theory and observed result. The theory predicts that the resonant growth of harmonics takes place for frequencies greater than 100 MHz, given the typical inductance of the bulk and capacitance of the sheath. On the other hand, the frequencies of the harmonics which are commonly observed to grow tend to be lower than 100 MHz. By taking into account the external circuit in the series resonance condition, the resonance is possible at a frequency below 100MHz. We have experimentally demonstrated the resonant growth of the second, third and forth harmonics of a 13.56MHz drive frequency by tuning an external circuit [2]. We also observed an increase in electron density as the amplitude of the harmonics grows [3]. Thus, the external circuit modifies the impedance of the electrode and the change in impedance has significant effect on the growth of the harmonics, and the growth of these harmonics brings about an increase in electron density. \\[4pt] [1] T. Mussenbrock and R. P. Brinkmann, Appl. Phys. Lett. 88, 151503 (2006) \\[0pt] [2] Y. Yamazawa, M. Nakaya, M. Iwata and A. Shimizu, Jpn. J. Appl. Phys., Part 1 46, 7453 (2007) \\[0pt] [3] Y. Yamazawa, Appl. Phys. Lett. 95, 191504 (2009) [Preview Abstract] |
Friday, October 8, 2010 5:30PM - 5:45PM |
VF1.00005: Effects of rf phase control in VHF-CCP system Yeonghun Han, Chul-ho Shin, Sang-min Jeong, Dougyong Sung On plasma parameters and characteristics in a plasma process, we studied in the influence of the phase control between top electrode and bottom electrode that was applied by rf power in a very high-frequency (VHF) Capacitively Coupled Plasma (CCP) triode system. The rf voltages at 100 MHz were individually applied to the top and bottom electrodes. The phase shift of each rf powers could be controlled between 0$^{\circ}$ and 360$^{\circ}$ by phase shifter. The electric field from top electrode to bottom electrode was minimum as phase shift 0$^{\circ}$ and maximum as phase shift 180$^{\circ}$. As changing phase shift, it made differences of electron density, electron temperature, plasma potential, chemical dissociation and plasma uniformity concerning OES intensity in 12 inch wafer. In spite of the same rf power condition, the phase controlled CCP was more useful from the plasma process point of view. We could verify that the phase-shift effect can control ion density, electron temperature and plasma potential in VHF-CCP system and that the phase-shift method could be a new knob to control plasma characters in large area plasma system. [Preview Abstract] |
Friday, October 8, 2010 5:45PM - 6:00PM |
VF1.00006: Confinement effect due to standing wave in VHF driven CCP Seok-Hwan Lee, Myung-Sun Choi, Gon-Ho Kim Capacitively coupled plasma (CCP) sources driven at very high frequency (VHF) are attractive in the deposition process of mc- Si for the fabrication of solar cells due to its capability of high density plasma generation with low electron temperature. Standing wave effect (SWE) is a major issue in increasing the size of the plasma source and has been investigated by many researchers. Most of studies were focused on the nonuniform plasma heating caused by the voltage distribution on the electrode. Although the heating of plasma is an important factor of plasma density distribution due to SWE, confinement of plasma is important as well. The potential of the bulk plasma is affected by the sheath voltage so the plasma potential also shows the standing wave pattern. Since the potential barrier corresponding to the spatial difference of the plasma potential is much larger than several times of the electron temperature, plasma is confined by the potential barrier and the plasma density distribution is similar to the plasma potential. In this study, the spatial distribution of the plasma potential is measured and compared with the plasma density in CCP with the 1 m x 1.2 m rectangular electrode driven at 60 MHz. [Preview Abstract] |
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