Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session KW1: Inductively Coupled Plasmas |
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Chair: Steven Shannon, North Carolina State University Room: Ballroom I |
Wednesday, October 2, 2013 1:30PM - 1:45PM |
KW1.00001: ICP Source with Immersed Ferromagnetic Inductor Valery Godyak Inductively coupled plasma (ICP) sources have found a wide range of applications in various areas of plasma science and technology. Among different ICP topology, ICPs with immersed inductors have benefits (compared to ICPs with helical side or flat top inductors) of better coupling and electromagnetic (EM) field self-screening by the plasma surrounding the inductor. This allows for EM-free otter plasma boundary, thus making an ICP chamber entirely of metal or glass, with no EM radiation outside the plasma. It's been long known that ICP enhanced with ferromagnetic core immersed inductor is applicable in rf light sources and has demonstrated good performance. In this presentation we report a detailed experimental study of the electrical and plasma characteristics of compact ICPs with immersed ferromagnetic inductors in argon and xenon gas. The extremely high plasma transfer efficiency of this plasma source has been demonstrated in a wide range of gas pressure and rf power. A compact plasma cathode built with ICP having an immersed ferromagnetic inductor, and operating at 70-200 W has shown high power transfer efficiency of 97{\%}, and electron emission efficiency of 25 mA/W. These data are superior compared to those demonstrated for other plasma cathodes. [Preview Abstract] |
Wednesday, October 2, 2013 1:45PM - 2:00PM |
KW1.00002: Three-coil inductively coupled plasma (ICP) source with individually controlled coil currents supplied from a single power generator Leonid Dorf, Shahid Rauf, Jonathan Liu, Jason Kenney, Steven Lane, Andrew Nguyen, Kartik Ramaswamy, Ken Collins As requirements on plasma uniformity get more stringent in the semiconductor industry, an ICP source with 3 coils becomes warranted. Designing a power distribution/50$\Omega $-tuning network (PDN) that delivers the power from a single generator to 3 coils is complicated, due to inductive coupling between the coils, and between coils and plasma. Our PDN comprises several capacitors, including 2 variable ones, C$_{1,2}$, connected in parallel to 2 coils. A set of equations for coils/plasma currents was solved over a wide parameter space to determine practical values/ranges for all capacitors. It was shown that by moving along a pre-determined programming path in C$_{1,2}$ space, one can attain various coil current ratios (CCR) without crossing resonance curves. The latter causes coil current reversal, which may result in plasma instabilities and affect uniformity. Based on modeling results, the PDN was built and tested using a specially made 3-coil source. A wide range of CCR was achieved by varying C$_{1,2}$, including maxima or minima in any 2 coils. With slight adjustments (to account for parasitics and actual plasma coupling), the model correctly predicted experimentally observed CCR for each tested C$_{1,2}$ pair. Likewise, the theoretical resonance structure was reproduced experimentally with good agreement. [Preview Abstract] |
Wednesday, October 2, 2013 2:00PM - 2:15PM |
KW1.00003: Synergistic Behavior of a Dual Tandem Plasma Source Lei Liu, Weiye Zhu, Shyam Sridhar, Vincent Donnelly, Demetre Economou, Michael Logue, Mark Kushner The electron energy distribution function (EEDF) is of paramount importance in plasma processing. To control the EEDF, a dual plasma source was developed, consisting of a lower (main) inductively coupled plasma (ICP), in tandem with an upper ICP. The two sources were separated by a grounded metal grid. A boundary electrode (BE) in the upper source could be DC biased to inject charged species between the two sources, in an effort to control the EEDF of the lower (main) source. A Langmuir probe was employed to measure plasma parameters and the EEDF in Ar plasmas. It was found that, without any bias on the BE, low energy electrons were depleted in the main source when both plasmas were cw powered. The low energy electron population in the main source increased with increasing positive BE bias. The reverse behavior was observed in the upper source. The main source was also power modulated at 10 kHz with 20{\%} duty cycle, while the upper plasma was cw powered. Low (0.2-0.8 eV), almost constant T$_{\mathrm{e}}$ was obtained in the afterglow of the main source, with high plasma density ($\sim$10$^{11}$ cm$^{-3})$ at 10 mTorr. T$_{\mathrm{e}}$ could be controlled by varying the BE bias. Simulations using the Hybrid Plasma Equipment Model agreed with experimental data and provided valuable insights regarding the interaction between the two sources. [Preview Abstract] |
Wednesday, October 2, 2013 2:15PM - 2:30PM |
KW1.00004: Large and powerful RF-driven hydrogen ion sources Ursel Fantz, Peter Franzen, Bernd Heinemann Large area plasma sources are desirable in many applications among them the heating systems of magnetically confined fusion devices such as ITER (www.iter.org). Here, the hydrogen plasma has to illuminate homogeneously an area of 1.9 x 1 m$^{2}$ at a pressure of 0.3 Pa maximum. The plasma is generated via inductively coupling in eight cylindrical drivers, each driver powered with up to 90 kW power at 1 MHz frequency. The modular concept allows for size scaling such that large surfaces are homogeneously illuminated. The ELISE test facility, recently commissioned at IPP, is equipped with a source of the same width but half the height of the ITER source, i.e. an area of 1 x 1 m$^{2}$. Target parameters in hydrogen and deuterium plasmas are high dissociation degree and high ionization degree: atomic to molecular density ratio of about 0.2 and a ratio of electron to neutral density of about 0.01 -- 0.1, respectively. The electron temperature and density are intended to decrease from about 10 eV and 10$^{18}$ m$^{-3}$ in the drivers to 1 eV and 10$^{17}$ m$^{-3}$ close the extraction surface by using a magnetic filter field. The plasma uniformity and the plasma parameters are measured by optical emission spectroscopy using multiple lines of sight allowing also for tomographic studies. The influence of surface bias and the influence of a magnetic filter field on the plasma uniformity is investigated as well. [Preview Abstract] |
Wednesday, October 2, 2013 2:30PM - 2:45PM |
KW1.00005: Measurements of collisionless heating effects in the H-mode of an inductively coupled plasma system Mujahid Zaka-ul-Islam, Bill Graham, Timo Gans, Kari Niemi, Deborah O'Connell Inductively coupled plasma systems (ICPs) for processing applications are often operated at low pressures, in the near-collisionless regime. In this regime, the electron mean free path is comparable or larger than the plasma dimensions. The electron dynamics in such ICPs has been investigated here, using phase and space resolved optical emission spectroscopy (PROES) and Langmuir probe measurements. The PROES measurements are also used to calculate the Fourier harmonics components of the 2D excitation (in the radial axial plane). The experimental system is a standard GEC cell with the axial gap of $\sim$4 cm, powered by 13.56 MHz RF power supply. The gas pressure was varied between 0.5 -- 2 Pa. The PROES measurements and Fourier harmonics components confirm many of the previous simulation results in comparable operational regimes. The results show that in the 2D (radial-axial) plane, the plasma power is deposited in a spatially non-uniform and non-linear manner, with axial layers of positive and negative power absorption. The contribution of these nonlinear effects decreases with an increase in the pressure, as observed in previous experimental and simulation results. [Preview Abstract] |
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