Bulletin of the American Physical Society
65th Annual Gaseous Electronics Conference
Volume 57, Number 8
Monday–Friday, October 22–26, 2012; Austin, Texas
Session ET3: Inductively Coupled Plasmas |
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Chair: Steve Shannon, North Carolina State University Room: Classroom 202 |
Tuesday, October 23, 2012 1:30PM - 2:00PM |
ET3.00001: Ferromagnetic Enhanced Inductive Plasma Sources Invited Speaker: Valery Godyak Inductively Coupled Plasma, ICP sources, or inductive discharges have been known for over a century. They have been used and studied in past decades mostly in two quite different regimes. At nearly atmospheric pressure, ICPs produce near equilibrium plasmas, while at low gas pressure, in the range of fraction and hundreds of mTorr, ICPs produce highly nonequilibrium plasmas. Low pressure ICPs have been used as ion sources for particle accelerators and thrusters for space propulsion. Recently, interest in low pressure ICPs has been revitalized due to their great advantages in plasma processing and lighting technology. The absence of electrodes, and the capability to provide large plasma densities, and high power transfer efficiency have made these discharges attractive for development of new technologies in various fields. The subject of this presentation is a review of ICP sources enhanced with a ferromagnetic core, FMICP, which found applications in plasma fusion, space propulsion, light sources, plasma chemistry and plasma processing of materials. Introduction of a ferromagnetic core to a magnetic rf circuit of ICP makes its operation close to that of an ideal transformer, thus enhancing its efficiency and power factor. The latter considerably simplifies ICP matching to a rf source. Application of a ferromagnetic core allows for considerable reduction of ICP driving frequency (up to 2-3 orders of magnitude) comparing to the standard in industry of 13.56 MHz. Reduction of the driving frequency allows for practical elimination of capacitive coupling and transmission line effects, inherent to ICP operating at 13.56 MHz. Utilization of lower frequencies also results in more efficient and less expensive rf power sources. However, the most valuable feature of FMICP for plasma processing is its ability for local rf power injection, which promises new possibilities in uniform processing over large substrate areas. The electrical and plasma characteristics of FMICPs, their matching to rf power sources, and their comparison with corresponding characteristics of conventional ICPs without a ferromagnetic core will be discussed in this review for various applications. [Preview Abstract] |
Tuesday, October 23, 2012 2:00PM - 2:15PM |
ET3.00002: High Pressure Discharge Negative Ion Source Lynn Olson, John Blandino, Nikolaos Gatsonis A high pressure discharge negative ion source has been developed with the goals of high duty cycle, high current, and good reliability, with the ultimate aim of providing a source for a facility such as the Spallation Neutron Source. The discharge itself has been characterized running on hydrogen and helium over pressure ranges of 10s to 100s of torr, with the pressure varied both by changing the flow rate and exit orifice diameter. A key part of the characterization was the power required for the E-H transition as a function of the pressure and gas flow. Running on hydrogen, a biased grid set has been used to extract negative current from a negative ion production region downstream from the discharge exit orifice and an electromagnet has been used to separate electrons from the negative ions. Initial measured efficiency for negative ion current has been in the range of 1-2 mA/kW. [Preview Abstract] |
Tuesday, October 23, 2012 2:15PM - 2:30PM |
ET3.00003: Three-Dimensional Electromagnetic Plasma Modeling of Inductively Coupled Plasma Source and Antenna Shahid Rauf, Ankur Agarwal, Jason Kenney, Ming-Feng Wu, Ken Collins Inductively coupled plasmas (ICP) are widely used for etching and deposition in the semiconductor industry. As device dimensions shrink with concomitant decreased tolerance for variability, it is critical to improve plasma and process uniformity in all plasma processes. In ICP systems, one of the major sources of non-uniformity is the radio-frequency (RF) antenna used to generate the electromagnetic wave. Discontinuities at current feed and grounding locations as well as electromagnetic field variations along the antenna coils can perturb the azimuthal electric field, resulting in a non-uniform plasma. For plasma modeling of ICP systems, a related problem is how capacitive coupling from the antenna is accounted for. ICP models have generally considered field variation along the antenna and capacitive coupling using simplified circuit models for the antenna structures. Modern ICP antennas are however quite complicated, making circuit approximations of the antenna too crude for system design. A three-dimensional parallel plasma model is described in this paper, where the full set of Maxwell equations are solved in conjunction with plasma transport equations for the plasma and the antenna. Several examples from the use of this model in ICP system design are presented. [Preview Abstract] |
Tuesday, October 23, 2012 2:30PM - 2:45PM |
ET3.00004: Evidence of weak plasma series resonance heating in the H-mode of neon and neon/argon inductively coupled plasmas A.E. Wendt, John B. Boffard, R.O. Jung, Chun C. Lin, L.E. Aneskavich The shape of the electron energy distribution function (EEDF) in low-temperature plasmas governs the relative rates of electron-impact processes that determine key discharge properties. Comparison of EEDFs measured with probes and optical emission [1] in argon and neon inductively coupled plasmas (ICP) has revealed a surplus of high-energy electrons in neon-containing plasmas. The abundance of these extra high energy electrons is correlated with the sheath thickness near the rf antenna and can be reduced by either adding a Faraday shield or increasing the plasma density. These trends suggest an association of the surplus high-energy electrons with stochastic heating of electrons in capacitively-coupled electric fields in the sheath adjacent to the antenna. Conventional stochastic heating, however, is found to be insufficient to account for the EEDF observations, and a comparison of modeled and experimental values of the 13.56 MHz time modulation of select neon emission lines strongly suggests plasma series resonance (PSR) heating adjacent to the ICP antenna as the source of the extra high-energy electrons. \\[4pt] [1] Plasma Sources Sci. Technol. \textbf{20}, (2011) 055006. [Preview Abstract] |
Tuesday, October 23, 2012 2:45PM - 3:00PM |
ET3.00005: Model of an Ar/O$_{2}$ inductive discharge used for plasma spray deposition Claudia Lazzaroni, Mehrdad Nikravech, Pascal Chabert A global model of a low pressure radio-frequency inductive discharge proposed to deposit thin layers of zinc oxide, the so-called spray-plasma device, is presented. This device consists in the injection of a precursor in the plasma reactor which is fed with an admixture of argon and oxygen and where the pressure is typically several tens of mTorr. This precursor is an aqueous solution of zinc nitrates, chlorates or acetates, which is transformed into an aerosol thanks to an ultrasonic sprayer. The droplets are then injected in the reactor through an aerosol conditioner and the ZnO layer is deposited on the substrate holder. The global model is based on the numerical resolution of the particle balance equations and the power balance equation. The model is run until the steady state is reached and we obtain the plasma parameters that are the species densities and the electron temperature. A parametric study is done varying the gas pressure, the RF power and the O$_{2}$ fraction in the reactor. Throughout the range investigated the electron density is found to be several 10$^{17}$ m$^{-3}$ and the electron temperature is between 2 and 3 eV. A great importance parameter for the deposition process is the flux of the reactive species (O, O$^{+}$, O$_{2}^{+})$ on the substrate holder and the model allows a fast parameter range exploration. [Preview Abstract] |
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