Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session LW1: Plasma Diagnostics I |
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Chair: Noah Hershkowitz, University of Wisconsin-Madison Room: Salon E |
Wednesday, October 15, 2008 1:30PM - 1:45PM |
LW1.00001: Formation and Propagation of the Plasma Bullets Emitted by a Pulsed Plasma Jet Asma Begum, Erdinc Karakas, Mounir Laroussi Recently non-thermal atmospheric pressure plasma jets have been playing an important role in plasma processing including biomedical applications. This is due to the ability of providing plasmas not confined by electrodes. In this paper we report experimental investigations on the characteristics of the plasma jet emitted by a pulsed plasma generator, the ``Plasma Pencil''. Two ring electrodes attached to the surface of alumina disk are inserted in a dielectric tube and separated by a small gap. One of the two electrodes is connected to a high voltage pulse generator. Using ICCD we show that the plume is a series of plasma packets/bullets traveling at high velocities. Correlation between the discharge current and ICCD images reveals when and how the bullets are emitted from the device. Using optical emission spectroscopy, we will present spatially resolved emission spectra which give indications of the evolution of the various chemical species contained in the plasma bullets. In addition, we will show the effects of an external electric field and gas flow on the evolution and chemistry of the plasma bullets. [Preview Abstract] |
Wednesday, October 15, 2008 1:45PM - 2:00PM |
LW1.00002: Stark broadening for determination of electron density and electron temperature in an atmospheric pressure arc Jenna R. Puckett, Matthew R. King, Christopher J. Oldham, Jerome J. Cuomo Determining basic plasma parameters for low frequency, atmospheric pressure discharges is often difficult. However, insight into these parameters is imperative for understanding fundamental processes in all plasma applications. Because Stark broadening of lines in the hydrogen Balmer series depend on electron temperature (T$_{e})$ and electron density (N$_{e})$, lineshape analysis can be used to determine these parameters. This technique has been developed in the literature and we find it can be applied to a low frequency, atmospheric pressure arc. The effects of power and frequency on N$_{e}$ and T$_{e }$were examined in a gas mixture of argon and 0.5{\%} hydrogen using an Ocean Optics HR2000 spectrometer (groove density of 2400mm$^{-1})$. Nitrogen was added to study the effect of other gases on plasma parameters with the Stark broadening technique. [Preview Abstract] |
Wednesday, October 15, 2008 2:00PM - 2:15PM |
LW1.00003: Measurement of Plasma density in High Intensity Discharge Lamps by THz Interferometry Alex Kieckhafer, John Curry A THz interferometer has been constructed with the goal of directly measuring plasma electron densities in High Intensity Discharge (HID) lamp plasmas. The use of THz frequencies has several advantages. Primary of these is the ability to measure high densities. The 0.6 THz system constructed is capable of measuring densities up to 4x10$^{15}$ cm$^{-3}$. Additionally, the short wavelength of 0.6 THz radiation will allow focal spot sizes smaller than a millimeter in diameter, thus enabling high spatial resolution measurements. The system also differs from traditional microwave interferometry in that heterodyning has been eliminated. In inductively driven lamps the plasma recombines twice per AC cycle, when the voltage drops below a critical value. This time-dependent phase shift of the THz beam will allow calculation of density as a function of time. Zero-points can be acquired during the measurement itself due to the twice-per-cycle recombination of the plasma. Detection using electro-optical or nonlinear optical methods can easily achieve the time resolution required for these measurements, while maintaining sufficient signal-to-noise levels for detection without the assistance of lock-in amplification. [Preview Abstract] |
Wednesday, October 15, 2008 2:15PM - 2:30PM |
LW1.00004: Microwave In-Phase and Quadrature Detection of E-Beam Generated Air Plasma Robert Vidmar, Chris Ramsayer, Kenneth Stalder Microwave In-phase and Quadrature (I/Q) measurements at 10 GHz are discussed in the context of determining plasma parameters. Plasma generated in laboratory air with a pressure from 1 mTorr to 636 Torr is modeled as collisional plasma. The electron temperature is close to the bulk gas temperature at high pressure or up to a few eV at low pressure. Plasma generation is produced with 10-ms pulses of electrons from a 100-keV 5-mA electron gun, which then propagate through a 12.7-$\mu $m aluminum transmission window into a 400-liter test cell. A differential measurement approach is described that extends the dynamic range of the I/Q magnitude measurement from tens of dB to a small fraction of a dB. Amplification of the phase measurement is used to increase sensitivity. Ultimate sensitivity and filtering of both measurements are discussed in the context of mixer shot noise, Johnson noise, and pulse duration. Representative measurements and the procedure to convert raw data into estimates of electron number density and electron momentum transfer collision rate are discussed. [Preview Abstract] |
Wednesday, October 15, 2008 2:30PM - 2:45PM |
LW1.00005: Laser Deflection (Schlieren) Measurements of Hg Density in an Ultra High Pressure Arc Lamp J. Kane, M. Kato, J.E. Lawler The very high gas densities and excellent quality arc tubes of Ultra High Pressure (UHP) Hg arc lamps create opportunities for unusual diagnostics. An experimentally derived density map of a 213 bar UHP lamp is reported. The deflection of a laser beam by temperature induced density/index gradients is reconstructed through an Abel inversion. This deflection technique is most sensitive in the mantle unlike emission techniques which are sensitive in the arc core. The resulting map is compared to previous measurements of the temperature in the arc core as well as theoretical models of the temperature in the arc mantle. [Preview Abstract] |
Wednesday, October 15, 2008 2:45PM - 3:00PM |
LW1.00006: N$_2(A^3\Sigma_u^+)$ density in ICP N$_2$ plasmas measured by diode laser cavity-ringdown absorption spectroscopy Y. Horikawa, K. Kurihara, K. Sasaki There are two candidates for the precursor for nitriding silicon surfaces by nitrogen plasmas: atomic nitrogen and molecular nitrogen at the metastable $A^3\Sigma_u^+$ state. The goal of our work is to identify the nitriding precursor by comparing the precursor densities with the nitriding performance. In this work, we measured the N$_2(A^3\Sigma_u^+)$ density in ICP nitrogen plasmas by cavity-ringdown absorption spectroscopy (CRDS) at the first positive band. By employing a diode laser as the light source, a sensitive detection limit of 10$^{-6}$ for absorption was obtained in our CRDS system. We observed that the increase in the N$_2(A^3\Sigma_u^+)$ density with the rf power was gentle and was saturated at a high rf power. The N$_2(A^3\Sigma_u^+)$ density decreased with the nitrogen gas pressure significantly, and the N$_2(A^3\Sigma_u^+)$ density at 100 mTorr was approximately 1/10 of that at 20 mTorr. We also measured the N atom density at the ground state by vacuum ultraviolet absorption spectroscopy at the $^4S^o- ^4P$ transition. As a result, it was observed that the increase in the N atom density with the rf power was steeper than that in the N$_2(A^3 \Sigma_u^+)$ density. In addition, the N atom density increased with the nitrogen gas pressure. At the conference, we will discuss the kinetics of N$_2(A^3 \Sigma_u^+)$ and N by comparing their densities. [Preview Abstract] |
Wednesday, October 15, 2008 3:00PM - 3:15PM |
LW1.00007: Estimating and controlling the atomic oxygen content in an argon-oxygen plasma Bernard Keville, Derek D. Monahan, Miles M. Turner Oxygen rich plasmas have been applied in many plasma processing applications for decades. In most such applications, process yield could be improved significantly by applying closed loop control of atomic oxygen radical concentration. The design of effective, real time, closed loop control algorithms is facilitated by simple dynamical models of the relationship between inputs, or actuators in control terminology, and the process quantities to be controlled. In the case of an oxygen rich plasma process, one requires the relationship between the inputs - flow-rate set points, forward power from the RF supply and residence time, for example - and the oxygen radical density. With the aid of an argon-oxygen plasma simulation, this presentation describes how, with the aid of simplified dynamical models of the process, one would design model-based control algorithms for the real-time, closed loop control of oxygen radical density. A sine qua non of real time, closed loop control is an accurate estimate of the process quantities to be controlled. Although actinometry provides a non-invasive method for estimating species densities, atomic oxygen actinometry is complicated by the fact that photon emission can occur through dissociative as well as direct excitation, leading to potential ambiguity between the emission intensity and the actual radical concentration in the plasma. Optimal estimation of process states given indirect measurements corrupted by process and measurement noise is a classical topic in control theory and has yielded some spectacular results, notably the ubiquitous Kalman filter. [Preview Abstract] |
Wednesday, October 15, 2008 3:15PM - 3:30PM |
LW1.00008: Integrated Plasma-Surface Kinetics Model to Predict Deposition Rates in an HDP-CVD Reactor Ananth Bhoj, Prashanth Kothnur, Ron Kinder A comprehensive model for HDP-CVD reactors used in semiconductor processing, such as the Novellus SPEED, remains ~challenging due to the complex coupling of plasma transport, gas-phase and surface chemical reaction pathways in the chamber. The Hybrid Plasma Equipment Model (HPEM) is employed here to predict deposition rates at the wafer. The HPEM has a Surface Kinetics Module (SKM) that accepts species fluxes from the plasma, computes deposition/etch rates and coverage of various surface resident species and modifies sticking coefficients of plasma species based on their surface reactivity. Discharges in Ar/O$_{2}$/SiH$_{4}$ generated at a few mTorr and 2 -- 6 kW power deposition in a dome-shaped 200-mm chamber are considered. The gas-phase and surface reaction mechanisms build on those used by Meeks \textit{et al} [1] for their well-mixed reactor model. The effect of varying power, pressure and wafer temperature on plasma characteristics and the ensuing effects on deposition rates and surface coverage of species at the wafer will be discussed. [1]~ E. Meeks, R. S. Larson, P. Ho, C. Apblett, S. M. Han, E. Edelberg, E. S. Aydil,~ J. Vac. Sci. Technol. A, \textbf{16}(2), 544 (1998). [Preview Abstract] |
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