Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session TF3: Diagnostics II (Electrical) |
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Chair: Tom Huiskamp, Tech. Universiteit, Eindhoven, & Guus Pemen, Tech. Universiteit, Eindhoven Room: Oregon Convention Center A106 |
Friday, November 9, 2018 9:30AM - 10:00AM |
TF3.00001: Expanding the Functionality of Plasma Diagnostics Invited Speaker: Steven Shannon As plasma processing demands grow, so does the range of conditions that plasma sources need to operate in. Higher sheath potentials, multi-frequency power delivery, transient operation, complex chemistries, engineered plasma facing surfaces, and extended pressure ranges all come together in some combination to enable fabrication of next generation devices using more exotic materials laid out with extraordinarily challenging topologies. These challenging conditions place demands on experimental diagnostic capabilities. In this talk, efforts to extend the operating capabilities and breadth of information obtained for three commonly used LTP diagnostics are summarized. 1.) extension of microwave hairpin probe diagnostic capability into high pressure regimes and transient conditions, where analysis techniques to measure collision frequency, plasma transients in pulsed RF operation, and direct measure of plasma perturbation due to the probe will be presented, 2.) extension of retarding field energy analyzers to high voltage operation by extending the spacing between grids, where a novel analysis technique that minimizes the distortion of reconstructed IEDF shape due to space charge accumulation between plates with sufficient separation for high voltage operation can improve measurement in this regime, and 3.) extension of Stark broadening measurement of electron density using Doppler Free saturation spectroscopy, where DFSS techniques are combined with Stark induced line shape and broadening analysis to estimate electron densities in the range of 10$^{\mathrm{12}}$ cm$^{\mathrm{-3}}$ with excellent comparison to Langmuir probe measurements in both magnitude and trend. [Preview Abstract] |
Friday, November 9, 2018 10:00AM - 10:15AM |
TF3.00002: Model-Experiment Comparison of Plasma Characteristics for Moderate Pressure Capacitively Coupled Discharges David Peterson, Steven C. Shannon, Wei Tian, Philip A. Kraus, Kallol Bera, Shahid Rauf, Thai Cheng Chua, Travis Koh, Hanhong Chen Spatial profiles of plasma parameters along with voltage and current characteristics in a parallel plate capacitively coupled discharge at moderate pressures are compared with 2-dimensional fluid plasma simulation results. Plasma parameters including electron density, effective collision frequency, effective electron temperature, and sheath thickness around a hairpin resonator probe are measured over different pressures and powers ranging from 13-530 Pa and 70-420 mW/cm$^{\mathrm{2}}$ in Ar, He, Ar-He, and N$_{\mathrm{2}}$ plasmas driven at 27 MHz with gap thicknesses ranging from 1-4 cm. Spatial measurements are made in the axial and radial directions. Probe sheath thickness is determined using a time resolved system capable of 25 ns resolution. Effective electron temperature is determined using effective collision frequency through the plasma conductivity equation but requires assuming an EEDF. The detailed model-experiment comparison proved useful for improving understanding of plasma chemistry mechanisms in these low temperature plasmas at moderately high pressure. All analysis and data acquisition use open source python scripts which are freely available to the public. [Preview Abstract] |
Friday, November 9, 2018 10:15AM - 10:30AM |
TF3.00003: Langmuir Probe Modifications for Use in Pulsed Plasma Alex Press, Keith Hernandez, Matthew Goeckner, Lawrence Overzet The kinetics of the transition periods in pulsed rf discharges is complex. This is in part because large changes in plasma conditions can occur within a few microseconds. Langmuir probes which are able to sample more quickly than this may still be unable to make reliable measurements. Adapting Langmuir Probes for time resolved measurements with time resolution less than 10 rf cycles requires conscious choices in the data collection methods and probe hardware. As the probe current collection time decreases, improving time resolution, the collection period becomes similar to the RF period. Under these conditions, it is important to choose collection periods that are integer multiples of the rf period to reduce error stemming from measuring fractions of rf cycles. During pulse turn-on and turn-off phases, the rf period averaged plasma potential can change by many volts, inducing displacement current in the probe circuitry. To accurately measure the plasma parameters during these phases, this displacement current must be minimized. This is achieved by modifying the Langmuir probe hardware/circuitry. This talk will show how this can be accomplished and some of the limitations to using Langmuir probes to measure plasma parameters during transition phases of pulsed rf discharges. [Preview Abstract] |
Friday, November 9, 2018 10:30AM - 10:45AM |
TF3.00004: Probe tip length effect of cutoff probe for measurement of high density plasma based on a new circuit cutoff model SiJun Kim, JangJae Lee, DaeWoong Kim, Jung-Hyung Kim, ShinJae You To improve the characteristics of the cutoff probe in measurement of high density plasma, we proposed a General Cutoff (GC) model based on transmission line theory. Although by virtue of this GC model we found the importance of the probe tip length on the measurement of high density plasma, the main effects of the tip length are not fully understood. In this research, we establish a new circuit model by approximating the GC model, and analyze the probe tip length effect in detail. As a results, we find that the ratio of the plasma inductance to the probe tip inductance plays an important role of the measurement limitation of the cutoff probe. This result also suggests a guideline for the design rule of the probe tip length for the measurement of high density plasma with cutoff probe. [Preview Abstract] |
Friday, November 9, 2018 10:45AM - 11:00AM |
TF3.00005: The multipole resonance probe: kinetic damping in its spectra Jens Oberrath The multipole resonance probe (MRP) has become an accepted diagnostic tool to measure electron densities in low pressure plasmas within the last decade. It excites a resonance of the dipole mode, where the resonance frequency is proportional to the electron plasma frequency. To allow for the measurement of electron density and temperature simultaneously, a second resonance parameter is necessary. A good candidate is the half width of the resonance peak, which is connected to the damping of the probe-plasma system and thus dependent on the electron temperature. However, in low pressure plasmas, the resonance peak is broadened due to kinetic effects, which requires a kinetic model. Such a model in electrostatic approximation based on functional analytic methods for a general probe geometry has been presented [1]. Based on the general solution of this model, the system response function Y of the MRP has to be approximated to determine specific spectra. These spectra show clearly a broadening of the resonance peak due to kinetic effects. The goal of ongoing research is to derive a relation between the half width and the electron temperature.\\ $[1]$ J. Oberrath and R.P. Brinkmann, Plasma Sources Sci. Technol. 23, 045006 (2014). [Preview Abstract] |
Friday, November 9, 2018 11:00AM - 11:15AM |
TF3.00006: Analysis of Kinetic Dynamics of the Multipole Resonance Probe Junbo Gong, Michael Friedrichs, Sebastian Wilczek, Denis Eremin, Jens Oberrath, Ralf Peter Brinkmann Active Plasma Resonance Spectroscopy (APRS) denotes a class of industry-compatible plasma diagnostic methods. One particular realization of APRS with a high degree of geometric and electric symmetry is the Multipole Resonance Probe (MRP). The Ideal MRP is an even more symmetric idealization which is suited for theoretical investigations. In this work, a spectral kinetic scheme is presented to investigate the behavior of the Ideal MRP in the low pressure regime. Similar to the particle-in-cell method, the scheme consists of two modules, the particle pusher and the field solver. A Green's function is defined to solve this potential problem. The spherical harmonics is employed to provide a general solution. With suitable truncation of the harmonics expansion, the complexity of the task can be reduced. The proposed kinetic model overcomes limitation of the cold plasma model and covers kinetic effects. Numerical results illustrate the resonance behavior and damping phenomena due to the escape of particles. [Preview Abstract] |
Friday, November 9, 2018 11:15AM - 11:30AM |
TF3.00007: Kinetic Spectra of the Planar Multipole Resonance Probe Michael Friedrichs, Jens Oberrath The planar multipole resonance probe is suitable for industrial plasma diagnostic purposes and consists of two half-disc electrodes, which can be integrated into the chamber wall of the reactor. Due to its minimal invasive character, inner plasma parameters can be monitored during the process. Based on a fluid model it is possible to determine the electron density from a detected resonance frequency in the measured spectrum. However, to monitor also the electron temperature an additional resonance parameter, e.g. the half-width of the resonance peak, is necessary. It is strongly influenced by kinetic effects, therefore a study of a kinetic model to obtain a relation between the half-width and the electron temperature is required. In this work such a kinetic model based on functional analytic methods and first spectra are presented. [Preview Abstract] |
Friday, November 9, 2018 11:30AM - 11:45AM |
TF3.00008: Real-time plasma impedance matching using an impedance mapping strategy. Mike Hopkins, David Gahan, Paul Scullin, Thomas Gilmore In plasma impedance matching, power transfer is not always the only desired outcome, for instance an accurate VI sensor at the output of the matching unit increases the accuracy of power delivery, accounts for matching network efficiency, increases impedance range, allows real time load impedance measurement and diagnostics, accurate load tracking, fast ignition, and in-pulse matching. In the current paper we use a VI sensor located at the output of the match, combined with the power forward and reflected, measured at the power supply to map the complex impedance of the matching unit and relate it to the system performance. To test the performance of different matching strategies, such as frequency tuning, we develop an electrical model of an ICP plasma etcher with a 13.56 MHz bias. We gather a wide range of experimental measurements to calibrate the model and show that it is accurate and predicts the behavior of the system. As an example, we observe a 20{\%} shift in ion energy with $+$/- 5{\%} range frequency tuning. We show in-pulse matching of power in the microsecond range. We confirm that impedance mapping is a powerful tool in delivering more stable and reliable plasma processes in the etcher studied and that it is the first step in a plasma chamber matching program. [Preview Abstract] |
Friday, November 9, 2018 11:45AM - 12:00PM |
TF3.00009: Novel voltage-based temperature measurement method for dielectric barrier discharges Robert Bansemer, Ansgar Schmidt-Bleker, Ursula van Rienen, Klaus-Dieter Weltmann For a multitude of processes based on dielectric barrier discharges (DBD), gas temperature is a crucial control parameter. One notable example is the production of ozone or different nitrogen oxides from air depending on pressure and temperature. In order to provide a means to control processes such as the species production, the suitability of a temperature determination based on changes of the gas-gap voltage in DBD has been evaluated. The method is destined for sine-driven devices and is based on a dependence of the gas-gap voltage on the gas density and hence on temperature and pressure in the active zone. It was found that the proposed method allows reaching a precision adequate for the designated purpose while being non-intrusive and working both in a stationary as well as in a flowing process gas. No equipment besides the setup for capturing the Lissajous-figure is needed. The method has been validated by thermistor measurements. Furthermore, computational fluid dynamics simulations were performed to investigate the temperature distribution within the device under test. [Preview Abstract] |
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