Bulletin of the American Physical Society
72nd Annual Gaseous Electronics Conference
Volume 64, Number 10
Monday–Friday, October 28–November 1 2019; College Station, Texas
Session HW2: Plasma Surface Interactons |
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Chair: Luc Stafford, Université de Montréal Room: Century II |
Wednesday, October 30, 2019 8:00AM - 8:15AM |
HW2.00001: Fabrication of a Micro Secondary Electron Detection System and Its Measurement Results Zhengyang Wang, Matthew Goeckner, Lawrence Overzet The presentation is about the fabrication of and measurement results from a micro-scale secondary electron detection system that should have the capability of imposing a variable surface electric field. To our knowledge, no experiments have been done to measure the ion induced secondary electron emission (IIEE) yield as a function of the surface electric fields. This is a critical factor in the operation of microplasmas since strong electric fields are present on all surfaces due to the plasma sheath. In our design, an electric field of at least 1V/$\mu $m will be applied on a chemically clean Si surface to simulate the E-field in a plasma sheath. Then low energy ions are directed onto the Si surface and produce IIEE. A collector layer is used to collect the secondary electron current. We have made our first working device and we are making test runs on it using a modified mass spectrometer as the ion source. We plan to present the fabrication of this micro detector together with results of its upcoming test runs. [Preview Abstract] |
Wednesday, October 30, 2019 8:15AM - 8:30AM |
HW2.00002: In-situ measurement of electron emission and electron reflection yields Mark Sobolewski Plasma simulations require values for electron emission yields at plasma-exposed surfaces. In-situ measurements can provide useful values for effective or total yields, summed over all incident, energetic particles produced by a given plasma. Here, measurements were performed at 5-10 mTorr of argon/CF4 mixtures in a radio-frequency (rf) biased, inductively coupled plasma (icp) system. The rf voltage and current across the sheath adjacent to the rf-biased electrode were measured, along with Langmuir probe measurements of ion current density and electron temperature. The measurements are analyzed by a numerical sheath model, which allows the emitted electron current to be distinguished from other current mechanisms. Also, electrons elastically reflected at the counterelectrode are detected by measuring the current component at twice the icp frequency, 2f. Although photon fluxes and photocurrents are also modulated at 2f, new measurements are now able to distinguish these effects. Values obtained for the elastic reflection coefficient are smaller and more precise than those reported previously, but the measured emission yields remain nearly unchanged. Using additional information, contributions to the total emission yield from each type of incident particle are identified. [Preview Abstract] |
Wednesday, October 30, 2019 8:30AM - 8:45AM |
HW2.00003: Glow discharge optical spectroscopy for sputter-depth profile analysis in plasmas Priyanka Arora, Junghyun Cho, Vincent Donnelly In-situ, real-time characterization of surfaces exposed to plasmas is of great interest. Chemical analysis methods are limited, however. Common chemical analysis methods, X-ray photoelectron spectroscopy and Auger electron spectroscopy, cannot be used because they require energy-resolved detection of electrons, as well as high-vacuum conditions. Consequently, another method for detection of sputtered species is needed. Here we discuss the use of optical emission spectroscopy for this purpose. In this study, a small coupon piece of aluminum coated with yttria, a common chamber wall coating in reactors used in plasma etching, was mounted on an rf-biased electrode and inserted into an opening in the reactor wall. Silicon or SiO$_{\mathrm{2}}$ substrates on a separately rf-biased electrode were etched in an inductively-coupled plasma (ICP) of Cl$_{\mathrm{2}}$/Ar or C$_{\mathrm{4}}$F$_{\mathrm{8}}$/O$_{\mathrm{2}}$, respectively. Pulsed bias was applied to sputter the surface of the coupon piece in an Ar ICP. The difference in optical emission intensity between the coupon bias on and off condition was used to determine what species were present on the surface. [Preview Abstract] |
Wednesday, October 30, 2019 8:45AM - 9:00AM |
HW2.00004: Surface production of negative ions from nitrogen doped diamond in a deuterium plasma Gregory Smith, James Ellis, Roba Moussaoui, Cedric Pardanaud, Jocelyn Achard, Riadh Issaoui, Timo Gans, James Dedrick, Gilles Cartry The production of negative ions is of significant interest for applications including mass spectrometry, material surface processing, and neutral beam injection. Diamond is of particular interest as it has a large band gap and can have negative electron affinity. Nitrogen doping introduces a deep donor level, thereby increasing the production of negative ions. In this study, we investigate the surface production of negative ions from nitrogen doped diamond via experiments and simulations. Negatively biased, nitrogen doped micro crystalline diamond films are introduced to a low pressure deuterium plasma. Negative ion energy distribution functions (NIEDFs) are measured via mass spectrometry with respect to the diamond surface temperature and dopant concentration, and are compared to simulations to infer the deuterium surface coverage. Mechanisms for the production of negative ions via continuous and pulsed sample biasing, and their influence on the surface structure, are discussed. [Preview Abstract] |
Wednesday, October 30, 2019 9:00AM - 9:15AM |
HW2.00005: Measurements of material induced chemistry effects on low pressure planar ICP Joel Brandon, Sang Ki Nam, Steven Shannon It is well known in capacitively coupled radio frequency plasmas that the cathode is a significant source of secondary electrons. It is also known that the cathode material, by way of differing work functions and therefore differing secondary electron emission coefficients, can affect the defining characteristics of the surrounding plasma. PIC/MCC models have shown that the energy of secondary electrons is dependent on the material as well as the gas and that the material can have an impact on overall plasma density. A novel approach using a rotating axle, Langmuir probe, and laser diagnostics has been developed to quantify material induced changes in a steady state CW plasma. With this method, the authors intend to show a material induced contribution to the high-energy tail of the EEDF in noble gasses, and a material induced contribution to species populations in electronegative gasses. This approach would allow the authors to observe the effects of electron temperature, densities, and negative ion densities due to material changes in a single plasma environment without intermediate chamber evacuation or contamination. [Preview Abstract] |
Wednesday, October 30, 2019 9:15AM - 9:30AM |
HW2.00006: Observation of Tungsten Blister-Generated Grain Orientation Change According to Hydrogen Ion Incident Angle Myeong-Geon Lee, Nam-Kyun Kim, Ki-Baek Roh, Gon-Ho Kim The hydrogen ions in the ITER divertor enter at an energy of less than 100 eV and generate blisters on tungsten surface. Preliminary studies showed that sub micrometer size small blisters are generated only in grain orientation (111) by vertically incident ions. However, the incident angle of the magnetic field to the ITER divertor is designed to be over 85 degree as the surface normal. In this study, we observed the variation of the grain orientation with small blister caused by deuterium ion incident angle. The ions were incident at an energy of 100 eV on a tungsten target tilted by 80 degrees to a magnetic field. We used fluid ion flux model in weakly collisional magnetized presheath and electric field dominant debye sheath to calculate ion incident angle. The incident angle was calculated at 17 degree from the surface normal. Small blisters were generated on (111) direction and (212) direction grain. (212) grain direction is same as those rotated 16 degrees of (111) grain. It is interpreted that small blisters are generated on the (212) grain with the lowest surface density in the direction of the ion motion and (111) plane with where migration of hydrogen in depth direction adsorbed on the surface occurs largely. [Preview Abstract] |
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