Bulletin of the American Physical Society
68th Annual Gaseous Electronics Conference/9th International Conference on Reactive Plasmas/33rd Symposium on Plasma Processing
Volume 60, Number 9
Monday–Friday, October 12–16, 2015; Honolulu, Hawaii
Session DT4: Basic Low Pressure Plasma Physics |
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Chair: Scott Baalrud, University of Iowa Room: 303 AB |
Tuesday, October 13, 2015 8:00AM - 8:15AM |
DT4.00001: Restructure of the plasma interior (presheath) caused by electron emission from surfaces Michael Campanell In the conventionally theorized ``space-charge limited'' regime of strong electron emission, the sheath potential is negative and the presheath is governed by Bohm ion acceleration towards the sheath edge. However, recent works found that sheath potentials at emitting surfaces can be positive, repelling ions. In this ``inverse sheath regime,'' the entire plasma interior (presheath) is also restructured [1]. Here we show at the presheath-sheath edge, due to their low velocities, the cold electrons entering the presheath have a higher spatial density than the hotter plasma electrons exiting the presheath. Therefore, assuming the emission collisionally thermalizes (reheats to the plasma temperature) in the presheath, it follows the quasineutral plasma density must increase towards the sheath edge, which is opposite from Bohm presheaths. The electron and ion force balance in the presheath becomes much different. A theoretical analysis with simulation and experimental evidence of ``inverted presheaths'' will be given. The results could be relevant to low temperature plasmas facing thermionically emitting surfaces and high temperature plasmas inducing strong secondary emission.\\[4pt] [1] M. D. Campanell, Phys. Plasmas 22, 040702 (2015). [Preview Abstract] |
Tuesday, October 13, 2015 8:15AM - 8:30AM |
DT4.00002: Influence of a phase-locked RF substrate bias on the E- to H-mode transition in an inductively coupled plasma Philipp Ahr, Edmund Schuengel, Julian Schulze, Tsanko V. Tsankov, Uwe Czarnetzki The influence of a capacitive radio frequency substrate bias on the E- to H-mode transition and the electron heating dynamics in a low pressure inductively coupled plasma (ICP) in hydrogen is investigated. The inductive and capacitive power sources are driven at the same frequency and can be operated in a phase-locked mode with a fixed, but adjustable phase between them. This approach of phase-locked discharge operation is a new feature which enables time-resolved studies of both the inductive and the capacitive energy coupling by phase-resolved optical emission spectroscopy (PROES). The inductive power at which the mode transition occurs, P$_{\mathrm{mtp}}$, is determined by PROES and from probe measurements of the electron density. For both, phase-locked and phase-unlocked operation, the plasma density in the E-mode is significantly influenced by the applied capacitive power: Already low values of bias power can reduce the value of P$_{\mathrm{mtp}}$. This coupling between the power sources is dependent on the adjustable phase between them and is attributed to a phase sensitive confinement mechanism for the energetic electrons produced by the expanding sheaths at the substrate and at the ICP coil. At higher pressures the effect diminishes. In contrast, by using electrodes with ring-shaped trenches the coupling is enhanced. [Preview Abstract] |
Tuesday, October 13, 2015 8:30AM - 8:45AM |
DT4.00003: Investigation of Self-Oscillation using Particle Balance Model Inshik Bae, Byungkeun Na, Hongyoung Chang Self-oscillation, which is obtained by using a DC-only power supply with specific anode voltage conditions, is investigated in a cylindrical system with thermal electrons using tungsten filaments. From analysis of the obtained oscillation profiles, the experimental data is consistent with the model derived from the particle balance model. The self-oscillation period characteristics with respect to the pressure and gas species are also analyzed. As the physics and particle motion of self-oscillation near the electron avalanche is analyzed in different perspective, this study may advance the understanding of this phenomenon. [Preview Abstract] |
Tuesday, October 13, 2015 8:45AM - 9:00AM |
DT4.00004: Measuring IVDF through high-aspect holes in pulsed ICP plasma Gilles Cunge, Maxime Darnon, Jerome Dubois, Philippe Bezard, Odile Mourey, Camille Petit-Etienne, Laurent Vallier, Emilie Despiau-Pujo, Olivier Joubert, Nader Sadeghi Plasma etching of high aspect-ratio (AR) structures is challenging. Several issues originate from the ion angular distribution: the feature sidewalls are bombarded by energetic ions and the ion flux at the bottom of the features is reduced. In ICP reactors at low pressure, this angular dispersion is due to two effects: the finite transverse velocity component of the ions when they enter the sheath region (i.e. the ion temperature Ti in plasma bulk) and charging effect of the feature sidewalls. To analyze those effects, we have measured the IVDF at the wafer surface in an industrial ICP reactor (AMAT) by using Semion multigrid ion energy analyzers. The plasma is operated in different chemistries (Ar, He, H$_{2}$ and CF$_{4}$) both in CW and pulsed mode. To analyze ion transport through high AR holes, we place 0.4 mm thick capillary plates with holes of AR 16, 8 and 4 in front of the RFA analyzer, which then probe IVDF at the exit of these holes. The results show that the ion flux drops dramatically when the AR is increased. By comparing the measured IVDF with an analytical model which calculates the transmission of a hole as a function of its AR and of T$_{\mathrm{i}}$ we concluded that Ti is about 3000 K. Charging effects are also observed and are shown to reduce significantly the ion energy at the feature bottom but with a ``minor'' effect on the ion flux and shape of the IVDF. We will discuss electropositive versus electronegative gases, pulsing and the role of ion mass on charging. [Preview Abstract] |
Tuesday, October 13, 2015 9:00AM - 9:15AM |
DT4.00005: Anomalous electron transport in magnetized plasmas with ExB drift A. Smolyakov, W. Frias, I. Romadanov, I. Kaganovich, Y. Raitses, M. Umansky Nonlinear fluid model has been developed for describing the fluctuations in Hall plasmas with magnetized electrons and non-magnetized ions. The plasma is immersed in externally applied crossed electric and magnetic fields. Plasma density gradient and collision destabilize the anti-drift and low hybrid modes resulting in turbulence. The conditions for excitation are tested with initial value simulations within the BOUT$++$ framework and with a linear eigenvalue solver. Nonlinear turbulence simulations are performed and levels of the anomalous transport are determined. The scalings of the turbulent transport with various plasma parameters are investigated. Nonlinear fluid simulations are compared with selected results of Particle-in-Cell simulations. [Preview Abstract] |
Tuesday, October 13, 2015 9:15AM - 9:30AM |
DT4.00006: Ion particle and energy flux uniformity control using a phase locked dual ICP coil design David Coumou, Steven Shannon Phase lock drive of multiple power sources to drive a single plasma discharge has demonstrated the ability to modify low pressure discharges in a variety of ways not achievable by other means including control of electrical asymmetry ion energy distribution function shape and uniformity. This work presents an experimental effort to elucidate the relationship between plasma parameters and locked phase between dual inductive coils and between the coils and bias cathode of a commercial 300 mm etching chamber. Adjusting parameters to maintain a constant electron density at the center of the discharge, both ion flux uniformity and average ion energy are impacted by these relative phase conditions. [Preview Abstract] |
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