Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session ET2: Electronegative Plasmas |
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Chair: Matt Goeckner, University of Texas at Dallas Room: Doubletree Crystal City Crystal Ballroom B |
Tuesday, October 2, 2007 4:00PM - 4:30PM |
ET2.00001: Plasma-Based Low Energy Ion Implantation Invited Speaker: After intense research and development of plasma doping systems, successful application of pulsed glow discharge in low energy ion implantation has been demonstrated. This approach offers great potential for both economic benefit, as a much higher throughput process than traditional beam line implantation, as well as enabling new fabrication options for advanced CMOS or non-planar implant. Understanding the discharge physics - collisions, ion energy distributions, plasma composition, secondary electron emission in the sheath of the dc pulsed plasma is indispensable for controlling the low energy ion implantation process. In this paper, ion energy distribution is directly measured from the high voltage sheath in a pulsed dc glow discharge using BF3 or BF3 mixed with inert gases as a gas feedstock. The impact of the ratio of BF3 mixed with inert gases on the ion energy distribution of the different ions and plasma parameters in the bulk and in the sheath is studied. The effects of elastic and inelastic collisions in the sheath on the ion energy distributions were experimentally and theoretically determined. It was found in several experiments that molecular ion such as BF2+ dominates the BF3 glow discharge. A possibility of negative ion formation is discussed with the recent experimental results taken into account. The analysis of the ion energy distribution and plasma parameters enabled a better understanding of the key parameters that control the nature, the concentration and the depth distribution of the implanted species. Based on the ion energy distributions measured with the mass spectrometer, the dopant depth profile is predicted and the plasma parameters are optimized in order to obtain shallow dopant depth distribution in the silicon after plasma doping implantation. This review of pulsed plasma-based implantation for semiconductor applications will focus on plasma diagnostics results thus far and the prospects for low energy implant applications. [Preview Abstract] |
Tuesday, October 2, 2007 4:30PM - 4:45PM |
ET2.00002: Theory and particle-in-cell simulation of ion-ion plasmas Gary Leray, Albert Meige, Jean-Luc Raimbault, Pascal Chabert Ion-ion plasmas have many potential applications such as in material processing (to minimize charging in the fabrication of microelectronic devices), in negative ion sources etc. In all these applications, the design of extracting grids implies a good knowledge of the sheath and the presheath in such plasmas. A full particle-in-cell simulation and a kinetic theory are developed to investigate ion-ion plasmas under the influence of a DC bias voltage. It is shown that high-voltage sheaths following the classical Child-law sheaths form within a few $\mu s$ after the DC voltage is applied. It is also shown that there exists the equivalent of a Bohm criterion with the corresponding presheath accelerating ions collected at one of the electrodes to the sound speed before entering the sheath. [Preview Abstract] |
Tuesday, October 2, 2007 4:45PM - 5:00PM |
ET2.00003: Propagating double layers in electronegative plasmas Albert Meige, Nicolas Plihon, Gerjan Hagelaar, Jean-Pierre Boeuf, Pascal Chabert, Rod Boswell Double layers have been observed to propagate from the source region to the diffusion chamber of a helicon-type reactor filled up with a low-pressure mixture of Ar/SF6 [N.~Plihon et al., \textit{J. Appl. Phys.}, \textbf{98}(023306), 2005]. In the present paper the most significant and new experimental results are reported. A full self-consistent hybrid model where the electron energy distribution function, the electron temperature and the various source terms are calculated is developed to investigate these propagating double layers. The spontaneous formation of propagating double layers is only observed in the simulation for system where the localized inductive heating is combined with small diameter chambers. The conditions of formation and the properties of the propagating double layers observed in the simulation are in good agreement with that of the experiment. By correlating the results of the experiment and the simulation, a formation mechanism compatible with ion two-stream instability is proposed. [Preview Abstract] |
Tuesday, October 2, 2007 5:00PM - 5:15PM |
ET2.00004: Very High Frequency Capacitively Coupled Plasmas of Electronegative Gases Shahid Rauf, Kallol Bera, Alex Paterson, Ken Collins Electromagnetic effects play an important role in determining the plasma behavior in large area capacitively coupled plasmas (CCP) generated using very high frequency (VHF) RF sources. A 2-dimensional model is used to elucidate the physics of VHF CCP discharges of electronegative gases. The model includes the full set of Maxwell equations in their potential formulation. The equations governing the vector potential, \textbf{\textit{A}}, are solved in the frequency domain after every cycle for multiple harmonics of the driving frequency. The coupled set of equations governing the scalar potential, \textit{$\phi $}, and drift-diffusion equations for all charged species are solved implicitly in time. The model also includes the electron temperature equation, Kirchhoff equations for the external circuit, and continuity equations for neutral species. The simulations focus on a 180 MHz CCP discharge, and examine the effect of gas mixture (Ar/CF$_{4}$, Ar/SF$_{6})$ and inter-electrode spacing on the plasma characteristics. It is found that spatial characteristics of the plasma are determined through a balance of electrostatic and electromagnetic effects. [Preview Abstract] |
Tuesday, October 2, 2007 5:15PM - 5:30PM |
ET2.00005: Fast silicon etching by plasma-sheath-lens focused negative ions Eugen Stamate Plasma processing technologies are based on radical-assisted, ion-induced surface modifications where ions accumulate energy within the sheath then strike the surface with a certain energy and incidence angle. Since reliable information on etching yields and a precise control of reactive species are of critical importance in attaining the desired process the use of plasma-sheath-lens and its discrete and modal focusing effects [1] can bring certain advantages (identical environment with that of real plasma processing; wide range of ion energies at high current densities; the passive surface can be used as a reference or as a collection surface of byproducts). Despite of high etching rates provided by high-density plasmas there are yet unsolved problems which can be avoided by bringing electrons to the bottom of the features, a case in which the etching needs to be performed by negative ions. In this work square and disk electrodes made of silicon have been exposed to different incident fluxes of negative ions focused by a plasma-sheath-lens. The etching pattern resulted by discrete and modal focusing effect was measured by phase-shift laser interferometry and compared with that from simulation performed for similar parameters. \newline [1] E. Stamate and H. Sugai, Phys. Rev. Lett. 94 (2005) 125004. [Preview Abstract] |
Tuesday, October 2, 2007 5:30PM - 5:45PM |
ET2.00006: Plasma Characterization of Electronegatively diluted VHF CCP Plasmas Alex Paterson, Ned Hammond, Shahid Rauf, Ed Barnat, Paul Miller, Greg Hebner In this study, the plasma characteristics of a VHF capacitively-coupled, 300 mm processing system were investigated. Spatially dependent ion and electron density, as well as electron energy distribution functions, were measured for frequencies between 27 and 170 MHz and for gas mixtures containing argon, SF$_{6}$ and CF$_{4}$. In argon plasmas, increasing the frequency above 120 MHz changed the ion and electron density spatial distributions from uniform to center high, producing a convex structure. This suggests that electromagnetic effects become important for this particular chamber geometry as the excitation frequency increases above 120 MHz. However, the addition of electronegative gas reduced the spatial non-uniformities, even at the highest frequencies investigated. For instance, diluting argon with SF6 resulted in the ion and electron density spatial uniformity changing from convex to uniform to concave. Similar effects were also observed with CF4 addition, but more dilution was required since it is less electronegative than SF6. This suggests the increasing negative ion density causes the electron density to reduce below a critical value, which results in the standing wave being ``damped,'' probably due to the increase in the plasma resistance. [Preview Abstract] |
Tuesday, October 2, 2007 5:45PM - 6:00PM |
ET2.00007: Formation of ion flux in low frequency and low pressure ccrf discharge I.V. Schweigert The formation of ion energy distribution function and ion angular distribution function are studied in 2-13.56 MHz discharge in Ar and BF3. The results are obtained with self-consistent kinetic simulations with using particle in cell Monte-Carlo collisions algorithm. For low gas pressure and high applied discharge voltages the models of electron and ion motion are modified to take into account the anisotropy of electron and ion scattering. [Preview Abstract] |
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