Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session EM1: Electronegative Plasmas |
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Chair: Miles Turner, Dublin City University Room: Doubletree Hotel Pine |
Monday, October 17, 2005 4:00PM - 4:15PM |
EM1.00001: Charged species' densities and fluxes in a dual-frequency capacitive plasma Garrett Curley, Jean-Paul Booth, Cormac Corr, Jean Guillon, Sebastien Dine Dual-frequency capacitively-coupled plasmas in fluorocarbon- based gases are widely used for etching holes in SiO$_{2}$- based dielectric films in integrated circuit manufacture. We are studying a customized 2 + 27 MHz industrial etch reactor, running in Ar/C$_{4}$F$_{8}$/O$_{2}$ gas mixtures at 50 mTorr. We have used an RF planar probe [1] to measure the positive ion flux and a microwave resonator probe [2] to measure the electron density. The ratio of the (central) electron density to the ion flux was observed to vary significantly with the feedstock composition, sometimes reaching values three times higher than that predicted by simple electropositive theories. We believe this indicates the presence of significant densities of F$^{-}$ negative ions. We are currently attempting to measure the F$^{- }$ density directly by high-sensitivity optical absorption techniques. \newline \newline [1] Braithwaite et al, PSST, 5 (1996), 677-684\newline [2] Piejak et al, J. Appl. Phys. 95 (2004), 3785-3791 [Preview Abstract] |
Monday, October 17, 2005 4:15PM - 4:30PM |
EM1.00002: Ion Transport in Ion-Ion Plasmas M. Lampe, R.F. Fernsler, S.P. Slinker, S.G. Walton, D. Leonhardt, G. Joyce When strongly electronegative source gases are used, the LAPPS e-beam-generated plasma device at NRL$^{\ast }$ is capable of producing a steady-state nearly electron-free positive ion / negative ion plasma. It is commonly thought that ion flux to a substrate, in such a plasma, is limited by thermal diffusion of ions in the core plasma. We present a new theoretical treatment which shows that strong ion flux occurs even in the limit of \textit{zero} ion temperature, if a DC bias is applied to the substrate. We show how this ion current scales with source strength, bias voltage, ion temperature, and device geometry. The theory will be used to interpret experimental results from the LAPPS experiment.$^{\ast }$ *See adjacent paper, ``Etching with Electron Beam-Generated Ion-Ion Plasmas,'' by S. G. Walton [Preview Abstract] |
Monday, October 17, 2005 4:30PM - 4:45PM |
EM1.00003: Electron and Ion Processes in Weak Plasmas Thomas M. Miller, Jane M. Van Doren, A.A. Viggiano \textbf{I. New Plasma Effects Observed in a Flowing-Afterglow Plasma.} In a study of electron attachment to C$_{6}$F$_{5}$Cl in a helium bath gas), we found the first case we know of in which a thermally-detaching ion product (C$_{6}$F$_{5}$Cl$^{-})$ results in competition with a thermally-stable ion product (Cl$^{-})$, at elevated temperatures (500-550 K). We hypothesize that the heavier ions are more confined to the core of the plasma, releasing fresh electrons all the while. A sudden transition is observed in the electron density decay as the C$_{6}$F$_{5}$Cl$^{-}$ concentration dies away. \textbf{II. Electron Attachment to Fluorinated Pyridines.} In this experiment we measured rate constants for electron attachment and electron detachment for C$_{5}$F$_{5}$N and C$_{5}$HF$_{4}$N. From the attachment/detachment reaction rate constants, electron affinities were determined to be EA(C$_{5}$F$_{5}$N) = 0.70 $\pm $ 0.05 eV and EA(C$_{5}$HF$_{4}$N) = 0.40 $\pm $ 0.08 eV. The neutrals are planar, but calculations show the negative ions to have the F or H opposite the N atom to be significantly out-of-plane. Experimental and calculated values show an average decrease in EA of 0.25 eV per substitution of H for F. \textbf{III. Ion-Molecule Reactions at High Temperatures.} We will present data on negative ion-molecule reactions with molecules, obtained in a high-temperature flowing afterglow apparatus at temperatures from 300-1440 K. [Preview Abstract] |
Monday, October 17, 2005 4:45PM - 5:00PM |
EM1.00004: Shading effect of electrons and positive ions in charging free plasma etching; In-situ measurement of temporal change of a contact hole charging in a pulsed two frequency CCP. Takeshi Ohmori, Takumi Akaike, Takeshi K. Goto, Takeshi Kitajima, Toshiaki Makabe Miniaturization in ULSI progresses toward device elements of nanometer size, and charging damages during plasma etching will be actualized. All kinds of particle injected into a trench or SiO${_2}$ contact hole with a miniaturized structure on a wafer is shaded base on the topographical and electrical profile. While it is common that the electron shading causes a bottom charging, we will exhibit an ion shading effect by using a measurement of the temporal change of the charging potential on the bottom surface in the pulsed 2f-CCP. In our previous work using an optical emission CT and contact hole potential[1], we showed a qualitative behavior of the charge reduction on the bottom during a short time by applying a single positive component (SPC) of the bias pulse in a pulsed 2f-CCP in CF${_4}$/Ar. In the present work, we analyze and discuss the details of a temporal change of a SiO$_{2}$ hole charging during one on/off period of the VHF. The charging potential on the bottom increases and decreases by the injection of low energy negative charges and high energy positive ions during the period of the VHF, respectively. In addtion, negative charges accelerated by a double layer structure decrease the charging potential in a phase of SPC. [1] T. Ohmori, T. Akaike. T. K Goto and T. Makabe, 2004 57th GEC (2004). [Preview Abstract] |
Monday, October 17, 2005 5:00PM - 5:30PM |
EM1.00005: Double Layers in the expanding region of electronegative plasmas Invited Speaker: Double layers (DL’s) have been studied over the past decades theoretically, numerically and experimentally (see the review by Raadu in Physics Report 178, 25 1989, and references therein). The biggest part of the literature treats the case of electropositive plasmas, however, DL’s were also found in electronegative plasmas (both theoretically and experimentally). Recently, Charles and co-workers (Appl. Phys. Lett. 82, 1356, 2003) have observed a current-free DL in the expanding region of a helicon wave excited plasma at very low pressures (typically less than a millitorr). A strongly diverging static magnetic field seemed to be required in order to reach the conditions for double layer formation. Their system also had an abrupt change in radius at the boundary between the source and the diffusion chambers, which could possibly be a source of DL formation. Following this work, we have observed and studied double layers in a system of similar geometry but without B field and with electronegative gas mixtures. The DL's were not observed in pure argon. They seem to have a spherical shape and be formed at the boundary between the source and the diffusion chambers. They act as an internal boundary between a high electron density, high electron temperature, low electronegativity plasma upstream, and a low electron density, low electron temperature, high electronegativity plasma downstream. They are only stable for a small window of electronegativity. In most of the parameter space explored, they periodically form at the interface between the two chambers and they propagate at low speed (about 150 m/s) in the expanding chamber. We measured their amplitude and their dynamics by space and time-resolved langmuir probe experiments. Some explanations for their formation and propagation will be given. [Preview Abstract] |
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