### Session BT1: Plasma Sources I

Chair: A.R. Ellingboe, Dublin City University, Ireland
Room: Holiday Inn Salon CD

 Tuesday, October 10, 2006 8:00AM - 8:15AM BT1.00001: Electron beam-generated ion-ion plasmas: Etching and diagnostics S.G. Walton , D. Leonhardt , R.F. Fernsler Positive ion-negative ion (ion-ion) plasmas are those where negative ions are the primary negative charge carrier and in the absence of any significant electron density, these negative ions are not confined to the bulk plasma. Thus, a nearly equal and anisotropic flux of positive and negative ions can be delivered to surfaces located adjacent to the plasma and eliminate electron-induced damage to substrates in etching applications. A requirement for the formation of ion-ion plasmas in low pressure, halogen-based gas backgrounds is a low electron energy so that the attachment rate is comparable to the ionization rate and the plasma electrons can be rapidly converted to negative ions. Electron beam-generated plasmas provide an opportunity to investigate ion-ion plasmas and their potential applications because of their uniquely low electron temperature compared to conventional discharges. In this presentation, we discuss recent investigations of ion-ion plasmas formed in pulsed, electron beam-generated plasmas produced in mixtures of SF$_{6 }$and their use in silicon etching. In this system, positive and negative ions were extracted using a low frequency (10-50 kHz), low voltage (0-300 V) bias. The results of Si etching experiments and plasma diagnostics will be presented with the goal of understanding the optimum system configuration and operating conditions. Tuesday, October 10, 2006 8:15AM - 8:30AM BT1.00002: Automated method for creating arbitrary substrate voltage wave forms for manipulating energy distribution of bombarding ions during plasma processing Amy Wendt , Marlann Patterson , Hsuan-Yih Chu Accurate and reproducible control of ion bombardment energy during plasma processing is a means to better understand the nature of plasma-surface interaction and to control process outcomes. Ion energy distribution (IED) control can be achieved by tailoring the wave form shape of an rf bias applied to the substrate during processing, through the use of a programmable wave form generator in combination with a power amplifier. Due to the frequency dependence of the amplifier gain and the impedance of the plasma in contact with the substrate, however, it is not practical to predict the shape of wave form needed at the generator to produce a desired result at the substrate. Introduced here is a systematic approach using feedback control in the frequency domain to produce arbitrary wave form shapes at the substrate. Specifically, a fast Fourier Transform (FFT) of the substrate wave form is compared, one frequency at a time, with the FFT of a desired “target” wave form, to determine adjustments needed at the generator. This iterative procedure, which is fully automated and tested for several target wave form shapes, is repeated until the substrate wave form converges to the targeted shape, providing a quick systematic method for producing an arbitrary IED at the substrate. Tuesday, October 10, 2006 8:30AM - 8:45AM BT1.00003: Scaling laws in dc micro discharges Marija Radmilovic-Radjenovic , Zoran Petrovic , Branislav Radjenovic , Paule Maguire , Charles Mahony In order to establish the operation regime of micro discharges we should start from the low pressure discharges and employ the standard scaling laws. Discharges should scale according to the reduced electric field $E/N$ and $p$d - product proportional to the number of collisions. Finally, the scaling should be made in accordance with the $jd^2$ - describing the space charge effects [1]. We have calculated the Paschen curves and Volt- Ampere characteristic by using a PIC code and appropriate data for argon in order to establish whether the standard micro discharges operate in Townsend regime or in Glow Regime. \newline [1] A.V.Phelps, Z.Lj.Petrovi\'{c} and B.M.Jelenkovi\'{c}, Phys. Rev. E \textbf{47} 2825 (1993) Tuesday, October 10, 2006 8:45AM - 9:00AM BT1.00004: Hydrodynamic models for the positive column with neutral gas depletion. Jean-Luc Raimbault , Laurent Liard , Pascal Chabert In the classical low-temperature plasma equilibrium, the ionization degree is sufficiently small that neutral density is considered constant. However, in many contemporary plasma reactors, such as helicons, the ionized fraction can be significant. This fraction may even reach 100\% in plasma thrusters. In such circumstances, neutral dynamics has to be included in order to solve the plasma equilibrium. We have revisited the plasma equilibrium models, from low-pressure (Tonks-Langmuir) to high pressure (ambipolar diffusion) regime, including the neutral dynamics. The results show that neutrals are pushed towards the wall by the electronic pressure, creating a neutral depletion at the center of the discharge. The effect is significant when the electronic pressure becomes comparable to the neutral pressure. The electron temperature becomes a function of the electron density, so that particle and power balance are not decoupled. Finally, we derived a new expression for the edge-to-center electron density ratio which accounts for neutral density depletion. Tuesday, October 10, 2006 9:00AM - 9:15AM BT1.00005: Numerical Simulation of the DC Discharge Using CFD-ACE+ Ning Zhou , Peng Zhang A low pressure DC discharge is simulated using the CFD-ACE+. The electron kinetics is obtained from the kinetic module. The local and non-local approaches are used separately for solving the kinetic equation. The results are compared at different locations in the discharge. It is shown that although the local approximation gives a good description of the electron energy distribution function (EEDF) in the bulk plasma, it fails to give accurate information of the EEDF near the wall, which is highly non-Maxwellian. As a result, the non-local approach is more appropriate for the kinetic treatment of plasma electrons in a low pressure DC discharge. The ion number density and momentum are obtained from a fluid model. For comparison, the electron continuity equations are also included. Based on the simulation model, the species' density profile, the power balance and the influence of the electron-electron coulomb collisions on the EEDF and discharge physics are investigated. The simulation results are also compared with results from pure fluid model without kinetic description. Tuesday, October 10, 2006 9:15AM - 9:30AM BT1.00006: Simulation of moving striations in rare gas plasmas Vladimir Kolobov , Robert Arslanbekov Ionization waves (moving striations) have been observed in classical DC discharges of rare gases in a wide range of gas pressures and discharge currents. Recently, striations have been also observed in plasma display cells and other micro-discharges. We have obtained moving striations in computer experiments using self-consistent discharge model. The model includes Boltzmann solver for electron kinetics, fluid model for ion transport, Poisson equation for the electric field and (optionally) an external circuit model. Simulations are performed from cathode to anode in 1d or 2d settings. Striations appear initially near the cathode and propagate towards the anode as observed in experiments. The model allows studies of nonlinear waves and effects of external circuit on the wave properties. We will discuss the mechanism of striations for different operating conditions and present results of simulations for a DC discharge in Argon gas for a typical pressure of 1 Torr, tube radius R=1 cm, for different discharge currents. High sensitivity of striations to the state of electron gas and ionization kinetics makes them an ideal tool for testing discharge models and advanced plasma diagnostics.