James K. Olthoff

Electron Interactions With SF6

Sulfur hexafluoride (SF6) is commonly used as a gaseous dielectric and as a plasma etching gas. In this work, the state of knowledge on electron-interaction cross sections and electron-swarm parameters in SF6 is comprehensively reviewed and critically assessed. Cross sections are presented and discussed for the following scattering processes: total electron scattering; differential elastic; elastic integral; elastic momentum; total vibrational; total and partial ionization; total dissociative and nondissociative electron attachment; and dissociation into neutrals. Coefficients for electron-impact ionization, effective ionization, electron attachment, electron drift, and electron diffusion are also reviewed and assessed. In addition, complementary information on the electronic and molecular structure of the SF6 molecule and on electron detachment and ion transport in parent SF6 gas is provided that allows a better understanding of the nature of the cross sections and swarm parameters. The assessed data are...

The Gaseous Electronics Conference radio‐frequency reference cell: A defined parallel‐plate radio‐frequency system for experimental and theoretical studies of plasma‐processing discharges

A “reference cell” for generating radio-frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self-bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.

Electron Interactions with CF4

Carbon tetrafluoride (CF4) is one of the most widely used components of feed gas mixtures employed for a variety of plasma‐assisted material‐processing applications. It has no stable excited states and, in a plasma environment, is an ideal source of reactive species, especially F atoms. To assess the behavior of CF4 in its use in manufacturing semiconductor devices and other applications, it is necessary to have accurate information about its fundamental properties and reactions, particularly its electronic and ionic interactions and its electron collision processes at low energies (<100 eV). In this article we assess and synthesize the available information on the cross sections and/or the rate coefficients for collisional interactions of CF4 with electrons. Assessed information is presented on: (i) cross sections for electron scattering (total, momentum, elastic differential, elastic integral, inelastic), electron‐impact ionization (total, partial, multiple, dissociative), electron‐impact dissociation (...

Sulfur hexafluoride and the electric power industry

The use of gas-insulated electrical equipment has a demonstrated value for society. The problems relating to SF/sub 6/ are not without solution and can lead to new opportunities. To this end, besides the current efforts to curtail the releases of SF/sub 6/ into the environment, a comprehensive and focused program is needed to develop alternative gaseous insulators and alternative high-voltage technologies.

Electron Interactions With Plasma Processing Gases: An Update for CF4, CHF3, C2F6, and C3F8

An update of electron–collision cross sections and electron transport parameters is presented for CF4, CHF3, C2F6, and C3F8.

Ion energy distributions and sheath voltages in a radio-frequency-biased, inductively coupled, high-density plasma reactor

Ion energy distributions were measured at a grounded surface in an inductively coupled, high-density plasma reactor for pure argon, argon–helium, and argon–xenon discharges at 1.33 Pa (10 mTorr), as a function of radio-frequency (rf) bias amplitude, rf bias frequency, radial position, inductive source power, and ion mass. The ground sheath voltage which accelerates the ions was also determined using capacitive probe measurements and Langmuir probe data. Together, the measurements provide a complete characterization of ion dynamics in the sheath, allowing ion transit time effects to be distinguished from sheath impedance effects. Models are presented which describe both effects and explain why they are observed in the same range of rf bias frequency.

Ion Energy Distributions in Inductively Coupled Radio-Frequency Discharges in Argon, Nitrogen, Oxygen, Chlorine, and Their Mixtures

We report ion energy distributions, relative ion intensities, and absolute total ion current densities at the grounded electrode of an inductively coupled Gaseous Electronics Conference radio-frequency reference cell for discharges generated in pure argon, nitrogen, oxygen, and chlorine, and in mixtures of argon with N2, O2, and Cl2. Measured current densities are significantly greater for pure argon and for mixtures containing argon than for pure N2, O2, and Cl2. For all three molecular gases, the ratio of molecular ions to the fragment ions decreases when argon is added to the molecular gas discharges. A possible destruction mechanism for the molecular ions involving metastable argon is discussed.

Kinetic‐energy distributions of ions sampled from argon plasmas in a parallel‐plate, radio‐frequency reference cell

Kinetic‐energy distributions are presented for ions sampled from 13.56‐MHz discharges in argon in a capacitively‐coupled, parallel‐plate, Gaseous Electronics Conference (GEC) radio‐frequency reference cell. The cell was modified to allow sampling of ions through an orifice in the grounded electrode. Kinetic‐energy distributions are presented for Ar+, Ar++, Ar+2, ArH+, and several trace ions for plasma pressures ranging from 1.3 Pa, where ion‐atom collisions in the plasma sheath are not important, to 33.3 Pa, where collisions are important. Applied peak‐to‐peak radio‐frequency (rf) voltages of 50, 100, and 200 V were used, and the current and voltage waveforms at the powered electrode were measured. Dependences of the ion fluxes, mean energies, and kinetic‐energy distributions on gas pressure and applied rf voltage are interpreted in terms of possible ion‐collision processes. The results agree with previously measured kinetic‐energy distributions of ions sampled from the side of the plasma through a ground...

Electron Interactions with CHF3

In this paper we assess and synthesize the available information on the cross sections and the rate coefficients for collisional interactions of trifluoromethane (CHF3) with electrons in an effort to build a database on electronic and ionic collision processes that will aid the understanding of the behavior of CHF3 in its use in manufacturing semiconductor devices and other applications. The limited data on the total and partial electron impact ionization cross sections, total and partial cross sections for electron impact dissociation of CHF3 into neutral species, electron-impact induced line and continuous light emission from CHF3, negative ion states of CHF3, and the energetics of ionization, dissociation, and attachment are summarized and discussed. Besides some recent unpublished measurements of the total electron scattering cross section below 20 eV, to our knowledge no measurements are available of the cross sections of any of the electron scattering processes (elastic, momentum, vibrational, inela...

Electron attachment cross sections and negative ion states of SF6

Abstract A comprehensive and critical assessment of published data on the total, dissociative and nondissociative electron attachment cross sections for SF 6 allowed us to recommend or suggest room temperature values for these cross sections over an energy range from 0.0001 eV to 15 eV. The total electron attachment cross section is dominated by the formation of SF 6 − below ∼0.2 eV, by the formation of SF 5 − between ∼0.3 eV and 1.5 eV, and by the formation of F − beyond ∼2.0 eV. This work, along with electron scattering and theoretical data, allowed us also to identify the energies and symmetry assignments of the negative ion states of SF 6 below ∼15 eV.