S. B. Radovanov

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...

Time‐resolved Balmer‐alpha emission from fast hydrogen atoms in low pressure, radio‐frequency discharges in hydrogen

Doppler‐broadened Hα emission (656.28 nm) detected from a 13.56 MHz, parallel‐plate, radio‐frequency discharge in hydrogen indicates the presence of fast excited H atoms throughout the discharge volume. Time and spatially resolved measurements of the Doppler‐broadened emission indicate that the fast H atoms are formed primarily at the surface of the powered electrode with kinetic energies exceeding 120 eV.

Ion kinetic‐energy distributions and Balmer‐alpha (Hα) excitation in Ar‐H2 radio‐frequency discharges

Excited neutrals and fast ions produced in a 13.56 MHz radio‐frequency discharge in a 90% argon −10% hydrogen gas mixture were investigated, respectively, by spatially and temporally resolved optical emission spectroscopy, and by mass‐resolved measurements of ion kinetic energy distributions at the grounded electrode. The electrical characteristics of the discharge were also measured and comparisons are made with results obtained for discharges in pure H2 under comparable conditions. Measurements of Balmer‐alpha (Hα) emission show Doppler‐broadened emission that is due to the excitation of fast atomic hydrogen neutrals formed from ion neutralization processes in the discharge. Temporally and spatially resolved emission profiles of the Hα radiation from the Ar‐H2 mixture are presented for the ‘‘slow’’ component produced predominately by electron‐impact dissociative excitation of H2, and for the ‘‘fast’’ component corresponding to energies much greater than can be derived from dissociative excitation. For t...

Ion kinetic‐energy distributions in argon rf glow discharges

Kinetic‐energy distributions have been measured for different mass‐selected ions sampled from 13.56 MHz rf glow discharges in argon inside a ‘‘GEC rf reference cell.’’ The electrode geometry of this cell produces an asymmetric discharge and the cell is operated in a pressure regime where ion‐molecule collisions in the sheath region of the discharge are significant. Ions are sampled from the side of the plasma perpendicular to the interelectrode axis using an electrostatic energy analyzer coupled to a quadrupole mass spectrometer. Kinetic‐energy distributions for Ar+, Ar2+, Ar++, and ArH+ are presented as functions of applied rf voltage, gas pressure, and distance of the mass spectrometer entrance aperture from the edge of the electrodes. The distributions obtained for the sampling orifice placed close enough to the electrodes to allow formation of a sheath in front of the orifice exhibit features similar to those observed previously when sampling ions through the grounded electrode of a parallel‐plate rea...

Studies of Ion Kinetic-Energy Distributions in the Gaseous Electronics Conference RF Reference Cell

A review is presented of kinetic-energy distribution measurements for ions striking grounded surfaces in a Gaseous Electronics Conference (GEC) rf Reference Cell. Two experimental arrangements that have been used to measure ion energies in the GEC Cell are described, and a comparison of their performance under different operating conditions is presented. Significant results from ion-energy analysis in the Reference Cell are highlighted, including evidence of effects due to surface conditions on ion sampling, verification of electrical behavior of the cell, inferences about ion-molecule reactions indicated by the shapes of measured ion kinetic-energy distributions (IEDs), and the use of measured IEDs for the validation of theoretical models. The paper concludes with a detailed study of IEDs measured for rf plasmas generated in mixtures of argon and oxygen, using both experimental arrangements.

Effect of electrode material on measured ion energy distributions in radio‐frequency discharges

Evidence is presented for a significant influence of electrode surface material and condition on the measurement of the kinetic energies of ions sampled from discharges through an orifice in the electrode. Significant differences in ion energy shifts and/or discrimination of low‐energy ions are found using aluminum and stainless‐steel electrodes in a radio‐frequency (rf) discharge cell. It is argued that the observed differences in energy shifts may be attributable in part to differences in charging of oxide layers on the electrode surface around the sampling orifice.

Kinetic-energy distributions of ions sampled from RF discharges in argon/helium gas mixtures

Summary form only given. The authors have studied the kinetic energies of ions created by RF discharges in argon/helium mixtures by sampling ions through the grounded electrode of a GEC RF Reference Cell. Ion kinetic-energy distributions (IED) of Ar/sup +/, Ar/sub 2sup +/, Ar/sup ++/, ArH/sup +/, He/sup +/, and ArHe/sup +/, as measured by an electrostatic energy analyzer with a quadrupole mass spectrometer, have been determined. The plasma conditions were as follows: pressures of 13.3 Pa or 1.33 Pa, peak-to-peak applied voltages from 200 to 500 V, helium concentrations in argon of 0 to 95%, and flow rates of 10 sccm.