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An oxygen plasma sustained at 13.56 MHz in a standardized reactor with a planar induction coil was used for biological decontamination experiments. Optical emission, mass spectrometry, Langmuir probe, and electrical measurements were applied to detection of chemical species and ion-energy and e ux analysis. These diagnostics identie ed a plasma-mode transition in the range of 13 ‐67-Pa pressure and 100 ‐330-W power to the induction coil. At higher pressure and lower power, the plasma was sustained in a dim mode (primarily by stray capacitive coupling). A primarily inductive bright mode was attained at lower pressure and higher power. The coupling mode of plasma operation was then monitored by emission spectroscopy on an analogous, scaled-down reactor for biological degradation tests. Plasmid DNA degradation efe cacies were compared in both plasma modes. DNA removal was »25% more efe cient in the inductively coupled mode than in the capacitively coupled mode at the same power. The fast degradation was attributed to synergetic mechanisms (photo- and ion-assisted etching by

In order to study the sterilization capabilities of radio frequency driven low pressure oxygen plasmas, the radiative emission was recorded at various pressures and input powers. A distinct transition from the bright mode (primarily inductively coupled) to a dim mode (primarily capacitively coupled) was observed as the pressure was increased and/or the power decreased. The data was further analyzed to estimate the electron temperature, rotational and vibrational temperatures, and various species concentrations. Based on the diffusion and rovibrational relaxation times, it is concluded that the rotational temperatures can be assumed to be in equilibrium with the translational temperature. The ions are produced “hot” and have little time to get equilibrated with the translational temperature. It is further determined that in the bright mode, which is more effective in microbe sterilization, the translational/rotational temperatures are in the 650–850 K range, the electron temperatures are low (3.5–4.5 eV), and the concentrations of atomic O and atomic metastables are at 1 order of magnitude higher than in the dim mode.

Characterization of CF4/O2/Ar inductively coupled plasmas by Fourier-transform infrared (FTIR) spectroscopy and optical emission spectroscopy (OES) in a Gaseous Electronics Conference reference cell has been carried out. Characterization was performed at three mixture compositions (80/10/10, 60/20/20, and 40/30/30), powers of 200 and 300 W and pressures between 10 and 50 mTorr. Quantitative estimates of CF4, CO, COF2, and SiF4 etch products are made via FTIR, while the OES combined with actinometry allows for qualitative characterization of conversion of CF4 to atomic C, CF, and C2, and molecular oxygen to atomic oxygen. Qualitative measurements of F density and etch products Si and SiF are also made by OES. Results are explained by a combination of electron-impact dissociation and recombination processes. In the absence of significant capacitive coupling, etch species are believed to be formed primarily by window interactions with atomic F. Rotational temperatures are estimated by both FTIR and analysis of emission spectra. The FTIR technique tends to estimate temperatures several hundred K lower than OES data due to the absorption of colder gas species outside of the plasma.

A global uncertainty and sensitivity analysis is performed for a detailed gas-phase reaction set in a CHF3 plasma. The goal of this paper is to ascertain the uncertainties in plasma reactor model results (plasma and radical densities) that originate from the uncertainties in the gas-phase chemistry database. We discuss the rates of reactions and their uncertainties. Comparisons with experimental data show that gas-phase rate uncertainties do not explain the disagreements at higher pressures (>30 mTorr). We also find that electron impact dissociation reactions of dominant neutrals are the largest sources of uncertainties. HF kinetics are also found to be critical in determining radical and feedstock gas densities. Relative ion densities are uncertain due to poor understanding of charge transfer mechanisms.

Positive ion fluxes, mean ion energies and ion energy distribution functions in low pressure CF4/Ar plasmas have been measured. The experiments were conducted in a Gaseous Electronics Conference cell using an inductively coupled plasma device powered by a 13.56 MHz radiofrequency (rf) power source. The measurements were made at 200 and 300 W of input rf power and at 10, 20, 30 and 50 mTorr gas pressures for three gas mixtures: (i) 20% CF4 : 80% Ar, (ii) 50% CF4 : 50% Ar and (iii) 80% CF4 : 20% Ar. A Langmuir probe was also used to measure plasma parameters such as ne, ni+ and electron energy distribution functions (EEDF) which were subsequently used to reconcile the mass spectrometer data. CF3+ is the most dominant fluorocarbon ion product of the plasma, followed by CF2+ and CF+. Ar+ is also detected in significant amounts with its relative flux increasing with the increase in Ar content in the gas mixture. Significant amounts of etch products, SiFx+/COF+x (x = 0−3), of the quartz window were also detected. The fluorocarbon ions are produced by direct electron impact and by ion–molecule reactions between Ar+ and CF4 as well as between CF3+ and CF4. However, the concentrations of CF2+ and CF+ are much larger than that which can be possibly produced from these two processes. The available cross-section data suggest that the direct electron impact ionization of the fragment neutrals and negative ion production by electron attachment may be responsible for the increase in the concentrations of the minor ions. F− densities, estimated by using the measured EEDF and positive ion flux data and the available cross-section data, agree well with the published experimental data.

Trifluoromethane (CHF3) is used in semiconductor plasma processing chambers to achieve high-etch selectivity of an oxide layer over a silicon substrate. Such surface etching is governed by the ion and molecule fluxes near the surface, the concentrations of which are dependent upon species interactions in and their transport through the plasma. In order to assist in the interpretation of ion flux measurements and to provide fundamental data required for plasma modeling, we report the first total cross sections for significant ion-molecule reactions occurring in CHF3 discharges. The reactions studied include collision-induced dissociation for CF3+ on CHF3, dissociative charge transfer for CF3+ and F+ on CHF3, and electron detachment from F− on CHF3. Collision energies range from a few to a few hundred electron volts. In addition, ion-flux energy distributions and relative ion intensities have been measured and are presented for dc townsend discharges with E/N values ranging from 5×10−18 to 25×10−18 V m2 [5 to 25 kTd]. The townsend discharge results are qualitatively interpreted using the cross-section measurements.

An inductively coupled Gaseous Electronics Conference (GEC) cell with modified viewing ports has been used to measure in situ absorption in CF4 plasmas via Fourier transform infrared spectroscopy, and the results compared to those obtained in a standard viewport configuration. The viewing ports were modified so that the window boundary is inside, rather than outside, of the GEC cell. Because the absorption obtained is a line of sight integrated absorption, measurements made represent an averaging of absorbing species inside and outside of the plasma. This modification is made to reduce this spatial averaging and thus allow a more accurate estimation of neutral species concentrations and temperatures within the plasmas. By reducing this path length, we find that the apparent CF4 consumption increases from 65% to 95% and the apparent vibrational temperature of CF4 rises by 50–75 K. The apparent fraction of etch product SiF4 decreases from 4% to 2%. The data suggest that these density changes may be due to s...

Electron and ion energy distribution functions and other plasma parameters such as plasma potential (Vp), electron temperature (Te) and electron and ion number densities (ne and ni) in low-pressure CF4 plasmas have been measured. The experiments were conducted in a GEC cell using an inductively coupled plasma device powered by a 13.56 MHz radiofrequency (rf) power source. The measurements were made at 300 W of input rf power at 10, 30 and 50 mTorr gas pressures. Langmuir probe measurements suggest that ne, ni and Vp remain constant over 60% of the central electrode area, beyond which they decrease. Within the limits of experimental error (±0.25 eV), Te remains nearly constant over the electrode area and peaks towards the electrode edge before falling rapidly. Te and Vp increase with a decrease in pressure. ne and ni are not affected as significantly as Te or Vp by variation in the gas pressure. The electron energy distribution function measurements indicate a highly non-Maxwellian plasma. CF3+ is the most dominant ion product of the plasma, followed by CF2+ and CF+. Significant amounts of etch products, SiFx/COFx(x = 0-3), of the quartz window were also detected. The concentrations of CF2+ and CF+ are much larger than that is possible from direct electron impact ionization of the parent gas. The cross-section data suggest that the direct electron impact ionization of fragment neutrals and negative ion production by electron attachment may be responsible for increase of the minor ions.

Fourier transform infrared spectroscopy (FTIR) has been used to characterize inductively coupled CF4 plasmas in a GEC reference cell in situ. In examining these FTIR spectra, several assumptions and approximations of FTIR analysis are addressed. This includes the density dependence of cross-sections, non-linear effects in the addition of overlapping bands and the effect of spatial variations in density and temperature. This analysis demonstrates that temperatures extracted from FTIR spectra may provide a poor estimate of the true neutral plasma temperature. The FTIR spectra are dominated by unreacted CF4, accounting for 40-60% of the gas products. The amount of CF4 consumption is found to have a marked dependence on power, and is nearly independent of pressure in the range of 10-50 mTorr. Small amounts of C2F6 are observed at low power. Also observed are etching products from the quartz window - SiF4, COF2 and CO - which occur in approximately equal ratios and together account for 17-19% of the gas at 300 W and 6-9% of the gas at 100 W. The concentrations of these species are nearly independent of pressure. CFx radicals are below the detection limit of this apparatus (~1013 cm-3).

Recently it has been recognized that the neutral gas in inductively coupled plasma reactors heats up significantly during processing. The resulting gas density variations across the reactor affect reaction rates, radical densities, plasma characteristics, and uniformity within the reactor. A self-consistent model that couples the plasma generation and transport to the gas flow and heating has been developed and used to study CF4 discharges. A Langmuir probe has been used to measure radial profiles of electron density and temperature. The model predictions agree well with the experimental results. As a result of these comparisons along with the poorer performance of the model without the gas-plasma coupling, the importance of gas heating in plasma processing has been verified.

Absolute fluxes and energy distributions of ions in inductively coupled plasmas of Ar, CHF3/Ar, and CHF3/Ar/O2 have been measured. These plasmas were generated in a Gaseous Electronics Conference (GEC) cell modified for inductive coupling at pressures 10-50 mTorr and 100-300 W of 13.56 MHz radio frequency (RF) power in various feedgas mixtures. In pure Ar plasmas, the Ar(+) flux increases linearly with pressure as well as RF-power. Total ion flux in CHF3 mixtures decreases with increase in pressure and also CHF3 concentration. Relative ion fluxes observed in the present studies are analyzed with the help of available cross sections for electron impact ionization and charge-exchange ion-molecule reactions. Measurements of plasma potential, electron and ion number densities, electron energy distribution function, and mean electron energy have also been made in the center of the plasma with a RF compensated Langmuir probe. Plasma potential values are compared with the mean ion energies determined from the measured ion energy distributions and are consistent. Electron temperature, plasma potential, and mean ion energy vary inversely with pressure, but increase with CHF3 content in the mixture.

Absolute cross sections have been measured for reactants typically found in carbon tetrafluoride (CF(4)) discharges for collision energies below a few hundred electron volts. The reactions investigated include collision-induced dissociation and dissociative electron transfer reactions for CF(+)(3) and F(+) colliding with CF(4), and collisional electron detachment for F(-) colliding with CF4. Also presented are measurements of energies and relative intensities of ions generated in dc Townsend CF4 discharges with E/N values ranging from 4 x 10(-18) V m(2) to 25 x 10(-18) V m(2) [4 to 25 kTd]. Ion energy and ion intensity data for the Townsend discharges are analyzed in light of the measured cross sections.

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...

Cross-sections, appearance energies and peak energies at which S − ion intensities are maximal have been measured for electron attachment to OCS as a function of electron impact energy in the energy range 0–20 eV using a time-of-flight mass spectrometer in a crossed-beams collision geometry. Maximum intensities of formation of S − were observed at four electron impact energies of 1.4, 4.7, 7.0, and 10.2 eV with an accuracy to ± 0.25 eV. The cross-sections measured at these energies were 2.6 × 10 −17 , 1.5 × 10 −19 , 1.8 × 10 −19 , and 0.4 × 10 −19 cm 2 respectively, with an uncertainty of about ± 15%. From appearance energies of various resonance processes for S − formation and by using thermochemical data we have been able to identify various dissociative electron attachment channels of OCS. Cross-section values for three additional dissociative channels for the formation of S − and time-of-flight spectra representing the kinetic energies of these ions are reported for the first time.

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 (

First measurements on the ionization cross sections for the production of and ( + ) ions from by electron impact are reported for an electron impact energy range of threshold energies to 1 keV and for at 100 eV. These measurements were carried out in a crossed-beams apparatus using the pulsed technique and the partial pressure method to determine the absolute cross sections. Total ionization cross sections at each electron impact energy were obtained by numerical summation of the respective partial ionization cross sections.

Normalized values of cross sections for the production of ions by electron impact on N(sub 2)O and NO have been obtained by utilizing the relative flow technique.

The present paper describes the design of a time-of-flight mass spectrometer (TOFMS) in which the single flight tube of a conventional TOFMS has been replaced by several cylindrical electrostatic lenses in tandem. By a judicious choice of voltages on these lenses, an improved TOFMS has been realized which has a superior mass and energy resolution, shorter flight lengths, excellent signal-to-noise ratio and less stringent requirements on the bias voltages.

Neutral temperatures in inductively coupled CF4/O2/Ar mixture plasmas have been characterized by fitting the rotational envelope of emission spectra in a gaseous electronics conference reference cell. CF and CO are found to present different rotational temperatures with opposite trends with respect to pressure. It is proposed that CF is created as a rotationally and translationally hot molecule due to CF4 dissociation and the disparity in temperatures and temperature trend is indicative of incomplete equilibration of the CF with other neutral species in the plasma. This may have important consequences from the standpoint of understanding neutral reaction chemistries.

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...

First measurements of cross sections for the formation of negative ions by electron attachment to SiF4 and CF4 are reported for an electron impact energy range of 0 to 50 eV. The energies at which the various ions appear and the positions at which the ionization efficiency curves peak have been obtained and compared with previous measurements. Thermochemical data have been used to predict and identify the various channels of dissociation. Cross sections for the production of ion pairs through the process of polar dissociation have also been measured.

Summary form only given. In this paper we present ion kinetic-energy distributions (IEDs), mean energies, and relative abundances of CF/sub 3//sup +/, CF/sub 2//sup +/, CF/sup +/, CHF/sub 2//sup +/, CH/sup +/, C/sup +/, and H/sup +/ ions produced in DC Townsend discharges in pure CHF/sub 3/. The discharges are generated between two circular parallel-plate electrodes at electric field-to-gas density ratios (E/N) ranging from 5/spl times/10/sup -18/ Vm/sup 2/ to 25/spl times/ 10/sup -18/ Vm/sup 2/ (5 to 25 kTd). A stable discharge could not be attained below 4/spl times/10/sup -18/ Vm/sup 2/ due to the electronegative nature of CHF/sub 3/. Ions sampled from the discharge through a small orifice in the center of the grounded electrode were energy and mass analyzed by a 45/spl deg/ electrostatic energy analyzer attached to a quadrupole mass spectrometer. The present apparatus is equipped with ion optics that allow measurements of ion energies up to 1000 eV.

Low-temperature or cold plasmas have been shown to be effective for the sterilization of sensitive medical devices and electronic equipment. Low-temperature plasma sterilization procedures possess certain advantages over other protocols such as ethylene oxide, gamma radiation, and heat due to the use of inexpensive reagents, the insignificant environmental impacts and the low energy requirements. In addition, plasmas may also be more efficacious in the removal of robust microorganisms due to their higher chemical reactivity. Together, these attributes render cold plasma sterilization as ideal for the surface decontamination requirements for NASA Planetary Protection. Hence, the work described in this study involves the construction, characterization, and application of an inductively-coupled, RF powered oxygen (O2) plasma.

The transport of positive and negative ions plays an important role in the initiation and behavior of discharges in gaseous dielectrics. in many cases, the identities, intensities, and kinetic energies of ions are determined by ion-molecule collisions experienced by ions while they are accelerated through the discharge. to help delineate the role of various collisional processes, such as charge-exchange collisions, collisional detachment, and ion conversion, we have measured the kinetic-energy distributions (KEDs) of positive and negative ions formed in dc Townsend discharges generated in O2 and SF6 at high electric field-to-gas density ratios (E/N). the relative abundances and mean energies of the ions are obtained from these measurements, and the effective cross sections for the ion-molecule reactions, in some cases, may be calculated. the availability of ion-molecule collision cross sections for the negative ions formed in O2 and SF6 enable a reasonable understanding of the KED data. However, attempts to analyze the positive ion KED data for these two gases highlight the lack of fundamental ion-molecule cross section data for positive ions formed in these discharges.

Technological advancement in the microelectronics industry requires an understanding of the physical and chemical processes occurring in plasmas of fluorocarbon gases used as etchants to optimize various operating parameters. This paper reports data on electron number density and temperature, electron energy distribution function (EEDF), and plasma potential measured using Langmuir probe in inductively coupled plasmas of CF 4 -Ar mixtures of various compositions. The probe data were recorded at several radial positions providing radial profiles of these plasma parameters at 10-50 mTorr and 200 and 300 W of radio frequency (rf) power. The measurements indicate that the electron and ion number densities increase with power; the plasma potential and electron temperature decrease with an increase in pressure, and they depend weakly on rf power. The radial profiles show that the electron and ion number densities and the plasma potential peak at the center of the plasma and drop toward the wall. Within the experimental error, the electron temperature is nearly constant in the electrode region and decreases toward the wall. As the CF 4 content increases in the mixture, the electron temperature increases hut the electron density decreases. At low CF 4 concentration, the electron and ion densities increase with pressure, but the densities are nearly independent of pressures at high CF 4 concentrations. The EEDFs have a characteristic drop near the low energy end at all pressures and powers and their shapes represent a non-Maxwellian plasma.

During oxide etch processes, buildup of fluorocarbon residues on reactor sidewalls can cause run-to-run drift and will necessitate time for conditioning and cleaning of the reactor. Various measurements in CF4 and Ar plasmas are made in an attempt to identify a metric useable to indicate the chamber condition. Mass spectrometry and Langmuir probe data show that the buildup of fluorocarbon films on the reactor surface causes a decrease in plasma floating potential, plasma potential, and ion energy in argon plasmas. This change in floating potential is also observed in CF4 plasma operation, and occurs primarily during the first hour and a half of plasma operation. A slight rise in electron density is also observed in the argon plasmas. Because the change is seen in an argon plasma, it is indicative of altered physical, not chemical, plasma-surface interactions. Specifically, the insulating films deposited on metal surfaces alter the electromagnetic fields seen by the plasma, affecting various parameters inc...

Water is present in the atmospheres of 6 of the 9 planets. Cross section values for the direct and partial ionization of H2O by electron impact have been measured and compared with previously published data. The present measurements have been carried out from thresholds to 1 KeV by utilizing a crossed electron beam and molecular beam collision geometry and an improved ion extraction technique.

Experiments were performed to measure, by electron impact, appearance potentials and the cross sections for ionization, dissociative ionization, and electron attachment for H2S. Results are presented, and discussed individually, for both positive and negative ions. A schematic diagram of the experimental setup is included.

A crossed electron beam-molecular beam collision geometry is used to measure cross sections for the production of positive ions by electron impact on NH3 and CS2. Ionization cross-section data for NH3 and the values of various cross sections are presented, as well as ionization efficiency curves for CS2. Considerable differences are found between the various results on NH3. The present values are close to the data of Djuric et al. (1981). The semiempirical calculations of Hare and Meath (1987) differ considerably in the absolute values of cross sections. Discrepancies were observed in comparisons of cross sections of other fragment ions resulting from the ionization and dissociate ionization of NH3.

Relative differential cross sections are presented for elastic scattering of electrons by sodium, potassium and rubidium atoms in the energy range from 150 to 500 eV. The data were obtained at angular intervals of 10 degrees from 30 degrees to 120 degrees . The cross section curves show a minimum around 100 degrees for sodium and potassium and 80 degrees for rubidium, the depth of the minimum decreasing with increasing energy. A comparison with previous experimental data and various theoretical models indicates the dominance of static and absorption potentials in the elastic scattering channel and the weak binding of valence electrons in the alkali atoms.