Electrostatic Probe Measurements Research Articles

In Situ Fourier Transform Infrared Measurements of Si Surface and Bulk Plasmas in Cl2/O2 and HBr/O2 Electron Cyclotron Resonance Plasma Etching: Influence of Oxygen on Reaction Products

In situ Fourier transform infrared (FTIR) absorption spectroscopy, electrostatic probe measurements and optical emission spectroscopy have been used to investigate reaction products during Si etching in HBr/O2 electron cyclotron resonance plasmas, in comparison with the results obtained in Cl2/O2 plasmas. In HBr/O2 plasmas, the plasma parameters were found to be almost constant within the range of the percentage of O2 gas flow rate to total gas flow rate of 0–10% by electrostatic probe measurements. The ratio of emission intensity of O atom to that of Br atom during Si etching was almost the same as that during SiO2 etching, while the ratio of emission intensity of O atom to that of Cl atom during Si etching was much lower than that during SiO2 etching. In FTIR absorption spectra, silicon bromides SiBrx (x=1–4) were not detected in the gas phase during Si etching in HBr/O2 plasmas at the present level of detection. A chemical shift of the position of a peak related to silicon oxides was observed, indicating the existence of silicon oxybromides on the Si surface. On the Si surface, FTIR absorption spectra revealed asymmetric Si–O stretching vibrational mode after Si etching even in pure HBr plasmas. Thus, Si etching mechanisms in HBr/O2 plasmas were considered to be different from those in Cl2/O2 plasmas.

Using the λ function to evaluate probe measurements of charged dielectric surfaces

The use of Pedersen's /spl lambda/ function to evaluate electrostatic probe measurements of charged dielectric surfaces is demonstrated. With a knowledge of the probe /spl lambda/ function, the procedure by which this function is employed is developed, and thereafter applied to a set of experimental measurements available in the literature. The values of surface charge density derived are in good agreement with the published data. Through this field-theoretical approach, it is readily shown that areas of charge remote from the probe location can produce a major part of the probe signal. If a circuit-theory approach were adopted to analyze such probe measurements, then as the held features of the probe response cannot be taken into account, a serious misinterpretation of the measurements could arise.

Mass spectrometric and electrostatic probe measurements of N2/O2 plasma flow

Plasma wind tunnels are used at the Laboratoire d'Aerothermique at Meudon to simulate the different parameters of the gas surrounding the surface of space vehicles during hypersonic flight in the upper atmosphere. In the present work, mass spectrometric and double electrostatic probe measurements in a stagnation point are performed in N2/O2 plasmas. Axial distributions of electron density and temperature are obtained from the fit between experimental data and Laframboise expression for the double cylindrical probe current. Neutral and ion distributions are measured by mass analysis for different axial positions, and are then compared with a chemical model for air, in order to evaluate the dominant reactions in the plasma flow.

Influence of substrate electrical bias on the growth of GaN in plasma-assisted epitaxy

A sample bias on the order of −15 V arises during electron cyclotron resonance plasma-assisted epitaxy of GaN on insulating substrates. In contrast, conducting substrates enable growth under zero or positive bias conditions. Surface morphology of GaN/Si(111) is progressively smoother with increasing bias (−10 to +10 V) for a microwave power of 30 W. Emission spectroscopy of the plasma suggests that both N and N+2 are produced from collisions involving N*2 and that for low power (10 W), the N and N+2 production is limited by the N*2 abundance. In contrast, at higher power (50 W), ion and atom production appears limited by the electron collision frequency. Electrostatic probe measurements near the growth stage indicate that the ion energy has a minimum of about 6 eV, attained at low plasma power or at medium power (30 W) with a positive substrate bias. Mg-doped films produced at 10 W and zero bias are highly resistive. p-n junction diodes formed by Si-doped GaN grown on Mg-doped GaN on p-type Si are operated at relatively low current densities of 100 A cm−2 and emit light near 2.5 eV at room temperature.

Multicusp Electron-Cyclotron-Resonance Plasma Source Working with Microwaves Radially Injected through an Annular Slit

A new-type electron-cyclotron-resonance (ECR) plasma source has been developed for materials processing. The reactor employed magnetic multicusp fields and microwaves radially injected through an annular slit; this configuration yielded stable, uniform discharges without contamination of the microwave entrance window by sputtered particles. Electrostatic probe and optical emission measurements were made to obtain the plasma properties in Ar. These measurements showed that high-density, uniform plasmas were produced by optimizing the width of the annular slit. Moreover, the electron temperature exhibited its strong peak around the ECR zone near the chamber wall. A simple model indicates the mechanisms responsible for the plasma uniformity obtained: the plasma was dominantly produced around the ECR zone, and then diffused preferentially toward the center of the chamber because of strong magnetic fields generated near the wall surface.

Translated from Nensho no Kagaku to Gijutsu, 1, 51-57 (1992) Electrostatic Probe Measurement to Explore Local Configuration of a High Intensity Turbulent Premixed Flame

Abstract The present study has been performed to explore the detailed configuration of the local reaction zone of a high intensity turbulent premixed flame by using a micro-electrostatic probe of two identical sensors. The local reaction zone configuration is shown to be determined by analyzing the ion current fluctuations. The radius of the local reaction zone curvature convex toward the unbumed mixlure is larger than that convex toward the burned gas. The radii of the local reaction zone curvature convex toward unburned mixture are distributed over a wider range than those convex toward burned gas. The frequency of the larger radius of the local reaction zone curvature increases in the downstream region. Therefore, the mean radius of the local reaction zone curvature in the downstream region is larger than that in the upstream region.

A modified theory for electrostatic probe measurements of particle mass flows in dense gas-solid suspensions

Measurements of mass flows of a dense gas-solid suspension have led to a modification of the electrostatic probe theory. Previous ball probe theory based on dilute gas-solid suspensions has been extended to account for the effects of multiple scattering and sliding when applied to a dense gas-solid suspension. The validation of the theory was shown by the experimental results.

A Fundamental Study of Electrostatic Probe Measurements to Explore the Structure of Turbulent Premixed Flames. 2nd Report. Dependence of the Characteristics of Ion Current on the Path of Curved Flames.

It is well known that the characteristics of ion current depend on the flame configuration and movement. Therefore, it is expected that the flame configuration can be examined by analyzing the ion current record. In the present study, an attempt has been made to elucidate the dependence of the characteristics of ion current on the local flame curvature and its path. It is shown that even though the local flame curvature is constant, the ion current changes its profile significantly as the flame path changes. As the angle between the flame front and the probe axis increases, the maximum ion current decreases and the half value period increases. As the distance from the center of flame curvature to the midpoint of a probe sensor increases, the half value period increases.

A fundamental study of electrostatic probe measurements to explore the microstructure of turbulent premixed flames. 1st Report. Effects of the curvature and path of the local flame front on ion current fluctuations.

In order to examine the structure of a high-intensity turbulent premixed flame to a further extent, an attempt has been made to examine the dependence of the characteristics of ion current on the flame configuration, i.e., the local flame curvature. When the curvature is smaller than the critical value, the maximum value of the ion current decreases and the half value period of the ion current increases as the flame curvature decreases. Even though the local flame curvature is constant, the ion current fluctuation changes its shape significantly as the flame path across the probe changes.

Cylindrical magnetron discharges. I. Current-voltage characteristics for dc- and rf-driven discharge sources

Direct current magnetron discharge sources are often characterized by current-voltage characteristics of the form I∝V n where n is typically in the range from 4 to 10. Similar I-V characteristics are found for dc hollow cathode discharges where the cathode configuration effectively provides electrostatic confinement of the primary electrons. Therefore, by analogy, it has been suggested that the exponent n provides an index to the effectiveness of the magnetic electron confinement in a magnetron discharge. When magnetron discharge sources are driven at rf frequencies, the I-V characteristics typically yield n values in the range 1–3. We have examined the I-V characteristics of cylindrical-post magnetron discharge sources of various diameters driven dc and at rf frequencies of 1.8 and 13.56 MHz. The rf-driven discharges yielded n values which, in most cases, were less than 2.5. Electrostatic probe measurements of the interelectrode voltage distribution showed that the low n values, that is, poor confinement, could be explained by the effect of the magnetic field on the electron transport during that portion of the rf cycle when the post electrode is serving as the anode.

Theory of H− formation in a weakly collisional plasma

A kinetic plasma model for the formation of negative hydrogen ions is developed, with particular emphasis on conditions prevailing in the NIBLI experiment [Nucl. Instrum. Methods A 243, 255 (1986)]. The overall picture of the plasma in the discharge and values of various parameters have been taken from experimental data, notably a series of electrostatic probe measurements. Physically reasonable electron and ion distributions have been assumed. The magnetic field has a mirror inhomogeneity, and analysis of the quasineutral steady states of isotropic ions with electrons having high perpendicular energy, due to gyroresonance, shows that the plasma is divided into two compartments, one with energetic electrons where vibrationally excited hydrogen molecules can be produced, the other with low-energy electrons where negative ions can be produced and maintained. The mutual interaction between the electric field necessary for quasineutrality and the H− formation from electrons and vibrationally excited hydrogen molecules has been studied. The position is determined as a function of the potential by solving an integrodifferential equation. Quasineutral solutions exist only for a limited range of position and potential, which may be related to transitions between subsonic and supersonic motion. Substantial produced fluxes of 10–100 mA/cm2 of H− are found. The influence of various factors on the flux, the magnitude of the potential, and the size of the structure is discussed, as well as a possible autocatalytic effect from the reaction-induced electric field, and the extraction of the negative ions without simultaneous depletion of the plasma in which they are formed.

Far-forward and forward CW. CO2 laser scattering measurements of ion-acoustic waves in a quiescent plasma

Far-forward and forward collective light scattering measurements of externally launched ion-acoustic waves in a low density argon plasma column have been performed with a c.w. CO2 laser. The scattering processes taking place are described theoretically by the same general formalism. Wave dispersive and damping properties are studied consistently from 2 to 200 cm-1. Plasma parameters are deduced and compared to electrostatic probe and antenna measurements. It is found that high frequency wave properties are erroneously measured with a grid antenna.

Electrostatic Probe Measurements in the Glow Discharge Plasma of a D. C. Magnetron Sputtering System

AbstractThe characteristics of the plasma surrounding the substrates in a planar magnetron sputtering system with a graphite target have been investigated by electrostatic probe measurements. The behaviour of the ion density ni and the electron temperature Te, determining the ion flux that can be extracted by the substrate, with the variation of the basic system parameters, has been studied.

Study of Intense Electron Beams Produced by High-Voltage Pulsed Glow Discharges

We report the generation of high-current-density (20 A/cm2) pulsed electron beams from high-voltage (48-100 kV) glow discharges using cathodes 7.5 cm in diameter. The pulse duration was determined by the energy of the pulse generator and varied between 0.2 μs and several microseconds, depending on the discharge current. The largest electron beam current (900 A) was obtained with an oxidized aluminum cathode in a helium-oxygen atmosphere. An oxidized magnesium cathode produced similar results, and a molybdenum cathode operated at considerably lower currents. A small-diameter (<1 mm) well-collimated beam of energetic electrons of very high current density (>1 kA/cm2) was also observed to develop in the center of the discharge. Electrostatic probe measurements show that the negative glow plasma density and the electron beam current have a similar spatial distribution. Electron temperatures of 1-1.5 eV were measured at 7 cm from the cathode. The plasma density (8.5 · 1011 cm-3 at 450 A) was found to depend linearly on the discharge current. In discharges at high currents a denser and higher temperature plasma region was observed to develop at approximately 20 cm from the cathode. We have modeled the process of electron beam generation and predicted the energy distribution of the electron beam. More than 95 percent of the electron beam energy is calculated to be within 10 percent of that corresponding to the discharge voltage.

Implantation and replacement of hydrogen isotopes in 304 stainless steel vacuum wall under RF discharge and RF-DC glow discharge

The saturation and replacement of hydrogen isotopes implanted into a 304 stainless steel vacuum wall at 300 K under RF discharge with and without DC bias potential on an RF antenna have been studied using partial pressure measurements of desorbed isotopes. The energy of ions hitting the wall was estimated to be 30–90 eV from electrostatic probe measurement for RF discharge plasmas. Nearly 90% of the desorbed gas in the isotopic exchange process was HD molecules. The amount of desorbed gas showed a tendency to saturate at a fluence of 2.3 × 10 16 cm −2. The desorption rate can be expressed by an inverse-exponential function with time; a two-component function is normally observed. The time constant of each component is evaluated by introducing an effective trapping coefficient.

Performance of a cw double electric discharge for supersonic CO lasers

The results of an experimental investigation of a cw double discharge in supersonic CO mixtures are reported. Stable discharges in CO/N2 and CO/Ar mixtures, with a maximum energy loading of 0.5 eV/CO molecule, were achieved in a small-scale continuous-flow supersonic channel. Detailed measurements of the discharge characteristics were performed, including electrostatic probe measurements of floating potential and electron number density and spectroscopic measurements of the CO vibrational population distributions. The results of these measurements indicate that the vibrational excitation efficiency of the discharge is approximately 60%, for moderate levels of main discharge current. These experiments, on a small scale, demonstrate that the double-discharge scheme provides adequate vibrational energy loading for efficient CO laser operation under cw supersonic flow conditions.

Probe Measurement in a High-density lonized Gas

Effects of probe temperature and probe material on electrostatic probe measurements in a partially-ionized high-density plasma were investigated. Probe measurements were performed in an atmospheric-pressure argon arc plasma and also in an argon arc plasma in which a small amount of hydrogen was added. Cylindrical probes of tungsten, rhenium and molybdenum were used at various temperatures. The work functions of these probes in atmospheric-pressure gases were estimated by the thermionic emission method. Further, ion saturation current to a cylindrical probe was calculated taking account of the local properties of the plasma. The ion current increases as the probe temperature rises but its increment is not large. The floating potential shifts in the negative direction at higher probe temperatures. This potential depends also on the material of the probe. These results are explained by the thermo-hydrodynamic effect and the variation in the work function of the probe.

Solar activity changes in the electron temperature at 1000‐km altitude from the Langmuir probe measurements on Isis 1 and Explorer 22 satellites

Electrostatic probe measurements of electron temperature from the Isis 1 satellite for the equinox season of high solar activity years 1969 and 1970 are analyzed for the 1000‐km altitude. These results are then compared with the Explorer 22 satellite measurements of electron temperature for the years 1965–1967. Large solar activity changes are found to occur in the latitudinal profiles of electron temperature during both day and night. At low and mid‐latitudes, the electron temperature increases from about 2000 to about 3500°K for the daytime and from about 800 to about 1700°K during the nighttime between low and high solar activity conditions. At high latitudes there is an increase in electron temperature by about a factor of 2 from low to high solar activity period. These solar activity changes in electron temperature are interpreted to be mainly due to the heat flux conducted down from the protonosphere, which increases with solar activity.

Caracteristiques electroniques d'un plasma cree par un faisceau d'ions acceleres

A neon plasma is created at high pressure (10–200 Torr) by an accelerated (60 MeV, 550 nA) 12C 5+ion beam. Microwave and electrostatic probe measurements and a simple kinetic model lead to a characterization of electron density, temperature and distribution function. This plasma is found to be a good simulation for nuclear reactor induced plasmas; hence it provides a quite suitable way to investigate basic phenomena in such plasmas.

Diagnostic methods for sputtering plasmas

This paper reviews the parameters that can be used to characterize glow discharge plasmas of the type used in many sputtering devices, and the methods available to measure those parameters. The review is also generally applicable to the plasmas used in ion plating and plasma-activated reactive evaporation. The objective is to provide a brief overview and a guide to the literature for thin-film specialists. The emphasis is on negative glow-type plasmas, and the diagnostic techniques of optical spectroscopy and electrostatic probes, since these methods are particularly effective for such plasmas and are relatively easy to implement in the laboratory. Guidelines are presented for a corona interpretation of absolute intensity line emission measurements in terms of the density of energetic electrons in an Ar-negative glow. Cases are described in which electrostatic probe measurements were used to investigate performance characteristics of cylindrical-post and cylindrical-hollow magnetron sputtering sources.