Axial emission profiles and apparent secondary electron yield in abnormal glow discharges in argon

This paper reports investigations of argon glow discharges established between flat disk electrodes, at pressure × electrode separation values between 45 Pa cm and 150 Pa cm. Parallel to the experimental studies the discharge is also described by a self-consistent hybrid model. The model uses as input data the measured electrical characteristics, this way making it possible to determine the apparent secondary electron emission coefficient. The model is verified through comparison of the measured and calculated spatial profiles of light emission, which are in good agreement for a wide range of conditions in the abnormal glow mode. Additionally, we investigate the dependence of the field reversal position on the discharge conditions and test the usual assumption that the position of the peak of emission closely coincides with the cathode fall - negative glow boundary. Received 21 May 2002 Published online 24 September 2002     

Ion energies at the cathode of the DC planar magnetron sputtering discharge

The energy distribution of the ions striking the cathode of the dc planar magnetron system was measured over a range of the typical sputtering conditions (magnetic field of 0.07–0.13 T, argon pressure of 0.01–10 Pa, discharge voltage of 250–600 V). The results obtained allow us to conclude that the major part of the incident ion flux originates in the cathode fall region. The theoretical model developed in terms of mobility theory makes it possible to evaluate the cathode fall voltage and its dependence on the sputtering conditions. It was found that the normalized integral form of the incident ions, energy spectrum is practically independent of the sputtering discharge parameters.     

Laser photochemical etching of silicon

Argon laser induced chemical etching of single crystal silicon with chlorine is studied. Etch rates are determined as a function of gas pressure, crystal orientation, laser power and wavelength. Analysis of gas phase and surface products by Fourier transform IR and X-ray photoelectron spectroscopy are used to probe the reaction mechanism. Contrary to previous reports, no thermally enhanced etch rate is observed for Si (111) and the presence of oxide on the surface is found to inhibit etching even at high laser power.     

Self-organized filaments in dielectric barrier glow discharges

The filamentation of a plasma created by a dielectric barrier discharge in conditions of low pd products (i.e., Townsend breakdown and not streamer breakdown) is investigated both experimentally and with a two-dimensional numerical discharge model. Complex stationary and dynamical domains and filaments are observed experimentally. Some of the properties of these systems are reproduced by the model     

High-frequency breakdown and paschen law

In the present paper an attempt has been made to draw theoretically a correlation between the well-known Paschen curve and the high-frequency breakdown characteristic of a gas device by interpreting electron mean free path in terms of the frequency of the applied field. The analytical high-frequency breakdown characteristic, so obtained, agree fairly well with the experimental results.     

Surface-science aspects of plasma-assisted etching

Plasma-assisted etching methods have been used in the manufacture of integrated circuits for more than 10 years and yet the surface-science aspects of this technology are poorly understood. The chemistry must be such that the reactive species generated in the plasma react with the surface being etched to form a volatile product. The chemistry is usually dominated by atoms, molecular radicals and low-energy (20–500 eV) positive ions. In microstructure fabrication, the positive ions are accelerated from the plasma towards the etched surface arriving essentially at normal incidence. Thus, the bottom surface of a very small feature being etched is subjected to both energetic ions and reactive neutral species, whereas the sidewalls of the feature are exposed to reactive neutral species only. The role of the energetic ions is primarily to accelerate the reaction between the neutral species and the etched surface (i.e., accelerate the etch rate), thereby reducing the steady-state top-monolayer coverage of the etching species on the etched surface. On the sidewalls, however, the reacting-species coverage is a saturation coverage. The present understanding of some of the surface-science aspects of this complex environment will be summarized, often using the Si-F system as an example, and some phenomena which are not well understood will be described.     

A time-of-flight study on the nanosecond laser induced etching of Cu with Cl2 at 308 nm

Chemical etching of Cu is studied using Cl₂ and a ns pulsed UV laser at 308 nm. At Cl₂ pressures in the range of 10^–6–10^–4mbar and a laser fluence up to 0.82 J/cm² the velocity distributions of the ejected species are determined. CuCl and Cu₃Cl₃ are the main products. The time-of-flight spectra of these particles can be fitted with Maxwell-Boltzmann distributions at high temperatures viz. 1750<T<6000 K. Starting with a clean Cu sample the system evolves to a steady state situation in which a considerable amount of Cl has diffused into the bulk. The chlorinated Cu layer has a pronounced influence on the coupling of the laser beam into the substrate, thereby determining the amount of particles desorbed and their time-of-flight distributions. A model is presented to explain the results.     

Properties and current-voltage characteristics of discharges in waveguide gas lasers

The paper deals with the properties andI-V characteristics of discharges in narrow capillaries used, for example, for He−Ne waveguide lasers. It has been observed that discharges in He−Ne waveguide lasers are unstable because of the strongly falling characteristic. A theory is presented which assumes that at low currents wall charges restrict the positive column to a narrow plasma channel and are the main reason for the observed falling characteristic. A numerical evaluation for helium gives results which agree well with experimental data.     

Radiation of pulsed and glow discharges in CCl4

The radiation of a pulsed-periodic discharge in CCl₄ has been investigated. Its spectrum is found to differ considerably from the spectrum of the glow discharge. It is found that ‖60% of the energy from the 215–650 nm region falls in the UV spectrum. Moscow Physicotechnical Institute, 9, Institutskii Per., Dolgoprudnyi, 141701, Moscow Region, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 302–305, March–April, 1998.     

Electron ionization rate in III–V ternary semiconductors

Theoretical calculations are presented for the ionization rate of electrons in III–V ternary semiconductor compounds considering alloy scattering and carrier-carrier interaction, in addition to optical phonon scattering and ionization scattering. However, alloy scattering is found to be a weak interaction. Fairly good agreement is obtained for Ga_1–x In _x As withx=0.14 and 0.53 with the experimental results and for Ga_0.5 Al_0.5 As with the existing theoretical result which used an indirect method. The alloy scattering potential has been taken in the form of energy band-gap difference. The calculations can be used for any ternary semi-conductor.     

Experiments on plane overvolted discharges in N2, and comparison with calculations

In this paper experimental and theoretical results for the development of overvolted discharges in N₂ between a plane-parallel gap are described. By suitable initial conditions laterally extended (plane) discharges can be realized instead of the usually observed filamentary streamers. In this discharges which were large in diameter compared with the gap distance, a quantitative comparison of the experimental results with one dimensional calculations is possible. It is shown that the discharges can be described by the well-known build-up theory of instationary discharges but an additional far-reaching electron generating mechanism (gas ionizing radiation) must be included. The development of our discharges is compared with that of the streamer.     

Studies on the applicability of slit metal vessels in fast theta-pinch discharges

The applicability of slit metal vessels for fast magnetic plasma compression was experimentally investigated. The results were encouraging for small diameter vessels when the time needed for plasma compression was not significantly longer than the time for the development of the limiting shortcircuiting arcs across the slit gaps. Applicability of large diameter slit metal vessels was only achieved after superposition of magnetic bias fields. The limiting effects were identified and the condition for the necessary bias field is presented. It is shown further that satisfactory efficiencies of shockwave heating in slit metal vessels can be achieved only if apart from superposition of bias fields the width of the metal strips is reduced to the order of centimeter.     

On the homogeneization of transverse gas discharges by preionization

Detailed data of the minimum preionization electron density (MPED)n ₀ necessary to initiate a homogeneous discharge mode in transverse gas discharges are computed. An upper limit for the inductance of the discharge circuit is set by the power balance during breakdown. The results are presented as functions of generalized parameters. Applicability of the computations is proved by experimental observations.     

缩比间隙中辉光放电相似性的初步研究

为了研究缩比实验在气体放电中的有效性, 对缩比间隙中的低气压氩气放电进行了数值模拟. 根据气体放电相似性的猜想, 如果间隙气压p和间隙距离d的乘积为常量, 即p₁d₁=p₂d₂, 并且约化电场E/p 在两个间隙中的空间分布相同, 那么这两个放电间隙的放电特性存在相似性. 数值模拟中设置三个缩比间隙: 气隙A的长度为30 mm, 气压为1 Torr (1 Torr=133.322 Pa); 气隙B的长度为15 mm, 气压为2 Torr; 气隙C的长度为10 mm, 气压为3 Torr. 仿真结果表明, 三个间隙均为辉光放电, 并存在明显的阴极位降区. 间隙A, B, C 的阴极位降区的厚度d_C分别为2.71, 1.35和0.87 mm, 相对应的pd值几乎相同, 即pd_C≈2.70 Torr·mm. 这与氩气辉光放电Paschen曲线最低点(pd≈2.86 Torr·mm)相近. 缩比间隙的放电参数的特性(如工作电压、电场、电流密度、电子密度和离子密度的沿“空间”px的分布)的数值计算结果与放电相似性猜想所预计的结果一致. 所以, 可以认为放电相似性猜想适用于低气压氩气缩比间隙的辉光放电. 关键词： 放电相似性 辉光放电 缩比间隙     

CO2-laser gas discharges in narrow gaps

We have studied RF discharges as excitation mechanisms for distributed feedback (DFB) CO₂ lasers. For CO₂ laser plasmas the reduced electric fieldE/N has to be in a well-defined range. The reduced electric fieldsE/N of gas discharges in the narrow gaps with widths of the order of 100 m required for DFB are considerably above this range. In order to study the feasibility of these RF-excited discharges for DFB CO₂ lasers we have measured the electron temperatureT _e in their plasmas. From helium-line-intensity ratios we have deduced a lower limit of the electron temperatureT _e of 4eV. The observed high intensities of bands of singly ionized nitrogen indicate an even higher electron temperature, but an efficient pumping of the upper laser level is not possible with an electron temperature above 2.5 eV.We have estimated the electron densityn _e and the current densityj _e from ratios of the intesities of forbidden and allowed helium lines. The high current densityj _e is in the range of abnormal glow discharges.In the gas discharges between narrow gaps the electron oscillation amplitudex _e is large than the electrode separationd. In order to replace the resulting high electron losses a high electron temperatureT _e is necessary to sustain the gas discharge. Because of this high electron temperatureT _e an efficient pumping of the upper laser level is not possible.     

Light emission during cathode sheath formation in preionizedhigh-pressure glow discharges

The cathode sheath formation in a transient spatially small X-ray preionized high-pressure glow discharge with parameters typical for neon buffered XeCl lasers is investigated experimentally. Pictures of the light emission are taken with high temporal (≈1 ns) and spatial (≈25 μm) resolution using a gated CCD-camera as well as a streak camera. Quantitative data on the spatial and temporal development of the sheath structure are given. The most prominent feature is an extremely fast formation of a thin and very bright cathode sheath at a time which could be time correlated with an accuracy of ±0.2 ns with the discharge current. The results can be used to check numerical model calculations of the sheath formation