Electron and Chemical Kinetics in the Low-Pressure RF Discharge Etching of Silicon in SF6

Monte Carlo simulation and Boltzmann equation solutions have been used to study the electron kinetics. All electronic excitation of SF6 is assumed to be dissociative in analogy with the known product channels in ionization and multiphoton dissociation. The electric-field-to-gas-density ratios are high (E/n ? 1000 Td, where 1 Td (Townsend) = 1 × 10-17 V . cm2) in low-pressure (p < 0.3 torr) radiofrequency (RF) discharges. At these high E/n values, the electron energy relaxation time is much shorter than the 74-ns period at 13.56 MHz. Furthermore, the time scale of the chemical kinetics is much longer than the period of the applied RF voltage. Therefore the electron energy distribution can "track" the time-varying electric field, and time- and space-averaged rate coefficients can be used in chemical kinetics models. A rate equation model has been used to study the chemical kinetic processes. Electron-impact dissociation and ionization are the dominant sources of chemically active species. An electron density of 1 × 108 cm-3 is estimated from the known average values of E/n and the discharge input power. Two limiting cases are studied for the positive and negative ion diffusion losses: a) trapped negative ions and positive ion loss at the ambipolar diffusion rate; and b) positive and negative ion losses at the free diffusion rates. Neutral particle diffusion losses are estimated by using an effective diffusion length which takes surface reflection into account and increases as the surface reflection probability increases.     

The Impact of Direct Ionization by Beam Electrons on the Electron Kinetics of the Beam Discharge Plasma in Molecular Hydrogen

In a recent paper the stationary beam plasma discharge in partially dissociated hydrogen was investigated where the electron component was described by the Boltzmann equation for a mixture of atomic and molecular hydrogen and the main heavy charged and neutral particles by balance equations. It was assumed that, via the quasilinear beam plasma interaction, the electron beam produces only the turbulent electric field whilst an additional production of plasma electrons due to direct ionization by the beam and thus a direct influence on the balances of charge carriers were neglected. Now the additional production of plasma electrons due to direct ionization by the beam is studied on the basis of a generalized Boltzmann equation but for the simpler model of a purely molecular hydrogen plasma. For experimentally obtainable values of the turbulence energy density, beam energy, beam ionization degree and electron life time the calculation of the electron energy distribution function and of the direct beam contribution to the electron particle balance shows a marked influence of the direct beam ionization with increasing degree of beam ionization.     

Plasma Beam Discharge in Carbon Dioxide

The paper deals with the dissociation of carbon dioxide in nonequilibrium plasma of a stationary plasma-beam discharge. Experimental results of spectroscopic and probe measurements of plasma parameters are given. Moreover, a mass-spectrometric analysis of gaseous products of the chemical reactions is presented. In addition the measurement of the deposition rate of solid products by means of a quartz oscillator is described. The results show that plasma beam discharge is an effective tool for inducing plasma-chemical reactions.     

Probe Measurements in a Beam Plasma Discharge

The influence of the beam energy and beam current density on the parameters of the plasma is investigated. The efficiency of carrier generation by collective interactions (Langmuir-oscillations) is compared with that by the single collision mechanism. The additional negative charging of the static probe caused by the beam electrons is used for the determination of the beam electron density.     

A Kinetic Model for Plasma Etching Silicon in a SF6/O2 RF Discharge

Time-dependent Boltzmann electron distribution calculations have been made at constant power and pressure in a SF6/O2 plasma with a varying oxygen mole fraction. The results show that as the oxygen fraction increases in a SF6/O2 plasma, the number of high-energy electrons in the tail of the electron distribution and the mean electron energy both increase significantly while the plasma is kept at the same reduced electric field E/N. Rate coefficients have been computed for the electron kinetic processes of these plasmas and merged within a kinetic equilibrium model for the plasma etch process, including neutral gas-phase chemistry, ion chemistry, and surface reactions. Model simulations show good agreement with experimental results for SF6/O2 etching of polysilicon and demonstrate that the anisotropic character of dilute SF6 plasma etching is related to the shift in the electron distribution with increasing oxygen fraction. Competition between F and O species for adsorption to silicon etching sites is also shown to be a factor in determining etch rates, but this competition is not significant until very large (> 80 percent) oxygen concentrations are present. Ionization rates and ion transport to the surface are shown to be much more important. The model simulations provide a rationale for explaining the very high etch rates observed at low-SF6 partial pressures and the increasing anisotropic etch character with greater oxygen dilution of SF6.     

On the Stationary Invariant Configurations of the Ideal Plasma

A system of magnetohydrodynamics equations for the compressible plasma, invariant for the one-parameter group of motions in the space E ₃ is integrated.     

Device for Producing and Investigating an Electron Beam Plasma Discharge

A survey on the properties and applications of the beam plasma discharge is given. A device for the experimental investigation of this discharge is described in which a magnetically guided (H = 0.05?0.1 T), ribbonlike electron beam (eU = 0.5–5 KeV, I = 10^?3?1 A) passes through a working chamber (p = 0.1–10 Pa; l = 10 cm, ø = 22 cm). The beam plasma discharge is sustained by collective beam plasma interaction. First results concerning the wall current and the ignition of the discharge as dependent on beam parameters are presented.     

Kinetics of the Electron Component in the Turbulent Electron-Beam Discharge Plasma in Diatomic Gases and Comparison of some Macroscopic Properties between the Plasmas of the Beam and the Glow Discharge

The present paper is devoted to the investigation of the kinetics of the electron component in the stationary beam discharge plasma in molecular nitrogen. Using the Boltzmann equation with the inclusion of the elastic and the main inelastic binary collisions and also the Coulomb interaction between the charged particles we have calculated the energy distribution function and some macroscopic quantities of the electrons within a large range of parameters. Using our earlier results for the beam discharge plasma in hydrogen, also the dependence of the macroscopic quantities on the kind of molecular gas is discussed. Finally, the comparison of some macroscopic properties of the beam and the glow discharge plasma was performed under the condition of equal power input per volume unit in both types of plasmas in nitrogen.     

Spatial Characteristics of the Beam Plasma Discharge in Crossed Electric and Magnetic Fields

The paper presents the results of the experimental investigation of the beam plasma discharge spatial structure in crossed fields induced by adding a high ionization potential gas to the discharge. Direct experimental evidence of the polarization mechanism of the radial current in a device with this type of discharge has been obtained.     

Deposition and Etching of Thin Films by Means of Beam Plasma Discharge with Tube-Like Electron Beam

The efficiency of energy dissipation caused by the mechanism of turbulent plasma heating from a tube-like electron beam in a electronegative gas is measured calorimetrically. Amorphous Si-layers are deposited from a SiH₄/Ar discharge both on conducting and nonconducting substrates and are analyzed by means of Auger-spectrometry. The velocity and specific energy of etching of SiO₂-layers in a CF₄-plasma are determined. Measured etching velocities of tungsten surfaces biased differently against the space potential provide information on the mechanism of plasma etching in a SF₆-plasma. Simultaneously performed Langmuir-probe measurements permit predictions to be made on the properties of the etching plasma.     

Kinetic Description of the Stationary Band-Like Weakly Turbulent Beam Discharge Plasma in Hydrogen II. Budget of Ions and Metastables — Analysis of the Balance Equation System

In the first part [1] of our paper a kinetic model for the band-like beam discharge plasma in hydrogen was derived, numerically obtained results on the ionization and dissociation degree were presented and a detailed explanation of the influence of the electron kinetic properties on the macroscopic plasma behaviour was given. Continuing these investigations, we now report and discuss the results on the ion- and metastable atom-budget. On this basis an analysis is made of the resulting balance equation system with a view to finding the most important physical processes, and a simplified equation system is derived which allows to interpret the essential features of the macroscopic plasma properties.     

电激励脉冲HF激光SF_6/C_2H_6工作气体的放电特性

研究了电激励脉冲HF激光工作介质SF6/C2H6混合气体的放电特性。通过对放电等离子体荧光图像和放电波形的测量,分析比较了不同条件下放电稳定性、剩余电压、能量沉积效率等特性参数的变化情况。实验结果表明:混合气体的放电过程存在主放电、剩余电压维持和电弧放电3个阶段,各阶段的放电特性有所差异;提高充电电压有利于放电能量的有效沉积,也会使不稳定的电弧放电提前;增加C2H6原子分数能起到抑制电弧放电的作用;混合气体总压的增加会导致剩余电压的提高以及辉光放电的能量沉积效率的降低;最佳的能量沉积出现在电弧放电阶段与辉光放电阶段即将融合的临界状态。     

On the Plasma Beam Instability of the Space Limited Electron Beam in a Magnetic Field

The present paper considers the plasma-beam instability of a space limited electron beam in a strong magnetic field (ω_H ? ω_o). The form of the beam was taken to be both cylindrical and plane. The threshold of the non-linear regime turned out to be weakly dependent on the beam form and independent of the magnetic field intensity. It is defined by the current and the directed velocity of the beam particles.     

均匀电场SF6短气隙放电过程动态模拟

根据基本物理定律和流体力学,构建均匀电场下SF₆短气隙放电流体模型,运用通量校正传输法(flux-corrected transport)数值分析大气压下4 mm间隙SF₆的放电过程,展现放电空间带电粒子产生、复合、附着、扩散以及光致电离动态过程,获得了放电间隙电场畸变、带电粒子动力学行为和放电通道形成发展历程和时空分布,根据R-M判据求出模型放电过程中电子崩转向流注的时空临界点,印证了光致电离在流注发展阶段的重要作用.     

SF_6气体及其衍生物的红外光谱分析

SF6气体大量应用于气体绝缘组合电器(GIS)中。通过化学方法检测SF6气体及其衍生物是检测GIS设备故障的一种重要方法。该文采用红外光谱技术分析了三种情况下的GIS设备内SF6气体组成情况,得出S2F10气体含量可以用来分析GIS故障原因是否为强火花或者电弧放电引起;CF4气体可以用来表征GIS设备内绝缘气体的绝缘状态。另外,研究表明,GIS设备在线运行时,绝缘气体气室密封失效、造成气体泄漏,引入新的气体杂质的问题比较严重。所以在进行GIS设备维护工作时,绝缘气室的密封维护工作十分重要。文章在研究GIS设备绝缘气体SF6红外谱图的基础之上提出了建立基于红外光谱技术的GIS设备故障诊断专家系统的意见。     

Plasma-Beam Discharge with a Pipe-like Electron Beam as the Generator of Large Flows of Active Radicals

Investigations on the device with a tube-like electron beam have been carried out. The behaviour of the plasma-beam discharge in active molecular gases at low pressures and at the pressure P = 1 Torr has been studied. The etching of crystalline silicon by active fluorine radicals has been carried out.     

Investigation of the Beam Plasma Discharge in Electronegative Gases Using the Second Derivative of Langmuir Probe Characteristics

The distribution of the charge carriers is measured and the influence of the attachment processes on the electron energy distribution function is demonstrated for beam plasma discharges in SF₆, CF₄ and O₂ with the aid of the second derivative of Langmuir probe characteristics. The structuration of the plasma into regions of predominating negative ions and regions of predominating electrons is determined by the the established radial T_e-profile. The dimension of the quasi electronfree plasma changes significantly as well at transition from the turbulent heating mechanism into the electron impact plasma generation as by occuring low-frequency instabilities. With increasing n_?/n_e a deficit of low energetic electrons appears in the electron energy distribution parallel to the formation of the negative ion peak. The saturation currents at n_e/n_?=0 yield the mass ratios between negative and positive ions.     

On the Conductance of the Gas Discharge Plasma at Space Anisotropic Excitation

The galvanic manifestation of two transformations of degenerate magnetic states of the neon atom, namely self‐alignment → non‐alignment and alignment ? orientation is studied by monitoring the voltage across the discharge in a range of hollow cathode discharge (HCD) lamps. The application of a magnetic field to the discharge disorders the self‐alignment. Alignment and orientation are optically induced and their effect on the discharge conductance is compared by measuring the optogalvanic signals. The degenerate states investigated are found to contribute to the gas discharge conductance in a manner which depends on their degree of coherence. Various hollow cathode discharge media are studied including Ne/As, Ne/Cu, Ne/Ni, Ne/Cd, Ne/Li and Ne/Ca in the corresponding trademarked HCD spectral lamps. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Kinetic Description of the Stationary Band-Like Weakly Turbulent Beam Discharge Plasma in Hydrogen. I. Basic Equations — Numerical Approach — Ionization and Dissociation Budget

On the basis of the electron Boltzmann equation and of the balances for the charge carriers (e, H⁺, H₂⁺, H₃⁺), the H-atoms and the metastable H(2s)-atoms for the H/H₂-mixture the behaviour of the weakly turbulent, band-like electron-beam discharge plasma in hydrogen has been calculated taking into account the main collision and transport processes. In dependence of the normalized discharge length, the life time of the neutral particles in the band-like plasma and the electron beam generated turbulence energy density the ionization and dissociation budget and in particular the most important electron-heavy particle collision rates, which appear in the balance equation system, are investigated in the present part of our paper. In a second part the results related to the budget of the ions and the metastable atomic state will be reported and an analysis of the main processes in the balances will be made.     

Fluorocarbon Barriers on Starch Foam Tray Surfaces Through SF6 Cold Plasma Treatment

Starch foam trays were produced using a laboratory model-baking machine. Surfaces of the trays were treated with SF₆ plasma to create fluorine-rich layers on the surfaces. RF power, gas pressure and reaction time were varied to evaluate the effects of each parameter on fluorination of surfaces. The fluorine concentrations of treated sample surfaces ranged from 43.6% to 57.9%. For reaction time dependence, the ratio of oxygen to carbon was decreased since hydroxyl groups might be replaced by fluoro-compounds. Gas pressure and RF power affected fluorination mechanism, which resulted in different shapes of carbon and fluorine ESCA high resolution spectra. Plasma-treated samples have higher contact angles and less uptakes of liquid and vapor water. AFM showed different morphology of untreated and SF₆ plasma-treated surfaces.