Showing papers in "Plasma Chemistry and Plasma Processing in 1984"

Parametric study of the flow and temperature fields in an inductively coupled r.f. plasma torch

Abstract: A theoretical investigation of the effect of different parameters on the flow and the temperature fields in a radiofrequency inductively coupled plasma is carried out. The parameters studied are: central injection gas flow rate, total gas flow rate, input power, and the type of plasma gas. The results obtained for argon and nitrogen plasmas at atmospheric pressure indicate that the flow and the temperature fields in the coil region, as well as the heat flux to the wall of the plasma confinement tube, are considerably altered by the changes in the torch operating conditions.

Effects of metallic vapor on the properties of an argon arc plasma

Abstract: During thermal plasma processing of materials, vapor generated from injected particulate matter will enter the plasma. Even traces of metallic vapors may have a strong effect on the properties and the behavior of the plasma and on the associated heat flux to the injected particles. In this paper a model system is considered in which an argon plasma at atmospheric pressure is “contaminated” by small amounts of copper vapor. By using the Chapman-Enskog approximation for a multicomponent gas mixture the transport properties are calculated for such a contaminated argon plasma. The results show that there is a drastic effect on the electrical properties. For temperatures below 104 K, the electrical conductivity, for example, increases by more than an order of magnitude if metallic vapor is present. The presence of metallic contaminants is also somewhat felt by the reactional thermal conductivity. In contrast, there is no effect on the heavy-particle properties as long as the percentage of the contaminants remains small.

Gas-phase reactions of CF2 with O(3P) to produce COF: Their significance in plasma processing

Abstract: Reactions between CF2 and O(3P) have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. The major reaction for CF2 has been found to be $$CF_2 + O \to COF + F$$ with $$CF_2 + O \to CO + 2F(F_2 )$$ more than a factor of three slower. The rate coefficient for all loss processes for CF2 on reaction with O is (1.8±0.4)×10−11 cm3 s−1. The COF produced in (18) undergoes a fast reaction with O to produce predominantly CO2. $$COF + O \to CO_2 + F$$ It is uncertain from the results whether or not $$COF + O \to CO + FO$$ occurs, but in any event (19) is the major route. The rate coefficient for the loss of COF in this system [i.e., the combined rate coefficients for (19) and (20)] is (9.3±2.1)×10−11 cm3 s−1. Stable product analysis reveals that for each CF2 radical consumed, the following distribution of stable products is obtained: COF2 (0.04±0.02), CO (0.21±0.04), and CO2 (0.75±0.05). Thus COF2, which we assume is produced via $$CF_2 + O \xrightarrow{M} COF_2$$ is a very minor product in this reaction sequence. The measured rate coefficients demonstrate that reactions (18) and (19) are important sources of F atoms in CF4/O2 plasmas.

Optical emission spectroscopy and actinometry in CCl4-Cl2 radiofrequency discharges

Abstract: Radiofrequency discharges fed with CCl4-Cl2 mixtures have been studied in the pressure range 0.3 to 0.6 torr by means of emission spectroscopic actinometry with Ar, He, and N2 as actinometers. Two different reactors, a parallel plate and a capacitively coupled tubular one, have been utilized for this study to obtain information for a large range of electron energy distributions. Analysis of the experimental results demonstrates the following: the utilization of actinometry and its range of validity, the importance of electron attachment to CClx species during the plasma decomposition process, and the effects of the presence of chlorine and “glowpolymer” in the discharge medium.

Decomposition of an organophosphorus material in a silent electrical discharge

Abstract: An organophosphorus compound, C7H16FO2P, was reacted with air in a silent ac discharge. This paper discusses the observed fragmentation and products of the reaction using Gas Chromatography-Mass Spectrometry.

Plasma chemical vapor deposition of TiN

Abstract: Experiments indicate that the temperature in chemical vapor deposition (CVD) of TiN can be decreased from about 1000°C in conventional CVD to about 500°C by the application of a D.C. nonequilibrium plasma. The hardness of the TiN film is greater than 2000 kg/mm2 (Vickers). The effect of pressure, ratio of gas mixture, and discharge parameters on the film deposition rate, its hardness, and microstructures has been studied.

Gas-phase reactions of CF3 and CF2 with hydrogen atoms: Their significance in plasma processing

Abstract: The use of hydrogen-rich CF4 plasmas leads to the selective etching of SiO2 in the presence of Si. The mechanisms which control this selectivity are poorly understood, and much more needs to be known about the fundamental chemical processes. In this work the reactions $$\begin{gathered} CF_3 + H \to CF_2 + HF \hfill \\ CF_2 + H \to CF + HF \hfill \\ \end{gathered} $$ have been studied at 295 K using a gas-flow reactor sampled by a mass spectrometer. The rate coefficients obtained are (8.9±1.8)×10−11 cm3 s−1 and (1.65±0.40)×10−13 cm3 s−1 for reactions (3) and (4) respectively. These values establish reaction (3) as a major source of CF2 while reaction (4) would be expected to be only a minor loss process in the etching environment.

Absolute partial and total electron ionization cross sections for CCl4 from threshold up to 180 eV

Abstract: Electron impact ionization of carbon tetrachloride was studied as a function of electron energy from threshold up to 180 eV. A double-focusing mass spectrometer system in combination with an improved electron impact ion source was used, alleviating the problems of ion extraction from the source and the transmission of the extracted ions through the mass spectrometer system. Absolute partial ionization cross sections for the occurrence of CCl3+, CCl2+, CCl+, Cl2+, Cl+, C+, CCl32+, and CCl22+ have been determined. In addition, the total ionization cross-section function of CCl4 is reported and compared with theoretical predictions based on a classical binary encounter approximation. Using nth root extrapolation the following ionization energies of the doubly ionized fragment ions have been derived: AE(CCl32+)=30.4±0.3 eV; and AE (CCl22+)=31.8±0.3 eV. In accordance with theoretical predictions and previous results, no stable CCl4+ has been detected, however, metastable dissociation processes CCl4+ → CCl3+ have been observed.

Thermal decomposition of carbon dioxide in an argon plasma jet

Abstract: The decomposition of carbon dioxide to carbon monoxide and oxygen in an argon plasma is studied. The overall kinetic and energy-related parameters of the process, as well as the quenching rates of the products, are evaluated on the basis of measured radial and longitudinal profiles of both temperature and degree of decomposition in the high-temperature reaction zone.

Plasma oxidation of liquids

Abstract: Liquid 2,2,4-trimethylpentane (I), 1-octene (II), and di-n-butylsulfide (III) were subjected to plasma of oxygen. II and III were also treated dissolved in alkanes. Conversion rates increased with decreasing temperature, with increasing gas velocity, and, in the case of II, also with the addition of nitrogen or helium to the gas stream. The selectivity of product formation is far superior to plasma oxidations in the gas phase, making these techniques attractive for preparative chemistry.

Radiofrequency plasma decomposition of C n F2n+2-H2 and CF4-C2F4 mixtures during Si etching or fluoropolymer deposition

Abstract: Microscopic decomposition processes and gas-solid interactions in CnF2n+2-H2 and CF4-C2F4 discharges are studied by comparing mass-spectrometric results with actinometric emission diagnostics. The role played by CFx radicals is evident in the various processes of gas-phase formation of saturates and unsaturates as well as in the “activation growth mechanism” of polymer deposition.

Chemical mechanisms in C3F8-H2 radiofrequency discharges

Abstract: Discharges fed with C3F8-H2 mixtures have been studied by means of mass spectrometry in a tubular reactor operated at 0.5 torr and 50 W. Comparison of the results with those obtained with emission actinometry give additional evidence that emission actinometry and mass spectrometry are powerful diagnostic tools to monitor stable and unstable species in discharges utilized for dry etching and polymer depositions. Mechanisms for end product formation and polymer deposition are also discussed.

Modeling of a free-burning, high-intensity arc at elevated pressures

Abstract: A previously established model has been applied to a free-burning high-intensity argon arc at elevated pressures for simulating the situations experienced, for example, in plasma processing or in underwater welding. With the calculated thermodyanmic and transport properties and appropriate boundary conditions, solutions of the entire arc are obtained with exception of the electrode sheath regions. The results show that the arc contracts as the pressure increases. As a consequence of this contraction, the current density, the enthalpy flux, and the voltage drop increase also while the velocity of the induced cathode jet decreases.

Titanium dioxide plasma treatment

Abstract: After a review of the literature on titanium production under plasma conditions, the main parameters controlling the reactions (residence time, type and relative quantity of reducer, reaction temperature, etc.) are emphasized. The controlled-atmosphere chamber where the rutile or anatase particles are heated and partly reduced in a crucible by a d.c. plasma torch with Ar-H2 as plasma gas is described. Study of the temperature dependence of the Gibbs free energy allows one to explain, at least qualitatively, the experimental results obtained which correspond at best to 10% (weight) of TiO2 reduced to TiO by carbon.

Mass spectrometric diagnosis of the surface nitriding mechanism in a d.c. glow discharge

Abstract: Reactive constituents have been investigated in a molecular beam generated in the cathode surface glow area and surface boundary layer. Mixtures of nitrogen and hydrogen form NHx(x=0–4) compounds, which are of relevance in heterogeneous, plasma vs. metal nitriding reactions. Ammonia decomposition leads to NHx(x=2–4). Strong cataphoretic enrichment of hydrogen has been observed in the cathode glow area. Heterogeneous reactions of NHx with iron lead to the formation of iron nitrides via intermediates such as FeNH2–3. In a pulsed d.c. glow discharge, increased sputtering and decreased hydrogen enrichment have been observed.

Synthesis gas production from peat using a steam plasma

Abstract: A steam plasma was used to convert peat into a synthesis gas, suitable for methanol production, in a cocurrent transport reactor. A cylindrical stainless-steel reactor 20 cm in diameter and 120 cm long was used. The effects of temperature and the carbon/ steam molar ratio on the product gas composition and carbon conversion were investigated. Finely ground peat (mean particle size, 63 µm; moisture content, 15.5%) was fed continuously through the reactor top and exposed to mean reaction temperatures ranging from 1250 to 1420 K. The plasma inlet temperature was calculated to be of the order of 3500 K and total powers as high as 62 kW were used. A carbon conversion of 89% and a hydrogen-to-carbon monoxide ratio of 1.8 in the product gas were obtained. A simple model of the reacting system suggested that a conversion of 90% (needed for an industrial process) and a hydrogen-to-carbon monoxide ratio of two could be obtained with equipment modifications.

Mass spectrometer-wall probe diagnostic of Ar discharges containing SF6 and/or O2: Reactive ions in etching plasmas

Abstract: Positive and negative ions of Ar/SF6 and Ar/SF6/O2 plasmas (etching plasmas) and of Ar/O2 plasmas (cleaning plasmas) in Pyrex tubes have been investigated using a mass spectrometer-wall probe diagnostic technique. The measurement of negative ions proved to be a very sensitive method for the detection of wall material. In etching plasmas with small admixtures of SF6, oxygen was found as the only representative of wall material. At larger amounts of SF6, silicon could be detected. In cleaning plasmas with small admixtures of O2 applied to a previously etched Pyrex surface, fluorine was found, indicating the reversal of fluoridation by oxygenation.

A transparent boron-nitrogen thin film formed by plasma CVD out of the discharge region

Abstract: A transparent boron-nitrogen thin film of thickness 550 nm was successfully deposited out of the discharge region by rf plasma CVD. The deposition was performed with diborane (4.8 vol % in N2) as the reactant gas and argon as the carrier gas by an inductively coupled reactor at a frequency of 13.56 MHz. The transparent films could be obtained at a low pressure of about 30 Pa, at a discharge power level of 30 W, and at room temperature without heating the substrate. The thin films obtained by rf plasma are compared with those obtained by microwave plasma. Both the refractive index and the deposition rate for the films deposited by microwave plasma are discussed according to the deposition conditions.

Nitriding of Titanium with Plasma Jet Under Reduced Pressure

Abstract: The nitriding of titanium with argon-nitrogen (3%) and argon-nitrogen (3%)-hydrogen (2%) plasma jets at pressures of 190 torr was studied. The reaction kinetics obeyed mainly a parabolic law. The parabolic kinetic constants were 10−10–10−8 g2 cm−4 s−1, which were 2–3 orders of magnitude larger than those in R.F. discharges. From emission spectroscopy, nitrogen atoms in the excited states were observed. The nitrogen atoms can promote the nitriding reaction. The effect of the addition of hydrogen to nitrogen is also briefly discussed.

Calculation of Thermodynamic and Transport Properties of a Typical Arc Furnace Plasma

Abstract: Using a previously developed computer program, thermodynamic and transport properties of a typical arc furnace plasma are calculated in order to single out those species and / or reactions which exert a dominating influence on the properties of such complex mixtures. The results indicate that dissociation of molecular species in the arc furnace atmosphere has a strong effect on the specific heat and on the thermal conductivity of the mixture. The electrical conductivity is strongly affected by metallic vapors from the molten metal pool and the slag cover.

H2 plasma development of X-ray imaged patterns on plasma-polymerized resists

Abstract: An X-ray imaged pattern on a plasma-polymerized film was successfully developed by H2 plasma etching. Plasma-polymerized MMA and 6FBMA were formed by using an inductively coupled argon flow type reactor. An X-ray imaged pattern on the film was attained through a knife-cut window of a gold plate. The X-ray was generated from a Cu target at 20 kV and main wavelength 1.54 A. The pattern development was performed using a tubular type reactor with parallel plate electrodes. The quality of plasma-polymerized resists in an X-ray lithography was evaluated by comparing it with the conventional polymer in the dry and wet process, and the minimum dose rate for a visible pattern fabrication was measured to be 4.1 J/cm2 for both resists in H2 plasma etching development.

Static pressure and heat flux measurements of a thermal argon plasma flow in a water-cooled tube

Abstract: The momentum and energy transfer phenomena with large temperature difference were investigated experimentally and theoretically, using an argon atmospheric thermal plasma. The plasma was generated by an arc discharge, 4–6 kW, and flowed into a water-cooled copper tube for static pressure measurements and into a copper block with the same size hole (8 mm i.d.) for measuring heat fluxes using a transient method. The argon flow rate was 2.77–8.31×10−4 kg/s. The static pressure of the plasma flow shows a different variation from that of an ordinary flow and does not decrease monotonically. The axial distributions of the numerical calculations are in fair agreement with those of the experiments, and it is concluded that the contributions of recombination and of physical properties play important roles in the behavior of the confined thermal plasma flow.

Chlorine incorporation in silicon films deposited by low-pressure rf discharges in gas mixtures of SiCl4+H2+Ar

Abstract: Silicon films were deposited from tetrachlorosilane by its dissociation in argon and hydrogen rf plasma at a pressure of 2 Torr. The concentration of chlorine incorporated in the films was found to be dependent on the macrovariables of the plasma such as power input and substrate position in the plasma reactor. Mass spectrometric measurements of the plasma showed that the concentration of HCl in the plasma was strongly dependent on the power input and on position in the plasma along the gas stream. At high input powers the HCl formed in the plasma dissociates to free radicals, contributing to a recombination process in the gas phase and codeposition with silicon on the substrate. The correlation between the HCl reactions in the plasma and the incorporation of Cl in the deposit is shown.

Intermediate and high-mass ion beams from a 10-cm Duopigatron

Abstract: Experimental studies of a 10-cm Duopigatron as a source of argon, krypton, and xenon ion beams are reported. Source plasma instabilities are examined, and the mass dependence of oscillation frequencies and instability onset conditions are determined. Arc current and density oscillations are found to be associated with ion acoustic fluctuations with frequencies scaling as 1/M1/2. Langmuir probe measurements within the source plasma double layer are used to indicate the physical mechanism responsible for the observed large-amplitude are current shifts. Ion beams have been extracted at energies up to 18 kV, and drain currents up to 540 mA for argon, 440 mA for krypton, and 520 mA for xenon have been achieved with source plasma densities in the range 1011–1012 cm–3. Excellent agreement with existing theoretical models has been obtained in the mass and density dependence of the extraction current, as well as the voltage at which transition from space-charge limited to ion saturation emission occurs.