Rf Glow Discharge Plasma Research Articles

Conductivity effects in hydrogenated amorphous silicon induced by gamma-ray irradiation

Hydrogenated amorphous silicon films 0.45 and 1.12 μm thick, grown by RF glow discharge plasma PECVD on Corning-7059 glass, were irradiated by a 60Co source (activity 2.8 × 10 15 Bq) in the dose range 10–450 kGy at different dose rates. The dark current of the samples, under 100 V applied voltage, was measured before, during and after gamma irradiation. When the irradiation starts, the dark current increases up to a level linearly dependent on the dose rate. When the irradiation is switched off, the dark current returns close to the initial value in a few days. Such behaviour suggests a possible application of hydrogenated amorphous silicon films in dosimetry and as gamma ray sensors. Moreover, the film optical constants were computed from the transmittance spectra measured in the range 500–2500 nm, before and after irradiation. After irradiation, the film optical absorption is slightly increased and the energy gap is substantially unchanged.

Zone-resolved mass spectroscopic study on RF plasma polymerization of styrene

The radiofrequency (rf) glow discharge plasma of styrene was investigated by direct sampling mass spectroscopy. Measurements were taken in three regions of the discharge : the plasma column and two dark zones before the electrodes. The plasma-polymerized styrene (PPS) thin films were analyzed by infrared spectroscopy (IR). The effects of monomer pressure and rf power on the ratios of mass peak heights C 4 H 2 + /C 4 H 3 + , C 6 H 6 + /C 6 H 5 CH=CH 2 + in the three discharge regions, the polymer deposition rate, and the polymeric structure of the PPS films were studied. It was found that in the different discharge regions and under various discharge conditions, a variety of reactive species were formed by electron impact on monomer molecules. The polymer deposition rate was mainly dependent on the total number of the reactive species produced in the discharge. The concentration of phenyl groups in PPS films was proportional to the relative concentration of phenyl ring-containing reactive species in the gas phase plasma.

Zone‐resolved mass spectroscopic study on RF plasma polymerization of styrene

The radiofrequency (rf) glow discharge plasma of styrene was investigated by direct sampling mass spectroscopy. Measurements were taken in three regions of the discharge: the plasma column and two dark zones before the electrodes. The plasma-polymerized styrene (PPS) thin films were analyzed by infrared spectroscopy (IR). The effects of monomer pressure and rf power on the ratios of mass peak heights C4H/C4H, C6H/C6H5()CH in the three discharge regions, the polymer deposition rate, and the polymeric structure of the PPS films were studied. It was found that in the different discharge regions and under various discharge conditions, a variety of reactive species were formed by electron impact on monomer molecules. The polymer deposition rate was mainly dependent on the total number of the reactive species produced in the discharge. The concentration of phenyl groups in PPS films was proportional to the relative concentration of phenyl ring-containing reactive species in the gas phase plasma. © 1996 John Wiley & Sons, Inc.

Control of Microstructure and Optoelectronic Properties of Si:H Films by Argon Dilution in Plasma-Enhanced Chemical Vapor Deposition from Silane

Structural and optoelectronic properties of thin films of silicon-hydrogen binary alloy (Si:H) deposited from silane and argon mixture in a rf glow discharge plasma have been studied for different argon dilutions and rf powers. It has been observed that with low rf power density ( 30-70 mW/cm3) increase of argon dilution up to 95% reduces the microstructure in the films, as determined from IR absorption spectra. Simultaneously, increase in refractive index and decrease in ESR spin density have been observed. Above 95% argon dilution or with higher rf powers, transmission electron microscopy (TEM) studies reveal a dominance of the columnar growth mechanism, and the optoelectronic properties of the films deteriorate. At 99% argon dilution, microcrystallites appear to form within columnar regions. Addition of a small amount of hydrogen to the silane-argon plasma improves the network significantly, which is manifested by the changes in the dark conductivities in the different rf power regimes.

ＥＣＤ／ＯＢＣにおける素材科学の進歩に基づいた製品開発

Advanced materials development has resulted in the commercialization of innovative new products at Energy Conversion Devices, Inc. such as thin-film amorphous silicon photovoltaic modules, nickel-metal hydride rechargeable batteries, phase change erasable optical memory disks, high-performance nonvolatile semiconductor memory devices, vapor barrier films for food packaging and long life electrophotographic photoreceptors.New materials have been engineered for these products through the use of chemical and structural disorder and unique processing technology has been developed to enable their manufacture. These advanced disordered materials range from multilayer thin film stacks of amorphous and microcrystalline silicon and amorphous silicon-germanium semiconductor alloys for solar cells, to thin film multielement chalcogenide (Te, Ge, Se, As) alloys for use in optical and electronic memories, to multiphase bulk hydride forming alloys such as VTiZrNiCrCoMnAlFe for use in nickel metal hydride rechargeable batteries.Processing technology for these materials ranges from RF glow-discharge and microwave plasma enhanced chemical vapor deposition for thin film semiconductor manufacturing to vacuum metallurgical bulk materials techniques utilizing induction melting, rapid solidification, hydrogen embrittlement and powder metallurgical processing. The materials, processing and commercialization status of each of these technologies is discussed, with particular emphasis on the NiMH battery.

Interface/Interphase Studies in Epoxy Matrix Composites

Abstract The effect of surface treatments and fiber sizings on the stress transfer characteristics and composite properties of AS-4 carbon/epoxy materials has been determined. Fiber surface chemistry was systematically varied from acidic to basic with RF glow discharge plasmas of CO2 and NH3 and characterized with ESCA techniques. Sizings applied to some of the treated fibers consisted of diglycidyl ether of bisphenol-A(DGEBA). Single fiber tension tests were used to measure the interfacial shear strength of samples made with DGEBA/metaphenylene diamine resin. Short beam shear and transverse flexure tests were used to examine the composite properties of modified materials. Results showed that the plasma treatments were effective in altering the surface chemistry of the fiber but that changes in surface chemistry had surprisingly little effect on the critical stress transfer length. Sizing had a more significant effect on the transfer length. The interlaminar shear strength of the composites were unaffecte...

Studies on diamondlike carbon films for antireflection coatings of infrared optical materials

Diamondlike carbon (DLC) films were directly deposited onto germanium (Ge) and zinc sulphide (ZnS) slices by a capacitively coupled 13.56 MHz rf glow discharge plasma with Ar-C2H2 gas mixtures. The IR transmittance was measured using a Fourier-transform infrared spectrometer. The maximum values of the IR transmission of Ge and ZnS with DLC films on both sides are 99% and 95.8%, respectively, which come up to the theoretical values. A nonuniform DLC film, of which the refractive index gradually changes along the thickness, has been successfully deposited onto a Ge slice for the first time and the IR transmission of a nonuniform DLC film coated onto both sides of a Ge substrate at the wider wave band of 2.5–15 μm is over 85%.

Measurements of potentials and sheath formation in plasma immersion ion implantation

Collecting and emitting probes have been used to explore the distribution of potentials and the dynamic behavior of the cathodic sheath in the rf glow discharge plasmas used for plasma immersion ion implantation (PI3). On application of a negative voltage pulse, the sheath expands rapidly but comes to a steady-state position within a few microseconds. The potential distribution then remains stable as long as there is sufficient plasma outside the sheath region to replace the ions lost to the cathode. The various dc potentials in the plasma that arise from rectification of the rf fields are also important. At power levels up to 500 W, the plasma potential is several hundred volts above the average dc potential of the antenna. The magnitude of this voltage difference depends on the antenna geometry, its insulation from the plasma and the dc potential that can exist between it and the chamber walls. The floating potential of a typical PI3 target can vary from 50 to 300 V below the plasma potential but in all cases the difference is sufficient to ensure that there is a sheath and presheath structure around the target before the application of the high voltage pulse.

Molecular surface tailoring of biomaterials via pulsed RF plasma discharges.

A pulsed RF plasma glow discharge is employed to demonstrate molecular level controllability of surface film deposits. Molecular composition of plasma deposited films is shown to vary in a significant manner with the RF duty cycle. Three fluorocarbon monomers are used to illustrate the process. All three exhibit a trend towards increased surface CF2 content with decreasing pulsed RF duty cycle, including exclusion of oxygen. Significant variations in carbon-fluorine surface functionalities are obtained over a controllable range of film thickness. Film growth rate measurements reveal the occurrence of surface reactions during significant portions of the off portion of the duty cycle. Albumin adsorption on fluorocarbon-treated PET films is unchanged from PET controls for a 100-fold range of bulk concentrations and 60-fold range of adsorption times. However, increased retention of albumin is observed following incubation with protein-denaturing sodium dodecyl sulfate solution, the retention decreasing with increasing bulk concentration of albumin. The increased retention of albumin suggests the treated surfaces may have promise as biocompatible materials.

High-photosensitivity a-SiGe: H films prepared by RF glow discharge plasma CVD method

Highly photosensitive and narrow band gap a-SiGe: H films have been prepared by the RF glow discharge plasma CVD method. The photosensitivity was 2.01 × 10 5 for the film with an optical band gap of E g = 1.47 eV. H 2 dilution and a relatively high RF power are attributed to the improving of the optoelectrical properties. Thermally induced changes of the a-SiGe:H films have been also investigated.

Fluidization and plasma characteristics of medium pressure RF glow discharge plasma fluidized bed reactors

Fluidization and plasma characterizations of medium pressure RF glow discharge plasma fluidized bed reactors are experimentally investigated. The results show that the particles are slightly positively charged by plasmas and that the oxidation of solid particles can be achieved effectively by present reactors using Ar-O 2 mixture gas plasmas.

Yellow emission bands produced during gold etching in O2-CF4 rf glow-discharge plasmas: Evidence for gas-phase AuF.

Distinctive optical emission bands have been observed during the etching of gold films in ${\mathrm{O}}_{2}$-${\mathrm{CF}}_{4}$ and ${\mathrm{O}}_{2}$-${\mathrm{SF}}_{6}$ rf glow-discharge plasmas. We suggest that the emission originates from gas-phase AuF, although AuO and the molecular ions ${\mathrm{AuF}}^{+}$ and ${\mathrm{AuO}}^{+}$ cannot be definitively ruled out as the emitting species. No optical spectra have previously been reported for any of these species in the gas phase. Conditions for producing the emission bands are outlined, and a representative spectrum is provided. Band positions for the tentatively identified (v\ensuremath{'}=v\ensuremath{''},v\ensuremath{''}) and (v\ensuremath{'}=v\ensuremath{''}-1,v\ensuremath{''}) progressions could be reproduced with a (0,0) band origin ${\ensuremath{\nu}}_{00}$=17 757 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, vibration frequencies ${\mathrm{\ensuremath{\omega}}}_{\mathrm{e}}^{\ensuremath{'}}$=529.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and ${\mathrm{\ensuremath{\omega}}}_{\mathrm{e}}^{\mathrm{\ensuremath{''}}}$=560 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and vibrational anharmonicities ${\mathrm{\ensuremath{\omega}}}_{\mathrm{e}}^{\ensuremath{'}}$${\mathrm{x}}_{\mathrm{e}}^{\ensuremath{'}}$=2.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and ${\mathrm{\ensuremath{\omega}}}_{\mathrm{e}}^{\mathrm{\ensuremath{''}}}$${\mathrm{x}}_{\mathrm{e}}^{\mathrm{\ensuremath{''}}}$=1.0 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, where the vibrational energies relative to the v=0 levels are given by ${\mathrm{G}}_{0}$(v)=(${\mathrm{\ensuremath{\omega}}}_{\mathrm{e}}$-${\mathrm{\ensuremath{\omega}}}_{\mathrm{e}}$${\mathrm{x}}_{\mathrm{e}}$)v-(${\mathrm{\ensuremath{\omega}}}_{\mathrm{e}}$${\mathrm{x}}_{\mathrm{e}}$)${\mathrm{v}}^{2}$. The band structure could be qualitatively accounted for by a ${\mathrm{\ensuremath{\Pi}}}^{1}$--${\mathrm{\ensuremath{\Sigma}}}^{1}$ band system with an assumed ${\mathrm{B}}_{\mathrm{e}}^{\mathrm{\ensuremath{''}}}$ of 0.24 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, ${\mathrm{B}}_{\mathrm{e}}^{\ensuremath{'}}$=${\mathrm{B}}_{\mathrm{e}}^{\mathrm{\ensuremath{''}}}$+2.75\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{e}}^{\ensuremath{'}}$=4.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{e}}^{\mathrm{\ensuremath{''}}}$=1.0\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, where the rotation constants are given by ${\mathrm{B}}_{\mathrm{v}}$=${\mathrm{B}}_{\mathrm{e}}$-${\mathrm{\ensuremath{\alpha}}}_{\mathrm{e}}$(v+12).

Numerical investigation of the kinetics and chemistry of rf glow discharge plasmas sustained in He, N2, O2, He/N2/O2, He/CF4/O2, and SiH4/NH3 using a Monte Carlo-fluid hybrid model

Capacitively coupled radio-frequency (rf) glow discharges are standard sources in plasma assisted materials processing. Theoretical analyses of rf discharges have been hampered by the computational difficulty of simultaneously resolving nonequilibrium electron transport and plasma chemistry. We have developed a hybrid Monte Carlo-fluid simulation that can simulate nonequilibrium electron transport while executing with the speed of a fluid simulation. An electron Monte Carlo simulation (EMCS) is used to calculate the electron energy distribution (EED) as a function of position and phase in the rf cycle. Collision rates and transport coefficients are calculated from the EED and used in a self-consistent fluid model (SCFM) of charged particle behavior and a neutral chemistry/transport model. Electric fields from the SCFM are cycled back to the EMCS, and the process is iterated until convergence. All pertinent heavy particle (charged and neutral) reactions can be included as well as collisions of electrons with ions, excited states, and reaction products. The hybrid model is applied to a variety of gas mixtures of interest to materials processing.

Time- and space-resolved electron-impact excitation rates in an rf glow discharge.

Abstract : Research on rf glow discharge plasmas was carried out to better understand the fundamental physics and chemistry of important aspects of plasma deposition and etching. A standard reference system for rf plasma processing research was utilized. Power, voltage and current waveforms were monitored and time and space resolved measurements were made using plasma induced emission (PIE). Nanosecond time resolution for PIE greatly expanded the utility of these plasma diagnostics over previous studies. Measurements were carried out with a prototype rf model discharge, atomic argon, concentrating on the important 4s levels 11.5eV above the ground state and the manifold of p levels coupled to these states by strong dipole transitions. Extensive analysis and computer modeling was carried out to reproduce the experimental data obtained and to test assumptions often used for this model system. Models of electron excitation waves were stringently tested and evaluated. The research concentrated on studying details of excitation waveforms as a function of pressure and rf power. Information on electron energy distribution functions were derived from the experimental results. New experimental techniques to enhance time and space resolution were developed.

Self-consistent kinetic calculations of helium rf glow discharges.

A theoretical study of low-pressure helium rf glow-discharge plasmas is presented. The numerical scheme provides a fully kinetic description of the electrons and singly charged He ions in one spatial dimension and predicts the electric fields present in a mutually consistent fashion. The results have implications for a variety of discharge geometries and gases. Realistic, detailed cross sections for He are used. Both the numerical algorithm and physical processes are discussed. Unlike previous theoretical studies, we find a low average electron energy (1 eV) in the central bulk region and a weak bulk field (\ensuremath{\approxeq}2 V/cm peak amplitude) that is out of phase with the strong sheath fields. The discussion emphasizes quantities that can be readily measured in order to facilitate comparison with experiment. Metastable-atom production rates are used as source terms in a diffusion-reaction model to predict metastable-atom densities. Multistep ionization due to metastable-atom--metastable-atom collisions is shown to be important for some of the conditions studied. The pressure dependence of the ion distribution at the electrode is studied. Some common approximations used in modeling discharges are examined for both suitability and possible improvement.

Characterization of Electron Cyclotron Resonance Plasma-Deposited Hydrogenated Amorphous Silicon and Related Alloy Films

ABSTRACTWe characterized a-Si:H films deposited by the electron cyclotron resonance (ECR) microwave plasma-enhanced CVD technique with the purpose of comparing ECR film quality widi that of films deposited by the rf plasma-enhanced CVD method. These ECR films were deposited in the 1–10 mT pressure region under a variety of growth conditions. Our investigations reveal the following typical properties for intrinsic ECR-deposited a-Si:H: (1) high photosensitivity as indicated by a light-to-dark DC conductivity ratio of up to 2×106, (2) a Tauc gap in the range of 1.75–1.85 eV, (3) an Urbach slope of 45–60 meV as determined by CPM and (4) an integrated deep defect density of 0.5–2×1016 cm-3 with Ec - Ef = 0.74–0.87 eV as determined by drive level profiling and junction capacitance vs. temperature scans. Variations of these quantities with deposition temperature, hydrogen dilution and magnetic field profile are discussed. Our results indicate that ECR-deposited a-Si:H is of comparable quality to a-Si:H deposited by the rf plasma glow discharge technique. ECR deposition conditions for a highly conductive type of a-Si:H film also are discussed. This material, while only slightly photosensitive and possessing an Urbach slope of over 100 meV, has a light DC conductivity of 3×10-4 (Ωcm)-1. Boron doping of this material produces a conductivity of 5×10-2 (Ωcm)-1.

Real-time detection of higher hydrides on the growing surface of hydrogenated amorphous silicon by infrared reflection absorption spectroscopy

Real-time in situ observations of the growth of a-Si:H films have been carried out in a rf glow discharge plasma reactor by use of infrared reflection absorption spectroscopy. Deuterium substitution of an interface layer is employed so as to differentiate the higher hydride species on the growing surface from those located at the film interface on the substrate. A three-layer model is presented to give a quantitative discussion on the absorption signal intensity in the reflection spectroscopy with respect to the normal incident transmission spectroscopy.

Growth Mechanism of ZnO Film by Reactive Sputtering Method –Significance of Thermodynamics in a Plasma System–

Zinc oxide films are prepared on a glass substrate by sputtering a zinc target in the rf glow discharge plasma of an argon/oxygen mixture. Growth rate, crystallographic structure, optical absorption, and the electrical conductivity of the films prepared are correlated experimentally with the conditions of the film growth process. The escape rate of zinc atoms from the growing surface, which depends solely on temperature, predominantly affects the chemical composition of the prepared film which includes Zn/ZnO mixture, Zn1+xO, and ZnO. The role of thermodynamic equilibrium in a glow discharge plasma system that is likely to be far from equilibrium and is kinetically controlled is pointed out for the first time.

Secondary ion formation from Langmuir-Blodgett films: Studies of positive molecular ions

Langmuir-Blodgett mono- and multi-layer (1–15 layers) systems consisting of stearic acid (SA) or barium stearate (BS) deposited on RF plasma glow discharge prepared Ag, Au, or Ge were studied by secondary ion mass spectrometry (SIMS). For the monolayer samples, substrate signals were not completely obscured (e.g. Ag +, AgCl − 2) even though sample related molecular ions persisted for extended periods. Ion beam induced damage and channeling of the primary and secondary ions may be responsible for these observations. ( M + H) + and ( M + H − H 2 O) + were observed for SA on Au and Ge but not Ag. An explanation involves the deprotonation of the SA by Ag oxide as opposed to the less active Au and oxidic Ge surfaces. For the analogous BS monolayers, no ( M + H) + or ( M + H − H 2 O) + were observed. Barium cationization (( M −- H + Ba 2+) +) was observed for all BS layers on any of the substrates. The only substrate cationization observed, ( M + Ag) + was for BS samples prepared on Ag. For SA and BS multilayers, attenuation of substrate signals increased with the number of layers; the attenuation is greater for equivalent numbers of BS layers than SA. In addition, the substrate has an effect, the attenuation being greatest for Ag, then Ge, then Au. Examination of molecular ion yields versus time under static sputtering conditions shows that initial ion beam damage-extends to approximately 250 Å. Studies of molecular ion yields versus time (while under ion beam irradiation) indicate that the substrate, packing density, and added cations can have an effect on the ion yield.

Modeling of a rf glow discharge plasma

A dynamic model for a rf glow discharge plasma in a parallel-plate geometry has been developed by considering the charged particle transport including the collisional relaxation kinetics. The model has been applied to low pressure and low gas temperature Ar discharge plasmas. A second-stage investigation, i.e., the study of the excited species, has been carried out in comparison with experiments. The effect of the frequency of the driving source has been investigated from the viewpoint of the ionization rate required to maintain the discharge in a rf plasma.