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Journal ArticleDOI

Control of powder formation in silane discharge by cathode heating and hydrogen dilution for high-rate deposition of hydrogenated amorphous silicon thin films

01 Oct 1993-Journal of Applied Physics (American Institute of Physics)-Vol. 74, Iss: 7, pp 4540-4545
TL;DR: In this paper, hydrogenated amorphous silicon (aSi:H) films have been deposited at high growth rates by increasing the rf power density while the optoelectronic quality of the films has been concurrently taken care of by controlling powder formation due to gas phase polymerization in the plasma.
Abstract: Hydrogenated amorphous silicon (a‐Si:H) films have been deposited at high growth rates by increasing the rf power density while the optoelectronic quality of the films has been concurrently taken care of by controlling powder formation due to gas‐phase polymerization in the plasma. This has been achieved by heating the cathode together with the anode in the capacitive coupling arrangement and keeping the cathode temperature close to that of the anode. This, together with hydrogen dilution of the source gas, has been used to control powder formation in the silane discharge. The films have been evaluated by optical and infrared vibrational spectroscopy, dark conductivity, secondary photoconductivity, and internal quantum efficiency measurements.
Citations
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Journal ArticleDOI
TL;DR: In this article, the model equations for particle formation, growth and transport were proposed for silane plasma chemical vapour deposition and were solved numerically, including the plasma chemistry of silane, particle nucleation by cluster formation, aerosol dynamics and transport of chemical species and particles.
Abstract: The model equations for particle formation, growth and transport were proposed for silane plasma chemical vapour deposition and were solved numerically. We included the plasma chemistry of silane, particle nucleation by cluster formation, aerosol dynamics and transport of chemical species and particles. The evolutions of gaseous species and particles along the reactor were presented for several conditions of process variables such as reactor pressure, total gas flow rate and electric field strength. To reduce the CPU time in numerical simulation, we used lower values of electric field strength in the sheath region then the actual values and analysed the effects of electric field strength qualitatively. It was found that the concentration profiles of positive ions show peaks at the centre of the plasma reactor, whereas most of the negative ions are located in the bulk plasma region owing to the electrostatic repulsion from the sheath region. Most of the particles in the plasma reactor are located around the sheath boundaries, owing to the balance of the electrostatic force and the ion drag force. As the reactor pressure increases, the contaminant concentration and diameter increase in the plasma reactor. The lower the total gas flow rate the higher the particle concentration and the larger the particle diameter. The particle concentration and diameter in the plasma reactor increase abruptly as the electric field strength in the sheath region increases.

23 citations

Journal ArticleDOI
TL;DR: A combination of Raman scattering, infrared absorption, and small angle x-ray scattering experiments was used to study the short-range order and microstructure of films deposited in different (dusty or otherwise) plasma conditions as mentioned in this paper.
Abstract: Hydrogenated amorphous silicon (a‐Si:H) films were deposited at high growth rates by increasing the rf power density in a (SiH4+H2) discharge, while powder formation due to gas phase polymerization was controlled by heating the cathode together with the anode. A combination of Raman scattering, infrared absorption, and small angle x‐ray scattering experiments was used to study the short‐range order and microstructure of films deposited in different (dusty or otherwise) plasma conditions. The results were correlated with initial and light‐soaked photoresponse to demonstrate that films with more microstructure and less short‐range order were generally poorer.

14 citations

Book ChapterDOI
01 Jan 2000
TL;DR: In this paper, the formation of particles in low-temperature, low-pressure plasmas is discussed and various technological aspects of the formation and characterization of the powders are discussed.
Abstract: Publisher Summary This chapter shows that low-pressure, low-temperature plasmas may generate a high particle nucleation rate and that they can allow for control of the composition, size, and atomic structure of the particles. These plasmas can produce nanometric particles of different composition, size, size distribution, and microstructure, depending on the discharge conditions. Besides the plasma parameters, modulation of the discharge and control of the duration of the plasma-on time can determine particle features. Results on the formation of powders of different alloys have also been presented. The scientific context of the formation of particles in low-temperature, low-pressure plasmas is reviewed. The basic studies of particles in interstellar space, the concern of the microelectronics industry about their contamination effect, the recent interest in nanostructured ceramics, and the new field of plasma crystals are also described. The various technological aspects of the formation and characterization of the powders are discussed. Detailed reports on the strong light emission observed in silicon nanoparticles produced in an rf discharge at low pressures showed that its origin is blackbody emission. In spite of using low laser intensities, nanoparticles heat up as a result of their low efficiency for dissipating heat through conduction between particles. This effect may be, in some cases, responsible for the light emission in other nanostructured materials.

11 citations

Journal ArticleDOI
TL;DR: In this article, the formation dynamics in the process of SiOx film deposition from a SiH4 and N2O gas mixture by a low frequency plasma enhanced chemical vapor deposition have been investigated using scanning electron microscopy and laser light scattering.
Abstract: Dust particle formation dynamics in the process of SiOx film deposition from a SiH4 and N2O gas mixture by a low frequency plasma enhanced chemical vapor deposition have been investigated using scanning electron microscopy and laser light scattering. The deposited films are confirmed to be SiOx from the measurements of Auger electron spectroscopy, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. It is observed by scanning electron microscopy that particles are deposited on Si substrate at the plasma power frequency f=5 kHz and above both with and without substrate heating (400 °C), while no particle is deposited below f=1 kHz. Moreover, the laser light scattering indicates that particles are generated at the plasma power frequency of f=3 kHz and above in the gas phase, and that they are not generated in the gas phase at below f=3 kHz. Properties (the refractive index, resistivity, and Vickers hardness) of the films with particles are inferior to those of the films without par...

8 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of interelectrode spacing on the properties of hydrogenated amorphous silicon (a•Si:H) films grown at high radio-frequency (rf) power density by rf plasma enhanced chemical vapor deposition method, with control of dusty plasma conditions by heating both the electrodes, was investigated.
Abstract: The effect of interelectrode spacing on the properties of hydrogenated amorphous silicon (a‐Si:H) films grown at high radio‐frequency (rf) power density by rf plasma enhanced chemical vapor deposition method, with control of dusty plasma conditions by heating both the electrodes, was investigated. The formation of precursors responsible for gas phase polymerization itself was sought to be controlled by preheating of the source gas mixture. Optimization of the interelectrode spacing for film characteristics was carried out for this novel deposition technique combining cathode heating and preheating of the source gases. The films were characterized by infrared vibrational spectroscopy, absorption and reflection measurements in the visible and near infrared regions, measurements of dark and photo‐conductivity (with light induced degradation), and electron spin resonance spectroscopy.

5 citations

References
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Journal ArticleDOI
TL;DR: A self-consistent fluid model of radio-frequency glow discharges has been used to analyze the existence of two different discharge regimes and of the transition between them, and a realistic description of the electron kinetics has been obtained by considering separately two electron groups representing, respectively, the tail and the bulk of the electrons distribution function.
Abstract: A self-consistent fluid model of radio-frequency glow discharges has been used to analyze the existence of two different discharge regimes and the transition between them The existence of these regimes had been previously established by Levitskii [Sov Phys Tech Phys 2, 887 (1958)] The self-sustaining and power-deposition mechanisms that characterize each of these regimes are drastically different In the first regime, termed as the ``wave-riding regime'' corresponding to low discharge power, most of the power deposition is due to bulk plasma electrons heated by the sheath expansions In the second regime termed as the ``secondary electron regime'' corresponding to higher discharge power, the discharge is sustained mainly by electrons emitted by the electrodes under ion bombardment and avalanching in the sheath regions The numerical results are in good agreement with previous experimental measurements by Godyak and Kanneh [IEEE Trans Plasma Sci PS-14, 112 (1986)] The results presented in this paper form the first self-consistent description of these different regimes and of the transition between them The validity domain of the model is restricted to pressure higher than a fraction of Torr and frequency less than a few tens of MHz The gas being considered is helium and the discharge power varies between 0 and 700 mW ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ The model is based on solutions of electron and ion fluid equations describing charged particle transport coupled with Poisson's equation for the electric field A realistic description of the electron kinetics has been obtained by considering separately two electron groups representing, respectively, the tail and the bulk of the electron distribution function The validity of the two-electron group fluid model has been checked with Monte Carlo simulations

324 citations

Journal ArticleDOI
TL;DR: In this paper, the generation and behavior of particles in a low-pressure silane-argon discharge have been analyzed under continuous and pulsed radio-frequency (rf) excitation conditions.
Abstract: The generation and behavior of particles in a low‐pressure silane‐argon discharge have been analyzed under continuous and pulsed radio‐frequency (rf) excitation conditions. In the continuous rf excitation regime, the influence of parameters such as gas temperature and silane partial pressure are determined. By using rf pulsed excitation, it is shown that gas‐flow effects play a predominant role for particle dynamics when the excitation is stopped. Radio‐frequency regimes with short and adjustable rf off sequences are used to study both the inhibition of particle formation and the elimination of particles from the dusty plasmas. The electrical properties of the discharge are shown to be sensitive to the presence of the particles. Simple models for particle trapping in the plasma edge and for particle dynamics when the discharge is turned off are presented.

283 citations

Journal ArticleDOI
TL;DR: In this article, the effect of plasma excitation frequency on the deposition rate and on the optical and electrical properties of amorphous silicon film was studied over the range 25-150 MHz.
Abstract: The effect of plasma excitation frequency on the deposition rate and on the optical and electrical properties of amorphous silicon film is studied over the range 25–150 MHz. Deposition rates as high as 21 A/sec are obtained at ∼70 MHz, which is a factor of 5–8 larger than typical rates obtained for the conventional 13.56-MHz silane glow-discharge system. Only minor changes occur in the defect density (as measured by the photothermal deflection spectroscopy method), the optical bandgap, and the electrical conductivity over this frequency range. In a preliminaryinterpretation given here, the large variation of the deposition rate as a function of excitation frequency is explained in terms of changes in the electron energy distribution function.

181 citations

Journal ArticleDOI
TL;DR: In this paper, a simple particle-scavenging arrangement based on thermophoresis was proposed to remove particles from glow discharges, where the particles are suspended in the discharge and move away from a heated electrode towards a cooled electrode.
Abstract: Particles in glow discharges are charged negatively and are therefore often suspended electrostatically since the plasma potential is usually more positive than the potential of surfaces bounding the plasma. However, in addition to responding to electrostatic and gravitational forces, particles are sensitive to forces associated with gradients in neutral gas temperature. A series of experiments were performed varying the temperature of water circulated through planar, parallel electrodes. When particles are present and are suspended in the discharge, they move away from a heated electrode and towards a cooled electrode. In the absence of particles, the discharge optical emission spatial profile and electrical characteristics did not change significantly for any combination of electrode heating or cooling. Particles remaining in the interelectrode gap after the discharge is extinguished appear to be uncharged. With particles present, the discharge electrical properties and time‐ and space‐resolved optical emission take on characteristics associated with discharges in electron attaching gases. We report on a simple particle‐scavenging arrangement based on thermophoresis that can be used to remove particles from a discharge.

162 citations

Journal ArticleDOI
TL;DR: In this article, the electron properties in a parallel plate capacitively coupled rf discharge were studied with results from a Monte-Carlo simulation, and the dc component of the sheath potential was found to be a function of the ratio λ/d, where is the electron mean free path and d is the electrode spacing.
Abstract: Electron properties in a parallel plate capacitively coupled rf discharge are studied with results from a Monte‐Carlo simulation. Time averaged, spatially dependent electron distributions are computed by integrating, in time, electron trajectories as a function of position while oscillating the applied electric field at rf frequencies. The dc component of the sheath potential is solved for in a self‐consistent manner during the simulation. For conditions where the secondary emission coefficient for electrons from the electrodes is large, the electron distribution is spatially differentiated, being dominated by an e‐beam component near the electrodes while being nearly in equilibrium with the applied electric field in the body of the plasma. The dc component of the sheath potential is found to be a function of the ratio λ/d, where λ is the electron mean free path and d is the electrode spacing.

159 citations