Christoph Hollenstein

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Results are presented which are geared towards an understanding of the influence of powder formation during film growth. Plasma chemistry is correlated with the morphology, structure (inferred through infrared spectroscopy, scanning electron microscopy and X-ray diffraction) electro-optical and density of states of intrinsic films deposited under continuous and power modulated operation. Results show that for modulation frequencies where no powder formation occurs and low substrate temperatures T (150 degre

Electromagnetic wave propagation effects can give rise to important limitations for processing uniformity in large area, radio-frequency (rf) capacitive plasma reactors. The electromagnetic wavefield solution is derived for a capacitive, high-frequency, cy ...

a-Si:H films were prepared using pure silane in the temperature range from 200 degrees C up to 400 degrees C by the very high frequency glow discharge (VHF-GD) technique. During deposition a He/Ne laser beam directed across the discharge monitored powder formation. H-content and microstructure were determined by IR-spectroscopy. The impurity contents of oxygen (O), nitrogen (N) and carbon (C) were analysed by SIMS. A surface profiler was used to measure the internal stress and thickness of the films. The sa

Stable negative ions containing up to sixteen silicon atoms have been measured by mass spectrometry in RF power-modulated silane plasmas for amorphous silicon deposition. These hydrogenated silicon cluster ions reach much higher masses than the positive ions, which have no more than six silicon atoms. This supports the view that negative ions are the precursors to particulate formation in silane plasmas. The time-dependent fluxes of positive and negative ions from the plasma are shown with a 5 mus time reso

It is now generally recognized that the excitation frequency is an important parameter in radio-frequency (rf) plasma-assisted deposition. Very-high-frequency (VHF) silane plasmas (50-100 MHz) have been shown to produce high quality amorphous silicon films up to 20 angstrom/s [H. Curtins, N. Wyrsch, M. Favre, and A. V. Shah, Plasma Chem. Plasma Processing 7, 267 (1987)], and therefore the aim of this work is to compare the VHF range with the 13.56 MHz industrial frequency in the same reactor. The principal

The fluctuating behavior of a Sulzer Metco F4 de plasma gun has been investigated by simultaneous measurement of the:time dependencies of the are voltage and of images from the nozzle interior. An end-on imaging arrangement using a mirror and a mask in the optical path from the are to the camera allows visualization of the anodic are attachment by strongly attenuating the bright emission from the are column, With the torch operating in the restrike mode, sequences of images have been acquired in synchroniza

Microcrystalline hydrogenated silicon films (muc-Si:H) have been deposited by a high current DC plasma in argon-silane-hydrogen mixtures at growth rates up to 10 nm/s and at substrate temperatures below 500 degreesC. Scanning electron microscopy, X-ray diffraction and FTIR analyses show that these films are highly crystallized. The surface morphology depends strongly on the experimental conditions and varies from a cauliflower structure to a prismatic one. The crystalline orientation of the films also chang

During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0 less than or equal to B-tor less than or equal to 1.46T, I-p less than or equal to 800kA, kappa less than or equal to 2.05, -0.7 less than or equal to delta less than or equal to 1. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000 s(-1) have been stabilized

Cost reduction constraints for microcrystalline silicon thin film photovoltaic solar cells require high deposition rates and high silane gas utilization efficiencies. If the requirements in deposition rate have sometimes been fulfilled, it is generally not ...

Charge-exchange collisions and radio frequency (RF) excitation combine to give peaks in the ion energy distribution measured at the ground electrode of an argon plasma in a capacitive reactor. These peaks are used as a diagnostic to reconstruct the profile of the time-averaged potential in the sheath. Particle-in-cell (PIC) simulations show that the method is accurate. The method is applied to investigate the sheath thickness as a function of excitation frequency at constant plasma power. The time-averaged

The growth and properties of nanosized silicon particles produced by gas-phase reaction in a low-pressure silane plasma has been studied. In situ ion-mass spectroscopy and Mie scattering measurements were used to monitor the formation of powders. High resolution transmission electron microscopic (HREM) studies confirmed the observations made by Raman spectroscopy that the nanoparticles grow from medium range ordered clusters. Onset of crystallization was similar to 700 degrees C when structures ranging from

Previous measurements of SixHm- anions and electrons in the afterglow of silane discharges are analyzed here. A model of plasma anion chemistry includes two sources of anions, two possible causes of x-->x+1 anion growth, and anion loss by mutual neutralization. Comparison to pulsed-discharge measurements for x=1-6, for a range of discharge times, clearly establishes radical reactions as the primary cause of anion growth; prior estimates generally suggested silane reactions. This comparison also indicates th

Plasma treatment of PET films was carried out under argon, followed by exposure to an oxygen atmosphere. The films underwent considerable changes in surface composition and morphology, as demonstrated by contact angle measurements, FTIR-ATR, AFM, and XPS. It was found that the surface acquired oxygen containing polar functional groups such as -C=O, -OH, and -OOH, which increased in number as the plasma treatment time increased. During storage, the treated films underwent significant surface reorganization,

Partial-depth modulation of the rf power in a capacitive discharge is used to investigate the relative importance of negative ions and neutral radicals for particle formation in low-power low-pressure silane plasmas. For less than 85% modulation depth, anions are trapped indefinitely in the plasma and particle formation ensues, whereas the polymerized neutral flux magnitudes and dynamics are independent of the modulation depth and the powder formation. These observations suggest that negative ions could be

Understanding particle dynamics requires comparison of spatially resolved measurements with two-dimensional (2-D) simulations, In this work, a cross section of a capacitive discharge is illuminated with an expanded laser beam, and global scattered light is recorded by camera, Plasma equipotentials are visualized using the scattered intensity from a small amount of particles trapped in an argon plasma. At low RF voltages, good agreement is found with 2-D fluid simulations, whereas displacement of the power c

A simple one-dimensional model for plasma deposition in a rectangular showerhead reactor with single side pumping has been developed in order to explain the mechanisms which yield uniform deposition using this gas flow configuration. Although the flow velocity increases linearly with distance towards the pumping side, the solution of the transport equations for the neutral species shows that their number densities are constant throughout the reactor. Consequently, the plasma and surface deposition reactions

An overview of the most recent experimental and modelling efforts on powder formation in reactive plasmas is given. The physics and chemistry of these dusty plasmas and their fundamental mechanisms leading to the production of nanometre-sized particles and their successive agglomeration leading to micrometre-sized particles are reviewed. The central role of particle charging and of charge fluctuations regarding the particle agglomeration is emphasised. Finally, the influence of the dust particles on the pla

Surface Dielelectric Barrier Discharges (DBD) are becoming very attractive in the field of flow control technologies for their promising effects on stabilising separating flows, at least at low speeds under the so-called ionic wind effect. Numerous experiments have been performed over the last few years to further study these effects. At high speeds, such as transonic aircraft or internal engine flow speeds, EPFL has performed studies showing a clear effect of the flow on the plasma, and a lesser effect on

The cavity ring-down technique is applied to an industrial-scale radio-frequency (rf) plasma reactor for the measurement of the density and spatial profile of negative ions in pure oxygen and hydrogen rf plasmas, and for the detection of nanometric particles in argon-silane plasmas. The real-time observation of powder formation is demonstrated to be feasible by the cavity ring-down technique. An observed plasma-induced spurious drift of the ring-down time is also studied and related to water desorption from

Boron nitride films were deposited by r.f. capacitively-coupled plasma (13.56 MHz) using two different gas mixtures: Ar-B2H6-NH3 and Ar-B2H6-N-2. In order to study the gas-phase reactions of the plasma in situ Fourier transform infrared absorption spectroscopy has been used. The study reveals that, in our conditions, mixing ammonia with diborane leads to the well-known creation of diammoniate of diborane. In the presence of the plasma, salt production is inhibited and creation of aminoborane is observed. Re

Christoph Hollenstein

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On the a-Si:H film growth: The role of the powder formation

Electromagnetic field nonuniformities in large area, high-frequency capacitive plasma reactors, including electrode asymmetry effects

Influence of Higher Deposition Temperature on a-Si-H Material Properties, Powder Formation and Light-Induced Degradation, Using the Vhf (70 Mhz) Glow-Discharge Technique

Negative Hydrogenated Silicon Ion Clusters as Particle Precursors in RF Silane Plasma Deposition Experiments

Frequency-Effects in Silane Plasmas for Plasma Enhanced Chemical Vapor-Deposition

Time-resolved imaging of anodic arc root behavior during fluctuations of a dc plasma spraying torch

Rapid deposition of hydrogenated microcrystalline silicon by a high current DC discharge

Recent Results from the Tcv Tokamak

Optimization of the microcrystalline silicon deposition efficiency

Reconstruction of the Time-Averaged Sheath Potential Profile in an Argon Radiofrequency Plasma Using the Ion Energy-Distribution

Growth, microstructure and sintering behavior of nanosized silicon powders

Anion reactions in silane plasma

Surface modification of polyester films by RF plasma

Partial-depth modulation study of anions and neutrals in low-pressure silane plasmas

Global visualization of powder trapping in capacitive RF plasmas by two-dimensional laser scattering

A gas flow uniformity study in large-area showerhead reactors for RF plasma deposition

The physics and chemistry of dusty plasmas

Surface DBD’s and plasma-flow interaction

Applications of the cavity ring-down technique to a large-area rf-plasma reactor

Diborane nitrogen/ammonia plasma chemistry investigated by infrared absorption spectroscopy