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Different types of antenna are used for helicon excitation but none of them generate a radio-frequency field that matches the helicon wave field determined by the dispersion equation. This match can be obtained to a very good approximation by using a birdcage type antenna.

High resolution transmission electron microscopic, infrared spectroscopic and Raman spectroscopic analyses show that silicon powder obtained in a low pressure silane plasma is heterogeneous. Silicon powders exhibit differential structural properties depending upon the location of their collection in the reactor. Infrared spectra indicates aggregated silicon-hydrogen phases and the existence of oxidized phases in the powder, when exposed to air. Annealing at 300 degrees celsius results in a crystalline silicon-like Raman vibrational band.

Mass spectroscopic measurements of time-resolved fluxes of negative ionic clusters in a power-modulated radio frequency silane plasma reveal that hydride anions percolate from the plasma with an energy of 0.5 electron volts, during afterglow. Modulation frequency influences the plasma composition. This dependency of the plasma composition is indicated by flux measurements for different ions masses.

Hydrogen evolution, elastic recoil detection analysis and infrared spectroscopy were used to investigate the effect of a high excitation frequency in the glow discharge technique on the process plasma and the characteristics of hydrogenated amorphous silicon. The results showed that as the substrate temperature decreased from 280 to 50 degrees celsius, significant changes occured in the structural and electrical properties of thin films prepared at the frequency of 13.56 MHz.

A resonant planar antenna as an inductive plasma source operating at 13.56 MHz inside a low pressure vacuum vessel is presented for potential plasma processing applications. Its principle consists in interconnecting elementary resonant meshes composed of inductive and capacitive elements. Due to its structure, the antenna shows a set of resonant modes associated with peaks of the real input impedance. Each of these modes is defined by its own current and voltage distribution oscillating at the frequency of the mode. A rectangular antenna of 0.55m×0.20m has been built, and first results obtained with argon plasmas are presented. Plasma generation is shown to be efficient as densities up to 4·1017m-3 at 2000 W have been measured by microwave interferometry at a distance of 4 cm from the source plane. It is also demonstrated that the plasma couples inductively with the resonating currents flowing in the antenna above a threshold power of about 60 W. A non-uniformity of less than ±5% is obtained at 1000 W at a few centimeters above the antenna over 75% of its surface. [ABSTRACT FROM AUTHOR]

One of the main challenges for silicon thin film deposition for solar cell applications is to achieve high rate deposition in order to reduce the manufacturing costs. However, when silane and hydrogen are used as precursor gas in parallel plate plasma-enhanced chemical vapor deposition, high rate deposition is generally synonymous of powdery discharge. In this work, time- and space-resolved light scattering experiments are presented. These were performed in an industrial-type large area reactor with a variable interelectrode distance. Results show that with a standard 25 mm interelectrode distance, the fraction of silane transformed into powder can be as high as 50% and that reducing the interelectrode distance shifts to higher pressure the appearance of powder in the discharge. From a standard 25 mm interelectrode distance to a 10 mm narrow gap reactor, the threshold pressure was increased from 2 to 7 mbars. More generally, it is proposed that the onset of powder formation depends mainly on the product of the interelectrode distance and the gas residence time in the discharge. [ABSTRACT FROM AUTHOR]

In large-area radio-frequency (rf) capacitive reactors, the redistribution of rf current to maintain current continuity near asymmetric sidewalls causes a perturbation in rf plasma potential to propagate along the resistive plasma between capacitive sheaths. The damping length of the perturbation can be determined by a telegraph equation. Experiments are described using a surface array of unbiased electrostatic probes in the ground electrode to verify the theoretical model of the telegraph effect in Howling et al. [J. Appl. Phys. 96, 5429 (2004)]. The measured spatial dependence of the plasma potential rf amplitude and circulating nonambipolar current agree well with two-dimensional numerical solutions of the telegraph equation. The rf plasma potential can be made uniform by using symmetric reactor sidewalls. [ABSTRACT FROM AUTHOR]

In small area capacitive reactors, the rf and dc components of the plasma potential can be assumed to be uniform over all the plasma bulk because of the low plasma resistivity. In large area reactors, however, the rf plasma potential can vary over a long range across the reactor due to rf current flow and the nonzero plasma impedance. A perturbation in rf plasma potential, due to electrode edge asymmetry or the boundary of a dielectric substrate, propagates along the resistive plasma between capacitive sheaths. This is analogous to propagation along a lossy conductor in a transmission line and the damping length of the perturbation can be determined by the telegraph equation. Some consequences are the following: (i) The spatial variation in sheath rf amplitudes causes nonuniform rf power dissipation near to the reactor sidewalls. (ii) The surface charge and potential of a dielectric substrate can be negative and not only positive as for a uniform rf plasma potential. The variation of sheath dc potential across a dielectric substrate causes nonuniform ion energy bombardment. (iii) The self-bias voltage depends on the plasma parameters and on the reactor and substrate dimensions—not only on the ratio of electrode areas. (iv) The nonuniform rf plasma potential in presence of the uniform dc plasma potential leads to nonambipolar dc currents circulating along conducting surfaces and returning via the plasma. Electron current peaks can arise locally at the edge of electrodes and dielectric substrates. Perturbations to the plasma potential and currents due to the edge asymmetry of the electrodes are demonstrated by means of an analytical model and numerical simulations. [ABSTRACT FROM AUTHOR]

Experiments using a lens-shaped circular electrode are described to measure the correction of plasma nonuniformity due to the standing wave effect in a large area very high frequency plasma reactor. This work is the experimental verification of the theoretical reactor design in cylindrical geometry recently presented by L. Sansonnens and J. Schmitt, Appl. Phys. Lett. 82, 182 (2003). It is found that the lens-shaped electrode effectively compensates the standing wave effects by creating a uniform rf vertical electric field in the plasma volume. The plasma is uniform, except for edge effects, for a wide range of parameters and consequently the design is suitable for plasma processing. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Previous measurements of Si[sub x]H[sub m][SUP ARRANGE="STAGGER"]-] 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 that electron attachment to radicals, not silane, is the largest source of SiH[sub m][SUP ARRANGE="STAGGER"]-] anions. Measured afterglow electron decay and SiH[sub m][SUP ARRANGE="STAGGER"]-] signals are also consistent with efficient, low energy electron attachment to radicals. Reasonable agreement with the observations is obtained using realistic estimates of the radical density, cation density, and the values of radical-anion (k[sub x]) and mutual neutralization rate coefficients. However, the x dependence of the k[sub x] required to fit the data is surprising. These conclusions have major consequences for silane-discharge, particle-nucleation models. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Time- and space-resolved light scattering experiments are performed in an industrial-type large area reactor with a variable interelectrode distance. The studies have shown that the onset of powder formation has depended on the product of the interelectrode distance and the gas residence time in the discharge.

The influence of excitation frequency on intrinsic stress in hydrogenated amorphous silicon during plasma enhanced chemical vapor deposition was investigated. The results showed that the diminished ion energy at higher excitation frequencies was the cause of the decrease in intrinsic stress and the increase in surface roughness. Very high frequency plasma enhanced chemical vapor deposition significantly reduced the intrinsic stress of hydrogenated amorphous silicon films.

Presents a study which performed intrinsic stress measurements on hydrogenated amorphous silicon (a-Si:H) films deposited with different excitation frequencies, by plasma-enhanced chemical vapor deposition. Method used in preparing the films; Plot of the intrinsic stress of the a-Si:H films; Change in the surface roughness in the films.