Search

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]

Helicon sources are known to produce high-density plasmas and have found many applications. Different types of antenna have been used for helicon excitation but none of them generate a radio-frequency (rf) field that matches the helicon wave field determined by the dispersion equation. We show that this match can be obtained to a very good approximation by using a birdcage type antenna. Our plasma experiments show that a helicon regime with electron densities up to 5×1012 cm-3 is obtained for very low rf power injection (typically 200 W), and at an unusual operating pressure up to 25 Pa. [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]

Presents a study that determined the time evolution of particle size and their number density through the use of in situ multi-angle polarization-sensitive laser light scattering. Discussion on the coagulation model; Comparison of multi-angle polarization-sensitive laser light scattering with other laser scattering methods; Demonstration on the existence of nonspherical agglomerates during the early phase of agglomeration.

Presents a study that observed visible photoluminescence at room temperature in amorphous hydrogenated silicon particulates during their formation in a silane radio-frequency plasma. Model consistent with the observations of visible photoluminescence; Source of contamination in plasma processing for the microelectronics industry; Description of crystalline silicon.

Presents information on a study that examined the structural properties of silicon powders produced in a low pressure silane plasma. Methodology of the study; Results and discussion on the study; Conclusions.

Presents a study which examined the influences of a high excitation frequency in the glow discharge technique on the process plasma and the properties of hydrogenated amorphous silicon. Experimental details; Results; Discussion.

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.

Plasma conditions for microcrystalline silicon deposition generally require a high flux of atomic hydrogen, relative to SiHα=0→3 radicals, on the growing film. The necessary dominant partial pressure of hydrogen in the plasma is conventionally obtained by hydrogen dilution of silane in the inlet flow. However, a hydrogen-dominated plasma environment can also be obtained due to plasma depletion of the silane in the gas mixture, even up to the limit of pure silane inlet flow, provided that the silane depletion is strong enough. At first sight, it may seem surprising that the composition of a strongly depleted pure silane plasma consists principally of molecular hydrogen, without significant contribution from the partial pressure of silane radicals. The aim here is to bring some physical insight by means of a zero-dimensional, analytical plasma chemistry model. The model is appropriate for uniform large-area showerhead reactors, as shown by comparison with a three-dimensional numerical simulations. The SiHα densities remain very low because of their rapid diffusion and surface reactivity, contributing to film growth which is the desired scenario for efficient silane utilization. Significant SiHα densities due to poor design of reactor and gas flow, on the other hand, would result in powder formation wasting silane. Conversely, hydrogen atoms are not deposited, but recombine on the film surface and reappear as molecular hydrogen in the plasma. Therefore, in the limit of extremely high silane depletion fraction (>99.9%), the silane density falls below the low SiHα densities, but only the H radical can eventually reach significant concentrations in the hydrogen-dominated plasma. [ABSTRACT FROM AUTHOR]

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 the case for the silane utilization. In this work, a reactor-independent methodology has been developed to determine the optimum plasma parameters in terms of deposition rate, silane utilization, and material microstructure. Using this optimization method, a microcrystalline layer has been deposited over a large area at a rate of 10.9 Å/s, with a silane utilization efficiency above 80%. [ABSTRACT FROM AUTHOR]

The electromagnetic standing wave effect can become the main source of nonuniformity limiting the use of very high frequency in large area reactors exceeding 1 m2 required for industrial applications. Recently, it has been proposed and shown experimentally in a cylindrical reactor that a shaped electrode in place of the conventional flat electrode can be used in order to suppress the electromagnetic standing wave nonuniformity. In this study, we show experimental measurements demonstrating that the shaped electrode technique can also be applied in large area rectangular reactors. We also present results of electromagnetic screening by a conducting substrate which has important consequences for industrial application of the shaped electrode technique. [ABSTRACT FROM AUTHOR]

Investigates the contamination in silane radio frequency plasma due to the generated and suspended particles. Detection of powder by illumination of the reactor volume; Uses of the simple diagnostic for global, spatio-temporal powder dynamics; Details on the power modulation.

Examines the negative ion mass spectra and particulate formation in radio frequency (rf) silane plasma deposition experiments. Use of mass spectrometer in measuring mass spectra; Presence of negative ion on lower power frequency; Effectiveness of low-frequency mixture in producing rf modulation.

Comments on issues related to ion energy uniformity in high-frequency capacitive discharges. Information that in recent times researchers have shown that the time-averaged plasma potential is uniform in a high frequency capacitive reactor; Opinion that ion energy will not be uniform when a dielectric substrate is on the electrode; Report that the ion bombardment energy is uniform only at conducting electrode surfaces.