Rfg Ralph Meulenbroeks

Plasma chemistry aspects of a-Si:H deposition using an expanding thermal plasma

The plasma chemistry of an argon/hydrogen expanding thermal arc plasma in interaction with silane injected downstream is analyzed using mass spectrometry. The dissociation mechanism and the consumption of silane are related to the ion and atomic hydrogen fluence emanating from the arc source. It is argued that as a function of hydrogen admixture in the arc, which has a profound decreasing effect on the ion-electron fluence emanating from the arc source, the dissociation mechanism of silane shifts from ion-electron induced dissociation towards atomic hydrogen induced dissociation. The latter case, the hydrogen abstraction of silane, leads to a dominance of the silyl (SiH3) radical whereas the ion-electron induced dissociation mechanism leads to SiHx (x<3) radicals. In the pure argon case, the consumption of silane is high and approximately two silane molecules are consumed per argon ion-electron pair. It is shown that this is caused by consecutive reactions of radicals SiHx (x<3) with silane. Almost indepe...

The argon-hydrogen expanding plasma: model and experiments

An argon expanding cascaded arc plasma, with small amounts (0-10 vol.%) of hydrogen added to the flow, is investigated by means of Thomson-Rayleigh scattering and optical emission spectroscopy. The results, especially the electron density behaviour as a function of the distance from the onset of the expansion, are interpreted by comparison with results of a quasi one-dimensional model. The associative charge exchange reaction between Ar+ ions and H2 molecules plays a dominant role in the model. Assuming that H2 molecules from the wall enter the plasma in the shock region, the large ionization loss can be explained. Good agreement between model and experiment is found for the electron and neutral density and the electron temperature behaviour. This makes plausible the existence of a recirculation flow inside the vacuum vessel, which transports wall-associated hydrogen molecules towards the plasma.

Emission spectroscopy on a supersonically expanding argon/silane plasma

Results from emission spectroscopy measurements on an Ar/SiH4 plasma jet which is used for fast deposition of amorphous hydrogenated silicon are presented. The jet is produced by allowing a thermal cascaded arc plasma in argon (I=60 A, V=80 V, Ar flow=60 scc/s and pressure 4 × 104 Pa) to expand to a low pressure (100 Pa) background. In the resulting plasma SiH4 is injected in front of the stationary shock front. Assuming a partial local thermal equilibrium situation for higher excited atomic levels, emission spectroscopy methods yield electron densities (∼ 1018 m−3), electron temperatures (∼5000 K) as well as concentrations of H+, Si+, and Ar+ particles. The emission spectrum of the SiH radical, the A 2Δ–X 2Π electronic transition, is observed. Numerical simulations of this spectrum are performed, resulting in upper limits for the rotational and vibrational temperatures of 4000 and 5600 K, respectively. The results can be understood assuming that, in the expansion, charge exchange and dissociative recombi...

Fabry–Pérot line shape analysis on an expanding cascaded arc plasma in argon

Fabry–Perot line profile measurements have been used to obtain heavy particle temperatures and electron densities for an expanding cascaded arc plasma in argon. This was done for the argon 415.9 and 696.5 nm neutral lines as a function of the distance from the onset of the expansion. Temperatures in the range of 2000–12 000 K were obtained. The electron density in the beginning of the expansion appeared to be 5.6×1021 m−3. The 696.5 nm line profiles appeared to be asymmetric because of self‐absorption by cool metastables around the plasma. The density and temperature of these metastables could be determined by fitting the measurements to a theoretical model, and appeared to be around 1017 m−3 and around 3000 K, respectively.

On expanding recombining plasma for fast deposition of a-Si:H thin films

A high-density expanding recombining plasma is investigated for deposition of a-Si:H thin films. The deposition method allows high growth rates and it relies on separation of plasma production in a high-pressure thermal arc, and transport of fragments of injected SiH4 monomer to the substrate. Some characteristics of the plasma are discussed together with an explanation of the dominant chemical kinetics, which proceed mainly through heavy-particle interactions. The deposition results indeed show very high growth rates from 2-30 nm s-1 on areas of 30 cm2. The properties of the layers are characterized by measuring their refractive index (in the range 3.1-3.8) and bandgap 1.2-1.5 eV). Analysis of the oxygen content in the deposited films shows oxidation of the samples in air, which is probably associated with the microstructure of the layers.

The role of hydrogen during plasma beam deposition of amorphous thin films

Abstract The influence of wall-associated H 2 molecules and other hydrogen-containing monomers on the degree of ionization in the expanding thermal plasma used for the fast plasma beam deposition of amorphous hydrogenated carbon (a-C:H) and amorphous hydrogenated silicon (a-Si:H) was determined. Deposition models are discussed with emphasis on the specific role of the ion during deposition. The connection between the role of atomic hydrogen and the degree of ionization in the plasma beam deposition of a-C:H and a-Si:H is addressed.

Atomic hydrogen and argon ground state density determination in a recombining plasma using visible light absorption spectroscopy

The atomic radical density in the first excited state, obtained by the technique of optical absorption spectroscopy, and a simple kinetic model are used to determine the radical ground state density in a recombining expanding plasma. The kinetic model used does not require knowledge of the shape of the electron energy distribution function. The information on electron density and electron temperature has been derived from the Thomson-Rayleigh scattering diagnostic. The method is demonstrated for the determination of the absolute ground state densities of atomic hydrogen H(n=1) and argon Ar(3p6) in a freely expanding plasma jet.

Optical Diagnostics for High Electron Density Plasmas

Nowadays high electron density plasmas are, beside their fundamental interest, widely used for many applications, e.g., light sources and plasma processing. The well known examples of high electron density plasmas can be found among the class of thermal plasmas as, e.g., the Inductively Coupled Plasma (ICP) and the Wall Stabilized Cascaded Arc (WSCA). Usually the pressure of the plasma is high, i.e., sub atmospheric to atmospheric. Other examples are the plasmas generated in tokamaks for fusion purposes and the recently exploited plasmas for etching and deposition devices such as the Electron Cyclotron Resonance plasmas. For the plasmas mentioned, the electron density is typical in the range of 1018 to 1023 m−3, and the electron velocity distribution is close to a Maxwellian velocity distribution.