van Mfam Maikel Hest

Analysis of the expanding thermal argon?oxygen plasma gas phase

An expanding thermal argon plasma into which oxygen is injected has been analysed by means of Langmuir and Pitot probe measurements. Information is obtained on the ion density profile and the flow pattern in the downstream plasma. A combination of Langmuir and Pitot probe measurements provide information on the total ion flux generated by the plasma source (cascaded arc). It has been found that the ion diffusion is mainly determined by the background pressure in the expansion vessel and the arc current. The ion density is determined by the total power input into the plasma as well as the gas flow in the plasma source. There is an optimum in the power transfer used for ionization from plasma source to the feed gas. Interaction of oxygen with the plasma results in a decrease in the argon ion density and the plasma beam radius. The recirculation pattern of the downstream plasma has been investigated experimentally using the Pitot probe. Due to the low downstream pressure (10?30?Pa), the conventional compressible Pitot probe theory no longer applies. It is concluded that viscous effects start to play an important role at these low pressures and should be taken into account in the analysis of the Pitot probe measurements.

Argon ion-induced dissociation of acetylene in an expanding Ar/C2H2 plasma

Mass spectrometric and Langmuir probe measurements reveal that the plasma chemistry of an expanding Ar/C2H2 plasma which is used for deposition of hydrogenated amorphous carbon is dominated by argon ion-induced dissociation of the precursor gas. The ion-induced dissociation is very efficient leading to complete depletion under certain conditions. The ion fluence as determined from modeling the mass spectrometry results is in good agreement with Langmuir probe measurements suggesting a one-to-one relation between the argon ion and acetylene consumption. The good correlation found between the growth rate and the acetylene consumption rate expresses the efficient use of the dissociation products.

Deposition of organosilicon thin films using a remote thermal plasma

Organosilicon thin films have been deposited using a remote plasma produced from an expanding thermal plasma. Hexamethyldisiloxane and oxygen have been used as precursor gases. It is shown that it is possible to deposit organosilicon thin films at high deposition rates (>60 nm/s). The film refractive index (at 632.8 nm) is a result of the presence of voids and carbon in the film. Analysis of the deposited films by means of elastic recoil detection analysis and Fourier transform infrared spectroscopy shows that the dissociation and deposition mechanism is complex. The deposited films contain carbon which is chemically bonded in a methyl configuration. From this fact the plasma gas phase chemistry and the surface chemistry have been hypothesized. The film deposition rate increases with a decrease in substrate temperature, which is highly beneficial for deposition of organosilicon thin films on substrate materials with low melting temperature.

Plasma chemistry of an expanding Ar/C2H2 plasma used for fast deposition of a-C:H

Mass spectrometric measurements in combination with Langmuir probe measurements reveal that the plasma chemistry of an expanding Ar/C2H2 is dominated by argon-ion-induced dissociation of the precursor gas. Under high arc current conditions complete depletion of acetylene is observed, indicating an efficient consumption of the injected acetylene. A clear correlation between the ion fluence emanating from the arc determined from modeling the mass spectrometry results and Langmuir probe measurements is observed. First measurements by means of cavity ring down and optical emission spectroscopy of the products of the dissociation of acetylene indicate that the dominant dissociation channel is C2H and H.

Use of in situ FTIR spectroscopy and mass spectrometry in an expanding hydrocarbon plasma

In situ Fourier transform infrared (FTIR) spectroscopy and mass spectrometry have been used to investigate the gas phase of an expanding thermal argon plasma into which hydrocarbons are injected. With both techniques it is possible to determine the depletion of the precursor gas and the densities of new species formed in the plasma, each of the techniques with its own advantages and disadvantages. To determine absolute densities of different species in the plasma by means of mass spectrometry it is necessary to deconvolute the obtained mass spectra, whereas by means of FTIR spectroscopy different species are easily recognized by their infrared absorption at specific positions in the absorption spectrum. With mass spectrometry the gas composition is measured locally, i.e. close to the gas extraction point. On the other hand with FTIR spectroscopy all particles in the infrared beam are included in the measurement. When both techniques are combined most of the individual disadvantages cancel, leading to a very powerful plasma diagnostic tool. Aside from the power resulting from the combination of both techniques, FTIR spectroscopy data also contain information on the temperature of the stable species inside the plasma. A method to extract the rotational particle temperature (within 100 K) by means of infrared absorption spectra simulation is presented.

Supersonically expanding cascaded arc plasma properties: comparison of Ne, Ar and Xe

Mathematical modelling was applied to study the dynamical and physical properties of the supersonically expanding rare gas plasma formed by a cascaded arc. Keeping constant the volume flow rate and the power input into the plasma, the Ne, Ar and Xe flows are compared. We demonstrate that the difference in mass flow rate affects the dynamic properties of plasma expansion. Modelling and experimental results show that the recombination heating of electrons is more significant in a gas that has a lower ionization potential.

Design of a fast in situ infrared diagnostic tool

Conventional Fourier transform infrared (FTIR) spectroscopes cannot be used to perform real time in situ infrared reflection absorption spectroscopy at monolayer sensitivity for high deposition rates (a couple of tens to hundreds of nm/s) which can be obtained when using an expanding thermal deposition plasma. Therefore a new analysis tool has been developed. The tool is based on a fast optical scanner in combination with conventional grating technology. This results in a loss of spectral range with respect to FTIR spectroscopes, but a significant gain is obtained in time resolution. For the combination used this makes it possible to measure at time resolution as low as 1.3 ms and resolution of 24 cm−1 at 1000 cm−1. The absorption sensitivity for single reflection at the best time resolution is approximately 10−2, but can be improved by using signal enhancement techniques. Here attenuated total reflection is used and the best sensitivity obtained is approximately 10−3, which is close to monolayer sensitiv...