Florian Sigeneger

Study of an atmospheric pressure glow discharge (APG) for thin film deposition

Abstract We studied a homogeneous atmospheric pressure dielectric barrier discharge in helium with small admixtures ( −3 ) of hexamethyldisiloxane (HMDSO) vapor for the deposition of thin silicon organic films on a technical aluminum sheet metal. The powered (100 kHz) plane electrode (80×15 mm 2 ) is covered by a glass insulator layer. Power absorption, sustaining voltage (2 kV pp ), gap voltage (700 V), current density (∼20 mA cm −2 ), and total light emission are monitored to characterize the discharge in the gap (1–1.5 mm). The gas composition of the exhaust gas is studied by mass spectrometry. During discharge operation a decrease of the precursor concentration is observed, due to dissociation and thin film deposition. Typical deposition rates range from approximately 0.2 to 2.0 nm s −1 , as measured by substrate weighing. The films display water contact angles of 63±3°. A protection of the Al sheet metal against 0.1n-NaOH for 3 min is observed. FT–IR (dominant SiOSi band) and XPS (low C content) measurements both reveal the dominance of non-organic components in the film. The spatially averaged electron concentration (2×10 11 to 5×10 11 cm −3 ) is experimentally determined by heterodyne interferometry. Discharge properties and thin film deposition are discussed in relation to the ionization rate of the precursor molecules and the current density.

Particles as probes for complex plasmas in front of biased surfaces

An interesting aspect in the research of complex (dusty) plasmas is the experimental study of the interaction of micro-particles with the surrounding plasma for diagnostic purposes. Local electric fields can be determined from the behaviour of particles in the plasma, e.g. particles may serve as electrostatic probes. Since in many cases of applications in plasma technology it is of great interest to describe the electric field conditions in front of floating or biased surfaces, the confinement and behaviour of test particles is studied in front of floating walls inserted into a plasma as well as in front of additionally biased surfaces. For the latter case, the behaviour of particles in front of an adaptive electrode, which allows for an efficient confinement and manipulation of the grains, has been experimentally studied in terms of the dependence on the discharge parameters and on different bias conditions of the electrode. The effect of the partially biased surface (dc and rf) on the charged micro-particles has been investigated by particle falling experiments. In addition to the experiments, we also investigate the particle behaviour numerically by molecular dynamics, in combination with a fluid and particle-in-cell description of the plasma.

Nonlocal transport and dissipation properties of electrons in inhomogeneous plasmas

The spatial evolution of the electron component in a neon plasma is investigated under the action of spatially inhomogeneous electric fields. In the center of the studies are those macroscopic quantities which describe the transport and the dissipation of power and momentum of the electrons. These quantities are determined from the velocity distribution function of the electrons obtained by the solution of the spatially inhomogeneous Boltzmann equation. Both a spatially limited disturbance of the field as well as a strongly modulated periodic field typical of s striations are considered. Moreover, the results of the strict kinetic treatment are compared with the corresponding ones obtained by the so-called local field approximation which corresponds to a hydrodynamic description of the electron component assuming a local compensation of power and momentum gain by the respective loss processes. The large deviation of both results from each other confirms the strongly nonlocal character of the electron transport and dissipation coefficients under the plasma conditions considered.

Modeling of Striated Filaments Occurring in a Nonthermal RF Plasma Jet at Atmospheric Pressure

The filaments occurring in an RF argon plasma jet at 27.12 MHz are investigated theoretically. The special setup of this jet leads to filaments in very regular spatiotemporal discharge patterns under certain conditions. Such a single filament generated in the active volume between the powered and grounded electrodes is described by a fluid model. A curved filament with a contracted radial profile and very pronounced striations along its trace has been obtained in accordance with experimental observations.

Spatiotemporal Relaxation of a Disturbed Neon Glow Discharge

In this paper, spatiotemporal relaxation of a neon glow discharge plasma is theoretically investigated. The study concerns the positive column and the adjacent anode region. The relaxation is initiated by a short laser pulse that disturbs the column plasma by depopulating the metastable atoms near the cathode-sided boundary of the considered region. The resulting decrease of the ionization rate initiates a spatiotemporal relaxation of the plasma in the downstream region, which is similar to ionization waves. In accordance with the chosen discharge parameters, ionization waves of p-type are generated. After about 3-4 ms, relaxation is finished, and the undisturbed state is reached. The theoretical investigations are based on a self-consistent hybrid model comprising a fluid description of all relevant plasma components, the solution of the Poisson equation, and a spatially resolved kinetic treatment of the electrons.

Deposition of Plasma Polymer Films by an Atmospheric Pressure Glow Discharge

Plasma assisted chemical vapor deposition is a proven method for the formation of thin films. The application of non-thermal low pressure plasmas containing organic compounds for thin film deposition by plasma polymerization is well known1. These films are successfully applied for corrosion protection and as diffusion barriers2. Operating non thermal discharges under atmospheric pressure conditions requires no vacuum devices, therefore the integration of the plasma process into production lines is greatly simplified. Batch processing can be avoided thus reducing production costs significantly. The plasma of the atmospheric pressure dielectric barrier discharge (DBD) has been used for technical applications for many years starting with ozone generation (Siemens, 1852). Other fields of application are flue gas cleaning, surface treatment of polymeric foils and films and thin film deposition3. The dielectric barrier discharge is usually a filamentary one and therefore strongly inhomogeneous. A homogeneous DBD without filaments was described by Okazaki et al. in a planar electrode configuration in He, later also in other gases and gas mixtures4. According to some similarities with the dc glow discharge this discharge is called atmospheric pressure glow discharge5. Its homogeneity favours this discharge for thin film deposition techniques.

Plasma Bubble in an RF Reactor

A pronounced local enhancement of the argon plasma of the capacitively coupled reactor PULVA-INP is generated by applying an additional RF voltage at the central pixel (CP) of its adaptive electrode. This enhancement is observed by a large increase of the light-emission intensity. A 2-D fluid model is applied to describe the plasma in this reactor configuration. A pronounced change of the electric potential and a large increase of the electron density are obtained around the CP. The spatial structure of the increased excitation rate of argon corresponds to the observed light emission.