Volkmar Hopfe

Atmospheric pressure pecvd coating and plasma chemical etching for continuous processing

Plasma processing at atmospheric pressure (APPlasmas) has attractions for both economic and technological reasons. Potential costs-saving factors are associated with online-processing capability and increase throughput due to high deposition rates. Capital cost savings for both equipment and line space (foot print), and relative ease of integration, are further benefits in comparison to low-pressure-technology approaches. Three types of APPlasmas are considered for coating: microwave chemical vapor deposition (CVD), dc ArcJet-CVD based on a linearly extended plasma source, and dielectric barrier glow discharge plasma CVD. Spectroscopic plasma characterization has shown that high fluxes of activated species are available in the plasma downstream region and can be used for deep fragmentation of even stable molecules. After precursor injection, a range of atomic and molecular intermediates, precursor fragments, and reaction products were identified leading to a conclusion that a complete conversion of the element-organic precursors into an inorganic materials take place. Alternatively, the dc ArcJet source is used for plasma chemical etching. All AP-plasma-enhanced chemical vapor deposition (PECVD), reactors are designed for continuous air-to-air processing on flat or slightly shaped substrates and allow deposition of nonoxide films. Reactor design is supported by fluid-dynamic modeling. Typical thin-film growth rates for PECVD are in the range of 5-100 nm/s (static) and up to 2 nm*m/s (dynamic). The rates for plasma chemical etching are typically ten times higher. Plasma activation substantially widens the range of potential applications, e.g., coating on steel, lightweight metals, preshaped glass, and plastics. Developments are underway to explore the use of the coating technologies in areas such as scratch-resistant coatings on metals, barrier layers, self-clean coatings, biocidal functional surfaces, and antireflective coatings. The coating materials range explored, so far, includes: silica, titania, carbon, silicon nitride/carbide, and metal oxides

NIR laser diode and FTIR based process control for industrial CVD reactors

Abstract Aiming toward process control of industrial high yield/high volume CVD reactors, the potential of optical sensors as a monitoring tool has been explored. The sensors selected are based on both Fourier transform infrared spectroscopy (FTIR) and tuneable diode laser spectroscopy (NIR-DLS). The former has the advantage of wide spectral capability and well-established databases. NIRLD spectroscopy has potentially high sensitivity, laser spatial resolution and the benefits of comparatively easier integration capabilities — including optical fibre compatibility. The proposed technical approach for process control is characterised by a ‘chemistry based’ feedback system with in-situ optical data as input information. The selected optical sensors continuously analyse the gas phase near the surface of the growing layer. The spectroscopic data has been correlated with process performance and layer properties, which, in turn establish data basis for process control. The new process control approach is currently being verified on different industrialised CVD coaters. One of the selected applications deals with the deposition of SnO 2 layers on glass based on the oxidation of (CH 3 ) 2 SnCl 2 , which is used in high volume production for low-E glazings.

In-Line Plasma Etching at Atmospheric Pressue for Edge isolation in Crystalline Si Solar Cells

In this contribution dry etching of crystalline silicon solar cells in a novel atmospheric pressure plasma is described. Dry etching has the potential to replace wet chemical etching steps in solar cell processing. Unlike in other dry etching systems described recently a plasma arc operating at atmospheric pressure is employed, offering the advantage of reduced investment costs and better process integration. Removal of the emitter from the rear surface is expected to lead to a reduction in surface recombination velocity and can be particularly useful for future cell concepts with dielectric rear surface passivation. Good shunt resistance values were achieved and the cell efficiencies are comparable to results from the reference process

FTIR monitoring of industrial scale CVD processes

The goal is to improve chemical vapour deposition (CVD) and infiltration (CVI) process control by a multipurpose, knowledge based feedback system. For monitoring the CVD/CVI process in-situ FTIR spectroscopic data has been identified as input information. In the presentation, three commonly used, and distinctly different, types of industrial CVD/CVI processes are taken as test cases: (i) a thermal high capacity CVI batch process for manufacturing carbon fibre reinforced SiC composites for high temperature applications, (ii) a continuously driven CVD thermal process for coating float glass for energy protection, and (iii) a laser stimulated CVD process for continuously coating bundles of thin ceramic fibers. The feasibility of the concept with FTIR in-situ monitoring as a core technology has been demonstrated. FTIR monitoring sensibly reflects process conditions.

FT-IR Investigations and Modelling of Anisotropic Materials: Application to Carbon Fibre Composites

The application of specular reflectance FT-IR spectroscopy for the investigation of carbon fibre reinforced epoxy composites is discussed. The use of the general 4 × 4 matrix algorithm allows determination of the dielectric functions of the sample, parallel and perpendicular to the optical axis. The parallel component shows a Drude-like spectral behaviour of the carbon fibre, and the perpendicular component is mainly determined by the polymer.