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D. Schäfer, J. Hell, C. Eisenmenger-Sittner, E. Neubauer:
"SUPPRESSION OF DE-WETTING OF COPPER COATINGS ON CARBON SUBSTRATES BY METAL (Cr, Mo, Ti) DOPED BORON INTERLAYERS";
Poster: 12 th Joint Vacuum Conference, 10 th European Vacuum Conference, 7 th Annual Meeting of the German Vacuum Society, Balatonalmadi/Ungarn; 22.09.2008 - 26.09.2008.

Novel heat sink materials consist of a highly thermal conductive matrix, e. g. copper with equally thermal conductive inclusions (e. g. carbon fibers, nanotubes or diamond particles). These inclusions allow for a reduction of the high Coefficient of Thermal Expansion (CTE) of copper (CTE copper: 16 ppm/K, various C modifications: approx. 2 ppm/K). The thermodynamic immiscibility of Cu and C leads to a high thermal resistance between matrix and inclusion. To overcome the problem of insufficient thermal transport across the Cu/C interface wetting promoting interlayers may be a solution. One candidate material for these interlayers is metal doped Boron.
B coatings doped with Cr, Ti or Mo were deposited on plane substrates of vitreous carbon ("Sigradur G") by magnetron sputtering from a composite target. The amount of included metal was determined by Auger Electron Spectroscopy and found to be in the range of 1 - 4 at%. The metal content relative to Boron was chosen to be in the range of 3at% for all interlayers. Onto these interlayers a Cu film of 300 nm thickness was deposited by magnetron sputtering. After that the Cu coated samples were subjected to heat treatment of 800 °C for 30 min.
The heat treated samples were investigated by Optical Microscopy, Scanning Electron Microscopy and Scanning Force Microscopy. Different intensities of de-wetting of the Cu coatings could be observed. It was possible to quantify the de-wetting process by determining the area density of holes formed within the Cu coating after thermal treatment. Interlayers which lead to the lowest hole density will be considered as candidate materials for optimizing the thermal properties of the Cu/C interface in subsequent experiments.
The financial support of the Austrian "Fonds zur Förderung der Wissenschaftlichen Forschung" (FWF), Grant No. P-19379-N16 is gratefully acknowledged.