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B. Schwarz, C. Schrank, C. Eisenmenger-Sittner, M. Stöger-Pollach, M. Rosner, E. Neubauer:
"ADHESION PROMOTION OF COPPER-COATINGS TO CARBON SURFACES BY PLASMA PRE TREATMENT AND MOLYBDENUM INTERLAYERS";
Poster: International Vacuum Congress 16, IVC-16, Venedig, Italien; 2004-06-28 - 2004-07-02.

The adhesion of sputter deposited Copper (Cu) coatings on plane glassy Carbon (C) substrates can be increased by a pre-treatment of the C-surface by Nitrogen-RF-Plasma and/or by the application of thin Molybdenum (Mo) interlayers which serve as bond layers. As a model for the interface between Cu and C-fibers in Cu-C Metal Matrix Composites (MMC's) the mechanical and thermal properties of the plane model system described above are of great interest.
If the Cu-coating is deposited directly on a Nitrogen-RF-Plasma treated C-substrate at room temperature (RT) the adhesion of Cu to C is excellent. In a further step the Cu coated C-samples are subjected to a thermal treatment at 800°C under high vacuum conditions for 1 hour to partially mimic the hot pressing step involved in the production of real MMC's. This thermal treatment drastically reduces the adhesion of Cu to C due to de-wetting of the Cu coating from the C substrate. De-wetting can effectively be suppressed if a 100 nm Mo interlayer is present. With this interlayer the thermal treatment procedure even leads to an increase of adhesion values.
This work shall clarify the microscopic bond mechanisms that are present at the C/Cu or at the C/Mo/Cu interfaces by Cross Sectional Transmission Electron Microscopy (X-TEM). At the C/Cu interface of Cu-films directly deposited on plasma treated substrates an intermixing zone between Cu and C of approximately 30-50 nm thickness could be detected by spatially resolved Energy Dispersive X-ray (EDX) analysis. Nitrogen, on the other hand, could not be detected by the microanalytical techniques attatched to the TEM (EDX, Electron Energy Loss Sspectroscopy (EELS)). Only Secondary Ion Mass Spectroscopy (SIMS), which is very sensitive to the presence of trace elements, could clearly identify the presence of Nitrogen at the interface. After heat treatment the intermixing zone has vanished and also the Nitrogen intensity recorded by SIMS was significantly decreased.
With a 100 nm Mo-interlayer, thermally treated samples could be prepared for TEM in cross section. Although Mo shows no or only very little intermixing with C, Cu and Mo obviously interdiffuse into each other. In addition the formation of grain boundary grooves at the C/Cu interface which is a main reason for the adhesion loss after thermal treatment for the systems without Mo interlayer, is effectively suppressed by the Mo bond layer. Therefore it can be concluded that Mo serves as a wetting promotor for Cu.
This work is supported by the Austrian Science Fund (FWF) under grant Nr. P-14534. The TEM-investigations were performed in collaboration with the University Service Centre for Transmission Electron Microscopy (USTEM) of the Vienna University of Technology.