Modification of wetting of copper (Cu) on carbon (C) by plasma treatment and molybdenum (Mo) interlayers

Manipulating wetting and adhesion between the chemically immiscible elements Cu and C is of high interest for the production of C-fiber reinforced Cu-C metal matrix composites (MMC's) which are potential materials for high performance heat sinks. This work presents two approaches to adhesion manipulation: (i) the activation of the C-surface by a treatment in nitrogen (N-2) radio frequency (RF) plasma and (ii) the deposition of a Mo-interlayer on the C-surface. Both approaches yield a significant increase in adhesion for Cu-coatings deposited immediately after pre treatment. Heat treatment (30 min, 800 degrees C, high vacuum furnace) leads to a drastic loss in adhesion for the plasma treated samples while the samples containing the Mo-interlayer retain excellent adhesion values. Results of thermal cycling experiments (RT-500 degrees C) combined with in situ X-ray diffraction (XRD) measurements show a similar picture. The Cu-coating on the plasma treated sample delaminates after one cycle. The sample with the Mo-interlayer can go through several cycles and is able to sustain thermally induced stresses. The difference in the response of the two sample types to post deposition thermal treatment can be tracked back to the de-wetting behavior of Cu on the different substrates. Void formation is observed at the Cu-C interface in the case of plasma treatment but not for samples with a Mo-interlayer. (c) 2005 Elsevier B.V. All rights reserved.