The influence of temperature treatment and carbon addition on the surface morphology and the surface energy of molybdenum layers on carbon substrates

Abstract

Molybdenum layers act as wetting and adhesion promotors for copper coatings to carbon substrates. A crucial step to initiate the adhesion promotion by Mo is a temperature treatment. Hundred nanometer thick Mo layers were deposited by magnetron sputtering on plane substrates of vitreous carbon (Sigradur G) and subjected to heat treatments of up to 8 min duration at 400 and 800 °C under high vacuum conditions (10-3 Pa). Changes in the surface morphology of the coating were recorded by atomic-force microscopy (AFM). The AFM measurements have shown significant recrystallization of the coatings. Grains with diameters of approximately 100 nm develop in the first stages of heat treatment. The grain diameter remains roughly constant with ongoing heat-treatment time. Surface-energy measurements that were performed with the sessile drop method have shown that temperature treatment at 800 °C significantly increases the surface energy of the Mo coating. Auger electron spectroscopy (AES) shows that heat treatment at 800 °C alters the chemical composition of the coating from pure Mo to a Mo-carbide while no carbide is formed at 400 °C. It is concluded that the carbide formation plays a significant role in the changes of the surface parameters of the Mo coating. This hypothesis is supported by comparing coatings produced by cosputtering Mo and C with the heat-treated coatings using the methods presented above. Copyright © 2008 John Wiley & Sons, Ltd.