Molybdenum layers act as wetting and adhesion promoters of Copper to Carbon. To trigger the adhesion promoting property of Mo a temperature treatment of at least 600°C under High Vacuum (HV) conditions is necessary. As it can be deduced from the phase diagram of the C-Mo-system this step transforms Mo to a Mo-carbide.
It is the intention of this paper to investigate the effects of heat treatment below and above the carbidzation temperature on Cu films located on top of a Mo interlayer. Cu films of 1 µm thickness were deposited on 100 nm thick Mo layers. Both films were deposited at room temperature by magnetron sputtering using Ar as working gas. Vitreous Carbon (Sigradur G) served as substrate.
The samples were subjected to a temperature treatment at 200°C, 400°C and 800°C under HV. The duration of the thermal treatment ranged from 1 to 15 minutes. Morphological changes of the Cu surface were followed by Atomic Force Microscopy (AFM) and by optical microscopy.
In the as deposited state the Cu coating exhibits features with an average diameter of approx. 100 nm separated by deep voids. This morphology results from the shadowing effect which determines film morphologies at low homologous temperatures.
While even prolonged temperature treatment at 200°C showed no significant effect on the Cu surface morphology, significant recrystallization occurred at 400 and 800°C. In both cases the crystallites formed shortly after the beginning of heat treatment. Afterwards their diameter remained roughly constant with a value of 5 - 10 µm
Temperature treatment at 400°C yields two dimensional flat crystallites after 15 minutes treatment time. Grain boundaries between the crystallites exist but no significant grain boundary grooving is observable. At 800°C three dimensional features form within the grains and significant grain boundary grooving is observed after 15 minutes, although no de-wetting or hole formation within the Cu film is visible.
It can therefore be concluded that the Mo interlayer promotes two-dimensional grain growth even at higher treatment temperatures, although an onset of three dimensional recrystallization can be observed at 800°C.
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