Stress relaxation and stability in thick amorphous carbon films deposited in layer structure

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Abstract
We have developed amorphous carbon films in sequential layers and studied their intrinsic stress, composition, and stress relief mechanisms. The films were deposited by sputtering either thin, with fixed bias voltage Vb or thick, with alternative (positive-layer A/negative-layer B) Vb. In situ spectroscopic ellipsometry and stress studies were used and supported by nanoindentation and x-ray reflectivity measurements. The films deposited with fixed negative (positive) Vb exhibit a thickness-dependent increase (decrease) of compressive stresses up to 200 Å and saturate at 6(1) GPa. In thick films deposited with alternative Vb the results demonstrate that: (1) the same modulation in stress values and sp3 content versus film thickness exists, supporting their direct interrelation; (2) the A layers (rich in sp2 sites) promote the stress relaxation of the films during a compositional rearrangement when a B layer is deposited; and (3) this process develops thick and stable films with lower stresses.