Pulsed laser deposition of diamond-like carbon films: reducing internal stress by thermal annealing

In order to obtain diamond-like carbon (DLC) films of relevant thickness (exceeding 1 μm), it is necessary to solve the critical problem related to the internal compressive stress (some GPa) leading to delamination at a threshold thickness value of the films. The Griffith’s theory explains the failure process by looking at the excess of elastic energy inside the film which overcomes the cohesive energy between film and substrate. To increase the above mentioned threshold thickness value there are two possibilities: (i) the improvement of the interface adhesion (for example, through surface micro-roughening and/or surface activation), and (ii) the reduction of the internal stress. In this work, stable DLC films, over silicon substrates, having thickness exceeding 1 μm, have been produced by appropriate steps of thermal annealing following pulsed laser deposition. Thin-film curvature measurements have been performed to evaluate the stored elastic energy in the films and the agreement between the fracture mechanical theory and experimental results has been proved.