The strong ion bombardment, applied during sputter deposition of diamond-like carbon films (DLC), which is needed to promote the growth of the sp3-bonded hard phase, inevitably is accompanied by compressive stress generation, thus limiting their maximum thickness. Gradient coatings with gradients in composition, constitution or properties are a well-known concept to manage such stress problems. The stepwise graded layer concept adjusts a graded constitution of the growing carbon film by a stepwise increase of the ion energy, i.e. the substrate bias voltage, during magnetron sputtering. To study the influence of the layer thickness on the expansion of the interface regions between the layers deposited with different bias voltage, samples with increasing deposition time of the top layer and thus thickness ratio were investigated by using the small angle cross-section nanoindentation method (SACS). It was revealed that the thickness of the interface regions is linearly dependent on the thickness ratio of the graded layers, which might be an evidence for stress-induced diffusion and relaxation processes in the carbon network. By using microindentation with a Berkovich indenter and ex-situ AFM-imaging it was found that all graded films exhibited higher Berkovich thresholds for crack development and thus better crack resistance than the hardest single-layer film and kept a high hardness value of about 4000 HV0.005.