Adhesion and structural changes of multi-layered and multi-doped a-C:H films during annealing

High residual stress in hydrogenated amorphous carbon (a-C:H) films makes them rather difficult to integrate to substrates whose reactivity for carbide formation is low at the deposition temperature. Additionally, when exposed to thermal cycling, a-C:H films not only soften (i.e., graphitization), but also peel off because of thermal stresses. To improve adhesion and reduce the graphitization at high temperatures, we studied multi-element doped a-C:H films with multi-layered buffer structures on austenitic stainless steel substrates. A multi-layered structure was deposited in the order of TiC/ TiCN/TiN/Ti/stainless steel prior to depositing multi-element doped a-C:H films using de reactive sputtering and plasma-enhanced CVD methods. The a-C:H films were doped with Ti and Si. Chemical analyses of the multi-layer structure was performed using X-ray photoelectron spectroscopy. Adhesion of the films with the multi-layered buffers was better than those without buffer layers at high temperatures (T=600 degrees C). The critical scratching load was maximum at around 400 degrees C on (Si:Ti)-a-C:H films. Similarly, as observed by Raman spectroscopy Si:Ti doped films had higher resistance to the graphitization than undoped films.