Structural and mechanical properties of a-C:H thin films grown by RF-PECVD

Abstract

a-C:H thin films have been deposited by plasma enhanced chemical vapor deposition at 13.56 MHz in a large bias voltage range (200–600 V). Their mechanical properties have been studied through different techniques such as nanoindentation, profilometry and finally X-ray reflectometry in order to determine their hardness, elastic modulus, stress level, interfacial fracture energy and density. We show that the hardness, the Young modulus, the density and the stress level decrease with increasing bias voltage contrary to the interfacial fracture energy, hence the adhesion of the deposits. To understand this behavior, films microstructure has been characterized through the determination of hydrogen and sp 3 hybridized carbon contents by ERDA, FTIR, Raman diffusion and ESR. We have demonstrated that a graphitization and a loss of hydrogen occur when the bias increases. Such evolutions are explained in terms of the subplantation model proposed by Lifshitz. Finally, hard and dense coatings can be grown at low bias as the sp 3 carbon content is high, but their corresponding adhesion is low.