Stress and interfacial defects induced by amorphous carbon film growth on silicon

Abstract

Amorphous hydrogenated carbon ( a-C:H) films deposited on silicon substrate were characterized by positron annihilation spectroscopy (PAS) and mechanical measurements with the aim of studying the possible relations existing between the residual intrinsic stress and the distribution of open-volume defects in the films and at the film–substrate interface. The carbon thin films were deposited by graphite sputtering in a RF Ar–H 2 plasma. Internal stress in films deposited with different thickness was measured in order to follow the film growth process and the induced mechanical effects in the films. PAS measurements were carried out with a slow positron beam coupled to a high purity Ge detector to record the Doppler broadening of the positron-electron annihilation line as a function of the positron implantation depth. The positron data have been analysed by the stationary diffusion equation to extract the main information about the open volume depth distribution in the films and in the film–Si interface. It was found that the films were homogeneous over all their thickness and presented an equal distribution of open-volumes whatever the thickness value. On the contrary, the growth process was accompanied by a strong modification at the film–Si interface. Here, the formation of a defected region, extending deeply in the Si, was found in all the samples. The region is more marked and more extended in depth in the thinnest and the thickest films, which on the other hand contained the highest compressive stress levels. The defects were identified as divacancy-like defects. The strong correlation between induced defects in the substrate and the stress is discussed.