Microstructure and stress in nano-crystalline diamond films deposited by DC glow discharge CVD

Abstract

Direct current glow discharge (DC GD) CVD from a methane–hydrogen mixture enables deposition of a nano-crystalline carbon film of a prevailing diamond character on a pristine silicon substrate without any surface pretreatment. The deposited films were investigated by various techniques including: X-ray diffraction (XRD); high resolution transmission electron microscopy (HR TEM); and Raman spectroscopy. From the XRD analysis, development of the diamond phase from the graphitic precursor layer and the nano-crystalline character of the deposited films were determined. The presence of multiple defects in the silicon substrate were established by measurements of the silicon rocking curves. TEM confirmed the nano-dimensional size of the crystallites in the deposited films as well as the highly dislocated character of the underlying silicon. Raman spectroscopy indicated the presence of large local stresses in the nano-diamond. The values of these stresses, calculated from the shift of the G-peak that belongs to the graphitic phase present in these films, were shown to reach critical values necessary for the graphite–diamond transformation. It is assumed that these stresses stem from the subplantation process of the energetic ions accelerated by the electric field and surface strains of carbon nano-clusters. The relaxation of these stresses is suggested to lead to the transformation of the graphite material into the diamond phase. The narrow range of temperatures (880±10 °C), which enables the formation of the diamond phase, indicates the importance of hydrogen adsorption/desorption processes in the nucleation and growth of the nano-crystalline diamond films deposited by DC GD.