THE INTERFACIAL STRUCTURE AND COMPOSITION OF DIAMOND FILMS GROWN ON VARIOUS SUBSTRATES

Diamond thin films have been successfully grown on monocrystalline Si and various polycrystalline substrates, such as Mo, Nb, Zr, Cu, SiC, SiO2, and WC, by microwave plasma CVD in gas mixtures of methane and hydrogen. For instance, high purity and dense diamond films can be deposited on structurally matched substrates of Si and SiC, in hydrogen containing 0.2% methane. SEM, TEM, XRD, AES, EELS, EDS, and Raman spectroscopy have been utilized to study and characterize the morphology, microstructure, and composition of the deposited films. Results indicate that tetrakaidecahedra are the dominant forms of crystalline diamond. Both {100} and {111} facets were observed on all substrates studied. SiC, SiOx, amorphous carbon, and carbides of refractory metals were the dominant interphases in this study. The composition and microstructure of the interphase appear to have significant effects on the adhesion strength, as shown in the diamond/Mo and diamond/Hf systems. Structural defects such as twins and stacking faults were frequently observed inside the diamond grains, while line defects of dislocations were mainly constrained to the grain boundaries. The diamond nucleation rate could be increased by first modifying the surface of the substrate material using a process that ultrasonically stimulated cavitation-erosion in an aqueous suspension of diamond dust. The diamond crystallites growing on this roughened surface were of a much more uniform size than was achieved after the more conventional lapping process.