INVESTIGATIONS OF DIAMOND NUCLEATION ON AC FILMS GENERATED BY DC BIAS AND MICROWAVE PLASMA

By the application of a negative d.c. bias to a Si(100) substrate in a CH4(5-15%)-H-2 microwave plasma, a SiC interface is formed covered by an amorphous carbon (a-C) layer. The diamond nucleation on these a-C films as a function of the bias voltage and the methane concentration has been studied by Raman spectroscopy, scanning electron microscopy, X-ray diffraction and atomic force microscopy. Measurements of the actual ion energy distribution by a retarding field probe showed that the ion energies for maximum nucleation are about 90 eV and are over a rather wide range independent of the methane concentration. In contrast, C+ ions with energies of about 90 eV possess the optimum energy for sp3 cluster formation in a-C films because of subplantation. Owing to the different etching efficiencies of a-C and sp3 clusters by atomic hydrogen, the films become granular, with grain sizes of up to 100 nm. The grain number density after 10 min and the nucleation density of diamond (after 30 min diamond deposition conditions) are identical and between 10(9) and 10(10). From XRD line width measurements we estimate sp3 cluster diameters of 20 nm.