COMPLEMENTARY APPLICATION OF ELECTRON-MICROSCOPY AND MICRO-RAMAN SPECTROSCOPY FOR MICROSTRUCTURE, STRESS, AND BONDING DEFECT INVESTIGATION OF HETEROEPITAXIAL CHEMICAL-VAPOR-DEPOSITED DIAMOND FILMS

The evolution and interdependence of microstructure, stress, and bondi ng defects of heteroepitaxial diamond films deposited on silicon subst rates has been investigated by applying scanning electron microscopy, transmission electron microscopy (TEM), and micro-Raman spectroscopy t o the same places in the films. For this purpose, TEM plane-view speci mens were prepared and the same grains in the electron transparent are as were characterized by all three methods that allowed crystalline de fects and their relation to spectral features of the Raman spectrum to be identified. To the authors' knowledge, this is the first successfu l complementary application of these methods to diamond films. Concern ing microstructure evolution, dislocations in the silicon substrate an d a residual plastic deformation of the silicon wafer prove that plast ic deformation of the silicon substrate had occurred with the presence of mechanical stress during deposition. Evolutionary selection of ran domly oriented, highly defective diamond grains observed at a film thi ckness of 300 nm leads to a textured film at 4 mu m (an intermediate s tate) consisting of truncated pyramids with defect-free {001} growth s ectors, bounded by four {111} growth sectors which exhibit a high dens ity of twins and stacking faults. During further growth, merging of {0 01} growth sectors begins and apart from the formation of low-angle gr ain boundaries, the formation of partial wedge disclinations takes pla ce, partly accommodating the misorientation between grains by elastic deformation. The latter process is shown to be more favorable than the formation of low-angle grain boundaries below a certain misorientatio n. Merging of grains introduces a high number of dislocations and mech anical stress into the {001} growth sectors. The comparison of the Ram an spectra with electron micrograph images shows that the G band of th e Raman spectrum originates exclusively from grain boundaries having a n associated {111} growth sector. Very localized luminescence sources have been detected, not correlating to microstructure elements. Stress inhomogeneities measured within single grains and an earlier observed transition of the biaxial stress state in the film plane to a more co mplicated stress state after grain merging is shown to originate from disclinations. (C) 1998 American Institute of Physics.