Library

Notes: The evolution and interdependence of microstructure, stress, and bonding defects of heteroepitaxial diamond films deposited on silicon substrates has been investigated by applying scanning electron microscopy, transmission electron microscopy (TEM), and micro-Raman spectroscopy to the same places in the films. For this purpose, TEM plane-view specimens were prepared and the same grains in the electron transparent areas were characterized by all three methods that allowed crystalline defects and their relation to spectral features of the Raman spectrum to be identified. To the authors' knowledge, this is the first successful complementary application of these methods to diamond films. Concerning microstructure evolution, dislocations in the silicon substrate and a residual plastic deformation of the silicon wafer prove that plastic deformation of the silicon substrate had occurred with the presence of mechanical stress during deposition. Evolutionary selection of randomly oriented, highly defective diamond grains observed at a film thickness of 300 nm leads to a textured film at 4 μm (an intermediate state) consisting of truncated pyramids with defect-free {001} growth sectors, bounded by four {111} growth sectors which exhibit a high density of twins and stacking faults. During further growth, merging of {001} growth sectors begins and apart from the formation of low-angle grain boundaries, the formation of partial wedge disclinations takes place, 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 misorientation. Merging of grains introduces a high number of dislocations and mechanical stress into the {001} growth sectors. The comparison of the Raman spectra with electron micrograph images shows that the G band of the Raman spectrum originates exclusively from grain boundaries having an 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 complicated stress state after grain merging is shown to originate from disclinations. © 1998 American Institute of Physics.

Notes: The growth kinetics of diamond films deposited at low substrate temperatures (600–400 °C) from the carbon–hydrogen gas system have been studied. When the substrate temperature alone was varied, independently of all other process parameters in the microwave plasma reactor, an activation energy in the order of 7 kcal/mol was observed. This value did not change with different carbon concentrations in hydrogen. It is supposed that growth kinetics in this temperature range are controlled by a single chemical reaction, probably the abstraction of surface bonded hydrogen by gas phase atomic hydrogen. © 1997 American Institute of Physics.

Notes: The stress distribution in heteroepitaxial chemical vapor deposited diamond films has been investigated by Raman spectroscopy. A new method for stress determination based on polarized confocal micro-Raman is presented and used for the measurement of the stress evolution across the film thickness in the center of the sample. The presence of highly inhomogeneous stresses at a microscopic scale is first demonstrated. The interface appears to be under compressive stress which rapidly decreases and then stabilizes, but remains compressive. The strain tensor is also shown to vary. Near the interface, the common assumption of biaxial stress in the plane of the film has been confirmed. Near the growth surface, the stress tensor appears to be more complicated. Grain boundaries are suggested to be mainly responsible for the intrinsic stress generation when the grain boundary density is high. Inhomogeneous impurity distribution could be related to stress inhomogeneities near the growth surface, where the grain boundary density becomes small. Agreement has been obtained between micro- and macro-Raman stress measurements. The average stress (over film thickness) as determined by macro-Raman is shown to increase by 30%–40% from the sample center to the edge. © 1997 American Institute of Physics.