Stress distribution in heteroepitaxial chemical vapor deposited diamond films

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. (C) 1997 American Institute of Physics.