Polycrystalline
diamond films were synthesized by microwave plasma
chemical vapor deposition. Films were mechanically stable until 30
μm thickness, while further deposition led to catastrophic film
delamination and rupture. This coincided with fracture of the single-crystal
silicon substrate, creating polycrystalline silicon with clear shear
markings. Films grown to 12, 18, 21, and 30 μm were subjected
to detailed investigations. Larger film thickness modified intrinsic
stresses (estimated from Raman shift) from mildly compressive to strongly
tensile. However, normal in-plane residual stresses and dislocation
densities, as estimated from X-ray diffraction, dropped. Film growth
enhanced anisotropies in crystallographic texture brought changes
to grain morphology and significantly increased out-of-plane residual
shear stress. Though different models of film delamination/rupture
were deliberated, they fail to assimilate all aspects of experimental
observations. Shear anisotropy-induced lateral stresses, on the other
hand, can explain film rupture and relate the same with substrate/film
microstructural developments.
Extensive bulk and micro-texture measurements are used to characterize single and polycrystalline diamond thin films of different film thicknesses produced using CVD. With increasing film thickness, texturing improves and in-grain misorientation drops. This is observed for both single and polycrystalline films. Improved texturing in polycrystalline diamond can be rationalized from growth selection/advantage, however explanation(s) on the in-grain misorientation development and its relationship with texturing, if any, remain pending.
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