Delamination/Rupture of Polycrystalline Diamond Film: Defining Role of Shear Anisotropy

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.