Investigation on crystalline structure, boron distribution, and residual stresses in freestanding boron-doped CVD diamond films

摘要

Growth orientation, crystalline structure, boron-doping distribution, and residual stresses of freestanding boron-doped chemical-vapor-deposited (CVD) diamond films have been comprehensively investigated. The introducing boron source of trimethylborate (B(OCH_3)_3) in a doping level region favorably leads to a predominant [110] texture growth. By analyzing the asymmetry parameter q related to Fano-type interference obtained from micro-Raman spectroscopy, it is qualitatively deduced that the boron concentration in the films is spatially inhomogeneous in a large scale, either on the growth surface (between different grain facets and boundaries) or along the cross-section. The boron distribution on the cross-section is attributed to the increase of growing temperature on top surface and, consequently, the high-temperature-induced diffusion enhancement of boron atoms in diamond lattices as well as the boron contamination accumulated in CVD chamber. Combining X-ray diffraction (XRD) with sin~2ψ method, scanning electron microscopy, and Raman spectroscopy, we demonstrate that the residual stress is related not only to boron-doping level and inhomogeneous boron distribution but also to grain size, crystalline texture, and appearance of twins in the boron-doped diamond films.