Influence of growth conditions on microstructure and defects in diamond coatings grown by microwave plasma enhanced CVD

Abstract

Diamond coatings were grown on SiO₂/Si substrate under various process conditions by microwave plasma chemical vapour deposition (MPCVD) using CH₄/H₂ gas mixture. In this paper, we present a microstructural study to elucidate on the growth mechanism and evolution of defects, viz., strain, dislocations, stacking faults, twins and non-diamond impurities in diamond coatings grown under different process conditions. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the diamond coatings. It has been shown that our new approach of prolonged substrate pre-treatment under hydrogen plasma yielded a new growth sequence that the SiO₂ layer on the Si substrate was first reduced to yield Si layer of ∼150 nm thickness before diamond was allowed to grow under CH₄–H₂ plasma, created subsequently. It has also been shown that Si and O as impurity from the substrate hinders the initial diamond growth to yield non-diamond phases. It is being suggested that the crystal defects like twins, stacking faults, dislocations in the diamond grains and dislocations in the intermediate Si layer are generated due to the development of non-uniform stresses during diamond growth at high temperature.