Microstructure Evolution and Defect Incorporation in Highly Oriented and Textured CVD Diamond Films

A series of highly oriented and textured microwave CVD diamond films, where only the deposition time was varied, was deposited on silicon wafers in order to follow the evolution of the microstructure and defect content with film thickness. SEM, XRD, Raman spectroscopy, luminescence measurements, and ESR were applied to determine the microstructure and the defect density. It is shown that the growth of highly oriented and textured film proceeds in two stages. The first is characterized by marked changes of the microstructure (size, orientation, and shape of the grains) which directly influence the generation of defects. The second stage, which begins as soon as the film surface is covered with {100} tiles, leads to minor changes in the microstructure and defect incorporation. The defect-related part of the Raman spectrum has been decomposed into two contributions, the D-band which mainly responds to grain boundary defects, and the G-band which is more sensitive to volume defects. ESR measures volume defects, grain boundaries provide only a minor contribution. In this respect, ESR and Raman G-band are similar. {111} growth sectors produce defect densities which are three to four times higher than their {100} counterparts. The thermal conductivity is shown to depend not only on the grain boundary density but also on bulk defects. Optical transparency in the visible range is strongly affected by surface roughness, however, using a new method, it has been possible to determine an absorption coefficient for the second stage which is consistent with recently published literature data.