Etch-pit formation mechanism induced on HPHT and CVD diamond single crystals by H2/O2 plasma etching treatment

H2/O2 plasma treatments offer advantages over other etching processes of diamond as a technique to prepare the substrate surface prior to chemical vapor deposition (CVD) diamond growth. It allows removing defects induced on the surface by polishing, thus leading to an improved morphology and limiting the stress within the grown crystal. Moreover, they present the advantage to be performed in situ just before the CVD diamond growth. In this work, H2/O2 plasma treatments were performed so that threading dislocations and other defects are etched preferentially, thus leaving typical etch-pits. The defect densities in several high pressure high temperature (HPHT) and CVD diamond crystals were then quantified and compared; in particular defects originating from polishing could be distinguished from extended defects inside the crystal. Furthermore, the defect density was found to be of the order of 105/cm2 for HPHT crystals, which was approximately one order of magnitude lower than that measured in low cost commercial CVD monocrystals. The use of laser microscopy also allowed observing the morphology, size and depth of different etch-pits of < 001 >-oriented and misoriented crystals and their evolution with etching time in order to get a better understanding of defect density and formation during CVD growth.