Towards Large Area Diamond Substrates: The Mosaic Process

Abstract

ABSTRACTA method has been developed for producing large area single-crystal diamond plates, suitable for optical and electronic applications. It starts with orienting and closely packing a set of diamond seed crystals with (001) top faces. This assembly, or mosaic, is then joined by a single-crystal overgrowth using a CVD process. A number of assembling techniques have been tested for compatibility with homoepitaxial diamond growth by hot filament assisted CVD and/or growth and etching by the acetylene-oxygen combustion flame. Furthermore a two-step process is described. First an initial layer (20-50/μm) is deposited by hot filament assisted CVD at a low growth rate in order to bridge the gap between the seeds. Subsequently the fast growth rate of the acetylene-oxygen combustion flame is employed to increase the layer thickness (>250,μm). It was found that both the basic mosaic process as well as the two step process can produce a single-crystal diamond layer on top of mosaics consisting of seed crystals with well aligned crystallographic directions. The width of the gaps between the seed crystals (up to 25 μm) was found to be less critical, while the orientation of the side faces and the direction of the misorientation (i.e. the step flow direction) seem not to effect the successful overgrowth. Apart from the alignment of the seed crystals the most severe problem, which has to be overcome in order to obtain one single-crystal overgrowth, is the occurrence of penetration twins in the joint regions. The largest mosaic structure -up to now- overgrown by CVD consists of seven seed crystals and has a surface area slightly in excess of 1 cm2