Diamond Growth by Microwave Plasma CVD for Electronic Devices

Diamond growth for electronic devices requires both high quality substrates and high quality epi-layers including intrinsic, p-type and n-type diamond. Additionally, the desire to increase the diamond substrate area is also important for the future. Diamond substrates and epi-layers have many factors that are important for electronic device applications including minimizing threading dislocation density, reducing undesired impurities that can degrade carrier mobility and cause compensation of dopants, and achieving controlled uniform doping. As diamond deposition technology and processes advance we learn that more parameters must be controlled and their impact on the grown diamond quality understood. The list of parameters that must be controlled continues to expand and includes diamond substrate preparation (off-cut angle and off-cut direction of the growth surface from a crystal plane, removal of polishing damage from the substrate, and cleanliness of the starting substrate); and the plasma CVD process (gas mixture, growth rate, substrate temperature and uniformity, dopant gas concentrations, cleanliness of input gases, substrate holder structure and growth start-up process). The impact of these parameters have been studied since the start of work on CVD deposition of single crystal diamond by many researchers. This paper will overview the many parameters and their impact on the growth of diamond from both results reported in the literature and work we have performed in recent years.<br/><br/>Work will be reported on the growth of thick plates of diamond and the evolution and propagation direction of threading dislocations from growths up to 4 mm thick. The possibilities of control of the direction of threading dislocations will be discussed. Experiments that use X-ray diffraction, X-ray topography, cathodoluminescence, photoluminescence, optical imaging and etch pit techniques to understand dislocations will be presented. The correlation of the off-cut nature of the growth surface to the dislocation propagation will also be presented. Another aspect studied recently is the impact of temperature uniformity during diamond deposition and its influence on the substrate bending during CVD deposition. The issue of how much the substrate bends and its relationship to cracking or potential cracking of the substrate is studied.<br/><br/>Recent work on the expansion of the area of diamond substrates using the mosaic tiling approach will be reported including both our work and work in the literature. Our results showing the tiling of multiple tiles with crystallographic alignment of better than 0.2 degrees will be shown. X-ray rocking curve measurements are used to determine alignment and any tiling related substrate bending.