Improving purity and size of single-crystal diamond plates produced by high-rate CVD growth and lift-off process using ion implantation

The lift-off process using ion implantation has recently been applied to produce large and thick single-crystal diamond plates by chemical vapor deposition (CVD). CVD growth conditions for undoped, as opposed to nitrogen-doped, diamond were investigated to improve the purity of plates produced by this technique. This utilized apparatus identical to that for high-rate growth with nitrogen addition under high-density plasma. By lowering the growth temperature to 900 °C, an undoped single-crystal CVD diamond plate with a maximum length of 9 mm and thickness of 0.47 mm was successfully produced without formation of non-epitaxial crystallites. The UV–Vis–NIR transmission spectrum of this plate was identical to high-pressure high-temperature (HPHT) synthetic IIa diamond, suggesting high purity of the plate. To increase the size of single-crystal CVD diamond plates, a process to enlarge the seed crystal by combining the lift-off process and a side-surface growth technique is proposed. By this process, a half-inch single-crystal CVD diamond seed crystal was successfully synthesized and half-inch freestanding single-crystal CVD diamond plates were produced from the seed.