Exploring constant substrate temperature and constant high pressure SCD growth using variable pocket holder depths

Abstract

SCD substrates were successfully synthesized using an optimized pocket holder design. The pocket holder design creates an appropriate thermal environment to shield the diamond substrate from the intense microwave discharge. This substrate configuration allows for a polycrystalline diamond (PCD) rimless, uniform single crystal diamond (SCD) growth process. Square shaped pocket holders with a constant width but with varying depths were used. The SCD growth procedures were carried out via microwave plasma assisted chemical vapor deposition (MPACVD) in a 2.45GHz microwave cavity plasma reactor C at a constant pressure of 240Torr and high power density of ~500W/cm3. By continuously adjusting incident microwave power (Pinc), the substrate temperature (Ts) was held at 1020°C±5°C throughout the entire process cycle. Under these growth conditions, the crystal morphologies exhibited a smooth and flat surface. The average growth rate of the SCDs varied between 30 and 24μm/h as the pocket depth increased from 2.0 to 2.9mm. The PCD rim was eliminated for all pocket depths and the shape of the final, as grown, top SCD surface varied from a square to a circular shape as the pocket holder depth increased. When using the 2.0mm and 2.3mm pockets, the final top SCD surface area increased to almost twice the original HPHT diamond seed area and the lateral growth rate was slightly larger than the vertical growth rate. Birefringence imaging of the grown CVD diamond indicated low stress and SIMS analysis indicated nitrogen concentration levels in the freestanding, CVD diamond plates were in the range of 50ppb to 140ppb. Prime novelty statementSingle crystal diamond is grown by high power density, microwave plasma assisted chemical vapor deposition in a pocket holder held at a constant temperature of 1020°C, a constant pressure of 240Torr and with 5% CH4/H2. Experimental variables were pocket depth and deposition time. Thick, PCD rimless growth was achieved, and for shallow holders, top growth surface area gains of 1. 4–1.9 were demonstrated.