Large Area Single-Crystal Diamond Synthesis by 915 MHz Microwave Plasma-Assisted Chemical Vapor Deposition

A 75 kW, 915 MHz microwave plasma-assisted chemical vapor deposition system was adapted and utilized to scale up production of high-quality single-crystal diamonds at high growth rates. A 300 mm diameter plasma discharge was achieved with uniform temperature distributions of +/- 250 degrees C on up to 300 single-crystal diamond substrates. Diamond single crystals were synthesized from H-2/CH4/N-2 gas mixtures at pressures between 90 and 180 Torr, with recorded growth rates from 10 to 30 mu m/h. The source of N-2 was from vacuum chamber leakage, and it greatly affected synthesis chemistry. Optical emission spectroscopy was used to probe the localized plasma chemistry and plasma uniformity at different gas pressures. Production rates of up to 100 g/day of single-crystal diamonds were demonstrated, with 25% of the material categorized as colorless. Crystals up to 3.5 mm in thickness could be produced during a single deposition run. The quality of the crystals produced was assessed by photoluminescence and UV-visible absorption spectroscopies.