Unusual Dependence of the Diamond Growth Rate on the Methane Concentration in the Hot Filament Chemical Vapor Deposition Process

Although the growth rate of diamond increased with increasing methane concentration at the filament temperature of 2100 degrees C during a hot filament chemical vapor deposition (HFCVD), it decreased with increasing methane concentration from 1% CH4 -99% H-2 to 3% CH4 -97% H-2 at 1900 degrees C. We investigated this unusual dependence of the growth rate on the methane concentration, which might give insight into the growth mechanism of a diamond. One possibility would be that the high methane concentration increases the non-diamond phase, which is then etched faster by atomic hydrogen, resulting in a decrease in the growth rate with increasing methane concentration. At 3% CH4 -97% H-2, the graphite was coated on the hot filament both at 1900 degrees C and 2100 degrees C. The graphite coating on the filament decreased the number of electrons emitted from the hot filament. The electron emission at 3% CH4 -97% H-2 was 13 times less than that at 1% CH4 -99% H-2 at the filament temperature of 1900 degrees C. The lower number of electrons at 3% CH4 -97% H-2 was attributed to the formation of the non-diamond phase, which etched faster than diamond, resulting in a lower growth rate.

Automated summary

The growth rate of diamond in HFCVD is influenced by methane concentration, with high levels potentially leading to the formation of non-diamond phases that are etched faster by atomic hydrogen, resulting in a decrease in growth rate. The presence of graphite coating on the hot filament also affects electron emission, with lower electron emission at higher methane concentrations attributed to the formation of non-diamond phases, leading to slower growth rates.