INVESTIGATION OF THE ROLE OF CHARGED SPECIES IN HOT FILAMENT ASSISTED CVD OF DIAMOND

Low pressure formation of diamond is well known, and has been accomplished by activating hydrocarbon/hydrogen mixtures near a heated substrate by means of a hot filament, dc glow discharge, etc. Many researchers have reported that externally applied voltages strongly affect the CVD process, and this is often attributed to electron bombardment effects. For this work, a filament assisted CVD reactor was modified by placing a grid between the filament and substrate, enabling independent control of the substrate potential and the filament to substrate current. Growth experiments under various bias conditions indicate that negatively charged species participate in the growth process, and that the reaction rate depends on the substrate potential. The growth rate becomes negligible when the substrate is held at a negative potential, even in the presence of a large current, which calls into question the electron bombardment explanation of the growth rate dependence on electrical bias.