Deposition by coiled and grid filaments using high methane concentrations

Carburized tantalum filaments in coiled and grid geometries were used individually to deposit diamond at high methane concentrations. The filaments can be used for multicycles of deposition at filament temperatures of 2400 degrees C (grid) and 2890 degrees C (coiled) without geometric deformation. At these temperatures for coiled and grid filaments, methane concentrations of 12% and 8% respectively can be applied. Silicon wafers were used as substrates, placed 5 mm below the filaments. Diamond films were deposited at rates of 10 mu m h(-1) using a coiled filament and 5 mu m h(-1) using a grid filament. A further increase in the grid filament temperature resulted in overheating of the substrate. Although the rate of diamond deposition by the grid filament is lower than that by the coiled filament, this drawback can be compensated by deposition over a larger area. By grid filament deposition, diamond films appeared to be uniform over an area of 2 cm x 3 cm. The films were characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. Using a grid filament, it is expected that the deposition system may be scaled-up for larger area diamond deposition.