Synthesis of thick, uniform, smooth ultrananocrystalline diamond films by microwave plasma-assisted chemical vapor deposition

The deposition of uniform, low-stress, thick and thin films of ultrananocrystalline diamond (UNCD) is investigated. The process methods and apparatus that enable the uniform and smooth deposition of both thin and thick (> 50 μm) UNCD across 3 in. diameters are described. UNCD films are synthesized by microwave plasma-assisted CVD using Ar/H2/CH4 input gas mixtures over a wide pressure range (60–240 Torr) and temperature range (400–850 °C). Films were grown on 3 in. diameter silicon substrates with thicknesses ranging from 58 nm to greater than 50 μm. Film surface roughness as low as 10 nm (AFM) was obtained. Film uniformities of 70 to over 95% were achieved on 3 in. diameter silicon substrates. The growth rate increased as pressure, percent hydrogen and percent methane in the gas mixture, and microwave power increased. The highest growth rate 1.12 μm/h was achieved at 180 Torr, H2/Ar/CH4 = (4:100:2) sccm and 1.5 kW absorbed power. Overall, a robust, repeatable process has been demonstrated for the deposition of UNCD films.