Investigation of a distributed antenna array microwave system for the three-dimensional low-temperature growth of nanocrystalline diamond films

In this paper the aptitude of a distributed antenna array (DAA) microwave system composed of planar matrix sources for the NanoCrystalline Diamond (NCD) film conformal coating of complex-shape 3D substrates is investigated using H-2/CH4/CO2 gas mixture at low pressure and low temperature (< 500 degrees C). First, NCD films are synthesized on 2- and 4-in. silicon wafers aligned perpendicularly (vertical samples) with respect to the plan of plasma sources. A strong heterogeneity of the layer thickness and microstructure along the vertical direction is observed but can be improved by decreasing the working pressure down to 0.25 mbar. At this pressure, NCD films synthesized on 4-in. silicon wafer at a substrate holder temperature of 400 degrees C show a homogeneous thickness with deviation below 15% on 3 cm along the vertical direction, which highlights the ability of the DAA reactor to treat three-dimensional substrates of a few centimeters size. A first concretization is then presented by coating a cylindrical-shape titanium implant of 6.3 mm height for biomedical applications with NCD films characterized by satisfactory purity and uniformity.