Deposition and post-processing of polycrystalline diamond for freestanding films and substrates

Summary form only given. In this paper, we report on the synthesis of high quality diamond and the fabrication of optical quality windows and uniform thickness ion beam stripping foils. Both of these applications require the deposition of high quality diamond, the laser cutting of the diamond to a desired shape, the post processing of the diamond by etching, lapping and polishing steps to produce smooth, flat and uniformly thick films or substrates. The polycrystalline diamond films are grown in a microwave plasma-assisted CVD reactor using hydrogen/methane chemistry. The methane percentage is nominally 1%. The deposition reactor is a microwave cavity applicator with the plasma confined inside a 12 cm diameter quartz dome. The substrates utilized are 5 and 7.5 cm diameter silicon wafers with thickness in the range of 1-2 mm. The substrate is actively cooled with a water cooled substrate holder to achieve a substrate temperature of 750-1100degC. The pressure utilized is 80-200 torr and the microwave power is 3-6 kW. The silicon substrates are prepared using mechanical polishing with diamond powder for nucleation. The typical post processing steps include laser cutting, lapping and polishing of the growth side of the diamond, removal of the silicon substrate, and plasma etching to remove a thin layer on the nucleation side of the diamond film. The polishing system has been used to achieve surface roughness values of 3 nm. Once the diamond is removed from the silicon substrate by etching the silicon away, a diamond film bowing often occurs due to the intrinsic stresses within the diamond film itself. A gradient in the stress within the diamond film in the direction of growth leads to a bending of the freestanding film. Techniques to compensate for this bowing such as removal of a layer of the film on the nucleation side are explored