Adaption of a microwave plasma source for low temperature diamond deposition

Summary form only given. This report describes the adaption of a microwave plasma reactor for low temperature diamond deposition. The reactor is of a resonant cavity design. Three approaches have been taken to establish plasma conditions for diamond deposition on substrates which are in the range of 450 C to 550 C. In the first, the substrate is heated only by the plasma and the source is operated at pressures on the order of 10 torr, such that the volumetric power density is sufficiently low to achieve these temperatures. In the second, the plasma pressure and microwave input power were reduced and a substrate heater was used to maintain the desired deposition temperatures. In the third approach, the plasma pressure and microwave power were increased and a substrate cooler was used to keep the substrate temperature in the desired range. In all three cases it was possible to maintain a plasma in contact with the deposition surface while the cavity was nominally tuned to a TM/sub 01n/ mode. However, in a resonant cavity, even a simple substrate holder assembly can represent an appreciable perturbation and some substrate assemblies that worked well for high pressure (50 to 100 torr) and high temperature (700 C to 900 C) diamond deposition conditions did not work well for low pressure operation. A design solution for low pressure operation is described. In addition, cavity design modifications for the incorporation of a resistively heated substrate holder and a closed-loop liquid-cooled substrate holder will be described. Both heated and cooled substrates utilized temperature control via feedback.