ABSTRACT
Microwave plasma-assisted diamond synthesis has been demonstrated over a wide operating pressure regime from a few millitorr to 1 atmosphere. The maximum film deposition rates vary from less than a tenth of a micrometer per hour at the low pressures of 10 mtorr to well over 10 µm/hr at operating pressures of 200 torr or greater. As the operating pressure is changed the behavior and properties of a typical microwave discharge vary significantly. At the low pressure of 10 mtorr to a few tens of torr the discharge usually fills the entire discharge chamber and is a relatively cold (gas temperature) nonequilibrium discharge where the electron temperatures are over 10,00020,000 K and the gas temperatures are less than 500-1500 K. As pressure is increased to 50 torr and above, the electron temperatures decrease and the gas temperatures increase. The discharge contracts and separates from the chamber walls as pressure is increased and takes on a ball-like or spherical shape that depends on the excitation electromagnetic fields and the geometry of the chamber. At higher pressures the gas temperatures usually are in excess of 1500 to 2000 K and the microwave discharge becomes a more spatially inhomogeneous discharge.
