Characterization of cascade arc assisted CVD diamond coating technology

Cascade arc plasma-assisted CVD (CACVD) technology is based on an innovative reactor design which utilizes the properties of a linear-arc plasma column. While operating in the same pressure range, from 0.1 Torr up to atmospheric pressure, the CACVD reactor overcomes the disadvantages of conventional Arc Torch CVD reactors by creating a homogeneous concentrated plasma column in a cylindrical or rectangular reaction chamber with a length of 1 m or more. Substrate holders are configured to act as a virtual liner confining the arc in a channel containing the substrates. In the CACVD reactor channel, an arc plasma is shaped by magnetic fields, creating a uniform plasma environment over extended lengths. It has been used to deposit polycrystalline diamond and related coatings on 3D substrates. In the cascade arc process, the temperature gradient and flow of energy are directed transversal to the hydrodynamic flow, which allows protection of the deposition area from direct impact with high-speed plasma flow. In high temperature CACVD processes, the temperature of substrates is determined by the balance between energy flow conveyed from the plasma column, radiative losses, and heat removal through cooling of the substrate holders and reactor wall. Precise control of the substrate temperature in high temperature CVD processes is critical for depositing polycrystalline diamond coatings. Composite powder variable conductance insulation (CPVCI) has been developed to control substrate temperature during deposition of polycrystalline diamond coatings in the CACVD reactor. Direct measurements of the substrate temperature vs. incoming energy flow from arc plasma allow estimation of the thermal balance of the substrates. The voltage-ampere characteristics as well as plasma transfer processes in an Ar-H2-CH4 cascade arc in relation to the thermal balance of substrates and deposition rate of polycrystalline diamond coatings are discussed.