DC arc plasma jet was introduced to the field of diamond film synthesis in the late 1980s. It heats an Ar/CH4/H2 gas mixture to a high temperature plasma of more than 3000 K by DC arc discharge, then ejects it at high speed onto the substrate to form diamond films. The whole system is composed of a vacuum deposition chamber, a DC high-voltage current source, discharge cathode and anode, a gas input system, a reaction gas system, a water-cooled stage and so on.
The basic process of DC arc plasma jet is applying a DC voltage between a pole cathode and a circular anode. An arc is generated when the gas flows into the electric field, and the gas is heated. The hot, expanding gas jets from the anode nozzle at high speed and forms the plasma jet. The starting arc gas is argon. When the reacting gases methane and hydrogen are introduced into the plasma jet, the CH4/H2 mixture is ionised by the high temperature plasma and jetted onto the substrate on the water-cooled stage, where diamond films nucleate and grow. Due to the high energy density of the plasma and the hydrogen atoms from the accompanying reaction, the density of methyl radicals and other active radicals is very high. Hence DC arc plasma jet CVD has a high diamond deposition rate and can be used for large-area deposition.
Because arc plasma is characterised by high temperature and high heat, the gases in the plasma are fully decomposed and ionised. When the plasma jets at high speed onto the relatively low temperature substrate, a great many active atoms and radicals do not recombine in time. This is so favourable to diamond deposition, since a high supersaturation of hydrogen atoms and active radicals (such as CH3 and C2H2) is generated, that DC arc plasma jet can increase the growth rate by two orders of magnitude compared with other CVD methods.
