PRESSURE LIMITS FOR THE VACUUM-ARC DEPOSITION TECHNIQUE

Observations of the cathodic copper plasma expansion at low pressures of He, Ar, and SF6 showed that, for background gas mass densities of ρg = 1 to 4 × 1- -4 kg/m3 and higher, the plasma and gas are separated into two volumes. A shock wave acts as a boundary between the two volumes. The boundary attains a stationary position once its expansion velocity decreases to the velocity of sound in the background gas. This position corresponds to a distance Rc to the cathode that agrees with a snowplow expansion model, giving Rcβf = Er, where f is a function of the arc current and background gas characteristics, Er is the erosion rate of the cathode, and β varies between 2.1 and 2.5. The interaction model is based on kinetic energy exchanges between two gas-like volumes without other energy losses. A maximum pressure limit for vacuum arc deposition is set for ρg/I = 2 to 9 × 10-6 kg/m3A.