Pressure limits for the vacuum arc deposition technique

Observations of the cathodic copper plasma expansion at low pressures of He, Ar, and SF/sub 6/ showed that, for background gas mass densities of rho /sub g/=1 to 4*10/sup -4/ kg/m/sup 3/ 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 R/sub c/ to the cathode that agrees with a snowplow expansion model, giving R/sub c//sup beta /f=E/sub r/, where f is a function of the arc current and background gas characteristics, E/sub r/ is the erosion rate of the cathode, and beta 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 rho /sub g//I=2 to 9*10/sup -6/ kg/m/sup 3/ A.<
>