Reduction of outgassing rate by glow discharge cleaning

Abstract

The effectiveness of glow discharge cleaning (GDC) as a means of decreasing the pump-down time of vacuum systems was studied. We measured the outgassing rate of an electropolished stainless steel surface after it was exposed to glow discharges fueled by various gases (He, He/1%–3%H2, He/1%–3%CH4, H2, Ar) following a standard 1 h of venting to ambient air. It is shown that He GDC is most effective in reduction of outgassing rate: a He GDC trial with a dose of 0.8 C/cm2 reduces the outgassing rate and subsequently the pump-down time by a factor of 13. For given glow discharge currents, the outgassing reduction factor is directly proportional to the glow discharge duration. The reduction of post-GDC outgassing is a result of enhanced desorption of H2, CO, and CO2 by He GDC as observed by residual gas analysis during the discharge. The GDC results are consistent with our previously proposed diffusion models for water outgassing from metal surfaces.