Sputtering in the presence of a rapid gas flow

• Published in: Journal of applied physics Vol. 64; no. 3; pp. 1418 - 1424
• Main Authors: RAE, S. C, TOBIN, R. C
• Format: Journal Article
• Language: English
• Published: Woodbury, NY American Institute of Physics 01.08.1988
• Subjects: Electric discharges; Exact sciences and technology; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Hollow cathode; Atom density; Glow discharge; Gas jet; Theoretical study; Noble gas; Copper; Experimental study; Electric discharge; Sputtering
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.341814

A rapid flow of noble gas through a hollow cathode glow discharge can be used to entrain a proportion of the sputtered metal atoms and form an extended high-concentration jet. This technique has been used previously to demonstrate copper i and gold i laser action at room temperature. We develop a model to predict the dependence of the ground-state metal atom concentration on the current density and the entrainment in such a system. The sputtering process depends on charge transfer collisions between metal atoms and noble gas ions. By fitting experimental results for a copper cathode to the theoretical predictions, values are found for the rate constant of this reaction and for the entrainment efficiency. In an argon/helium gas mixture, the optimum volume fraction of helium is approximately 90%. The main effects of the helium are to decrease the number of ion collisions in the cathode dark space (leading to increased sputtering yields) and to improve the charge transfer process, although there are a number of additional effects. The time and current dependencies of the copper atom concentration in the cathode region are compared with corresponding measurements taken downstream in the jet.