Ionization of copper in gas and gasless modes of continuous high-power magnetron sputtering

Abstract

The results of studies of magnetron sputtering of copper at discharge currents from 2 to 15 A in a 76 mm diameter planar magnetron are presented. In addition to the standard gas mode at an argon pressure of 0.12 Pa, a gasless mode was also implemented in which no argon was supplied to the vacuum chamber and the base pressure was 1·10−3 Pa. The stable gasless mode is realized at a discharge current higher than 8 A. The electrical discharge parameters as well as the copper sputtering rate, the ion current density on the substrate and the degree of ionization of the sputtered target material were measured and compared for the two modes mentioned. The plasma composition was also measured by optical spectrometry. The experimental data were used to calculate the density and composition of the neutral and ion fluxes to the substrate. It is shown that the gasless mode provides a higher ion current density on the probe and a higher degree of ionization of the sputtered copper compared to the gas mode at the same discharge current. The degree of ionization of the sputtered material reaches 14–15 % in gasless mode, whereas in gas mode it varies from 2 to 13 % depending on the discharge current.