A positively biased external anode for energy control of plasma ions: hollow cathode and magnetron sputtering discharge

Abstract

The performance of a positively biased external ring anode in combination with a hollow cathode (HC) discharge or a magnetron sputtering (MS) discharge, both with a Ti cathode and with Ar as working gas, is investigated. Plasma and floating potential increase as function of anode voltage. Energy-resolved mass spectrometry reveals that the kinetic energy of argon and titanium ions is enhanced by a positive anode voltage allowing for an effective energy control of plasma ions.

Ion energy distribution of plasma ions of a hollow cathode discharge in Ar + N$$_2$$ and Ar + O$$_2$$ gas mixtures

“…Figure 4 compares ion energy distributions of singly charged Ar + , Ti + , and Ar + 2 and doubly charged Ar 2+ and Ti 2+ ions plotted versus reduced energy Ẽ = E/z, where E is the kinetic energy divided by the charge number z. Similar results have been published before [20]. Singly and doubly charged argon ions show a pronounced low-energy tail which presumably is caused by resonant charge changing collisions, e.g., Ar z+ + Ar → Ar + Ar z+ .…”

“…A hollow cathode (HC) made from titanium rod (purity 99.95%, length 40 mm, outer diameter 12 mm, inner diameter of 5 mm) is mounted inside a vacuum chamber (Fig. 1) [20]. The HC tube is open on one end Guest editors: Jose L. Lopez, Michael Brunger, Holger Kersten.…”

“…The observed Ar 2+ /Ar + ion ratio is about 10% for Ar, in fair agreement with more recent observations [26], but considerably smaller (about 2%) for Ar + N 2 and Ar + O 2 gas mixtures. The ratio is quite large considering the plasma conditions which are characterized by a small electron temperature of 0.8 eV only [20] which is typical for DC and pulsed HC discharges [15,27]. Semi-empirical cross sections for single and multiple ionization of argon atoms by electron impact are available from Deutsch et al [28][29][30][31].…”

“…To stabilize the HC discharge, an extra ring anode was recently implemented [18,19]. A biased ring anode offers the additional benefit of controlling the plasma potential outside the HC and the kinetic energy of plasma ions impinging on a substrate [20].…”

Time-resolved ion energy distribution functions during a HiPIMS discharge with cathode voltage reversal

“…In addition to increasing deposition rate, the positive pulse allows one to control the ion energy reaching the substrate. Since changes to electric field are felt by ionized sputtered material and process gas alike, the need to understand and to separate the effects of metal and gas ions has arisen [22][23][24]. The importance of tuneable ion energies of deposited material are difficult to understate given the wide range of material properties [25] accessible at relatively modest gas temperatures.…”