Pulsed vacuum-arc plasma source operating in the reflective-discharge mode

Abstract

Plasma sources based on vacuum arc discharge have an important disadvantage that is a high share of droplets exists in the cathode erosion material. To ldquocut offrdquo droplets, various kinds of bent magnetic filters are used. We have suggested one more approach to reduce droplet content in arc discharge plasma which is intense evaporation of droplets in a discharge cell, caused by ignition of ldquodroplet spotsrdquo. A Penning-type arc discharge cell was recognized to be providing favourable conditions for ignition of droplet spots. At such a cell, a uniform plasma column is formed, the temperature and concentration are much higher than those of a routine vacuum arc of the same discharge current. Further increase in energy density in plasma of a reflective-discharge cell could be achieved by means of both increase in discharge current and B-field optimisation. The present paper presents results of development and characterisation of a plasma source combining well-known high-current vacuum arc evaporator with a Penning discharge cell. It has been recognized that ion current density amplitude at the source output is as high as 800 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , plasma density up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , and electron temperature 6-8 eV. Those conditions lead to intensive evaporation of droplets in fly. Copper film deposition rate was measured to be of 1.5 nm per pulse, which corresponds to instantaneous deposition rate of 2000 nm/s.