3484 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 47, NO. 8, AUGUST 2019 Plasma Generation in a Double Anode Vacuum Arc I. I. Beilis , Senior Member, IEEE , Y. Yankelevich, and R. L. Boxman, Fellow, IEEE Abstract—The hot refractory anode vacuum arc (HRAVA) plasma source was previously developed with a consumed cath- ode and a refractory anode to reduce the macroparticle (MP) contamination in vacuum arc deposited films. The HRAVA had open cylindrical electrodes and demonstrated that it not only reduced MP sizes and numbers but also converted MP material to plasma, and thus increased the deposition rate. This paper presents a new HRAVA configuration with a double arc between a common water-cooled Cu cathode with two active surfaces and two refractory graphite or tungsten anodes, with the aim of depositing film over a wider area. The arc current in each of the two arcs was 125 A for graphite and 150 A for tungsten. The radially expanding plasma plumes from each of the cathode–anode gaps merged, forming a wider common plasma. Cu films were deposited and over a 150 mm length parallel to the arc axis, while the corresponding length from a single-HRAVA source was only 75 mm. Index Terms— Double arc, merged plasma plume, refractory anode, vacuum arc. I. I NTRODUCTION T HE metallic plasma is used for thin film deposition, tool coatings, ion implantation, spacecraft thrusters, and pro- ducing interconnections in microelectronics [1], [2]. Vacuum arcs are used as metallic plasma sources to deposit thin films. The vacuum arc plasma can produce larger deposition rates than the sputtering and electrolysis. However, conventional “cathodic” vacuum arc coatings are degraded by macroparti- cles (MPs) produced as a part of the cathode spot process [3]. While magnetic filtering can significantly reduce the MP contamination, it also significantly reduces the deposition rate and uses a complicated and bulky apparatus. To overcome these difficulties, another techniques use arc modes where MP generation is repressed such as in the hot cathode vacuum arc [4] with the distributed current on an evaporated cathode and the hot anode vacuum arc [5] with an evaporated anode. Two plasma sources were developed with not expendable hot anode: the hot refractory anode vacuumarc (HRAVA) [6], which has an open gap between the parallel anode and cathode surfaces, and the vacuum arc with a blackbody assembly (VABBA), which has an interelectrode cavity enclosed by a hot cup-shaped refractory anode with one or more plasma exit apertures [7]. Manuscript received January 8, 2019; revised March 3, 2019; accepted April 23, 2019. Date of publication May 22, 2019; date of current version August 9, 2019. The review of this paper was arranged by Senior Editor K. W. Struve. (Corresponding author: I. I. Beilis.) The authors are with the Faculty of Engineering, Electrical Discharge and Plasma Laboratory, School ofElectrical Engineering, Tel Aviv University, Tel Aviv 69978, Israel (e-mail: beilis@tauex.tau.ac.il). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2019.2914996 The HRAVA was sustained between a nonconsumed cylin- drical anode facing a water-cooled consumable cathode with a 10–20 mm gap for up to 180 s of arcing [8]. The anode was thermally isolated by surrounding shields to reduce radiative heat loss. The anode surface temperature was found to increase with time, reaching 2000–2500 K, depending on arc current and anode material. The arc initially (t < 20 s) operated as a conventional vacuum arc, and cathode material was deposited on the cold anode. When the anode was sufficiently heated, the material deposited on it was reevaporated and the generated plasma radially expanded and deposited a metallic film on substrates. The HRAVA was investigated as a plasma source for depositing materials with intermediate thermophysical properties (Cu, Cr, Ti) with a tungsten anode [9], volatile materials (Al, Zn, Sn) with graphite and Mo anodes [10], and refractory material (Zr, W) with a W anode [11]. The above HRAVA plasma sources can deposit metallic films on a substrate placed at a distance of 110 mm from the arc axis with deposition rates up to ∼3 μm/min but only onto a relatively limited area corresponding to a few times the interelectrode gap (10–15 mm) [6]. The VABBA with multiple exits, resembling a shower head, likewise deposits films close to it on an area close to the shower head dimen- sions [7]. However, much larger coating areas are required for many applications of interest, such as transparent conductive films for large flat displays, energy conserving coatings on architectural glass, films on flexible polymers, and aerospace applications [12], [13]. Usually, these films are currently deposited by sputtering, which has a relatively low deposition rate [6]. It would be useful to develop a vacuum arc source that can deposit MP-free metallic coatings on large areas with high deposition rate, and this was the goal of the present project. This paper presents a new configuration with a double arc between a common cathode and two refractory anodes, which produced plasma flux over a wider area. II. EXPERIMENTAL SETUP A schematic of the double-HRAVA system is presented in Fig. 1. Two parallel lateral sides of a water-cooled Cu cath- ode of 30 mm diameter (Fig. 2) faced toward two refractory anodes (indicated as 1 and 2, see also Fig. 1), forming two d = 10 mm gaps. One of the cathode sides is a port for cooling water inflow through a channel. The cathode face wall is the bulk wall, which served as an additional cooling body and for return the water flow from the cathode body. A BN shield isolated the cathode face surface (see Fig. 3). The anodes were 32 mm diameter, either 10-mm-thick graphite or 40-mm-thick tungsten. 0093-3813 © 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.