Interaction of a vacuum arc plasma beam with an obstacle positioned normal to the plasma flow

Abstract

The effect of an obstacle positioned normal to a plasma jet produced by a vacuum arc plasma source on the radial distribution of ion flux in the vicinity of the obstacle was studied. This study was motivated by interest in the mutual influence of tightly packed substrates on coatings in industrial vacuum arc deposition systems. The experimental system consisted of a vacuum arc plasma source, a straight plasma duct, and a multi-probe consisting of a removable disc obstacle and a set of ring probes for measuring the radial ion flux. A dc arc discharge was ignited in vacuum between a truncated cone-shaped Cu cathode and an annular anode. The plasma jet produced by cathode spots passed through the anode aperture into the straight plasma duct. An axial magnetic field guided the plasma jet in the duct. The multi-probe consisted of a removable disc obstacle and a set of five ring probes for measuring the radial plasma flux as a function of distance from the disc obstacle. The rings and the disc probes were coaxially arranged on the multi-probe assembly and positioned so that plasma from the source passed through the ring probes and then encountered the disc. The influence of the obstacle was determined by measuring the ring ion currents, both in the presence of the obstacle, and when the disc obstacle was removed. The difference between the measured ion currents with and without the obstacle was interpreted to be the contribution of reflected or sputtered particles from the obstacle to the radial ion flux. The ring probes were biased by −60 V with respect to the grounded anode, to collect the saturated ion current. The multi-probe was connected to a movable stem, and positioned at different distances from the plasma source.A plasma density of ∼6 × 1017 m−3 was estimated in this study based on the ion current to the obstacle. The radial ion flux collected by the ring probes increased by 20–25% due to the presence of the obstacle. As the calculated mean free path for collisions between the plasma ions and sputtered or reflected particles is much larger than the plasma path length, the plasma jet should not be affected by returning particles. Hence, the increase of the radial flux is most probably due to ion reflection from the obstacle and ionized neutral atoms sputtered from the obstacle.

Current Distribution on the Substrate in a Vacuum Arc Deposition Setup

“…We suppose that in our conditions, the saturated current is collected 20. In our setup, the ion current increases when applying the bottle configuration of the magnetic field, as it may be seen in Figure 2c) and 3c).…”

Plasma Jet Interaction With a Spherical Target in Magnetic Field

“…The number of electron "runs" along the stream may be estimated (4) where is the electron transit time across the stream, is the electron transit time along the stream, is the electron velocity along the stream (i.e., along the magnetic field), is the electron velocity across the magnetic field, is the stream thickness, and m is the distance between the target and duct. The electron velocity in general form may be calculated (5) where is the electron mobility tensor and is the electrical field vector. From this relation, we have and , where is the electron mobility along the magnetic field, is the electron cross-field mobility, is the electrical field along the stream, and is the electrical field across the stream (transversal electrical field).…”

“…In the plasma immersion implantation, the interaction of plasma and ion fluxes with an object of a complex shape causes rearrangement of electrical field [3], [4] and the following redistribution of the ion current to the target surface. The interaction of a vacuum arc plasma jet with the biased object may represent an interest for studying the uniformity of deposition on close located substrates, and for reflecting the plasma beams [5]. Besides, plasma transport in the curved ducts [6], [7] may be considered as a special case of a plasma-object interaction.…”

Design and Performance of the Transverse Rotating Magnetic Field Steered Arc Source Used in Vacuum Arc Deposition

“…However, to date the main magnetic field configurations are limited to static magnetic field. There are two typical magnetic field configurations: one is the axial magnetic field employed with a dished cathode [15][16][17][18][19], or with a frustum cone cathode [20][21][22][23][24]. In the dished cathode case, there is an increasing tendency for the cathode spot to rotate and drift toward the cathode target edge due to the axisymmetric "retrograde motion" and "acute angle rule", respectively.…”