E Gidalevich

Recent progress in filtered vacuum arc deposition

Abstract During this decade significant advances have been made both in the understanding and implementation of filtered vacuum are deposition. Rigid rotor models have been analyzed statistically, and new models which treat the mutual influence of the electrons and ions on each other self-consistently, take into account the centrifugal force on the ions, and take into consideration collisions, have been formulated. It was shown that the plasma transport efficiency is limited by drifts caused by the centrifugal force and by the electric field generated by charge separation in the plasma. For a range of magnetic fields strengths for which the ions are not magnetized, i.e., confined to a Larmor radius less than the duct radius, the transport efficiency for Cu plasma is about 10%, and depends only weakly on the magnetic field strength. Increased transmission is found when the ions are magnetized, reaching about 50% for a 36–60 mT field in typical configurations. The plasma transport efficiency and spatial distribution has been measured over a large parameter range, and correlated with the various theories. The plasma beam may be approximated as a Gaussian distribution which is displaced in the B × G direction, where G is in the direction of the centrifugal force, while a displacement in the plane of symmetry is surprisingly found in the − G direction. The total convected ion current decreases exponentially with distance from the toroidal filter entrance. Macroparticle transport within the magnetic filter has been analyzed, and it has been shown that electrostatic reflection from the walls can occur if the magnetic field is weak. Filtered arc sources with improved throughput performance and novel geometries have been built, and are now available commercially. The range of coatings deposited with FVAD has been expanded to include metals, oxides, and nitrides, as well as diamond-like carbon. In several cases, coatings having the highest quality reported in the literature have been fabricated with the FVAD technique, and one commercial application has been reported.

Vacuum arc plasma jet propagation in a toroidal duct

A two fluid magneto‐hydrodynamic theory of vacuum arc plasma jet propagation in a magnetized toroidal duct is developed. The physical mechanisms of jet transverse displacement and plasma losses are analyzed and the centrifugal force on the ions is shown to play the principle role in these processes. Optimal conditions for jet propagation occur when the centrifugal force is balanced by the electrical force on the ions. An analytical solution of the nonlinear problem of plasma beam transport through a toroidal duct is obtained for the two cases where ions are magnetized or not magnetized. The ion mass current decreases with the azimuthal distance along the torus as (1+φ/φ0)−1 where φ0 is a characteristic angular distance, for the case when ions are magnetized, and exponentially when the ions are not magnetized. Numerical calculations show that the decrease of plasma density leads to a longitudinal electric field and current. This current, together with the current due to the centrifugal drift, form a curren...

Filtered vacuum arc deposition of semiconductor thin films

The cathode spot vacuum arc produces a jet of highly ionized plasma plus a spray of liquid droplets, both consisting of cathode material. The droplets are filtered from the plasma by passing the plasma through a curved, magnetized duct. A radial magnetic field may be applied to the face of the cathode to rotate and distribute the cathode spots in order to obtain even erosion and avoid local overheating. The choice of axial magnetic field strength in the vicinity of the cathode is a compromise between a relatively high field desired to collimate a large fraction of the plasma flux, and the need to collect a substantial fraction of the plasma at the anode in order to reduce arc voltage and insure arc stability. The transmission of the filter duct increases with magnetic field strength until a saturation value is reached. Entrainment of the droplets in the plasma jet can decrease the effectiveness of the filter at high plasma flux. Semiconducting thin films of amorphous silicon were prepared using cathodes of heavily B-doped Si. Arcs of 35-A current produced a deposition rate of 10 /spl Aring//s. The electrical conductivity of the films was similar to conventional a-Si:H films deposited by conventional Silane based PACVD at high temperatures, but had a higher room-temperature conductivity. Transparent conducting films of Sn-O were deposited at rates of up to 100 /spl Aring//s using 160-A arcs on a Sn cathode while injecting O/sub 2/ gas in the vicinity of the substrate. Adjustment of the O content is critical for optimizing conductivity, and complicated by pumping effects of the arc. Optimal conductivity was achieved at an oxygen pressure of 6 mtorr. Conductivities equal to the best reported to date were achieved by subjecting the room-temperature deposited films to a 30-s rapid thermal annealing at 350/spl deg/C. Both the deposited and annealed films are amorphous. The deposition rates achieved by the filtered vacuum arc technique for these semiconductor films are an order of magnitude greater than achieved with conventional methods, while the conductivities are equivalent or better.

Magnetic control, in vacuum arc deposition - a review

The use of magnetic fields to control cathode spot location and motion and to collimate and direct the plasma flow in vacuum arc deposition apparatus is reviewed. Retrograde and acute angle motion are used to control the location and motion of cathode spots, in order to confine them to the cathode surface facing the substrates, to prevent local overheating, and to reduce macroparticle production. Axial fields are use to collimate cathode spot produced plasma jets, and to bend them around macoparticle occluding obstacles in filtered vacuum arc deposition. Advances have been made in understanding these phenomena, but theoretical models have not yet been formulated which can predict plasma behavior sufficiently well for apparatus design.

The numerical calculation of plasma beam propagation in a toroidal duct with magnetized electrons and unmagnetized ions

Electron-magnetized vacuum arc plasma transport in a magnetic toroidal duct is calculated numerically taking in account electron - ion collisions, electron and ion temperatures, and the high conductivity of the duct wall. The longitudinal magnetic field in the duct, the fully ionized plasma density and the electric potential distribution at the torus entrance are given, while the plasma density, electrical field and current, and macroscopic plasma velocity across the magnetic field inside the duct are calculated. Toroidal coordinates are used to describe plasma beam propagation. A Runge - Kutta routine is used for the calculations along the torus while a finite difference method is used across the torus cross section. It is found that plasma loss due to particle flux to the duct wall depends on the electron and ion temperatures and the plasma density distribution at the torus entrance cross section. With an electron temperature of , 30 000 K and 50 000 K, an ion temperature and a Gaussian distribution of plasma density at the torus entrance with a maximum value , we found that the duct efficiency was less than 10% for longitudinal magnetic field strengths of 10 mT and 20 mT. In the case where only the electrons are magnetized, filter efficiency depends only weakly on the magnetic field strength, on , and on .

Theory and modelling of the interaction of two parallel supersonic plasma jets

The objective of the present work is to predict the profile of the shock front formed by the interaction of two parallel diverging supersonic plasma jets. The form of the front is determined by the divergence of the plasma jets and by the distance between their sources, but the maximum angle of the front inclination at the head point of the shock wave is determined by the plasma properties only. The streamlines of the two plasma jets are diverging before the front and are parallel behind it. The diffusion of the ions flying from two different sources was calculated numerically up to a distance of 10 times the source separation in the region bounded by two symmetric shock fronts. For an ion temperature of K, a jet velocity of , and initial densities of and (corresponding to a Mach number of 10 and Knudsen numbers of 0.04 and 0.4 respectively) the partial and total density distribution in the diffusion zone was found. The ion distribution is not homogeneous in all of investigated regions. The most homogeneous distribution was obtained with an initial density of . The shock model predictions were compared with a free expansion model, and the densities are radically different.

Sub- and supersonic expansion of an arc channel in liquid

Post-breakdown expansion of a submerged discharge was considered taking into account the curvature of the plasma boundary and the sound and shock wave fronts. Numerical calculations were performed for an inter-electrode gap of 10−5 m, electrical current and voltage of 10 A and 100 V, respectively and a water medium. With an initial temperature of T0 = 2 × 104 K, a subsonic solution was found. The maximum expansion velocity is 1200 m s−1. The electrical current increases up to 9 A during ~60 ns. With an initial temperature of T0 = 3 × 104 K, the plasma channel expansion starts as subsonic but after ~5 ns it reaches the sonic velocity and transits it. The maximum velocity of the plasma boundary of about 2000 m s−1 is reached after ~17 ns, and a shock wave appears in the undisturbed water. At this stage, water intensively evaporates into the plasma cavity. The electrical current jumps at the sonic transition point up to 10 A. The calculated pressure maximum is about 8 × 1010 Pa.

Propagation of a magnetized plasma beam in a toroidal filter

A two-fluid magneto-hydrodynamic model for the motion of a vacuum-arc-produced magnetized plasma beam in a toroidal magnetic filter is presented. The model takes into account in a self-consistent way electron-ion collisions and electrical, magnetic, centrifugal and pressure forces. An analytical solution is obtained that describes the distribution of the plasma density, the electron and ion velocities, the electric field and the current in the plasma. Analytical expressions for the filter efficiency as a function of the toroidal magnetic field are also derived. The effect of the centrifugal and diamagnetic ion drifts on the polarization electric field is studied. It is shown that the efficiency increases exponentially when the polarization field decreases. A decrease of the polarization field can take place when a current path outside the plasma short-circuits the electrical currents generated by the magnetic field in the plasma. When there is no polarization electric field, the filter efficiency increases with the magnetic field as where , is the ion mass, is the total input ion flux, is the transverse plasma conductivity and R and are the major and minor radii of the torus, respectively.

Hydrodynamic effects in liquids subjected to pulsed low current arc discharges

Hydrodynamic phenomena in liquids associated with low current electrical discharges were analysed theoretically and the radial plasma column expansion was considered as an arbitrary discontinuity propagation. For assumed initial discharge channel radii of R0 = 10 −6 and 10 −5 m, the initial temperatures in the discharge channel was found to be T0 = 1.4 × 10 6 and 6.5 × 10 4 K for a discharge current of I = 1 A, and T0 = 6.5 × 10 6 and 3 × 10 5 K for I = 10 A. The temperature decreases during the initial ∼10 −8 s, due to radial plasma column expansion. During the initial 10 −8 s the velocity of the plasma column expansion exceeds the speed of sound in the undisturbed water (by 5–15 times), creating a shock wave in the water with a pressure discontinuity of ≈10 5 atm, and a relaxation length of 10 −4 m.

Shock discontinuity in high-current vacuum arcs

The deceleration of a cathode plasma jet caused by interaction with a secondary ion cushion at the anode is analyzed. Copper electrodes are considered. The secondary ions are assumed to be sputtered and/or reflected from the anode. The sputtering coefficient was found by integrating the energy distribution of the cathode spot plasma jet, weighed by the copper-copper self-sputtering yield. The system of equations of motion and continuity for the primary plasma jet and the secondary ions was solved numerically for arc current densities in the range of (3/spl times/10/sup 4/-5/spl times/10/sup 5/) A/m/sup 2/. It was found that for an interelectrode gap of 2 cm, and a secondary ion velocity of 10/sup 3/ m/s, there is no upper limit for the current density for continuous jet motion. For secondary ion velocities <0.25/spl times/10/sup 3/ m/s, the upper limit is 10/sup 5/ A/m/sup 2/, above which a shock front forms between the primary and secondary plasma.