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Cathode spots are the locus for plasma production in cathodic vacuum arcs, and measurements of the discharge voltage provide information about the physics. The voltage noise and cathode-erosion patterns of a high-current pulsed titanium arc were studied as a function of time, current, and pulse shape. Enhanced noise and a 1/f3 trend in the spectral power density were observed when cathode spots are close together at the initiation of an arc for fast rising currents (>1.3 kA in 30 mus) or when the total current exceeds a threshold value of 1.6 kA. We propose a model in which the individual currents associated with the spot substructure can act as noise generators coupled via magnetic fields or coherent spot nucleation.

The disturbance resulting from the presence of a positively biased Langmuir probe at an equilibrium steady-state ion sheath boundary in the drifting plasma is simulated by the two-dimensional particle-in-cell (PIC) method in rectangular coordinates. The positive potential of the probe was found to shield electrons on the side of the probe away from the sample surface from the negative potential of the sample surface and thereby cause an increase in the electron current drawn by the probe. The drifting ions on the same side of the probe are slowed by it and thereby raising the ion density in front of the probe. The electron currents of the probe are calculated at different probe positions from the sample surface. It is found that the sheath boundary as defined by the probe current is wider than the unperturbed boundary. The widening of the sheath boundary agrees well with experimental sheath boundary measurements.

A one-dimensional (1-D) particle-in-cell (PIC) numerical method is developed to determine the equilibrium steady-state sheath width established in a drifting plasma. The simulated and measured steady-state sheath widths are in approximate agreement although the measured width is slightly larger than the simulated. The probe is biased to +90 V and this greatly influences the potential structure within the sheath boundary. The simulation shows that the mean-charge state and mean-atomic-mass approach to dealing with multiple ion species with a range of charge states does not accurately predict the position of the equilibrium sheath when the difference between the charge-to-mass ratios of the ion species is large. A more robust approach is to simulate the steady sheath by a 1-D-PIC method that can handle multiple ion species. In experimental situations where the sample stage is finite in size, the assumption that the equilibrium ion sheath expands from a biased plate of infinite extent may be violated. A two-dimensional PIC numerical method expressed in r-z cylindrical coordinates has been developed to investigate the condition where the 1-D assumption becomes inaccurate. The results confirm that the 1-D-PIC method becomes inaccurate when the steady-state sheath width has dimensions comparable with the sample stage diameter.

The almost fully ionized cathodic arc plasma is a versatile source for the deposition of thin films. The ion energies impinging on the growth surface can easily be controlled by the application of substrate bias. The natural energy of the depositing ions is moderate (/spl sim/10s eV) and generates substantial compressive stress in most materials. In hard materials such as tetrahedral-carbon and titanium nitride the high yield stress makes the problem particularly severe. Work has shown that stress relaxation can be achieved by pulses of high ion energy bombardment (/spl sim/10 kV) applied to the substrate during growth. In this paper we describe the variation of intrinsic stress as a function of applied pulsed bias voltage (V) and pulse frequency (f) for the deposition of carbon and titanium nitride films. We show that the stress relaxation depends on the parameter Vf, so that it is possible achieve the same level of stress relief for a range of voltages by selecting appropriate pulsing frequencies. With the right choice of parameters it is possible to almost completely eliminate the intrinsic stress and deposit very thick coatings. Our experimental results show correlations between intrinsic stress and film microstructures, such as the preferred orientation. This leads to the possibility of controlling microstructure with high energy ion pulsing during growth. Molecular dynamics computer simulations of isolated impacts provide insight into the atomic scale processes at work. Using the results of such simulations, we describe a model for how the stress relief might take place, based on relaxation in thermal spikes occurring around impact sites of the high-energy ions.

High-voltage sheath dynamics near a negatively biased substrate in cathodic arc plasmas are investigated using a biased electrical probe. Since the sheath is devoid of electrons, the sheath boundary can be inferred from the position where a positively biased probe draws no electron current. The extent of the sheath is primarily dependent on the plasma density, the ion velocity and the applied voltage. Using insulating substrates, the sheath boundary eventually retracts due to a dynamic reduction in the applied voltage. This reduction is caused by positive charge accumulation on the insulator surface. The collapse time of the sheath is dependent on the plasma density and the substrate characteristics. We believe this to be the first direct observation of the reduction in the width of the high-voltage sheath when implanting an electrical insulator using plasma-based ion implantation (PBII). This information is important when determining the optimal parameters for plasma-based ion implantation of insulators. Our measurements are compared with theoretical predictions based on the Child-Langmuir equations for high-voltage sheaths. By choosing appropriate values for the secondary electron coefficient the theory could be made to fit the experimental data. A discussion of the validity of the choice of secondary electron coefficients is presented.

Vacuum arc or cathodic arc metal plasma sources are attractive and convenient for depositing high-quality thin metal films and metallurgical coatings. It is a common practice to use a curved magnetic filter duct to eliminate macroparticle contamination and to bias the duct wall with a positive voltage to enhance the throughput of the metal plasma. The metal plasma usually consists of several charge states and time-of-flight (TOF) experiments show that the mean charge state of the metal ions decreases with increasing bias and magnetic field applied to the filter duct. We also derive the throughput of ions with different charge states at different bias voltage and magnetic field by the particle-in-cell (PIC) method. The ion trajectory is simulated neglecting the influence of electron charge. Our results show that the simulated mean charge state displays a similar decreasing trend as the bias voltage and magnetic field strength are increased. Phenomena such as reduction of the mean charge state at high magnetic field strength and bias can be explained in terms of standalone multiply charged metal ions under the influences of magnetic and electric forces inside the filter duct.

In this paper we report the effects of transmission through a 90/spl deg/ solenoidal magnetic filter on the ion charge state distribution of a vacuum arc plasma as a function of the magnetic field strength and the injection distance between the cathode and filter entrance. The mean ion charge state, measured using the time of flight technique, increased compared with the unfiltered value at low magnetic fields and then steadily decreased as the filter field was increased. At high fields, it was significantly lower than the unfiltered value.

The cathodic vacuum are is a simple means of creating a highly ionized metal or carbon plasma, which can be used to produce a wide variety of metal and metal compound thin films. In order to produce smooth, defect-free films suitable for optical and electronic applications, the plasma needs to be filtered of micrometer-sized molten and solid cathode debris known as macroparticles. To date, most of the research effort on plasma filtering has been focused on development and optimization of magnetic filter designs based on curved solenoids. Ryabchikov et al. (1998) proposed and employed novel filter designs for a combined plasma and ion beam source. The new designs are based on a nested set of conical plates in one version and a set of angled plates ("venetian blind") in another. We report on a detailed characterization of the operation of a filter employing a linear venetian blind geometry. The effects of parameters such as plate and arc currents, as well as plate bias on the throughput and deposition profile are reported.

Filtering of plasmas by curved solenoidal ducts is well established as a method of removing macroparticles. By analyzing the interactions of planar probes with the drifting plasma of the cathodic arc, new insights have been obtained into the operation of these ducts. Theoretical modeling of these interactions suggests, and experiment confirms, that the use of a separate biased electrode on the inside of the duct gives enhanced transmission without drawing excessive electron current. Theoretical modeling of a negatively biased planar electrode lying parallel to the drift velocity as well as experiment both show that ions are captured effectively onto the electrode producing a macroparticle free film at good deposition rates. The application of pulsed high voltage to the substrate placed at the exit of the duct is treated theoretically, and a model is proposed which gives a good agreement with the experimental concentration profile for a silicon surface coated and simultaneously implanted with titanium.

Ion transport in a magnetically filtered cathodic arc thin film deposition system is investigated. The plasma floating potential, ion current and deposition rate profiles are used to show that the ion density profile is a function of the magnetic field configuration alone although the magnitude of the ion density increases linearly with magnetic field strength. The magnetic mirror effect, electron diffusion and ion centrifugal drift are identified as the dominant loss mechanisms. The results can be used to design optimal filter systems and to control deposition rate profiles. The effect of reactive gas pressure is also examined.

Curved magnetic ducts are frequently used to remove macroscopic-sized droplets from the plasma stream of cathodic vacuum arcs. The plasma of a cathodic vacuum arc in a magnetic filter is characterized by a strongly directional ion velocity (corresponding to 20-100 eV) and magnetized electrons. In the first section of this paper the effects of these features on the I-V characteristic curves of planar probes are identified and explained using a simple model. This is then used to interpret the interaction of the plasma with the walls of a biased quarter torus duct. Two small electrodes placed on the outer and inner sections of the curved duct wall show that the I-V characteristic is determined primarily by the electron-ion current balance at the wall on the outside of the curve. The application of a bias to a planar electrode on the outer wall section was found to give the same increase in throughput as a positive bias applied to the entire duct with the advantage of a much smaller electron current being drawn by the biasing power supply. The improvement in duct throughput achievable with positive-biasing of the duct wall was found to depend on both the configuration and strength of the magnetic field in the quarter torus filter. The plasma density profile and potential were unaffected by the application of the bias.