Diamond-like carbon: state of the art

High power pulsed magnetron sputtering (HPPMS) is an emerging technology that has gained substantial interest among academics and industrials alike. HPPMS, also known as HIPIMS (high power impulse ...

High power pulsed magnetron sputtering: A review on scientific and engineering state of the art

The high power impulse magnetron sputtering (HiPIMS) discharge is a recent addition to plasma based sputtering technology. In HiPIMS, high power is applied to the magnetron target in unipolar pulse ...

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High power impulse magnetron sputtering discharge

Diamond-like carbon (DLC) films combine several excellent properties like high hardness, low friction coefficients and chemical inertness. The DLC coating material can be further classified in two main groups, the hydrogenated amorphous carbon (a-C:H, ta-C:H) and the hydrogen free amorphous carbon (a-C, ta-C). By adding other elements like metals (a-C:H:Me) or non-metal elements like silicon, oxygen, fluorine or others (a-C:H:X), several modifications of the properties can be adjusted according to application requirements. First reports on hard amorphous carbon films were published in the 1950s and about 20 years later there began worldwide intensive research activities on DLC. In the following years the number of publications increased continuously and the importance for industrial applications became more and more evident. Several deposition techniques were applied to prepare a-C:H, ta-C, metal containing a-C:H:Me and non-metal containing a-C:H:X coatings. In parallel the structure and deposition mechanisms of DLC coatings were extensively studied. An essential obstacle for a broad industrial application was the high compressive stress level in a-C:H films causing delamination and limiting the film thicknesses. With metal based intermediate layer systems most adhesion problems could be solved satisfactorily and thus from the mid-1990s the pre-conditions for a broad application especially in the automotive industry were given. With modified a-C:H:X and a-C:X coatings a considerable friction reduction or surface energy adjustments could be achieved.

History of diamond-like carbon films — From first experiments to worldwide applications

An overview on the tribological behavior of diamond-like carbon in technical and medical applications

A new type of arc evaporator, the so-called HCA (high-current pulsed arc), was developed to increase the deposition rate by several times in comparison with conventional arc evaporation units. This device makes use of pulsed arc discharges with nearly sinusoidal current shapes (duration 0.1–1 ms, peak current > 5 kA), which are ignited repeatedly (0–300 s-1) in the centre of a circular cathode. The high pulse current drives the cathode spots radially at high velocity, but before touching the cathode border the arc is switched off and another cycle is started in the centre. The new arc evaporator can work with an average arc current as high as 1000 A. This represents an increase of more than five times over the d.c. currents of 100–200 A usually used. The controllable arc duration and repetition frequency mean that only a well defined circular area of erosion is affected by the arc evaporation. Besides the high rate, there are some other advantages: the deposition rate can easily be controlled and adjusted in a range from zero to a maximum value. The pulsed arc operates with peak deposition rates about 20 times higher than an ordinary arc evaporation unit. Using this method a modified film structure and/or composition can be expected. The number of droplets will be strongly diminished. Using two or more evaporation units, films with a well defined modulated composition and structure (e.g. multilayer films with single film densities of some nanometres) can be produced effectively and with high reproducibility. All the advantages of vacuum arc deposition (high degree of ionisation, ion energies of about 20–50 eV, option for reactive deposition) are enhanced or preserved.

High-current arc-a new source for high-rate deposition

Though the vacuum arc cathode spot has been under investigation for more than a century, its structure and operation is still discussed controversially. Experimentally measured parameters and descriptions of the visible structures given by different authors far from provide a uniform picture. In the present paper, the wide range of findings, parameter values and phenomenological descriptions are explained as different semblances of a complex structured object. The random behavior of all arc spot related parameters, mostly stated as a factor complicating their accessibility, gives the key to a better understanding of its nature. It is shown that the arc spot is mainly characterized by the statistical self-similarity of its structure. Recognizing fractal structures as one of the main features of the arc spot, its comparable appearance on different spatial scales is understandable. Scale dependent values of structure dimensions and time constants are inevitable consequences of this "fractal picture".

Investigation of cathode spots and plasma formation of vacuum arcs by high speed microscopy and spectroscopy

The transport of vacuum arc plasmas through a 90/spl deg/ curved magnetic macroparticle filter was investigated using a high-current pulsed arc source with a carbon cathode. The peak arc current was in the kiloampere range, exceeding considerably the level of what has been reported in the literature. The main question investigated was whether magnetic macroparticle filters could be scaled up while maintaining the transport efficiency of small filters. In front of the cathode, we found that arc current dependent total ion saturation currents were in the range from 10% to 23% of the arc current. The best relative transmission was 25% (time integrated output/time integrated input) at a duct wall bias of 12.5 V and at an axial magnetic field of about 100 mT. The measured relative transmission of the used high-current arrangement is comparable to what has been observed with other low-current filters. The absolute measurable ion saturation currents at the filter exit reached 70 A at an arc current of about 1000 A.

Macroparticle filtering of high-current vacuum arc plasmas

Special features of the filtered high-current pulsed arc deposition (φ-HCA) are presented in comparison with the conventional dc-arc method. The high-current arc technique allows pulse currents of some kiloamperes and averaged arc currents of approximately 1 kA. Due to the high spot velocity the droplet density is already markedly reduced. The remaining particles may be completely eliminated by combination with a magnetic filter. The optimum design of this device together with the high efficiency of the pulsed arc source yields ion currents at the filter exit above 100 A during a pulsed arc and above 10-A averaged current. High quality films with deposition rates of industrial relevance may be produced by advanced arc techniques. Various coatings such as metal refractory nitrides, oxides and hard coatings are investigated and compared with the conventional dc-arc deposition. It is shown that the φ-HCA module is a promising supplementary device that can be attached to industrial standard equipment for various applications demanding smooth mirror-like metallic hard coatings.

Comparison of filtered high-current pulsed arc deposition (φ-HCA) with conventional vacuum arc methods

A pulsed high current metal ion source that produces a metallic plasma flux was designed and successfully used for film deposition. The plasma flux consists of the fully ionized plasma beam produced by a pulsed high current vacuum arc transported through a curved magnetic duct. Deposition rates of more than ten nm/s were achieved. The deposited layers are free of macroparticles, holes, and pits. Films of about 50 nm thickness have been deposited homogeneously (thickness variation below 5%) on a 4 in substrate after 300 pulses. Repetition rates are adjustable from more than 100 Hz down to a single pulse depending on the acceptable thermal input. Several applications are described in the paper: 1) deposition of hard, amorphous carbon films (diamond like carbon), 2) droplet-free TiN films for advanced applications, 3) transparent Al/sub 2/O/sub 3/ protective coatings, and 4) metallization for microelectronics.

Peter Siemroth

Papers

High-current arc-a new source for high-rate deposition

Investigation of cathode spots and plasma formation of vacuum arcs by high speed microscopy and spectroscopy

Macroparticle filtering of high-current vacuum arc plasmas

Comparison of filtered high-current pulsed arc deposition (φ-HCA) with conventional vacuum arc methods

Deposition of droplet-free films by vacuum arc evaporation-results and applications