The majority of all plasma processes still refers to low-pressure non-equilibrium plasmas. Over the years scaleable high density plasma sources have been developed for a wide variety of different applications. Meanwhile there is a whole range of plasma excitation schemes available including advanced capacitively/inductively coupled rf-sources, helicons and a variety of microwave plasma sources. As an example the so-called SLot ANtenna 2.45 GHz microwave plasma source SLAN with active plasma diameters of up to 67 cm will be presented. The smallest of these sources with a plasma diameter of 4 cm (μmSLAN) allows for the formation of a free standing plasma beam with extraordinary properties. Using argon as a feed gas electron temperatures of well below 1 eV with plasma densities in the range of 10¹³ cm^-3 have been observed more than 30 cm downstream the source outlet. With such a system high quality DLC films with deposition rates close to 40 µm/hour have been deposited for automotive applications.

Maximum plasma densities, excellent homogeneity, contamination issues, scaleability and reduced cost of ownership were the most important driving forces for “traditional” low pressure plasma sources. Because of the relatively high power levels needed for a homogenous stable plasma generation and the widespread energy distribution functions of charged plasma particles a more selective plasma chemistry is difficult to achieve. A major step to overcome this barrier relates to the use of time-modulated power coupling or the operation at extremely low average cw-power levels. As a consequence a substantial retention of the original monomer structure is possible as well as the incorporation of dopants/additives in certain limits. This is especially important for the deposition of highly functionalised polymer thin films for biomedical applications.

A novel 13.56 rf Hollow Cathode Plasma Source developed at the Microstructure Research Center fmt has been proven to satisfy those requirements including scaleability and very low parasitic contamination. Process examples spanning from optical SiO_x hard coatings, SiN_x thin films for photovoltaics to DLC for optical and biomedical applications.

Increasing the workable pressure range to atmospheric pressure without loosing the technological benefits of low-pressure non-equilibrium plasmas is highly attractive and has stimulated massive research worldwide. Because of their comparable low lifetime charged plasma particles play a less significant role in atmospheric pressure plasma processing. Instead, metastable engineering on a molecular level is becoming more important. Here so-called surface and coplanar discharges operating (at least partially) in the glow discharge regime without any restricion to the use of molecular gases are promising. This talk will address some novel innovative schemes together with process examples, too.

Employing thermal evaporators, very high deposition rates can be achieved. However, layer properties lack sufficient density typically. This drawback can be overcome by introduction of a suitable plasma activation.

Plasma properties like plasma density in the range of 10¹²/cm³ and electron temperature of about 3 eV in the positive plasma column as well as the very wide operation parameter range including different evaporation materials and different gases in a wide pressure range between 0.1 Pa to 30 Pa make the hollow cathode arc sources to be first choice tools for plasma activation. A wide variety of configurations for different applications and process conditions has been developed and optimized.

Most configurations are dedicated to web coating. For uniform plasma activation of the vapor generated by a line evaporator, the hollow cathode plasma sources are arranged side by side and are equipped with ring anodes. Directed electrons from the cathodes pass through the ring anodes and activate the vapor cloud close to the substrate. The resulting ion current density impinging on the substrate amounts to 5...10 mA/cm². For higher degree of activation, the plasma electrons can be drawn towards additional anodes arranged close to the crucible. In combination with an external transversal magnetic field, an internal electrical field within the plasma is generated. It accelerates ions towards the substrate. In this setup, ion current densities from 30 to 60 mA/cm² can be achieved.

In directed vapor deposition (DVD) technology developed recently, vapor stemming from a point source is focused by a carrier gas to propagate as a tight beam. Operation pressures up to 30 Pa are typical for this process. The hollow cathode arc source has to be adapted to these conditions. Furthermore, the drop of the self bias voltage due to electron collision processes in dense atmosphere has to be compensated by an external bias voltage applied to the substrate which enhances the energy of the condensing ions. For deposition of non-conductive layers, this bias voltage must be AC pulsed.