EP1767068A2

EP1767068A2 - Device for the treatment of a substrate by means of at least one plasma jet

Info

Publication number: EP1767068A2
Application number: EP05753782A
Authority: EP
Inventors: Jürgen ENGEMANN; Darius Korzec; Markus Teschke
Original assignee: JE PlasmaConsult GmbH; Maschinenfabrik Reinhausen GmbH
Current assignee: Maschinenfabrik Reinhausen GmbH
Priority date: 2004-06-16
Filing date: 2005-06-08
Publication date: 2007-03-28
Anticipated expiration: 2025-06-08
Also published as: DE102004029081A1; DE502005007992D1; WO2005125286A2; EP1767068B1; WO2005125286A3

Abstract

The invention relates to a device (10) for treating a substrate (11) with the aid of at least one plasma jet (13). Said device comprises a receptacle (15) through which a carrier gas flows along a certain direction of flow (x), a first electrode (17), and a second electrode (18). The inventive device is characterized in that the two electrodes (17, 18) are separated from each other by means of at least one dielectric barrier (15) while an alternating voltage is applied between the electrodes (17, 18) in order to create an atmospheric pressure glow discharge plasma. Furthermore, the first electrode (17) is axially (L) and radially (R) spaced apart from the second electrode (18) relative to the direction of flow (x) of the carrier gas.

Description

Device for processing a substrate using at least one plasma jet

The invention relates to a device for processing a

Substrate by means of at least one plasma jet according to the preamble of claim 1.

The invention is based on a device according to DE 197 22 624 C2, which goes back to the applicant. An apparatus for generating a large number of low-temperature plasma jets is described there. The plasma jets are generated using hollow cathode discharges. Openings in single hollow cathodes and in the anode form axially aligned pairs of holes. The plasma jets each penetrate an area between the cathode bore and the anode bore and extend beyond the bore areas into a process space. With the device of the prior art, a homogeneous disposition of a functional layer on a web-shaped and possibly temperature-sensitive substrate is possible.

Based on this prior art, the object of the invention is to develop a device according to the preamble of claim 1 in such a way that it can be used to generate plasma jets in an efficient manner, even at working pressures in the range of atmospheric pressure, while enabling a large machining depth.

The invention solves this problem with the features of claim 1, in particular with those of the identification part, and is accordingly characterized in that the two electrodes are separated from one another by at least one dielectric barrier an AC voltage is applied between the electrodes for generating an atmospheric pressure glow discharge plasma, and that the first electrode is axially and radially spaced from the second electrode with respect to the flow direction of the carrier gas.

The principle of the invention is first of all to provide an atmospheric pressure glow discharge instead of a hollow cathode discharge as proposed by the prior art. An atmospheric pressure glow discharge plasma requires a dielectric barrier between the two electrodes and, compared to the hollow cathode discharge, represents a completely different physical principle of plasma generation, which leads to a different type of plasma. In this context, the term “atmospheric pressure glow discharge plasma” makes it clear that this plasma can also burn at atmospheric pressure and the device can be operated accordingly at atmospheric pressure. Working pressures in the range between 50 mbar and 10 bar are possible and useful.

The device according to the invention thus differs from the device according to DE 197 22 624 C2, which conventionally can only be operated at a few mbar using a vacuum pump. According to the invention, the vacuum pump required in the prior art can be dispensed with. In theory, operation with the device according to DE 197 22 624 C2 is also conceivable at higher working pressures. The discharge channels must then have a very small diameter in the range of a few μm, taking into account the free path length of the electrons, which leads to a complex construction. In this case, however, plasma jets would not be generated, but hollow micro-cathode discharges. The intended with the device according to the invention

Processing of substrates, especially with large ones

Substrate surfaces, as well as substrates that have a special topography and require a large processing depth, are not possible with the known device.

A plasma jet in the sense of the invention is an atmospheric pressure glow discharge plasma which, when viewed optically in the operating state of the device, has a jet or jet shape and is extracted from the device, in particular from the container, and is distanced up to one extends from the device arranged substrate. It should be noted that the substrate can be arranged in a stationary manner during processing by the device or can undergo movement relative to the device.

Processing of a substrate in the sense of the invention is understood to mean any treatment, in particular surface treatment, of a substrate, in particular a coating, structuring (lithography), cleaning or modification of the substrate surface or of the substrate. The plasma jet is a cold, chemically reactive plasma jet that burns at low temperatures of a few 10 ° C. In the device according to the invention, the chemically reactive and physically excited species are provided to each plasma jet with the aid of a dielectrically impeded primary discharge.

In order to supplement and deepen the understanding of the invention, an overview is given below of a large number of further devices of the prior art which work with arc discharges. For arc discharges, however, is between the first and the second electrode no dielectric barrier, so that it is not comparable plasmas.

The plasma jets in the form of arc discharge have been known for a long time. There are different variants and applications

The subject of numerous patent specifications. For example, in U.S. 5,272,979 describes a device in which an arc discharge is ignited between an inner electrode and an outer electrode. It transfers the electrical energy to a gas flow that exits from an outlet nozzle in the form of a plasma jet and is guided to a substrate. Such a plasma jet is used for structuring or cleaning lithographic plates. A similar device for lithographic purposes is given in US 5,062,364. Another

Device that focuses on improved gas flow is described in US 6,408,755.

The manner in which the gas is fed into the device also plays an important role in the devices of the prior art. This deals with e.g. WO 01/43512. The gas is introduced into the discharge zone at a certain azimuthal and axial angle, so that a swirling of the gas flow occurs. This leads to an increase in the efficiency of the interaction of the discharge with the gas. This device is used for cleaning rollers and belts (cf. EP 1 170 066).

An "atmospheric-pressure plasma jet" according to US Pat. No. 5,961,772 has, in addition to a narrowing nozzle area, also a coaxial space between the inner electrode and the outer electrode, in which the carrier gas is treated over a considerably longer distance than in the device discussed above helium the device is operated in the “Atmospheric Pressure Glow Discharge (APGD) mode. This means that a non-equilibrium, relatively cold (gas temperature below 250 ° C) plasma with high energy stored in metastably excited species is formed in the coaxial space, which allows the generation of a long plasma jet. Supplementing this device with means for supplying the process gas in the vicinity of the outlet nozzle according to WO 99/20809 enables the generation of a chemically reactive plasma jet. This avoids the introduction of the process gas together with the carrier gas in order to avoid the chemical reactions of the primary discharge with the electrodes or the layer deposition on the electrodes and to prevent the quenching of the metastably excited species in this area. The parasitic layer deposition, overheating and the chemical attack of the discharge electrodes are serious problems with all devices for the production of chemically reactive plasma jets. WO 01/40543 solves the problem with the aid of an inner envelope gas guided on the surface of the outer electrode, which separates the zone of the plasma generated with process gas from the electrode surface.

The solution for providing the process gas, which is often described in the literature, is a direct supply into the zone of the plasma jet, e.g. the supply of a carbon-containing monomer for the construction of diamond films using a method and a device according to EP 0388861.

The disadvantage of the numerous devices described above that work with arc discharges is that a direct electrical connection between the two is electrical only through the plasma electrodes separated from each other. Even small variations in the electrode spacing or the nature of the electrode surface lead to the focus of the discharge and the creation of a hot spot or other types of spatial inhomogeneity.

To avoid these disadvantages, devices are also known which provide a dielectric barrier between the two electrodes. For example, FIG. 2 of US 2002/0097295 describes a device in which two electrodes, the “up-stream” electrode 1 and the “down-stream” electrode A, are attached to a common dielectric tube. The two electrodes 1, A are essentially sleeve-shaped and surround the dielectric tube. They are axially spaced apart. The primary discharge 4 forms in the axial direction between the two electrodes and can pass into a plasma jet 5b, provided that suitable geometric dimensions and operating parameters are selected. However, the generation of plasma jets is not a primary goal of the device described in this patent application. A problem with this arrangement is, moreover, that the ignition distance between the electrodes inside and outside the tube is of the same length and thus a parasitic discharge in the outer region cannot be ruled out.

Various coaxial arrangements of the electrodes known from the literature with an also coaxially arranged dielectric barrier between the electrodes are freed from this disadvantage.

Koinuma et al describe a device in US Pat. No. 5,221,427 and a method for treating surfaces under atmospheric pressure with a plasma jet in US Pat. No. 5,198,724. A working gas typically a helium gas mixture, passed through a coaxial area between the axially positioned inner electrode and the electrically insulating outer tube and the outer electrode and converted to a primary discharge with the electromagnetic field built up there between the inner electrode and the outer electrode with the aid of a voltage generator and then in the form of a chemically and physically activated plasma jet in the direction of the substrate. There the plasma jet effects surface modification, layer deposition, cleaning or other plasma processes. In a variant of this device described in US Pat. No. 5,369,336, means for generating a magnetic field are applied behind the substrate in order to influence the shape of the plasma jet and its direction.

A complex configuration of magnetic fields is also described for controlling the position of the plasma jet in WO 01/88220 (also US 2002/0030038).

In US 5,523,527 and US 6,221,268, Kim Li and M. Tanielian describe a device for generating an atmospheric pressure glow discharge which is generated with the aid of high-frequency power (13.56 MHz) in the form of a jet. The discharge scheme and the electrode geometry correspond to the principle according to US Pat. No. 5,221,427. The modification of plastic surfaces is mentioned as an application example.

EP 0921713 A2 is based on the reverse arrangement of the coaxial electrodes and the dielectric barrier. In this case, the working gas in the coaxial zone between the outer electrode and the dielectric sheath of the inner electrode is guided in the axial direction. The device according to the invention also differs significantly from the devices described above by its electrode geometry. It is provided according to the invention that the first electrode is axially and radially spaced from the second electrode in relation to the flow direction of the carrier gas. Such an electrode geometry initially requires a flow direction of the carrier gas. It is assumed that the carrier gas essentially flows along a straight line in the region of the two electrodes. In particular, the direction of flow of the carrier gas in the region of the electrodes corresponds to the longitudinal extent of the container in the region of the electrodes, for example a central longitudinal axis of the container. According to the invention, the first electrode and the second electrode are spaced axially and radially from one another. The carrier gas flows along the direction of flow between the two electrodes, main discharge channels being formed between the two electrodes due to the AC voltage applied. The main discharge channels essentially form along the shortest connecting lines between the two electrodes. Since the first electrode is axially and radially spaced from the second electrode, the shortest connecting line between the two electrodes is arranged essentially obliquely to the direction of flow of the carrier gas. This enables a particularly intensive interaction between the carrier gas and the discharge.

Due to the special arrangement of the electrodes with respect to one another according to the invention, a particularly long shortest connecting line, which runs obliquely to the flow direction of the carrier gas, can be achieved. The longer the shortest connecting line is selected, the more volume fractions of the carrier gas can interact with the plasma. However, it should also be noted that the shortest connecting lines between the two electrodes, which are selected too long, have a disadvantageous effect on the plasma generation. There is an optimal length of the shortest connecting line.

The electrode geometry according to the invention differs from an electrode geometry which only provides electrodes which are radially spaced apart from one another by an inclination of the shortest connecting line relative to the flow direction of the carrier gas, which improves the interaction between plasma and carrier gas. The electrode geometry according to the invention differs from an electrode arrangement which only axially spaces electrodes by an essential component of the shortest connecting line and a main discharge channel aligned essentially along the shortest connecting line, essentially transverse to the flow direction of the carrier gas.

Since main discharge channels form according to the invention along a direction oblique to the flow direction of the carrier gas, a large volume fraction of the carrier gas can interact with the plasma, so that an efficient mode of operation is possible.

It should be noted that in the sense of the invention an axial spacing of the two electrodes from one another means a spacing along the flow direction of the carrier gas. A radial spacing of the two electrodes from one another in the sense of the present patent application means a spacing of the two electrodes from one another transversely to the direction of flow of the carrier gas. The design of the main discharge channels according to the invention brings about a substantial increase in the efficiency of the device through increased interaction with the carrier gas. The electromagnetic energy is coupled into a much larger volume of carrier gas, whereby a higher proportion of helium atoms is brought into a metastable excited state. The energy stored in this way facilitates the ionization processes and other plasma processes in the plasma jet, as a result of which both the length and the intensity of the plasma jet are increased in the sense of the electron concentration and in the sense of its chemical reactivity.

The consequence of this increase in efficiency is that you need significantly less power and less helium flow to achieve a certain process effect. Accordingly, the economy of the operation of a device according to the invention improves. At the same time, the device can be realized in the form of a much lighter, more easily scalable and thus less complex construction. The gas flow in the device according to the invention, in particular within the container, enables a laminar flow to be maintained, as a result of which, according to the experiments carried out, the plasma jet becomes longer and the treatment area of a plasma jet becomes larger.

With the device according to the invention it is also possible to supply a process gas in addition to the carrier gas. For example, a separate container in the manner of an inner tube can be provided for this purpose, which is arranged concentrically with the outer container. The annulus between the inner tube and the The container is flowed through by carrier gas, with process gas flowing through the inner tube. In the area of an outlet of the device for the plasma jet, a core area consisting of process gas and a jacket area are formed, which is formed by the plasma jet. The process gas is brought up to the substrate within the plasma jacket and through the plasma jacket. Since the carrier gas has a much higher concentration of metastably excited species than the process gas, a much higher degree of ionization can be achieved in the carrier gas with the same coupled power than in the process gas. Therefore, a higher electron concentration and consequently a higher electrical conductivity can be achieved in a jacket area consisting of carrier gas. The electromagnetic power can be transported along such a plasma jet over longer distances and over larger substrate areas. The process depth, i.e. the processing depth, and the process homogeneity are significantly improved.

The device according to the invention operates, for example, in a frequency range from approximately 1 kHz to a few tens of kHz, which is sufficient to work in the operating mode of the atmospheric pressure glow discharge and which enables the capacitive coupling of power through the dielectric barrier. In principle, depending on the geometric design and operating conditions, higher frequencies up to the MHz range can also be used. However, an expensive tuning unit can be dispensed with when operating in the low kHz range. The dielectric losses are also significantly lower compared to high frequency or microwaves. All of these technical advantages lead to a significant increase in the cost-effectiveness of the device in comparison with the devices of this type belonging to the prior art. The economic benefit of the device according to the invention is that it offers completely new technological possibilities for also treating in three-dimensional substrates , Three-dimensional substrates are those substrates which have a special surface topography, which has, for example, wave troughs and wave crests or some other structuring. Thanks to the high production of metastably excited atoms or molecules and their direct delivery to the substrate surface, it is possible to carry out the already known processes such as surface modification, cleaning, degreasing with higher process rates and better homogeneity. In addition, it is possible to carry out the deposition processes analogously to low-pressure PECVD processes, since it is possible according to the invention to expose the substrate surface or even its internal structure to the action of metastably excited species. This can be achieved by additionally supplying monomers in the form of gas, steam or liquid to the substrate surface or into the substrate structure.

A new circle of interesting applications that have so far remained largely unexplored is the influencing of biological material or organic tissue through the action of metastably excited species. It is also conceivable to influence the substrate properties in the nanometer range.

According to an advantageous embodiment of the invention, the container is a cylindrical, in particular circular cylindrical, tube educated. This enables a laminar flow of the carrier gas to be generated. In addition, such a container enables the concentric arrangement of an inner container within which a process gas can additionally be guided. Finally, the arrangement of the electrodes on the container can be carried out in a simple manner, advantageously in such a way that one electrode is arranged outside the container, or on its outer surface, and the other electrode is arranged in the interior of the container. A particularly simple radially and axially spaced arrangement of the electrodes can be achieved in this way.

Any axially elongated container which has a substantially constant cross section over its axial extent is regarded as a cylindrical tube in the sense of the present patent application. The cross section can be rectangular, in particular square, but also elliptical. The container is preferably a circular cylindrical tube. Any other cross sections are also conceivable, e.g. Polygon trains, or pipe cross sections, which have straight sections and curved sections.

According to a further advantageous embodiment of the invention, the tube consists of a dielectric material, in particular an oxide or nitride ceramic or glass. This enables a particularly simple embodiment of the device according to the invention in such a way that a wall area of the tube directly provides the dielectric barrier.

According to a further advantageous embodiment of the invention, a second (inner) container for a process gas is arranged within the container. This enables a concentric arrangement of the inner container and the (outer) container, so that the Plasma jet emerging from the (outer) container envelop an inner core area of process gas in a jacket-like manner and can thus lead to the substrate surface. According to a further advantageous embodiment of the invention, the ratio of the cross section of the area of the container through which carrier gas flows to the cross section of the inner container is equal to the ratio of the flow of carrier gas to the flow of process gas. This enables a particularly efficient operation of the device according to the invention.

According to a further advantageous embodiment of the invention, the flow direction of the process gas is essentially parallel to the flow direction of the carrier gas. This enables laminar flows to be achieved in a particularly simple manner.

According to a further advantageous embodiment of the invention, the inner container consists of a dielectric material, in particular of an oxide or nitride ceramic or of glass. This embodiment of the invention enables a particularly simple construction of the device and a simple arrangement of the radially inner electrode on the inner container.

According to a further advantageous embodiment of the invention, at least one electrode is essentially ring-shaped or sleeve-like. This enables a particularly simple design of the electrodes. Furthermore, this embodiment of the invention also enables an at least partial rotational symmetry of the device, which can ensure a particularly efficient interaction of the plasma with the carrier gas, since a large number of possible discharge channels can be formed. In a simple embodiment of the invention, both electrodes are essentially ring-shaped or sleeve-like. The two electrodes are axially spaced from one another and have different diameters, so that an inner and an outer electrode are formed, which means that the electrodes are radially spaced apart. With this arrangement, an infinite number of shortest connecting lines between the two electrodes is conceivable. This is because the two electrodes have active edges facing one another, which are of circular marginal edges of the two electrodes. In this case, the shortest connecting lines between the two electrodes are those which are perpendicular to the two active edges. The active edge of an electrode is the outermost boundary edge that is closest to the other electrode. If, for example, as shown in FIGS. 7 and 8 of this patent application, there are essentially plate-shaped electrodes 17 and 18 arranged parallel to one another, the active edges are the mutually parallel, immediately adjacent or opposite edge edges 25a, 25b.

In the case of two annular or sleeve-like electrodes, as is shown schematically, for example, in FIG. 1 of the present patent application, the circular, radially outer edge 25a of the inner electrode 17 facing the second electrode 18 and the radially inner, the inner electrode 17 act as active edges facing edge 25b of the outer electrode 18.

The active edges of the electrodes are the outermost edges of the electrodes which are immediately adjacent to one another. According to a further advantageous embodiment of the invention, at least one electrode has an active edge facing the other electrode which deviates from a circular shape. For example, projections can be provided on the active edges for this purpose, which shorten the shortest connecting line between the electrodes. This results in a predetermined number of precisely defined and geometrically defined shortest connecting lines. The discharge channels are primarily formed along these shortest connecting lines between the two electrodes. The interaction between the plasma and the carrier gas can be further optimized by calculating the geometry of the electrodes and by calculating the spatial arrangement and the length of the shortest connecting line or several shortest connecting lines between the two electrodes.

According to a further advantageous embodiment of the invention, the shortest connecting line between two active edges of the two electrodes is curved. The shortest connecting line between two active edges of the two electrodes is the geometric vector that connects the two electrodes to one another in the shortest possible way. A shortest connecting line in the sense of the present patent application also cuts through the dielectric barrier. A curved shortest connecting line in the case of a concentric arrangement of the inner tube and outer tube does not, however, cut through the dielectric inner tube, but rather, for example, nestles helically against the inner tube. This definition of a shortest connecting line takes into account the electromagnetic fields actually created. Likewise, a curved shortest connecting line between two active edges of the electrodes can also be formed by that a radially outer electrode is formed by segmentation in such a way that a shortest connecting line consists of different sections of different directions and thus overall forms a connecting line approximating a curved connecting line.

A curved shortest connecting line enables a further improved interaction between the plasma and the carrier gas. For example, the shortest connecting line between the two active edges can be designed to be helical and thus wind around the inner tube in a helical manner, at least in sections.

According to a further advantageous embodiment of the invention, at least one electrode is segmented. This means that at least one electrode consists of at least two electrically conductive electrode components, for example electrode surfaces, which are separated from one another. As a result, a voltage is only applied to a first electrode segment. A voltage is induced in the second electrode segment. The shortest connecting line between the two electrodes advantageously runs essentially overall between the first electrode segment and the other electrode. In fact, a first section of a shortest connecting line runs between the second electrode segment and an inner electrode and another section of the shortest connecting line runs between the second electrode segment and the first electrode segment. The shortest connecting line between the two electrodes therefore comprises a total of two sections of different directions or has a basic shape approximating the two sections. Segmentation of an electrode can be used to influence the discharge channel and, for example, to give it a previously determined and pre-calculated spatial shape. In this way, the interaction between plasma and carrier gas can be further optimized.

According to a further advantageous embodiment of the invention, the first electrode is arranged upstream and the second electrode downstream, based on the direction of flow of the carrier gas. In particular, the first electrode can be arranged on an outer lateral surface of the inner container and can face the carrier gas with its electrically conductive, in particular metallic outer lateral surface. This embodiment of the invention enables a particularly simple contacting of the first electrode for connection to a voltage generator. In addition, the carrier gas can flow past the metallic outer surface of the first electrode before it is supplied to the plasma. The electrode geometry can therefore be achieved with comparatively little design effort.

According to a further advantageous embodiment of the invention, the device is combined with at least one further device to form a row arrangement. This enables a device that can generate a large number of plasma jets for processing a substrate. A plurality of devices, for example five to ten devices, advantageously extend along a row. Several rows can also be composed of devices in a grid-like arrangement, a so-called “array”. It is particularly advantageous if several devices have a common carrier gas supply and / or a common one Have process gas supply. The design effort for such a device can be kept low in this way.

Further advantages of the invention result from the subclaims not cited and from the following description of the exemplary embodiments shown in the figures. In it show:

1 is a partially sectioned, schematic view of a first embodiment of the device according to the invention,

2 shows, in a representation according to FIG. 1, a second exemplary embodiment of the device according to the invention in the manner of a multi-jet plasma source,

3 shows a cylindrical projection of the two electrodes of a device according to FIG. 1 in a schematic illustration,

4 shows a further exemplary embodiment of an electrode geometry in a representation according to FIG. 3,

5 shows a third exemplary embodiment of an electrode geometry in a representation according to FIG. 3,

6 shows a fourth exemplary embodiment of an electrode geometry in a representation according to FIG. 3,

Fig. 7 shows a third embodiment of the device according to the invention in a schematic, partially sectioned side view similar to Fig. 1, and FIG. 8 shows the device according to FIG. 7 in a schematic, partially sectioned illustration approximately along section line VIII-VIII in FIG. 7. The principle according to the invention should first be described with reference to the third

Embodiment according to Figures 7 to 8 are explained. It should first be noted that the device according to the invention is designated 10 in its entirety. For the sake of clarity, identical or comparable parts or elements of the device have been given the same reference numerals, sometimes with the addition of small letters.

7 shows a device 10 according to the invention for processing a substrate 11 or in particular for processing a surface 12 of the substrate 11 in a very schematic manner. A plasma jet 13 can be extracted from the device 10 through an outlet 14 of the device 10 and can be brought up to the substrate 11. There he can carry out a processing of the surface 12, for example coating, structuring, modifying or the like.

FIG. 7 already shows that the substrate to be processed is arranged at a distance from the device 10. The electrodes 17, 18 described below are thus arranged on the same side of the substrate 11. In the device according to the invention, it is also irrelevant whether the substrate 11 or its surface 12 is made conductive or insulating. The substrate 11 brought up to the device 10 does not influence the electrode potentials. The device 10 comprises a cylindrical container 15, which in the embodiment consists of an insulating, that is dielectric, material is made. 8 shows that the container 15 has an essentially square cross section, which is formed by four side walls 16a, 16b, 16c, 16d. A carrier gas, in particular helium, flows through the container 15 essentially along the direction of flow of the arrow x. The flow direction x essentially corresponds to the direction of a longitudinal central axis of the container 15.

A first, essentially plate-shaped electrode 17 is arranged on the lower side wall 16a of the container 15. With its bare upper side, ie with its metallic outer surface 19, it faces the interior 24 of the container 15.

A second, essentially plate-shaped electrode 18 is arranged with respect to FIGS. 7 and 8 above the upper side wall 16c of the container 15. The second electrode 18 is provided with an insulating sheath 20.

For the sake of clarity, the first electrode 17 is referred to as the upstream electrode and the second electrode 18 as the downstream electrode, which takes into account the direction x of the flow of the carrier gas.

The upstream electrode 17 is spaced from the downstream electrode 18 by the distance L in the axial direction, that is to say in the direction of the flow direction x of the carrier gas. At the same time, the upstream electrode 17 is spaced from the downstream electrode 18 by an amount R in the radial direction, that is to say transversely to the flow direction x of the carrier gas. The two electrodes 17, 18 are therefore axially and radially spaced apart. The shortest connecting line between the two electrodes 17, 18 is designated 21. This is the line that connects an outer edge 25a of the first electrode 17 with an outer edge 25b of the second electrode 18 in the shortest possible way. In the exemplary embodiment in FIGS. 7 and 8, the electrodes 17, 18 are essentially plate-shaped. Accordingly, the two mutually facing edge edges 25a, 25b of the two electrodes 17, 18, which are referred to below as active edges, are each aligned along a straight line and parallel to one another.

If an alternating voltage of a suitable frequency and a suitable amplitude is applied between the two electrodes 17, 18, which is done via a voltage generator not shown in FIGS. 7 and 8, a main discharge channel 22 is formed in the region of the shortest connecting line 21, specifically in the Essentially along the shortest connecting line 21. The main channel 22 of the discharge is shown schematically in FIGS. 1, 7 and 8 in cross section in the manner of a narrow, elongated cloud. Such an image also results for an observer if a suitable image is taken of the device in operation.

The interaction of the main discharge channel with the carrier gas forms a plasma 23, a so-called primary discharge, in the manner of a plasma cloud, which opens into a plasma jet 13 in the direction of the substrate 11. With a suitable choice of the flow of the carrier gas, the substrate 11 can be processed by means of the plasma jet.

Because the main discharge channel 22 has a particular spatial position and length, essentially along the shortest connecting line 21, based on the direction x of the flow of the carrier gas occupies, a particularly long and intense plasma jet 13 can be formed. The predeterminable spatial arrangement of the main discharge channel 22 maximizes the coupling of power into the chemically and physically excited species in the carrier gas. Because the main discharge channel 22 is inclined at an acute angle α to the flow direction x of the carrier gas, the carrier gas can cooperate with the main discharge channel 22 in a large volume and is thus conducted particularly well in terms of space and time. Because of a longer and more intensive plasma jet 13, the substrate can be treated more efficiently.

A second exemplary embodiment of the device 10 according to the invention will now be described with reference to FIG. 1, in which the container 15 is designed as a circular cylindrical hollow tube 15. Within the outer tube 15, a second inner tube 26 is arranged concentrically to this. A process gas can flow through the inner tube 26 along the flow direction y, that is to say essentially parallel to the flow direction x of the carrier gas. The inner tube 26 is also made of dielectric material.

The first electrode 17 is essentially sleeve-like, that is to say in the form of an axially elongated ring, and is applied to the outer circumferential surface 33 of the inner tube 26. With its outer side 19, it faces the annular interior 24 of the container 15.

The second, downstream electrode 18 is attached to the outer lateral surface 34 of the outer tube 15. It is also essentially ring-shaped or sleeve-like and surrounds the outer tube 15 in the circumferential direction. On its outer surface 35 is the downstream electrode 18 surrounded by an insulating jacket 20. The ring end face directed toward the substrate 11, including the edge 36 of the second electrode 18, is also surrounded by a region 20a of the insulating sheath 20.

The first electrode 17 is connected to an AC voltage generator 27 via a connecting line 28a and the second electrode 18 via a connecting line 28b. When an AC voltage of a frequency is typically applied between 1 and 30 kHz and with an amplitude of 100 V to 10 kV, a main discharge channel 22 is formed essentially along a shortest connecting line 21 between an active edge 25a and the first electrode 17 and an active edge 25b second electrode 18. FIG. 1 schematically shows a realistic pictorial snapshot of the device in operation, from which it becomes clear that the main discharge channel 22 actually only slightly deviates from the shortest connecting line 21. One reason for this is the flow velocity of the carrier gas along the flow direction x.

Furthermore, with regard to FIG. 1, it must be noted that FIG. 1 represents an image recording at a specific point in time. If one looked at the state of the device according to FIG. 1 a few microseconds earlier or later, it would be found that main discharge channels 22 are formed in another area between the two electrodes 17 and 18.

In the exemplary embodiment in FIG. 1, the first electrode 17 and the second electrode 18 each have, for example, a circular active edge 25a, 25b. The shortest connecting lines 21 between each the two active edges 25a, 25b are therefore distributed rotationally symmetrically around the central longitudinal axis M of the device 10. Since the main discharge channels 22 each remain only a few microseconds, which is described in more detail below, different main discharge channels are formed in succession within a short time.

The interaction of the carrier gas with the main discharge channels 22 leads to the formation of a plasma cloud 23, which opens into a plasma jet 13, which is extracted from the device 10 from the plasma jet opening 14.

The process gas enters the plasma jet 13 through a process gas outlet 32, that is to say the left end of the inner tube 26 with respect to FIG. 1, and there forms a core zone 29 of process gas which extends to the substrate surface 12. The plasma jet 13 forms a type of jacket zone 30 which surrounds the core zone 29. The plasma jet 13 widens in the foot region 31 of the plasma jet 13, in which it hits the substrate surface 12, a core zone 29a and a jacket zone 30a also being recognizable in the region of the foot 31. This formation of core zone 29 and cladding zone 30 enables a particularly homogeneous processing of the substrate 11 with a particularly large processing depth. The outer jacket region 30 has a higher concentration of metastably excited species, as a result of which a higher electron concentration is achieved in this region and a transfer of the electromagnetic power to a greater distance along the plasma jet 13 and over a larger area of the substrate 11 in the foot region 31 of the plasma jet 13 is possible. With such a structure of the plasma jet 13, the carrier gas mixes with the Process gas only on the surface 12 of the substrate, as a result of which there is intensive energy transfer by quenching and Penning impacts from the particles from the jacket region 30a with the particles from the core region 29b. Not only the metastably excited helium atoms and molecules are located in the cladding region 30a. Part of the metastable excitation energy is transferred to the nitrogen molecules contained in the surrounding air. Very long-lived metastably excited nitrogen molecules are generated, which contribute to the transfer of chemical as well as electromagnetic energy to substrate 11.

The inner tube 26 and the outer tube 15 are formed from an electrical insulator. In the area of the second electrode 18, the outer tube 15 therefore directly forms the dielectric barrier.

In an embodiment not shown, a second dielectric barrier can of course also be arranged between the first electrode 17 and the second electrode 18. For example, a further insulating sheath can be attached to the outer circumferential surface 19 of the first electrode 17.

The first electrode 17 is spaced from the second electrode 18 by an axial distance L. The radial distance R between the first electrode 17 and the second electrode 18 is constant in the circumferential direction around the central longitudinal axis M.

The second electrode 18 is closer to the substrate 11 than the first electrode 17. This enables a particularly advantageous construction. For given operating conditions there is a distance L at which the length I of the plasma jet 13 is at a maximum. If the distance L is too short, the length of the discharge channels 22 between the electrode edges 25a and 25b offers too little interaction with the carrier gas, as a result of which the concentration of the excited species in the plasma jet 13 drops. If the distance is too long, the alternating electrical field that arises between the electrodes 17, 18 along the shortest connecting line 21 is reduced, as a result of which the intensity of the primary discharge decreases. This also leads to a reduction in the concentration of the excited species in the plasma jet 13. With increasing concentration of the metastably excited species in the plasma jet 13, the energy required to achieve a given degree of ionization of the plasma jet decreases. With constant power, this leads to a higher electron concentration and a larger volume, especially a greater length I, of the plasma jet.

The most efficient method of power supply is a resonance circuit. In such a case, the voltage signal has the form of a sine function. In principle, the discharge can also be supplied with voltage signals of other forms. The use of a resonance circuit as a voltage generator for the plasma jet 13 enables the highest efficiency of the power coupling and the dispensing with a tuning unit. During the experiments with this embodiment of the invention, it was found that the longest plasma jet 13 can be reached with a grounded inner electrode 17 and polarized outer electrode 18. In principle, however, the device also works with an earthed outer electrode 18 or with an earth point lying between the electrode potentials. The electrical displacement of the electrode potentials in relation to the earth point, for example by using a voltage divider, can be used check the length I of the jet 13, which can be used to specifically adjust the treatment depth of the plasma jet 13.

The outer electrode 18 is provided with an insulating seal 20, 20a, which prevents the spread of corona discharges starting from the edge 36 of the outer electrode 18, over the ring end face 37 of the outer tube 15. Such parasitic discharges lead to the generation of ozone and nitrogen oxides in the ambient air with concentrations that far exceed the permissible limit values. They also cause the formation of a "virtual" outer electrode, the area of which is increased by the area of the corona discharges. A large part of the electrical energy is also coupled into these parasitic corona discharges. For these reasons, this undesirable effect is to be avoided constructively very important.

It has also been experimentally proven that a much longer plasma jet 13 can be achieved under laminar flow conditions. In practice, it means that the length I of the jet 13 does not increase monotonously with increasing gas flow, but instead reaches a maximum for a specific gas flow and that the plasma jet length I is reduced as the gas flow increases further. Not only the entire gas flow has an impact on the transition from laminar to turbulent flow, but also the way in which the process gas is supplied to the carrier gas.

In the device according to the invention it is important that the exit speeds of the carrier gas and the process gas are similar in order to avoid turbulence. This is fulfilled if the ratio of the cross-sectional area of the coaxial region 24 (annular space) between the outer tube 15 and the inner tube 26 and the Cross-sectional area of the opening of the inner tube 26 is approximately equal to the ratio of the carrier gas flow to the process gas flow.

The distance d between the process gas outlet 32 and the carrier gas outlet 14 is also important for the optimal design of the structure of the plasma jet 13. FIG. 1 shows an embodiment in which the outlet 32 of the process gas is closer to the substrate 11 than that Outlet 14 of the plasma jet 13 or the carrier gas outlet 14. The distance d can be approximately up to twice the inner diameter 38 of the outer tube 15.

Alternatively, it is also conceivable that the outlet 14 of the container 15 for the carrier gas is closer to the substrate 11 than the outlet 32 of the process gas. The distance between the outlet 14 and the outlet 32 can in this case be up to ten times the inner diameter 38 of the outer tube 15. The choice of the distance d depends on the process gas and the process conditions. The embodiment of FIG. 2 shows a device 40 in a representation according to FIG. 1, in which several of the devices 10 shown in FIG. 1 are arranged in a row. The exemplary embodiment in FIG. 2 shows four devices 10 arranged in series, each of which generates a plasma jet 13a, 13b, 13c, 13d. The processing width B is thus approximately four times the processing width of the device 10 according to FIG. 1. For reasons of illustration, the main discharge channel 22 and the core zone 29 according to FIG. 1 are not shown in the exemplary embodiment in FIG. 2. The multi-jet plasma source, designated 40 in its entirety in FIG. 2, has an insulating housing 39, to which the outer tubes 15a, 15b, 15c, 15d are fastened in a parallel alignment to one another. The inner tubes 26a, 26b, 26c, 26d are fastened to a fastening plate 43. The fastening plate 43 also provides for an electrical connection of the four inner electrodes 17a, 17b, 17c, 17d to one another, which are connected together to a ground pole 45 and to the voltage supply 27 via the connecting line 28a. The outer electrodes 18a, 18b, 18c, 18d are connected to one another via line sections 44a, 44b, 44c and to the voltage source 27 via a line section 28b. All outer electrodes 18a, 18b, 18c, 18d are thus at the same potential. All internal electrodes 17a, 17b, 17c, 17d are also each at the same potential. A first gas distribution space 41 for the process gas supplies the four inner tubes 26a, 26b, 26c, 26d with process gas via a common process gas inlet opening 46. A second gas distribution space 42 supplies the four containers 15a, 15b, 15c, 15d with carrier gas via a common carrier gas inlet opening 47.

When observing a plasma jet 13 and its primary discharge 22 with the naked eye or with a camera with exposure times in the ms range, one gets the impression that the discharge type is spatially homogeneous and stable over time. This impression turns out to be wrong when viewing ICCD recordings in the microsecond range. The discharge consists of partial discharges, the discharge channels 22, which form radially inside the outer electrode 18 between the edge 25a of the inner electrode and the inner surface 48 (FIG. 1) of the outer tube 15. The dielectric inner surface 48 of the outer tube 15 has only a certain capacity for the electrical charge. Since this charge on the Outer tube surface 48 lingers longer than a period of voltage supply, the next discharge takes place in another area of the inner surface 48 of the outer tube 15. This effect can be used for the targeted control of the formation of the main channel 22 of the discharge.

In the device 10 according to the invention, the influence of the main discharge channel 22 is influenced by the basic geometry of the

Electrodes 17, 18 reached. Various designs of an optimized electrode design will now be explained by way of example with reference to FIGS. 3 to 6.

3 shows an example of the geometric shape of the outer electrode 18 and the inner electrode 17 in a cylindrical projection. For a better understanding, it should be noted that this cylindrical projection, which is also referred to as a cylindrical development or an azimuth shark projection, the two electrodes 17, 18 in a cut, flat lying state. The azimuth angle on the coordinate of the diagram thus indicates the circumferential angle, based on the longitudinal central axis M of the device 10 in FIG. 1, the axial course of the two electrodes 17, 18 being shown on the abscissa of the coordinate system in FIG. 3.

3 that the active edge 25a of the inner electrode 17 and the active edge 25b of the outer electrode 18 deviate from a circular shape. By contrast, projections 49a, 49b, 49c, 49d are provided in the two electrodes 17, 18, which lead to an active edge 25a, 25b of the electrodes 17, 18, which has precisely defined, shortest connecting lines 21a and 21b. 3 results in two shortest connecting lines of exactly the same length, namely the Connection lines 21a and 21b between the protrusions 49a and 49c and between the protrusions 49b and 49d, respectively.

3 furthermore shows that the projections 49a, 49b of the first electrode 17 to the projections 49c, 49d of the second

Electrode 18 are offset circumferentially. Accordingly, the shortest

Connecting line 21a, 21b, also in the illustration in FIG. 3, is not formed parallel to the flow direction x of the carrier gas, but extends obliquely to it at an acute angle. Furthermore, the shortest connecting line 21a, 21b should not be imagined to run along a straight line, but taking into account the geometrical arrangement of inner tube 26 and outer tube 15 such that the shortest connecting line 21a, 21b is a section of a helix. The shortest connecting line 21a, 21b is thus curved since, by definition, it cannot cut the inner tube 26.

The arrangement of the projections 49a, 49b, 49c, 49d leads to the formation of a main discharge channel 22 which runs obliquely to the gas flow direction x and which is substantially approximated to the shortest connecting line 21a, 21b.

In the case of circular parallel electrode edges 25a, 25b, which are not shown in FIG. 3, main discharge channels 22 form which, in a representation according to FIG. 3, occur parallel to the gas flow x and under certain circumstances only in a narrow region of the azimuthal position , As a result, most carrier gas can flow through the zone of the primary discharge 22 without interacting with the main discharge channels 22. By favoring the formation of more than one main discharge channel 22 and by its position deviating from the parallelism to the main axis direction x, the volume in which the interaction between the carrier gas and the main discharge channel 22 takes place is substantially increased. This creates the metastably excited species in a much larger amount and in a much larger volume. This leads to the formation of a longer and more intense plasma jet.

3 are formed accordingly

Main discharge channels 22, which are essentially the shortest

Connecting lines 21a, 21b are approximated. The main discharge channels 22 thus also run along a section of one

Wendel.

The number of projections 49a, 49b, 49c, 49d on the two electrodes 17, 18 is only to be understood as an example and depends on the type of application of the device 10.

FIG. 4 shows a further exemplary embodiment of an electrode arrangement in a representation according to FIG. 3. It is clear from FIG. 4 that the outer electrode 18 has two spiral arms 50a and 50b. The two electrode arms 50a, 50b are designed in the manner of elongated projections and extend helically around the inner tube 26 according to FIG. 1, not shown in FIG. 4. In this connection, it should be noted that the electrode arrangements according to FIGS. 3 to 6 can all be used in devices according to FIG. 1.

In the embodiment of FIG. 4, the shortest connecting line between the two electrodes 17, 18 is the distance between the free end 51 of a spiral arm 50a, 50b and Effective edge 25a of the electrode 17. Since the radial distance between the inner electrode 17 and the outer electrode 18 is constant, and since a main discharge channel 22 cannot develop through the dielectric barrier of the wall of the container 15, but only in that through which the carrier gas flows 4 leads to a main discharge channel 22b which is composed of two sections 22'b and 22 "b and which is bent. Likewise, the main discharge channel 22a is composed of a first channel section 22'a and a second channel section angled to it 22 "a together.

The total discharge channel 22a (or 22b) is essentially helical, that is curved, and extends around the inner tube 26 according to FIG. 1.

5 shows a further exemplary embodiment of an electrode arrangement according to the invention, in which the outer electrode 18 has five electrode segments 52a, 52b, 52c, 52d, 52e. The electrode segments 52a, 52b, 52c, 52d, 52e are not electrically connected to one another. The electrode segment 52a is essentially ring-shaped and is connected to the voltage source 27, not shown in FIG. 5. An electrode segment 52b and an electrode segment 52c are arranged in series, circumferentially offset from one another. A further electrode segment 52d and a further electrode segment 52e are likewise arranged offset in circumference.

By applying a voltage to the electrode segment 52a, voltages are induced in the electrode segments 52b and 52d. This also induces voltages in the electrode segments 52c and 52e.

The active edge 25a and the active edge 25b of the second electrode 18 are directly connected to one another via shortest connecting lines, not shown, which lead to the two active edges 25a and 25b in FIG

Stand essentially vertically. The arrangement of the electrode segments

52b, 52c, 52d, 52e, however, leads to the fact that the potential applied to the active edge 25a of the first electrode 17 "sees" a potential applied to the electrode segments 52c and 52d. Likewise, the potential applied to the electrode segments 52c and 52e "sees" that potentials applied to the adjacent electrode segments 52b and 52d.

Overall, main discharge channels 22a and 22b are again formed, which are composed of main discharge sections 22 "b and 22'b or 22" a and 22'a.

The duct sections 22'b and 22 "b or 22'a and 22" a are arranged at an angle to one another. The main discharge channels 22a and 22b resulting overall from the electrode geometry are again essentially helical.

In a further exemplary embodiment according to FIG. 6, the outer electrode 18 is generally substantially helical, that is to say helical. This leads to several main discharge channels 22a, 22b, 22c.

The shortest possible main discharge channel is designated with 22a, with 22b the main discharge channel moving azimuthally in the coaxial space of the primary discharge 23 and with the reference symbol 22c the longest possible main discharge channel. It should be pointed out that the exemplary embodiments in FIGS. 1 to 6 are shown and described with circular-cylindrical outer tubes 15 and inner tubes 26 and with annular or sleeve-shaped electrodes 17 and 18. In the exemplary embodiments, a plasma jet 13 is located at the outlet 14 of the outer tube 15 and formed at the outlet 32 of the inner tube 26. The process gas flowing through the inner tube 26 is required for certain types of processing of the substrate. However, the invention also includes devices in which a plasma jet 13 is generated without a process gas being additionally supplied.

The essentially rotationally symmetrical design of the tubes 15, 26 and the electrodes 17, 18 is advantageous, but not absolutely necessary. Protrusions 49a, 49b, 49c, 49d or spiral or helical arms 50a, 50d can equally be provided in devices such as those outlined in FIGS. 7 and 8.

The distance L between the two electrodes 17, 18 is advantageously adapted in such a way that the formation of axially elongated and intensive main discharge channels 22 is effected or promoted. It is particularly important if the discharge channels 22 have at least one directional component that is oriented transversely to the gas flow direction x.

In the exemplary embodiments in FIGS. 1 to 6, the inner electrode 17 is advantageously grounded. However, this is also not necessary. Alternatively, a segment of the outer electrode, in the case of a segmented outer electrode 18 in particular the segment 52a furthest away from the inner electrode 17, can also be grounded. Finally, it is also possible for neither of the two electrodes 17, 18 is grounded, but the ground potential lies between the two electrode potentials.

It should be emphasized that in all the exemplary embodiments of the device 10 according to the invention, both electrodes 10, 11, the container 15 and the containers 15, 26 are assigned. The substrate 11 is located in a process space into which the plasma jets 13 are extracted from the device 10. The process space is thus located outside the device 10 having the electrodes 17, 18.

Claims

Expectations

1. Device (10) for processing a substrate (11) by means of at least one plasma jet (13), comprising a container (15) through which a carrier gas flows along a flow direction (x), and comprising a first electrode (17) and a second electrode (18), characterized in that the two electrodes (17, 18) are separated from one another by at least one dielectric barrier (15), that between the electrodes (17, 18) for generating an atmospheric pressure glow discharge plasma AC voltage is applied, and that the first electrode (17) from the second electrode (18) with respect to the flow direction (x) of the carrier gas is spaced axially (L) and radially (R).

2. Device according to claim 1, characterized in that the

Container (15) is formed by a cylindrical, in particular circular cylindrical, tube.

3. Device according to claim 2, characterized in that the tube (15) consists of a dielectric material, in particular of an oxide or nitride ceramic or glass.

4. The device according to claim 2 or 3, characterized in that the tube (15) has an inner diameter (38) between 1 and 10 mm.

5. Device according to one of the preceding claims, characterized in that the carrier gas is helium.

6. Device according to one of the preceding claims, characterized in that a second (inner) container (26) for a process gas is arranged within the container (15).

7. The device according to claim 6, characterized in that the ratio of the cross section of the area of the container (15) through which carrier gas flows to the cross section of the inner container (26) is substantially equal to the ratio of the flow of carrier gas to the flow of process gas.

8. The device according to claim 6 or 7, characterized in that the process gas flow is between 0.1 and 5% of the carrier gas flow.

9. Device according to one of claims 6 to 8, characterized in that the process gas is a molecular gas or a gas mixture of molecular gases.

10. Device according to one of claims 6 to 9, characterized in that the flow direction (x) of the process gas is substantially parallel to the flow direction (y) of the carrier gas.

11. Device according to one of claims 6 to 10, characterized in that the inner container (26) is formed by a cylindrical, in particular circular cylindrical, tube (inner tube).

12. The apparatus according to claim 11, characterized in that the inner tube has an inner diameter between 0.1 and 5 mm.

13. Device according to one of claims 6 to 12, characterized in that the inner container (26) is arranged concentrically to the (outer) container (15).

14. Device according to one of claims 6 to 13, characterized in that the inner container (26) consists of a dielectric material, in particular an oxide or nitride ceramic or glass.

15. Device according to one of the preceding claims, characterized in that at least one electrode (17, 18) is substantially annular or sleeve-shaped.

16. The apparatus according to claim 15, characterized in that both electrodes (17, 18) are substantially annular or sleeve-like.

17. Device according to one of the preceding claims, characterized in that at least one electrode (17) has an active edge (25a, 25b) facing the other electrode (18) which deviates from a circular shape.

18. The device according to claim 17, characterized in that the active edge (25a, 25b) of an electrode (17, 18) comprises at least one projection (49a, 49b, 49c, 49d) directed towards the other electrode (18, 17).

19. The device according to claim 17 or 18, characterized in that the active edge (25a, 25b) of an electrode (17, 18) comprises a plurality of projections (49a, 49b, 49c, 49d) directed towards the other electrode (18, 17) ,

20. Device according to one of claims 17 to 19, characterized in that the active edges (25a, 25b) of both electrodes (17, 18) comprise projections (49a, 49b, 49c, 49d) directed towards one another.

21. Device according to one of claims 18 to 20, characterized in that a projection from a free end (51) of a helical electrode arm (50a, 50b) is provided.

22. Device according to one of claims 17 to 21, characterized in that the shortest connecting line (21, 21a, 21b) between the two active edges (25a, 25b) of the two electrodes (17, 18) has a directional component transverse to the flow direction (x) of the carrier gas.

23. The device according to one of claims 17 to 22, characterized in that the shortest connecting line (21, 21a, 21b) between two active edges (25a, 26b) is curved.

24. Device according to one of claims 17 to 23, characterized in that the shortest connecting line (21, 21a, 21b) between two active edges (25a, 25b) is substantially helical or comprises a helical section.

25. Device according to one of the preceding claims, characterized in that at least one electrode (18) is segmented.

26. The device according to claim 25, insofar as it relates to one of claims 17 to 24, characterized in that at least one electrode segment (52b, 52c, 52d, 52e) together with the two electrodes (52a, 17) essentially one overall provides the shortest curved connecting line (21a, 21b) between the two active edges (25a, 25b).

27. Device according to one of the preceding claims, characterized in that the first electrode (17) upstream and the second electrode (18) downstream, based on the flow direction (x) of the carrier gas, are arranged.

28. Device according to one of the preceding claims, characterized in that the first electrode (17) within the interior

(24) of the (outer) container (15) is arranged.

29. Device according to one of the preceding claims, characterized in that the first electrode (17) is arranged on an outer circumferential surface (33) of the inner container (26).

30. Device according to one of the preceding claims, characterized in that the first electrode (17) with its electrically conductive, in particular metallic, outer surface (19) faces the carrier gas.

31. Device according to one of the preceding claims, characterized in that the second electrode (18) is arranged on an outer lateral surface (34) of the (outer) container (15).

32. Device according to one of the preceding claims, characterized in that the electrodes (17, 18) are applied galvanically or by vapor deposition or by atomization.

33. Device according to one of the preceding claims, characterized in that the second electrode (18) on its outer lateral surface (35) is surrounded by an insulating sheath (20, 20a).

34. Device according to claim 33, characterized in that the insulating sheath (20, 20a) is formed by a layer of oxide ceramic or of glass or of a polymer with low dielectric losses.

35. Apparatus according to claim 33 or 34, characterized in that the insulating sheath (20, 20a) has a thickness between a few 10 microns and a few mm.

36. Device according to one of the preceding claims, characterized in that a wall of the (outer) container (15) provides the dielectric barrier between the two electrodes (17, 18).

37. Device according to one of the preceding claims, characterized in that a controller is provided, by means of which the potential difference between the electrodes (17, 18) can be changed in order to change the jet length (I).

38. Device according to one of the preceding claims, characterized in that the applied AC voltage has a frequency between 1 and 30 kHz.

39. Device according to one of the preceding claims, characterized in that the applied AC voltage has a voltage in a range between 100 V and 10 KV.

40. Device according to one of the preceding claims, characterized in that the operating pressure of the device is between 50 mbar and 10 bar.

41. Device according to one of the preceding claims, characterized in that it is combined with at least one further device (10) to form a multi-jet plasma source (40), in particular in the manner of a row arrangement.

42. Device according to one of the preceding claims, characterized in that it is combined with at least two further devices (10) to form a grid-like arrangement, in particular consisting of several row arrangements (40).

43. Device according to claim 41 or 42, characterized in that several devices (10) have a common carrier gas supply (47) and / or a common process gas supply (46).