WO2008074312A2

WO2008074312A2 - Arrangement and method for the removal of contaminants or modification of surfaces of substrates by means of electric arc discharge

Info

Publication number: WO2008074312A2
Application number: PCT/DE2007/002286
Authority: WO
Inventors: Otmar Zimmer; Frank Kaulfuss
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2006-12-19
Filing date: 2007-12-14
Publication date: 2008-06-26
Also published as: TW200902733A; WO2008074312A3; DE102006062375A1; DE102006062375B4

Abstract

The invention relates to an arrangement and a method for the removal of contaminants or modification of surfaces of substrates by means of electric arc discharge. It is an object of the invention to provide possibilities by which, in a simple and cost-effective form, contaminants can be removed from substrate areas or such surfaces can be modified without a non-uniform removal of contaminants or surface modification occurring over the substrate surface. According to the invention, an internally hollow housing element (5) is in this case fixed in an electrically insulating manner on the anode (2), which is arranged at a distance from a substrate (1), connected as cathode. The housing element forms a processing space for the electric arc discharge. The surface of the substrate and anode with housing element can be moved relative to one another and the surface of the substrate is larger than the active area of the anode.

Description

Arrangement and method for removing impurities or modifying surfaces of substrates by means of electrical arc discharge

The invention relates to an arrangement and a method for the removal of impurities or modification of surfaces of substrates by means of e-lektrischer arc discharge. It can be used before the actual performance of coating processes in vacuum, for descaling, degreasing, the removal of impurities on surfaces of substrates, but also in a surface modification for example, a roughening.

It is known to treat surfaces of a wide variety of electrically conductive substrates by means of electrical arc discharges. In this case, the respective substrate is usually connected as a cathode and the arc discharge is initiated by means of an anode held at a distance from the surface of the substrate. In the known solutions, it is not or only with great difficulty, the respective Defined area of influence of the electric arc discharge on the substrate surface to be observed or even limited. This is due to the fact that the focal points or bases of the arc discharge move chaotically over the respective substrate surface and thereby also local jumps are performed, so that no uniform, homogeneous influence over the entire desired surface of the substrate can be achieved. Consequently, certain surface areas are more influenced by the electric arc discharge and a significantly higher material removal is achieved than at other surface areas and it may even happen that surface areas of a substrate surface are completely unaffected by the electric arc discharge, which of course is undesirable.

To counteract this problem, it was attempted to locally influence the electrical arc discharges locally by the influence of magnetic fields. For this purpose, however, a very high energy demand is required, which of course adversely affects the overall efficiency. In this possibility of influencing there is also the problem that coupled magnetic fields in substrates which are formed from or with ferromagnetic materials, are strongly distorted therein and so a targeted local influence on the electric arc discharges is no longer possible.

Another alternative to counteract this problem is to increase the pressure. However, the gas is strongly excited or ionized in the vicinity of the electrical arc discharges. However, this is also undesirable in the most common cases. It is therefore an object of the invention to provide ways in which contaminants can be removed from substrate surfaces in a simple and cost-effective manner or such surfaces can be modified without there being an uneven removal of impurities or surface modification via the substrate surface.

According to the invention, this object is achieved by an arrangement having the features of claim 1. It can be worked with a method according to claim 25. Advantageous embodiments and further developments can be achieved with features described in the subordinate claims.

An arrangement according to the invention is designed such that electrical arc discharges, as in the prior art, are initiated between the respective surface of the substrate connected as a cathode and an anode arranged at a distance from the substrate. In addition, a hollow housing element is present at the anode inside. The housing member may be formed of a dielectric material and thereby be directly connected to the anode. But it is also possible to provide a housing element to an anode, which is electrically isolated from this and connected to the anode. The inside hollow case member forms a processing space for the arc discharge between the surface of the substrate and the anode, so that the electric arc discharge and the flow of electrons in its surface can be restricted by the case member. It is obvious that the housing element has a corresponding opening at least in the direction of the substrate surface. Thus, a coating on the outer circumferential surface form a housing element. The coating can be formed from at least one layer (electrically non-conducting) or, for example, an electrically non-conductive and an electrically conductive outer layer. But it can also be used as a housing element, a sleeve-shaped element that surrounds the anode. In these cases, a cavity which is open in the direction of the substrate can be formed on the anode, which is enclosed radially on the outside by such a housing element.

A housing member may be made of a non-ferromagnetic material (metal), e.g. Aluminum, optionally iron or an alloy, but also be formed of a preferably electrically non-conductive ceramic.

For a meaningful removal of impurities or a modification of a substrate surface, the surface of the substrate and the anode are movable together with the housing member relative to each other to thereby affect a significantly larger surface area than the housing element actually allows. In addition, the surface of the substrate is larger than the effective anode area and this also applies in connection with the opening of the housing element in the direction of the substrate surface.

It is possible to move the anode with housing element alone, the substrate alone or substrate and anode with housing element simultaneously.

In the arrangement according to the invention, between the direction pointing towards the surface of the substrate should be between the the gap between the end face of the housing element and the substrate surface can be maintained, so that touching contact can be avoided. Due to the dielectric material or the electrically insulated arrangement of the housing element at the anode, this gap can be kept relatively small and only have a few mm gap.

A housing element can have different geometric configurations and can also be adapted to the respective substrate. Thus, it is possible to use a cylindrical housing element with an anode in the inventive arrangement. However, square or rectangular cross-sectional shapes are also suitable. In any case, the free cross-section within a housing element should be limited so that the disadvantages of the prior art can be avoided by the uncontrolled movement of the electrical arc discharge.

The arrangement according to the invention can be used in vacuum chambers, but also for applications in continuous operation.

In particular, in the latter case, it is advantageous to arrange at least one anode perpendicular to a feed direction of the respective substrate, which extends at least approximately over the entire width of the substrate surface, in order to be able to free as much as possible of the entire substrate surface impurities or to modify the surface. For larger substrate widths, however, it is also possible to use a plurality of anodes in a series arrangement, wherein a separate housing element, but also a common housing element for all anodes can be present for each individual anode. Several A- However, nodes can also be arranged in a slightly staggered arrangement and thereby perpendicular to the feed direction overlapping.

In particular, in one, as explained above, a housing element may then be formed with two spaced apart and perpendicular to the feed direction, plate-shaped elements and thereby the processing space is formed in the gap between these two plate-shaped elements.

It is also possible to form a housing element with at least two segments. These may be bowl-shaped and have different geometric shapes. Thus, in addition to plate-shaped and cylindrical segments may be present. They can also be detachably connected to one another, which has a beneficial effect on any cleaning required.

A housing element, in particular if it is not formed from a dielectric material, does not necessarily have to have closed walls, but openings can certainly be formed thereon or a housing element can be designed as a Faraday cage. In addition to the openings mentioned slots may also be present or formed on the housing element. Slots may also be formed between segments that form a housing member.

Since, as a result of the surface treatment, contamination at the anode can often at least not be completely avoided, it is advantageous to provide a mechanical cleaning device with which Help the active surface of an anode can be freed from such impurities. In this case, a mechanical cleaning device can remove such impurities from the anode surface by purely mechanical contact and relative movement.

Since heating during process control can not be avoided, the one or more anode (s) should be cooled. This can be achieved advantageously by a suitable water cooling.

A preferred material for anodes is graphite. Graphite has suitable electrical properties and is sufficiently thermally stable under the prevailing conditions.

However, it is particularly advantageous to use an anode which is formed with a gradient material. In this case, a gradient material can be designed so that its thermal conductivity is increased at the side of the anode (s) facing away from the substrate. The thermal conductivity therefore increases starting from the active anode surface up to the side facing away from it, if necessary up to a cooling device, a continuous increase being preferred.

Such a gradient material may be graphite, in which metal is contained, wherein the metal content should increase in the direction of the side facing away from the substrate. The metal contained in the graphite also provides increased physical density which results in improved tightness for a coolant that may be passed through an area of the anode.

The effective anode surface should be completely off Graphite may be formed in order to achieve a more uniform distribution of the electric arc discharge over the effective area of the anode and to avoid a preferred point-like burn-up at the anode.

The arrangement according to the invention can also be developed advantageously by having at least one device for monitoring the state reached on the respectively already treated surface of the substrate. For this purpose, a housing element, which is at least partially optically transparent, be used in an optical monitoring. In this case, the housing element can be formed entirely from an optically transparent material, but also be provided with optically transparent windows. The optical monitoring can take place with the aid of a video camera, advantageously in conjunction with electronic image processing, by means of FTIR spectroscopy or by means of reflectometry.

The monitoring can also be done by means of evaluation of the electrical arc discharge parameters. Thus it is possible to determine the integral of the electric current which has flowed over predefinable time intervals. The integrals can be compared with, for example, empirically determined threshold values and from this it is possible to infer the achieved state of the respective surface treatment of the substrate.

However, monitoring can also be carried out by determining the electrical conductivity at the substrate surface. In this case, an electrical contact element can be guided over the already treated substrate surface, which can be achieved, for example, by means of a sliding contact or an electrically conductive contact. pressure roller or a similar element is possible.

When removing impurities or modifying substrate surfaces, the electric arc discharge can be operated with an electric voltage in the range of 10 V to 100 V and with electric current in the range of 10 A to 50 kA, preferably up to 10 kA. Particularly with higher electrical currents, it is advantageous to operate the arc discharge in a pulsed manner.

When carrying out the method, it is advantageous to maintain a pressure of less than 1000 Pa, preferably less than 100 Pa, which should apply at least to the processing area within the housing element. In the absence of a housing element, even at significantly higher pressure, namely at pressures above 1000 Pa, an areal limitation of the movement of the electric arc discharge on the respective substrate surface can be achieved.

When carrying out the method according to the invention, an inert gas can also be introduced at least into the processing space within the housing element, in order to avoid undesired chemical reactions, which in turn could lead to undesired impurities or deposits. It is particularly advantageous to supply a gas mixture which, in addition to nitrogen, additionally contains hydrogen. Of the

Proportion of hydrogen contained should be kept at a maximum of 5%, preferably at 2%.

Below, the invention will be explained in more detail by way of example. Showing:

Figure 1 in schematic form an example of an inventive arrangement;

Figure 2 shows an example of an arrangement with a

Cleaning device waiving the representation of a housing element and

Figure 3 in schematic form an uncontrolled electrical arc discharge according to the prior art.

In the example of an arrangement according to the invention shown in FIG. 1, a relatively large-area, here plate-shaped, substrate 1, which is formed from steel, is present.

At a distance from the surface of the substrate 1 is a cylindrical anode 2, which is formed with graphite and, as already mentioned in the general part of the description, may also contain metal arranged. At the anode 2, a housing member 5 is electrically isolated from the anode 2 in the form of a hollow cylinder, so that the anode 2 and housing member 5 can be moved together with each other over the entire surface of the substrate.

6 shows possible electron paths in an electrical arc discharge in FIG. 1, the electron flow of focal spots 7 being directed at the substrate surface in the direction of the active anode surface.

The housing element 5 is formed in this example of a steel, wherein the wall thickness of the housing Elements 5 only the thermal conditions prevailing in the implementation of the method should take into account.

FIG. 2 is intended to illustrate a possibility for removing impurities at the anode surface. In this example, the anode 2 is provided as a cylinder, optionally provided with an internal water cooling, which can rotate about an axis, as indicated by the arrow.

Above the anode 2, which is static except for the rotational movement, the substrate 1 can be moved translationally with as constant a distance to the anode 2. The length of the anode 2 in the direction of its axis of rotation should at least approximately correspond to the width of the substrate, perpendicular to the translational feed movement. With broader substrates 1, as already mentioned in the general part of the description, it is also possible to use a plurality of anodes 2 in a row arrangement.

In this example, a plate-shaped element, as a mechanical cleaning device 3 is present, one end face is in touching contact with the anode surface and by the rotational movement of the anode 2 impurities on the surface can be mechanically removed. Instead of a plate-shaped element but can also see a mechanical cleaning device 3, similar to a

Brush is designed to be used. However, a cleaning device can not only be arranged below the anode 2, but also laterally next to the anode 2 in order to avoid that the contaminants can reach the actual substrate surface to be treated. In the example, as in 2, a container 8 is also arranged below the anode 2 and the cleaning device 3, with which the mechanically removed impurities can be collected.

Of course, an arrangement as shown in FIG. 2 can also have a housing element 5, which is not shown here for reasons of clarity. A housing element 5 may in this case be formed with two plates aligned parallel to the axis of rotation of the anode 2, which plates are arranged between the anode 2 and the substrate surface and a processing region for electrical arc discharges is formed in the gap between these plate-shaped elements.

FIG. 3 is intended to illustrate how, in contrast to the technical solution according to the invention, the electrical arc discharges can take place uncontrolled over the entire surface of the substrate 1. In this case, an anode 2 without a housing element 5 is arranged at a distance from the respective surface of a substrate 1, the substrate 1 is connected as a cathode and the electrical arc discharges run uncontrolled over the entire surface of the respective substrate 1. In this case, the electron trajectories 6, starting from the focal spots 7, are shown by the substrate surface in FIG. It becomes clear that the course is completely uncontrolled and chaotic. Thus, the surface of the substrate 1 is not uniformly processed in the actually desired shape and in particular a material removal takes place on a variety of surface areas in different forms, which of course is not desirable.

Claims

claims

1. Arrangement for the removal of impurities or modification of surfaces of substrates by means of electrical arc discharge, in which

Arc discharges are initiated between the respective surface of the substrate connected as a cathode and an anode arranged at a distance from the substrate, characterized in that an inside hollow housing element (5) is fixed to the anode (2) electrically insulated therefrom with the housing element (2). 5) a processing chamber for the arc discharge is formed between the surface of the substrate (1) and the anode (2); the surface of the substrate (1) and anode (2) with the housing element (5) are movable relative to each other, and wherein the surface of the substrate (1) is greater than the effective anode area.

2. Arrangement according to claim 1, characterized in that between the in the direction of the surface of the substrate (1) facing end face of the housing element (5) and the substrate surface

Gap is maintained.

3. Arrangement according to claim 1 or 2, characterized in that the housing element (5) is cylindrical, formed with a square or rectangular cross-section.

4. Arrangement according to one of the preceding claims, characterized in that the housing element (5) is formed of a non-ferromagnetic material.

5. Arrangement according to one of the preceding claims, characterized in that the housing element (5) is formed of a dielectric material.

6. Arrangement according to one of the preceding claims, characterized in that the housing element (5) is formed of a ceramic material

7. Arrangement according to one of the preceding claims, characterized in that at least one or more anode (s) (2) extend in an array perpendicular to a feed direction at least approximately over the entire width of the substrate surface / rich.

8. Arrangement according to claim 7, characterized in that the housing element (5) is formed with two at a distance from each other and aligned perpendicular to the feed direction plate-shaped ele- ments.

9. Arrangement according to one of the preceding claims, characterized in that a housing element (5) is formed with at least two elements.

10. Arrangement according to one of the preceding claims, characterized in that openings are formed on the housing element (5).

11. Arrangement according to one of the preceding claims, characterized in that on a housing element (5) slots are present.

12. Arrangement according to one of the preceding claims, characterized in that at the anode (2) a mechanical cleaning device (3) is present.

13. Arrangement according to claim 12, characterized in that the anode (s) (2), is designed as a cylinder rotating about an axis / are.

14. Arrangement according to claim 12 or 13, characterized in that the cleaning device (3) a the surface of the anode (s) (2) with an end face contacting and parallel to the rotation axis aligned plate-shaped or as

Brush is a trained element.

15. Arrangement according to one of claims 12 to 14, characterized in that cleaning device (5) and anode (s) (2) are arranged laterally next to or vertically below the substrate (1).

16. Arrangement according to one of the preceding claims, characterized in that the anode (s) (2) is cooled / are.

17. Arrangement according to one of the preceding claims, characterized in that the anode (s) (2) is / are formed with graphite.

18. Arrangement according to one of the preceding claims, characterized in that the anode (s) (2) is / are formed with a gradient material and the heat conductivity at the side facing away from the substrate of the anode (s) (2) is increased.

19. Arrangement according to claim 17 or 18, characterized in that a metal is contained in the graphite.

20. The arrangement according to claim 17 or 19, characterized in that the metal content, starting from the substrate (1) side facing increases.

21. Arrangement according to one of claims 17 to 20, characterized in that the effective anode surface is formed entirely of graphite.

22. Arrangement according to one of the preceding claims, characterized in that at least within the processing space, a pressure of less than 1000 Pa is maintained.

23. Arrangement according to one of the preceding claims, characterized in that a device for monitoring the achieved state of the surface of the substrate (1) is present.

24. Arrangement according to claim 23, characterized in that the housing element (5) is at least partially optically transparent.

25. A method for the removal of impurities or modification of surfaces of substrates with an arrangement according to one of claims 1 to 24, characterized in that between a connected as a cathode substrate (1) and at least one anode (2) electric arc discharges ignited and with impingement points of the arc discharges, impurities are removed or the surface is modified; while the anode (s) (2) and the substrate (1) are moved relative to each other and the arc discharge by means of a housing element

(5) between substrate surface and anode (s) (2) within a processing space and on a limited surface area of the substrate (1) is held.

26. The method according to claim 25, characterized in that the electrical arc discharge with an electrical voltage in the range 10 V to

100 V and operated with electric current in the range of 10 to 50 kA.

27. The method according to claim 25 or 26, characterized in that the arc discharge is operated pulsed.

28. The method according to any one of claims 25 to 27, characterized in that a pressure <1000 Pa is maintained.

29. The method according to any one of claims 25 to 28, characterized in that at least in the

Processing space an inert gas is introduced.

30. The method according to any one of claims 25 to 29, characterized in that N is introduced at least in the processing space with a proportion of hydrogen of not more than 5%.

31. The method according to any one of claims 25 to 30, characterized in that the reached state of the substrate surface is monitored by means of the electrical arc discharge parameters.

32. The method according to claim 31, characterized in that the integral of the electrical current is determined and thus the state is monitored.

33. The method according to any one of claims 25 to 30, characterized in that the state of the O berfläche is optically monitored.

34. The method according to claim 33, characterized in that the state is monitored with a camera, by FTIR spectroscopy or by reflectometry.

35. The method according to any one of claims 25 to 31, characterized in that the state is monitored by determining the electrical conductivity of the substrate surface by means of an electrical contact element guided over the surface.