Target arrangement

The invention relates to a target arrangement comprising a tubular-shaped carrier element and a hollow-cylindrical target having at least one target material, said target comprising at least one one-piece tube segment which at least partially surrounds the carrier element. Said carrier element and the tube segment are partially interconnected in a material fit by at least two plastically deformable compensating means. The invention also relates to a method for producing said type of target arrangement and a tubular segment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/EP2007/001295, filed Feb. 14, 2007, and which claims the benefit of German Patent Application No. 10 2006 009 749.1, filed Mar. 2, 2006, the disclosures of both applications being incorporated herein by reference.

The invention relates to a target arrangement comprising a tubular carrier member and a hollow cylindrical target comprising at least one target material and including at least one tube segment made in one piece and surrounding the carrier member at least section-wise.

Target arrangements of this type, which are also called atomization targets or sputter targets, are generally known. They are used as a material source, for example in the thin coating of large-area substrates by means of cathode atomization or sputtering. The thin coating by means of such target arrangements is used, for example, for the manufacture of heat protection films or sun protection films on flat glass or plastic foils.

The fastening of the target to the carrier member is problematic with target arrangements of the initially named kind. This in particular applies to those target arrangements in which the target is not applied directly to the carrier member by a casting process or by a thermal injection molding process, for example because the target material would sublimate on casting or thermal injection.

Target arrangements are thus known in which the target is fastened to the carrier member in a force-transmitting manner with the help of elastic clamping elements. However, only a moderate thermal dissipation between the target and the carrier member is achieved by means of such a force-transmitting connection.

An improved thermal dissipation could be achieved by a full-area connection with material continuity between the target and the carrier member. Full-area, connections with material continuity of this type are used, for example, in planar targets in which a planar target segment is fastened to a support plate by means of a throughgoing solder layer. A semi-cylindrical target segment can accordingly be attached to a tubular carrier member in this manner.

Full-area, solder connections with material continuity are, however, not suitable for target arrangements in which the target is made of at least one tube segment. Since the carrier members of tubular target arrangements, for example, comprise a metal material and the target tube segments comprise a ceramic material, the carrier members and the tube segments have thermal coefficients of expansion which differ significantly from one another. There is not only the risk of a loosening of the connection between the carrier member and the tube segment due to the resulting difference in the thermal expansion of the carrier member and the tube segment and due to the brittleness of the ceramic material, but also the risk of damage to the tube segments.

To compensate the different coefficients of expansion between the metallic material and the ceramic material, an adhesive bonding of the carrier member and the tube segment by means of a plastically deformable adhesive had also been considered. Apart from the fact that an adhesive of this type does not have sufficiently high heat conduction properties, a reliable adhesive bonding of two joint partners moreover requires a certain pressure on the joint partners. An adhesive bonding of the carrier member and the target segment may therefore be considered for target arrangements having planar or semi-cylindrical target segments. However, due to the stiffness of both the tube segment and the carrier member and owing to the coaxial arrangement of the carrier member and the tube segment, an adhesive introduced between the carrier member and the tube segment cannot be acted on viewed in the radial direction. An adhesive bonding of the carrier member and the target segment can therefore hardly be realized in practice with target arrangements having tubular target segments.

It is the underlying object of the invention to provide a target arrangement of the initially named kind in which the carrier member and the target are connected to one another in a simple and reliable manner and simultaneously an improved heat transfer is ensured between the target and the carrier member.

The object is satisfied in accordance with the invention by a target arrangement having the features of claim1and in particular in that the carrier member and each tubular segment are partially connected to one another with material continuity by at least two plastically deformable compensation means.

Since the carrier member and the tube segment or the tube segments of the target are not in direct contact with one another in accordance with the invention, but are connected to one another by plastically deformable compensation means, the joint partners, i.e. the carrier member and the target, can expand to different degrees in the event of heating, for example during a sputtering process, in accordance with their different thermal coefficients of expansion without strains being caused in the target material which could result in damage to the target, e.g. in cracks in the target material. Different thermal expansions of the carrier member and the target are so-to-say compensated or balanced by the plastically deformable compensation means.

At the same time, a heat transfer between the target and the carrier member which is improved in comparison with force-transmitting joint variants is achieved by the connection with material continuity of the compensation means both to the target and to the carrier member. The heat introduced into the target during a sputtering process can thus be dissipated to the carrier member up to ten times better via the connection with material continuity than by a force-transmitting connection.

This permits a use of the target arrangement in so-called heavy-duty sputtering processes, i.e. that is a use of the target arrangement in sputtering with increased power densities and in particular increased voltages. Furthermore, the connection with material continuity also permits an increased target utilization of up to 80% since there is no risk of parts of the target being able to enter the sputtering plant on too low a residual density due to a failure caused thereby. Both ultimately result in an improved economy of the respective sputtering process.

The expression “partially connected to one another” is to be understood here such that the carrier member and the tube segment are not connected to one another over the full-area, but rather only regionally. A gap located between the tube segment and the carrier member is therefore not completely filled by the compensation means. It is rather the case that the compensation means establish a partial connection between the carrier member and the target, i.e. they form locally limited bridges separate from one another between the joint partners. The deformability of the compensation means is thereby substantially increased and the different thermal expansion of the target and the carrier member can be particularly effectively compensated.

Advantageous embodiments of the invention can be seen from the dependent claims, from the description and from the drawing.

In accordance with a preferred embodiment, the compensation means are free of flux. The target arrangement is thereby particularly well-suited for use in a vacuum plant in which there is generally a risk of an evaporation of volatile substances such as fluxes.

It is particularly advantageous when the compensation means include a solder, and in particular a soft solder. Solder not only has a particularly high thermal conductivity, but is also very easily plastically deformable. Furthermore, a Sn solder, for example, has a thermal coefficient of expansion of approximately 24·10−6K−1, whereas ZnO has a thermal coefficient of expansion of approximately 5.3·10−6K−1and stainless steel has a thermal coefficient of expansion of approximately 16·10−6K−1. Compensation means comprising Sn solder can consequently particularly effectively compensate the different thermal expansions of a ZnO target and a stainless steel carrier member. Furthermore, solder can be processed particularly easily, whereby the manufacture of the target arrangement is simplified overall.

Furthermore, solder can be liquefied again under a corresponding supply of heat, whereby it is possible to separate the connection between the joint partners and to release the target from the carrier member. A damaged tube segment can thus be replaced by an undamaged tube segment in a simple manner. The separation of the target and the carrier member moreover permits a reuse of the carrier member after the target material has been used up in a sputtering process or in a plurality of sputtering processes.

In accordance with a preferred embodiment, regions of a gap provided between the target and the carrier member and spaced apart from one another are filled up with solder. The compensation means are, in this case, therefore formed by locally limited solder bridges which are separate from one another and which partially connect the target and the carrier member to one another. The solder bridges have a particularly good deformability, whereby thermally induced strains between the target and the carrier member can be compensated even better.

It is particularly advantageous for the solder to be provided between the target and projections of the carrier member. Regions are pre-set by the projections in which the solder connects the joint partners to one another.

The projections are preferably spaced apart from one another, viewed in the axial or radial direction, and are then in particular arranged distributed over substantially the whole length of the target. On the one hand, different thermal expansions of the joint partners in the axial direction can thereby be compensated particularly easily. On the other hand, a thermal coupling of the target to the carrier member can be ensured over the total length of the target.

The projections advantageously include webs substantially extending in the peripheral direction of the carrier member. Projections of this type can be manufactured particularly simply, for example by a corresponding introduction, e.g. milling or cutting, of elongate cut-outs or grooves into the carrier member.

In accordance with an embodiment, a plurality of web-like projections extend at right angles to the longitudinal axis of the carrier member. The projections preferably extend in a ring-like manner over the whole periphery of the carrier member. Alternatively or additionally, a web-like projection can extend around the carrier member in spiral form. A projection of this type can be formed, for example, in that a spiral cut-out is cut into the carrier member in the manner of a threaded groove. Both the ring-like projections and the spiral projections permit the manufacture of target arrangements of any desired length in a simple manner.

The cut-outs of the carrier member bounded by the projections advantageously form a receiving space for the solder in a pre-assembly state of the target arrangement. On the assembly of the target arrangement, the solder therefore does not have to be applied directly to the projections, but can rather be arranged in the cut-outs, for example in the form of half-stock. The cut-outs thus so-to-say form a reservoir for the solder. The manufacture of the target arrangement is thereby simplified even further.

Fixing means are preferably arranged between the tube segment and the carrier member to fix, and in particular to center, the target with respect to the carrier member in a pre-assembly state. Even before the target and the carrier member are connected to one another with material continuity by the solder, a correct positioning of the joint partners relative to one another is ensured by the fixing means. This, on the one hand, facilitates the manufacture of the target arrangement and, on the other hand, ensures a correct seat of the target on the carrier member.

Alternatively, the target can also be centered with respect to the carrier member without fixing means while utilizing the different heat expansions of the target and the carrier member.

In accordance with a further embodiment, the compensation means each include a spring member. The connection of the carrier member and the target therefore does not take place via solder bridges in this joint variant, but via spring members connected with material continuity to the carrier member and the target. This joint variant combines the advantages of a force-transmitting connection with those of a connection with material continuity. A particularly good compensation is thus achieved between the different coefficients of expansion of the carrier member and the target by the elasticity of the spring members and a particularly efficient thermal dissipation from the target to the carrier member is achieved by the connection with material continuity of the spring members both to the carrier member and to the target.

Advantageously, each spring member is connected to the carrier member and to the tube segment with material continuity by means of a solder, in particular a soft solder. As has already been mentioned above, solder has particularly good thermal dissipation properties so that the thermal coupling of the target to the carrier member is improved even further.

Cut-outs for the spring members can be provided on the outer side of the carrier member. The spring members are already fixed to the carrier member in a pre-assembly state through the cut-outs and are in particular secured against an axial displacement with respect to the carrier member. This facilitates the pushing of the tube segment or of the tube segments onto the carrier member.

In accordance with a further embodiment, the target is metallized, in particular over the full area, at its inner side and/or the carrier member is metallized, in particular over the full area, at its outer side. A metallization of this type ensures a particularly reliable connection with material continuity between the joint partners, in particular when a soft solder free of flux is used as the compensation means or as the connection means for the connection of spring members to the target and to the carrier member and when the target comprises a ceramic material such as ZnO. The target can be coated, for example electroplated, at its inner side and the carrier member can have solder applied at its outer side.

To prevent melted solder from penetrating to the outer side of the target on the manufacture of the connection with material continuity of the target and the carrier member, a respective sealing material, in particular a heat-resistant sealing material, e.g. a silicone material, can be provided between two adjacent tube segments.

A further subject of the invention is moreover a method having the features of claim17. The aforesaid advantages are achieved accordingly by the method in accordance with the invention.

In accordance with an embodiment of the method in accordance with the invention, the carrier member and the tube segment are connected to one another by means of a solder, in particular of a soft solder, and preferably by means of a soft solder free of flux.

The solder is preferably arranged between projections of the carrier member spaced apart from one another and in particular formed in the manner of webs in a pre-assembly state of the target arrangement. This represents a particularly simple method for the application of the solder to the carrier member. The solder can, for example, be inserted into the cut-outs formed between the projections as half-stock.

The solder must be liquefied so that it can establish a connection with material continuity between the carrier member and the target. It is particularly advantageous in this connection for the target and the carrier member to be rotated such that the liquefied solder moves under the effect of centrifugal forces and capillary forces into gaps formed between the target and the projections of the carrier member to contact the target and the carrier member.

The liquefied solder therefore moves out of a pre-assembly position into an end position by the rotation of the target and the carrier member, namely out of the cut-outs into the gaps formed between the projections and the target. As soon as so much solder has moved onto the projections that the gaps between the projections and the target are completely filled with solder, the heat input and the rotation of the target arrangement can be ended so that the solder can cool and can connect with material continuity both to the target and to the projections of the carrier member.

Since the solder moves into the gaps between the projections and the target due to the centrifugal forces and the capillary forces, a correct positioning of the solder in the regions provided for the connection with material continuity of the target and the carrier member is automatically achieved. This simplifies the manufacture of the target arrangement and permits the manufacture of target arrangements of any desired length. In this connection, it is not necessary to melt the solder or to let it solidify simultaneously over the whole length of the target arrangement, but the target arrangement can rather be moved through a correspondingly made heat source, e.g. a continuous furnace, for the liquefying of the solder.

In accordance with a further embodiment of the method in accordance with the invention, each compensation means includes a spring member which is connected by solder to the carrier member and to the tube segment. It is possible by a corresponding heat input to melt the solder located between the spring members and the carrier member and the solder located between the spring members and the target simultaneously to establish the connection with material continuity of the spring members to the carrier member and to the target simultaneously.

Alternatively or additionally, the spring members can also already be connected with material continuity to the carrier member before the pushing of the tube segments onto the carrier member. In this way, the spring members are fixed to the carrier member and cannot be displaced in an axial direction on the pushing of the tube segments onto the carrier member. The same effect can alternatively or additionally be achieved in that receivers for the spring members are provided in the carrier member.

In order to improve the adhesion of the solder to the target and to the carrier element—as was already described above—the tube segment can be metallized, in particular over the full area, at its inner side and/or the carrier member can be metallized, in particular over the full area, at its outer side before the application of the solder.

A further object of the invention is moreover a tube segment of a hollow cylindrical target which comprises a ceramic material and a metal coating, in particular over the full area, at the inner side of the tube segment. The coating can e.g. include a layer comprising Ni, a layer comprising Cu and a layer comprising SnPb. The Ni layer has a particular good adhesion strength to a ceramic material comprising ZnO, whereas the Cu layer protects the Ni layer from corrosion and reduces the porosity of the SnPb layer. The Cu layer can optionally also be omitted. The SnPb layer is the actual functional layer which provides an optimum adhesion of a solder free of flux to the tube segment.

The ceramic material of the tube segment can comprise ITO (indium tin oxide).

The target arrangement in accordance with the invention shown inFIG. 1includes a tubular carrier member10comprising a metal material such as titanium, steel, in particular stainless steel or copper. The chain-dotted line12represents the longitudinal central axis of the carrier member10. The carrier member10is provided at its outer side with a solder layer, for example a layer of soldering tin.

Furthermore, at the outer side of the carrier element10, a plurality of groove-like cut-outs14are introduced, for example milled or cut, into the carrier member10. In the embodiment shown, the cut-outs14have a round and in particular an approximately semi-circular cross-section, but the cut-outs14can generally also have a round section which does not have the shape of a partial circle or can even have an angular cross-section.

Furthermore the cut-outs14in the embodiment shown extend transversely to the longitudinal central axis12, i.e. in the peripheral direction of the carrier member10, and indeed in each case along the total periphery of the carrier member10. The cut-outs14are, in other words, made in the manner of ring grooves. Alternatively, a cut-out can also expand in the manner of a spiral, i.e. in the manner of a threaded groove, around the carrier member. Mixed forms are also conceivable in which, viewed in the axial direction, a plurality of cut-outs14are provided sectionally in the form of ring grooves or a cut-out in the manner of a threaded groove is provided.

As is shown inFIG. 1, the cut-outs14are spaced apart from one another such that a projection16is in each case formed by and lies between two adjacent cut-outs14. In accordance with the configuration of the cut-outs14, the projections16also extend along the total periphery of the carrier member10in the peripheral direction, i.e. transversely to the longitudinal central axis12. In the case of a cut-out in the manner of a threaded groove, a projection would correspondingly extend around the carrier member in the manner of a spiral.

The spacings between adjacent cut-outs14are selected such that the projections16have a flattened plateau region18in each case at their outwardly facing upper sides18. The width of the plateau region18can amount to approximately half the width of the cut-outs14.

As is shown inFIG. 1, the target arrangement furthermore includes a hollow cylindrical target20comprising at least one tube segment21which is made in one piece and which comprises a target material, in particular a ceramic material such as ZnO.

Each tube segment21has a metal coating at its inner side, for example an electroplated coating19(FIG. 4). The coating comprises three sequential layers, namely an inner layer19aof Ni, a middle layer19bof Cu and an outer layer19cof SnPb, with the middle layer19bof Cu also being able to be omitted.

Each tube segment21surrounds the carrier member10at least section-wise. If the target20is composed of a plurality of tube segments21, a respective heat resistant sealing material (not shown), e.g. a silicone material, is provided between two adjacent tube segments21.

The inner diameter of each tube segment21is matched to the outer diameter of the carrier member10in the region of the projections16such that a gap22is formed between the plateau region18of each projection16and the inner side of the tube segment21. In the non-heated state of the target arrangement, i.e. at room temperature for example, the gaps22can have a gap width which lies in the range of some tenths of a millimeter.

A plurality of plastically deformable compensation means are provided for the connection of the carrier element10and the target20and are formed in the embodiment shown inFIGS. 1 to 3by a soft solder24which is free of flux and comprises e.g. SnIn or SnPb.

The soft solder24is introduced into the cut-outs14, e.g. is inserted into the cut-outs14as half-stock, for the assembly of the target arrangement. Subsequently, the tube segment21or the tube segments21are pushed onto the carrier member10and positioned over the cut-outs14receiving the soft solder24.

As is indicated inFIG. 1, the cut-outs14, viewed in the axial direction, are arranged distributed over substantially the total length of the target20. Fixing means, not shown, for example spring members, are arranged in those cut-outs14which are located in the region of the axial ends of the or each tube segment21for the fixing and centering of the target20with respect to the carrier member10in the pre-assembly state shown inFIG. 1.

The soft solder24present as half-stock in the cut-outs14is liquefied by means of a direct heat input26for the connection with material continuity of the target20to the carrier member10, as is shown inFIG. 2. The heating of the soft solder24can take place, for example in a continuous furnace, from outside via the target20and/or from inside via the carrier member10by means of a heat source introducible into the carrier member10.

On the melting of the soft solder24, the carrier member10and the target20are also heated. The carrier member10and the target20expand to different degrees due to this heating, whereby the width of the gaps22between the projections16of the carrier member10and the tube segment21or the tube segments21is reduced, for example to a gap width of 0.05 mm to 0.1 mm.

In addition to the liquefaction of the soft solder24, the carrier member10and the target20are set in rotation together around the longitudinal central axis12. The rotation of the target arrangement is selected such that the liquefied soft solder24moves out of the cut-outs14onto the plateau regions18of the projections16and contracts in and at the gaps22due to centrifugal forces and capillary forces. It is prevented by the sealing material between adjacent tube segments21that melted solder24can reach the outer side of the target20.

The heating and the rotation of the target arrangement are maintained for so long until so much solder24has collected in the gaps22that they are completely filled with solder24. The solder24is now in contact both with the plateau regions18of the projections16of the carrier member10and with the target20and thus bridges the intermediate space between the target20and the carrier member10.

The heat supply26is subsequently ended so that the target arrangement can cool down, preferably under continued rotation. The soft solder24solidifies due to this cooling down, with it simultaneously connecting to the target20and the carrier member10with material continuity.

The spacing between the target20and the carrier member10becomes larger again on the cooling of the target arrangement as a result of the different thermal expansions of the target20and the carrier member10. As is shown inFIG. 3, the soft solder24located in the gaps22is drawn apart while forming solder bridges or solder fillets28. Strains in the target20which could occur in the target20during the cooling due to the different thermal expansion of the joint partners10,20and which could result in damage to the target20are avoided by the plastic deformability of the solder fillets28.

The result is a target arrangement whose target20is connected with material continuity to the carrier member10via the plastically deformable solder fillets28of soft solder24. A particularly good thermal coupling of the target20to the carrier member10is thereby achieved, on the one hand, and a reliable mechanical fastening of the target20to the carrier member10, on the other hand, without there being a risk of damage to the target20due to strains which could result from the different thermal expansion of the joint partners.

In the second embodiment shown inFIG. 5, the target20made from one or more tube segments21and the carrier member10are not connected to one another by solder fillets24. Instead, the different degrees of expansion of the carrier member10and the target20on the warming of the target arrangement, e.g. during a sputtering process, are compensated by spring members30which are arranged between the carrier member10and the tube segment21or the tube segments21. The spring members30form the compensation means of this embodiment in that they are compressed on a heating of the target arrangement and expand again on a cooling of the target arrangement.

To ensure a particularly good heat transfer from the target20via the spring members30to the carrier member10, the spring members30are connected with material continuity both to the tube segment21or to the tube segments21and to the carrier member10.

A soft solder is provided as the connection means and is introduced between the spring members30and the tube segment21or tube segments21as well as between the spring members30and the carrier member10. A connection with material continuity is in each case established between the spring members30and the carrier member10or the target20by a corresponding melting and cooling process.

As with the first embodiment described above, a metal coating19, comprising a Ni layer19a, an optional Cu layer19band a SnPb layer19c, is also provided at the inner side of each tube segment21in the second embodiment (FIG. 4) to improve the connection with material continuity of the soft solder and the target20. The carrier member10is accordingly provided at its outer side with a solder layer, for example a layer of soldering tin.

The fastening of the spring members30to the carrier member10can take place simultaneously with the fastening of the spring elements30to the target20e.

In the embodiment shown inFIG. 6, the carrier element10and the target20are connected via spring members30located in cut-outs14. The soft solder24connects the spring members24with the carrier element10and with the target20.

Alternatively or additionally, the spring members30can also be connected with material continuity to the carrier member10before the pushing of the tube segment21or the tube segments21onto the carrier member10. In this manner, the spring members30are already fixed to the carrier member10on the assembly of the target20and are secured against an axial displacement by the tube segment21or the tube segments21. Alternatively or additionally, the spring members30can also be supported in cut-outs (not shown) of the carrier member10for this purpose.

REFERENCE NUMERAL LIST