Device, method and system for coating a substrate and superconducting tape conductor

Abstract

The present invention relates to an apparatus, a method and a system for coating a substrate and a superconducting strip conductor. The method comprises the steps of generating a metal material in a gas phase, introducing the gaseous metal material into an expansion space, wherein the expansion space is configured to expand the gaseous metal material and point it toward the substrate, and depositing the metal material on at least a portion of the surface of the substrate. The coated superconducting strip conductor comprises: at least one superconducting layer, at least one metal coating, the metal coating being deposited on the strip conductor, wherein the thickness of the metal coating is at least 1 μm and varies by no more than 10%, preferably no more than 5%, over the width of the coated strip conductor.

Description

Technical Field

[0001] The invention relates to a method and a device for coating substrates, in particular heat-sensitive thin substrates, with metal, such as films, strips for electronic devices and high-temperature superconductor (HTS) strip conductors. In particular, dense, well-conducting metal layers, for example, noble metals such as gold, silver, copper, tin and alloys thereof (for example bronze) should be deposited onto such substrates at high deposition rates and with high material efficiency. Background Art

[0002] Various methods for depositing metallic protective or contact layers are known from the prior art. In the case of metallic substrates, galvanic deposition is usually used, since in this case the metal can be selectively deposited on the substrate surface and thus a high material efficiency can be ensured.

[0003] For thick metal layers, so-called plasma spraying or screen printing slurries with the aid of metal nanoparticles are also often used. Plasma or particle spraying is usually carried out at atmospheric pressure. In order to achieve a directional effect, work is sometimes also carried out with the aid of nozzles. In the case of spraying cold particles, WO 2008074064 A1 proposes the use of nozzles in order to direct powder particles carried by the process gas onto the substrate with high kinetic energy. This application is limited to high gas pressures of the process gas, since the process gas must accelerate the carried powder particles by impact.

[0004] PVD (physical vapor deposition) techniques are usually used for thin layers, such as sputtering or vapor deposition from a heated boat or crucible in a high vacuum. Very dense, smooth metal layers can be produced in this way, but these usually have only a very small thickness.

[0005] In order to ensure sufficient heat dissipation, the film substrate can be passed over cooled rollers in the coating region and the heat can be dissipated away. Such an arrangement is described, for example, in US Pat. No. 7,871,667. However, this has the disadvantage that in the coating region, due to the arc of the circle, a significant change in the angle of incidence occurs, which can locally lead to shadowing effects and columnar growth of the coating.

[0006] However, all of these methods have other special disadvantages, especially when the substrate is sensitive to corrosive chemicals and / or high temperatures. Therefore, corrosive electrolytes (strong acids or cyanides) are mostly used in electroplating, which can corrode sensitive substrate types or coatings. In addition, the substrate surface must have good electrical conductivity everywhere so that deposition can be carried out evenly. Here, at the corners and edges of the substrate, due to the excessive field strength, thickening is almost inevitably caused, the so-called dog bone effect (Hundeknochen-Effek), so that the coating is uneven at the edges, especially in the case of thin substrates. Therefore, such unevenly coated substrates may not be suitable for applications such as tightly packed magnetic coils.

[0007] Furthermore, hydrogen is released during electrolysis and is embedded in the metal, which can change the material properties (e.g. copper) (e.g. by hydrogen embrittlement). In addition, there is the risk of liquid accumulating in recesses or cavities, especially in the case of film- or tape-shaped substrates that already carry other functional layers, such as HTS tape conductors. This can lead to corrosion or the formation of bubbles (so-called gassing) during brazing.

[0008] Plasma spraying locally generates a high heat input and leads to porous coatings, which prevents the use of sensitive substrates. Screen printing pastes and inks must be subjected to a heat treatment after application to remove organic solvents and therefore have a high pore density. This makes it difficult to achieve a uniform or even outer surface of the substrate and adhesion at edges is problematic.

[0009] Wet chemical coating methods or plasma spraying or particle sputtering methods that can also apply thick metal layers always provide coatings with high porosity and surface roughness, because the metal particles present here are baked in. The particle diameter also determines the size of the pores and the surface properties.

[0010] In contrast, PVD methods provide very uniform, smooth and compact coatings at low deposition rates of a few nm / s and substrate temperatures of <100°C. However, during sputtering, the substrate is very close to the plasma and the high-energy ions lead to a high heat input. During sputtering, in addition to metal atoms and ions, clusters of metal fragments can also be released. As a result, the metal layer grows more coarsely than in the case of evaporation where the evaporation source is far from the substrate and the metal atoms collide at a thermal rate.

[0011] However, at low coating rates, PVD methods are generally uneconomical for producing thicker metal layers of more than 1 μm to 3 μm.

[0012] PVD processes carried out in a vacuum are usually used for thin metal layers. For economic reasons, high deposition rates are desirable, but at high deposition rates and a cold base substrate, columnar growth occurs in the PVD layer due to local shadowing effects, resulting in rough and porous coatings.

[0013] This phenomenon is well documented in the literature. See for example Donald M. Mattox, "Handbook of physical vapour deposition (PVD) processing" ISBN: 0-8155-1422-0, 1998, p. 498, and can be described by the zone model of BA Movchan, AV Demchishin, Fiz. Met. Metalloved. 28 (1969) 653. With conventional PVD methods, even with good metal target conductivity, it is not possible to reach the extremely high rate range with deposition rates > 50 nm / s.

[0014] DE 10 2009 019146 describes measures for scattering metal vapor directed toward the chamber wall of the coating chamber back into the chamber and thereby increasing efficiency. However, due to this and the ballistic propagation of the vapor from the source, most of the metal atoms hit the substrate strip non-directionally and partially at very gentle angles. As mentioned above, the gentle impact at the required low substrate temperature and at high coating rates inevitably leads to columnar growth of the coating. As a result, the coating can be penetrated by deep gaps and holes and its airtightness (protective function) and electrical conductivity can be greatly affected. Summary of the invention

[0015] The present invention is intended to overcome at least some of the disadvantages described in the prior art and thereby provide an economical alternative for depositing uniform and dense metal layers at a high deposition rate and improved material efficiency. In particular, HTS tape conductors can thereby be equipped with stable metal layers or metal sheaths in a very cost-effective manner.

[0016] In one embodiment, the present invention provides a method for coating a substrate, in particular a superconducting strip conductor, in a vacuum environment, wherein the method comprises the following steps: generating a metal material in a gas phase, introducing the gaseous metal material into an expansion space, wherein the expansion space is configured to expand the gaseous metal material and direct it toward the substrate, and depositing the metal material on at least a portion of the surface of the substrate.

[0017] In particular, the expansion space can be configured to convert a lateral impulse component of the particles of the gaseous metal material into a longitudinal impulse component toward the substrate; and / or can be configured to generate a supersonic flow of the gaseous metal material in a direction toward the substrate; and / or can be configured to align the particles of the gaseous metal material with the substrate so that the particles impact at an angle of no more than 15°, preferably no more than 10°, and most preferably no more than 5° relative to the surface normal of the substrate.

[0018] The invention can be used, for example, to coat a substrate surface by evaporating metal from a crucible or a diffusion furnace in a high vacuum. The crucible of the evaporation source or gas source can be heated by common devices such as a resistance heater, an inductor or an electron beam, so that the metal to be evaporated melts therein and produces a gaseous metallic material within the crucible.

[0019] The method is characterized by very high deposition rates and material efficiency, which in turn allows high throughput and favorable production costs. The method also avoids the columnar and porous layer growth that usually occurs at high coating rates and thus allows for a dense, smooth and uniformly thick metal layer that follows the shape of the substrate, especially at the edges, and can thus also be used for uniform full-surface coating.

[0020] The above method enables substrates, such as HTS tape conductors, to be provided with a very uniform, dense, impermeable and well-conducting metal coating, wherein coating thicknesses of more than 1 μm can be achieved at deposition rates of more than 20 nm / s, more than 50 nm / s, or even >80 nm / s.

[0021] In addition, the method can also achieve very high material efficiencies (ie the ratio of the amount of material deposited on the substrate to the amount of material evaporated) of more than 50%, more than 70%, or even more than 80%. It can also be achieved that the resulting coating has essentially no pores or gaps.

[0022] In addition, in a vacuum environment, there can be up to 1×10 -1 Pascal, preferably up to 1×10 -2 Pascal, preferably up to 1×10 -3 The ambient gas pressure in Pascals.

[0023] This reduces undesired oxidation of the coating material and / or the substrate. In addition, hydrogen embedded in the substrate and / or the coating can also be reduced thereby.

[0024] In an alternative embodiment, the method may also be carried out in a suitable inert gas environment (eg, Ar, N2, etc.).

[0025] Furthermore, the substrate can be moved preferably continuously past the outlet of the expansion space, which also allows the coating of film- or strip-shaped substrates of any length.

[0026] In some embodiments, the gaseous metal material particles have an average free path length of less than 1 mm, preferably less than 0.1 mm, and more preferably less than 0.05 mm when flowing out of the gas source. In addition, the vapor pressure of the metal material in the gas source is at least 10 1 Pascal, preferably at least 10 2 Pascal, more preferably at least 10 3 Pascal.

[0027] These process parameters make the gaseous metal material have properties similar to those of a classical gas system due to frequent collisions and interactions with each other. Here, the expansion of the gaseous metal material in the expansion space can convert thermal energy into kinetic energy and, if necessary, generate a supersonic flow toward the substrate. The lateral impulse component of the metal particles is converted into a component toward the front, and the gas flow is directed toward the substrate parallel to the axis of the expansion space.

[0028] In another embodiment, the present invention provides a device for coating a substrate, in particular a superconducting tape conductor, wherein the device includes: a gas source for producing a metal material in a gas phase; wherein the gas source has an opening, and the gaseous metal material flows from the opening into an expansion space, and wherein the expansion space is configured so that the gaseous metal material expands and is aligned with the substrate.

[0029] In addition, as described above, the expansion space is configured to convert at least one lateral impulse component of the particles of the metal material into a longitudinal impulse component toward the substrate; and / or is configured to generate a supersonic flow of gaseous metal material in a direction toward the substrate, and / or is configured to align the particles of the gaseous metal material with the substrate so that the particles impact at an angle of no more than 15°, preferably no more than 10°, and most preferably no more than 5° relative to the surface normal of the substrate.

[0030] In particular, the device comprises a side surface surrounding the expansion space, wherein at least a portion of the side surface can have an anti-adhesion coating, preferably a perfluoropolyether, PFPE anti-adhesion coating. Furthermore, at least a portion of the side surface can be treated in such a way that the absorption of thermal radiation is increased. Furthermore, at least a portion of the side surface can be actively cooled.

[0031] This means, for example, that gaseous metallic material is not deposited on the side surfaces of the expansion space. Suitable anti-adhesion coatings of the long-chain perfluoropolyether (PFPE) type are known, for example, from US Pat. No. 4,022,928. The enclosed expansion space has two decisive advantages. The metal vapor flow is parallelized, so that even at high coating rates and low substrate temperatures, a dense layer growth is achieved. Secondly, the material efficiency is greatly improved, so that even in the case of a large distance between the evaporation source and the substrate, more than 50%, more than 70%, or even more than 80% of the evaporated metal is deposited on the substrate under high vacuum. Here, active cooling protects the anti-adhesion coating from overheating and, together with the increased absorption of thermal radiation, reduces the undesired heat input caused by the thermal radiation of the gas source in some substrate types (for example in HTS strip conductors). In particular, it is possible to achieve that, even at very high deposition rates, heat-sensitive substrates do not overheat and that the substrate temperature remains below 180° C., or even below 150° C. during coating.

[0032] Alternatively, in the case of substrate types which are less temperature-sensitive, at least a portion of the side surface also has a temperature which reduces the deposition of the metal material on the side surface.

[0033] In addition, in some embodiments, the expansion space can have an exhaust port facing the substrate and an inlet port facing the gas source, wherein the ratio of the diameter of the exhaust port to the diameter of the inlet port can be at least 1.5, preferably at least 1.75, more preferably at least 2.0; and / or wherein the ratio of the spacing between the inlet port and the substrate to the spacing between the inlet port and the exhaust port can be at least 1.0 and at most 1.4; and / or wherein the ratio of the spacing between the exhaust port and the inlet port to the diameter of the exhaust port can be at least 1.5.

[0034] It has been found that the geometrical properties of the expansion space can advantageously influence the directional effect of the expansion space, thereby ensuring in particular a uniform, dense and pore-free layer growth even at high coating rates.

[0035] Furthermore, in some embodiments, the expansion space can expand from the gas source to the substrate, in particular conically or bell-shaped. In particular, the expansion space can have the shape of a diffuser of a Laval nozzle.

[0036] Such Laval nozzles or supersonic nozzles are used in rocket technology to produce a directional airflow in a rocket engine, which is produced under high pressure and expands into free space. In order to produce the highest possible directional forward thrust, the gas flow expanding in the Laval nozzle is parallelized.

[0037] Although the gas pressure is many orders of magnitude lower than that of rocket engines, the embodiments described transfer the principle to applications in vacuum environments. As discussed above, the generation of supersonic flow is sufficient to cause the gas pressure in the vapor of metal atoms at the output of the gas source to be in the range of 10 when operating at high rates. 2In the range of Pascals, and thus the average free path length in the metal vapor is in the sub-millimeter range, so that the gas pressure behaves like a classical gas system due to the frequent collisions and interactions of atoms. The pressure reduction of the gas (metal vapor) in the dispersion portion of the Laval nozzle converts thermal energy into kinetic energy and forms a supersonic flow. Here, the lateral impulse component of the metal atoms is converted into a component toward the front and the gas flow is oriented parallel to the nozzle axis. Here, the average free path length in the expansion gas is significantly smaller than the geometric dimensions of the Laval nozzle. In order to effectively utilize this effect, in several embodiments of the present invention, an expansion space is added in the space between the evaporation source and the substrate coating plane, and the expansion space corresponds to the dispersion portion (expansion portion) of the Laval nozzle. The conical or bell-shaped expansion space can have a circular to slightly elliptical diameter to match the geometric structure of the coating surface.

[0038] In particular, in several embodiments, the expansion space may have an elliptical or rectangular cross-section with an aspect ratio of at least 1.2, preferably at least 1.5, more preferably at least 2.0, and most preferably at least 3.0.

[0039] As a result, the flow cross section of the gaseous metallic material flowing from the expansion space toward the substrate can be adapted to the elongated shape of the film-like or strip-like substrate, thereby increasing the available coating surface on the substrate.

[0040] In addition, the opening of the gas source can have a perforated plate, and the perforated plate preferably has at least one thin plate. In addition, the gas source and / or the perforated plate can be made of a high melting point material, preferably made of tungsten, tantalum, molybdenum, carbon and / or heat-resistant ceramic.

[0041] The build-up of vapor pressure in the gas source can thereby be intensified. In this context, the preferably layered partitions also reduce splashing of liquid metal droplets from the gas source, which splashing can occur due to overheating and / or turbulent flow processes.

[0042] In another embodiment, the present invention provides a system for coating a substrate, in particular a superconducting tape conductor, wherein the system comprises: at least one coating zone, in which a metal material is deposited on the substrate, wherein the substrate passes through the at least one coating zone at least twice; or comprises at least two coating zones, in which a metal material is deposited on the substrate, wherein the substrate passes through the at least two coating zones at least once each.

[0043] Such a system enables, for example, thicker layers to be deposited on a substrate in a single process step.

[0044] In particular, the system may also comprise means for changing the orientation of the substrate after a first pass through the at least one coating zone and before a second pass through the at least one coating zone or before passing through the second coating zone.

[0045] Such a system enables, for example, both sides of a strip-shaped substrate, such as an HTS strip conductor, to be coated uniformly; in particular, if a stream of coating material particles is directed onto the substrate to be coated, as by some of the above-mentioned devices.

[0046] In another embodiment, the present invention provides a system for coating a substrate, in particular a superconducting tape conductor, wherein the system comprises: at least one coating zone, in which a metal material is deposited on the substrate, wherein the substrate passes through the at least one coating zone at least twice; or comprises at least two coating zones, in which a metal material is deposited on the substrate, wherein the substrate passes through the at least two coating zones at least once each; and comprises a device for cooling the substrate after a first passage through the at least one coating zone and before a second passage through the at least one coating zone or before passing through the second coating zone.

[0047] In the case of high-rate coating, the main heat input on the substrate is the condensation energy released during the layer formation. Since the substrate can also be in a high vacuum in some embodiments, the substrate cannot release this heat input via solid or gas heat conduction and heats up according to its heat capacity. The heat capacity is very low, especially in thin films and ribbons, which limits the maximum layer thickness that can be deposited per pass through at least one coating zone in temperature-sensitive substrates. In the case of HTS tape conductors, for example, the maximum temperature should be kept below 180° C., preferably below 150° C., because above this temperature, the HTS layer properties, especially the critical current carrying capacity, will deteriorate due to oxygen losses.

[0048] This embodiment also allows the deposition of metal layers thicker than 1 μm by passing the substrate through the coating zone several times and being cooled by a coolant during this process.

[0049] In particular, in some embodiments, the speed at which the substrate passes through the coating zone can be selected so that the temperature is kept below the desired threshold temperature during a single pass through the coating zone. The substrate can then be moved through a device for cooling before it passes through another coating zone or repeatedly passes through the same coating zone. This process can be performed as frequently as desired until the desired total layer thickness is reached. The intermediate cooling mechanism can also be located outside the coating zone and can be effectively separated from the coating zone. Here, for example, the substrate can be cooled down via cooled rollers and solid heat conduction or via higher gas heat conduction so that the entry temperature is low enough to compensate for the temperature rise during coating.

[0050] In another embodiment, the present invention provides a system for coating a substrate, in particular a superconducting tape conductor, wherein the system comprises: at least one coating zone, in which a metal material is deposited on the substrate, wherein the substrate passes through the at least one coating zone at least twice; or comprises at least two coating zones, in which a metal material is deposited on the substrate, wherein the substrate passes through the at least two coating zones at least once each; and comprises at least one gas reflector arranged in or around at least one coating zone, which reflects particles of the metal material toward the substrate.

[0051] In particular, at least a portion of at least one gas reflector may have an anti-adhesion coating; and / or at least a portion of at least one gas reflector may be treated in such a way that the absorption of thermal radiation is increased; and / or at least a portion of the gas reflector may be actively cooled.

[0052] Such a gas reflector significantly increases the material efficiency of the system, allows the substrate to be coated more evenly from all directions and / or reduces the heat input into the substrate.

[0053] In particular, in several embodiments, a metallic material may be deposited in one or more coating zones of the above-described system by using one of the above-described apparatuses and / or methods.

[0054] In particular, the above-mentioned systems can also be combined with one another, so that, depending on the field of application of the coating system, a change in the orientation of the substrate, intermediate cooling and / or the gas reflector can be used.

[0055] In another embodiment, the present invention provides a coated superconducting tape conductor, comprising: at least one superconducting layer, at least one metal coating, which is deposited on the tape conductor, wherein the thickness of the metal coating is at least 1 μm and varies over the width of the coated tape conductor by no more than 10%, preferably no more than 5%.

[0056] Such superconducting tape conductors are particularly suitable for applications where multiple tape conductors are stacked on top of each other, or where there are multiple windings stacked one on top of the other, such as in a magnetic coil. Small thickness variations of the tape conductors reduce cavities or gaps and / or clamping forces between the individual layers / windings. In addition, coating thicknesses of more than 1 μm make the superconducting layer hermetic, achieve good thermally conductive cooling and provide an effective alternative flow path in the event of local (extrusion) fractures of the superconductor.

[0057] In particular, at least one metallic coating of a strip conductor can be produced by means of one of the above-described coating methods, coating devices and / or coating systems.

[0058] Furthermore, in several embodiments, less than 5%, preferably less than 3%, more preferably less than 1% of the volume of at least one metallic coating consists of cavities, gaps and / or pores.

[0059] Furthermore, in some embodiments, the area density of metal particles having an average diameter of at least 10 μm embedded in or deposited on the metal coating may be less than 5 / cm 2 , preferably less than 3 / cm 2 , more preferably less than 1 / cm 2 , most preferably less than 0.1 / cm 2 .

[0060] Furthermore, the metal coating can comprise gold, silver, copper and / or tin and alloys thereof or metals of the same group and / or surround the strip conductor.

[0061] Furthermore, the thickness of the at least one metal coating is at least 1 μm and at most 30 μm, preferably at least 1 μm and at most 10 μm, more preferably at least 3 μm and at most 10 μm.

[0062] The coating uniformity and roughness that can be achieved by the present invention increases the electrical and thermal conductivity of the coating and improves its airtightness and mechanical properties. For example, a uniform and pure coating is less likely to detach from the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The following describes selected solutions of the present invention with reference to the accompanying drawings. The accompanying drawings show:

[0064] Figure 1 A schematic structural diagram of a device for PVD metallization of a substrate according to an embodiment of the present invention is shown;

[0065] Figure 2 A schematic structural diagram of a device for PVD metallization of a strip-shaped substrate with a winding device according to an embodiment of the present invention is shown;

[0066] Figure 3a shows a cross-sectional microstructural image of a conventional electroplated copper HTS tape conductor;

[0067] Figure 3b shows a cross-sectional microstructural image of an edge of an HTS tape conductor having a surrounding copper coating according to an embodiment of the present invention;

[0068] Figure 4a shows a cross-sectional microstructural image of a 12 μm thick silver layer made by a conventional high-rate PVD method;

[0069] Figure 4b A cross-sectional microstructural image of a 12 μm thick copper layer according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0070] exist Figure 1The first embodiment of the present invention is schematically shown in FIG. 1. The vacuum device / vacuum chamber 1 is evacuated to a pressure less than 10 -2 Pascal, preferably less than 10 -3 Pascal residual gas pressure, so that the active metals (such as Al, Mg, etc.) will not oxidize during the evaporation process. An evaporation source / gas source 2 for evaporating the metal without splashing is arranged in the chamber 1. This is, for example, a diffusion furnace or a crucible, which can be heated by an electron beam, a resistance heater or an induction coil until the evaporation material melts and reaches a temperature of more than 10 in the evaporation source / gas source. 2 High evaporation pressure in the Pascal range. Preferably, the evaporator 2 has a cover plate, which includes a sheet made of a high melting point material, such as W, Ta, Mo, C or ceramic, to prevent splashing.

[0071] In the upper region of the vacuum chamber 1, the substrate 4 to be coated in the form of a flexible thin strip or film is continuously moved through the coating zone 5 via the evaporation source 2. Here, the strip can come from an unwinding and winding mechanism in the vacuum chamber or continuously enter the vacuum chamber, as described in DE 10 2009 052 873.

[0072] In order for the metal vapor 9 to impinge on the substrate 4 in the region of the coating zone 5 as vertically as possible (within an angular distribution of ±15° relative to the substrate normal) and thus avoid the above-mentioned columnar growth and high coating porosity, an expansion space 3 is provided between the evaporation source 2 and the coating zone 5. In the embodiment shown, the expansion space is functionally equivalent to the diverging expansion part of a Laval nozzle, which is mainly used in the aerospace industry or in turbines to generate and bundle supersonic flows. The expansion space or Laval nozzle 3 has an inwardly concave bell shape and a circular to slightly elliptical diameter. The lower inlet opening (diameter Q i ) is slightly wider than the outlet of the evaporation source 2 to allow them to be thermally separated. The upper outlet (diameter Q a ) basically determines the lateral dimension of the coating area 5.

[0073] In some embodiments, the expansion space 3 of length L is close to the coating zone 5, so that as little metal vapor 9 as possible is lost laterally in the gap between the expansion space 3 and the substrate 4. The distance DL is dimensioned in this case so that the substrate strip 4 does not come into contact with the expansion space 3 even if it sags slightly and is not contaminated, for example, by the anti-adhesion coating. Typically, the ratio D:L=1-1.4.

[0074] The geometric proportions of the expansion space or Laval nozzle 3 shown are as follows: the ratio Q between the outlet and the inlet of the nozzle a :Q i In this case, it is preferably greater than 1.5, particularly preferably greater than 2. The ratio of the nozzle length to the diameter of the outlet opening is greater than L:Q a= 1.5. The effect of the Laval nozzle is thus a high separation rate of the parallel vapor flows 9 and a very high material efficiency.

[0075] However, the nozzle shape of the expansion space described here (eg, Laval nozzle) is only one possible way to achieve the directional effect provided by the expansion space. Other shapes and / or types of expansion spaces are also conceivable and are part of the present invention.

[0076] In order to prevent the metal vapor 9 from adhering and condensing on the side surfaces of the expansion space 3, the expansion space is provided with an anti-adhesion coating. Suitable coatings are preferably composed of long-chain PFPE compounds (trade name, for example, Fomblin). In order to keep the evaporation pressure of the PFPE coating low and to remove the thermal radiation from the gas source 2, the side surfaces of the expansion space 3 are actively cooled, for example, by a well-thermally coupled, water-flowing pipeline. In order to prevent the side surfaces of the expansion space 3 from reflecting the thermal radiation of the gas source 2 onto the heat-sensitive substrate 4, it is recommended to blacken the surface of the expansion space before the anti-adhesion coating, so that the expansion space absorbs the thermal radiation and discharges it into the cooling water.

[0077] This arrangement enables extremely high coating rates to be achieved on the substrate 4. For economic reasons, the goal is a coating rate greater than 20 nm / s, preferably greater than 50 nm / s and particularly preferably greater than 80 nm / s. Even with copper as the coating material, the last proposed coating rate can be easily achieved by the present invention. Another important economic aspect is the material efficiency, i.e. the ratio of the amount of material deposited on the substrate 4 to the amount of material evaporated. In normal non-directional vacuum evaporation and when the common spacing D between the source 2 and the substrate 4 is 30 cm and 50 cm, the material efficiency is usually mostly only in the low double-digit percentage range. The material efficiency that can be easily achieved by the present invention is greater than 50%, preferably greater than 70%, and particularly preferably greater than 80%.

[0078] High coating rates on films or ribbons in a vacuum or high vacuum inevitably lead to a high energy input due to the released heat of condensation, so that the substrate 4 heats up very quickly. Many substrate materials, such as plastics or HTS tape conductors, are temperature-sensitive and are irreversibly damaged when a temperature threshold is exceeded. Therefore, how much material can be deposited during the passage through the coating zone 5 is determined on the one hand by the maximum permissible temperature of the substrate 4 and on the other hand by the heat capacity of the substrate 4.

[0079] The transport speed of the strip-shaped substrate 4 is thus calculated with the aid of the coating rate. If a thicker layer is required, the substrate 4 must be coated several times. This is achieved by installing several evaporation units in succession, winding the strip several times through the device over its entire length, or passing the strip several times through the same coating zone 5 via a winding device 6. The latter is particularly suitable for strips that are narrower than the width of the coating zone 5. Of course, all three measures can also be combined with each other. In addition, in all cases of multiple coating, after passing through the coating zone 5, the intermediate cooling device 8 can be used to remove heat from the strip-shaped substrate and reduce the temperature so that re-coating can be carried out.

[0080] Figure 2 An embodiment of a system for coating substrates and in particular strip conductors is shown. For the following investigations, a 12 mm wide HTS strip conductor was coated around its periphery with silver and copper. The HTS strip conductor consists of a thin metal strip (e.g. Hastelloy C 276) with a thickness of 30-100 μm, on which a metal oxide buffer layer (e.g. MgO) and an HTS functional layer, e.g. a cuprate of the RBa2Cu3O7 (R=yttrium or rare earth element) type, e.g. GdBa2Cu3O7, are deposited. The metallization serves for contacting, protection and electrical stabilization of the strip conductor, so that the strip conductor does not burn out in the event of an overload.

[0081] What is desired here is a metallization that is as dense as possible, smooth and all-round with very good layer thickness uniformity. However, when heated in a vacuum, superconducting cuprates lose oxygen by diffusion, thereby reducing their most important function, namely the critical current carrying capacity. Figure 2 The coating mechanism in the HTS tape conductor 4 is provided with a coating having, for example, 15 tracks (in Figure 2 The winding device 6 (shown only schematically in FIG. 1 ) passes through the coating zone 5 several times.

[0082] Outside the coating zone 5, each track runs through an intermediate cooling device 8. In this way, the substrate temperature can be reliably kept below 180°C, preferably even below 150°C, during the entire coating period and at copper layer thicknesses of more than 30 μm.

[0083] In addition, rear reflectors 7a, 7b are installed in the winding machine 6, which scatter the material evaporated backward through the gap between the tracks back to the substrate rear side at the rear reflector 7a or back to the substrate front side at the rear reflector 7b. Similar to the outer surface of the Laval nozzle 3, the rear reflector is water-cooled and provided with an anti-adhesion coating. This can increase the material efficiency by about 10%. In this case, the HTS strip conductor 4 is surrounded by copper. For this reason, the strip is turned over by the device when returning, that is, the rear side is driven forward. The layer thickness on the two main faces and edges of the strip 4 can be arbitrarily set according to requirements by the number of channels, the position of the upper reflectors 7a, 7b and the width of the gap between different winding tracks.

[0084] When producing HTS tape conductors, metal layers consisting of silver, copper, gold and tin, their alloys or sequences of these metals are preferably used. Even though the method described here is not limited to these metals, these metals are important applications. HTS tape conductors were therefore coated with silver and copper and investigated in detail with and without the method according to the invention. These HTS tape conductors have unique features that can be directly distinguished from tape conductors coated with other metallization methods.

[0085] The metal layers produced by electroplating on the strip conductors in this way have a characteristic increase in layer thickness at the edges, which is unavoidable due to the excessively high electric fields at the edges and the large solid angles at which the metal ions can accumulate.

[0086] Figure 3a By way of example, a cross-sectional microstructure image of the edge of a 12 mm wide and approximately 100 μm thick HTS tape conductor coated in a conventional manner, ie electroplated, with a nominally 20 μm thick copper layer is shown. All cross-sectional microstructure images shown ( Figure 3a , 3b , 4a, 4b) are all produced by ion beam etching with Ar ions to ensure smooth cutting edges without mechanical damage to the coating structure.

[0087] exist Figure 3a In the electron microscope image of the cut edge of the strip, the buffer layer and the HTS layer are clearly visible as bright strips on the front side of the metal substrate. Above and around it is the electroplated copper layer. The copper layer has a dimensionally stable thickness of 20 μm over most of the strip surface, but becomes continuously thicker towards the strip edge and reaches more than twice as high values ​​of 45 μm at the edge. Although the so-called dog bone effect can be reduced by suitable arrangement of the anodes in the electroplating bath, it does not completely disappear in the economically important deposition rate of more than 20 nm / s and is a unique distinguishing feature from PVD coatings, the layer thickness of which is practically constant right up to the edge.

[0088] In the case of electroplated metallized strip conductors, in the best case, a thickness ratio of 1.2 to 1.3 is observed at the edge to the center. Figure 3b ), the ratio is below 1.1, preferably even below 1.05. This dimensional accuracy is particularly desirable for the construction of magnetic coils, since uneven conductor thicknesses cause unnecessary gaps between the winding layers.

[0089] In comparison, Figure 3b FIG. 3 shows a cross-sectional microstructure image of a ribbon conductor 300 coated with copper around the periphery using the high rate PVD method of the present invention. Figure 3b In the electron micrograph of the cut edge in FIG. , the buffer layer and the HTS layer 310 are visible as bright stripes above the front side of the metal substrate. Figure 3b In the strip conductor of , the front and rear sides are coated with different thicknesses, in this case 14 μm on the front side and 6 μm on the rear side. The remarkable uniformity of the layer thickness 320 and the edge shielding can be clearly seen. The variation of the metal layer thickness 320 is less than 10%, preferably less than 5%, of the average value.

[0090] The invention thus enables high quality of the PVD vapor-deposited metal layer even in the region of high coating rates and large metal layer thicknesses. The method is particularly suitable for metallizing HTS tape conductors when a metal layer thickness of between 1 and 30 μm, preferably between 1 and 20 μm, particularly preferably between 3 and 20 μm, is applied on each side.

[0091] Figure 4a and Figure 4b Combining two HTS tape conductors coated with 12 μm metal layer thickness shows that conventional high rate evaporation ( Figure 4a ) and the present invention ( Figure 4b ) comparison results.

[0092] Figure 4a The cross section of a silver layer is shown, which is produced at a high rate of >50 nm / s and by intermediate cooling, but without the expansion space 3 provided by the invention. The vapor from the source is reflected from the side walls of the chamber into the chamber until it impinges on the substrate and is built into the metal layer there. The vapor thus reaches the substrate surface from all spatial directions (i.e. non-directionally) up to critical incidence or grazing incidence.

[0093] exist Figure 4aIn the 440, only the interface with the HTS layer and a thin 1.5 μm crystalline silver layer can be seen from below the HTS tape conductor, which was annealed at >300°C after the first PVD coating. In this arrangement, columnar growth is very clearly shown in the high-rate silver layer, which causes large pores and gaps in the layer and surface features 440. The thickness variations and roughness are a few μm and are greater than 20% of the average layer thickness.

[0094] and Figure 4b A cross section of a 12 μm thick copper layer deposited on a similar HTS tape conductor surface by means of the present invention is shown. Upon closer inspection, a coating structure can be seen in the copper layer 320, which is caused by multiple passes through the coating area. Figure 4a Unlike the sintered carbon foam, the coating is very dense and smooth. Figure 4a The holes and gaps 440 in the are almost completely gone.

[0095] In the cross-sectional microstructure image obtained by ion beam etching perpendicular to the substrate surface and observed by electron microscopy (magnification 5000×) used here, the cavity or hole 440 is less than 1% of the cross-sectional area and volume of the metal layer 320. The thickness variation of the metal layer 320 measured on the cross-sectional microstructure image obtained by ion beam etching is at least less than 10% of the average local layer thickness, and in some embodiments, even at least less than 5%.

[0096] The HTS conductor strip 300 produced by one of the embodiments of the present invention is also characterized by a very low surface density of metal splashes 450 on the surface. During high-rate evaporation, turbulent processes and splash formation are usually caused in the metal melt due to severe overheating in the crucible. The resulting metal droplets 450 have a diameter of >10 μm, which can damage the substrate due to local overheating during impact, or press the substrate into the HTS layer 310 located thereunder and cause it to break when the substrate is guided on rollers. Splashing can be effectively avoided by an evaporation source with a cover plate made of a high-melting-point material, such as W, Ta, Mo, C or ceramic. The metal layer 320 produced here is therefore also characterized by splashes with an average diameter greater than 10 μm and a very low density of less than 0.1 / cm2 of embedded particles 450. 2 Surface density.

[0097] Reference numerals list

[0098] 1 Vacuum chamber / vacuum environment

[0099] 2 Evaporation source / gas source

[0100] 3 Expansion space / expansion nozzle for water cooling

[0101] 4 Moving base band (thin film)

[0102] 5 Coating area

[0103] 6 Belt winder / winding mechanism

[0104] 7a, 7b Water-cooled rear reflector / gas reflector

[0105] 8 Intermediate cooling mechanism

[0106] D The distance between the evaporation source and the substrate

[0107] L Expansion space / length of the spreading nozzle

[0108] Q i Entrance diameter of expansion space

[0109] Q a Expansion space outlet diameter

Claims

1. A method for coating a substrate (4) with a metal coating in a vacuum environment (1), wherein: In the vacuum environment (1), there is a maximum of 1 × 10 -1 The ambient gas pressure in Pascals, the method comprising: a. generating a metal material (9) in a gas phase in a splash-free manner in a gas source (2), wherein the vapor pressure of the metal material (9) in the gas source (2) is at least 10 1 Pascal; b. introducing the gaseous metal material (9) into the expansion space (3); c. wherein the expansion space (3) has the shape of an expansion portion of a Laval nozzle and is configured to expand the gaseous metal material (9) and direct it toward the substrate (4); and d. depositing the metal material (9) on at least a portion of the surface of the substrate (4), wherein the expansion space (3) is arranged directly adjacent to the gas source (2), and The peripheral surface of the expansion space (3) is coated with an anti-adhesion coating.

2. The method according to claim 1, wherein: The expansion space (3) is configured to convert a lateral impulse component of the particles of the gaseous metal material (9) into a longitudinal impulse component toward the substrate (4); and / or wherein The expansion space (3) is configured to generate a supersonic flow of the gaseous metal material (9) in a direction toward the substrate (4); and / or wherein: The expansion space (3) is arranged such that particles of the gaseous metallic material (9) are directed toward the substrate (4) in such a way that they impinge at an angle of no more than 15° relative to a surface normal of the substrate (4).

3. A method according to any one of the preceding claims, wherein: In the vacuum environment (1), there is a maximum of 1 × 10 -2 Ambient gas pressure in Pascals; and / or wherein, The substrate (4) moves through the outlet of the expansion space (3).

4. The method according to claim 1 or 2, wherein: The particles of the gaseous metal material (9) have a mean free path length of less than 1 mm when flowing out of the gas source (2); and / or wherein: The vapor pressure of the metal material (9) in the gas source (2) is at least 10 2 Pascal.

5. A device for coating a substrate (4) with a metal coating in a vacuum environment (1), wherein: In the vacuum environment (1), there is a maximum of 1 × 10 -1 Pascal's ambient gas pressure, the device comprising: a. A gas source (2) for producing a metal material (9) in a gas phase in a splash-free manner, wherein the vapor pressure of the metal material (9) in the gas source (2) is at least 10 1 Pascal; b. wherein the gas source (2) has an opening, and the gaseous metal material (9) flows from the opening into the expansion space (3); and c. wherein the expansion space (3) is formed as an expansion portion of a Laval nozzle and is arranged directly adjacent to the gas source (2), The peripheral surface of the expansion space (3) is coated with an anti-adhesion coating, and The expansion space (3) is configured to allow the gaseous metal material (9) to expand and align with the substrate (4).

6. The device according to claim 5, wherein: The expansion space (3) is configured to convert at least one lateral impulse component of the particles of the gaseous metal material (9) into a longitudinal impulse component toward the substrate (4); and / or wherein: The expansion space (3) is configured to generate a supersonic flow of the gaseous metal material (9) in a direction toward the substrate (4); and / or wherein: The expansion space (3) is configured so that particles of the gaseous metallic material (9) are directed toward the substrate (4) so ​​that the particles impact at an angle of no more than 15° relative to a surface normal of the substrate (4).

7. The device according to any one of claims 5 to 6, wherein At least a portion of the peripheral surface is treated in such a way as to improve the absorption of thermal radiation; and / or wherein At least a portion of the peripheral side surface is actively cooled.

8. The device according to claim 5 or 6, wherein: The expansion space (3) has an outlet facing the substrate (4) and an inlet facing the gas source (2), wherein the ratio of the diameter of the outlet to the diameter of the inlet is at least 1.5; and / or wherein, The ratio of the distance between the inlet opening and the substrate to the distance between the inlet opening and the outlet opening is at least 1.0 and at most 1.4, and / or wherein, A ratio of a distance between the outlet opening and the inlet opening to a diameter of the outlet opening is at least 1.

5.

9. The device according to claim 5 or 6, wherein: The expansion space (3) extends from the gas source (2) to the substrate (4); and / or wherein The opening of the gas source (2) has a perforated plate; and / or wherein The gas source (2) and / or the orifice plate are made of a material with a high melting point.

10. A system for coating a substrate (4) with a metal coating in a vacuum environment (1), the system comprising: a. at least one coating zone (5), in which a metallic material (9) is deposited on the substrate (4) by using an apparatus according to any one of claims 5 to 9, wherein the substrate (4) passes through the at least one coating zone (5) at least twice; or b. At least two coating zones (5), in which a metal material (9) is deposited on the substrate (4) by using an apparatus according to any one of claims 5 to 9, wherein the substrate (4) passes through the at least two coating zones (5) at least once in each case.

11. The system according to claim 10, further comprising means (6) for changing the orientation of the substrate (4) after a first passage through the at least one coating zone (5) and before a second passage through the at least one coating zone or before a passage through the second coating zone (5), means (8) for cooling the substrate (4) after a first pass through the at least one coating zone (5) and before a second pass through the at least one coating zone or before passing through a second coating zone (5); and / or At least one gas reflector (7a, 7b) is arranged in or around the at least one coating region (5), the gas reflector reflecting particles of the metallic material (9) towards the substrate (4).

12. The system according to claim 11, wherein: At least a portion of the at least one gas reflector (7a, 7b) has an anti-adhesion coating; and / or wherein, At least a portion of the at least one gas reflector (7a, 7b) is treated in such a way that the absorption of thermal radiation is increased; and / or wherein, At least a portion of the gas reflector (7a, 7b) is actively cooled.

13. A coated superconducting tape conductor (300), comprising: a. at least one superconducting layer (310); b. at least one metal coating (320) deposited on the strip conductor (300); and c. wherein the thickness of the metal coating (320) is at least 1 µm and varies by no more than 10% over the width of the coated strip conductor (300), The at least one metallic coating (320) is produced by means of a method according to any one of claims 1 to 4 and / or a device according to any one of claims 5 to 9 and / or a system according to any one of claims 10 to 12.

14. The coated superconducting tape conductor (300) according to claim 13, wherein: Less than 5% of the volume of the at least one metallic coating (320) consists of cavities, gaps and / or pores (440); and / or wherein The area density of metal particles (450) having an average diameter of at least 10 µm embedded in or deposited on the metal coating is less than 5 / cm 2 ; and / or where The at least one metal coating (320) comprises gold, silver, copper and / or tin and alloys thereof or a sequence of these metals; and / or wherein The at least one metallic coating (320) surrounds the strip conductor (300).

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