Textured substrate for forming epitaxial film and method for producing the same

Abstract

The present invention provides a textured substrate for forming an epitaxial film, including a textured metal layer on at least one surface of the layer, the textured metal layer including a copper layer having a cube texture, the textured metal layer having, on a surface of the layer, palladium added in an amount of 10 to 300 ng/mm.sup.2 per unit area, the hydrogen content of the surface of the textured metal layer being 700 to 2000 ppm. This textured substrate is produced through a step of adding 10 to 300 ng/mm.sup.2 per unit area of palladium by strike plating to a surface of the copper layer having a cube texture.

Claims

1. A textured substrate for forming an epitaxial film, comprising a textured metal layer on at least one surface of the textured substrate, wherein the textured metal layer comprises a copper layer having a cube texture, the textured metal layer has, on a surface of the layer, palladium added in an amount of 10 to 300 ng/mm.sup.2 per unit area, and a hydrogen content of the surface of the textured metal layer is 700 to 2000 ppm.

2. The textured substrate for forming an epitaxial film according to claim 1, wherein the textured metal layer has a nickel layer on a surface of the copper layer.

3. The textured substrate for forming an epitaxial film according to claim 2, wherein the nickel layer has a thickness of 100 to 20000 nm.

4. The textured substrate for forming an epitaxial film according to claim 3, wherein the copper layer of the textured metal layer has a {100}<001> cube texture, and a drift angle , of a crystal axis of the surface of the copper layer is , 6.

5. The textured substrate for forming an epitaxial film according to claim 3, wherein the textured metal layer includes a reinforcing material for reinforcing of the layer.

6. A superconductive material comprising at least one intermediate layer and a superconductor layer made of an oxide superconductive material formed on the textured metal layer of the textured substrate for forming an epitaxial film defined in claim 3.

7. The textured substrate for forming an epitaxial film according to claim 2, wherein the copper layer of the textured metal layer has a {100}<001> cube texture, and a drift angle , of a crystal axis of the surface of the copper layer is , 6.

8. The textured substrate for forming an epitaxial film according to claim 2, wherein the textured metal layer includes a reinforcing material for reinforcing of the layer.

9. A superconductive material comprising at least one intermediate layer and a superconductor layer made of an oxide superconductive material formed on the textured metal layer of the textured substrate for forming an epitaxial film defined in claim 2.

10. The textured substrate for forming an epitaxial film according to claim 1, wherein the copper layer of the textured metal layer has a {100}<001> cube texture, and a drift angle , of a crystal axis of the surface of the copper layer is , 6.

11. The textured substrate for forming an epitaxial film according to claim 10, wherein the textured metal layer includes a reinforcing material for reinforcing of the layer.

12. A superconductive material comprising at least one intermediate layer and a superconductor layer made of an oxide superconductive material formed on the textured metal layer of the textured substrate for forming an epitaxial film defined in claim 10.

13. The textured substrate for forming an epitaxial film according to claim 1, wherein the textured metal layer includes a reinforcing material for reinforcing of the layer.

14. A superconductive material comprising at least one intermediate layer and a superconductor layer made of an oxide superconductive material formed on the textured metal layer of the textured substrate for forming an epitaxial film defined in claim 1.

15. The superconductive material according to claim 14, wherein the intermediate layer has at least a barrier layer and a cap layer, the barrier layer is made of an oxide containing zirconium oxide, and the cap layer is made of a composite oxide containing a rare earth element oxide or a rare earth element.

16. The superconductive material according to claim 14, wherein the superconductor layer is made of a RE-based superconductive material.

17. A method for producing the textured substrate for forming an epitaxial film defined in claim 1, comprising a step of adding by strike plating 10 to 300 ng/mm.sup.2 per unit area of palladium to a surface of a copper layer having a cube texture.

18. The method for producing a textured substrate for forming an epitaxial film according to claim 17, wherein conditions of the strike plating are such that plating is performed by use of a plating solution having a metal palladium concentration of 0.4 to 0.6 g/L and a pH of 8.5 to 9.5.

19. The method for producing a textured substrate for forming an epitaxial film according to claim 17, comprising a step of, before the step of adding palladium, forming a nickel layer by epitaxial growth on the surface of the copper layer having a cube texture.

20. The method for producing a textured substrate for forming an epitaxial film according to claim 17, comprising a step of, after the a step of adding palladium, heating the substrate to 400 C. or higher in a non-oxidizing atmosphere to perform a heat treatment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the results of oxygen concentration XPS analysis of the surfaces of the textured substrates of the example and comparative examples.

(2) FIG. 2 shows the results of X-ray diffraction analysis of epitaxial films formed on the textured substrates of Example 1 and the conventional example.

(3) FIG. 3 shows X-ray pole figures of epitaxial films formed on the textured substrates of Example 1 and the conventional example.

(4) FIG. 4 shows X-ray pole figures of an epitaxial film on the textured substrate of Example 1 in the length direction (front end portion, central portion, rear end portion).

(5) FIG. 5 shows the results of oxygen concentration analysis of the surfaces of textured substrates in the second embodiment, when the treatment conditions for the addition of palladium are varied.

DESCRIPTION OF EMBODIMENTS

(6) Hereinafter, best modes for carrying out the present invention will be described.

First Embodiment

(7) In this embodiment, first, various kinds of precious metals were added to the surface of a textured substrate including a copper layer as a textured metal layer, and the effects of the addition of palladium were tested. For the formation of a textured metal layer, a 1000-m-thick, tape-shaped copper plate was prepared and cold-rolled at room temperature by use of a pressure roll set to have a reduction ratio of 95%, to give a tape material of 50 m. After rolling is performed, the copper plate was subjected to a heat treatment to orient the crystalline structure to give a {100}<001> cube texture. This heat treatment was performed by the application of heat for 2 hours at a temperature of 750 C. in an atmosphere containing 95% nitrogen gas and 5% hydrogen gas.

(8) On the crystal-orientation-treated copper layer, a nickel layer to serve as a crystal orientation improving layer was formed by plating. For nickel plating, the substrate was subjected to acid degreasing and electrolytic degreasing, and then to electrolytic plating in a nickel plating bath (Watts's bath). The plating conditions were as follows: temperature: 40 C., current density: 1 A/dm.sup.2. The plating time was adjusted to give a 1000-nm-thick nickel plating. Incidentally, when a nickel plating is formed as a crystal orientation improving layer, the conditions are preferably set within the following range: current density: 1 to 5 A/dm.sup.2, bath temperature: 40 to 60 C.

(9) For the textured substrate formed of a copper layer provided with a nickel layer, various precious metals containing palladium were added to the surface. Precious metals were each added by strike plating. This treatment was performed by use of a plating solution having a metal palladium concentration to 0.5 g/L and a pH of 9 (product name: PALLADEX STRIKE2) as a plating bath at a bath temperature of 35 to 45 C. and a current density 3 to 8 A/dm.sup.2 for a plating time of 20 seconds. In this plating treatment, the amount of addition was set at 60 ng/mm.sup.2 per unit area. After the addition of each precious metal, a heat treatment was performed in a non-oxidizing atmosphere (nitrogen-hydrogen mixed gas) at 700 C. for 1 hour.

(10) The hydrogen content of the surface of the textured substrate produced as above was analyzed by an inert gas fusion method (analyzer: OHN836, manufactured by LECO Japan). Then, to examine whether a natural oxide film was formed, the oxygen concentration of the substrate surface 180 minutes after production was analyzed by X-ray photoelectron spectroscopy analysis (XPS). The analysis was performed on the outermost surface of the substrate and also near the surface by sputtering. The results are shown in Table 1 (hydrogen content) and FIG. 1 (oxygen concentration).

(11) TABLE-US-00001 TABLE 1 Added metal Hydrogen content Example 1 Pd 783 ppm Comparative Example 1 Pt 4.8 ppm Comparative Example 2 Ag 3.2 ppm Comparative Example 3 Au 3.7 ppm Comparative Example 4 Ru 3.1 ppm Conventional example Not added 3.3 ppm

(12) Referring to Table 1, the hydrogen content of the textured substrate surface is extremely high in the substrate having palladium added thereto. Referring to the results of the measurement of surface oxygen concentration (FIG. 1), the oxygen concentration of the substrate having palladium added thereto is almost zero even in the outermost surface, and no oxide is confirmed to be produced. In contrast, it is shown that in the conventional example having no metal added thereto, oxygen is present near the outermost surface and also near the surface, which indicates that an oxide was produced. Additionally, regarding the effects of other precious metals, platinum, gold, silver, and ruthenium resulted in lower oxygen concentrations than when no metal is added, which suggests that they are somewhat effective although the mechanism seems to be different from the surface hydrogen content. However, as compared with palladium, the suppressing effect on the formation of an oxide film can be said to be lower. From the above examination results, the addition of palladium was confirmed to be extremely effective to suppress the production of a natural oxide film.

(13) Next, epitaxial films were formed by use of the textured substrates of Example 1 and the conventional example, and the orientation was evaluated. For the formation of an epitaxial film, a 100-m-thick, tape-shaped stainless steel (SUS304) plate was bonded to the textured substrate as a reinforcing material. For the bonding of the stainless steel plate, the bonding surfaces of the copper substrate and the stainless steel plate were both surface-activated with a fast atomic beam (argon) by a surface-activated bonding device, and they were bonded together by a pressure roll. The conditions for surface-activated bonding are as follows. Degree of vacuum: 10.sup.5 Pa
(Inside the vacuum chamber and etching chamber: argon gas atmosphere) Applied voltage: 2 kV Etching time: 5 minutes Applied pressure during bonding: 2 MPa

(14) Additionally, the substrate of the conventional example was subjected to an argon beam treatment before the formation of an epitaxial film to remove the surface oxide film much as possible (the argon beam treatment was not performed in Example 1). For the formation of an epitaxial film, a 100-nm-thick stabilized zirconia (YSZ) thin film was formed by PLD method, and further a 400-nm-thick cerium oxide (CeO.sub.2) thin film was formed thereon.

(15) After the formation of the two-layer epitaxial film, the structure and crystal orientation of the epitaxial film were evaluated. The epitaxial film surface was subjected to X-ray diffraction analysis (XRD), and the crystal orientations of YSZ and CeO.sub.2 forming the epitaxial film were examined by a 2- method. Then, the crystal orientation was evaluated by a pole figure method (Shultz reflection method).

(16) FIG. 2 shows the results of X-ray diffraction (2- method) of the epitaxial films (YSZ/CeO.sub.2 continuous films) formed on the textured substrates of Example 1 and the conventional example. In the epitaxial film of Example 1, only YSZ (002) peak and CeO.sub.2 (200) peak are seen, and it can be observed that each substance grows epitaxially along the crystal orientation of the layer immediately thereunder. Meanwhile, in the epitaxial film of the conventional example, there are only YSZ (101) peak and CeO.sub.2 (111) peak. This indicates that the film grows along the preferred orientation of each substance independently of the orientation of the layer immediately thereunder, which indicates that the function of the textured substrate is not exerted.

(17) This can be also understood also from the pole figures. FIG. 3 shows X-ray pole figures of the continuous epitaxial films (YSZ/CeO.sub.2) formed on the textured substrates of Example 1 and the conventional example. In the epitaxial film of Example 1, YSZ and CeO.sub.2 are shown to have high orientation. In contrast, in the conventional example, it can be observed that YSZ and CeO.sub.2 each grow along its preferred orientation, and, as a result, the CeO.sub.2 crystal orientation is significantly inferior.

(18) Additionally, FIG. 4 shows X-ray pole figures of the YSZ/CeO.sub.2 continuous film on the textured substrate of Example 1 in the length direction, showing a front end portion, a central portion, a rear end portion. In the epitaxial film of Example 1, the same crystal orientation is seen in every point, and no variation can be observed in the length direction. Accordingly, it was confirmed that even when an elongated epitaxial film was formed, the textured substrate of Example 1 having palladium added thereto allowed for the formation of a film with stable crystal orientation.

(19) From the above examination results, it was confirmed that when palladium was added to a textured substrate by a suitable treatment while increasing the hydrogen content, such a substrate allowed for the growth of an epitaxial film while maintaining good crystal orientation. This is attributable to the suppressive action on the production of a natural oxide film caused by palladium, and it appears that other metals have no such action. Additionally, the addition of palladium allows for formation of a good epitaxial film even without cleaning the substrate surface before the epitaxial film formation (argon beam treatment), and it can be said that this technique is also excellent in terms of efficiency.

Second Embodiment

(20) Here, when the treatment conditions for the addition of palladium were varied and a different addition method was applied, it was examined whether there would be any difference in the hydrogen content of the textured substrate surface. Palladium was added under strike plating conditions varied from the first embodiment. Additionally, the treatment was performed by use of general electrolytic plating as a method for adding palladium to produce textured substrates (Comparative Examples 5 and 6). This electrolytic plating was performed by use of a commercially available plating solution (product name: PALLADEX ADP720) at a bath temperature 30 to 50 C. and a current density 0.5 to 1.0 A/dm.sup.2 for a plating time of 1 second. Incidentally, in each case, the amount of addition of palladium was set at 60 ng/mm.sup.2 per unit area.

(21) Then, the hydrogen content and oxygen concentration of the substrate surface were measured in the same manner as in the first embodiment. The results are shown in Table 2 and FIG. 5.

(22) TABLE-US-00002 TABLE 2 Added metal Hydrogen content Example 2 Pd 795 ppm Example 3 751 ppm Example 4 801 ppm Comparative Example 5 418 ppm Comparative Example 6 637 ppm

(23) From the results of Table 2 and FIG. 5, it appears that there is correlation between the hydrogen content and oxygen concentration of the substrate surface. However, in order for the effect to be exerted, certain hydrogen content is necessary. Additionally, it can be observed that even though palladium has hydrogen absorbability, it is difficult to introduce a sufficient amount of hydrogen by usual plating, and a treatment in which hydrogen can be forcibly introduced, such as strike plating, is suitable.

INDUSTRIAL APPLICABILITY

(24) As described above, the textured substrate for forming an epitaxial film according to the present invention ensures crystal orientation and also considers the quality of an epitaxial film formed thereon. The present invention is suitable as a substrate for various materials and devices using an epitaxial film, and is useful as a substrate for forming an oxide thin film for a superconductive material, a solar cell, or the like.