JPH04163808A - Manufacture of superconductive device - Google Patents

Abstract

PURPOSE:To prevent degradation due to fabrication of a superconductive film and to obtain a superconducting device with high quality by fabricating a substrate surface into a pattern shape prepared in advance and, forming an oxide superconductive film on the projection surface of the processed surface. CONSTITUTION:A device pattern 2B prepared in advance is formed on a surface of a SrTiO3 substrate 2 by a separation processing. Then, an oxide superconductive film 1A is formed on the projection surface of the processed substrate 2 by means of epitaxial growth. Degradation of superconductive characteristics in the edge side of the pattern due to ions collision can be prevented because no processing is added to such a superconductive film 1A. Furthermore, since no resist is applied to the surface of the superconductor, oxygen plasma arcing becomes unnecessary, degradation of superconductive characteristics in surface and side of the pattern due to excess or insufficiency of oxygen is not generated. High quality superconducting device can be obtained accordingly.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides superconductivity using a thin film of an oxide superconductor that has a crystal structure including CuO or vO structures and has a high critical temperature (Tc). The present invention relates to a method for manufacturing a device.

[Conventional technology 1] As is well known, high Tc oxide superconductors such as YBaCuO and B15rCaCuO are heated at liquid nitrogen temperature (77K).
It exhibits superconductivity even at temperatures above this temperature. Therefore, if a superconducting device that operates at liquid nitrogen temperature is realized using such an oxide superconductor, the cooling cost will be significantly lower than that of a superconducting device that uses a Nb-based alloy and requires liquid helium cooling. A significant reduction is expected.

For this reason, a superconducting quantum interference magnetometer (SQUID) using the above-mentioned high Tc oxide superconductor
ingQuantum Interference D
Research is being carried out on superconducting devices such as (Vice), Josephson elements, microwave passive circuits, optical sensors, and strong magnets. In particular, thin films grown epitaxially on single crystal substrates have good crystallinity, so not only do they have a high Tc, but they also have a high critical current density (Je), making it possible to fabricate devices with high current density, and high-frequency surface resistance. (R1
) is low, making it possible to create low-loss high-frequency devices; and since the magnetic field penetration length (λL) is short, high-frequency devices can be created by making only the surface layer of about 1 μm of superconductor. It has many advantages and is currently being actively researched.

However, when prototyping thin film devices, it is necessary to form a pattern of oxide superconductor, but the superconducting properties such as Tc, Jc, R, etc. may be significantly deteriorated during the pattern formation process. It has been reported that it is not easy to obtain a device that combines pattern processing and superconducting properties.

Normally, for pattern formation, a resist film is formed on a superconducting thin film, the resist material is altered in quality by exposure to light through a mask, and the altered parts are removed with a solution to transfer the pattern on the mask to the resist. After that, using the resist as a mask, the unnecessary parts of the oxide superconducting thin film are dissolved using a solution such as phosphoric acid, or using the resist as a mask and irradiating with ions such as Ar, etching the unnecessary parts of the oxide superconducting thin film. Methods such as removing the Finally, when the resist is removed by ashing with oxygen plasma, an oxide superconductor with the same pattern as the resist pattern is formed.

However, in wet etching using phosphoric acid or the like, the liquid diffuses through the grain boundaries of the oxide superconductor, and the etching rate is extremely high. As a result, the edge shape on the side surface of the pattern is easily disturbed (the shape accuracy is significantly deteriorated and precision controllability is lacking, and the superconducting properties are deteriorated due to the reaction between the etchant and the oxide superconductor). There's a problem.

In addition, in the dry etching method using ions, as unnecessary parts of the oxide superconducting thin film are removed, high-energy ions also collide with the sides of the pattern, so oxygen is easily removed from the structure of the oxide superconductor such as CuO. The disadvantage is that the superconducting properties of the side surfaces of the pattern deteriorate as the superconductivity is taken away by the superconducting material. Furthermore, in the ashing process for removing the resist pattern, the upper surface and side surfaces of the oxide superconducting pattern are exposed to oxygen plasma, so oxygen may be supplied excessively to structures such as CuO, or oxygen may be removed. The disadvantage is that the superconducting properties are significantly degraded.

[Problem to be Solved by the Invention 1] An object of the present invention is to provide a method for manufacturing a superconducting device that can eliminate such conventional drawbacks and avoid processing deterioration of an i-oxide superconducting thin film.

[Means for Solving the Problems j] In order to achieve the above-mentioned object, the present invention processes a substrate surface into a pattern shape in advance, and forms an oxide superconductor thin film on the convex portions of the processed surface. It is characterized by forming.

[Operation 1] In the device fabrication method of the present invention, a rough single crystal substrate is processed into a device pattern, and a high quality oxide superconducting thin film is grown on the surface of the single crystal substrate pattern to fabricate a superconducting device pattern. By doing so, a device with excellent superconducting properties can be manufactured by omitting the process of processing the oxide superconductor. Since this method does not process the oxide superconducting thin film, it is possible to prevent deterioration of the superconducting properties of the side surfaces of the pattern edges due to ion collisions. Furthermore, since no resist is applied to the superconductor surface, oxygen plasma ashing is not required when removing the resist, and superconducting properties do not deteriorate due to excess or deficiency of oxygen on the surface or side surfaces of the device pattern. Device pattern accuracy depends on the processing accuracy of the single-crystal substrate, which is achieved using normal exposure methods.

A strip line pattern produced by the method of the present invention and a strip pattern produced by the conventional method are schematically shown in FIGS. 1(A) and 1(B), respectively.

In the method of the present invention, the surface 2A of the convex part and the surface 2B of the flat part of the substrate 2 which has been processed into a pattern shape in advance (if a plurality of convex parts are provided, the surface of the concave part sandwiched between them) ) on top of the superconducting thin films IA and IB, respectively.
are formed, and the two are electrically isolated. The device used here is a superconducting thin film I on the surface of the convex part.
A, and the superconducting thin film IB on the flat or concave surface is not normally used. In the conventional method shown in FIG. 1(B), a superconducting thin film 1 formed on the surface of a substrate 2 is processed into a device pattern.

[Example 1 The present invention will be explained below by way of examples.

5rTiO whose surface is polished to a smooth (110) crystal plane
A pattern was formed on a single crystal substrate using the following method. The pattern forming method is shown in FIG.
Figure (A)). Next, a Ta thin film 5 with a thickness of 1000 nm was formed on the resist film 4 by sputtering, and a positive resist film (upper resist) 6 was further formed on top of it to form a three-layer structure (second Figure (B)). Next, the upper resist 6 was exposed to light using a mask, and the resist was developed to produce an upper resist pattern 6'. Upper resist 6
The Ta thin film 5 is exposed in the removed portion (second
Next, the exposed portion of the Ta thin film 5 was removed by etching using Ar ions to form a pattern 5' of the Ta thin film 5 (FIG. 2(D)). Furthermore, etching was performed using nitrogen ions. As a result, the upper resist pattern 6' is removed, but the Ta mask pattern 5' is hardly etched by the nitrogen ions, so the 5rTLO and single crystal of the substrate are etched after the upper resist pattern 6' and the lower resist layer 4 are removed. As a result, a 5rTiOs pattern 3' is formed (FIG. 2(E)). When the 5rTiOi is etched to a predetermined depth, the nitrogen ion etching is terminated. Finally, the remaining lower resist 4' and Ta mask 5' were removed by exposure to oxygen plasma, leaving only the 5rTiO pattern 3' (FIG. 2(F)). The fabricated pattern shape is a 4-terminal electrical resistance measurement pattern consisting of lines with a width of 5 μm, and S
The step difference in the rTi0m pattern is 5 μm.

The surface of the 5rTiOs pattern was polished to a degree of ILLm to obtain a clean (110) crystal plane, and then 30
A YBazCusOa 118 thin film with a thickness of 0.00 mm was epitaxially grown. YBatCusOs grown on the surface of a 4-terminal electrical resistance measurement pattern of 5rTiOs,
Y grown on the os thin film and the etched 5rTiOi lower surface.
There was no electrical continuity between the BaxCusOs and ms thin films. In the vapor deposition method, since the vapor deposited particles move in a straight line, it is thought that the film on the surface of the pattern and the film on the parts other than the pattern grew independently. Curve A in FIG. 3 shows the temperature dependence of the critical current density Jc of this thin film measured by the four-terminal method.

Normal (110) 5rTiO, which does not form a pattern, is coated with YBaiCu with a thickness of 3000 nm by reactive vapor deposition on a single crystal substrate.
YBatCus for 4-terminal electrical resistance measurement by forming a sOs□ thin film and using the above-mentioned three-layer structure of resist/Ta/resist together with Ar ion etching and nitrogen ion etching.
Patterns of Os and ws were prepared. Curve B in Figure 3 is 4
The temperature dependence of the critical current density J of this thin film measured by the terminal method is shown.

As is clear from comparing the characteristics of curves 1IIA and B in Figure 3, curve A does not involve the patterning process of YBazCus'Oa, is thin film, so J at liquid nitrogen temperature (77K)
c shows an excellent value of 2.5 x 10'A/cm'',
The superconducting critical temperature is also 92, YBazCusOs, ms
is the original value. On the other hand, in curve B, although no deterioration of the superconducting critical temperature is observed, Je at 77 is clearly deteriorated to 2×10'A/cm''.

This is the result of YBazCusOs using nitrogen ions.
s During thin film etching, nitrogen ions collide with the side surfaces of the pattern to remove oxygen from the oxide superconductor, and during resist ashing, YBa proverbial CuJ@. This appears to be because the superconducting properties of the pattern surface and side surfaces deteriorated due to excessive supply of oxygen into the oxide superconductor as the surface and side surfaces of the pattern were exposed to oxygen plasma.

The current introduction terminal part (2
Micro-XPS (X-
rayPhotoelectron 5pectros
The Cu2ps/2 spectrum was measured using the copy method.

The results are shown by curve A in FIG. The Cu2psz□ spectrum has a main spectrum near 933eV and a satellite spectrum around 942eV, but the area intensity ratio (satellite intensity/main intensity) is 0.33, which is clean YBazC.
This corresponds to the intensity ratio at the usOslls surface.

The current introduction terminal part (2 m
Curve B in FIG. 4 shows the Cu2pxy* spectrum of the surface of the material (mx 2 mm). Area intensity ratio (satellite intensity/
Main strength) is 0.35 and clean YBaaCusOslls
The intensity ratio is slightly larger than that at the surface, indicating that oxygen is in excess. It appears that the surface and sides of the pattern were exposed to oxygen plasma, resulting in a decrease in critical current density. In addition, the current introduction terminal part (
2! Curve C in FIG. 4 shows the Cu2psyz spectrum measured after irradiating nitrogen ions onto the sample (111×2fflIfi). The area intensity ratio (satellite/main intensity ratio) is 0
．． 12, and the half width of the main peak also decreased, indicating that oxygen was removed from the CuO structure by nitrogen ion irradiation and the superconducting properties were significantly deteriorated. Therefore, since the side surfaces of the 4-terminal electrical resistance measurement pattern fabricated using the same method as the thin film pattern with the characteristics shown in curve B in Figure 3 are exposed to nitrogen ions, the critical current density characteristics are significantly degraded. That is clear.

As is clear from the surface XPS measurement results, normal Cu
A device pattern having an O structure and having excellent superconducting properties can be manufactured using the method of the present invention.

[Advantageous Effects of the Invention 1] As explained above, oxide superconductors interact with ions and plasma and easily deteriorate their superconducting properties. Therefore, by using a substrate that has been pre-processed into the pattern of a superconducting device and simply forming a thin film on it, it is possible to create a superconducting device that, in principle, does not suffer from characteristic deterioration. . In the above-mentioned examples, the effects of the present invention on Tc and Jc were shown as superconducting properties, but R3 and magnetic field entry length, which are essential for high frequency devices,
It is easily understood that the basic properties such as 1.

In addition, in the example, YBazCusOa, 9! Only the case where a thin film was epitaxially grown on a pattern of a 5rTiOs single crystal substrate is shown. However, the deterioration mechanism of oxide superconductors due to various ions and plasmas occurs through the mechanism of removing or injecting oxygen from the oxide superconductor, so oxide superconductors with compositions in which Y is replaced with other elements It is obvious that the device manufacturing method of the present invention is also effective for superconductors such as B15rCaCuO-based oxide superconductors and B15rCaCuO-based oxide superconductors. Furthermore, since the deterioration mechanism caused by ions and plasma is the same even in thin films that are not epitaxially grown, it is obvious that the device manufacturing method of the present invention is effective. Furthermore, in addition to the 5rTiOs single crystal substrate, there are poly(YAlOm, LaGa0m, MgO, etc.) single crystals as substrates on which oxide superconductors are epitaxially grown, and the method of the present invention is limited only to 5rTiOs single crystal substrates. Also, depending on the device to be manufactured, it may not be possible to create all patterns using the method of the present invention;
It is also clear that the method of the present invention does not limit the types of devices that can be produced, as it is only necessary to produce the required portions with the best superconducting properties by the method of the present invention in combination with conventional methods.

As described above, since the device fabrication method of the present invention does not, in principle, cause deterioration of superconducting properties during the fabrication process, it is possible to fabricate various electronics and communication devices using epitaxial thin films with ideal performance. . For example, this method is particularly useful in high-frequency devices such as filters and delay circuits, where it is essential to maintain the superconducting properties of epitaxial thin films. Furthermore, even in the 5QUID element that utilizes crystal grain boundaries, the weakly coupled portions are not subject to processing deterioration, so the reproducibility and controllability of device performance are significantly improved. As a result, it will be possible to bring out the excellent superconducting properties of oxide superconductors to the maximum and provide high-performance superconducting devices, which will have immeasurable future industrial effects. be.

[Brief explanation of drawings]

Figures 1 (A) and (B) are schematic diagrams of stripline patterns produced by the method of the present invention and the conventional method, respectively. Figures 2 (A) to (F) are schematic diagrams of the substrate pattern forming method according to the present invention. FIG. 3 is a schematic diagram of the sequential steps showing examples of YBa produced by the method (A) of the present invention and the conventional method (B).
*Critical current density J of Cu5Os, os thin film. Figure 4 is a Cu2psz□ spectrum diagram measured by the xPS method. A: Measurement results for a 4-terminal electrical resistance pattern produced by the method of the present invention. B: Measurement results using a 4-terminal electrical resistance measurement pattern prepared using a conventional method. C: Measurement results after nitrogen ion irradiation was performed on the surface of the 4-terminal electrical resistance pattern produced by the method of the present invention. DESCRIPTION OF SYMBOLS 1... Oxide superconductor, 2... Substrate, 3--.5rTiOs substrate, 4... Lower resist, 5... Ta thin film, 6... Upper resist.

Claims (1)

[Claims] 1) A method for producing a superconducting device, which comprises processing the surface of a substrate in advance into a pattern, and forming an oxide superconductor thin film on the surface of the convex portions of the processed surface.