JPH065940A - Superconductor thin-film board - Google Patents

Abstract

PURPOSE:To lessen the influence of scattered light by a board incident from the rear of a photoresist film, by using a composite layer board for suppressing scattered ultraviolet light from a transparent board for resist exposing. CONSTITUTION:A Bi2Sv2CuOx normal conductor layer 2 and a Bi2Sr2Cu2Ox superconductor 3 are deposited on a plane (100) MgO board 1 by halide CVD, for example. And plane (001) MgO has a lattice constant approximate to those of the normal conductor layer 2 and a superconductor thin-film 3. And the Bi2Sr2CuOx normal conductor layer 2 absorbs ultraviolet rays emitted from the openings of a glass mask 5 effectively, in case of the patterning of a photoresist film 4. Accordingly, it becomes possible to make the patterning precision higher, improve the performance of the superconducting element, and increase reproducibility, since the light-absorbing oxide normal conductor layer 2 absorbs scattered light too which has come back after being reflected by the rear of the MgO single crystal board 1 in groove 6 regions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconductor thin film substrate, and more particularly to a superconductor thin film substrate having an oxide high temperature superconductor thin film formed thereon.

[0002] In recent years, the high temperature oxide superconductors that have been discovered one after another have attracted attention for their practicality because their critical temperature is liquid nitrogen temperature (77K) or higher. These are Y by material
It was clarified that the Cu-O surface contained in each of the groups was roughly divided into the group of Bi-based, Bi-based, and Tl-based, and had a superconducting property.

When these high-temperature oxide superconductors are applied to devices in the field of electronics such as superconducting wirings, Josephson devices, superconducting transistors, SQUIDs, etc., grain boundary noise is suppressed, the current density is increased, and Superconductors are used in the form of thin films in order to perform precise shape processing and connect with peripheral electronic circuits.

[0004]

2. Description of the Related Art The higher the crystallographic quality of a superconductor thin film deposited on a substrate is, the more excellent the superconducting properties are, for example, the critical temperature Tc and the critical current density. Properties such as flatness and etching characteristics are improved.

Therefore, it is usually deposited with a C-axis orientation on a specific surface of the oxide single crystal substrate, for example, the (001) surface. Most preferred is an epitaxial growth film, but C
Highly practical superconducting properties can be obtained even with axially oriented polycrystals.
The C-axis oriented superconductor thin film is patterned by using a normal photolithography technique when the device is processed.

By the way, the substrate for depositing the superconductor thin film is usually MgO, Al ₂ O ₃ or SrTiO 3.
₃ single crystal substrates are used. In some cases, MgO grown on a substrate made of another material may be used. These substrate crystals generally have a wide band gap and are transparent from the visible region to the ultraviolet region of a considerably short wavelength.

The selective etching of the superconductor thin film using the patterned photoresist film as a mask is performed by dry etching using Ar ion beam, wet etching using hot phosphoric acid, or the like.

[0008]

As mentioned above, the use of "transparent" oxides in substrate crystals for superconducting thin film deposition is due to the fact that these materials are chemically stable at high temperatures.
This is because the lattice constant is relatively close to that of a superconductor, and a large-sized high quality single crystal can be obtained.

However, if a superconductor thin film is deposited on the substrate by, for example, the CVD method, and a photoresist film is applied on the thin film and patterned by ultraviolet (UV) light, the substrate is "transparent". Occurs.

FIG. 2 is a diagram for explaining this problem. In FIG. 2, an oxide single crystal substrate 11, for example, a MgO substrate having a (001) plane, is formed on the superconductor thin film 12 by a CVD method, for example, Bi-Sr-Ca-Cu having a thickness of 0.05 to 0.4 μm. -O-based oxide thin film is deposited.

On top of that, a positive type photoresist film 1
Glass mask 15 coated with 4 to form a metal pattern
Selectively expose by overlapping. The ultraviolet rays for resist exposure differ depending on the fineness of the pattern, but the g-line (4
36 nm) or i-line (365 nm) is often used. Eximer laser light (248 nm light for KrF or 193 nm light for ArF) is used for line width processing of 0.3 μm or less.
Is sometimes used.

However, the band gap of the oxide single crystal as the substrate is 10 eV or more, and it is "transparent" to the ultraviolet rays for resist exposure. As a result, the ultraviolet light transmitted through the opening of the glass mask 5 and exposed to the photoresist film is
It partially penetrates the "thin" superconductor thin film 12.

Then, the light is reflected by the surface of the oxide single crystal substrate 11 to become scattered light, which passes through the superconductor thin film 12 and is exposed from the back surface of the photoresist film 14. In particular, the light that once enters the oxide single crystal substrate 11, is reflected on the back surface and returns, has a pattern considerably different from that of the mask opening. For this reason, the patterning accuracy of the photoresist film 14 is significantly reduced, and it becomes difficult to perform sub-micron fine processing.

As the superconducting element becomes finer and has higher functionality, it is necessary to increase the aspect ratio and increase the number of layers. Therefore, the superconductor thin film 12 needs to be thin. As a result, after passing through the superconductor thin film 12, the amount of scattered light that reflects and exposes the photoresist film 14 from the back surface is further increased, and the adverse effect is further spread.

An object of the present invention is to provide a technique for reducing the influence of substrate scattered light incident from the back surface of the photoresist film at the time of selective exposure of the photoresist mask for device processing of the superconductor thin film.

[0016]

According to the present invention, a composite layer substrate is used to suppress scattered light of ultraviolet rays for resist exposure from a transparent substrate.

That is, the superconductor thin film substrate of the present invention is
An oxide single crystal substrate having a predetermined plane orientation and transparent to an exposure wavelength, a light absorbing oxide normal conductor layer deposited on the substrate and opaque to the exposure wavelength, and the light absorbing oxide. And a superconductor thin film deposited on the normal conductor layer.

[0018]

[Function] The light-absorbing oxide normal conductor layer exists between the superconducting thin film and the "transparent" oxide single crystal substrate for resist exposure ultraviolet light, and penetrates the photoresist film and the superconducting thin film. It effectively absorbs the ultraviolet light. Therefore, in this path, the ultraviolet light incident on the oxide single crystal substrate is attenuated, and the generated scattered light is further attenuated.

On the other hand, after depositing the superconductor thin film, the first patterning is performed for element isolation, and the superconductor thin film and the light absorbing oxide normal conductor layer are selectively removed to form a groove. The surface of the oxide single crystal substrate is exposed in the groove region. In this case, when the second patterning is performed for processing each element, the ultraviolet light for exposure penetrates into the oxide single crystal substrate from the exposed portion, and the scattered light is generated.

However, since the light-absorbing normal conductor layer is arranged in each element region, the scattered light enters from the lower surface of the normal conductor layer and is absorbed. Therefore, also in this case, scattered light is attenuated before reaching the lower surface of the photoresist film.

The present invention will be described in more detail below based on examples.

[0022]

EXAMPLE FIG. 1 is a sectional view showing a state in which a photoresist film is patterned in order to process an element on a superconductor thin film substrate on which a superconductor thin film is deposited.

In the figure, 1 is Mg having a plane orientation (001).
An oxide single crystal substrate made of O is formed by CVD on the substrate 2.
A light-absorbing oxide normal conductor layer made of a deposited Bi ₂ Sr ₂ CuO _x layer having a thickness of 0.4 μm and a Bi ₂ Sr ₂ CaCu layer having a thickness of 0.1 μm deposited by CVD on the normal conductor layer.
₂ shows a superconductor thin film composed of a ₂ O _x layer.

Reference numeral 4 denotes a positive photoresist film coated on the superconductor thin film 3, and reference numeral 5 denotes a patterning glass mask which is closely adhered to the photoresist film.
Further, 6 is a groove provided for element isolation.
The depth reaches the surface of the oxide single crystal substrate.

Bi ₂ Sr ₂ CuO _x as shown in FIG.
The normal conductor layer 2 and the Bi ₂ Sr ₂ Cu ₂ O _x superconductor thin film 3 can be continuously deposited on the (100) MgO substrate 1 by using, for example, a halide-based CVD method.

The halide source material is BiCl ₃ --Sr.
I-CaI-CuBr, each of which is temperature-controlled independently in the source chamber and is transported to the substrate region using He as a carrier gas. Oxygen and moisture are transported to the substrate region in the reaction tube through another inlet, join with the halide source gas and react with each other to continuously deposit the normal conductor layer 2 and the superconductor thin film 3 on the substrate. . Growth temperature 810
At 830 ° C., a C-axis oriented polycrystalline layer having a grain size of 40 to 100 μm is obtained on the (001) MgO substrate 1 with a smooth growth surface.

The (001) plane MgO has a lattice constant similar to that of the normal conductor layer 2 and the superconductor thin film 3 described above. The Bi ₂ Sr ₂ CuO _x normal conductor layer 2 effectively absorbs the ultraviolet light emitted from the opening of the glass mask 5 when the photoresist film 4 is patterned. The light-absorbing oxide normal conductor layer 2 is reflected not only by the ultraviolet light penetrating from the upper surface through the photoresist film 4 but also by being reflected by the back surface of the MgO single crystal substrate 1 in the groove region and returns. It also has the function of absorbing scattered light.

In the embodiment described above, the Bi-based normal conductor layer 2 is used.
The superconductor layer 3 and the superconductor layer 3 are deposited on the MgO substrate 1 by the halide CVD method, but can be deposited on the oxide single crystal substrate 1 having a slightly different lattice constant, for example, sapphire.

In this case, it is desirable to use the plasma CVD method for the purpose of lowering the substrate temperature and reducing the thermal strain. The oxidizing component (O ₂ + H ₂ O) gas is caused to flow between the electrodes and plasma excitation is performed to promote the deposition.

In addition to the combination of the Bi-based normal conductors described above, other examples of Bi-based compounds include Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x as a superconductor and Bi as a light-absorbing oxide normal conductor. 0.5 to 1 wt% of ₂ Sr ₂ Ca ₇ Cu ₈ O _x and metal component M (M = Nb, Zr or Ta)
It is also possible to use M-SrTiO ₃ , which is SrTiO ₃ contained in%, CuO, Cu ₂ O or the like.

In addition, a combination of a Y-type normal conductor and a superconductor
For example, as a superconductor, YBa₂Cu₃O_xOr
YBa₂Cu_FourO_x, Pr as a light-absorbing oxide normal conductor
Ba ₂Cu₃O_xAnd M-SrTiO described above₃, Cu
O, Cu₂O or the like can be used.

The above-mentioned composite substrate of the translucent single crystal substrate and the light-absorbing oxide normal conductor layer can be utilized not only for absorbing scattered light but also for forming a current-carrying element in the stacking direction using a superconductor thin film.

For example, as shown in FIG. 3, there is a method of using a normal conductor layer as a current-carrying path to an electrode. In FIG. 3, a light-absorbing oxide normal conductor layer 2 is formed on an oxide single crystal substrate 1, and a superconductor thin film 3A, a normal conductor thin film 7, and a superconductor thin film 3B are deposited thereon. An SNS type Josephson element is formed. A normal conductor electrode 8 is formed on the superconductor thin film 3B.

The oxide single crystal substrate 1, the light-absorbing oxide normal conductor layer 2, and the superconductor thin film 3 are made of the same materials as those in the above-mentioned embodiments. In order to pass a current in the vertical direction to the SNS type Josephson element, the normal conductor thin film 7 is replaced by the superconductor thin films 3A, 3A, 3
The configuration sandwiched between B is adopted. The light-absorbing oxide normal conductor layer 2 also functions as a lower electrode.

The translucent oxide single crystal substrate 1 is made of, for example, SrTiO 3 in addition to the above-mentioned MgO and sapphire.
₃ may be used. Although the present invention has been described above with reference to the embodiments, the present invention is not limited thereto. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0036]

As described above, according to the present invention,
In the photolithography process for converting the superconductor thin film deposited on the substrate into a device, the patterning accuracy can be improved. As a result, it is possible to improve the performance and reproducibility of the superconducting device.

[Brief description of drawings]

FIG. 1 is a sectional view showing a photolithography process using a superconductor thin film substrate according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a photolithography process using a conventional superconductor thin film substrate.

FIG. 3 is a diagram showing an application example of the substrate of the present invention.

[Explanation of symbols]

1 Oxide Single Crystal Substrate 2 Absorbing Oxide Normal Conductor Layer 3 Superconductor Thin Film 4 Positive Photoresist Film 5 Glass Mask 6 Groove 11 MgO Single Crystal Substrate 12 (Bi-Sr-Ca-Cu-O System) Oxide Superconductor thin film 14 Positive photoresist film 15 Glass mask

Claims (3)

[Claims] 1. An oxide single crystal substrate (1) having a predetermined plane orientation and transparent to an exposure wavelength, and a light absorbing oxide deposited on the substrate (1) and opaque to the exposure wavelength. A superconductor thin film substrate comprising a material normal conductor layer (2) and a superconductor thin film (3) deposited on the light absorbing oxide normal conductor layer (2). 2. The oxide single crystal substrate (1) is Mg
The superconductor thin film substrate according to claim 1, which is formed of O, Al ₂ O ₃ or SrTiO ₃ , and the superconductor thin film (3) is formed of a Bi-based or Y-based superconductor. 3. The light absorbing oxide normal conductor layer (2) comprises:
For Bi-based superconductors, M-SrTiO ₃ (however,
M is Nb, Zr or Ta, SrTiO ₃ M-SrTiO ₃ is containing these 0.5~1wt%), C
uO, Cu ₂ O, Bi ₂ Sr ₂ CuO _x and Bi ₂ S
One or more materials from the group consisting of r ₂ Ca ₇ Cu ₈ O _x, M-SrTiO ₃ for Y-based superconductors (where M is Nb, Zr or Ta, and M-SrTiO 3
₃ is SrTi containing 0.5 to 1 wt% of these
The superconductor thin film substrate according to claim 2, which is made of one material selected from the group consisting of O ₃ ), CuO, Cu ₂ O, and PrBa ₂ Cu ₃ O _x .