JP2716138B2 - Method and apparatus for forming composite oxide superconducting thin film by facing target type sputtering method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus capable of forming a complex oxide superconducting thin film on a substrate as-depo by a facing target type sputtering method.

(Related Art) In recent years, remarkable research and development of superconducting thin films have been observed, and various superconducting materials have been searched for by methods such as vacuum evaporation, sputtering, CVD, and screen printing.

In particular, research on materials for high-temperature superconducting thin films has been remarkable, for example,
The Y-Ba-Cu-O-based superconductor (YBCO) is a substance having a critical temperature of 90K or more, and its practical application is expected to be hotter than in the fields of both weak electricity and strong electricity.

Also, very recently, it has been reported that the critical temperature of a Bi-based Bi-Sr-Ca-O-based superconductor reaches 120K.

In sputtering, which is one of the typical methods of forming a thin film, intensive research has been conducted toward the practical use of a sputtering apparatus together with the search for a superconductor material.

For example, as a sputtering apparatus, as proposed in Japanese Patent Application Laid-Open No. 57-158300, there is a facing target type sputtering apparatus, which widens and uniforms a target surface to be sputtered to improve the use efficiency of the target. In addition, a compact and inexpensive device that can improve the cooling efficiency of the target to form a thin film at a low temperature and at a high speed and that does not require an external coil has been developed.

(Problems to be Solved by the Invention) However, according to the facing target type sputtering apparatus, although the composition deviation between the target material and the thin film is reduced, there is a problem of reactivity with the ceramic substrate, and At least 600 ° C to obtain a superconducting thin film at −depo.
There are also problems such as the need for a high substrate temperature as described above and the need for annealing.

The present invention has been made in order to solve the problem when forming a composite oxide superconducting thin film by the facing target type sputtering method, and has a small composition deviation from a target material and a low reactivity with a substrate. It is an object of the present invention to provide a method and an apparatus capable of obtaining a composite oxide superconducting thin film having a small and excellent uniformity by a simple process.

(Means for Solving the Problems) In order to achieve the above object, the present inventors assume that the facing target type sputtering apparatus according to the above proposal is used, and as-depo. has good c-axis oriented, superposed high Tc, Jc, intensive research to find a method capable of forming a low substrate temperature as possible a complex oxide superconducting thin film showing the Hc _2.

First, focusing on the fact that substrate materials were limited to ceramics such as SrTiO ₃ , MgO, and YSZ, Si, SiO ₂
An attempt was made to use a silica-based substrate such as As a result, by using thermally oxidized Si as a substrate,
It was found that a thin film having excellent surface smoothness with almost no composition deviation from the target material could be obtained at a substrate temperature of 500 ° C. However, all the obtained thin films were insulators.

Therefore, we consider that this is because oxygen is not effectively taken into the film, and considering that oxygen escapes from the film even at a substrate temperature of 100 ° C in a vacuum, as a result, In order to prevent dissociation of oxygen, a process for introducing oxygen at the time of cooling the substrate has been established here.

That is, in short, the method according to the present invention uses a composite oxide as a target and a semiconductor substrate as a substrate when forming a composite oxide superconducting thin film on a substrate by a facing target type sputtering method. By introducing oxygen during substrate cooling,
The present invention is characterized in that a superconducting thin film is obtained as it is, and that the obtained thin film is annealed to improve superconductivity as necessary.

Further, according to the present invention, a pair of targets serving as cathodes are provided so that the surfaces to be sputtered face each other in parallel with a space therebetween, and a magnetic field generating means for generating a magnetic field in a direction perpendicular to the surface to be sputtered is provided. In a facing target type sputtering apparatus provided with a configuration in which a thin film is formed by sputtering on a substrate disposed so as to face the space on the side of the space between the targets, the magnetic field generating means is generated only between the targets. A means for introducing oxygen at the time of cooling the substrate after film formation by sputtering is provided, and a composite oxide is used as a target material,
A semiconductor substrate is used as the substrate.

 Hereinafter, the present invention will be described in more detail.

(Operation) FIG. 1 is a view schematically showing a facing target type sputtering apparatus of the present invention.

First, a pair of targets T ₁ and T ₂ are arranged in the vacuum chamber 1 so that the surfaces on which the pair of targets T ₁ and T ₂ are sputtered are parallel to each other with a space therebetween. The target holders 2 and 3 have a hollow structure and are attached to the vacuum chamber 1 via an insulating member.
The cooling water can be cooled by the supply pipes 4a and 5a and the discharge pipes 4b and 5b.

On the other hand, the substrate 6 is arranged on the side of the space between the targets by the substrate holder 7 provided on the side of both targets so as to face the space. This substrate holder is substrate 6
Is provided with a heater 8 so that the substrate temperature can be adjusted.

The magnetic field generating means sets the permanent magnets 11 and 12 so that the magnetic fields formed by the magnetic poles in the target holder behind each target are all in the same direction perpendicular to the sputtering surface of the target, and It is located in the periphery of. Therefore, the magnetic field is formed only in the space between the targets.

9 is an exhaust port connected to the exhaust system, and 10 is an inlet connected to the sputtering gas introduction system. The introduction port 10 is also connected to an oxygen introduction system, and can switch between a sputtering gas introduction system and an oxygen introduction system.

FIG. 2 is a view for explaining the principle of the facing target type sputtering method of the present invention. A magnetic field is applied perpendicularly to the two targets with the two targets facing each other. Sputtering is performed by supplying sputter power from the sputter power supply to the shield ring and the target. Most of the γ-electrons and negative ions emitted from the target are confined in the space between both targets due to the E × B drift, so that plasma is formed in the space between both targets. Therefore, since the substrate is not exposed to the plasma,
It is possible to form a film without high energy particles colliding with the substrate.

As a result, a thin film having excellent surface smoothness and having almost no composition deviation can be obtained at a lower substrate temperature as compared with other sputtering methods.

Moreover, in the present invention, a composite oxide is used as a target, and a semiconductor substrate (eg, surface thermally oxidized Si) is used as a substrate, but the obtained thin film has no problem of interdiffusion between atoms in the film and substrate atoms. .

As the target material, various composite oxides and compositions exhibiting superconductivity can be used. For example, Y
In the case of -Ba-Cu-O system, Y: Ba: Cu = 1: 2: 3, Bi-Sr-Ca-
In the case of Cu-O system, Bi: Sr; Ca: Cu = 1: 2: 3: 4, 1: 1: 1: 1, 1:
Those having a composition ratio such as 1: 1: 2 can be mentioned.

FIG. 3 shows an example of a process for forming a composite oxide superconducting thin film by the opposed target type sputtering method of the present invention. In the sputtering apparatus shown in FIG. 1, after evacuation of the vacuum chamber, a predetermined substrate temperature was set. And a sputtering gas (eg, Ar
After introducing + O ₂ ), pre-sputtering is performed for a predetermined time, and then main sputtering is performed. Then, introduction of sputter gas is stopped, the substrate is cooled while introducing oxygen gas, and the sample is taken out after baking. The sputtering conditions are not particularly limited.

(Example) Next, an example of the present invention will be described.

Example 1 In the facing target type sputtering apparatus shown in FIG. 1, a target having a composition ratio of Y: Ba: Cu = 1: 2: 3 was used, and a surface thermally oxidized Si was used as a substrate. A Y ₁ Ba ₂ Cu ₃ O _7-δ superconducting thin film was formed by the process shown in FIG.

FIG. 4 shows the change of the c-plane orientation index f _00l in the obtained thin film with respect to the substrate temperature (Ts). When the c-plane orientation index is 1, it is completely c-plane orientation, and when it is 0, it is random orientation. Therefore, as shown in FIG. You can see that it is. In a magnetron sputtering method or the like, a substrate temperature Ts of 600 ° C. or more is required to obtain a c-plane oriented film even when a ceramic substrate that can be expected to grow epitaxially is used. In view of this, the decrease in the substrate temperature Ts is due to the fact that the energetic particles collide with the substrate much less than the other methods.

FIG. 5 shows the dependence of the film composition on the substrate temperature (Ts), and it can be seen that the composition deviation is very small as compared with other sputtering methods.

FIG. 6 shows the relationship between the oxygen introduction pressure and the c-axis length. It is apparent that the c-axis is reduced by introducing oxygen, and the oxygen amount in the film and the c-axis length are negatively correlated. Shows that oxygen is effectively taken into the film by oxygen introduction. In fact, the oxygen-introduced film exhibited a drastic decrease in resistivity at room temperature, and showed a value of several to several tens mΩ · cm. Incidentally, the oxygen introduction pressure is suitably from 1 to 100 × 10 ⁻⁶ Torr.

Note that the magnitude of the c-axis length also depends on the substrate cooling rate, and as shown in FIG. 7, it can be seen that the c-axis becomes shorter as the substrate cooling rate increases.

As described above, by introducing oxygen at the time of cooling the substrate, the obtained thin film has a short c-axis, can prevent a decrease in the amount of oxygen in the film, and exhibits superconductivity.

FIG. 8 shows the temperature change of the resistivity of the obtained thin film. The film composition is Y: Ba: Cu = 1: 2.19: 3.05, Tc (onset) = 70K, Tc (zero) = 32K and ΔTc = 38K were shown.

FIG. 9 shows the Auger profile in the depth direction of the film, and it is apparent that no interdiffusion between atoms in the film and Si of the substrate has occurred.

Example 2 The superconducting thin film obtained in Example 1 was annealed at various temperatures. Annealing is performed in an oxygen atmosphere of 1 atm at 500 ° C to 900 ° C for 1 hour, and then at 400 ° C for 4 hours.
Hold for hours.

FIG. 10 shows the dependence of the c-axis length on the annealing temperature (Ta), and the c-axis length increases as the annealing temperature increases. Each annealing temperature (500 ℃, 600 ℃, 700 ℃, 800 ℃,
The temperature change of the resistivity of the film at 900 ° C,
As shown in the figure, at Ta = 500 ° C., the Tc is higher than that of the as-depo. Film, but the superconductivity deteriorates as the annealing temperature rises. At Ta = 900 ° C., the resistance at room temperature is 10 MΩ or more. Yes, it became an insulator.

As described above, the reason why Tc was improved at Ta = 500 ° C. is considered to be that the film took in oxygen by annealing, and the superconductivity of the film can be improved by performing an appropriate annealing treatment. However, an excessive increase in the annealing temperature promotes the reaction between the film and the substrate and deteriorates the superconductivity.

In the above embodiment, an example of a YBCO superconducting thin film is shown, but a thin film of another composite oxide having superconductivity can be similarly formed.

(Effects of the Invention) As described in detail above, according to the present invention, the composite oxide superconductivity having a small composition deviation from the target material, little reactivity with the substrate, excellent uniformity, and excellent surface smoothness. A thin film can be obtained as-depo. In addition, superconductivity can be further improved by performing appropriate annealing after sputtering. It is particularly effective for forming a high-temperature superconducting thin film.

Further, a complicated power supply device or the like is not required for the sputtering device for that purpose, and the reliability of the entire device is improved and the device is inexpensive.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a facing target type sputtering apparatus according to the present invention, FIG. 2 is an explanatory view showing the principle of the facing target type sputtering method according to the present invention, and FIG. 3 is a composite oxide superconducting thin film according to the present invention. FIG. 4 is a diagram showing the substrate temperature dependence of the c-plane orientation index, FIG. 5 is a diagram showing the substrate temperature dependence of the film composition, and FIG. 6 is an oxygen introduction pressure of the c-axis length. FIG. 7 is a diagram showing the dependence of the c-axis length on the substrate cooling rate, FIG. 8 is a diagram showing the temperature change of the resistivity of the film at as-depo. FIG. FIG. 10 shows the Auger profile in the depth direction. FIG. 10 shows the dependence of the c-axis length on the annealing temperature. FIGS. 11 to 14 show the temperature change of the resistivity of the film at different annealing temperatures. It is. 1 ... Vacuum chamber, 2, 3 ... Target holder, 4a, 5a
... cooling water supply pipe, 4b, 5b ... cooling water discharge pipe, 6 ... substrate, 7 ... substrate holder, 8 ... heater, 9 ... exhaust port, 10 ... sputter gas, oxygen introduction port, 11 , 12… permanent magnet, 13, 14… shield ring, T ₁ , T ₂ … target.

Claims (4)

(57) [Claims] 1. A composite oxide superconducting thin film is formed on a substrate by a facing target sputtering method in which a pair of targets serving as cathodes are provided so that their surfaces to be sputtered face each other in parallel with a space therebetween. Using a composite oxide and a semiconductor substrate as the substrate, a magnetic field in a direction perpendicular to the surface to be sputtered by the magnetic field generating means is generated only in the space between the opposing targets, and the substrate is formed in the space between the opposing targets. Is characterized by obtaining a superconducting thin film by introducing oxygen at the time of cooling the substrate after the film is formed by sputtering, and is disposed at a position distant from the space between the targets at the side and orthogonally facing this space. Of forming a composite oxide superconducting thin film by facing target type sputtering method. 2. The composite oxide as a target is Y-Ba-
The method for forming a composite oxide superconducting thin film according to claim 1, wherein the substrate is a Cu-O-based composite oxide and the substrate is a thermally oxidized Si substrate. 3. A method for forming a composite oxide superconducting thin film, wherein the thin film obtained by the method according to claim 1 is annealed. 4. A pair of targets serving as cathodes are provided so that their sputtered surfaces face in parallel with a space therebetween, and a magnetic field generating means for generating a magnetic field in a direction perpendicular to the sputtered surfaces of the targets is provided. In a facing target type sputtering apparatus having a configuration in which a thin film is formed by sputtering on a substrate disposed so as to be orthogonal to this space on the side thereof away from the space between the facing targets, and the magnetic field generating means, Along with disposing so as to generate a magnetic field only in the space between the opposing targets, a means for introducing oxygen during substrate cooling after film formation by sputtering is provided,
A facing target type sputtering apparatus for forming a composite oxide superconducting thin film, wherein a composite oxide is used as a target material and a semiconductor substrate is used as a substrate.