Production of oxide superconductor film and apparatus therefor

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a manufacturing method and an apparatus for producing a Bi-based oxide superconducting film, which has a uniform film thickness of a single-phase structure on the entire substrate surface and can obtain a film having a good surface morphology. ..

【0002】

[Conventional technology]

Oxidation of the vapor-deposited film is indispensable for the production of the oxide superconducting film, and the oxidation method includes a method of introducing an oxidizing gas into the chamber where the film is formed at the same time as the vapor deposition, and an oxidizing atmosphere after the vapor deposition. There is a method of annealing.

【0003】

With the laser vapor deposition method, vapor deposition is possible even when the pressure inside the chamber is around 1 Torr, so it is generally O at the same time as the vapor deposition.₂, O₃Oxidizing gas such as is introduced into the chamber to oxidize the film. As a method of introducing the oxide gas into the chamber, a method of introducing the oxide gas directly from the flange portion of the film-forming chamber to make the entire chamber into a uniform oxygen partial pressure is common. (See, for example, Applied Physics Letter. 53 (1988), P1557 ~ 1559) However, it is difficult to increase only the oxygen partial pressure near the substrate by this method, and the target surface irradiated with the laser is also oxidized. As a result, the composition shifts in the film, the evaporation particle size becomes non-uniform, the film surface physics is adversely affected, and the reproducibility is poor even under certain vapor deposition conditions. That is, in the conventional laser vapor deposition method, it is generally difficult to match the composition of the target with the film formation composition.

【0004】

[Problems to be Solved by the Invention]

An object of the present invention is that in the production of an oxide superconductor film by a laser vapor deposition method in which an oxide gas is introduced into a chamber and oxidation is performed at the same time as the film formation, the crystal structure of the vapor deposition film is a single layer and a uniform film thickness. It is an object of the present invention to provide a method and an apparatus for producing a film having a good film surface morphology.

【0005】

[Means for solving problems]

The gist of the present invention lies in the device with the following method.

【0006】

An oxide superconductor sintered material or a precursor thereof is used as a target, and a single crystal or polycrystal of an oxide of at least one of Group IIa, IIIa and IVa elements is used as a substrate material, and the substrate temperature is 550. ~ 700 ° C, oxygen partial pressure on the substrate surface is 10⁰~10^-3Under the condition of Torr, the oxide gas is parallel to the substrate surface and 0.1 to 100 cm in the direction opposite to the exhaust direction in the chamber.³A method for producing an oxide superconducting film, which comprises introducing at a flow rate of / min. And performing laser vapor deposition.

【0007】

A chamber having a laser incident window and an exhaust port is arranged in a direction substantially diagonally opposite to the exhaust port in the chamber, and the oxide gas flowing out from the opening flows in the direction opposite to the substrate surface so as to flow parallel to the substrate surface. An oxide superconductor film manufacturing apparatus characterized by having a nozzle for introducing an exhaust gas located in.

【0008】

In the above method of the present invention, the target oxide superconductor sintered material is, for example, repeated a cycle of calcining, pulverization, pressing and sintering, and has the same crystal structure and substantially the same composition as the target film formation. The precursor thereof is an amorphous material having a composition almost the same as that of a film formed by heating at a high temperature.

【0009】

The substrate material must be selected according to the type of superconductor membrane to be produced. It is an oxide of at least one element selected from Group IIa, IIIa and IVa elements (eg MgO, SrTiO).₃) Is a single crystal or a polycrystal.

【0010】

In the present invention, in order to obtain a film having a uniform film thickness and composition and a single-phase crystal structure, the substrate temperature and the oxygen partial pressure on the substrate surface are determined as described above, and the oxidation gas is applied to the substrate surface. Flow at a specific flow rate in parallel and in the direction opposite to the exhaust direction in the chamber. The above device is suitable for carrying out such a method of the present invention.

【0011】

[Action]

Hereinafter, the configuration and operation / effect of the present invention will be described in detail with reference to FIG. 1 showing an example of the apparatus of the present invention.

【0012】

(A) of FIG. 1 is a vertical sectional view, and (b) of FIG. 1 is AA of (a).^,It is a cross-sectional view taken along the arrow. 1 is a film forming chamber, 2 is an introduction gas, 3 is a gas nozzle, 4 is a substrate, 5 is a target, 6 is a laser beam, 7 is a laser incident window, 8 is a chamber exhaust port, and 9 is a flange. As shown in the figure, the mouth of the gas nozzle 3 is located substantially diagonally opposite to the chamber exhaust port 8, and the mouth of the gas nozzle is parallel to the substrate surface and the gas introduction direction is opposite to the substrate surface. It is arranged.

【0013】

The laser beam 6 incident from the outside of the film-forming chamber irradiates the target 5 located at the substantially central portion in the chamber, and the elements evaporated from the target 5 are formed on the substrate surface. At the same time, O_2,O₃Oxidizing gas is introduced from the gas nozzle and becomes a parallel gas flow as if stroking the substrate surface, and is discharged from the chamber exhaust port located substantially diagonally to the gas nozzle.

【0014】

When the oxidation gas is introduced from the flange of the chamber (9 in Fig. 1) at the time of film formation as in the past to increase the oxygen partial pressure in the chamber, the effect of oxidation of the target cannot be ignored, and the evaporated particle component. The composition of the particles shifts, and the instability of the evaporation rate is induced, which makes it difficult to control the film thickness.

【0015】

As will be described later, as a gas introduction method, an attempt was made to install a gas nozzle port near the substrate, blow oxidation gas onto the substrate surface to reduce the oxidation of the target, and increase the oxygen partial pressure on the substrate surface. However, it was found that the surface morphology of the film was deteriorated by the influence of the sprayed gas. Further, non-uniformity was generated in the evaporation component on the substrate surface, and the crystallinity of the film was also deteriorated.

【0016】

In the present invention, in order to reduce the influence of target oxidation and increase the oxygen partial pressure near the substrate, the mouth of the gas nozzle is provided at a position in the chamber away from the target. When the oxide gas introduced by the gas nozzle is blown onto the substrate surface with the mouth of the gas nozzle facing the substrate surface, the evaporated particles from the target are unevenly deposited on the substrate surface, so that the oxide gas flow rate direction is set to the substrate surface. On the other hand, the nozzle openings are directed upward so that they are parallel to each other to reduce the influence of the blown gas. In addition, the direction of the introduced gas flow is closely related to the positions of the gas nozzle port and the chamber exhaust port, and when the gas nozzle port is directed toward the exhaust direction, the partial pressure of the oxide gas on the substrate surface becomes non-uniform. Become.

【0017】

Therefore, in the present invention, the gas inlet is arranged so that the direction of the gas flow is parallel to the substrate surface. In this way, it is possible to prevent the evaporation particles and the gas particles from colliding with each other on the substrate, or the accumulated particles already formed on the substrate from being removed by the blowing gas, which is very efficient. A film is formed.

【0018】

In the present invention, a single crystal or polycrystal composed of oxides of at least one of Group IIa, IIIa, and IVa elements is used as the substrate. The reason for this is that the difference in lattice constant from the obtained oxide superconductor is relatively small and the crystallinity of the film formation is high. The temperature of the substrate shall be 550 to 700 ° C. The reason is that when the temperature is lower than 550 ° C, the vapor-deposited film becomes amorphous and loses superconductivity, and when the temperature exceeds 700 ° C, the superconducting phase becomes formed due to the precipitation of Ca or Cu oxides. This is because it is not formed. If the flow rate of the oxidizing gas is excessively excessive, the effect of oxidation of the target cannot be ignored. Therefore, in the present invention, the flow rate of the oxidizing gas is 0.1 to 100 cm.³Limited to / min. 0.1 m³If the gas flow rate is less than / min., The obtained film is not sufficiently oxidized, so that the composition of the superconductor is difficult to obtain. On the other hand, 100 cm³If the gas flow rate exceeds / min., The effect of collision with the evaporated particles from the target cannot be ignored, and a vapor-deposited film having a uniform composition and a uniform film thickness cannot be obtained.

【0019】

[Example]

Br with a high critical temperature (Tc 110 K) in the Bi-based oxide superconducting phase₂Sr₂Ca₂Cu₃O_XA thin film film formation experiment was conducted.

【0020】

As the conditions for film formation, the substrate temperature is 650 ° C and the oxygen partial pressure is 2 × 10.^-2Torr, laser energy 1.5J / cm²Therefore, a sintered material having a charged composition ratio of Br: Sr: Ca: Cu = 2: 2: 2: 3 was used as the target material. As a method of forming a film of the present invention, as shown in FIG. 1, a gas nozzle is provided parallel to the substrate surface, and the port is directed to the opposite side located substantially diagonally to the chamber exhaust port. As a comparative example, one in which the oxide gas is introduced from the flange portion without providing the gas nozzle in the film forming chamber, and the other in which the gas nozzle is provided in the film forming chamber and the gas nozzle port is brought close to the substrate and the oxide gas is blown onto the substrate surface. The vapor deposition was carried out by the above-mentioned apparatus. As an oxidation gas, O₂The gas flow rate is 5 cm.³It was set to / min. The film formation time was 20 minutes in each case.

【0021】

Table 1 shows the ICP analysis results of the target composition and the film formation composition.

【0022】

[table 1]

<img file="JPH0543390A_D0001.tif" />【0023】

The analysis was performed by ICP spectroscopic analysis, and the values in Table 1 show the composition ratio of the entire membrane. The film formation composition in the comparative example has a large deviation from the target composition, but the composition deviation in the example of the present invention is small.

【0024】

FIG. 2 shows the measurement results of the surface morphology of the film formation obtained by observing the smoothness of the sample films of Examples 2, 4 and 7 in Table 1 with a profilometer. (A) is an example of Example 2 and (B) is an example. 4, (C) is the result of Example 7. In Examples 2 and 4, a large number of irregularities were observed and the film thickness distribution was disturbed, but in the sample film of Example 7, the uniformity of the film thickness was extremely good. When these sample films were examined by SEM images, in Examples 2 and 4, particles having a composition shift were considerably adhered, but in Example 7, the particles were extremely smooth.

【0025】

FIG. 3 shows the observation results of the crystal phase from the sample film X-ray diffraction patterns of Example 2, Example 4, and Example 7 in Table 1. (A) is the result of Example 2, (B) is the result of Example 4, and (C) is the result of Example 7. S, L, and H in Fig. 4 are Bi, respectively.₂Sr₂Cu₁O_X, Bi₂Sr₂Ca₁Cu₂O_X'(Low Tc phase), Bi₂Sr₂Ca₂Cu₃O_X' It is a diffraction spectrum of (high Tc phase). In Example 2 and Example 4, the target Br₂Sr₂Ca₂Cu₃O_X'Not only (high Tc phase) but also other phases are mixed, and an unidentifiable unknown phase () is also generated. But in Example 7, Br₂Sr₂Ca₂Cu₃O_X'No diffraction spectrum other than (high Tc phase) is found, and it can be seen that the film is a high Tc phase monophasic film.

【0026】

[Effect of the invention]

As shown in the examples, according to the method of the present invention, it is possible to obtain a film of a superconducting oxide having a single-phase crystal structure having a uniform film thickness and composition.

[Simple explanation of drawings]

[Figure 1]

It is a schematic cross-sectional view from the front surface and the top surface of the film formation chamber for forming the superconducting oxide of the present invention.

[Figure 2]

This is the measurement result of the surface morphology of the film formation obtained by observing the smoothness of the sample film with a profilometer.

[Fig. 3]

It is the observation result of the crystal phase from the sample film X-ray diffraction pattern.