JPS63247362A - Sputtering target - Google Patents

Abstract

PURPOSE:To obtain a sputtering target particularly suitable for manufacturing a thin-film compound superconductor by means of sputtering vapor deposition, by providing a composition composed principally of one or more kinds among Sc-, Y- and La-series elements, one or more kinds among group-IIa elements, Cu, and O in the prescribed mol.% ratio. CONSTITUTION:The sputtering target of this invention has the principal components represented by (A1-xBx)2CuO4-delta. At this time, A and B mean one or more kinds among Sc-, Y, and La-series elements (atomic number 57-71) and one or more kinds among group-IIa elements, respectively, and the symbols (delta) and (x) stand for 0-4 and 0-1, respectively. A thin-film superconductor formed by using the above-mentioned target is reduced in thickness, and the thin film is prepared by depositing a superconductor material on a substrate after decomposing the material into an atomic state of submicron particles. Accordingly, the composition of the resulting superconductor is essentially homogeneous as compared with that of the conventional sintered compact, and a superconductor having extremely high accuracy can be manufactured by using the target of this invention.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a sputtering target used in the production of superconductors. In particular, it relates to sputtering targets used for producing compound thin film superconductors by sputter deposition.

Conventional technology Niobium nitride (NbN) and germanium niobium (NbsGe) are used as A15 type binary compounds as high-temperature superconductors.
were known, but the superconducting transition temperature of these materials was at most 24°. On the other hand, perovskite-based ternary compounds are expected to have even higher transition temperatures, and Ba-
A La-Cu-0-based high-temperature superconductor was proposed [J,
G. Bend.

rz and K, A, Muller, Zetshrift Fairphysik
f Q rphysik B)-Condensed
Matter 64.189-193 (1986)
].

Although the details of the superconducting mechanism of this type of material are not clear,
The transition temperature may be higher than the liquid nitrogen temperature.
However, Ba-
La-Cu-0-based materials can only be formed through the process of sintering with current technology, so they can only be obtained in the form of ceramic powder or blocks. On the other hand, when this type of material is to be put to practical use, there is a strong demand for processing it into a thin film, but it is considered extremely difficult to form a thin film using conventional techniques.

The present inventors have discovered that when a thin film of this kind of material is deposited by an ion process, a thin film-like high-temperature superconductor is formed, and based on this, a suitable method for manufacturing a thin film superconductor has been found. The purpose is to provide sputtering targets.

Means for Solving the Problems The sputtering target of the present invention is characterized in that its main components are (Ari-, Bo)gcut-a. Here, A represents at least one of Sc, Y, and lanthanum series elements (atomic numbers 57 to 71), and B represents at least one or two or more of the group ■a elements. δ is O ≦δ≦4, and X is 0≦x≦1
It is.

Function The basic structure of the thin film superconductor formed using the sputtering target of the present invention is that the main component is (A+-
It is characterized by a layered structure to which a ternary compound coating of OBK)2CuO4 is attached. The present inventors have developed this type of layered structure superconductor by depositing the main component (
The present invention discovered that a composite oxide film consisting of A t -*B This is what happened. Here A is Sc
, Y and lanthanum series elements (atomic number 57-7.1
) (at least one kind, B is Ba, Sr, Ca, B
At least one element of group IIa elements such as e, Mg, etc.

The thin film superconductor formed using the target of the present invention is made into a thin film, and the thin film is made thin because the superconductor material is decomposed into ultrafine particles in the atomic state and then deposited on the substrate. The composition of superconductors is essentially homogeneous compared to conventional sintered bodies. Superconductors of very high precision are therefore realized using the targets of the invention.

Example Embodiments of the present invention will be described with reference to the drawings.

The ternary compound film 12 shown in FIG. 1 is formed by a sputtering method using the target of the present invention. In this case, the base 11 has a ternary compound coating 12 exhibiting superconductivity.
The purpose is to maintain the The superconductor of the invention therefore essentially consists of a layered structure. This layered structure is usually formed at a high temperature of several hundred degrees Celsius, and since superconductors are operated at a low temperature, for example, liquid nitrogen temperature (-195 degrees Celsius), the adhesion between the base 11 and the coating 12 is particularly poor, and the layered structure is often damaged. The present inventors have confirmed that. Furthermore, as a result of investigating the detailed thermal characteristics of the base for various materials, the present inventors found that the linear thermal expansion coefficient α>l Q-8/
It has been confirmed that the above-mentioned layered structure will not be damaged if the layered structure is thick.For example, if quartz glass with α<l Q-6/mu is used as the substrate, the coating 12 will have numerous cracks and become discontinuous. The present inventors have confirmed that the resulting film is difficult to put into practical use.

Furthermore, the present inventors have discovered that there is an optimal material for the layered structure substrate 11 shown in FIG. 1 from the viewpoint of functionality.

That is, the highly crystalline ternary compound coating 12 is applied to the substrate 11.
A single crystal substrate is effective for forming it on the surface 13 of. The present inventors investigated in detail the optimal substrate material for the composition range x = 0.05 to 0.2, which is effective as a superconductor for a ternary compound film. As a result, we found that magnesium oxide, sapphire (α-A Igo3 ), spinel, strontium titanate, silicon, gallium arsenide, and other single crystals were confirmed to be effective. However, since this is for effectively growing a highly crystalline coating 12 on the surface 13, it is sufficient if at least the substrate surface 13 is a single crystal.

The present inventors have confirmed that sintered porcelain is more effective as a base material than single crystal when processing this type of superconductor into an arbitrary shape, such as a cylindrical shape. Found the material. In other words, the present inventors have found that alumina, maglucium oxide, derconium oxide, steatite, forsterite, beryllia, spinel, etc. are used as the porcelain substrate to provide optimal adhesion of the superconducting coating 12 to the substrate 11 during processing of the substrate. confirmed. In this case as well, it is preferable that even the surface of the substrate is made of this type of porcelain, as in the case of single crystals.

To form a thin film superconductor, first, (As-B-)tcu
The main components are (A+-, Bx
) 2 CuOa-s is deposited on the substrate by sputter deposition using a sputtering target. In this case, the composite oxide film consists of components A, B and C.
The present inventors have confirmed that it is sufficient that the stoichiometric ratio of u matches.

The present inventors have confirmed that when a composite oxide film is attached to the surface 13 of the base 11, there is an optimal temperature range for the base. That is, the optimum temperature range for the substrate is 200 to 1000°C. In addition, below 200℃,
The adhesion of the composite oxide film to the substrate surface deteriorates. Also, ioo.

At temperatures above .degree. C., the deviation from the stoichiometric ratio of components A, B and Cu in the composite oxide film increases.

Furthermore, the present invention has shown that the temperature of the substrate when depositing the composite oxide film is particularly in the range of 500 to 700°C from the viewpoint of the function of this type of vapor deposition apparatus and the reproducibility of the properties of the composite oxide film. They confirmed. In this case, the formed composite oxide film exhibits superconductivity (A s −* B
x) Shows a structure similar to the layered perovskite structure of the lICuOa sintered body.

Surprisingly, however, this type of coating exhibits semiconducting properties and no superconductivity is observed even at liquid He temperatures (4°K).

The present inventors have discovered that superconductivity can be generated by further heat-treating this type of composite oxide film in an oxidic atmosphere such as air at normal pressure, a mixed gas of argon and oxygen, or pure oxygen. In this case, the optimal heat treatment temperature is 900
~1000°C, and the heat treatment time is 1 to 100 hours, and the heat treatment time is particularly long, which is unconventional for thin film materials.

If the heat treatment time is less than 1 hour, superconducting properties cannot be obtained with good reproducibility of semiconductor properties. Moreover, when the time is longer than 100 hours, the resistivity becomes high and the characteristics of the film become unstable.

In order to further understand the contents of the present invention, more specific examples will be shown below.

(Specific Example) <Lao, eS ro, +) tcUO4 target (x=0.1.A=La,B =Sr) is sputter-deposited in an Ar gas atmosphere to form crystalline (Sr) on the above substrate.
Lao, ss ro, 5) Deposited as a 2CuO4 coating to form a layered structure.

In this case, the Ar gas pressure was 0.5 Pa, the sputtering power was 150 W, the sputtering time was 10 hours, the film thickness was 6 μm, and the substrate temperature was 600° C. The formed layered structure was further heat treated in air at 9-00°C for 70 hours.

The room temperature resistivity of the film was 100 μΩ (up to), and the superconducting transition temperature was 28°.

FIG. 2 shows that the main component is (A+-Bx) 2Cub4 (x=
0.1. X of the ternary compound coating 12 in the example when the ternary compound coating 12 of A=La, B=Sr)
A line diffraction spectrum is shown. In FIG. 2, spectrum a is obtained from the coating 12, and spectrum b is obtained from the layered perovskite structure exhibiting superconductivity.

As shown in the figure, the coating spectrum a is similar to the spectrum b of the layered perovskite, and superconductivity occurred in the coating 12 as well, as seen in the temperature change 31 of electrical resistance in FIG.

In this example, the film thickness of the coating 12 is 6 μm, but it has been confirmed that superconductivity occurs even when the film thickness is as thin as 0.1 μm or less, or as thick as 10 μm or more. Furthermore, although this example shows the case where the composition ratio of the ternary compound is X=O,l, a change in the value of X causes a change in the superconducting transition temperature, and the essential difference is X=0.05. ~0.2. However, when X<0.01, superconductivity is not significant.

The present inventors experimentally investigated in detail the effectiveness of crystalline substrates other than magnesium oxide.

Figure 4 shows (A
t-xB, )2Cu04 structure (x=0.1.A=La,
B=Sr) coatings were deposited by sputtering deposition as in the case of magnesium single crystals, and the X-ray diffraction spectra obtained from these coatings are shown.

Spectra in the same figure, (a) (sapphire), (b)
The characteristics of spinel (spinel) are similar to the spectra in FIGS. 2(a) and (b). In addition to these substrates, strontium titanate, silicon, and gallium arsenide single crystals were also investigated, and similar X-ray diffraction spectra were obtained. It was confirmed that all of these cases exhibited superconductivity.

In sputtering deposition of this type of oxide film, for example, A
Although a mixed gas of r and 02 is used as a sputtering gas, the present inventors have found that the presence of 02 gas may deteriorate the crystallinity of the formed oxide film. The present inventors have experimentally confirmed that inert gases such as Ar, Xe, Ne, and Kr, or mixed gases of these inert gases, are effective as sputtering gases.

The present inventors have confirmed that all sputtering vapor deposition methods, such as high-frequency bipolar sputtering, direct current bipolar sputtering, and magnetron sputtering, are effective.

Particularly in the case of DC sputtering, it is necessary to lower the resistivity of the sputtering target to less than 10<-3 >Ω, and if the resistivity is higher than this, sufficient sputtering discharge will not occur. Note that the resistivity of the target is usually adjusted by adjusting the sintering conditions of the target.

FIG. 5 shows the sputtering deposition method improved by the inventors. That is, the sputtering vapor deposition is performed using a plurality of targets 1 (At-IB-1)tcuO4,2(
At-x2Bxg)gCu 04...3(At-*
n B X! l) 2 Cu 04 is simultaneously deposited by sputtering. In this case, by varying the sputtering power to each target,
The chemical composition of the composite oxide film formed on the substrate 4 (11 in FIG. 1) can be imparted by sputtering.

5 is an inert gas, 6 is a heater, and 7 is a vacuum container.

Therefore, it becomes possible to actively adjust the chemical composition of the film and create artificial fluctuations in the chemical composition, such as an artificial lattice.

Particularly in this type of apparatus, the present inventors have confirmed that DC sputtering is effective for precise control of sputtering power, etc., and that DC magnetron sputtering or a DC magnetron sputter gun is particularly effective.

In addition, as a method for forming a composite oxide film on the substrate surface, the main metal component is deposited on the substrate by sputtering vapor deposition, and the film is further irradiated with an oxygen beam or oxygen ions during film formation, so that the main metal component is deposited on the surface of the substrate. It is also possible to oxidize.

The detailed characteristics of this type of coating, such as its crystal structure, are such that because the coating is constrained on the substrate, there are large strains and defects within the coating that do not exist in ordinary sintered bodies. For this reason, it is not possible to infer the method of manufacturing a coating from the method of manufacturing the coating. Although the details of the physical meaning of the heat treatment of the film are not clear, it can be roughly considered as follows. That is, in the composite oxide film deposited on the substrate by sputtering vapor deposition, the divalent B element is not completely replaced by the trivalent A element (As-11B-) I! cuO
It does not form a compound called "ban". In this case, for example, A
A composite oxide is formed in which the oxide of element B is dispersed in a network of gCuO4 structure.

Naturally, the Cu atom is divalent. Superconducting properties also have good reproducibility (not obtained.Superconductivity is caused by the replacement of element A by element B, and subsequent generation of trivalent Cu atoms by oxidation of divalent Cu atoms, and this process is caused by heat treatment. Related: The reason why superconductivity cannot be obtained when the heat treatment time is 1 hour or less is thought to be due to insufficient substitution of the B element for the B element.

This type of ternary compound superconductor (A + - * B *
) The details of changes in superconducting properties due to changes in constituent elements A and B of 2Cu04 are not clear. However, it is true that A indicates trivalence and B indicates divalence, and the B element replaces a part of the hexavalent element. The explanation has been given using La as an example of element A, but Sc, Y, and even lanthanum series elements (atomic numbers 57 to 71) can change the essential properties of the layered structure of the invention to the extent that the superconducting transition temperature changes. It's not a thing.

Also, regarding the B element, changes in Ha group elements such as Sr and Ca%Ba change the superconducting transition temperature by about 10°, but this does not essentially change the characteristics of the layered structure of the present invention.

The present inventors have discovered, for example, sputtering targets 1, 2, .
3, the main component is (At-YoB-)2Cu Oa -J
I confirmed that it is fine. where 0≦x≦1.0≦δ
≦4, A is at least one of Sc, Y, and lanthanum series elements (atomic numbers 57 to 71), and B is one of the na group elements. In this case, the composition of the target is Sintered bodies such as disks, cylinders, etc. are useful.

However, it does not necessarily have to be a molded product (for example,
As shown in the figure, even if the target is in the form of powder, granules, or chuck, the ratio of the constituent metal elements of the target is as described above (
As long as A s −* B * ) 2 Cu Oa −a is satisfied. In particular, if a container 9 is filled with a powder or granular target 8 as shown in FIG. 6, it becomes possible to supply the target in any shape, and the composition ratio when forming a superconducting thin film can be optimized. , which is extremely convenient. It was also confirmed that it is possible to easily create a uniform target for superconducting materials that tend to have non-uniform composition when sintered, and that powder or granular targets are very effective.

Furthermore, since the constituent elements of the target are deposited in atomic form by sputtering, the target is not necessarily sintered (A
I-XBX)gcuo4-J compound.

Even if a compound of metal elements constituting the target, such as a small amount (AOx, Boy, CuOZ, etc.) is mixed in, as a result, these metal elements A, B, and Cu are sputtered in atomic form, so the metal element concentration in the target is However, (AI-
B.) It is sufficient as long as it satisfies gCuoa-J. X here.

Y, Z≧0゜Also, the target does not need to have a single composition, for example, A
OX, BOY, CuOZ, (AI-XB11)2Cu
Even if there is a composite target with a different composition composed of 04-J or these compounds, the total metal element concentration in the composite target is (A I-IT B *) t C
It is sufficient as long as u04-J is satisfied.

In addition, even if multi-component sputtering is used and the constituent elements constituting these composite targets are AOx, Boy, and CuOz, and these are sputtered simultaneously, the metal element concentration deposited on the substrate will be (AI-, B-). It is only necessary to satisfy tcUOa-J.

In particular, the powder target according to the present invention does not require molding and has the advantage that it can be continuously supplied during sputtering, making it more effective in producing this type of superconductor.

Effects of the Invention When forming a superconducting thin film using the sputtering target of the present invention, it is possible to form the target into a powder or granule form, which makes it easy to adjust the composition particularly required for forming a superconducting thin film, and to form a uniform film. It is possible to create a target material composition, making it possible to obtain highly reliable and stable superconductors with good reproducibility. Therefore, the superconductor produced using the target according to the present invention can be formed as a stable thin film. In other words, using a homogeneous target with an optimally controlled composition, the superconductor material is decomposed into ultrafine particles in the atomic state and then deposited on the substrate, so the composition of the formed superconductor is essentially: It is more homogeneous than conventional sintered bodies.

Therefore, a superconductor with very high precision is realized with the present invention.

As explained above (according to the method for manufacturing a thin film superconductor using the target of the present invention, it is formed in the form of a thin film on a crystalline substrate, for example, so it is essentially more precise than a sintered body, and is made of Si or GaAs). It is possible to integrate devices with other devices, and it is also used in the production of various superconducting devices such as Josephson devices.In particular, the transition temperature of this type of compound superconductor may be room temperature, making it difficult for conventional practical applications. The scope of this invention is wide (and the industrial value of the present invention is high).

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of a thin film superconductor formed using the target of the present invention, FIGS. 2, 3, and 4 are basic characteristic diagrams of a thin film superconductor formed using the present invention, FIG. 5 is a basic configuration diagram of a manufacturing apparatus used in the method for manufacturing a thin film superconductor of the present invention, and FIG. 6 is a diagram showing a state of sputtering using a target according to an embodiment of the present invention. 1.2.3... Sputtering target, 8...
Powder target, 11...substrate, 12... ternary compound coating. Name of agent: Patent attorney Toshio Nakao and 1 other military, 1 school (K)

Claims (5)

[Claims] (1) The main component is (A_1_-_xB_x)2CuO_4
A sputtering target characterized by being ____δ. Here, A represents at least one kind of Sc, Y, and lanthanum series elements (atomic numbers 57 to 71), and B represents at least one kind or two or more kinds of group IIa elements. δ is 0≦δ≦4, and x is 0≦x≦1. (2) The sputtering target according to claim 1, characterized in that it is made of a sintered body. (3) The sputtering target according to claim 1, wherein the sintered body is in the form of powder or particles. (4) The sputtering target according to claim 1, which contains at least AO_X, BO_Y, CuO_Z, or a compound thereof. X here,
Y, Z≧0 (5) The sputtering target according to claim 1, which is made of AO_X, BO_Y, CuO_Z, or a composite of these compounds.