JPH01160828A - Oxide superconducting thin film creation method - Google Patents

Abstract

PURPOSE:To contrive homogenization of element distribution and obtain a thin film having excellent superconductivity characteristics, by thermally vaporizing a Ba oxide, Cu and rare earth element, jetting the vaporized raw materials onto a substrate, respectively forming cluster ions, accelerating the ions and heat-treating the substrate. CONSTITUTION:A Ba oxide, Cu and rare earth element are respectively used as vapor deposition raw materials, initially heated and vaporized. The above- mentioned vaporized vapor deposition raw materials are then jetted onto a substrate to respectively form clusters of the vapor deposition raw materials. The aforementioned clusters are then ionized and accelerated so as to collide with the substrate. The above-mentioned substrate is subsequently heat-treated to prepare the aimed oxide superconducting thin film. The Ba oxide in this method for preparing the thin film has properties of not decomposing into the respective elements but evaporating in the state of nearly the Ba oxide. Since the evaporation temperature thereof is close to that of other vapor deposition raw materials, the evaporation rate can be readily controlled and element distribution in the film can be homogenized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing an oxide superconducting thin film.

[Prior art] Conventionally, the temperature at which normal conductivity transitions to superconductivity (hereinafter referred to as 'I')
Nb was said to have the highest value (abbreviated as c).

Even Ge has a temperature of about 23'C, and when it is used it generally has to be cooled using expensive liquid helium.

On the other hand, in recent years Bednorz and Muter (1Jiil 1erl, etc.) have reported that metal oxides (L a −)3 a with C of about 30 to 40
-S r -Ca-C11-0 system) was discovered (Magazine: Z, Phys, ) 364.189 (19861
1, sohnitniiC1M, ni, w-(v.

A Y-Ba-C11-0 type substance with a Tc of about 80 to 93 was discovered by K., Wul et al. (Magazine: Phys, Rev, Left, 58.90F
l (!987) ), and in the later study Y 13 a
It has been found that m Cus Oy (near the composition of 6≦y≦7) exhibits the best characteristics. Also, Y is La, Nd
, Sm, Eu, Gd, Ha, Er, Yb, Ln. These superconducting materials use liquid nitrogen (boiling point 77K), which is inexpensive as a refrigerant.
) is the fiJ ability, and the sintered body is 77K
The critical current density (hereinafter abbreviated as Jc) at lo'A/
cm", and has extremely useful properties in practice.On the other hand, the application of this material is to Josephson elements and magnetic detection elements. Development in this direction is also progressing rapidly.

Several methods have been proposed for making thin films of this substance, and a typical example is vapor deposition.
A method has been adopted in which metals such as n and Cu are vaporized as raw materials and heated with a resistor or an electron beam to simultaneously deposit eight metals on the E element. When the film attached to the substrate is heated to about 900°C in an oxygen atmosphere, M a −L n
A perovskite-type compound of -Cu -0 can be obtained, and since it is the simplest film formation method, it has the advantage that it can be produced relatively easily. Further, the use of a cluster ion beam deposition method (hereinafter abbreviated as IBC method), which is a type of the above-mentioned deposition method, is being considered. The advantage of this method is that it usually produces a homogeneous, dense film with high adhesion, combined with the effect of electric field acceleration due to the formation of clusters and their ionization. considered to be the most suitable. The principle of this method will be explained based on FIG. When the vapor deposition raw material (2) is heated with a heater (4), neutral molecules (2A) are evaporated from the crucible (11), and clusters (2B) are formed as a result of adiabatic expansion. Ionized filament (7)
Ionize the cluster (2C) with an electron shower from
This is accelerated by one acceleration. Accelerated cluster ions (2C) collide and adhere to the substrate (IO) surface,
Forms a film.

[Problems to be Solved by the Invention] As described above, the method for producing an oxide superconducting thin film by the conventional ICB ternary simultaneous vapor deposition method is as follows. Because their evaporation temperatures are different (for example, the raw material temperatures to obtain a vapor pressure of 1O-3 torr are 862K and 1750K, respectively.
problems such as difficulty in controlling the deposition rate, non-uniform distribution of elements in the film thickness direction of the formed film, and difficulty in obtaining a film with a uniform composition after heat treatment. was there.

This invention was made to solve the above-mentioned problems, and aims to make the element distribution uniform within the film and, as a result, obtain an oxide superconducting thin film with excellent superconducting properties. do.

[Means for Solving the Problems] The method for producing an oxide superconducting thin film according to the present invention involves heating and vaporizing Ba oxide, Cu, and rare hepta elements (hereinafter abbreviated as Ln) as vapor deposition raw materials. 1, a second stage in which each of the vaporized evaporation raw materials is ejected toward the substrate to form clusters of the evaporation raw material, and a third stage in which each of the clusters is ionized to form cluster ions, A fourth step of accelerating the Nikiya cluster ions so as to collide with the substrate, and a fifth step of heat-treating the substrate in an oxygen atmosphere are sequentially performed.

[Function] The Ba oxide in this invention has the property of not decomposing into individual elements and evaporating mostly in the state of 13a oxide,
Its evaporation temperature (for example, 1O-3t, orr + 7', the temperature at which vapor pressure is obtained is 1694K) is close to the evaporation temperature of other evaporation raw materials, so it controls the evaporation rate (easy to dispose of and uniform element distribution within the film). Can be converted into three elements at the same time?A
Since the deposited film is oxidized by heat treatment in an oxygen atmosphere, there is no problem even if Ba oxide rather than Ba metal is deposited on the substrate.

[Example] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

Embodiment FIG. 1 is a sectional view showing a CB ternary simultaneous vapor deposition apparatus according to an embodiment of the present invention. Fill the crucible (11) with about 5 g of barium carbonate powder (2). After evacuating the outer vacuum container (3) to a high vacuum (~l O-"torr), the heater (4)
Electrify and heat to about 1250K, then gradually heat to about 1450K to prevent sudden thermal decomposition, and confirm that the degree of vacuum does not deteriorate. In this state, we know that the reaction of [3a CO3-B a O+ COz has been completed.

Crucibles (5) and (6) are filled with Cu and Y, respectively, and during this pretreatment, these crucibles (
5) and (6) are not heated and ionized filament
It goes without saying that ionization is not performed in (7). The shutter (8) is also closed. After this operation, all heaters (4) are energized to ensure the optimum evaporation rate while evaporating (
1) and place the crucible (11) towards the substrate (10).
, (5), (6) to form a cluster (
2nd step), ionization with the ionization filament (7) (3rd step), acceleration with 1 acceleration (II) so that it collides with the substrate (1O) (4th step), and open the shutter (8). Film formation is started on the M a O'31 final substrate (10), and the film is deposited to a thickness of about 1 μm.

The results of Auger analysis of the film thus obtained are shown in FIG. 2. From this figure, it can be seen that the distribution of Ba is extremely good.

After heating this film at approximately 900°C for 1 hour in an oxygen atmosphere,
When it was slowly cooled at 00° C./hour (fifth step) and measured using the four-probe method to measure the resistance-temperature characteristics, it was found that Tc was present at about 85 K as shown in FIG. In addition, when we investigated the crystalline phase of this oxide superconducting thin film using X-ray analysis, we found that
As shown in the figure, it was found that the main component was Ba-Y-Cu-0 and a slight amount of CuO was included. Furthermore, when comparing a simple evaporation method without electric field acceleration and this method using ICB, although there is almost no difference in 'rc of 116, the Jc value is about twice as high, about several hundred A/c, for the same thickness. m2 was obtained. This shows that this ICB method is extremely useful in terms of film density.

Comparative Example Metals Y, Ba, and Cu were used as vapor deposition raw materials and evaporated under the same conditions as in the above example, and films were formed by the I CB method. An example of Auger analysis of this film is shown in FIG. From the figure, it can be seen that the distribution of l(a is uneven.

Furthermore, the resistance-temperature characteristics and crystal phase were examined by heat treatment in the same manner as in the above examples, and the results were as shown in FIGS. 6 and 7. From these figures, T' c is 40
It is also clear that the superconducting phase is of a low degree, and that a different phase other than the superconducting phase is precipitated.

In the above example, barium carbonate is thermally decomposed to produce B a
Although the oxide, namely barium oxide, was used, the raw material for B(1 oxide) may be anything that can be thermally decomposed to become Ba oxide, such as barium nitrate, barium acetate, barium sulfate, etc. However, if the temperature at which barium oxide is thermally decomposed is higher than 1600, barium oxide itself becomes A1 during thermal decomposition, which is disadvantageous.Also, barium oxide itself can be used, but Normally, the composition is denatured by water, carbon dioxide, etc., so when using barium oxide itself, it is desirable to heat treat it in the same way as for Ba compounds.However, it is difficult to obtain high-purity products. It is desirable to use compound a as described above.

In addition, in the L-Example, the component system is Y-Ba-Cu-0
Although the case of the system is shown, Y is, for example, La.

Nd, Sm, Eu, Gd, t)y, Ho, Er, Yb,
Ln-Ba- replaced with other rare earth elements such as L+i
A similar effect can be obtained in the case of Cu-0 type.

[Effects of the Invention] As described above, according to the present invention, Ba oxide, Cu,
and a rare earth element (hereinafter abbreviated as Ln) as vapor deposition raw materials by heating and vaporizing them, and a second step of ejecting the vaporized vapor deposition raw materials toward the substrate to form clusters of the vapor deposition raw materials. , a third step of ionizing each of the clusters to form cluster ions,
Since the fourth step of accelerating each of the cluster ions to collide with the substrate and the fifth step of heat-treating the substrate in an oxygen atmosphere are performed in order, the deposition rates of the three elements are similar and B
This has the effect of making the a distribution uniform and obtaining an oxide superconducting thin film that is dense, has a large Jc value, and has good superconducting properties.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an ICB ternary co-evaporation apparatus according to an embodiment of the present invention, and FIG. 2 shows the element distribution in the thickness direction of an oxide superconducting thin film produced by the method according to an embodiment of the present invention. FIG. 3 is a characteristic diagram showing the resistance-temperature characteristics of an oxide superconducting thin film produced by a method according to an embodiment of the present invention, and FIG. A characteristic diagram showing the crystal phase of an oxide superconducting thin film obtained by X-ray analysis. Figure 5 is a characteristic diagram showing the element distribution in the thickness direction of an oxide superconducting thin film according to a comparative example. Figure 6 is a characteristic diagram showing the element distribution in the thickness direction of an oxide superconducting thin film according to a comparative example. Characteristic diagram showing resistance-temperature characteristics, 7th
The figure is a characteristic diagram showing the crystal phase by X-ray analysis of an oxide superconducting thin film according to a comparative example, and FIG. 8 is a cross-sectional configuration diagram illustrating the principle of a general ICB vapor deposition method. In the figure, (1), (5), and (6) are the crucible, (4) is the heater, (7) is the ionization filament,
(8) is a shutter, (101 is a substrate, and (II) is an accelerating double positive. In each figure, the same reference numerals indicate the same or H1 portions.

Claims (4)

[Claims] (1) In creating an oxide superconducting thin film by ternary simultaneous vapor deposition, Ba oxide, Cu, and rare earth elements (
A first step of heating and vaporizing each of the vapor deposition materials (hereinafter abbreviated as Ln), a second step of ejecting the vaporized vapor deposition materials toward the substrate to form clusters of the vapor deposition materials, and each cluster of the vapor deposition materials described above. A third step of ionizing and forming cluster ions, a fourth step of accelerating each of the cluster ions to collide with the substrate, and a fifth step of heat-treating the substrate in an oxygen atmosphere are sequentially performed. A method for creating oxide superconducting thin films. (2) The method for producing an oxide superconducting thin film according to claim 1, wherein the Ba oxide is obtained by thermally decomposing a Ba compound in vacuum. (3) The method for producing an oxide superconducting thin film according to claim 2, in which a compound that decomposes into Ba oxide by 1600K is used as the Ba compound. (4) The method for producing an oxide superconducting thin film according to claim 3, wherein the Ba compound is any one of barium carbonate, barium nitrate, barium acetate, and barium sulfate.