JPH01246355A - Formation of multiple oxides superconducting thin film by counter target-type sputtering method and device therefor - Google Patents

Abstract

PURPOSE:To easily produce the title thin film with a small deviation in composition from a target material and having low reactivity toward a substrate by using a multiple oxides as the target and a semiconductor substrate as the substrate, and introducing oxygen at the time of cooling the substrate on which the film is formed. CONSTITUTION:In a counter target-type sputtering device, for example, a material contg. a 1/2/3 ratio of Y, Ba and Cu is used, thermally oxidized Si is used for the substrate 6, and a superconducting thin film of Y1Ba2Cu3O7-delta is formed. A magnetic field generated by a magnetic field generating means and vertical to the sputtering plane is formed only in the space between targets. When the substrate 6 is cooled after the film is formed, oxygen is introduced from a sputtering gas and oxygen inlet 10. By this method, a superconducting thin film with a small deviation in composition from the target material, hardly reacting with the substrate, and having excellent uniformity can be formed by as-depo.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for forming a composite oxide superconducting thin film on a substrate as-dapo by a facing target sputtering method.

(Prior Art) Recently, research and development of superconducting thin films has been remarkable, and various superconducting substances are being searched for by methods such as vacuum evaporation, sputtering, CVD, and screen printing.

In particular, research into materials for high-temperature superconducting thin films has been remarkable; for example, Y
A -Ba-Cu-○ system superconductor (YBC○) is a substance exhibiting a critical temperature of 90 or higher, and its practical application is highly anticipated in both the weak and strong electric fields.

Also, very recently, it has been reported that a Bi-based B1-5r-Ca-O superconductor has a critical temperature of 120K.

Sputtering, which is one of the representative methods for forming thin films, is also being actively researched to find superconducting materials and to put sputtering equipment into practical use.

For example, as a sputtering device, JP-A-57-1583
As proposed in Japanese Patent Application No. 00, there is a facing target type sputtering device, which improves the usage efficiency of the target by making the sputtered surface of the target wide and uniform.
A compact and inexpensive device has been developed that can improve the cooling efficiency of the target and form thin films at low temperatures and at high speed, and does not require an external coil.

(Problem to be Solved by the Invention) However, although the facing target type sputtering apparatus described above reduces the compositional deviation between the target material and the thin film, there is a problem of reactivity with the ceramic substrate, and Obtaining a superconducting thin film by -depo requires a high substrate temperature of at least 600° C., and also requires annealing.

The present invention was made in order to solve the problems encountered when forming a composite oxide superconducting thin film by the facing target sputtering method. The object of the present invention is to provide a method and apparatus that can produce a small and highly uniform composite oxide superconducting thin film through a simple process.

(Means for Solving the Problems) In order to achieve the above object, the present inventors applied an as-depo method to a substrate on the premise of using the facing target type sputtering apparatus according to the previous proposal.

We have conducted extensive research to find a method for forming composite oxide superconducting thin films with good C-axis orientation and high Tc, Jc, and Hc at the lowest possible substrate temperature.

First, conventionally, 5rTiO, Mgo,
Focusing on the point that it was limited to ceramic-based substrates such as ysz, we attempted to use silica-based substrates such as Si and Sin. As a result, it was found that by using thermally oxidized Si, which is a semiconductor, as a substrate, a thin film with almost no compositional deviation from the target material and excellent surface smoothness could be obtained at a substrate temperature of 500°C. However, all of the obtained thin films were insulators.

Therefore, we consider that this is because oxygen is not effectively incorporated into the film, and that the substrate temperature is 100°C in vacuum.
Taking into account that oxygen is also extracted from the film, we established a process to introduce oxygen during cooling of the substrate in order to prevent dissociation of elements during cooling of the substrate.

That is, in short, the method according to the present invention uses a complex oxide as a target and a semiconductor substrate as a substrate when forming a composite oxide superconducting thin film on a substrate by facing target sputtering method, and after forming the film by sputtering. The method is characterized in that a superconducting thin film can be obtained by sputtering by introducing oxygen during cooling of the substrate.

Furthermore, if necessary, the obtained thin film is annealed to improve its superconductivity.

Further, the present invention relating to a sputtering apparatus provides a pair of targets serving as cathodes so that their surfaces to be sputtered face each other in parallel with a space in between, and generate a magnetic field in a direction perpendicular to the surfaces to be sputtered. In a facing target sputtering apparatus configured to form a thin film by sputtering on a substrate which is provided with a magnetic field generating means and is disposed on the side of a space between the targets so as to face the space, the magnetic field generating means is provided with a thin film formed by sputtering on a substrate that is arranged to face the space between the targets. The present invention is characterized in that it is arranged so that oxygen is generated only between the layers, is provided with a means for introducing oxygen during cooling of the substrate after film formation by sputtering, and uses a composite oxide as the target material and a semiconductor substrate as the substrate. It is something.

The present invention will be explained in more detail below.

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

First, a pair of targets T1 and T2 are arranged in a vacuum chamber 1 so that the surfaces on which the sputtering targets T1 and T2 are sputtered are parallel to each other with a space between them. The target holder 2.3 has a hollow structure, is attached to the vacuum chamber 1 via an insulating member, and can be cooled by cooling water supply pipes 4a, 5a and discharge pipes 4b, 5b.

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

The magnetic field generation means are permanent magnets 11 and 12, and at the same time,
The magnetic fields formed by the magnetic poles in the target holder behind each target are all oriented in the same direction perpendicular to the sputtering surface of the target, and are arranged at the periphery of the target. Therefore, a magnetic field is created only in the space between the targets.

9 is an exhaust port connected to an exhaust system, and 1o is an inlet port connected to a sputtering gas introduction system.

Note that this introduction port 10 is also connected to an oxygen introduction system, and can be switched between the sputtering gas introduction system and the oxygen introduction system.

FIG. 2 is a diagram illustrating the principle of the facing target sputtering method of the present invention. Place two targets facing each other,
Apply a magnetic field perpendicular to the target. Sputtering is performed by supplying sputtering power to the shield ring and target from a sputtering power source. Most of the γ electrons and negative ions emitted from the target are confined in the space between the two targets due to EXB drift, so that plasma is formed in the space between the two targets. Therefore, since the substrate is not exposed to plasma, film formation is possible without collision of high-energy particles with the Fi group.

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

Moreover, in the present invention, although a composite oxide is used as a target and a semiconductor substrate (e.g., surface thermally oxidized Si) is used as a substrate, the obtained thin film does not have the problem of interdiffusion between the atoms in the film and the atoms of the substrate. .

As the target material, it is possible to use various composite oxides and compositions that exhibit superconductivity.

For example, in the case of Y-Ba-Cu-0 system, Y:Ba:Cu
= 1:2:3, in the case of Bi-5r-Ca-Cu-0 system, Bi: Sr: Ca: Cu = 1: 2: 3
: 4.1:1:1:1.1:1:1:2.

FIG. 3 shows an example of the process of forming a composite oxide superconducting thin film using the facing target sputtering method of the present invention. In the sputtering apparatus shown in FIG. 1, the vacuum chamber is evacuated and then set to a predetermined substrate temperature. and sputter gas (e.g. A
r+02), press sputtering is performed for a predetermined time, then main sputtering is performed, the introduction of sputtering gas is stopped, and the substrate is cooled while introducing oxygen gas,
After baking, remove the sample. Note that sputtering conditions are not particularly limited.

(Example) Next, examples of the present invention will be shown.

In the facing target type sputtering apparatus shown in Fig. 1, a target having a composition ratio of Y:Ba:Cu=1:2:3 is used, and a surface thermally oxidized Si is used for the substrate. , YiBa, Cu30□- by the process shown in FIG.
8 superconducting thin films were formed.

Figure 4 shows the C-plane orientation index f oak in the obtained thin film.
This figure shows the change in temperature (Ts) of the substrate.

When the C-plane orientation index is 1, it is completely C-plane oriented, and when it is 0, it is random orientation, so from the same figure, 480-500℃
It can be seen that there is a transition from random orientation to C-plane orientation in a narrow range of 20°C. Even when using a ceramic substrate on which epitaxial growth can be expected using magnetron sputtering, it takes 60 mL to obtain a C-plane oriented film.
A substrate temperature Ts of 0°C or higher is required, and considering that the substrate used in this example is amorphous, this substrate temperature Ts
The reduction in is due to the fact that the substrate is bombarded with much less energetic particles than 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 compared to other sputtering methods.

Figure 6 shows the relationship between the oxygen introduction pressure and the C-axis length. It is clear that the C-axis shrinks due to oxygen introduction, and there is a negative correlation between the amount of oxygen in the film and the C-axis length. , indicating that oxygen is effectively incorporated into the film by introducing oxygen. In fact, the resistivity of the oxygen-introduced film at room temperature was extremely reduced, reaching a value of several to several tens of Ω·cm. In addition, the oxygen introduction pressure is 1 to 100 x 10-'T
orr is appropriate.

Note that the size of the C-axis length also depends on the substrate cooling rate;
As shown in the figure, it can be seen that the faster the substrate cooling rate is, the shorter the C-axis becomes.

In this way, by introducing oxygen during substrate cooling,
The resulting thin film has a short C-axis, can prevent a decrease in the amount of oxygen in the film, and exhibits superconductivity.

Figure 8 shows the temperature change in resistivity of the obtained thin film, and the film composition was Y:Ba:Cu~1:2.1
9:3.05 and Tc (onset) = 70 K
, Tc (zero) = 32K, and ΔTc = 38K.

Figure 9 shows the Auger profile in the depth direction of the membrane.
It can be seen that interdiffusion between atoms in the film and Si of the substrate does not occur.

In addition, the superconducting thin film obtained in Example 1 was annealed at various temperatures. Annealing is done in an oxygen atmosphere of 1 atm.
Hold at 500°C to 900'C for 1 hour, then 400°C
It was kept at ℃ for 4 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℃, 900'C1), as shown in FIGS. 11 to 14, Ta=500
℃, the Tc is improved compared to the as-depo film, but as the annealing temperature increases, the superconductivity deteriorates, and Ta=
At 900°C, the resistance at room temperature was more than IOMΩ, making it an insulator.

Thus, the reason why Tc was improved when Ta=500° C. is thought to be because the film took in oxygen through annealing, and the superconductivity of the film can be improved by performing an appropriate annealing treatment. However, an excessive increase in annealing temperature promotes the reaction between the film and the substrate, degrading superconductivity.

In the above embodiment, an example of a YBCO superconducting thin film was shown, but it is also possible to form a thin film of other composite oxides exhibiting superconducting properties.

(Effects of the Invention) As detailed above, according to the present invention, a composite oxide superconductor with little compositional deviation from the target material, almost no reactivity with the substrate, excellent uniformity, and excellent surface smoothness. Thin films can be obtained as-depo. Furthermore, superconductivity can be further improved by performing appropriate annealing after sputtering. It is particularly effective for forming high-temperature superconducting thin films.

Further, the sputtering apparatus for this purpose does not require a complicated power supply device, etc., and the reliability of the entire apparatus is improved and the cost is low.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a facing target type sputtering apparatus of the present invention. Fig. 2 is an explanatory diagram showing the principle of the facing target sputtering method according to the present invention. Fig. 3 is a diagram showing the formation process of a composite oxide superconducting thin film according to the present invention. Fig. 4 is a diagram showing the dependence of C-plane orientation index on substrate temperature. Figure 5 is a diagram showing the dependence of film composition on substrate temperature, and Figure 6 is a diagram showing the dependence of film composition on substrate temperature.
A diagram showing the dependence of the axial length on oxygen introduction pressure, FIG. 7 is a diagram showing the dependence of the C-axis length on the substrate cooling rate, and FIG. 8 is a diagram showing the dependence of the C-axis length on the substrate cooling rate.
Figure 9 is a diagram showing the Auger profile in the depth direction of the film, Figure 10 is a diagram showing the dependence of the C-axis length on the annealing temperature, and Figures 11- FIG. 14 is a diagram showing temperature changes in film resistivity at different annealing temperatures. 1... Vacuum chamber, 2.3... Target holder, 4
a, 5a... Cooling water supply pipe, 4b, 5b... Cooling water discharge pipe, 6... Board, 7... Board holder, 8...
·heater. 9...Exhaust port, 10...Sputter gas, oxygen inlet, 11.12...Permanent magnet, 13.14...Shield ring, T,,T,...Target. Patent applicant Takashi Nakamura, Patent attorney representing the New Technology Development Corporation Figure 1 Figure 2 Figure 3
↓ ↓ Premata Pub 7 (1h) ↓ Main snowboard (a, ri↓ Gasu introduction #1↓ ↓ He-yang 72 ↓ Section ``1 work, Figure 6 Figure 7 Board cooling, (French I^ ) to B/Y, Cu/Y c11!l orientation 11 number Fig. 8 si: L 屓 (to) Fig. 9 inclination (parrot - Fig. 10 annealing si 1 hawk (°C) Fig. 11 si 1! Figure 12: 98 degrees (K) Figure 13: Temperature /i (K)

Claims (4)

[Claims] (1) When forming a composite oxide superconducting thin film on a substrate using the facing target sputtering method, a composite oxide is used as the target and a semiconductor substrate is used as the substrate, and after the film is formed by sputtering, oxygen is introduced during cooling of the substrate. A method for forming a composite oxide superconducting thin film by a facing target sputtering method, which is characterized by obtaining a superconducting thin film as sputtered. (2) The method according to claim 1, wherein the composite oxide is a Y-Ba-Cu-O-based composite oxide, and the substrate is a thermally oxidized Si substrate. (3) The method according to claim 1, wherein the obtained thin film is annealed. (4) A pair of targets serving as cathodes are provided so that their surfaces to be sputtered face each other in parallel with a space between them, and a magnetic field generating means for generating a magnetic field in a direction perpendicular to the surfaces to be sputtered is provided, and In a facing target type sputtering apparatus configured to form a thin film by sputtering on a substrate disposed on the side of a space between the targets so as to face the space, the magnetic field generating means is configured to generate the magnetic field only between the targets. At the same time, a means for introducing oxygen during cooling of the substrate after film formation by sputtering is provided, and
A facing target sputtering apparatus for forming a composite oxide superconducting thin film, characterized in that a composite oxide is used as a target material and a semiconductor substrate is used as a substrate.