JPH0333003A - Superconducting thin film production equipment - Google Patents

Abstract

PURPOSE:To form an oxide superconducting thin film exhibiting high superconductivity in the chemical vapor growth method using an organometallic compd. as the raw material by providing a mechanism for generating a DC discharge in the vicinity of a substrate. CONSTITUTION:The mechanism for generating a DC discharge is provided in the vicinity of a substrate in the MOCVD device for an oxide superconductor thin film. A mechanism for keeping an electrode on the evacuation side at 200-400 deg.C is preferably furnished. Furthermore, the boron compd. of a metal or preferably at least one boron compd. of yttrium, barium, lanthanum or strontium is used for the electrode to achieve the objective. In this device, the DC discharge is used for exciting the organometallic compd. and oxygen with a high-speed electron or UV and accelerating the oxidation reaction of the organometallic compd. In addition, the deposition of the by-product and unreacted material on the electrode is prevented by the mechanism for keeping the electrode on the evacuation side at 200-400 deg.C.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an apparatus for forming a thin film of an oxide superconductor. In particular, it relates to an apparatus for forming thin films of oxide superconductors by MOCVD.

[Conventional technology]

Chemical vapor deposition method using organic metals as raw materials, so-called MO
CVD has excellent features such as easy upscaling of equipment and the ability to form films on complex-shaped substrates and large-area substrates, making it a promising method for producing thin films of oxide superconductors. (For example, "High Temperature Superconductivity Data Book" supervised by New Technology Development Corporation, p. 59, round neck stock % formula %)) However, with conventional technology, the substrate temperature during thin film production is approximately 800°C. Therefore, the interaction between the oxide thin film and the substrate occurs, causing problems such as deterioration of the performance of the superconducting thin film, deterioration of the substrate, and occurrence of peeling.

[Problem to be solved by the invention] An object of the present invention is to provide a means for producing a thin film of an oxide superconductor exhibiting excellent superconducting properties at a lower temperature. [Means to solve the problem]

An object of the present invention is to provide a mechanism for generating DC discharge near a substrate in an MOCVD apparatus for forming an oxide high temperature superconductor thin film, and preferably a mechanism for maintaining the temperature of the electrode on the exhaust system side at 200 to 400°C. This can be achieved by providing the electrode, and more preferably by using a metal boride, particularly preferably at least one of yttrium, barium, lanthanum, and strontium boride.

[Effect]

In the present invention, the DC discharge has the effect of exciting the organometallic compound and oxygen with high-speed electrons and ultraviolet rays, thereby promoting the oxidation reaction of the organometallic compound. In addition, the mechanism that maintains the exhaust side electrode at 200 to 400°C is
It has the effect of preventing by-products and unreacted substances from adhering to the electrode. Also, metal borides, especially Y, can be used as electrodes. The use of borides of Ba, Sr, and La has the effect of lowering the discharge voltage and preventing destabilization of the discharge due to oxidation of the electrode.

【Example】

Below, representative oxide superconductors, Y B a, C
The present invention will be explained using an apparatus for forming a thin film of u307-x as an example. The thin film forming apparatus used is shown in Figure 1. The reaction tube 11 is made of quartz and is heated by the electric furnace 10. A raw material side electrode 1 and an exhaust system side electrode 2 are enclosed outside the electric furnace 10. Both electrodes 1.2 are Ni wires whose surfaces are coated with LaB. DC discharge is generated by setting the raw material side electrode 1 at ground potential and applying a positive DC potential to the exhaust side electrode 2, and the magnitude of the discharge current is controlled by inserting a resistor 4 in series in the circuit. Metal raw materials include dipivaloyl methanato complexes of Y, Ba, and Cu (generally Y (DPM), Ba (DPM)2
, Cu(DPM)2) was used. These raw materials 6.7.8 are 110℃, 240℃, and 120℃, respectively.
It is placed in a container maintained at a temperature of 0.degree. C., and is transported by a carrier gas (Ar) and introduced into a reaction tube. Also,
Oxygen supplied from a cylinder 9 was used as the oxidizing gas. Using this device, the discharge current was 10 mA, and the substrate temperature was 600°C.
Figure 2 shows the temperature dependence of the resistance of a thin film formed on a magnesium oxide substrate under these conditions. Furthermore, as a comparative example, FIG. 2 also shows the temperature dependence of the resistance of a thin film prepared without generating discharge. Note that the vertical axis in FIG. 2 is the resistance at the measured temperature with respect to the resistance at 250°C. As shown in the figure, the resistance of the thin film created by generating electric discharge decreased as the temperature decreased, and further became zero resistance due to superconducting transition (curve 21). The critical temperature at which the resistance value became zero was 90°C. on the other hand. The resistance of the thin film created without generating an electric discharge increased as the temperature decreased, and did not exhibit superconducting transition even at 4.2 K (curve 22). In other words, this result shows that a superconducting thin film can be created even at low temperatures by direct current discharge. Incidentally, in the above embodiment, Ni wires whose surfaces were coated with L a B were used as electrodes, but the same effect can be obtained by using Ni wires as they are instead. however,
In the case of Ni wire, the voltage required to generate a discharge increases by about 100V. Also, metals such as iron and copper oxidize the electrode surface. Discharge becomes unstable. That is, as an electrode, LaB&
A Ni wire coated with is more desirable. In addition, instead of the above LaB, YB, , SrB, , Ba
Good results can also be obtained using boron compounds such as CeB. Furthermore, as a matter of course, similar effects can be obtained by using these boron compounds themselves. The effect of discharge increases as the discharge current increases, and the effect saturates at a constant discharge current, after which it has a rather negative effect. Although the saturated discharge current value changes depending on the shape of the device, the fact that a superconducting thin film can be created by discharge is an advantage of the present invention. In the above example, Y Ba 2 Cu 307-
Although the apparatus for producing an X thin film has been described, the film growth mechanism is the same for MOCVD of other oxide superconductors, and it is possible to produce superconducting thin films at low temperatures using the present invention.

【Effect of the invention】

According to the present invention, thin films of oxide superconductors can be formed at low temperatures. This will enable the production of high-performance superconducting electronic devices, superconducting wires, and superconducting shielding materials.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a thin film forming apparatus used for forming a thin film in an example of the present invention, and FIG. 2 is a resistance-temperature characteristic diagram of IAS showing the effect of improving electrical characteristics according to the present invention. Explanation of symbols 1... Raw material supply side electrode, 2... Exhaust system side electrode, 3...
...DC power supply, 4...Resistance for controlling discharge current, 5...
Board, 6・Y (DPM) 3.7”・B a (D
P M ) z, 8-Cu (D P M ) 2.9
...Oxygen cylinder, 10...Electric furnace curve 21...Curve showing the temperature change in the resistance of a thin film created by generating an electric discharge, Curve 22...Curve showing the change in resistance of a thin film created without generating an electric discharge Curve 1III showing temperature change

Claims (3)

[Claims] 1. A superconducting thin film forming apparatus characterized in that the MOCVD apparatus for producing an oxide high-temperature superconducting thin film includes a mechanism for generating a direct current discharge near a substrate. 2. 2. The superconducting thin film forming apparatus according to claim 1, further comprising a mechanism for controlling the temperature of the electrode on the exhaust system side to 200 to 400°C. 3. Metal boride, preferably yttrium, for the electrode.
3. The superconducting thin film forming apparatus according to claim 1, wherein at least one member selected from the group consisting of barium and lanthanum strontium borides is used.