JP2559413B2 - Oxide superconducting integrated circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oxide high temperature superconducting thin film integrated circuit, and relates to an insulating film for the purpose of electrical insulation, mechanical protection and corrosion / reaction prevention of an electrode film. .

[Prior Art] A tunnel-type Josephson junction element is a switching element that applies a superconducting tunnel phenomenon at a very low temperature (4.2K) with a sandwich structure in which an extremely thin tunnel obstacle layer is sandwiched between two superconducting thin films. . Compared with conventional semiconductor devices, this device has a switching speed of about an order of magnitude and power consumption of about three orders of magnitude, and is expected as a theoretical calculation element and storage element for future ultra-high speed computers. There is. The superconducting thin film for forming those devices is mainly composed of Pb-In-Au alloy, Pb-Bi alloy, Nb and NbN.
Are used. Az-Zn alloy, M
o, or MoNx is used. Further, an SiO film or a SiO ₂ film is used as an interlayer insulating film for electrically insulating the superconducting thin film and the low antibody thin film from each other.

By the way, the Josephson junction device has conventionally exhibited desired characteristics while being cryogenically cooled (up to 4.2 K) using liquid helium as a coolant. Recently, however, the layered perovskite-like structure composed of a complex oxide of rare earth elements and copper exhibits a significantly higher superconducting critical temperature than conventional metal-based superconducting materials. (1986) p. 189 (Zeitsc
hrift fur Physik, B-Condensed Matter, 64 (1986) 18
Discussed in 9.). Later research by La
-Sr-Cu-O-based material is about 30-40K, and Y-Ba
It was revealed that the -Cu-O-based material exhibits superconductivity at 88K and zero resistance. These oxide superconducting materials may be prepared by using oxides or carbonates, reacting them at a high temperature of about 900 ° C. after mixing, further mixing and pulverizing, and then heat-treating at 900 ° C. to 1000 ° C. In order to make the above-mentioned oxide superconducting material into a thin film, a sputtering film forming method using a sintered body produced by a high-temperature heat treatment as a target is used. The thin film prepared in this way
By heat treatment in a high temperature oxygen atmosphere around 0 ° C,
A film having the above-mentioned high critical temperature characteristics can be obtained. With the advent of such oxide superconducting materials, it has become possible to fabricate Josephson junction devices that operate using liquid nitrogen refrigerant, which has been impossible until now.

As a main element of the oxide superconducting Josephson junction element formed by the above method, a logical operation circuit,
When manufacturing an integrated circuit of a memory circuit, it is necessary to form electrode films, thin film components such as resistors, inductors, and capacitors in the same chip, and these are generally realized by a laminated structure. Therefore, it is necessary to electrically isolate the thin film components from each other, and an interlayer insulating film is used for that purpose. Usually, in conductors, Si is used as such an interlayer insulating film.
O ₂ , SiO, Si ₃ N ₄ , poly-Si or amorphous SiAl ₂ O ₃ film or the like is used. However, when these films are used as the insulating film of the above-mentioned oxide superconducting ultra-thin film, the oxide superconducting thin film reacts with the Si element in the oxide superconducting thin film and the insulating film by the heat treatment in the oxygen and superconducting thin film. For example, a decrease in the superconducting critical temperature Tc or the disappearance of the superconducting property occurs. On the other hand, when an oxide superconducting thin film is subjected to a heat treatment at about 900 ° C, Cu element is deposited from the surface of the thin film, compositional deviation occurs, and further, the deposited Cu element is oxidized and Cu
₂ O is formed and it exhibits a P-type semiconductor property.
Therefore, it is especially important to completely suppress the precipitation of Cu in order to prevent the characteristic deterioration of the superconducting thin film. In other words, it is an essential condition that the characteristics of the superconducting electrode material are not affected by the above heat treatment.

Furthermore, since YBa ₂ Cu ₃ O ₇ and other YBa-based perovskite structure oxide superconducting material, and SrBa ₂ Cu ₃ O ₇ and other SrBa-based perovskite structure oxide superconducting material both react with moisture, When cooling is repeatedly performed using a refrigerant, moisture in the atmosphere is condensed to infiltrate the moisture from the superconductor surface layer, and eventually superconducting properties change, and there is a problem that Tc decreases or superconducting properties disappear. .
Therefore, in order to prevent such a change or deterioration of the properties at the end, it is extremely important to provide a protective film so that the oxide superconductor does not react with moisture and improve the moisture resistance.

[Problems to be Solved by the Invention] As described above, the prior art does not consider the reaction between the oxide superconducting thin film and the interlayer insulator and the water resistance, and has a problem in the development of the high temperature oxide superconducting thin film device. .

An object of the present invention is to provide an oxide superconducting integrated circuit having an insulating film (including a protective film) which is stable to high temperature and heat treatment and has excellent moisture resistance.

[Means for Solving Problems] The above object is achieved by using ZrC, ZrN, and ZrB ₂ as an interlayer insulating film and a protective film.

[Function] ZrC is a type of dielectric crystal with a high melting point and excellent in insulating property. It has a monoclinic crystal structure at low temperature and a tetragonal crystal structure at high temperature, and is a typical YBa of high temperature oxide superconductor material. ₂ Cu ₃ O ₇
And the lattice constants of the a and b axes of the crystal lattice are almost equal,
YB using ZrC as a substrate, which is stabilized by including Ca and Mg in several%.
When a ₂ Cu ₃ O ₇ is deposited in a thin film form, a strong thin film in the C-axis direction is obtained. As described above, ZrC and YBa ₂ Cu ₃ O ₇ have extremely good matching of crystal growth with each other and are suitable for forming a thin film laminated structure. On the other hand, contrary to the above, Z on the YBa ₂ Cu ₃ O ₇ film is
When the rC film is formed, the YBa ₂ Cu ₃ O ₇ film can serve as an interlayer insulating film. That is, the high temperature mentioned above,
Mutual diffusion does not occur even in heat treatment in an oxygen atmosphere, and a thermally stable laminated film can be formed.The ZrC film is used as an interlayer insulating film thin film of an integrated circuit element using an oxide superconducting thin film. Further, it can be sufficiently used as a protective film against moisture. Further, nitrides and borides containing Zr as a main component have almost the same effect as ZrC. [Embodiment] An embodiment of the present invention will be described below with reference to FIG. Sr
Y-Cu-O and Ba-Cu are formed on the main surface of the TiO ₃ insulating substrate 1.
A YBa ₂ Cu ₃ O ₇ film is deposited to a thickness of about 1 μm by a magnetron sputtering method using two sputtering targets made of —O material. At that time, the atmosphere of the discharge gas is Ar or Ar +
Either atmosphere may be selected as long as it is under 10% O ₂ low pressure. In addition to the above-mentioned SrTiO ₃ crystal, MgO and YSZ were used as the substrate material.
Any of the crystals may be used. The substrate temperature is normal temperature. Then, the YBa ₂ Cu ₃ O ₇ film is crystallized by performing heat treatment at 920 ° C. for 2 hours in an oxygen pressure atmosphere.

Next, a desired resist pattern is formed on the YBa ₂ Cu ₃ O ₇ film by exposure / phenomenon treatment in a photoetching process using an AZ resist. Then, using the resist pattern as a mask, the YBa ₂ Cu ₃ O ₇ film was etched with a 5% HNO ₃ aqueous solution (volume%) to form a desired pattern, and the lower electrode film 2 was formed.
To form. In this embodiment, the pattern formation of the YBa ₂ Cu ₃ O ₇ film may be carried out by the dry etching method by ion bombardment of Ar or the like in addition to the chemical etching method.

Next, ZrC to be an interlayer insulating film is deposited on the lower electrode film 2. The film thickness of ZrC is 1.8 μm, and an insulating film having a desired film thickness is formed on the entire main surface of the substrate by a magnetron sputtering method using a ZrC sintered body as a sputtering target. An example of deposition conditions is as follows. Using Ar + 10% O ₂ mixed gas, gas pressure is 10 mTorr, discharge voltage is 1 Kv,
The deposition rate of the film is about 16 nm / min. Then, an AZ resist is applied on the main surface of the substrate 1 on which the ZrC film is formed, and heat-cured, and then exposed and developed using a desired photomask to form a resist pattern. Then, by the plasma etching method whose main component is freon gas,
ZrC is formed into a desired pattern, and then the resist is removed to form the interlayer insulating layer 3. At that time, the opening 4 is provided so that a part of the lower electrode film 2 is exposed. Next Ar
The surface of the YBa ₂ Cu ₃ O ₇ film exposed from the opening of the interlayer insulating film is cleaned by the plasma discharge method of. The cleaning conditions are Ar pressure of 10 mTorr, rf discharge voltage of 800 V, and discharge time of 20 minutes. After that, subsequently, a YBa ₂ Cu ₃ O ₇ film to be the upper electrode is formed by the sputtering method. The thickness of the deposited YBa ₂ Cu ₃ O ₇ film is 3 μm. Next, the substrate 1 on which each thin film is laminated is heat-treated at 900 ° C. for 2 hours in a pressurized oxygen atmosphere, and then gradually cooled at a rate of 100 ° C./h. During this heat treatment, the main surface of the substrate 1 was made of YBa ₂ Cu ₃ O produced by a sintering method.
₇ Place the membrane so that it directly contacts the pellet surface. The high resistance layer (existing as an insulating film due to composition shift or crystal disorder) formed on the surface of the lower electrode film 2 by this heat treatment step is partially changed to a low resistance layer, and a slight residual high resistance. The layer acts as a tunnel barrier layer. After performing the above heat treatment, the YBa ₂ Cu ₃ O ₇ film is processed into a desired pattern by a photoetching process to form the upper electrode 5. Finally, a ZrC film is deposited on the entire surface of the substrate to form a protective film 6 for the electrode film.

By the above method, a Josephson integrated circuit using an oxide superconducting thin film can be manufactured. Typical junction characteristics of the element thus manufactured are Jc = 3000A / cm ² , Rj / Rnn =
8 is shown.

In addition to the above-mentioned embodiment, as a method of forming a tunnel barrier layer, the surface of the YBa ₂ Cu ₃ O ₇ lower electrode film 2 exposed by the opening 4 of the interlayer insulating film 3 is cleaned by rf discharge under reduced pressure of Ar, and After completely removing the high-resistivity layer existing on the surface of the lower electrode, Al was deposited to about 30Å, and further thermal oxidation treatment was performed to modify Al into Al ₂ O ₃ and YBa ₂ Cu _{3 of the} upper electrode film was also formed.
A tunnel junction can be produced by forming an O ₇ film.
In this case as well, the same superconducting characteristics as the above results can be obtained.

In the above examples, the case where the ZrC film is used as the layer insulating film has been described, but the same results as in the above examples can be obtained when the ZrN film and the ZrB ₂ film are used as the insulating film materials. Although the sputtering film formation method has been described as a method for forming the insulating film, a chemical vapor deposition method (CVD method) may be used.

Further, when the thin film containing any two or more of ZrC, ZrN, and ZrB ₂ is used as the insulating film, the same result as in the case of the above embodiment can be obtained.

[Effects of the Invention] As described above, according to the present invention, the use of a thin film of ZrC, ZrN, or ZrB ₂ as an interlayer insulating film or a protective film for an oxide superconducting thin film causes a conventional problem. Heat treatment at high temperature in an oxygen atmosphere (for example, 920 ° C-2
No deterioration such as deterioration or loss of superconducting properties after the treatment (in hr O ₂ gas), and prevention of moisture intrusion by repeated immersion in liquid nitrogen refrigerant, corrosion of oxide superconducting electrode film It is possible to completely prevent the change due to.

As described above, the stability of the device is remarkably improved by the present invention.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of an embodiment of the present invention. 1 ... Substrate, 2 ... Lower electrode film, 3 ... Interlayer insulating film, 4
…… Aperture, 5 …… Upper electrode film, 6 …… Protective film.

Claims (2)

(57) [Claims] 1. A superconducting device comprising a Josephson junction formed by laminating oxide superconductor thin films as a main circuit element, and forming an interlayer insulating film for electrically insulating the thin film components constituting the circuit from each other. In integrated circuits, ZrC film, ZrN film,
An oxide superconducting integrated circuit, characterized in that one of the ZrB ₂ films is used as an interlayer insulating film including a protective film. 2. The ZrC film, Z according to claim 1
An oxide superconducting integrated circuit characterized in that a thin film containing at least _{two of an} rN film and a ZrB ₂ film is used as an interlayer insulating film including a protective film.