JPH09219118A - Superconducting wiring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the reduction of the critical current value owing to the oxidation of a superconducting wiring in a high temperature processing, by providing one of an aluminum oxide film, a magnecium oxide film, a zirconium oxide, and the like, on the upper surface of a superconductor. SOLUTION: An insulating liner layer 2 is formed by laminating a silicon dioxide on a silicon substrate 1. Then, a two-layer membrane of niobium and aluminum oxide is formed on the layer 2. Then, a part of the aluminum oxide and the niobium is etched to form the first wiring protective layer 4, and the niobium is etched by making the layer 4 as the mask, so as to form the first superconducting wiring 3. Then, a layer-to-layer insulating layer 5 is formed. After that, the second wiring protective layer 7 which consists of an aluminum oxide is formed. Then, the niobium is etched by making the layer 7 as the mask to form the second superconducting wiring 6. And after that, the silicon dioxide is laminated so as to make into a protective insulating layer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting integrated circuit device, and more particularly to a superconducting wiring structure suitable for integrating multi-layered superconducting wiring.

[0002]

2. Description of the Related Art Regarding the structure of conventional superconducting wiring, M. B. Ketjen, Dee Pearson, A. W. Kleinzasser, CK Fu, M.
Smith, Jay Logan, Kay Stowiats, E. Balun, Em Jaso, Tee Ross, Kay Petrilo, Em Manny, S. Basavaia, S. Brodsky, S. B. Caplan, and W. Jay Gallagher "Sub-micrometer, planarized, niobium-aluminum oxide-niobium Josephson Process for 125";
Mm Wafers Developed Inn
Partnership With Silicon Technology ”
Applied Physics Letters, Volume 59,
No. 20, November 1991, pp. 2609-261
Up to 1 page (MB Ketchen, D. Pearson, AW Kleins
sasser, CK Hu, M. Smyth, J. Logan, K. Stawiasz,
E.Baran, M. Jaso, T. Ross, K. Petrillo, M. Manny,
S. Basavaiah, S. Brodsky, SB Kaplan, and WJ
Gallagher; "Sub-μm, planarized, Nb-AlOx-Nb Josep
hson process for 125 mm wafers developed in partne
rship with Si technology "Appl. Phys. Lett., Vol.
59, No. 20, November, 1991, pp.2609-2611), it was composed of niobium (Nb).

[0003]

In the prior art, the superconducting wiring was made of niobium. When manufacturing a superconducting integrated circuit using multilayer niobium superconducting wiring,
The niobium wiring once formed may be subjected to a high temperature step later. When the niobium wiring undergoes a high temperature process, oxygen in the air or oxygen diffused from the material used in the film forming process reacts with niobium to form niobium oxide (Nb ₂ O ₅ ), which causes Part of it changes to an insulator, and the superconducting critical current value that can flow in the wiring decreases. This may hinder the operation of the integrated circuit, causing a problem in terms of circuit reliability.

The object of the present invention is to prevent oxygen from diffusing into the superconductor constituting the superconducting wiring even when a high temperature process is performed after the superconducting wiring is formed, and the superconductor changes to an insulator to change the superconducting property. An object of the present invention is to provide a superconducting wiring structure suitable for suppressing a decrease in the critical current value.

[0005]

Means for Solving the Problems The above-mentioned problem is to form a superconducting wire, and then to form a film at or near the superconducting wire forming portion at a high temperature. Before the film formation process in step 1, the surface of the formed superconducting wiring (that is, the surface not bonded to the substrate material or the insulating film) is covered with a material having a standard enthalpy larger than that of the oxide of the superconducting material forming the wiring. Will be solved. When the superconducting wiring is formed under reduced pressure (so-called vacuum) and the surface of the superconducting wiring is covered with a metal oxide, it is desirable to form a metal film on the surface of the superconducting wiring under reduced pressure and then oxidize it. .

The above-mentioned object of the present invention is to provide a superconducting wiring which is provided in a superconducting integrated circuit and is capable of flowing a superconducting current. At least a part of the superconducting wiring is in contact with a superconductor forming the superconducting wiring. On the upper surface of the superconductor, an aluminum oxide film (Al ₂ O ₃ ), a magnesium oxide film (MgO), a zirconium oxide film (ZrO ₂ ), a hafnium oxide film (Hf ₂ O ₃ ), and a tantalum oxide film (TaO).
_This is achieved by providing a structure having at least one of ₃ ).

Another object of the present invention is to provide, in the above-mentioned superconducting wiring, a superconductor which constitutes the superconducting wiring,
This is achieved by constructing a material selected from niobium nitride and niobium carbon nitrogen.

Further, the object of the present invention is achieved by providing the above-mentioned superconducting wiring in a superconducting integrated circuit using a Josephson junction element.

As described above, when the superconducting wiring is provided in the superconducting integrated circuit in the present invention, an aluminum oxide film, a magnesium oxide film, in contact with the superconductor, is formed on the upper surface of the superconductor forming the superconducting wiring. At least one of a zirconium oxide film, a hafnium oxide film, and a tantalum oxide film is provided. The standard enthalpy of formation of Nb ₂ O ₅ per mol of oxygen atoms is −380 kJ / mol, whereas the standard enthalpies of formation of Al ₂ O ₃ , MgO, ZrO ₂ , Hf ₂ O ₃ , and TaO ₃ are respectively: -559, -602, -55
0, -572, and -409 kJ / mol. For example, when the superconductor is made of niobium, since the absolute value of the enthalpy of formation of oxides of aluminum, magnesium, zirconium, hafnium, and tantalum is larger than that of niobium oxide, aluminum, magnesium, zirconium, hafnium, and Oxygen atoms bonded to tantalum are less likely to react with niobium, and even if a high temperature process is performed, niobium forming a superconductor is less likely to be oxidized and the superconducting critical current value be lowered.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. FIG. 1 is a sectional view showing a part of a superconducting wire according to an embodiment of the present invention. 280 nm of silicon dioxide is deposited on the silicon substrate 1 by a high frequency magnetron sputtering method using an argon gas with a pressure of 1.3 Pa (that is, under reduced pressure) to form a base insulating layer 2. Niobium having a thickness of 280 nm was formed on the base insulating layer 2 by a DC magnetron sputtering method using argon gas at a pressure of 1.3 Pa.
Aluminum is continuously deposited to a thickness of 5 nm without breaking the vacuum, and aluminum is oxidized to form a two-layer film of niobium and aluminum oxide. A photoresist pattern including a wiring of 1 μm width and a space of 1 μm width is formed on the above two-layer film, and a part of aluminum oxide and niobium (10 nm in thickness) is formed by an ion beam etching method using argon gas. Is etched to form a first wiring protection layer 4 made of aluminum oxide, and the photoresist is removed. Using this first wiring protection layer 4 as a mask, pressure 13
Niobium is etched by the reactive ion etching method using CF ₄ gas of Pa to form the first superconducting wiring 3.

Next, again, silicon dioxide is deposited to a thickness of 360 nm by a high frequency magnetron sputtering method using an argon gas having a pressure of 1.3 Pa, and is processed by a reactive ion etching method using a CHF ₃ gas to form an interlayer insulating layer 5. Form. When the silicon dioxide is deposited, the temperature of the entire sample rises to about 180 ° C, but the first superconducting wiring 3
Since there is the first wiring protection layer 4 on the first superconducting wiring 3,
The niobium forming the film is less likely to be oxidized by reacting with oxygen in silicon dioxide during film formation. Therefore, the decrease in the superconducting critical current value of the first superconducting wiring 3 is small. The surface of the sample is sputter-etched using an argon gas having a pressure of 2 mTorr, and the first wiring protection layer 4 on the first superconducting wiring 3 is formed.
After removing the exposed part of the above, niobium (360 nm) and aluminum (5 nm) were continuously deposited without breaking vacuum by a direct current magnetron sputtering method using argon gas at a pressure of 1.3 Pa to oxidize aluminum. A two-layer film of niobium and aluminum oxide is formed. 2 above
A photoresist pattern containing a 1 μm wide wiring and a 1 μm wide space is formed on the layer film, and a part of aluminum oxide and niobium (made into a film thickness) is formed by an ion beam etching method using argon gas. 10 nm) is etched to form a second wiring protection layer 7 made of aluminum oxide, and the photoresist is removed. Using the second wiring protection layer 7 as a mask, niobium is etched by the reactive ion etching method using CF ₄ gas at a pressure of 13 Pa to form the second superconducting wiring 6. First superconducting wire 3 and second
The planar dimension of the contact portion of the superconducting wiring 6 is 0.7 μm square. Further, 440 nm of silicon dioxide is deposited by a high frequency magnetron sputtering method using an argon gas having a pressure of 1.3 Pa to form a protective insulating layer 8. When the silicon dioxide is deposited, the temperature of the entire sample rises to about 200 ° C.
Since the wiring protection layer 7 is provided, niobium forming the second superconducting wiring 6 is less likely to be oxidized by reacting with oxygen in the silicon dioxide during film formation. Therefore, the decrease in the superconducting critical current value of the second superconducting wiring 6 is small. As described above, the superconducting wiring according to the example of the present invention could be manufactured.

If the above-mentioned superconducting wiring is cooled to 4.2K using liquid helium, the superconducting critical current value that can flow from the first superconducting wiring 3 through the second superconducting wiring 6 becomes 40 mA, and the above-mentioned superconducting wiring is It can be used in superconducting integrated circuits using Josephson junction devices.

FIG. 2 is a sectional view showing a part of the superconducting wiring in the case where there is no wiring protective layer in contact with the superconductor made of niobium in the above embodiment. When the superconducting wire of FIG. 2 is cooled to 4.2K using liquid helium, the superconducting critical current value that can flow through the first superconducting wire 13 and the second superconducting wire 15 is 20 mA. Therefore,
In order to obtain a critical current value of 40 mA with the same structure as in FIG. 2, it is necessary to widen the width of the superconducting wiring to about twice the width of the embodiment of the present invention.

[0014]

As described above, according to the present invention, in the superconducting wiring provided in the superconducting integrated circuit, the superconducting critical current value is lowered even when a high temperature process is performed after the superconducting wiring is formed. There is little, and it does not interfere with the operation of the superconducting integrated circuit. Moreover, in order to prevent malfunction of the integrated circuit, it is not necessary to increase the line width and film thickness of the superconducting wiring in consideration of the amount of decrease in the critical current value due to the high temperature process. Can be integrated.

[Brief description of drawings]

FIG. 1 is a sectional view showing a part of a superconducting wiring according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a part of a superconducting wire manufactured by using a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Base insulating layer, 3 ... 1st superconducting wiring, 4 ... 1st wiring protective layer, 5 ... Interlayer insulating layer, 6 ... 2nd superconducting wiring, 7 ... 2nd wiring protective layer, 8 ... Protection Insulating layer, 11
... Silicon substrate, 12 ... Base insulating layer, 13 ... First superconducting wiring, 14 ... Interlayer insulating layer, 15 ... Second superconducting wiring, 16
… Protective insulation layer.

Claims (3)

[Claims] 1. In a superconducting wiring which is provided in a superconducting integrated circuit and is capable of flowing a superconducting current, at least a part of the superconducting wiring is in contact with a superconductor constituting the superconducting wiring and is on the upper surface of the superconductor. A superconducting wire comprising at least one of an aluminum oxide film, a magnesium oxide film, a zirconium oxide film, a hafnium oxide film, and a tantalum oxide film. 2. The superconducting wiring according to claim 1, wherein the superconductor forming the superconducting wiring is selected from niobium, niobium nitride, and niobium carbon nitrogen. 3. The superconducting wiring according to claim 1, wherein the superconducting wiring is provided in a superconducting integrated circuit using a Josephson junction element.