JPS60208874A - Manufacture of josephson junction element - Google Patents

Abstract

PURPOSE:To form a tunnel barrier part having high dimensional accuracy, by performing the anisotropic etching of the mask of the tunnel barrier part, and completely etching the part other than the mask by ion beam, which is projected at an angle of 30-50 deg. with respect to the direction normal to a substrate. CONSTITUTION:On an insulating substrate 11, a first superconductive electrode 12 of Nb, a tunnel barrier layer 15 and a second superconductive electrode 21 of Pb, i.e. three-layer films, are formed. A resist mask 22 is formed at a place, which is to become the tunnel barrier part on the second superconductive electrode 21. Thereafter, the second superconductive electrode 21 is etched by ions by using an obliquely inputting ion beam at an angle of 30-50 deg. with respect to the direction normal to the substrate 11. Then an insulator layer 14 comprising SiO and the like is deposited on the entire surface of the substrate by a film forming method having excellent directivity. The resist mask 22 is lifted off and a pattern is formed. Thereafter, a third superconductive electrode 23 is formed by the same way for the first superconductive electrode 12 and the second superconductive electrode 21.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a Josephson junction device, and more particularly to a method for manufacturing a tunnel barrier type Josephson junction device.

(Prior art and its problems) In general, logic circuits and memory circuits composed of Josephson junction elements have excellent junction characteristics, and variations in these characteristics between elements are small, and they are easily affected by thermal cycles. Elements with minimal characteristic deterioration are required. Niobium (Nb) or a Nb compound is used for the first superconductor electrode as a device that satisfies both the integration requirements of excellent bonding properties and high reliability.

Those using lead (pb) or a Pb alloy for the second superconductor electrode are attracting attention. however.

Since this Pb-based material is chemically unstable, conventional patterning methods have been limited to the lift-off method.

As a conventional example of this, 19
In October 1980, American magazine “IEEE Transac
t-ions on Electron Device
There is a paper published in ED-27, No. 10, pages 1998-2008 of ``S'', Vol.

First, as shown in FIG. 1 (al), a first superconductor electrode 12 made of Nb is formed on an insulating substrate or a substrate 11 having an insulating layer on its surface by vapor deposition or sputtering. The patterning of the first superconductor electrode 12 is carried out using a conventional photoresist process, a ching method, or a lift-off method.Next, as shown in FIG. A resist mask 13 with an undercut shape is formed in the part that will become the barrier part, and as shown in FIG. 11(C).
As shown in Figure 2, silicon monoxide (8i0), silicon dioxide (Sin,
), etc., and then lift-on to form a tunnel barrier section with an opening as shown in FIG. In addition, it can be obtained by immersing it in an organic solvent such as chlorobenzene or bromobenzene before or after exposure.Next, as shown in Figure 1(e), several layers are applied to the tunnel barrier section by thermal oxidation method or plasma oxidation method. A tunnel barrier layer 15 having a thickness of 1 OA is formed.Thereafter, as shown in FIG. 1(f), a second superconductor electrode 16 is formed by a vapor deposition method and a lift-off method.

This manufacturing method requires an undercut-shaped resist mask 13 to form the tunnel barrier, but the shape of this mask is easily influenced by resist pre-baking conditions, organic solvent temperature, dipping time, etc. . In particular, it is very difficult to accurately adjust the dimensions of the lower part of the resist mask 13, which defines the effective area of the tunnel barrier.Also, during sputter cleaning or plasma oxidation of the tunnel barrier, sputtered materials from the insulator layer 14 may There were also five drawbacks when the barrier became contaminated.

(Objects of the Invention) It is an object of the present invention to provide a method for manufacturing a Josephson junction element that eliminates such conventional drawbacks, eliminates overetching, and allows formation of a tunnel barrier portion with high dimensional accuracy.

(Structure of the Invention) The structure of the method for manufacturing a Josephson junction element of the present invention is such that a first superconducting electrode of a predetermined pattern made of Nb or a Nb compound is formed on a substrate, a tunnel barrier layer is formed on the first superconducting electrode, and a tunnel barrier layer is formed on the first superconducting electrode. A first step of successively forming a second superconducting electrode made of Pb or a Pb alloy on the tunnel barrier layer, and forming an etching mask at a location on the second superconducting electrode that will become the tunnel barrier layer. The second superconducting electrode portion at a location other than 30° relative to the normal direction of the substrate.
A second step of completely ion etching with an ion beam incident at an angle of ~50 degrees, and depositing an insulating layer so as to fill the etched portion of the second superconducting electrode and the surface of the substrate other than the pattern. and then a third step of removing the etching mask, and a fourth step of depositing a third superconducting electrode on the insulator layer including a portion in contact with the second superconducting electrode. Features.

(Example) The present invention will be explained in detail below with reference to the drawings.

FIGS. 2(a) to ω are cross-sectional views explaining the embodiments of the present invention in the order of steps. First, as shown in FIG. 2(a), an insulating substrate or a substrate having an insulating layer on the surface ll, a first superconducting electrode 12 made of Nb or a Nb compound
, tunnel barrier layer 15. A three-layer film of the second superconductor electrode 21 made of Pb or a Pb gold alloy is formed. These first
And the second superconductor electrode 12.21 is formed by a vapor deposition method or a sputtering method. Further, the tunnel barrier layer 15 is
The superconductor electrode 12 is formed by oxidizing the surface of the superconductor electrode 12 by heat or plasma, or by depositing an insulating film or a semiconductor film. Patterning of these three-layer films 11i5 and 2t is performed by an etching method using a normal resist process or a lift-off method.

Next, as shown in FIG. 2 Φ), the second superconductor electrode 21
After forming a resist mask 22 at a location that will become the upper tunnel barrier section, as shown in FIG. 2 (C1 and (d)),
The second superconductor electrode 21 is ion-etched using an ion beam incident obliquely at an angle of 30 to 50 degrees with respect to the normal direction of the substrate 11 . As shown in FIG. 2 (C1), in the just-etched state, the base of the second superconductor electrode 21 is widened, but by over-etching for approximately the same amount of time, the second superconductor electrode 21 is widened. is shown in Figure 2 (
As shown in d), it becomes a rectangular pattern.

Next, as shown in FIG. 2 (el), an insulating layer 14 made of 8i0.SiO□ or the like is deposited on the entire surface of the substrate by a film forming method with good directionality such as vapor deposition or ion beam deposition. The resist mask 22 is lifted on to form a pattern as shown in FIG. 2(f).After this, as shown in FIG. A third superconductor electrode 23 is formed using the same film forming method and processing method as in 21.

When using oblique incidence etching as in this embodiment, as shown in FIG. 2(C), the second superconductor electrode 2
1 and the shadow effect of the resist pattern 22.
This produces a skirt on the superconductor electrode 21, which can be removed by overetching for approximately the same time as the just etching time. At this time, there is a concern that the substrate 11 and the first superconductor electrode 12 may be etched, but there is no problem because a large selectivity can be obtained with the element having this configuration. Also, the second superconductor electrode 1 after etching
2. Since the resist pattern 22 has excellent rectangularity,
Subsequent lift-off can be performed easily and accurately.

FIG. 3 is a characteristic diagram showing the relationship between pattern width change amount Δw/b and beam incident angle θ in pb ion beam etching. Here, the pattern width change amount Δw/d is P with respect to the resist mask width normalized by the etching depth d.
6 The increase in pattern width is ΔW, and the beam incidence angle θ is:
This is the angle that the incident ion beam makes with respect to the normal direction of the substrate. As is clear from this figure, it is possible to form a workpiece pattern with a beam incident angle θ of about 40 degrees and almost no pattern width variation Δ−/·d. Pb and Pb
The optimal beam incidence angle θ for alloys depends somewhat on the material, but
It is thought to be between 30 and 50 degrees.

In this manufacturing method, if a rectangular resist mask with good reproducibility can be used to form the tunnel barrier portion, it is possible to transfer a pattern with high precision from the resist mask 22 to the M2 superconductor electrode 21 using the ion etching method. from,
It is easier to control the dimensions of the tunnel barrier compared to methods used in conventional lift-off methods.

(Concrete example) Next, the present invention will be explained in detail.

A silicon (Si) substrate (11) whose surface is coated with thermal oxidation 5in2 is heated to a substrate temperature of 30% by electron beam evaporation.
A Nb film (12) with a thickness of 2000A is deposited at 0C. Subsequently, in the same apparatus, argon containing 2% oxygen (02) (
Using a mixed gas of Ar)-0, the total pressure lXl0 To
rr, cathode voltage -170V-? 'Nb film surface 10
Plasma oxidize for 20-30X niobium oxide (N
b20g) Form a film (15).

After this, the Pb film (21) was continuously deposited at room temperature to a thickness of 2000 mm.
Deposit λ. After forming a resist mask 22 with a film thickness of 1.5 μm on this film using a normal photoresist process using a positive type photoresist (AZ1350J manufactured by Silaplay Co., Ltd.), Argon etching was performed using a parallel plate type sputter etching device.
, Freon 13 (CF,)pb(21), Nb respectively
/Nb2O, (15) is continuously etched to form a first superconductor electrode pattern.

Next, after patterning a resist mask with a diameter of 1.5 μm and a film thickness of 5000 A at the location on the three-layer film 12s15s21 that will become the tunnel barrier, the PB film (21) is etched using an ion etching method using a beam incidence angle of 40 degrees. is completely removed to form a second superconductor electrode pattern. , this etching condition is Ar pressure 2X] 0'Torr,
Accelerating voltage 500V, current density 0, g m A/c
It is n2. Next, on the substrate 11, a 5 inch (2000λ)
14) is deposited, and the resist mask 22 is removed by ultrasonic cleaning in acetone. After sputter cleaning the substrate surface with Ar, a third superconductor electrode 23 made of a 3000A Pb film is formed in the same manner as in forming the second superconductor electrode pattern.

In this manufacturing method, the etching rate ratio of Pb to AZ1350JKN is as large as 5 to 9 of the second superconductor f with a weight of >21. There is almost no change in pattern dimensions of the tunnel barrier section with respect to the mask. In addition, Pb is the superconductor electrode of Mud 1, Nb is the base insulation 1i) S
Selective etching of Pb is possible because they have large etching speed ratios of 7-8 and 4-5 for t02, respectively.

In addition, in this specific example, Nb is used as the pole 12 of the superconductor 12, and P is used as the second and third superconductor electrodes 21t.
Although the case where B is used has been described, similar results can be obtained with N b compounds and Pb alloys, respectively. However, for the superconductor electrode 23 of the butterfly 3.

Nb or N,b compounds can also be used.

Further, the tunnel barrier layer 15 is provided with a first superconductor electrode 12.
In addition to the oxide layer on the surface, an insulator layer formed by deposition,
When oxidizing the tunnel barrier layer, metal layers and semiconductor layers can also be used. Furthermore, although AZ1350J was used as a mask for forming the tunnel barrier section, other organic resists or inorganic resists may also be used.

(Effects of the Invention) As explained above, according to the present invention, since the tunnel barrier portion is formed by an excellent anisotropic etching method,
A Josephson junction device having a tunnel barrier portion with high dimensional accuracy can be manufactured.

[Brief explanation of drawings]

FIGS. 1(a) to 1(f) are cross-sectional views illustrating a conventional method for manufacturing a Josephson junction device in the order of steps, and FIGS.
(B) is a cross-sectional view of an element explaining one embodiment of the present invention in the order of steps, and FIG. : etching depth) and beam incident angle θ. In the figure, 11...Substrate, 12...First superconductor electrode, 13.22...Resist mask, 14
...Insulator layer, 15...Tunnel barrier layer, 16, 21...Second superconductor electrode, 23
...This is the third superconductor electrode. ″、−１−ノ′ Stone/Figure

Claims (1)

[Claims] A first superconducting electrode of a predetermined pattern made of Nb or a Nb compound is formed on a substrate, a tunnel barrier layer is formed on this first superconducting electrode, and a second superconducting electrode made of Pb or a Pb alloy is continuously formed on this tunnel barrier layer. a first step of forming the second superconducting electrode, and forming an etching mask at a portion of the second superconducting electrode that will become the tunnel barrier portion, and etching the second superconducting electrode portion other than the mask with respect to the normal direction of the substrate; te3
A second step of completely ion etching with an ion beam incident at an angle of 0 to 50 degrees, and covering the insulating layer so as to fill the etched portion of the second superconducting electrode and the surface of the substrate other than the pattern. and a fourth step of depositing a third superconducting electrode on the insulating layer including a portion that contacts the second superconducting electrode. A method for manufacturing a Josephson junction element characterized by: