JPS60107876A - Manufacture of josephson element - Google Patents

Abstract

PURPOSE:To form a throughhole for junction eliminating any burrs by a method wherein SnO2 is utilized for a throughhole insulating material for junction and an interlayer material. CONSTITUTION:A thermal oxide film 32 is formed on an Si substrate 31. Firstly a resist tensile mask 33 for forming a lower electrode is provided on the film 32. Secondly a layer to be a lower electrode 34 is formed and lifted off to form the lower electrode 34. Thirdly a throughhole forming mask 35 is formed. Fourthly an SnO2 film is evaporated to form an interlayer insulating film 36. Fifthly the film 36 with throughhole for junction is left by lift off process. Sixthly a lift off mask 37 is formed. Seventhly a tunnel barrier layer 38 is formed by plasma oxidation process. Eighthly SnO2 is evaporated for a protecting film 40. Finally the mask 37 is lifted off to form an upper electrode 39 and the protecting film 40. Through these procedures, any burrs to be generated in case of forming a minute pattern especially a throughhole for junction may be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the production of Pb alloy-based and Nb-based Josephson elements, and relates to a method of producing a through hole for bonding to bamboo.

[Background of the invention]

In the conventional Josephson element, there are problems in the method of manufacturing the through-pole for the junction, making it difficult to form the through-hole according to the design dimensions, and the '1-flow tightness varies greatly between each junction, resulting in a decrease in the operating margin. It was the cause.

First, a conventional manufacturing process and its problems will be explained using one drawing.

FIGS. 1(a) and 1(t) are explanatory diagrams of the manufacturing process of a through hole for bonding in a conventional Josephson element.

In the figure, 11 is a substrate, 12 is a stencil mask (hereinafter referred to as lift-off mask) made of AZ-based resist (manufactured by Hoechst Co., Ltd.) and has an overhang, and 13
is a StO film.

As shown in FIG. 1(a), a lift-off mask 12 was used to deposit an SiO film 1.3i as an insulating material, and a lift-off process was performed to form a pattern.

However, the deposition particles of SiQ are strongly scattered and adhere to the bottom and side walls of the overhang of the lift-off mask 12, and in the subsequent lift-off process, as shown in FIG.
As a result, holes (indicated by dotted circles) remained, making it impossible to form a through hole according to the design dimensions.

For this reason, as described above, variations in current density between the respective junctions and a reduction in the operating margin occur.

[Purpose of the invention]

It is an object of the present invention to provide an element having a through-hole pattern for Josephine junctions having the same design dimensions and no holes, etc., and a method for manufacturing the same.

[Summary of the invention]

In the present invention, in order to realize this, various insulating materials were used. That is, %Qe.

The targets were In20B, 8nOt, etc. As a result,
S n Ox can be deposited relatively easily by the resistance heating method, and moreover, the deposition rate is %l! 1 lil! It was found that a through-hole pattern consistent with the design could be formed with almost no penetration.

FIGS. 2(a) and 2(b) are explanatory diagrams of a through hole for bonding according to the present invention, and FIG. 2(a) shows a lift-off mask having an overhang portion formed on a substrate 21 as in the conventional case.

It shows the cross-sectional shape of the 8n02 film 23 deposited. In addition, (- indicates the cross-sectional shape of the through-hole pattern after lift-off. As is clear from the figure,
There are no cracks or the like, and the pattern is formed according to the design dimensions.

In addition, in the manufacturing process of di,′:1 Cefson device,
Pattern formation by photolithography and lift-off steps are repeated in various steps in addition to forming through-holes, but it is desirable that each lift-off mask formed in each step has an overhang portion. It is also used in various steps in the Josephson fabrication process of the present invention.

69. How to form a lift-off mask with a hank part using a known method. For details, see IBM Tech B
Ull, 19.4048 (1977).

Normally, positive type AZ1350J resist (manufactured by Hoechst)
, a positive PMMA resist (also known as 0EBRiooo, Tokyo Ohdaisha #!i) is used.The former AZ1350J resist forms a modified layer on the resist surface by chlorobenzene immersion treatment after pattern exposure, and is exposed to storm light during development. By making the surface of the portion particularly difficult to dissolve in the developer, an undercut is formed to form an overhang portion. On the other hand, in the case of the latter PMMA, the bottom of the resist becomes lightless due to the pax kick effect from the substrate that is irradiated with the electron beam, causing undercuts during development processing, and it is possible to form an overhang part. . Furthermore, if PMMA is irradiated with far ultraviolet light (wavelength of 300 nm or less), subjected to chlorobenzene immersion treatment, and then developed, it is possible to cause undercuts and form overhang portions.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

Embodiment 1 FIGS. 3(a) to 3(0) are explanatory diagrams of the manufacturing process showing one embodiment of the present invention, and FIG. Diagram order (a) to (
The main steps will be explained in correspondence with i).

(ω: The substrate has a thickness of 50 m + φ and a thickness of 450 μm.

A <100> Si substrate 31 is used, and a 600 nm
321-&fT top (
A resist stencil mask (lift-off mask) 33 for bath formation is provided. The 7-off mask is positive type AJ1.
350J resist (Hoechst product) with a thickness of 800
After applying the nanometer coating, pre-baking at 70C for 30 minutes, applying ultraviolet light (360 to 450N) emitted from a high-pressure mercury lamp.
Perform pattern exposure using step m) and chlorobenzene treatment.
0 minutes, and then developed with an alkaline developer.

(b): The 8i substrate 31 on which the lift-off mask is formed is inserted into a vacuum chamber, and sputter cleaning is performed using Ar to remove moisture and dirt adsorbed on the surface of the thermal oxide film 32. At this time, the conditions were: high frequency 1 power 5W, Ar pressure 3
X 10-” Torr, sputtering time 5 minutes.

Next, after reducing the degree of vacuum in the vacuum chamber to 5 x 10-7 Torr, the resistance heater was turned on.

Pb and In are deposited in this order to form a layer that will become the lower electrode 34. - As an example, the film thickness is 4 nm each.
, 160 nm, and 36 nm.

(C) Lift-off is carried out in the near seven-ton lower electrode 34
get.

(d) A secondary bonding through-hole formation mask (lift-off mask) 35 is formed in the same process as in the formation of the lower electrode 34. The material, film thickness, etc. of the resist used may be the same as above.

(e): After performing Ar sputter cleaning in the vacuum chamber again, a film with a thickness of 5nOze and 270
An interlayer insulating film (<8n02 film) 36 is formed by vapor deposition.

(f): Lift-off is performed in acetone to leave the interlayer insulating film 36 completely covering the bonding through holes.

(g) The lift-off mask 37 for secondary upper electrode formation is a positive PMMA resist (also known as 0EBI-LlooO).

After applying Xe-Hg (manufactured by Tokyo Ohka) to a thickness of 1.2 μm and pre-baking for 1° 60 minutes.

Far ultraviolet light (200-300nm) emitted from a 500W lamp
) pattern exposure and chlorobenzene treatment at 15
Do it for a minute AIIBK (, j chill' so/chill 亥ton):
After forming by developing with a mixed solution of IPA ((sopro and χ rule): 1:2), sputter cleaning of iAr on the surface of the lower electrode 34 exposed in the through hole is performed in a vacuum chamber. The conditions at this time are the same as the previous conditions.Next, 02 gas is introduced into the vacuum chamber, and the pressure is 2×
10″2'l' o r r then high frequency power 5W
, plasma oxidation was performed for 15 minutes at an acceleration voltage of 360 V, and the lower s! A tunnel barrier layer 38 made of a polar oxide film (PbO+In2O3) is formed.

(h) Second, increase the degree of vacuum in the vacuum chamber to 5 x 10-' To
After reducing the pressure to rr, P b-B is
i (29 wt %) film (to be the upper electrode) 31 to a thickness of 450 nm n nl is deposited. On top of this, 5nQ2 is continuously deposited as a protective film 40 to a thickness of 120 nm.

(i): The lift-off mask 37 is lifted off with acetone in the same manner as in the formation of the lower electrode 34, and an upper electrode (Pb-Bi film) 39 and a protective film (Sn02 film) 40 are formed. Next, a resist mask (not shown) for forming a protective film was formed in the same manner as the mask for forming the upper electrode. However, the thickness of the resist mask was set to 1.5 μm in consideration of ease of lift-off since the thickness of the protective film 4 in which the nuclide will be formed later is 1 μm, for example. After inserting it into a vacuum chamber and performing Ar sputter cleaning, snow was deposited to a thickness of 1 μm. Lift-off was performed in the same manner as for forming the upper electrode described above, and the protective film 41 was formed.

Through the above steps, the pb-based Josephson device of the present invention is completed.

As described in the examples, the Josephson element according to the present invention uses an insulating material of 5nOzf, and as a result, it is clear from SEM (scanning electron microscope) observation images that the junction dimensions are extremely faithful to the design dimensions. , those with the same characteristics were confirmed. In addition, it was revealed that 8nO211''1. did not cause any damage to device characteristics such as reaction with PB or stress, and had sufficient dielectric strength, making it an extremely stable insulating film.Furthermore, It became clear that 5nOz was extremely stable without dissolving in solvents or aqueous solutions.

〔Effect of the invention〕

As explained above, in the present invention, 5iOtSnOz, which has been conventionally used as an insulating material, is replaced, but 5n02 can be replaced with 5iOtSnOz, for example, using the same method as SiO since Ut.
A film can be easily formed by evaporation using a resistance heater, and no difficulties arise with respect to Lfq in the manufacturing process.

5. According to the present invention, the formation of fine patterns, especially the formation of through holes for bonding, has been completely eliminated, making it possible to create patterns according to the designed dimensions, and with uniform characteristics. The element can be easily obtained.
The effect is profound.

Furthermore, as a result of applying the present invention 'e to the production of a Nb-based Josephson element, an element with uniform characteristics similar to that of a Pb-based Josephson element was obtained with good reproducibility.

Note that the present invention is applicable to devices other than Josephson devices that have a lift-off process (for example, bubble memory devices, C1a
It goes without saying that this method can be applied to the production of As elements, etc., and has great effects.

[Brief explanation of drawings]

Figures 1 (a) and (b) are explanatory diagrams of the manufacturing process of a through hole for bonding in a conventional Josephson element, and Figure 2 (a).
) and (b) are explanatory diagrams of the bonding through-hole according to the present invention, and Figures 3 (a) to (i) are manufacturing process diagrams showing one embodiment of the present invention, and Figure 3 (i) is a diagram of the completed PB. 1 is a cross-sectional view schematically showing the main parts of a Josephson-based Josephson element. 11.21.31...Substrate% 12.22...Stencil mask (lift-off mask)% 13...si
o film, 23 ・5nO1 film, 32... thermal oxide film, 33
, 35° 37... Lift-off mask % 34... Lower electrode (Pb-Au-i-n film), 36... Interlayer insulating film (8nOa film), 38... Tunnel barrier layer, 3
9...Top electrode, (p b 1 Figure\JZ Figure 3 Figure'fJ 3 Figure

Claims (1)

[Scope of Claims] 1. 5n02'e is used as a through-hole insulating film material and interlayer insulating film material for junction that separates a lower electrode and an upper electrode made of a superconducting film to form a Josephson junction. Method for manufacturing a Josephson device. 2. The superconducting film material described in item 1 outside the scope of claims is Pb
Alloy-based, Nb-based, NbN, MON, N1)ssn. A method for manufacturing a Josephson device characterized by being made of Nb5AL, VaSi, and N0Re.