JPS60160186A - Terminal electrode of superconductive integrated circuit - Google Patents

Abstract

PURPOSE:To obtain the electrode structure of strong adhesive strength and low contact resistance by using two-layer film composed of Ti as the bottom layer and a metallic film of one of Au, Ag and Cu as the upper layer for a base metallic film of a projecting electrode. CONSTITUTION:A Ti film 10 is vapor-deposited on a surface of a terminal electrode 4 for a projecting electrode and subsequently an Au film 11 is vapor-deposited. After that, liftoff is performed to form the desired pattern shape. Next, by using a metal mask prepared previously, positions of the electrode 4 and an aperture part of the mask are adjusted and then In, Sn and Bi are vapor deposited. After removing the metallic mask, a substrate 1 is heated under the predetermined conditions and In, Sn and Bi are reflown to form a hemispherical projection electrode 12. The projecting electrode base metallic film thus fabricated has the low contact resistance and the adhesive property which is enough mechanically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a base metal film for a superconducting protrusion electrode used for an external S connection of a superconducting integrated circuit, particularly a di-Cefnon junction element.

[Background of the invention]

Tunnel Kajita Cefnon junction element has two superconductors w#
Extremely thin II with a thickness of several nm between the films! 0, which is a switch/ch/g device that uses superconducting tunneling at extremely low temperatures (~4K) and has a sandwich structure with three edge films, has a switching speed of approximately Because it is one order of magnitude faster and consumes about three orders of magnitude less power and power, it is expected to be used as a logic operation element for future ultra-high-speed computers.

The company develops superconducting thin films to construct these devices.

Mainly Pb-In-Au alloy, Pb-Au alloy, or N
In addition, oxides of PB and In or oxides of Nb are used for the ultra-thin tunnel barrier layer. By the way, in order to use these D1Sefson junction devices as elements for ultra-high-speed computers, we implemented a large number of chips that were integrated into the L8 level by Nana et al., and developed logic operation circuits and memory circuits that were integrated into the L8 Lebel. 0 Things to be especially careful about when mounting these LSI chips on a module board.

(1) Superconducting LSI chips and other superconducting LSI chips.

If you connect the pools via wires, those wires.

The connection electrode (input/output signal extraction #IL4Iii) is.

V. Everything must be made of superconducting metal.

(2)] bonding the L8I chip to the mounting board.

The above two items are major differences from conventional semiconductor processes.

Aui (polar-Au wire bonding, AI electrode-an plated lead or solder electrode-solder electrode) four-bonding, etc. are used. Among these methods, the method applicable to superconducting LSI assembly is reflow bonding using solder electrodes.

This is because the solder electrode itself exhibits superconducting properties, and it is suitable for high-density packaging because the wiring length can be shortened compared to other methods of expanding the wiring length by chip mounting. Pb is the component ratio of solder generally used for reflow bonding.
It is a pb-8n alloy (eutectic alloy) consisting of 60 parts of 8n and 40 parts of 8n, and its melting point is 183°C. ◎Usually, an LSI (8i-LSI) with solder deposits formed is reflow bonded onto a mounting board. In this case, the LSI and board are approximately 2
The purpose is achieved by heating to 00-300°C and melting the solder IE electrode. When this method is adopted as a mounting method for a superconducting LSI chip on a mounting board.

The following problems arise: ◎In other words, Josephson junction elements use an extremely thin oxide barrier layer with a thickness of 20 to 40λ, but due to the heat during reflow bonding, the oxide l- In the case of a superconducting LSI using OPb as a superconducting electrode, oxygen molecules diffuse into the lower part or inside the superconducting electrode, deteriorating the so-called superconducting properties.
The permissible temperature limit for preventing the above-mentioned deterioration is approximately 90°C, and when Nb is used, the temperature limit is approximately 200°C.
It is ℃. Therefore, in the case of conventional solder electrodes, superconducting L
It cannot be applied to the assembly of SI.

For this reason, it is necessary to develop protruding electrode materials that melt S at temperatures below 90°C and exhibit superconducting properties themselves. Typical materials for these are I n-8n #1m-8n
-Bi etc. Another problem is that when forming the above-mentioned protruding electrodes on the terminals of superconducting LSIs, 1. mechanically sufficient adhesive strength is obtained, and electrically superconducting connection or contact resistance is low. Since connection is required, a metal film for connection (metal film underlying the protruding electrode) is provided between the protruding VT pole and the terminal portion of the superconducting LSI. Generally, these metal films are made of Au/Pd 814 (upper layer Au, lower layer Pd). oAu is a protruding electrode and an underlying Pd device, and a Pd device is a 4-terminal electrode provided on a superconducting LSI chip (generally (Nb film is used) and protruding IE electrode material LSI chip * Since there is no projection of a diffusion prevention film to prevent diffusion inside the electrode, a slight resistance (contact resistance) is exhibited. , a fever due to dill fever occurs. Therefore, liquid kL of cryogenic refrigerant
e vaporizes and foams, and the cooling effect of the superconducting LI 91 is severely reduced. To change the cooling effect, use the connection command l14.
It is necessary to use gold Mll, which exhibits superconducting properties, or a metal film with low contact resistance.

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned problems. 1) A protruding electrode base which has a mechanically sufficient adhesive strength, has low contact resistance, and has a poor diffusion prevention effect. The purpose is to provide gold j14-.

[Mourning of invention]

In the present invention, the bottom layer is Ti and the upper layers are Au and Ag.

A two-layer film composed of one of the metal films of Cu is superconducting I! As a metal base for continuous protruding electrodes.

It is formed on the external connection terminal electrode provided inside the superconducting LSI chip.

The Ti film has sufficient adhesion to Nb, which is the external connection terminal electrode of the superconducting LSI chip, even under low-temperature film formation, and also has excellent adhesion to Au, Mug, and Cu formed in the upper layer. ing. Moreover, ICTIm is Au.

It is also extremely stable against metallic diffusion with Ag and Cu. On the other hand, since the specific resistance of the Ti machine is higher than that of the conventional Pd machine, the contact resistance becomes large. To address these drawbacks, the influence of υ contact resistance can be reduced by setting the Ti film thickness to 300 to 500λ, and even with such a thin film, the aforementioned adhesion and diffusion prevention effects can be obtained. It has been found that it can be used as a base metal film for protruding electrodes for connecting superconducting LSI chips.

All of those films are protruding electrode materials. 1
t-=:' alloy, In-8n-Bi gold alloy has meltability (same bath), and the superconducting transition temperature Tc of the protruding electrode material itself
Sufficient adhesion was obtained without affecting the Ti
It has been found that it can be used as a multistable base metal film by using it in combination with 1l [.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, approximately 6,000 p.p.
8i0 of λ. Form layer 2. After cleaning the substrate again, apply Nb to a thickness of about 3000λ in a high vacuum of 1 x 10 Torr or less.The Nb film can also be formed by sputtering in addition to the evaporation method described above. stomach. Next, a ground plane 3 is formed by etching and etching Nb into a desired pattern using a No. 7 photoresist and a hydrofluoric acid-nitric acid aqueous solution. In addition to the external magnetic shielding effect for the Girosefson junction formed in the active element part of the superconducting LSI and the mirroring effect of the magnetic flux generated from the control aS, this ground plane is used for the ground terminal and protrusion IIC inside the LSI. It plays the role of the terminal electrode 4. Next, the surface of the Nb exchange layer other than the Nb film used for the ground terminal and the terminal electrode for the protruding electrode is anodized to form the ground plane protective film 5, and then the first interlayer insulation made of 840 is formed. f
Ull! form 6. Next IIc A u l n
Resistance consisting of 2.

Further, a wiring connection layer 7 made of a Pb-In-Au alloy and a lower layer 11c are formed. Next, after forming the third M insulating layer made of SiO, using the plasma oxidation method)
The tunnel barrier layer button is then formed on the desired lower electrode surface, and then the upper electrode film is formed. Furthermore, the third M insulation layer is then controlled? Is and wiring layer 8 are further formed to form a protective film 9.Next, the surface of the Itako electrode 40M for the protruding electrode is sputter-cleaned under a reduced pressure of 10" Tolr of Ar gas, and then evaporated to a thickness of TIIrO2500λ. Subsequently, an Au film 11 was deposited to a thickness of 1000λ, and then lift-off was performed to obtain the desired pattern shape.
- In the M layer of F6 and Ayu, the temperature of the substrate is 50°C.
The temperature was maintained at about 0.degree. C. and the dimension (opening) of the terminal electrode 4 was 60 .mu.m. Next, using a metal mask prepared in advance, the terminal electrode 4 described in @ and the opening of the metal mask were positioned, and then In, Sn, and Bi were evaporated to a thickness of about 40 μm, and the metal mask was removed. The substrate was coated with water for 5 hours. The contact resistance of the base electrode for the nine electrodes produced by the method described above is 0.001~
0.0050 mm, 1/2 to 1/2 that of conventional base metal film
We were able to reduce it to 3k. We also confirmed that the adhesion strength of the protruding electrodes was 45 to 155 g (shear strength per piece), and that sufficient mechanical strength was obtained.

1. In this example, the results were obtained using a two-layer film of Au/Ti, but the same results as in the previous example were also obtained for two-layer films of Ag/Ti and Cu/Ti.

Furthermore, in this example, the case of a superconducting LSI using a Pb alloy was described, but a superconducting LSI using a Nb-based material
It has been confirmed that similar effects can be obtained when using In that case, the temperature of the protrusion ti glue 70 can be raised to 200°C.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to stably form the electrode base metal replacement on the external connection protrusion 1 of the super-conducting LSI, and an electrode structure with high adhesive strength and low contact resistance can be reproduced. Now it can be easily manufactured.

[Brief explanation of drawings]

FIG. 41 is a diagram showing a cross-sectional structure of a protruding electrode portion for external connection of a superconducting LSI according to an embodiment of the present invention. In the figure, l...substrate, 2... insulating layer (layer to Si), 3
--Ground plane, 462. Superconducting L81 terminal, electrode, 5...ground brain protective film, 6...w
41 Interlayer insulation film, 7... Wiring connection layer, 8... Wiring layer, 9... Protective film. 10 ・Ti MIA, 11 ・Au1ll! , 12-
...Superconducting protrusion - @1 pole. Patent applicant Hirobe Yoda, Director of the Agency of Industrial Science and Technology Figure 1

Claims (1)

[Claims] 1. The main element is a Santoichi structure in which an extremely thin tunnel barrier layer is sandwiched between two superconducting thin films. In the 11-way superconducting device in which superconducting protruding electrodes are connected to the element, the lowermost layer is made of TI and the upper layer is made of one of Au, Ag, and Cu metal films as the base metal film for the protruding electrodes. A terminal electrode for a superconducting integrated circuit characterized by using a two-layer device.