JPS5877266A - Bump electrode for connection terminal of superconductive thin film functional element and manufacture thereof - Google Patents

Abstract

PURPOSE:To form a bump electrode, whereon a reflowing junction can be formed at the superconductive critical tempeature of 6.5K or above and the melting temperature of 100 deg.C or below by a method wherein at least one of Sn, In and Cd is added to the superconductive alloy having Pb and Bi as main components. CONSTITUTION:A laminated film 9 of Pb/Au is vapor-deposited on the whole surface of an Si substrate 1 including the Nb upper electrode 6 of the Josephson element which was formed by performing a prescribed process. A resist mask is provided, Pb and Bi are successively laminated by soaking the above in succession into the Pb plating solution having borofluoric lead as a main component and the Bi plating solution having bismuth chloride as a main component, and lastly, Sn is superposed on the above by soaking into the Sn plating solution having tin chloride as a main compoenent. Then, a dome-shaped bump 10 is formed by instantaneously fusing the laminated plated film at approximately 120 deg.C. The plated resist is then removed, an unnecessary underlayer 9 is removed using the bump 10 as a mask, and the bump electrode is completed. Using this bump electrode, the yield rate of assembling and the reliability of Josephson LSI can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Application of the Invention The present invention relates to a superconducting thin film functional device, particularly a protrusion used in a wire of a Josephson junction device and a method for manufacturing the same.

(2) Conventional technology The Josephson choreography element made by Tunnel has a sandwich structure with two superconducting thin films several nanometers thick sandwiched between them. A switching element using a 1m tunnel wall is used. This element has a switching speed of fJ1 compared to conventional semiconductor wires.
The power consumption is about 3 orders of magnitude lower, and it is expected to be used as a logical IJI cable and memory element for future ultra-fast nose-resistant aircraft. A pb-4n-Au alloy, a Pb-Au alloy, or Nb is mainly used in the superconductor for constructing these elements. Pb oxide or Nb oxide is used in the tunnel barrier layer of the Kakitabakuhiro. By the way, in order to use these Josephson choreography elements as elements for Miii 6-speed drunkenness control, it is necessary to develop a logic is circuit and a memory circuit lNr that integrate them at the LSI level. When creating these circuits, the following points should be kept in mind: (11) Josephson elements and other Josephson elements
When installing FTC via tM, all seven wirings and electric screws (input/output JrFi connection) are super
WIIL An essential curse made of conductive metal.

(2) The bonding of the circuit chip to the mounting board is carried out at the lowest possible temperature to prevent deterioration of the ultra-thin tunnel barrier layer.
(100C or less) must have a must-see view.

The above two items are different from the conventional gyudou process.'t')7'c
This is one of the things that is very different.

Conventionally, the connection between the L81 chip and the external electrode was At electric m-h.
Ultrasonic wire bonding by tm warehouse, Au1 to pole-
Au#1Ml! , AjKm-Aua line Kjru ,.

Thermopressure layer wire bonding %Au' [pole - 8n plated lead, or solder 11L etc. - reflow bonding with solder electrodes, etc. are used.

Among these methods, the method applicable to the assembly of the Josephson LSI is 70-bonding using solder electrodes. This is because the solder electrode material exhibits superconducting properties. Generally, the components of the solder used for reflow bonding are PB-Sn alloy (eutectic alloy), which is composed of 60% PB and 40% Sn, and one of them is 183C.
It is. Normally solder is formed by z billion tons of *Lsr (st-
When reflow bonding an LSI (LSI) onto an AI board, the purpose is achieved by heating the LSI and the board to about 200C to 230C and melting the solder 11IL poles in a bath.

When this method is adopted as a mounting method for a mounting board of a Josephson LSI chip, the following problem occurs. In other words, the Josephson junction element is used on a 20-30A thick oxide layer barrier layer, but the heat during reflow bonding causes zero atoms in the oxide layer to form on top or bottom S. It diffuses into the superconducting electrode, deteriorating its so-called superconducting properties. In the case of a Josephson LSI using Nb as a superconducting electrode, the allowable temperature limit for preventing the above-mentioned deterioration is about 120C or less.

Therefore, in the case of the conventional No. 1
It is rarely possible to apply it directly to SI assembly.

(3) Purpose of the Invention The present invention has been made in order to solve the above-mentioned problems, and has been made in order to provide a protruding electrode that exhibits superconducting properties and is capable of reflow bonding at temperatures below 100C. I can buy things.

(4) Detailed description of the invention At least one metal selected from S8''*IntCd is sewn onto gold to achieve a superconducting critical temperature of 6.5.
A ternary eutectic alloy with a melting temperature of 100 C or higher and a melting temperature of 100 C or lower is prepared, and this is used as a bump electrode for Josephson LSI glue flow bonding.

The composition of the ternary association that satisfies the above-mentioned ultra-tIIL supercritical temperature and bath M temperature is as follows.

In other words, in the case of pb-Bi-Sn ternary eutectic alloy, Bi
12 ~ 25%, Sn20 ~ 25% (wt%) remaining P
b% p b - f3 i - In the case of In-based ternary eutectic alloy, Bi12 ~ 25% * In20 ~ aO% (wt
%) residue pb, and in the case of pb-BiQd ternary alloy, at1s~25%. This is an alloy group consisting of 5 to 25% (wt%) Cdl and the balance 1 pb. Furthermore, each of the protruding electrodes mentioned above can be manufactured by vapor deposition method, laminated plating method, alloy plating method,
etc. are used. Protruding electrodes can be easily produced by either method.

On the other hand, the protruding electrodes are Nb formed inside the LSI chip.
'IIt to the extreme putting part. A diffusion barrier at- is provided to prevent mutual diffusion between Nblft and the solder electrode.

Generally, Pb-Au is often used.

(5) Examples Hereinafter, the present invention will be explained in detail with reference to examples. 1st
As shown in the figure, a silicon dioxide layer 2 having a thickness of approximately 6,000 layers is formed on a silicon single crystal substrate 1 which has been previously cleaned by thermal oxidation.

After cleaning the board again, 16”'1'1'or
Niobium is deposited to a thickness of approximately 3000 nm in a high vacuum below r. Next, a desired pattern is etched using a photoresist and a hydrofluoric acid-nitric acid bath solution, and the lower electrodes (3, 3'
) to form. Next, silicon monoxide is formed as an interlayer insulating film 4 on the surface of the niobium electrode. At that time, a lift-off process is used to provide an opening so that a portion of the niobium electrode is exposed. Next, the pressure on the niobium electrode surface exposed in the opening was reduced to 5×10'''5 TOrr, and fch
After sputter cleaning in an r atmosphere, the pressure was subsequently reduced to 5 x 10" Torr, Ar gas was released, 0.0" gas was introduced, and the pressure was reduced to 10" Torr.
Nb is exposed for about 10 minutes to @ elemental plasma generated with a high frequency output of 20W.

According to the above method, a tunnel barrier layer 5 made of a niobium oxide film having a thickness of about 40 nm is formed on the exposed surface of the niobium electrode. Next, Nb is deposited to a thickness of approximately 4000 nm to form the upper electrode 6. Next, 3t□ was vapor-deposited and
An interlayer insulating layer or a tumor film 7 is formed on the surface. In addition to sio, these interlayer insulating layers are 810. Or 8i
aN4, polyimide resin, etc. may also be used. Next, a wall metal for preventing diffusion and a bump base metal 9 for improving adhesion are deposited on the entire surface of the wafer. Generally, a Pd/Au laminated film with a thickness of about 100 OA is used as the bump base metal. This bump base metal film is used as an electrode when forming bumps by electroplating. Next, a photoresist is applied to the entire surface of the wafer, and in order to form bumps, openings are provided at desired locations to form a plating resist pattern that exposes the bump underlying metal. Next, the wafer is immersed in a PB plating solution containing boron fluoride as a main component, and a PB film with a thickness of about 40 μm is formed on the mouth of the resist by the electroplating method. Next, the wafer is immersed in a Bi plating solution containing bismuth chloride as the main component, and the same process as Pb is performed. Approximately 40mm thick is applied to the top of the PB using the L-air plating method.
Form μmoB1.

Finally, the wafer is immersed in a Bn plating solution containing tin chloride as a main component to form a Bn layer with a thickness of approximately 20 μm. Thereafter, the wafer is pushed into a preheated electric furnace, and the laminated plating layer is instantly melted at about 120C, and a hemispherical pb-Bi-Sn superconducting bump electrode (bump) 10 is formed.
form. In general, if the size of the opening window in the bump underlayer for plating is 60 μm, the above-mentioned method can create a hemispherical memory with a height of about 130 μm in diameter. Next, after removing the Metsuki Resistant, use the hemispherical protruding electrode as a mask to remove unnecessary /
Au/Pd) is removed. According to the method described above, pb
A low single point superconducting protrusion electrode made of -ai-sn can be created.

In addition, in the example, a method for making a protruding electrode for a connection terminal made of pb-Bi-f3n alloy was described, but pb-Bi-f3n alloy
For j3i-In or pb-Bi-cd, protruding electrodes for multi-connection terminals can be created in the same manner. In that case, an acid plating solution containing indium chloride or cadmium chloride as a main component may be used as the In or CD plating solution, respectively.

Furthermore, in this example, p b -Bi-8n, p b -B
Although the electroplating method has been described in detail as a method for forming the laminated film (i-In, FiP b-B 1-Cdty), exactly the same results can be obtained by using a vacuum evaporation method in addition to the above method.

Furthermore, in the embodiments of the present invention, a method was described in which a hemispherical electrode was obtained by laminating the respective metals constituting the protruding electrode and then instantaneously melting them. i3i alloy layer.

PB, Bi alloy plating method or simultaneous vapor deposition method)
The same results as in the above example were obtained.

(6) Summary As explained above, according to the present invention, protruding electrodes for external connection of a tunnel junction type Josephson LSI can be produced with good reproducibility, and the LSI can be reflowed onto a mounting board at a low temperature of 100C or less. Since bonding has become possible, the assembly yield and reliability of Josephson LSIs have improved significantly.

[Brief explanation of the drawing]

FIG. 1 shows a cross-sectional view of a tunnel junction type Josephson junction device. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Insulating layer, 3 and 3'... Lower electrode, 4... Interlayer insulating film, 5... Thon barrier layer, 6... Upper electrode, 7... ...Protective layer, 8 and 9...
・Bump base electrode film, 10...Protruding electrode for connection terminal (
Bamboo). Agent Patent Attorney Toshiyuki Hakata

Claims (1)

[Claims] 1. In a superconducting thin film functional element having a sandwich structure in which an ultra-thin tunnel barrier layer is placed between two superconducting thin films, cough al! The terminal electrode for external connection of the functional element is pb-B.
1. A protruding electrode for a connection terminal of a superconducting thin film functional element, characterized in that it is composed of a M'tlL4 composite formed by adding at least one element selected from the group consisting of gold alloys gn, Jn and cd. 2. In the method for manufacturing a terminal for external S connection of a superconducting thin film functional element consisting of a sandwich structure in which an ultra-thin 1 m tunnel wall layer is sandwiched between two superconducting thin films, PB is placed at the specified position, Then, after sequentially forming Bit-'t, at least one gold maple selected from the group consisting of Bn, In, and CD is sequentially laminated on -'t, and these laminated metals are melted to form a hemispherical shape. A method for manufacturing a protruding electrode for a connecting terminal of a superconducting thin film functional element, characterized in that: 3. In a method for manufacturing a terminal electric wire for removing the outer S wire of a super wire conductor consisting of a sand inch structure with a tunnel barrier layer between the two wires. , after forming a Pb-B1 skin at the shortening position, sn
A superconducting thin film functional element characterized in that at least one metal selected from the group consisting of A method for manufacturing a protruding electrode for a connection terminal.