JPS5867081A - Josephson ic - Google Patents

Abstract

PURPOSE:To change the unevenness of the surface into a plane by an insulating film, eliminate disconnections of wirings and improve the quality and reliability, by providing a poly siloxane film or an Si oxide film produced from a poly siloxane film as an insulating film. CONSTITUTION:An Nb film 3 is adhered on a substrate 1 resulting in the lower electrode. Cellosolve acetate solution of terminal etoxy group blocked siloxane copolymer is spin-coated on the upper surface thereof and heated resulting in the removal of the solvent. Next, it is heated in N, and accordingly the hardening film 11 of poly siloxane is formed. The entire surface is etched, thus the surface of the lower electrode 3 constituted of an Nb film is exposed, an etching is performed by an etching gas, and accordingly the poly siloxane film with the same thickness as the lower electrode 3 is left resulting in a flat surface. After the SiO film 12 is adhered and patterned, a tunnel oxide film 2 is formed, the upper electrode 4 constituted of an Nb film is formed, and the poly siloxane hardening film 13 is formed thereon. Further, an SiO film 14 and a control line 7 are successively formed resulting in an element with less stepwise differences, and therefore disconnections of the upper electrode and the control line can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an integrated circuit including a Josephson device, and more particularly to a novel insulating film-provided di-Sefson integrated decoy path.

Josephson elements are attracting attention as switching elements and memory elements for next-generation electronic computers, but integrated circuits that include such Josephson elements, that is, Josephson integrated circuits, are similar to conventional semiconductor integrated circuits. In order to further connect them, it is necessary to miniaturize them and form them densely.

However, since the Josephson element is an element formed by stacking thin films, the surface tends to be extremely uneven, and has a structure that is prone to disconnections and short circuits. Figure 1 shows a typical structural cross-section of a conventional Josephson element9, in which a tunnel oxide film several tens of microns thick is sandwiched between layers of niobium (Nb) and Nb compounds on a substrate 1.

Alternatively, there is a lower electrode 3 and an upper electrode 4 formed of a superconducting film made of a lead (Pb) alloy, and these two electrodes are made of silicon monoxide (Si) in areas other than the tunnel oxide film 2.
n) is insulated by an insulating film 5 made of a film. Then, on the upper surface thereof, an insulating film 6 made of the same <5iOIK is formed.
A signal control line 7 formed by superconducting expansion similar to that described above is provided via.

Because of such a laminated structure, the control line 7 and upper electrode 4 of the Josephson element are wired over multiple steps caused by superconducting wiring and openings in the insulating film arranged in the lower layer. become. Therefore, the upper layer has a high probability of disconnection or short circuit, and in order to prevent this, conventional wires are used.

In the manufacturing method of the Cefson element, a method is adopted in which the film thickness is increased from the lower layer to the upper layer as the layers are improved.

However, as the shape of the Josephson element becomes smaller and the line width of the wiring becomes narrower, disconnections and short circuits are more likely to occur. Similarly, there is a risk of disconnection in signal propagation lines made of thin films. Therefore, in Josephson integrated circuits having such a laminated structure, the most important issue is to reduce interconnect disconnections in order to increase the degree of integration.

On the other hand, in semiconductor integrated circuits, in recent years, multilayer wiring structures formed on the surface have been planarized. However, in Josephson integrated circuits, an oxidation process is essential to form a tunnel oxide film, and plasma oxidation or thermal oxidation is used as a means for this. When using an organic resin composed of nitrogen (he), oxygen (0, etc.),
It is difficult to use these as insulating films because the films eventually disappear due to plasma etching or oxidative decomposition at high temperatures.

The present invention is based on such a Josephson integrated circuit,
We propose a di-Sefson integrated circuit in which surface irregularities are flattened with an insulating film to eliminate disconnection of wiring, and the insulating film has a composition formula of R15i04t (2≧X≧0.
R is a hydrogen atom or a monovalent organic J having 1 to m carbon atoms!
This can be achieved by means of a Josephson integrated circuit characterized in that it is provided with a polysiloxane film represented by .

The polysiloxane used in the present invention has a composition after the curing reaction of Rx Si 04i! ...(υ, Tazoshi2≧X≧
0° is preferably expressed as 1.8≧X≧0.25, where R is a hydrogen atom or a monovalent organic group having 1 to 10 carbon atoms, such as a methyl group, an ethyl group, or a propyl group.

Indicates phenyl group, vinyl group, methacrylic group, aminoethyl group, etc. The molecular constituent unit of the polysiloxane film having the above composition is (RR'5iO) (2).

(R5iO1)...(3), (St (OR)*O
)...(4), and can be obtained by preparing a solution of a silane monomer or siloxane polymer having a terminal reactive group OR, or a mixture or copolymer thereof in an organic solvent, applying the solution, and then heating and curing the solution. In the above formulas (2), (3), and (4), R'J6 and R' are the same as R in formula (1), and R and R' may be the same or different. That is, in siloxane polymers, the reactive group OR at the end of the molecule or in the main chain has a 5i
-OR+R0-5i→St -0-St + ROR・
...5i-0- according to the reaction formula expressed by (5)
3. Cures by forming biobonds.

Silsesquioxane, which consists of the unit of formula (3), has a so-called ladder structure in its molecules, so it is fluid.

It has excellent heat resistance and good adhesion to the inorganic layer. Adding diorganosiloxane consisting of units of formula (2) to this silsesquioxane improves flexibility, while adding tetrafunctional siloxane consisting of units of formula (4) improves adhesion and heat resistance.

It can improve intuition and hardness. Excessive addition of siloxane diorganosiloxane or tetrafunctional oxane will actually reduce heat resistance and crank resistance.Thus, the siloxane polymer used in the present invention has a siloxane oxane unit of 100 to 100 siloxane units. 30 tetrafunctional siloxane units
0 or less, with addition of 400 or less diorganosiloxane units, that is, after the curing reaction, X in the above formula (1) is 1.8≧
A polysiloxane in the range of X≧0.25 is suitable.

Nb and N are used as superconductors constituting Josephson elements.
When a melting point metal such as compound b is used, the properties of the superconducting metal are not changed in the above-mentioned curing reaction of polysiloxane. Also, when using a low melting point metal such as Pb alloy, calcium.

By adding a curing accelerator such as a carboxylate of a metal such as potassium or titanium or an amine to the siloxane polymer, a cured film of polysiloxane can be formed by heat treatment at a low temperature, for example, 10 a'c or less.

Such a polysiloxane film is made of silicon dioxide (Sin
,) has excellent planarization properties compared to inorganic layers such as films, and has better adhesion to inorganic substances than organic resins such as polyimide, and in particular, there is no decrease in adhesion due to moisture.

It also has high heat resistance, and the following table shows the flatness, adhesion, and
Comparison of heat resistance.

This is the surface level difference when the flat part is coated with a film thickness of 300i1λ on the back surface.
The value when 100 W-shaped squares were formed and beaded with cellophane adhesive tape is shown in ■, and the value when beaded again after 1 hour of boiling is shown in 1. None of the squares came off. The first remaining number represents the number of eyes. Moreover, heat resistance indicates the temperature at which the weight decrease reaches 5% by increasing the temperature by 5V.

In addition, polysiloxanes can be physically and chemically etched, and fluorocarbon gases such as CF4,
A desired pattern can be formed by plasma etching using a mixed gas of CF, ;Iv'02, etc., ion milling using argon (Ar), or chemical etching mainly containing hydrofluoric acid.

Furthermore, by irradiating polysiloxane with an electron beam or ultraviolet rays and developing it, a pattern can be formed in layers in the same manner as with resist.

Also. The major feature of polysiloxane is that it contains a high proportion of Si and O atoms, so the etching rate is very low even when exposed to 02 plasma, and when oxidized at high temperatures, the organic groups decompose and disappear. It remains as a wood oxide film (mainly composed of Sin). For this reason,
(b) When plasma oxidation is performed on the surface of the lower electrode exposed through the opening by providing an opening in a part of the insulating layer using a white insulating layer, as in the case of using a normal organic resin as the insulating layer, Q plasma will not enlarge the opening and oxidize the polarized surface other than the designated area, and the thickness of the insulating layer will not decrease, and the insulating film will not disappear even if it is oxidized at high temperatures for a long time. .

Furthermore, the polysiloxane group was heated to 5θO in an oxygen-containing atmosphere.
℃ or higher, preferably 700 to 1200℃,
Through decomposition and removal of the organic group (8) and simultaneous oxidation reaction, it is transformed into a resin oxide film, which can be used as an insulating layer of a Jiso Sefson device.

In the polysiloxane used at this time, the organic group (t) bonded to the 51 atom does not contain a phenyl group and is composed of a monovalent hydrocarbon group with a small number of carbon atoms, such as a methyl group, an ethyl group, or a hydrogen atom. things are suitable. This is because phenyl groups have strong high-temperature oxidation resistance and are prone to graphitization, making it difficult to completely decompose and remove them.Also, large organic groups with a large number of carbon atoms can cause damage to the paint film during decomposition and removal. This is because it is easy to cause distortion due to volumetric contraction.

Although the thickness of the silicon oxide film obtained as described above is reduced to I-% compared to the cured polysiloxane film, the heat resistance and adhesion are further improved, and CF, M It has the characteristic that no residue remains during plasma etching using gas or the like. In addition, taking advantage of its high heat resistance,
Nb compounds, such as Nb, Sat Nb3G, which require a high substrate temperature of 500-1000°C for film formation.
Super conductive materials such as e, V, si, NbN, etc. can be used for the upper layer wiring.

Taking advantage of the fact that a Josephson element with a flattened layered structure is obtained as described above, a superconducting ground plane is further formed in the upper layer, and a polysiloxane insulating layer is formed on top of this, and the wiring process is repeated. By returning it, integrated circuits can also be manufactured in multilayer Josephson #.

Hereinafter, embodiments will be described in detail with reference to the drawings.

Figure 2 shows the polysiloxane film and St 071! In this embodiment of the Josephson device using both insulating films, the polysiloxane film is of course interposed for planarization. Among them, the method for flattening the step using the lower electrode is shown in Figure 3 (a).
- Shown in (c). First, a film with a thickness of 5000 mm is deposited on the substrate l.
! (1) A Nb film 3 is deposited by vapor deposition or sputtering, and patterned by lift-off or etching.
(Fig. 13(a)). Next, 25 mol % of (Si (Oc2Hs)! 0 ) units were added to the upper surface.

[(CHDSj 04 ) unit 63 moles out, [(C Tao 2
Spin code a hepterosol acetate solution of a terminally blocked ethoxy group copolymer (IWW8X103) consisting of 12 mo/L/% of SiO) units, and heat it to 100°C to remove the solvent. Then, it was heated in nitrogen at 350°C for 1 hour to form a cured polysiloxane film ((CHslO,s
65101.57) form 11. The film thickness is lμ
I11. The thickness on the Nb film is 60(3), and the step height is 10.
00λ (Fig. 3(b)). Next, the polysiloxane film 11 formed in this way is etched over the entire surface using a parallel plate plasma thinner. CF is used as the etching gas, the gas pressure is 0.ITorr, and the output is 150.
Etching is performed with W for 7 minutes to leave a polysiloxane film with the same thickness as the lower electrode 3 and obtain a flat surface (third
Figure (C)).

After flattening the lower electrode in this way, as shown in FIG. The electrode 4 was formed, and the same polysilo cow sun bag film B as above was formed thereon, and then 510M114. Control lines 7 are sequentially formed to provide an element with fewer steps.

In addition, the Josephson chord having the structure shown in Fig. 2 [here,
When a PB alloy film is used as a superconducting film instead of a dental membrane, the above method for forming a polysiloxane film is not possible, although heat curing at 350' is the same as the melting point of PB, which is 1'M temperature. Become. In that case, the polysiloxane is [:*(QC
□□ (0 loose 0) unit 8 mole tsuba.

((CHDSj (￥) A silica copolymer (Fv! W- 2 do.

This polysiloxane solution is spin-coded, dried at room temperature for 30 minutes, and then heated at 100° C. for 1 hour to form a cured polysiloxane film. As a Pb alloy film,
For example, Au 45L Pb 1600 people, In 35
FIG. 4 shows another example in which both a polysiloxane film and a 5iOj insulating film are used, similar to the example shown in FIG. 2. In this example, the polysiloxane film 11 is selectively etched using a resist film as a mask so that only the portion where the tunnel oxide film 2 is to be formed is exposed.
Compared to the example shown in FIG. 2, the structure eliminates the need for the S10 film 12,
This simplifies the process accordingly.

Next, FIG. 5 shows an embodiment in which a silicon oxide film formed from the polysiloxane side is used as an insulating layer.

Polysiloxane is C8i (OCRρ(OH) 03 units 33 molsi.

[(Formula 0)”Si%] unit 62 mol%, [(C~,
510) Siloxane co-J1 complex consisting of 5 mol% units and terminally capped with methoxy groups (yrw-1.5X io4
) in cyclohexanone. Such a solution was spin-coded onto a substrate 1 on which a lower electrode 3 made of an Nb film with a film thickness of 50 (io Then, the resinous wood oxide film 15 is formed.Then, the resinous wood oxide film [15
A photoresist film mask is formed on top, and 50% hydrofluoric acid (H
F) , :4o% ammonium fluoride (NH4F) −1
Etching is performed using a solution of +6 to make the surface of the dental membrane on which the tunnel oxide film 2 is formed 11'fl. The etching rate is comparable to that of a thermally generated SiO film (1000 minutes). The following is ton warehouse 4C:. Membrane 2.

An upper electrode 4 is formed, and then a resin oxide M16 is formed in the same manner as above, and a control line 7 is formed to obtain the Josephson element shown in the figure.

As can be seen from these examples, it is possible to flatten the polysiloxane group or a silicon oxide film produced from it as an insulating layer and eliminate the disconnection of the upper electrode or control line. FIG. 6 shows an example of a six-layer Cefson integrated circuit. In this way, it is also possible to stack two or more layers of D-Cefson integrated circuits to form an integrated circuit. 6th
In the structure shown in the figure, in order to prevent magnetic interference between the upper and lower elements, superconducting ground layers 17 and 18 are provided, and an insulating layer 19 of the polysiloxane group is used to connect the lower element (shown in the conventional structure).
The unevenness of the surface has been flattened.

As is clear from the above description, according to the present invention, it is possible to improve the quality and reliability of the compact and highly integrated Sefson integrated circuit, and the effects thereof are extremely significant.

[Brief explanation of drawings]

FIG. 1 shows a diy-Sefson element with a conventional structure, and FIG. 2 shows it. 4, 5, and 46 show structural examples of a di-Cefson device or a di-Cefson integrated circuit according to the present invention, and FIGS. 3(a) to (c) show a part of the forming process. FIG. In the figure, 1 is the substrate, 2 is the tunnel oxide layer, 3 is the lower electrode,
4 is elegant m+jAs 5, 6.12.14 is SiQ
JM, 7 is a control line, 11.13.19 is a polysiloxane family, 15.16 is a wood oxide film produced from a polysiloxane family, and 17.18 is a ground layer. Figure 1 Figure 2 Figure 3 Figure 3 Figure 4 Figure 5

Claims (2)

[Claims] (1) It is composed of thin films of superconductors, normal conductors, and insulators, and is used as an insulating film in Cefson integrated circuits with the composition formula Rx St 04? 1. An integrated circuit comprising a polysiloxane film represented by (2≧X≧0.R is a hydrogen atom or a monovalent organic group having 1 to 10 carbon atoms). (2) In Josephson integrated circuits composed of thin films of superconductors, normal conductors, and insulators, the composition formula Rx S
l 04? (2 ≧ Josephson integrated circuit.