JPS58158981A - Manufacture of tunnel type josephson junction element - Google Patents

Abstract

PURPOSE:To obtain a barrier layer of high quality with good reproducibility by RF sputtering the surface of base electrode made of an Nb superconductive thin film in Ar-CF4 gas or Ar-CF4-O2 gas, then oxidizing or accumulating different material and forming by oxidizing a tunnel barrier layer. CONSTITUTION:An Si substrate formed with a thermally oxidized film on the surface is held at 400 deg.C, and a base electrode Nb thin film of 2,000Angstrom thick is formed by an electron beam deposition method in vacuum of 2X10<-8>Torr by using Nb tablet of 99.99%. Then, this substrate is coated with resist, exposed, developed, and etched as the base electrode of the prescribed width. Thereafter, this surface is RF sputtered in Ar-10%CF4 or Ar-5%CF4-2%O2 gas, oxidized, and a tunnel barrier layer is formed. After sputtering, different substance is accumulated by discharging of SiH4 gas, and then similarly oxidized.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for manufacturing a tunnel-type, Senoson junction element,
In particular, it relates to a method for forming a stable tunnel barrier layer.

[Technical background of the invention and its problems]

Tunnel-type junction devices basically have a substrate (St
It has a structure in which there is a base electrode (superconductor) on top of (or sapphire, etc.), an electrically insulating tunnel barrier layer on top of that, and an upper electrode (superconductor) on top of that. This tunnel barrier layer is a very thin insulating layer with a thickness of 20 to 50X, and it greatly influences the characteristics of the tree. For example, if the thickness of the tunnel barrier layer changes by 1111, the Cefnon current will change by one order of magnitude.

Furthermore, the material and quality of the tunnel barrier have a large influence on the device characteristics. Therefore, developing a method for forming a high-quality barrier layer with good control is important from the viewpoint of improving device reliability and yield. ! The first stage of production will be poor.

In general, tunnel-shaped nosesons can be roughly divided into 1) Formation of a superconducting thin film on a base electrode, 2) Formation of an arm turn of this thin film, 2) Formation of a tunnel barrier, and 2) Formation of a counter electrode. There are two methods for forming the tunnel/soriya layer (2).

One method is to form a predetermined barrier layer by oxidizing the base electrode t-i (natural oxidation or glazema oxidation) after forming a large turn.
1, Si, Bi, To, etc.) by steaming N or CVD.
In this method, a tunnel barrier layer is formed by forming an extremely thin film (with a thickness of several 1 OX) to form a barrier, or by oxidizing 7fL. In the former case, it is easy to control the thickness of the tunnel barrier layer, or only a predetermined barrier material can be obtained depending on the type of underlying electrode. On the other hand, the latter is a method of forming a barrier with a low electrical resistivity such as At205, 8102, B1, Te, etc., which is different from the single-layer electrode, but it is not easy to control the thickness of the ultra-thin O film. As described above, both barrier layer formation methods have advantages and disadvantages. Controlling the Barrier Layer 14I One point to note is that the barrier layer is formed by directly forming a line on the underlying electrode, but there are the following problems when this method is applied to Nb. The first problem is that if the tunnel barrier growth penalty is used to clean the vines using Ar gas, the yield of vines will be small. The surface of the underlying electrode is damaged by the collision, and the subsequent oxidation results in Nb2o
Metallic Nb-0 compounds other than No. 5 are formed. The problem with the second inspection is that Nb is very easily oxidized, and for graph 1 oxidation, Ar -02 mixed gas is mixed at 0.01 To
Even if about rr is introduced, an oxide film of several X will grow before discharge, so the thickness W of the tunnel barrier layer depends only on the discharge time.
i-control lacks controllability. As above, Ar
Although the surface was cleaned by cleaning the surface, defects were introduced into the Nb surface, and when the whole bamboo was then subjected to iL image densification, the 1IIJ characteristics of the oxidation glands were lost. .

[Object of the Invention and A View] The object of the present invention is to provide a tabulation method for 17-funon confectionery (tunnel-shaped) that can form a high-quality tunnel barrier layer with good properties.0 The present invention According to Mr. No-no, the surface of the base electrode made of Nb superconducting thin film was coated with kr-CF41f or Ar-cF4-
A method for fabricating a tunnel-type junction device is provided, in which the oxidized tunnel barrier layer is formed after RF sintering in an 02trx, and the oxidized tunnel barrier layer is formed to have a t-% mold.

According to another aspect of the present invention, the surface of the base electrode made of the Nb superconducting thin film is heated with Ar-CFA gas or Ar-CF4-
02 is in the air RF i! A method for manufacturing a tunnel-type Sefson junction device is provided, which comprises depositing a foreign material after forming a vine, and then oxidizing the foreign material to form a tunnel barrier layer.

In the above method of the present invention, preferably Ar-CF4-
The CF4 concentration of O2 gas is 0.5% to 20%, and 02%
The concentration is less than 20%, and the RF level is 0 in the evening.
．． The ritual is performed at a gas pressure of 0.003 to 0.1 Torr.

When producing a tunnel type device using a photo process, the ViNb surface may be contaminated with renost, acid, and alkali during tanning of the underlying electrode, or the surface of the underlying electrode may be contaminated by adsorption of atmospheric oxygen. is covered with an oxide film.

For this reason, before forming the tunnel 191 layer, smear it in At gas! After nail etching treatment, Ar-02
The cage barrier is formed by RF plasma oxidation in mixed gas. 5. The method of 5th generation is better than the conventional method for Pb and Nb layers, and does not necessarily provide a better barrier for Nb layers.
T-cannot be formed (, Arff etching using Arff is used for the physical effect of knocking out particles from the !li! cabinet due to the collision of Ar ions, but the yield is small for Nb. Therefore, in order to remove a contamination layer of about 100X near the base surface in a relatively short time (660 minutes), it is necessary to increase the self-bias to about 400V. Nb
Gold noodle-like Nb-0 compounds other than 2O5 are also formed and the barrier quality deteriorates. In addition, surface damage can be avoided by performing 9 ivy etching at a depth of 200 m degrees on self/4 Ias 1, but it takes a long time (more than 8 hours) to remove the contaminated layer and speeds up the wood graining process. It will be missing. Also N
The clean surface of b is very easily oxidized, and when an Ar-02 mixed gas is introduced after sputter etching, an oxide layer of several X grows before the I discharge starts, and this becomes the initial value of the oxide film thickness, so the discharge A predetermined oxide film thickness cannot be obtained by controlling only by time. The above S/9 etching treatment using Ar gas is recommended as a pretreatment for RFf plasma oxidation.
It has a drawback that the controllability of the b-element is limited. Therefore, it is possible to form a high-quality Nb2o5 barrier in the Nb4 film with good reproducibility and to improve the efficiency of the process.
In order to achieve this, while maintaining the speed of etching, lower the voltage when etching the horns to avoid damage to the surface, and immediately after etching the clean Nb surface to maintain its sublimation properties. It is necessary to cover with one film to prevent deterioration during replacement. The chemical action of CF4 gas can be used to satisfy these conditions. CF4 gas zolazma not only removes Nb by converting it to fluorine, but also converts Al accumulation in the surface oxide to C02.
Removed as gas. Further, in a state of oxygen deficiency, sublimable carbon is deposited as shown in Table 11. Ninth A of discharge stabilization
In order to improve the etch rate and control carbon deposition, a specified amount of 02 was mixed with a specified CF4 gas using r, but if RF snotting in the gas was carried out, the Nb surface would be damaged at low voltage. Not only can the contaminated film be quickly removed without giving any damage, but the clean surface of Nb is protected by a sublimable amorphous carmen of several tens of times, and the carbon film thickness can be controlled, so the subsequent kr +02 In the plasma oxidation process, carmen is first extracted as CO2.
The thickness of the Nb2O5-only barrier can be controlled by the discharge time.Table 1 shows the etch rate of Nb by CF4 and the mura. As is clear from this table, the etching rate of Ar is significantly lower than that of CF4.
Even if the discharge is stabilized by increasing the gas pressure, the controllability of the etching rate does not change at all. Also, Figure 1 shows 02 of Ar-CF4-02 mixed gas.
The graph shows the thickness of carton deposited on the Nb surface when the concentration is changed. FIG. 2 shows the carbon film thickness when changing the self-bias in an Ar-CF4-02 mixed gas. Nb in Ar-CF4-02 mixed gas,
Carbon pile in the evening! If R violet is in the range of lO number Plasma oxidation is then performed at low voltage to remove the carbon as CO2, and then a high quality barrier consisting only of Nb2O5 is formed.

[Embodiments of the Invention] Example 199.99 Nb tablets were used to produce 81 groups with thermal oxidation (5iOz
Agriculture JII100OX) Upper IC400℃ (D board temperature [
't'2
@(A Nb thin film was formed on the D base for 11 electrodes. The superconducting critical temperature of this thin film was 9.2 K. This thin film substrate was coated with light, exposed, developed, and etched.
A 0 μm underlayer llIc& was formed. Next, tunnel-shaped elements were fabricated using these thin film substrates. In other words,
! K11l12500 on two turned base boards
One 810 stencil was formed by the lift-off method, and one was coated on the surface of the underlying electrode in an Ar1f bath (20 mTo
rr + v, , - = aoov, 20 minutes), and the other one is a 9-horned ivy (20 m) in Ar-10% CF4.
Torr, V (11; 200 V + 20 min) was replaced with 0 S. 9 Ivy 1 Ar-10*O27/S and plasma oxidized (30 mTorr, V = 10 QV, 5 min)
Nb for the upper electrode is formed by electron beam evaporation on a water-cooled C1 substrate (
4000X) L-edited by light, development, and etching. The characteristics of the obtained device were flat in Ar, and the one obtained in the evening had Pritsuno type characteristics, but Ar-10%CF4
As shown in Fig. 3, the one with the horn of 4V had the characteristics of a single-particle tunneling device with little leakage. The gear and gummy pressure at this time was 3.0 mV at 4.2K.

Example 2 The four substrates on which the base was removed and SiO stencils were formed in Example 1 were treated with an Ar-CF4-02 mixed gas (
10mTorr) by changing the CF4 concentration.
Ivy (■(s+s=200V, 20 minutes) sifc
After, Ar-5102, /7 speed (30znTorr)
After plasma oxidation (V, = 100 V, 2 minutes), a Nb 2 O soil IB electrode was formed to fabricate the device. Table 2 shows the characteristics of these four types of confectionery. It is thought that when the CF4 concentration was high, the amount of carbon deposited increased and even the subsequent oxidation could not remove carmene.

Table 2 Example 3 Four substrates on which base electrodes and StO stencils were formed in Example 1 were treated with lr-CF4-02 mixed scum (
After converting the 02 concentration (30mTorr) to i and performing bis-concentration (VCl, = 250V, 20 minutes), it becomes ^r-3%.
Plasma oxidation (VC) in 02 gas (40 mTorr)
, 1=80 V, 4 minutes) and then A & t-water.

From above, Nb for the upper electrode was evaporated, and elements were fabricated by turning. 3
Shown below.

Table 3 As shown in the above, if the acid system is not applied once, the oxidation will occur at the same time as the etching during slubbing in the Ar-CF4-02 gas, and the oxide film will become thicker due to subsequent oxidation.

Example 4 In Example 1, F base wax and SiO stencil f
: By changing the gas pressure of the CF4-2%02 mixed gas in the four substrate warehouses Ar-5, the gas and mother ivy (VC,,=
20UV, 20 minutes) Solarization (Vo,
,=70V.

3 minutes) After that, the Nb upper electrode was deformed to produce a device. Table 4 shows the characteristics of each element.

Table 4: If the gas pressure is low, etching is insufficient; if the gas pressure is too high, etching progresses and causes damage. The substrate was grown with snow ivy (■.,,=
200V, 20 minutes), one sheet was heated to a St of about 1 by resistance heating.
After introducing 00X steam into an atmospheric pipe and naturally oxidizing it to form a 5102 barrier, it was exhausted and placed in a gas atmosphere (30 mTorr).
) sputtering (vcsm=100V, 5 minutes), and then an Nb upper electrode was formed to fabricate a device. The obtained device characteristics were tunnel type, but as shown in Figure 5, they had characteristics with a lot of leakage. This is a result of pinholes created during the deposition of St. On the other hand, the other one was exposed to RF radiation (0,2
Torr, V (B=200V.

100 minutes) c and about 100! (2) Bit-
After deposition, some or all of the Si is naturally oxidized to form 510
2 barrier was formed and treated with Ar (30 mTorr).

VC, = 100 V for 5 minutes), the entire Nb soil electrode was formed and a device was fabricated.The device characteristics obtained were tunnel-shaped characteristics with less IJ-resistance, similar to the characteristics shown in Figure 4. .

In addition to this characteristic point, the method of depositing the foreign material 'X on the substrate by RF discharge of SiH4 gas is simple because it is sufficient to simply introduce Ar-5IH4 into the reaction vessel. One root with a high rate can produce a t-seed with good characteristics.

[Young fruit of invention]

As explained above, the Nb agricultural surface is changed to Ar −CFa −0
If you follow the mixing ratio of the two mixed gases and apply RF gas, you can obtain a clean Nb surface in a short time even at low voltage without damaging the Nb surface. Because it is protected by the carmen, it is possible to prevent the deterioration of Table (3) during gas exchange.Then, the shibariya is formed by direct oxidation method or foreign material deposition method by passing through the photo process. There is an advantage that all the deterioration of Nb can be recovered.

[Brief explanation of drawings]

Figure 1 is a graph showing the thickness of carmen deposited on the Nb surface when the O2 concentration of the Ar-CF4-O2 mixed gas is changed, and Figure 2 is the graph showing the thickness of carmen deposited on the Nb surface when the O2 concentration of the Ar-CF4-O2 mixed gas is changed. A graph showing the deposition film thickness of carb/ on the Nb surface when sputtering with varying self-bias. Figure 3 is a graph showing the V-I% characteristic of quasiparticle tunneling with little leakage. @41:d is A graph showing V-1%i of a tunnel-shaped junction, and Fig.
3 is a graph showing the VI characteristics of a 5102 barrier element formed by t-oxidation. Figure 4 Figure 5

Claims (2)

[Claims] (1) The surface of a ground electrode made of a Nb superconducting thin film was exposed to RF snow in Ar-CF4 gas or Ar-CF'4-0.2 gas. After it vines, it oxidizes and forms a ton-i-rubarya layer.
Process for manufacturing bonding elements. (2) Table of the base electrode extending from the Nb superconducting thin film (8)
1. Deposit a foreign material and then oxidize the foreign material to form a tunnel barrier layer. A method for producing a 1-in-1 type noyosefun/jewel element imitating gold.