JPH0446084A - Method and device for surface-treating oxide superconducting thin film - Google Patents

Abstract

PURPOSE:To remove the deteriorated layer on the surface of an oxide superconducting thin film without damaging the surface by irradiating a substrate covered with the oxide superconducting thin film with an ion beam in a vacuum. CONSTITUTION:A substrate 2 covered with an oxide superconducting thin film 9 is held by a holding and cooling mechanism 1 set in a vacuum vessel 8, and the vessel 8 is evacuated to <=10<-4>Torr through an evacuating system 7. The surface of the thin film 9 is irradiated with the inert gas ion beam having 10-200eV energy and ion beam with a halogen element as the constituent element respectively from ion sources 3 and 4 to remove the deteriorated layer on the surface, a metal layer is then continuously deposited from a metal depositing mechanism 5, and then an insulating layer is formed by an insulating layer depositing mechanism 6.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a surface treatment method and surface treatment apparatus for oxide superconducting thin films, which are essential for manufacturing wiring and electrode contacts of electronic devices using superconductors. It is related to.

[Prior Art] Electronic devices that utilize superconducting phenomena can be widely applied as, for example, high-speed switching elements, highly sensitive electromagnetic wave detection elements, and highly sensitive magnetometers. Additionally, since superconductors have zero direct current electrical resistance, they are expected to be used as wiring for integrated circuits. Therefore, in order to form devices and wiring layers with high practical value, superconducting B
A thin film made of an oxide superconductor having a high temperature (Tc) (77 or higher) is used.

Depending on these uses and purposes, superconducting thin films are used in the form of layers or patterns. At this time, the superconducting thin film is exposed to the atmosphere, moisture, and chemicals, so its surface becomes contaminated and its surface deterioration layer, whose superconductivity is extremely weakened, forms its Fii
Formed on the surface of the membrane.

Therefore, when producing various superconducting devices and wiring layers, it is essential to perform surface treatment to remove this surface deteriorated layer without damaging the thin film.

As a conventional surface treatment method, there is a method of performing surface treatment by high frequency discharge (reverse sputtering) in an atmosphere containing an inert gas. It is known that by using this method, the surface deteriorated layer of metallic superconductors can be effectively removed. For example, it is possible to create tunnel-type Josephson junctions, which are typical superconducting devices, and to make electrode contacts. The formation of
This is achieved using this method.

However, compared to conventional metallic superconductors, oxide superconductors have a very short superconductor coherence length (ξ) (2 to 50 A) and are easily damaged. It is very difficult to perform effective surface treatment depending on the method.

In other words, in the case of an oxide superconducting thin film, even if the surface is treated using this method, the surface deterioration layer is hardly removed, and on the contrary, oxygen desorption from the oxide superconducting thin film, surface damage, etc. It was found that there were negative effects.

Further, as a variation of this method, it is possible to take measures such as mixing oxygen, halogen gas, etc. into the discharge atmosphere or lowering the discharge voltage, but none of these methods are effective surface treatments. For this reason, a Tonnell-type Josephson junction using an oxide superconductor that exhibits sufficient characteristics has not yet been realized.

In addition, when forming noble metal electrodes such as Au and Ag on oxide superconducting thin films, sufficient contact characteristics cannot be obtained with this surface treatment alone, so after electrode deposition, SOO℃
High-temperature heat treatment is required.

As explained above, it is extremely difficult to remove the degraded layer shown in Table 1 from oxide superconducting thin films using conventional methods, and there has been no effective surface treatment technology for oxide superconducting thin films. .

[Problems to be Solved by the Invention] An object of the present invention is to be able to remove the surface-deteriorated layer of an oxide superconducting thin film without damaging the surface, and to improve the wiring, electrode contacts, etc. of high-performance superconducting devices. An object of the present invention is to provide a surface treatment method and a surface treatment apparatus for an oxide superconducting thin film, which can facilitate the production of oxide superconducting thin films.

[Means for Solving the Problems] In the method for surface treatment of an oxide superconducting thin film of the present invention, a substrate on which an oxide superconducting thin film is formed is placed in a vacuum chamber evacuated to vacuum, and the surface of the thin film is The method is characterized in that an ion beam having an energy in the range of 10 to 200 eV generated from an ion source installed in the vacuum chamber is irradiated.

The surface treatment apparatus for an oxide superconducting thin film of the present invention includes at least a vacuum chamber and an exhaust system; a holding/cooling mechanism for holding and cooling the substrate on which the oxide superconducting thin film is formed in the vacuum chamber; : at least two or more electron cyclotron resonance ion sources for generating an ion beam and irradiating the ion beam onto the substrate surface; after irradiation with the ion beam, a metal layer and/or an insulating layer on the substrate surface; A thin film deposition mechanism for continuously forming a thin film;

[Effect] The operation of the present invention will be explained below along with the detailed configuration.

According to the present invention, a surface-deteriorated layer is irradiated with an ion beam having a predetermined energy.

Here, an inert gas element (
For example, He, Ne, Ar, KrXe, etc.) can be used, and efficient surface treatment can be performed due to its physical Nitstig action. In this ion beam irradiation, setting the ion energy is important. If this energy exceeds 200 eV, it will damage the crystallinity of the surface of the oxide thin film, and if it is less than 10 eV, no irradiation effect (ie, the effect of removing surface deterioration 1) can be expected. For this reason, the energy is set in the range of 10 to 200 eV.

In addition, in order to further reduce surface damage, for example,
A gas containing a halogen element such as F, Cfl, or Br (for example, C, F2..2. CCf1a).

CBr4. CCn□F2. Preferably, an ion beam of CBrF, etc.) is mixed into the inert gas ion beam. In this case, in addition to the physical etching effect, a chemical etching effect is also taken into account, so that the irradiation effect becomes very significant.

A first method for implementing this is to simultaneously irradiate an ion beam of an inert gas and an ion beam of a gas containing a halogen element (Claim 2).
).

On the other hand, as a second method, there is a method of irradiating with an ion beam generated using a mixed gas of a gas containing a halogen element and an inert gas as a source (Claim 3)
.

In addition, in the second method, the mixing ratio of the inert gas and the halogen gas is set as follows. If the amount of gas containing a halogen element as a constituent element is too large, a large amount of halogenated oxide layer will be formed on the surface of the oxide thin film.
In order to prevent effective etching from proceeding, the volume fraction of the gas containing halogen elements in the mixed gas should be reduced to 10%.
The following shall apply.

The degree of vacuum in the vacuum chamber during irradiation with the ion beam is preferably 10-' Torr or less, and 10-'Torr or less, for example.
-8 or less is more preferable.

As a source for generating such an ion beam, a Kauffman type ion source can be considered. In the case of a Kauffman type ion source, a filament made of tungsten or other material is used for thermionic emission to generate plasma, so if the source gas contains active halogen gas, the ion source will stop operating due to filament breakage. The lifespan is short, only a few hours, and the filament gradually deteriorates before it breaks, resulting in large fluctuations in the -ion current value.
Difficult to adequately control. Therefore, as the ion beam generation source, it is preferable to use an ECR (cyclotron and OS) type ion source in which plasma is generated by microwaves.

In the case of an ECR type ion source, since a filament is not used, it is possible to stably generate an ion beam containing a reactive gas, and it is also easy to generate a low-energy ion beam.

Therefore, in the surface treatment apparatus of the present invention, an ECR type ion source is used as an ion source, and at least two or more ECR type ion sources are provided. ! A f# film deposition mechanism is provided.

Note that this surface treatment device is suitable for use in combination with an ion beam of an inert gas and an ion beam of a gas containing a halogen element. can also be used. In this case, all but one of the two or more ECR type ion traps may be left inactive.

On the other hand, examples of the FF film deposition mechanism include those having functions such as vapor deposition, sputtering, ion blating, and chemical vapor deposition.

In the apparatus of the present invention, a metal layer or an insulating layer can be continuously formed after the surface deterioration layer is removed, so the surface of the clean oxide conductive thin film exposed after the surface deterioration layer is removed can be maintained clean. A metal layer or an insulating layer made of a noble metal or the like can be formed on the clean surface, making it possible to form tunnel-type Josephson junctions, electrode contacts, etc. with excellent characteristics.

As described above, since the present invention utilizes the physical and chemical etching effect of a low-energy ion beam, it is different from the conventional technology in that surface damage to the oxide superconducting thin film can be minimized. different.

[Examples] The present invention will be described in more detail below based on Examples.

(Example 1) In this example, a surface treatment apparatus shown in FIG. 1 was used.

This device has a vacuum AI 8 and an exhaust system 7, a holding/cooling mechanism 1 that holds and cools a substrate 2 on which an oxide superconducting thin film 9 is formed in a vacuum chamber 8, and generates an ion beam.
and a first ECR ion source 3 and a second ECR ion 'a, 4 for irradiating the surface of the substrate 2 with an ion beam, and a metal layer is continuously formed on the surface of the substrate 2 after irradiation with the ion beam. A metal layer deposition mechanism 5 for continuously forming an insulating layer and an insulating layer deposition mechanism 6 for continuously forming an insulating layer are provided.

In this example, the following surface treatment was performed using this apparatus.

The details will be explained below.

First, a Y-Ba-Cu-O thin film (thickness: 2000 Å) was formed on a 5rTi◯ substrate. As a result of examining this thin film by X-ray diffraction method, the lattice constant of the C axis was 11.7A,
It was found that it has a superconductor crystal structure exhibiting a superconducting transition temperature Tc = 90K, and that the orientation of the crystal (in the C-axis direction) is extremely high.

Next, the substrate on which this thin film was formed was subjected to high-speed reflection electron diffraction (RHEED), Auger electron spectroscopy (AES), EC
Substrate holding/cooling mechanism 1 in a vacuum chamber 8 equipped with an R ion beam irradiation device and a reverse sputtering mechanism (both not shown)
Fixed. At this time, the substrate 1 was exposed to the atmosphere.

For the surface of the thin film before surface treatment, RHEED
A mixed pattern of weak spots and rings was observed in the pattern, and as a result of surface composition analysis by AES, several tens of percent of C and N were detected in addition to YBa, Cu, and O, which are component elements of the thin film. In other words, it was found that a contaminant layer with low crystallinity was formed on the surface by taking it out into the atmosphere.

As mentioned above, after measuring the characteristics before surface treatment,
Surface treatment was performed according to the following procedure.

First, the inside of the vacuum chamber 8 is heated to about 10-'T using the exhaust system 7.
Exhausted to orr.

Next, using the ECR ion beam source 4, 100 eV
Ar ion beam (beam current density 0.5 mA
The surface treatment was performed by irradiating the thin film surface with /cm2) for 10 minutes.

After the surface treatment, the RHEED pattern of this sample was examined, and it was observed that the RHEED pattern had a regular array of spots that were strong against non-customers.

Therefore, it was found that the surface had excellent crystallinity.

Furthermore, as a result of surface composition analysis performed on this sample by AES, the component elements of the thin film, Y, Ba, Cu,
Elements other than O were not detected with the detection sensitivity of AES (05%) or lower. Therefore, it was found that the contamination layer existing on the surface was removed.

In addition, an experiment was conducted using an ECR ion beam with He, Ne, Kr, and Xe ion species instead of Ar, and other conditions were the same as in the above example, but the same effect as the Ar ion beam was obtained. I found out that I have it.

As described above, it was confirmed that the surface deteriorated layer of the oxide superconducting thin film could be removed without causing surface damage according to this example.

(Comparative Example) In this example, an ion beam having an energy of 10 eV and an ion beam having an energy exceeding 200 eV were irradiated.

Other conditions were the same as in Example 1.

After the irradiation, we analyzed the crystallinity and surface composition using RHEED and AES, and found that in the case of 10 eV grooves, the surface deteriorated layer was hardly removed, and no irradiation effect could be expected. It was confirmed that the crystallinity was affected when the amount was exceeded.

(Conventional Example 1) Next, another sample was introduced into the same apparatus, and surface treatment was performed by a conventional method, that is, by reverse sputtering (bias voltage Vp-p=800V) in Ar gas SPa.

On the surface of this thin film, a pattern with a mixture of weak spots and rings was observed in the RHEED pattern, and Y, which is a component element of the thin film, was observed in AES.

In addition to Ba, Cu, and O, several tens of percent of C and N were detected.

That is, it was found that the contamination layer with low crystallinity formed on the surface was hardly removed and remained as it was.

In addition, in the conventional method, the Ar gas pressure is set in the range of 1 to 50 Pa,
The surface treatment was performed by changing the bias voltage in the range of 100 to 100 OV, but similar results were obtained with RHEED and AES, indicating that the surface contamination layer was not removed.

The results of Example 1 and Conventional Example 1 described above are summarized in Table 1.

Table 1 Results of RHEED observation and AES analysis of superconducting thin film surfaces treated by the present invention and conventional methods (Example 2, Conventional Example 2) B1-5r-Ca-Cu-0 formed on M30 substrate
Using a superconducting thin film, we compared the difference in electrode contact resistance between the present invention and the conventional surface treatment.

The thickness of the B1-3r-Ca-Cu-0 thin film is 3000A,
The superconducting transition B temperature Tczsro was 105.

The thin film was patterned into a shape for 4-terminal electrical resistance measurement using a photo process (resist coating, exposure, development) and ion beam etching.

Then, a lift-off stencil for the Au electrode was formed by a photo process (resist coating, exposure, and development). here,! The area of the extreme part is 200μm x 200μm, electric g! The number of parts was 10.

Two such samples were prepared and surface treated using the present invention and the conventional method. Thereafter, a 500A thick Au thin film was deposited and lift-off was performed in acetone to form an Au contact electrode pattern.

Here, in the present invention, the surface treatment is (Ar+5%
The experiment was carried out by bombarding an ECR ion beam (ion beam energy: 50 eV, beam current density: 0.3 A/cm') with a mixed gas of CF, ) as the source gas for 5 minutes.

On the other hand, in the conventional method, RF sputter cleaning (Vp-p
=500V, 5m1n).

Using the sample thus prepared, the contact resistance between the superconducting thin film and the Au thin film was evaluated. In the V material prepared according to the present invention, the contact resistance is I x 10-' ~
A low value of I x 10-'Ωcm2 was obtained on the non-palate side, indicating that good contact was formed. On the other hand, in the sample prepared by the conventional method, the contact resistance was l
It was found that the contact formation was in the range of Xl0-' to 1 ΩCm'', with large variations and large values overall, indicating that the contact formation was insufficient.

In addition, CF4 in a mixed gas as a source gas is generally replaced with C, F2. In addition, the mixed gas is a mixed gas of (Ar + 2% CCl12), (Ar
+6%CCu2F2) mixed gas, (Ar + 8%cBr
Similar experiments were conducted using the mixed gas of 4) and the mixed gas of (Ar+1o%CBrF3), respectively.
Results similar to those above were obtained.

In addition, Ar in these mixed gases can be replaced with other inert gas (He
, Ne, Kr, Xe), similar results were obtained. The mixing ratio of the gas containing a halogen element as a constituent element must be 10% or less; if it exceeds this, a large amount of halogenated oxide layer will be formed on the surface of the oxide thin film, making effective etching impossible. It was also confirmed that the disease did not progress.

Furthermore, it was also recognized that in this case as well, the ion energy of the mixed gas needs to be kept within the range of 10 to 200 eV, similar to the example of Tsuta 1.

(Example 3) E was deposited on a L a A fl O3 substrate by sputtering.
A u-Ba-Cu-0 superconducting thin film was deposited to a thickness of 1500A. This thin film is processed through photo process (resist coating, exposure, development)
Then, the lower electrode shape was patterned by ion beam etching. Then photo process (resist coating,
A lift-off stencil for the upper electrode was formed by exposure and development. Here, the area of the joint is 50μm x 50μ
It was set as m. Two such samples were prepared, and tunnel-type dicocephalic junctions were fabricated using the present invention and the conventional method.

Here, too, the surface treatment apparatus according to the present invention shown in FIG. 1 was used. In this example, an electron gun evaporation source 5 is used as the metal layer deposition mechanism.
A vapor deposition apparatus 5 having a structure was used.

Further, an AC magnetron sputtering device 6 was used as an insulating layer deposition mechanism. Note that an MgO target was used as the target 6a.

A sample is placed in the substrate holding/cooling mechanism in the vacuum chamber of this device, and an Ar ion beam (energy:
120 eV, ion current density 0.2 A/cm2) and an ion beam of a gas containing a halogen element (source gas: CCf14. Energy 20 eV, ions;
Irradiated with a current density of 0.1 A/cm' for 10 minutes,
Then, 2OA of Mgo was deposited as a barrier layer using an AC magnetron sputtering cathode, and finally, an upper electrode Nb was formed to a thickness of 1200A using an electron gun evaporation source to form a tunnel-type Josephson junction.

On the other hand, RF sputter cleaning (V
p-p = 500 V, 15 min), then 2 OA of MgO was deposited as a barrier layer in the same manner, and finally an upper electrode Nb of 120 OA was formed to form a tunnel type Josephson junction.

The current-voltage characteristics of the tunnel-type Josephson junction created as described above were measured at a liquid temperature of 4.2°C. A superconducting gap structure was observed. In contrast, the junction fabricated by the conventional method did not exhibit nonlinearity, and no Josephson current 1 superconducting gap structure was observed.

As an inert gas, instead of Ar, He NeKr, X
When using CCj2.e, and as a gas containing a halogen element as a constituent element, CCj2. Instead, CnFin+2.
CBrn, CCuzF2. CB rF3
When experiments were conducted using each case, the same results as above were obtained. In this case as well, it was confirmed that the energy of each ion beam must be kept within the range of 10 to 200 eV.

[Effects of the Invention] As explained above, according to the present invention, for example, the surface deterioration layer and the contaminated layer of the oxide superconducting thin film caused by exposure to the atmosphere, photo process, etc. 2
By irradiating the ion beam with an energy of 00 eV, efficient etching is performed without leaving any damage to the surface layer, and the surface is recovered and cleaned. It has the advantage of achieving good interfacial properties with the barrier layer and the metal layer. Therefore, it becomes possible to form tunnel junctions and electrode contacts using oxide superconductors.

In particular, the above effect becomes even more remarkable when irradiating with an ion beam of an inert gas and an ion beam of a gas containing a halogen element (Claims 2 and 3).

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of a surface treatment apparatus of the present invention. (Explanation of symbols) 1... Board holding/cooling mechanism 2...Base board) 3...First ECR ion source 4...Second ECR ion source 5...Metal layer deposition mechanism (evaporation device) 5a...electron gun evaporation source 6...Insulating layer deposition mechanism 6a...Target (Sputtering equipment) 7...Vacuum exhaust system 8...Vacuum chamber 9...Oxide superconducting thin film

Claims (4)

[Claims] (1) A substrate on which an oxide superconducting thin film is formed is placed in a vacuum chamber that is evacuated, and the surface of the thin film is coated with 10 to
A method for surface treatment of an oxide superconducting thin film, which comprises irradiating an ion beam with an energy in the range of 200 eV. (2) Two ion sources are used as the ion sources, and the ion beam of inert gas generated from the first ion source and the halogen element generated from the second ion source are the constituent elements. 2. The method for surface treatment of an oxide superconducting thin film according to claim 1, wherein the surface of the thin film is simultaneously irradiated with an ion beam of a gas. (3) Ions generated using a mixed gas of an inert gas and a gas containing a halogen element as a source, in which the volume fraction of the gas containing a halogen element as a constituent element is 10% or less. 2. The method for surface treatment of an oxide superconducting thin film according to claim 1, wherein the surface of the thin film is irradiated with a beam. (4) having at least a vacuum chamber and an exhaust system; a holding/cooling mechanism for holding and cooling the substrate on which the oxide superconducting thin film is formed in the vacuum chamber; generating an ion beam and at least two ion beams for irradiating the
at least one electron cyclotron resonance ion source; and a thin film deposition mechanism for continuously forming a metal layer and/or an insulating layer on the substrate surface after irradiation with the ion beam. Surface treatment equipment for oxide superconducting thin films.