JPH0585703A - Active gas generating device and forming method for oxide high temperature superconductive thin film using this device - Google Patents

Abstract

(57) [Summary] [Object] To provide an active gas generator having sufficient oxidizing power under high vacuum and easy to handle, and a method for forming an oxide-based high temperature superconducting thin film. [Structure] A cylindrical discharge tube 1 having a small hole at one end, and a coil 2 made of a conductor wound around the outer periphery of the discharge tube, and a small hole 1a provided at one end of the discharge tube 1 In an active gas generator in which a gas is ejected and a high frequency current is passed through the coil 2 to turn the gas into a plasma, the length of the cylindrical body of the discharge tube 1 is (L), and the coil 2 is a discharge tube. The length of the range wound around the cylinder of No. 1 is (L
c) and the mean free path of the electron is (λe),
The length (L) of the cylindrical body of the discharge tube 1 is set to L> Lc + 2λe, and an oxide-based high temperature superconducting thin film is formed under high vacuum using this apparatus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active gas generator, and more particularly to an active gas generator for forming an oxide thin film under high vacuum and an oxide-based high temperature superconducting thin film using this device. It relates to a forming method.

[0002]

2. Description of the Related Art Generally, in order to deposit a metal element and obtain an oxide thin film thereof, oxygen is introduced into a vacuum layer under high vacuum (less than -10 ^-6 Torr), and so-called reactive deposition is performed. The method is known. When a thin film of an oxide-based high temperature superconducting thin film is formed on the substrate, the substrate is SrT.
iO ₃ or MgO is used. In order to grow a superconducting thin film on the surface of these substrates, it is necessary to remove carbon and hydrogen attached to the surface in advance. Conventionally, the removal method is to wash with dilute acid (ethanol + 10% nitric acid). The substrate is heated to 600-700 ° C under high vacuum. O ₂ gas is applied while being heated to 600 to 700 ° C. Ar Ar beam is applied to the surface. Etc. are taken.

[0003]

However, the oxidizing power is not sufficient in the method in which only oxygen is introduced into the vacuum layer and the reactive vapor deposition is carried out. Therefore, a method of providing a high frequency coil in a vacuum layer and applying a high frequency to the high frequency coil to convert oxygen into plasma or using ozone, which is more oxidative than oxygen, is also used. However, in order to generate plasma, it is necessary to keep the oxygen partial pressure at 10 ^-3 Torr or more,
Therefore, there is a problem that it affects the deposition rate of the deposition source (Knudsen cell or electron beam deposition source), making it difficult to control the film thickness and composition. In addition, the method using ozone has a problem that due to toxicity and explosiveness of ozone, it requires a great deal of attention in handling. Also in the method of cleaning the substrate surface, the method of cleaning with a dilute acid is very likely to dissolve because the substrate itself is an ionic crystal, and it is difficult to uniformly clean only the surface of an extremely shallow portion. ..
The method of heating under a vacuum or applying O ₂ gas in a heated state has a problem that complete cleaning is difficult, and the method of using Ar ions further gives a problem that the substrate surface is damaged. The present invention has been made to solve the above-mentioned problems of the prior art, and provides an active gas generator that has sufficient oxidizing power under high vacuum and is easy to handle, and further provides an oxide using the device. An object is to provide a method for forming a high temperature superconducting thin film.

[0004]

In order to solve the above-mentioned problems, the present invention provides, in claim 1, a cylindrical discharge tube having a small hole at one end, and a conductor wound around the outer circumference of the discharge tube. An active gas generator for ejecting a gas from a small hole provided at one end of the discharge tube and applying a high-frequency current to the coil to turn the gas into a plasma. Let (L) be the length of the cylinder of the discharge tube, (Lc) be the length of the range in which the coil is wound around the cylinder of the discharge tube, and let the average free path of the electrons be (λe). The length (L) of the cylindrical body is set to L> Lc + 2λe.
As a source of oxygen for forming a high temperature oxide superconducting thin film, the surface of the substrate which is placed in a vacuum container and is inert to oxygen is irradiated with active oxygen from the active gas generator of FIG. It is characterized by being used.

[0005]

Since the length of the cylinder is the sum of the length of the coil wound around the cylinder and twice or more of the mean free path of electrons, a sufficient plasma generation space is secured. By irradiating the surface of the substrate, which is inert to oxygen, with active oxygen from this device, a good cleaned surface was obtained, and two-dimensional epitaxial growth was performed by oxidizing the deposited metal elements in a high vacuum. An oxide-based superconducting thin film can be obtained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram for explaining an embodiment of the active gas generator of the present invention. In the figure, reference numeral 1 is a cylindrical discharge tube having a length (L) and an inner diameter of about 10 to 20 mm, which is formed of an insulator such as quartz or ceramics. A small hole 1a that functions as an orifice is formed at the tip of the discharge tube 1 and is connected to the gas introduction tube 4 via the connection tube 3. The gas introduction pipe 4 is airtightly fixed near the center of the vacuum flange 5, and one end thereof is connected to a gas (oxygen in the drawing) cylinder (not shown).

Reference numeral 2 denotes a conductor coil wound a plurality of times within a predetermined range (Lc) of the discharge tube 1, and both ends thereof are airtightly fixed while being insulated from the vacuum flange. Cooling water is introduced into the coil 2 from one end, and the cooling water makes a circuit in the coil 2 and is then discharged from the other end. Although not shown in the drawing, a high frequency power source (not shown) is connected to the coil 2 via a terminal 6 to apply a high frequency.

Generally, when vapor deposition is performed using a high vacuum apparatus, a vacuum degree of 10 ^-6 Torr or less is usually required in order to secure the mean free path of atoms between the evaporation source and the substrate. Therefore, when flowing oxygen into the active gas source, it is necessary to suppress the flow rate to the extent that the degree of vacuum can be maintained. The flow rate of oxygen depends on the exhaust speed of the exhaust pump, but for example, 3000 l /
When a minute cryopump is used, the relationship between the pressure inside the vacuum device and the oxygen flow rate is as shown in FIG.

In FIG. 1, the shape of the orifice is 0.1.
Below scc / min (standard cc per minute), it is almost 0.
A 1mm ² ~1mm ² about. Oxygen plasma is generated in the discharge tube by applying a high-frequency current to the coil 2 in this state, but by adjusting the applied current, it is possible to realize a state of extremely high emission intensity called arc discharge.

On the other hand, the inventors generated oxygen plasma by using a commercially available active gas generator having the structure shown in FIG. 1, but no satisfactory result was obtained. Therefore, the inventors have noticed that the generation of oxygen plasma is related to the length of the discharge tube and the winding range of the coil, and as a result of various experiments, the length L of the discharge tube is
It was confirmed that arc discharge can be obtained by making the length of the coil winding range Lc longer than the sum of twice the mean free path λe of electrons in the discharge tube.

FIG. 3 shows the result of analyzing the emission spectrum of such plasma with a spectroscope.
A sharp peak is seen at 7.4 nm. This piece
It is known that the emission is from the excited state (oxygen radical) of atomic oxygen, indicating that extremely active oxygen is generated. In addition, this arc discharge-like plasma has a spread approximately equal to the coil length. On the other hand, in plasma, O 2 + e → O ^* + O + e, e + O → O ^* + e
A reaction such as (O ^* ; active oxygen) is occurring, and in the oxygen molecule, electrons collide with atomic oxygen to promote the reaction. The mean free path λe of this electron is given by λe = (1 / αn) n and n = 9.68 × 10 ³⁴ (P / T). α: Collision cross section of gas molecule (mm ² ) n; Molecular density (m ^-3 ) P; Pressure (Torr) T; Temperature (° C)

Here, the cross-sectional area of the oxygen molecule is 3.6 × 10.
^-10 m ² , pressure (P) 10 ^-2 Torr, temperature (T)
Substituting 300K into the above equation gives λe = 3 cm (about 30 cm for P = 10 ⁻³ Torr). This indicates that the electrons can diffuse out of the plasma by a distance of λe. That is, by using a discharge tube in which the length of plasma (corresponding to Lc) is at least 2λe or more, the generation efficiency of the active oxygen source can be increased.

FIG. 4 is a block diagram showing a state in which the active gas generator 10 having the above structure is attached to the MBE device 11. 1
2 is a substrate holder having a heater, 13 is a substrate attached to the substrate holder, 14 is a material crucible, and 15 is Q-MAS
The gas generator 10 is installed in an MBE device (high vacuum device) in which a substrate 13 on which an oxide thin film is to be formed is placed by a vacuum flange, and gas from a gas cylinder (not shown) is gasted at a predetermined pressure. Introduced into the introduction pipe 4 (see Fig. 1),
A high-frequency current is applied to the coil 2 while being ejected from the small hole 1a of the discharge tube. As a result, the gas ejected from the small holes 1a is turned into plasma and ejected.

Using the active gas generator 10 described above, MB
Under ultra-high vacuum of E unit 11, SrTiO3 and MgO
The substrate 13 is heated to 600 to 700 ° C., and the wavelength is 777.4.
Irradiation with active oxygen gas having a μm spectrum for about 5 minutes
did. As a result, both substrates have uneven surface atoms
Confirmed that no cleaning was done. 5 and 6
Cleans the MgO (100) substrate using the MBE machine,
Subsequently, using the elements Dy, Ba, and Cu, the oxide-based superconductivity
A conductive thin film is formed, and the temperature-resistance characteristics and
It is a figure which shows an example of the result of having performed X-ray diffraction measurement. Na
The film forming conditions were as follows. Dy cell temperature ... 950 ° C., Ba cell temperature ... 568 ° C.,
 Cu temperature… 1000 ° C, substrate temperature… 600 ° C, acid
Elementary pressure… 2 × 10^-6(Torr), film thickness ... 300 angstrom
-, According to Fig. 5, the resistivity (mΩ-cm) near 88K
Indicates that the superconducting critical temperature (Tc) becomes 0.
ing. In addition, in the X-ray diffraction measurement result of FIG.
There is a strong peak of 0l), and the thin film is oriented in the C-axis direction.
It shows that it is doing. MBE device as described above
When using ultra-high vacuum, for example, in the first stage, turbo
After pre-evacuating with a molecular pump, the second stage is cryo
It is pulled by the pump. In that case, the degree of vacuum in the device is 10
^-8It is about Torr. By the way, for example, forming a superconducting thin film
In doing so, the MgO substrate 13 is heated to 600 to 700 ° C.
In such a case, the temperature inside the device may be several hundred degrees depending on the location.
To rise. The vacuum container is constructed by this temperature rise.
H occluded in a metal (for example, stainless steel)₂But
Most of the residual molecules are H because they are released into the vacuum container.
₂Becomes However, H₂Is N₂Or O₂Saturated vapor pressure compared to
Is large, there is a problem that exhaust efficiency is poor.
In the invention, the excited state oxygen radical is used as the oxygen source.
Therefore, there is an effect that it contributes to the improvement of exhaust efficiency.
That is, oxygen radicals (O^*) Supply and leave
Done H₂Is H₂+ O^*→ H ₂It becomes the shape of O. This H₂O is steam
Exhaust can be performed efficiently because the atmospheric pressure is large. Fruit
According to the test, the hydrogen partial pressure before oxygen radical supply is 2 × 10^-8To
About rr is 1.7 × 10^-8To reduce to about Torr
I was able to. In the present invention, since the superconducting thin film is formed
Since oxygen radicals are constantly supplied to the
Power is 2 × 10^-6Torr level, but for example partial heating
Means for efficiently exhausting hydrogen released into the vacuum container by
If oxygen radicals are supplied for a certain period of time,
I hate the existence of hydrogen because the hydrogen partial pressure can be lowered.
It can be used for processes. In the present embodiment, claim 1
Oxygen is the gas generated from the active gas generator
I made it clear that hydrogen, nitrogen, and other gases will do the same.
It can be activated.

[0015]

As described above in detail with reference to the embodiments, in the active gas generator of the present invention, the length of the discharge tube is (L) and the length of the range in which the coil is wound around the discharge tube. (Lc) and the mean free path of electrons is (λe), the length of the discharge tube is L> Lc + 2λe, so that plasma can be efficiently generated, and in the high vacuum of the deposited metal element. Can be efficiently oxidized. Further, if the surface of the substrate is cleaned by using this apparatus to form an oxide-based superconducting thin film, a superconducting thin film with good characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of an active gas generator of the present invention.

FIG. 2 is a diagram showing a relationship between a pressure in a vacuum device and an oxygen flow rate.

FIG. 3 is a diagram showing a result of analyzing an emission spectrum of plasma by a spectroscope.

FIG. 4 is a configuration diagram showing a state in which the active gas generator of the present invention is attached to an MBE device.

FIG. 5 is a diagram showing temperature-resistance characteristics of a superconducting thin film.

FIG. 6 is a diagram showing an X-ray diffraction measurement result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge tube 1a Small hole 2 Coil 3 Connection tube 4 Gas introduction tube 5 Vacuum flange 6 Terminal 10 Active gas generator 11 MBE device 12 Substrate holder 13 Substrate 14 Material crucible 15 Q-MASS

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location H01B 13/00 565 D 8936-5G H01L 39/24 ZAA B 8728-4M // H01B 12/06 ZAA 8936-5G

Claims (2)

[Claims] 1. A tubular discharge tube having a small hole at one end, and a coil made of a conductor wound around the outer circumference of the discharge tube, wherein gas is supplied from a small hole provided at one end of the discharge tube. In an active gas generator which is made to jet and a high frequency current is passed through the coil to turn the gas into plasma,
When the length of the tube of the discharge tube is (L), the length of the range in which the coil is wound around the tube of the discharge tube is (Lc), and the mean free path of electrons is (λe), An active gas generator, wherein the length (L) of the cylindrical body of the discharge tube is L> Lc + 2λe. 2. The surface of a substrate placed in a vacuum container, which is inert to oxygen, is irradiated with active oxygen from the active gas generator according to claim 1 to clean the surface of the substrate and increase the temperature of the oxide. A method for forming an oxide high temperature superconducting thin film, which is used as an oxygen source when forming a superconducting thin film.