JPH1180939A - Formation of thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming thin film in which the irradiating conditions of a laser are optimized, the cracking of a target is prevented and capable of forming thin film on a based material having a wide area by effectively using the structural material of the target. SOLUTION: This method is the one in which a target is intermittently irradiated with laser light to beat out or evaporate the structural particles of the target, and the structural particles are deposited on a base material to form thin film, and at the time of intermittently applying the laser light while scanning is executed by moving the irradiating position of the laser light on the surface of the target and executing laser vapor deposition, the scanning rate of the laser light to be applied to the target is regulated to 2 to 20 mm/sec, the irradiating energy of the laser light is regulated to 200 to 400 mj, and the irradiating frequency at the time of intermittently applying the laser light is regulated to 10 to 200 Hz.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to formation of a thin film by forming a thin film by irradiating a target with a laser beam to beat or evaporate constituent particles of the target and depositing the constituent particles on the surface of a substrate. It is about the method.

[0002]

2. Description of the Related Art In order to use an oxide superconductor as a conductor, it is necessary to form a thin film of an oxide superconductor having good crystal orientation on a long base material such as a tape. In general, since the metal tape itself is a polycrystalline material and its crystal structure is significantly different from that of the oxide superconductor, a thin film of the oxide superconductor with good crystal orientation cannot be formed.

[0003] The inventors of the present invention have proposed a method of forming yttrium-stabilized zirconia (Y) having excellent crystal orientation on a base material 1 made of a metal tape such as a Hastelloy tape as shown in FIG.
(SZ) or the like, and a critical temperature of about 9 among oxide superconductors is formed on the polycrystalline intermediate thin film 2.
A 0K, good oxide superconducting superconducting properties by forming a thin film 3 of Y ₁ Ba ₂ Cu ₃ O _x based oxide superconductor having excellent stability can be used in liquid in nitrogen (77K) Attempts have been made to manufacture the conductor 4, and the present inventors have previously described Japanese Patent Application Nos. 3-126636 and 3-12.
No. 6837, Japanese Patent Application No. 3-205551, Japanese Patent Application No. 4-1
Patent applications have been filed in Japanese Patent Application No. 3443 and Japanese Patent Application No. 4-293364.

In the techniques described in these patent applications, a method of forming a thin film by a laser vapor deposition method is employed to form a thin film 3 of a Y ₁ Ba ₂ Cu ₃ O _x -based oxide superconductor. ing. Laser vapor deposition is a method of moving a laser beam irradiation position on the surface of a target while scanning to strike or evaporate constituent particles of the target and deposit the constituent particles on the surface of the base material to form a thin film. This is a method of forming a thin film for forming a thin film. As a laser, if it can strike out constituent particles,
Any of a YAG laser, a CO ₂ laser, an excimer laser and the like can be used. The target has a composition similar to or close to the composition of the oxide superconductor to be formed into a film, and a sintered body of the oxide superconductor or the like is used.

According to the method for forming a thin film described above, only one target having a composition equal to or close to the composition of the oxide superconductor to be formed is required. In addition, since the intensity of laser light does not attenuate even in the air, it can be deposited in an oxygen atmosphere, and crystal growth is preferably performed in an oxygen atmosphere, which is convenient for forming a thin film of an oxide superconductor. It is. Furthermore, since the irradiation energy of the laser beam acts only on the portion of the target irradiated with the laser beam and does not affect the surrounding area, the composition of the oxide superconductor is heated by the heat of the irradiation energy of the laser beam. Is not locally changed, and even when a thin film is formed on a substrate, a thin film having a uniform composition can be obtained. Furthermore, since the constituent particles of the target that are beaten out or evaporated by the laser beam are deposited on the polycrystalline intermediate thin film having good crystal orientation while growing epitaxially, the oxide superconductor having excellent crystal orientation is formed. A thin film can be obtained, and the superconducting characteristics such as a critical current value and a critical current density of the obtained oxide superconducting conductor can be improved.

[0006]

However, in a conventional method of forming a thin film by a laser vapor deposition method, usually, a scanning speed of a laser beam is 1 mm / sec, an irradiation frequency of a laser beam is 10 to 200 Hz, and a laser beam irradiation is performed. Although the energy is 200 to 400 mJ, the scanning speed is relatively slow, and the thermal energy of the laser beam received by the target is large, so that the temperature of a portion of the target irradiated with the laser beam locally rises, and this temperature rise As a result, there is a problem that the oxide is locally expanded and the target which is a sintered body is cracked or a hole is generated.

[0007] Further, under the above-mentioned irradiation conditions, the surface of the target once irradiated with the laser beam cannot be irradiated with the laser again. That is, the surface of the target
The constituent particles of the target are beaten out or evaporated by the laser light to become concave, the smoothness of the surface is impaired, and even if the same part is irradiated again with the laser light, the direction in which the blown out constituent particles fly is changed. This is because the particles are unbalanced and the constituent particles cannot be uniformly deposited on the base material. Therefore, even if the sintered body of the oxide superconductor still remains, there is a problem in that the target has a lifetime if the laser beam is irradiated once on the entire surface of the target, and the target cannot be used effectively. Another problem is that the area of a thin film that can be formed by one target cannot be increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to prevent a target from cracking and to form a thin film on a substrate having a large area by effectively using a constituent material of the target. It is an object of the present invention to provide a method of forming a thin film capable of performing the following.

[0009]

In order to achieve the above object, the following configuration is adopted. The method for forming a thin film according to claim 1, wherein the target is intermittently irradiated with a laser beam to beat out or evaporate constituent particles of the target and deposit the constituent particles on the surface of the base material. A laser beam irradiation position is moved over the surface of the target, and the laser beam is intermittently irradiated while performing laser deposition. ~ 20mm /
Second, irradiation energy of laser light is 200-400m
J, Irradiation frequency for intermittent irradiation of laser beam is 10
It is characterized by being set to 200 Hz.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a thin film 3 of an oxide superconductor.
1 shows an example of a laser vapor deposition apparatus for forming a film. The laser vapor deposition apparatus 11 of this example has a processing vessel 12, and a thin film laminate 14 and an oxide superconductor target 15 can be installed in a vapor deposition processing chamber 13 inside the processing vessel 12. I have. That is, a base 16 is provided at the bottom of the vapor deposition processing chamber 13, and the thin film laminate 14 can be installed on the upper surface of the base 16.
A target 15 of an oxide superconductor supported by a support holder 17 is provided diagonally above. Further, reference numeral 18 in the drawing denotes a delivery device for the thin film laminate 14,
Reference numeral 19 denotes a winding device of the thin film laminate 14. Further, the processing container 12 is connected to a vacuum exhaust device 21 via an exhaust hole 20 so that the pressure in the vapor deposition processing chamber 13 can be reduced to a predetermined pressure.

The thin film laminate 14 is formed by forming a polycrystalline intermediate thin film 2 of YSZ on a metal tape-shaped substrate 1 such as Hastelloy by an ion beam assisted sputtering method or the like. Stainless steel,
A long metal tape appropriately selected from various metal materials such as copper or alloys such as nickel alloys such as Hastelloy can be used. The thickness of the substrate 1 is 0.01 to
It is 0.5 mm, preferably 0.02 to 0.15 mm. When the thickness of the substrate 1 is 0.5 mm or more, the thickness is larger than the thickness of the oxide superconductor thin film 3 described later, and the critical current density per overall (total cross-sectional area of the oxide superconductor) decreases. . On the other hand, when the thickness of the substrate 1 is 0.0
If it is less than 1 mm, the strength of the base material 1 is significantly reduced, and the effect of reinforcing the oxide superconducting conductor 4 is lost. The polycrystalline intermediate thin film 2 is composed of a large number of fine crystal grains in which crystals having a cubic crystal structure are aggregated and joined together via a crystal grain boundary. The c-axis is oriented substantially at right angles to the upper surface (film-forming surface) of the substrate 1, and the a-axes and b-axes of the crystal axes of the crystal grains are oriented in the same direction and are in-plane oriented. I have. The thickness of the polycrystalline intermediate thin film 2 is set to 0.1 to 1.0 μm. Even if the thickness of the polycrystalline intermediate thin film 22 is increased beyond 1.0 μm, the effect cannot be expected to increase anymore, which is economically disadvantageous.
On the other hand, if the thickness of the polycrystalline intermediate thin film 2 is less than 0.1 μm, there is a possibility that the thin film 3 of the oxide superconductor cannot be sufficiently supported because it is too thin. As a constituent material of the polycrystalline intermediate thin film 2, MgO, SrTiO ₃ or the like can be used in addition to YSZ.

The oxide superconductor target 15 has a composition similar or similar to that of the oxide superconductor thin film 3 to be formed, or a composite oxide containing many components that easily escape during film formation. It is made of a body such as a binder or an oxide superconductor. Therefore, the target 15 of the oxide superconductor is composed of Y ₁ Ba ₂ Cu ₃ O _x , Y ₂ Ba ₄ Cu ₈ O _x ,
The composition of Y ₃ Ba ₃ Cu ₆ O _x , (Bi, Pb) ₂ Ca ₂ Sr ₂
Cu ₃ O _x , (Bi, Pb) ₂ Ca ₂ Sr ₃ Cu ₄ O _x , or Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _x , Tl ₁ Ba ₂ C
Since used to form _{a 2 Cu 3 O x, Tl} 1 Ba 2 Ca 3 Cu 4 O x becomes thin film 3 having a high critical temperature oxide superconductor represented by like composition, or the same composition as this It is preferable to use one having a similar composition.

The base 16 has a built-in heater.
The thin film laminate 14 can be heated as needed. On the other hand, a laser light emitting device 22, a first reflecting mirror 23, a condenser lens 24, and a second reflecting mirror 2
5 is provided so that the laser beam generated by the laser light emitting device 22 can be focused and irradiated on the target 15 through the transparent window 26 attached to the side wall of the processing container 12. As the laser light emitting device 22, any device such as a YAG laser, a CO ₂ laser, an excimer laser, or the like may be used as long as it can strike out constituent particles from the target 15.

As means for scanning a laser beam on a target and adjusting the scanning speed, a support holder 17 of an oxide superconductor target 15 is connected to a drive source such as a motor so that the position can be moved. It is configured to be able to. Adjustment of the laser irradiation output can be performed by adjusting the output of an amplifier (not shown) that supplies power to the laser light emitting device 22. Further, the irradiation frequency of the laser indicates the number of laser pulses intermittently oscillated per second. This adjustment is performed by intermittently supplying power to the laser light emitting device 22 at a constant frequency. It can be adjusted by providing a mechanical shutter such as a rotating sector somewhere in the path through which the laser beam passes, and operating this mechanical shutter at a constant frequency.

FIGS. 3 (a) and 3 (a) show an example of a trajectory (dashed line) when the laser beam moves on the surface of the target 15. FIG.
(B). In FIG. 3A, the laser light is:
Scanning is performed along the circumference of the circular target 15a so as to gradually rotate toward the center of the target 15a.
In FIG. 3B, the laser beam moves along the short side of the rectangular target 15b, and then moves to the target 15b.
The target 15b is moved so as to slightly move along the longitudinal direction thereof, and is moved again along the short side of the target 15b.

Next, Y is placed on the thin film laminate 14.₁Ba_TwoCu
_ThreeO_XFor forming thin film 3 of oxide superconductor
explain. Thin film on which YSZ polycrystalline intermediate thin film 2 is formed
The laminate 14 is placed on the base 1 with the polycrystalline intermediate thin film 2 side facing up.
6 and placed as an oxide superconductor target 15
Y ₁Ba_TwoCu_ThreeO_XIs installed and the deposition chamber 1
3 is depressurized by the evacuation device 21. Here as needed
Oxygen gas is introduced into the evaporation processing chamber 13 to
An oxygen atmosphere may be used. Also, the heater of the base 16
To heat the thin film stack 14 to a desired temperature.
good.

While sending the thin film stack 14 from the sending device 18, the laser beam is applied to the target 1 of the oxide superconductor.
5 is focused and irradiated. As a result, the constituent particles of the target 15 are removed or evaporated, and the particles are deposited on the polycrystalline intermediate thin film 2.

The polycrystalline intermediate thin film 2 has crystal grains of c
Since the oxide superconductor thin film 3 is formed by the ion beam assist method so as to be oriented in the axial direction and also in the a-axis and the b-axis, the c-axis, the a-axis, and the b-axis of the crystal of the oxide superconductor thin film 3 are also polycrystalline intermediate thin
And is crystallized by epitaxial growth so as to match the crystal. Thereby, Y ₁ Ba ₂ Cu _{3 having} good crystal orientation can be obtained.
O _X thin film 3 of an oxide superconductor is obtained. After the film formation, a heat treatment for adjusting the crystal structure of the oxide superconductor thin film 3 may be performed, if necessary. The thickness of the oxide superconductor thin film 3 is about 0.5 to 5 μm.

The scanning speed when irradiating the target with laser light is preferably in the range of 2 to 20 mm / sec. When the scanning speed is 2 mm / sec or less, the thermal energy of the laser beam received by the target increases, and cracks are generated due to a local temperature rise of the target, which is not preferable. In addition, the degree of beating or evaporation of the constituent particles becomes large, and the surface smoothness of the portion once irradiated with the laser light is impaired, so that the same portion cannot be irradiated with the laser light again. It is not preferable because the life cannot be extended. If the scanning speed is at least 20 mm / sec, the constituent particles cannot be beaten out or vaporized sufficiently from the target, and the formation speed of the oxide superconductor thin film will be reduced, which is not efficient.

When the target is irradiated with laser light in the above-mentioned scanning speed range, the irradiation energy of the laser light needs to be in the range of 200 to 400 mJ. When the irradiation energy of the laser beam is 200 mJ or less, even if the scanning speed is set to 2 mm / sec, the thermal energy given to the target is too small and the constituent particles of the target cannot be sufficiently beaten out or evaporated. The formation speed of the superconductor thin film is reduced, which is not efficient. If the output of the laser beam is 400 mJ or more, even if the scanning speed is set to 20 mm / sec, the energy given to the target is too large and the target is cracked, which is not preferable.

Further, the irradiation frequency of the laser beam is 10 to 2
It must be in the range of 00 Hz. When the irradiation frequency of the laser beam is 10 Hz or less, the irradiation output becomes 400
Even if the scanning speed is set to 2 mm / sec, the energy given to the target is too small to sufficiently squeeze out the constituent particles of the target. Not a target. If the irradiation frequency of the laser beam is higher than 200 Hz, even if the irradiation output is set to 200 mJ and the scanning speed is set to 20 mm / sec, the energy given to the target is too large, and the target is cracked.

According to the above-described method for forming a thin film, the scanning speed of the laser beam irradiating the target is 2 to 20 mm /
Second, irradiation energy of laser light is 200-400m
J. Since the irradiation frequency is set to 10 to 200 Hz, the surface of the target is not locally heated by the laser light, and the expansion of the oxide due to the temperature rise is prevented, so that the target which is a sintered body is broken. Can be prevented. In addition, the target is moderately suppressed from hitting or evaporating constituent particles by laser light,
Since the surface smoothness is maintained, it is possible to irradiate the laser light again to the same portion, and the remaining sintered body of the oxide superconductor can be beaten out or evaporated again by one laser irradiation. Because it is possible, the target can be used effectively. Further, the area of a thin film that can be formed by one target can be increased.

[0023]

【Example】

 (Example 1) A scanning speed of a laser beam was set to 2 mm / sec.
Irradiation energy of 200 mJ, irradiation frequency of 1
YSZ polycrystalline intermediate thin film with a frequency of 00 Hz and a thickness of 0.7 μm
For 5 Hastelloy tapes with 0.3m length
I mean, Y ₁Ba_TwoCu_ThreeO_xSystem material
Use a 1 μm thick Y on each Hastelloy tape.
₁Ba_TwoCu_ThreeO_x5 layers of oxide superconductor
A conductor was produced. In this case, the laser light is targeted.
When the entire surface of the kit is irradiated, at least one
5 sets because a thin film can be formed on Roy tape
In order to fabricate an oxide superconductor of
The target is repeatedly irradiated several times. (Example 2) The scanning speed of the laser beam was 5 mm / sec,
Implemented except that the irradiation energy of the laser light was 400 mJ
Five sets of oxide superconductors were prepared in the same manner as in Example 1.
Was.

(Embodiment 3) The scanning speed of the laser beam is set to 10
mm / sec, the irradiation output of the laser beam was set to 400 mJ, and the irradiation frequency was set to 200 Hz.
Five sets of oxide superconductors were prepared. (Example 4) The scanning speed of the laser beam was 2 mm / sec, the irradiation output of the laser beam was 400 mJ, and the irradiation frequency was 200 H.
A set of oxide superconductors was produced in the same manner as in Example 1 except that z was used. (Example 5) The scanning speed of the laser beam was 20 mm / sec, the irradiation output of the laser beam was 200 mJ, and the irradiation frequency was 10 H.
A set of oxide superconductors was produced in the same manner as in Example 1 except that z was used.

(Comparative Example 1) Scanning speed of laser beam was 1 m
Five sets of oxide superconducting conductors were produced in the same manner as in Example 1 except that the irradiation energy of the laser beam was changed to 400 mJ / m / sec. (Comparative Example 2) The scanning speed of the laser beam was 1 mm / sec, the irradiation energy of the laser beam was 400 mJ, and the irradiation frequency was 2
Five sets of oxide superconductors were produced in the same manner as in Example 1 except that the frequency was set to 00 Hz. Comparative Example 3 A set of oxide superconductors was produced in the same manner as in Example 1 except that the scanning speed of the laser beam was 25 mm / sec, the irradiation energy of the laser beam was 100 mJ, and the irradiation frequency was 100 Hz.

(Comparative Example 4) Scanning speed of laser light was 1 m
A set of oxide superconductors was prepared in the same manner as in Example 1 except that the irradiation energy of the laser beam was 450 mJ and the irradiation frequency was 100 Hz. (Comparative Example 5) The scanning speed of the laser beam was 2 mm / sec, the irradiation energy of the laser beam was 400 mJ, and the irradiation frequency was 5
A set of oxide superconductors was produced in the same manner as in Example 1 except that the frequency was changed to Hz.

The critical current value and the critical current density under the conditions of 77 K and 0 T were measured while cooling the oxide superconducting conductors produced in the examples and comparative examples with liquid nitrogen. Table 1 shows the results
Shown in Further, the surface of the target after irradiation with the laser light was visually observed. Table 2 shows the results.

[0028]

[Table 1]

[0029]

[Table 2]

The oxide superconductors of Examples 1 to 5 have good critical current values and critical current densities. Comparative Examples 1, 2, 4
The oxide superconducting conductor of Table 1 is compared with Examples 1 to 5 in Table 1.
Therefore, some have the same critical current density, but the critical current density decreases as the irradiation of the target with the laser beam progresses. In the case of Comparative Examples 1 and 2, only two sets of oxide superconductors having good characteristics were obtained. Further, when the targets of Comparative Examples 1 and 2 are observed, cracks and holes are confirmed. Furthermore, in Comparative Example 4, cracks occurred in the target immediately after the irradiation with the laser. This is because the irradiation conditions of the laser beam are too strong, the thermal energy given to the target is large, the surface smoothness of the target is impaired, or cracks are generated, so that the second and subsequent sets of oxide superconductors It is presumed that the thin film could not be formed uniformly.

Table 1 shows that the critical current values of all the oxide superconductors of Comparative Examples 3 and 5 are lower than those of Examples 1 to 5. This is presumed to be due to the fact that the laser irradiation conditions were too weak, the formation of the oxide superconductor thin film was insufficient, and the overall size was small.

[0032]

As described above in detail, the method of forming a thin film of the present invention intermittently irradiates a target with laser light to strike out or evaporate the constituent particles of the target, thereby forming a substrate. A method for forming a thin film by depositing the constituent particles on a surface, wherein the irradiation frequency of the laser light applied to the target is 10 to 20.
0 Hz, a scanning speed of 2 to 20 mm / sec, and a laser beam irradiation energy of 200 to 400 mJ,
The temperature of the target is not locally increased by the laser beam, the expansion of the oxide is prevented, and the crack of the target that is a sintered body can be prevented. In addition, since the surface of the target is appropriately suppressed from beating or evaporating the constituent particles by the laser beam, the smoothness of the surface is maintained, so that the same portion can be irradiated with the laser beam again. The remaining sintered body of the oxide superconductor can be beaten out or evaporated again by the laser irradiation, and the target can be used effectively. Further, the area of a thin film that can be formed by one target can be increased.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a laser deposition apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective sectional view showing an oxide superconducting conductor according to an embodiment of the present invention.

3A and 3B are diagrams illustrating a trajectory of laser light when a target is irradiated with laser light in the laser vapor deposition apparatus according to the embodiment of the present invention. FIG. 3A illustrates a trajectory of laser light in a circular target. FIG.
(B) is a schematic diagram showing a trajectory of a laser beam on a square target.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Polycrystalline intermediate thin film 3 Oxide superconductor thin film 4 Oxide superconductor 11 Laser vapor deposition device 14 Thin film laminate 15 Target 22 Laser light emitting device 23 First reflecting mirror 24 Condensing lens 25 Second reflecting mirror

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takashi Saito 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Co., Ltd.

Claims (1)

[Claims] 1. A method for forming a thin film by intermittently irradiating a target with a laser beam to beat or evaporate constituent particles of the target and depositing the constituent particles on a surface of a substrate. When laser irradiation is performed by intermittently irradiating laser light while scanning by moving the irradiation position of the laser light on the surface of the target, the scanning speed of the laser light irradiating the target is 2 to 20 mm / sec. A method for forming a thin film, wherein the irradiation energy is 200 to 400 mJ and the irradiation frequency for intermittent irradiation of laser light is 10 to 200 Hz.