JPH0885865A - Formation of thin film by laser vapor depositing method - Google Patents

Abstract

PURPOSE: To produce an oxide superconducting thin film of high quality having a large area, in a laser vapor depositing method in which a substrate is arranged vertically to the face of a target to be irradiated and the substrate and target are rotated, by scanning a laser beam on the surface of the target. CONSTITUTION: A target 5 is arranged at a target holder 45 in a sealed chamber 40 in which the pressure and atmosphere can be regulated and is rotated by a motor 47. Simultaneously, a substrate 6 is disposed at a substrate holder 46 vertically to the face of the target 5 to be irradiated and is rotated by a motor 36. A laser beam 10 oscillated by a laser device 1 is reflected by a mirror 2, is transmitted through a lens 3, passes through an incident window and converges on the target 5. In this case, when the face of the substrate 6 is extended in the direction of the target 5, the mirror 2 is rotated in such a manner that the laser beam scans the surface of the diameter of the target in the case of being crossed with the face of the target 5 to grow an oxide superconducting thin film on the face of the substrate 6 to be film-formed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a thin film. More specifically, the present invention relates to a method of producing a high quality thin film by laser vapor deposition.

[0002]

2. Description of the Related Art A laser vapor deposition method is a method of irradiating a target with a high-energy laser beam under reduced pressure to generate a deposit and grow a thin film on a substrate. The laser vapor deposition method has advantages that the composition of the thin film can be easily controlled and that the film formation rate is high. Also, since it does not require any electromagnetic field,
The presence of charged particles in the deposit will not be affected. Therefore, it is considered to be a suitable method for producing a high quality thin film.

On the other hand, the oxide superconductor is a multi-component complex oxide, and even if the composition ratio is a little off, the superconducting properties are significantly deteriorated. As described above, since the composition of the thin film to be formed is easily controlled by the laser vapor deposition method, research has been conducted on producing an oxide superconducting thin film having excellent characteristics by using the laser vapor deposition method. For example, the material of the Optical and Quantum Device Research Group by the Institute of Electrical Engineers of Japan (Document number OQD
-92-53) pp.69-77 (October 28, 1992), a high-quality Y-Ba was produced by a laser deposition method using an excimer laser.
A method of forming a -Cu-O-based oxide superconducting thin film is disclosed.

When a thin film is formed by the laser deposition method, as shown in the above-mentioned document, the substrate and the target are placed in a chamber which can be evacuated to a high vacuum and into which an arbitrary atmospheric gas can be introduced. A laser beam emitted from a laser device arranged outside the chamber is guided by an optical means, and is condensed as necessary to irradiate a target.

[0005]

However, as described in the above document, the laser vapor deposition method has a narrow film forming range and it is difficult to form a thin film having a large area. Therefore, in the film formation by the laser vapor deposition method, the film formation rate itself is high, but the substantial film formation efficiency is low. Therefore, an object of the present invention is to provide a method for forming a high-quality oxide superconducting thin film having a large area by a laser deposition method.

[0006]

According to the present invention, a target is irradiated with laser light in an airtight chamber whose internal pressure and atmosphere can be adjusted to form a film on a substrate arranged perpendicularly to the surface to be irradiated of the target. A method for growing an oxide superconducting thin film on a surface, comprising: rotating a substrate and scanning a target with a laser beam to form a film. .

In the method of the present invention, it is preferable that the minimum length by which the laser beam can scan the target is larger than 1/2 of the typical length of the substrate. In this case, the representative length of the substrate means the length of the diameter of the substrate when the substrate is substantially circular, and the length of the diagonal line of the substrate when the substrate is substantially rectangular.

On the other hand, in the method of the present invention, the substantial scanning speed of the laser light is slowed at the position corresponding to the peripheral portion of the substrate,
It is preferable to increase the speed at a position corresponding to the center of the substrate. The substantial scanning speed of the laser light may be adjusted by keeping the scanning speed of the laser light constant and temporarily stopping the scanning of the laser light.

[0009]

According to the method of the present invention, when the oxide superconducting thin film is formed by the laser vapor deposition method, the substrate is placed perpendicular to the irradiation surface of the target, the substrate and the target are rotated, and the laser beam is irradiated on the target. Where it scans is its main feature. In the laser vapor deposition method, when the substrate is placed perpendicular to the irradiation surface of the target, laser light is generated from the portion where the target hits, and a portion close to the target along the light emission of the deposit called a plume-shaped plume. A thin film grows that reflects the shape of the plume that is thick and thick on the plume centerline.

Therefore, in the method of the present invention, in order to make the film thickness distribution uniform, the laser light is scanned so that the side surface of the plume hits the substrate uniformly, and the substrate is rotated. In the method of the present invention, for this purpose, the minimum length by which the laser light can scan the target is the representative length of the substrate, that is, the diameter of the substrate (for a circle), the diagonal line (for a rectangle). Is preferably greater than 1/2 of the length. As can be easily understood, when the size of the target is smaller than the above value, it is impossible to scan the laser light so that the side surface of the plume hits the substrate uniformly.

Further, in the method of the present invention, the substantial scanning speed of the laser beam is made slower at the position corresponding to the peripheral portion of the substrate and faster at the position corresponding to the central portion of the substrate, so that a more uniform thin film can be obtained. Can be formed. More specifically, it is preferable to change the substantial scanning speed of the laser light at the corresponding position so that it is inversely proportional to the linear velocity of each part of the rotating substrate or has a negative correlation.

However, when it is difficult to actually change the scanning speed of the laser light, even if the substantial scanning speed of the laser light is adjusted by temporarily stopping the scanning of the laser light. Good.

The oxide superconductors used in the method of the present invention are Y ₁ Ba ₂ Cu ₃ O _7-X , Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x , Tl ₂ Ba ₂ Ca ₂ Cu ₃
A high-temperature oxide superconductor such as O _x is preferable, and as the laser, it is preferable to use a harmonic wave of an excimer laser or a YAG laser.

Hereinafter, the present invention will be described in more detail with reference to examples, but the following disclosure is merely examples of the present invention and does not limit the technical scope of the present invention.

[0015]

EXAMPLE FIG. 1 (a) shows a schematic view of an example of a laser vapor deposition apparatus for carrying out the method of the present invention. The laser vapor deposition apparatus shown in FIG. 1A includes a laser apparatus 1, an airtight chamber 40, a mirror 2 and a lens 3 that collect the laser light 10 oscillated by the laser apparatus 1 and guide it into the chamber 40. . Mirror 2
And the lens 3 operates in synchronization with the scanning means 21,
Scan with laser light. The airtight chamber 40 includes an entrance window 41 through which the laser light 10 is incident, an exhaust unit 42, and a gas introduction unit 43, and the internal pressure and atmosphere can be arbitrarily changed. In addition, inside the airtight chamber 40, the motor
The target holder 45, which can rotate the target 5 mounted by the 47, emits the laser light incident from the incident window 41.
The position 10 is arranged so as to hit the target 5. Further, inside the airtight chamber 40, a substrate holder 46 for mounting the substrate 6 perpendicularly to the target 5 is provided. The substrate holder 46 can rotate the substrate 6 by a motor 48, and can also move the position of the substrate 6 in the axial direction and the direction perpendicular to the axis. A heater (not shown) is built in the substrate holder 46, and the substrate 6
Can be heated.

The laser light 10 oscillated by the laser device 1 is reflected by the mirror 2, passes through the lens 3, and is focused on the target 5 through the entrance window 41. In this embodiment, when the substrate surface is extended in the target direction, the mirror 2 is rotated so that the laser beam is scanned over the target diameter when it intersects the target surface. In the lens 3, the length of the optical path from the laser device 1 to the lens 3 is a on the plane formed by the optical path of the laser light when the laser light is scanned in synchronization with the rotation operation of the mirror 2. Three
When the optical path length from the target to the target 5 is b, the two-dimensional operation is performed so that the reduction ratio b / a on the target 5 becomes constant. However, when the length a of the optical path from the laser device 1 to the lens 3 is sufficiently larger than the diameter of the target 5, even if the lens 3 is one-dimensionally operated in parallel with the diameter of the irradiated surface of the target 5, The reduction rate b / a can be regarded as substantially constant. When such an arrangement is possible, the lens 3 is one-dimensionally operated in parallel with the diameter of the irradiation surface of the target 5. The focal length f of the lens 3 is 1 / f = 1
/ A + 1 / b. Laser light 10 is shown in Figure 1.
The target 5 is scanned as shown in (b). Laser light 1
When 0 is irradiated on the target 5, light emission called a plume is generated almost perpendicularly to the surface to be irradiated. In the above apparatus, the substrate 6 and the target 5 are rotated and the laser light 10
By irradiating the target 5 while scanning the target 5, the entire target 5 is used and the side surface of the plume is the substrate 6
The film is evenly contacted with the surface of the to form a uniform thin film.

Example 1 An oxide superconducting thin film is formed by the conventional method of rotating only the target 5, the conventional method of rotating the target 5 and the substrate 6, and the method of the present invention, using the above laser deposition apparatus. did. For the substrate 6, a Si single crystal substrate on a disk with a diameter of 75 mm and a thickness of 0.4 mm is used, and for the target 5, a Y ₁ Ba ₂ Cu ₃ O _7- on a disk with a diameter of 75 mm and a thickness of 5 mm is used. _A sintered body of _X oxide superconductor was used. The film forming process will be described below.

First, the target 5 is attached to the target holder.
The substrate 6 was set on the substrate holder 46 at 45. The inside of the airtight chamber 40 was evacuated to 1 × 10 ⁻⁶ Torr and then O ₂ was introduced to adjust the pressure to 1 Torr. As shown in FIG. 2, the substrate 6
The target 5 and the target 5 are arranged such that the film formation surface of the substrate 6 and the irradiation surface of the target 5 are perpendicular to each other, and the normal line standing at the center of the irradiation surface of the target 5 passes through the center of the film formation surface of the substrate. The common film forming conditions are shown below. Substrate surface temperature 300 ° C Distance between substrate center and target 90 mm Oxygen pressure 1 Torr Laser energy (on target) 330 mJ / pulse Laser irradiation area 4 × 1 mm ² Laser pulse rate 30 Hz Target rotation speed 20 rpm Substrate rotation speed 72 rpm Film formation time 5 minutes

In the method of the present invention, the laser beam is scanned at a scanning speed of 1.9 within a range of 72 mm in diameter parallel to the target substrate film formation surface.
Scanning was performed at mm / sec, and the scanning was stopped for 4 seconds at both scanning ends and 0.4 seconds at 20 mm and 30 mm positions from both scanning ends, respectively. As a result, the Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film formed by the method of the present invention had a thickness of 180 ± 7 nm, but in the conventional method in which only the target was rotated, The conventional method of rotating 100 to 1400 nm and both the target and substrate resulted in a film thickness distribution of 200 to 500 nm. Figure 3 (a)-
(c) illustrates the film thickness distribution of the thin film formed by each of the above methods. 3A is a conventional method in which only the target is rotated, FIG. 3B is a conventional method in which both the target and the substrate are rotated, and FIG. 3C is in which both the target and the substrate are rotated. ₂ is a diagram showing the film thickness distribution of a Y ₁ Ba ₂ Cu ₃ O _{7 -X} oxide superconducting thin film formed by the method of the present invention which is rotated and further scanned with a laser beam.

Example 2 An oxide superconducting thin film was formed by the method of the present invention using the laser deposition apparatus shown in FIG. The substrate 6 has a diameter of 75 m
m, using a 0.5 mm thick LaAlO ₃ single crystal substrate on a disk,
The target 5 is Y ₁ B on a disk with a diameter of 75 mm and a thickness of 5 mm.
A sintered body of a ₂ Cu ₃ O _7-X oxide superconductor was used.

The target 5 and the substrate 6 were set in the same manner as in Example 1, the inside of the hermetic chamber 40 was evacuated to 1 × 10 ^-6 Torr, and then O ₂ was introduced to adjust the pressure to 1 Torr.
The film forming conditions are shown below. Substrate surface temperature 650 to 690 ℃ Substrate center-target distance 90 mm Oxygen pressure 1 Torr Laser energy (on target) 330 mJ / pulse Laser irradiation area 4 × 1 mm ² Laser pulse rate 30 Hz Target rotation speed 20 rpm Rotation speed 72 rpm Film formation time 10 minutes

Similar to the first embodiment, laser light was scanned at a scanning speed of 1.9 mm / sec over a range of the target diameter of 72 mm for 4 sec at both scanning ends, and 0.4 sec at 20 mm and 30 mm positions from both scanning ends, respectively. The film formation was performed after stopping. As a result, the obtained thin film was smooth on the entire surface of the substrate, had an average thickness of 220 nm, and had a film thickness distribution of ± 4%. Furthermore, the critical temperature was in the range of 88 to 91 K, and the film was a high quality thin film with extremely high uniformity. FIG. 4 shows the film thickness distribution of the thin film obtained in this example, and FIG. 5 shows the critical temperature distribution.

Example 3 Under the same conditions as in Example 2, the Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film was formed by the method of the present invention by changing the size and arrangement of the target and the laser beam scanning method. Was formed. In this embodiment, a disk-shaped LaAlO ₃ single crystal substrate having a diameter of 75 mm and a thickness of 0.5 mm is used as the substrate 6, and the target 5 is
A sintered body of Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconductor on a disk having a diameter of 38 mm and a thickness of 5 mm was used. As shown in FIG. 6, with respect to the substrate 6 and the target 5, the film formation surface of the substrate 6 and the irradiation surface of the target 5 are perpendicular to each other, and the normal line standing on the irradiation surface of the target 5 is the film formation surface of the substrate 6. It was arranged so as to be parallel to and overlap with the substrate surface. Further, the diameter of the target 5 was larger than ½ of the diameter of the substrate 6, and the target 5 was arranged so that the normal line at its end passes through the center of the substrate. As a specific example, the normal line at 0.5 mm from the end of the target 5 is arranged so as to pass through the center of the substrate 6.

The laser light scans a range of 36 mm of the target diameter at a scanning speed of 1.9 mm / sec, and the scanning edge corresponding to the periphery of the substrate is 4 seconds, and 20 mm and 30 mm from the scanning edge, respectively.
The film was formed by stopping for 0.4 seconds at the position. As a result, the obtained thin film was smooth on the entire surface of the substrate, and had an average of 220n.
It had a thickness distribution of ± 4% or less at a thickness of m 2. Further, the critical temperature was in the range of 88 to 91 K on the entire surface of the substrate, and it was a high quality thin film with extremely high uniformity.

Example 4 A Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film was formed by the method of the present invention under the same conditions as in Example 2 except that only the target scanning method was changed. In this embodiment, the laser beam stops the range of 74 mm of the target diameter for 0.1 seconds at both scanning ends, and the scanning speed is 25 mm / second at the center of the target, and the scanning speed during that time is the distance from the rotation center of the target. Scanning was performed symmetrically with respect to the center of rotation of the target at a scanning speed inversely proportional to the square. As a result, the obtained thin film was smooth on the entire surface of the substrate, had an average thickness of 220 nm, and had only a ± 3% film thickness distribution. Further, the critical temperature was in the range of 88 to 91 K on the entire surface of the substrate, and it was a high quality thin film with extremely high uniformity. FIG. 7 shows the film thickness distribution of the thin film obtained in this example, and FIG. 8 shows the distribution of the critical temperature.

Example 5 A Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film was formed by the method of the present invention under the same conditions as in Example 3 except that only the target scanning method was changed. In the present embodiment, the laser light stops the range of 37 mm of the diameter of the target for 0.1 seconds at the scanning end corresponding to the peripheral portion of the substrate, and 25 m at the scanning end corresponding to the rotation center of the substrate.
Scanning was performed at a scanning speed of m / sec, during which the scanning speed was inversely proportional to the square of the distance from the center of rotation of the target. As a result, the obtained thin film was smooth on the entire surface of the substrate, had an average thickness of 220 nm, and had a film thickness distribution of ± 3. Further, the critical temperature was in the range of 88 to 91 K on the entire surface of the substrate, and it was a high quality thin film with extremely high uniformity.

[0027]

As described above, according to the method of the present invention, a high-quality oxide superconducting thin film having a smooth surface, a small film thickness distribution and a small critical temperature distribution and a large area is formed by the laser deposition method. Membrane is possible. According to the present invention, a high-quality oxide superconducting thin film can be produced at low cost because the laser deposition method has a high film forming rate and a simple apparatus.

[Brief description of drawings]

FIG. 1 (a) is a schematic view of an apparatus for carrying out the method of the present invention, and (b) is a schematic view showing the arrangement of characteristic parts of the apparatus of (a).

FIG. 2 is a diagram showing an arrangement of a substrate and a target in Examples 1, 2 and 4.

FIG. 3 is a diagram showing film thickness distributions of an oxide superconducting thin film formed by a conventional method and an oxide superconducting thin film formed by a method of the present invention. (a) and (b) shows the film thickness distribution of the oxide superconducting thin film formed by the conventional method,
(c) shows the film thickness distribution of the oxide superconducting thin film formed by the method of the present invention.

FIG. 4 is a diagram showing a film thickness distribution of an oxide superconducting thin film formed by the method of the present invention in the examples described in the present specification.

5 is a diagram showing a distribution of critical temperature of an oxide superconducting thin film formed by the method of the present invention in the example in which the result of FIG. 4 was obtained.

FIG. 6 is a diagram showing an arrangement of a substrate and a target in Examples 3 and 5.

FIG. 7 is a diagram showing a film thickness distribution of an oxide superconducting thin film formed by the method of the present invention in another example described in the present specification.

8 is a diagram showing a distribution of critical temperature of an oxide superconducting thin film formed by the method of the present invention in the example in which the result of FIG. 7 was obtained.

[Explanation of symbols]

 1 Laser Device 2 Mirror 3 Lens 5 Target 6 Substrate 10 Laser Light 40 Airtight Chamber 41 Entrance Window 42 Exhaust Means 45 Target Holder 46 Substrate Holder

Claims (4)

[Claims] 1. A method of irradiating a target with a laser beam in an airtight chamber in which an internal pressure and an atmosphere can be adjusted to grow a thin film on a film forming surface of a substrate arranged perpendicularly to a surface to be irradiated of the target. A method of forming a thin film by a laser vapor deposition method, characterized in that the substrate is rotated, and a film is formed by scanning a laser beam on a target. 2. The production of a thin film by the laser deposition method according to claim 1, wherein the minimum length by which the laser light can scan the target is larger than 1/2 of the typical length of the substrate. Method. 3. The scanning speed of the laser beam is slowed at a position corresponding to the peripheral portion of the substrate and is increased at a position corresponding to the central portion of the substrate. Method of forming thin film by laser deposition method. 4. The method for producing a thin film by the laser vapor deposition method according to claim 3, wherein the substantial scanning speed of the laser light is adjusted by temporarily stopping the scanning of the laser light.