JP3083327B2 - Thin film manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin film such as an oxide high-temperature superconductor by a laser ablation method.

[0002]

2. Description of the Related Art Recently, a laser ablation method has been actively used as a method for forming a film of an oxide high-temperature superconductor. The feature of this method is that a heat treatment at about 900 ° C. after film formation, which is indispensable in the conventional sputtering method or the like, is not required, and a high-quality film can be obtained. To obtain a film. Various improved processes of such a laser ablation method have been proposed.

[0003] A method has been proposed in which a ring-shaped electrode is provided between a target and a substrate, and charged particles among atoms scattered by irradiating the target with a laser trigger a plasma near the electrode. (S. Witanach
chi, H .; S. Kwok, X .; W. Wang and D.M. T. Shaw, Applied PhysicsL
eters, vol. 53, pp. 234 to 236 (J
uly1988)). According to this method, once a discharge plasma is generated by the first pulse of the laser, the discharge continues as long as a voltage is applied to the electrodes thereafter. By this process, the substrate temperature is reduced from the conventional 650 to 700 ° C.
Even if the temperature falls from about 400 ° C. to about 400 ° C., a high quality film can be obtained.

In another process, a second laser beam is passed in the vicinity of the substrate in parallel with the substrate, and a film is formed in a state in which particles which are to reach the substrate are activated by the second laser. (G. Koren, A. Goup
ta, and R.A. Bareman, Applied P
physics Letters, vol. 54, pp1
920-2022 (May 1989)).

The oscillation of the second laser is performed in a pulsed manner with a certain time delay from the irradiation of the target with the laser. This process raises the substrate temperature from 700 ° C to 60 ° C.
Even if the temperature is reduced to 0 ° C., a good film can be formed.

As yet another process, pulsed plasma deposition for generating plasma in a pulsed manner has been proposed (G. Scarsbrook, IP.
Llewellyn, S .; M. Ojha, and R.A.
A. Heinecke, Vacuum, vol. 38,
No. 8-10, pp. 627-631 (1988)).

[0007]

FIG. 4 is a chart for explaining a conventional process for generating discharge plasma in a region between a ring and a substrate. As shown in FIG. 4, the particles scattered by irradiating the target with the pulsed laser beam pass through the ring electrode and reach the substrate.
Since a discharge is generated and active oxygen is generated, the particle bundle and the active oxygen react before reaching the substrate. This makes it difficult for active oxygen and particle bundles to reach the substrate in an active state, which has a negative effect on thin film formation. In addition, when the discharge plasma is continuously generated as in this example, the material and structure of the electrode are restricted, so that it is difficult to increase the discharge power when the particles pass through the ring electrode to increase the degree of activation. It is.

In the case of pulse plasma deposition, there is also a problem that the scattered particles react with active oxygen before the scattered particles reach the substrate.

In the method using the second laser, the above-mentioned problems can be solved, but a device for oscillating the second laser (λ = 193 nm) is required, and the device becomes expensive. The problem arises. Also, N ₂
There is also a problem that the effect can be exhibited only by using O gas, O ₂ gas cannot be used, and the type of gas to be used is limited.

An object of the present invention is to solve the conventional problems and to provide a method capable of forming a high-speed and high-quality thin film.

[0011]

According to a thin film manufacturing method according to the present invention, a pulse laser beam is repeatedly irradiated on a target surface, whereby constituent atoms of the target are scattered as scattered particles and a film is deposited on a substrate. In a method of manufacturing a thin film by a laser ablation method, an electrode is provided in a region between a target and a substrate, a pulse discharge is generated in a region between the target and the substrate, and a timing for applying a pulse voltage to this electrode is determined. , By adjusting the time when the scattered particles from the target reach the vicinity of the substrate,
It is characterized in that the timing at which the pulse discharge occurs is adjusted to the time at which the scattered particles from the target reach the vicinity of the substrate.

As a discharge plasma generating means for generating a pulse discharge, for example, an RF power supply, a DC pulse power supply, a microwave power supply and the like can be used.

As a method of generating a pulse discharge in accordance with the time at which scattered particles from the target reach the vicinity of the substrate, a delay pulse generator is used, and one of two pulses having different timings is applied to a laser device. To emit a pulsed laser beam, and another pulse to an apparatus for generating a discharge to generate a pulsed discharge.

In this case, the difference between the timings of the two pulses is set to about the time from when the laser is irradiated to the target until the particles reach the vicinity of the substrate. With this setting, the timing of the pulse discharge can be adjusted to the time when the scattered particles from the target reach the vicinity of the substrate.

FIG. 1 is a block diagram showing an apparatus for explaining the present invention. Referring to FIG. 1, a ring-shaped electrode 3 for generating discharge plasma is provided in a region between substrate 1 and target 2. A laser device 4 is installed on the target 2 so that the pulse laser beam 5 is irradiated. The electrode 3 is connected to a plasma generator 6. A delay pulse generator 7 is connected to the laser device 4 and the plasma generator 6 so that pulse signals having different timings are provided.

Different pulse signals are supplied from the delay pulse generator 7 to the laser device 4 and the plasma generator 6, respectively, and a pulse laser beam 5 is applied from the laser device 4 to the target 2 in accordance with the supplied pulse signal. And the constituent atoms of the target 2 are scattered as scattered particles and reach the substrate 1.

At the electrode 3, discharge plasma is generated by a pulse signal given from the delay pulse generator 7 so as to coincide with the arrival time of the scattered particles on the substrate 1.

[0018]

FIG. 2 is a chart showing timings of a discharge pulse and a laser light pulse for explaining the present invention. As shown in FIG. 2, a short time after the generation of the laser light pulse, the particle bundle of the scattered particles passes near the electrode 3 and reaches the substrate 1.

A discharge pulse is generated at the same time as the arrival time of the particle flux on the substrate 1. This discharge pulse activates oxygen. Therefore, according to the method of the present invention, a large amount of the particle flux from the target and the activated carbon are present on the substrate 1 at the same time. Therefore, a high-quality thin film can be obtained at high speed.

Further, the duty ratio of the discharge pulse can be reduced because the discharge of the duration of the particle flux is sufficient. As a result, even if the average applied voltage is limited by the electrode structure or the material, the peak power of the discharge pulse can be increased by reducing the duty ratio, so that a higher degree of activation can be provided to the particle flux. Becomes

Further, in the present invention, discharge plasma is used as the activating means. When producing an oxide high-temperature superconducting thin film as a thin film, it is necessary to activate oxygen gas, and when using a conventional process of photoexcitation,
Light of 180 nm or less is required as light for such excitation, and laser light of such a wavelength is not practical with current laser technology. In contrast, in the present invention, since discharge plasma is used, activation by dissociated electrons is easy, and by selecting discharge power,
Activation of oxygen gas can be easily performed.

[0022]

EXAMPLES In the following examples, Y ₁ was used as a thin film.
An experimental example in which a Ba ₂ Cu ₃ O _7-Y oxide high-temperature superconducting thin film is manufactured will be described.

Example 1 KrF excimer laser (λ = 24
(8 nm) as an ablation laser was irradiated onto the target surface at an energy density of ² J / cm ² . The repetition frequency of the laser light pulse was 5 Hz. A coil-shaped electrode is provided between the target and the substrate, and an RF power source (f =
13.56 MHz). The RF power supply was driven at 5 Hz so as to have a pulse width of 10 μsec delayed by 10 μsec by the laser light pulse. The output was 1 kW.

A film was formed at a substrate temperature of 350 ° C. using MgO (100: substrate surface) as a substrate.

The critical temperature of the resulting superconducting thin film was measured and found to be 82K. Comparative Examples 1 and 2R
A superconducting thin film was formed on a substrate in the same manner as in Example 1 except that the F plasma pulse was set at the same timing as the laser light pulse (Comparative Example 1). Further, the RF plasma pulse was driven to be delayed by 150 μsec from the laser pulse, and a superconducting thin film was formed on the substrate in the same manner as in Example 1 except for the above conditions (Comparative Example 2).

Comparative Examples 1 and 2 obtained as a result
No film showed a superconducting transition at 4.2 K or higher.

Embodiment 2 FIG. 3 is a perspective view showing a discharge plasma generating means in this embodiment. Referring to FIG. 3, a cylindrical resonator 13 is provided between target 12 and substrate 11, and microwave resonator 14 is provided in resonator 13.
And a discharge plasma was generated inside the resonator 13, and a superconducting thin film was formed on a substrate in the same manner as in Example 1 except for the other conditions. Note that the microwave is pulse-driven, and 10 μsec later than the laser pulse by 10 μsec.
It was driven at 5 Hz with a pulse width of c.

As a result, the thin film formed on the substrate exhibited a critical temperature of 81K. Example 3 A DC pulse power source was used as a discharge plasma generator, this was connected to a ring-shaped electrode, and the repetition frequency of the laser light pulse was 100 Hz.
The time delay from the pulsed laser light pulse is 10 μsec, and the pulse width of 10 μsec is 1
Driven at 00 Hz. The output was 20 kW.

A superconducting thin film was formed on the substrate by using a KrF excimer laser in the same manner as in Example 1 above, using MgO (100: substrate surface) at a substrate temperature of 600 ° C. The superconducting thin film obtained as a result is 8
It showed a critical temperature of 0K. In this example, a high repetition frequency was employed, and the film formation rate was 4500 Å / min.

In the following examples, B was used as a thin film.
An experimental example in which an i ₂ Sr ₂ Ca ₂ Cu ₃ O _x oxide high-temperature superconducting thin film is manufactured will be described.

Embodiment 4 ArF excimer laser (λ = 19)
(3 nm) as an ablation laser was irradiated onto the target surface at an energy density of 1.5 J / cm ² .
The target used is a sintered body of Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x . Repetition frequency of laser light pulse is 20Hz
And A coil-shaped electrode was provided between the target and the substrate, and connected to an RF power supply (f = 13.56 MHz).

The RF power source is set to 20 so that the pulse width becomes 10 μsec, which is delayed by Δt (μsec) from the laser light pulse.
Hz. The input power of RF was 1.5 kW. The substrate temperature was set to 450 ° C., and MgO (11
Film formation was performed using the 0) plane. 0 μs delay time Δt
Table 1 shows the results of a plurality of experiments performed in the range of ec to 150 μsec.

[0033]

[Table 1]

As can be seen from this result, in this embodiment,
Is the time for the laser irradiation time of 60 to 100 μsec.
By giving the delay to the RF pulse, Bi_TwoSr_TwoCa
_TwoCu _ThreeO_xThe critical temperature of the thin film became the best. this
The result is that the distance from the target to the substrate is 70mm
Is the optimal time due to this difference in distance.
It is naturally expected that the delay will be different. this
Will be described in the following examples.

Example 5 In this example, the distance from the target to the substrate was 120 mm, and the same experiment as in Example 4 was performed. Table 2 shows the results corresponding to Table 1.

[0036]

[Table 2]

In this embodiment, the optimal time delay is 120
130 μsec, which is larger than that of Example 4. This is due to ablation
At a time when the protruding particles reach the vicinity of the substrate, R
This suggests that excitation by F discharge and supply of active particles are important for realizing a high quality film.

As is clear from the above results, in the embodiment according to the present invention, a high-quality film is produced at a high speed by adjusting the timing of the pulse discharge to the time when the scattered particles from the target reach the vicinity of the substrate. be able to.

In the above embodiments, the description has been made by taking the oxide high-temperature superconducting thin film as an example of the thin film. However, the manufacturing method of the present invention is not limited to these oxide superconducting thin films, but may be applied to other thin films. Applicable.

[0040]

According to the present invention, the timing of the pulse discharge is adjusted to the time when the scattered particles from the target reach the vicinity of the substrate, so that the particle bundle reacts with the active oxygen before reaching the substrate as in the prior art. This prevents more particles and active oxygen from reaching the substrate.

Therefore, according to the manufacturing method of the present invention,
High quality thin films can be manufactured at higher speed.

Further, since a high quality film can be formed at a low temperature and at a high speed, even if a metal such as stainless steel or silver is used as the substrate material, diffusion at the film / substrate interface can be suppressed, and a long substrate material can be formed. High-speed film formation can be expected. For this reason,
The thin film manufacturing method of the present invention can be useful, for example, as a method for manufacturing a high-temperature superconducting wire.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an apparatus for explaining the present invention.

FIG. 2 is a chart showing timings of a discharge pulse and a laser light pulse for explaining the present invention.

FIG. 3 is a perspective view showing a discharge plasma generating means in one embodiment of the present invention.

FIG. 4 is a chart showing timings of discharge and laser light pulse in a conventional laser ablation method.

[Explanation of symbols]

1, 11 Substrate 2, 12 Target 3 Electrode 4 Laser device 5, 15 Pulsed laser beam 6 Plasma generator 7 Delayed pulse generator 13 Resonator 14 Microwave waveguide

────────────────────────────────────────────────── ─── Continuing on the front page (51) Int.Cl. ⁷ Identification symbol FI H01B 12/06 H01B 12/06 (72) Inventor Kiyoshi Okaniwa 2-4-1 Nishi-Atsujigaoka, Chofu City, Tokyo Inside TEPCO ( 72) Inventor Takahiko Yamamoto 2-4-1, Nishi-Atsujigaoka, Chofu-shi, Tokyo Examiner, Tokyo Electric Power Company, Inc. Satoshi Sera (56) References JP-A-1-172214 (JP, A) JP-A-63-264819 (JP, A) JP-A-63-262879 (JP, A) JP-B-52-42152 (JP, B1) JP-T-57-500492 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) C23C 14/00-14/56 H01B 13/00 565 H01L 39/24 C01B 13/14 C01G 29/00 H01B 12/06 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A thin film manufacturing method by a laser ablation method in which a pulse laser beam is repeatedly irradiated on a target surface to scatter constituent atoms of the target as scattered particles and deposit a film on a substrate. An electrode is provided in a region between the substrate and a pulse discharge is generated in a region between the target and the substrate. A method for producing a thin film, characterized in that the timing at which the pulse discharge occurs is adjusted to the timing at which the scattered particles from the target reach the vicinity of the substrate by adjusting the timing to reach the vicinity.