JPH05139735A - Thin film forming device by laser ablation method - Google Patents

Abstract

PURPOSE:To provide a thin film forming device by the laser ablation method favorable to make a thin film composition uniform. CONSTITUTION:The device consists of a vacuum vessel 1, a target 20 (oxide superconductor), pulse laser generator 3 (excimer laser: ArF), a substrate 40, to which negative charge is given, a dome shaped grid 5 and a dome shaped screen 6. By irradiating the target 20 with pulse laser beam in a state that the target 20 is rotated by the motor 21 and the substrate 40 is rotated by the motor 41, laser abration which is explosive dissociation, is generated to form a ionized material high in speed and a neutralized material relatively slow in speed. The neutralized material flies in wide range and the ion is diffused in wide angle by electric field of the screen 6 and the grid 5 to film-form on the substrate 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film forming apparatus using a laser ablation method. The present invention can be used, for example, in forming a thin film of an oxide superconductor.

[0002]

2. Description of the Related Art In recent years, a thin film forming apparatus using a laser ablation method has been developed. This equipment uses a laser beam with an extremely high energy density, generally a pulsed laser beam of an excimer laser with a high output in the ultraviolet region, irradiates the laser beam on a solid target in a high vacuum state, and explodes on its surface. Laser ablation, which is a typical dissociation, is generated, and particles such as atoms and ions emitted by the laser ablation are deposited on the substrate to grow a thin film.

The above-mentioned laser ablation is said to have a non-thermal property, and the ionization rate and the kinetic energy of emitted particles are extremely large as compared with the thermal laser process. The thin film formed by the above-mentioned thin film forming apparatus by the laser ablation method had nonuniform composition and thickness. The reason is believed to be as follows. That is, in the laser ablation, an ionized substance having a high velocity and a neutral substance having a relatively low velocity are mainly generated on the surface of the target material, and both of them fly toward the substrate. Here, since the neutral substance is emitted with a distribution of cos θ with respect to the normal line direction of the irradiation point, the neutral substance flies toward the substrate in a considerably wide range. On the other hand, the ionized substance is cos ⁿ θ (n >>) with respect to the normal direction of the irradiation point.
Since it is emitted in the distribution of 1), it does not spread almost from the irradiation point and concentrates on the substrate. Therefore, in the thin film formed on the thin film formation surface of the substrate, the ionized substance is increased in the central part and the neutral substance is relatively increased in the peripheral part, resulting in nonuniform composition of the thin film.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and an object thereof is to provide a thin film forming apparatus by a laser ablation method which is advantageous for uniformizing the composition of a film. To do.

[0005]

A thin film forming apparatus using a laser ablation method according to the present invention includes a vacuum container having a vacuum chamber, a target holding portion for holding a target arranged in the vacuum chamber, and laser ablation of the target. A laser oscillator that irradiates a high energy density laser beam, a substrate holding unit that holds a substrate having a thin film formation surface that is placed in a vacuum chamber and is given a negative potential, and between the substrate holding unit and the target holding unit. It is composed of a grid that is located in a passage through which particles generated by laser ablation pass and is given a negative potential. To do.

The laser oscillator is generally a high-power excimer laser in the ultraviolet region or an Nd: YAG laser.
-Pulse oscillate with a switch. For the excimer laser, ArF, KrF, XeCl or the like can be adopted. As the target, a metal, a nonmetal, a semiconductor, an insulator, or a multi-component oxide superconductor can be adopted. As a multi-component oxide superconductor, YBa ₂ Cu ₃ 07 _-x ,
Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ is present. It is preferable to arrange the grid having a small radius of curvature of the grid at a position close to the target. This is because the ions can be effectively diffused at a position close to the target, so that the diffusivity of the ions can be increased. However, it should be noted that if the grid is too close to the target, the laser beam may damage the grid.

[0007]

[Operation] Ions and neutral substances (including clusters) generated by laser ablation fly toward the substrate,
Ions are diffused in the grid. Therefore, the ions fly to the substrate in a wide range.

[0008]

EXAMPLES Examples of the present invention will be described below. As shown in FIG. 1, the thin film forming apparatus according to the present embodiment includes a vacuum container 1 having a vacuum chamber 10, a target holding unit 2 holding a target 20, a pulse laser oscillator 3, and a target 2.
0, a substrate holder 4 for holding a substrate 40 that is placed in the vacuum chamber 10 and is provided with a negative potential, and a dome-shaped grid located between the substrate holder 4 and the target holder 2. 5 and a dome-shaped screen 6 close to the grid 5. The potential of the grid 5 is given by the variable voltage source 53. The potential of the screen 6 is applied by the variable voltage source 63. The openings of the grid 5 and the screen 6 are set to face each other. This is for ensuring the permeability of ions and neutral substances generated by laser ablation and applying a hemispherical electric field. Further, the vacuum container 10 is provided with a convex lens 11 and an optical window 12, and the laser beam L is irradiated toward the target 20 through the convex lens 11 and the optical window 12.
The material of the target 20 is solid YBa ₂ Cu ₃ O _7-x . The target holding unit 2 is rotated by the motor 21. The substrate holder 4 is rotated by the motor 41.

The pulse laser oscillator 3 is an ultraviolet excimer laser beam (ArF, oscillation wavelength: 193 nm, pulse: 10 to 300 Hz, peak output: 100 W (300
mJ)) is oscillated. In this embodiment, the distance d ₀ between the center K of the screen 6 and the target 20 is 10 to 30.
It is set to mm. The radius r of the screen 6 is 15 to 30
It is set to 0 mm. The distance between the grid 5 and the screen 6 is 2 to 10 mm.

In this embodiment, the screen 6 is provided with a negative V _Sg potential with respect to ground, the grid 5 is provided with a negative V _ag potential with respect to ground, and the substrate 40 is provided with a negative V _{sub with respect to} ground. A potential of (-500V) is applied. Further, the target holding unit 2 is grounded. At the time of film formation, the inside of the vacuum chamber 10 is brought to an ultrahigh vacuum state of 10 ⁻⁷ to 10 ⁻⁸ Torr, the target 20 is rotated by the motor 21, and the substrate 40 is rotated by the motor 41. In that state, the target 20 is irradiated with the pulse laser beam L from the pulse laser oscillator 3 through the convex lens 11 and the optical window 12. The maximum intensity of the laser beam is about 10 ⁸ W / cm ² . As a result, laser ablation, which is an explosive dissociation, occurs on the surface of the target 20, and the ionized substance having a high velocity and the neutral substance having a relatively low velocity fly in. Here, the neutral substance basically does not receive the suction effect due to the potentials of the grid 5 and the screen 6. That is, a part of the neutral substance adheres to the grid 5 and the screen 6, but most of the rest is wide in a wide range and is straight.
Fly towards.

On the other hand, the ionized substance (velocity: up to 3 ×
Originally, about 10 ⁵ m / s) is mainly scattered along the normal line P of the laser irradiation position, but in this embodiment, it is diffused by being attracted by the potential of the grid 5 and the screen 6. And then gather in the direction of the dome-shaped grid 5. At this time, in this embodiment, by setting V _ag = -10 to 100 V, it is possible to efficiently collect the ions in the grid 5 without damaging the grid 5. Further, in this embodiment, since the potential of V _ag -V _Sg = -100 to -200 V is applied, the ions are diffused in a wide angle while being accelerated by the electric field between the screen 6 and the grid 5. Therefore, as in the case of the neutral substance, ions are widely spread over the substrate 40.
To the thin film formation surface 40 of the substrate 40 as a result.
A thin film of uniform composition with a thickness of about 1000Å is formed by being deposited on the whole a.

FIG. 2 shows the degree of diffusion of ions and neutral substances. The horizontal axis of FIG. 2 represents the angle θ, and the vertical axis represents the relative number. Here, the relative number is {(number of particles flying at angle θ nθ / (number of particles flying at angle θ = 0 n0)}
Means In FIG. 2, ○ indicates a neutral substance, Δ indicates an ion (without grid 5), ⋄ indicates an ion (with grid 5, r = 50 mm, V _ag = −150 V), and □ indicates an ion. (With grid 5, r = 25 mm,
V _ag = -200 V) is shown.

As shown by the characteristic line A0 in FIG. 2, in the case of the neutral substance, the decrease in the relative number is relatively small even if the angle θ becomes large, that is, the neutral substance flies over a wide range. .. In the case of ions, as shown by the characteristic line A1 in FIG. 2, in the case of no grid 5, the relative number decreases as the angle θ increases. That is, the ions fly in a narrow range. Further, as shown by the characteristic line A2 in FIG. 2, in the case where the grid 5 is provided, the decrease in the relative number is small even if the angle θ is large, that is, it is understood that the ions fly in a relatively wide range. Furthermore, as shown by the characteristic line A3 in FIG. 2, there is a grid 5, and r = 25 mm, V _ag =
In the case of −200 V, since the radius of curvature of the grid 5 is small and the attraction force by the electric potential is strong, the decrease in the relative number is further reduced even when the angle θ is increased, that is, the characteristic line A3 and the characteristic line A0. As can be understood by comparison with, it is understood that ions can fly over a wider range than neutral substances. Therefore, it can be seen that the provision of the grid 5 is advantageous for making the composition ratio of the thin film uniform. In the above test example, the neutral substances are YO _{2 -x} , BaO _1-x , Cu ₂ O.
_1-x, etc., and the ions are YBa ₂ Cu ₃ O _7-x ^-1 , Y
It is considered to be O ^-12 _-x .

FIG. 3 shows another test example. In this test example, basically, the same conditions as in the above-mentioned test example were used. In this case, the target 20 is an oxide superconductor (YBa).
₂ Cu ₃ 07 _-x ). Therefore, the target 20
When laser ablation occurs, basically, ions and neutral substances fly from the target 20 toward the thin film formation surface 40a of the substrate 40 at a ratio of 1 Y atom, 2 Ba atoms, and 3 Cu atoms. It will be. Therefore, originally, Cu / Y in the thin film is 3, Ba / Y is 2, Cu / Y
The ratio is /Ba1.5. In addition, Y, C
Both u and Ba are considered to be ions and neutral substances. In this test example, the laser intensity is 50 J / c.
m ² , radius of the grid 5 R = 50 mm, V _Sg = −50
It was performed under the conditions of V, V _ag = -150V and V _sub = -100V.

The test results are shown in FIG. Here, the vertical axis of FIG. 3 represents the composition ratio and the critical temperature of the superconducting phenomenon, and the horizontal axis represents the angle θ. In addition, △ mark is Cu / when there is no grid 5.
Y represents, and ▲ represents Cu / Y with grid. ○ indicates Ba / Y without grid 5, ●
The mark indicates Ba / Y when the grid 5 is present. □ indicates Cu / Ba without the grid 5, and ■ indicates Cu / Ba with the grid 5.

Cu / Y will be described. That is, when the grid 5 is not provided, θ is 0 to 20 as indicated by a triangle mark.
Cu / Y is about 3 in the degree range, but θ is 30
At 40 degrees, Cu / Y decreases to about 2.5. On the other hand, in the case where the grid 5 is provided, as indicated by the triangle, Cu / Y is about 3 even in the region where θ is about 30 degrees, and even if θ is 40 degrees, Cu / Y is about 2.8. Maintained at.

Ba / Y will be described. That is, when the grid 5 is not provided, θ is 0 to 20 as indicated by the circle.
Ba / Y is about 2 in the range of degrees, but θ is 30
At 40 degrees, Ba / Y decreases from 1.6 to about 1.5. On the other hand, when the grid 5 is present, Ba / Y is about 2 even in the region where θ is about 30 degrees, and Ba / Y is 1.8 to 1.9 even when θ is 40 degrees, as shown by the mark ●. Maintained to a degree.

Cu / Ba will be described. That is, there is no grid 5 shown by □, and grid 5 shown by ■
The case of presence is about 1.5 for both Cu / Ba,
does not change. It is presumed that the reason is mainly that the flying amounts of both Cu and Ba decrease. Further, in FIG. 3, the characteristic line W1 shows the critical temperature without the grid 5, and the characteristic line W2 shows the critical temperature with the grid 5. As shown by the characteristic line W1 and the characteristic line W1,
In the region where the angle θ is up to about 20 °, the composition ratio deviates from the predetermined value when the angle θ reaches 30 ° and 40 °, although the critical temperature is not so different between the case without the grid 5 and the case with the grid 5. It can be seen that when the grid 5 is not provided, the critical temperature is greatly reduced, but when the grid 5 having a small composition ratio deviation is provided, the critical temperature is not significantly reduced.

As can be understood from the above test results,
When the grid 5 is not provided, the composition ratio of the thin film deviates from a predetermined value, and the critical temperature Tc indicating the superconducting phenomenon also drops. In this respect, it is understood that the ion diffusion action by the grid 5 according to the present example is effective in making the composition ratio of the thin film uniform, and is advantageous in maintaining the critical temperature at which the superconducting phenomenon occurs at a high temperature.

In both the test results shown in FIG. 2 and the test results shown in FIG. 3, the elements in the thin film were identified by Auger electron spectroscopy ESCA or the like. (Other Embodiments) A drive motor is arranged in a separate chamber of a vacuum chamber, and one of a grid and a target is equipped on a movable body that is moved by the drive motor, and the movable body is moved by the drive motor, whereby the grid and the target are moved. It is also possible to adopt a configuration in which the interval distance of is adjusted. In this case, since the distance between the grid and the target can be adjusted, the effect of adjusting the degree of ion diffusion that diffuses the ions generated on the target surface by the grid can be obtained.

[0021]

According to the thin film forming apparatus by the laser ablation method of the present invention, it is possible to diffuse the ions, which tend to be concentrated and fly, and therefore it is advantageous to make the composition of the thin film uniform. Furthermore, if a grid having a diffusing action is brought close to the target, it can diffuse near the target, which is advantageous in increasing the degree of ion diffusion, and is more advantageous in homogenizing the composition of the thin film. When the device of the present invention is applied to the formation of a thin film made of a superconducting material, the composition of the superconducting material can be made uniform, which is advantageous for maintaining the critical temperature at which the superconducting phenomenon occurs at a high temperature. In addition, ITO (Indium Ti
When used for a multi-component transparent conductive electrode such as a (n oxide) film, it can contribute to improvement of light transmittance and film conductivity.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of an apparatus.

FIG. 2 is a graph showing the degree of spread of ions and neutral substances when a grid is provided and when a grid is not provided.

FIG. 3 is a graph showing a relationship between a composition ratio and an angle in another test example.

[Explanation of symbols]

In the figure, 10 is a vacuum chamber 10, 1 is a vacuum container, 20 is a target 20, 2 is a target holder, 3 is a pulse laser oscillator, 4 is a substrate holder, 40 is a substrate, 5 is a grid, 6
Indicates a screen.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C30B 29/22 501 H 7821-4G // H01B 12/06 8936-5G

Claims (1)

[Claims] 1. A vacuum container having a vacuum chamber, a target holding unit arranged in the vacuum chamber for holding a target, a laser oscillator for irradiating the target with a high energy density laser beam for causing laser ablation, and A substrate holding part, which is placed in a vacuum chamber and holds a substrate having a thin film forming surface to which a negative potential is applied, and a path through which particles generated by laser ablation are located between the substrate holding part and the target holding part. A thin film forming apparatus by a laser ablation method, characterized in that it is arranged with a grid to which a negative potential is applied, and ions generated by laser ablation are diffused and scattered toward the substrate by the grid.