JPH04214864A - Film forming method - Google Patents

Abstract

PURPOSE:To prevent the contamination of a laser beam injecting window and to stably execute a film forming operation for a long time, at the time of forming a film by a laser ablation apparatus, by specifying the incident angle of a laser beam against a target. CONSTITUTION:The atmosphere in a vacuum chamber 8 provided with a substrate 18 against a target material 9 is regulated to an oxygen one, and while the target is rotated by a rotation 11, a laser beam 12 is generated from a laser generating apparatus 13. The laser beam 12 is condensed by a condenser lens and is penetrated into a vacuum chamber 8 from a window 15 provided at the edge part of a projecting port 16 in a vacuum chamber 8, and the whole face of the rotated target 9 is irradiated with it to evaporate the target material and to form an oxide superconducting film on the substrate 18. By regulating the incident angle of a laser beam against the target 9 to >=60 degrees, contamination of the inside of the window 15 caused by the sticking of the evaporated grains of the target 9 is prevented, and a film forming operation for a long time is permitted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film forming method using laser ablation, and in particular to an improvement to enable continuous film forming over a long period of time.

0002

[Prior Art] Laser ablation methods (1) have no compositional deviation between the target and the deposited film;
2) It has the characteristics of being able to form films at low temperatures and at high speeds, and has recently attracted attention as a method for producing oxide superconducting thin films.

[0003] When forming a film by laser ablation, a vacuum chamber is prepared, and inside the vacuum chamber,
A target and a substrate to be deposited facing the target are placed. For example, a laser generator that generates excimer laser light is placed outside the vacuum chamber, and the laser beam from the laser generator is transmitted through a condensing lens placed outside the vacuum chamber and a quartz or The target is irradiated through a window made of spradil. Usually, the angle of incidence of the laser beam on the target (the angle between the direction of incidence of the laser beam on the target surface and the normal line perpendicular to the target surface) is selected to be 45 degrees.

0004

Problems to be Solved by the Invention When forming a film by the above-described laser ablation method, there is a problem in that particles scattered from the target by the ablation also adhere to the window and contaminate the window.

[0005] Such window contamination absorbs or scatters laser light. This causes a change in the energy density and its distribution of the laser light that reaches the target surface, and as a result, the performance of the obtained film also changes. Therefore, windows provided in the vacuum chamber must be frequently replaced with clean ones, and contaminated windows must be polished or otherwise prepared for reuse.

However, although window replacement as described above is applicable when film formation is performed in a batch manner for a relatively short time, it is necessary to perform continuous film formation or repeated film formation for a relatively long time. It cannot be easily applied in certain cases. Therefore, when performing continuous film formation or repeated film formation over a relatively long period of time, even if the energy density and its distribution that can form a film with excellent properties are initially set, over time, There was a problem that the properties of the obtained film changed. Therefore, for example, it has been difficult to continuously form a film on a long substrate with stable quality.

[0007] Therefore, an object of the present invention is to provide a film forming method that can prevent windows from becoming dirty and thereby stably obtain a film having predetermined characteristics for a long period of time. .

[0008]

[Means for Solving the Problems] The present invention is directed to a film forming method using laser ablation, and in order to solve the above-mentioned technical problems, the incident angle of the laser beam to the target is 60 degrees or more. It is characterized by being

The present invention is preferably applied to the formation of oxide superconducting thin films. Further, it is more preferable that the incident angle of the laser beam to the target is 70 degrees or more.

0010

[Operation] Particles scattered from the target surface by laser ablation are distributed in a direction substantially perpendicular to the target surface. The scattering direction of the particles hardly depends on the irradiation direction of the laser beam, that is, the angle of incidence on the target surface.

The inventor of the present invention irradiated the main surface 2 of the target 1 with a laser beam 3 as shown in FIG. 2, and investigated the scattering direction of particles. As a result, it was found that most of the particles fell within a cone 6 having an elevation angle 5 from the laser spot 4 on the main surface 2, and the magnitude of the elevation angle 5 at this time was 140 degrees.

[0012] The state of distribution of the scattered particles is affected by various conditions provided within the vacuum chamber, particularly by the oxygen gas pressure. Generally speaking, when the oxygen gas pressure is high, the scattering direction of particles scattered by ablation tends to spread. The commonly used oxygen gas pressure is 10
In the case of mTorr, if the target and window are separated by 30 cm or more, the scattered particles will mostly fall within a cone 6 with an elevation angle 5 of 120 degrees at the window location. Therefore, in this case, placing the window outside the cone 6 with an elevation angle 5 of 120 degrees will prevent the window from being contaminated by flying particles. When a window is placed outside a cone 6 whose elevation angle 5 is 120 degrees, the laser beam 3 is irradiated toward the target 1 through this window, so the incident angle of the laser beam 3 on the target 1 is set to 60 degrees. The above is sufficient.

On the other hand, when the oxygen gas pressure is made higher, for example, from 100 to 1000 mTorr, the elevation angle 5 of the cone 6 indicating the particle scattering area becomes larger, and this elevation angle 5 is outside the 120 degree cone 6. Some scattering of particles is also observed in the vicinity. However, the elevation angle 5 is 14
Most particles will fit within the 0 degree cone 6. Therefore, in order to more completely prevent contamination of the window in consideration of the case where the acidic gas pressure is increased, it is preferable that the incident angle of the laser beam 3 to the target 1 is set to 70 degrees or more.

[0014]

[Effects of the Invention] According to the present invention, the angle of incidence of the laser beam on the target is selected so that there is almost no scattering of particles to the window through which the laser beam passes, so that it can be used continuously for a long time. Alternatively, even if film formation is performed multiple times, a film of the same or substantially the same quality can be stably obtained.

[0015] Therefore, the film forming method according to the present invention is
Particularly remarkable effects are exhibited when applied to the case where a film is continuously formed on a long substrate. Therefore, the film forming method according to the present invention is particularly advantageous when applied to the case where an oxide superconducting thin film is formed on a long substrate to obtain an oxide superconducting wire.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram showing a laser ablation apparatus 7 for carrying out an embodiment of the present invention.

Referring to FIG. 1, the inside of vacuum chamber 8 has an atmosphere containing, for example, oxygen. A target 9 is placed within such a vacuum chamber 8 . The target 9 is held by a rotating shaft 11 that rotates as indicated by an arrow 10, so that as wide a region of the main surface of the target 9 as possible can be used as the irradiation portion of the laser beam 12.

A laser generator 13 is arranged outside the vacuum chamber 8 . Laser light 12 generated by laser generator 13 passes through condensing lens 14 and window 15 and is irradiated onto target 9 . The window 15 is made of quartz or spradil, for example. The window 15 is attached to the tip of a port 16 that protrudes from the main body of the vacuum chamber 8 .

A substrate pedestal 17 is provided at a position facing the target 9, and a substrate 18 is placed on the substrate pedestal 17. The substrate stand 17 has a built-in heater for heating the substrate 18.

Laser ablation device 7 as described above
When the target 9 is irradiated with the laser beam 12, a plume 19 is generated from the target 9 to the substrate 18. "Plume" refers to the plasma specific to laser ablation, which includes ions, atoms, molecules, ions, etc.
A state in which electrons and excited particles coexist. This plume 19 forms a thin film on the substrate 18 .

In this embodiment, the angle of incidence 20 of the laser beam 12 with respect to the target 9 is set to be 60 degrees or more, more preferably 70 degrees or more. As a result, particles scattered from the target 9 due to laser ablation are removed from the window 15.
This is intended to prevent the window 15 from becoming contaminated due to adhesion to the window.

Next, an experimental example carried out according to the present invention will be explained. Experimental Example 1 Using a sintered disk of YBa2 Cu3 O7-X with a diameter of 5 cm as a target, film formation was repeated under the conditions shown in the table below. As a substrate, (100) plane Mg
An O single crystal substrate was used. Further, the film forming time per time was set to 4 hours. Further, the distance between the laser spot position on the target and the window was 40 to 50 cm. In addition, in Table 1, condition No. Those marked with * are comparative examples.

[0023]

[Table 1]

The critical current density at liquid nitrogen temperature (77.3 K) was measured every time the film forming operation was performed, and the results shown in FIG. 3 were obtained. As shown in FIG. 3, No. 3 within the scope of this invention. 2 and no. In No. 3, the initial critical current density could be almost maintained even if the film-forming operation was repeated. On the other hand, No. 1, which is outside the scope of this invention. 1 and no. In No. 4, in the second film-forming operation, a film with such poor superconducting properties that the critical current density could not be measured at liquid nitrogen temperature was obtained.

Experimental Example 2 Bi-
A Pb-Sr-Ca-Cu-O high temperature oxide superconducting thin film was fabricated.

Target: Bi1.8 Pb0.6 Sr2 Ca2
Cu3.4 Ox Sintered body substrate temperature: 200°C Laser: Q-switch Nd:YAG laser (1064
nm) Energy density: 2 J/cm2 Repetition frequency: 200 Hz Oxygen pressure: 200 mTorr Target-to-substrate distance: 35 mm Deposition rate: 40 to 60 angstroms/min Deposition time:
The film obtained by laser ablation under the above conditions for 1 hour was amorphous and did not exhibit superconducting properties even at 4.2K.

[0027] Therefore, in the atmosphere, at 850°C, 60°C
Heat treatment was carried out for an hour. By changing the incident angle of the laser beam,
The change in critical temperature depending on the number of times the film was formed was measured. At this time,
At the same time as changing the incident angle of the laser beam, the energy was also changed to maintain a constant energy density on the target. Also,
The critical temperature was measured by the usual four-terminal method.

Table 2 shows the effect of increasing the total film forming time on the critical temperature when the incident angle of the laser beam is changed. In order to shorten the experiment time, only when measuring the critical temperature, the film deposition operation was temporarily stopped, the vacuum was released, a new substrate was installed, and the film was deposited for 1 hour. During the process, film formation was performed continuously without using a substrate.

[0029]

[Table 2]

As can be seen from Table 2 above, sample Nos. 1 and 2 have laser beam incident angles of "60°" and "70°".
In samples No. 2 and 3, the angle is "50°". 1
Excellent results have been obtained compared to . Also, in particular,
Sample No. 70°. In Sample No. 3, the angle is "60°". Even better results were obtained compared to 2.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a laser ablation device 7 for carrying out an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing the direction of particles scattered from the target 1 by laser ablation.

FIG. 3 is a diagram showing the relationship between the critical current density of a superconducting thin film and the number of times of film formation obtained through an experiment conducted to confirm the effects of the present invention.

[Explanation of symbols]

7 Laser ablation device 9 Target 12 Laser light 15 Window 18 Board 20 Incident angle

Claims (3)

[Claims] 1. A film forming method using laser ablation, characterized in that the incident angle of the laser beam to the target is 60 degrees or more. 2. The film forming method according to claim 1, wherein the target has a component of an oxide superconducting substance and is applied to forming an oxide superconducting thin film. 3. The film forming method according to claim 1, wherein the incident angle is 70 degrees or more.