JPH10209512A - Dielectric thin film and method and device for forming meal thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film which has a crystal structure of a growing initial stage, excellent crystallinity and pyroelectric characteristic at a speed higher than conventional, by depositing first dielectric thin film at a low deposition speed at a high density and forming a second (Pb1-(x+y) Lax Mgy )Ti1-(x+y) /4 O3 deposition film on the first dielectric thin film at a high deposition speed, in a process of forming a perovskite compound thin film made of (Pb1-(x+y) Lax Mgy ) Ti1-(x+y) /4 O3 . SOLUTION: In a dielectric thin film forming apparatus, a first layer thin film is formed by arranging a shielding plate 6 whose 1/2 area is opened between a target 5 and a substrate holder 2 and rotating the substrate holder 2 at 3rpm. At the time of forming a second layer thin film, the shielding plate 6 is removed. A (Pb1-(x+y) Lax Mgy )Ti1-(x+y) /4 O3 thin film is formed by at lest two processes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for forming a thin film, and more particularly to a method and an apparatus for forming a dielectric thin film and a metal thin film.

[0002]

2. Description of the Related Art Thin-film technology is used in the field of electronics,
In particular, it has developed mainly in the semiconductor manufacturing process, and has progressed with the development of new materials. These thin films are extremely rare in the case of a single element, and are generally alloys or compounds in many cases, and the characteristics are significantly changed depending on the forming method. The creation of these new materials and their deviceization often depend on improvements in thin film technology, as typified by artificial lattice materials.

[0003] ABO ₃
Is a dielectric material having a perovskite structure. Here, the A site is Pb, Ba, Sr, La
Alternatively, at least one kind of Mg and the B site contain at least one kind of element of Ti and Zr. (Pb
_{1- (x + y)} La _x Mg _y ) (Zr _z Ti _1-z ) _{1- (x + y) / 4} O
₃ (hereinafter referred to as PLMT) and ferroelectric materials represented by BaTiO ₃ exhibit excellent ferroelectricity, piezoelectricity, pyroelectricity, and electro-optical properties, and various functional devices using the same are being studied. Have been. In particular, a pyroelectric material represented by a PLMT thin film converts a temperature change into an electric signal by detecting infrared rays, and is therefore expected to be applied to a pyroelectric infrared sensor.

[0004] In order to improve the characteristics of these materials or to integrate them, it is very important to make them thinner. In addition, when this thin film is used as a pyroelectric infrared sensor, it depends greatly on how the thin film is grown with good crystallinity, and it is necessary to sufficiently consider the influence of the underlying material. In general, a MgO single crystal substrate is often used for forming a PLMT thin film because of the relationship between a lattice constant and a thermal expansion coefficient, and a Pt thin film is considered to be optimal as a base electrode material.

[0005] A film forming technique for improving the crystallinity of a thin film laminated on these dissimilar materials has been developed in each research period. Further, it is difficult to improve mass productivity because the film formation time is long, which is a problem of the thin film process.

[0006]

The crystallinity of a thin film formed by a deposition method such as sputtering or CVD (Chemical Vapor Deposition) used in the prior art basically depends on the substrate material, chemical composition, and formation temperature. Is controlled by In the sputtering method most commonly used in the past for thinning an oxide dielectric material, a chemical composition easily shifts between an oxide sintered body as a target material and a formed thin film. It was very dependent on the conditions.

[0007] Recently, with the development of a thin film deposition method utilizing a non-thermal equilibrium process having a high activity, the formation temperature of this process has been considerably reduced, but it is still necessary to obtain a thin film of good crystallinity by 600 times. A high substrate temperature of about ° C. is required, which causes a problem that interdiffusion occurs between the substrate and the deposited thin film.

When performing high-speed film formation due to the necessity of mass production, R
It is necessary to change film forming conditions such as an increase in F power and a reduction in the distance between the substrate and the target. In this case, the deposited film may be damaged by collision of ions or the like having high energy, or may have a low density of porous material. There has been a problem that pinholes and defects are generated when the film grows. Therefore, in order to obtain a thin film that is dense and capable of high-speed film formation, it is necessary to use a thin film deposition method with better crystallographic controllability.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, it is an object of the present invention to improve the crystal structure of a thin film in an initial growth process, and to obtain a thin film having good crystallinity and pyroelectric properties in a shorter time than before. I do.

In general, the formation of a PLMT thin film is generally performed using M
Although a gO single crystal substrate is used, and a Pt thin film can be used as a base electrode, there is a problem that a part of the laminated Pt / PLMT / MgO is peeled off by a high-temperature heating or an etching process by a chemical. Is also an issue. Accordingly, an object of the present invention is to improve the crystal structure of a thin film in the initial growth stage and to obtain a thin film having good adhesion in order to solve the above problems.

[0011]

In order to achieve this object, the present invention provides a perovskite-type composite compound (Pb
_In the production of _{1- (x + y)} La _x Mg _y ) Ti _{1- (x + y) / 4} O ₃ thin film, a first dielectric thin film is deposited at a high deposition rate at a low deposition rate, and a first dielectric thin film is deposited thereon. Two (Pb _{1- (x + y)} La _x Mg _y ) Ti
_{Since a 1- (x + y) /} 4O ₃ deposited film is formed, a thin film having better crystallinity and pyroelectric properties can be obtained at higher speed than before.

In the production of a Pt thin film which is a base metal thin film, the first Pt thin film is formed such that 0.20 ≦ O ₂ / Ar ≦
A gas flow ratio of 1.00 is formed, and a second Pt thin film is formed on the first Pt thin film at a gas flow ratio of O ₂ /Ar≦0.50. Thus, a thin film having good adhesion can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention
Is a perovskite-type composite compound (Pb _{1- (x + y)}
La_xMg_y) Ti_{1- (x + y) / 4}O_ThreeIn the production of thin films,
As low as 0.15 nm / sec or less for forming one dielectric thin film
High density (Pb_{1- (x + y)}La_xMg_y) Ti
_{1- (x + y) / 4}O_ThreeA thin film is formed and 0.15 nm / sec is formed on it.
With the above high deposition rate (Pb_{1- (x + y)}La_xMg_y) Ti
_{1- (x + y) / 4}O_ThreeA thin film formed, dense and grain-grown
PLT thin film with sufficient thickness was formed as the first layer
Function to improve the crystal structure at the beginning of thin film growth
Having.

According to a sixth aspect of the present invention, in the production of a Pt thin film, the first Pt thin film has a thickness of 0.20 ≦ O ₂ / A.
r ≦ 1.00, and the first P
A second Pt thin film is formed on the t thin film at a gas flow ratio of O ₂ /Ar≦0.50.
Since the structure of the t thin film can be improved, it has an effect that the adhesion between the MgO substrate and the Pt thin film can be improved.

Embodiment 1 Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings. First, FIG. 1 shows a schematic view of an apparatus for forming a dielectric thin film. This apparatus is the most commonly used magnetron sputtering apparatus when producing a perovskite oxide dielectric thin film.

Here, this apparatus uses a p-BN heater 1 in which a boron nitride film is coated on one side of the heater so that heat is uniformly radiated from the carbon heater, instead of the conventional sheath heater. Further, a substrate holder 2 was set at a position 10 mm away from the heater 1. Here, a black body stainless steel plate having a thickness of 2 mm was used as the soaking plate 3 between the substrate holder and the p-BN heater.

Therefore, the substrate heating in this embodiment is performed by p-
The mechanism is such that the soaking plate 3 is heated by radiation from the BN heater 1 and the MgO substrate 4 attached to the substrate holder 2 is further heated by heat conduction.

In the present embodiment, the sintered (Pb
_0.9 La _0.1 ) Ti _0.975 O ₃ (moreover, PbO is 20 to 30)
A 10-inch oxide ferroelectric material (sintered with an excess of mol%) was mounted as a target 5 and set so that the MgO substrate 4 was located directly above the erosion portion of the ceramic target 5. The linear distance between the MgO substrate 4 and the ceramic sintered body target 5 is 100 mm.

In such a thin film forming apparatus, RF power = 1200 W, substrate temperature = 600 ° C., gas pressure = 0.15
A (Pb _0.9 La _0.1 ) Ti _0.975 O ₃ (hereinafter, PLT) thin film was deposited under the film forming conditions of Pa, Ar / O ₂ gas flow ratio = _25/1 . The thickness was about 2 μm. At this time, the deposition rate was 0.20 nm / sec, and the deposition time was about 2 hours and 47 minutes. Furthermore, the crystallinity of the deposited PLT thin film was evaluated by X-ray diffraction, and the MgO substrate was etched to release the film, and by attaching electrodes on the front and back surfaces, the electrical properties in the film thickness direction, mainly pyroelectric properties, were evaluated. .

First, the PLT (0
01) The half width of the peak is 0.24 ° and the peak intensity is 18
9 kcps and a c-axis orientation ratio of 92% showed good crystallinity. However, for the electrical characteristics, ε-40
0, γ to 3.0 × 10 ⁻⁸ C / cm ² · K, which was insufficient for obtaining sufficient pyroelectric properties. These results are considered to be problems due to morphology or stability such as the growth state of crystal grains. Therefore, in order to improve the characteristics of the thin film, a formation method for forming a film while ensuring sufficient growth and stabilization of crystal grains is required.

Next, in order to stabilize the PLT thin film, in forming the PLT thin film, a stabilizing step in which the thin film is not deposited or the deposition rate is low is intermittently and periodically introduced during the thin film deposition time. We tried a method of forming a film. In this embodiment, when depositing a thin film, a stainless steel shielding disk (5 mm thick) 6 having an open half was placed between the target and the substrate holder, and the substrate holder was further rotated at 3 rpm.

With this device structure, when the substrate is on the open portion of the shielding plate, sputtered particles from the target fly near the substrate and form a thin film, but when the substrate rotates and is positioned on the shielding plate ( (The half of the deposition time) is an annealing step in which deposited particles from the target are blocked by the shielding plate and do not reach the vicinity of the substrate, and only the formed thin film is heated. By periodically repeating such a deposition step and an annealing step, the thin film was stabilized as needed.

Here, the conditions for forming the PLT thin film were the same as those in the above experiment, and the film thickness was the same as 2 μm. This PL
The half width of the PLT (001) peak in the X-ray diffraction of the T thin film was 0.23 °, the peak intensity was 187 kcps, and the c-axis orientation ratio was 95%, indicating good crystallinity as in the case of continuous film formation. . On the other hand, regarding electrical characteristics, ε ~ 190, γ ~
An extremely high pyroelectric property of 4.0 × 10 ⁻⁸ C / cm ² · K was obtained.

However, in this case, the total deposition rate is 0.09 nm / sec, which is slower than the conventional one due to the addition of the time when the thin film is not deposited by the shielding plate.
The deposition time to form a μm thin film also took about 6 hours and 10 minutes. Considering the mass productivity of these dielectric thin films, it is not desirable that the deposition rate is slow and the deposition time is long. Therefore, how to form a thin film having good crystallinity and electric characteristics in a short time is an important issue.

In the present embodiment, in order to solve these problems, the formation of a PLT thin film is performed in two steps. First, as a method of forming a first PLT thin film, the above-mentioned shielding plate is set between a target and a substrate holder,
RF power = 1200 W, substrate temperature = 600 ° C., gas pressure =
A film of about 0.3 μm was formed under a film forming condition of 0.15 Pa and an Ar / O ₂ gas flow rate ratio of 25/1. Thereafter, the shielding plate was removed, and a second PLT thin film was formed on the first PLT thin film under the same conditions at a thickness of 1.7 μm.

Therefore, the overall thickness of the PLT thin film is 0.3
μm (first PLT thin film) +1.7 μm (second PLT thin film)
(Thin film). In other words, the first layer, 0.3 μm
In the early stage of the growth of 0.09 nm / sec using a shielding plate
This means that a dense and stabilized PLT thin film was formed at a very low deposition rate, and then a PLT thin film was deposited as a second layer at a high speed of 0.20 nm / sec.

The crystallinity of the 2 μm PLT thin film formed in this way is such that the PLT (001) peak has a half-value width of 0.22 °, a peak intensity of 191 kcps, and a c-axis orientation ratio of 96%.
And the electrical characteristics are ε-200, γ-4.0 ×
High pyroelectric properties of 10 ⁻⁸ C / cm ² · K were obtained. In particular, the improvement in the pyroelectric properties in this experiment was achieved by forming a dense and grain-grown PLT thin film as the first layer by a deposition method with a step of stabilizing the deposited film itself, thereby achieving an initial state of thin film growth. This is because the crystal structure of was improved.

At this time, the deposition time of the first layer is 55 minutes and the deposition time of the second layer is 2 hours and 20 minutes. The total deposition time is 3 hours and 15 minutes, and the P layer having a thickness of 2 μm is short.
The formation of the LT thin film was achieved. In addition, including the substrate cooling time for removing the shielding plate and the time for removing the shielding plate, the time was 5 hours and 10 minutes, and the time was consistently reduced by one hour as compared with the case where the film was formed using the shielding plate. .

Conventionally, considering the necessity of mass production,
In order to perform high-speed film formation, it is necessary to change film formation conditions such as an increase in RF power and a reduction in the distance between substrate targets, so that the deposited film may be damaged by collision with ions having high energy, or may be damaged. There has been a problem that the growth of a porous film having a high density causes pinholes and defects.

However, as shown in this embodiment, in the step of forming the PLT thin film, the PLT
Forming a T thin film at a low deposition rate of 0.15 nm / sec or less;
By using a method of manufacturing a PLT thin film at a high deposition rate of 15 nm / sec or more and comprising a thin film including at least two steps, a PLT thin film exhibiting high pyroelectric characteristics and crystallinity can be realized at a high throughput. .

Embodiment 2 Hereinafter, Embodiment 2 of the present invention will be described with reference to the drawings. Similarly, the magnetron sputtering apparatus shown in FIG. 1 was used for forming the PLT thin film.

In the first embodiment, in order to stabilize the thin film, in forming the dielectric thin film, a stabilizing step in which the thin film is not deposited during the thin film deposition time or a deposition rate is low is intermittently and periodically introduced. An example of film formation was shown while
Specifically, this is performed by installing a stainless shielding disk (5 mm thick) having a half opening between the target and the substrate holder.

Therefore, before forming the PLT thin film of the second layer at a high speed, it is necessary to return the vacuum in the vacuum chamber to the atmosphere and remove the shielding plate. Actually, it is not desirable to expose the substrate holder heated to a high temperature of about 600 degrees to the air in view of contamination of the film into the film and oxidation of the heater, and it also takes time and labor to remove the shield plate. Was gone. In the second embodiment, the first layer PL
In order to form a PLT thin film on the second layer continuously after the formation of the T thin film, the structure of the shielding plate was changed without breaking the vacuum chamber.

FIG. 2A is a schematic view of the shielding plate.
Two 5 mm-thick stainless steel discs with three-quarters opened were stacked. This shielding plate was set between the target and the substrate holder. First, the first layer, 0.
When forming a 3 μm PLT thin film, as shown in FIG. 2 (b), a half-opened disk is formed, and this is used to form a 1.7 μm PLT thin film of the second layer. Figure 2 (c)
The shape was changed to a disk having a 3/4 opening as shown in FIG.
The structure of the shielding plate can be changed by a manual lever outside the vacuum chamber.

Using a thin film forming apparatus having such a shielding plate, a film is formed at an RF power of 1200 W, a substrate temperature of 600 ° C., a gas pressure of 0.15 Pa, and an Ar / O ₂ gas flow ratio of 25/1. Under the conditions, a PLT thin film of about 2 μm was formed. At this time, the PLT (001) peak of the X-ray diffraction of the PLT thin film had a half value width of 0.23 °, a peak intensity of 197 kcps, and a c-axis orientation ratio of 90%, indicating good crystallinity as in the case of continuous film formation. The electrical characteristics are shown as ε-178, γ-
An extremely high pyroelectric characteristic of 4.2 × 10 ⁻⁸ C / cm ² · K was obtained.

Also, by using the method and the apparatus of the present embodiment, the time for forming a PLT thin film having a thickness of 2 μm is 55 minutes (first layer PLT thin film) +3 hours 5
Minutes (second layer PLT thin film), and the time was reduced by 2 hours without lowering the figure of merit as compared with the case where the film was formed using the shielding plate.

Therefore, according to the present embodiment, a PLT thin film exhibiting high pyroelectric characteristics and crystallinity can be realized at high throughput without the work of removing the shielding plate.

(Embodiment 3) Hereinafter, embodiments of the present invention will be described.
State 3 will be described with reference to the drawings. Similarly, the shape of the dielectric thin film
RF magnetron sputtering equipment with 4 inch cathode
Was used. In the present embodiment, SrTiO_Three(Hereinafter ST
O) For the purpose of forming a thin film. Here, the sintered SrT
iO_ThreeTarget 4 inch oxide dielectric material
And put it right above the erosion part of this target
It was set so that the substrate was positioned. Further substrate and target
The linear distance of the set is 80 mm. Such thin film forming equipment
RF power = 200 W, substrate temperature = 200
° C, gas pressure = 0.15 Pa, Ar / O _TwoGas flow ratio = 10
An STO thin film was deposited under a film forming condition of / 1. The film thickness is
It was about 0.2 μm. At this time, the S
rTiO_ThreeThe peak half width is 0.40 ° and the peak intensity is 5k
cps.

Next, a two-step method of forming an STO thin film was performed in the same manner as in the embodiment of the PLT thin film. First, for the formation of the first layer of STO thin film, a stainless shielding disk (5 mm) with a half portion opened between the target and the substrate holder
Thickness) was set, and the substrate holder was rotated at 3 rpm. Thereafter, a second PbTiO ₃ thin film was formed on the first thin film under the same conditions as the device structure with the shielding plate removed. The Sr of the X-ray diffraction of the STO thin film at this time
The half width of the TiO ₃ peak is 0.35 ° and the peak intensity is 21 k.
The crystallinity was improved as compared with the above results of continuous film formation under the same conditions as cps.

(Embodiment 4) When a pyroelectric element is formed, before forming a PLT thin film, a Pt thin film is formed on a MgO single crystal substrate by a 6-inch cathode RF magnetron sputtering apparatus as a base electrode. 2 .mu.m. Thereafter, a PLT thin film is formed, and patterning and formation of an upper electrode are performed. Therefore PLT / Pt / M
The gO element is subjected to many etching and high-temperature heating steps after forming the PLT thin film. During this process, Pt peeling at the Pt / MgO interface rarely occurs. Sputtering condition: substrate temperature 6
00 ° C, gas pressure 10mTorr, RF power 50W, O ₂ / Ar
After forming a Pt thin film of 0.15 μm with a gas flow rate of 0.25, RF power = 1200 W, substrate temperature = 600 ° C. by a 10-inch RF magnetron sputtering apparatus,
Gas pressure = 0.15 Pa, Ar / O ₂ gas flow ratio = 25/1
When a 2 μm PLT thin film is deposited under
The peeling failure rate of the LT / Pt / MgO element was about 30%.

As a measure for improving the adhesion between the MgO substrate and the Pt thin film interface, a method of forming a buffer thin film of Ti or the like having a thickness of several tens of nm between layers has been reported. , Or a multi-target sputtering apparatus needs to be used.

Therefore, in the present invention, in the step of forming the Pt thin film, a method of manufacturing a metal thin film comprising at least two or more steps is used. Sputtering conditions common to all processes
Substrate temperature 600 ° C, gas pressure 10mTorr, RF power 50W
Only the Ar / O ₂ gas flow ratio was changed during the film formation. A first Pt thin film is formed with a gas flow ratio of O ₂ /Ar=0.25 at 50 nm, and a second Pt thin film is formed on the first Pt thin film.
A thin film was continuously formed at a gas flow ratio of O ₂ / Ar = 0 of about 150 nm. Thereafter, similarly, a 2 μm PLT thin film is formed using a 10-inch RF magnetron sputtering apparatus under the conditions of RF power = 1200 W, substrate temperature = 600 ° C., gas pressure = 0.15 Pa, and Ar / O ₂ gas flow ratio = 25/1. In the case where was deposited, the peeling failure rate of the PLT / Pt / MgO element could be reduced to about 0%.

The improvement in the adhesion between the MgO substrate and the Pt thin film in the present invention is due to the fact that the structure of the Pt thin film in the initial stage of growth could be improved.

[0044]

As described above, according to the present invention,
In the step of forming a perovskite-type composite compound thin film composed of (Pb _{1- (x + y)} La _x Mg _y ) Ti _{1- (x + y) / 4} O ₃ , the first (Pb _{1- ( x + y)} La _x Mg _y ) Ti
Forming a _{1- (x + y) / 4} O ₃ thin film at a low deposition rate of 0.15 nm / sec or less; and forming a second (Pb) film on the first thin film.
_{1- (x + y)} La _x Mg _y ) Ti _{1- (x + y) / 4} O ₃ thin film is 0.15 n
By using a method of forming a dielectric thin film comprising at least two steps for forming a film at a high deposition rate of m / sec or more, high pyroelectric characteristics and crystallinity are exhibited (Pb _{1- (x + y)} La _x M
g _y ) Ti _{1- (x + y) / 4} O ₃ thin film can be realized with high throughput.

In the step of forming a Pt thin film,
A first Pt thin film is formed on a substrate by 0.20 ≦ O ₂ / Ar ≦ 1.
A metal thin film comprising at least two steps of forming a second Pt thin film on the first Pt thin film at a gas flow ratio of O ₂ /Ar≦0.50. By using the manufacturing method, PLT / Pt
/ MgO when processed as pyroelectric element
The peeling failure between the O substrate and the Pt thin film can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a basic configuration of a dielectric thin film forming apparatus according to an embodiment of the present invention.

FIG. 2A is a cross-sectional view illustrating a configuration of a shield plate according to an embodiment of the present invention. FIG. 2B is a cross-sectional view illustrating a configuration of a first layer of the shield plate according to an embodiment of the present invention when a thin film is formed. FIG. 2 is a cross-sectional view illustrating the configuration of the shielding plate according to the embodiment of the present invention when the second layer is formed as a thin film

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate heater (p-BN heater) 2 Substrate holder 3 Heat equalizing plate 4 MgO substrate 5 PLT ceramic sintered compact target 6 Shield plate (slit plate)

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI G01J 1/02 G01J 1/02 Y 5/02 5/02 A H01L 21/316 H01L 21/316 Y 41/187 41/18 101C 41/24 41/22 A

Claims (6)

[Claims] 1. (Pb _{1- (x + y)} La _x Mg _y ) Ti
_In the step of forming a perovskite-type composite compound thin film composed of _{1- (x + y) /} 4O ₃ , the first (Pb <sub>1- (x
+ y)</sub> La _x Mg _y ) Ti _{1- (x + y) / 4} O ₃ thin film of 0.15 nm / s
forming the following low deposition rate ec, the second to the first thin film _{(Pb 1- (x + y)} La x Mg y) Ti 1- (x + y) / 4 O
_{3. A} method for forming a dielectric thin film comprising at least two or more steps of forming a thin film at a high deposition rate of 0.15 nm / sec or more. 2. The first (Pb _{1- (x + y)} La _x Mg _y ) Ti
_{1- (x + y) / 4} O 3 as a method of forming the thin film, the dielectric of the opening degree is made of carrying out the thin film formation by installing at least one smaller shielding plate between the target and the substrate holder according to claim 1, wherein Method of forming body thin film. 3. The second (Pb _{1- (x + y)} La _x Mg _y ) Ti
_{1- (x + y) / 4} O 3 as a thin film forming method, placed claims 1 dielectric thin film forming method according consisting carrying out the thin film formed after increasing the opening degree of the shield plate. 4. A second (Pb _{1- (x + y)} La _x Mg _y ) Ti
_{As a} method for forming a _{1- (x + y) /} 4O ₃ thin film, an apparatus for forming a dielectric thin film for forming a thin film after increasing the aperture of an installed shielding plate. 5. A process for forming a SrTiO ₃ thin film, comprising: forming a first SrTiO ₃ thin film on a substrate at 0.15 nm / sec.
Forming a dielectric thin film comprising at least two steps of forming a second SrTiO ₃ thin film on a first thin film at a high deposition rate of 0.15 nm / sec or more, Method. 6. The method of forming a Pt thin film, comprising: forming a first Pt thin film on a substrate in a range of 0.20 ≦ O ₂ /Ar≦1.00.
Forming a second Pt thin film on the first Pt thin film at a gas flow ratio of O ₂ /Ar≦0.50. Method.