JP2003105533A - Method for producing transparent conductive film and transparent conductive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a transparent conductive film without crystallizing an a-Si layer as an underlayer and not causing diffusion of doped impurities, and a low resistance at a substrate temperature of about 150 ° C. And a transparent conductive film exhibiting high transmittance at a film thickness of 100 nm or less. SOLUTION: In a vacuum vessel, a film material III
A sputtering source having a ZnO target to which 1 to 7% by weight of an oxide of a Group B element or an oxide of a Group IVB element is added,
Arranged facing the substrate, a process gas consisting of a rare gas and a hydrogen gas is introduced into the vacuum vessel, a high frequency is applied to the ZnO target to generate a discharge, and sputter particles made of a film material are generated from the surface of the ZnO target. Let out,
Sputter ZnO particles are deposited on the substrate in a hydrogen atmosphere.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a transparent conductive film having excellent electrical conductivity and a transparent conductive film.

[0002]

2. Description of the Related Art For example, amorphous silicon (hereinafter a)
A transparent conductive film is used as an electrode of a solar cell. As shown in FIG. 7, in a conventional a-Si solar cell, a transparent conductive film 102 made of tin oxide (SnO ₂ ) is used as a surface transparent electrode on a glass substrate 101.
A-Si layer 1 consisting of a p-layer, an i-layer and an n-layer on a part thereof
03, and indium oxide
Transparent conductive film 104 made of tin oxide composite oxide (ITO)
Are sequentially laminated, an aluminum electrode 105 as a metal electrode is further laminated thereon, and an aluminum electrode 106 as a collector electrode is separately formed on the transparent conductive film 102. When the light 107 enters the a-Si layer 103 through the substrate 101 and the transparent conductive film 102, a-S
Photoelectric power is generated by photoelectric conversion in the i layer 103.

The transparent conductive film 102 is formed by a known thermochemical vapor deposition method and has a thickness of about 1 μm. Also,
The interface between the transparent conductive film 102 and the a-Si layer 103 (the surface where the film is exposed) has irregularities of 0.1 μm or less. These irregularities greatly contribute to increase in photovoltaic power, that is, improvement in power generation efficiency. The reason is that the light 107 incident from the glass substrate 101 side is less likely to be reflected by the unevenness of the interface between the transparent conductive film 102 and the a-Si layer 103, and is efficiently taken into the a-Si layer 103. is there. Here, the transparent conductive film 104
Is to increase the reflectance of the long-wavelength light reaching the interface with the a-Si layer 103 to the a-Si layer 103 and further improve the power generation efficiency.

[0004]

Conventionally, ITO has been used as a material for the transparent conductive film 104.
Since ITO is expensive, low-cost alternative materials are being demanded from various fields. In response to this, one of the alternative material candidates
One of them is tin oxide (ZnO).

Reactive vacuum deposition is one of the methods for forming a film of ZnO. However, with the reactive vacuum deposition method, 1 ×
Although it is possible to manufacture the transparent conductive film 104 having a low resistance of 10 ⁻³ Ω · cm, it is necessary to heat the base material to a temperature of 350 ° C. or higher. Further, unless the film thickness is 300 nm or more, this resistivity cannot be obtained.

Further, in the temperature range of 350 ° C. or higher, a-Si
When the transparent conductive film 104 is deposited on the layer 103, a-
The Si layer 103 is crystallized and diffusion of the doped impurities causes a problem that power generation efficiency is significantly reduced.

From such a background, a method for manufacturing a ZnO transparent conductive film in which the a-Si layer is not crystallized during film formation, and the doped impurities are not diffused,
Low resistance at a substrate temperature of about 150 ° C or less and a film thickness of 1
It is strongly desired to develop and put into practical use a ZnO transparent conductive film having a high transmittance of 00 nm or less.

The present invention has been made in order to solve the above problems, and is for producing a transparent conductive film without crystallizing an a-Si layer as an underlayer and without causing diffusion of a doped impurity. The purpose is to provide a method.

It is another object of the present invention to provide a transparent conductive film having a low resistance at a substrate temperature of about 150 ° C. and a high transmittance at a film thickness of 100 nm or less.

[0010]

The method for producing a transparent conductive film according to the present invention is a film material in a vacuum container III
A sputtering source having a ZnO target to which 1 to 7% by weight of an oxide of a group B element or an oxide of a group IVB element is added,
The substrate is arranged so as to face the substrate, a process gas composed of a rare gas and a hydrogen gas is introduced into the vacuum container, and the ZnO
A high frequency is applied to the target to generate a discharge, and the Z
It is characterized in that sputtered particles made of a film material are ejected from the surface of the nO target and the ZnO sputtered particles are deposited on the substrate in an atmosphere containing hydrogen.

The above process gas is 80 to 99% by volume.
It is preferable that the rare gas and hydrogen gas of 20 to 1 volume% are included. If the amount of hydrogen gas added falls below 1% by volume,
Since the resistivity of the film rapidly increases as shown in, the lower limit of the amount of hydrogen gas added was set to 1% by volume. Further, when the added amount of hydrogen gas exceeds 20% by volume, the resistivity of the film gradually increases so that it cannot be ignored as shown in FIG. 2, so the upper limit of the added amount of hydrogen gas was set to 20% by volume.

The rare gas may be any of argon, neon, krypton and xenon, but it is particularly preferable to use argon gas.

According to the method for producing a transparent conductive film of the present invention, Zn containing 1 to 7% by weight of an oxide of a IIIB group element or an oxide of a IVB group element serving as a film material is added in a vacuum container.
An evaporation source having an O vapor deposition material is arranged facing the substrate, and a process gas consisting of oxygen gas or a mixed gas of oxygen / rare gas and hydrogen gas is introduced into the vacuum container to heat the ZnO vapor deposition material. And vaporized, and the ZnO vapor is deposited on the substrate in a hydrogen atmosphere.

The above process gas preferably contains 99.0 to 99.9% by volume of oxygen gas or a mixed gas of oxygen / rare gas and 1.0 to 0.1% by volume of hydrogen gas. When the amount of hydrogen gas added falls below 0.1% by volume, the resistivity of the film sharply increases as shown in FIG. 5, so the lower limit of the amount of hydrogen gas added was set to 0.1% by volume. Further, when the added amount of hydrogen gas exceeds 1.0% by volume, the resistivity of the film gradually increases so that it cannot be ignored as shown in FIG. 5, so the upper limit of the added amount of hydrogen gas was set to 1.0% by volume.

The rare gas may be any of argon, neon, krypton and xenon, but it is particularly preferable to use argon gas.

Further, gas discharge plasma is generated between the evaporation source and the substrate, and ZnO that has passed through this discharge plasma
It is desirable to deposit the vapor on the substrate. A high deposition rate can be obtained by the action of the discharge plasma.

The transparent conductive film according to the present invention is a transparent conductive film formed on an amorphous silicon layer as a base layer, and is II in an inert gas atmosphere containing hydrogen.
1 to 7 group IB element oxides or IVB group element oxides
The sputtered particles ejected from the ZnO target added by weight% are deposited on the amorphous silicon layer, or in an oxygen gas atmosphere containing hydrogen, II
1 to 7 group IB element oxides or IVB group element oxides
It is characterized by being formed by depositing vapor evaporated from a ZnO vapor deposition material added by weight% on the amorphous silicon layer.

[0018]

Various preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

(Embodiment 1; Sputtering method) The outline of the structure of the sputtering apparatus used in Embodiment 1 will be described with reference to FIG. The sputtering apparatus includes a vacuum container 1 that is evacuated through an exhaust port 16 by a vacuum exhaust device (not shown). In this vacuum container 1, a sputter source 2 and a substrate electrode 12 are arranged so as to face each other.

The sputtering source 2 is Zn containing Al ₂ O ₃ added.
A target 3 made of O and a plurality of magnetic field generating magnets 4
And a target holder 5 as an electrode having a water cooling function
A shield 6 and an insulator 7 having a vacuum sealing function.

The target holder 5 is connected to a high frequency power source 9 via a matching unit 8. When the target 3 is held by the target holder 5 and energized, a desired component is ejected from the target 3 by the sputtering action and is deposited on the substrate 10. The target holder 5 and the vacuum container 1 are insulated by the insulator 7. In addition to the high frequency power source, a DC power source may be used as the power source 9. When using a DC power supply, the matching box 8 is unnecessary.

A substrate electrode 12 having a heater 11 is arranged so as to face the target 3. Substrate electrode 12
Is provided with a holding mechanism for holding the substrate by suction.
0 is held on the lower surface of the electrode 12.

A gas introduction pipe 15 penetrates the side wall of the vacuum container 1 and is inserted into the interior of the container, and a gas introduction port is opened above the vicinity of the target 3. The gas introduction pipe 15 communicates with a gas supply source equipped with a flow rate control device (not shown), and a predetermined flow rate of argon gas and a predetermined flow rate of hydrogen gas are introduced into the vacuum container 1, respectively. The argon gas and the hydrogen gas may be mixed in a desired ratio in advance before being introduced into the vacuum container 1, and may be introduced into the vacuum container 1 as a mixed gas.

Next, a case where a ZnO transparent conductive film is formed on a glass substrate using the above sputtering device will be described.

The substrate 10 made of non-alkali glass is ultrasonically cleaned in an organic solvent (for example, acetone), placed on the substrate electrode 12 in the vacuum container 1 and pre-evacuated to 2 × 10 ^-6 torr or less. The addition amount of Al ₂ O ₃ , which is an oxide of a Group IIIB element, to the ZnO target 3 is 2% by weight.
The substrate 11 is heated to 150 ° C. by the heater 11.

Then, as a rare gas, an argon gas 75-
100% by volume and 25 to 0% by volume of hydrogen gas are vacuumed respectively.
It is introduced into the container 1. The internal pressure of the vacuum container 1 at this time is 5 ×
10 ^-3Adjust so that it becomes torr.

When high frequency power is applied from the power source 9 to the target holder 5 through the matching unit 8, a discharge is generated, the generated argon ions collide with the surface of the target 3, sputter particles fly out from the target surface, and hydrogen is generated. Sputtered particles are sequentially deposited on the substrate 10 in an atmosphere containing the sputtered particles.
As a result, the ZnO film 14 having a desired component and thickness is formed on the substrate 10.
Formed on. The thickness of the ZnO film 14 is 80 nm.
Met.

FIG. 2 is a characteristic line showing the results of investigating the correlation between the hydrogen gas composition (volume%) on the horizontal axis and the film resistivity (× 10 ⁻³ Ω · cm) on the vertical axis. It is a figure.
As is clear from the figure, the ZnO film containing no hydrogen gas (0% by volume) exhibits a high resistivity of 20 × 10 ⁻³ Ω · cm. On the other hand, it was found that the resistivity of the ZnO film containing 1% by volume of hydrogen gas was significantly reduced to 3 × 10 ⁻³ Ω · cm. Further, it was found that the ZnO film containing 8% by volume of hydrogen gas has a low resistivity of 0.7 × 10 ⁻³ Ω · cm.

The film resistivity was 3 × 10 ⁻³ Ω · cm or less when hydrogen gas was added in an amount of 20% by volume or less, whereas the film resistivity was 8 × 10 when hydrogen gas was added in an amount of 25% by volume.
It increased to ^-3 Ω · cm. The reason for this is that the ZnO film was reduced and oxygen vacancies were generated in large numbers.

The amount of Al ₂ O ₃ added is preferably 1 to 7 mass%. When Al ₂ O ₃ is less than 1 mass% or exceeds 7 mass%, the resistivity increases up to the order of 1 × 10 ⁻² Ω · cm. Even if the additive material to ZnO was an oxide of a group IIIB element other than Al ₂ O ₃ or an oxide of a group IVB element, both showed low resistivity of about 0.7 × 10 ⁻³ Ω · cm.
In addition, when the rare gas is changed to neon, krypton, or xenon other than argon, 0.7 × 10 ⁻³ Ω ·
It showed a low resistivity of around cm.

FIG. 3 shows a short circuit current of an a-Si solar cell having a ZnO transparent conductive film (Example 1) prepared in the presence of 95% by volume of argon gas and 5% by volume of hydrogen gas, and a conventional ITO transparent conductive film. It is a graph figure which compares with the short circuit current of the a-Si solar cell which has a film (Comparative example 1). Example 1
The solar cell of both Comparative Example 1 and Comparative Example 1 had the structure shown in FIG. When the short circuit current of Comparative Example 1 was set to the reference value 1, the short circuit current of Example 1 was about 1.1. From this, it was found that the solar cell having the ZnO transparent conductive film of Example 1 had a photoelectric conversion efficiency equal to or higher than that of the conventional product.

According to the method for producing a transparent conductive film of this embodiment, a high-quality transparent conductive film can be obtained without crystallizing the a-Si layer of the underlayer and without diffusing the doped impurities. It can be formed on the Si layer. Therefore, the yield of solar cell products can be improved and the production cost can be significantly reduced.

Further, the transparent conductive film of this embodiment is 150 ° C.
It has a low resistance and a high transmittance at the following substrate temperatures, and a solar cell using the same can obtain a large short-circuit current and greatly improve the photoelectric conversion efficiency.

(Embodiment 2; Plasma deposition) Next, an outline of the configuration of the plasma deposition apparatus used in Embodiment 2 is shown in FIG.
Will be described with reference to.

The plasma deposition apparatus is equipped with a vacuum container 21 which is evacuated by an unillustrated vacuum evacuation device through an evacuation port 31. In this vacuum container 21, an evaporation source 22
And the substrate holder 29 are opposed to each other.

The evaporation source 22 is a refractory crucible provided with a melting and heating means, in which an appropriate amount of the vapor deposition material 23 made of ZnO containing 1 to 7% by weight of Al ₂ O ₃ is contained. An electron beam, a resistance heating coil, or the like can be used as the melting and heating means of the evaporation source 22.

A substrate holder 29 having a heater 30 is arranged so as to face the evaporation source 22. Board holder 2
9 has a holding mechanism for sucking and holding the substrate, and the substrate 10 is held on the lower surface of the holder 29.

A gas introduction pipe 28 penetrates the side wall of the vacuum container 21 and is inserted into the interior of the container, and a gas introduction port is opened above the vicinity of the evaporation source 22. The gas introduction pipe 28 communicates with a gas supply source equipped with a flow rate control device (not shown) so that a predetermined flow rate of oxygen gas and a predetermined flow rate of hydrogen gas are introduced into the vacuum container 21, respectively. The oxygen gas and the hydrogen gas may be mixed in advance in a desired ratio before being introduced into the vacuum container 21, and may be introduced into the vacuum container 21 as a mixed gas.

A high frequency coil 24 for generating discharge plasma is arranged between the evaporation source 22 and the substrate holder 29.
The high frequency coil 24 is connected to a power source 27 via a matching unit 26. The high frequency coil 24 is introduced into the vacuum container 21 via an insulator 25 having a vacuum sealing function.

Next, the case of forming a ZnO transparent conductive film on a glass substrate using the above plasma deposition apparatus will be described.

After ultrasonically cleaning the substrate 10 made of non-alkali glass or the like with an organic solvent (for example, acetone), the vacuum container 2
It is installed on the substrate holder 29 in 1 and pre-evacuated to 2 × 10 ⁻⁶ torr or less. The added amount of Al ₂ O ₃ , which is an oxide of a Group IIIB element, to the ZnO vapor deposition material 23 was 3% by weight. The substrate 10 is heated to 150 ° C. by the heater 30.

Next, 100 to 99% by volume of oxygen gas,
0 to 1.4% by volume of hydrogen gas is introduced. At this time, the internal pressure of the vacuum container 21 is adjusted to 8 × 10 ⁻⁴ torr.

The evaporation material 23 is heated by the evaporation source 22,
At the same time as evaporating the ZnO component, high-frequency power is applied to the high-frequency coil 24 from the high-frequency power source 27 via the matching device 26, and plasma 33 is generated by discharge. ZnO vapor is sequentially deposited on the substrate 10 in an atmosphere containing hydrogen, whereby a ZnO film 14 having a desired component and film thickness is formed on the substrate 10. The film thickness of the ZnO film 14 was 80 nm.

FIG. 5 is a characteristic line showing the results of investigating the correlation between hydrogen gas composition (volume%) on the horizontal axis and film resistivity (× 10 ⁻³ Ω · cm) on the vertical axis. It is a figure.
As is clear from the figure, the ZnO film with no hydrogen gas added (0% by volume) shows a high resistivity of 15 × 10 ⁻³ Ω · cm. On the other hand, ZnO added with 0.2% by volume of hydrogen gas
The resistivity of the film was significantly reduced to 3 × 10 ⁻³ Ω · cm. Further, the ZnO film added with 0.6% by volume of hydrogen gas had a low resistivity of 0.7 × 10 ⁻³ Ω · cm.

The resistivity up to 1% by volume of hydrogen gas is 2 × 10 ⁻³ Ω · cm or less, but the resistivity increases to 7 × 10 when the amount of hydrogen gas added increases to 1.4% by volume. ^-3 Ω ・ c
increased to m. This is because the ZnO film was reduced and many oxygen vacancies were generated.

The amount of Al ₂ O ₃ added is preferably 1 to 7 mass%. If the added amount of Al ₂ O ₃ is less than 1% by mass or exceeds 7% by mass, the resistivity increases to the order of 1 × 10 ⁻² Ω · cm. Other than Al ₂ O ₃ as the additive material to ZnO II
Both of the oxides of Group IB elements and the oxides of Group IVB elements showed low resistivity around 0.7 × 10 ⁻³ Ω · cm. Moreover, when a mixed gas of oxygen gas and argon gas is used instead of oxygen gas, the adhesion of the ZnO film is improved.

FIG. 6 shows the short-circuit current of an a-Si solar cell having a ZnO transparent conductive film (Example 2) prepared in the presence of 99.4% by volume of oxygen gas and 0.6% by volume of hydrogen gas.
A-Si having a conventional ITO transparent conductive film (Comparative Example 2)
It is a graph figure which compares with the short circuit current of a solar cell. The solar cells of both Example 2 and Comparative Example 2 were configured as shown in FIG. When the short-circuit current of Comparative Example 2 is set to the reference value 1,
The short-circuit current of Example 2 was 1.05. From this, it was revealed that the solar cell having the ZnO transparent conductive film of Example 2 had a photoelectric conversion efficiency equal to or higher than that of the conventional product.

According to the method for producing a transparent conductive film of this embodiment, a high quality transparent conductive film can be obtained without crystallizing the a-Si layer of the underlayer and without causing diffusion of the doped impurities. It can be formed on the Si layer. Therefore, the yield of solar cell products can be improved and the production cost can be significantly reduced.

Further, the transparent conductive film of this embodiment is 150 ° C.
It has a low resistance and a high transmittance at the following substrate temperatures, and a solar cell using the same can obtain a large short-circuit current and greatly improve the photoelectric conversion efficiency.

[0050]

According to the present invention, a high-quality transparent conductive film is formed on an a-Si layer without crystallizing the a-Si layer as an underlayer and without causing diffusion of doped impurities. Therefore, the yield can be improved and the production cost can be significantly reduced.

Since the transparent conductive film of the present invention has not only excellent conductivity but also excellent transparency in the entire visible region,
It is particularly useful as a light-transmitting display or an electrode for solar cells.

[Brief description of drawings]

FIG. 1 is a block cross-sectional view showing an outline of an apparatus used in a method for manufacturing a transparent conductive film according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a correlation between a hydrogen gas composition and a resistivity of a transparent conductive film.

FIG. 3 is a graph showing a short circuit current of a transparent conductive film in comparison between Example 1 and Comparative Example 1.

FIG. 4 is a block cross-sectional view showing an outline of an apparatus used in a method for manufacturing a transparent conductive film according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing the correlation between the hydrogen gas composition and the resistivity of the transparent conductive film.

FIG. 6 is a graph showing a short circuit current of a transparent conductive film in comparison with Example 2 and Comparative Example 2.

FIG. 7 is a schematic sectional view showing a solar cell having a conventional transparent conductive film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum container, 2 ... Sputter source, 3 ... Target, 4 ... Magnet for magnetic field generation, 5 ... Target holder, 6 ... Shield, 7 ... Insulator, 8 ... Matching device, 9 ... High frequency power supply, 10 ... Substrate, 11 ... heater, 12 ... substrate electrode, 13 ... insulator, 14 ... ZnO film, 15 ... gas introduction pipe, 16 ... exhaust port, 21 ... vacuum container, 22 ... evaporation source, 23 ... deposition material, 24 ... high frequency coil, 25 ... Insulator, 26 ... Matching device, 27 ... High frequency power supply, 28 ... Gas introduction tube, 29 ... Substrate holder, 30 ... Heater, 31 ... Exhaust port, 33 ... Plasma, 101 ... Glass substrate, 102 ... Transparent conductive film (SnO) ₂ ), 103 ... a-Si layer, 104 ... Transparent conductive film (ITO), 105 ... Metal electrode film (Al), 106 ... Current collecting electrode (Al), 107 ... Light.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuhiko Kondo             3-5-1, 717-1, Fukahori-cho, Nagasaki-shi, Nagasaki             Hishi Heavy Industries Ltd. Nagasaki Research Center F-term (reference) 4K029 AA09 BA49 BC09 BD00 CA03                       CA05 DC05 DD02 EA05                 5F051 AA05 BA16 FA02

Claims (9)

[Claims] 1. A film material III in a vacuum container
A sputtering source having a ZnO target to which 1 to 7% by weight of an oxide of a group B element or an oxide of a group IVB element is added,
A process gas composed of a rare gas and a hydrogen gas is introduced into the vacuum container, and a high frequency is applied to the ZnO target to generate a discharge, which is formed of a film material from the surface of the ZnO target. A method for producing a transparent conductive film, characterized in that sputtered particles are ejected and the ZnO sputtered particles are deposited on a substrate in an atmosphere containing hydrogen. 2. The process gas is a rare gas of 80-9.
The method according to claim 1, characterized in that it contains 9% by volume and 20 to 1% by volume of hydrogen gas. 3. The process gas is argon gas 8
The method according to claim 1, comprising 0 to 99% by volume and 20 to 1% by volume of hydrogen gas. 4. A film material III in a vacuum container
An evaporation source having a ZnO vapor deposition material added with an oxide of a group B element or an oxide of a group IVB element in an amount of 1 to 7% by weight is arranged to face a substrate, and oxygen gas or oxygen / rare gas is placed in the vacuum container. A process gas comprising a mixed gas of 1) and a hydrogen gas is introduced, the ZnO vapor deposition material is heated and evaporated, and the ZnO vapor is deposited on a substrate in a hydrogen atmosphere. . 5. The process gas contains 99.0 to 99.9% by volume of oxygen gas or a mixed gas of oxygen / rare gas and 1.0 to 0.1% by volume of hydrogen gas. Item 4. The method according to Item 4. 6. The process gas contains 99.0 to 99.9% by volume of oxygen gas or a mixed gas of oxygen / argon gas and 1.0 to 0.1% by volume of hydrogen gas. Item 4. The method according to Item 4. 7. A discharge plasma of the gas is generated between the evaporation source and the substrate, and Z is passed through the discharge plasma.
The method of claim 4, wherein nO vapor is deposited on the substrate. 8. A transparent conductive film formed on an amorphous silicon layer as a base layer, wherein an oxide of a Group IIIB element or an oxide of a Group IVB element is added in an inert gas atmosphere containing hydrogen. A transparent conductive film formed by depositing sputtered particles, which are ejected from a ZnO target added by up to 7% by weight, on an amorphous silicon layer. 9. A transparent conductive film formed on an amorphous silicon layer as a base layer, wherein an oxide of a Group IIIB element or an oxide of a Group IVB element is added in an inert gas atmosphere containing hydrogen. A transparent conductive film formed by depositing vapor evaporated from a ZnO vapor deposition material added to ˜7 wt% on an amorphous silicon layer.