JPS63102109A - Transparent conducting film - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a transparent conductive film with corrosion resistance, particularly to a transparent conductive film that is most suitable as a substrate for a solar cell.

[Prior Art] Generally, transparent conductive films that are transparent in the visible light region and have conductivity are used as transparent electrodes in new display systems such as liquid crystal displays and EL displays, and as transparent electrodes in amorphous silicon solar cells.

It is also used by forming a film on a transparent glass substrate to prevent photomasks from being charged. Indium oxide containing tin as a dopant and tin oxide containing antimony or fluorine as a dopant are mainly used as materials for these transparent conductive films. In particular, indium oxide has a lower resistance, which is currently about 1O-4Ω, C
The results were as follows.

[Problems to be solved by the invention] As described above, transparent conductive films, especially indium oxide films, have excellent conductivity properties, but when considering acid resistance or reduction resistance, they are extremely weak films. 0 for example 100
When a film formed by vapor-depositing indium oxide with a thickness of 500 to 1000 people on a glass plate is immersed in hydrochloric acid with a concentration of 500% to 1000%.
In some cases, it dissolves away in 1 to 3 seconds and is completely useless. Indium oxide is an oxygen-deficient transparent conductive film and has donor type conductivity. In this film, the bond between indium and oxygen is weak, so when ion bombardment is performed in a high-temperature atmosphere containing hydrogen or in plasma, oxygen is liberated and metallic indium precipitates, resulting in devitrification. . This becomes a big problem when using this indium oxide film as a semiconductor film for solar cells. This is because the amorphous silicon film currently used as a semiconductor film for solar cells is mainly produced by a plasma CVD method using hydrogen plasma. As a method to improve this problem, Ti02 is added as a blocking layer on the indium oxide film.
Although it has been considered to form an oxide layer such as 5i02 or 5i02, it has drawbacks such as impairing conductivity and insufficient plasma resistance. Further, transparent conductive films mainly composed of tin oxide were also insufficient in terms of plasma reactivity resistance.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes hydrogen and boron on the surface of a transparent conductive film whose main component is indium oxide or tin oxide. The present invention provides a transparent conductive film with improved corrosion resistance, characterized in that a protective film is formed, at least one of which is doped with carbon.

The present invention will be explained in more detail below.

FIG. 1.2 is a drawing showing an embodiment of the transparent conductive film according to the present invention, in which 1 is a substrate, 2 is a transparent conductive film whose main component is indium oxide or tin oxide, 3 is titanium nitride, or a protective film made of titanium nitride containing oxygen, and 4 represents an alkali barrier film.

In the present invention, the transparent conductive film containing indium oxide as a main component contains tin in an amount of about 0.5 to 30% by weight, preferably about 5 to 10% by weight, based on indium oxide, and is a tin-doped oxide film that is imparted with electrical conductivity. In a transparent conductive film which is an indium conductive film and whose main component is tin oxide, fluorine is contained in an amount of 0.1 to 5% by weight, preferably 0.3 to 2% by weight based on tin oxide, and the conductivity is improved. The applied fluorine-doped tin oxide conductive film or antimony has a 0.0.
It is an antimony doped tin oxide conductive film which contains about 1 to 30% by weight, preferably about 0.3 to 5% by weight, and is imparted with electrical conductivity.

Such a tin-doped indium oxide conductive film can be manufactured by a sputtering method, a vacuum evaporation method, etc., and a fluorine-doped tin oxide conductive film can be manufactured by a CVD method (Chemical
The antimony-doped tin oxide conductive film can be manufactured by a CVD method, a sputtering method, a vacuum deposition method, a solution spray method, etc. be able to. The thickness of such a transparent conductive film is determined depending on the desired resistance value, optical properties, etc., but it is usually 500 to 2μ.
The range is about m.

The substrate 1 on which the transparent conductive film 2 described above is formed may be a soda lime silicate glass plate, an aluminosilicate glass plate, a borosilicate glass plate, or a lithium silicate glass plate from the viewpoint of transparency, optical properties, durability, electrical properties, etc. An alkali-containing glass plate such as an aluminosilicate glass plate, a low alkali-containing glass plate, an alkali-free glass plate, a quartz glass plate, etc. are preferable, but a transparent plastic plate or a transparent plastic film may also be used depending on the case. . In addition, for alkali-containing glass plates such as soda lime silicate glass plates, or low-alkali glass plates, alkaline components on the surface of the glass plates dissolve and cause haze (clouding) on the transparent conductive film formed thereon. SiO2 and Al2O3 are placed on the side of the glass plate on which the transparent conductive film is to be formed, so as not to cause any damage.

It is preferable to form an alkali barrier film 4 mainly composed of an oxide such as Zr02.

In the present invention, a protective film made of carbon doped with at least one of hydrogen and boron is used as a transparent conductive film to improve the corrosion resistance, especially plasma resistance, of a transparent conductive film mainly composed of indium oxide or tin oxide. Formed on the surface of the membrane.

It is optimal for the protective film made of carbon containing hydrogen and boron to contain 5 to 50% of at least one of hydrogen and boron.

Carbon in the protective film of the present invention can have two types of crystal structures, a diamond structure and a graphite structure, which is a two-dimensional layered material, depending on its bonding state. The diamond structure is an insulator with strong wear resistance, but the graphite structure wears out easily and has electrical conductivity comparable to that of metal.

Generally, a carbon film is formed to a thickness of several tens of people.

Although there are differences depending on the film forming method and conditions, amorphous carbon films do not have a clear crystalline structure and do not have the fragility to wear of graphite-structured carbon and the electrical conductivity of metals, but have strong wear resistance. Although it has a low electrical conductivity and is similar to a diamond structure in these two respects, it is a non-transparent and absorbent film. In addition, since there are no crystal grains, it grows over the entire uneven surface of the substrate on which it is grown, and has good covering properties, covering the entire surface. Bonds between carbon atoms have high energy and are excellent in chemical reactivity resistance, and in particular, in terms of plasma reactivity resistance, it is thought that since it is not an oxide film, it is difficult to change against reducing plasma containing H2 and the like. This fact indicates that when producing amorphous silicon for solar cells, when a dimont structure, a graphite structure, or an amorphous carbon film is used as an overcoat on a transparent conductive film, an oxide overcoat is used. As mentioned above, carbon films have excellent covering properties, but carbon films are optically absorptive films and have low conductivity, so they can be used for solar cells. In order to obtain sufficient visible light transmittance (for example, 70% or more) and surface resistance without affecting conversion efficiency when used as a substrate, the protective film must be extremely thin, for example, 20 Å or less. However, if it is too thin like this, there is a problem that the material will deteriorate in terms of plasma reactivity resistance.

As a result of repeated studies on how to improve these problems, we found that in terms of electrical conductivity, carbon doped with boron shows no change in plasma reactivity resistance and surface coverage compared to undoped carbon films. It was also found that since this film exhibits acceptor type conductivity, the protective film made only of carbon does not need to be extremely thin, and the sheet resistance does not increase.

On the other hand, regarding the issue of transmittance, the transmittance of carbon doped with hydrogen and carbon doped with both hydrogen and boron decreases, and an overcoat with a thickness of about 100 people is applied. A transmittance of about 70% could be obtained with the transparent conductive film.

In particular, a carbon film doped with both hydrogen and boron has excellent plasma reactivity resistance, transmittance, and electrical conductivity, and a transparent conductive film overcoated with this has excellent properties as a solar cell substrate. It turns out.

The ratio of hydrogen introduced into the carbon film, the ratio of boron introduced into the carbon film, each ratio when both hydrogen and boron are introduced, and the total ratio are optimally 5 to 50%.

The optimum thickness of the carbon film H containing at least one of hydrogen and boron is 10 to 100 Å, preferably 20 to 50.

The method for forming the protective film in the present invention is not limited to specific methods such as vapor deposition and sputtering, but in order to achieve effective plasma reactivity resistance with the film thickness as shown above, It is necessary to create a film with properties as close to those of the bulk as possible, and for this purpose, it is desirable to use plasma-assisted film manufacturing methods such as sputtering, ion plating, and plasma CVD. When sputtering, a carbon target or a carbon target and a poron target are set in the vacuum chamber of a sputtering device, and at least one of argon gas, methane gas, hydrogen, and diporane gas is introduced, and RF main voltage is applied to the target to perform sputtering. A dense film can be obtained. In order to obtain a carbon film doped with hydrogen and boron that has high conductivity, high transmittance, and plasma reactivity resistance at the same time, a carbon target and a boron target are set in a vacuum chamber, and hydrogen gas is 1 Ma O 1%. Sputtering is performed by mixing hydrogen gas with argon gas in the range of 1% to 20%, or setting a carbon target in a vacuum chamber and adding 1% hydrogen gas.
VO1% ~ 20 ma 01%, Diporane gas 1 ma oj% ~
An optimal film can be obtained by mixing argon gas in a range of 30 mmol or 1% and sputtering the mixture. Under these conditions, the in-plane specific resistance and transmittance of the transparent conductive film, which was overcoated with carbon doped with hydrogen and boron for about 30 hours, remained unchanged from before the overcoat. It is thought that a dense film close to the bulk also acts as an effective diffusion barrier. Furthermore, if the underlying transparent conductive film is also produced by the CVD method, and the film of the present invention is also produced by the plasma CVD method, online production up to amorphous silicon is possible.

Since the transparent conductive film of the present invention has high plasma reactivity resistance,
Each insertion/removal hole can be formed on such a transparent conductive film by a plasma CVD method. Therefore, such a transparent conductive film is most suitable as a transparent electrode for an amorphous solar cell.

In manufacturing an amorphous solar cell, for example, a p-type amorphous Si film, an i-type amorphous Si film, and an n-type amorphous Si film are deposited on the transparent conductive film of the present invention formed on a glass substrate by plasma CVD. Manufactured by sequential formation.

"Example" The present invention will be explained in detail below.

Example 1 A metallic indium target containing 10 at % tin and a pure carbon sputtering target are each set on a cathode in a vacuum chamber of a sputtering device. A soda lime silicate glass substrate (thickness: 1.1 m), which is a silica/alkali barrier film material whose surface has been cleaned by ceria polishing and water washing, is placed in a vacuum chamber and evacuated to 5, OX 1O-5 Torr or less using an oil diffusion pump. do. The substrate temperature is raised to 250 to 400°C, preferably about 370°C.The vacuum chamber is filled with a mixed gas of Ar:02=62:3B, and the degree of vacuum is set to 2.2X 1O-3Torr.
500mm on a tin-indium alloy target.
Apply a DC voltage of , and perform press sputtering for 10 minutes.
After press sputtering, the shutter was opened and sputtering was performed for 5 minutes, and a transparent In2O3 conductive film containing 10 at% of tin was obtained with a film thickness of 4,200 mm.The atmosphere in the vacuum chamber was changed to Ar: CH4- without breaking the vacuum. Completely replace the gas with an 80:20 mixture and reduce the vacuum to 1.5 x 1O-3 Torr.
After adjusting the carbon target to r, a main RF voltage of 3 KV was applied to the carbon target and pre-sputtering was performed for 5 minutes followed by sputtering for 6 seconds to obtain a hydrogen-doped carbon overcoat film (film n: about 40 people). The specific resistance of the transparent conductive film thus obtained was measured using the four-probe method and found to be 5, OXl0
-4 Ω-cm, transmittance 82%.Although the resistivity was slightly higher than that without thio-barcoding, there was almost no change in the resistivity.

A normal plasma CVD device for producing amorphous silicon was used on these transparent conductive film substrates, and the inside of the chamber of the device was heated to lXl0-5 Torr by an oil diffusion pump.
After exhausting to a certain extent, SiH4 gas and 1000pp
5ZH6 gas diluted with hydrogen and fat was introduced into the chamber at a volume ratio of 1:10, RF output was 5W, and substrate temperature was 250°C.
After forming a P-type amorphous silicon film, the amorphous silicon M was etched away using hydrazine hydrate, and the specific resistance and transmittance of the transparent conductive film were measured. As a result, with the film without any overcoat, the specific resistance changed by 1.8 times and the transmittance changed by 0.9 times, whereas the hydrogen-doped carbon protective film of this example was coated with The resistivity and transmittance of the membrane did not change at all.

Example 2 A metallic indium target containing 10 at % (atomic ratio %) of tin and a pure sputtering target were each set on a cathode in a vacuum chamber of a sputtering device. A 110m thick soda lime silicate glass substrate whose surface had been cleaned by ceria polishing and water washing was placed in a vacuum chamber, and an oil diffusion pump was used for 5. Evacuate to OX 1O-5 Tarr or less. Also, raise the substrate temperature to about 370°C. Fill the vacuum chamber with a mixed gas of Ar:02=82:38.
Set the vacuum degree to 2.2X 1O-3 Torr, and
After press sputtering, apply a DC voltage of 500μ to the indium alloy target and perform press sputtering for 10 minutes.
When the shutter was opened and sputtering was performed for 5 minutes, the film thickness was 4.
A transparent In2O3 conductive film containing 10 at% of tin was obtained.To break the vacuum, the atmosphere in the vacuum chamber was changed to A.
r: Completely change to a mixed gas of B2:B2H6=90:5:5 and reduce the degree of vacuum to 1.6×1O-3To
After adjusting to rr, a constant RF voltage of 3 KV was applied to the carbon target to perform press sputtering for 5 minutes and then sputtering for 6 seconds. The overcoated hydrogen and boron doped carbon protective film thickness was 40.

The transparent conductive film thus obtained has a specific resistance of 2.5
The transmittance of 10-4Ω-C was 82%, which was almost the same as that without overcoating.

A normal plasma CVD device for producing amorphous silicon was used on these transparent conductive film substrates, and the inside of the chamber of the device was heated with IX 1O-5Tar by an oil diffusion pump.
After exhausting to about r, SiH4 gas and 1ooopp
- S2) 1b gas diluted with hydrogen in volume ratio l:1
Introduced into the chamber at 0, RF output 5W, substrate temperature 25
After forming a P-type amorphous silicon film at 0°C, the amorphous silicon film was removed by etching using hydrazine hydrate, and the specific resistance and transmittance of the transparent conductive film were measured. As a result, with the film without any overcoat, the specific resistance changed by 1.8 times and the transmittance changed by 0.9 times, whereas the hydrogen and boron doped carbon protective film of this example changed. In the overcoated membrane, both specific resistance and transmittance did not change at all.

Example 3 S formed by CVD method as alkali barrier film
A soda lime silicate glass substrate (plate ff 2.0 mm) having a silica Φ alkali barrier film material having an i02 film (film thickness 800 mm) on its surface was thoroughly washed off, and then this glass substrate was placed in a CVD equipment. After heating the glass substrate to 5001, tin tetrachloride IX 1 was applied to the surface of the glass substrate.
Steam (1, I x 101mo
A transparent conductive film made of tin oxide doped with fluorine at a rate of approximately 5,000 people/min was sprayed with nitrogen gas containing water vapor (30), methyl alcohol (1), and hydrofluoric acid (l/min), water vapor (30), methyl alcohol (1), and hydrofluoric acid (l/min). Next, the glass substrate with the transparent conductive film was placed in a vacuum chamber of a sputtering apparatus in which boron and carbon sputtering targets were set, and the vacuum chamber was heated to a thickness of 4,000 mm. OX 101T
After exhausting to orr, Ar: CH4=80:20
Add a mixed gas of 1.5 x 1 O-3 Tar
After adjusting to r, 3K was applied to boron and carbon targets.
After press sputtering was performed for 5 minutes by applying a constant RF voltage of V, sputtering was performed for 8 seconds.

The overcoated hydrogen and boron doped carbon film thickness was approximately 40 nm.

The transparent conductive film thus obtained had a specific resistance of 3, OXl
It had a transmittance of 0-4 Ω·cm and a transmittance of 82%, which was almost the same as that without overcoating.

A normal plasma CVD device for producing amorphous silicon was used on these transparent conductive film substrates, and the inside of the chamber of the device was heated with IX 1O-5Tar by an oil diffusion pump.
After exhausting to about r, 5iHa gas and 1000pp
S2 H6 gas diluted with hydrogen in a volume ratio of 1:10
Introduced into the chamber with RF output of 5W and substrate temperature of 250.
After forming a P-type amorphous silicon film at 0.degree. C., the amorphous silicon film was etched and removed using hydrazine hydrate, and the specific resistance and transmittance of the transparent conductive film were measured. As a result, with the film without any overcoat, the specific resistance changed by 1.6 times and the transmittance changed by 0.9 times, whereas in the case of the film without any overcoat, the resistivity changed by 1.6 times and the transmittance changed by 0.9 times, whereas the film with the overcoat of the oxidized titanium nitride protective film of this example There was no change in specific resistance or transmittance of the membrane.

Example 4 S formed by CVD method as alkali barrier film
A soda lime silicate glass substrate (thickness: 1.1 layers) having an i02 film (M thickness: 800) on its surface and a silica-alkali barrier film material was thoroughly cleaned, and then this glass substrate was placed in a CVD apparatus. After heating the glass substrate to 500°C, tin tetrachloride IX 10 was applied to the surface of the glass substrate.
Nitrogen gas containing 30 liters of water vapor, 1 liter of methyl alcohol, and 1 liter of hydrofluoric acid is sprayed at a rate of -212/min, approximately 500
A transparent conductive film (+112 thickness, 4000 layers) made of tin oxide doped with 1 wt % fluorine was formed at 0 layers/minute.

Next, the above-mentioned glass substrate with a transparent conductive film was placed in a vacuum chamber of a sputtering apparatus in which boron and carbon sputtering targets were set, and the vacuum chamber was heated 1. OX 1O
After evacuating to -5 Torr, +lr gas was added and the degree of vacuum was adjusted to 1.5X 1O-3 Torr, 3 KV RF main voltage was applied to boron and carbon targets, press sputtering was performed for 5 minutes, and then sputtering was performed for 8 seconds. , a boron-doped carbon overcoat film was formed. The thickness of the overcoat film was about 30.

The transparent conductive film thus obtained has a specific resistance of 2.8
It had a transmittance of 10 −4 Ω·cm and a transmittance of 82%, which was almost the same as that without overcoating.

A normal plasma CVD device for producing amorphous silicon was used on these transparent conductive film substrates, and the inside of the chamber of the device was heated to IX 1O-5 Tor by an oil diffusion pump.
After exhausting to about r, Sih gust 11000pp
S2 H6 gas diluted with dihydrogen at a volume ratio of 1:10
Introduced into the chamber with RF output of 5W and substrate temperature of 250.
After forming a P-type amorphous silicon film at a temperature of .degree. C., the amorphous silicon film was removed by etching using hydrazine hydrate, and the specific resistance and transmittance of the transparent conductive film were measured. As a result, with the film without any overcoat, the specific resistance changed by 1.8 times and the transmittance changed by 0.9 times, whereas with the film without any overcoat, the resistivity changed by 0.9 times, whereas the film with the overcoat of the oxidized titanium nitride of this example There was no change in specific resistance or transmittance of the membrane.

[Effects of the Invention] As described above, according to the present invention, the durability against reducing plasma can be significantly improved without impairing the transparency and conductivity of a transparent conductive film, particularly an indium oxide film and a tin oxide film. This is very advantageous for using this film composition as a substrate for solar cells using amorphous silicon as a substrate.

Furthermore, since the protective films according to the present invention have very good covering properties, these films can be used as a protective layer for so-called uneven structure films for solar cells.

[Brief explanation of the drawing]

FIG. 1.2 shows a cross-sectional view for explaining the transparent conductive film according to the present invention. 1: Substrate, 2: Transparent conductive film,

Claims (3)

[Claims] (1) Improved corrosion resistance characterized by forming a protective film made of carbon doped with at least one of hydrogen and boron on the surface of a transparent conductive film mainly composed of indium oxide or tin oxide. Transparent conductive film. (2) The transparent conductive film according to claim 1, wherein the protective film contains at least one of hydrogen and boron in an atomic ratio of 5 to 50 at% based on carbon. (3) The thickness of the protective film is 10 to 100 Å, preferably 20 Å
The transparent conductive film according to claim 1, wherein the transparent conductive film has a thickness of 50 Å.