JP2014037604A - Substrate with transparent conductive oxide film attached thereon and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate with transparent conductive oxide film attached thereon in which the mobility of carrier electrons is high, a haze ratio is high, and light absorption is low in a near-infrared region due to the low electron density of sheet carriers, and a method for manufacturing the substrate.SOLUTION: In a method for manufacturing a substrate with transparent conductive oxide film attached thereon in which a transparent conductive oxide film is provided on a substrate having a smooth surface, the transparent conductive oxide film includes at least a first layer composed of a tin oxide film with non-doped fluorine and formed on the substrate, and a second layer composed of a tin oxide film with doped fluorine and formed on the first layer. The first layer and the second layer are formed under pressure of 200 Pa or less by using a CVD method. The film thickness of the first layer is 1200nm or more, the film thickness of the second layer is 100nm or more, the total film thickness of the tin oxide film with doped fluorine included in the transparent conductive oxide film is 1200 to 2000nm, and the total film thickness of the tin oxide film with doped fluorine 100 to 600nm.

Description

  The present invention relates to a substrate with a transparent conductive oxide film and a method for producing the same. Specifically, the present invention relates to a method for manufacturing a substrate with a transparent conductive oxide film having high mobility of carrier electrons and low light absorption in the near infrared region (wavelength 800 to 2000 nm). The substrate with a transparent conductive oxide film obtained by the method of the present invention is suitably used as an incident light side electrode of a photoelectric conversion element such as a thin film solar cell.

  Thin film solar cells that are photoelectric conversion elements include amorphous silicon (a-Si) and polycrystalline silicon depending on the type of power generation layer. These thin film silicon solar cells include an incident light side. A transparent conductive oxide film is used as an electrode. This transparent conductive oxide film is required to have low resistance and high transparency and high light scattering performance in order to increase photoelectric conversion efficiency.

  As the transparent conductive oxide film, a tin oxide film, an indium oxide film, and the like are known. Among these, tin oxide film is a chemically stable material and is inexpensive, and is therefore useful as a transparent conductive oxide film used as an incident light side electrode of a photoelectric conversion element. In particular, fluorine is used as a dopant. The fluorine-doped tin oxide film to be contained is preferable because the film has little light absorption and is highly transparent.

Generally, a transparent conductive oxide film is required to have low resistance and high transparency, but light absorption gradually increases from near infrared to visible light as the carrier electron density that affects conductivity is increased. Therefore, it is extremely difficult to achieve both low resistance and high transparency. However, it is important that the transparent conductive oxide film used as the incident light side electrode of the photoelectric conversion element is transparent while maintaining the conductivity as high as possible.
The fluorine-doped tin oxide film has a specific resistance as high as 10 ⁻⁴ Ω · cm, and a film having high conductivity tends to be obtained relatively easily, whereas a film having a high transmittance tends to be difficult to obtain. This is because, in the fluorine-doped tin oxide film, it is possible to reduce the resistance by increasing the carrier electron density relatively easily. However, the increase in carrier electrons causes optical absorption, resulting in a decrease in transmittance. It is.

As a method for forming the fluorine-doped tin oxide film, a CVD method is preferably used because of easy control of the film thickness and good coverage (see Patent Document 1).
As described in Patent Document 1, an atmospheric pressure CVD method has been conventionally used for forming a fluorine-doped tin oxide film.
On the other hand, when using a low pressure CVD method in which a CVD method is carried out under a pressure of 10 kPa or less, a fluorine-doped tin oxide film with less impurities can be formed, so that the fluorine doping with high carrier electron mobility is possible. It is considered that a tin oxide film can be obtained.
In Non-Patent Document 1, a mobility of 75.8 cm ² / V · s is achieved with a fluorine-doped tin oxide film formed by using a low pressure CVD method.

Another problem in the fluorine-doped tin oxide film is that it is difficult to increase the haze ratio.
One means for increasing the photoelectric conversion efficiency in the thin film solar cell is to increase the current flowing in the fluorine-doped tin oxide film used as the incident light side electrode of the thin film solar cell. For this purpose, it is known to increase the haze ratio. For example, a method of providing irregularities on the surface of a fluorine-doped tin oxide film is known (see Patent Document 2). Here, in order to increase the haze ratio, it is preferable to increase the thickness of the fluorine-doped tin oxide film, but when the thickness of the fluorine-doped tin oxide film is increased under the same carrier electron density, Since the number of carrier electrons in the entire fluorine-doped tin oxide film increases, the light transmittance decreases due to optical absorption, so the thickness of the fluorine-doped tin oxide film cannot be increased, and the haze ratio can be increased. It was difficult.
Note that, as described in paragraph [0072] of Patent Document 2, the haze ratio is required to be 10% or more in terms of the C light source haze ratio.

In Patent Document 2, the transparent conductive oxide film is a laminated film of a tin oxide film doped with fluorine and a tin oxide film not doped with fluorine. In the vertical direction, a region with a large amount of fluorine to be doped and a region with a small amount of fluorine are provided, and while ensuring excellent conductivity in the surface direction in a region with a large amount of fluorine, the total amount of fluorine is reduced to reduce Absorption can be reduced. Note that the transparent conductive oxide film of Patent Document 2 is a laminate in which a fluorine-doped tin oxide film is laminated on a fluorine-doped tin oxide film as shown in FIG. It is configured as a membrane.
In Patent Document 2, the tin oxide film doped with fluorine and the tin oxide film not doped with fluorine are formed using an atmospheric pressure CVD method.

JP-A-2-168507 No. 2007/05811

“Full spectrum TCO-Improving mobility of SnO2: F by LP-CVD-” Masanobu Isshiki, Junich Okubo, Toru Ikeda and Satoru Takaki, ASAHI GLASS CO., LTD. October 7-8, 2010, Venue: Tokyo Tech Front

As described in paragraph [0031] of Patent Document 2, it is preferable to increase the thickness of the tin oxide film to some extent in order to increase the haze ratio. This is because when the thickness of the tin oxide film is increased, irregularities are formed on the surface of the tin oxide film. As described in paragraph [0038] of Patent Document 2, irregularities are formed on the surface of the tin oxide film. This is because the haze ratio is increased when there is.
As shown in FIG. 1, the C light source haze ratio of the fluorine-doped tin oxide film increases in proportion to the film thickness of the fluorine-doped tin oxide film. FIG. 1 shows the film thickness of a fluorine-doped tin oxide film for a fluorine-doped tin oxide film formed by an atmospheric pressure CVD method and a fluorine-doped tin oxide film formed by a low-pressure CVD method as described in Patent Documents 1 and 2. And a graph showing the relationship between the fluorine-doped tin oxide film and the C light source haze ratio.
Here, the atmospheric pressure CVD method and the reduced pressure CVD method were performed under the following conditions, respectively. Moreover, the base | substrate which forms a fluorine dope tin oxide film | membrane used the base | substrate similar to the Example mentioned later, ie, an alkali free glass substrate.
[Atmospheric pressure CVD method]
SnCl ₄ was used as the main material, H ₂ O was used as the auxiliary material, and HF was added to form a fluorine-doped tin oxide film on a glass substrate having a substrate temperature of 550 ° C. while changing the film thickness. The pressure during film formation was atmospheric pressure.
[Low pressure CVD method]
Source gas flow rate SnCl ₄ : 2 sccm
H ₂ O: 400 sccm
HF: 8 sccm
Atmospheric pressure: 100Pa
Substrate temperature: 360 ° C
As is clear from FIG. 1, the fluorine-doped tin oxide film formed by the low pressure CVD method has a lower C light source haze ratio than the fluorine-doped tin oxide film formed by the atmospheric pressure CVD method even if the film thickness is the same. .
Therefore, in order to achieve the same C light source haze ratio with the fluorine-doped tin oxide film formed by the atmospheric pressure CVD method, it is formed by the atmospheric pressure CVD method. It is necessary to make the film thickness larger than the fluorine-doped tin oxide film.

When the thickness of the fluorine-doped tin oxide film is increased under the same carrier electron density, the number of carrier electrons in the entire fluorine-doped tin oxide film increases, and thus the light transmittance decreases due to optical absorption. For this reason, in order to increase the thickness of the fluorine-doped tin oxide film without reducing the light transmittance, it is necessary to reduce the carrier electron density of the fluorine-doped tin oxide film.
However, it has been clarified that when the carrier electron density of the fluorine-doped tin oxide film is lowered, the mobility of carrier electrons is lowered as shown in FIG.

FIG. 2 shows the carrier electron density (number / cm ³ ) of the fluorine-doped tin oxide film and the mobility of carrier electrons (cm ² / V · s) for the fluorine-doped tin oxide film formed by using the low pressure CVD method. It is the graph which showed the relationship.
Here, the low pressure CVD method was performed under the following conditions. Moreover, the base | substrate which forms a fluorine dope tin oxide film | membrane used the base | substrate similar to the Example mentioned later, ie, an alkali free glass substrate.
Source gas flow rate SnCl ₄ : 2 sccm
H ₂ O: 400 sccm
HF: 0 to 8 sccm
Atmospheric pressure: 100Pa
Substrate temperature: 360 ° C
Deposition time: 20 minutes (equivalent to a film thickness of 800 nm)
The carrier electron mobility and carrier electron density of the fluorine-doped tin oxide film were measured in the same procedure as in the examples described later.
As shown in FIG. 2, the carrier electron density of the fluorine-doped tin oxide film can be lowered by reducing the flow rate of HF in the source gas. However, as apparent from FIG. 2, when the carrier electron density of the fluorine-doped tin oxide film is lowered, the mobility of carrier electrons is lowered.

In FIG. 2, in order to lower the carrier electron density of the fluorine-doped tin oxide film, the flow rate of HF was reduced among the source gases, but the substrate temperature at the time of film formation was reduced, and among the source gases, H ₂ O The carrier electron density of the fluorine-doped tin oxide film can also be lowered by increasing the flow rate of. Although not shown, the applicant of the present application tried these means, but in any of the methods, when the carrier electron density of the fluorine-doped tin oxide film was lowered, the mobility of carrier electrons was lowered.

The above problem will be described using the following equation regarding the sheet resistance of the fluorine-doped tin oxide film.
Sheet resistance R [Ω / □] = 1 / (sheet carrier electron density n_sheet [piece / cm ² ] × carrier charge e [C] × carrier electron mobility μ [cm ² / V · s]) (1)
Here, the sheet carrier electron density (n_sheet) is expressed by the following equation.
n_sheet [pieces / cm ² ] = carrier electron density n [pieces / cm ³ ] × fluorine-doped tin oxide film thickness d [nm] × 10 ⁻⁷ (2)
From the above formulas (1) and (2), if the sheet carrier electron density n_sheet and the carrier electron mobility μ are kept constant, the sheet resistance R is constant even if the thickness d of the fluorine-doped tin oxide film is changed. Will be kept.
However, if the thickness d of the fluorine-doped tin oxide film is increased while keeping the sheet carrier electron density n_sheet constant, the carrier electron density n decreases.
As shown in FIG. 2, when the carrier electron density n decreases, the carrier electron mobility μ decreases, so the sheet resistance R increases.
Here, in order to keep the sheet resistance R constant, it is necessary to increase the carrier electron density n or increase the thickness d of the fluorine-doped tin oxide film as much as the carrier electron mobility μ decreases. When any of these is increased, the sheet carrier electron density n_sheet increases.

When the sheet carrier electron density n_sheet increases, light absorption in the near infrared region (wavelength 800 to 2000 nm) increases as shown in FIG.
FIG. 3 shows the sheet carrier electron density n_sheet (number / cm ² ) of the fluorine-doped tin oxide film and the respective wavelengths of 500 nm, 1000 nm, 1500 nm, and 2000 nm for the fluorine-doped tin oxide film formed by using the low pressure CVD method. It is the graph which showed the relationship with the light absorptivity (%).
Here, the low pressure CVD method was performed under the following conditions. Moreover, the base | substrate which forms a fluorine dope tin oxide film | membrane used the base | substrate similar to the Example mentioned later, ie, an alkali free glass substrate.
Source gas flow rate SnCl ₄ : 2 sccm
H ₂ O: 400 sccm
HF: 0 to 8 sccm
Atmospheric pressure: 100Pa
Substrate temperature: 360 ° C
Deposition time: 20 minutes (equivalent to a film thickness of 800 nm)
As shown in FIG. 3, when the sheet carrier electron density n_sheet increases, light absorption in the near-infrared region with wavelengths of 1000 nm, 1500 nm, and 2000 nm increases.

In order to solve the above-described problems of the prior art, the present invention has a high carrier electron mobility, a high haze ratio, and a low sheet carrier electron density. An object is to provide a substrate with a conductive oxide film and a method for producing the same.
The substrate with a transparent conductive oxide film produced by the method of the present invention has a carrier electron mobility μ of 70 [cm ² / V · s] or more, a C light source haze ratio of 10% or more, and The sheet carrier electron density n_sheet is preferably 7.5 × 10 ¹⁵ (pieces / cm ² ) or less.

  The inventors of the present invention have prepared a laminated film of a tin oxide film not doped with fluorine and a tin oxide film doped with fluorine as a transparent conductive oxide film, and the film thickness satisfies a predetermined condition. Thus, it has been found that a substrate with a transparent conductive oxide film having a high carrier electron mobility and a low sheet carrier electron density can be obtained by using the low pressure CVD method.

The present invention has been made based on the above findings, and is a method for producing a substrate with a transparent conductive oxide film in which a transparent conductive oxide film is provided on a substrate having a smooth surface,
The transparent conductive oxide film is formed of a tin oxide film not doped with fluorine, and is formed of a first layer formed on the substrate and a tin oxide film doped with fluorine, and formed on the first layer. And at least a second layer,
The first layer and the second layer are formed using a CVD method under a pressure of 200 Pa or less,
The film thickness of the first layer is 1200 nm or more, the film thickness of the second layer is 100 nm or more,
The total film thickness of the tin oxide film not doped with fluorine contained in the transparent conductive oxide film is 1200 to 2000 nm,
Provided is a method for producing a substrate with a transparent conductive oxide film, characterized in that the total film thickness of a fluorine-doped tin oxide film contained in the transparent conductive oxide film is 100 to 600 nm.

In the method for producing a substrate with a transparent conductive oxide film according to the present invention, the substrate temperature at the time of forming the first layer by a CVD method is preferably 300 to 400 ° C.
In the method for producing a substrate with a transparent conductive oxide film according to the present invention, the substrate temperature at the time of forming the second layer by a CVD method is preferably 300 to 400 ° C.

In the method for producing a substrate with a transparent conductive oxide film of the present invention, the amount of water relative to tin tetrachloride in the raw material gas at the time of forming the first layer by the CVD method is a flow rate ratio (H ₂ O / SnCl ₄ ). It is preferable that it is 100-200.
In the method for producing a substrate with a transparent conductive oxide film of the present invention, the amount of water relative to tin tetrachloride in the raw material gas at the time of forming the second layer by the CVD method is a flow rate ratio (H ₂ O / SnCl ₄ ). It is preferable that it is 100-200.

In the method for producing a substrate with a transparent conductive oxide film of the present invention, the amount of hydrogen fluoride with respect to tin tetrachloride in the raw material gas at the time of forming the second layer by the CVD method is a flow rate ratio (HF / SnCl ₄ ). It is preferable that it is 4-16.

  Moreover, this invention provides the base | substrate with a transparent conductive oxide film manufactured by the manufacturing method of the base | substrate with a transparent conductive oxide film of this invention.

The substrate with a transparent conductive oxide film of the present invention has a carrier electron mobility μ of 70 [cm ² / V · s] or more, a C light source haze ratio of 10% or more, and a sheet carrier electron density. It is preferable that n_sheet is 7.5 × 10 ¹⁵ (pieces / cm ² ) or less.

Further, the substrate with a transparent conductive oxide film of the present invention has a haze ratio at a wavelength of 1000 nm of 1.5% or more, a sheet resistance of 10 Ω / □ or less, and a carrier electron mobility μ of 70 [cm ^2. / V · s] and the light absorptance at a wavelength of 1500 nm is preferably 8% or less.

In the method of the present invention, as the transparent conductive oxide film, a laminated film of a tin oxide film not doped with fluorine and a tin oxide film doped with fluorine is used. Thus, by forming using the low pressure CVD method, a substrate with a transparent conductive oxide film having high carrier electron mobility, high haze ratio, and low sheet carrier electron density is obtained. Specifically, the carrier electron mobility μ is 70 [cm ² / V · s] or more, the C light source haze ratio is 10% or more, and the sheet carrier electron density n_sheet is 7.5 × 10 ^15. A substrate with a transparent conductive oxide film of (pieces / cm ² ) or less is obtained.
Since the substrate with a transparent conductive oxide film obtained by the method of the present invention has a low sheet carrier electron density, there is little light absorption in the visible to near-infrared wavelength region, and particularly in the near-infrared wavelength region. Light absorption is less than that of a conventional substrate with a transparent conductive oxide film using a fluorine-doped tin oxide film. Moreover, since the film thickness of the transparent conductive oxide film can be increased, the C light source haze ratio is as high as 10% or more, and in particular, the haze ratio in the near infrared wavelength region is improved. Due to these optical characteristics in the near-infrared wavelength region, when used as an incident light side electrode of a so-called tandem solar cell in which a photoelectric conversion layer made of amorphous silicon and a photoelectric conversion layer made of microcrystalline silicon are laminated. , The light utilization efficiency is improved.

FIG. 1 shows a fluorine-doped tin oxide film formed by atmospheric pressure CVD method and a fluorine-doped tin oxide film formed by low-pressure CVD method. It is the graph which showed the relationship between C light source haze rate (%). FIG. 2 shows the carrier electron density (number / cm ³ ) of the fluorine-doped tin oxide film and the mobility of carrier electrons (cm ² / V · s) for the fluorine-doped tin oxide film formed by using the low pressure CVD method. It is the graph which showed the relationship. FIG. 3 shows the sheet carrier electron density n_sheet (number / cm ² ) of the fluorine-doped tin oxide film and the respective wavelengths of 500 nm, 1000 nm, 1500 nm, and 2000 nm for the fluorine-doped tin oxide film formed by using the low pressure CVD method. It is the graph which showed the relationship with the light absorptivity (%). 4, the laminated film formed by low pressure CVD method (laminated film of a SnO ₂ film and the fluorine-doped SnO ₂ film), a carrier electron density of the laminated film (the number / cm ^3), the carrier electrons It is the graph which showed the relationship with mobility (cm < ² > / V * s). In FIG. 4, the plot of FIG. 2 is also shown. FIG. 5 is a diagram illustrating a laminated film (a laminated film of a SnO ₂ film and a fluorine-doped SnO ₂ film) formed by using a low pressure CVD method, a sheet carrier electron density n_sheet (number / cm ² ) of the laminated film, and 500 nm. , 1000 nm, 1500 nm, and 2000 nm are graphs showing the relationship with the light absorption rate (%) for each wavelength. FIG. 6 is a graph in which only the plot relating to the light absorption rate at a wavelength of 1500 nm is extracted from the plots of FIGS. 3 and 5. FIG. 7 shows the film thickness of the laminated film (stacked film of SnO ₂ film and fluorine-doped SnO ₂ film) formed by using the low pressure CVD method and the haze ratio for each wavelength of 550 nm and 1000 nm. It is the graph which showed the relationship with (%).

Hereinafter, the manufacturing method of the base | substrate with a transparent conductive oxide film of this invention is demonstrated.
The method for producing a substrate with a transparent conductive oxide film of the present invention is a method for producing a substrate with a transparent conductive oxide film in which a transparent conductive oxide film is provided on the substrate.
In the production method of the present invention, the transparent conductive oxide film formed on the substrate is made of a tin oxide film (SnO ₂ film) not doped with fluorine, and the first layer formed on the substrate, fluorine A tin oxide film doped with (fluorine-doped SnO ₂ film), and at least a second layer formed on the first layer. The transparent conductive oxide film of the present invention forms a laminated film in which the first layer and the second layer are formed on a substrate. In addition, it is described in the above that the first layer and the second layer are included in a small amount because one or more sets of stacked films (SnO ₂ film) are further formed on the stacked films of the first layer and the second layer. And a fluorine-doped SnO ₂ film formed in this order).

In the production method of the present invention, SnO ₂ film serving as the first layer, and, using the CVD method for forming fluorine-doped SnO ₂ film serving as the second layer. The reason for this is the ease of control of the film thickness and the good coverage.
However, SnO ₂ film serving as the first layer, and, during the formation of the fluorine-doped SnO ₂ film serving as the second layer, using a CVD method at a pressure of at 200 Pa. Hereinafter, in this specification, a CVD method performed under a pressure of 200 Pa or less is referred to as a “low pressure CVD method”.
Here, it is more preferable that the atmospheric pressure when performing the low pressure CVD method is 100 Pa or less.
However, if the atmospheric pressure when performing the low pressure CVD method is too low, the film material (the number of atoms of the film material) reaching the surface of the substrate is decreased, so that the film formation rate is lowered and is not practical. For this reason, it is preferable that the atmospheric pressure at the time of implementing low pressure CVD method is 10 Pa or more, It is more preferable that it is 20 Pa or more, It is further more preferable that it is 50 Pa or more.

In the present invention, the SnO ₂ film as the first layer and the fluorine-doped SnO ₂ film as the _second layer are formed by performing CVD under a pressure of 200 Pa or less, thereby reducing SnO _2. A film and a fluorine-doped SnO ₂ film can be formed.
In Patent Document 2, the transparent conductive oxide film is a laminated film of a tin oxide layer doped with fluorine (fluorine-doped SnO ₂ film) and a tin oxide layer not doped with fluorine (SnO ₂ film). However, since the atmospheric pressure CVD method is used for forming these tin oxide layers (fluorine-doped SnO ₂ film and SnO ₂ film), the formed tin oxide layers (fluorine-doped SnO ₂ film and SnO ₂ film) It contains a lot of impurities. For this reason, if the film thickness is increased, the transmittance of light in the visible to near-infrared wavelength region is reduced by light absorption, so the film thickness of the tin oxide layer (fluorine-doped SnO ₂ film and SnO ₂ film) is increased. Therefore, the upper limit of the total film thickness of the laminated film is set to 1200 nm. In Patent Document 2, the ratio of the thickness of the tin oxide layer (SnO ₂ film) not doped with fluorine to the thickness of the tin oxide layer doped with fluorine (fluorine-doped SnO ₂ film) in the laminated film is disclosed. 3/7 to 7/3, but in order to reduce the sheet resistance of the transparent conductive oxide film, a tin oxide layer (SnO ₂ film not doped with fluorine) is used. ), The thickness of the tin oxide layer doped with fluorine (fluorine-doped SnO ₂ film) needs to be increased. For this reason, in the Example described in this document, the thickness of the tin oxide layer doped with fluorine (fluorine-doped SnO ₂ film) is larger.

In contrast, in the present invention, by using the low pressure CVD method, SnO ₂ film serving as the first layer, and, since the impurity of fluorine-doped SnO ₂ film serving as the second layer is reduced, increasing the thickness Even so, there is little decrease in the transmittance of light in the wavelength range from visible light to near infrared due to light absorption.
In the present invention, the film thickness of the SnO ₂ film as the first layer is 1200 nm or more, and the film thickness of the fluorine-doped SnO ₂ film as the second layer is 100 nm or more. Therefore, the upper limit of the total film thickness of the laminated film is set to 1200 nm, and the thickness of the tin oxide layer (fluorine-doped SnO ₂ film) doped with fluorine rather than the tin oxide layer (SnO ₂ film) not doped with fluorine. The structure of the laminated film is clearly different from that of Patent Document 2 in which the thickness needs to be increased.

Since the laminated film of Patent Document 2 includes a tin oxide layer (fluorine-doped SnO ₂ film and SnO ₂ film) constituting the laminated film by an atmospheric pressure CVD method, since it contains a large amount of impurities, visible light due to light absorption Although the film thickness could not be increased in order to reduce the decrease in light transmittance in the near-infrared wavelength region, the SnO ₂ film as the first layer is used in the present invention because the reduced pressure CVD method is used. Even if the film thickness is 1200 nm or more, impurities contained in the SnO ₂ film are reduced. Therefore, a decrease in light transmittance in the wavelength range from visible light to near infrared due to light absorption is also reduced. Here, since the crystallinity of the SnO ₂ film as the first layer increases as the film thickness increases, the vicinity of the surface of the SnO ₂ film having a film thickness of 1200 nm or more is in a state of high crystallinity. The crystallinity of the fluorine-doped SnO ₂ film as the second layer increases as the film thickness increases. However, since the vicinity of the surface of the SnO ₂ film serving as the base is in a state of high crystallinity, the second layer The fluorine-doped SnO ₂ film has a high crystallinity even if the film thickness is small. Then, the higher the crystallinity of the fluorine-doped SnO ₂ film, the higher the mobility of carrier electrons. Therefore, as shown in FIG. 4, high carrier electron mobility can be achieved with a lower carrier electron density.

FIG. 4 shows a layered film formed by using a low pressure CVD method, that is, a layered film of a SnO ₂ film as a first layer and a fluorine-doped SnO ₂ film as a second layer. 5 is a graph showing the relationship between electron density (pieces / cm ³ ) and carrier electron mobility (cm ² / V · s). In FIG. 4, the plot of FIG. 2 is also shown.
Here, the low pressure CVD method was performed under the following conditions. Moreover, the base | substrate which forms a fluorine dope tin oxide film | membrane used the base | substrate similar to the Example mentioned later, ie, an alkali free glass substrate.
Source gas flow rate SnCl ₄ : 2 sccm
H ₂ O: 400 sccm
HF: 0 sccm (SnO ₂ film), 8 sccm (fluorine-doped SnO ₂ film)
Atmospheric pressure: 100Pa
Substrate temperature: 360 ° C
By changing the film formation time of the SnO ₂ film and the fluorine-doped SnO ₂ film, the film thickness of these films in the laminated film was changed. The total film thickness of the laminated film ranges from about 800 nm to about 3200 nm, and the film thicknesses of the SnO ₂ film and the fluorine-doped SnO ₂ film range from about 200 nm to about 2700 nm and from about 200 nm to about 600 nm, respectively. there were.
As shown in FIG. 4, in the laminated film of the SnO ₂ film as the first layer and the fluorine-doped SnO ₂ film as the second layer, the carrier electron density as compared with the case of only the fluorine-doped SnO ₂ film. There was very little decrease in the mobility μ of carrier electrons with respect to the decrease in n.

FIG. 5 shows a sheet carrier electron density n_sheet of a laminated film of a SnO ₂ film as a first layer and a fluorine-doped SnO ₂ film as a second layer formed by using a low pressure CVD method. It is the graph which showed the relationship between (piece / cm < ² >) and the light absorptivity (%) for each wavelength of 500 nm, 1000 nm, 1500 nm, and 2000 nm.
As shown in FIG. 5, the laminated film of the SnO ₂ film as the first layer and the fluorine-doped SnO ₂ film as the second layer also includes the case of only the fluorine-doped SnO ₂ film shown in FIG. Similarly, when the sheet carrier electron density n_sheet increases, light absorption in the near infrared region increases.
FIG. 6 is a graph in which only the plot relating to the light absorption rate at a wavelength of 1500 nm is extracted from the plots of FIGS. 3 and 5.
As shown in FIG. 6, when the sheet carrier electron density is the same, the light absorption rate at a wavelength of 1500 nm is as follows: a fluorine-doped tin oxide film, a laminated film (SnO ₂ film as the first layer, and There was no difference between the fluorine-doped SnO ₂ film and the laminated film. From this result, it is understood that when the sheet carrier electron density is the same, the light absorption rate at a wavelength of 1500 nm does not depend on the film thickness of the transparent conductive oxide film.
Although not shown, the light absorptance in other near-infrared wavelength regions (wavelengths 1000 nm and 2000 nm) also shows the same tendency as in FIG.

From the results of FIGS. 4 to 6, it is preferable to lower the sheet carrier electron density in order to reduce the light absorption in the near infrared wavelength region as long as the required carrier electron mobility can be achieved. I understand.
Here, from the relational expression (the above formula (2)) regarding the sheet carrier electron density (n_sheet), in order to reduce the sheet carrier electron density, among the carrier electron density n and the film thickness of the fluorine-doped tin oxide film, One of them can be lowered. Of these, the setting of conditions is easier when the thickness of the fluorine-doped tin oxide film is reduced.
For this reason, in the present invention, the film thickness of the fluorine-doped SnO ₂ film as the _second layer is made smaller than the film thickness of the SnO ₂ film as the first layer.

Next, the film thicknesses of the first layer and the second layer constituting the laminated film will be described.
In the present invention, the thickness of the SnO ₂ film as the first layer is set to 1200 nm or more. When the film thickness of the SnO ₂ film as the first layer is less than 1200 nm, the crystallinity near the surface of the SnO ₂ film is lowered. Therefore, the crystallinity of the fluorine-doped SnO ₂ film as the second layer is also lowered, and the mobility of carrier electrons is lowered. Increasing the film thickness increases the crystallinity of the fluorine-doped SnO ₂ film, but in this case, the light absorption increases, so that the light transmittance in the visible to near-infrared wavelength range decreases.
The film thickness of the SnO ₂ film as the first layer is preferably 1400 nm or more, more preferably 1600 nm or more, and further preferably 1800 nm or more.
However, if the thickness of the SnO ₂ film as the first layer is too large, the light absorption increases and the light transmittance in the wavelength range from visible light to near infrared decreases, so the thickness of the SnO ₂ film is 2000 nm. The following. Here, when one or more sets of laminated films (a laminated film in which a SnO ₂ film and a fluorine-doped SnO ₂ film are formed in this order) are further formed on the laminated film of the first layer and the second layer, all The total film thickness of the SnO ₂ film is 2000 nm or less.
The SnO ₂ film as the first layer is a film that contains fewer dopants and has less light absorption than the second layer doped with fluorine (fluorine-doped SnO ₂ film). As the thickness increases, light absorption increases even in the case of the first layer of SnO ₂ film.
Here, since the SnO ₂ film containing no dopant is a film with few carrier electrons, the light absorption in the visible light region tends to increase more than the light absorption in the near infrared region. For this reason, the thickness of the SnO ₂ film as the first layer should be 2000 nm or less when combined with a solar cell having high power generation efficiency particularly in the visible light region (for example, an amorphous-Si solar cell). Is preferred.
In addition, since the low pressure CVD method generally has a lower film formation rate than the atmospheric pressure CVD method, it is preferable from the viewpoint of film formation cost that the SnO ₂ film as the first layer is smaller.

In the present invention, the fluorine-doped SnO ₂ film as the _second layer is 100 nm or more. If the fluorine-doped SnO ₂ film as the second layer is less than 100 nm, the mobility of carrier electrons decreases.
The film thickness of the fluorine-doped SnO ₂ film as the second layer is preferably 200 nm or more, more preferably 300 nm or more, and further preferably 400 nm or more.

However, if the thickness of the fluorine-doped SnO ₂ film as the second layer is too large, it increased light absorption, since light transmittance in the wavelength range of near infrared from the visible light is lowered, the fluorine-doped SnO ₂ film The film thickness is 400 nm or less. Here, when one or more sets of laminated films (a laminated film in which a SnO ₂ film and a fluorine-doped SnO ₂ film are formed in this order) are further formed on the laminated film of the first layer and the second layer, all The total film thickness of the fluorine-doped SnO ₂ film is 600 nm or less.
The total film thickness of the fluorine-doped SnO ₂ film is preferably 500 nm or less.

The fluorine content in the fluorine-doped SnO ₂ film as the second layer is preferably 0.01 to 4 mol% in terms of fluorine content with respect to SnO ₂ , since the carrier electron density becomes appropriate.
The fluorine content in the fluorine-doped SnO ₂ film is more preferably 0.01 to 2 mol%, further preferably 0.02 to 1 mol% in terms of the fluorine content relative to SnO ₂ .

Next, with regard to the conditions for the low-pressure CVD method used for forming the substrate on which the transparent conductive oxide film is formed, the SnO ₂ film as the first layer, and the fluorine-doped SnO ₂ film as the second layer, Describe.

<Substrate>
As the substrate on which the transparent conductive oxide film is formed, a substrate having a smooth surface on which the transparent conductive oxide film is formed is used. Here, the smooth surface means that the arithmetic average roughness (Ra) is 10 nm or less. In addition, arithmetic mean roughness (Ra) is based on JIS B 0601 (2001).
The surface on which the transparent conductive oxide film is formed is required to be smooth because if the surface on which the transparent conductive oxide film is formed is not smooth, the light beam of the transparent conductive oxide film formed on the surface This is because absorption increases. The surface on which the transparent conductive oxide film is formed is preferably 2 nm or less in Ra, more preferably 1 nm or less in Ra.

Since the surface on which the transparent conductive oxide film is formed is required to be smooth, the shape of the substrate is a plate having a smooth flat surface. Examples of the substrate include a glass substrate, a ceramic substrate, a plastic substrate, and a metal substrate. The substrate is preferably a transparent substrate excellent in translucency, and a glass substrate is preferable from the viewpoint of strength and heat resistance. As the glass substrate, use a transparent glass plate made of colorless and transparent soda lime silicate glass, aluminosilicate glass, borate glass, lithium aluminosilicate glass, quartz glass, borosilicate glass substrate, non-alkali glass substrate, and other various glasses. Can do.
When used as an incident light side electrode of a photoelectric conversion element such as a solar cell, the glass substrate preferably has a thickness of 0.2 to 6.0 mm. Within this range, the strength of the glass substrate is high and the transmittance is high. Moreover, it is desirable that it is sufficiently insulating and has high chemical and physical durability.
In addition, in the case of a glass substrate made of glass containing sodium such as soda lime silicate glass or a glass substrate made of low alkali content glass, an alkali component from the glass to the transparent conductive oxide film formed on the upper surface thereof In order to minimize the diffusion of silicon, an alkali barrier layer such as a silicon oxide film, an aluminum oxide film, or a zirconium oxide film may be provided on the glass substrate surface.
Moreover, you may further have the layer for reducing the difference in the refractive index of the surface of a glass substrate, and the layer provided on it on the surface of a glass substrate.

<Formation of SnO ₂ film by low pressure CVD method>
The formation of the SnO ₂ film by the low pressure CVD method may be performed by the following procedure.
In a state where the chamber is maintained at a predetermined pressure of 200 Pa or less, a substrate disposed at a predetermined position in the chamber is maintained at a predetermined substrate temperature, tin tetrachloride (SnCl ₄ ) as a source gas, and By simultaneously spraying water (H ₂ O) from a source gas supply nozzle together with a carrier gas such as nitrogen or argon, a SnO ₂ film can be formed on the substrate.

When the low pressure CVD method is performed, the amount of water (H ₂ O) to tin tetrachloride (SnCl ₄ ) in the raw material gas is preferably 100 to 200 in terms of a flow rate ratio (H ₂ O / SnCl ₄ ). H ₂ O acts as an oxidizing agent for proceeding the oxidation reaction from SnCl ₄ to SnO ₂ . Therefore, if the amount of H ₂ O is too small, the oxidation reaction becomes insufficient and the formed film may be colored. Therefore, the flow rate ratio (H ₂ O / SnCl ₄ ) is preferably 100 or more. On the other hand, when H ₂ O is large, because there is no problem in the characteristic of the film formed, which becomes difficult to supply a large amount of H ₂ O on the equipment, the flow rate ratio (H ₂ O / SnCl ₄₎ And preferably 200 or less.
The flow rate ratio (H ₂ O / SnCl ₄ ) is more preferably 120 to 200, and further preferably 150 to 200.

When the low pressure CVD method is performed, the substrate temperature is preferably 300 to 400 ° C. When the substrate temperature is lower than 300 ° C., the film formation rate of the SnO ₂ film is lowered, and the carrier electron density of the formed SnO ₂ film is increased, so that the sheet carrier of the formed transparent conductive oxide film The electron density increases. When the substrate temperature is higher than 400 ° C., the mobility of carrier electrons in the formed transparent conductive oxide film decreases.
The substrate temperature is more preferably 340 to 390 ° C, and further preferably 360 to 380 ° C.

When carrying out the low pressure CVD method, the amount of carrier gas (for example, nitrogen) with respect to tin tetrachloride (SnCl ₄ ) in the raw material gas is preferably 1 to 50 in terms of a flow rate ratio (carrier gas / SnCl ₄ ).

When carrying out the low pressure CVD method, the amount of carrier gas (for example, nitrogen) with respect to water (H ₂ O) in the raw material gas is preferably 0.2 to 5 in terms of flow rate ratio (carrier gas / H ₂ O).

<Formation of fluorine-doped SnO ₂ film by low pressure CVD method>
The formation of the fluorine-doped SnO ₂ film by the low pressure CVD method may be performed according to the following procedure.
With the chamber maintained at a predetermined pressure of 200 Pa or less, the substrate on which the SnO ₂ film is formed by the above procedure is placed at a predetermined position in the chamber, and the substrate is held at a predetermined substrate temperature. By simultaneously blowing the source gas tin tetrachloride (SnCl ₄ ), water (H ₂ O), and hydrogen fluoride (HF) together with the carrier gas such as nitrogen and argon from the source gas supply nozzle, it is possible to form a fluorine-doped SnO ₂ film on the SnO ₂ film.

When the low pressure CVD method is performed, the amount of water (H ₂ O) to tin tetrachloride (SnCl ₄ ) in the raw material gas is preferably 100 to 200 in terms of a flow rate ratio (H ₂ O / SnCl ₄ ). H ₂ O acts as an oxidizing agent for proceeding the oxidation reaction from SnCl ₄ to SnO ₂ . Therefore, if the amount of H ₂ O is too small, the oxidation reaction becomes insufficient and the formed film may be colored. Therefore, the flow rate ratio (H ₂ O / SnCl ₄ ) is preferably 100 or more. On the other hand, when H ₂ O is large, because there is no problem in the characteristic of the film formed, which becomes difficult to supply a large amount of H ₂ O on the equipment, the flow rate ratio (H ₂ O / SnCl ₄₎ And preferably 200 or less.
The flow rate ratio (H ₂ O / SnCl ₄ ) is more preferably 120 to 200, and further preferably 150 to 200.

When the low pressure CVD method is performed, the amount of hydrogen fluoride (HF) to tin tetrachloride (SnCl ₄ ) in the raw material gas is preferably 4 to 16 in terms of a flow rate ratio (HF / SnCl ₄ ). If the amount of HF that is a dopant raw material is too small, the carrier concentration in the film to be formed becomes low. Therefore, the flow rate ratio (HF / SnCl ₄ ) is preferably 4 or more. If the amount of HF is too large, it does not work as a dopant for forming carriers, but fluorine taken as a simple impurity increases and causes a decrease in mobility. Therefore, the flow rate ratio (HF / SnCl ₄ ) is preferably 16 or less.

When the low pressure CVD method is performed, the substrate temperature is preferably 300 to 400 ° C. When the substrate temperature is lower than 300 ° C., the deposition rate of the fluorine-doped SnO ₂ film is extremely lowered, and the reaction does not proceed sufficiently, so that the amount of impurities remaining in the film increases. The reason is unknown when the substrate temperature is higher than 400 ° C., but the inventors have found that the mobility of the transparent conductive oxide film formed tends to decrease.
The substrate temperature is more preferably 340 to 390 ° C, and further preferably 360 to 380 ° C.

When carrying out the low pressure CVD method, the amount of carrier gas (for example, nitrogen) with respect to tin tetrachloride (SnCl ₄ ) in the raw material gas is preferably 1 to 50 in terms of a flow rate ratio (carrier gas / SnCl ₄ ).

When carrying out the low pressure CVD method, the amount of carrier gas (for example, nitrogen) with respect to water (H ₂ O) in the raw material gas is preferably 0.2 to 5 in terms of flow rate ratio (carrier gas / H ₂ O).

The substrate with a transparent conductive oxide film of the present invention obtained by the above-described procedure has high carrier electron mobility, and the carrier electron mobility μ measured by the procedure described in Examples described later is 70 [cm ^2. / V · s] or more.
As a result, the sheet resistance of the substrate with a transparent conductive oxide film of the present invention is 10Ω / □ or less.

Further, the substrate with a transparent conductive oxide film of the present invention obtained by the above-described procedure has a sheet carrier electron density n_sheet of 7.5 × 10 ¹⁵ (pieces / cm ² ) or less. As a result, the light absorptance in the near infrared wavelength range is reduced. Specifically, the light absorptance at a wavelength of 1500 nm measured by the procedure described in the examples described later is 8% or less.

  Moreover, the base | substrate with a transparent conductive oxide film of this invention obtained by an above-described procedure has a high haze rate, and C light source haze rate becomes 10% or more. In addition, the haze ratio in the near-infrared wavelength range is also increased. Specifically, the haze ratio at a wavelength of 1000 nm measured by the procedure described in the examples described later is 1.5% or more.

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to this.
Example 1
A tin oxide film not doped with fluorine was formed as a first layer on an alkali-free glass substrate under the following film formation conditions.
SnCl ₄ : 2 sccm
H ₂ O: 400 sccm
HF: 0 sccm
Atmospheric pressure: 100Pa
Substrate temperature: 360 ° C
Next, a tin oxide film doped with fluorine was formed as the second layer under the following film formation conditions.
SnCl ₄ : 2 sccm
H ₂ O: 400 sccm
HF: 8 sccm
Atmospheric pressure: 100Pa
Substrate temperature: 360 ° C
About the obtained base | substrate with a transparent conductive oxide film, a carrier electron mobility, a carrier electron density, and sheet resistance cut a sample into 1 cm x 1 cm, and used Van der Pauw method using BioRad HL5500. It was obtained by performing the measurement.
The film thickness was measured with a stylus type surface shape measuring device DEKTAK150 manufactured by Veeco.
The results are shown in Table 1.

Similarly, Example 2 and Comparative Examples 1 to 3 were formed by changing the film thicknesses of the first layer and the second layer as shown in Table 1.
From the results of Table 1, the substrate with a transparent conductive oxide film of the present invention has a carrier electron mobility μ of 70 [cm ² / V · s] or more, a C light source haze ratio of 10% or more, In addition, the sheet carrier electron density n_sheet was 7.5 × 10 ¹⁵ (pieces / cm ² ) or less.
Since the sheet carrier electron density is 7.5 × 10 ¹⁵ (pieces / cm ² ), it can be estimated from FIG. 3 that the light absorption at a wavelength of 1500 nm is 8% or less.

Claims (9)

A method for producing a substrate with a transparent conductive oxide film in which a transparent conductive oxide film is provided on a substrate having a smooth surface,
The transparent conductive oxide film is formed of a tin oxide film not doped with fluorine, and is formed of a first layer formed on the substrate and a tin oxide film doped with fluorine, and formed on the first layer. And at least a second layer,
The first layer and the second layer are formed using a CVD method under a pressure of 200 Pa or less,
The film thickness of the first layer is 1200 nm or more, the film thickness of the second layer is 100 nm or more,
The total film thickness of the tin oxide film not doped with fluorine contained in the transparent conductive oxide film is 1200 to 2000 nm,
The manufacturing method of the base | substrate with a transparent conductive oxide film characterized by the total film thickness of the tin oxide film | membrane doped with the fluorine contained in the said transparent conductive oxide film being 100-600 nm.   The manufacturing method of the base | substrate with a transparent conductive oxide film of Claim 1 whose base | substrate temperature at the time of formation of the said 1st layer by CVD method is 300-400 degreeC.   The manufacturing method of the base | substrate with a transparent conductive oxide film of Claim 1 or 2 whose base | substrate temperature at the time of formation of the said 2nd layer by CVD method is 300-400 degreeC. The amount of water with respect to tin tetrachloride in the raw material gas at the time of forming the first layer by the CVD method is 100 to 200 in flow rate ratio (H ₂ O / SnCl ₄ ). Of manufacturing a substrate with a transparent conductive oxide film. 5. The amount of water relative to tin tetrachloride in the raw material gas at the time of forming the second layer by a CVD method is 100 to 200 as a flow rate ratio (H ₂ O / SnCl ₄ ). Of manufacturing a substrate with a transparent conductive oxide film. The amount of hydrogen fluoride with respect to tin tetrachloride in the raw material gas at the time of formation of the second layer by a CVD method is ₄ to 16 in terms of a flow rate ratio (HF / SnCl ₄ ). Of manufacturing a substrate with a transparent conductive oxide film.   A substrate with a transparent conductive oxide film produced by the method for producing a substrate with a transparent conductive oxide film according to claim 1. The carrier electron mobility μ is 70 [cm ² / V · s] or more, the C light source haze ratio is 10% or more, and the sheet carrier electron density n_sheet is 7.5 × 10 ¹⁵ (pieces / cm ^2). The substrate with a transparent conductive oxide film according to claim 7, wherein: A haze ratio at a wavelength of 1000 nm is 1.5% or more, a sheet resistance is 10 Ω / □ or less, a carrier electron mobility μ is 70 [cm ² / V · s] or more, and a light beam having a wavelength of 1500 nm The substrate with a transparent conductive oxide film according to claim 7 or 8, wherein the absorptance is 8% or less.