JP2001291882A - Thin film manufacturing method - Google Patents

Abstract

[PROBLEMS] For example, a silicon-based thin film that is an n-type impurity semiconductor and a silicon-based thin film that is a p-type impurity semiconductor, which are components of a photovoltaic element such as an amorphous silicon solar cell, are intrinsic. A method for forming a thickest intrinsic semiconductor layer at a high speed and without causing damage to a base which adversely affects device performance in manufacturing a laminated body bonded via a silicon-based thin film as a semiconductor. SOLUTION: A reaction gas such as a silane-based gas is supplied into a reaction chamber such as an inductively coupled plasma generator maintained in a vacuum state, and a reaction gas is supplied to a plasma generation electrode disposed inside or outside the reaction chamber. 10 ¹⁰ cm by applying an RF power ^{- 3} or more of the reaction gas plasma is generated in the electron density, in forming a thin film such as a silicon-based thin film on the surface of the installed base in the reaction chamber The high-frequency power applied to the plasma generating electrode is set low at the start of film formation, and the high-frequency power is increased continuously or stepwise when a film having a specific thickness is formed, thereby forming a thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a thin film,
And a method for manufacturing a photovoltaic element represented by a solar cell using the method for manufacturing a thin film.

[0002]

2. Description of the Related Art At present, as a photovoltaic element used for a solar cell or the like, a photovoltaic element using an amorphous silicon film as a photoelectric conversion layer (hereinafter referred to as an amorphous photovoltaic element) because of its high performance and ease of manufacture. Is also widely used.

A typical amorphous photovoltaic element currently used has a structure in which a transparent conductive film, a semiconductor layer made of amorphous silicon, and a collecting electrode are laminated in this order on a transparent substrate such as glass or resin. Have. In the photovoltaic element, a semiconductor layer is a p-type semiconductor layer in order from a lower layer,
Since it is an intrinsic (i-type) semiconductor layer and an n-type semiconductor layer,
It is generally called a pin type structure.

Further, a metal electrode made of a metal such as aluminum or silver, a transparent conductive film layer, a transparent conductive layer, or the like is formed on a substrate made of glass, silicon, a heat-resistant polymer or the like or a metal substrate made of stainless steel or the like.
In recent years, a photovoltaic element having a nip type structure in which a type semiconductor layer, an intrinsic (i-type) semiconductor layer, a p-type semiconductor layer, and a transparent conductive film layer are sequentially stacked has also become common.

[0005] In these conventional amorphous photovoltaic devices, the lamination of semiconductor layers is performed by chemical vapor deposition (CVD).
Physical vapor deposition (PVD)
Method) or the like, but it is possible to suppress the generation of structural defects such as dangling bonds (unbonded hands) to a low level and efficiently form a three-dimensional silicon network structure. For this reason, generally, a capacitively coupled plasma (CVD) CVD method (the CVD method generally uses an RF from a high frequency wavelength range to be used).
Although it is often referred to as a -CVD method, in this specification, CCP-CVD is used in the following, focusing on a plasma generation method.

In this method, a film-forming material gas such as monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used as it is.
Alternatively, a high-frequency electric field is generated by applying high-frequency electric power between two electrodes arranged opposite to each other in the vacuum reaction chamber while being introduced into the vacuum reaction chamber together with a hydrogen gas for dilution or the like. In this electric field, electrons collide with neutral molecules of the source gas to form high-frequency plasma to decompose the source gas and form a silicon thin film on the surface of the substrate placed on one electrode. is there.

However, the CCP-CVD method requires a high reaction gas pressure, so that a polymer-like decomposition product is generated by a secondary reaction in a gas phase, There is a possibility that the quality of the thin film may be deteriorated due to the contamination of the chamber wall due to the discharge or the adhesion of the substance to the electrode due to the discharge.

Further, in this method, since the electron density of the plasma is as low as, for example, 10 ⁹ cm ⁻³ or less, the deposition rate of silicon is about 0.1 to 0.3 nm / sec. Although it has the characteristic of being obtained, it takes a long time to form an intrinsic semiconductor layer requiring a thickness of several hundred nm, which is inefficient. A hydrogen dilution method in which a film forming material gas such as monosilane (SiH ₄ ) is accompanied by a hydrogen gas for dilution at a flow rate of 5 to 100 times and introduced into a vacuum reaction chamber {“Towards Large-Area, High Efficiency a
-Si / a-SiGe Tandem Solar Cells ", S.Okamoto, etc., 11 ^th
International Photovoltaic Science and Engineerin
g Conference Proceedings (1999), pp.45-48}, it is possible to increase the deposition rate without deteriorating the quality of the thin film. It is necessary to use a large amount of high-risk gas, which not only increases the equipment and labor required for storage and processing, but also increases the cost.

In order to efficiently stack the intrinsic semiconductor layers, instead of the conventional CCP-CVD method, the decomposition efficiency of the source gas is high, and the electron density of the high electron density can be reduced. Attempts have been made to increase the film formation rate by using a plasma CVD method using plasma. As the high-density plasma CVD method, inductively coupled plasma (IC
P) CVD (hereinafter sometimes abbreviated as ICP-CVD), ECR-CVD, helicon-wave CVD, microwave CVD, etc. are known.
Since the CVD method is capable of forming a thin film at a high speed over a large area without unevenness in thickness, the CVD method is attracting attention as a method for manufacturing a silicon-based thin film or the like.

[0010] In the ICP-CVD method, high-frequency power is applied to a high-frequency coil (antenna) to generate inductively coupled plasma (ICP), and a silicon-based material is placed on a substrate placed opposite to the high-frequency coil. It is intended to form a thin film or the like, for example, ¹⁰ 10 ~10 ¹² cm ^- high electron density plasma of about ³ is obtained, the effective radical species by adjusting the plasma generation condition (SiH ₃ radicals) can often generate a It is. In addition, the generation of ionic species that may adversely affect the growth surface of the thin film or the interface with the underlying layer is small, and the reaction can be performed even at a low pressure of, for example, 0.3 to 30 mTorr.

The apparatus used for the IPC-CVD method is as follows:
Unlike an apparatus used in the conventional CCP-CVD method, there is no need to use a counter electrode, so that the space inside the apparatus has a degree of freedom. For this reason, for example, it is possible to increase the effective utilization rate of the reaction gas by installing a reaction gas supply nozzle facing the substrate stage.

As such an apparatus for the IPC-CVD method, Japanese Patent Laid-Open Publication No. Hei 10-27762 discloses a spiral high-frequency coil installed above the reaction chamber via a window made of an insulator such as quartz. The new device has also been replaced by the Japanese Journal of Applied Physics.
{Jpn. J. Appl. Phys. Vol. 36 (1997), pp.3714-3720}
Discloses an internal excitation type inductively coupled plasma CVD apparatus capable of generating a stable plasma at a low reaction pressure and a low voltage by disposing a high frequency coil inside a reaction chamber.

[0013]

SUMMARY OF THE INVENTION However, the ICP
-When laminating an intrinsic semiconductor layer by a method using high-density plasma such as a CVD method, a lower conductive semiconductor layer (p-type semiconductor layer or n-type semiconductor layer) is damaged by the high electron density plasma, and as a result, As a result, there has been a problem that the characteristics of the photovoltaic element are impaired.

In order to avoid such a problem, a buffer layer is provided between the conductive semiconductor layer and the intrinsic semiconductor layer to protect the surfaces of the transparent conductive film and the conductive semiconductor layer from high electron density plasma. Has been done. In this method, the larger the thickness of the buffer layer, the greater the protection effect and the better the characteristics of the photovoltaic element. However, the buffer layer is formed by another method using an RF-CVD method, which generally has a low silicon deposition rate. Since they are stacked in a reaction vessel, not only does the operation become complicated,
When a sufficient protective effect is to be obtained, there has been a problem that the production time is long.

[0015]

Means for Solving the Problems The present inventors have made intensive studies in order to solve the above-mentioned problems in the case of manufacturing a photovoltaic element having an intrinsic semiconductor layer by a high-density plasma CVD method. As a result, it has been found that the above problem does not occur when the high-frequency power applied to the plasma generating electrode is reduced at the beginning of film formation and then increased. As a result of further study based on the findings, the damage to the underlayer is caused by the impact of ions and the like generated by the high-density plasma. Damage can be prevented, that the underlying layer will not be damaged even if the applied power is increased after a certain amount of intrinsic semiconductor layer is formed, and that the film formation speed determines the initial applied power. It has been found that the solar cell characteristics, particularly the open-circuit voltage and the fill factor, are improved when the control is performed so as to fall within the range, and the present invention has been completed.

That is, the first aspect of the present invention is to supply a reaction gas into a reaction chamber maintained in a vacuum state,
By applying high-frequency power to a plasma generating electrode placed inside or outside the reaction chamber, 10 ¹⁰ cm ^−
A method of producing a thin film on a surface of a substrate installed in the reaction chamber by generating a reactive gas plasma having an electron density of ³ or more, wherein the plasma generating electrode is formed after the start of film formation. A method for producing a thin film, characterized in that high-frequency power applied to a thin film is increased continuously or stepwise.

In the method for producing a thin film according to the present invention,
For example, by setting the high-frequency power applied to the plasma generating electrode at the start of the thin film formation to 50% or less of the maximum high-frequency power applied to the plasma generating electrode during the formation of the thin film, the lowering can be performed without significantly affecting the efficiency of film formation. Damage to the stratum can be suppressed. In particular, when a thin film having a large thickness is formed, the feature of the present invention, that is, high-speed film formation using plasma having a high electron density, is effectively exhibited.

Further, according to a second aspect of the present invention, a reaction gas is supplied into a reaction chamber maintained in a vacuum state.
By applying high-frequency power to a plasma generating electrode placed inside or outside the reaction chamber, 10 ¹⁰ cm ⁻
A reaction gas plasma having an electron density of ³ or more is generated, and a thickness of 10 μm is formed on the surface of the base material installed in the reaction chamber.
A method for producing a thin film having a thickness of not less than 10 nm, wherein the film forming speed until the thickness of the formed thin film reaches 10 nm is 0.01 to 0.5 nm / sec. It is a manufacturing method.

By controlling the film forming speed in this way, for example, when the intrinsic semiconductor layer of the photovoltaic element is formed by the method, the characteristics of the obtained photovoltaic element can be improved. .

In the first and second aspects of the present invention, by using a reaction gas containing a silane-based gas, a silicon-based thin film that can be suitably used as various semiconductor layers of a photovoltaic device can be manufactured.

In a third aspect of the present invention, a silicon-based thin film as an n-type impurity semiconductor and a silicon-based thin film as a p-type impurity semiconductor are joined via a silicon-based thin film as an intrinsic semiconductor. A method for manufacturing a photovoltaic element having a laminate in which at least one of the thin films has a thickness of 10 nm or more, wherein the thickness of the laminate is 10 n
A method for manufacturing a photovoltaic element, wherein at least one of the silicon-based thin films having a thickness of m or more is manufactured by the method for manufacturing a thin film according to claim 4.

According to the method, a photovoltaic device having excellent characteristics can be manufactured efficiently.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method for producing a thin film of the present invention, 10
Producing a thin film using ^three or more reactive gas plasma electron density ^{- 10} cm. By using such a high electron density plasma, it is possible to increase the film forming speed.
Incidentally, the electron density of the reaction gas plasma in all periods during film formation 10 ¹⁰ cm in the present invention ^- it is not necessary to be ³ or more, temporarily 10 ¹⁰ cm ^- may be a less than ³ electron density but from the viewpoint of film forming speed, 10 ¹⁰ cm the total casting time ^- percentage of time using a reaction gas plasma of ^three or more electron density the higher is preferred.

[0024] ¹⁰ 10 cm ^- reactive gas plasma of ^three or more electron density aforementioned (ICP) CVD method (hereinafter, IC
P-CVD method), ECR-CVD method,
It can be generated by a high-density plasma CVD method such as a helicon wave CVD method or a microwave CVD method. In these high-density plasma CVD methods, a reaction gas is supplied into a reaction chamber maintained in a vacuum state, and a high-frequency power is applied to a plasma generation electrode disposed inside or outside the reaction chamber. A high-electron-density reactive gas plasma can be generated.

Here, as the plasma generating electrode, those generally used for each plasma generating method to be used can be used. For example, when using the ICP-CVD method,
A coil or a spiral antenna made of a metal conductive material, an open waveguide when using the ECR-CVD method, and a microwave when using the microwave CVD method in the reaction vessel. An antenna made of metal or an apertured waveguide that propagates through the antenna can be used.

A high-frequency generator is connected to the above-mentioned plasma generating electrode via a matching circuit, so that high-frequency power in a frequency range usually used can be applied in accordance with a plasma generating method to be employed. . For example,
When ICP-CVD method is adopted, usually 5 to 200M
A high frequency of Hz is used. Preferably, 10-1
Preferably, the frequency is 00 MHz. The high frequency power means high frequency energy generated by the high frequency generator, and a desired high frequency power can be set by the high frequency generator. For example, a commercially available general radio frequency (RF) generator can generate RF of any high frequency power in the range of 10 W to 3 kW.

The reaction chamber to be used has a structure that can be maintained in a vacuum, has a plasma generating electrode inside or outside thereof, a base material can be placed inside the reaction chamber, and a reaction gas can be supplied inside. There is no particular limitation as long as the reaction chamber used in the conventional high electron density plasma CVD method can be used without any limitation. -27762, Jpn. J. Appl. Phys. Vol. 3
6 (1997), pp. 3714-3720}.
A reaction chamber for the CVD method can be suitably used.

Further, the substrate on which the thin film is formed is provided in the reaction chamber and is not particularly limited. For example, it is used when forming various silicon-based thin films when manufacturing a photovoltaic device. Base material can be used. As such a substrate, a substrate made of a material such as quartz glass, soda lime glass, heat-resistant polymer, single crystal silicon, polycrystalline silicon, stainless steel, ceramics, and a thin film such as a silicon film formed on these substrates Can be used without any restrictions. The thickness and shape of these substrates may be appropriately determined according to the purpose (for example, the photovoltaic element to be used), but generally, a plate or sheet having a thickness of about 50 nm to 5 mm is preferably used. Can be used.

When a photovoltaic element is manufactured by the method for manufacturing a thin film according to the present invention, a substrate obtained by attaching electrodes to the above substrate may be used as a base material. As the electrode, Sn
A conductive film (transparent conductive layer) in which an oxide such as O ₂ , In ₂ O ₃ , ZnO, CdSnO ₄ , and TiO ₂ is formed to have a light transmittance of about 80% or more is preferable. Can be used.
The thickness of the transparent conductive film layer is not particularly limited, but is generally about 0.1 to 1 μm. Further, the transparent conductive film layer may be formed, for example, by using JP-A-9-69642 or JP-A-9-2964.
In the case of a texture structure (a fine uneven structure) as disclosed in JP-A-83780, the use efficiency of incident light increases due to a “light confinement effect”, and thus such a structure is desirable.

Further, a metal is deposited on the entire surface of the substrate,
A substrate having the metal layer as an electrode may be used.
As the metal layer, for example, a layer made of silver, aluminum, an alloy thereof, or the like and having a light reflectance of 80% or more is preferably used. The thickness of the metal layer is not particularly limited, but is generally about 0.1 to 1 μm.

The reaction gas is not particularly limited as long as it is a gas containing various compound gases (source gases) that can be converted into plasma and can precipitate semiconductors such as silicon and metals from the plasma. A gas generally used as a reaction gas in the plasma CVD method can be used depending on the kind of the target thin film. For example, when a silicon-based thin film is formed, the general formula SiH _m
A silane-based gas represented by Cl _(4-m) (where m is an integer of 0 to 3) is generally used, and such a source gas can be suitably used in the present invention. In addition,
When it is desired to obtain a silicon-based thin film that is a p-type impurity semiconductor, a source gas is obtained by mixing a gas of a compound containing a Group III element such as boron or gallium as a dopant with the silane-based gas. When it is desired to obtain a silicon-based thin film as an n-type impurity semiconductor, a source gas may be obtained by mixing a compound gas containing a Group V element such as phosphorus or arsenic as a dopant.

These source gases may be used alone as a reaction gas, or may be diluted with a non-depositing gas such as hydrogen, helium, argon, xenon, etc. to obtain a reaction gas.

In the manufacturing method of the present invention, the vacuum is maintained.
10 in a closed reaction chamber^Tencm ^{― Three}Electron density above
Generates a reactive gas plasma on the surface of the substrate
When forming a film, a plasma generating electrode is
Reduce the applied high-frequency power and start film formation before
RF power must be increased continuously or stepwise.
Su. Generates high-frequency power from plasma at the start of film formation
Apply to the raw electrode, and keep the high frequency power constant during the film formation period
To reduce high-frequency power from high-frequency power.
Inevitably damages the underlayer, and can provide a good thin film.
Can not. The electron density and electron density of the reaction gas plasma
The temperature is controlled by a metal electrode made of Pt, W, Mo, etc. in the plasma.
A current-voltage characteristic obtained by inserting a pole and applying a voltage to it
Measured by Langmuir probe method, etc.
Can do things.

The value of the high-frequency power (initial high-frequency power) applied to the plasma generating electrode at the start of the film formation cannot be specified unequivocally because it differs depending on the apparatus used, the type of the reaction gas, and the like. In order to obtain the same, it is preferable that the maximum high-frequency power applied to the plasma generating electrode during the formation of the thin film is 50% or less, particularly 20% or less.
Further, since the deposition rate depends on the applied high-frequency power, the initial high-frequency power can be defined by the deposition rate. If the initial high-frequency power is expressed by the initial deposition rate, 0.01
０．５0.5 nm / sec, particularly 0.05-0.3 nm / sec.

The time for keeping the applied high-frequency power low is not particularly limited, but the thickness is 10 nm or more, especially 50 nm.
In the case of manufacturing the above thin film, it is preferable to reduce the applied electric power until the thickness of the film reaches 10 nm after the start of the film formation. If the applied power is too low for a long time, the film forming time becomes long, and a thin film cannot be manufactured efficiently. The thickness of the formed film can be determined from the film forming time by checking the relationship between the applied high-frequency power and the film forming time (application time) and the film thickness in advance.

In the method of manufacturing a thin film according to the present invention, after starting film formation with a low initial high-frequency power, the high-frequency power applied to the plasma generating electrode is increased in order to increase the film formation speed and increase the film manufacturing efficiency. Increase continuously or stepwise. The increase pattern of the applied high-frequency power is not particularly limited, and may be appropriately determined according to the device to be used, the type of the reaction gas, the final film thickness, the intended manufacturing time, and the like. Normally, the film forming speed depends on the magnitude of the applied high-frequency power. Therefore, after a lapse of a predetermined time from the start of film forming, it is preferable to quickly increase the high-frequency power to a stable high-speed film forming.
However, if the high-frequency power is suddenly changed, the plasma becomes unstable and may adversely affect the film quality.
It is preferable to control the computer so as to reproduce the optimum pattern using a computer. Although there is no particular advantage in manufacturing, it is of course possible to temporarily reduce the applied high-frequency power.

The maximum value when the applied high-frequency power is increased is not particularly limited, but is usually set to a value that enables stable film formation and maximizes the film formation speed. Since the specific value differs depending on the apparatus used, the type of reaction gas, and the like, it cannot be described unconditionally. For example, a single-coil plasma having a diameter of 3 to 30 cm and installed in a reaction chamber in an ICP-CVD method is used. The preferred maximum applied high frequency power when applied to the generating electrode is:
It is about 10 W to 3 kW, more preferably about 100 to 300 W.

According to the method of manufacturing a thin film of the present invention, a thin film such as a silicon-based thin film can be efficiently manufactured without damaging the underlying layer. Thus, for example,
At least one silicon-based thin film of a photovoltaic element having a laminate in which a silicon-based thin film as an n-type impurity semiconductor and a silicon-based thin film as a p-type impurity semiconductor are joined via a silicon-based thin film as an intrinsic semiconductor When is manufactured by the method for manufacturing a thin film of the present invention, the damage at the interface can be reduced, so that a photovoltaic device having a high open-circuit voltage and a fill factor can be efficiently obtained. In this case, since the silicon-based thin film, which is an intrinsic semiconductor, is the thickest of the three types of silicon-based thin films, it is most preferable to manufacture the silicon-based thin film by the thin-film manufacturing method of the present invention in terms of manufacturing speed. It is advantageous.

Hereinafter, using a plasma CVD apparatus having a reaction chamber (ICP reaction vessel) to which the ICP-CVD method can be applied as shown in FIG.
The method for manufacturing a photovoltaic element according to the present invention will be described in more detail by taking, as an example, a method for manufacturing an intrinsic semiconductor layer of an in-type photovoltaic element using the method for manufacturing a thin film according to the present invention.

The plasma CVD apparatus 100 shown in FIG.
Mainly include a vacuum pump (mechanical booster pump 121, a turbomolecular pump 122, and an oil diffusion pump 131) communicating with each reaction vessel (120, 130) and the sample introduction chamber 110, each reaction vessel and the sample introduction chamber, and each reaction vessel. High-frequency generators (141, 142) communicating with plasma generating electrodes (not shown) installed in the inside, and gas supply devices (151, 15) communicating with respective reaction vessels.
2).

In each of the above-mentioned reaction vessels, the kind of plasma to be used and the kind of gas that can be introduced are set in advance according to the kind of film to be formed, and a gate valve 171 is provided between each reaction vessel and the sample introduction chamber. , 172 are provided, and the sample (photovoltaic element in the manufacturing process) can be moved while maintaining the vacuum state using the transfer rod 160. In the apparatus shown in FIG. 1, the reaction vessel is a CCP reaction vessel 120 for forming an n-type semiconductor layer or a p-type semiconductor layer using capacitively-coupled plasma generated by a high-frequency generator 141; It is divided into an ICP reactor 130 for forming an intrinsic semiconductor layer using inductively coupled plasma generated by a coil. In each reaction vessel, a silane gas such as monosilane, disilane, or halogenated silane, which is a raw material of a silicon film, and hydrogen, helium, argon,
A diluting gas such as neon or xenon is added to the CCP reaction vessel 120 in addition to B ₂ H ₆ , BF ₃ , P
A gas containing an element of Group III or Group V of the periodic table such as H ₃ or AsH ₃ (hereinafter also referred to as a dopant gas), and carbon such as CH ₄ for introducing carbon atoms into the p-type semiconductor layer. The contained gas can be introduced from the gas supply device 151.

If a sputtering apparatus or a vapor deposition apparatus is connected to the apparatus shown in FIG. 1 by a vacuum line in the same manner as each of the above-described reaction vessels, a transparent conductive layer 220 and a second transparent conductive layer
40, the metal layer 250 can also be manufactured while maintaining a vacuum state.

In the method of manufacturing a photovoltaic device according to the present invention, first, a transparent conductive film layer 220 is formed on a substrate 210. The manufacturing method is not particularly different from the manufacturing method for manufacturing a conventional pin type photovoltaic element, and may be appropriately selected from known methods such as a sputtering method, an electron beam evaporation method, and a CVD method. The manufacturing conditions are not particularly different from the conventional method.

For example, when the transparent conductive film layer 220 is formed by a sputtering method, argon sputtering may be performed using a metal oxide having the same composition as that constituting the transparent conductive film layer. Note that the thickness of each layer can be adjusted by previously examining the relationship between the sputtering time and the film thickness under the same conditions and controlling the sputtering time.

Further, a texture structure can be introduced into the transparent conductive film layer 220 by performing appropriate etching or the like.

Next, the substrate 2 formed as described above
10. A semiconductor layer 230 is formed by a plasma CVD method on a stacked body in which the transparent conductive film layers 220 are stacked.

The semiconductor layer 230 includes a p-type semiconductor layer 231,
It is composed of an intrinsic semiconductor layer 232 and an n-type semiconductor layer 233. Here, the p-type semiconductor layer has a thickness of about 5 to 50 nm and has a periodic table of boron, gallium, or the like as a dopant.
It is a layer made of silicon containing a group III element. The intrinsic semiconductor layer is a layer made of silicon having a thickness of 100 to 1000 nm. The n-type semiconductor layer has a thickness of 5 to 50.
This layer is made of silicon having a thickness of about nm and containing a Group V element of the periodic table such as phosphorus or arsenic as a dopant.

The p-type semiconductor layer 231 and the n-type semiconductor layer 2
Since the layer 33 is a very thin layer as described above, even if a method having a low deposition rate such as the CCP-CVD method is used for forming these layers, the layer formation time is hardly affected. On the other hand, when the method of forming a thin intrinsic semiconductor layer 232 by using the above-described method with a low deposition rate is used, the film formation time becomes extremely long. Therefore, the thin film manufacturing method of the present invention is used. Is preferred. Note that the method for manufacturing a thin film of the present invention may be used for forming the p-type semiconductor layer 231 and the n-type semiconductor layer 233 without any problem.

The p-type semiconductor layer 231 is transferred to the CCP
In the case of manufacturing within 0, if a gas containing carbon such as methane is mixed with a monosilane gas to form a raw material gas, a silicon film having a wide optical gap can be manufactured by mixing carbon into the silicon film. By increasing the hydrogen dilution ratio of the source gas, a microcrystalline silicon layer having a small absorption coefficient may be obtained. The film forming conditions are the same as those of ordinary CCP-
There is no particular difference from the CVD method. For example, preferable conditions for forming an amorphous silicon semiconductor layer are as follows: high frequency output: 5 to 50 W, SiH ₄ flow rate: 5 to 100 sccm, substrate temperature: 150 to 300 ° C., reaction pressure: 0.1 to 1 Torr
It is. The dopant is introduced by using a gas containing a Group III element of the periodic table such as B ₂ H ₆ as a dopant gas at the time of producing the p-type semiconductor layer at 1 to 10000 ppm with respect to the SiH ₄ flow rate.
It may be carried out by using the mixture as a source gas.

Under the above manufacturing conditions, the p-type semiconductor layer
After the formation of 50 nm, the sample is transferred to the ICP reaction vessel 120,
According to the thin film manufacturing method of the present invention, the intrinsic semiconductor layer 232 is
It is formed to a thickness of 00 to 1000 nm. The reaction conditions at this time depend on the installation condition and shape of the plasma generation electrode, the size of the substrate, and the like. For example, a plasma generation electrode composed of a single coil having a diameter of about 15 cm is installed in the ICP reaction vessel 120. Suitable reaction conditions when a substrate having an area of about 100 cm ² is used are as follows. That is, the reaction pressure is preferably 5 to 50 mTorr, and the distance between the coil and the substrate is 2 to 30 cm, preferably 8 to 30 cTorr.
m and the substrate temperature are preferably 150 to 300 ° C. When high-frequency power is applied, the initially applied high-frequency power is set to 20 to 50 W, and the high-frequency power is applied to a film thickness of 10 to 50 W.
nm, and then continuously (or stepwise, for example, every 10 W) at a rate of 1 to 20 W / sec.
After increasing the applied power from 0 W to 3 kW, it is preferable to form a film while maintaining the applied power.

After the formation of the intrinsic semiconductor layer 232 in this manner, the sample is transferred to the CCP reaction vessel 130 again, and the dopant gas is changed to a gas containing a group V element of the periodic table such as PH ₃ , except that it is a p-type. An n-type semiconductor layer 233 is formed in a thickness of 5 to 50 nm in the same manner as the formation of the semiconductor layer 231.

On the semiconductor layer thus manufactured,
Similarly to the above-mentioned transparent conductive film layer, the second transparent conductive film layer 24
0 is formed, and a metal layer 250 of a current collecting electrode made of silver (Ag) or the like is further deposited thereon.

The manufacturing method may be appropriately selected from known methods such as a sputtering method, an electron beam evaporation method, and a resistance heating method. The manufacturing conditions are not particularly different from the conventional method.

For example, the metal layer 250 is formed by a sputtering method.
Is manufactured, a metal of the same type as the metal constituting the metal layer is used as a target, and a pressure of 1 to 100 mTo
Ar sputtering may be performed under conditions such as rr and Ar flow rates of 1 to 100 sccm in the presence of oxygen as necessary. Note that the thickness can be adjusted by checking the relationship between the sputtering time and the film thickness under the same conditions in advance and controlling the sputtering time.

Although the manufacturing example of the pin type photovoltaic element as shown in FIG. 2 has been described above, the method of manufacturing the photovoltaic element of the present invention is different from the pin type photovoltaic element shown in FIG. The present invention is also applicable to the manufacture of a power element or a nip type photovoltaic element. Further, the reactor and the method of generating high electron density plasma are not limited to the embodiment shown in the above-described manufacturing example, and it is a matter of course that other types of reactors and other methods of generating high electron density plasma can be employed.

[0056]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Each thin film in each of the examples and comparative examples was formed using the apparatus having the basic structure shown in FIG.
In the CCP reaction vessel 120 of the apparatus, a plasma generating electrode composed of a generally used parallel plate type counter electrode is installed, and an RF generator (anelva) as a high frequency generator 141 is provided on the electrode. Is connected. Further, a ring-shaped plasma generating electrode having a diameter of 15 cm made of an Al pipe is installed in the ICP reaction vessel 130, and an R-type high frequency generator 142 is mounted on the electrode.
An F generator (manufactured by Anelva) is connected.

Example 1 First, a sputtering apparatus (SPC-35 manufactured by Anelva) was used.
Quartz glass substrate (24 mm x 16)
mm × 0.5 mmt), and Zn as a target
1000 nm Z by argon sputtering using O
A transparent conductive film layer made of nO was laminated. The sputtering was performed at an Ar flow rate of 10 sccm and an O ₂ gas flow rate of 0.0
2 sccm, pressure 5 mTorr, high frequency power (hereinafter also referred to as RF power) 100 applied to the plasma generating electrode
W, the substrate temperature was 300 ° C., and the sputtering time was 15 minutes.

The substrate in which the transparent conductive layer is laminated on the glass substrate in this manner is set in the sample introduction chamber 110 of the plasma CVD apparatus 100, and after performing vacuum suction,
It is transferred to a P reaction vessel 120 and has a thickness of about 10 n by a CCP-CVD method using plasma having an electron density of about 10 ⁷ / cm ^3.
m p-type semiconductor layers were formed. The conditions at this time were as follows: SiH ₄ flow rate 3 sccm, B ₂ H ₆ (1 vol.
l. % Diluted) flow rate 3 sccm, hydrogen flow rate 30
sccm, CH ₄ flow rate 9 sccm, a reaction pressure 100mT
orr, RF power 5 W, substrate temperature 200 ° C., reaction time 1 minute 30 seconds.

After the formation of the p-layer, the sample is placed under vacuum
Has a single-coil plasma generating electrode with a diameter of 15 cm
To the ICP reaction vessel 130 where the electron density is about 10^Ten/
cm ^ThreeThickness by ICP-CVD method using plasma
A 300 nm intrinsic semiconductor layer was formed. At this time,
Condition is SiH_FourFlow rate 30 sccm, RF power 20
0W, reaction pressure 20mTorr, substrate temperature 200 ° C,
The response time was 15 minutes. However, RF for 30 seconds from the start
The power was set to 20W. At this time, after starting film formation
The film formation rate for 30 seconds is about 0.3 nm / sec.
The thickness of the film formed in a minute was about 10 nm.

After the formation of the intrinsic semiconductor layer, the sample was transferred to the CCP reaction vessel 120 again, and an n-type semiconductor layer having a thickness of 20 nm was formed by CCP-CVD using plasma having an electron density of about 10 ⁷ / cm ³ . The condition at this time is SiH
₄ Flow rate 20 sccm, PH ₃ (diluted to 1 vol.% With hydrogen) flow rate 5 sccm, reaction pressure 100 mTorr
r, RF power 5 W, substrate temperature 200 ° C., and reaction time 4 minutes.

After the formation of the n-type semiconductor layer, the sample is placed in the sample introduction chamber 1
After being transferred to No. 10, it was taken out of the plasma CVD apparatus, mounted again on the above-mentioned sputtering apparatus, and was 70 nm thick by an argon sputtering method using ZnO as a target.
A second transparent conductive film layer made of m ZnO was laminated. At this time, sputtering was performed at an Ar flow rate of 10 sccm, a pressure of 5 mTorr, an RF power of 10 W, a substrate temperature of 200 ° C.
The sputtering was performed under the condition of a sputtering time of 20 minutes.

Further, a metal layer having a thickness of 800 nm was laminated by an argon sputtering method using silver as a target.
The sputtering was performed at an Ar flow rate of 10 sccm, a pressure of 5 mTorr, an RF power of 200 W, and a substrate temperature of 200.
C. and a sputtering time of 20 minutes.

The IV characteristics of the photovoltaic device thus obtained were measured. The measurement of the IV characteristics was performed using a microammeter (4140 manufactured by Hewlett-Packard Company).
B) was carried out under irradiation of white light of 100 mW / cm ² .

When the open-circuit voltage and short-circuit current were obtained from the obtained IV characteristic curve, the open-circuit voltage was 0.872 V, the short-circuit current was 11.56 mA / cm ² , and the fill factor was 0.60.
3, and the conversion efficiency was 6.08%.

Example 2 An optical semiconductor device was produced in the same manner as in Example 1, except that the RF power at the start of the production of the intrinsic semiconductor layer was changed to 100 W. The open-circuit voltage and short-circuit current of the obtained photovoltaic device were determined in the same manner as in Example 1. The open-circuit voltage was 0.854 V, and the short-circuit current was 11.71 m.
A / cm ² , fill factor was 0.573, and conversion efficiency was 5.73%.

Comparative Example 1 An optical semiconductor device was manufactured in the same manner as in Example 1, except that the RF power at the start of the fabrication of the intrinsic semiconductor layer was changed to 200 W from the beginning instead of 20 W. The open-circuit voltage and short-circuit current of the obtained photovoltaic element were determined in the same manner as in Example 1. The open-circuit voltage was 0.849 V, the short-circuit current was 12.61 mA / cm ² , and the fill factor was 0.455.
And the conversion efficiency was 4.87%.

From the comparison between the results of Examples 1 and 2 and Comparative Example 1, it can be seen that when the intrinsic semiconductor layer is manufactured by the method for manufacturing a thin film of the present invention, the open-circuit voltage and the fill factor are improved.

[0069]

According to the method for producing a thin film of the present invention, the high density plasma C can be formed without damaging the underlying layer.
A thin film such as a silicon-based thin film can be manufactured by the VD method (that is, at a high speed). When an intrinsic semiconductor layer in a photovoltaic element such as an amorphous silicon solar cell is formed by the method, excellent values such as a high open-circuit voltage and a fill factor and a small short-circuit current can be obtained without providing a buffer layer. A photovoltaic element having characteristics can be obtained.

As described above, the method for manufacturing a photovoltaic element using the method for manufacturing a thin film according to the present invention has a feature that a photovoltaic element having good characteristics can be efficiently obtained in a short time. It can be said that this is an industrially superior production method.

[Brief description of the drawings]

FIG. 1 is a schematic view of a typical plasma CVD apparatus that can be used in the method for producing a thin film of the present invention.

FIG. 2 is a diagram showing a structure of a typical pin type photovoltaic element.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Plasma CVD apparatus 110 Sample introduction chamber 120 CCP reaction vessel 130 ICP reaction vessel 121 Mechanical booster pump 122 Turbo molecular pump 131 Oil diffusion pump 141 High frequency generator 142 High frequency generator 151 Gas supply device 160 Transfer rod 171 Gate valve 172 Gate valve Reference Signs List 200 photovoltaic element 210 glass substrate 220 transparent conductive layer 230 semiconductor layer 231 p-type semiconductor layer 232 intrinsic semiconductor layer 233 n-type semiconductor layer 240 second transparent conductive layer 250 metal layer

Claims (5)

[Claims] To 1. A reaction chamber maintained in a vacuum state, supplies the reaction gas by applying RF power to a plasma generating electrode arranged inside or outside of the reaction chamber 10 ¹⁰ cm ^{- 3} or more A method of producing a thin film on a surface of a substrate installed in the reaction chamber by generating a reactive gas plasma having an electron density of: A method for producing a thin film, characterized by continuously or stepwise increasing high-frequency power to be applied. 2. The method of manufacturing a thin film according to claim 1, wherein the high frequency power applied to the plasma generating electrode at the start of the thin film formation is set to 50% or less of the maximum high frequency power applied to the plasma generating electrode during the thin film formation. Method. To 3. A reaction chamber maintained in a vacuum state, supplies the reaction gas by applying RF power to a plasma generating electrode arranged inside or outside of the reaction chamber 10 ¹⁰ cm ^{- 3} or more A method for producing a thin film having a thickness of 10 nm or more on a surface of a substrate provided in the reaction chamber by generating a reaction gas plasma having an electron density of Film forming speed until reaching 10 nm is 0.01-0.5 n
m / sec. 4. The method for producing a thin film according to claim 1, wherein a silicon-based thin film is produced using a reaction gas containing a silane-based gas. 5. A silicon-based thin film as an n-type impurity semiconductor and a silicon-based thin film as a p-type impurity semiconductor are joined via a silicon-based thin film as an intrinsic semiconductor, and the thickness of at least one of these silicon-based thin films is A method for producing a photovoltaic device having a laminate having a thickness of 10 nm or more, wherein at least one of the silicon-based thin films having a thickness of 10 nm or more constituting the laminate is produced by the method for producing a thin film according to claim 4. A method for manufacturing a photovoltaic device.