JP2002217114A - Method and apparatus for manufacturing silicon based thin film, and photovoltaic device and method for manufacturing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for manufacturing a silicon-based thin film having a good priority orientation and grown columnar crystal, and a photovoltaic device and a method for manufacturing it. SOLUTION: A substrate is heated to a predetermined temperature in a reaction chamber, silicon-containing gas and hydrogen gas are supplied between the substrate and a discharge electrode, a high frequency electric power of a source frequency of 100 MHz to 300 MHz is applied between the discharge electrode and the substrate to produce a discharge plasma, and a thin-film- crystal-like silicon thin film is stack-formed on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a silicon-based thin film, a manufacturing apparatus therefor,
The present invention relates to an in-type or nip-type silicon-based thin-film photovoltaic device and a method of manufacturing the same, and more particularly to a method of manufacturing a silicon-based thin film used for a solar cell or a sensor, a manufacturing apparatus thereof, a photovoltaic device, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A typical example of a photovoltaic element using a silicon-based thin film is an amorphous silicon-based solar cell. Amorphous silicon is usually manufactured by a plasma CVD method using a silicon hydride gas such as silane or disilane as a source gas. For generating plasma, a high-frequency power source having a frequency of 13.56 MHz is generally used. Amorphous silicon is characterized in that it can be formed on an inexpensive substrate such as glass, metal or plastic at a low temperature of 200 ° C. or lower, and that a large-area film can be formed.
Since amorphous silicon-based solar cells have such characteristics, cost reduction in mass production is expected.

However, when the amorphous silicon-based solar cell is irradiated with light, defects occur in the i-layer, which is a photoelectric conversion layer, and the photoelectric conversion efficiency is reduced by about 10 to 30% as compared with the initial state. The photo-deterioration phenomenon is a major obstacle in practical use. Regarding the mechanism of the photodegradation phenomenon, although various studies have been conducted energetically, it has not been completely elucidated yet, and at present, no drastic solution has been established.

On the other hand, in recent years, attempts have been reported to use microcrystalline silicon instead of amorphous silicon as the i-type photoelectric conversion layer (J. Meier et al., Mat. Res. S.
oc. Symp. Proc. Vol. 420, p3 (1996)). According to this report, a pin-type photoelectric conversion element is formed by a high-frequency plasma CVD method using a power supply in a VHF band at a frequency of 110 MHz, and it is reported that the pin-type photoelectric conversion element is not accompanied by a light degradation phenomenon such as amorphous silicon.

A photovoltaic element using microcrystalline silicon is:
Since the film can be formed by the plasma CVD method as in the case of amorphous silicon, it has the potential of increasing the area and reducing the cost during mass production. A photovoltaic element using microcrystalline silicon as the photoelectric conversion layer has a peak in the spectral sensitivity spectrum on the longer wavelength side, compared to a photovoltaic element using amorphous silicon. Is a top cell and microcrystalline silicon is a photoelectric conversion layer of a bottom cell.

As described above, a photovoltaic element using microcrystalline silicon is basically a plasma CVD device similar to the conventional one.
There is an advantage that a film can be formed by a technique and there is no light deterioration phenomenon.

In order to promote microcrystallization, it is necessary to generate high-density hydrogen radicals, terminate dangling bonds on the growth surface, and promote surface diffusion of active species (radicals) involved in film formation. It is essential. In the case where a conventionally used power supply having a frequency of 13.56 MHz is used as a power supply for generating plasma, high-density hydrogen radicals are generated and micro-crystallization is performed by using hydrogen with respect to a source gas containing silicon. It is necessary to increase the gas flow ratio extremely or increase the high frequency power. Such a condition is required for frequency 1
When a power supply of 3.56 MHz is used, the reason is that the plasma density is low.

[0008]

However, when the flow rate ratio of hydrogen gas to the raw material gas containing silicon is extremely increased, there is a problem that the productivity is reduced in industrial use because the film forming speed is reduced. . In addition, when forming a film by increasing the high-frequency power, local abnormal discharge occurs in the vacuum vessel, and powder is easily generated in the gas phase. The microcrystalline silicon formed in such a situation has a problem that the quality of the film is remarkably deteriorated because the powder generated in the gas phase is taken into the film.

The structure of microcrystalline silicon used for the photovoltaic element is preferably a so-called columnar crystal in which the crystal has developed in the direction of current flow, that is, in the film thickness direction. In the microcrystalline silicon film formation by the plasma CVD method, in order to develop columnar crystals, that is, to preferentially orient to a specific crystal orientation, it is necessary to raise the film formation temperature and to use high frequency power for generating plasma. Need to be higher. In a photovoltaic element using microcrystalline silicon for forming a photoelectric conversion layer under such conditions, a doping element, phosphorus (or boron), is formed from the underlying n-layer (or p-layer) during the formation of the photoelectric conversion layer. Is diffused into the photoelectric conversion layer, and the characteristics as an intrinsic semiconductor deteriorate. In addition, when plasma containing hydrogen gas as a main component is generated at a high temperature on a transparent conductive film made of a metal oxide, the transparent conductive film is reduced, the transmittance is reduced, and the metal oxide is reduced and deposited. There is a problem that the deposited metal diffuses into the silicon layer and significantly degrades semiconductor characteristics. Furthermore, if the high-frequency power during film formation of the photoelectric conversion layer is increased, the nucleation density is high, so that a large number of crystal nuclei generated in the initial stage of film formation interfere with each other during the growth process, and the grain size increases. Since growth is inhibited, microcrystalline silicon of fine crystal grains in which columnar crystals have not sufficiently developed is eventually formed. A photovoltaic element using microcrystalline silicon having fine crystal grains as a photoelectric conversion layer has insufficient photoelectric conversion characteristics due to the influence of a large number of crystal grain boundaries in the direction in which current flows, that is, in the film thickness direction. is there.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method of manufacturing a silicon-based thin film having excellent preferential orientation and having developed columnar crystals, an apparatus for manufacturing the same, a photovoltaic element, and manufacturing thereof. The aim is to provide a method.

[0011]

According to a method of forming a silicon-based thin film according to the present invention, a substrate is heated to a predetermined temperature in a reaction vessel, and a silicon-containing gas and a hydrogen gas are supplied between the substrate and a discharge electrode. Supply and power frequency is 10MHz
A high-frequency power of 300 MHz or less is applied between the discharge electrode and the substrate to generate discharge plasma, and a thin film crystalline silicon thin film is formed on the substrate.

In the present invention, when a high frequency (VHF) having a frequency of 10 MHz or more and 300 MHz or less is applied to generate a discharge plasma in the coexistence of a hydrogen gas and a silicon-containing gas, high-density hydrogen radicals are generated in the discharge plasma. Is generated, dangling bonds on the growth surface are terminated, and surface diffusion of active species is promoted. Thus, a film having a preferred orientation and a columnar crystal is obtained.

In the present invention, a film forming surface heater is disposed between the substrate heating heater and the discharge electrode to heat the growing film surface. This further promotes the diffusion of radicals involved in film formation adsorbed on the growth surface, and promotes crystal growth, so that columnar crystals develop.

Further, in the present invention, by forming a film using the above-described method, a photovoltaic element using a silicon-based thin film excellent in preferential orientation and having well-developed columnar crystals as a photoelectric conversion layer, and a photovoltaic element using the same. A manufacturing method is provided.

Further, in the present invention, by the above method,
Pin-type or nip using a p-layer or n-layer formed in a temperature range where the transparent conductive film is not deteriorated or reduced
A photovoltaic device of the type and a method of manufacturing the same are provided.

[0016]

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

FIG. 1 is a schematic perspective cross-sectional view showing an example of a plasma CVD apparatus used for forming a thin film crystalline silicon film. The outside of the plasma CVD apparatus is covered with a reaction vessel 1 made of stainless steel. An exhaust pipe 3 is opened at an appropriate position in the reaction vessel 1, and the inside of the reaction vessel 1 is evacuated to a predetermined pressure by a vacuum pump 8 through the exhaust pipe 3.

In a reaction vessel 1, a discharge electrode 2, a substrate heating heater 7, a gas mixing box 11, and a film forming surface heater 1 are provided.
2 are respectively located at appropriate places. The discharge electrode 2 and the substrate heating heater 7 are arranged facing each other, and a film forming surface heater 12 is inserted between the electrode 2 and the heater 7.
The substrate 9 is held in close contact with the heater 7 with the film-forming surface facing downward.

The discharge electrode 2 is arranged at a position facing the substrate heater 7, and is connected to the impedance matching device 5 and the high frequency power supply 4 via a coaxial cable 10. A film forming surface heater 12 made of a stainless steel mesh is provided near the substrate 9. The film forming surface heater 12 is connected to a power supply 13. A power supply (not shown) is also connected to the substrate heating heater 7.

The gas mixing box 11 supports the discharge electrode 2 substantially horizontally so as to back up the discharge electrode 2. However, the gas mixing box 11 and the discharge electrode 2 are electrically insulated by the insulating member 11a. The gas mixing box 11 contains a porous dispersion pipe communicating with the raw material gas introduction pipe 6. The source gas is evenly dispersed and supplied from the porous dispersion tube toward the substrate 9.

The raw material gas introduction pipe 6 communicates with a gas supply source (not shown). The gas supply source is a gas mixing box made of a gas containing silicon as a source gas, specifically, a gas obtained by diluting a silicon hydride gas such as silane or disilane, a halosilane gas such as silicon fluoride gas or dichlorosilane with a hydrogen gas, or the like. 11 or a single silicon-containing gas and a single hydrogen gas are supplied to the gas mixing box 11.

Next, a method for forming a thin film crystalline silicon will be described.

The substrate 9 is degreased and washed, dried, carried into the reaction vessel 1, and held in close contact with the substrate heating heater 7.
The discharge electrode 2 is provided at a position facing the heater 7. A film forming surface heater 12 is inserted between the heater 7 and the discharge electrode 2. In order to minimize the contamination of the film with impurities, the inside of the reaction vessel 1 is evacuated to 1 × 10 ⁻⁶ Torr or less by the vacuum pump 8 via the exhaust pipe 3.

Next, a raw material gas at a predetermined flow rate is introduced into the gas mixing box 11 through the raw material gas introducing pipe 6. The flow rate of the source gas is controlled by a mass flow controller (not shown). As a source gas, a silicon-containing gas, specifically, a gas obtained by diluting a silicon hydride gas such as silane or disilane, a silicon fluoride gas or a halosilane gas such as dichlorosilane with hydrogen is used.

In this case, the ratio of the flow rate of the hydrogen gas to the flow rate of the silicon-containing gas is desirably 5 times or more and 100 times or less. The flow rate ratio of hydrogen gas / silicon-containing gas is 5
If the ratio is less than twice, the amount of generated hydrogen radicals in the plasma becomes insufficient, and the termination of dangling bonds on the surface of the growing film becomes insufficient. As a result, the surface diffusion of the radicals involved in the film formation becomes insufficient and the crystal growth of the thin-film crystalline silicon does not proceed sufficiently, so the lower limit is set to 5 times. On the other hand, when the flow ratio of hydrogen gas / silicon-containing gas is 10
If it exceeds 0 times, the thin film crystalline silicon grows, but the film formation speed is extremely low, and the thin film crystalline silicon photovoltaic element requiring a photoelectric conversion layer thicker than amorphous silicon is industrially required. Since it is uneconomical without being on a suitable production base, its upper limit is set to 100 times.

Next, the inside of the reaction vessel 1 is adjusted to a predetermined pressure by a pressure adjusting valve (not shown). It is desirable that the pressure in the reaction vessel 1 be 0.1 Torr or more and 5 Torr or less. If the pressure is lower than 0.1 Torr, the film forming speed becomes extremely low, and the productivity is greatly reduced. Therefore, the lower limit is set to 0.1 Torr. On the other hand, if the pressure exceeds 5 Torr, particles are likely to be generated in the gas phase during film formation, so the upper limit is set to 5 Torr. Particles generated during the film formation are not only taken into the film and extremely deteriorate the film quality of the thin-film crystalline silicon, but also increase the frequency of open maintenance inspection of the reaction vessel 1 and lower the equipment operation rate. This is because it has an adverse effect.

At the same time as adjusting the pressure in the reaction vessel 1, the substrate heater 7 and the film forming surface heater 12 are energized and heated.
Is heated to a predetermined temperature. The surface temperature of the substrate 9 can be arbitrarily controlled by a combination of the electric power supplied to the substrate heater 7 and the film forming surface heater 12, but a temperature range of 500 ° C. or lower where an inexpensive material such as glass or stainless steel can be used. It is desirable that In this case, the lower limit of the substrate temperature is 100 ° C. If the substrate temperature is set to less than 100 ° C., the surface diffusion of radicals involved in film formation adsorbed on the substrate surface becomes insufficient, so that the thin-film crystalline silicon does not grow sufficiently.

The electric power supplied to the film forming surface heater 12 is 5
It is desirable to set it to W or more and 500 W or less. If the power supplied to the film forming surface heater is less than 5 W, the amount of heat input to the growing film surface is insufficient, the diffusion of surface-adsorbed radicals is not promoted, and the development of columnar crystals becomes insufficient. The value is 5W. On the other hand, the power supplied to the film forming surface heater is 5
When the temperature exceeds 00 W, the surface of the film forming surface heater 12 itself becomes high temperature, and the raw material gas containing silicon is supplied to the film forming surface heater 1.
2 Pyrolyzed on the surface, producing fine powder in the gas phase. The powder generated during the film formation is taken into the film and not only extremely deteriorates the film quality of the thin-film crystalline silicon, but also increases the frequency of open maintenance of the reaction vessel 1 and lowers the operation rate of the apparatus. And other adverse effects. Therefore, the upper limit of the power supplied to the film forming surface heater is set to 500 W.

While the substrate temperature and pressure are stable, high frequency power of a predetermined frequency is supplied from the high frequency power supply 4 to the discharge electrode 2 to generate plasma, and a thin film crystalline silicon is formed on the surface of the substrate 9. At this time, the impedance matching unit 5 is adjusted so that the reflected power is minimized.

The frequency of the high frequency power supply 4 is 10 MHz or more and 3
It is desirable that the frequency be 00 MHz or less. 10M frequency
When the frequency is lower than Hz, the plasma density decreases, the number of hydrogen radicals excited in the plasma decreases, and the termination of dangling bonds on the surface of the growing film becomes insufficient. As a result, the surface diffusion of the radicals involved in the film formation becomes insufficient and the columnar crystals develop insufficiently. Therefore, the lower limit of the power supply frequency is set to 10 MHz. On the other hand, the frequency is 300 MHz
Is exceeded, the voltage distribution in the discharge electrode 2 becomes large, and uniform discharge over the entire surface of the discharge electrode 2 becomes difficult. Therefore, the upper limit is set to 300 MHz.

After forming the film under the above conditions for a predetermined time, the raw material gas is exhausted from the reaction vessel 1, the substrate 9 is cooled, and the substrate 9 is taken out from the reaction vessel 1. On this substrate 9, a thin-film crystalline silicon layer of a predetermined thickness with columnar crystals developed is formed.

The above is a method of forming microcrystalline silicon having essentially intrinsic semiconductor characteristics used as a photoelectric conversion layer. Note that B ₂ H ₆ , BF ₃
When a gas containing trivalent impurities such as boron is added,
A p-type thin film crystalline silicon can also be formed. Further, when a gas containing a pentavalent impurity such as phosphorus such as PH ₃ is added to the source gas, an n-type thin film crystalline silicon can be formed.

Next, a method for manufacturing a photovoltaic device according to the present invention will be described.

FIG. 2 shows an example of the structure of a photovoltaic element using thin-film crystalline silicon according to the present invention. First and second lower electrode layers 14 and 15 are formed on a substrate 9 made of glass, stainless steel, or the like. First lower electrode layer A14
Is made of a metal such as Al, Ag, Ti, Ni, Cr, Cu or an alloy thereof, and is formed by lamination using a physical vapor deposition method such as a vacuum vapor deposition method or a sputtering method. On the other hand, the second lower electrode layer B15 is made of ZnO, SnO ₂ or ITO.
And the like, and is formed by lamination using a CVD method or a sputtering method.

Next, the n-type (or p-type) thin-film crystalline silicon layer 16, the i-type thin-film crystalline silicon layer 17, and the p-type (or n-type) thin film A system silicon layer 18 is sequentially formed on the substrate 9.

The thickness of the n-type thin film crystalline silicon layer 16 is 5
It is desirable that the thickness be not less than nm and not more than 50 nm. When the film thickness of the n-type thin film crystalline silicon layer 16 falls below 5 nm, the entire surface of the lower electrode layer B15 is no longer covered with the n-type thin film crystalline silicon layer 16, and a part of the lower electrode layer B15 is exposed in a patchy manner. That is, the n-type thin film crystalline silicon layer 16 grows in an island shape. In this case, a portion not covered with the n-type thin film crystalline silicon layer 16 does not form a normal semiconductor pn junction, so that characteristics as a photovoltaic element are significantly reduced. On the other hand, if the thickness of the n-type thin film crystalline silicon layer 16 exceeds 50 nm,
In this case, the effect of light absorption by the light source becomes large, and the light reflected by the lower electrode layer A14 cannot be effectively used for photoelectric conversion. This causes a problem in device performance that sensitivity to long-wavelength light is reduced.

The thickness of the i-type thin film crystalline silicon layer 17 is
Although it depends on the light confinement state depending on the surface shape of the lower electrode layer B15 and the i-type thin-film crystalline silicon layer 17, it is determined that the lower limit value is 0.1.
It is desirable that the thickness be 5 μm or more and 10 μm or less. If the thickness of the i-type thin-film crystalline silicon layer 17 is less than 0.5 μm, the incident light cannot be sufficiently absorbed and the short-circuit current as a photovoltaic element becomes small.
5 μm. When the thickness of the i-type thin film crystalline silicon layer 17 exceeds 10 μm, the internal electric field generated in the i-type thin film crystalline silicon layer 17 becomes weak, and not only the open voltage as a photovoltaic element decreases, but also Since the film formation time is prolonged and the productivity is reduced, the upper limit is set to 10 μm.

The thickness of the p-type thin film crystalline silicon layer 18 is 5
It is desirable that the thickness be not less than nm and not more than 50 nm. When the thickness of the p-type thin film crystalline silicon layer 18 falls below 5 nm, the entire surface of the i-type thin film crystalline silicon layer 17 is not covered with the p-type thin film crystalline silicon layer 18 and Partially exposed in a patch-like manner, that is, the p-type thin film crystalline silicon layer 18 grows in an island shape. In this case,
Since a normal semiconductor pn junction is not formed in a portion where the p-type thin film crystalline silicon layer 18 is not formed, the characteristics as a photovoltaic element are significantly reduced. The lower limit of the thickness is 5 nm. On the other hand, when the film thickness of the p-type thin film crystalline silicon layer 18 exceeds 50 nm, the influence of light absorption in the p-type thin film crystalline silicon layer 18 becomes large, and the amount of light reaching the i-type thin film crystalline silicon layer 17 is reduced. Since this causes a problem in element performance that the short-circuit current of the photovoltaic element is small, the upper limit is set to 50 nm.

Next, ZnO, SnO ₂ or ITO
A transparent conductive film layer 19 made of the above is laminated. The transparent conductive film layer 19 is preferably formed by a CVD method, a sputtering method, or the like.

Next, Al, Ag, Ti, Ni, Cr,
When the comb-shaped collector electrode 20 made of one or more metals selected from the group of Cu or an alloy thereof is formed, the photovoltaic element shown in FIG. 2 is completed. The collecting electrode 20 is formed by a physical vapor deposition method such as a vacuum vapor deposition method or a sputtering method, or a printing method. In the photovoltaic element having the structure shown in FIG. 2, light enters from the transparent conductive film layer 19 side.

Next, a photovoltaic element according to another embodiment of the present invention will be described with reference to FIG.

In the photovoltaic element of this embodiment, glass,
A light-transmitting substrate 9 such as plastic is used. On the translucent substrate 9, a metal oxide transparent conductive film layer 19a made of ZnO, SnO _2, ITO, or the like is formed by lamination by a CVD method, a sputtering method, or the like.

Next, the n-type (or p-type) thin film crystalline silicon layer 16, the i-type thin film crystalline silicon layer 17, and the p-type (or n-type) thin film A system silicon layer 18 is sequentially formed on the translucent substrate 9. The thickness of each of the n-type (or p-type) thin-film crystalline silicon layer 16, the i-type thin-film crystalline silicon layer 17, and the p-type (or n-type) thin-film crystalline silicon layer 18 depends on the first embodiment. Same as the form.

Next, ZnO, SnO ₂ or ITO
Is formed on the thin-film crystalline silicon layer 16 by a CVD method, a sputtering method, or the like. Finally, Al, Ag, Ti, Ni, Cr, C
back electrode layer 2 made of a metal such as u or an alloy thereof
When 1 is formed, the photovoltaic element shown in FIG. 3 is completed.
In the photovoltaic element having the structure shown in FIG. 3, light enters from the light transmitting substrate 9 side.

Next, as a specific embodiment of the present invention, a substantially intrinsic i-type thin film crystalline silicon film formed on the substrate 9 will be described in comparison with a comparative example. (Example 1-1)
-1-2) The degreased and cleaned glass substrate 9 was set in the film forming apparatus shown in FIG. 1, and an i-type thin film crystalline silicon film was formed by the method described above. The source gas is silane SiH ₄
And using hydrogen _{H 2.}

Table 1 shows Examples 1-1 and 1-2 and Comparative Example 1.
The film forming condition of -1 is shown. The conditions of Comparative Example 1-1 were substantially the same as those of Example 1-2 except that the film-forming surface heater 12 was not used. In Example 1-1 in which the film was formed using the film forming surface heater 12, the set temperature of the substrate heater 7 was adjusted so that the same substrate surface temperature as in Comparative Example 1-1 was obtained. The film forming time was adjusted so that the thickness of each test piece was 1.0 μm.

Regarding the film formed on the glass substrate 9, X
X-ray diffraction was performed, and the diffraction intensity of (22) was
The diffraction intensity ratio of the 0) plane was compared. Table 1 shows the results. As is clear from Table 1, Examples 1-1 and 1-2
Is (111) in X-ray diffraction as compared with Comparative Example 1-1.
The ratio of the diffraction intensity of the (220) plane to the diffraction intensity of the plane increased, and the (220) preferred orientation increased. Incidentally, although the substrate surface temperature of Example 1-1 is the same as that of Comparative Example 1-1, since the film forming surface heater 12 is used, (2
20) It was found that an i-type thin film crystalline silicon film having strong columnar orientation and columnar crystals was obtained. This tendency is more remarkable in the comparison between Example 1-2 in which a film is formed at the same substrate heater temperature and Comparative Example 1-1. this is,
As compared with Comparative Example 1-1 in which heating is performed only by the substrate heater 7,
In Examples 1-1 and 1-2, since the surface of the growing film is heated by the film forming surface heater 12, the surface diffusion of the radicals adsorbed on the film surface is promoted, and the crystal growth proceeds. 220) This is because the structure has developed a columnar structure with strong preferential orientation.

(Embodiments 2-1 to 2-2) In the following, FIG.
Examples of the photovoltaic element having the structure shown in FIG.

On a substrate 9 made of glass, a lower electrode layer A
As No. 14, Ag having a thickness of 500 nm was formed by a vacuum evaporation method. Next, as the lower electrode layer B15, a film thickness of 50 nm
Was formed by sputtering. Next, an n-type thin-film crystalline silicon layer 16 to which phosphorus was added, an i-type thin-film crystalline silicon layer 17 and a p-type thin-film crystalline silicon layer 18 to which boron was added were formed by the aforementioned plasma CVD method.

The thicknesses of the n-type thin film crystalline silicon layer 16 and the p-type thin film crystalline silicon layer 18 were 20 nm and 30 nm, respectively. Next, an 80 nm-thick transparent conductive film layer 19 made of ITO was formed by a sputtering method. Finally, a comb-shaped current collecting electrode 20 made of Al was formed by a vacuum evaporation method. Simulated sunlight (AM1.5, AM1.5) was applied to the photovoltaic element thus formed from the transparent conductive film layer 19 side.
100 mW / cm ² ), and the photoelectric conversion efficiency was measured.

Table 2 shows film forming conditions of the i-type thin film crystalline silicon layer 17 for Examples 2-1 to 2-2 and Comparative example 2-1. Comparative Example 2-1 had basically the same film forming conditions as Example 2-2 except that the film forming surface heater 12 was not used. In Example 2-1, the set temperature of the substrate heater 7 was adjusted so that the same substrate surface temperature as that of Comparative Example 2-1 was obtained. In each test piece, the thickness of the i-type thin-film crystalline silicon layer 17 was 2.0 μm.

Table 2 shows a comparison of the photoelectric conversion efficiencies of Examples 2-1 to 2-2 and Comparative Example 2-1 in which the films were formed. The conversion efficiency in Table 2 indicates a relative value when the photoelectric conversion efficiency of Comparative Example 2-1 in which the i-type thin film crystalline silicon 17 was formed without using the film forming surface heater 12 was 1.0. Was. Comparative Example 2-1
In comparison, in Examples 2-1 and 2-2 in which the i-type thin-film crystalline silicon layer 17 was formed using the film forming surface heater 12, the photoelectric conversion efficiency was improved to 1.06 and 1.13, respectively. did. In Examples 2-1 and 2-2 in which the i-type thin-film crystalline silicon layer 17 was formed using the film-forming surface heater 12, the i-type thin-film crystal was compared with Comparative Example 2-1 for the reason described above. The columnar structure of the system silicon layer 17 further develops. Therefore, the number of crystal grain boundaries crossing the direction in which current flows decreases, and carriers generated by light in the i-type thin-film crystalline silicon layer 17 become
Since it was efficiently taken out to an external circuit without being lost by recombination, the photoelectric conversion efficiency was improved as compared with Comparative Example 2-1.

(Example 3-1) Hereinafter, Example 3-1 of the photovoltaic element using the translucent substrate 9 shown in FIG. 3 will be described together with Comparative Example 3-1. On a translucent substrate 9 made of glass, SnO _{2 having a} thickness of 700 nm and ZnO having a thickness of 40 nm were each applied as a transparent conductive film layer 19 a by thermal CV.
It was formed by the D method and the sputtering method.

Next, the n-type thin-film crystalline silicon layer 16, the i-type thin-film crystalline silicon layer 17, to which phosphorus is added by the above-mentioned plasma CVD method using the film forming surface heater heating,
Then, a p-type thin film crystalline silicon layer 18 to which boron and boron were added was sequentially formed.

The thicknesses of the n-type thin film crystalline silicon layer 16 and the p-type thin film crystalline silicon layer 18 are 20 nm and 3 nm, respectively.
It was set to 0 nm. Next, an 80 nm-thick transparent conductive film layer 19b made of ITO was formed by a sputtering method. Finally, a back electrode 21 made of Al was formed by a vacuum evaporation method. Simulated sunlight (AM 1.5, 100 mW / cm) was applied to the photovoltaic element thus formed from the transparent substrate 9 side.
² ) was irradiated, and the photoelectric conversion efficiency was measured.

Table 3 shows the conditions for forming the i-type thin film crystalline silicon layer 17 for Example 3-1 and Comparative example 3-1. In Comparative Example 3-1, the i-type thin film crystalline silicon layer 17 was formed without using the film forming surface heater 12.
In Example 3-1, the i-type thin film crystalline silicon layer 17 was formed using the film forming surface heater 12. In Example 3-1, the set temperature of the substrate heater 7 was adjusted so that the substrate surface temperature was the same as in Comparative Example 3-1. In each test piece, the thickness of the i-type thin-film crystalline silicon layer 17 is
2.0 μm.

Table 3 also shows the photoelectric conversion efficiency of each element of Example 3-1 and Comparative example 3-1. Table 3 shows that the i-type thin film crystalline silicon layer 1 was used without using the film forming surface heater 12.
7 shows a relative value when the photoelectric conversion efficiency of Comparative Example 3-1 in which a film No. 7 was formed was 1.0. Example 3 as compared with Comparative Example 3-1
The photoelectric conversion efficiency of -1 was significantly improved to 1.12. This is because in Example 3-1 in which the i-type thin-film crystalline silicon layer 17 was formed using the film-forming surface heater 12, the columnar crystals of the i-type thin-film crystalline silicon layer 17 were further developed for the reasons described above. In addition, in Comparative Example 3-1, in forming the i-type thin-film crystalline silicon layer 17, the transparent conductive film layer 19a made of an oxide is reduced, the light transmittance is reduced, and the transparent conductive film 19a is reduced. The metal deposited by the reduction of the film layer 19a is
This is because they diffused into the semiconductor layer and reduced the semiconductor junction characteristics. On the other hand, in Example 3-1, the heater 12 for the film forming surface was used.
As a result, since the film surface is heated and the substrate heater 7 is kept at a relatively low temperature, the reduction of the transparent conductive film layer 19a does not occur, so that the photoelectric conversion efficiency is improved as compared with Comparative Example 3-1. .

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

[0061]

According to the present invention, a substrate heater for setting a substrate in a reaction vessel and a discharge electrode are arranged opposite to each other, and a gas containing silicon and hydrogen are used as raw material gases.
And the frequency of the high frequency power supply is 10MHz or more and 300MHz
In the formation of a silicon-based thin film characterized in that the film is formed by the following high-frequency plasma CVD method, a film forming surface heater for heating active species contributing to film formation is provided between a substrate and a discharge electrode. By using a silicon-based thin film manufacturing apparatus characterized by being arranged, a silicon-based thin film having a strong preferential orientation and a columnar structure is developed, and a silicon-based thin film photovoltaic device using the silicon-based thin film having excellent photoelectric conversion characteristics. A power element can be formed.

[Brief description of the drawings]

FIG. 1 is a block sectional view schematically showing an apparatus used for a method of forming a silicon-based thin film according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a photovoltaic device according to an embodiment of the present invention.

FIG. 3 is a schematic sectional view showing a photovoltaic element according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reaction container, 2 ... Discharge electrode, 3 ... Exhaust pipe, 4 ... High frequency power supply, 5 ... Impedance matching device, 6 ... Source gas introduction pipe, 7 ... Heater for substrate heating, 8 ... Vacuum pump, 9 ... Substrate, DESCRIPTION OF SYMBOLS 10 ... Coaxial cable, 11 ... Gas mixing box, 11a ... Insulating member, 12 ... Film forming surface heater, 13 ... Heater power supply, 14 ... Lower electrode layer A, 15 ... Lower electrode layer B, 16 ... n-type (or p-type) Type) thin-film crystalline silicon layer, 17 ... i-type thin-film crystalline silicon layer, 18 ... p-type (or n-type) thin-film crystalline silicon layer, 19 ... transparent conductive film layer, 20 ... current collecting electrode, 21 ... back electrode .

Continued on the front page (72) Inventor Yoshiaki Takeuchi 5-717-1, Fukahori-cho, Nagasaki-city, Nagasaki Prefecture Inside the Nagasaki Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Katsuhiko Kondo 5-717-1, Fukahori-cho, Nagasaki-city, Nagasaki Prefecture (72) Inventor Tatsuyoshi Nishinomiya 5-7-17-1 Fukahori-cho, Nagasaki-shi, NagasakiMitsuhishi Heavy Industries, Ltd. F-term (reference), 57-17-1 Mitsuhishi Heavy Industries, Ltd. Nagasaki Research Laboratory 4K030 AA06 AA17 BA29 CA06 FA03 HA04 JA18 KA24 KA30 LA16 5F045 AA08 AB02 AC01 AD07 AE19 AE21 BB12 BB15 BB16 CA13 DA65 DP05 EH04 EK07 AEK05A05A05 A055 CA16 CA24 CA34 DA04 FA04 FA06

Claims (8)

[Claims] A substrate is heated to a predetermined temperature in a reaction vessel,
A silicon-containing gas and a hydrogen gas are supplied between the substrate and the discharge electrode, and a power frequency of 10 MHz to 300 MHz is applied between the discharge electrode and the substrate to generate discharge plasma. A method of manufacturing a silicon-based thin film, comprising laminating thin-film crystalline silicon on a substrate. 2. The method according to claim 1, further comprising disposing a film forming surface heater between the substrate heating heater and the discharge electrode, and heating the thin film surface on the substrate by the film forming surface heater. Manufacturing method. 3. A reaction vessel, a substrate heating heater for holding and heating a substrate in the reaction vessel, a discharge electrode arranged to face the substrate held by the substrate heating heater, 10 MHz or more and 300 MHz for the discharge electrode
A manufacturing apparatus comprising: a high-frequency power source that applies a high-frequency power of the following frequency; and a gas supply source that supplies a silicon-containing gas and a hydrogen gas as a source gas between the discharge electrode and the substrate. An apparatus for manufacturing a silicon-based thin film, comprising a film forming surface heater between a heater and said discharge electrode. 4. A substrate, a first electrode layer composed of a metal or alloy film laminated on the substrate, and a first electrode layer composed of a metal oxide-based transparent conductive film laminated on the first electrode layer. A first conductive type thin film crystalline silicon layer laminated on the second electrode layer by using the method according to claim 1; and a first conductive type thin film crystalline silicon layer. An i-type thin-film crystalline silicon layer formed on the layer by using the method according to claim 1, and a lamination formed on the i-type thin-film crystalline silicon layer by using the method according to claim 1. A second conductive type thin film crystalline silicon layer, a third electrode layer made of a transparent conductive film laminated on the second conductive type thin film crystalline silicon layer, and a third electrode layer formed on the third electrode layer. A photovoltaic element comprising: a provided current collecting electrode. 5. The thin film crystalline silicon layer of the first conductivity type, the i-type thin film crystalline silicon layer, and the thin film crystalline silicon layer of the second conductivity type are arranged between a substrate heating heater and a discharge electrode. 5. The photovoltaic device according to claim 4, wherein each of the photovoltaic devices is formed by heating the surface of a thin film on a substrate using a formed film forming surface heater. 6. The thin film crystalline silicon layer of the first conductivity type and the second conductivity type is formed on the surface of the thin film on the substrate by using a film forming surface heater disposed between the substrate heating heater and the discharge electrode. 5. The photovoltaic device according to claim 4, wherein said photovoltaic device is formed by heating each of said photovoltaic devices. 7. A first electrode layer made of a metal or alloy film is laminated on a substrate by a physical vapor deposition method, and a second electrode layer made of a metal oxide-based transparent conductive film is formed by a CVD method or a sputtering method. A first conductive type thin film crystalline silicon layer formed on the second electrode layer by using the method of claim 1;
And an i-type thin film crystalline silicon layer is stacked on the first conductive type thin film crystalline silicon layer by using the method of claim 1, and using the method of claim 1. A second conductive type thin film crystalline silicon layer is laminated on the i-type thin film crystalline silicon layer, and a third electrode layer made of a transparent conductive film is formed by a CVD method or a sputtering method. A method for manufacturing a photovoltaic element, comprising laminating on a system silicon layer, and forming a current collecting electrode on the third electrode layer by a physical vapor deposition method or a printing method. 8. A film forming surface heater is disposed between a substrate heating heater and a discharge electrode, and the thin film surface on the substrate is heated by the film forming surface heater to form the first conductive type thin film crystal. 8. The manufacturing method according to claim 7, wherein a system silicon layer, an i-type thin film crystal silicon layer and a second conductivity type thin film crystal silicon layer are formed.