JP2002075877A - Method and device for forming polycrystalline semiconductor thin film, and solar cell using polycrystalline semiconductor thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in the conventional technique where process costs increase in the plasma CVD method using such special high-pressure gas as SiH4, the crystal particle diameter of Si film is small, light trapping is not sufficient, and the area of a semiconductor film to be formed cannot be increased easily. SOLUTION: A substrate for forming a semiconductor film is arranged in a chamber for introducing an etching gas, at the same time a solid-like semiconductor material is provided, further a heating catalyst body for activating the etching gas to be introduced into the chamber is provided, the etching gas is brought into contact with the heating catalyst body for activation, then the activated etching gas is allowed to collide with the solid-like semiconductor to form a volatile compound, and the volatile compound is transported to the surface of the substrate to form the semiconductor thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for forming a polycrystalline semiconductor thin film and a solar cell using the polycrystalline semiconductor thin film.

[0002]

2. Description of the Related Art In recent years, research and development of next-generation solar cells that achieve both low cost and high conversion efficiency have been actively promoted. In particular, thin-film polycrystalline S mainly composed of Si
An i-solar cell is considered to be the most promising next-generation solar cell after comprehensively considering costs, conversion efficiency, resource issues, environmental issues, and the like.

In this thin-film polycrystalline Si solar cell, cost reduction such as material cost and equipment cost is required in order to reduce the cost, but it is currently the mainstream method of forming a Si thin film for a solar cell. SiH ₄ , Si ₂ H ₆ , SiH _x Cl
_In a plasma CVD method using a special high-pressure gas such as _y as a process gas, strict response processing is required at various stages, such as gas production, transportation, management, and exhaust gas treatment. It is a factor that increases.

On the other hand, the formation of a high-quality photoactive layer and the formation of a light trapping structure are the most important requirements for improving the efficiency of a thin-film solar cell using polycrystalline Si for the photoactive layer. Regarding the crystal structure factor, it can be said that ideally, the polycrystalline Si film has a large crystal grain size and the surface of the crystal layer has an appropriate texture shape.

[0005] Regarding this, for example, Japanese Patent Laid-Open No. Hei 10-11
No. 7006 describes that a photoactive layer is formed by using a plasma CVD method and a spontaneous uneven structure of 0.05 to 3 μm is formed on the surface of the Si layer.
A problem is that the crystal grain size of the film is as small as several nm to several hundred nm.

In this film forming method, plasma CVD is used.
Since the method is used, there is a problem that it is difficult to form a large-area film as compared with the catalytic CVD method or the like due to the configuration of the apparatus.

[0007] The present invention has been made in view of such problems of the prior art, and the plasma CVD method using a special high-pressure gas such as SiH ₄ increases the process cost.
Since the crystal grain size of the Si film is small, light trapping is not sufficient, and it is difficult to increase the area of the semiconductor film to be formed. It is an object of the present invention to provide a forming device and a semiconductor device using the polycrystalline semiconductor thin film.

[0008]

According to a first aspect of the present invention, there is provided a method for forming a polycrystalline semiconductor thin film.
After activating the etching gas by contacting the heating catalyst with the heating catalyst, the activated etching gas collides with the solid semiconductor to form a volatile compound, and transports the volatile compound to the surface of the substrate. The method is characterized in that a semiconductor thin film is formed.

In the method of forming a polycrystalline semiconductor thin film, it is preferable that the etching gas is one or more of a hydrogen gas, a fluorine-based gas, and a chlorine-based gas.

In the method of forming a polycrystalline semiconductor thin film, it is preferable that the solid semiconductor is made of one or more of silicon, germanium, and selenium.

In the method of forming a polycrystalline semiconductor film, the volatile compound may be brought into contact with the heating catalyst and then transported to the surface of the substrate to form a semiconductor film.

In the method for forming a polycrystalline semiconductor thin film, it is preferable that the heating catalyst is heated at a temperature of 1500 to 2000 ° C.

In the method of forming a polycrystalline semiconductor thin film, it is preferable that the substrate temperature is set higher than the temperature of the solid semiconductor.

In the apparatus for forming a polycrystalline semiconductor film according to the present invention, a substrate for forming a semiconductor film is provided in a chamber into which an etching gas can be introduced, and a solid semiconductor material is provided. Further, a heating catalyst for activating the etching gas introduced into the chamber is provided.

In the above-described apparatus for forming a polycrystalline semiconductor film, it is preferable that the heating catalyst is made of one or more of tungsten, tantalum, platinum, and molybdenum.

In the above-described apparatus for forming a polycrystalline semiconductor film, it is preferable that the heating catalyst is disposed between the substrate and the solid semiconductor.

According to a tenth aspect of the present invention, there is provided a solar cell using a polycrystalline semiconductor thin film formed by the method according to the first to sixth aspects.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail.

FIG. 1 is a view showing one embodiment of an apparatus for forming a polycrystalline semiconductor thin film according to the present invention.
2 is a gas inlet, 3 is a solid semiconductor, 4 is a heating catalyst,
5 is a substrate.

A substrate 5 is disposed downward in the upper part of the chamber 1, a solid semiconductor 3 is disposed in a lower part of the chamber 1, and a heating catalyst is provided between the substrate 1 and the solid semiconductor 3. 4 is provided, and a gas inlet 2 is provided in the lower part of the chamber 1.

The substrate 5 is made of an insulating substrate such as glass, SUS, or the like, and can be heated to a temperature of about 500 ° C. by providing a heating means (not shown) such as a heater in the support plate. Have been.

The heating catalyst 4 is made of one or more of tungsten, tantalum, platinum, and molybdenum.

The heating catalyst 4 is preferably disposed between the solid semiconductor 3 and the substrate 5 in order to uniformly etch the solid semiconductor 3 with an etching gas. If the position can activate
Not limited to that.

Using such an apparatus, an etching gas is brought into contact with the heating catalyst 4 to be activated, and then the activated etching gas is caused to collide with the solid semiconductor 3 to form a volatile compound. This volatile compound is transported to the surface of the substrate 5 to form a semiconductor thin film. That is, the polycrystalline semiconductor film obtained by such a formation method has crystal grains having a crystal grain size of 0.1 to 1 μm in a direction parallel to the substrate 5. This is because the etching gas is activated by the heating catalyst to have an etching action, and the nucleation density on the surface of the substrate 5 in the initial stage of the growth of the semiconductor film and the generation rate of the secondary nuclei during the growth are moderate. It is considered that this is because In addition, the ratio of the crystal component to the whole film is 90% or more, and in this polycrystalline semiconductor thin film, the surface of the film has an uneven structure of 0.05 to 0.5 μm.

As the etching gas, hydrogen gas is used.
Gas, fluorine-based gas, or chlorine-based gas
Alternatively, a plurality of types can be used. As fluorine-based gas
Is CF _Four, C_TwoF₆, SF₆, BF_FourEtc., as chlorine-based gas
Is CCl_Four, OCI_Three, BCl_Three, Cl_TwoEtc., fluorine-chlorine
The system gas is CCIF_Three, CCl_TwoF_Two, CCl_ThreeF, C
_TwoClF_Five, C_TwoCl_TwoF_FourAre used. This etchin
Gas can control the inside of the chamber 1 to about 13 Pa
Such a flow rate may be set.

The solid semiconductor is a main raw material of a polycrystalline semiconductor film formed on the substrate 5.
It is made of one or more of germanium and selenium.

In order to form a good semiconductor film on the substrate 5, the volatile compound may be brought into contact with the heating catalyst 4 again. When formed in this manner, the volatile compound becomes more active, and high-speed deposition can be expected.

The heating catalyst 4 has a temperature of 1500 to 2000 ° C.
Heat to If this temperature is 1500 ° C. or lower, a situation where the heating catalyst 4 reacts with a volatile compound to cause deterioration is induced. Further, when the temperature becomes 2000 ° C. or higher, the components of the heating catalyst 4 evaporate, are taken in as impurities in the deposited film, and the quality of the semiconductor film deteriorates.

The temperature of the solid semiconductor 3 is set at about 0 to 300.degree. The temperature of the substrate 5 is higher than the temperature of the solid semiconductor 3 by one.
The temperature is set to be about 00 ° C. higher, that is, 100 to 500 ° C. That is, the higher the temperature, the lower the etching rate. Therefore, by setting the temperature of the substrate 5 higher than the temperature of the solid semiconductor 3 as described above, while maintaining the etching rate of the solid semiconductor high, This is because the etching rate on the substrate surface can be reduced.

Next, an example of forming a thin-film polycrystalline Si solar cell will be described with reference to FIG.

The thin-film solar cell shown in FIG.
1, Ti, Ni, W, Mo, Cu, Ag, or A
1, a thin film layer 12a formed of at least one kind of a metal film, a nitride film thereof, or a silicide film thereof, an oxide layer 12b containing at least one of In, Sn or Zn, a p-type polycrystalline Si An underlayer 13, a p-type polycrystalline Si photoactive layer 14, an n-type non-single-crystal Si layer 15,
And a conductive antireflection film 16 also serving as a light receiving surface electrode layer. In the figure, reference numeral 17 denotes a front extraction electrode formed on the upper surface of the antireflection film 16, and reference numeral 18 denotes the oxide layer 1.
It is a back extraction electrode formed on the upper surface of 2b.

In manufacturing such a thin film solar cell, first, a thin film layer 12a is formed on a glass substrate 11 by a vacuum film forming method such as an electron beam evaporation method or a sputtering method so that the sheet resistance becomes about 1 Ω / □ or less. To an appropriate thickness. Specifically, a Ti film is formed to a thickness of 0.1 μm, an Ag film is formed thereon to a thickness of 1 μm, and a Ti film is further formed to a thickness of 0.1 μm.
When the film is formed, a sheet resistance of 0.1Ω / □ or less is realized.
The Ti and Ag films may be replaced with other metals or the like in the following steps as long as there is no problem.

Next, an oxide layer 12b is formed on the thin film layer 12a by a vacuum film forming method such as a sputtering method or an ion plating method. Specifically, an ITO film having an uneven shape on the surface is formed. Next, the polycrystalline Si underlayer 1
3 is formed on the oxide. Specifically, a polycrystalline Si layer containing B at about 1E18 to 1E22 / cm ³ is formed on the oxide layer 12b to a thickness of about 1 μm or less by a plasma CVD method or a catalytic CVD method. , High BS
An underlayer having an F function is used.

Next, a polycrystalline or microcrystalline Si layer serving as a Si photoactive layer 14 of the same conductivity type (ie, p-type) as the same layer is formed on the polycrystalline Si layer 13 by using the apparatus shown in FIG. To a thickness of about 1 μm to 30 μm. At this time, such as H ₂ as a process gas, a single-crystal Si substrate of the polycrystalline Si layer 13 of the same conductivity type is used as solid semiconductor 3, H ₂ = 10 sccm, a substrate temperature of 350 ° C. to 500
° C, the temperature of the solid semiconductor 3 is 150 ° C, and the diameter is 0.5 mm.
Input voltage to the W (tungsten) catalyst 4 is ~ 50 W
/ M, the distance between the catalyst body and the element substrate 11 is up to 5 cm, and the deposition pressure is up to 13 Pa. A polycrystalline or microcrystalline Si layer formed under this condition has a crystal component occupying 90% or more of the entire film by Raman spectroscopy.
It has been confirmed by SEM observation that crystal grains having a crystal grain size of 0.1 to 1 μm are contained. The SEM observation also confirms that the surface of the layer has an uneven structure of 0.05 to 0.5 μm.

Here, the polycrystalline Si underlayer 13 functions as an underlayer of the Si photoactive layer 14 and can promote the expansion of the crystal grain size and the crystal quality of the Si photoactive layer 14, and optimize the film forming conditions. In this case, epitaxial growth can be performed.

Next, the Si underlayer 1 is formed on the Si photoactive layer 14.
A non-single-crystal Si layer 15 containing an amorphous, polycrystalline or microcrystalline of the opposite conductivity type (ie, n-type) to the plasma C
It is formed to a thickness of 1 μm or less by a vacuum film forming method such as a VD method, a catalytic CVD method, or a sputtering method.

Here, the Si photoactive layer 14 and the non-single-crystal Si
Depending on the quality of the pn junction formed with layer 15, Si
Between the photoactive layer 14 and the non-single-crystal Si layer 15, an intrinsic type (i
(Type) non-single-crystal Si layer may be interposed. In particular, when the same layer is formed of hydrogenated amorphous Si, the thickness is set to about 2 to 40 nm. Further, the non-single-crystal Si layer 15
In addition, when the intrinsic non-single-crystal Si layer is formed in an atmosphere containing hydrogen, in particular, the interface of each layer and a defect level in the vicinity thereof can be inactivated by terminating with hydrogen, and a higher quality pn can be obtained.
A junction or a pin junction can be obtained.

When the RIE method is used to form fine and random irregularities on the element surface independent of the crystal orientation of crystalline Si to increase the light use efficiency and improve the element conversion efficiency, the pn junction must be formed. Before forming, the Si photoactive layer 1
4 is subjected to RIE, and then a non-single-crystal Si layer 15 is formed. Depending on the substrate to be used, an uneven shape may be formed on the surface of the element substrate 11 by using the RIE method before forming the thin film layer 12a. In any case, this R
Light wavelength 400 contributing at least to power generation by IE processing
Within the range of nm to 1000 nm, the reflectance of the bare Si surface can be reduced to 10% or less.

Next, on the non-single-crystal Si layer 15, a conductive anti-reflection film 16 such as ITO or SnO ₂ or an insulating anti-reflection film 16 such as a silicon nitride film or a silicon oxide film is formed by a plasma CVD method or a sputtering method. Is formed in a thickness of about 60 to 100 nm by using the vacuum film forming method described above.

Next, a front extraction electrode 17 is formed on the antireflection film 16 by using a vacuum film forming technique, a printing and baking technique, and a plating technique. When an antireflection film having a green color is formed on the non-single-crystal Si layer 15, an insulating antireflection film is formed in a region where the front electrode 17 is formed by an etching technique using a suitable chemical such as buffered hydrofluoric acid. Removing the film to expose the non-single-crystal Si layer 15;
What is necessary is just to make the front extraction electrode 17 contact here.

The back electrode 18 is also formed on the thin film layer 12b by vacuum film forming technology, printing and baking technology,
Further, it can be formed using a plating technique or the like. In some cases, the back electrode layer 12a may be exposed, and the back extraction electrode 18 may be formed thereon.

As described above, a low-cost and highly efficient thin-film solar cell can be obtained.

In the above embodiment, an example was described in which the polycrystalline semiconductor thin film was used for the photoactive layer of the solar cell. However, the polycrystalline semiconductor thin film can be used for other layers of the solar cell.

[0044]

As described above, according to the method for forming a polycrystalline semiconductor thin film according to the first aspect, after the etching gas is brought into contact with the heating catalyst to be activated, the activated etching gas is removed. A volatile compound is formed by colliding with a solid semiconductor, and the volatile compound is transported to the surface of the substrate to form a semiconductor thin film.
1 μm, the proportion of this crystal component in the whole film is 90%
As described above, a polycrystalline semiconductor thin film suitable for a photoactive layer or the like of a solar cell can be formed. Further, a polycrystalline thin film having a relatively large particle size can be obtained at low cost without using a dangerous gas as a process gas, and the manufacturing cost of various thin film polycrystalline devices can be reduced.

According to the apparatus for forming a polycrystalline semiconductor film of the present invention, a substrate for forming a semiconductor film is provided in a chamber into which an etching gas can be introduced, and a solid semiconductor material is formed. Since the heating catalyst is provided for activating the etching gas introduced into the chamber, the above-described polycrystalline semiconductor film can be easily manufactured.

Further, according to the solar cell according to the tenth aspect, since the above-described polycrystalline semiconductor thin film is used,
Since the polycrystalline semiconductor film has a small surface area of the crystal grain boundary and can suppress the recombination disappearance of photoexcited carriers at this interface, the short-circuit current and open-circuit voltage of a thin-film solar cell represented by a thin-film polycrystalline Si solar cell are reduced. Can be improved. In particular, in order to increase the short-circuit current in a thin-film polycrystalline Si solar cell, it is extremely important to increase the optical path length by forming a light trapping structure and improve long-wavelength light sensitivity. It changes greatly depending on the height difference of the unevenness and the aspect ratio.
Generally, in a device having a polycrystalline Si photoactive layer of about 1 to 2 μm, a height difference of about 0.1 μm is considered to be preferable, and the height difference of the unevenness of the polycrystalline semiconductor thin film is relatively small to this optimum value. It is a close value. As described above, a polycrystalline thin film suitable for a high-efficiency thin-film solar cell can be obtained at low cost.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a polycrystalline semiconductor thin film forming apparatus of the present invention.

FIG. 2 is a view showing one embodiment of a thin-film solar cell using a polycrystalline semiconductor thin film of the present invention.

[Explanation of symbols]

 1 chamber 2 gas inlet 3 solid semiconductor 4 heating catalyst 5 substrate 11 element substrate 12a back electrode layer 12b oxide layer 13 polycrystalline Si underlayer 14 polycrystalline Si photoactive layer 15 non-single crystalline Si layer 16 anti-reflection film 17 Front extraction electrode 18 Back extraction electrode

Continued on front page F-term (reference) 4G069 AA02 BC56A BC59A BC60A BC60B BC75A CD10 DA05 EE03 4K030 AA03 AA04 BA09 BA29 BA32 BB03 CA06 FA17 HA03 HA04 JA02 JA10 KA49 LA16 5F045 AB01 AB03 AB04 AB05 AC02 AD07 AD07 AF09 BP17 DQ08 EK07 5F051 AA03 CB04 CB29 CB30 GA04

Claims (10)

[Claims] After activating an etching gas by contacting the heating gas with a heating catalyst, the activated etching gas is caused to collide with a solid semiconductor to form a volatile compound. Forming a semiconductor thin film by transporting to a surface of a semiconductor. 2. The method for forming a polycrystalline semiconductor thin film according to claim 1, wherein the etching gas comprises one or more of a hydrogen gas, a fluorine-based gas, and a chlorine-based gas. 3. The method according to claim 1, wherein the solid semiconductor is made of one or more of silicon, germanium, and selenium. 4. The method according to claim 1, wherein the volatile compound is brought into contact with the heating catalyst, and then transported to the surface of the substrate to form the semiconductor thin film. Method. 5. The heating catalyst is heated to a temperature of 1500 to 2000 ° C.
The method for forming a polycrystalline semiconductor thin film according to claim 1, wherein the heating is performed at a temperature of: 6. The method according to claim 1, wherein the substrate temperature is set higher than the temperature of the solid semiconductor. 7. A substrate for forming a semiconductor film is provided in a chamber into which an etching gas can be introduced, a solid semiconductor material is provided, and the etching gas introduced into the chamber is further removed. An apparatus for forming a polycrystalline semiconductor film provided with a heating catalyst for activation. 8. The polycrystalline semiconductor film forming apparatus according to claim 7, wherein the heating catalyst is made of one or more of tungsten, tantalum, platinum, and molybdenum. 9. The heating catalyst according to claim 7, wherein the heating catalyst is disposed between the substrate and the solid semiconductor.
3. The apparatus for forming a polycrystalline semiconductor film according to claim 1. 10. A solar cell using a polycrystalline semiconductor thin film formed by the method according to claim 1.