JPH0766437A - Manufacture of substrate for photoelectric transducer - Google Patents

Abstract

PURPOSE:To uniformly form a semiconductor film of few defects by a low temperature film forming means which film is provided with a texture trench. CONSTITUTION:A silicon oxide thin film 2 is formed, by a sputtering method, on the surface of single crystal silicon 1 on which surface etch-pits 10 constituting a texture trench are formed. The silicon oxide thin film and the signal crystal silicon surface are etched by using etching agent of 30wt.% KOH aqueous solution. Crest parts and valley parts of the etch-pits are worked into a curved surface while the texture trench is left as it is. By this working process, an amorphous silicon layer 4 which has few defects and is excellent in film characteristics can be simply formed, so that the photoelectric conversion efficiency of an obtained film forming type solar battery can be improved.

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 substrate for a photoelectric conversion device applied to a photoelectric conversion device such as a film-forming solar cell or an image sensor, and more particularly to a low temperature film formation having a texture groove on the surface. The present invention relates to a method for manufacturing a substrate for a photoelectric conversion device, by which a semiconductor film having few defects can be uniformly formed.

[0002]

2. Description of the Related Art A film-type solar cell will be described as an example of this type of photoelectric conversion device.
As shown in FIGS. 2 and 3A, for example, a p-type single crystal silicon substrate a and an n-type that forms a pn junction between the silicon substrate a provided on the light incident side surface of the single crystal silicon substrate a. Amorphous silicon layer b and this amorphous silicon layer b
The comb-teeth-shaped electrode c provided above and the back surface electrode d uniformly provided on the back surface side of the single crystal silicon substrate a constitute a main part thereof, and electrons and holes generated due to light incidence are generated. There is known a structure in which is extracted as a current from the electrodes c and d.

In this type of photoelectric conversion device such as a film-forming solar cell, in order to effectively absorb light and obtain high photoelectric conversion efficiency, conventionally, a substrate for a photoelectric conversion device has a light confining function on its surface. A single crystal silicon substrate in which the textured groove a1 is formed is applied (see FIG. 3B). That is, the single crystal silicon substrate having the textured groove is formed by, for example, etching single crystal silicon having a (100) crystal orientation with a strong alkali such as KOH to form a pyramid-shaped etch pit on the surface. Was obtained.

[0004]

By the way, FIG. 3 (B)
As shown in, the surface of a single crystal silicon substrate having a high degree of texture (that is, the tops and valleys of the above etch pits having a square shape) is subjected to, for example, a sputtering method or a plasma CVD (chemical vapor deposition) method. When a semiconductor film such as an amorphous silicon layer is formed by a film forming means whose film forming conditions are relatively low, defects occur in the semiconductor film formed at the top and the valley of the etch pit as shown in FIG. There is a defect that the film characteristics of the semiconductor film formed easily are not good. For this reason, in the photoelectric conversion device such as a film-forming solar cell obtained due to this, the photoelectric conversion efficiency does not increase so much despite the fact that the texture grooves act to effectively absorb light. Had.

Therefore, conventionally, there is adopted a method in which the surface of the single crystal silicon substrate on which the etch pits are formed is isotropically etched, and the tops and valleys of the etch pits are processed into a curved shape to reduce the texture. It was being done.

However, when the surface of the single crystal silicon substrate on which the etch pits are formed is subjected to isotropic etching, not only the tops and valleys of the etch pits but also the inclined surfaces of the etch pits are uniformly etched. Therefore, there is a drawback that the surface of the substrate becomes flat as a whole and the texture groove is easily lost. Then, due to this, the light confinement effect is lowered, so that there is a problem that the photoelectric conversion efficiency thereof does not increase so much as in the case of applying a substrate having a high texture.

When the above-mentioned substrate having a high degree of texture is applied, a method of applying a thermal CVD method instead of the above-mentioned low temperature film forming method such as the sputtering method or the plasma CVD method may be considered. That is, by applying this thermal CVD method and appropriately setting the film forming conditions, it is possible to improve the film characteristics of the semiconductor film formed on the top and the valley of the etch pit. is there.

However, the thermal CVD method requires a large amount of heat energy as compared with the low-temperature film forming method such as the sputtering method or the plasma CVD method, and the control of the film forming conditions becomes complicated. It is disadvantageous in that the cost is high and is not suitable as a method for manufacturing an inexpensive solar cell or the like.

The present invention has been made by paying attention to such a problem, and a problem thereof is that a semiconductor film having a texture groove on the surface and having a low number of defects can be uniformly formed by a low temperature film forming means. It is to provide a method for manufacturing a substrate for a photoelectric conversion device.

[0010]

That is, the invention according to claim 1 is premised on a method for manufacturing a substrate for a photoelectric conversion device having a textured groove, and a single crystal in which an etch pit forming the textured groove is formed. A thin film is formed on the surface of silicon by a low temperature film-forming method, and the thin film and the single crystal silicon surface are etched using an etchant having an etching rate for crystalline silicon higher than the etching rate for the thin film, and the top of the etch pit is etched. It is characterized in that the valley and the valley are each processed into a curved shape.

As a method of forming an etch pit on the surface of single crystal silicon by such a technical means, for example, single crystal silicon having a (100) crystal orientation is etched with a strong alkali such as KOH as in the conventional method. The method of processing is mentioned.

On the surface of the single crystal silicon in which the etch pits are formed, silicon oxide (S
A thin film such as iO ₂ ) is formed. Since this thin film is formed by the low temperature film forming method, as described in the prior art, the thin film formed on the top and valley of the etch pit is larger than the thin film formed on the inclined surface of the etch pit. Have defects. When the thin film and the surface of the single crystal silicon are subjected to an etching treatment with an etchant having an etching rate for crystalline silicon higher than the etching rate for the thin film, the thin film formed at the top and the valley of the etch pit has a sloped surface of the etch pit. Since the film characteristics are worse than those of the thin film formed in the above step, they are more likely to be etched by the etching agent, and this etching agent passes through the defects in the thin film and etches the tops and valleys of the etch pits. On the other hand, the film characteristics of the thin film formed on the inclined surface of the etch pit are better than those of the thin film formed on the top and the bottom of the etch pit, and thus are less susceptible to etching by the above-mentioned etching agent. The sloped surface of the etch pit covered with is also less susceptible to etching. Therefore, since the tops and valleys of the etch pits are selectively etched, it is possible to process the tops and valleys of the etch pits into curved shapes while leaving the texture grooves. In addition to the above-described silicon oxide, examples of materials applicable to the thin film include silicon nitride (SiN _x ), tin oxide (SnO ₂ ), titanium oxide (TiO ₂ ), and zinc oxide (ZnO). Can be mentioned.

When an etching agent having a lower etching rate for crystalline silicon than a thin film such as silicon oxide is applied as the etching agent, the thin film is uniformly etched regardless of the film characteristics of the thin film. Therefore, it becomes difficult to process the top and valley of the etch pit into a curved shape while leaving the texture groove. Therefore, it is necessary to apply an etching agent having an etching rate for crystalline silicon higher than that for the thin film. Examples of such an etching agent include the following, depending on the type of material forming the thin film. That is, when the thin film is silicon oxide (SiO ₂ ), a highly concentrated alkaline aqueous solution (for example, an aqueous solution of KOH, NaOH, etc.) or a mixed system of HF and HNO ₃ (HF: HNO ₃ = 1: 5 to 5).
1:10), and the thin film is silicon nitride (Si
In the case of N _x ) or titanium oxide (TiO ₂ ), the mixed system of HF and HNO ₃ can be applied. When the thin film is tin oxide (SnO ₂ ), about 5% dilute alkaline (KOH, NaOH, etc.) aqueous solution can be applied, and when the thin film is zinc oxide (ZnO), about 1%. A dilute alkaline (KOH, NaOH, etc.) aqueous solution or the like can be used.

Further, as an etching agent for removing the thin film remaining on the surface of the single crystal silicon after the top and the valley of the etch pit are processed into a curved surface shape, HF or the like for the silicon oxide thin film is used. About 1% dilute alkali (KOH or NaO) for silicon thin film and titanium oxide thin film
H or the like), an aqueous solution of a strong acid such as hydrochloric acid, sulfuric acid or nitric acid can be applied to the tin oxide thin film, and a diluted acid aqueous solution of about 1% can be applied to the zinc oxide thin film.

Next, as a low temperature film forming method capable of intentionally forming a thin film having bad film characteristics on the top and the valley of the etch pit,
PVD (Physical Vapor Deposition) method such as vacuum deposition method, sputtering method, ion beam devolution method and plasma CV
D method etc. are mentioned. The invention according to claim 2 relates to the invention which specifies the above-mentioned low temperature film forming method.

That is, the invention according to claim 2 is premised on the method for manufacturing a substrate for a photoelectric conversion device according to claim 1, wherein the low temperature film forming method is PVD or plasma CVD.
It is characterized by being a law.

Regarding the film thickness of the thin film formed on the surface of the single crystal silicon on which the etch pits are formed and the etching treatment time for the thin film and the surface of the single crystal silicon, the depth of the previously formed etch pits is It may be set to an appropriate value in consideration of the type of etching agent applied and the curved shapes of the top and valley of the etch pit.

Further, examples of application of the obtained substrate include substrates such as film-forming solar cells and image sensors.

[0019]

According to the first and second aspects of the invention, since the thin film is formed on the surface of the single crystal silicon in which the etch pits are formed by the low temperature film forming method, the thin film formed on the inclined surface of the etch pits. In comparison with the above, the thin film formed on the top and the valley of the etch pit has many defects. Then, when the thin film and the single crystal silicon surface are subjected to an etching treatment with an etching agent having an etching rate for crystalline silicon higher than the etching rate for the thin film, the tops and valleys of the etch pits covered with the thin film having many defects are selectively removed. Since it is subjected to etching, it is possible to process the tops and valleys of the etch pits into curved surfaces while leaving the textured grooves.

[0020]

EXAMPLES Examples of the present invention will be described in detail below.

First, n-type single crystal silicon having a (100) crystal orientation and a thickness of 0.6 mm (specific resistance 1
10 Ω · cm) 8 in 5% by weight KOH aqueous solution
It was immersed at 0 ° C. for 20 minutes to form 1.0 to 3.0 μm pyramid-shaped etch pits 10 (see FIG. 1A).

The single crystal silicon 1 in which the etch pits 10 are formed is introduced into a high frequency magnetron sputtering apparatus, and a silicon oxide thin film 2 having a thickness of 0.1 μm is formed on the surface of the single crystal silicon 1 by a sputtering method under the following film forming conditions. A film was formed (see FIG. 1B).

[Film Forming Conditions] Sputtering target; Si reactive gas type; O ₂ reactive gas supply rate; 1 SCCM to 20 SCCM reactive gas pressure; 1 mTorr to 10 mTorr discharge power; 50 W to 200 W single crystal silicon heating temperature; 100 C.-300.degree. C. Next, the single crystal silicon 1 on which the silicon oxide thin film 2 is formed is etched for about 1 minute using an etching agent of a 30 wt% KOH aqueous solution, and the oxidation formed on the inclined surface of the etch pit 10 is performed. The top and the valley of the etch pit 10 are processed into a curved surface shape through the silicon oxide thin film 22 having poor film characteristics as compared with the silicon thin film 21, and then an etchant of H is added.
Instead of F, an etching process was performed again, and the remaining silicon oxide thin film 2 was dissolved and removed to manufacture a substrate 3 as shown in FIG. 1 (C).

Then, the obtained substrate 3 was applied as a substrate for a film-forming solar cell. That is, a thickness of 2 is formed on the surface of the substrate 3 by the plasma CVD method under the following film forming conditions.
A 00Å p-type amorphous silicon layer 4 was formed (see FIG. 1D).

[Film forming conditions] Kind of reaction gas: B ₂ H ₆ / SiH ₄ = 0.05% to 5
% Reaction gas supply rate; 5 SCCM to 100 SCCM Reaction gas pressure; 50 mTorr to 1 Torr discharge power; 5 W to 100 W Heating temperature of single crystal silicon; 100 ° C. to 300 ° C. Next, on the p-type amorphous silicon layer 4 A comb-teeth-shaped electrode is formed of silver paste, and aluminum is uniformly deposited on the back surface side of the substrate 3 made of n-type single crystal silicon by a sputtering method to form a back surface electrode. Manufactured.

Then, the film-forming solar cell thus obtained was subjected to current-voltage measurement using a solar simulator of AM1: 100 mW / cm ² , and as a result, V _oc was 0.5.
The voltage was 7 V, J _sc was 35 mA / cm ² , FF was 0.71, and the photoelectric conversion efficiency η was 14.2%.

Further, when the surface reflection characteristics of this solar cell were measured, it was confirmed that the reflectance was reduced over the entire wavelength range, and that the light trapping function due to the texture groove was functioning.

[Comparative Example 1] Next, in order to confirm the effect of the substrate according to the embodiment, a p-type single crystal silicon in which the tops and valleys of the etch pits are not processed into a curved shape is used. A film-forming solar cell having the same structure was manufactured.

[0029] Then, this film forming solar cell, similar to the Example AM1: current by using a solar simulator of 100 mW / cm ² - result of voltage measurement, V _oc
Was 0.54 V, J _sc was 35 mA / cm ² , FF was 0.70, and photoelectric conversion efficiency η was 13.2%.

When the surface reflection characteristics of this solar cell were measured, the reflectance was reduced over the entire wavelength range,
It was also confirmed that the light confinement function due to the texture groove was functioning as in the example.

[Comparative Example 2] As in Comparative Example 1, in order to confirm the effect of the substrate according to the example, the top and valley of the etch pit were processed into a curved shape by etching without forming a silicon oxide thin film. A film-forming solar cell having the same structure as that of the example was manufactured using conventional p-type single crystal silicon.

[0032] Then, this film forming solar cell, similar to the Example AM1: current by using a solar simulator of 100 mW / cm ² - result of voltage measurement, V _oc
Was 0.58 V, J _sc was 32 mA / cm ² , FF was 0.71, and photoelectric conversion efficiency η was 13.2%.

When the surface reflection characteristics of this solar cell were measured, the reflectance increased over the entire wavelength range,
It was confirmed that the optical confinement function did not function sufficiently unlike the examples.

[0034]

According to the first and second aspects of the present invention, it becomes possible to manufacture a photoelectric conversion device substrate in which the tops and valleys of the etch pits are processed into a curved shape while leaving the texture grooves. .

Therefore, it becomes possible to easily form a semiconductor film having few defects and good film characteristics on the surface of the substrate, and thus it is possible to improve the photoelectric conversion efficiency of the obtained photoelectric conversion device. .

[Brief description of drawings]

1A to 1C are explanatory views showing a manufacturing process of a substrate for a photoelectric conversion device according to an embodiment, and FIG. 1D shows a semiconductor film formed on the obtained substrate. Explanatory drawing which shows a state.

FIG. 2 is a schematic perspective view of a film-forming solar cell.

3 (A) is a sectional view taken along line III-III in FIG.
FIG. 3B is a partially enlarged view of FIG.

FIG. 4 is a conceptual diagram showing film characteristics of a semiconductor film formed on the surface of a single crystal silicon substrate having a high texture.

[Explanation of symbols]

 1 Single Crystal Silicon 2 Silicon Oxide Thin Film 3 Substrate 4 Amorphous Silicon Layer 10 Etch Pit 21 Silicon Oxide Thin Film 22 Silicon Oxide Thin Film

Claims (2)

[Claims] 1. A method for manufacturing a substrate for a photoelectric conversion device having a textured groove, wherein a thin film is formed by a low temperature film forming method on the surface of single crystal silicon in which the etch pits forming the textured groove are formed, and The photoelectric conversion device characterized in that the thin film and the surface of the single crystal silicon are etched using an etchant having an etching rate for crystalline silicon higher than the etching rate for the thin film, and the tops and valleys of the etch pits are each processed into a curved shape. A method for manufacturing a substrate for a conversion device. 2. The low temperature film forming method is a PVD method or a plasma C method.
The method for manufacturing a substrate for a photoelectric conversion device according to claim 1, which is a VD method.