WO2011132340A1

WO2011132340A1 - Method for producing low reflection substrate, method for manufacturing photovoltaic device, and photovoltaic device

Info

Publication number: WO2011132340A1
Application number: PCT/JP2010/069618
Authority: WO
Inventors: 秀一檜座; 松野　繁; 邦彦西村
Original assignee: 三菱電機株式会社
Priority date: 2010-04-21
Filing date: 2010-11-04
Publication date: 2011-10-27
Also published as: JPWO2011132340A1; JP5430751B2

Abstract

A method for producing a low reflection substrate according to one embodiment of the present invention comprises: a step wherein a high concentration impurity diffusion layer (2) is formed on a main surface of a (100) single crystal silicon substrate (1a); a step wherein an etching-resistant film (3) is formed on the high concentration impurity diffusion layer (2); a step wherein the etching-resistant film (3) is subjected to a sandblasting process so that an opening (4), which penetrates through the etching-resistant film (3) and reaches the high concentration impurity diffusion layer (2), is formed; a step wherein anisotropic etching is carried out via the opening (4) using an aqueous alkaline solution to which the etching-resistant film (3) is resistant, while having the etching-resistant film (3) provided with the opening (4) serve as a protective mask; and a step wherein the etching-resistant film (3) is removed after the etching.

Description

Low reflective substrate manufacturing method, photovoltaic device manufacturing method, and photovoltaic device

The present invention relates to a method for manufacturing a low reflection substrate, a method for manufacturing a photovoltaic device, and a photovoltaic device.

In order to improve the performance of photoelectric conversion devices such as solar cells, it is important to efficiently incorporate sunlight into the substrate constituting the solar cell. For this reason, texture processing is performed on the substrate surface on the light incident side, and light once reflected on the substrate surface is incident again on the substrate surface, so that more sunlight is taken into the substrate and the photoelectric conversion efficiency is improved. ing. Here, the texture processing is processing for intentionally forming fine irregularities having dimensions of several tens of nm to several tens of μm on the substrate surface.

As a method of forming a texture having a desired shape on the substrate, a thin film layer (protective film) serving as a mask formed on the entire surface of the substrate is partially provided with an opening by a method such as sandblasting, and then the etching solution is used. A technique for forming a recess in a substrate portion corresponding to a mask opening by dipping has been disclosed (see, for example, Patent Document 1).

JP 2004-287372 A

As a method of forming a texture on a silicon substrate, when the substrate is a single crystal substrate, anisotropy using the crystal orientation by an aqueous alkali solution such as sodium hydroxide or potassium hydroxide having a crystal orientation dependency on the etching rate. Etching is widely used. For example, when this anisotropic etching is performed on the (100) silicon substrate surface, a pyramidal texture with the (111) plane exposed is formed on the substrate surface.

However, when the (100) single crystal silicon substrate having a protective film provided with a partial opening is anisotropically etched using such an alkaline aqueous solution, the etching rate of the (111) plane is very slow. For this reason, the concave portion spreading speed in the lateral direction from the partial opening of the protective film is slow. Therefore, in order to form a uniform texture on the entire surface of the substrate and reduce reflection, a long-time anisotropic etching process and a protective film having a film thickness that can withstand long-time anisotropic etching are required. .

The present invention has been made in view of the above, and a method for manufacturing a low-reflection substrate, a method for manufacturing a photovoltaic device, and a higher method capable of reducing the reflection of the substrate by shorter-time anisotropic etching An object is to obtain a photovoltaic device having photoelectric conversion efficiency.

In order to solve the above-described problems and achieve the object, the present invention includes a step of forming a high concentration impurity diffusion layer on a main surface of a (100) single crystal silicon substrate, and a resistance to the high concentration impurity diffusion layer. A step of forming an etchable film, a step of subjecting the etch resistant film to a sandblasting process to form an opening penetrating the etch resistant film and reaching the high-concentration impurity diffusion layer; and Using the formed etching resistant film as a protective mask, performing an anisotropic etching using an alkaline aqueous solution with which the etching resistant film has resistance through the opening, and the etching resistance after the etching And a step of removing the film.

According to the present invention, since a high-concentration diffusion layer exists on the substrate surface directly under the protective film, the anisotropic etching rate of silicon by the alkaline aqueous solution can be increased, and etching for uniformly forming the texture on the entire surface of the substrate. There is an effect that the time can be shortened.

FIG. 1 is a cross-sectional view showing a p-type single crystal silicon substrate whose surface has been subjected to low reflection by the substrate roughening method according to the first embodiment of the present invention. FIGS. 2-1 is sectional drawing explaining the process of the manufacturing method of the low reflection board |

substrate concerning Embodiment

1 and 2 of this invention. FIG. 2-2 is a cross-sectional view for explaining a process of the method for manufacturing the low reflection substrate according to the first and second embodiments of the present invention. FIG. 2-3 is a cross-sectional view for explaining a process of the method for manufacturing the low-reflection substrate according to the first embodiment of the present invention. FIGS. 2-4 is sectional drawing explaining the process of the manufacturing method of the low reflection board | substrate concerning Embodiment 1 of this invention. FIGS. 2-5 are cross-sectional views for explaining a process of the method for manufacturing the low-reflection substrate according to the first embodiment of the present invention. FIG. 3A is a top view of the photovoltaic device manufactured by using the low reflection substrate manufactured by the method of manufacturing the low reflection substrate according to the first embodiment of the present invention. FIG. 3-2 is a cross-sectional view of the photovoltaic device manufactured using the low reflection substrate manufactured by the low reflection substrate manufacturing method according to the first embodiment of the present invention. FIGS. 4-1 is sectional drawing explaining the process of the manufacturing method of the low reflection board | substrate concerning Embodiment 2 of this invention. FIGS. FIG. 4-2 is a top view for explaining a process of the method for manufacturing the low-reflection substrate according to the second embodiment of the present invention. FIGS. 4-3 is sectional drawing explaining the process of the manufacturing method of the low reflection board | substrate concerning Embodiment 2 of this invention. FIGS. FIGS. 4-4 is sectional drawing explaining the process of the manufacturing method of the low reflection board | substrate concerning Embodiment 2 of this invention. FIGS. FIGS. 4-5 is sectional drawing explaining the process of the manufacturing method of the low reflection board | substrate concerning Embodiment 2 of this invention. FIG. 5A is a top view of the photovoltaic device manufactured using the low-reflection substrate manufactured by the low-reflection substrate manufacturing method according to the second embodiment of the present invention. FIG. 5B is a cross-sectional view of the photovoltaic device manufactured using the low reflection substrate manufactured by the method of manufacturing the low reflection substrate according to the second embodiment of the present invention. FIG. 6 is a diagram comparing the effect of reducing the substrate reflection according to the first embodiment of the present invention with the comparative example in terms of the reflectance at a wavelength of 628 nm and the weight difference before and after etching.

Embodiments of a low reflection substrate manufacturing method, a photovoltaic device manufacturing method, and a photovoltaic device according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment, In the range which does not deviate from the summary, it can change suitably.

In the embodiment described below, the material of the substrate and the use of the substrate with low reflection are not particularly limited, but as an example, low reflection of a (100) single crystal silicon substrate will be described. In addition, the substrate will be described as being used for manufacturing a single crystal silicon solar cell. Further, in the drawings shown below, the scale of each member may be different from the actual for easy understanding, and the same applies to the drawings.

Embodiment 1 FIG.
FIG. 1 shows a p-type single crystal silicon substrate 1 (a solar cell substrate that is a photovoltaic device) that has been subjected to low surface reflection by the substrate manufacturing method according to the present embodiment. 1 is a cross-sectional view showing a substrate 1). In this substrate 1, textured recesses 5 having pyramidal irregularities with an average pitch between holes of about 1 to 10 μm are formed substantially uniformly on the substrate surface.

Next, a method for manufacturing the low reflection substrate according to the first embodiment for forming such a substrate 1 will be described. The manufacturing method of the low reflection substrate according to the first embodiment includes a first step of forming a protective film on the surface of the substrate, and a first step of forming a partial opening in the protective film by subjecting the protective film to a blasting process. Two steps, a third step of etching the surface of the substrate on which the protective film is formed using the protective film having an opening as a mask, under a condition that the protective film is resistant, and a fourth step of removing the protective film Including.

FIGS. 2-1 to 2-5 are cross-sectional views for explaining the steps of the manufacturing method of the low reflection substrate according to the first embodiment. Hereinafter, the manufacturing method of the low reflection substrate according to the first embodiment will be described with reference to these drawings.

First, in the first step, as shown in FIG. 2-1, a high concentration is applied to the surface of one surface side of a p-type single crystal silicon substrate 1a (hereinafter referred to as substrate 1a) which is a target for reducing the reflection of the substrate surface. An n-type diffusion layer 2 is formed.

The substrate 1a in the present embodiment is a (100) single crystal silicon substrate that is widely used for consumer solar cells. In this method, after slicing from a silicon ingot with a multi-wire saw, damage during slicing is removed by wet etching using an acid or alkali solution. For example, the thickness of the substrate 1a after removing the damage is 200 μm and the dimensions are 156 mm × 156 mm. In addition, the dimension of the board | substrate 1a is not limited to this, It can change suitably.

The high-concentration n-type diffusion layer 2 is formed by introducing the substrate 1a into a thermal oxidation furnace and heating it in the presence of phosphorus oxychloride (POCl ₃ ) vapor to form phosphorus glass on the surface of the substrate 1a. Formed by diffusing phosphorus inside. The diffusion temperature is set to 840 ° C., for example. After forming the diffusion layer, it is immersed in a hydrofluoric acid solution to remove the phosphorus glass layer.

In the second step, as described in FIG. 2B, the surface of the substrate 1a on which the high-concentration n-type diffusion layer 2 that is a target for reducing the reflection of the substrate surface is formed as a protective film on the surface to be described later. A film 3 having etching resistance (hereinafter referred to as an etching resistant film) 3 is formed.

The etching resistant film 3 is a 100 nm thick silicon thermal oxide film (hereinafter referred to as SiO ₂ film) formed by thermal oxidation. Here, although the SiO ₂ film is used as the etching resistant film 3, the silicon nitride film (SiN), silicon oxynitride film (SiON), and amorphous silicon film (SiON film) formed by the plasma CVD method as the etching resistant film 3 are used. а-Si), diamond-like carbon film or the like may be used.

In the third step, fine hole processing is performed on the etching resistant film 3 as shown in FIG. That is, a plurality of fine openings 4 are opened in the etching resistant film 3 by sandblasting. The fine opening 4 formed here penetrates the etching resistant film 3 and reaches the high concentration n-type diffusion layer 2.

At this time, alumina abrasive grains are used as abrasive grains for blast processing. The inventors of the present application searched for the most suitable abrasive for opening an opening in the SiO ₂ film that is the etching resistant film 3 without causing cracks in the substrate, and as a result of repeated research, the alumina abrasive grains were the most suitable. It came to the knowledge that it was suitable. However, the abrasive grains for the blasting treatment are not limited to this, and other abrasive grains other than the alumina abrasive grains may be used as long as the fine openings 4 can be opened in the etching resistant film 3.

In the fourth step, an alkali is applied to one surface of the substrate 1a on which the high-concentration n-type diffusion layer 2 is formed on the side on which the etching resistance film 3 is formed, using the etching resistance film 3 subjected to micro-hole processing as a mask. An anisotropic etching with an aqueous solution is performed to form a textured recess 5 through the fine opening 4 as shown in FIG. 2-4.

As an alkaline aqueous solution used for etching, for example, a sodium hydroxide aqueous solution is used. The concentration of the aqueous alkaline solution is 1 weight percent, and the temperature is 80 ° C. Further, an additive such as isopropyl alcohol may be added to the alkaline aqueous solution. Here, the concentration and temperature of the alkaline aqueous solution can be appropriately changed according to the required etching amount and time.

In the fifth step, the textured recess 5 is exposed by removing the etching resistant film 3. For example, a hydrofluoric acid aqueous solution can be used to remove the etching resistant film 3. As a result, as shown in FIG. 2-5, a texture structure having a fine pattern of, for example, about 10 μm can be formed on the surface of the substrate 1a. The p-type single crystal silicon substrate in which the substrate surface has been subjected to low reflection through the above steps is the substrate 1 in FIG.

Next, using the substrate 1 having a textured structure formed on the substrate surface using the above-described method for manufacturing a low-reflection substrate, the photoluminescence shown in the top view of FIG. 3-1 and the cross-sectional view of FIG. 3-2 is used. A process for manufacturing the power device 10 will be described. In addition, since the process demonstrated here is the same as the manufacturing process of the photovoltaic apparatus using a general single crystal silicon substrate, the process in the middle is not illustrated in particular.

The substrate 1 that has been subjected to the process of the fifth step is put into a thermal oxidation furnace and heated in the presence of phosphorus oxychloride (POCl ₃ ) vapor to form phosphorous glass on the surface of the substrate 1. Then, phosphorus is diffused to form an n-type diffusion layer 11a in the surface layer of the substrate 1 (FIG. 3-2). The diffusion temperature is 840 ° C., for example.

Next, after removing the phosphor glass layer of the substrate 1 in a hydrofluoric acid solution, a SiN film is formed on the n-type diffusion layer 11a as the antireflection film 12 by plasma CVD. The antireflection film 12 is formed in a region excluding the formation region of the light receiving surface side electrode 13 to be formed later (FIG. 3-2). The film thickness and refractive index of the antireflection film 12 are set to values that most suppress light reflection. Note that two or more layers having different refractive indexes may be stacked. Further, the antireflection film 12 may be formed by a different film forming method such as a sputtering method.

Next, a paste mixed with silver is printed on the light-receiving surface of the substrate 1 in a comb shape by screen printing, and a paste mixed with aluminum is printed on the entire back surface of the substrate 1 by screen printing, and then a baking process is performed. Thus, the light receiving surface side electrode 13 and the back surface electrode 14 are formed. Firing is performed at 760 ° C. in an air atmosphere, for example. The light-receiving surface side electrode 13 includes a bus electrode 13a and a grid electrode 13b of the photovoltaic device 10 (FIG. 3-1), and FIG. 3-2 shows a cross-sectional view in a cross section perpendicular to the longitudinal direction of the grid electrode 13b. Yes. As described above, the photovoltaic device 10 shown in FIGS. 3-1 and 3-2 is manufactured.

The photovoltaic device 10 includes a semiconductor substrate 1 having an n-type diffusion layer 11a on a substrate surface layer, an antireflection film 12 and a light receiving surface side electrode 13 formed on a light receiving surface side (front surface) of the semiconductor substrate 1, A photovoltaic device of 15 cm □ is provided that includes a back electrode 14 formed on a surface (back surface) opposite to the light receiving surface.

The results of evaluating the performance of the photovoltaic device 10 manufactured through the above steps will be described. In producing the photovoltaic device 10, the reflectance characteristics of the substrate 1 were evaluated with a spectrophotometer at the time when the low reflection of the substrate 1 was performed. Of these, the reflectance at a wavelength of 628 nm and the weight difference before and after etching are shown in FIG.

As a comparative example, the first and second steps were not carried out, but the second and subsequent steps were carried out to produce a concavo-convex substrate. At this time, the alkali anisotropic etching time in the fourth step is the same as the alkali anisotropic etching time in the substrate 1 subjected to low reflection by the substrate manufacturing method according to the first embodiment. Yes. The light reflection characteristics of the substrate of the comparative example were evaluated with a spectrophotometer. Of these, the reflectance at a wavelength of 628 nm and the weight difference before and after etching are also shown in FIG.

As can be seen from FIG. 6, the weight difference before and after the etching is compared with the substrate 1 that has been roughened by the roughening method of the substrate according to the first embodiment, even though the etching time is the same. A difference of about 1.8 times occurs with the substrate of the example, which shows that the etching of silicon progressed at a higher etching rate by using the substrate roughening method according to this example.

As can be seen from FIG. 6, the reflectance at a wavelength of 628 nm is 19.1% in the substrate of the comparative example, whereas the surface is roughened by the method of roughening the substrate according to the first embodiment. In the case of the substrate 1, it can be suppressed to 13.9%. As a result, the substrate 1 roughened by the substrate roughening method according to the first embodiment has a non-etched flat region remaining on the surface even when alkali anisotropic etching is performed for the same time. It was a little, and it turned out that the better reflectance suppression effect is exhibited.

It can be explained as follows that the silicon etching progressed at a higher etching rate than the comparative example in the manufacturing method of the low reflection substrate according to the present embodiment.

Generally, the etching reaction of silicon with an aqueous alkali solution occurs when hydroxide ions present in the aqueous solution act on the silicon substrate surface. At this time, in the silicon crystal having a diamond structure, anisotropic etching in which the (111) plane having the highest atomic density is exposed occurs. On the other hand, since the formed high-concentration n-type diffusion layer is excessively doped with impurities, the silicon crystal contains more impurities and defects than a region with a low doping concentration. For this reason, the lattice arrangement of silicon tends to be disturbed as compared with a region where high concentration doping is not performed. This tendency is particularly remarkable on the outermost surface where the impurity density is high. When silicon with such a disordered lattice arrangement is immersed in an aqueous alkali solution, etching anisotropy, that is, an etching rate difference due to the crystal structure is less likely to occur, and the etching progress of silicon is somewhat isotropic. proceed.

For the above reason, in the method for manufacturing a low-reflection substrate according to the present embodiment, the high-concentration n-type diffusion layer 2 (doping) that exists directly under the mask made of the etching-resistant film 3 partially provided with the fine openings 4. Layer) The etching of the outermost part proceeds somewhat close to isotropic. Therefore, an undercut occurs in a very thin region below the etching resistant film 3 simultaneously with the alkali immersion. Subsequently, in the p-type single crystal silicon substrate 1a, which is a non-high-concentration doping region existing under the high-concentration n-type diffusion layer 2 (doping layer), the silicon (111) spatially limited by the undercut region is formed. ) Anisotropic etching proceeds so that the surface is exposed. Therefore, in the method for manufacturing the low reflection substrate according to the present embodiment, the region of the high-concentration n-type diffusion layer 2 is etched by alkali, not the etching rate of the (111) plane in the p-type single crystal silicon substrate 1a. As a result, anisotropic etching controlled by the lateral spreading speed of the undercut region is generated.

On the other hand, in the comparative example, the high-concentration n-type diffusion layer 2 does not exist below the etching resistant film 3 (protective film), and the lattice state is maintained from directly below the protective film. When such a sample is immersed in an alkaline aqueous solution, there is no region subjected to high-concentration n-type diffusion below the etching-resistant film 3, so that an undercut is difficult to form, and a partial coating applied to the etching-resistant film 3. The (111) plane that is spatially limited in the opening region is exposed. Further, in the subsequent time zone, the etching progress is limited by the lateral spreading speed due to the etching of the silicon (111) surface not subjected to high concentration doping.

The ratio of the lateral spread rate of the undercut region formed by etching of the high-concentration n-type doped region and the lateral spread rate by etching of the silicon (111) surface not subjected to high-concentration doping is the concentration of the alkaline aqueous solution used for etching. However, according to the research conducted by the inventors of the present invention, the result that the lateral spread of the former proceeds about 2-8 times faster can be obtained. It was. For this reason, the etching rate of silicon obtained by the manufacturing method of the low reflection substrate according to the present embodiment is higher than the etching rate of silicon obtained by the comparative example, and the texture on the entire surface of the substrate in a shorter time. It is thought that the formation was possible.

As described above, according to the method for manufacturing a substrate according to the first embodiment, the high concentration n-type diffusion layer 2 is formed in the lower layer of the etching resistant film 3 in the first step. This makes it possible to increase the etching rate of the (111) plane in alkali anisotropic etching, that is, to increase the etching speed, and to form uniform irregularities in the plane in a shorter time. become.

As a result, the reflectance of the substrate surface can be suppressed even in a short anisotropic etching process.

Due to the presence of the diffusion layer under the protective film, the lateral spreading etching rate from the opening is increased compared to the case without a diffusion layer even in the case of using a highly anisotropic alkaline solution, and the time is reduced. A uniform texture can be formed on the entire surface of the substrate by this anisotropic etching process.

Also, since the alkali anisotropic etching time required for texture formation on the entire surface of the substrate is shortened, there is an effect of reducing the required film thickness of the etching resistant film 3.

In addition, according to the method for manufacturing the photovoltaic device 10 according to the first embodiment, the photovoltaic device using the substrate 1 whose surface has been subjected to low reflection by the substrate manufacturing method according to the first embodiment. Therefore, the surface light reflection loss on the substrate surface on the light incident side is greatly reduced. Therefore, the photoelectric conversion efficiency can be improved, and a photovoltaic device having higher photoelectric conversion efficiency can be manufactured.

Embodiment 2. FIG.
FIGS. 4-1 to 4-5 are a cross-sectional view and a top view for explaining the steps of the manufacturing method of the low reflection substrate according to the second embodiment. The substrate roughening method according to the second embodiment will be described below with reference to these drawings. The same members as those shown in FIGS. 2-1 to 2-5 are denoted by the same reference numerals, and detailed description thereof is omitted.

First, the first step is the same as the first step of the manufacturing method of the low reflection substrate according to the first embodiment. As shown in FIG. A high-concentration n-type diffusion layer 2 is formed on the surface of one side of the crystalline silicon substrate 1a (hereinafter referred to as the substrate 1a).

The high-concentration n-type diffusion layer 2 is formed by putting the substrate 1a into a thermal oxidation furnace and heating it in the presence of phosphorus oxychloride (POCl ₃ ) vapor to form phosphorus glass on the surface of the substrate 1a. Forms by diffusing phosphorus. The diffusion temperature is set to 840 ° C., for example. After forming the diffusion layer, it is immersed in a hydrofluoric acid solution to remove the phosphorus glass layer.

The second step is the same as the second step of the manufacturing method of the low-reflection substrate according to the first embodiment, and as shown in FIG. An etching resistant film 3 having etching resistance to etching described later is formed as a protective film on the surface on one side of the substrate 1a on which the layer 2 is formed.

In the third step, as shown in the cross-sectional view of FIG. 4A and the top view of FIG. 4B, the surface of the substrate 1a that has completed the second step has resistance to the subsequent sandblasting process. A blast-resistant protective film 21 is partially formed. 4A is a cross-sectional view of the substrate 1a to be subjected to low reflection, and FIG. 4-2 is a top view of the substrate 1a. As shown in FIG. 4B, the blast resistant protective film 21 includes a blast resistant protective film 21a for a bus electrode part and a blast resistant protective film 21b for a grid electrode part. A sectional view in a section perpendicular to the longitudinal direction of the film 21b is shown.

For the blast resistant protective film 21, for example, a polyurethane resin having a film thickness of 100 μm formed by a screen printing method is used. The thickness and material of the blast resistant protective film 21 may be different from each other as long as the underlying etching resistant film 3 can be protected from blasting. Moreover, the formation method of the blast-resistant protective film 21 is not limited to the screen printing method, and may be formed by different means such as a gravure printing method and an ink jet method.

In the fourth step, as shown in FIG. 4-3, a sand blast process is performed on the substrate 1a after the completion of the third process, and a fine hole process is performed on the etching resistant film 3. That is, a plurality of fine openings 4 are opened in the etching resistant film 3 by blast processing. At this time, the blast-resistant protective film 21 is used as a mask at the portion where the blast-resistant protective film 21 is formed in the third step, and processing of the etching-resistant film 3 is hindered. In the etching resistant film 3 on which the blast protective film 21 is not formed, a fine opening 4 is formed so as to penetrate the high resistance n-type diffusion layer 2.

In the fifth step, after removing the blast-resistant protective film 21 by chemical treatment, the etching-resistant film 3 on which micro-hole processing has been performed is used as a mask on one surface of the substrate 1a on the side where the etching-resistant film 3 is formed. On the other hand, anisotropic etching with an aqueous alkali solution is performed to form a textured recess 5 through the fine opening 4 as shown in FIG. 4-4. As the alkaline aqueous solution used for etching, for example, a sodium hydroxide aqueous solution is used. The concentration of the aqueous alkaline solution is 1 weight percent, and the temperature is 80 ° C. Further, an additive such as isopropyl alcohol may be added to the alkaline aqueous solution.

Here, the concentration and temperature of the alkaline aqueous solution can be appropriately changed according to the required etching amount and time. At this time, since the etching resistant film 3 in which the fine openings 4 are not formed remains in the portion where the blast resistant protective film 21 is formed in the third step, the texture recess 5 is not formed.

In the sixth step, the texture recess 5 is exposed by removing the etching resistant film 3. For example, a hydrofluoric acid aqueous solution can be used to remove the etching resistant film 3. As a result, as shown in FIG. 4-5, a texture structure having a fine pattern of about 10 μm, for example, is formed on the surface of the substrate 1a other than the portion where the blast resistant protective film 21 is formed in the third step. Can do. A p-type single crystal silicon substrate in which the substrate surface has been subjected to low reflection through the above steps is referred to as a substrate 1 '. The region where the blast resistant protective film 21 is formed in the third step is a flat region 22 where the high concentration n-type diffusion layer 2 formed in the first step is exposed on the surface.

Next, the light shown in the top view of FIG. 5-1 and the cross-sectional view of FIG. 5-2 using the substrate 1 ′ having a texture structure formed on the substrate surface by using the above-described method for manufacturing a low reflection substrate. A process for manufacturing the electromotive force device 20 will be described.

The substrate 1 ′ after the processing in the sixth step is put into a thermal oxidation furnace and heated in the presence of phosphorus oxychloride (POCl ₃ ) vapor to form phosphorus glass on the surface of the substrate 1 ′. Phosphorus is diffused into 1 ′ to form a low-concentration n-type diffusion layer 31b in the surface layer of the substrate 1 ′ (FIG. 5-2). The diffusion temperature is 800 ° C., for example. At this time, since the high-concentration n-type diffusion layer 31a already formed in the flat region 22 already has a high-concentration impurity dopant, the high-concentration n-type diffusion layer 31a is subjected to the low-concentration diffusion process in this step. The sheet resistance value of is equal to or less than that before the process.

Next, after removing the phosphor glass layer of the substrate 1 ′ in a hydrofluoric acid solution, an SiN film is formed on the low-concentration n-type diffusion layer 31 b by the plasma CVD method as the antireflection film 12. The antireflection film 12 is formed in a region excluding the formation region of the light receiving surface side electrode 13 to be formed later (FIG. 5-2). The film thickness and refractive index of the antireflection film 12 are set to values that most suppress light reflection. Note that two or more layers having different refractive indexes may be stacked. Further, the antireflection film 12 may be formed by a different film forming method such as a sputtering method.

Next, a paste mixed with silver is printed by screen printing on the flat region 22 which is a non-textured region of the light receiving surface of the substrate 1 ′, and the paste mixed with aluminum is screened on the entire back surface of the substrate 1 ′. After printing by printing, a baking process is performed to form the light receiving surface side electrode 13 and the back surface electrode 14. Firing is performed at 760 ° C. in an air atmosphere, for example.

The light-receiving surface side electrode 13 includes the bus electrode 13a and the grid electrode 13b of the photovoltaic device 20 (FIG. 5-1), and the bus electrode portion of the flat region 22 where the high-concentration n-type diffusion layer 2 is exposed on the surface, respectively. It is formed immediately above the flat region and the grid electrode portion flat region. FIG. 5-2 shows a cross-sectional view in a cross section perpendicular to the longitudinal direction of the grid electrode 13b. As described above, the photovoltaic device 20 shown in FIGS. 5A and 5B is manufactured.

The photovoltaic device 20 is formed on a semiconductor substrate 1 ′ having a high-concentration n-type diffusion layer 31a and a low-concentration n-type diffusion layer 31b on the surface of the substrate, and a light-receiving surface side surface of the semiconductor substrate 1 ′. The photovoltaic device of 15 cm □ is provided with the antireflection film 12, the light receiving surface side electrode 13, and the back surface electrode 14 formed on the surface (back surface) opposite to the light receiving surface.

As described above, according to the method for manufacturing a substrate according to the second embodiment, the high-concentration n-type diffusion layer 2 is formed in the lower layer of the etching resistant film 3 in the first step. This makes it possible to increase the etching rate of the (111) plane in alkali anisotropic etching, that is, to increase the etching speed, and to form uniform irregularities in the plane in a shorter time. become.

As a result, the reflectance of the substrate surface can be suppressed even in a short anisotropic etching process. In addition, when performing micro-hole processing by blast processing, by forming the anti-blast protective film 21 in advance on the light receiving surface side electrode corresponding portion of the photovoltaic device, the high concentration n-type diffusion layer 2 on the electrode corresponding portion, that is, It is possible to leave the high concentration n-type diffusion layer 31a.

According to the method for manufacturing the photovoltaic device 20 according to the second embodiment, the photovoltaic device 20 using the substrate 1 ′ having the substrate surface reduced in reflection using the substrate manufacturing method according to the second embodiment described above is used. Since the power device is manufactured, the surface light reflection loss on the substrate surface on the light incident side is greatly reduced. Therefore, the photoelectric conversion efficiency can be improved. Further, since the high-concentration n-type diffusion layer 31a having a low sheet resistance is formed in advance on the portion corresponding to the light receiving surface side electrode, it is possible to improve electrical contact, that is, contact resistance.

Furthermore, a low concentration n-type diffusion layer 31b is formed in the light receiving surface region other than the portion corresponding to the light receiving surface side electrode, and recombination of surplus minority carriers generated by light incidence can be suppressed. Due to the above effects, a photovoltaic device having high photoelectric conversion efficiency can be manufactured.

Furthermore, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention in the implementation stage. Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent requirements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and is described in the column of the effect of the invention. When an effect is obtained, a configuration in which this configuration requirement is deleted can be extracted as an invention. Furthermore, the constituent elements over different embodiments may be appropriately combined.

As described above, the method for manufacturing a low-reflection substrate, the method for manufacturing a photovoltaic device, and the photovoltaic device according to the present invention are useful for texture processing for improving photoelectric conversion efficiency. It is suitable for shortening the battery manufacturing time and improving the performance of solar cells.

DESCRIPTION OF SYMBOLS 1, 1 'p-type single crystal silicon substrate made low-reflection 1a p-type single

crystal silicon substrate

2, 31a High concentration n type diffused layer 3 Etching-resistant film 4 Fine opening 5 Texture recessed

part

10, 20 Photovoltaic device 11a N-type diffusion layer 12 Antireflection film 13 Light receiving surface side electrode

13a Bus electrode

13b Grid electrode 14 Back electrode 21 Anti-blast protective film 21a Anti-blast protective film for bus electrode part 21b Anti-blast protective film for grid electrode part 22 Flat region 31b Low Concentration n-type diffusion layer

Claims

(100) forming a high concentration impurity diffusion layer on the main surface of the single crystal silicon substrate;
Forming an etching resistant film on the high-concentration impurity diffusion layer;
Performing a sandblasting treatment on the etching resistant film to form an opening that penetrates the etching resistant film and reaches the high-concentration impurity diffusion layer;
Performing the anisotropic etching using the aqueous alkali solution having resistance to the etching resistant film through the opening, using the etching resistant film in which the opening is formed as a protective mask;
Removing the etching resistant film after the etching;
The manufacturing method of the low-reflection board | substrate characterized by including this.
Forming a blast-resistant protective film that protects a part of the etching-resistant film from the sandblasting after the formation of the etching-resistant film and before the sandblasting treatment;
Removing the blast resistant protective film after forming the opening;
The method for manufacturing a low reflection substrate according to claim 1, further comprising:
The method for manufacturing a low-reflection substrate according to claim 1 or 2, wherein the conductivity type of the single crystal silicon substrate is p-type, and the conductivity type of the high-concentration impurity diffusion layer is n-type.
The said sandblasting process is performed using an alumina abrasive grain. The manufacturing method of the low reflective board | substrate of Claim 1, 2, or 3 characterized by the above-mentioned.
A photovoltaic device is manufactured using the low-reflection substrate manufactured by the method for manufacturing a low-reflection substrate according to any one of claims 1 to 4. A method for manufacturing a photovoltaic device, comprising:
Using the low reflection substrate manufactured by the low reflection substrate manufacturing method according to claim 2,
A photovoltaic device is manufactured by forming a light-receiving surface side electrode on the high-concentration impurity diffusion layer under the region where the blast-resistant protective film is formed.
A (100) p-type single crystal silicon substrate;
An n-type high concentration impurity diffusion layer formed on a part of the main surface of the substrate;
A light-receiving surface side electrode formed on the n-type high concentration impurity diffusion layer;
A back electrode formed on the back surface opposite to the main surface of the substrate;
With
A photovoltaic device, wherein a texture structure having irregularities is formed in a region where the light receiving surface side electrode is not formed on the main surface.