WO2011122353A1

WO2011122353A1 - Method for roughening substrate and method for manufacturing photovoltaic device

Info

Publication number: WO2011122353A1
Application number: PCT/JP2011/056311
Authority: WO
Inventors: 邦彦西村; 松野　繁; 秀一檜座
Original assignee: 三菱電機株式会社
Priority date: 2010-03-29
Filing date: 2011-03-16
Publication date: 2011-10-06
Also published as: JPWO2011122353A1; JP5220237B2

Abstract

Disclosed is a method for roughening a substrate, which includes: a step of forming an etching resistant film on the surface of the substrate; a step of attaching a mesh-like blast mask (3) to the etching resistant film; a step of forming, by blast processing, a fine opening (4) in an etching resistant film region having no blast mask (3) attached thereto; a step of removing the blast mask; a step of performing etching using the etching resistant film having the opening formed therein; and a step of removing the etching resistant film.

Description

Substrate roughening method and photovoltaic device manufacturing method

The present invention relates to a method for roughening a substrate and a method for manufacturing a photovoltaic device.

In order to improve the performance of photovoltaic devices such as solar cells, it is important to efficiently incorporate sunlight into the substrate constituting the solar cell. For this reason, in the photoelectric conversion device, texture processing is performed on the substrate surface on the light incident side, and light once reflected on the substrate surface is incident on the substrate surface again, so that more sunlight is taken into the substrate and photoelectric conversion is performed. Improving efficiency. 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 for forming a texture on a substrate for a solar cell, when the substrate is a single crystal substrate, anisotropic etching having crystal orientation dependency on the etching rate is widely used. In anisotropic etching, the crystal orientation is used to perform etching using an aqueous alkali solution such as sodium hydroxide or potassium hydroxide. For example, when this anisotropic etching is performed on a silicon substrate having a (100) plane, a pyramidal texture with the (111) plane exposed is formed on the substrate surface.

When forming a texture on a single crystal substrate, an ideal inverted pyramid texture can be formed on the substrate surface using an etching mask. At this time, a method of forming an etching mask by photolithography or the like has been put into practical use. However, the photoengraving method has drawbacks that the process cost is high and it is difficult to apply to a large substrate.

Further, as a groove processing method that does not depend on the surface orientation, for example, an etching mask film having an opening is formed on the surface of a silicon substrate, and air blasting is performed on the surface of the mask film to thereby form a mask opening. A method of forming a groove or a recess as a texture has been proposed (see Patent Document 1 below).

On the other hand, as a texture forming method using an etching mask forming method instead of photolithography, the present inventors have proposed the texture forming method described in Patent Document 2 below. In the method described in Patent Document 2 below, an etching mask film is formed on the surface of the silicon substrate, and air blasting is performed on the surface of the mask film to form an opening in the mask surface. A texture is formed by carrying out.

JP 2002-43601 A International Publication No. 2009/128324

However, the texture forming method using the etching mask formed by the conventional photoengraving method has a problem that the process cost is high and it is difficult to apply to a large substrate.

In the texture forming method described in Patent Document 1, air blasting is performed only through the opening of the protective mask. For this reason, the area | region to which the protective mask has adhered has maintained the original board | substrate surface shape, ie, a flat shape. In this case, there is a problem that the light confinement effect cannot be exhibited with respect to the light incident on the flat surface, and a good light reflection suppressing effect cannot be obtained.

Also, in the texture forming method described in Patent Document 1, a resin film is formed as a protective mask by printing or the like. For this reason, there is a problem that a fine pattern of about 10 μm cannot be formed on the substrate surface. Further, even if a fine pattern can be formed on the protective mask, blasting using abrasive grains having a diameter of about 10 μm is performed when the texture of the substrate is formed. For this reason, there exists a problem that a fine uneven | corrugated pattern about 10 micrometers cannot be formed in the substrate surface. Furthermore, in the texture forming method described in Patent Document 1, since blasting is used for the texture formation of the substrate, there is a problem that damage such as microcracks caused by collision of abrasive grains occurs on the substrate surface. is there.

Furthermore, the texture forming method described in Patent Document 1 has a problem that a process for printing the protective mask and a process for removing the protective mask after blasting are required, which complicates the process.

Further, according to the technique described in Patent Document 2, since the blast process is used to form the opening in the etching mask film, the position, shape, size, etc. of the opening of the etching mask film are random. There is a problem that uniform and good texture cannot be formed.

The present invention has been made in view of the above, and can form a good texture without causing damage such as microcracks on the substrate surface, and can evenly finely roughen the substrate surface by an easy process. It is an object of the present invention to obtain a substrate roughening method and a photovoltaic device manufacturing method that can be performed.

In order to solve the above-described problems and achieve the object, the present invention provides a first step of forming a protective film on the surface of a substrate, and the detachable blast mask having regularly arranged openings. A second step of depositing on the film; a third step of forming an opening in a region of the protective film where the blast mask is not deposited by performing a blasting process through the blast mask; and the blast mask. And a step of performing etching on the surface of the substrate on which the protective film is formed under the condition that the protective film is resistant, using the protective film on which the opening is formed as an etching mask. And a sixth step of removing the protective film.

According to the present invention, it is possible to form a good texture without causing damage such as microcracks on the substrate surface, and to achieve an effect that uniform fine roughening of the substrate surface can be performed by an easy process. .

FIG. 1 is a cross-sectional view showing an example of a substrate whose surface has been roughened by the substrate roughening method of the first embodiment. FIG. 2A is a sectional view for explaining a first step of the substrate roughening method according to the first embodiment. FIG. 2-2 is a sectional view for explaining a second step of the substrate roughening method according to the first embodiment. FIG. 2-3 is a cross-sectional view for explaining a third step of the substrate roughening method according to the first embodiment. FIG. 2-4 is a cross-sectional view for explaining a fourth step of the substrate roughening method according to the first embodiment. 2-5 is a cross-sectional view for explaining a fifth step of the substrate roughening method according to the first embodiment. FIG. FIG. 2-6 is a cross-sectional view for explaining a sixth step of the substrate roughening method according to the first embodiment. FIG. 3 is a schematic diagram illustrating a configuration example of a blasting apparatus. FIG. 4A is a diagram of an example of a blast mask according to the first embodiment. FIG. 4B is a diagram of another example of the blast mask according to the first embodiment. FIGS. 5-1 is a figure for demonstrating the difference in the shape of the texture hollow by the difference in a formation method. FIG. 5B is a diagram for explaining a difference in the shape of the texture depression due to a difference in formation method. FIG. 5C is a diagram for explaining the difference in the shape of the texture depression due to the difference in formation method. FIG. 6A is a cross-sectional view illustrating a configuration example of the photovoltaic device according to the first embodiment. FIG. 6B is a top view of the configuration example of the photovoltaic device according to the first embodiment. FIG. 7 is a diagram illustrating an example of an evaluation result of power generation characteristics of the photovoltaic device according to the first embodiment. FIG. 8 is a top view showing an example of the configuration of a blast mask for forming a selective emitter structure. FIG. 9A is a diagram illustrating a configuration example in a state where the substrate subjected to the diffusion process in advance is subjected to the etching process using the selective emitter structure forming blast mask. FIG. 9B is a diagram illustrating a configuration example of the substrate in a state where the etching resistant film is removed. FIG. 9C is a diagram illustrating a configuration example in a state where the diffusion process is performed again on the substrate. FIG. 10 is a diagram illustrating an example of an evaluation result of power generation characteristics of the photovoltaic device according to the second embodiment. FIG. 11 is a perspective view showing an example of the configuration of a blast mask for forming a selective emitter structure according to the third embodiment.

Embodiments of a substrate roughening method and a photovoltaic device manufacturing method 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 of this invention, it can change suitably. In the present invention, the material of the substrate and the use of the roughened substrate are not particularly limited, but in the following description, roughening of a single crystal silicon substrate will be described as an example. 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 is a cross-sectional view showing an example of a substrate 1 whose surface has been roughened by the method of roughening a substrate according to the first embodiment of the present invention. A substrate 1 shown in FIG. 1 is a p-type single crystal silicon substrate which is a substrate for a solar cell which is a photovoltaic device. In this substrate 1, texture depressions 5 having an inverted pyramid shape with an average pitch between holes of about 10 μm are formed substantially uniformly on the substrate surface.

Next, the substrate roughening method of the present embodiment for forming such a substrate 1 will be described. FIGS. 2-1 to 2-6 are cross-sectional views for explaining the steps of the substrate roughening method according to the present embodiment. The substrate roughening method of the present embodiment includes first to sixth steps, FIG. 2-1 shows the first step, FIG. 2-2 shows the second step, and FIG. 3 illustrates the third step, FIG. 2-4 illustrates the fourth step, FIG. 2-5 illustrates the fifth step, and FIG. 2-6 illustrates the sixth step. The substrate roughening method of the present embodiment will be described below with reference to these drawings.

In the first step, as shown in FIG. 2-1, a protective film is formed on the surface of one side of a p-type single crystal silicon substrate 1a (hereinafter referred to as substrate 1a) to be roughened as described later. A film (hereinafter referred to as an etching resistant film) 2 having an etching resistance to the etching performed in the fifth step is formed.

The substrate 1a of the present embodiment is a single crystal silicon substrate that is often used for consumer solar cells. For example, after slicing from a single crystal silicon ingot with a multi-wire saw, wet using an acid or alkali solution This removes the damage at the time of slicing by etching. As an example, here, the thickness of the substrate 1a after removing the damage is 200 μm, and the dimensions are 15 cm square. In addition, the thickness and dimension of the board | substrate 1a are not limited to this, It can change suitably.

The etching resistant film 2 is a silicon oxide film (SiO2, SiO) having a thickness of 100 nm formed by a thermal oxidation method. Although a silicon oxide film is used as the etching resistant film 2 here, a silicon nitride film (SiN), a silicon oxynitride film (SiON), an amorphous silicon film (а-Si), diamond, and the like are used as the etching resistant film 2. Other materials such as a like carbon film may be used.

The film thickness of the etching resistant film 2 is preferably 10 nm to 500 nm. When the film thickness of the etching resistant film 2 is 10 nm or more, the etching resistant film is etched when etching is performed on one surface of the substrate 1a on the side where the etching resistant film 2 is formed in the fifth step described later. Even if the film is slightly cut, it functions as an etching resistant film. Moreover, if the film thickness of the etching resistant film 2 is 500 nm or less, the fine hole processing can be surely performed on the etching resistant film 2 in the third step described later. In addition, the film thickness of the etching resistant film 2 is not limited to this, and functions reliably as an etching resistant film in the fifth step described later, and fine hole processing is reliably performed in the third step described later. It is sufficient if the thickness is sufficient.

In the second step, a removable blast mask 3 having an opening is attached to the etching resistant film 2 as shown in FIG. As the blast mask 3, for example, a stainless mesh can be used. If the number of meshes is 500, openings of about 20 to 40 μm can be formed at a pitch of 50 μm. The blast mask 3 may be in the form of a mesh having an opening, and the material of the blast mask 3 and the shape and size of the mesh are not limited thereto.

In the third step, as shown in FIG. 2-3, fine hole processing is performed on the etching resistant film 2 at a position corresponding to the opening of the blast mask 3 (portion not covered by the blast mask 3). That is, a plurality of fine openings 4 are opened in the etching resistant film 2 by blast processing. At this time, for example, alumina abrasive grains are used as the abrasive grains used for the blast processing. The inventors have sought the most suitable abrasive for forming an opening in the SiO 2 film, which is the etching resistant film 2 without causing cracks in the substrate 1, and as a result of repeated research, the alumina abrasive grains are 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 2.

FIG. 3 shows a configuration example of an apparatus (hereinafter referred to as a blast processing apparatus) used when forming a plurality of fine openings 4 in the etching resistant film 2 in the substrate roughening method of the present embodiment. It is a schematic diagram. The blasting apparatus shown in FIG. 3 includes an abrasive grain injection nozzle 11, an abrasive grain tank 12, and a compressed air cylinder 13. In this blast processing apparatus, the blast abrasive grains 14 supplied from the abrasive tank 12 are ejected from the abrasive grain injection nozzle 11 by the compressed air supplied from the compressed air cylinder 13, and the ejected blast abrasive grains 14 are processed. The surface is cut by colliding with the surface (here, the etching resistant film 2 formed on the substrate 1a). In the present embodiment, the blast mask 3 is deposited on the etching resistant film 2, and the etching resistant film 2 is not cut at the portion where the blast mask 3 is present, and the portion without the blast mask 3 ( Only the portion corresponding to the opening of the blast mask 3 is cut.

Although not shown in FIG. 3, the blast abrasive grains 14 are moved in the substrate plane by moving the substrate 1 a in the in-plane direction of the substrate 1 a in a state where the blast abrasive grains 14 are ejected from the abrasive spray nozzle 11. Can act on the entire surface. Thereby, the fine opening 4 can be opened in the etching resistant film 2 by cutting the entire surface of the substrate uniformly.

FIG. 4A is a diagram illustrating an example of the blast mask 3 of the present embodiment. FIG. 4A is a schematic diagram when the blast mask 3 is an orthogonal woven mesh having square lattice openings. By aligning the mesh of the mesh with the 100 directions of the crystal orientation, the inverted pyramid-shaped texture depressions 5 can be formed in a square lattice arrangement on the substrate 1a.

FIG. 4B is a diagram showing another example of the blast mask 3. The blast mask 3 shown in FIG. 4-2 is a 45-degree oblique weave mesh having triangular lattice openings, and is a mesh having a streak-like opening with one weave being narrower than the other. Using this mesh, the longitudinal direction of the opening of the mesh is aligned with the 110 direction of the crystal orientation (the diagonal direction of the inverted pyramid), and the streak-like fine opening 4 is formed in the etching resistant film 2. In this way, the inverted pyramid-shaped textured dents 5 can be formed in a square lattice pattern on the substrate 1a. If the shape and arrangement of the blast mask 3 shown in FIG. 4-2 are used, it is possible to form the inverted pyramid-shaped texture depression 5 even with a small opening area.

Here, as an example of a mesh shape, a plurality of first members arranged so as to be spaced apart from each other and parallel to each other, intersecting the first member, and spaced apart from each other. Although the blast mask 3 that is formed by a plurality of second members that are open and arranged in parallel with each other (configured by members in two directions) is shown, the blast mask 3 is not limited to this. For example, a sheet formed by opening an opening in a plate-like member may be used as long as it has openings of a certain shape and size at regular intervals. In general, in order to form a fine opening, a mesh composed of members in two directions is easier to process than a plate-like mesh having openings.

In the fourth step, the blast mask 3 is removed as shown in FIG. Although the method of removing the blast mask 3 is not particularly limited, the use of a stainless steel mesh or the like as the blast mask 3 makes it easier to remove compared to the case where a resin film or the like is used as the blast mask.

In the fifth step, etching is performed on one surface of the substrate 1a on which the etching resistant film 2 is formed, using the etching resistant film 2 that has been subjected to fine hole processing as a mask, as shown in FIG. 2-5. Thus, the texture depression 5 is formed. As the etching performed in the fifth step, for example, wet etching using an alkaline aqueous solution such as NaOH or KOH is performed. In this case, the shape of the texture recess 5 varies depending on the crystal plane orientation. Note that the etching method is not limited to wet etching using an alkaline aqueous solution, and wet etching using a hydrofluoric acid nitric acid mixture may be used, or dry etching may be used. FIGS. 5A to 5C are diagrams for explaining the difference in the shape of the texture recess 5 due to the difference in the forming method.

FIG. 5A shows an example in which the texture depression 5a is formed on the surface of the substrate 1a with the (100) plane exposed by etching using an alkaline aqueous solution. FIG. 5A is an example corresponding to the case where a resin film having an opening formed by printing or the like is used as an etching mask as conventionally performed. In the conventional method, when the etching progresses and the (111) plane is exposed, the etching progresses very slowly, and the side etching under the etching resistant film 2 does not proceed sufficiently, and the surface of the substrate 1a. The flat portion 6 remains, and becomes a factor that hinders the suppression of reflectance later.

FIG. 5-2 shows an example in which the recess 7 is formed by blasting. As shown in FIG. 5B, the recess 7 formed by blasting is formed almost directly below the opening of the protective mask during blasting. Therefore, when the dent 7 formed by blasting is used as a texture dent, the region where the protective mask is applied remains in the original substrate surface shape, which is a factor that hinders the suppression of reflectance. On the other hand, in the present embodiment, since the blasting is used when forming the opening in the etching resistant film 2, the depression 7 by the blast abrasive grains 14 shown in FIG. 5-2 is formed to the inside of the silicon substrate. The That is, after the fourth step, a depression similar to the depression 7 in the example of FIG. Therefore, in the fifth step, as in the example shown in FIG. 5A, this recess 7 is also used when etching is performed using an alkaline aqueous solution on the surface of the substrate 1a with the (100) plane exposed. As a result, the etching spread in the lateral direction is promoted, and the etching proceeds to some extent again from the time when the (111) plane is exposed, and the remaining flat portion 6 is reduced.

FIG. 5-3 shows an example in which the texture depression 5a is formed on the surface of the substrate 1a with the (111) plane exposed by etching using an alkaline aqueous solution. As shown in FIG. 5-3, the etching hardly progresses on the surface of the substrate 1a where the (111) plane is exposed, and the texture depression 5 is not formed.

Here, a method for determining conditions for the blasting process in the second step will be described. In blasting, it is necessary to adjust air pressure, air flow, nozzle-substrate distance, and sweep speed as blasting conditions. In the present embodiment, the size and shape of the diameter of the hole (fine opening 4) opened in the etching resistant film 2, that is, the size and shape of the opening of the blast mask 3, the thickness of the etching resistant film 2, etc. Adjust these conditions accordingly. Further, the blast abrasive grains 14 collide a plurality of times with the etching resistant film 2 below the opening of the blast mask 3, thereby opening the etching resistant film 2 below the opening of the blast mask 3. Is equivalent to Therefore, it is necessary to adjust the blast processing conditions and the processing time so that a desired opening state can be obtained in the etching resistant film 2.

The opening diameter of the etching resistant film 2 is defined by the opening diameter of the blast mask 3, and the depth of the inverted pyramid increases as the opening diameter increases. Therefore, the opening diameter of the blast mask 3 is limited by the thickness of the substrate 1a.

In the sixth step, as shown in FIG. 2-6, the texture dent 5 is exposed by removing the etching resistant film 2. For example, a hydrofluoric acid aqueous solution can be used to remove the etching resistant film 2. Note that the etching resistant film 2 may be removed by any method. Through the above steps, an inverted pyramid texture structure having a pattern of about 20 μm, for example, can be formed on the surface of the substrate 1 as shown in FIG.

FIGS. 6A and 6B are diagrams illustrating a configuration example of a photovoltaic device manufactured using the substrate 1 described above. FIG. 6A is a cross-sectional view of the photovoltaic device, and FIGS. FIG. 3 is a top view of the photovoltaic device. The photovoltaic device shown in FIGS. 6A and 6B includes a first conductivity type semiconductor substrate 21 having an n layer 21a in which a second conductivity type impurity is diffused in the surface layer of the substrate, and a light receiving surface of the semiconductor substrate 21. The antireflection film 22 formed on the side surface (front surface), the light receiving surface side electrode 23 formed on the light receiving surface side surface (front surface) of the semiconductor substrate 21, and the surface opposite to the light receiving surface of the semiconductor substrate 21 A back electrode 24 formed on the back surface.

The light-receiving surface side electrode 23 includes a grid electrode 23a and a bus electrode 23b of a photovoltaic device. FIG. 6A shows a cross-sectional view in a cross section perpendicular to the longitudinal direction of the grid electrode 23a. For the semiconductor substrate 21 (the portion excluding the n layer 21a of the semiconductor substrate 21), the substrate 1 having a texture structure formed on the substrate surface using the substrate roughening method described above is used. A photovoltaic device is configured.

Next, steps for manufacturing the photovoltaic device shown in FIGS. 6A and 6B using the substrate 1 described above will be described. Note that the process described here is the same as the process for manufacturing a photovoltaic device using a general single crystal silicon substrate, and is not particularly shown. Moreover, the process demonstrated here is an example, The process for manufacturing a photovoltaic apparatus other than the manufacturing process of the board | substrate 1 is not restricted to these, You may use what processes.

The substrate 1 that has been processed 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 to form an n layer 21 a on the surface layer of the substrate 1. The diffusion temperature is set to 840 ° C., for example.

Next, after removing the phosphor glass layer of the substrate 1 in a hydrofluoric acid solution, a region where the light-receiving surface side electrode 23 is formed is formed on the n layer 21a by forming a SiN film as the antireflection film 22 by plasma CVD (Chemical Vapor Deposition). Except for forming. The film thickness and refractive index of the antireflection film 22 are set to values that most suppress light reflection. Note that two or more layers having different refractive indexes may be stacked. The antireflection film 22 may be formed by a film formation method different from the above, 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, followed by a baking process. Thus, the light receiving surface side electrode 23 and the back surface electrode 24 are formed. Firing is performed at 760 ° C. in an air atmosphere, for example. As described above, the photovoltaic device shown in FIGS. 6-1 and 6-2 is manufactured.

The results of the performance evaluation of the photovoltaic device manufactured by the above process will be described. In the case of the photovoltaic device, the light reflection characteristics of the substrate 1 were evaluated with a spectrophotometer when the surface of the substrate 1 was roughened (after the sixth step). As a result of this evaluation, the reflectance at a wavelength of 628 nm was about 10%.

On the other hand, as a comparative example, the reflectance of a substrate that did not form a texture on the substrate surface was evaluated, and as a result, it was about 30% at a wavelength of 628 nm. Therefore, it turned out that the board | substrate 1 which gave the roughening by the roughening method of the board | substrate of this Embodiment has exhibited the favorable reflectance suppression effect.

Next, the produced photovoltaic device was actually operated, and the power generation characteristics were measured and evaluated. FIG. 7 is a diagram illustrating an example of the evaluation result of the power generation characteristics of the photovoltaic device according to the present embodiment. FIG. 7 shows the open circuit voltage Voc (mV), short circuit current density Jsc (mA / cm ² ), fill factor FF, and photoelectric conversion efficiency Eff (%) obtained as a result.

As a comparative example, a 15 cm square photovoltaic device was produced using the substrate of the above comparative example. The photovoltaic device of this comparative example was actually operated, and the power generation characteristics were measured and evaluated. As a result, the open circuit voltage Voc (mV), the short circuit current density Jsc (mA / cm ² ), the fill factor FF, and the photoelectric conversion efficiency Eff (%) are also shown in FIG.

As can be seen from FIG. 7, in the photovoltaic device of the present embodiment, the short-circuit current density is significantly increased as compared with the photovoltaic device of the comparative example (compared to 35.6 [mA / cm 2] of the comparative example). 37.1 [mA / cm 2]), the photoelectric conversion efficiency is improved (18.02% compared to 17.37% in Comparative Example). Thereby, the suppression of the surface reflection loss of the substrate 1 succeeded by configuring the photovoltaic device using the substrate 1 roughened by the method of roughening the substrate of the present embodiment, It has been found that the short-circuit current density is greatly increased and contributes to the improvement of photoelectric conversion efficiency.

As described above, according to the substrate roughening method of the present embodiment, an expensive apparatus such as lithography and a redundant manufacturing process are required because blast processing is used for micro-hole processing of the etching resistant film 2. The fine hole processing of the etching resistant film 2 can be realized without making it, and the fine roughening can be easily and uniformly performed on the surface of the substrate 1a.

In addition, according to the substrate roughening method of the present embodiment, since a process such as resin printing is not used for patterning the etching resistant film 2, a fine roughening is performed on the surface of the substrate 1a in a simple process. Surfaceization can be performed uniformly.

Further, according to the substrate roughening method of the present embodiment, since the wet or dry etching is used for roughening the substrate 1a, it is possible to carry out fine unevenness processing regardless of the abrasive grain size. In addition, since the etching proceeds isotropically to the lower side of the etching resistant film 2 and so-called side etching processing can be performed, an unnecessary flat portion does not remain below the etching resistant film 2. Thus, the roughening can be easily and uniformly performed on the surface of the substrate 1a.

Also, since wet or dry etching is used for roughening the substrate 1a instead of blasting, substrate damage such as microcracks caused by blasting can be prevented. Thereby, a fine roughening can be implemented with respect to the surface of the board | substrate 1a, without reducing the quality of the board | substrate surface resulting from roughening.

Further, in the present embodiment, the fine opening 4 is provided in the etching resistant film 2 by blasting using the mesh blast mask 3 having the opening. Therefore, the position, shape, size, etc. of the opening of the etching mask film can be made uniform as compared with the case where the fine opening 4 is provided in the etching resistant film 2 by blasting using the blast mask 3. Therefore, it is possible to uniformly roughen the surface of the substrate 1a.

Therefore, according to the substrate roughening method of the present embodiment, it is possible to uniformly fine the surface of the substrate while maintaining the quality of the substrate surface, and exhibits an excellent antireflection effect. The substrate to be roughened can be roughened.

In addition, according to the method for manufacturing a photovoltaic device of the present embodiment, a photovoltaic device is used by using the substrate 1 having the substrate surface roughened by using the substrate roughening method of the present embodiment. In order to manufacture the power device, a photovoltaic device having good photoelectric conversion efficiency can be manufactured in which the surface light reflection loss on the substrate surface on the light incident side is greatly reduced and the photoelectric conversion efficiency is improved. . As a result, when manufacturing a photovoltaic device having the same photoelectric conversion efficiency as the conventional one, the area of the substrate is reduced, the amount of the raw material of the substrate is reduced, and the photovoltaic device is reduced in size and weight. It is possible to reduce the volume.

Embodiment 2. FIG.
Next, a substrate surface roughening method according to the second embodiment of the present invention will be described. In the present embodiment, a previously diffused substrate is used as the substrate 1a, and a portion for masking the electrode region portion is added to the blast mask 3. Thereby, it is possible to form a selective emitter structure capable of increasing the efficiency of the solar cell. The selective emitter structure is a structure in which only the electrode portion is diffused twice so that the resistance of the electrode portion is lower than that of the light receiving surface portion. The rough surface of the substrate of the present embodiment except that a substrate that has been diffused in advance is used as the substrate 1a, and that a mask obtained by adding the electrode mask 25 to the blast mask 3 of the first embodiment is used as a mask used during blast processing. The roughening method is the same as the substrate roughening method of the first embodiment. Hereinafter, a different part from Embodiment 1 is demonstrated.

In this embodiment, a diffused substrate in which an n layer (diffusion layer) is formed by heating a p-type single crystal silicon substrate in the presence of phosphorus oxychloride vapor, for example, is used as the substrate 1a. Then, using the substrate 1a, the first step is performed in the same manner as in the first embodiment. Next, the second step is carried out in the same manner as in the first embodiment. In this case, a mask in which an electrode mask 25 is added as a blasting mask to be deposited on the etching resistant film 2 (hereinafter, selected) Called an blast mask for forming an emitter structure). In the third step, blasting is performed using this selective emitter structure forming blast mask.

FIG. 8 is a top view showing an example of the configuration of a blast mask for forming a selective emitter structure. As shown in FIG. 8, the blast mask for forming the selective emitter structure includes a blast mask 3 similar to that in the first embodiment having an opening for forming a texture, and an electrode without an opening for forming an electrode portion. And a mask 25. In the third step, by performing blasting using this selective emitter structure forming blast mask, the electrode portion is not blasted and texture is not formed. The electrode mask 25 is a non-opening mask having no opening, and is composed of a wide portion of about 1 to 2 mm corresponding to the bus electrode 23b and a narrow portion of about 100 to 500 μm corresponding to the grid electrode 23a. The The electrode mask 25 is not limited to the shape described above, and the shape may be determined according to the region of the electrode to be formed. Thereafter, the fourth to sixth steps are performed as in the first embodiment.

FIG. 9A is a diagram showing a configuration example in a state where the substrate 1a that has been subjected to the diffusion process in advance is subjected to the etching process using the selective emitter structure forming blast mask of the present embodiment. FIG. 9A shows the first to fifth steps similar to those of the first embodiment using the blast mask for forming the selective emitter structure of the present embodiment on the substrate 1a which has been subjected to the diffusion treatment in advance. A cross-sectional view of the substrate 1a after implementation is shown. The electrode region 26 is a portion corresponding to the region of the electrode mask 25 in the etching resistant film 2 and is a portion that remains without being opened at the time of blasting by being covered with the electrode mask 25. Further, the etching process in the fifth step removes the diffusion layer from the surface of the substrate 1a where the electrode region 26 is not deposited, but the under-electrode diffusion layer to which the electrode region 26 is deposited. In 27, a diffusion layer remains.

FIG. 9-2 is a diagram showing a configuration example of the substrate 1a in a state where the etching resistant film 2 is removed by the sixth step. FIG. 9-2 shows a state where the etching resistant film 2 is removed from the substrate 1a shown in FIG. By removing the etching resistant film 2, the substrate 1 on which the under-electrode diffusion layer 27 is exposed is generated. Thereafter, using this substrate 1, a photovoltaic device is manufactured by a manufacturing method similar to the manufacturing method of the photovoltaic device described in the first embodiment.

FIG. 9C is a diagram illustrating a configuration example in a state where the diffusion process is performed again on the substrate 1. FIG. 9-3 illustrates the diffusion process in the process of manufacturing the photovoltaic device described in the first embodiment using the substrate 1 generated by the first to sixth steps of the present embodiment. The state after performing is shown. In this embodiment, since a substrate that has been subjected to diffusion processing is used as the substrate 1a, this diffusion processing is the second diffusion processing.

As a result of this second diffusion treatment, the under-electrode re-diffusion layer 28 is subjected to two diffusion treatments with the diffusion layer formed by the first diffusion treatment remaining, so that the resistance value is low. On the other hand, in the texture region 29, which is a region where the electrode region 26 is not deposited during the etching process, the diffusion layer formed by the first diffusion process during the etching process is removed. A diffusion layer corresponding to one diffusion process is formed, and the resistance value is higher than that of the diffusion layer 28 under the electrode. By forming such a selective emitter structure, the light receiving surface has a low diffusion concentration, and recombination of electrons generated by light irradiation is suppressed, while the electrode region has a high diffusion concentration and low resistance, and thus collects the generated electrons. Becomes easy. Thereby, the conversion efficiency can be improved.

Next, the photovoltaic device produced by the manufacturing process of the present embodiment was actually operated, and the power generation characteristics were measured and evaluated. FIG. 10 is a diagram illustrating an example of an evaluation result of the power generation characteristics of the photovoltaic device according to the present embodiment. FIG. 10 shows open circuit voltage Voc (mV), short circuit current density Jsc (mA / cm ² ), fill factor FF, and photoelectric conversion efficiency Eff (%) obtained as evaluation results. In FIG. 10, the evaluation result of the photovoltaic apparatus of Embodiment 1 is also shown collectively.

As can be seen from FIG. 10, in the photovoltaic device of the present embodiment, compared with the photovoltaic device of the first embodiment, the open circuit voltage (in the first embodiment, 630 [mV], in the present embodiment, 635 [mV]) and short circuit current density (38.1 [mA / cm ² ] in this embodiment compared to 37.1 [mA / cm ² ] in Embodiment 1) and photoelectric conversion efficiency are improved. is doing. Thus, it was found that the photovoltaic device is configured using the substrate 1 roughened by the substrate roughening method according to the present embodiment, which contributes to the improvement of photoelectric conversion efficiency. .

As described above, in the present embodiment, a diffused substrate is used as the substrate 1a, and the blast mask for forming a selective emitter structure in which the electrode mask 25 is added to the blast mask 3 of the first embodiment at the time of blasting is used. . Therefore, the same effect as in the first embodiment can be obtained, and a selective emitter structure can be formed, and the photoelectric conversion efficiency can be improved as compared with the first embodiment.

Embodiment 3 FIG.
Next, a substrate surface roughening method according to the third embodiment of the present invention will be described. FIG. 11 is a perspective view showing an example of the configuration of a blast mask for forming a selective emitter structure according to the present embodiment. In this embodiment, a mask in which an emulsion portion (second mask portion) 31 is attached to a mesh portion (first mask portion) 30 and integrated as a blast mask for forming a selective emitter structure as shown in FIG. use.

The thickness of the emulsion part 31 is, for example, 20 to 100 microns. For example, a mask used in screen printing may be used as the emulsion part 31. The emulsion part 31 can be patterned by photolithography.

The emulsion part 31 blocks the mesh opening across the plurality of meshes of the mesh part 30 and prevents the passage of blast abrasive grains. Thereby, a selective emitter is formed. The patterning of the emulsion part 31 is performed by photolithography or the like. Although the emulsion part 31 is gradually scraped by the blast abrasive grains, it is possible to suppress the scraping of the emulsion part 31 by using, for example, a rubber-based material. Moreover, since the mesh part 30 and the emulsion part 31 are integrated, it is not necessary to align both.

The substrate roughening method using the selective emitter structure forming blast mask of the present embodiment is the same as the substrate roughening method of the second embodiment, and the description thereof will be omitted.

As described above, the method for roughening a substrate and the method for manufacturing a photovoltaic device according to the present invention uniformly maintains a fine surface roughness of the substrate surface while maintaining the quality of the substrate surface. Useful when doing.

DESCRIPTION OF SYMBOLS 1,1a Substrate 2 Etch-resistant film 3 Blast mask 4 Fine opening 5 Texture depression 6 Flat part 7 Dimple 11 Abrasive spray nozzle 12 Abrasive grain tank 13 Compressed air cylinder 14 Blast abrasive 21 Semiconductor substrate 21a n layer 22 Antireflection film 23 Photosensitive surface side electrode

23a Grid electrode

23b Bus electrode 24 Back electrode 25 Electrode mask 26 Electrode region 27 Electrode diffusion layer 28 Electrode re-diffusion layer 29 Texture region 30 Mesh part 31 Emulsion part

Claims

A first step of forming a protective film on the surface of the substrate;
A second step of depositing a removable blast mask having regularly arranged openings on the protective film;
A third step of forming an opening in a region of the protective film where the blast mask is not deposited by performing a blasting process through the blast mask;
A fourth step of removing the blast mask;
A fifth step of performing etching on the surface of the substrate on which the protective film is formed, under the condition that the protective film has resistance, using the protective film in which the opening is formed as an etching mask;
A sixth step of removing the protective film;
A method for roughening a substrate, comprising:
The blast mask is
A plurality of first members spaced apart from each other and arranged parallel to each other;
A plurality of second members intersecting the first member, spaced apart from each other and arranged parallel to each other;
The method for roughening a substrate according to claim 1, comprising:
The blast mask is configured such that the first member and the second member are orthogonal to each other.
The method for roughening a substrate according to claim 2.
The blast mask is configured such that an angle formed by the first member and the second member is 45 degrees.
The method for roughening a substrate according to claim 2.
The blast mask has a larger interval between the adjacent first members than between the adjacent second members.
The method for roughening a substrate according to claim 4.
The etching is anisotropic alkali etching,
The method for roughening a substrate according to any one of claims 1 to 5, wherein:
In the second step, an arrangement of the first member or the second member with respect to the substrate is determined based on a crystal orientation of the substrate, and the blast mask is placed on the protective film so as to be the determined arrangement. To wear,
The method for roughening a substrate according to claim 6.
The etching is isotropic etching;
The method for roughening a substrate according to any one of claims 1 to 5, wherein:
The substrate is a single crystal silicon substrate;
9. The method for roughening a substrate according to claim 1, wherein the surface is roughened.
The material of the blast mask is stainless steel,
The method for roughening a substrate according to any one of claims 1 to 9, wherein:
In the second step, a non-opening mask without opening is applied to the protective film, and the blast mask is applied to a region of the protective film where the non-opening mask is not applied,
11. The method for roughening a substrate according to claim 1, wherein the surface is roughened.
The substrate is a semiconductor substrate which is the first conductivity type semiconductor substrate and has a diffusion layer formed by diffusing an impurity element of the second conductivity type on the surface;
The region where the non-opening mask is deposited is a region where an electrode is formed,
The method for roughening a substrate according to claim 11.
A roughening step of roughening one surface side of the first conductivity type semiconductor substrate by the method of roughening a substrate according to any one of claims 1 to 12,
An impurity diffusion layer forming step of diffusing an impurity element of a second conductivity type to form an impurity diffusion layer on one surface side of the semiconductor substrate;
Forming an electrode on the other surface side of the semiconductor substrate and an electrode forming region on the one surface side of the semiconductor substrate; and
A method for manufacturing a photovoltaic device, comprising:
The blast mask is
A plurality of first members arranged so as to be spaced apart from each other and parallel to each other, and a plurality of first members arranged so as to cross the first member and be spaced apart from each other and parallel to each other A first mask portion comprising two members;
A second mask part formed integrally with the first mask part so as to block a part of the opening of the first mask part;
The method for roughening a substrate according to claim 1, comprising: