JP2011238846A - Solar cell manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solar cell manufacturing method with which it becomes possible to form a texture having a uniform size efficiently at a high density and achieve a superior photoelectric conversion efficiency.SOLUTION: A solar cell manufacturing method includes: a first step for forming a mask layer on a surface of a single-crystal silicon substrate of a first conductivity type; a second step for performing blast processing on the surface of the single-crystal silicon substrate, on which the mask layer is formed, thereby forming an opening in the mask layer; a third step for performing anisotropic etching on the surface of the single-crystal silicon substrate, on which the mask layer is formed, using the mask layer, in which the opening is formed, as an etching mask, thereby forming a recessed part in a region below and in the vicinity of the opening; a fourth step for removing the mask layer; a fifth step for diffusing an impurity element of a second conductivity type on one surface side of the single-crystal silicon substrate, on which the recessed part is formed, thereby forming an impurity diffusion layer; and a sixth step for forming electrodes in an electrode formation region, which is on one surface side of the semiconductor substrate, and on the other surface side of the semiconductor substrate.

Description

  The present invention relates to a method for manufacturing a solar battery cell using a single crystal silicon substrate.

  In crystalline silicon solar cells, a texture structure is formed on the surface of the substrate in order to improve light absorption. Generally, this texture structure is formed by wet etching in which a propanol solution is added to an alkaline solution.

  However, when texture formation is performed by such wet etching, the consumption of propanol solution, which is a dangerous substance, increases, so expensive explosion-proof equipment is required, or processing is performed because the etching rate is significantly reduced by additives. There is a problem that the time becomes longer.

  As a conventional technique for solving such a problem, a technique is proposed in which a damaged layer of about 0.5 to 5 μm is formed by, for example, blasting or grinding, and then the damaged layer is etched to improve the etching rate. (For example, refer to Patent Document 1).

JP 2005-209726 A

  However, when a texture is formed by the above-described conventional solar cell manufacturing method, the size of the formed texture is non-uniform because the processing damage in the damage layer is non-uniform. There is a problem that the open circuit voltage of the cell is lowered.

In addition, in order to form a texture with high density with the above-mentioned conventional technology, since it is necessary to give high-density processing damage by one blast processing, a problem that a very long blast processing time is required There is. For example, in order to uniformly form a texture shape of about 3 μm in a plane with a density of about 0.2 to 0.8 / μm ^2, a blasting process of about 30 minutes must be performed on a cell of about 150 mm square. I must.

  This invention is made in view of the above, Comprising: It aims at obtaining the manufacturing method of the photovoltaic cell excellent in the photoelectric conversion efficiency which can form the texture of uniform size efficiently in high density. To do.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a solar battery cell according to the present invention includes a first step of forming a mask layer on the surface of a first conductivity type single crystal silicon substrate, A second step of forming an opening in the mask layer by blasting the surface of the single crystal silicon substrate on which the mask layer is formed, and using the mask layer in which the opening is formed as an etching mask, A third step of forming a recess in the lower part of the opening and the vicinity thereof by performing anisotropic etching on the surface of the single crystal silicon substrate on which the mask layer is formed, and removing the mask layer A fourth step, a fifth step of diffusing an impurity element of a second conductivity type to form an impurity diffusion layer on one surface side of the single crystal silicon substrate where the recess is formed, and one surface of the semiconductor substrate On the side Characterized in that it comprises a sixth step of forming a pole forming region and electrodes on the other surface of the semiconductor substrate.

  According to the present invention, it is possible to efficiently form a texture having a uniform size at a high density and to obtain a solar cell excellent in photoelectric conversion efficiency.

FIG. 1 is a flowchart for explaining a texture forming process flow according to the first embodiment of the present invention. FIGS. 2-1 is sectional drawing for demonstrating the texture formation process flow concerning Embodiment 1 of this invention. FIGS. FIGS. 2-2 is sectional drawing for demonstrating the texture formation process flow concerning Embodiment 1 of this invention. FIGS. FIGS. 2-3 is sectional drawing for demonstrating the texture formation process flow concerning Embodiment 1 of this invention. FIGS. FIGS. 2-4 is sectional drawing for demonstrating the texture formation process flow concerning Embodiment 1 of this invention. FIGS. FIGS. 2-5 is sectional drawing for demonstrating the texture formation process flow concerning Embodiment 1 of this invention. FIGS. FIG. 3 is a flowchart for explaining a texture forming process flow according to the second embodiment of the present invention. FIG. 4-1 is a cross-sectional view of the solar battery cell according to the third embodiment of the present invention. FIG. 4-2 is a top view of the solar battery cell according to the third embodiment of the present invention.

  Embodiments of a method for manufacturing a solar battery cell according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.

Embodiment 1 FIG.
In the first embodiment, an example in which a large number of textures having a size of about 3 μm effective for light absorption are uniformly formed on the surface of a single crystal silicon substrate at a high density is shown as an example in FIGS. The present invention will be described with reference to FIG. FIG. 1 is a flowchart for explaining a texture forming process flow according to the first embodiment of the present invention in a basic solar cell manufacturing process. FIGS. 2-1 to 2-5 are cross-sectional views for explaining the texture forming process flow according to the first embodiment of the present invention in the basic solar cell manufacturing process.

  Usually, a silicon substrate used for a solar battery cell is made into a wafer by slicing an ingot with a wire saw regardless of single crystal or polycrystal. For this reason, a damage layer having a depth of 5 to 10 μm generated during slicing is formed on the surface of the silicon substrate.

  This damaged layer is generally removed by wet etching using an alkaline solution such as a sodium hydroxide solution or a potassium hydroxide solution, or by wet etching using an acid such as a hydrofluoric acid solution.

Therefore, for example, a damaged layer caused by slicing is removed by wet etching using a sodium hydroxide solution on the (100) plane of a prepared P-type single crystal silicon substrate 1 (hereinafter referred to as silicon substrate 1) ( Step S10). Next, the silicon substrate 1 from which the damaged layer has been removed is subjected to an oxidation treatment in an oxygen atmosphere at 1,000 ° C. for about 500 seconds, and a blast buffer material for blasting and etching in the etching process A thermal oxide film is formed as the mask layer 2 functioning as a mask (step S20, FIG. 2-1). Here, a silicon oxide film (SiO ₂ film) is formed as the thermal oxide film.

Next, the texture formation process in the first stage is performed. First, a first drilling process of the mask layer 2 is performed by a blasting method (step S30, FIG. 2-2). In order to process the surface of the silicon substrate 1 below the mask layer 2 to a depth of about 4 μm to 8 μm at a maximum pitch of 10 μm, a silicon substrate using a 500th polishing material 3 made of aluminum oxide (Al ₂ O ₃ ) is used. 1 is subjected to sandblasting to form an opening in the mask layer 2. Here, the sandblasting is performed so that the hole density is about 0.01 to 0.05 / μm ² , for example. Further, a processing mark having a depth of about 4 μm to 8 μm is formed on the surface of the silicon substrate 1 exposed at the opening of the mask layer 2 by sandblasting.

  Next, the first anisotropic etching process is performed (step S40, FIG. 2-3). In the first texture formation step, the mask layer 2 with the opening formed thereon is used as a mask to perform anisotropic etching on the surface of the silicon substrate 1 on which the mask layer 2 is formed to A first recess (first texture) 4 is formed in the vicinity region. The anisotropic etching is performed by wet etching using a sodium hydroxide solution, which is an alkaline solution, as an etchant.

  By performing the above steps S20 to S40, anisotropic etching is performed starting from the opening of the mask layer 2 formed by sandblasting and the processing trace on the surface of the silicon substrate 1, and the like. The (111) surface having a slower etching rate than the surface remains, and the inverted quadrangular pyramid-shaped first recess (first texture) 4 is formed. At this time, the processing trace on the surface of the silicon substrate 1 is about 4 to 8 μm, and since the mask layer 2 serving as an etching mask is formed, a transfer defect is generated on the surface of the silicon substrate 1 by sandblasting. Hard to do. For this reason, the cross-sectional state in the vicinity of the surface of the silicon substrate 1 after step S40 is as shown in FIG. 2-3, and the texture size of the first concave portion (first texture) 4 is approximately 4 μm to 8 μm in depth. is there.

In addition, since the pitch of the openings formed in the mask layer 2 is 10 μm or less, the length of the unprocessed region is also 5 μm or less. Furthermore, by using the abrasive _{3 made of} aluminum oxide (Al ₂ O ₃ ), the abrasive 3 embedded in the silicon substrate 1 is etched simultaneously with the silicon substrate 1 during the wet etching using the alkaline solution in step S40. . For this reason, the abrasive 3 buried in the silicon substrate 1 can be easily peeled off from the silicon substrate 1, and the abrasive 3 buried in the silicon substrate 1 may cause damage in a later process, or after etching. Does not change the texture shape.

After the first-stage texture formation process (steps S30 and S40), the second-stage texture formation process is performed. First, a second drilling process of the mask layer 2 is performed by a sandblasting process (step S50, FIG. 2-4). Here, sandblasting is performed using a 2000th abrasive 5 made of aluminum oxide (Al ₂ O ₃ ) so that the processing pitch is 3 μm at the maximum. That is, sandblasting is performed using the abrasive 5 having a size smaller than that of the abrasive 3 used in the sandblasting in step S30.

By this sandblasting, as shown in FIG. 2-4, the abrasive 3 is sprayed at a high density onto the mask layer 2 or the first concave portion (first texture) 4 formed by the texture formation process in the first stage. Then, drilling of the mask layer 2 and transition of less than 1.0 μm are generated in the first recess (first texture) 4 of the silicon substrate at a high density of about 0.2 to 0.8 pieces / μm ² .

  Next, a second anisotropic etching step is performed (step S60, FIG. 2-5). In the second texture formation step, the mask layer 2 in which openings are formed in the second mask layer 2 drilling step is used as a mask, and the surface of the silicon substrate 1 on which the mask layer 2 is formed is anisotropic. Etching is performed to form a second recess (second texture) 6 in the lower part of the opening and in the vicinity thereof. The anisotropic etching is performed by wet etching using a sodium hydroxide solution, which is an alkaline solution, as an etchant.

  As a result, in the portion where the mask layer 2 remains after the first-stage texture formation process, anisotropic etching proceeds from the new opening and the (111) plane remains. In the region where the first concave portion (first texture) 4 having a depth of about 4 μm to 8 μm is formed in the first-stage texture formation process, anisotropic etching proceeds from the transition of less than 1.0 μm. , (111) plane remains. Thereby, as shown in FIG. 2-5, both the remaining portion of the mask layer 2 in the first-stage texture formation process and the formation portion of the first recess (first texture) 4 of about 4 μm to 8 μm are 2 μm to 2 μm. Second recesses (second texture) 6 of about 3 μm are uniformly formed at a high density.

By selecting the etching process time suitable for the etching rate of the mask layer 2 made of a silicon oxide film (SiO ₂ film) and the thickness of the mask layer 2, the removal process of the mask layer 2 becomes unnecessary, but step S60. After that, there is no problem even if the removal process of the mask layer 2 is adopted as step S70.

  By performing the above steps, the second recesses (second texture) 6 of about 2 μm to 3 μm can be formed on the surface of the silicon substrate 1 with high density and uniformity.

  In the first embodiment described above, since the sand blast process is performed using the mask layer 2, the size of the transfer defect generated during the sand blast process can be suppressed, and the etching can be performed without losing the anisotropy thereafter. .

  In the first embodiment described above, sandblasting is performed in two stages with different abrasive sizes. A deep and low-density process is performed in the first stage of sandblasting, and then textures of irregular sizes are formed starting from this processed point by wet etching using an alkaline solution. After that, a second textured sandblasting process is performed on the large-sized texture and the remaining portion of the mask layer 2 of the light receiving portion, and a shallow and high-density processing is performed, and a new texture is formed starting from this processing point. By carrying out such a process, a texture having a size of about 3 μm effective for light absorption can be uniformly formed on the surface of the silicon substrate 1 at a high density.

  That is, when blasting is performed only once using the same size abrasive, processing damage is non-uniform and it is difficult to control the size and density of the texture to be formed. Further, if processing damage is uniformly and densely applied to the silicon substrate 1 by one blast processing, the blast processing time significantly increases or the etching time significantly increases.

  However, in the first embodiment, since two-step sandblasting is performed and anisotropic etching is performed, a texture having the same size can be formed on the surface of the silicon substrate 1 with high density.

  Moreover, in Embodiment 1 mentioned above, since the process trace by a blast process does not remain on the surface of the silicon substrate 1, the fall of the open voltage of the electrical characteristic of the photovoltaic cell resulting from the process trace by a blast process, or electric current Leakage is prevented.

Further, in the first embodiment, by performing the two-stage sand blast processing, each processing time can be shortened, and the first blast processing time of about 3 μm is performed on the silicon substrate 1 of about 150 mm by about 15 minutes. Two concave portions (second texture) 6 can be uniformly formed in the plane at a density of about 0.2 to 0.8 pieces / μm ² . Therefore, the texture can be efficiently formed in a short time.

  In the first embodiment, since the mask layer 2 serves as both a buffer material and an etching mask for blasting, it is not necessary to separately form the buffer material and the etching mask for blasting, and the process is simplified. Is done.

In the first embodiment, the abrasives 3 and 5 made of aluminum oxide (Al ₂ O ₃ ) are used, so that the abrasives 3 and 5 buried in the silicon substrate 1 are obtained by wet etching using an alkaline solution. Since it is etched, it is easily peeled off from the silicon substrate 1. This prevents the abrasives 3 and 5 from remaining on the etched silicon substrate 1 and causing damage or changing the texture shape after etching.

  Therefore, according to the first embodiment, a texture structure having a uniform size of about 3 μm with high efficiency of light absorption of visible light can be efficiently and densely formed on the surface of the silicon substrate 1 in a shorter time than before. Can be formed. And the solar cell excellent in photoelectric conversion efficiency can be efficiently produced by using this silicon substrate 1. FIG.

Embodiment 2. FIG.
In the second embodiment, the case where the mask layer 2 made of a silicon nitride film is formed as the mask layer 2 using a plasma CVD method will be described with reference to FIG. 3 and FIGS. 2-1 to 2-5. FIG. 3 is a flowchart for explaining a texture forming process flow according to the second embodiment of the present invention in the basic solar cell manufacturing process.

First, the damaged layer resulting from the slice is removed by wet etching using a sodium hydroxide solution on the prepared (100) surface of the silicon substrate 1, for example (step S10). Next, a blast buffer material at the time of blasting and a mask layer 2 functioning as an etching mask in the etching process are formed on the silicon substrate 1 from which the damaged layer has been removed (step S120). FIG. 2-1). Here, a silicon nitride film (SiN film) is formed as the mask layer 2. A silicon nitride film (SiN film) can also be used as the mask layer 2 similarly to the silicon oxide film (SiO ₂ film) formed in the first embodiment.

  Thereafter, the steps described in step S30 and FIGS. 2-2 to S60 and FIG. 2-5 in the first embodiment are performed.

  As in the case of the first embodiment, the removal process of the mask layer 2 is performed by selecting the etching process time suitable for the etching rate of the mask layer 2 made of the silicon nitride film and the thickness of the mask layer 2. Although unnecessary, there is no problem even if the removal process of the mask layer 2 is adopted as step S70 after step S60.

  By performing the above steps, the second recesses (second texture) 6 of about 2 μm to 3 μm can be formed on the surface of the silicon substrate 1 with high density and uniformity.

  In the second embodiment described above, since the sand blast process is performed using the mask layer 2 as in the first embodiment, the size of the transfer defect generated during the sand blast process is suppressed, and the anisotropy is also maintained thereafter. Etching can be performed without loss.

  Further, in the second embodiment described above, sandblasting is performed in two stages with different abrasive sizes as in the case of the first embodiment. A deep and low-density process is performed in the first stage of sandblasting, and then textures of irregular sizes are formed starting from this processed point by wet etching using an alkaline solution. After that, a second textured sandblasting process is performed on the large-sized texture and the remaining portion of the mask layer 2 of the light receiving portion, and a shallow and high-density processing is performed, and a new texture is formed starting from this processing point. By carrying out such a process, a texture having a size of about 3 μm effective for light absorption can be uniformly formed on the surface of the silicon substrate 1 at a high density.

  Moreover, in Embodiment 2 mentioned above, since the process trace by a blast process does not remain on the surface of the silicon substrate 1 like the case of Embodiment 1, the electrical characteristic of the photovoltaic cell resulting from the process trace by a blast process A reduction in the open circuit voltage or the occurrence of current leakage is prevented.

Further, in the second embodiment, by performing the two-stage sandblasting as in the first embodiment, each processing time can be shortened, and about 15 minutes for the silicon substrate 1 of about 150 mm square. The second recesses (second texture) 6 of about 3 μm can be uniformly formed in the plane at a density of about 0.2 to 0.8 pieces / μm ^{2 in} the blasting time of. Therefore, the texture can be efficiently formed in a short time.

  In the second embodiment, the mask layer 2 also serves as a buffer material and an etching mask for blasting as in the case of the first embodiment. Therefore, the buffer material and the etching mask for blasting are individually formed. There is no need to do so, and the process is simplified.

Further, in the first embodiment, as in the case of the first embodiment, by using the abrasives 3 and 5 made of aluminum oxide (Al ₂ O ₃ ), the silicon substrate 1 is obtained by wet etching using an alkaline solution. Since the abrasives 3 and 5 buried in are etched, they are easily separated from the silicon substrate 1. This prevents the abrasives 3 and 5 from remaining on the etched silicon substrate 1 and causing damage or changing the texture shape after etching.

  Therefore, according to the second embodiment, as in the first embodiment, a texture structure having a uniform size of about 3 μm, which has a high light absorption efficiency of visible light, is formed on the surface of the silicon substrate 1 compared to the conventional case. It can be formed efficiently and densely in a short time. And the solar cell excellent in photoelectric conversion efficiency can be efficiently produced by using this silicon substrate 1. FIG.

Embodiment 3 FIG.
FIGS. 4-1 and FIGS. 4-2 are figures which show the photovoltaic cell produced using the silicon substrate 1 by which the texture was formed by the method concerning Embodiment 1 mentioned above, FIG. 4-1 is sectional drawing. FIG. 4B is a top view. The solar battery cell shown in FIGS. 4A and 4B includes a first conductivity type semiconductor substrate 101 having an N type impurity layer 101a which is an impurity diffusion layer in which impurities of the second conductivity type are diffused in the substrate surface layer. The antireflection film 102 formed on the light receiving surface side surface (front surface) of the semiconductor substrate 101, the light receiving surface side electrode 103 formed on the light receiving surface side surface (front surface) of the semiconductor substrate 101, and the semiconductor substrate 101 A back electrode 104 formed on a surface (back surface) opposite to the light receiving surface.

  Moreover, as the light-receiving surface side electrode 103, the grid electrode 103a and bus electrode 103b of a solar cell are included, In FIG. 4-1, sectional drawing in the cross section perpendicular | vertical to the longitudinal direction of the grid electrode 103a is shown. And the solar cell is comprised for the semiconductor substrate 101 using the board | substrate 101 which formed the fine texture (not shown) on the substrate surface using the texture formation method mentioned above.

  Next, steps for manufacturing the solar battery cell shown in FIGS. 4-1 and 4-2 using the substrate 101 described above will be described. In addition, since the process demonstrated here is the same as the manufacturing process of the photovoltaic cell using a general silicon substrate, it does not show in particular in figure.

The substrate 101 in which the process of step S60 in Embodiment 1 is completed 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 101. Phosphorus is diffused in 101 to form a second conductivity type N-type impurity layer 101 a in the surface layer of the substrate 101. The diffusion temperature is set to 840 ° C., for example. Thereby, the semiconductor substrate 101 having the N-type impurity layer 101a on the substrate surface layer is obtained. Since a p-type silicon substrate is used here, phosphorus of different conductivity type is diffused to form a pn junction. However, when an n-type silicon substrate is used, p-type impurities may be diffused.

  Next, after removing the phosphor glass layer of the substrate 101 in a hydrofluoric acid solution, a SiN film is formed on the N-type impurity layer 101a as the antireflection film 102 by plasma CVD. The film thickness and refractive index of the antireflection film 102 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 102 may be formed by a different film formation method such as a sputtering method.

  Next, a paste mixed with silver is printed on the light receiving surface of the substrate 101 in a comb shape by screen printing, and a paste mixed with aluminum is printed on the entire back surface of the substrate 101 by screen printing, and then a baking process is performed. Thus, the light receiving surface side electrode 103 and the back surface electrode 104 are formed. Firing is performed at 760 ° C. in an air atmosphere, for example. As described above, the solar cell shown in FIGS. 4-1 and 4-2 is manufactured. Moreover, also when using the silicon substrate 1 in which the texture was formed by the method concerning Embodiment 2 mentioned above, a photovoltaic cell can be produced similarly to the above.

  According to the manufacturing method of the solar cell according to the third embodiment described above, the silicon substrate 1 in which the texture is formed on the substrate surface using the texture forming method according to the first embodiment or the second embodiment is used. Therefore, it is possible to produce a solar cell having a good photoelectric conversion efficiency, in which the surface light reflection loss on the substrate surface on the light incident side is significantly reduced and the photoelectric conversion efficiency is improved. it can. As a result, when producing a photovoltaic cell having photoelectric conversion efficiency equivalent to the conventional one, the area of the substrate is reduced, the amount of the raw material of the substrate is reduced, and the solar cell is reduced in size, weight, and reduction. It is possible to make it easier.

  As described above, the method for manufacturing a solar battery cell according to the present invention is useful for efficiently forming a uniform-sized texture with high density.

1 P-type single crystal silicon substrate 2 Mask layer 3 Abrasive material 4 1st recessed part (1st texture)
5 Abrasive material 101a N-type impurity layer 101 Semiconductor substrate 102 Antireflection film 103 Light receiving surface side electrode 103a Grid electrode 103b Bus electrode 104 Back surface electrode

Claims (6)

A first step of forming a mask layer on a surface of a first conductivity type single crystal silicon substrate;
A second step of forming an opening in the mask layer by blasting the surface of the single crystal silicon substrate on which the mask layer is formed;
Using the mask layer in which the opening is formed as an etching mask, anisotropic etching is performed on the surface of the single crystal silicon substrate on which the mask layer is formed, so that the lower portion of the opening and the vicinity thereof are formed. A third step of forming a recess;
A fourth step of removing the mask layer;
A fifth step of forming an impurity diffusion layer by diffusing an impurity element of a second conductivity type on the one surface side of the single crystal silicon substrate where the concave portion is formed;
A sixth step of forming an electrode on one side of the semiconductor substrate and an electrode on the other side of the semiconductor substrate;
The manufacturing method of the photovoltaic cell characterized by including. Between the third step and the fourth step, perform the second step and the third step for the second time again,
In the second second step, blasting is performed using an abrasive having a size different from that of the first second step,
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these. In the second step of the second time, blasting is performed using a larger abrasive than the abrasive used in the second step of the first time,
The manufacturing method of the photovoltaic cell of Claim 2 characterized by these. The anisotropic etching is wet etching using an alkaline solution,
The mask layer is made of a material having a high selectivity to the alkaline solution;
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these. The mask layer is made of silicon oxide or silicon nitride;
The manufacturing method of the photovoltaic cell of Claim 4 characterized by these. In the second step, blasting is performed using an abrasive made of aluminum oxide,
The manufacturing method of the photovoltaic cell of Claim 4 characterized by these.

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