JP2005136062A - Manufacturing method of solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of manufacturing, more efficiently than conventionally, a solar battery in which a region with a surface electrode provided on the front face side of a substrate is formed to be flat and parts other than the region are formed to be uneven. <P>SOLUTION: The method of manufacturing a solar battery includes at least a step of forming a dielectric film on the front face side of a semiconductor substrate having a photoelectric conversion function, a step of forming a coating layer on the dielectric film positioned in an electrode formation region, a step of etching the semiconductor substrate using the dielectric film as a mask, and a step of removing the dielectric film from the semiconductor substrate. Alternately, the method includes at least a step of forming the dielectric film on the surface of the semiconductor substrate having the photoelectric conversion function, a step of removing the dielectric film positioned in the electrode formation region, a step of etching the semiconductor substrate using the dielectric film as a mask, and a step of removing the dielectric film from the semiconductor substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming irregularities on a semiconductor surface for reducing the reflectance of a semiconductor substrate and improving the short-circuit current of the solar cell, and a method for manufacturing a solar cell that improves the characteristics by flattening the bottom of the electrode of the solar cell. Is.

  For example, in a solar cell using a crystalline substrate such as a silicon solar cell, light reflection is reduced by reducing the reflection of light on the surface side of the substrate (the side where light is intended to be incident when the solar cell is used). It is important as one of elemental technologies for improving the efficiency of photoelectric conversion that the substrate is well absorbed. As a method for reducing the reflection of light, for example, a method of forming irregularities on the surface side of a substrate is known. Specifically, a structure in which fine pyramid-like or inverted pyramid-like irregularities are continuously formed on the surface side of the crystalline substrate (such a surface structure is called a “texture structure”) is made incident. Methods for reducing the reflection of incoming sunlight are known. When such a texture structure is formed, since multiple reflections in which light reflected downward on a certain pyramid surface enters another pyramid can be utilized, reflection on the surface side of the substrate as a whole is reduced. Further, when the texture structure is formed, light incident on the silicon is refracted and travels a long distance, so that there is an advantage that the absorption coefficient is equivalently increased (corresponding to an increase in the diffusion distance).

  In the case of a single crystal silicon substrate, in general, anisotropic etching using an alkaline solution or the like is performed on the surface side of the single crystal silicon substrate, so that a fine pyramid or inverted pyramid as described above is formed on the surface side. As a result, a textured structure is realized. The formation of the texture structure by this anisotropic etching utilizes the fact that the etching rate of single crystal silicon differs between the Si (100) crystal orientation plane and the Si (111) crystal orientation plane. Formation of a texture structure by such anisotropic etching is a very useful technique when a solar cell is formed using an expensive single crystal silicon substrate.

  However, when a solar cell is formed using a polycrystalline silicon substrate effective for cost reduction, the polycrystalline silicon substrate has various surfaces even if anisotropic etching is performed as in the case of the single crystal silicon substrate. Since crystal grains having an orientation are included, it is difficult to form a texture structure.

  For this reason, conventionally, various methods for forming irregularities on the surface side of a polycrystalline silicon substrate have been proposed without depending on anisotropic etching. For example, in Patent Document 1, a groove having a substantially V-shaped or substantially U-shaped cross-section is formed by a wheel-shaped multi-blade grindstone having a large number of blades having a substantially V-shaped or U-shaped cross section on a ground surface. A method is disclosed in which irregularities can be mechanically formed on the surface side by forming the surface at the same time on the surface side without depending on the crystal plane orientation. Further, in Patent Document 2, a groove having an appropriate shape is formed on the surface side of a polycrystalline silicon substrate by processing by irradiating a laser beam while changing the irradiation shape at a predetermined speed according to the processing shape. Methods that can be formed are described. Further, in Patent Document 3, after a semiconductor substrate is carried into a dry etching apparatus, a mask forming gas and an etching gas are simultaneously introduced into the dry etching apparatus to form minute irregularities on the surface side of the semiconductor substrate. A method is disclosed. Further, in Patent Document 4, a first step is formed by partial chemical oxidation of the surface with an oxidizing solution containing fluorine ions to form a layer with a porous silicon surface, and the layer is dissolved. A method for organizing the surface of p-type polycrystalline silicon and its alloys in combination with a second step to obtain a textured surface is disclosed. In Patent Document 5, the first step of forming the protector with a random distribution on the surface of the semiconductor wafer, the groove is formed by immersing the semiconductor wafer in an isotropic etching solution and etching the unformed region of the protector. The manufacturing method of the semiconductor wafer for solar cells including the 2nd process to form and the 3rd process to remove a protector is disclosed.

In addition, if the region where the surface electrode is installed is formed flat on the substrate surface while using the texture structure as a basic structure, the leakage current and ohmic loss are reduced, the electric output is improved, and as a result, the photoelectric conversion efficiency is further increased. It is also known that improved solar cells can be obtained. As a method of forming the region flatly, a method of selectively etching using a photo etching technique is known (for example, refer to Patent Document 6).
JP-A-9-148603 Japanese Patent Laid-Open No. 3-89518 JP-A-9-102625 JP-A-9-167850 JP 2002-217439 A JP 62-35582 A

  As described above, various methods are known for forming irregularities on the surface of a polycrystalline silicon substrate in order to improve photoelectric conversion efficiency. However, among the methods for forming irregularities on the surface of the polycrystalline silicon substrate, the mechanical processing method described in Patent Document 1, the processing method using a laser described in Patent Document 2, and Patent Document 3 The described dry etching method has the disadvantages that the operation time is long and expensive equipment is required. In addition, the wet etching method using an acid aqueous solution described in Patent Document 4 is not an effective method because it is difficult to perform multiple reflection and the light absorption rate is reduced. Furthermore, in the case of etching using the protector described in Patent Document 5, a drying process for forming the protector and a removal process of the protector are essential, so that a long working time is required and the production efficiency is inferior. There's a problem.

  In addition, when manufacturing a solar cell that is basically provided with a textured structure and in which the region on the surface of the substrate where the surface electrode is installed is formed flatly, it must be selectively etched. There was a problem that complicated processes such as laser processing were required and efficient production was difficult.

  The present invention has been made in order to solve the above-described problems, and the object of the present invention is to form a flat region where the surface electrode on the surface side of the substrate is installed, and a portion other than the region. It is to provide a method capable of manufacturing a solar cell having irregularities much more efficiently than before.

  According to a method for manufacturing a solar cell according to an aspect of the present invention, a step of forming a dielectric film on the surface side of a semiconductor substrate having a photoelectric conversion function, and a coating layer is formed on the dielectric film located in the electrode formation region And a step of etching the semiconductor substrate using the dielectric film as a mask, and a step of removing the dielectric film from the semiconductor substrate. May be referred to as a "production method"). In the first manufacturing method, it is preferable to form a coating layer in the electrode formation region using a masking tape or a resist.

  Moreover, according to the method for manufacturing a solar cell according to another aspect of the present invention, a step of forming a dielectric film on the surface of a semiconductor substrate having a photoelectric conversion function, and a step of removing the dielectric film located in the electrode formation region And a step of etching the semiconductor substrate using the dielectric film as a mask, and a step of removing the dielectric film from the semiconductor substrate. Sometimes referred to as "manufacturing method"). In the second manufacturing method, a metal mask is placed on the electrode formation region before forming the dielectric film, and after the formation of the dielectric film, the dielectric film located in the electrode formation region together with the metal mask is removed. Alternatively, it is preferable to remove the dielectric film located in the electrode formation region by forming a coating layer in a portion other than the portion located in the electrode formation region on the dielectric film and performing etching.

  In any of the first manufacturing method and the second manufacturing method of the present invention described above, the dielectric film is preferably a film formed of silicon nitride (silicon nitride film). In addition, when the silicon nitride film is formed by plasma CVD, the surface and interface of the semiconductor substrate are inactivated by hydrogen atoms in the decomposition gas during film formation, and the characteristics of the polycrystalline silicon solar cell are particularly improved. ,preferable.

  In either of the first production method and the second production method of the present invention, it is preferable to perform etching using an acidic etching solution, and a mixed liquid of hydrofluoric acid and nitric acid as the acidic etching solution. Is more preferable.

  Furthermore, in any of the first manufacturing method and the second manufacturing method of the present invention, it is preferable to remove the dielectric film from the semiconductor substrate using hydrofluoric acid.

  According to the present invention, it has been difficult to form a texture structure by anisotropic etching, and various attempts to form irregularities on the surface side have been difficult in terms of production efficiency. Even in a polycrystalline silicon substrate, irregularities can be easily formed on the surface side thereof. In addition, according to the present invention, not only the above-described polycrystalline silicon substrate, but also a single crystal silicon substrate that has been capable of forming a texture structure by anisotropic etching in a relatively simple manner is the surface on the surface side of the substrate. It is possible to manufacture a solar cell in which the region where the electrode is installed is flat and the surface is uneven except for the region, which is much more efficient than in the past. Thus, the solar cell obtained in the present invention has an improved short circuit current compared to the conventional solar cell manufactured by removing the damage layer, and further, by flattening the lower part of the electrode, the leakage current In addition, solar cell characteristics other than short-circuit current, such as a reduction in ohmic loss, are improved, and as a result, a solar cell with significantly improved photoelectric conversion efficiency can be realized.

  FIG. 1 is a diagram showing a first manufacturing method in a stepwise manner in the solar cell manufacturing method of the present invention. Hereinafter, the first production method of the present invention will be described with reference to FIG.

  The first manufacturing method of the present invention includes a step of forming a dielectric film on the surface side of a semiconductor substrate having a photoelectric conversion function, a step of forming a coating layer on the dielectric film located in the electrode formation region, and a dielectric At least a step of etching the semiconductor substrate using the body film as a mask and a step of removing the dielectric film from the semiconductor substrate are included.

  First, as shown in FIG. 1A, a dielectric film 2 is formed on the surface side of a semiconductor substrate 1 having a photoelectric conversion function. The semiconductor substrate 1 having a photoelectric conversion function is not particularly limited as long as it is a semiconductor substrate that has been widely used in the manufacture of solar cells. Crystalline silicon such as a single crystal silicon substrate and a polycrystalline silicon substrate can be used. Not only the substrate but also an amorphous silicon substrate which is an amorphous silicon substrate may be used. Among them, a polycrystalline silicon substrate, which has been difficult to form a texture structure by conventional anisotropic etching, is preferable because it can exert a particularly remarkable effect by the manufacturing method of the present invention. The “surface side of the semiconductor substrate 1” refers to a side intended to receive light when it is later formed as a solar cell among the two sides related to the thickness direction of the substrate 1 (the semiconductor substrate in the thickness direction). The side opposite to the front side is sometimes referred to as the “back side”).

  The material for forming the dielectric film 2 is not particularly limited as long as it is a dielectric material capable of forming a film. For example, silicon nitride, silicon oxide, alumina, titanium oxide, magnesium fluoride In particular, it is preferable to form the dielectric film 2 using silicon nitride from the standpoint of resistance as a mask during silicon etching and simplicity of the film removal method. Even if the manufacturing method of the present invention is performed except that the surface side of the semiconductor substrate is covered with a material other than a dielectric, there is a problem that the resistance as an etching mask or the substrate is affected as an impurity. The problem of the invention cannot be solved.

  The method for forming the dielectric film 2 is not particularly limited, and can be formed by a conventionally known appropriate method such as a plasma CVD method, a low pressure CVD method, or a sputtering method. Since the surface and interface of the silicon substrate are sometimes inactivated by hydrogen atoms in the decomposition gas and a polycrystalline silicon substrate is used, the characteristics of the solar cell are particularly improved, which is preferable. The conditions for film formation by the plasma CVD method may be in accordance with appropriate conditions conventionally performed in this field.

  The dielectric film 2 preferably has a substantially uniform film thickness and is formed so as to cover the surface side of the semiconductor substrate 1. The dielectric film 2 may be formed so as to cover the entire surface of the semiconductor substrate 1 or may be formed so as to cover only a part thereof. Although there is no restriction | limiting in particular in the thickness of the dielectric material film 2, It is preferable that it is 10 nm-100 nm, and it is more preferable that it is 30 nm-70 nm. When the thickness of the dielectric film 2 is less than 10 nm, the resistance of the dielectric film as a mask is low, the dielectric film is removed during etching, and the surface shape is almost flat, and a surface shape with small unevenness is formed. If the thickness of the dielectric film 2 exceeds 100 nm, the resistance of the dielectric film as a mask is high, and the back surface where the etched dielectric film is not formed is excessively etched. This is because there is a fear of it.

  Next, as shown in FIG. 1B, a coating layer 4 is formed on the dielectric film 2 located in the electrode formation region on the surface side of the semiconductor substrate 1. Here, the “electrode formation region” in the present specification refers to one or a plurality of regions on the surface side of the semiconductor substrate where the surface electrode is scheduled to be installed in a later step. In the first manufacturing method, masking is performed on a portion of the dielectric film 2 located in the electrode formation region in the thickness direction of the semiconductor substrate 1 to form the coating layer 4. The material for forming the coating layer 4 is not particularly limited, and for example, a conventionally known appropriate material such as a masking tape (UV tape or the like), a resist, a wax, a paste, or a film can be used. Among them, the use of masking tape has the advantage that it is resistant to acid and can be easily formed and removed, and if a resist is used, it can be finely formed and used as a mask in accordance with fine electrodes. It is particularly preferable to form the coating layer 4 with a masking tape or a resist because of the advantage that it can be done.

  In the subsequent process, the semiconductor substrate 1 is etched using the dielectric film 2 as a mask. Here, when the dielectric film 2 is formed so as to cover a part of the surface side of the semiconductor substrate 1, the etching of the semiconductor substrate 1 is performed using the portion where the dielectric film 2 is formed as a mask. Good. However, when the dielectric film 2 is formed so as to cover the entire surface of the semiconductor substrate 1 as shown in FIG. 1A, the dielectric film 2 can be used as a mask as it is. Can not. Therefore, in such a case, it is preferable to first etch the dielectric film 2 as a pretreatment for etching the semiconductor substrate 1 using the dielectric film 2 as a mask. As an etching solution used for etching the dielectric film 2, a known solution can be appropriately used according to the material for forming the dielectric film 2. For example, when the dielectric film 2 is realized by a silicon nitride film, hydrofluoric acid (hydrofluoric acid; HF) or a mixed liquid of hydrofluoric acid and nitric acid can be used as a suitable etching solution. By etching the silicon nitride film using hydrofluoric acid or a mixed liquid of hydrofluoric acid and nitric acid, the thickness of the silicon nitride film is reduced as shown in FIG. As a result, holes are randomly formed in the silicon nitride film. At this time, the portion where the silicon nitride coating layer 4 is formed in the above process remains without being etched. In this way, the semiconductor substrate can be etched using the dielectric film 2 as a mask using the holes randomly formed in the dielectric film 2. If etching is performed using a mixed solution of hydrofluoric acid and nitric acid, the etching of the semiconductor substrate proceeds from the portion where the holes of the silicon nitride film are formed. Since the semiconductor substrate can be etched using the silicon nitride film as a mask, it is particularly suitable.

  In the etching of the dielectric film 2, when hydrofluoric acid is used as an etching solution, the concentration is preferably 0.5% (w / w) to 50% (w / w), preferably 5% ( More preferably, it is w / w) -20% (w / w). The time for etching the dielectric film 2 with hydrofluoric acid is preferably within a range of 1 minute to 20 minutes, and more preferably within a range of 2 minutes to 10 minutes.

  In the etching of the dielectric film 2, when a mixed solution of hydrofluoric acid and nitric acid is used as an etching solution, the mixing ratio is as follows: hydrofluoric acid: nitric acid = 1: 3 to 1:50 (volume ratio) ), And hydrofluoric acid: nitric acid = 1: 5 to 1:20 (volume ratio) is more preferable. The time for etching the dielectric film 2 with the mixed liquid of hydrofluoric acid and nitric acid is preferably within a range of 1 minute to 15 minutes, and more preferably within a range of 2 minutes to 8 minutes. .

  As an etching solution used for etching the semiconductor substrate 1 using the dielectric film 2 as a mask, a known etching solution can be appropriately used according to the material for forming the semiconductor substrate 1 and the dielectric film 2. It is preferable to use an acidic etching solution such as a mixed solution of hydrofluoric acid and nitric acid or a mixed solution of hydrofluoric acid, nitric acid and acetic acid. When the dielectric film 2 is formed of a silicon nitride film as described above, it is particularly preferable to perform etching using a mixed liquid of hydrofluoric acid and nitric acid for the reasons described above. As a result, as shown in FIG. 1 (d), except for the region located on the portion of the dielectric film 2 on which the coating layer 4 is formed on the surface side of the semiconductor substrate 1 (that is, the electrode formation region), Unevenness can be formed on the surface side of the semiconductor substrate 1.

  In the etching of the semiconductor substrate 1 using the dielectric film 2 as a mask, when a mixed solution of hydrofluoric acid and nitric acid is used as an etching solution, the mixing ratio is preferably the same as described above. The etching time of the semiconductor substrate 1 using the dielectric film 2 as a mask with a mixed liquid of hydrofluoric acid and nitric acid is preferably within a range of 1 minute to 10 minutes, and is preferably 2 minutes to 8 minutes. More preferably, it is performed within the range.

  The etching (etching of the silicon nitride film, etching of the semiconductor substrate) may be performed by immersion in a bath containing an etching solution. At this time, the back surface of the semiconductor substrate is mixed with a liquid mixture of hydrofluoric acid and nitric acid. Etching is also performed on the side to reduce the unevenness on the back side. Thereby, the surface area of the back surface is reduced, recombination on the back surface is suppressed, and there is an advantage that the characteristics when the solar cell is manufactured are improved.

  Next, as shown in FIG. 1E, the dielectric film 2 is removed from the semiconductor substrate 1. In this process, the removal of the dielectric film 2 can be performed by an appropriate method according to the material for forming the dielectric film 2. When the dielectric film 2 is realized by a silicon nitride film, it can be removed by immersion in hydrofluoric acid, hot phosphoric acid, a mixed solution of hydrofluoric acid and nitric acid, or the like. Among these, hydrofluoric acid is preferably used because there is an advantage that the silicon nitride film can be removed relatively easily without requiring heating and without affecting the substrate. When hydrofluoric acid is used to remove the dielectric film 2, the concentration is preferably 2% (w / w) to 50% (w / w), and 10% (w / w) to 50%. (W / w) is more preferable.

  According to the first manufacturing method of the present invention, by including at least each of the steps described above, the surface of the semiconductor substrate 1 is formed flat in the electrode formation region, and the portions other than the electrode formation region are uneven. The formed solar cell structure can be manufactured.

  If the manufacturing method of this invention is a method including each said process, the process normally performed in manufacture of a solar cell (for example, the doping process of a semiconductor substrate, the formation process of an antireflection layer, a surface electrode, and a back surface) Of course, it may also include an electrode forming step and the like.

  In the doping process of the semiconductor substrate, for example, after the step of removing the dielectric film 2 and before the formation of the surface electrode 3, the semiconductor substrate 1 is doped with phosphorus, and the light is intended to enter when the solar cell is formed. A PN junction is formed on the side to be processed. The doping of phosphorus into the semiconductor substrate 1 can be suitably performed by a thermal diffusion method that has been widely used in the art.

  The process of forming the antireflection film is a process of forming a film that can prevent reflection of incident light on the surface side of the semiconductor substrate 1 in order to improve the photoelectric conversion efficiency. The material for forming the antireflection film is not particularly limited as long as it has been conventionally used in this field. For example, SiN, TiO, SiO and the like are exemplified. Such an antireflection film can be formed by a method such as a plasma CVD method or a spin coating method. For example, an antireflection film is formed on a SiN film by performing a plasma CVD method using a mixed gas of silane and ammonia as a raw material. A film can be formed.

The surface electrode 3 can be formed, for example, by applying a silver paste to the electrode forming region of the semiconductor substrate by a printing method such as screen printing and firing it (FIG. 1 (f)). Preferably, the silver paste is screen-printed on a portion located in the electrode formation region on the antireflection film provided on the surface side of the semiconductor substrate 1 on which the PN junction is formed, and this is baked to produce a surface electrode It is preferable that the surface electrode 3 is formed by passing through the antireflection film and bonding it to the N ⁺ layer.

  The back electrode (not shown) can be formed, for example, by screen-printing an aluminum paste and a silver paste on the back side of the semiconductor substrate and firing it.

  FIG. 2 is a diagram showing an example of the second manufacturing method in a stepwise manner in the solar cell manufacturing method of the present invention, and FIG. 3 is a second manufacturing method in the solar cell manufacturing method of the present invention. It is a figure which shows the other example of a method in steps. Hereinafter, the second manufacturing method of the present invention will be described with reference to FIGS. In addition, about the 2nd manufacturing method of this invention, about the part which is common with the 1st manufacturing method of this invention, description of the 1st manufacturing method of this invention mentioned above shall be considered, and description is abbreviate | omitted. Sometimes.

  The second manufacturing method of the present invention includes a step of forming a dielectric film on the surface of a semiconductor substrate having a photoelectric conversion function, a step of removing the dielectric film located in the electrode formation region, and using the dielectric film as a mask. At least a step of etching the semiconductor substrate and a step of removing the dielectric film from the semiconductor substrate are included. In the second manufacturing method of the present invention, after the formation of the dielectric film, the dielectric film located in the electrode forming region is removed prior to etching of the semiconductor substrate. A metal mask is placed on the electrode formation region before forming the dielectric layer, and after the dielectric film is formed, the dielectric film located in the electrode formation region together with the metal mask is removed (in the case of FIG. 2), or the dielectric film This is preferably carried out by removing the dielectric film located in the electrode formation region (in the case of FIG. 3) by forming a coating layer other than the portion located in the upper electrode formation region and performing etching.

  In the former case, first, as shown in FIG. 2A, the metal mask 5 is placed on the electrode formation region on the surface side of the semiconductor substrate 1. Specific metal materials for the metal mask 5 include SUS (stainless steel), nickel, and the like, and are not particularly limited. Usually, the same SUS as the metal mask is used for the dielectric film forming apparatus. Therefore, SUS is particularly preferable.

  In the subsequent step, a dielectric film 2 is formed on the surface side of the semiconductor substrate 1 as shown in FIG. The dielectric film 2 is preferably a silicon nitride film formed by plasma CVD as in the first manufacturing method described above. Here, the dielectric film 2 may be formed so as to cover the entire surface of the semiconductor substrate 1 or may be formed so as to cover a part thereof. Here, the dielectric film 2 is formed on the metal mask 5 in the electrode formation region where the metal mask 5 is placed in the above-described process.

  Next, the dielectric film located in the electrode formation region together with the metal mask 5 is removed. Since the metal mask 5 is merely placed on the electrode formation region as described above, the entire dielectric film formed thereon can be easily removed. Thereby, as shown in FIG. 2C, the dielectric film 2 located in the electrode formation region is removed.

  In the latter case, first, a dielectric film 2 is formed on the surface side of the semiconductor substrate 1 as shown in FIG. The dielectric film 2 is preferably a silicon nitride film formed by plasma CVD as in the first manufacturing method described above. The dielectric film 2 may be formed so as to cover the entire surface of the semiconductor substrate 1 or may be formed so as to cover a part thereof.

  Next, as shown in FIG. 3 (b), a coating layer 7 is formed in a portion other than the portion located in the electrode formation region on the dielectric film 2, and then etching is performed as shown in FIG. 3 (c) to form an electrode. The dielectric film located in the region is removed. The material for forming the coating layer 7 is not particularly limited, and those listed as the material for forming the coating layer 4 in the first manufacturing method can be used without any particular limitation. Among these, it is preferable to form the coating layer 7 with a resist. Etching of the dielectric film 2 located in the electrode formation region may be performed according to a conventionally known appropriate technique and condition depending on the material for forming the coating layer 7, and is not particularly limited. After the etching, the covering layer 7 is removed, so that a structure (FIG. 3C) from which the dielectric film 2 is removed only at the portion located in the electrode formation region can be obtained.

  Next, the semiconductor substrate 1 is etched using the dielectric film 2 as a mask.

  Also in the second manufacturing method of the present invention, as in the first manufacturing method, when the dielectric film 2 is formed so as to cover a part of the portion other than the electrode formation region, the dielectric film 2 Etching of the semiconductor substrate 1 may be performed using the portion where the is formed as a mask. When the dielectric film 2 is formed so as to cover the entire surface other than the electrode formation region as shown in FIGS. 2C and 3C, the dielectric film 2 is used as a mask. As a pretreatment for etching the semiconductor substrate 1, it is preferable to first etch the dielectric film 2. The etching solution used for etching the dielectric film 2 is preferably hydrofluoric acid or a mixed solution of hydrofluoric acid and nitric acid, as in the first manufacturing method. By etching the dielectric film 2, the thickness of the silicon nitride film is reduced, and holes are formed in the silicon nitride film at random locations due to stress.

  As an etching solution used when etching the semiconductor substrate 1 using the dielectric film 2 as a mask, a known etching solution can be appropriately used depending on the material for forming the semiconductor substrate 1 and the dielectric film 2. It is preferable to use an acidic etching solution such as a mixed solution of hydrofluoric acid and nitric acid or a mixed solution of hydrofluoric acid, nitric acid and acetic acid. When the dielectric film 2 is formed of a silicon nitride film as described above, if a mixed liquid of hydrofluoric acid and nitric acid is used, the semiconductor substrate is etched from the portion where the holes of the silicon nitride film are formed. Therefore, the etching of the semiconductor substrate using the silicon nitride film as a mask can be performed together with the etching of the silicon nitride film as the pretreatment, which is particularly preferable.

  In this etching, the electrode forming region which is a region not covered with the dielectric layer 2 on the surface side of the semiconductor substrate 1 is also etched. At this time, if a mixed solution of hydrofluoric acid and nitric acid is used as an etching solution, isotropic etching is performed in the electrode formation region, and the electrode is formed flat in the region and embedded in the electrode formation region. Since the surface electrode 3 can be formed, the shadowed portion of the electrode is reduced and the characteristics are improved, which is particularly preferable (FIGS. 2D, 3E, 3D, and 3E).

  Next, as shown in FIGS. 2 (f) and 3 (f), the dielectric film 2 is removed from the semiconductor substrate 1. This step may be performed in the same manner as in the first manufacturing method described above.

  Also according to the second manufacturing method of the present invention, a structure for a solar cell in which the electrode formation region is formed flat on the surface side of the semiconductor substrate 1 and unevenness is formed on the portion excluding the electrode formation region is obtained. Can be produced. After each of the above steps, as shown in FIGS. 2 (g) and 3 (g), a surface is formed on the electrode forming region held flat on the surface side of the semiconductor substrate in the same manner as in the first manufacturing method. The electrode 3 may be formed. Also in the second manufacturing method, if each of the above-described steps is included, as in the first manufacturing method, a step conventionally performed in the manufacture of a solar cell (for example, a doping step of a semiconductor substrate) Of course, it may also include a step of forming an antireflection layer, a step of forming front and back electrodes, and the like.

Example 1
The damage layer was removed from the polycrystalline silicon substrate having a thickness of 300 μm and a size of 125 mm × 125 mm with an aqueous sodium hydroxide solution. Thereafter, a silicon nitride film (thickness: about 70 nm) is formed by plasma CVD, UV tape is applied to the electrode formation region on the surface side of the polycrystalline silicon substrate, and the polycrystalline silicon substrate is bonded with hydrofluoric acid and nitric acid. Was immersed in an etching solution mixed at a ratio of 1:10 (volume ratio) for 4 minutes for etching. Then, UV irradiation is performed for 1 minute, the UV tape is peeled off, and the remaining silicon nitride film is removed by immersion in a 5% (w / w) hydrofluoric acid solution for 15 minutes. A polycrystalline substrate having irregularities was obtained.

  This polycrystalline substrate was doped with phosphorus using a thermal diffusion method to form a PN junction. Next, an antireflection film made of a silicon nitride film was formed by a plasma CVD method using a mixed gas of silane and ammonia as a raw material. Next, an aluminum paste and a silver paste are formed on the back surface of the substrate as a back electrode by screen printing, a surface electrode is screen-printed with a silver paste on a flat portion on the antireflection film on the substrate surface, and baked to form an electrode. Further, after flux is applied to the entire surface, the solar cell is immersed in a solder bath filled with melted solder, and solder is pulled up on the front electrode and the silver electrode on the back surface. Thereby, the solar cell was completed.

Comparative Example 1
The damage layer was removed from the polycrystalline silicon substrate having a thickness of 300 μm and a size of 125 mm × 125 mm with an aqueous sodium hydroxide solution. Thereafter, a silicon nitride film was formed by plasma CVD, and the substrate was immersed in a solution in which hydrofluoric acid and nitric acid were mixed at a ratio of 1:10 for 4 minutes for etching. Thereafter, the remaining silicon nitride film was removed by immersion in a 5% hydrofluoric acid solution for 15 minutes to obtain a polycrystalline substrate having irregularities formed on the surface. Using this substrate, a solar cell was fabricated in the same process as in Example 1.

Comparative Example 2
Similar to the production of a solar cell using a conventional polycrystalline silicon substrate, the polycrystalline silicon substrate having a thickness of 300 μm and a size of 125 mm × 125 mm is removed from the damaged layer with a sodium hydroxide aqueous solution, and then the polycrystalline silicon substrate is used. As is, a solar cell was produced.

For the solar cells obtained in Example 1 and Comparative Examples 1 and 2, solar cell characteristics (short circuit current (A), open circuit) under irradiation of AM (Air Mass) 1.5, 100 mW / cm ² The voltage (V), fill factor, and photoelectric conversion efficiency (%) were measured.

  The results are shown in Table 1.

Example 2
The damage layer was removed from the polycrystalline silicon substrate having a thickness of 300 μm and a size of 125 mm × 125 mm with an aqueous sodium hydroxide solution. After that, a metal mask is installed, a silicon nitride film (thickness: 70 nm) is formed by plasma CVD, and the substrate is immersed in a mixed solution of hydrofluoric acid and nitric acid in a ratio of 1:10 for 4 minutes for etching. I do. Thereafter, the remaining silicon nitride film is immersed in a 5% hydrofluoric acid solution for 15 minutes to remove the remaining silicon nitride film, so that a region where the surface electrode on the surface side is installed is formed flat, and irregularities are formed in portions other than the region. A polycrystalline silicon substrate formed of was obtained.

It is a figure which shows the 1st manufacturing method in steps among the manufacturing methods of the solar cell of this invention. It is a figure which shows an example of the 2nd manufacturing method in steps among the manufacturing methods of the solar cell of this invention. It is a figure which shows in stepwise another example of the 2nd manufacturing method among the manufacturing methods of the solar cell of this invention.

Explanation of symbols

1 semiconductor substrate, 2 dielectric film, 3 surface electrode, 4 coating layer, 5 metal mask, 7 coating layer.

Claims (10)

  A step of forming a dielectric film on the surface side of the semiconductor substrate having a photoelectric conversion function, a step of forming a coating layer on the dielectric film located in the electrode formation region, and etching the semiconductor substrate using the dielectric film as a mask A method for manufacturing a solar cell, comprising at least a step of applying and a step of removing the dielectric film from the semiconductor substrate.   The method according to claim 1, wherein a covering layer is formed on the electrode forming region using a masking tape or a resist.   Forming a dielectric film on the surface of the semiconductor substrate having a photoelectric conversion function; removing the dielectric film located in the electrode formation region; etching the semiconductor substrate using the dielectric film as a mask; A method for producing a solar cell, comprising at least a step of removing a body film from a semiconductor substrate.   4. The metal mask is placed on the electrode formation region before forming the dielectric film, and the dielectric film located in the electrode formation region together with the metal mask is removed after the formation of the dielectric film. The method described.   4. The method according to claim 3, wherein the dielectric film located in the electrode formation region is removed by forming a coating layer in a portion other than the portion located in the electrode formation region on the dielectric film and performing etching. .   The method according to claim 1, wherein the dielectric film is a silicon nitride film.   The method according to claim 1, wherein the dielectric film is formed by a plasma CVD method.   The method according to claim 1, wherein the etching is performed using an acidic etching solution.   The method according to claim 8, wherein the acidic etching solution is a mixture of nitric acid and hydrofluoric acid.   The method according to claim 1, wherein the dielectric film is removed from the semiconductor substrate using hydrofluoric acid.

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