JP2016032073A - Method and device for manufacturing solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell capable of improving the quality and yield of the solar cell without increasing an environmental load.SOLUTION: A method for manufacturing a solar cell includes: a first step of forming an uneven structure on a surface of a silicon-based substrate of a first conductivity type; a second step of forming an impurity diffusion layer in a surface layer of the silicon-based substrate by diffusing an impurity of a second conductivity type to the surface of the silicon-based substrate; and a third step of removing a compound layer including the impurity formed on the impurity diffusion layer and a material of the silicon-based substrate. The third step further includes: a fourth step of etching the surface of the silicon-based substrate using the solution containing hydrofluoric acid; a fifth step of cleaning the solution containing hydrofluoric acid remaining on the surface of the silicon-based substrate using pure water; a sixth step of uniformly forming an oxide film on the surface of the silicon-based substrate using oxidizing chemicals; a seventh step of cleaning the oxidizing chemicals remaining on the surface of the silicon-based substrate using pure water; and an eighth step of drying the surface of the silicon-based substrate.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a solar cell manufacturing method and a solar cell manufacturing device, and more particularly to a solar cell manufacturing method and a solar cell manufacturing device that suppress the generation of watermarks.

There is a thermal diffusion process for forming a pn junction in a manufacturing process of a semiconductor device using a silicon substrate, for example, a solar battery cell. For example, when phosphorus diffusion is performed on a p-type silicon substrate, the following thermal diffusion process is performed. That is, a p-type silicon substrate is put into a thermal oxidation furnace, the p-type silicon substrate is heated in the presence of phosphorus oxychloride (POCl ₃ ) vapor, and a phosphorus glass that is an oxide film containing phosphorus is added to the p-type silicon substrate A film is formed on the surface. Then, phosphorus is thermally diffused from the phosphorus glass into the p-type silicon substrate, thereby forming a phosphorus diffusion layer serving as an n-type impurity diffusion layer on the surface of the p-type silicon substrate to form a pn junction.

  On the surface of the phosphorous diffusion layer after the thermal diffusion step, phosphorous glass containing glass as a main component is formed. If phosphorous glass remains on the surface of the phosphorous diffusion layer, the photoelectric conversion efficiency of the solar battery cell is lowered, so that a cleaning step for removing the phosphorous glass is required.

In general, the cleaning step for removing phosphorus glass is performed by first using a solution containing HF such as hydrofluoric acid (HF) or a mixed acid of HF, nitric acid (HNO ₃ ), and sulfuric acid (H ₂ SO ₄ ). From the removal processing of phosphorus glass by the wet etching process used, the cleaning process of cleaning the solution containing HF remaining on the surface of the silicon substrate with pure water, and the drying process of draining and drying the pure water on the surface of the silicon substrate Become.

  In the production of solar cells, it is required to produce solar cells at low cost. For this reason, the above-mentioned cleaning process is performed by a batch method in which a large number of silicon substrates are collectively processed at a time. In addition, the drying process is performed by dry air blowing in which heated dry air is blown from the top, bottom, left, and right directions toward the silicon substrate in order to reduce tact time and reduce costs.

However, with dry air blow, it is difficult to uniformly dry all the silicon substrates in one batch. Furthermore, since the uneven structure called texture structure is formed on the surface of the silicon substrate of the solar battery cell, the surface state is likely to change due to the shape effect of the texture, and in the case of hydrophobicity, it becomes more hydrophobic and hydrophilic. In this case, the surface becomes more hydrophilic and unevenness occurs in the surface state of the silicon substrate. For the above reasons, in the method for manufacturing a solar cell described above, the surface state and drying time of the silicon substrate are uneven, and silicon oxide (SiO _x ) called a watermark is likely to be generated on the surface of the silicon substrate.

  When the watermark is generated, the surface of the silicon substrate becomes cloudy and the appearance is deteriorated, and the yield of solar cells is reduced due to the appearance failure. The generation of the watermark is affected by conditions such as the drying method, the hydrogen bonding state of the substrate surface, and the surface shape.

  As a method for suppressing the generation of a watermark, for example, in Patent Document 1, after a silicon substrate is immersed in a dilute hydrofluoric acid aqueous solution in order to remove phosphorous glass, the silicon substrate is immersed in the dilute hydrofluoric acid aqueous solution. The substrate surface is hydrophilized by mixing an oxidizing aqueous solution with a hydrofluoric acid aqueous solution.

JP-A-4-144131

  However, according to the above conventional technique, since the silicon substrate is immersed in a mixed solution obtained by mixing an oxidizing aqueous solution with a dilute hydrofluoric acid aqueous solution, the formation of the oxide film and the etching of the oxide film and the phosphor glass on the surface of the silicon substrate are performed. Progress at the same time. In the production of solar cells, in order to obtain a solar cell with high photoelectric conversion efficiency, the phosphorus concentration of the phosphorus diffusion layer that becomes the n-type impurity diffusion layer formed on the surface of the p-type silicon substrate in the previous step is important. . Therefore, fluctuations in the phosphorus concentration on the surface of the phosphorus diffusion layer due to etching must be suppressed. In addition, the surface roughness of the texture structure formed on the surface of the silicon substrate is increased by the etching, and the photoelectric conversion efficiency improvement effect by the texture structure cannot be obtained as designed. Further, since the oxidizing aqueous solution is mixed with the dilute hydrofluoric acid aqueous solution, it is necessary to newly prepare the dilute hydrofluoric acid aqueous solution for each batch, and there is a problem that the environmental load is large.

  The present invention has been made in view of the above, and a method for manufacturing a solar cell capable of improving the quality of the solar cell and improving the yield of the solar cell without increasing the environmental load, and the solar cell It aims at obtaining the manufacturing apparatus of the photovoltaic cell which implement | achieves this manufacturing method.

  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 concavo-convex structure on the surface of a silicon substrate of a first conductivity type, and the silicon system. A second step of diffusing impurities of a second conductivity type on the surface of the substrate to form an impurity diffusion layer on a surface layer of the silicon-based substrate; the impurities formed on the impurity diffusion layer; and a material of the silicon-based substrate And a third step of removing a compound layer including: a fourth step of etching the surface of the silicon substrate using a solution containing hydrofluoric acid; and a surface of the silicon substrate. A fifth step of cleaning the solution containing hydrofluoric acid remaining in the substrate with pure water, a sixth step of uniformly forming an oxide film on the surface of the silicon-based substrate using an oxidizing chemical solution, and The acid remaining on the surface It characterized in that it comprises a seventh step of washing the sexual chemical with pure water, and an eighth step of drying the surface of the silicon-based substrate.

  According to the present invention, it is possible to improve the quality of solar cells and the yield of solar cells without increasing the environmental load.

Sectional drawing of the principal part of the photovoltaic cell produced using the manufacturing method of the photovoltaic cell concerning embodiment of this invention The top view of the photovoltaic cell produced using the manufacturing method of the photovoltaic cell concerning embodiment of this invention Sectional drawing of the principal part explaining the manufacturing method of the photovoltaic cell concerning embodiment of this invention Sectional drawing of the principal part explaining the manufacturing method of the photovoltaic cell concerning embodiment of this invention Sectional drawing of the principal part explaining the manufacturing method of the photovoltaic cell concerning embodiment of this invention Sectional drawing of the principal part explaining the manufacturing method of the photovoltaic cell concerning embodiment of this invention The flowchart explaining the flow of the phosphorus glass removal process in the manufacturing method of the photovoltaic cell concerning embodiment of this invention. The schematic diagram which shows schematic structure of the manufacturing apparatus of the photovoltaic cell which implements the phosphorus glass removal process in the manufacturing method of the photovoltaic cell concerning embodiment of this invention The flowchart explaining the flow of the phosphorus glass removal process of a comparative example Characteristic diagram showing the incidence of watermarks with or without an oxide film formation step with ozone water after a phosphorous glass etching step with a solution containing hydrofluoric acid Characteristic diagram showing the rate of occurrence of watermarks with and without the oxide film formation step with hydrogen peroxide after the phosphor glass etching step with a solution containing hydrofluoric acid

  EMBODIMENT OF THE INVENTION Below, embodiment of the manufacturing method of the photovoltaic cell concerning this invention and the manufacturing apparatus of a photovoltaic cell is described in detail based on drawing. 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 The present embodiment relates to the manufacture of solar cells, and particularly relates to the suppression of the generation of watermarks resulting from the cleaning process after the diffusion process. Specifically, the present embodiment is performed after the impurity diffusion layer is formed in the surface layer of the silicon substrate by thermally diffusing the second conductivity type impurity in the surface layer of the first conductivity type silicon substrate. The present invention relates to a removal process of a compound layer formed between an impurity and a silicon substrate formed on the surface of the silicon substrate. More specifically, the compound layer is a compound layer mainly composed of impurities of the second conductivity type, silicon that is a material of the silicon-based substrate, and oxygen.

  First, the solar battery cell produced using the manufacturing method of the solar battery cell concerning this Embodiment is demonstrated. FIG. 1 and FIG. 2 are views showing a solar battery cell manufactured using the method for manufacturing a solar battery cell according to the present embodiment, FIG. 1 is a cross-sectional view of the main part of the solar battery cell, and FIG. It is a top view of a battery cell. 1 and 2 includes a silicon substrate 11 having an n-type impurity diffusion layer 11b in the substrate surface layer of a p-type silicon substrate 11a and having a pn junction formed thereon, and a light-receiving surface side of the silicon substrate 11. The antireflection film 12 formed on the surface, the light receiving surface side electrode 13 formed on the light receiving surface side surface of the silicon substrate 11, and the back electrode formed on the back surface that is the surface facing the light receiving surface of the silicon substrate 11 14. A P + layer 11c containing a p-type impurity at a higher concentration than the p-type silicon substrate 11a is formed in the lower region of the back electrode 14 in the surface layer portion on the back surface side of the silicon substrate 11. The P + layer 11c is provided in order to obtain a BSF (Back Surface Field) effect.

  The light receiving surface side electrode 13 includes a grid electrode 13a and a bus electrode 13b, and FIG. 1 shows a cross-sectional view in a cross section perpendicular to the longitudinal direction of the grid electrode 13a. A silicon oxide film 21 is formed between the n-type impurity diffusion layer 11 b and the antireflection film 12. On the surface on the light receiving surface side of the silicon substrate 11, that is, the surface of the n-type impurity diffusion layer 11b, a texture structure 15 that is a fine uneven structure is formed.

  Below, the process for manufacturing the photovoltaic cell shown in FIG.1 and FIG.2 is demonstrated. 3-6 is principal part sectional drawing explaining the manufacturing method of the photovoltaic cell concerning embodiment.

  First, the p-type silicon substrate 11a is cut out from the silicon ingot by slicing. The p-type silicon substrate 11a may be a single crystal silicon substrate or a polycrystalline silicon substrate. In the present embodiment, a single crystal silicon substrate is used as the p-type silicon substrate 11a. On the surface of the p-type silicon substrate 11a cut out from the silicon ingot by slicing, organic impurities and metal impurities, which are contaminants made of chips and abrasives generated by cutting the wire during slicing, are attached. . For this reason, the p-type silicon substrate 11a cut out from the silicon ingot is subjected to a cleaning removal process of organic impurities and metal impurities that are residues when cut out by slicing.

  The p-type silicon substrate 11a that has been subjected to the cleaning and removing process of organic impurities and metal impurities is finely formed on the substrate surface as shown in FIG. 3 in the wet etching process so that the solar cells can absorb more sunlight. A texture structure 15 that is a rough structure is formed. The texture can be formed on the surface of the p-type silicon substrate 11a by anisotropic etching utilizing the property that the etching rate differs depending on the plane orientation of silicon. In texture formation, a p-type silicon substrate is added to a wet etching solution that is a high-temperature chemical solution obtained by adding an organic substance such as isopropyl alcohol (IPA) to an alkaline aqueous solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution. Immerse 11a. Note that the p-type silicon substrate 11a may not be immersed in the wet etching solution as long as the wet etching solution can be supplied to the surface of the p-type silicon substrate 11a to form the texture.

Next, the p-type silicon substrate 11a having a texture formed on the surface is put into a thermal diffusion furnace, and in the presence of an atmosphere containing phosphorus such as phosphorus oxychloride (POCl ₃ ) vapor or phosphorus hydride (PH ₃ ) vapor. A phosphorus glass layer is deposited on the surface of the p-type silicon substrate 11a by heating. Then, phosphorus is diffused into the p-type silicon substrate 11a by supplying phosphorus from the phosphorus glass layer. As a result, the n-type impurity diffusion layer 11b is formed on the entire surface of the p-type silicon substrate 11a, and a pn junction is formed. The surface of the n-type impurity diffusion layer 11b is in a state in which a phosphorus glass layer is formed. The phosphorus glass layer is a compound layer containing phosphorus, which is an impurity of the second conductivity type, and silicon, which is a material of the p-type silicon substrate 11a, which is a silicon substrate of the first conductivity type. More specifically, the compound layer is a compound layer containing phosphorus, silicon, and oxygen as main components.

  Here, immediately after the formation of the n-type impurity diffusion layer 11b, a phosphorus glass layer 31 is formed on the surface of the p-type silicon substrate 11a including the n-type impurity diffusion layer 11b as shown in FIG. For this reason, the phosphorus glass removal process which removes this phosphorus glass layer 31 by wet etching using an etching liquid is performed.

  FIG. 7 is a flowchart for explaining the flow of the phosphorus glass removing step in the method for manufacturing a solar battery cell according to the present embodiment. The phosphorus glass removing process according to the present embodiment includes a phosphorus glass etching process performed in step S10, a first cleaning process performed in step S20, an oxide film forming process performed in step S30, and step S40. The 2nd washing process performed in and a drying process performed in Step S50 are included.

In the phosphor glass etching process of step S10, n-type impurity diffusion is performed by wet etching using a solution containing HF such as hydrofluoric acid (HF) or a mixed acid of HF, HNO ₃ and H ₂ SO ₄ as an etchant. The phosphorus glass layer 31 formed on the surface of the p-type silicon substrate 11a including the layer 11b is removed by etching. The concentration of hydrofluoric acid in the solution containing HF is not particularly limited, and may be set as appropriate depending on various conditions such as the conditions for forming the n-type impurity diffusion layer 11b. Further, the immersion time of the p-type silicon substrate 11a in the etching solution that is a solution containing HF may be set as appropriate depending on various conditions such as the formation conditions of the n-type impurity diffusion layer 11b and the concentration of hydrofluoric acid.

In the phosphorous glass etching step, for example, the p-type silicon substrate 11a is immersed in an HF solution prepared at HF: H ₂ O = 1: 10 for 450 seconds, and the surface of the p-type silicon substrate 11a including the n-type impurity diffusion layer 11b. The phosphorus glass layer 31 formed in the step is removed by etching.

  In the first cleaning process of step S20, after the phosphorus glass etching process is performed, pure water is supplied to the surface of the p-type silicon substrate 11a, whereby the solution containing HF remaining on the surface of the p-type silicon substrate 11a. The 1st washing process which wash | cleans with pure water is performed. In the first cleaning step, for example, the p-type silicon substrate 11a is immersed in pure water, and the HF solution remaining on the surface of the p-type silicon substrate 11a is washed away.

At this time, the surface of the p-type silicon substrate 11a is hydrophobic because it is immersed in the HF solution. For this reason, the p-type silicon substrate 11a lifted from the pure water repels water, but the pure water may partially remain in the form of water droplets. Then, the pure water remaining in the form of water droplets on the surface of the p-type silicon substrate 11a drawn from the pure water causes the generation of a watermark made of silicon oxide (SiO _x ).

  Therefore, as a countermeasure for preventing the occurrence of the watermark, in the oxide film forming process in step S30, after the first cleaning process is performed, an oxidizing chemical solution having an oxidizing action is supplied to the surface of the p-type silicon substrate 11a, thereby causing p. A silicon oxide film 21 is uniformly formed on the surface of the p-type silicon substrate 11a by wet oxidation to uniformly hydrophilize the surface of the p-type silicon substrate 11a. Examples of the oxidizing chemical solution include ozone water and hydrogen peroxide solution in which ozone gas is dissolved.

  In the oxide film forming step, after cleaning with pure water in step S20, for example, the p-type silicon substrate 11a is immersed in a storage tank in which an oxidizing chemical solution is stored, so that the surface of the p-type silicon substrate 11a as shown in FIG. Then, a silicon oxide film 21 which is an oxide film is uniformly formed to uniformly hydrophilize the surface of the p-type silicon substrate 11a.

  As the oxidizing chemical solution, for example, ozone water in which ozone gas is dissolved is used. And after immersing the p-type silicon substrate 11a in the storage tank in which ozone water is stored, ozone water whose dissolved ozone concentration is adjusted to a predetermined concentration is constantly supplied to the storage tank, and the dissolved ozone in the ozone water in the storage tank Keep the concentration constant. The dissolved ozone concentration of ozone water should just be 0.1 mg / L or more, and the hydrophilic treatment in a short time is possible, so that it is high concentration. The dissolved ozone concentration of ozone water is more preferably 1 mg / L or more. In addition, the upper limit of the dissolved ozone density | concentration of ozone water is 180 mg / L from a viewpoint of the reason on manufacture of high concentration ozone water. When the dissolved ozone concentration of the ozone water is about 0.1 mg / L, the immersion time of the p-type silicon substrate 11a in the ozone water may be 30 seconds or more.

  In addition, the silicon oxide film 21 formed on the n-type impurity diffusion layer 11b on the light-receiving surface side of the silicon substrate 11 among the silicon oxide film 21 formed in the oxide film forming process in step S30 is an antireflection film or a passivation film. Can be used as Of the silicon oxide film 21 formed in the oxide film forming process in step S30, the silicon oxide film 21 formed on the back surface and side surface of the silicon substrate 11 is an unnecessary n-type impurity diffusion layer after the phosphorus glass removing process. A part or the whole is removed when etching and removing 11b.

  When the n-type impurity diffusion layer 11b is formed only on one side of the p-type silicon substrate 11a in advance, the unnecessary n-type impurity diffusion layer 11b is not required to be etched, so the p-type silicon substrate 11a. The silicon oxide film 21 also remains on the back surface and side surfaces other than the light receiving surface side. The back and side silicon oxide films 21 on the p-type silicon substrate 11a may or may not be removed.

  In the second cleaning process of step S40, after the oxide film forming process is performed, pure water is supplied to the surface of the p-type silicon substrate 11a, thereby purifying the oxidizing chemical remaining on the surface of the p-type silicon substrate 11a. A second washing process is carried out with water. In the second cleaning step, for example, the p-type silicon substrate 11a is immersed in pure water, and the oxidizing chemical remaining on the surface of the p-type silicon substrate 11a is washed away.

  In each step of Step S10 to Step S40, if the target processing can be performed by supplying each processing solution to the surface of the p-type silicon substrate 11a, the p-type silicon substrate 11a does not have to be immersed in each processing solution. Also good.

  In the drying process of step S50, the pure water remaining on the surface of the p-type silicon substrate 11a is drained and dried after the second cleaning process. In the drying step, for example, pure water remaining on the surface of the p-type silicon substrate 11a is drained and dried by blowing or evaporating pure water by blowing hot air of about 150 ° C. on the p-type silicon substrate 11a. I do. In the substrate drying by the warm air drying method using warm air, the substrate is blown with warm air of 100 ° C. or higher, preferably 140 ° C. or higher so that the surface temperature of the substrate becomes 50 ° C. or higher, and adheres to the surface of the substrate. The substrate is dried by blowing away or evaporating the water. The above-described step S50 is performed, and the series of phosphorus glass removal processing is completed.

  In the phosphorus glass removing process according to the present embodiment, the surface of the p-type silicon substrate 11a is uniformly covered with the silicon oxide film 21 in the oxide film forming process in step S30, and the surface of the p-type silicon substrate 11a is uniformly hydrophilic. It becomes. Therefore, pure water does not remain in the form of water droplets on the surface of the p-type silicon substrate 11a after the second cleaning step, and active silicon on the surface of the p-type silicon substrate 11a reacts with oxygen in the air. There is nothing. That is, due to the hydrophilicity of the surface of the p-type silicon substrate 11a, water drainage on the surface becomes worse. When the surface of the p-type silicon substrate 11a is hydrophilized unevenly, pure water remains in the form of water droplets on the surface of the p-type silicon substrate 11a. Therefore, in the phosphorus glass removing process according to the present embodiment, the surface of the p-type silicon substrate 11a is uniformly made hydrophilic to prevent pure water from remaining in the form of water droplets on the surface of the p-type silicon substrate 11a. . Thereby, it is possible to prevent the occurrence of a watermark due to the pure water remaining on the surface of the p-type silicon substrate 11a, and it is possible to prevent the occurrence of the watermark even if the p-type silicon substrate 11a is dried by the hot air drying method. .

  The phosphorus glass removing step according to the present embodiment described above can be performed using the solar cell manufacturing apparatus shown in FIG. FIG. 8 is a schematic diagram showing a schematic configuration of a solar cell manufacturing apparatus that performs the phosphorus glass removing step in the solar cell manufacturing method according to the present embodiment.

  The solar cell manufacturing apparatus shown in FIG. 8 includes an etching treatment tank 101 that is a first tank in which a chemical solution containing hydrofluoric acid (HF) for removing an oxide film on the surface of a silicon-based substrate is stored, A first cleaning treatment tank 102 which is a second tank in which pure water for cleaning a chemical solution containing hydrofluoric acid (HF) remaining on the surface of the substrate is stored, and an oxidization property for oxidizing the surface of the silicon-based substrate. An oxidation treatment tank 103 that is a third tank in which a chemical solution is stored, and a second cleaning treatment tank 104 that is a fourth tank in which pure water for cleaning the oxidizing chemical solution remaining on the surface of the silicon-based substrate is stored. A drying tank 105, which is a fifth tank for draining and drying pure water remaining on the surface of the silicon substrate, is arranged in the order of the processing steps.

  In the production of solar cells, a batch processing method for processing a large number of substrates at a time is used from the viewpoint of mass productivity. The solar cell manufacturing apparatus shown in FIG. 8 sequentially immerses a large number of silicon-based substrates housed in a carrier (not shown) in a solution stored in a tank from the etching treatment tank 101 to the second cleaning treatment tank 104. (Not shown).

  In the drying tank 105, after the immersion process up to the second cleaning tank 104 is completed, the substrate is dried by blowing high-temperature dry air or an inert gas such as nitrogen onto the silicon substrate housed in the carrier. In addition, as for the tank from the etching process tank 101 to the 2nd washing process tank 104 in the manufacturing apparatus of the photovoltaic cell shown in FIG. 8, all should just be one tank, and all the tanks are the systems which circulate a chemical | medical solution, or a chemical | medical solution. Or you may have a system which always supplies a pure water. In addition, for example, water such as ion exchange water may be used as the solvent and pure water of the chemical solution, and the liquid temperature adjusting mechanism may be provided.

  Next, after the phosphorus glass removing step described above, the n-type impurity diffusion layer 11b formed on the one surface side of the p-type silicon substrate 11a is protected with a resist, and then only on one main surface of the p-type silicon substrate 11a. Etching is performed on the p-type silicon substrate 11a so as to leave the impurity diffusion layer 11b. As a result, as shown in FIG. 6, the n-type impurity diffusion layer 11b formed on the other surface side and the side surface of the p-type silicon substrate 11a, which is an unnecessary n-type impurity diffusion layer 11b, is removed by etching to have a pn junction. A silicon substrate 11 is formed. In the p-type silicon substrate 11a, the side where the n-type impurity diffusion layer 11b is left is the light-receiving surface side.

  Here, since the silicon oxide film 21 formed on the removed n-type impurity diffusion layer 11b is also removed, the silicon oxide film 21 is only on the n-type impurity diffusion layer 11b left on the light receiving surface side. Remains. The residual resist after the treatment is removed using an organic solvent or the like.

  In addition, after the phosphorus glass removing step described above, the p-type silicon substrate 11a which is a p-type impurity diffusion layer is obtained by etching and removing the n-type impurity diffusion layer 11b at the end of the p-type silicon substrate 11a by plasma treatment. The silicon substrate 11 may be formed by separating it from the n-type impurity diffusion layer 11b on the light receiving surface side of the p-type silicon substrate 11a. In this state, the n-type impurity diffusion layer 11 b still remains on the back surface of the silicon substrate 11. Here, since the silicon oxide film 21 formed on the removed n-type impurity diffusion layer 11b is also removed, the silicon oxide film 21 is formed on the n-type impurity diffusion layer 11b left on the light receiving surface side and the back surface side. Remain on top. When the n-type impurity diffusion layer 11b is formed only on one side of the p-type silicon substrate 11a in advance, the unnecessary etching process of the n-type impurity diffusion layer 11b is not necessary.

  Next, a silicon nitride film (SiN film) is formed on the n-type impurity diffusion layer 11b with a film thickness of, for example, about 70 nm to 90 nm by a film forming method such as a plasma CVD method as the antireflection film 12 made of an insulating film. Specifically, since the silicon oxide film 21 is formed on the n-type impurity diffusion layer 11b as will be described later, the antireflection film 12 is formed on the silicon oxide film 21. The film thickness and refractive index of the antireflection film 12 are set to values that most suppress light reflection. As the antireflection film 12, two or more films having different refractive indexes may be laminated. The antireflection film 12 may be formed by a different film forming method such as a sputtering method.

  Next, the silver paste mixed with silver is screen-printed in a comb shape on the light receiving surface of the silicon substrate 11 and dried, and the aluminum paste mixed with aluminum is screen-printed on the entire back surface of the silicon substrate 11 and dried. Further, usually, silver paste is overprinted on a part or opening on the aluminum paste surface.

  Thereafter, the printed paste is baked to form the light receiving surface side electrode 13 and the back surface electrode 14. The light-receiving surface side electrode 13 penetrates the antireflection film 12 and the silicon oxide film 21 by so-called fire through and is connected to the n-type impurity diffusion layer 11b. On the back surface side of the silicon substrate 11, the aluminum paste reacts with the silicon on the back surface of the silicon substrate 11 to obtain a back electrode 14, and aluminum diffuses from the aluminum paste to the surface layer on the back surface of the silicon substrate 11, thereby forming the back electrode 14. A P + layer 11c is formed immediately below. Further, when the silicon oxide film 21 is present on the back surface of the silicon substrate 11, the back electrode 14 penetrates the silicon oxide film 21 by so-called fire-through and forms a p-type silicon substrate 11 a that is the back surface of the silicon substrate 11. Connecting.

  Further, as described above, when only the n-type impurity diffusion layer 11b at the substrate end portion of the p-type silicon substrate 11a is removed to form the silicon substrate 11, n-type impurities are formed on the back surface of the p-type silicon substrate 11a. The diffusion layer 11b remains. In this case, the aluminum paste reacts with the silicon of the n-type impurity diffusion layer 11b remaining on the back surface of the silicon substrate 11 to obtain the back electrode 14, and the n remaining on the back surface of the p-type silicon substrate 11a. Aluminum is diffused from the aluminum paste into the type impurity diffusion layer 11b, and a P + layer 11c is formed immediately below the back electrode. As described above, the solar battery cell shown in FIGS. 1 and 2 is manufactured.

  Next, as a comparative example, a phosphorus glass removing process in which the above-described oxide film forming process and the second cleaning process are not performed will be described. FIG. 9 is a flowchart for explaining the flow of the phosphorus glass removing step of the comparative example. The phosphorus glass removal process of the comparative example includes a phosphorus glass etching process performed in step S110, a cleaning process performed in step S120, and a drying process performed in step S130.

  In the phosphorus glass etching process performed in step S110, the same processing as the phosphorus glass etching process performed in step S10 of the phosphorus glass removing process according to the above-described embodiment is performed. In the cleaning process performed in step S120, the same process as the first cleaning process performed in step S20 of the phosphorus glass removing process according to the above-described embodiment is performed. In the drying process performed in step S130, the same process as the drying process performed in step S50 of the phosphorus glass removing process according to the present embodiment described above is performed.

In the flow of the phosphorus glass removing process of the comparative example, the surface of the silicon substrate is hydrophobized by immersing the silicon substrate in a solution containing hydrofluoric acid in step S110. Then, after cleaning with pure water in step S120, uneven water residue may occur on the surface of the silicon substrate. Here, the phosphorus glass etching process in step S110 is a process of immersing the silicon substrate in an HF solution prepared at, for example, HF: H ₂ O = 1: 10 for 450 seconds.

  Further, depending on the processing conditions for removing phosphorus glass with a solution containing phosphorus concentration or hydrofluoric acid in the n-type impurity diffusion layer in which phosphorus is diffused, the surface of the silicon substrate is roughened, and the surface of the silicon substrate after the cleaning process in step S120. It has been found that water residue is likely to occur. Water residue on the surface of the silicon substrate after the cleaning process is likely to occur in the silicon substrate having a fine concavo-convex structure, and the water residue induces a reaction between silicon and oxygen in the air in the subsequent drying process by hot air drying. It becomes a factor which forms a mark.

  In the technique of Patent Document 1, since the silicon substrate is immersed in a mixed solution obtained by mixing an oxidizing aqueous solution with a dilute hydrofluoric acid aqueous solution, the formation of the oxide film and the etching of the oxide film proceed simultaneously on the surface of the silicon substrate. . For this reason, the phosphorus concentration of the phosphorus diffusion layer, which is the n-type silicon layer formed on the surface of the silicon substrate in the previous step, varies, and the phosphorus concentration of the phosphorus diffusion layer varies within the plane of the silicon substrate, The desired phosphorus concentration cannot be obtained. Further, there arises a problem that the surface roughness of the texture structure formed on the surface of the silicon substrate is increased. Furthermore, it is necessary to newly prepare a dilute hydrofluoric acid aqueous solution for each batch, which causes a problem that the environmental load is large.

  On the other hand, the phosphorus glass removing step in the method for manufacturing the solar cell according to the present embodiment is performed after removing the phosphorus glass layer on the surface of the p-type silicon substrate 11a by wet etching with a solution containing hydrofluoric acid. A wet oxidation process is performed to uniformly form a silicon oxide film 21 on the surface of the p-type silicon substrate 11a, thereby uniformly rendering the surface of the p-type silicon substrate 11a hydrophilic. Since the surface of the p-type silicon substrate 11a is uniformly made hydrophilic, the surface of the p-type silicon substrate 11a is purely formed on the surface of the p-type silicon substrate 11a after the second cleaning step due to the non-uniformity of hydrophilicity on the surface of the p-type silicon substrate 11a. It is suppressed that water remains in the form of water droplets. Further, even when the surface of the p-type silicon substrate 11a is roughened due to the processing conditions for removing phosphorous glass with a solution containing hydrofluoric acid, the surface of the p-type silicon substrate 11a is uniformly made hydrophilic so that the p-type silicon substrate 11a becomes hydrophilic. Due to the roughness of the surface of the silicon substrate 11a, pure water is prevented from remaining on the surface of the p-type silicon substrate 11a after the second cleaning step.

  Further, since the surface of the p-type silicon substrate 11a is uniformly covered with the silicon oxide film 21, active silicon on the surface of the p-type silicon substrate 11a is prevented from reacting with oxygen in the air. Therefore, the formation of watermarks on the surface of the p-type silicon substrate 11a can be suppressed by performing the phosphorus glass removing step according to the present embodiment.

  In addition, in the phosphorus glass removing process according to the present embodiment, unlike Patent Document 1, the formation of the oxide film and the etching of the oxide film do not proceed simultaneously on the surface of the p-type silicon substrate 11a. The generation of watermarks can be suppressed without changing the phosphorus concentration on the surface of the n-type impurity diffusion layer 11b doped with phosphorus on the surface, and without increasing the surface roughness of the texture structure. In addition, hydrofluoric acid, which is a chemical solution used for removing the phosphorus glass layer, can be reused, and the chemical solution cost and the environmental load can be reduced.

  Below, the manufacturing method of the photovoltaic cell concerning this Embodiment is demonstrated based on a specific Example. An experiment for verifying the suppression effect of watermark generation by the method for manufacturing a solar battery cell according to the present embodiment described above was performed as follows.

Example 1
First, surface treatment is performed by immersing the p-type silicon substrate for 20 minutes in an alkaline chemical solution having a concentration of 1% by mass mixed with an additive such as IPA, and a texture structure is formed on the surface of the p-type silicon substrate. did. After that, the p-type silicon substrate having a texture structure formed on the surface is put into a thermal diffusion furnace, heated in the presence of phosphorous oxychloride (POCl ₃ ) vapor, and diffused into the surface of the p-type silicon substrate by thermal diffusion. An n-type impurity diffusion layer as a layer was formed.

  Next, the phosphorus glass removing step according to the present embodiment was performed on the p-type silicon substrate on which the n-type impurity diffusion layer was formed, according to the flowchart shown in FIG. In the oxide film forming step of step S30, ozone water having a dissolved ozone concentration of 5 mg / L was used as an oxidizing chemical solution, and the p-type silicon substrate was immersed in the ozone water for 180 seconds. Thus, the p-type silicon substrate which performed the phosphorus glass removal process concerning this Embodiment was used as the sample of Example 1. FIG.

  Further, the phosphorus glass removing step according to the comparative example in which the oxide film forming step is not performed according to the flowchart shown in FIG. went. Thus, the p-type silicon substrate which performed the phosphorus glass removal process concerning a comparative example was made into the sample of a comparative example.

  FIG. 10 shows a result of comparison of the occurrence rate of the watermark on the surface of the sample of Example 1 and the sample of the comparative example. FIG. 10 is a characteristic diagram showing the rate of occurrence of watermarks depending on the presence or absence of an oxide film forming step using ozone water after a phosphor glass etching step using a solution containing hydrofluoric acid.

  Assuming that the watermark occurrence probability of the sample of the comparative example is 1, the probability of occurrence of the watermark of the sample of the example 1 was 0. This is because active silicon on the surface of the p-type silicon substrate reacts with oxygen in the air by uniformly covering the surface of the p-type silicon substrate with a silicon oxide film in the wet oxidation process after removing the phosphorous glass layer. This is thought to be due to the fact that the surface of the p-type silicon substrate was made hydrophilic and the water on the surface of the p-type silicon substrate was prevented from remaining on the surface of the p-type silicon substrate. This comparison confirmed the effect of reducing the probability of watermark generation by the method for manufacturing a solar battery cell according to the present embodiment.

(Example 2)
In the oxide film forming process of step S30 in the phosphorus glass removing process according to the present embodiment, it is possible to use hydrogen peroxide solution as the oxidizing chemical solution. The concentration of hydrogen peroxide solution in the case of using hydrogen peroxide solution as the oxidizing chemical solution may be 0.01% by weight (w / v%) or more, more preferably 0.1% by weight (w / v). v%) or more. From the viewpoint of wastewater treatment in consideration of environmental load, the upper limit of the concentration of the hydrogen peroxide solution is 30% by weight (w / v%). In Example 2, the texture formation and the n-type impurity diffusion layer, which is a phosphorus diffusion layer, were performed on the p-type silicon substrate by the same method as in Example 1 described above. The weight volume% (w / v%) is a unit representing how many grams of the solvent is dissolved in 100 ml of the solution.

  Next, the phosphorus glass removing step according to the present embodiment was performed on the p-type silicon substrate on which the n-type impurity diffusion layer was formed, according to the flowchart shown in FIG. In the oxide film forming step of step S30, a hydrogen peroxide solution having a concentration of 0.1 (w / v%) was used as an oxidizing chemical solution, and the p-type silicon substrate was immersed in the hydrogen peroxide solution for 180 seconds. Thus, the p-type silicon substrate which performed the phosphorus glass removal process concerning this Embodiment was used as the sample of Example 2. FIG.

  FIG. 11 shows the result of comparison of the occurrence rate of watermarks on the surface of the sample of Example 2 and the sample of the comparative example. FIG. 11 is a characteristic diagram showing the rate of occurrence of watermarks depending on the presence or absence of an oxide film forming step using hydrogen peroxide after the phosphor glass etching step using a solution containing hydrofluoric acid.

  When the watermark occurrence probability of the sample of the comparative example is 1, the probability of occurrence of the watermark of the sample of Example 2 was 0.2. This is because active silicon on the surface of the p-type silicon substrate reacts with oxygen in the air by uniformly covering the surface of the p-type silicon substrate with a silicon oxide film in the wet oxidation process after removing the phosphorous glass layer. This is thought to be due to the fact that the surface of the p-type silicon substrate was made hydrophilic and the water on the surface of the p-type silicon substrate was prevented from remaining on the surface of the p-type silicon substrate. This comparison confirmed the effect of reducing the probability of watermark generation by the method for manufacturing a solar battery cell according to the present embodiment.

  Further suppression of the generation of watermarks by the phosphorus glass removing process according to the present embodiment is achieved by increasing and optimizing the processing temperature in the oxide film forming process of step S30, extending and optimizing the processing time, multi-tank processing, etc. Therefore, it is possible to achieve formation of an oxide film having an appropriate thickness in a short time.

  In the above description, a p-type silicon substrate is used. However, an n-type silicon substrate may be used. When an n-type silicon substrate is used, an impurity diffusion layer is formed by diffusing boron (B) as an impurity into the surface layer of the n-type silicon substrate by thermal diffusion. In this case, a borosilicate glass layer is formed on the surface of the n-type silicon substrate. Also in this case, by performing the borosilicate glass removal step in the same manner as the above-described phosphorus glass removal step, generation of watermarks can be suppressed and prevented similarly to the phosphorus glass removal step. The borosilicate glass layer is a compound layer containing boron, which is an impurity of the second conductivity type, and silicon, which is a material of an n-type silicon substrate, which is a silicon substrate of the first conductivity type.

  The borosilicate glass removing process includes a borosilicate glass etching process, a first cleaning process, an oxide film forming process, a second cleaning process, and a drying process. The borosilicate glass removing step is the same as the phosphorous glass removing step except for having a borosilicate glass etching step instead of the phosphorous glass etching step.

The borosilicate glass etching step includes an n-type impurity diffusion layer by wet etching using a solution containing HF such as hydrofluoric acid (HF) or a mixed acid of HF, HNO ₃ and H ₂ SO ₄ as an etchant. The borosilicate glass layer formed on the surface of the p-type silicon substrate is removed by etching. The concentration of hydrofluoric acid in the solution containing HF is not particularly limited, and may be set as appropriate according to various conditions such as the conditions for forming the n-type impurity diffusion layer.

  As described above, in the present embodiment, the phosphorus glass layer on the surface of the p-type silicon substrate 11a is removed by wet etching with a solution containing hydrofluoric acid, and then wet oxidation is performed to perform p-type silicon substrate 11a. A silicon oxide film 21 is uniformly formed on the surface of the p-type silicon substrate 11a so that the surface of the p-type silicon substrate 11a is made hydrophilic. Due to the hydrophilicity of the surface of the p-type silicon substrate 11a, water drainage on the surface becomes worse. When the surface of the p-type silicon substrate 11a is hydrophilized unevenly, pure water remains in the form of water droplets on the surface of the p-type silicon substrate 11a. Therefore, in the present embodiment, the surface of the p-type silicon substrate 11a is uniformly made hydrophilic to prevent pure water from remaining in the form of water droplets on the surface of the p-type silicon substrate 11a. That is, by making the surface of the p-type silicon substrate 11a uniformly hydrophilic, it is possible to prevent pure water from remaining in the form of water droplets on the surface of the p-type silicon substrate 11a after the subsequent cleaning process. Further, since the surface of the p-type silicon substrate 11a is uniformly covered with the silicon oxide film 21, active silicon on the surface of the p-type silicon substrate 11a is prevented from reacting with oxygen in the air. Thereby, in this Embodiment, formation of the watermark in the surface of the p-type silicon substrate 11a can be suppressed.

  In the present embodiment, unlike Patent Document 1, the formation of the oxide film and the etching of the oxide film and phosphor glass etching do not proceed simultaneously on the surface of the p-type silicon substrate 11a. The generation of watermarks can be suppressed without changing the phosphorus concentration on the surface of the n-type impurity diffusion layer 11b doped with phosphorus on the surface and without increasing the surface roughness of the texture structure. In addition, hydrofluoric acid, which is a chemical solution used for removing the phosphorus glass layer, can be reused, and the chemical solution cost and the environmental load can be reduced.

  Therefore, according to the present embodiment, it is possible to improve the quality of solar cells and the yield of solar cells without increasing the environmental load.

  11 silicon substrate, 11a p-type silicon substrate, 11b n-type impurity diffusion layer, 11c P + layer, 12 antireflection film, 13 light-receiving surface side electrode, 13a grid electrode, 13b bus electrode, 14 back electrode, 21 silicon oxide film, 101 Etching tank, 102 First cleaning tank, 103 Oxidation tank, 104 First cleaning tank, 105 Drying tank.

Claims (12)

A first step of forming a concavo-convex structure on the surface of a first conductivity type silicon-based substrate;
A second step of diffusing impurities of a second conductivity type on the surface of the silicon substrate to form an impurity diffusion layer on a surface layer of the silicon substrate;
A third step of removing a compound layer including the impurity and the material of the silicon-based substrate formed on the impurity diffusion layer;
Including
The third step includes
A fourth step of etching the surface of the silicon-based substrate using a solution containing hydrofluoric acid;
A fifth step of cleaning the solution containing hydrofluoric acid remaining on the surface of the silicon-based substrate with pure water;
A sixth step of uniformly forming an oxide film on the surface of the silicon-based substrate using an oxidizing chemical solution;
A seventh step of washing the oxidizing chemical remaining on the surface of the silicon-based substrate with pure water;
An eighth step of drying the surface of the silicon-based substrate;
The manufacturing method of the photovoltaic cell characterized by including. In the eighth step, blowing hot air to the surface of the silicon substrate to dry the surface of the silicon substrate;
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these. The silicon-based substrate is a p-type silicon substrate;
The impurity is phosphorus;
The manufacturing method of the photovoltaic cell of Claim 1 or 2 characterized by these. The silicon-based substrate is an n-type silicon substrate;
The impurity is boron;
The manufacturing method of the photovoltaic cell of Claim 1 or 2 characterized by these. The oxidizing chemical solution is ozone water or hydrogen peroxide solution in which ozone gas is dissolved;
The manufacturing method of the photovoltaic cell as described in any one of Claim 1 to 4 characterized by these. The dissolved ozone concentration of the ozone water is 0.1 mg / L or more and 180 mg / L or less,
The manufacturing method of the photovoltaic cell of Claim 5 characterized by these. The concentration of the hydrogen peroxide solution is 0.01 w / v% or more and 30 w / v% or less,
The manufacturing method of the photovoltaic cell of Claim 5 characterized by these. A solar cell manufacturing apparatus for cleaning the silicon substrate in which a compound containing an impurity and a material of the silicon substrate is formed on the surface of the silicon substrate,
A first tank in which a solution containing hydrofluoric acid for etching the compound is supplied and the silicon-based substrate is immersed in the solution containing hydrofluoric acid;
Pure water for cleaning the solution containing hydrofluoric acid remaining on the surface of the silicon-based substrate etched with the compound in the first tank is supplied, and the silicon-based substrate is immersed in the pure water. The second tank;
A third tank in which an oxidizing chemical solution for forming an oxide film on the surface of the silicon-based substrate cleaned in the second tank is supplied, and the silicon-based substrate is immersed in the oxidizing chemical solution;

Pure water for cleaning the oxidizing chemical remaining on the surface of the silicon substrate on which the oxide is formed in the third tank is supplied, and the silicon substrate is immersed in the pure water. 4 tanks,
A fifth tank for drying the surface of the silicon-based substrate cleaned in the fourth tank;
The manufacturing apparatus of the photovoltaic cell characterized by including. The silicon-based substrate has an uneven structure on the surface,
The solar cell manufacturing apparatus according to claim 8. In the fifth tank, spraying warm air on the surface of the silicon-based substrate to dry the surface of the silicon-based substrate;
The manufacturing apparatus of the photovoltaic cell of Claim 8 or 9 characterized by these. In the first tank, the second tank, the third tank, the fourth tank, and the fifth tank, processing is performed in a state where a plurality of the silicon-based substrates are stored in a carrier,
The solar cell manufacturing apparatus according to any one of claims 8 to 10, wherein: The oxidizing chemical solution is ozone water or hydrogen peroxide solution in which ozone gas is dissolved;
The solar cell manufacturing apparatus according to any one of claims 8 to 11, wherein:

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