JP5908096B2 - Solar cell manufacturing apparatus and solar cell manufacturing method using the same - Google Patents

Description

  The present invention relates to a solar cell manufacturing apparatus and a solar cell manufacturing method using the same, and more particularly to a solar cell manufacturing apparatus having high light utilization efficiency and a solar cell manufacturing method using the same.

  In a conventional solar cell substrate (hereinafter sometimes referred to as a substrate), the light incident surface (hereinafter referred to as a light receiving surface) is formed with irregularities (hereinafter referred to as texture) to reduce the reflectance of the light receiving surface, There is a technique for increasing the amount of light incident on the inside of a substrate. That is, the number of carriers generated in the solar cell substrate greatly depends on the amount of light incident on the substrate, and a texture is formed to increase the amount of incident light.

  One texture structure is composed of pyramidal irregularities. As a method for forming such a texture, the substrate is immersed in a chemical solution in which a surfactant such as caprylic acid is mixed in an alkaline chemical solution such as an aqueous solution of sodium hydroxide or potassium hydroxide, and etching is performed according to the crystal orientation of the substrate. A method using the difference in rate is generally used.

  In such a forming method, a technique is disclosed in which dopant ions eluted from the substrate during etching are removed, deterioration of the function of the chemical solution for etching is prevented, and the number of times the chemical solution is reused is increased (for example, Patent Document 1). reference).

JP 2006-278409 A

  However, according to the above conventional technique, in a manufacturing method including a collecting part for collecting dopant ions eluted from the substrate or an adsorbing part for adsorbing dopant ions, it is uniform in size, for example, an etching solution, in comparison with the dopant ions. In the case where a component that does not dissolve in the water is floating as a foreign substance (hereinafter referred to as an insoluble product), a phenomenon that it cannot be collected or adsorbed due to a difference in solubility occurs. When such an insoluble product is present, the insoluble product and the surfactant in the chemical solution interact with each other, the function of the surfactant is inhibited, and depending on the area of the substrate, the texture formation may not proceed. Occurs. For this reason, variation occurs in the texture shape after completion of etching, and it becomes difficult to form an ideal texture on the entire light receiving surface. In addition, the insoluble product adheres to the light-receiving surface of the substrate, and the supply of the alkali component or the surfactant to the texture forming portion is rate-controlled to inhibit the texture formation. As a result, there is a problem that the amount of light incident on the substrate is reduced due to the variation in texture shape, the light use efficiency is lowered, and the photoelectric conversion efficiency is lowered. Here, ideal texture formation means that a uniform texture is formed in the light receiving surface.

  The insoluble product as described above is easily generated by increasing the concentration of the silicate generated by etching the impurities or silicon that are brought into the etching solution by the substrate with alkali. We have found that an increase in the amount of insoluble products present in the etchant is one of the factors that determine the lifetime of the etchant because good etching becomes difficult. By removing this insoluble product from the etching solution, extending the life of the etching solution and increasing the number of substrates that can be processed are problems for reducing the costs associated with manufacturing.

  This invention is made | formed in view of the above, Comprising: It aims at obtaining the manufacturing apparatus and manufacturing method of a solar cell which can obtain the solar cell with high light utilization efficiency and excellent photoelectric conversion efficiency.

  In order to solve the above-described problems and achieve the object, a solar cell manufacturing apparatus according to the present invention is used for manufacturing a solar cell in which a pn junction is formed on the surface of a silicon-based semiconductor substrate, and has a texture on the surface of the semiconductor substrate. An etching apparatus for forming an etching tank that holds a strong alkaline etching solution and an etching solution and performs texture etching by immersing a semiconductor substrate in the etching solution, and filters the etching solution And a filtration part provided with a hydrophilic fiber part, wherein the hydrophilic fiber part is entangled without being bonded at the point where the fibers intersect.

  According to the solar cell manufacturing apparatus of the present invention, the same shape texture can be uniformly formed on the light receiving surface side of the semiconductor substrate, the solar cell has high light utilization efficiency and excellent photoelectric conversion efficiency. There is an effect that can be obtained.

FIG. 1 is a conceptual diagram showing the structure of a solar cell manufacturing apparatus according to Embodiment 1 of the present invention. FIG. 2 is an explanatory view of an etching tank of the apparatus. FIG. 3: is sectional drawing for demonstrating the structure of the solar cell using the solar cell board | substrate formed with the solar cell manufacturing apparatus concerning Embodiment 1 of this invention. FIGS. 4-1 is process sectional drawing which shows the texture etching process using the manufacturing apparatus of the solar cell concerning Embodiment 1 of this invention. FIGS. FIGS. 4-2 is process sectional drawing which shows the texture etching process using the manufacturing apparatus of the solar cell concerning Embodiment 1 of this invention. FIGS. FIG. 5 is a perspective view of a semiconductor substrate on which a texture is formed. FIG. 6A is a flowchart illustrating a manufacturing process of the solar cell. FIG. 6B is a flowchart of the texture etching process in the manufacturing process of the solar cell. FIG. 7 is a conceptual diagram showing the structure of the solar cell manufacturing apparatus according to the second embodiment of the present invention. FIG. 8: is a conceptual diagram which shows the structure of the manufacturing apparatus of the solar cell concerning Embodiment 3 of this invention. FIG. 9: is a conceptual diagram which shows the structure of the manufacturing apparatus of the solar cell concerning Embodiment 4 of this invention. FIG. 10: is a perspective view which shows the cassette used with the manufacturing apparatus of the solar cell concerning Embodiment 4 of this invention. FIG. 11 is a perspective view showing Modification 1 of the cassette. FIG. 12 is a perspective view showing a second modification of the cassette. FIG. 13: is a perspective view which shows the hydrophilic fiber attachment part of the cassette used with the manufacturing method of the solar cell concerning Embodiment 5, and remove | excludes the hydrophilic fiber from the cassette. FIG. 14 shows the cassette and is a perspective view showing what is drawn including hydrophilic fibers. FIG. 15 is a conceptual diagram showing the structure of the solar cell manufacturing apparatus according to the fifth embodiment. FIG. 16 is a conceptual diagram showing the structure of the solar cell manufacturing apparatus according to the sixth embodiment.

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

Embodiment 1 FIG.
FIG. 1 is a conceptual diagram showing the structure of a solar cell manufacturing apparatus according to Embodiment 1 of the present invention. FIG. 2 is an explanatory view of an etching tank of the apparatus. FIG. 3: is sectional drawing for demonstrating the structure of the solar cell using the solar cell board | substrate formed with the solar cell manufacturing apparatus concerning Embodiment 1 of this invention. The solar cell manufacturing apparatus according to the first embodiment is a (wet) etching apparatus, which includes a filtration unit including a hydrophilic fiber part for filtering an etching solution, and the hydrophilic fiber part has a fiber diameter of 0.1. A substrate for a solar cell in which a large number of textures 10T are uniformly formed can be stabilized over a long period of time by being composed of hydrophilic fibers of 10 μm and being entangled without being bonded at the point where the fibers cross each other. Can be formed.

  The solar cell formed using the solar cell manufacturing apparatus according to the first embodiment has a first conductivity type constituting a solar cell substrate provided with a number of textures 10T, as shown in a sectional view in FIG. A functional layer is formed on the semiconductor substrate 10. That is, this solar cell includes a second conductivity type layer 11 that is a second conductivity type impurity diffusion layer on the surface of the first conductivity type semiconductor substrate 10, and an insulating layer 12 that covers a part of the surface of the texture 10T, for example. A light receiving surface side electrode 13 electrically connected to the second conductive type layer 11 and formed on the light receiving surface side of the first conductive type semiconductor substrate 10, and opposite to the light receiving surface of the first conductive type semiconductor substrate 10. The first conductivity type layer 14 formed on the surface layer of the side surface (back surface) and the back surface side electrode 15 formed on the back surface side of the first conductivity type layer 14 are provided as functional layers.

  In the first conductivity type semiconductor substrate 10 which is a solar cell substrate according to the present embodiment, a plurality of textures 10T are formed on the light receiving surface side. The texture 10T is formed by processing the surface on the one surface side of the semiconductor substrate 10 of the first conductivity type. As the solar cell substrate (first conductivity type semiconductor substrate 10), for example, a p-type single crystal or polycrystalline silicon substrate can be used. In this case, the second conductivity type layer 11 is an impurity diffusion layer (n-type impurity diffusion layer) in which, for example, phosphorus is diffused in the surface layer of the first conductivity type semiconductor substrate 10. The first conductivity type layer 14 is a diffusion layer in which an electrode material of the back surface side electrode 15, for example, aluminum is diffused in the surface layer on the back surface side of the first conductivity type semiconductor substrate 10. The first conductivity type semiconductor substrate 10 is not limited to this, and an n-type silicon substrate may be used. The insulating layer 12 is provided as an antireflection film, and is formed of, for example, a silicon nitride film or a silicon oxide film.

  On the light-receiving surface side of the first conductivity type semiconductor substrate 10 of the solar cell according to the first embodiment configured as described above, the same and fine pyramidal texture 10T having a uniform height and shape is uniformly formed on the entire surface. Is formed. The texture 10T having a uniform height and shape increases the probability that the light reflected by the texture 10T re-enters the adjacent texture 10T, and increases the light use efficiency of the solar cell. Increasing the light use efficiency can increase the number of carriers generated in the solar cell and realize improvement in photoelectric conversion efficiency.

  Further, in this solar cell, generation of a fine texture having a different shape from other textures formed due to a lack of etching solution in the forming process or a region where no texture is formed is suppressed. Therefore, an unintended increase in surface area of the light receiving surface is suppressed, a uniform texture can be formed, and a high open circuit voltage can be obtained.

  Therefore, according to the solar cell concerning Embodiment 1, the solar cell which has high light utilization efficiency and high open circuit voltage, and was excellent in photoelectric conversion efficiency is implement | achieved.

  First, the manufacturing apparatus of the solar cell concerning Embodiment 1 mentioned above is demonstrated with reference to FIG. 1 and FIG. This apparatus is an etching apparatus for forming a uniform texture 10T on the surface of the first conductivity type semiconductor substrate 10 constituting the solar cell substrate. This apparatus includes an etching tank 2 for holding an etching solution 1, a cassette 3 for supporting a semiconductor substrate 10 and immersing in the etching solution 1, and a circulation unit 4 having a pipe for circulating the etching solution 1. Have. And the pump 5 provided on the pipe which comprises the circulation part 4, the filtration part 6 which removes an insoluble product, the insoluble product removed by the filtration part 6 is detected, and the etching assistance in etching liquid is detected. An addition mechanism 9 serving as a replenishment unit for adding a shortage of the agent and a control unit 7 for controlling the addition mechanism 9 are provided. The top surface of the cassette 3 is open so that the semiconductor substrate 10 can be taken in and out, or a gap is opened by a slit or the like. A plurality of ribs 3b are provided on the inner walls of the side surface 3a and the bottom surface 3c, and a holding groove is formed between the ribs 3b. Further, both ends of the holding groove on the bottom surface 3c of the cassette 3 are connected to the holding grooves on the inner walls of the left and right side surfaces 3a. This is mounted on the cassette 3 and the held semiconductor substrate 10 is immersed in the etching solution 1 together with the cassette 3.

  The addition mechanism 9 includes an alkali addition mechanism 9a and an etching auxiliary agent addition mechanism 9b. The control unit 7 detects the insoluble product removed by the filtering unit 6, calculates the alkali component and the etching auxiliary component in the insoluble product, and controls the alkali addition mechanism 9a and the etching auxiliary agent addition mechanism 9b. The alkali component and the etching auxiliary component are replenished. The control unit 7 outputs a chemical supply signal for supplying the etching solution 1 with an alkali component and an etching auxiliary component, and is connected to the alkali addition mechanism 9 a and the etching auxiliary agent addition mechanism 9 b via the control line 8. The alkali addition mechanism 9 a has an alkaline chemical solution a for replenishing the etching solution 1, and adds the alkaline chemical solution a to the etching solution 1 through a signal from the control line 8. Similarly, the etching auxiliary agent addition mechanism 9 b has an etching auxiliary agent b for replenishing the etching liquid 1, and adds the etching auxiliary agent b to the etching liquid 1 in the etching tank 2 through a signal of the control line 8. The amounts of the alkaline chemical solution a and the etching aid b added to the etching solution 1 are adjusted so that the above-described ideal etching can be performed according to the amount of the insoluble product removed. Although it is ideal that the alkali addition mechanism 9a and the etching auxiliary agent addition mechanism 9b are controlled individually, they may be controlled collectively and do not limit the present invention.

  Next, the texture etching process using the solar cell manufacturing apparatus according to the first embodiment will be described with reference to FIG. 1 and FIGS. First, for example, a p-type single crystal silicon substrate is prepared as the semiconductor substrate 10 (FIG. 4A). Next, anisotropic etching is performed to form a texture on the semiconductor substrate 10. That is, a semiconductor substrate 10 made of a p-type single crystal silicon substrate is mixed with 0.5 to 10% by mass of sodium hydroxide and a surfactant, for example, 0.05 to 0.2 mol / l caprylic acid, to 60 to 90 ° C. The substrate is immersed in the etching solution 1 heated in the step. In this step, the etching of the semiconductor substrate 10 (p-type single crystal silicon substrate) proceeds anisotropically to form convex portions and form a uniform texture 10T (FIG. 4-2). FIG. 5 is a perspective view of the semiconductor substrate 10 on which the texture 10T is uniformly formed. The AA cross section of FIG. 5 corresponds to FIG. FIG. 6A is a flowchart illustrating the manufacturing process of the solar cell, and FIG. 6B is a flowchart illustrating the texture etching process.

  In FIG. 1, a semiconductor substrate 10 inserted in a cassette 3 is immersed in an etching solution 1. This etching apparatus has a circulation section 4, and the etching solution 1 is circulated by a pump 5 in the direction of arrow A in FIG. The circulation unit 4 includes a filtration unit 6, and the etching solution 1 passes through the filtration unit 6 during circulation. The filtration unit 6 has a filter and removes insoluble products mixed in the etching solution 1 by filtration, and returns the etching solution 1 to the etching tank 2. The filter has a thickness for effectively removing insoluble products and accumulating in the filter, for example, a thickness of 2 mm or more. The filter of the filtration part 6 is comprised with a hydrophilic fiber. This apparatus is equipped with a mechanism for detecting the amount of insoluble products removed by the filtration unit 6 for removing insoluble products, and a control unit for calculating the alkali components and etching auxiliary components in the removed insoluble products. 7 is provided. The control unit 7 outputs a chemical supply signal for supplying the etching solution 1 with an alkali component and an etching auxiliary component, and is connected to the alkali addition mechanism 9 a and the etching auxiliary agent addition mechanism 9 b via the control line 8. The alkali addition mechanism 9 a has an alkaline chemical solution a for replenishing the etching solution 1, and adds the alkaline chemical solution a to the etching solution 1 through a signal from the control line 8. Similarly, the etching auxiliary agent adding mechanism 9 b has an etching auxiliary agent b for replenishing the etching liquid 1, and adds the etching auxiliary agent b to the etching liquid 1 through a signal of the control line 8. The amounts of the alkaline chemical solution a and the etching aid b added to the etching solution 1 are adjusted so that the above-described ideal etching can always be performed according to the amount of the insoluble product removed. Although it is ideal that the alkali addition mechanism 9a and the etching auxiliary agent addition mechanism 9b are controlled individually, they may be controlled collectively and do not limit the present invention.

  The insoluble product in the present invention is a foreign substance that is not dissolved homogeneously and is floating in the etching solution generated in the etching solution during texture etching. Residue of coolant when slicing the substrate, oil and grease adhering from fingers and containers, components contained in the substrate such as dopants, floating dust on the work site, etching tank 2 and attached devices Various impurities are mixed in the etching solution 1 such as surfactants, contaminants, impurities contained in the raw material of the etching solution 1. During etching, these impurities promote the generation of insoluble products. In the etching of silicon-based substrates, silicon and water in the etchant react with alkali to produce silicate. This silicate is also a component of the insoluble product. As the number of substrates to be processed increases, the concentration of silicate increases and insoluble products tend to be generated. The insoluble product may be a solid particle having a clear surface in the etching solution, but often has a gel-like form with an unclear boundary.

  If such an insoluble product exists on the surface of the substrate being etched, the etching is affected, and the formation of a pyramid structure at that portion is hindered to generate a defect. By removing the insoluble product from the etching solution, texture defects can be suppressed.

  Insoluble products can be removed by filtration. Filtration is a preferable removal method because the apparatus is simple and the efficiency is high. The removal of the insoluble product does not have to be all separated, and the effect can be obtained only by removing the coarse insoluble product with an appropriate filter medium. The method of grasping the shape of insoluble products is possible to some extent with light scattering and ultrasonic particle size distribution analyzers, but it is difficult to grasp clearly because there are many shapes with unclear boundaries. is there. The removal state of the insoluble product can be detected by measuring the viscosity in addition to the particle size distribution. The simplest method is to detect the turbidity of the etching solution. Turbidity increases due to light scattering by insoluble products. Reduce turbidity values by filtration or centrifugation. The method of measuring turbidity at this time is not particularly limited because it only performs a relative comparison of homogeneous liquids, and may be simple.

  The amount of insoluble product that decreases each time it passes through the filtration unit 6 is preferably 30% or more, and more preferably 40% or more. When the amount of reduction is less than 30%, a large amount of floating matter remains, so that a sufficient effect of suppressing defects cannot be obtained.

  The insoluble product contains a high concentration of silicate, and removing this from the etching solution also removes the silicate. As a cause of the deterioration of the etching solution, accumulation of silicate can be cited. Conventionally, the only way to remove the silicate from the deteriorated etchant is to replace the etchant. However, in the method for removing insoluble products of the present invention, the silicate can be removed. It is possible to extend the life. Since not only the silicate but also the impurities coexisting with it are removed at the same time, a preferable result is obtained. In terms of extending the life of the etching solution, it is also preferable to replenish with decreasing alkali components and etching auxiliary components. That is, a detection unit that detects the amounts of the alkali component and the etching auxiliary component removed by the filtering unit 6 is provided, and the alkali component and the etching auxiliary component are supplied to the etching solution based on the detected amount.

  The replenishment of the alkali component is preferably performed by adding more than the amount removed as silicate. The amount of silicate removed can be used as a detection unit without providing a special detection unit. That is, it can be quantified from the weight of the filter medium after drying with a weigh scale. In normal operation, it is possible to estimate the amount of silicate removed by filtration from measured values such as filtration rate and filtration pressure, and to add an amount of alkali corresponding to the amount of silicate. In this case, it is often preferable to add an amount of alkali more than the amount of alkali equivalent to the removed silicate because the etching state can be maintained. It is considered that the silicate remaining in the etching tank without being filtered has an influence on the etching, and this influence can be reduced by the excessively added alkali. The alkali amount to be added is preferably 120% or more and less than 500% of the equivalent amount of the removed silicate, more preferably 150% or more and less than 300%. If it is less than 120%, the amount of alkali is small and the etching rate tends to decrease gradually, or the amount of insoluble products generated tends to increase. If the addition amount exceeds 500%, the amount of alkali becomes too much, and the texture defects may increase on the contrary.

  The replenishment amount of the etching auxiliary component varies depending on the chemical used, and thus cannot be defined unconditionally, but is preferably 50% or less of the amount used for the initial etching solution preparation. It is preferable to consider the balance between the alkali component and the etching aid in the etching solution that varies depending on the addition of the alkali component.

  As a filter medium used for filtration, a non-woven fabric formed by collecting fibers, a woven fabric, a porous body formed by collecting particulate matter, a paper accumulated with short fibers, or a composite thereof is used. it can. Among these, the nonwoven fabric is preferable because it is easy to form as a filter medium that can achieve both the permeability of the etching solution and the removability of the insoluble product.

  A preferred filter medium is a non-woven fabric having a filtration performance of capturing fibers having a fiber diameter of 200 μm or less and capturing spherical resin particles having a diameter of 1 μm of 70% or more and 95% or less. When the trapping rate is less than 70%, the trapping property of the insoluble product is deteriorated, and it may be difficult to obtain the effect. A filter medium exceeding 95% is less likely to cause a problem, but it is likely to be clogged, and frequent filter medium replacement may be required. More desirably, the nonwoven fabric is preferably composed of hydrophilic fibers having a fiber diameter of 50 μm or less.

  As a material constituting the filtration part, a material formed by entanglement without binding fibers without using a hydrophilic fiber having a fiber diameter of 0.1 μm or more and 10 μm or less, particularly a nonwoven fabric is preferable. If the fiber diameter of the hydrophilic fiber is not 0.1 μm, the contact area with the filtrate becomes small, and the infiltrated product in an irregular shape is cut and passes, so that the filtrate that should remain originally passes. . On the other hand, when the fiber diameter of the hydrophilic fiber exceeds 10 μm, the fiber becomes too thick, and the elasticity of the fiber itself is lowered. For example, a nonwoven fabric made by entanglement of fibers by a hydroentanglement method can move fibers flexibly. For this reason, it is possible to flexibly change the shape to match the shape of the insoluble product, which is indefinite, and it is possible to increase the contact area between the fiber and the insoluble product, and to keep many insoluble products in the fiber. Is preferable.

  In addition, it is preferable that the thickness of the filter medium made of the nonwoven fabric is formed to be thick to some extent. Since insoluble products are often in a flexible form, they are easily clogged. By giving the filter medium a thickness, it is possible to make clogging difficult. The thickness of the nonwoven fabric is preferably 1 mm or more, more preferably 2 mm or more, as measured by JIS L1913. Several non-woven fabrics can be stacked to obtain this thickness. If the thickness is less than 1 mm, it is difficult to secure a sufficient volume for accumulating insoluble products, which is not preferable because clogging tends to occur.

  The fiber used for the filter medium can be made of various materials. Polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, rayon, nylon, acrylic fiber vinylon, aramid fiber, cotton, pulp, silk, and combinations thereof can be used. A binder or a surface treatment material may be adhered. Polyolefin is suitable as a filter material because it has chemical resistance, releases less impurities, and has low moisture absorption. In particular, polypropylene is preferable because it also has heat resistance. Polyester has a high heat resistance and a low hygroscopic property, and is widely used as a general-purpose material and is suitable as a filter medium. Acrylic fibers are excellent in chemical resistance, have little deterioration due to heat and light, and are suitable as filter media. Vinylon and aramid fibers can form a strong filter medium, and are preferable as a filter medium.

  In the filtration of insoluble products, it is preferable to use a fiber having a hydrophilic surface because the collection efficiency is increased. Hydrophilicity can be determined by contact angle. The contact angle of water on the flat surface of the material is preferably 60 ° or less, and more preferably 45 ° or less. Polypropylene, polyethylene terephthalate, etc. have low hydrophilicity as a material. It can be used by increasing the hydrophilicity of the surface by irradiation with ultraviolet rays or electron beams, reaction with active chemical species such as peroxides or radicals, and coating with a hydrophilic resin. The peroxides and radicals used here start polymerization of ozone, hydrogen peroxide, persulfuric acid / percarbonate / performic acid / peracetic acid and their salts, benzoyl peroxide, cumene hydroperoxide, azobisisobutyronitrile, etc. Compounds used as agents can be used. Such a hydrophilization treatment is effective in that the performance of capturing insoluble products is improved by using a material having performance such as alkali resistance and low cost such as polypropylene.

  Since the fiber used as a filter medium in the filtration part comes into contact with an alkaline etching solution, it is preferable to use after subjecting polypropylene, polyethylene terephthalate, polyethylene or vinylon exhibiting alkali resistance to a hydrophilic treatment.

  The filter medium is preferably washed with an alkaline aqueous solution before contacting with the etching solution. If a substance adhering to the filter medium or a substance eluted from the filter medium is mixed in the etching solution, the etching performance is greatly affected, and the texture quality may be deteriorated. Such contamination can be suppressed by washing with an alkaline aqueous solution, and stable and good etching can be performed. In general, washing is often performed with water or water mixed with a surfactant, but with such washing, it is possible to remove deposits to some extent, but the solubility can be reduced by reaction with alkali. In addition, since a substance that dissolves in the etching solution cannot be removed, a sufficient cleaning effect cannot be obtained. Further, when a surfactant is used, if the surfactant cannot be reliably removed, the surfactant itself becomes a contaminant. The alkaline aqueous solution used for washing can be an inorganic alkali such as NaOH, KOH, sodium carbonate, or an organic alkaline aqueous solution such as ammonium hydroxide and choline and tetramethyl ammonium hydroxide. It is preferable to use the same alkali as the etching solution because there is no problem even if it is mixed into the filtered etching solution.

  For washing with an alkaline aqueous solution, a method of immersing the filter medium in an alkaline aqueous solution, a method of sprinkling the alkaline aqueous solution with a spray or the like on the filter medium, and the like can be used. The alkaline aqueous solution may be at room temperature or heated. It is also preferable to remove the contaminants peeled off from the alkaline aqueous solution by washing with water after washing.

  The concentration of the aqueous alkali solution is preferably 0.1% by mass or more and 15% by mass or less in the case of an inorganic alkali. In the case of 0.1% by mass or less, the effect of alkali cannot be obtained. If it is 15% by mass or more, it is not preferable because it becomes difficult to manage the water after washing with an alkaline aqueous solution, or when the water washing is omitted, the alkali concentration of the etching solution tends to fluctuate. In the case of organic alkali, 0.5 mass% or more and 25 mass% or less are preferable. In the case of 0.5% by mass or less, the effect of alkali cannot be obtained. If it is 25% by mass or more, it becomes difficult to manage the water after washing with an aqueous alkali solution, or if the water washing is omitted, the alkali concentration of the etching solution tends to fluctuate. In the case of organic alkali, when it exceeds 5% by mass, there is an advantage that the hydrophobic substance is easily removed compared to the case of inorganic alkali.

  With respect to the concentration of the aqueous alkali solution, an effect can be obtained in the above-mentioned range, but it is particularly effective to select with a focus on the alkali concentration of the etching solution in terms of obtaining a reliable effect. By setting the alkali concentration higher than the alkali concentration of the etching solution, a more stable effect can be obtained. In the cleaning with an alkaline aqueous solution, the components to be eluted differ depending on the alkali concentration. Therefore, if the alkali concentrations of the cleaning liquid and the etching liquid are different, the elution in the etching liquid may not be reliably suppressed. The concentration of the alkaline aqueous solution based on the etching solution is preferably 50% by mass to 200% by mass of the alkali concentration of the etching solution. Even if it is out of this range, if it is within the preferable range of the alkali concentration, the effect of cleaning can be obtained, but there is a possibility that a small amount of dissolved substance in the etching solution is generated.

  The component dissolved in the etching solution from the filter medium can be suppressed by washing with the alkaline aqueous solution, but it is difficult to suppress elution due to long-term deterioration of the material due to swelling or slow decomposition reaction. Deterioration over a long period of time can be suppressed by modifying the material of the filter medium. For the modification, irradiation with electron beams or gamma rays is effective. In particular, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, acrylic resin and its derivative resins, cotton, pulp and the like can be suppressed because it can suppress swelling and solubility in an etching solution.

  Washing with an aqueous alkaline solution uses an alkaline solution of a solution at a temperature of 25 ° C. or room temperature to 100 ° C. or less. The effect can be obtained even at a treatment of 25 ° C. or lower, but the treatment time may be prolonged. If the temperature exceeds 100 ° C., the aqueous alkaline solution may evaporate, making concentration management difficult.

  First, when the texture is formed on the semiconductor substrate 10 (step S10 in FIGS. 6-1 and 6-2), the filter medium is previously washed with an alkaline aqueous solution (step S101). Then, the filter medium is mounted and the filtration unit 6 is set (step S102). Then, the semiconductor substrate 10 is immersed in an etching tank, and texture etching is performed (step S100). And it returns to step S101 again. At this time, the insoluble product is adsorbed by the filtering material in the filtration unit 6 and the alkali component concentration, the silicon concentration, etc. in the etching solution are lowered, so an alkali component and an etching auxiliary component are added (step S103).

  The pretreated fiber is hydroxylated at the end of the molecular chain and exhibits hydrophilic properties, so that hydrophilic insoluble products can be captured sufficiently and can be used in the filtration unit 6. Become. The filtration unit 6 removes insoluble products generated during the etching of the p-type single crystal silicon substrate, and inhibits the formation of texture or the interface due to adhesion of the insoluble product to the semiconductor substrate 10 which is the p-type single crystal silicon substrate. Etching can be performed while preventing the act of the activator from being hindered. As a result, the texture 10T is uniformly formed on the first conductivity type semiconductor substrate 10 without gaps (FIGS. 4-2 and 5).

  The semiconductor substrate 10 having the texture 10T formed on the surface in this manner is subjected to a generally used process, and then the second conductivity type layer 11, the insulating layer 12, and the like to the first conductivity type semiconductor substrate 10, The light receiving surface side electrode 13, the first conductivity type layer 14, and the back surface side electrode 15 are formed to form a solar battery cell. FIG. 6A is a flowchart illustrating a method for manufacturing a solar cell.

For example, the semiconductor substrate 10 on which the texture forming process (step S10) has been completed is put into a thermal diffusion furnace and heated in the presence of phosphorus oxychloride (POCl ₃ ) vapor to form phosphorus glass on the surface of the semiconductor substrate 10. Phosphorus is diffused in the semiconductor substrate 10 to form the second conductivity type layer 11, and a pn junction is formed (step S20). Since a p-type silicon substrate is used here, phosphorus of different conductivity type is diffused to form a pn junction. However, when an n-type silicon substrate is used, a p-type impurity may be diffused.

  Next, after removing the phosphorus glass layer of the semiconductor substrate 10 in a hydrofluoric acid solution and removing the second conductivity type layer 11 formed on the surface other than the light receiving surface side of the semiconductor substrate 10 (pn separation: step S30), As the insulating layer 12, a SiN film is formed on the second conductivity type layer 11 by plasma CVD (formation of an antireflection film: step S40). The film thickness and refractive index of the insulating layer 12 are set to optimum values that are compatible with each other in consideration of a value that suppresses light reflection or a value that terminates surface defects. Note that layers having different refractive indexes may be deposited. The insulating layer 12 may be formed by a different film formation method such as a sputtering method.

  Next, a paste mixed with silver is printed on the light receiving surface of the semiconductor substrate 10 in a comb shape by a screen printing method (step S50), and a paste mixed with aluminum is printed on the entire back surface of the semiconductor substrate 10 by a screen printing method. After printing (step S60), a baking process is performed (step S70), and the light-receiving surface side electrode 13 and the back surface side electrode 15 are formed. Firing is performed at 800 ° C., for example, in an air atmosphere. Moreover, the component of the back surface side electrode 15 spread | diffuses to the back surface side of the semiconductor substrate 10 which consists of an n-type single crystal silicon substrate by baking, and the 1st conductivity type layer 14 is formed. The solar cell shown in FIG. 3 is produced as described above.

  As described above, the solar cell manufacturing apparatus according to the present embodiment is produced by a reaction between the semiconductor substrate 10 and the etching solution 1 in the etching apparatus for texture formation, or mixed with the etching solution 1 from the environment. The filtration part 6 which can remove the insoluble product produced | generated is comprised. The filtration unit 6 is made of a polymer material (resin fiber) added with hydrophilicity by being washed with an alkaline solution or a polymer material (resin fiber) added with hydrophilicity by ozone treatment.

  Insoluble products cannot be removed by the conventional method of removing dopant ions eluted from a silicon substrate. Therefore, an insoluble product adheres to the surface of the silicon substrate, and texture formation of the adhesion portion is hindered. In addition, the function of a surfactant component that promotes anisotropy in the etching solution, such as caprylic acid, is hindered by the insoluble product, and it is difficult to realize ideal texture formation.

  However, since the solar cell manufacturing apparatus of the first embodiment includes the filtration unit 6 that can remove insoluble products in the etching solution 1, the insoluble products are removed from the etching solution 1 and the etching solution 1 is circulated. Therefore, the texture formation on the semiconductor substrate 10 proceeds uniformly over the entire surface, and an ideal texture is formed.

  In addition, by adding and replenishing the alkali component and the etching auxiliary component contained and removed in the insoluble product in the filtration unit 6, the alkaline component and the etching auxiliary agent in the etching solution 1 when continuously processed are added. Can be maintained in an ideal balance. Therefore, an ideal texture can be continuously formed on a large number of silicon substrates without changing the chemical solution.

  Therefore, according to the first embodiment, a solar cell having a high light utilization efficiency and a high open-circuit voltage in which a uniform texture is formed on the light-receiving surface side of the solar cell and having an excellent photoelectric conversion efficiency is realized. Is done.

  As described above, the first embodiment is an etching apparatus used for manufacturing a solar cell in which a pn junction is formed on the surface of a silicon-based semiconductor substrate, and for forming a texture on the surface of the semiconductor substrate. This apparatus includes a strong alkaline etching solution, an etching tank that holds the etching solution, and performs texture etching by immersing the semiconductor substrate in the etching solution, and a hydrophilic fiber portion that filters the etching solution. And a filtration part. And this etching tank comprises the circulation part which circulates etching liquid, and is comprised so that it may be repeatedly used by circulation. With this configuration, it is possible to remove contaminants that inhibit texture formation due to adhesion to a semiconductor substrate or bonding with a surfactant, and a texture can be formed uniformly. By previously removing impurities eluted from the hydrophilic fiber into the etching solution, it is possible to avoid the adverse effect on texture formation. As a result, an ideal texture can be formed on the semiconductor substrate, the amount of light incident on the semiconductor substrate can be increased, and photogenerated carriers can be increased.

Embodiment 2. FIG.
In the second embodiment, a modification of the etching apparatus for texture formation in the solar cell manufacturing apparatus described in the first embodiment will be described. Since the manufacturing method of the solar cell concerning Embodiment 2 is the same as that of Embodiment 1 except the etching apparatus for texture formation, detailed description is abbreviate | omitted as referring to Embodiment 1. FIG. FIG. 7: is a conceptual diagram of the apparatus structure for demonstrating the etching apparatus for the texture formation of the solar cell concerning Embodiment 2 of this invention.

  In the etching apparatus according to the first embodiment described above, an apparatus configuration having the filtration unit 6 capable of removing insoluble products is used. In the etching apparatus according to the second embodiment, when the filtration unit 6 has the bypass flow path 4b, a large amount of flexible insoluble suspended matter accumulates on the filter of the filtration unit 6 and the filtration flow rate of the etching solution 1 decreases. Prevents an increase in the pressure applied to the filter.

  For example, the filtration unit 6 shown in Embodiment 1 is provided with an outlet 6o upstream from the filtration surface 6s, for example, in the filtration unit 6 separated by 50 mm, so that the etching solution 1 flows out from the filtration unit 6. The outlet 6o is connected to the circulation unit 4 after the filtration unit 6 via the bypass channel 4b, and the etchant 1 flowing out is returned to the circulation unit 4 through the outside of the filtration unit 6. As a result, even when insoluble products accumulate in the filtration unit 6 and clogging of the filter occurs, the etching solution 1 flowing into the filtration unit 6 passes through the outlet 6o and passes through the bypass channel 4b to the etching tank 2. Returned. Since the filtration part 6 provided with the outflow port 6o does not hold | maintain a certain amount or more of etching liquid, it can prevent the pressure increase to the filter by an etching liquid. In addition, the outflow of the insoluble product captured on the filter surface can be prevented by providing the outlet 6o away from the filtration surface 6s on the upstream side. It is also possible to precipitate an insoluble product having a higher specific gravity than the etching solution 1 in the etching solution 1 on the filter. Therefore, it is possible to accumulate insoluble products corresponding to the bulky distance from the filter surface to the outlet 6o. Therefore, an increase in insoluble products can be prevented even when a large amount of p-type silicon substrate is processed for the same etching solution.

  In addition, since the control unit 7 that detects and feeds back alkali components and etching assistants contained in the flexible insoluble product removed in the filtration unit 6 as in the first embodiment, the chemical solution is exchanged. An ideal texture can be formed on a silicon substrate without any problems.

  As described above, in the etching process for forming a texture in the solar cell manufacturing method according to the second embodiment, an increase in insoluble products in the etching solution is prevented even after a large amount of the p-type single crystal silicon substrate is processed. Thus, adhesion of insoluble products to the p-type single crystal silicon substrate or inhibition of the function of the surfactant is prevented, and a uniform texture is formed over the entire surface of the p-type single crystal silicon substrate. Therefore, even when a large amount of p-type single crystal silicon substrate is processed, a solar cell having high light utilization efficiency and high open circuit voltage and excellent photoelectric conversion efficiency is realized.

  In addition, after a large amount of the semiconductor substrate is etched, insoluble products may accumulate in the filtration part and the filtration filter may be clogged. However, by providing a bypass flow path in the filtration part, it is possible to prevent pressure from being applied to the clogged filtration filter, and it is possible to prevent insoluble products from passing through the filtration filter. Therefore, a texture can be uniformly formed on the semiconductor substrate, and photogenerated carriers can be increased.

Embodiment 3 FIG.
In the third embodiment, a modification of the etching apparatus for texture formation in the solar cell manufacturing apparatus described in the first embodiment will be described. Since the solar cell manufacturing method using the solar cell manufacturing apparatus according to the third embodiment is the same as that of the first embodiment except for the etching apparatus, the detailed description is omitted with reference to the first embodiment. To do. FIG. 8: is a conceptual diagram of the apparatus structure for demonstrating the etching apparatus for the texture formation of the solar cell concerning Embodiment 3 of this invention.

  In the etching apparatus according to the first embodiment described above, the filtration unit 6 capable of removing insoluble products is provided outside the etching tank 2. In the etching apparatus according to the third embodiment, an etching tank 2 includes an inner tank 2a and an outer tank 2b, and an overflow etching tank in which the etching solution 1 overflows from the inner tank 2a and is supplied to the outer tank 2b is used. For ease of understanding, the outer tub 2b is described only on one side of the inner tub 2a. However, the outer tub 2b may be installed so as to face any or all of the periphery of the inner tub 2a. A semiconductor substrate 10 made of a p-type single crystal silicon substrate and a cassette 3 are immersed in the inner tank 2a, and the etching solution 1 overflowing from the inner tank 2a flows in the direction of the arrow in the figure and moves to the outer tank 2b. The overflowing etching solution 1 passes through the filtration unit 6 including a filtration filter installed in the outer tub 2b, and joins the pooled etching solution 1S below the outer tub 2b. The pooled etching solution 1S returns to the inner tank 2a via the circulation unit 4S and the pump 5S. In FIG. 8, the filtration unit 6 made of a filtration filter is shown in only one place for easy understanding. However, a plurality of filtration units may be installed, and the number of filtration filters is not limited. Moreover, what is necessary is just to install a filtration filter in the whole area or a part of outer tank 2b, and does not restrict | limit the installation area of a filtration filter.

  The filtration part 6 which consists of a filtration filter is comprised by the hydrophilic fiber which gave the pre-process similarly to the filtration part 6 of the etching apparatus in Embodiment 1. FIG. As the hydrophilic fiber, a fiber added with hydrophilicity by washing with an alkaline solution, such as polyolefin or polyester, or a fiber added with hydrophilicity using oxidation treatment by ozone treatment, such as polypropylene, is used. Since the filtration part 6 which consists of a filtration filter is installed in the outer tank 2b, it can increase a filtration area easily rather than the filtration part 6 in the manufacturing apparatus of the solar cell concerning the above-mentioned Embodiment 1-2. In addition, only the etching solution 1 overflowing from the inner tank 2a is supplied to the filtration filter of the filtration unit 6. Since the overflowing etching solution 1 does not pass through the pump 5S, the flow rate is slow, and the pressure applied to the filtration unit 6 composed of a filtration filter is only due to gravity. The pressure due to gravity is lower than the pressure applied by the pump, so that a flexible insoluble product can remain in the filter, and the flexible insoluble product can be efficiently removed from the etching solution 1. In addition, the filtration unit 6 installed in the outer tub 2b can easily exchange the filtration filter, and since the filtration unit 6 is installed outside the circulation unit 4S, the filtration filter can be exchanged without interrupting the texture forming process.

  According to Embodiment 3 described above, the filtration area of the filtration unit 6 made of a filtration filter can be designed widely, and the pressure of the etching solution 1 supplied to the filtration filter is low, so that a flexible insoluble product can be efficiently produced. It can be removed from the etching solution 1. As a result, there is no occurrence of a phenomenon in which the function of the surfactant is hindered by the flexible insoluble product or the flexible insoluble product adhering to the p-type silicon substrate, and the p-type single crystal silicon substrate is uniform without gaps. A texture is formed. In addition, since the filtration filter is installed in the outer tank 2b of the etching tank 2, it is possible to replace the filtration filter without stopping processing, thereby improving the continuous operability of the apparatus and increasing productivity.

  Further, as in the first embodiment, an alkali addition mechanism 9a for replenishing the alkali component removed by filtration and the etching auxiliary agent and an etching auxiliary agent addition mechanism 9b are provided, and the control unit 7 and the control line 8 Etching solution 1 is controlled to be in an ideal state. For this reason, it is possible to prevent poor texture formation due to the loss of the balance between the alkali component and the etching aid during continuous processing, and a uniform and ideal texture can be formed.

  Therefore, according to the solar cell manufacturing apparatus according to the third embodiment, a solar cell having high light utilization efficiency and high open-circuit voltage and excellent in photoelectric conversion efficiency is realized, and the solar cell has high productivity. Can be manufactured below.

  As described above, according to the present embodiment, the etching solution 1 overflowing from the inner tank 2a is supplied to the filtration filter installed in the outer tank 2b. It becomes possible to filter with. In addition, the filtration part (filtration filter) can be exchanged without stopping the treatment, and a texture can be continuously formed uniformly on the semiconductor substrate, and a solar cell with increased photogenerated carriers can be manufactured.

Embodiment 4 FIG.
Since the solar cell manufacturing apparatus according to the fourth embodiment is the same as that of the first embodiment except for the apparatus configuration of the etching apparatus for texture formation, detailed description will be omitted with reference to the first embodiment. To do. FIG. 9: is a conceptual diagram of the apparatus structure for demonstrating the etching apparatus for the texture formation of the manufacturing apparatus of the solar cell concerning Embodiment 4 of this invention. FIG. 10 is a perspective view showing a cassette used in this etching apparatus.

  In the etching apparatus according to the fourth embodiment, the etching bath 2 is filled with the etching solution 1, and the semiconductor substrate 10 made of a p-type single crystal silicon substrate is inserted into the cassette 3 and immersed therein. The cassette 3 is provided with hydrophilic fiber portions 16 on the side surface and the bottom surface. As in the first embodiment, the hydrophilic fiber portion 16 constituting the filtration portion is made hydrophilic by adding a hydrophilic property by washing with an alkaline solution, for example, polyolefin or polyester, or an oxidation treatment by ozone treatment. Fibers such as polypropylene are used.

  The hydrophilic fiber portion 16 attached to the cassette 3 is exposed to the convection of the etching solution 1 in the etching tank 2. During the etching process, the etchant 1 collides with the hydrophilic fiber part 16 so that the etchant 1 passing through the hydrophilic fiber part 16 is present, and the insoluble product flowing together with the etchant 1 becomes hydrophilic fiber part. 16 entangled.

  The insoluble product in the etching solution is captured by the hydrophilic fiber portion 16 attached to the cassette 3, and the insoluble product in the etching solution is removed. In addition, the cassette 3 is taken out from the etching tank 2 after the texture formation is completed, and is carried to a cleaning process. In the cleaning step, the entire cassette 3 is subjected to a cleaning process, so that the hydrophilic fiber portion 16 provided in the cassette 3 is also cleaned. The insoluble product captured during the etching process is accumulated in the hydrophilic fiber part 16, but the accumulated insoluble product can be removed during the cleaning process, and the insoluble product is generated in the hydrophilic fiber part 16. There is no residue. Therefore, after completion of the washing process, the hydrophilic fiber portion 16 is in a state where the insoluble product can be captured again, and can be repeatedly used together with the cassette 3 without replacing the hydrophilic fiber portion 16. In addition, since the insoluble product is taken out of the texture forming apparatus every time it is processed, it is possible to prevent the insoluble product in the etching solution 1 from increasing with time when it is repeatedly processed. As a result, the insoluble product can be removed repeatedly without requiring a hydrophilic fiber replacement step, and the insoluble product in the etching solution 1 can be removed. That is, the insoluble product in the etching solution 1 adheres to the surface of the p-type single crystal silicon substrate (semiconductor substrate 10) and can prevent the action of inhibiting the texture formation and the action of the surfactant. A texture can be uniformly formed on the entire surface of the type single crystal silicon substrate. Furthermore, even when the same etching solution 1 is repeatedly used, an increase in insoluble products in the etching solution can be prevented, and the number of times the etching solution is used can be increased.

  In addition, the fourth embodiment includes a mechanism for measuring the amount of alkali components and etching aids contained in the flexible insoluble product captured by the hydrophilic fiber portion 16 during cassette transport to the cassette transport machine 17, for example, A weight change measuring mechanism for measuring the weight before and after processing is provided. And the alkali addition mechanism 9a or the etching adjuvant addition mechanism 9b is connected via the control part 7 and the alkali addition mechanism control line 8a or the etching adjuvant addition mechanism control line 8b. The alkali component and the etching auxiliary agent are added by the alkali addition mechanism 9a and the etching auxiliary agent addition mechanism 9b, and the etching solution 1 is maintained in the ideal state described above. Therefore, even if the treatment is repeatedly performed, the treatment can be performed without losing the balance between the alkali component and the etching aid in the etching solution 1, and an ideal texture can be formed on the semiconductor substrate 10.

  According to the present embodiment, the hydrophilic fiber portion 16 capable of capturing the insoluble product is provided in the cassette 3 immersed in the etching solution 1 together with the semiconductor substrate 10. Both the cassette 3 and the hydrophilic fiber portion 16 are taken out to the cleaning process after the etching process of the semiconductor substrate 10. For this reason, since the insoluble product in the etching solution is captured by the hydrophilic fiber portion 16 and taken out, it is removed from the etching tank 2. In addition, in the cleaning process, it is possible to remove the insoluble product captured by the hydrophilic fiber portion 16, and the hydrophilic fiber portion 16 together with the cassette 3 returns to the initial state before capturing the insoluble product. Can be used repeatedly. Since the hydrophilic fiber having the same trapping performance of the insoluble product as that in the initial state is immersed in the etching tank 2, the effect of removing the insoluble product can be maintained. As a result, even when it is repeatedly processed, insoluble products in the etching solution 1 are effectively removed, and a texture can be uniformly formed on the semiconductor substrate 10. In addition, since a mechanism for replenishing the etching solution with the alkali component and the etching auxiliary component captured by the hydrophilic fiber is provided, the alkali component and the etching auxiliary component in the etching solution can always be maintained in an ideal balance. As a result, an ideal texture can be stably formed, and a solar cell with increased photogenerated carriers can be produced.

  As described above, according to the solar cell manufacturing apparatus of the fourth embodiment, a solar cell with high light utilization efficiency and excellent photoelectric conversion efficiency is realized. In addition, an apparatus capable of efficiently producing the solar cell is realized.

  Next, as a modified example 1 of the cassette used in the etching apparatus of the fourth embodiment, as shown in FIG. 11, it is also useful that the side surface 23a and the bottom surface 23c of the cassette 23 are formed with hydrophilic fiber boards 26. . Reference numeral 23 b denotes a rib for supporting the semiconductor substrate 10. In this example, the surface area of the hydrophilic fiber can be made larger than that of the cassette of the fourth embodiment, and the capture efficiency of insoluble products can be increased. The insoluble product trapped during the etching process accumulates on the hydrophilic fiberboard 26. When the cassette is pulled up from the etching solution 1 after the etching is completed, the insoluble product inside the cassette 23 is more efficiently removed. Can be captured. As in the case of the fourth embodiment, the accumulated insoluble product can be removed during the cleaning process of the cassette 23, and the insoluble product does not remain in the hydrophilic fiberboard 26. Therefore, after completion of the cleaning process, the hydrophilic fiber board 26 is in a state in which insoluble products can be captured again, and can be repeatedly used together with the cassette 23 without replacing the hydrophilic fiber board 26. In addition, since the insoluble product is taken out of the texture forming apparatus every time it is processed, it is possible to prevent the insoluble product in the etching solution 1 from increasing with time when it is repeatedly processed. As a result, the insoluble product can be removed repeatedly without requiring a hydrophilic fiber replacement step, and the insoluble product in the etching solution 1 can be removed.

  Next, Modification 2 of the cassette used in the etching apparatus of the fourth embodiment will be described. In this example, as shown in FIG. 12, a cassette 33 in which a hydrophilic fiber portion 36 is added and the internal space is expanded will be described. In this example, the hydrophilic fiber part 36 is added to the vicinity of the region where the rib 33b for supporting the semiconductor substrate 10 is formed, and the internal space for holding the etching solution is expanded. In the present embodiment, the entire four side surfaces 33 a are formed of the hydrophilic fiber portion 36 except for the bottom surface 33 c of the cassette 33 and the region where the ribs 33 b are formed. Also in this example, the etching solution used for etching and containing an insoluble product is temporarily held in the cassette 33, and the etching solution is filtered when the cassette 33 is pulled up.

  For this reason, an insoluble product can be captured more efficiently. As in the case of the fourth embodiment, the accumulated insoluble product can be removed during the cleaning process of the cassette 33, and the insoluble product does not remain in the hydrophilic fiber portion 36. Therefore, also in this case, the hydrophilic fiber portion 36 is in a state in which the insoluble product can be captured again after the cleaning process is completed, and can be repeatedly used together with the cassette 33 without replacing the hydrophilic fiber portion 36. In addition, since the insoluble product is taken out of the texture forming apparatus every time it is processed, it is possible to prevent the insoluble product in the etching solution 1 from increasing with time when it is repeatedly processed. As a result, the insoluble product can be removed repeatedly without requiring a hydrophilic fiber replacement step, and the insoluble product in the etching solution 1 can be removed.

  In addition, if the hydrophilic fiber portion 36 is made detachable from the cassette body of the cassette 33, after the etching is finished, it is removed from the cassette body, and another hydrophilic fiber portion 36 is attached and used. The hydrophilic fiber part 36 can be cleaned more efficiently. In addition, the cleaning time for repeated use can be shortened.

  In Embodiment 4 and Modifications 1 and 2, when the semiconductor substrate 10 and the etching solution 1 react, an upward flow of the etching solution is generated in the etching tank 2 and a flow of the etching solution is generated. Since the etching solution exits from the cassettes 3, 23, and 33 to the top surface, inflow of the etching solution from the top surface is prevented and inflow of insoluble products is also prevented.

  On the other hand, the etching solution rises, and the etching solution 1 that has flowed out of the cassettes 3, 23, 33 to the top surface passes again through the hydrophilic fiber part 16, the hydrophilic fiber plate 26, and the hydrophilic fiber part 36, and then the cassette 3, Return to 23, 33. When the etching solution passes through the hydrophilic fiber part 16, the hydrophilic fiber plate 26, and the hydrophilic fiber part 36, the insoluble product is entangled with the fiber and does not flow into the cassettes 3, 23, and 33.

  Therefore, a texture is formed on the semiconductor substrate 10 without being affected by the insoluble product having an irregular shape. In addition, the amorphous insoluble product entangled with the hydrophilic fibers is transported to the next cleaning step together with the cassettes 3, 23, 33, and the hydrophilic fiber portion 16, the hydrophilic fiber plate 26, the hydrophilic The amorphous insoluble product in the fiber part 36 is also washed and removed. Therefore, after completion of the cleaning process, the hydrophilic fiber portion 16, the hydrophilic fiber plate 26, and the hydrophilic fiber portion 36 are in a state in which the insoluble insoluble product can be captured again, and the hydrophilic fiber portion 16, the hydrophilic fiber plate 26, It becomes possible to repeatedly use the hydrophilic fiber portion 36 together with the cassettes 3, 23, and 33 without exchanging the hydrophilic fiber portion 36.

Embodiment 5 FIG.
Since the solar cell manufacturing apparatus according to the fifth embodiment is the same as that of the fourth embodiment except for the apparatus configuration of the etching apparatus for texture formation, detailed description will be omitted with reference to the fourth embodiment. To do. FIG. 13 shows a hydrophilic fiber attachment portion of a cassette used in this etching apparatus, and is a perspective view drawn with the hydrophilic fiber removed from the cassette for easy understanding. FIG. 14 is a perspective view illustrating the cassette shown in FIG. 13 including hydrophilic fibers. FIG. 15 is a conceptual diagram showing the structure of the solar cell manufacturing apparatus according to the fifth embodiment, and schematically shows the flow of an etching solution when a cassette holding a semiconductor substrate is immersed in an etching bath and reacted. FIG. Although hydrophilic fibers are described on a part of the side surface and the bottom surface, in order to realize the maximum fiber area, the side surface of the cassette itself may be configured using hydrophilic fibers within the range in which the shape of the cassette can be maintained. Good.

  As shown in FIG. 13, the etching apparatus in the fifth embodiment is provided with openings 38, 39, and 40 on the side surface and the bottom surface constituting the cassette 37. In the present embodiment, as shown in FIG. 14, hydrophilic fibers 43, 44, and 45 are installed in the opening 42 of the cassette 41, that is, the portion corresponding to the openings 38, 39, and 40 in FIG. 13. As in the first embodiment, a hydrophilic fiber such as polyolefin or polyester, or a hydrophilic fiber such as polypropylene with an oxidation treatment using ozone treatment is used as the hydrophilic fiber. In order to remove in advance the eluate from the fibers, it is preferable to perform washing with an alkaline solution. The cassette 41 comes into contact with the etching solution in the etching tank 46 through the side and bottom openings 42 and the hydrophilic fibers 43.

  FIG. 15 shows the flow of the chemical solution when the etching solution 47 is introduced into the etching bath 46 and the cassette 48 holding the semiconductor substrate 49 is immersed in the etching bath 46. When the semiconductor substrate 49 and the etching solution 47 react, an upward flow of the etching solution 47 is generated in the etching tank 46, and an etching solution flow 50 is generated. Since the etching solution 47 exits from the inside of the cassette 48 to the top surface, the inflow of the etching solution 47 from the top surface is prevented and the inflow of insoluble products is also prevented.

  On the other hand, the etching solution 47 flows after the flow 50 as shown in the flow 51 and the flow 52 of the etching solution 47, and the bottom opening and the hydrophilic fiber portion 54 again, the side opening and the hydrophilic fiber portion 53, And return to the cassette 48. When the etching solution 47 passes through the hydrophilic fiber portions 53 and 54, the insoluble product is entangled with the fibers and does not flow into the cassette 48.

  Accordingly, a texture is formed on the semiconductor substrate 49 without being affected by the insoluble product having an irregular shape. In addition, the amorphous insoluble product entangled with the hydrophilic fibers is transferred to the next washing step together with the cassette 48, and the amorphous insoluble products in the hydrophilic fibers are also washed and removed. Therefore, after completion of the cleaning process, the hydrophilic fiber portions 53 and 54 are in a state in which the insoluble insoluble product can be captured again and can be repeatedly used together with the cassette 48 without replacing the hydrophilic fiber portions 53 and 54. It becomes.

  Furthermore, since the insoluble product is taken out of the texture forming apparatus every time it is processed, it is possible to prevent the insoluble product in the etching solution 47 from increasing over time when it is repeatedly processed. As a result, the insoluble product can be removed repeatedly without the need for a hydrophilic fiber replacement step, and the amorphous insoluble product in the etching solution 47 can be removed. That is, it is possible to prevent the insoluble product in the etching solution 47 from adhering to the surface of the p-type single crystal silicon substrate (semiconductor substrate 49) and inhibiting the texture formation or the surfactant. A uniform texture can be formed on the entire surface of the type single crystal silicon substrate.

  Furthermore, even when the same etching solution 47 is repeatedly used, an increase in insoluble products in the etching solution can be prevented, and the number of times the etching solution is used can be increased.

  According to the present embodiment, the hydrophilic fiber part 53 and / or the hydrophilic fiber part 54 capable of capturing insoluble products are provided in the cassette 48 immersed in the etching solution 47 together with the semiconductor substrate 49. Both the cassette 48 and the hydrophilic fiber portions 53 and 54 are taken out to the cleaning process after the etching process of the semiconductor substrate 49.

  For this reason, the insoluble product in the etching solution is captured by the hydrophilic fiber portions 53 and 54 and removed from the etching bath 46.

  In addition, it becomes possible to remove insoluble products captured by the hydrophilic fiber portions 53 and 54 in the washing process, and the hydrophilic fiber portions 53 and 54 together with the cassette 48 are in an initial state before capturing the insoluble products. Can be used repeatedly. The etching tank 46 is soaked with hydrophilic fibers that are washed and have the same insoluble product capture performance as in the initial state, so that the removal effect of the insoluble product can be maintained.

  As a result, even when it is repeatedly processed, insoluble products in the etching solution 47 are effectively removed, and a texture can be uniformly formed on the semiconductor substrate 49. As a result, an ideal texture can be stably formed, and a solar cell with increased photogenerated carriers can be produced.

  As described above, according to the solar cell manufacturing apparatus of the fifth embodiment, a solar cell with high light utilization efficiency and excellent photoelectric conversion efficiency is realized. In addition, an apparatus capable of efficiently producing the solar cell is realized.

Embodiment 6 FIG.
The solar cell manufacturing apparatus according to the sixth embodiment is the same as that of the fifth embodiment except for the etching solution circulation part of the texture-forming etching apparatus. Therefore, detailed description is omitted with reference to the fifth embodiment. To do. FIG. 16: is a conceptual diagram of the apparatus structure for demonstrating the etching apparatus for the texture formation of the manufacturing apparatus of the solar cell concerning Embodiment 6 of this invention.

  The etching apparatus according to the sixth embodiment is configured such that a circulation flow outlet 59 of an etching solution circulation system 57 is located below a hydrophilic fiber 56 installed on the bottom surface of a cassette 55. The circulation system 57 circulates the etching solution 61 from the etching tank 60 via the pump 58, and the insoluble product passes through the circulation system 57 and returns to the lower part of the etching tank 60. The etching solution 61 is blown out from the outlet 59 of the circulation flow. The etching solution blown out from the circulation flow outlet 59 passes through the hydrophilic fibers 56 installed on the bottom surface of the cassette 55 and enters the cassette 55. The insoluble product in the blown etching solution 61 is entangled with the hydrophilic fiber 56 on the bottom surface of the cassette 55 and does not enter the cassette. In particular, when the reaction between the semiconductor substrate 62 at the end of the process and the etching solution 61 ends and the upward flow of the etching solution 61 in the cassette 55 due to the reaction becomes weak, the chemical solution is supplied from the circulation flow outlet 59 at the bottom of the cassette 55. It is possible to forcibly supply and continuously generate an upward flow. Thereby, it is possible to prevent the insoluble product from entering the cassette 55 from the opening on the top surface, and it is possible to create a state where there is no insoluble product in the cassette even in the final stage of the process. Therefore, a texture is formed on the semiconductor substrate 62 without being affected by insoluble products from the start to the end of the process.

  According to the present embodiment, the circulation flow outlet 59 is installed so that the hydrophilic flow 56 on the bottom surface of the cassette 55 is in contact with the circulation flow of the etching solution 61. Even when the reaction between the semiconductor substrate 62 at the end of the process and the etching solution 61 stops, the etching solution 61 is supplied from the bottom of the cassette 55, and the etching solution 61 enters the cassette 55 from the opening where no hydrophilic fibers are installed. Can prevent intrusion. That is, only the etchant that has passed through the hydrophilic fiber is supplied into the cassette even in the final stage of the process, and the insoluble insoluble product contained in the etchant is captured by the hydrophilic fiber 56. Therefore, a uniform texture can be formed on the semiconductor substrate 62. As a result, an ideal texture can be stably formed, and a solar cell with increased photogenerated carriers can be produced.

  In this embodiment, for easy understanding, the outlet of the circulation flow is installed on the bottom surface and the hydrophilic fiber on the bottom of the cassette is opposed to the outlet, but the circulation flow is applied so that the hydrophilic flow on the side surface of the cassette hits the hydrophilic flow. However, the present invention is not limited thereto.

  Furthermore, as a semiconductor substrate applicable by this method, it is needless to say that it can be applied not only to single crystal and polycrystalline silicon substrates but also to all silicon substrates treated with a strong alkaline chemical solution.

  As described above, the solar cell manufacturing apparatus according to the present invention is useful for manufacturing solar cells with high light utilization efficiency and excellent photoelectric conversion efficiency, and in particular, manufacturing of solar cells using a crystalline silicon-based substrate. Suitable for This is because, in particular, when the pn junction is formed by diffusion on the surface of the crystalline silicon substrate on which the texture is formed, the distribution of the texture affects the photoelectric conversion characteristics.

DESCRIPTION OF SYMBOLS 1 Etching liquid, 2 Etching tank, 2a Inner tank, 2b Outer tank, 3,23,33 Cassette, 4 Circulation part, 4b Bypass flow path, 5 Pump, 6 Filtration part, 7 Control part, 8 Control line, 9 Addition mechanism , 9a Alkali addition mechanism, 9b Etching auxiliary agent addition mechanism, a Alkaline chemical solution, b Etching auxiliary agent, 10 First conductivity type semiconductor substrate (p-type single crystal silicon substrate), 10T texture, 11 Second conductivity type layer, 12 Insulating layer, 13 Light receiving surface side electrode, 14 First conductivity type layer, 15 Back surface side electrode, 16 Hydrophilic fiber part, 26 Hydrophilic fiber board, 36 Hydrophilic fiber part, 37 Cassette, 38 Opening part, 39 Opening part, 40 opening, 41 cassette, 42 opening, 43 hydrophilic fiber, 44 hydrophilic fiber, 45 hydrophilic fiber, 46 etching tank, 47 etching 48 cassette, 49 semiconductor substrate, 50 etchant flow, 51 etchant flow, 52 etchant flow, 53 hydrophilic fiber part, 54 hydrophilic fiber part, 55 cassette, 56 hydrophilic fiber, 57 circulation system, 58 pump, 59 outlet of circulating flow, 60 etching tank, 61 etching solution, 62 semiconductor substrate.

Claims (21)

An etching apparatus used for manufacturing a solar cell having a pn junction formed on the surface of a silicon-based semiconductor substrate, for forming a texture on the surface of the semiconductor substrate,
A strongly alkaline etchant;
An etching tank that holds the etching solution and performs texture etching by immersing the semiconductor substrate in the etching solution;
Comprising a filtration part having a hydrophilic fiber part for filtering the etching solution;
The said hydrophilic fiber part is a manufacturing apparatus of the solar cell characterized by not being combined in the point which fibers cross | intersect, but being entangled.   The said hydrophilic fiber part was comprised with the hydrophilic fiber with a fiber diameter of 200 micrometers or less, The manufacturing apparatus of the solar cell of Claim 1 characterized by the above-mentioned.   The said hydrophilic fiber part was comprised with the hydrophilic fiber with a fiber diameter of 0.1-10 micrometers, The manufacturing apparatus of the solar cell of Claim 2 characterized by the above-mentioned. Comprising a cassette for supporting the semiconductor substrate;
The semiconductor substrate is immersed in an etching solution for each cassette, and is configured to be pulled up from the etching solution for each cassette after completion of etching,
The said filtration part is a hydrophilic fiber part with which the said cassette was mounted | worn, The manufacturing apparatus of the solar cell of Claim 3 characterized by the above-mentioned.   The solar cell manufacturing apparatus according to claim 4, wherein an opening is provided on a side surface or a bottom surface of the cassette, and the opening is covered with the hydrophilic fiber. The solar cell manufacturing apparatus according to claim 4 , wherein the etching tank includes a circulation unit that circulates the etching solution.   The solar cell manufacturing apparatus according to claim 6, wherein an outlet of the circulation unit is installed so that an etching solution is jetted toward the hydrophilic fiber installed in the opening of the cassette.   A detection unit that detects the amounts of the alkali component and the etching auxiliary component removed by the filtration unit; and a replenishment unit that replenishes the etching solution with the alkali component and the etching auxiliary component based on the detected amount. The solar cell manufacturing apparatus according to claim 1, wherein the solar cell manufacturing apparatus is a solar cell manufacturing apparatus.   2. The solar cell manufacturing apparatus according to claim 1, further comprising a bypass channel connected to the filtration unit and returning directly to the etching tank without passing through the filtration unit. The etching tank is an overflow tank including an inner tank and an outer tank,
The said filtration part is a filtration filter which consists of a hydrophilic fiber part provided in the said outer tank, The manufacturing apparatus of the solar cell of any one of Claims 1-3 characterized by the above-mentioned.   The said hydrophilic fiber part consists of polymeric materials by which the surface was hydrophilized, The manufacturing apparatus of the solar cell of any one of Claims 1-10 characterized by the above-mentioned.   The said hydrophilic fiber part is 1 mm or more in thickness, The manufacturing apparatus of the solar cell of Claim 11 characterized by the above-mentioned.   The said hydrophilic fiber part is 2 mm or more in thickness, The manufacturing apparatus of the solar cell of Claim 12 characterized by the above-mentioned. A strongly alkaline etchant;
An etching tank that holds the etching solution and performs texture etching by immersing a silicon-based semiconductor substrate in the etching solution;
Using a solar cell manufacturing apparatus, comprising a filtration part including a hydrophilic fiber part for filtering the etching solution, and the hydrophilic fiber part is entangled without being bonded at a point where the fibers cross each other.
An etching step of performing texture etching by immersing the semiconductor substrate in an etching tank holding a strong alkaline etching solution;
A step of forming a pn junction on the surface of the semiconductor substrate on which the texture is formed,
The method of manufacturing a solar cell, wherein the etching step performs etching while filtering the etching solution by the filtration unit having the hydrophilic fiber part.   Prior to the etching step, the method includes a step of immersing the hydrophilic fiber part in an alkali solution having an alkali concentration of 50% by mass or more and 200% by mass or less of the alkali concentration of the etching solution. 14. A method for producing a solar cell according to 14.   The method for manufacturing a solar cell according to claim 14, wherein the hydrophilic fiber portion is made of a hydrophilic fiber having a fiber diameter of 0.1 to 10 μm. The filtration part is a hydrophilic fiber part attached to a cassette that supports the semiconductor substrate,
The etching step includes
Mount the semiconductor substrate on the cassette,
For each cassette, the semiconductor substrate is immersed in an etching solution,
Etching while circulating the etchant by the upward flow due to the etching reaction,
The method for manufacturing a solar cell according to claim 16, further comprising a step of pulling up the cassette from the etching solution after completion of etching. The etching step includes
The method for manufacturing a solar cell according to claim 17, wherein the semiconductor substrate is etched while circulating the etching solution using a circulating unit that circulates the etching solution. The etching step includes
19. The solar cell manufacturing method according to claim 18, wherein the semiconductor substrate is etched while jetting an etching solution from an outlet of the circulation portion toward the hydrophilic fiber portion installed in the cassette. Method. Detecting the amount of alkali components and etching auxiliary components removed by the filtration unit;
The method for manufacturing a solar cell according to any one of claims 14 to 19, further comprising a step of replenishing the etching solution with the alkali component and the etching auxiliary component based on the detected amount. 21. The method of manufacturing a solar cell according to claim 20, wherein the etching liquid can be returned directly to the etching tank without passing through the filtration unit by a bypass flow path connected to the filtration unit. .

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