JP2013098301A - Etching apparatus, etching method, and method for manufacturing solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an etching apparatus which is capable of suppressing a texture formation failure as compared with conventional ones in a texture etching process in solar cell manufacturing.SOLUTION: The etching apparatus for etching a silicon substrate 100 by immersing it in an etchant 13 includes: an etching bath 11 in which the etchant 13 is stored and the silicon substrate 100 is etched; and a hydrophobic organic substance collection part 15 for collecting a hydrophobic organic substance eluted into the etchant 13.

Description

  The present invention relates to an etching apparatus and method, and a solar cell manufacturing method.

  A silicon solar cell is a clean energy source because it is a device that converts sunlight, which is an inexhaustible energy source, into electrical energy. In the production of silicon solar cells, it is important to stably produce solar cells having high power generation efficiency by suppressing variations in characteristics in mass production as much as possible in addition to improving power generation efficiency.

  The silicon (including single crystal silicon and polycrystalline silicon) substrate used as a substrate for solar cells increases the light absorption rate by forming fine quadrangular pyramid irregularities called texture on the surface on the light irradiation side, Power generation efficiency can be improved. A silicon substrate having a texture on the surface (hereinafter referred to as a texture substrate) is generally composed of, for example, an alkaline solution of KOH or NaOH (concentration is, for example, 0.05 to 2.0 mol / l) and isopropyl alcohol (concentration is, for example, 0). Texture etching in which a silicon substrate is immersed in a solution for etching (hereinafter referred to as an etching solution) as a mixed solution with .05 to 2.0 mol / l) or the like at a temperature of about 70 to 90 ° C. for several minutes to several tens of minutes. It is formed by executing a process. As a system of an apparatus used for texture etching, there are a batch processing type and a single wafer processing type.

  In such a texture etching process, since the quality of the texture depends on the concentration of impurities dissolved in the etching solution, in-plane non-uniformity of the texture substrate becomes a problem. A texture substrate on which an in-plane uneven texture is formed lacks the light confinement effect. Therefore, when a solar battery cell is manufactured using such a substrate, the characteristics are deteriorated.

  For example, if a silicon substrate is etched several times with the same etchant, elution of the dopant metal (phosphorus, etc. for n-type silicon substrates, boron, etc. for p-type silicon substrates) in the silicon substrate causes the silicon substrate to be etched in each etch process The cation concentration increases, the texture becomes non-uniform, and the light reflectance of the texture substrate increases. In order to remove cations in the etching solution, which is a cause of such uneven texture formation, a metal adsorbent is installed in the circulation pipe of the etching apparatus, or an electrode is installed and a voltage is applied. A technique for lowering the metal impurity concentration in the etching solution by installing a mechanism for precipitating the metal or by precipitating the metal by adjusting the pH or adjusting the temperature is disclosed (for example, see Patent Document 1). .

  In addition, a method for suppressing the influence on the silicon device by removing organic substances attached to the silicon substrate by ozone treatment during the immersion treatment in the solution has been proposed (for example, see Patent Document 2).

JP 2006-278409 A JP 2005-136377 A

  However, even if the dopant metal in the etching solution is removed by the technique described in Patent Document 1 or the organic substance attached to the silicon substrate is removed by the technique described in Patent Document 2, the texture formation becomes non-uniform. There was a problem that it was. That is, the texture for enhancing the solar cell characteristics could not be efficiently formed only by removing the dopant metal or the organic matter adhering to the silicon substrate.

  The present invention has been made in view of the above, and it is an object of the present invention to provide an etching apparatus and method capable of suppressing poor texture formation as compared with conventional processes and a solar cell manufacturing method in a texture etching process of solar cell manufacturing. And

  To achieve the above object, an etching apparatus according to the present invention is an etching apparatus for immersing and etching a silicon substrate in an etching solution, storing the etching solution and etching the silicon substrate, And a hydrophobic organic substance collecting part for collecting the hydrophobic organic substance eluted in the etching solution.

  According to the present invention, since the hydrophobic organic substance collecting part for collecting the hydrophobic organic substance eluted in the etching solution is provided, the eluted hydrophobic organic substance in the etching solution that adversely affects the etching is affected by the etching. As a result of collecting so as not to give, and suppressing the residue of hydrophobic organic matter on the texture substrate surface, it has the effect that the texture effective for improving the characteristics of the solar cell can be efficiently formed on the surface of the silicon substrate. .

FIG. 1 is a diagram showing the relationship between the presence or absence of a hydrophobic organic substance in an etching solution and the reflectance of a silicon substrate prepared with the etching solution. FIG. 2 schematically shows a schematic configuration of the etching apparatus according to the first embodiment of the present invention. FIG. 3 is a diagram schematically showing a schematic configuration of an etching apparatus according to Embodiment 2 of the present invention. FIG. 4 is a cross-sectional view schematically showing the structure of the solar battery cell.

  Exemplary embodiments of an etching apparatus and method and a solar cell manufacturing method according to the present invention will be explained below in detail with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments. In the following, after describing the cause of etching failure in the conventional process, an embodiment for solving it will be described. Furthermore, the drawings of the etching apparatus and solar cell used in the following embodiments are schematic, and the ratio of size and length is different from the actual one.

  As a result of experiments conducted by the present inventors, in the texture etching process, when the etching solution from which hydrophobic organic substances are eluted is used and when the etching liquid not containing hydrophobic organic substances is used, the texture of the silicon substrate is obtained. It was found that there was a large difference in the reflectance. This point will be described below. In the present invention, the hydrophobic organic substance refers to an organic compound having low solubility in an etching solution.

  FIG. 1 is a diagram showing the relationship between the presence or absence of a hydrophobic organic substance in an etching solution and the reflectance of a silicon substrate prepared with the etching solution. As shown in FIG. 1, the reflectance is about 18% when an etching solution containing a hydrophobic organic material is used, whereas the reflectance is about 10% when an etching solution containing no hydrophobic organic material is used. Decreases to about 12%. Therefore, a texture substrate formed using an etchant containing a hydrophobic organic substance has poor light absorption efficiency into the substrate, and high characteristics are expected even when solar cells are produced using such a texture substrate. Can not.

  As described above, in the etching solution containing the hydrophobic organic substance, when the concentration of the hydrophobic organic substance increases, the substrate surface of the product formed by the interaction between the hydrophobic organic substance or the component eluted by the etching and the hydrophobic impurity. It is considered that the adhesion to the surface increases and inhibits etching of silicon by alkali. That is, if the hydrophobic organic substance (hydrophobic impurity) is present in the etching solution at a certain concentration or more, the etching rate and uniformity are adversely affected. As a result, it is considered that the form of the texture to be generated becomes poor, or texture formation unevenness is generated by local adhesion.

  There are various types of hydrophobic organic substances and mixing routes. The main mixing routes include those mixed in raw materials of etching solution and pure water, those that adhere to the silicon substrate, those that are brought in by the wafer cassette that holds the silicon substrate, those that enter from the air, Some are due to contamination of equipment components.

  Included in the raw material is an impurity dissolved in a solvent-based raw material such as isopropyl alcohol, which is often not only an impurity at the time of production, but also a lubricating oil or a rust preventive agent mixed in the middle. . These impurities include higher alcohols, various hydrocarbons, ethers and esters. In addition to various fatty acids and esters contained in fingerprints, what is brought into the silicon substrate includes lubricants, rust preventives, plastic plasticizers such as phthalates and adipates, etc. . In addition to adhering to the silicon substrate via a container or a conveying part, these may be adsorbed by adsorbing a minute amount of vapor in the air. Oil mist generated from a heat source, spray particles, or the like may become a problem as a material that enters the etching solution from the air.

  Such a hydrophobic organic substance cannot be removed by the method of Patent Document 1 in which only the cation of the dopant of the silicon substrate is removed. Further, in the treatment with ozone as in Patent Document 2, intentionally added organic substances such as isopropyl alcohol are decomposed first, so that it is difficult to selectively remove only hydrophobic organic substances. . That is, conventionally, no method has been proposed for removing hydrophobic organic substances in the etching solution. As described above, in the prior art, a sufficiently clean etching solution cannot be provided, so that it is impossible to stably form a uniform texture in the surface on the texture substrate, which hinders improvement in power generation efficiency in the solar cell. At the same time, the yield was reduced.

  Therefore, in the following, by removing the hydrophobic organic substance present in the etching solution, the hydrophobic organic substance concentration in the etching solution is lowered, that is, the eluted hydrophobic organic substance concentration does not affect the texture etching reaction. An embodiment will be described in which better texture etching can be realized by maintaining the state, that is, a uniform texture substrate with low reflectance can be manufactured.

Embodiment 1 FIG.
FIG. 2 schematically shows a schematic configuration of the etching apparatus according to the first embodiment of the present invention. The etching apparatus includes an etching tank 11 that stores an etching solution 13. A wafer cassette 12 that holds a silicon substrate 100 to be etched is immersed in the etching tank 11. Here, a plurality of silicon substrates 100 are held in the wafer cassette 12, and texture etching is performed simultaneously.

  The etching tank 11 is provided with a circulation pipe 14, and a pump 16 used for circulation of the etching solution 13 is provided on the circulation pipe 14. The etching liquid 13 is circulated by the pump 16 in the direction of the arrow in FIG. Although not shown, the etching tank 11 or the circulation pipe 14 is provided with a heater as a heating unit, and the etching solution 13 can be heated to a predetermined temperature. Furthermore, when the etching solution 13 needs to be stirred, the etching solution 13 can be stirred by providing the etching tank 11 with a stirring means (not shown).

  Further, the circulation pipe 14 is provided with a hydrophobic organic substance collecting unit 15 for collecting hydrophobic organic substances. By circulating the etching solution 13 through the circulation pipe 14 by the pump 16, the hydrophobic organic matter eluted in the etching solution 13 can be collected by the hydrophobic organic matter collecting unit 15 and removed from the etching solution 13. In the example of FIG. 2, the hydrophobic organic substance collection unit 15 is provided in the circulation pipe 14, but may be provided in the etching tank 11. In this case, for example, it is fixed to the side surface of the bottom of the etching tank 11 so as not to contact the silicon substrate 100 in the wafer cassette 12.

  The hydrophobic organic matter collecting unit 15 is formed by incorporating an adsorbent having a hydrophobic surface, for example. As long as the surface of the adsorbent is hydrophobic and has a sufficient surface area, it can take various forms such as fibrous, granular, plate-like, porous, and composites thereof.

  By making the surface hydrophobic, the hydrophobic organic substance existing in excess in the etching solution 13 can be adsorbed on the adsorbent surface. The surface hydrophobicity depends on the surface area of the adsorbent, but if it is equal to or greater than the hydrophobicity of the textured substrate during etching, the adsorbent adsorbs hydrophobic organic matter to suppress the amount adsorbed on the textured substrate. can do. Since the hydrophobicity of the textured substrate during etching varies depending on the etching state and the composition of the etching solution 13, it is difficult to determine it as a single value. Therefore, as a result of various studies on the hydrophobicity, it is desirable that the contact angle of water when the material of the adsorbent is processed into a flat surface is 60 ° or more, and more preferably 80 ° or more. I found it desirable. When the contact angle is less than 60 °, the amount of the hydrophobic organic substance adsorbed on the texture substrate cannot be sufficiently suppressed, and the adverse effect on etching may not be suppressed.

  The larger the surface area of the adsorbent, the more efficiently the hydrophobic organic substance can be adsorbed. If the flow rate of the etching solution 13 in contact with the adsorbent is sufficiently large, the effect can be obtained if the surface area is equal to or greater than the surface area of the texture substrate. In order to maintain the effect in the long term, a larger surface area may be provided. Considering the lifetime of the etching solution 13, the surface area of the adsorbent is preferably 5 times or more, more preferably 8 times or more the surface area of the textured substrate. If it is less than 5 times, there is a high possibility that the etching will vary as the etching is repeated.

  The adsorbent can take various forms as long as the above requirements are satisfied. Here, two types of particles and fibers are taken up and described. In the particulate form, the average particle size is preferably 7 mm or less and 1 μm or more, more preferably 5 mm or less and 10 μm or more. Handling can be facilitated by bonding the particles to each other to form a porous shape. If the average particle size exceeds 7 mm, the amount of adsorbent for obtaining a sufficient surface area becomes too large, and the amount of etching solution and the cost for temperature control become excessive. If the average particle diameter is less than 1 μm, the risk of leakage of the adsorbent from the hydrophobic organic substance collecting unit 15 increases, and handling of the adsorbent becomes difficult.

  In the case of a fiber, the fiber diameter is preferably 0.5 mm or less and 0.5 μm or more, more preferably 0.1 mm or less and 1 μm or more. When the fiber diameter exceeds 0.5 mm, the amount of the adsorbent for obtaining a sufficient surface area becomes too large. When the fiber diameter is less than 0.5 μm, the strength of the fiber is low and it may be difficult to handle. The length of the fiber is preferably 10 mm or more so that the fiber does not flow into the etching solution 13. The cross section of the fiber may be circular, but it is also preferable to increase the adsorption efficiency of impurities by increasing the surface area. The fibers can be used in a bundled state as they are, but the use as a woven fabric or a non-woven fabric is preferable in terms of handling and can also function as a filter for removing particulate foreign matter in the etching solution 13. There are advantages.

  The material of the adsorbent is preferably a material having a hydrophobic surface and not deteriorated by the etching solution 13 during etching. Olefin resins such as polyethylene and polypropylene are preferably used because of their high durability against alkalis and low cost. Chlorinated resins such as vinyl chloride and vinylidene chloride, PTFE (polytetrafluoroethylene), PFA (copolymer of tetrafluoroethylene and perfluoroalkoxyethylene), FEP (copolymer of tetrafluoroethylene and hexafluoropropylene) ), ETFE (a copolymer of tetrafluoroethylene and ethylene), PVDF (polyvinylidene fluoride), PCTFE (polychlorotrifluoroethylene) and the like are preferable because of their high hydrophobicity and durability. In addition, vinyl resins such as acrylic resin and polystyrene can be used. In addition, it is also preferable to use a combination of these materials, and by coating polyethylene with a core having a high melting point, such as polypropylene, a nonwoven fabric or the like is formed as a material having both heat resistance and heat fusion properties of polyethylene. It is also possible to use a combination of various materials, such as making it easier to form, or forming an aggregate of fibers and particles of other materials using polypropylene powder as a binder.

  In addition to the above hydrophobic resin, hydrophilic fibers such as cellulose and rayon can be used after being subjected to a reaction with a silane coupling agent or the like, or a hydrophobic treatment with plasma or the like. Carbon fibers, metal fibers, metal foils, various metal oxides and metal nitride particles and plates can also be used. However, when using the above-mentioned fibers, particularly hydrophilic fibers such as cellulose and rayon, use high-purity ones or those previously washed with an alkaline aqueous solution, It is desirable that no components elute as impurities.

  An etching method in the etching apparatus having such a configuration will be described. After the etching bath 11 is filled with the etching solution 13, the wafer cassette 12 holding the silicon substrate 100 is immersed in the etching bath 11 for a predetermined time. At this time, a part of the etching solution 13 is guided to the circulation pipe 14 by operating the pump 16. The etching liquid 13 that moves through the circulation pipe 14 passes through the hydrophobic organic substance collecting unit 15, thereby removing the hydrophobic organic substance in the etching liquid 13 and returning it to the etching tank 11 again. In this way, the concentration of the hydrophobic organic substance in the etching solution 13 of the etching tank 11 is set to be a predetermined value or less. As a result, the in-plane non-uniformity of the texture caused by the hydrophobic organic substance can be prevented, so that the production of solar cells with high power generation efficiency can be realized with a high yield. After immersing the silicon substrate 100 in the etching solution 13 for a predetermined time, the wafer cassette 12 is pulled up, and the wafer cassette 12 holding another silicon substrate 100 that has not been subjected to the etching process is immersed in the etching solution 13. The process is repeated.

  In addition, when the use time of the adsorbent is lengthened, the removal efficiency of the hydrophobic organic matter is lowered. Therefore, it is possible to maintain the effect by exchanging the adsorbent in the hydrophobic organic substance collecting unit 15 with a new one every appropriate time. The adsorbent according to this embodiment is different from the adsorption of molecules to the micropores by removing impurities with activated carbon or the like, and uses an action only to attach a hydrophobic organic substance to the hydrophobic surface. There is an advantage that impurities can be easily removed. That is, the adsorbent can be reused.

  There are several methods for removing the hydrophobic organic substance from the adsorbent, but the most reliable method is a method of cleaning with an organic component such as alcohol added to the etching solution 13 such as isopropyl alcohol. . In this method, the hydrophobic organic substance is dissolved and removed in the organic component. Moreover, since the components used for the etching solution 13 are used, the adsorbent can be used without being dried after washing.

  In addition, the solubility of the hydrophobic organic substance is higher than that of the etching liquid 13 which contains the hydrophobic organic substance or silicate which is soluble by repeated use. There is also a method of removing impurities adhering to the adsorbent using the higher one. When the etching solution 13 in the etching tank 11 is replaced with a new one, it is possible to clean some of the etching solution 13 by discarding it through the adsorbent. This method has an advantage that a part of the etching solution 13 is wasted, but it can be processed without any special effort. Further, the device needs to be devised, but the impurities can be removed from the adsorbent by the new etching solution 13 not only at the time of replacement with the new etching solution 13 but also during the etching.

  Further, there is a method of removing impurities adhering to the adsorbent by utilizing the fact that the solubility of the hydrophobic organic substance varies depending on the temperature of the etching solution 13. When the old etching solution 13 is discharged from the etching tank 11, it is possible to dissolve and remove the adsorbed hydrophobic organic matter by raising the temperature to a temperature higher than the etching temperature and discharging it through the adsorbent. is there. In addition to the method of raising the temperature of the entire etching solution 13, there are a method of raising the temperature of a part of the etching solution 13 for regeneration of the adsorbent and a method of raising the temperature of only the adsorbent portion. These methods have the advantage that hydrophobic organics can be removed from the adsorbent without generating extra waste.

  Next, specific examples of the adsorbent are given. For any of these examples, the hydrophobic organics can be reduced to a level that does not adversely affect texture formation.

(1) When using a nonwoven fabric made of polypropylene fibers A nonwoven fabric made of polypropylene fibers having a fiber diameter of 2 μm prepared by a melt blow method is wound into a cylindrical shape to create an adsorbent having a diameter of 100 mm and a length of 200 mm. This is sealed in a cylindrical container having an inner diameter of 100 mm provided with an introduction hole and a discharge hole at the upper and lower ends to form a hydrophobic organic matter collecting unit 15. When 50 kg of the etching solution 13 (isopropyl alcohol 2%, NaOH 4%) containing 10 ppm of bis (2-ethylhexyl) phthalate as the hydrophobic organic substance is passed through the hydrophobic organic substance collecting unit 15 thus created. , Hydrophobic organics are reduced to 0.5 ppm.

(2) When polypropylene powder is used Polypropylene powder having an average particle size of about 200 μm is packed in a container similar to the above to form the hydrophobic organic matter collecting unit 15. After the powder is first wetted with isopropyl alcohol, the hydrophobic organic substance is reduced to 0.3 ppm by passing the etching solution 13 containing 10 ppm of bis (2-ethylhexyl) phthalate, as described above.

(3) In the case of using polypropylene fibers A bundle of 100 g of polypropylene fibers having a fiber diameter of 10 μm and a length of 200 mm is used as an adsorbent to form a hydrophobic organic matter collecting unit 15. While this is immersed in the etching tank 11, the silicon substrate 100 that is slightly contaminated with bis (2-ethylhexyl) phthalate is etched. Etching is performed by fixing the bundle of polypropylene to the side surface at the bottom of the etching tank 11 so as not to come into contact with the silicon substrate 100 being etched. When etching is performed without adding polypropylene fiber, bis (2-ethylhexyl) phthalate in the etching solution 13 rises to 32 ppm, but in the case where polypropylene fiber is put, the rise remains to 0.9 ppm.

  As described above, in the first embodiment, in the etching apparatus that forms the texture structure on the silicon substrate 100 for solar cells, the hydrophobic organic substance collecting unit that removes the hydrophobic organic substance that adversely affects the uniform formation of the texture structure. 15 is provided, the hydrophobic organic substance from the etching solution 13 can be reduced to a predetermined concentration or less. As a result, the texture structure can be formed uniformly on the silicon substrate 100.

Embodiment 2. FIG.
FIG. 3 is a diagram schematically showing a schematic configuration of an etching apparatus according to Embodiment 2 of the present invention. This etching apparatus has a configuration in which an etching tank 11 that stores an etching solution 13 and two hydrophobic organic substance removal tanks 21a and 21b are connected by circulation pipes 14a to 14f. In this example, the case where the etching tank 11 and the two hydrophobic organic substance removal tanks 21a and 21b are connected in series is shown.

  A wafer cassette 12 that holds a silicon substrate 100 to be etched is immersed in the etching tank 11. Here, a plurality of silicon substrates 100 are held in the wafer cassette 12, and texture etching is performed simultaneously.

  One end of the circulation pipe 14a is connected to the etching tank 11, and the other end branches to the circulation pipes 14b and 14c. The circulation pipe 14c is connected to the hydrophobic organic substance removal tank 21a through the valve 31b. A pump 16a for circulating the etching solution 13 is provided on the circulation pipe 14a.

  One end of the circulation pipe 14d is connected to the hydrophobic organic substance removal tank 21a, and the other end is connected to the hydrophobic organic substance removal tank 21b. The circulation pipe 14d is provided with a valve 31c and a pump 16c. One end of the circulation pipe 14e is connected to the hydrophobic organic matter removal tank 21b, and the other end joins the circulation pipe 14b via the valve 31d and is connected to the circulation pipe 14f. The circulation pipe 14 f is provided with a pump 16 b and one end thereof is connected to the etching tank 11. The circulation pipe 14b is provided so as to connect between the circulation pipe 14a and the circulation pipe 14f, and is provided with a valve 31a. The plurality of valves 31 a to 31 d are appropriately opened and closed according to the circulation and transport operation of the etching solution 13. The circulation pipe 14b is used when the etching solution 13 is circulated without passing through the hydrophobic organic substance removal tanks 21a and 21b.

  The hydrophobic organic substance removing tank 21a is a septic tank for the etching liquid 13 for removing the hydrophobic organic substance eluted in the etching liquid 13 obtained by subjecting the silicon substrate 100 to the texture etching process a predetermined number of times (for example, once or a plurality of times) in the etching tank 11. It is.

  The hydrophobic organic substance removing tank 21a is provided with a circulation pipe 22a, and a pump 24a used for circulation of the etching solution 13 is provided on the circulation pipe 22a. The etching solution 13 can be circulated in the direction of the arrow in the figure by the pump 24a. In addition, the circulation pipe 22a is provided with a hydrophobic organic matter collecting part 23a for collecting a hydrophobic organic matter. By circulating the etching solution 13 in the circulation pipe 22a by the pump 24a, the hydrophobic organic matter eluted in the etching solution 13 is collected by the hydrophobic organic matter collecting unit 23a provided in the circulation pipe 22a and removed from the etching solution 13. Can do.

  The hydrophobic organic substance removing tank 21b removes the hydrophobic organic substance from the etching liquid 13 from which the hydrophobic organic substance has been sufficiently removed by the hydrophobic organic substance removing tank 21a, and further reduces the hydrophobic organic substance concentration in the etching liquid 13.

  The hydrophobic organic matter removing tank 21b is provided with a circulation pipe 22b, and a pump 24b used for circulation of the etching solution 13 is provided on the circulation pipe 22b. The etching solution 13 can be circulated in the direction of the arrow in FIG. Further, the circulation pipe 22b is provided with a hydrophobic organic matter collecting part 23b for collecting hydrophobic organic matter. By circulating the etching liquid 13 in the circulation pipe 22b by the pump 24b, the hydrophobic organic substance is further collected by the hydrophobic organic substance collecting part 23b, and the concentration of the hydrophobic organic substance contained in the etching liquid 13 is reduced. Thus, the etchant 13 having a sufficiently reduced hydrophobic organic substance concentration is used again in the etching tank 11 as the etchant 13 for the silicon substrate 100, and the hydrophobic organic substance removal tank 21 b is a chemical solution for the etching tank 11. It also serves as a standby tank for chemicals for supply.

  An etching method in the etching apparatus having such a configuration will be described. After the etching bath 11 is filled with the etching solution 13, the wafer cassette 12 holding the silicon substrate 100 is immersed in the etching bath 11 for a predetermined time. Thereafter, the wafer cassette 12 is pulled up. After such processing is performed a predetermined number of times, for example, the valves 31a, 31c, and 31d are closed, the valve 31b is opened, the pump 16a is operated, and the etching solution 13 is moved to the hydrophobic organic matter removing tank 21a. After the movement, the valve 31b is closed.

  In the hydrophobic organic matter removing tank 21a, the pump 24a is operated to guide a part of the etching solution 13 to the circulation pipe 22a and to pass through the hydrophobic organic matter collecting part 23a. As a result, the hydrophobic organic substance in the etching solution 13 is removed and returned to the hydrophobic organic substance removing tank 21a again. By circulating the etching solution 13 in this way, the hydrophobic organic substances eluted in the etching solution 13 are removed.

  In the hydrophobic organic matter removing tank 21a, for example, after the concentration of the hydrophobic organic substance becomes a predetermined value or less, the valves 31a, 31b, 31d are closed, the valve 31c is opened, and the pump 16c is operated to operate the hydrophobic organic substance removing tank. The etching solution 13 in 21a is moved to the hydrophobic organic substance removal tank 21b. After the movement, the valve 31c is closed.

  In the hydrophobic organic matter removing tank 21b, the pump 24b is operated to guide a part of the etching solution 13 to the circulation pipe 22b and pass through the hydrophobic organic matter collecting unit 23b. As a result, the hydrophobic organic substance in the etching solution 13 is removed and returned to the hydrophobic organic substance removing tank 21b again. By circulating the etching solution 13 in this way, the hydrophobic organic matter in the etching solution 13 is further collected, and the concentration of the hydrophobic organic matter contained in the etching solution 13 is reduced. The etching solution 13 having a sufficiently reduced hydrophobic organic substance concentration is used again in the etching tank 11 as the etching solution 13 for the silicon substrate 100.

  In the apparatus shown in FIG. 3, for example, when the etching process is performed in the etching tank 11, the hydrophobic organic substance removal process from the etching solution 13 is performed in the hydrophobic organic substance removal tanks 21a and 21b. Further, after the etching solution 13 is moved from the etching tank 11 to the hydrophobic organic substance removing tank 21a by the pump 16a, the valves 31a to 31d are switched as appropriate, and the hydrophobic organic substance removing tank 21b is pumped to the etching tank 11 by the pump 16b. It is possible to move the etching solution 13 from which the organic material has been removed to continue the next etching process.

  In addition, when newly creating the etching solution 13 from the chemical solution or pure water, the chemical solution and pure water may be mixed in the etching tank 11, but as described above, the chemical solution and pure water also contain a hydrophobic organic substance. Therefore, it is preferable to mix the new etching solution 13 in the hydrophobic organic substance removal tank 21a or the hydrophobic organic substance removal tank 21b in order to remove the hydrophobic organic substance mixed in the chemical solution or pure water. Moreover, although the case where there were two hydrophobic organic substance removal tanks here was shown, you may use three or more hydrophobic organic substance removal tanks. Further, the form and material of the adsorbent and the adsorbent regeneration method can be the same as those in the first embodiment and the method.

  In the second embodiment, the hydrophobic organic substance contained in the etching liquid 13 is removed from the etching liquid 13 by being adsorbed by the hydrophobic organic substance collecting units 23a and 23b of the hydrophobic organic substance removing tanks 21a and 21b. In-plane non-uniformity of the texture caused by the organic material can be prevented.

  Moreover, since the lifetime of the etching solution 13 is extended, the replacement frequency of the etching solution 13 can be reduced, the amount of the etching solution 13 used can be reduced, and the chemical solution cost and the manufacturing cost can be reduced. Moreover, the fall of the manufacturing efficiency of a solar cell by the loss of the replacement | exchange time of the etching liquid 13 can also be avoided.

Embodiment 3 FIG.
A solar cell can be manufactured using the silicon substrate etched by the etching apparatus of Embodiments 1 and 2.

  FIG. 4 is a cross-sectional view schematically showing the structure of the solar battery cell. In this solar cell, a p-type inversion layer 112 is formed on the surface (light-receiving surface) of the n-type single crystal silicon substrate 111 where the texture structure is formed, and the n-type single crystal silicon substrate 111 and the inversion layer 112 are formed. A photoelectric conversion layer is formed. Further, an antireflection film 113 is formed on the inversion layer 112, and a light receiving surface side electrode 114 having a predetermined shape is formed so as to penetrate the antireflection film 113 at a predetermined position on the light receiving surface. On the other hand, n-type impurities that can prevent recombination of minority carriers generated by light irradiation in the n-type single crystal silicon substrate 111 are diffused on the back surface of the n-type single crystal silicon substrate 111 facing the light receiving surface. A BSF (Back Surface Field) layer 115 is formed, and a back-side electrode 116 is formed on the BSF layer 115. Note that the BSF layer 115 is provided as necessary.

  In such a solar battery cell, the p-type inversion layer 112 is formed on the light-receiving surface on which the texture structure of the n-type single crystal silicon substrate 111 formed by the etching process of the first and second embodiments is performed. Then, an antireflection film 113 is formed on the inversion layer 112, and an n-type BSF layer is formed on the back surface of the n-type single crystal silicon substrate 111. Then, the light receiving surface side electrode 114 is formed on the antireflection film 113, and the back surface side electrode 116 is formed on the back surface of the n-type single crystal silicon substrate 111. Thus, a solar battery cell can be formed. Also, by arranging a plurality of solar cells formed in this way and electrically connecting adjacent solar cells in series or in parallel, it has a good light confinement effect and excellent photoelectric conversion efficiency A solar cell module can be realized.

  In this example, a single crystal silicon substrate is used as the substrate. However, the present invention is not limited to this, and a polycrystalline silicon substrate may be used. Further, although the conductivity type of the substrate is n-type, it may be p-type. In that case, the conductivity type of the inversion layer 112 is n-type, and the conductivity type of the BSF layer 115 is p-type.

  In the conventional etching apparatus, the amount of hydrophobic organic substances eluted from the raw material of the etchant 13, pure water, silicon substrate, wafer cassette, air, contamination of apparatus constituent materials, etc. increases, resulting in poor texture formation on the texture substrate surface. As a result, the production yield of the solar battery cells was reduced. On the other hand, since the solar cell is manufactured by the method according to the third embodiment, the concentration of the hydrophobic organic substance in the etching solution 13 can be kept low in the texture etching step. Can be formed. As a result, the production yield of solar cells having high power generation efficiency can be increased.

  According to the third embodiment, the solar battery cell is formed using the silicon substrate etched using the etching solution 13 in which the concentration of the hydrophobic organic substance described in the first and second embodiments is set to a predetermined value or less. Therefore, it has the effect that manufacture of the photovoltaic cell of high power generation efficiency is realizable with a high yield.

DESCRIPTION OF SYMBOLS 11 Etching tank 12 Wafer cassette 13 Etching liquid 14, 14a-14f, 22a, 22b Circulation piping 15, 23a, 23b Hydrophobic organic substance collection part 16, 16a-16c, 24a, 24b Pump 21a, 21b Hydrophobic organic substance removal tank 31a- 31d Valve 100 Silicon substrate 111 Single crystal silicon substrate 112 Inversion layer 113 Antireflection film 114 Light receiving surface side electrode 115 BSF layer 116 Back surface side electrode

Claims (13)

An etching apparatus for immersing and etching a silicon substrate in an etching solution,
An etching tank for storing the etching solution and etching the silicon substrate;
A hydrophobic organic substance collecting unit for collecting the hydrophobic organic substance eluted in the etching solution;
An etching apparatus comprising:   The etching apparatus according to claim 1, wherein the hydrophobic organic substance collecting unit is immersed in the etching solution so as not to contact the silicon substrate in the etching tank. An etching apparatus for immersing and etching a silicon substrate in an etching solution,
An etching tank for storing the etching solution and etching the silicon substrate;
A hydrophobic organic substance removal tank having a hydrophobic organic substance collecting section for storing the etching liquid from the etching tank and removing the hydrophobic organic substance in the etching liquid;
Piping connecting between the etching tank and the hydrophobic organic matter removal tank;
A valve for switching the flow of the etching solution flowing through the pipe;
An etching apparatus comprising: When etching the silicon substrate, the valve is closed and the etching solution is retained in the etching tank,
After the etching of the silicon substrate is completed, the valve is opened to move the etching solution in the etching tank to the hydrophobic organic substance removing tank, and then the valve is closed and the etching liquid is used in the hydrophobic organic substance removing tank. The etching apparatus according to claim 3, wherein the hydrophobic organic substance is removed.   The etching apparatus according to claim 3, comprising a plurality of the hydrophobic organic substance removal tanks.   The etching apparatus according to claim 1, wherein the hydrophobic organic substance collecting unit contains a substance having a hydrophobic surface.   The substance having a hydrophobic surface is composed of one material or a combination of a plurality of materials selected from the group consisting of olefin resins, chlorinated resins, fluororesins, acrylic resins, and vinyl resins. The etching apparatus according to claim 6.   The etching apparatus according to claim 6, wherein the substance having a hydrophobic surface is a hydrophilic substance whose surface is modified to be hydrophobic.   9. The etching apparatus according to claim 8, wherein the hydrophilic substance whose surface is modified to be hydrophobic is made of at least one of cellulose and rayon or a combination of both. Forming a texture structure on the first surface of the silicon substrate of the first conductivity type with the etching apparatus according to claim 1;
Forming an inversion layer having a second conductivity type dopant on the first surface side of the silicon substrate;
Forming an antireflection film on the inversion layer;
Forming a light receiving surface side electrode on the first surface of the silicon substrate so as to penetrate the antireflection film;
Forming a back-side electrode on a second surface opposite to the first surface of the silicon substrate;
A method for producing a solar cell comprising: An etching step of immersing and etching a silicon substrate in an etching solution;
A hydrophobic organic substance collecting step of collecting the hydrophobic organic substance eluted in the etching solution by contacting with an adsorbent containing a substance having a hydrophobic surface;
An etching method comprising:   The etching method according to claim 11, wherein the etching step and the hydrophobic organic substance collecting step are performed simultaneously.   The etching method according to claim 11, wherein the hydrophobic organic substance collecting step is performed on the etching solution used in the etching step after the etching step.

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