JP2015142890A - Manufacturing method of solar cell substrate and manufacturing apparatus of solar cell substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a solar cell substrate capable of preventing the occurrence of a water mark in a washing process immediately after wet etching.SOLUTION: A manufacturing method of a solar cell substrate in which a treatment substrate having etching liquid remaining on the surface is immersed in washing liquid and is washed includes; a first washing process of immersing the treatment substrate having a surface on which the etching liquid remains, into pure water supplied to a first washing tank as the washing liquid and washing the etching liquid remaining on the surface of the treatment substrate while replacing at least a part of the washing liquid in the first washing tank continuously or intermittently with new pure water; and a second washing process of immersing the treatment substrate washed in the first washing process into pure water supplied to a second washing tank as the washing liquid and performing the washing. Therein, in the first washing process, electric conductivity of the washing liquid in the first washing tank is continuously measured and, based on the measured electric conductivity, it is judged whether the first washing process is completed or not.

Description

  The present invention relates to a solar cell substrate manufacturing method and a solar cell substrate manufacturing apparatus.

  In a photovoltaic power generation system that converts light energy of sunlight into electric energy, a pn junction is often provided on a polycrystalline silicon (Si) substrate, and electrons and holes generated by the light energy are transmitted from the front and back of the polycrystalline silicon substrate. Each of them (photoelectromotive force) is taken as its principle. The manufacturing method of the photovoltaic cell used for such a photovoltaic power generation system will be described.

  Usually, the first stage of the formation of the solar cell is a step of performing an alkaline wet etching process called a texture process on the surface of a square p-type silicon substrate for a solar battery. Then, an n-type impurity diffusion layer is formed on the surface of the p-type silicon substrate on which the texture is formed by texture treatment, for example, by diffusing (thermally diffusing) phosphorus (P), for example, and inverting the conductivity type. .

Usually, phosphorus oxychloride (POCl ₃ ) is often used as a phosphorus diffusion source. In general, the n-type impurity diffusion layer is formed on the entire surface of the p-type silicon substrate. The sheet resistance of the n-type impurity diffusion layer is, for example, about several tens of Ω / □, and the depth is, for example, about 0.3 μm to 0.5 μm.

  Subsequently, after the n-type impurity diffusion layer formed on one side of the p-type silicon substrate is protected with a resist, an etching process is performed so that the n-type impurity diffusion layer is left only on one main surface of the p-type silicon substrate. The residual resist after the treatment is removed using an organic solvent or the like.

  Next, a silicon nitride film as an insulating film (antireflection film) is formed on the n-type impurity diffusion layer with a thickness of about 700 to 900 by plasma CVD or the like. Next, aluminum paste is screen-printed on the back surface of the p-type silicon substrate (the surface on which the n-type impurity diffusion layer is not formed) and dried. Usually, a silver paste is printed over a part or opening on the aluminum paste surface, and the wiring is soldered thereon. On the silicon nitride film, a silver paste to be a front electrode is screen printed in the same manner as the back surface and dried.

Thereafter, the front and back surfaces of the p-type silicon substrate are simultaneously fired at 700 ° C. to 900 ° C. for several minutes to several tens of minutes in a near infrared lamp furnace. As a result, on the back side of the p-type silicon substrate, aluminum as an impurity diffuses from the aluminum paste into the p-type silicon substrate during firing, and a p ⁺ layer containing a high concentration impurity of aluminum is formed. This layer is generally called a BSF (Back Surface Field) layer and contributes to the improvement of the energy conversion efficiency of the solar cell. The solar cell substrate thus formed is generally called a solar cell (see, for example, Patent Document 1).

  In the so-called diffusion step in which phosphorus diffusion is performed by sublimation of phosphorus oxychloride, adhesion to the surface of the p-type silicon substrate, and heating at about 800 ° C., which is performed to form the above-described n-type impurity diffusion layer, A layer mainly composed of phosphorus, silicon, and oxygen is formed on the surface of a p-type silicon substrate (including an n-type impurity diffusion layer). For this reason, the process (phosphorus glass etching process) of carrying out the etching removal of this phosphorus glass layer with a hydrofluoric acid is required. In the phosphor glass etching step, the surface of the p-type silicon substrate (including the n-type impurity diffusion layer) is brought into a hydrogen-terminated state by hydrofluoric acid. For this reason, the drainage in the water washing process performed after the phosphorous glass etching process in which the hydrofluoric acid remaining on the surface of the p-type silicon substrate (including the n-type impurity diffusion layer) is washed is good, and the p-type silicon substrate (n-type impurity diffusion) Usually, no watermark is generated on the surface of the substrate (including the layer). A watermark is a stain formed on the surface of a p-type silicon substrate (including an n-type impurity diffusion layer) made of silicon oxide.

JP 2004-207493 A

  However, a stain called a watermark may be generated in the washing process. The cause of the occurrence of the watermark is not completely elucidated, but if the watermark is generated in the initial stage of the water washing process performed after the phosphor glass etching process, the silicon oxide does not dissolve in the subsequent process. The watermark cannot be removed. That is, when the p-type silicon substrate is transported from the hydrofluoric acid etching tank in which the phosphorus glass etching process has been performed to the first water-washing tank and the first water-washing process is performed, the p-type silicon substrate from the first water-washing tank is performed. If a watermark is formed during the pulling-up stage, the watermark cannot be removed.

  The appearance on the light receiving surface side of the solar battery cell is generally blue or black due to the effect of the silicon nitride film, and the reflectance of visible light is desirably about 10% or less and uniform. However, once a silicon oxide film as a watermark is formed on a p-type silicon substrate (including an n-type impurity diffusion layer), the light reflectance increases in the region where the silicon oxide film is formed, and the white color is increased. Because of discoloration, it is difficult to ship as it is from the viewpoint of characteristics and appearance.

  On the other hand, even when the generation of such a watermark causes discoloration of the appearance of the solar battery cell, the surface of the p-type silicon substrate (including the n-type impurity diffusion layer) after the phosphor glass etching process is not discolored. First, it is determined whether or not the discoloration region is generated for the first time after the formation of the silicon nitride film.

  This invention is made in view of the above, Comprising: Obtaining the manufacturing method of a solar cell substrate which can suppress and prevent generation | occurrence | production of the watermark in the water washing process immediately after wet etching, and the manufacturing apparatus of a solar cell substrate Objective.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a solar cell substrate according to the present invention is a method for manufacturing a solar cell substrate in which a processing substrate having an etching solution remaining on the surface is immersed in a cleaning solution and cleaned. The processing substrate having the etching solution remaining on the surface is immersed in pure water supplied to the first water washing tank as a cleaning liquid, and at least a part of the cleaning liquid in the first water washing tank is continuously or intermittently provided. A first water washing step for washing the etching solution remaining on the surface of the processing substrate while replacing with fresh pure water, and supplying the processing substrate washed in the first water washing step to the second water washing tank as a washing solution A second water washing step of immersing and washing in the purified water, wherein in the first water washing step, the conductivity of the cleaning liquid in the first water washing tank during the cleaning of the processing substrate is continuously measured, Measured conductivity And wherein the, to determine whether or not to end the first washing step based on.

  According to the present invention, it is possible to suppress and prevent the generation of watermarks in the water washing process immediately after wet etching.

FIG. 1 is a cross-sectional view of a main part of a solar battery cell using a solar battery substrate formed by applying a method for manufacturing a solar battery substrate according to an embodiment of the present invention. FIG. 2 is a top view of a solar battery cell using the solar battery substrate formed by applying the solar battery substrate manufacturing method according to the embodiment of the present invention. FIG. 3 is an image showing a result of observing whether or not a watermark is generated due to the hydrofluoric acid concentration. FIG. 4 is a characteristic diagram showing the relationship between the hydrofluoric acid concentration and the conductivity in the hydrofluoric acid aqueous solution in the first water washing tank after the first water washing step experiment has been performed a plurality of times. FIG. 5 is a flowchart for explaining the flow of the method for manufacturing the solar cell substrate according to the embodiment of the present invention. FIG. 6 is a schematic diagram showing a schematic configuration of a solar cell substrate manufacturing apparatus that implements the solar cell substrate manufacturing method according to the embodiment of the present invention.

  EMBODIMENT OF THE INVENTION Below, embodiment of the manufacturing method of the solar cell substrate concerning this invention and the manufacturing apparatus of a solar cell substrate is described in detail based on drawing. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.

Embodiment.
The present embodiment relates to the manufacture of a solar cell substrate, and particularly relates to the suppression / prevention of the generation of watermarks resulting from the cleaning process after the diffusion process.

  First, the solar cell substrate (solar cell) produced using the manufacturing method of the solar cell substrate concerning this Embodiment is demonstrated. 1 and 2 are views showing a solar battery cell formed by applying the method for manufacturing a solar battery substrate according to the present embodiment. FIG. 1 is a cross-sectional view of the main part of the solar battery cell, and FIG. It is a top view of a photovoltaic cell. 1 and 2 are formed on, for example, a silicon substrate 11 having an n-type impurity diffusion layer 11b on the surface layer of a p-type silicon substrate 11a and a surface (front surface) of the silicon substrate 11 on the light-receiving surface side. The antireflection film 12, the light receiving surface side electrode 13 formed on the light receiving surface side surface (front surface) of the silicon substrate 11, and the back surface electrode formed on the surface (back surface) opposite to the light receiving surface of the silicon substrate 11. 14. The light receiving surface side electrode 13 is formed to be surrounded by the antireflection film 12 in the surface direction of the silicon substrate 11.

  The light receiving surface side electrode 13 includes a grid electrode 13a and a bus electrode 13b, and FIG. 1 shows a cross-sectional view in a cross section perpendicular to the longitudinal direction of the grid electrode 13a. And the solar cell is comprised for the silicon substrate 11 using the silicon substrate by which the water washing process was implemented using the manufacturing method of the solar cell substrate concerning this Embodiment.

  Below, the process for manufacturing the photovoltaic cell shown in FIG.1 and FIG.2 is demonstrated. In addition, since the process demonstrated here is the same as the manufacturing process of the general photovoltaic cell using a silicon substrate, it does not show in particular in figure.

  First, the p-type silicon substrate 11a is cut out from the silicon ingot by slicing. The p-type silicon substrate 11a may be a single crystal silicon substrate or a polycrystalline silicon substrate. On the surface of the p-type silicon substrate 11a cut out from the silicon ingot by slicing, organic impurities and metal impurities, which are contaminants made of chips, abrasives, etc. generated by cutting the wire during slicing, are attached. . For this reason, the p-type silicon substrate 11a cut out from the silicon ingot is subjected to a cleaning process such as a water cleaning process. However, these contaminants remain on the surface of the cleaned p-type silicon substrate 11a without being removed. Therefore, it is necessary to clean these contaminants attached to the surface of the p-type silicon substrate 11a.

  Further, the processing strain due to the slice called a damage layer is generated on the surface layer of the sliced substrate up to a depth of about 5 μm. If this damaged layer remains in the solar cell, the damaged layer promotes recombination of electrons, leading to deterioration of the characteristics of the solar cell. For this reason, it is necessary to remove the damaged layer.

  In addition, a high-temperature chemical solution (wet etching solution) obtained by adding an organic substance such as IPA as an additive to an alkaline aqueous solution was used on the surface of the p-type silicon substrate 11a so that the solar cell can absorb more sunlight. By anisotropic etching, for example, a texture structure composed of irregularities having quadrangular pyramidal convex portions surrounded by the (111) plane of silicon is formed.

  Therefore, also in the present embodiment, cleaning for removing these contaminants adhering to the surface of the p-type silicon substrate 11a described above, removal of the damaged layer, and formation of the texture structure are performed.

Next, the p-type silicon substrate 11a having a texture formed on the surface is put into a thermal diffusion furnace and heated in the presence of phosphorus oxychloride (POCl ₃ ) vapor to form a phosphorus glass layer on the surface of the p-type silicon substrate 11a. By forming, phosphorus is diffused into the p-type silicon substrate 11a. As a result, the n-type impurity diffusion layer 11b is formed on the entire surface of the p-type silicon substrate 11a, and a pn junction is formed. The surface of the n-type impurity diffusion layer 11b is in a state in which a phosphorus glass layer is formed. The sheet resistance of the n-type impurity diffusion layer 11b is, for example, about several tens of Ω / □, and the depth thereof is, for example, about 0.3 μm to 0.5 μm.

  Here, a phosphorus glass layer is formed on the surface of the n-type impurity diffusion layer 11b immediately after the formation of the n-type impurity diffusion layer 11b. For this reason, the phosphorus glass etching process of removing this phosphorus glass layer by wet etching using etching liquid, such as a hydrofluoric acid, is performed. In the present embodiment, the phosphorus glass etching step is performed by immersing the p-type silicon substrate 11a on which the n-type impurity diffusion layer 11b is formed in a hydrofluoric acid etching tank in which hydrofluoric acid is stored. The concentration of hydrofluoric acid is not particularly limited, and may be set as appropriate according to various conditions such as conditions for forming the n-type impurity diffusion layer 11b. Further, the immersion time of the p-type silicon substrate 11a in the hydrofluoric acid etching tank may be appropriately set according to various conditions such as the formation conditions of the n-type impurity diffusion layer 11b and the concentration of hydrofluoric acid.

  After the phosphor glass etching step, a water washing step for washing the hydrofluoric acid remaining on the surface of the p-type silicon substrate 11a (the surface of the n-type impurity diffusion layer 11b) is performed, and then a drying step is performed. The water washing process will be described later.

  Subsequently, after protecting the n-type impurity diffusion layer formed on one side of the p-type silicon substrate 11a with a resist, etching is performed so as to leave the n-type impurity diffusion layer only on one main surface of the p-type silicon substrate 11a. . Thereby, the silicon substrate 11 is formed. In the p-type silicon substrate 11a, the side where the n-type impurity diffusion layer is left is the light-receiving surface side. The residual resist after the treatment is removed using an organic solvent or the like.

  Next, a silicon nitride film (SiN film) is formed as an antireflection film 12 made of an insulating film on the n-type impurity diffusion layer 11b by a plasma CVD method or the like with a film thickness of about 700 to 900 mm, for example. As the antireflection film 12, two or more films having different refractive indexes may be laminated. The antireflection film 12 may be formed by a different film forming method such as a sputtering method.

  Next, the silver paste mixed with silver is screen-printed in a comb shape on the light receiving surface of the silicon substrate 11 and dried, and the aluminum paste mixed with aluminum is screen-printed on the entire back surface of the silicon substrate 11 and dried. Usually, silver paste is overlaid and printed on a part or opening on the aluminum paste surface, but the description is omitted here.

  Thereafter, the printed paste is baked to form the light receiving surface side electrode 13 and the back surface electrode 14. As described above, the solar battery cell shown in FIGS. 1 and 2 is manufactured.

On the back side of the silicon substrate 11, aluminum as an impurity diffuses from the aluminum paste into the p-type silicon substrate during firing, and a p ⁺ layer containing a high concentration impurity of aluminum is formed. Is omitted. This layer is generally called a BSF (Back Surface Field) layer.

  Next, the water washing process performed after the phosphorus glass etching process will be described. In the water washing step, the treatment for washing the hydrofluoric acid remaining on the surface of the p-type silicon substrate (hereinafter referred to as the processing substrate W) after the phosphorus glass etching step in which the n-type impurity diffusion layer 11b is formed on the entire surface is performed multiple times. Done. That is, after the phosphorus glass etching step, the first water washing step, the second water washing step,. This embodiment is characterized by the first water washing step among the plurality of water washing treatments.

  In the phosphorus glass etching process in the manufacturing process as described above, the surface of the processing substrate W after the phosphorus glass etching process is brought into a hydrogen-terminated state by hydrofluoric acid. For this reason, in general, water drainage in the water washing step of washing the hydrofluoric acid remaining on the surface of the processing substrate W after the phosphor glass etching step is good, and no watermark is usually generated on the surface of the processing substrate W. It is. The watermark is a stain made of silicon oxide and formed on the surface of the processing substrate W.

  However, a stain called a watermark may be generated in the water washing process. The cause of watermarks has not been fully elucidated. If the watermark is generated in the initial stage of the water washing process performed after the phosphorus glass etching process, the silicon oxide is not dissolved in the subsequent process, and thus the watermark cannot be removed. In the rinsing process, a plurality of rinsing processes are performed, but when the processing substrate W is transported from the hydrofluoric acid etching tank in which the phosphorus glass etching process has been performed to the first rinsing tank and the first rinsing process is performed, If a watermark is formed at the stage of pulling up the processing substrate W from the first washing tank, the watermark cannot be removed. Therefore, it is required to suppress and prevent the generation of the watermark in the stage of pulling up the processing substrate W from the first water washing tank in the first water washing step.

  In the first water washing step, which is the next step of the phosphorus glass etching step, the processing substrate W in a state where the hydrofluoric acid in the hydrofluoric acid etching tank remains on the surface is immersed in pure water stored in the first water washing tank as a cleaning liquid. The For this reason, hydrofluoric acid dissolves in the pure water of the first washing tank from the surface of the immersed processing substrate W, and the pure water changes to a hydrofluoric acid aqueous solution having a relatively high concentration when the processing substrate W is immersed. In addition, in order to distinguish from the hydrofluoric acid stored in the hydrofluoric acid etching tank and the hydrofluoric acid remaining on the surface of the processing substrate W, here, the hydrofluoric acid remaining on the surface of the processing substrate W is pure water in the first washing tank. The hydrofluoric acid dissolved in the inside is called a hydrofluoric acid aqueous solution.

  Thereafter, although depending on the method of supplying pure water, the concentration of hydrofluoric acid in the hydrofluoric acid aqueous solution in the first washing tank is gradually reduced by further supplying pure water. Therefore, the hydrofluoric acid concentration of the hydrofluoric acid aqueous solution is changing (decreasing) every moment until the completion of the first water washing step. That is, the cleaning liquid in the first washing tank changes from a pure water state to a relatively high concentration hydrofluoric acid aqueous solution when the processing substrate W is immersed, and then gradually changes to a hydrofluoric acid aqueous solution having a low concentration. Go.

  The inventors diligently studied when the substrate is pulled from such a hydrofluoric acid aqueous solution, and when the liquid property of the hydrofluoric acid aqueous solution is easy to form a watermark. As a result, when the hydrofluoric acid aqueous solution containing fluorine (fluorine concentration conversion) in the range of 25 to 50 ppm as the hydrofluoric acid concentration is present as water droplets on the surface of the processing substrate W terminated with hydrogen, I found that it was easy to mark. The description of ppm in the following represents the fluorine concentration conversion.

  FIG. 3 is an image showing a result of observing whether or not a watermark is generated due to the hydrofluoric acid concentration. In FIG. 3, after a plurality of hydrofluoric acid aqueous solutions having different concentrations are dropped and dried on the surface of the processing substrate W sufficiently hydrogen-terminated with 10% hydrofluoric acid, a silicon nitride film is formed on the surface of the processing substrate W. And the result of having observed the presence or absence of the production | generation of a watermark is shown. The concentration of the hydrofluoric acid aqueous solution was 7 conditions of 0 ppm, 10 ppm, 25 ppm, 50 ppm, 100 ppm, 250 ppm, and 500 ppm as the hydrofluoric acid concentration. Further, in FIG. 3, what appears to be white and substantially circular is a watermark.

  As can be seen from FIG. 3, in the case of a hydrofluoric acid aqueous solution having a hydrofluoric acid concentration of 100 ppm or more, no watermark is generated, and a water mark is easily generated in a hydrofluoric acid aqueous solution having a hydrofluoric acid concentration in the range of 50 ppm or less, particularly 25 ppm. It has been clarified that a watermark is easily generated in a hydrofluoric acid aqueous solution having a hydrofluoric acid concentration in the range of ˜50 ppm.

  The water mark is fundamentally generated by dissolution and accumulation as a silicate caused by oxidation and hydration of the silicon surface by oxygen dissolved in the water drop at the peripheral edge of the water drop. That is, in the first water washing step, when the water droplets adhering to the surface of the processing substrate W are dried at the stage of lifting the processing substrate W from the first water washing tank, the silicon oxide accumulates at the peripheral edge of the water droplets. A watermark is formed.

  Such a watermark basically occurs even when pure water is present as water droplets on the surface of the processing substrate W terminated with hydrogen. However, in a dilute hydrofluoric acid aqueous solution having a hydrofluoric acid concentration of 25 ppm to 50 ppm, it is considered that the dissolution of the silicon oxide film generated by the oxidation of the silicon surface further proceeds. In addition, when the concentration of the hydrofluoric acid aqueous solution is higher, naturally, even if a silicon oxide film is formed at the peripheral edge of the water droplet of the hydrofluoric acid aqueous solution, it is immediately dissolved in the water droplet by hydrofluoric acid, Since no silicon accumulation occurs, no watermark is considered to occur.

  In general, when the processing substrate W is washed with, for example, overflow rinsing, pure water is supplied at a predetermined pure water supply amount to a first water washing tank in which a carrier containing the processing substrate W is disposed. The carrier is pulled up after a lapse of a predetermined time while overflowing from the washing tank. Then, after elapse of a predetermined time, for example, 30 seconds later, the carrier is transported and installed in the second washing tank which is the next stage. In this case, it is held on the surface of the processing substrate W and is brought from the hydrofluoric acid etching tank into the pure water of the first water washing tank, and the hydrofluoric acid is sequentially diluted with pure water. For this reason, the concentration of hydrofluoric acid in the cleaning liquid (hydrofluoric acid aqueous solution) in the first water rinsing tank gradually decreases.

  Usually, the maximum hydrofluoric acid concentration at the time when the carrier containing the processing substrate W is installed in the first washing tank from the hydrofluoric acid etching tank often exceeds 1000 ppm. However, the amount of hydrofluoric acid held on the processing substrate W varies greatly, and the concentration of hydrofluoric acid brought into the first washing tank varies greatly. For this reason, although the concentration of hydrofluoric acid in the cleaning liquid (hydrofluoric acid aqueous solution) in the first water washing tank decreases due to the overflow of the cleaning liquid (hydrofluoric acid aqueous solution), the immersion is performed for a predetermined time, for example, about 3 minutes. The hydrofluoric acid concentration varies from about 10 ppm to about 500 ppm. Accordingly, it is difficult to predict the hydrofluoric acid concentration of the cleaning liquid in the first water rinsing tank only by the passage of a predetermined time, that is, only the immersion time of the processing substrate W.

  Inventors etc. earnestly researched about the measurement of the fluorine concentration of the washing | cleaning liquid (hydrofluoric acid aqueous solution) of the 1st washing tank after the actual 1st washing process was performed. As a result, it was found that the change in the fluorine concentration of the hydrofluoric acid aqueous solution can be monitored every time, and that the measurement of the conductivity of the hydrofluoric acid aqueous solution is appropriate as a measurement method that has a unique correspondence with the hydrofluoric acid concentration. That is, it has been found that measuring the conductivity of a hydrofluoric acid aqueous solution is appropriate as a means for measuring that the hydrofluoric acid aqueous solution is in a specific hydrofluoric acid concentration range.

  FIG. 4 is a characteristic diagram showing the relationship between the hydrofluoric acid concentration and the conductivity in the cleaning liquid (hydrofluoric acid aqueous solution) in the first water washing tank after the first water washing step experiment was actually performed a plurality of times. The experiment of the first water washing step was performed at different dates and times on the first implementation date, the second implementation date, the third implementation date, and the fourth implementation date. Moreover, on each implementation day, the experiment of the 1st water washing process was implemented in multiple times. The hydrofluoric acid concentration of the hydrofluoric acid aqueous solution was analyzed by ion chromatography. The conductivity of the hydrofluoric acid aqueous solution was measured with a conductivity meter. Moreover, since a new pure water is used for every 1st water washing process, the influence of the hydrofluoric acid aqueous solution of the 1st water washing process implemented at the other date does not arise. FIG. 4 also shows the results of measuring the conductivity of dilute hydrofluoric acid having different concentrations.

  From FIG. 4, it became clear that the hydrofluoric acid concentration can be uniquely determined by measuring the conductivity. And it became clear that 25 ppm to 50 ppm, which is the concentration of hydrofluoric acid that easily generates the watermark, has a relationship corresponding to about 25 mS / m to 45 mS / m in terms of conductivity. From this, the conductivity of the hydrofluoric acid aqueous solution in the first washing tank is in a range other than 35 ± 10 mS / m, and preferably the conductivity is 60 mS / m (fluorine with a margin for the higher conductivity). When the concentration is in the range of 100 ppm or more in terms of concentration, it is considered that it is difficult to generate a watermark when it is lifted from the first washing tank.

  In addition, hydrofluoric acid from the pH meter using a method of directly measuring the fluorine concentration of the hydrofluoric acid aqueous solution in the first washing tank by the ion chromatography method and the relationship between the pH calculated from the dissociation constant of hydrofluoric acid and the hydrofluoric acid concentration. A method for estimating the concentration is also conceivable. However, the ion chromatograph method is an off-line analysis means, and is not suitable for measuring liquid properties that change every moment. In addition, as a result of intensive research, the pH is changed by anions such as phosphate ions dissolved in the first washing tank in addition to the hydrofluoric acid concentration, so it is still unsuitable for unambiguously defining the hydrofluoric acid concentration. is there.

  Based on the above examination results, in the present embodiment, in order to form a solar cell substrate in which the generation of watermarks in the first water washing step is suppressed / prevented, the processing shown in FIG. 5 is performed as the first water washing step. . FIG. 5 is a flowchart for explaining the flow of the method for manufacturing the solar cell substrate according to the present embodiment. In this Embodiment, a 1st water washing process and a 2nd water washing process are implemented after the phosphorus glass etching process mentioned above as a water washing process.

  The 1st water washing process in the water washing process concerning this Embodiment can be implemented using the manufacturing apparatus of the solar cell board | substrate shown in FIG. FIG. 6 is a schematic diagram showing a schematic configuration of a solar cell substrate manufacturing apparatus that implements the solar cell substrate manufacturing method according to the present embodiment. The solar cell substrate manufacturing apparatus shown in FIG. 6 immerses the treated substrate W after the phosphor glass etching step in the pure water as the first water washing step to suppress / prevent the generation of watermarks, and thereby the surface of the treated substrate W It is a manufacturing apparatus of the solar cell substrate which can wash the hydrofluoric acid which remains in water.

  A standard washing scheme in the present embodiment will be described below. A 1st water washing process is implemented after a phosphorus glass etching process. This first water washing step is performed using, for example, a technique called overflow rinsing. First, the carrier 21 in which a plurality of the processing substrates W after the phosphor glass etching process are stored is transferred from the hydrofluoric acid etching tank (not shown) to the first water washing tank 31 by using the carrier lifting and transporting device 22 which is a transporting part. To be transported and installed. The carrier 21 may be held and fixed in the first washing tank 31 by, for example, a holding unit (not shown). The first rinsing tank 31 is disposed inside the outer rinsing tank 41. Here, batch processing for processing a plurality of processing substrates W at the same time has been described, but processing substrates W may be processed one by one.

  Next, a pure water supply valve 33 provided in a pure water supply pipe 32 as a pure water supply unit is opened, and pure water 37 as a cleaning liquid is supplied into the first water washing tank 31 through the pure water supply pipe 32. . One end of the pure water supply pipe 32 is disposed in the first washing tank 31, and the other end is connected to the pure water supply source 34. The pure water supply pipe 32 is disposed at a position that does not hinder the carrier 21 from being transported by the carrier lifting and transporting device 22. The pure water supply valve 33 is constituted by an electric valve, for example. In addition, the pure water 37 is supplied into the first flush tank 31 and the pure water 37 (hydrofluoric acid aqueous solution) in the first flush tank 31 is supplied to the lower part of the first flush tank 31 in the first flush tank drain pipe. Drain from 35. Drainage by the first flush tank drain pipe 35 is controlled by opening and closing a first flush tank drain valve 36 provided in the first flush tank drain pipe 35.

  Here, in order to overflow the pure water 37 (hydrofluoric acid aqueous solution) from the first flush tank 31, the supply amount of the pure water 37 to the first flush tank 31 is made larger than the amount of drainage from the first flush tank 31. The The pure water 37 (hydrofluoric acid aqueous solution) overflowed from the first water washing tank 31 flows out to the outer water washing tank 41 disposed so as to surround the outside of the first water washing tank 31. The drainage from the first flush tank drain pipe 35 may be stopped according to the amount of pure water 37 supplied to the first flush tank 31.

  An outer flush tank drain pipe 42 for draining pure water 37 (hydrofluoric acid aqueous solution) in the outer flush tank 41 is provided below the outer flush tank 41. The amount of water in the outer flush tank 41 is adjusted by controlling the drainage state from the outer flush tank drain pipe 42 by opening and closing the outer flush tank drain valve 43 provided in the outer flush tank drain pipe 42. The pure water 37 (hydrofluoric acid aqueous solution) stored in the tank is adjusted so as not to flow again into the first washing tank 31. The outer flush tank drain valve 43 is constituted by, for example, an electric valve.

  In this manner, the replacement of the hydrofluoric acid held on the surface of the processing substrate W by the pure water 37 (hydrofluoric acid aqueous solution) in the first water washing tank 31 is performed, and the water washing is performed. However, as described above, it is difficult to predict the hydrofluoric acid concentration of the cleaning liquid (hydrofluoric acid aqueous solution) in the first water rinsing tank 31 only after the elapse of a predetermined time, that is, only the immersion time of the processing substrate W.

  Therefore, in the present embodiment, the cleaning liquid (hydrofluoric acid aqueous solution) drained from the first water washing tank 31 connected to the first water washing tank drain pipe 35 connected to the lower part of the first water washing tank 31 is provided. A conductivity meter 51 which is a conductivity measuring unit for measuring conductivity is provided. Then, the carrier 21 in which the processing substrate W is stored is immersed in pure water 37 (hydrofluoric acid aqueous solution) so that the cleaning liquid (hydrofluoric acid aqueous solution) overflows from the first washing tank 31 and changes (decreases) every moment. The conductivity of the cleaning liquid (hydrofluoric acid aqueous solution) in the first water washing tank 31 is measured using the cleaning liquid (hydrofluoric acid aqueous solution) flowing through the first water washing tank drain pipe 35. The conductivity is measured by the conductivity meter 51 by opening and closing the first flush tank drain valve 36 provided in the first flush tank drain pipe 35 so as to be drained by the first flush tank drain pipe 35. This is done by measuring the electrical conductivity of the cleaning liquid (hydrofluoric acid aqueous solution).

  Then, the conductivity value of the hydrofluoric acid aqueous solution measured by the conductivity meter 51 is not less than 50 ppm in terms of hydrofluoric acid concentration, and the hydrofluoric acid on the surface of the processing substrate W as the first step of the water washing step is replaced with pure water. Is reduced to 60 mS / m (100 ppm in terms of hydrofluoric acid concentration), for example, when supply of pure water 37 to the first water washing tank 31 is stopped, and the first water washing tank is also achieved. Control for stopping the drainage of the cleaning liquid (hydrofluoric acid aqueous solution) 31 is performed by automatic control of the closing operation of the pure water supply valve 33 and the first water washing tank drain valve 36 which are electric valves, respectively.

  Automatic control of the pure water supply valve 33 and the first flush tank drain valve 36 is performed by a control unit 52 connected to the conductivity meter 51, the pure water supply valve 33, and the first flush tank drain valve 36, for example. The control unit 52 acquires the conductivity of the hydrofluoric acid aqueous solution in the first washing tank 31 that changes (decreases) every moment from the conductivity meter 51, and determines whether the acquired conductivity is greater than 60 mS / m. (Step S10).

  When the acquired electrical conductivity is larger than 60 mS / m (step S10, Yes), the controller 52 does not control the closing operation of the pure water supply valve 33 and the first flush tank drain valve 36, One water washing step, that is, the replacement of hydrofluoric acid on the surface of the processing substrate W by the supply of pure water with pure water is continued (step S20). And the control part 52 returns to step S10 and continues a process.

  When the obtained conductivity is not greater than 60 mS / m, that is, 60 mS / m or less (No in Step S10), the control unit 52 closes the pure water supply valve 33 and the first flush tank drain valve 36. The valve operation is controlled to stop the overflow and terminate the first water washing step, and start the movement of the carrier 21 to the second water washing tank as the next stage (step S30). Basically, the controller 52 preferably ends the first water washing step when the acquired conductivity reaches 60 mS / m, but the numerical value of 60 mS / m is not necessarily measured. For this reason, the control part 52 complete | finishes a 1st water washing process, when the electrical conductivity of 60 mS / m or less is acquired from the conductivity meter 51. FIG. The control part 52 transmits the valve closing command which closes a valve with respect to the pure water supply valve 33 and the 1st flush tank drain valve 36, when the electrical conductivity of 60 mS / m or less is acquired. In the pure water supply valve 33 and the first flush tank drain valve 36, an operation of closing the valves is performed in accordance with the valve closing command transmitted from the control unit 52.

  Moreover, the control part 52 transmits the completion | finish information of a 1st water-washing process with respect to the apparatus 22 for carrier pick-up conveyance. In the carrier lifting and transporting device 22, the lifting operation of the carrier 21 from the first water washing tank 31 is executed according to the end information of the first water washing process transmitted from the control unit 52. Thereby, when the electrical conductivity of the hydrofluoric acid aqueous solution in the first water washing tank 31 becomes 60 mS / m, or when it becomes 60 mS / m or less, the end of the first water washing step can be automatically controlled. The carrier pulling and conveying device 22 conveys the carrier 21 to the second washing tank after a predetermined time has elapsed. In the second washing tank, the processing substrate W is cleaned by, for example, overflow rinsing. In other words, in the second water washing step, the hydrofluoric acid on the surface of the processing substrate W on which the first water washing step has been performed is further replaced with pure water.

  In addition, the method of automatic control of the pure water supply valve 33 and the 1st flush tank drain valve 36 is not limited to this. For example, a control means capable of acquiring the conductivity from the conductivity meter 51 and automatically controlling the closing operation of the electric valve based on the conductivity is separately provided for the pure water supply valve 33 and the first flush tank drain valve 36. It may be provided. And you may transmit the completion | finish information of a 1st flush process from the control means by the side of the pure water supply valve 33 and the 1st flush tank drain valve 36. FIG.

  However, in the measurement of the conductivity of the hydrofluoric acid aqueous solution in the first washing tank 31 by the conductivity meter 51, there is a possibility that the electrode of the conductivity meter 51 may be damaged when the hydrofluoric acid concentration of the hydrofluoric acid aqueous solution is high. . For this reason, in actual measurement, for example, when the overflow of the hydrofluoric acid aqueous solution in the first water rinsing tank 31 is continued until, for example, about 2/3 of the predetermined time of the dipping process in the general first water rinsing process, the electric conduction is not performed. Measurement of the rate meter 51 is performed by opening a supply valve provided in the conductivity meter 51.

  The concentration of hydrofluoric acid used in the phosphor glass etching step, the amount of hydrofluoric acid held on the surface of the processing substrate W and brought into the pure water 37 of the first washing tank 31, and the processing substrate W stored in the carrier 21. Although depending on various conditions such as the number of sheets, in many cases, the concentration of the hydrofluoric acid aqueous solution in the first washing tank 31 is about 100 ppm to 200 ppm at this time. Therefore, it is necessary to set a predetermined time so that the concentration of the hydrofluoric acid aqueous solution at the start of measurement by the conductivity meter 51 does not fall below 100 ppm for automatic termination control of the first water washing step.

  At that time, since the hydrofluoric acid concentration of the water droplets held on the surface of the processing substrate W is 100 ppm, very fine water droplets are generated on the surface of the processing substrate W when pulled up from the first washing tank 31 and are short. Even if it dries in time, the watermark is hardly generated.

  In the present embodiment, by using a quantitative parameter called conductivity as a method for measuring the concentration of hydrofluoric acid, variation in the concentration of the hydrofluoric acid aqueous solution in the first water washing tank 31 at the end of the first water washing step is achieved. In addition to being able to suppress, the hydrofluoric acid concentration of the hydrofluoric acid aqueous solution at the time of pulling up the processing substrate W from the first water rinsing tank 31 is not reduced to about 10 ppm, and the concentration of the hydrofluoric acid aqueous solution at the end of the first water washing step is reduced. Can be set higher. By the latter effect, it becomes possible to prevent the surface state of the processing substrate W in the final rinsing step of the rinsing step performed a plurality of times from becoming more hydrophilic than necessary.

  Moreover, in the above, although the case where the 1st water washing process was implemented by overflow rinse was demonstrated, discharging | emitting the hydrofluoric acid aqueous solution hold | maintained in the 1st water washing tank 31 in a short time, and supplying a lot of pure water after that Even when a repeated washing process called quick dumpling is applied to the first washing process, the generation of watermarks can be suppressed / prevented using the measurement of conductivity as described above.

  Moreover, in said overflow rinse, supplying pure water continuously in the 1st washing tank 31, and replacing a part of pure water (fluid solution) in the 1st washing tank 31 with new pure water Although water washing is performed, pure water is intermittently supplied into the first water washing tank 31, and water is washed while replacing a part of the pure water (hydrous aqueous solution) in the first water washing tank 31 with new pure water. You may go. In addition, when the quick dump rinse is applied to the first water washing step, it is not always necessary to replace all of the pure water (water solution) in the first water washing tank 31 with new pure water at one time. You may replace at least one part of the pure water (fluid solution) in the 1st washing tank 31 with new pure water.

  Moreover, in the above, although the discrimination | determination reference | standard of the completion | finish of the 1st water washing process in the 1st water washing tank 31 was made into the time of the electrical conductivity measurement value of the fluorinated aqueous solution in the 1st water washing tank 31 reaching 60 mS / m, If the criterion for determining the end of the first water washing step is out of the range of 25 mS / m to 45 mS / m, preferably greater than 60 mS / m, the generation of watermarks can be greatly suppressed / prevented. Therefore, it is possible to employ a scheme in which the first water washing step is terminated when the measured conductivity value of the aqueous solution of the water in the first water washing tank 31 is within this range.

  Moreover, although the case where the 1st water washing process and the 2nd water washing process were implemented as the water washing process in the above was demonstrated after the 1st water washing process concerning this embodiment, not only the 2nd water washing process, The 3 water washing process, the 4th water washing process ..., and multiple water washing processes should just be implemented as needed.

  As described above, in the present embodiment, the conductivity of the cleaning liquid (hydrofluoric acid aqueous solution) in the first water washing tank 31 is measured by the conductivity meter 51 in the first water washing step performed after the phosphorus glass etching step. Then, when the measured conductivity is in a range where it is difficult to generate a watermark, the first water washing step is finished, and the processing substrate W is pulled up from the first water washing tank 31. The range of the conductivity at which it is difficult to generate a watermark is 25 mS / m to 45 mS / m (35 ± 10 mS / m) corresponding to a hydrofluoric acid concentration of 25 ppm to 50 ppm. Further, the conductivity is 60 mS / value as a value that allows the higher conductivity to have a sufficient margin and sufficiently replaces hydrofluoric acid on the surface of the processing substrate W as the first step of the water washing step with pure water. It is preferable to end the first washing step at the time of m (100 ppm in terms of hydrofluoric acid concentration).

  In such an embodiment, when the processing substrate W is pulled up from the first water rinsing tank 31, an effect that the generation of watermarks on the surface of the processing substrate W can be suppressed / prevented can be obtained. Thereby, the fall of the performance of the photovoltaic cell by the increase in the light reflectivity resulting from a watermark can be prevented, and the photovoltaic cell excellent in photoelectric conversion efficiency is obtained. Moreover, there is no discoloration caused by the watermark when irradiated with light, and a solar cell having a good appearance can be obtained.

  Therefore, according to the present embodiment, it is possible to prevent the occurrence of a watermark in the first water washing step immediately after the wet etching.

  As described above, the method for manufacturing a solar cell substrate according to the present invention is useful for preventing the generation of watermarks in the water washing step immediately after wet etching.

  11 silicon substrate, 11a p-type silicon substrate, 11b n-type impurity diffusion layer, 12 antireflection film, 13 light-receiving surface side electrode, 13a grid electrode, 13b bus electrode, 14 back electrode, 21 carrier, 22 carrier lifting and conveying device, 31 1st water washing tank, 32 Pure water supply pipe, 33 Pure water supply valve, 34 Pure water supply source, 35 1st water washing tank drain pipe, 36 1st water washing tank drain valve, 37 Pure water, 41 Outside water washing tank, 42 Outer flush tank drain pipe, 43 Outside flush tank drain valve, 51 conductivity meter, 52 control unit, W processing substrate.

Claims (10)

A method of manufacturing a solar cell substrate in which a processing substrate having an etching solution remaining on a surface is immersed in a cleaning solution and cleaned.
The processing substrate with the etching solution remaining on the surface is immersed in pure water supplied to the first washing tank as a washing liquid, and at least a part of the washing liquid in the first washing tank is continuously or intermittently renewed. A first water washing step of washing the etching solution remaining on the surface of the processing substrate while replacing with pure water;
A second water washing step of washing the treated substrate washed in the first water washing step by immersing it in pure water supplied to the second water washing tank as a cleaning liquid;
Including
In the first water washing step, the conductivity of the cleaning liquid in the first water washing tank during the cleaning of the processing substrate is continuously measured, and whether or not the first water washing step is terminated based on the measured conductivity. Determining
The manufacturing method of the solar cell board | substrate characterized by these. The processing substrate is unloaded from the first water washing tank after it is determined that the cleaning of the processing substrate in the first water washing tank is completed;
The method for producing a solar cell substrate according to claim 1. The processing substrate is a substrate in which an n-type impurity diffusion layer in which phosphorus is diffused by thermal diffusion is provided on the surface of a p-type silicon substrate, and the surface of the n-type impurity diffusion layer is etched with hydrofluoric acid,
In the first water washing step, it is determined that the first water washing step is finished in a range where the measured conductivity of the cleaning liquid is larger than 45 mS / m.
The manufacturing method of the solar cell substrate of Claim 1 or 2 characterized by these. In the first water washing step, it is determined that the first water washing step is finished when the measured conductivity of the washing liquid is reduced to 60 mS / m or less.
The method for manufacturing a solar cell substrate according to claim 3. In the first washing step, measuring the conductivity of the washing liquid drained from the first washing tank during washing of the processing substrate,
The method for manufacturing a solar cell substrate according to any one of claims 1 to 4, wherein: A solar cell substrate manufacturing apparatus for immersing and cleaning a processing substrate having an etching solution remaining on a surface thereof,
A rinsing tank in which pure water is supplied as the cleaning liquid and the treatment substrate is immersed in the cleaning liquid;
A transport unit that carries the treated substrate into the washing tank and unloads the treated substrate from the washing tank;
A supply unit for supplying the pure water to the washing tank;
A drainage section provided in connection with the flushing tank, for draining the washing liquid supplied to the flushing tank;
A conductivity measuring unit that is connected to the drainage unit and measures the conductivity of the cleaning liquid drained from the washing tank and flowing through the drainage unit;
A control unit for determining whether or not to end the cleaning of the processing substrate in the washing tank based on the conductivity measured by the conductivity measuring unit;
With
The processing substrate is cleaned while continuously or intermittently replacing at least a part of the cleaning liquid in the water washing bath in which the processing substrate is immersed,
The conductivity measuring unit continuously measures the conductivity of the cleaning liquid drained from the washing tank and flowing through the drainage unit during the cleaning of the processing substrate.
An apparatus for manufacturing a solar cell substrate characterized by the above. The control unit, when it is determined that the cleaning of the processing substrate in the washing tank is finished, to control the removal of the processing substrate from the washing tank by the transport unit;
The apparatus for manufacturing a solar cell substrate according to claim 6. The processing substrate is a substrate in which an n-type impurity diffusion layer in which phosphorus is diffused by thermal diffusion is provided on the surface of a p-type silicon substrate, and the surface of the n-type impurity diffusion layer is etched with hydrofluoric acid,
Determining that the cleaning of the processing substrate is finished in a range where the measured conductivity of the cleaning liquid is greater than 45 mS / m,
The manufacturing apparatus of the solar cell substrate according to claim 6 or 7. The control unit determines to end the cleaning of the processing substrate when the measured conductivity of the cleaning liquid is reduced to 60 mS / m or less,
The apparatus for manufacturing a solar cell substrate according to claim 8. The conductivity measuring unit is configured to supply the conductivity measuring unit with the cleaning solution flowing through the drainage unit after a lapse of a preset time after the treatment substrate is immersed in the cleaning solution. The measurement starts,
The apparatus for manufacturing a solar cell substrate according to any one of claims 6 to 9, wherein: