JP5377762B2 - Substrate roughening method - Google Patents

Abstract

Disclosed is a method for roughening a substrate, which includes: a disposing step wherein a mask plate having a plurality of rectangular openings previously formed is disposed on the side of the substrate surface to be processed; and a blast step wherein abrasive grains are blasted to the surface to be processed through the mask plate.

Description

  The present invention relates to a method for roughening a substrate and a method for manufacturing a photovoltaic device.

  In order to improve the performance of photoelectric conversion devices such as solar cells, it is important to efficiently incorporate sunlight into the substrate. Therefore, texture processing is performed on the substrate surface on the light incident side, and the light reflected by the slope of the convex portion on the surface is incident on the slope of the other convex portion, so that more sunlight is taken into the substrate. The photoelectric conversion efficiency is improved. Here, the texture processing is processing for intentionally forming a texture (fine irregularities) having a size of several tens of nanometers to several tens of micrometers on the substrate surface.

  As a texture processing method, when the substrate is a single crystal substrate, an anisotropic etching process using an alkaline aqueous solution (sodium hydroxide, potassium hydroxide, etc.) having crystal orientation dependence on the etching rate is widely used. That is, when an anisotropic etching process is performed in the presence of an appropriate additive on the surface of the silicon substrate where the flat (100) surface is exposed, the pyramidal texture (fine irregularities) where the (111) surface is exposed is silicon. It is formed on the surface of the substrate.

  At this time, a crystal plane slightly different from the (111) plane is exposed at the top of the pyramid, and etching for breaking the pyramid shape from the top progresses simultaneously. Thus, in order to form a pyramid shape on the entire surface of the silicon substrate while maintaining an equilibrium state between the action of forming the pyramid and the action of breaking it, a long etching time of about 30 minutes is required.

  In order to shorten the etching time, a method of forming a texture structure on the entire surface of the silicon substrate without depending on anisotropic etching has been proposed. One such method is a method of grooving the substrate surface with a laser. This method is not practical because the processing time is very long because the entire surface needs to be processed by sweeping a laser beam having a small diameter on the substrate surface. The other method is a method of mechanically grooving the substrate surface with a cutting blade or the like. This method is not suitable for microfabrication of 1 mm or less, and the substrate strength is remarkably lowered when implemented on a solar cell substrate having a substrate thickness of about several hundred μm. Still another method is a method applying air blasting.

  Patent Document 1 discloses that a protective mask is formed by coating a photosensitive resin on the surface of a polycrystalline silicon substrate, etching and opening, and spraying first abrasive grains onto the surface of the silicon substrate through the opening of the protective mask. In addition, it is described that the second abrasive grains having a particle size smaller than that of the first abrasive grains are sprayed on the surface of the silicon substrate to remove the protective mask. Thus, according to Patent Document 1, it is said that a large number of inverted pyramid-shaped recesses can be formed on the surface of the silicon substrate as a low reflection shape.

JP 2002-43601 A

  In the technique described in Patent Document 1, in order to process the surface of a single silicon substrate, it is necessary to pattern a photosensitive resin on the surface of the silicon substrate to form a protective mask. Two blasting operations using the grains are required. This complicates the processing for processing the surface (surface to be processed) of the silicon substrate as a whole.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a method for roughening a substrate and a method for manufacturing a photovoltaic device, which can simplify a process for processing a processed surface of the substrate. To do.

  In order to solve the above-described problems and achieve the object, a method for roughening a substrate according to one aspect of the present invention provides a mask plate on which a plurality of rectangular openings are formed in advance on the processed surface side of the substrate. And a blasting step of spraying abrasive grains onto the surface to be processed through the mask plate.

  According to the present invention, blasting is performed through a mask plate in which a plurality of openings are formed in advance. Accordingly, blasting for forming a texture (fine irregularities) can be performed on the processed surface of the substrate without forming a protective mask on the processed surface of the substrate. Further, it is not necessary to remove the protective mask after blasting. That is, the process for processing the processed surface of the substrate can be simplified.

FIG. 1 is a diagram illustrating a substrate roughening method according to the first embodiment. FIG. 2 is a diagram for explaining the positional relationship between the region to be blasted and the opening. FIG. 3 is a diagram illustrating a blasting apparatus. FIG. 4 is a table (Table 1) showing the results of performance evaluation of the photovoltaic device produced by the substrate roughening method according to the first embodiment. FIG. 5 is a table (Table 2) showing the results of performance evaluation of the photovoltaic device produced by the substrate roughening method according to the first embodiment. FIG. 6 is a diagram for explaining the steps of the substrate roughening method according to the second embodiment. FIG. 7 is a table (Table 3) showing the results of performance evaluation of the photovoltaic device produced by the substrate roughening method according to the second embodiment. FIG. 8 is a table (Table 4) showing the performance evaluation results of the photovoltaic device manufactured by the substrate roughening method according to the second embodiment. FIG. 9 is a diagram illustrating a photovoltaic device. FIG. 10 is a diagram for explaining the positional relationship between the blast-resistant mask used in the substrate roughening method according to the third embodiment and the blast-resistant mask for bus electrodes. FIG. 11 is a diagram for explaining a blasted region and an unprocessed region formed by the substrate roughening method according to the third embodiment. FIG. 12 is a diagram illustrating the shape of a blast-resistant mask for bus electrodes.

  Embodiments of a method for roughening a substrate according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to these embodiments.

  Hereinafter, roughening of a single crystal silicon substrate will be described as an example. Moreover, it demonstrates as what is used in order to manufacture a single crystal silicon solar cell as a use of a board | substrate.

Embodiment 1 FIG.
The substrate roughening method according to the first embodiment will be described with reference to FIG. FIG. 1 is a process cross-sectional view for explaining the substrate roughening method according to the first embodiment.

  In the step (arrangement step) shown in FIG. 1A, the substrate 1 is prepared. The substrate 1 is made of, for example, single crystal silicon. For example, the substrate 1 is obtained by slicing a single-crystal silicon ingot with a multi-wire saw and then removing damage during slicing by wet etching using an acid or alkali solution. The thickness of the substrate 1 after removing the damage is, for example, 200 μm, and the size of the substrate 1 is, for example, 156 mm × 156 mm.

  Then, a blast-resistant mask (mask plate) 2 is disposed on the processed surface 1 a side of the substrate 1. In the anti-blast mask 2, for example, a plurality of openings (a plurality of rectangular openings) 5 arranged in a two-dimensional manner are formed in advance (see FIG. 2). As the blast-resistant mask 2, for example, a stainless steel plate having a thickness of 100 μm formed with an opening 5 having a predetermined dimension by etching is used with a resin coating on the surface. The purpose of the resin coating is to impart elasticity to the surface of the blast-resistant mask 2 and to suppress the wear of the plate material due to the collision of abrasive grains. The dimensions and shape of the opening 5 will be described later.

  In the step (blasting step) shown in FIG. 1B, blasting is performed while moving the substrate 1 through the anti-blast mask 2. That is, while moving the substrate 1 relative to the blast mask 2, the abrasive grains 6 are sprayed through the blast mask 2 onto the surface 1 a to be processed. Thereby, a plurality of grooves 3 are formed on the surface of the substrate 1. As the abrasive grains 6, for example, No. 1200 alumina abrasive grains are used. Our test revealed that the abrasive grains 6 suitable for grooving the processed surface 1a of the substrate 1 while minimizing microcracks in the substrate 1 are alumina abrasive grains. Note that other abrasive grains may be used as long as desired groove processing is possible.

  Here, the positional relationship between the region FR to be blasted and the opening 5 of the anti-blast mask 2 will be described with reference to FIG. FIG. 2 is a view when the substrate 1 is viewed from the processing surface 1a side in a state where the blast-resistant mask 2 is arranged on the processing surface 1a side of the substrate 1. FIG.

  Consider a case where the shape of the opening 5 is a stripe shape extending from one end of the substrate 1 to the other end in order to form a plurality of grooves 4 each having a stripe shape on the processing surface 1a. In this case, the width of the opening 5 in the longitudinal direction is very long, and vibration is generated in the blast-resistant mask 2 during blasting, so that a normal blasting shape cannot be formed on the processing surface 1a.

  On the other hand, in the first embodiment, as shown in FIG. 2, for example, a blast resistant mask 2 in which a plurality of rectangular openings 5 are arranged two-dimensionally is used. In the blast-resistant mask 2, for example, the opening width 5b in the short direction is 100 μm, the opening pitch 5a in the short direction is 200 μm, the opening width 5d in the long direction is 300 μm, and the opening pitch 5c in the long direction is 400 μm. Then, blasting is performed while moving the substrate 1 along the longitudinal direction of the opening 5 (for example, in a parallel direction 7). Thereby, the to-be-processed area | region FR which has the groove | channel 4 each extended from the one end of the board | substrate 1 to the other end by blasting can be obtained. Although the method of moving the substrate 1 is employed here, the substrate 1 may be fixed and the blast resistant mask 2 and the abrasive spray nozzle 108 (see FIG. 3) may be moved together. Alternatively, both the substrate 1 and the anti-blast mask 2 may be moved.

  A blasting apparatus 100 used for blasting will be described with reference to FIG. The blasting apparatus 100 simultaneously ejects abrasive grains supplied from the abrasive tank 110 while ejecting compressed air supplied from the abrasive jet nozzle 108 by the compressed air cylinder 109, and covers the ejected abrasive grains 111. The processed surface 1a is cut by colliding with the processed surface 1a.

  Although not particularly shown in FIG. 3, by moving the substrate 1 in parallel, the abrasive grains can be applied to the entire surface to be processed 1a, and the entire surface to be processed 1a can be uniformly cut. Further, in FIG. 3, the abrasive grains are directly ejected by compressed air, but a method of ejecting a liquid in which abrasive grains are mixed by compressed air and a method of ejecting the liquid in which abrasive grains are mixed by directly applying pressure are employed. May be.

  In the step (etching step) shown in FIG. 1C, an etching process is performed on the processing surface 1a of the substrate 1 that has undergone the blasting step. This makes it possible to remove damage such as microcracks that occur in the vicinity of the processed surface 1a in the substrate 1 during blasting, and to form a plurality of grooves 8 on the processed surface 1a of the substrate 1 as textures (fine irregularities). Can be formed. For the etching treatment, for example, a 1% sodium hydroxide aqueous solution was treated at 80 ° C. for 1 min. Other chemicals may be used, or dry etching such as reactive ion etching or gas etching may be used.

  Below, the process for manufacturing a photovoltaic apparatus is demonstrated easily using the roughening method of the board | substrate mentioned above. Note that the process described here is the same as the process for manufacturing a photovoltaic device using a general single crystal silicon substrate, and is not particularly shown.

The substrate 1 (for example, single crystal silicon) that has been processed in the process shown in FIG. 1C is put into a diffusion furnace and heated in the presence of phosphorus oxychloride (POCl ₃ ) vapor to form phosphorus glass. Thereby, phosphorus is diffused in the substrate 1 to form an N layer. The diffusion temperature was 840 ° C., for example.

  Next, after removing the phosphor glass layer in a hydrofluoric acid solution, a SiN film is formed as a reflection preventing film by plasma CVD. The film thickness and refractive index are set to values that most suppress light reflection. Note that two or more layers having different refractive indexes may be stacked. Further, it may be formed by a different film forming method such as a sputtering method.

  Next, a paste mixed with silver as an upper electrode is formed in a comb shape by screen printing, and a paste mixed with aluminum is formed as a back electrode on the entire surface by screen printing. Then, a baking process is implemented. Firing was performed at 760 ° C. in an air atmosphere, for example. In this way, a photovoltaic device is produced.

  The results of performance evaluation of the photovoltaic device manufactured through the above steps will be described. First, the reflection characteristics at the time of roughening were evaluated with a spectrophotometer. Of these, the reflectance at a wavelength of 628 nm is shown in Table 1 of FIG. In the comparative example in which the texture (fine irregularities) is formed on the single crystal silicon substrate with an alkaline aqueous solution, the reflectance is 30%, whereas the substrate roughening method according to the first embodiment is applied. It was found that the substrate 1 was able to suppress the reflectance to 15% and exhibited a good reflectance suppressing effect.

  Next, the results of evaluating the power generation characteristics of the produced 156 mm square photovoltaic device are shown in Table 2 of FIG. In the photovoltaic device to which the substrate 1 subjected to the substrate roughening method according to the first embodiment is applied, the suppression of the surface reflection loss is more effective than the comparative example, and the short-circuit current density is significantly increased. It was found that it contributes to the improvement of conversion efficiency.

  Here, let us consider a case where a protective mask is formed by coating a photosensitive resin on the processing surface 1a of the substrate 1, etching and opening without using the anti-blast mask 2. In this case, the first abrasive grains are sprayed onto the processing surface 1a of the substrate 1 through the opening of the protective mask, and then the second abrasive grains having a particle size smaller than the first abrasive grains are sprayed onto the processing surface 1a of the substrate 1. The protective mask will be removed. That is, in order to process the processing surface 1a of one substrate 1, it is necessary to form a protective mask by patterning a photosensitive resin on the processing surface 1a of the substrate 1, and further, abrasive grains having different particle sizes are formed. The two blasting processes used are required. Thereby, the process for processing the to-be-processed surface 1a of the board | substrate 1 becomes complicated as a whole.

  On the other hand, in the first embodiment, blasting is performed through the blast-resistant mask 2 which is a plate in which a plurality of openings 5 are formed in advance. Thus, blasting for forming a texture (fine irregularities) can be performed on the processed surface 1 a of the substrate 1 without forming a protective mask on the processed surface 1 a of the substrate 1. Further, it is not necessary to remove the protective mask after blasting. That is, according to Embodiment 1, the process for processing the to-be-processed surface 1a of the board | substrate 1 can be simplified.

  Moreover, when forming a protective mask in each to-be-processed surface 1a of the some board | substrate 1, the process of forming the protective mask becomes a single wafer process by the lithography method (or screen printing method). Thereby, the process efficiency with respect to the several board | substrate 1 is bad, and mass-productivity falls.

  On the other hand, in the first embodiment, since the plurality of openings 5 are formed in advance in the anti-blast mask 2, it is not necessary to form openings in the anti-blast mask 2 every time. Thereby, the process efficiency with respect to the several board | substrate 1 can be improved, and mass productivity can be improved.

  Furthermore, when a protective mask is formed on the processed surface 1a of the substrate 1, the protective mask is removed by spraying the second abrasive grains onto the processed surface 1a of the substrate 1, and therefore the protective mask cannot be completely removed. . In addition, crystalline silicon used as a substrate in a solar cell is more fragile than a photosensitive resin used as a protective mask for blasting, and in the process of removing the protective mask even if the grain size of the abrasive is adjusted, The processed surface of the substrate receives damage such as microcracks.

  In contrast, in the first embodiment, since the protective mask is not formed on the processed surface 1a of the substrate 1, it is not necessary to remove the protective mask. Further, as shown in FIG. 1A, since the blast resistant mask 2 is disposed in a non-contact state on the processed surface 1a side of the substrate 1, the blast resistant mask 2 itself may damage the substrate 1. Is low.

  Alternatively, if the shape of the opening 5 is a stripe shape (stripe opening) extended from one end of the substrate 1 to the other end in order to form the plurality of grooves 4 each having a stripe shape on the processing surface 1a. think of. In this case, the width of the opening 5 in the longitudinal direction is very long, and vibration is generated in the blast-resistant mask 2 during blasting, so that a normal blasting shape cannot be formed on the processing surface 1a.

  On the other hand, in the first embodiment, the abrasive grains are removed from the blast resistant mask 2 while moving the substrate 1 relative to the blast resistant mask 2 along the longitudinal direction of the rectangular opening (strip opening) 5. It injects over the to-be-processed surface 1a over. Thus, the stripe region can be processed even when a strip opening is used instead of the stripe opening. That is, the groove 3 extending from one end to the other end of the outer dimension of the substrate 1 can be processed even though the long side of the rectangle of the opening 5 is shorter than the outer dimension of the substrate 1. In addition, since a plurality of openings 5 are arranged in the longitudinal direction, the grooves 3 can be reliably processed. Furthermore, since a plurality of openings 5 are arranged in a direction intersecting the longitudinal direction (for example, the short direction), the plurality of grooves 3 can be processed in parallel. That is, a plurality of grooves 3 that extend in a stripe shape in a direction corresponding to the longitudinal direction of the rectangular opening and are aligned with each other are formed on the processing surface 1a. Thereby, the efficiency of the process at the time of forming the some groove | channel 3 can be improved, and mass productivity can be improved.

  Alternatively, suppose that no etching process is performed in the step shown in FIG. 1C after blasting. In this case, damage such as microcracks due to blasting remains in the vicinity of the surface 1a to be processed in the substrate 1. When such a substrate 1 is applied to a photovoltaic device, characteristics (for example, power generation characteristics) of the photovoltaic device are deteriorated.

  On the other hand, in the first embodiment, in the step shown in FIG. 1C after the blasting process, the processing surface 1a of the substrate 1 that has undergone the blasting process is subjected to an etching process. For this reason, damage (damage) such as micro cracks generated on the processed surface of the substrate by blasting can be removed, and favorable characteristics (for example, power generation characteristics) of the photovoltaic device can be obtained.

  Further, in the first embodiment, in the step shown in FIG. 1C, damage such as micro cracks generated in the vicinity of the processing surface 1a in the substrate 1 at the time of blasting can be removed and the substrate 1 is covered. Since the plurality of grooves 8 can be formed as texture (fine irregularities) on the processed surface 1a, compared to the case where the process of removing damage and the process of forming textures (fine irregularities) are performed in separate steps. The process of forming a texture (fine irregularities) on the processed surface 1a can be simplified as a whole.

Embodiment 2. FIG.
A substrate roughening method according to the second embodiment will be described with reference to FIG. FIG. 6 is a process cross-sectional view for explaining the substrate roughening method according to the second embodiment. Below, it demonstrates focusing on a different part from Embodiment 1. FIG.

  In the step shown in FIG. 6A, after removing damage to the substrate 11i, an impurity diffusion region (first impurity diffusion region) 21i is formed on the processed surface 11ia of the substrate 11i. At this time, the impurity diffusion region 22 is also formed on the back surface 11ib of the substrate 11i. As the substrate 11i, for example, a boron diffused P-type substrate is used. Therefore, the impurity diffusion regions 21i and 22 are N-type layers in which phosphorus is diffused, and PN junctions are formed. The purpose of forming the impurity diffusion region 21i in this step is to improve the performance by reducing the contact resistance when forming the current collecting electrode later, and to improve the performance as a photovoltaic device. The diffusion regions 21i and 22 are not essential.

In the step (formation step) shown in FIG. 6B, an etching resistant film 13i that covers the impurity diffusion region 21i is formed on the processing surface 11ia. At this time, an etching resistant film 23 covering the impurity diffusion region 22 is also formed. The etching resistant films 13i and 23 are films having etching resistance, and are, for example, oxide films (hereinafter referred to as “SiO ₂ films”) having a thickness of 50 nm formed by thermal oxidation. Although a SiO ₂ film is used here, a silicon nitride film (SiN), a silicon oxynitride film (SiON), an amorphous silicon film (а-Si), a diamond-like carbon film, or the like may be used. In addition, since thermal oxidation is used here, the film is formed not only on the processed surface 11ia of the substrate 11i but also on the back surface 11ib and the end surface. I do not care.

  In the step shown in FIG. 6C, first (placement step), the blast-resistant mask 12 in which a plurality of openings 15 are arranged is placed on the processed surface 11ia side of the substrate 11i. As the anti-blast mask 12, for example, a mask having an opening width of 1.9 mm in the short direction, an opening pitch of 2.2 mm in the short direction, an opening width of 3 mm in the longitudinal direction, and an opening pitch of 3.3 mm in the longitudinal direction is prepared. Here, the opening pitch of 2.2 mm is the same as the pitch of the current collecting electrodes 18 formed in a later step.

  Next (blasting step), blasting is performed in which the abrasive grains 16 are sprayed onto the processing surface 11a through the anti-blast mask 12 while the substrate 11 is moved relative to the anti-blast mask 12. For example, blasting is performed while moving the substrate 11 through the anti-blast mask 12. By this blast processing, for example, a region to be processed FR10 having a plurality of belt-like patterns with a pitch of 2.2 mm and a width of 1.9 mm is formed. Blasting conditions are set so that a plurality of micro openings 14 are formed in the etching resistant film 13 in the processing area FR10.

  In FIG. 6C, the blasting process is performed only on the etching resistant film 13, whereas the blasting process may actually extend to the impurity diffusion region 21 directly below. Thus, no problem arises because the etching process is performed after blasting.

  In the step shown in FIG. 6D (second etching step), the processed surface 11a of the substrate 11 is etched using the etching resistant film 13 having a plurality of minute openings 14 formed in the processed region FR10 as a mask. Apply. Thereby, for example, a plurality of texture recesses (a plurality of recesses) 11c are formed on the processing surface 11a so that the flat portion 11a1 remains. At this time, the impurity diffusion region 21 in the processing region FR10 is partially removed so that the impurity diffusion region 21 of the flat portion 11a1 remains. Etching is performed for 10 minutes using, for example, a 1% aqueous sodium hydroxide solution heated to 80 ° C. When etching with alkali is performed, for example, an inverted pyramid-shaped texture recess 11c is formed. The concentration of the etching solution and the etching temperature can be changed to appropriate values in view of the etching rate and the etching shape.

  In the step (removal step) shown in FIG. 6E, the etching resistant film 13 is removed from the processing surface 11a. Thereby, the texture hollow 11c of the to-be-processed surface 11a is exposed. For example, a hydrofluoric acid aqueous solution is used to remove the etching resistant film 13. Thereby, for example, the flat portion 11a1 having a pitch of 2.2 mm and a width of 0.3 mm is exposed. The impurity diffusion region 21 remains in the flat portion 11a1.

  In the step shown in FIG. 6F, an impurity diffusion region (second impurity diffusion region) 17 is left so as to leave the impurity diffusion region 21 in the flat portion 11a1 where the plurality of texture depressions 11c are not formed on the processing surface 11a. Form. The phosphorus concentration (impurity concentration) of the impurity diffusion region 17 is set to be lower than the phosphorus concentration of the impurity diffusion region 21. As a result, the phosphorus concentration in the flat portion 11 a 1 is maintained at a high concentration by the impurity diffusion region 21, while the phosphorus concentration in the texture recess 11 c becomes a low concentration by the impurity diffusion region 17. Thus, since the phosphorus concentration of the texture depression 11c to be the light receiving portion is low, the lifetime of the photogenerated electron-hole pair can be extended, and the power generation characteristics can be improved. Thereafter, although not shown, a SiN film is formed on the entire light receiving surface (surface of the textured dent 11c) by plasma CVD as an antireflection film.

  In the step shown in FIG. 6G, the current collecting electrode 18 is formed on the flat portion 11a1 by screen printing a silver-containing paste. Since the high-concentration impurity diffusion region 21 is disposed in the flat portion 11a1, the contact resistance with the current collecting electrode 18 can be easily reduced. Further, the back electrode 19 is formed on the back surface 11 b side of the substrate 11 by screen printing an aluminum-containing paste. Thereafter, the substrate 11 is heated to 760 ° C. in the atmosphere, and the collector electrode 18 (silver-containing paste) and the back electrode 19 (aluminum-containing paste) are fired. Thereby, a photovoltaic device is produced.

  The results of performance evaluation of the photovoltaic device manufactured through the above steps will be described. The reflection characteristics at the time of roughening were evaluated with a spectrophotometer. Of these, the reflectance at a wavelength of 628 nm is shown in Table 3 of FIG. In the comparative example in which the texture (fine irregularities) is formed on the single crystal silicon substrate with an alkaline aqueous solution, the reflectance is 30%, whereas the substrate is subjected to the substrate roughening method according to the second embodiment. 11, it was found that the reflectivity was suppressed to 11%, and a good reflectivity suppressing effect was exhibited.

  Next, Table 4 in FIG. 8 shows the results of evaluating the power generation characteristics of the produced 156 mm square photovoltaic device. In the photovoltaic device to which the substrate 11 subjected to the substrate roughening method according to the second embodiment is applied, compared to the comparative example, the suppression of the surface reflection loss and the improvement of the contact of the collecting electrode have been successful. It was found that the short circuit current density and the fill factor greatly increased and contributed to the improvement of the conversion efficiency. Furthermore, since the impurity diffusion concentration on the light receiving surface is low, an improvement in open circuit voltage was confirmed.

  In the second embodiment, abrasive grains 16 are sprayed through the blast resistant mask 12 toward the etching resistant film 13 i covering the processing surface 11 a to form a plurality of micro openings 14 in the etching resistant film 13. That is, since the etching resistance film 13 is mainly subjected to blasting and the substrate 11 is hardly subjected to blasting, damage to the processed surface 11a of the substrate 11 is suppressed.

  Then, the processed surface 11a is etched using the etching resistant film 13 having a plurality of minute openings 14 as an etching mask, so that the inverted pyramid-shaped texture depressions 11c starting from the minute openings (blast openings) 14 are formed. A plurality are formed. Thereby, damage (damage) such as micro cracks generated on the processed surface 11a of the substrate 11 by blasting can be removed, and favorable characteristics (for example, power generation characteristics) of the photovoltaic device can be obtained.

  Further, an impurity diffusion region 17 having an impurity concentration lower than that of the impurity diffusion region 21 is formed in each texture recess 11c so as to leave the impurity diffusion region 21 in the flat portion 11a1 where the plurality of texture recesses 11c are not formed on the processing surface 11a. To do. Thereby, since the impurity concentration of the texture hollow 11c which should become a light-receiving part is low, the lifetime of the electron-hole pair produced | generated can be extended. Further, since the high-concentration impurity diffusion region 21 is disposed in the flat portion 11a1, the contact resistance between the flat portion 11a1 and the collector electrode 18 can be easily reduced. Therefore, the power generation characteristics of the photovoltaic device can be improved by manufacturing the photovoltaic device using the substrate 11 subjected to the substrate roughening method according to the second embodiment.

Embodiment 3 FIG.
A method for roughening a substrate according to the third embodiment will be described. Below, it demonstrates centering on a different part from Embodiment 1 or Embodiment 2. FIG.

  First, FIG. 9 shows a top view of the photovoltaic device 200 manufactured by using the substrate roughening method according to the third embodiment. The photovoltaic device 200 has a plurality of current collecting electrodes 18 and a plurality of bus electrodes 202 on one main surface 201 thereof. The plurality of current collecting electrodes 18 are aligned with each other (for example, in parallel), and each intersect with each bus electrode 202 (for example, at a right angle). The plurality of bus electrodes 202 are aligned with each other (for example, in parallel), and each intersect with each collector electrode 18 (for example, at a right angle).

  Each bus electrode 202 plays a role of further collecting and extracting the current collected by the current collecting electrode 18. For example, the current collecting electrode 18 has a width of 100 μm, an interelectrode pitch of 2 mm, and a number of 76. The bus electrodes 202 have, for example, an electrode width of 2 mm, an inter-electrode pitch of 76 mm, and two pieces.

  The bus electrode 202 plays a role of further collecting the current collected by the current collecting electrode 18. However, since the bus electrode 202 itself is arranged on the substrate 1 (or 11), the flat portion 11 a 1 is disposed immediately below the bus electrode 202. The contact resistance between the bus electrode 202 and the impurity diffusion region 21 can be reduced when the high-concentration impurity diffusion region 21 is disposed at the same position.

  Next, a mask used in the substrate roughening method according to the third embodiment will be described with reference to FIG. FIG. 10 shows the substrate 1 (or 11) in a state where the blast resistant mask 203 for bus electrodes and the blast resistant mask 2 (or 12) are arranged on the processed surface 1a (or 11a) side of the substrate 1 (or 11). It is a figure at the time of seeing from the to-be-processed surface 1a (or 11a) side.

  In the step shown in FIG. 1B (or the step shown in FIG. 6C), before blasting, the bus electrode anti-blast mask (mask member) 203 (see FIG. 10), the substrate 1 (or 11i), and The bus electrode blast-resistant mask (mask member) 203 is arranged so that the blast-resistant mask 2 (or 12) is positioned between them. A bus electrode blast-resistant mask (mask member) 203 shown in FIG. 10 is provided in the opening 5 so as to suppress blasting in a region where a plurality of bus electrodes 202 should be arranged on the processing surface 1a (or 11a). This is a mask for shielding the part, and is arranged at a position corresponding to the plurality of bus electrodes 202 to be formed in the photovoltaic device 200. For example, two bus electrode blast-resistant masks 203 are arranged in a positional relationship orthogonal to the longitudinal direction of the opening 5, and the interval is 76 mm.

  In the blasting step, the abrasive grains 6 (or 16) are transferred to the processing surface 1a (or the etching-resistant film 13 on the processing surface 11ia via the bus electrode blast-resistant mask 203 and the blast-resistant mask 2 (or 12). To spray. At this time, when blasting the substrate 1 (or 11) relative to the blast resistant mask 2 (or 12), the bus electrode blast resistant mask 203 is moved relative to the substrate 1 (or 11). Blasting in a stationary state. That is, in the blasting process, the substrate 1 (or 11) is moved relative to the blast-resistant mask 2 (or 12) along the longitudinal direction of the rectangular opening 5, and the substrate 1 (or 11) is moved. The abrasive grains 6 (or 16) are transferred to the processing surface 1a via the bus electrode blast resistant mask 203 and the blast resistant mask 2 (or 12) while being relatively stationary with respect to the bus electrode blast resistant mask 203 ( Or sprayed to the etching resistant film 13 on the surface 11 ia to be processed).

  As a result, on the processing surface 1a of the substrate 11 (or the etching resistant film 13 on the processing surface 11ia), as shown in FIG. 11, the processing region FR204 extended from one end to the other end in the longitudinal direction, Two unprocessed regions 205 that are orthogonal to each other are formed at intervals of 76 mm.

  FIG. 12 shows the shape of the blast resistant mask 203 for bus electrodes. The bus electrode blast-resistant mask 203 has, for example, a triangular prism shape with a ridge line disposed on the abrasive grain spray nozzle 108 (see FIG. 3) side, and the surface thereof is coated with resin. By adopting the triangular prism shape, it is possible to avoid a direct collision with the bus electrode blast resistant mask 203 when the abrasive grains 6 (or 16) are sprayed, and to reduce the impact on the bus electrode blast resistant mask 203. .

  As described above, in the third embodiment, before blasting, the bus electrode anti-blast mask 2 (or 12) is positioned between the bus electrode anti-blast mask 203 and the substrate 1 (or 11i). An anti-blast mask 203 is arranged. In the blasting step, the abrasive grains 6 (or 16) are transferred to the processing surface 1a (or the etching-resistant film 13 on the processing surface 11ia via the bus electrode blast-resistant mask 203 and the blast-resistant mask 2 (or 12). To spray. Thereby, since the blasting of the region where the plurality of bus electrodes 202 should be arranged on the processing surface 1a (or 11a) can be suppressed, the region is defined as the flat portion 11a1 (see FIG. 6D). Similarly to the second embodiment, each bus electrode 202 can be formed on the flat portion 11a1 on which the high-concentration impurity diffusion region 21 (see FIG. 6D) is arranged. As a result, the power generation characteristics of the photovoltaic device can be further improved, for example, the open circuit voltage of the photovoltaic device to be created can be further increased.

  In the third embodiment, in the blasting process, the substrate 1 (or 11) is moved relative to the anti-blast mask 2 (or 12) along the longitudinal direction of the rectangular opening 5, and the substrate 1 (or 11) is kept relatively stationary with respect to the blast resistant mask 203 for bus electrodes, and the abrasive grains 6 (or 16) are passed through the blast resistant mask 203 for bus electrodes and the blast resistant mask 2 (or 12). Sprayed to the processing surface 1a (or to the etching resistant film 13 on the processing surface 11ia). This suppresses blasting of the region where the plurality of bus electrodes 202 should be arranged on the processing surface 1a (or 11a), while blasting the plurality of processing regions FR204 (for example, in FIG. 1B). The formation of the groove 3 shown or the formation of the minute opening 14 shown in FIG. 6C) can be performed in parallel.

  The shape of the bus electrode blast resistant mask 203 is not limited to that shown in FIG. For example, the blasting process of the bus electrode 202 on the processing surface 1a (or 11a) should be shielded in the region where the plurality of bus electrodes 202 should be arranged. It may be cylindrical.

  FIG. 10 illustrates the case where the bus electrode blast resistant mask 203 is disposed on the abrasive spray nozzle 108 (see FIG. 3) side with respect to the blast resistant mask 2 (or 12). The method is not limited to this case. For example, the blast-resistant mask 203 for bus electrodes is resistant to the substrate 1 (or 11) because the blast processing in the region where the plurality of bus electrodes 202 should be arranged on the processing surface 1a (or 11a) is to be shielded. You may arrange | position between blast masks 2 (or 12). Even in this case, since the blasting of the region where the plurality of bus electrodes 202 should be arranged on the processing surface 1a (or 11a) can be suppressed, the region is flattened 11a1 (see FIG. 6D). Similarly to the second embodiment, each bus electrode 202 can be formed on the flat portion 11a1 on which the high-concentration impurity diffusion region 21 (see FIG. 6D) is arranged. .

  In the blasting process, the substrate 1 (or 11) is moved relative to the blast-resistant mask 2 (or 12) along the longitudinal direction of the rectangular opening 5, and the substrate 1 (or 11) is moved. The abrasive grains 6 (or 16) are transferred to the processing surface 1a via the bus electrode blast resistant mask 203 and the blast resistant mask 2 (or 12) while being relatively stationary with respect to the bus electrode blast resistant mask 203 ( (Or to the etching-resistant film 13 on the processed surface 11a) by spraying, while suppressing the blast processing of the region where the plurality of bus electrodes 202 should be arranged on the processed surface 1a (or 11a), Blasting (for example, formation of the groove 3 shown in FIG. 1B or formation of the minute opening 14 shown in FIG. 6C) on the processing region FR204 can be performed in parallel.

  As described above, the method for roughening a substrate according to the present invention is useful for texture processing of a substrate.

1, 11i, 11 Substrate 2, 12 Blast resistant mask 3 Groove 4 Groove 5a Short-side opening pitch 5b Short-side opening width 5c Long-side opening pitch 5d Long-side opening width 6, 16, 111 Abrasive grain 7 Progression direction of substrate 8 Groove 11a1 Flat portion 11c Texture depression 13i, 13 Etching resistant film 14 Micro opening 17, 21i, 21, 22 Impurity diffusion region 18 Current collecting electrode 19 Back electrode 108 Abrasive spray nozzle 109 Compressed air cylinder 110 Abrasive grain Tank FR, FR10, FR204 Work area 200 Photovoltaic device 201 One main surface 202 Bus electrode 203 Blast-resistant mask for bus electrode 205 Unprocessed area

Claims (4)

An arrangement step of arranging a mask plate in which a plurality of rectangular openings are formed in advance on the processing surface side of the substrate;
A blasting step of injecting abrasive grains onto the work surface through the mask plate;
Including
In the arranging step, the mask member is further arranged such that the mask plate is positioned between the mask member that shields a part of the rectangular opening and the substrate,
In the blasting step, the abrasive grains are sprayed onto the processing surface via the mask member and the mask plate,
In the blasting step, the abrasive is moved while moving the substrate relative to the mask plate along the longitudinal direction of the rectangular opening, and while making the substrate stationary relative to the mask member. said mask member and roughening methods board, which comprises injecting through the mask plate to the workpiece surface. An arrangement step of arranging a mask plate in which a plurality of rectangular openings are formed in advance on the processing surface side of the substrate;
A blasting step of injecting abrasive grains onto the work surface through the mask plate;
Including
In the arranging step, a mask member for shielding a part of the rectangular opening is further arranged between the mask plate and the substrate,
In the blasting step, the abrasive grains are sprayed onto the processing surface via the mask plate and the mask member,
In the blasting step, the abrasive is moved while moving the substrate relative to the mask plate along the longitudinal direction of the rectangular opening, and while making the substrate stationary relative to the mask member. said mask member and roughening methods board, which comprises injecting through the mask plate to the workpiece surface. An arrangement step of arranging a mask plate in which a plurality of rectangular openings are formed in advance on the processing surface side of the substrate;
A blasting step of injecting abrasive grains onto the work surface through the mask plate;
Including
At least before the blasting step, further comprising a forming step of forming an etching resistant film on the work surface;
In the blasting step, a plurality of openings corresponding to the plurality of rectangular openings are formed in the etching resistant film,
In the mask plate, the plurality of rectangular openings are arranged in a direction intersecting at least the longitudinal direction of the rectangular openings,
In the blasting step, in the etching resistant film, the plurality of openings are formed in each of a plurality of regions to be processed that extend in a stripe shape in a direction corresponding to the longitudinal direction of the rectangular opening and are aligned with each other,
In the arranging step, the mask member is further arranged such that the mask plate is positioned between the mask member that shields a part of the rectangular opening and the substrate,
In the blasting step, the abrasive grains are sprayed to the etching resistant film on the processing surface through the mask member and the mask plate,
In the blasting step, the abrasive is moved while moving the substrate relative to the mask plate along the longitudinal direction of the rectangular opening, and while making the substrate stationary relative to the mask member. said mask member and roughening methods board, characterized in that through the mask plate for injecting into the anti-etching film on the processed surface. An arrangement step of arranging a mask plate in which a plurality of rectangular openings are formed in advance on the processing surface side of the substrate;
A blasting step of injecting abrasive grains onto the work surface through the mask plate;
Including
At least before the blasting step, further comprising a forming step of forming an etching resistant film on the work surface;
In the blasting step, a plurality of openings corresponding to the plurality of rectangular openings are formed in the etching resistant film,
In the mask plate, the plurality of rectangular openings are arranged in a direction intersecting at least the longitudinal direction of the rectangular openings,
In the blasting step, in the etching resistant film, the plurality of openings are formed in each of a plurality of regions to be processed that extend in a stripe shape in a direction corresponding to the longitudinal direction of the rectangular opening and are aligned with each other,
In the arranging step, a mask member for shielding a part of the rectangular opening is further arranged between the mask plate and the substrate,
In the blasting step, the abrasive grains are sprayed onto the etching resistant film on the processing surface through the mask plate and the mask member,
In the blasting step, the abrasive is moved while moving the substrate relative to the mask plate along the longitudinal direction of the rectangular opening, and while making the substrate stationary relative to the mask member. said mask member and roughening methods board, characterized in that through the mask plate for injecting into the anti-etching film on the processed surface.

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