JP2014007188A - Method of manufacturing solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method of manufacturing a solar battery, capable of manufacturing a selective emitter type solar battery by which a high conversion efficiency can be obtained, with stability and good reproductivity by a simple process.SOLUTION: A method of manufacturing a solar battery includes: an impurity diffusion step of selectively diffusing an impurity in a pattern-shape region of an impurity diffusion layer 6 to form a high concentration diffusion layer 7, as a diffusion layer formation step of forming the impurity diffusion layer 6 to a semiconductor substrate 1; a high concentration diffusion layer detection step of detecting a position where the high concentration diffusion layer 7 is formed in the impurity diffusion layer 6; and a light-receiving surface side electrode formation step of forming a light-receiving surface side electrode 3 on the high concentration diffusion layer 7. The high concentration diffusion layer detection step includes: a detection light supply step of supplying detection light to the impurity diffusion layer 6 after the impurity diffusion step; and a determination step of measuring a reflective index of the detection light at the impurity diffusion layer 6, and determining whether or not the high concentration diffusion layer 7 is formed at a position where the detection light is reflected, depending on the reflective index.

Description

  The present invention relates to a method for manufacturing a solar cell, and more particularly to a method for manufacturing a crystalline silicon solar cell.

  Conventionally, various techniques are known for improving the efficiency of crystalline silicon solar cells. Considering market development, it is desired to adopt a method suitable for mass production even if it is a high efficiency method. As a relatively simple technique for improving the efficiency, for example, many techniques relating to the introduction of a selective emitter structure have been developed. According to the selective emitter structure, the lower part of the light-receiving surface side electrode of the solar cell is made low resistance, and the other part that receives sunlight is made high resistance, thereby simultaneously realizing reduction of electric resistance and suppression of surface recombination. The aim is to increase efficiency.

  For example, Non-Patent Document 1, which is a paper reported at the 25th European Photovoltaic Solar Energy Conference and Exhibition (EUPVSEC), describes a selective emitter formation method currently under development. This includes a printing method using a paste containing impurities, an etching method using an oxide film mask, an ion implantation method, an etch back method, a laser doping method, and the like.

  Here, a method for manufacturing a selective emitter type crystalline silicon solar cell will be briefly described. Here, as an example, a selective emitter structure is formed by laser doping using a P-type single crystal silicon wafer as a substrate material.

  First, the surface of the sliced P-type single crystal silicon wafer is etched with an alkaline solution or a mixed acid, thereby removing the damage layer on the surface due to the slicing. Next, an unevenness (texture) structure for increasing light absorption is formed on the surface of the silicon wafer. For example, a pyramid structure using the anisotropy of silicon crystals can be formed by heating an etching bath containing an additive in an alkaline solution to about 70 ° C. to 100 ° C. and immersing the silicon wafer.

Next, in order to form a PN bond in the silicon wafer, phosphorus is added to the surface of the P-type single crystal silicon wafer heated to about 800 ° C. by, for example, a vapor phase diffusion method in phosphorus oxychloride (POCl ₃ ) gas. The n-type diffusion layer is diffused. At this time, the sheet resistance of the N-type diffusion layer is set to be the sheet resistance of the light receiving surface, for example, 100Ω / □.

A conventional solar cell having a uniform emitter is completed through diffusion of POCl ₃ , removal of phosphorous glass formed on the surface, formation of an antireflection film, electrode printing and firing. On the other hand, when the selective emitter structure is formed by the laser doping method, before removing the phosphor glass by etching, a portion of the surface of the silicon wafer under the light receiving surface side electrode is irradiated with laser light.

  The portion under the light receiving surface side electrode is heated by laser light irradiation, so that phosphorus atoms in the phosphor glass are selectively diffused into the silicon wafer in a pattern similar to the electrode pattern. The sheet resistance value decreases at the portion where phosphorus is selectively diffused, and the sheet resistance value increases at the other portions. A selective emitter type solar cell is then completed by removing phosphorous glass, forming an antireflection film, printing an electrode, and firing.

G.Hahn, “STATUS OF SELECTIVE EMITTER TECHNOLOGY”, Conference Proceedings of 25th EUPVSEC (2010) 1091-1096

  In the manufacture of a selective emitter type solar cell, the biggest issue is whether or not the electrode can be correctly positioned on the high-concentration diffusion layer with a reduced sheet resistance. In the selective emitter structure, as a method of aligning the electrodes formed by screen printing, for example, alignment with respect to three points around the silicon wafer is performed in order to align the pattern of the screen mask with the high concentration diffusion layer. It is known to do.

  However, in this alignment method, it is very difficult to accurately place an electrode having the same width as that of the high concentration diffusion layer on the high concentration diffusion layer due to an arrangement error of the screen mask or a slight displacement of the silicon wafer. difficult. For this, the width of the high-concentration diffusion layer is usually made larger than the width of the electrode so that the electrode can be formed on the high-concentration diffusion layer even if the position of the electrode is slightly shifted.

  In this way, by providing a certain tolerance for the positional deviation of the electrode, it is ideal that only the low-concentration diffusion layer is exposed on the light-receiving side surface, but the high-concentration diffusion layer Is also exposed on the light-receiving side surface. Most of the photocarriers generated by the sunlight incident on the exposed portion of the high-concentration diffusion layer will disappear due to recombination on the surface. Therefore, the advantage of improving the efficiency by introducing the selective emitter structure is hindered.

  On the contrary, when the electrode protrudes from the low concentration diffusion layer, a part of the sunlight that should enter the low concentration diffusion layer is blocked by the electrode, and the efficiency of taking in sunlight is reduced. In addition, the electrode is baked after printing, whereby the antireflection film and the surface of the silicon wafer are etched by a glass component contained in the electrode material to realize electrical contact. The low-concentration diffusion layer has a small diffusion depth, and the PN bond is easily broken by erosion of the electrode material. Since the PN bond is broken at the portion where the electrode protrudes from the low-concentration diffusion layer, the improvement in efficiency is hindered.

  The present invention has been made in view of the above, and provides a method for manufacturing a solar cell capable of stably manufacturing a selective emitter solar cell having high conversion efficiency with a simple process. For the purpose.

  In order to solve the above-described problems and achieve the object, the present invention provides a diffusion layer forming step for forming an impurity diffusion layer on a surface on the light receiving surface side of a semiconductor substrate. In this region, impurities are selectively diffused to form a high-concentration diffusion layer, and regions other than the region where the high-concentration diffusion layer is formed in the impurity diffusion layer have an impurity concentration higher than that of the high-concentration diffusion layer. Detected in an impurity diffusion step for forming a low-concentration diffusion layer, a high-concentration diffusion layer detection step for detecting a position of the impurity diffusion layer where the high-concentration diffusion layer is formed, and the high-concentration diffusion layer detection step A light-receiving surface-side electrode forming step for forming a light-receiving surface-side electrode on the high-concentration diffusion layer at a position, and the high-concentration diffusion layer detecting step detects light to the impurity diffusion layer that has undergone the impurity diffusion step. Supply And determining whether or not the high-concentration diffusion layer is formed at a position where the detection light is reflected by measuring a reflectance of the detection light in the impurity diffusion layer And a process.

  According to the present invention, instead of the alignment based on the peripheral position of the semiconductor substrate, the position of the high concentration diffusion layer is detected according to the reflectance of the detection light in the impurity diffusion layer, and the light receiving surface side electrode is formed. . By making it possible to directly detect the position of the high-concentration diffusion layer in the semiconductor substrate by reflectivity without using the peripheral position of the semiconductor substrate as a reference, the light-receiving surface side electrode can be easily and accurately placed on the high-concentration diffusion layer Can be formed. Thereby, there is an effect that a selective emitter type solar cell with high conversion efficiency can be stably manufactured with good reproducibility by a simple process.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a solar battery cell created by the solar battery manufacturing method according to the first embodiment. FIG. 2 is a top view of the solar battery cell viewed from the light receiving surface side. 3-1 is sectional drawing for demonstrating the procedure of the manufacturing method of the solar cell concerning Embodiment 1 (the 1). 3-2 is sectional drawing for demonstrating the procedure of the manufacturing method of the solar cell concerning Embodiment 1 (the 2). 3-3 is sectional drawing for demonstrating the procedure of the manufacturing method of the solar cell concerning Embodiment 1 (the 3). 3-4 is sectional drawing for demonstrating the procedure of the manufacturing method of the solar cell concerning Embodiment 1 (the 4). 3-5 is sectional drawing for demonstrating the procedure of the manufacturing method of the solar cell concerning Embodiment 1 (the 5). 3-6 is sectional drawing for demonstrating the procedure of the manufacturing method of the solar cell concerning Embodiment 1 (the 6). FIG. 4 is a diagram for explaining the detection of the position of the high concentration diffusion layer by the detection light. FIG. 5 is a diagram illustrating an example of a relationship between the reflectance of the detection light in the high concentration diffusion layer and the low concentration diffusion layer and the wavelength of the detection light. FIG. 6 is a diagram for explaining the detection of the position of the high-concentration diffusion layer in the method for manufacturing a solar cell according to the second embodiment of the present invention. FIG. 7 is a diagram for explaining the detection of the position of the high-concentration diffusion layer with detection light in the method for manufacturing a solar cell according to the fourth embodiment of the present invention.

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

Embodiment 1 FIG.
1 and 2 are diagrams illustrating a schematic configuration of a solar battery cell created by the solar battery manufacturing method according to the first embodiment. FIG. 1 is a cross-sectional view of a solar battery cell. FIG. 2 is a top view of the solar battery cell viewed from the light receiving surface side. FIG. 1 shows an AA cross section shown in FIG.

  The solar battery cell is a solar battery substrate having a photoelectric conversion function. The solar battery cell includes a semiconductor substrate 1, an antireflection film 2, a light receiving surface side electrode 3, and a back surface side electrode 4. The semiconductor substrate 1 has a PN junction. The antireflection film 2 is formed on the surface of the semiconductor substrate 1 on the light receiving surface side. The antireflection film 2 prevents reflection of incident light on the light receiving surface.

  The light receiving surface side electrode 3 is an electrode partially formed on the surface of the semiconductor substrate 1 on the light receiving surface side. The back surface side electrode 4 is an electrode formed on the back surface of the semiconductor substrate 1 which is the surface opposite to the light receiving surface.

  The semiconductor substrate 1 includes a P-type (first conductivity type) single crystal silicon 5 and an N-type (second conductivity type) impurity diffusion layer 6 in which the conductivity type of the surface of the P-type single crystal silicon 5 is inverted. Have. P-type single crystal silicon 5 and N-type impurity diffusion layer 6 constitute a PN junction.

  The N-type impurity diffusion layer 6 has a high concentration diffusion layer 7 and a low concentration diffusion layer 8. The high concentration diffusion layer 7 is formed in the N-type impurity diffusion layer 6 near the light receiving surface side electrode 3. The low-concentration diffusion layer 8 is formed in a portion that receives sunlight other than the high-concentration diffusion layer 7 where the light-receiving surface side electrode 3 is formed in the N-type impurity diffusion layer 6.

  The solar cell according to the present embodiment employs a selective emitter structure including a high concentration diffusion layer 7 having a low sheet resistance and a low concentration diffusion layer 8 having a high sheet resistance. A solar cell can obtain high conversion efficiency by reducing the electrical resistance of the part in which the light-receiving surface side electrode 3 is formed, and suppressing surface recombination in the part which receives sunlight.

  On the surface of the semiconductor substrate 1 on the light receiving surface side, fine irregularities (not shown) are formed at a high density as a texture structure. The minute unevenness has a function of confining light by changing the angle of the reflected light on the light receiving surface to suppress a substantial reflectance through a plurality of reflections.

  The light receiving surface side electrode 3 includes a front silver bus electrode 11 and a front silver grid electrode 12. The front silver grid electrodes 12 are arranged substantially in parallel with a predetermined width and interval. The front silver grid electrode 12 collects electricity generated inside the semiconductor substrate 1. The front silver bus electrode 11 is provided substantially orthogonal to the front silver grid electrode 12. The front silver bus electrode 11 takes out the electricity collected by the front silver grid electrode 12. The back surface side electrode 4 is formed on the entire back surface of the semiconductor substrate 1 except for the end portion.

  In the solar battery configured as described above, when sunlight passes through the antireflection film 2 and the N-type impurity diffusion layer 6 and is irradiated onto the semiconductor substrate 1, holes and electrons are generated. When the electrons generated in the P-type single crystal silicon 5 reach the PN junction surface, the electrons move toward the N-type impurity diffusion layer 6 by the electric field of the PN junction, and the holes move toward the P-type single crystal silicon 5. .

  As a result of excessive electrons in the N-type impurity diffusion layer 6 and holes in the P-type single crystal silicon 5, a photovoltaic force is generated. This photovoltaic power is generated in the direction of biasing the PN junction in the forward direction, the light receiving surface side electrode 3 connected to the N-type impurity diffusion layer 6 becomes a negative electrode, and the back surface side electrode 4 connected to the P-type single crystal silicon 5 As a positive pole, current flows through an external circuit (not shown).

  Next, an example of a method for manufacturing the solar battery cell shown in FIGS. 1 and 2 will be described. FIGS. 3-1 to 3-6 are cross-sectional views for explaining the procedure of the method for manufacturing the solar cell according to the first embodiment.

  For example, a P-type single crystal silicon wafer is prepared as a silicon-based substrate to be the semiconductor substrate 1 (see FIG. 3A). In this embodiment, as an example, the thickness of a P-type single crystal silicon wafer is 200 μm and the dimensions are 156 mm × 156 mm. The thickness and dimensions of the P-type single crystal silicon wafer are not limited to this, and can be changed as appropriate.

  A P-type single crystal silicon wafer is manufactured by slicing an ingot formed by cooling and solidifying molten silicon with a wire saw. On the surface of the manufactured P-type single crystal silicon wafer, a damaged layer caused by damage during slicing is left. Since this damaged layer has extremely poor crystallinity, it is necessary to remove the damaged layer in order to obtain a sufficient function as the semiconductor substrate 1. Therefore, the damaged layer on the surface due to slicing is removed by etching the surface of the P-type single crystal silicon wafer after slicing with an alkaline solution or mixed acid.

  Subsequent to the removal of the damaged layer, fine irregularities are formed as a texture structure on the light-receiving surface side surface of the P-type single crystal silicon wafer. The texture structure is formed, for example, by etching a P-type polycrystalline silicon substrate with an alkaline solution containing an additive. For example, an alkali hydroxide aqueous solution containing IPA (isopropyl alcohol) is placed in an etching tank, and the P-type single crystal silicon wafer is immersed in a state heated to about 70 ° C. to 100 ° C. Thereby, a pyramid structure utilizing the anisotropy of the silicon crystal is formed.

  By providing such a texture structure on the light receiving surface side of the semiconductor substrate 1, multiple reflection of light on the light receiving surface side of the solar battery cell is caused. A solar cell can efficiently photoelectrically convert incident sunlight by efficiently absorbing light incident from the light-receiving surface side into the semiconductor substrate 1 and effectively reducing the reflectance. In addition, in each figure, illustration of micro unevenness | corrugation is abbreviate | omitted.

Next, the semiconductor substrate 1 having fine textures formed on the surface as a texture structure is put into a thermal oxidation furnace and heated in an atmosphere of phosphorus which is an N-type impurity. For example, in a phosphorus oxychloride (POCl ₃ ) gas atmosphere, a P-type single crystal silicon wafer as the semiconductor substrate 1 is heated to about 800 ° C. to 900 ° C., and phosphorus is deposited on the surface of the semiconductor substrate 1 by a vapor phase diffusion method. Spread.

  In this diffusion layer forming step, phosphorus, which is an impurity element, is diffused on the surface on the light receiving surface side of the semiconductor substrate 1 to form an N-type impurity diffusion layer 6 (see FIG. 3-2). Actually, the N-type impurity diffusion layer 6 is formed on the entire surface of the semiconductor substrate 1, but here, in order to show the outline of the structure of the solar cell, the N-type formed on the surface other than the light-receiving surface side surface. The impurity diffusion layer 6 is omitted. Of the semiconductor substrate 1, the portion on the inner side of the surface layer where the N-type impurity diffusion layer 6 is formed is P-type single crystal silicon 5. Thereby, a PN junction is formed in the semiconductor substrate 1. At this time, phosphorus diffusion is controlled so that the sheet resistance of the N-type impurity diffusion layer 6 is, for example, 100Ω / □.

  Next, the portion of the N-type impurity diffusion layer 6 below the light receiving surface side electrode 3 is irradiated with laser light. The portion under the light receiving surface side electrode 3 is heated by laser light irradiation, so that phosphorus atoms in the phosphor glass are selectively diffused into the semiconductor substrate 1 in a pattern similar to the electrode pattern (laser doping). ).

  In this impurity diffusion step, impurities are selectively diffused in a pattern-like region similar to the pattern of the light-receiving surface side electrode 3 in the N-type impurity diffusion layer 6. A high-concentration diffusion layer 7 having a high impurity concentration is formed in the patterned region where the impurities are diffused (see FIG. 3-3). Of the N-type impurity diffusion layer 6, a region other than the region where the high concentration diffusion layer 7 is formed is a low concentration diffusion layer 8. The low concentration diffusion layer 8 is a portion of the N-type impurity diffusion layer 6 having a lower impurity concentration than the high concentration diffusion layer 7. By this impurity diffusion step, the high-concentration diffusion layer 7 which is a portion where phosphorus is selectively diffused has a lower sheet resistance value, and the other portion of the sheet resistance value is an N-type impurity diffusion layer formed by a vapor phase diffusion method. The resistance value of 6 is almost maintained.

  Next, phosphorus glass (not shown), which is a byproduct of diffusion in the diffusion layer forming step, is removed by etching. Subsequently, the antireflection film 2 is formed on the entire surface of the N-type impurity diffusion layer 6 (FIGS. 3-4). The semiconductor substrate 1 on which the antireflection film 2 is formed is set in a printing machine for screen printing.

  When the semiconductor substrate 1 is set in the printing press, the position where the high concentration diffusion layer 7 is formed in the N type impurity diffusion layer 6 is detected by the high concentration diffusion layer detection step. In the high-concentration diffusion layer detection step, infrared light L is supplied to the N-type impurity diffusion layer 6 through the antireflection film 2 to the semiconductor substrate 1 that has undergone the steps up to the formation of the antireflection film 2 (FIG. 3-5). . The infrared light L supplied in the detection light supply process is detection light for detecting the position of the high concentration diffusion layer 7. Following the detection light supply step, in the determination step, the reflectance of the infrared light L in the N-type impurity diffusion layer 6 is measured, and whether or not the high-concentration diffusion layer 7 is formed at the position where the infrared light L is reflected. Is determined according to the reflectance.

  Next, in the light receiving surface side electrode forming step, the light receiving surface side electrode 3 is formed on the high concentration diffusion layer 7 at the position detected in the high concentration diffusion layer detecting step (FIGS. 3-6). A silver paste that is a material of the light-receiving surface side electrode 3 is applied by screen printing to a portion of the antireflection film 2 where the high-concentration diffusion layer 7 is formed immediately below, and then the silver paste is dried. Moreover, after applying the aluminum paste which is the material of the back surface side electrode 4 to the back surface side of the semiconductor substrate 1 by screen printing, the aluminum paste is dried.

  Thereafter, by baking the paste, the front silver bus electrode 11 and the front silver grid electrode 12 as the light receiving surface side electrode 3 and the back surface side electrode 4 are obtained. Firing is performed at a temperature selected from a range of 750 ° C. to 850 ° C., for example, in an air atmosphere. The firing temperature is selected in consideration of the cell structure and paste type.

  The high-concentration diffusion layer 7 in the N-type impurity diffusion layer 6 and the light receiving surface side electrode 3 are electrically connected to each other when the silver component of the light receiving surface side electrode 3 penetrates the antireflection film 2. As a result, the N-type impurity diffusion layer 6 can obtain a good resistive junction with the light-receiving surface side electrode 3. By carrying out the steps as described above, the solar battery cell shown in FIGS. 1 and 2 is manufactured.

  FIG. 4 is a diagram for explaining the detection of the position of the high concentration diffusion layer by the detection light. The light source 13 emits infrared light L having a wavelength of 1064 nm, for example. The light source 13 is, for example, a YAG laser that oscillates a fundamental wave of 1064 nm. In the detection light supply step, the light source 13 scans the infrared light L in the two-dimensional direction in the N-type impurity diffusion layer 6. For scanning the infrared light L from the light source 13, for example, scanning means (not shown) such as a galvanometer mirror is used.

  The light receiving unit 14 detects the infrared light L reflected by the N-type impurity diffusion layer 6 and measures the reflectance of the infrared light L in the N-type impurity diffusion layer 6. The light receiving unit 14 determines whether or not the high-concentration diffusion layer 7 is formed at the position where the infrared light L is reflected, according to the reflectance that is the measurement result.

  FIG. 5 is a diagram illustrating an example of a relationship between the reflectance of the detection light in the high concentration diffusion layer and the low concentration diffusion layer and the wavelength of the detection light. In the N-type impurity diffusion layer 6, the higher the carrier concentration, the greater the amount of absorption of the infrared light L, so that the reflectance of the infrared light L decreases. For this reason, the reflectance R1 of the high concentration diffusion layer 7 is lower than the reflectance R2 of the low concentration diffusion layer 8. The light receiving unit 14 determines whether or not the high-concentration diffusion layer 7 is present at the position where the infrared light L is reflected, using such a difference in reflectance. By using the infrared light L as the detection light, it is possible to identify the portion of the N-type impurity diffusion layer 6 where the high concentration diffusion layer 7 is formed according to the difference in reflectance due to the absorption of the infrared light L. And

  For example, the scanning unit that scans the infrared light L scans the infrared light L in a predetermined direction from the vicinity of one corner of the semiconductor substrate 1. For example, the light receiving unit 14 detects a linear portion forming the front silver grid electrode 12 from the reflectance of the infrared light L scanned in the longitudinal direction (for example, the X direction) of the front silver grid electrode 12. . In the laser doping described above, laser light is continuously irradiated from the end of the semiconductor substrate 1 to the opposite end. For this reason, the scanning of the infrared light L in the X direction does not detect the end of the linear portion forming the surface silver grid electrode 12.

  Simultaneously or continuously with the scanning of the infrared light L at one corner of the semiconductor substrate 1, the surface silver grid electrode 12 is scanned by the scanning with the infrared light L in the X direction even at a position that is diagonal to the corner. Detect the linear part that forms. Thereby, the position of an electrode pattern is determined about the Y direction which is a direction orthogonal to the X direction among the two-dimensional directions on the semiconductor substrate 1.

  In addition, the light receiving unit 14 is obtained from the reflectance of the infrared light L scanned in the longitudinal direction (Y direction) of the front silver bus electrode 11 in the vicinity of the portion of the semiconductor substrate 1 where the front silver bus electrode 11 is formed. A linear portion forming the silver bus electrode 11 is detected. Thereby, the position of the electrode pattern is determined in the X direction among the two-dimensional directions on the semiconductor substrate 1. In addition, the scanning mode of the infrared light L in the high-concentration diffusion layer detection step is not limited to the case described in the present embodiment, and may be changed as appropriate.

  According to the present embodiment, the position of the high concentration diffusion layer 7 is detected according to the reflectance of the infrared light L in the N-type impurity diffusion layer 6 instead of the alignment based on the peripheral position of the semiconductor substrate 1. . By determining the position of the high-concentration diffusion layer 7 based on the reflectance of the infrared light L, the position of the high-concentration diffusion layer 7 in the semiconductor substrate 1 is directly determined, unlike the case where the peripheral position of the semiconductor substrate 1 is used as a reference. Can be detected automatically. By aligning the light receiving surface side electrode 3 with the position of the high concentration diffusion layer 7 detected directly, the light receiving surface side electrode 3 can be easily and accurately formed on the high concentration diffusion layer 7. Thereby, there is an effect that a selective emitter type solar cell with high conversion efficiency can be stably manufactured with good reproducibility by a simple process.

Embodiment 2. FIG.
FIG. 6 is a diagram for explaining the detection of the position of the high-concentration diffusion layer in the method for manufacturing a solar cell according to the second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and repeated description will be omitted as appropriate. In the second embodiment, when there is an abnormality in the detection of the position of the high concentration diffusion layer 7 in the high concentration diffusion layer detection step, the traveling direction of the detection light in the detection light supply step is changed to detect the detection light supply step. And the determination step is performed again.

  For example, as indicated by a broken-line arrow in the figure, when the infrared light L that is the detection light is irradiated, the infrared light L enters the texture structure formed on the light receiving surface side surface of the semiconductor substrate 1. Depending on the state of the portion, the infrared light L may be reflected in a direction different from that of the light receiving unit 14 (see FIG. 4).

  When the infrared light L reflected by the N-type impurity diffusion layer 6 travels in a direction other than a desired direction and the infrared light L is not sufficiently detected, and there is an error in the determination process, the light source 13 (FIG. 4) and the infrared light L is supplied again. For example, the traveling direction of the infrared light L is changed by adjusting the inclination of the principal ray of the infrared light L in accordance with the direction of the light source 13. It is assumed that the direction and amount of change for changing the inclination of the principal ray of the infrared light L can be set as appropriate.

  In the present embodiment, the traveling direction of the infrared light L is adjusted so as to realize a reflection characteristic suitable for detecting the position of the high concentration diffusion layer 7 by the infrared light L reflected by the semiconductor substrate 1. For example, it is assumed that the reflectance is normally measured in the light receiving unit 14 by changing the traveling direction of the infrared light L from the state indicated by the dashed arrow in the drawing to the state indicated by the solid arrow. When the reflectance is measured, it is determined whether or not the high-concentration diffusion layer 7 is formed at the position where the infrared light L is reflected by the determination process again.

  According to the present embodiment, as in the first embodiment, a selective emitter type solar cell capable of obtaining high conversion efficiency can be manufactured stably with good reproducibility by a simple process. Furthermore, according to the present embodiment, when there is an error due to the infrared light L reflected by the N-type impurity diffusion layer 6 traveling in a direction other than the desired direction, the traveling direction of the infrared light L is changed. Then, by performing the high concentration diffusion layer detection step again, it is possible to suppress the situation where the high concentration diffusion layer 7 cannot be detected due to an error in reflectance measurement.

Embodiment 3 FIG.
In the solar cell manufacturing method according to the third embodiment, the detection light wavelength in the detection light supply step is changed when there is an abnormality in the detection of the position of the high concentration diffusion layer 7 in the high concentration diffusion layer detection step. Then, the detection light supply step and the determination step are performed again. Detection of the position of the high concentration diffusion layer in the present embodiment will be described with reference to FIGS. The same parts as those in the first embodiment are denoted by the same reference numerals, and repeated description will be omitted as appropriate.

  The state of the portion where the infrared light L is incident in the texture structure formed on the surface of the semiconductor substrate 1 on the light receiving surface side when the infrared light L as the detection light is irradiated to the light receiving surface side of the semiconductor substrate 1 In some cases, the infrared light L may not be sufficiently detected by the light receiving unit 14 (see FIG. 4).

  When there is an error in the determination process because the infrared light L is not sufficiently detected, the wavelength of the infrared light L from the light source 13 (see FIG. 4) is changed and the infrared light L is supplied again. It is assumed that whether the wavelength of the infrared light L is changed to a long wavelength or a short wavelength, the amount of change in wavelength, and the like can be set as appropriate.

  In the present embodiment, the wavelength of the infrared light L is adjusted so as to realize a reflection characteristic suitable for detecting the position of the high-concentration diffusion layer 7 by the infrared light L reflected by the semiconductor substrate 1. When the reflectance is normally measured in the light receiving unit 14 by appropriately changing the wavelength of the infrared light L, the high-concentration diffusion layer 7 is formed at the position where the infrared light L is reflected by the determination process again. It is determined whether or not.

  According to the present embodiment, as in the first embodiment, a selective emitter type solar cell capable of obtaining high conversion efficiency can be manufactured stably with good reproducibility by a simple process. Furthermore, according to the present embodiment, when there is an error due to insufficient detection of the infrared light L, the wavelength of the infrared light L is changed, and the high-concentration diffusion layer detection step is performed again, so that the reflectance is increased. It is possible to suppress a situation in which the high concentration diffusion layer 7 cannot be detected due to a measurement error. In the high-concentration diffusion layer detection step, both the change of the traveling direction of the infrared light L in the second embodiment and the change of the wavelength of the infrared light L in the present embodiment may be performed.

Embodiment 4 FIG.
FIG. 7 is a diagram for explaining the detection of the position of the high-concentration diffusion layer with detection light in the method for manufacturing a solar cell according to the fourth embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and repeated description will be omitted as appropriate. In the present embodiment, in the detection light supply process, the entire surface of the impurity diffusion layer 6 is irradiated with detection light all at once.

  The light source 21 irradiates the entire light receiving surface side surface of the semiconductor substrate 1 with infrared light L as detection light. The light source 21 supplies infrared light having a wavelength region of 1000 nm to 1500 nm as the infrared light L, for example. For example, the light source 21 includes an optical system that diffuses the generated infrared light L in a two-dimensional direction. Such an optical system may be provided in the optical path of the infrared light L from the light source 21.

  The filter 23 is provided in a region through which the infrared light L traveling from the light source 21 to the semiconductor substrate 1 passes. For example, the filter 23 shields light having a wavelength of less than 1000 nm and transmits light having a wavelength of 1000 nm or more. The filter 23 has a function of removing light in a wavelength region that becomes noise in the reflectance measurement by the infrared camera 22 described later. Note that the filter 23 may be omitted depending on the situation where the influence of light in the wavelength region that causes noise is small.

  The infrared camera 22 collectively detects the infrared light L reflected by the N-type impurity diffusion layer 6. The infrared camera 22 measures the reflectance for each position in the two-dimensional direction of the light receiving surface side surface of the semiconductor substrate 1. The infrared camera 22 determines a portion of the N-type impurity diffusion layer 6 where the high-concentration diffusion layer 7 is formed from the reflectance distribution as a measurement result.

  According to the present embodiment, as in the first embodiment, a selective emitter type solar cell capable of obtaining high conversion efficiency can be manufactured stably with good reproducibility by a simple process. Furthermore, according to the present embodiment, it is possible to determine the position of the high concentration diffusion layer 7 by collectively irradiating the entire area of the semiconductor substrate 1 with the infrared light L, so that the time required for the high concentration diffusion layer detection step is reached. Can be shortened and the throughput can be improved.

  The method of aligning the high-concentration diffusion layer 7 and the light-receiving surface side electrode 3 described in each embodiment is not limited to being applied to the formation of a selective emitter structure through a laser doping method. The method of each embodiment is a method other than the laser doping method, for example, a printing method using a paste containing impurities, an etching method using an oxide film mask, an ion implantation method, an etch back method, or the like. The present invention can also be applied to the formation of a selective emitter structure. In any case, the position of the high concentration diffusion layer 7 can be detected from the difference in reflectance of the detection light between the high concentration diffusion layer 7 and the low concentration diffusion layer 8. This makes it possible to produce solar cells with high conversion efficiency in a simple process with high reproducibility, regardless of which method is used to form the selective emitter structure, as in the case of employing the laser doping method. The effect that it is possible can be obtained.

  In each embodiment, the case where a P-type silicon wafer is used as the semiconductor substrate 1 has been described. However, a reverse-conductivity solar cell in which a P-type diffusion layer is formed using an N-type silicon wafer as the semiconductor substrate 1. The effects of the present invention described above can also be obtained. In the above-described embodiment, a single crystal silicon wafer is used as the semiconductor substrate 1, but the above-described effects of the present invention can be obtained even when a polycrystalline silicon wafer is used as the semiconductor substrate 1.

  The N-type impurity diffused in the P-type silicon wafer is not limited to phosphorus, and any element that becomes an N-type diffusion source may be applied. For an N-type silicon wafer, for example, boron is used as a P-type impurity. As the P-type impurity, any element that becomes a P-type diffusion source in addition to boron may be used.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Antireflection film 3 Light-receiving surface side electrode 4 Back surface side electrode 5 P type single crystal silicon 6 N type impurity diffusion layer 7 High concentration diffusion layer 8 Low concentration diffusion layer 11 Table silver bus electrode 12 Table silver grid electrode 13 Light source 14 Light-receiving part 21 Light source 22 Infrared camera 23 Filter L Infrared light

Claims (6)

As a diffusion layer forming step for forming an impurity diffusion layer on the surface on the light receiving surface side of the semiconductor substrate, a high concentration diffusion layer is formed by selectively diffusing impurities in a patterned region of the impurity diffusion layer. An impurity diffusion step in which a region other than the region where the high concentration diffusion layer is formed in the impurity diffusion layer is used as a low concentration diffusion layer having an impurity concentration lower than that of the high concentration diffusion layer;
A high-concentration diffusion layer detection step for detecting a position where the high-concentration diffusion layer is formed in the impurity diffusion layer;
A light receiving surface side electrode forming step for forming a light receiving surface side electrode on the high concentration diffusion layer at the position detected in the high concentration diffusion layer detecting step,
The high concentration diffusion layer detection step includes:
A detection light supply step for supplying detection light to the impurity diffusion layer that has undergone the impurity diffusion step;
Determining a reflectance of the detection light in the impurity diffusion layer, and determining whether or not the high-concentration diffusion layer is formed at a position where the detection light is reflected, according to the reflectance. A method for manufacturing a solar cell.   The method for manufacturing a solar cell according to claim 1, wherein in the detection light supply step, infrared light as the detection light is supplied.   In the high concentration diffusion layer detection step, when there is an abnormality in the detection of the position of the high concentration diffusion layer, the traveling direction of the detection light in the detection light supply step is changed, and the detection light supply step and the The method for manufacturing a solar cell according to claim 1, wherein the determination step is performed again.   In the high concentration diffusion layer detection step, when there is an abnormality in the detection of the position of the high concentration diffusion layer, the detection light supply step and the determination are performed by changing the wavelength of the detection light in the detection light supply step. The method of manufacturing a solar cell according to claim 1, wherein the step is performed again.   5. The method for manufacturing a solar cell according to claim 1, wherein in the detection light supply step, the detection light is scanned by the impurity diffusion layer. 6.   3. The method for manufacturing a solar cell according to claim 1, wherein, in the detection light supplying step, the entire surface of the impurity diffusion layer is collectively irradiated with the detection light.

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