WO2009157052A1

WO2009157052A1 - Method for manufacturing photovoltaic system

Info

Publication number: WO2009157052A1
Application number: PCT/JP2008/061410
Authority: WO
Inventors: 濱本　哲
Original assignee: 三菱電機株式会社
Priority date: 2008-06-23
Filing date: 2008-06-23
Publication date: 2009-12-30

Abstract

In a method for manufacturing a photovoltaic system, the outermost surface of a diffused layer formed on the surface of a semiconductor substrate by a thermal diffusion method is removed with excellent controllability. The manufacturing method includes an N-type diffused layer formation step for forming an N-type diffused layer (102) by diffusing an N-type impurity on the light incident surface side of a P-type silicon substrate (101); a silicon oxide film formation step for forming a silicon oxide film (103) by oxidizing the outermost surface section of the N-type diffused layer (102) at a temperature where the N-type impurity is not diffused while containing the N-type impurity diffused in the outermost surface section; and a silicon oxide film removal step for removing the silicon oxide film (103).

Description

Method for manufacturing photovoltaic device

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

In general, in order to manufacture a photovoltaic device, an impurity having a conductivity type opposite to that of a semiconductor substrate is diffused on the surface of the substrate to form an impurity diffusion layer (hereinafter referred to as a diffusion layer), and a PN junction is formed. It forms (for example, refer patent document 1). In the photovoltaic device, since the photovoltaic power greatly depends on the level difference of each conductivity type, from the viewpoint, it is preferable that the impurity concentration (doping concentration) for determining the conduction level is higher. In addition, since the diffusion layer also functions as a part of an electrode for efficiently extracting the generated current to an external circuit, it is preferable that the dopant concentration is high from that viewpoint.

On the other hand, the crystal quality in a silicon semiconductor shows better characteristics as the concentration of impurities present therein is lower. If the dopant concentration is too high, the crystal quality as a semiconductor is greatly reduced and the recombination rate is increased, so that the photovoltaic power is reduced. Therefore, it is important to set the dopant concentration to an appropriate concentration while balancing these three.

JP-A-10-70296

By the way, as shown in the above-mentioned Patent Document 1, a thermal diffusion method is often used for forming a diffusion layer. The thermal diffusion method is a method in which a substance containing the element to be diffused is heated to a high temperature in contact with the substrate surface and penetrated into the solid using dissolution in the solid and movement by thermal vibration. In the case of crystalline silicon solar cells, phosphorus (P) diffusion is often used. In the thermal diffusion method, since the diffusion source is in contact with the surface, the dopant concentration in the outermost surface portion is extremely high, and in many cases, the solid solubility (the upper limit at which the element can be dissolved in the solid) Has reached. Such a portion has extremely poor characteristics as a semiconductor, and is a major factor for reducing the photovoltaic power.

In order to suppress the influence of the portion having a high dopant concentration as described above and improve the photovoltaic power, it is one of important methods to remove the outermost surface portion of the diffusion layer. The thickness of the portion to be obtained is very thin, around 10 nm. Therefore, there is a demand for a method for removing this thin portion with good controllability over a wide area. However, the removal by etching, which is a general method, has a problem that it is very difficult to remove this thin portion with good controllability over a wide area. Although removal by oxidation is also mentioned, since normal thermal oxidation is performed at a high temperature equal to or higher than the diffusion temperature, phosphorus moves again with heating, and the new interface also has a very high concentration. There was a problem that it was.

The present invention has been made in view of the above, and an object of the present invention is to obtain a method for manufacturing a photovoltaic device capable of removing the outermost surface of a diffusion layer formed on the surface of a semiconductor substrate by a thermal diffusion method with good controllability. To do.

In order to achieve the above object, a method for manufacturing a photovoltaic device according to the present invention comprises diffusing impurities of a second conductivity type on the light incident surface side of a semiconductor substrate of a first conductivity type. A first diffusion layer forming step of forming a first diffusion layer having a concentration; and the second diffusion layer diffused into the outermost surface portion of the first diffusion layer at a temperature at which the impurities of the second conductivity type do not diffuse. An oxide film forming step of forming an oxide film by oxidizing while containing conductive impurities and an oxide film removing step of removing the oxide film are included.

According to the present invention, after the first diffusion layer containing the second conductivity type impurity is formed on the light incident surface side of the first conductivity type semiconductor substrate, the second conductivity type impurity is dissolved. The outermost surface portion, which is included near the limit of the degree of crystallinity and is deteriorated, is oxidized and removed without re-diffusion of the impurity of the second conductivity type. The outermost surface portion of the diffusion layer can be removed easily and with good controllability. The resulting photovoltaic device can convert the captured optical energy into electrical energy with high current-voltage characteristics, improve the output characteristics of the photovoltaic device, and obtain a highly efficient photovoltaic device Has the effect of being able to.

FIG. 1-1 is a top view of the photovoltaic device. FIG. 1-2 is a rear view of the photovoltaic device. 1-3 is a cross-sectional view taken along the line AA of FIG. 1-2. FIG. 2-1 is a perspective view schematically showing one example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 1). FIG. 2-2 is a perspective view schematically showing one example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 2). FIG. 2-3 is a perspective view schematically showing one example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 3). FIG. 2-4 is a perspective view schematically showing one example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 4). FIG. 2-5 is a perspective view schematically showing an example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 5). FIG. 2-6 is a perspective view schematically showing one example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 6). FIG. 3-1 is a sectional view schematically showing an example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 1). FIG. 3-2 is a sectional view schematically showing an example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 2). FIG. 3-3 is a sectional view schematically showing one example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 3). FIG. 3-4 is a sectional view schematically showing an example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (part 4). FIG. 3-5 is a sectional view schematically showing one example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 5). FIG. 3-6 is a sectional view schematically showing one example of a processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment (No. 6). FIG. 4 is a diagram showing the relationship between the thickness of the oxide film and the oxidation treatment time at each heat treatment temperature. FIG. 5 is a diagram showing the diffusion coefficient of phosphorus in silicon. FIG. 6 is a diagram showing the solid solubility of phosphorus in silicon. FIG. 7-1 is a perspective view schematically showing an example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment (No. 1). FIG. 7-2 is a perspective view schematically showing an example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment (No. 2). FIG. 7-3 is a perspective view schematically showing one example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment (No. 3). FIG. 7-4 is a perspective view schematically showing an example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment (part 4). FIG. 7-5 is a perspective view schematically showing one example of a processing procedure of the manufacturing method of the photovoltaic device according to the second embodiment (No. 5). FIG. 7-6 is a perspective view schematically showing an example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment (No. 6). FIG. 7-7 is a perspective view schematically showing one example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment (No. 7). 7-8 is a perspective view schematically showing an example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment (No. 8). FIG. FIG. 7-9 is a perspective view schematically showing an example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment (No. 9). FIG. 7-10 is a perspective view schematically showing one example of a processing procedure of the method for manufacturing the photovoltaic device according to the second embodiment (No. 10). FIG. 7-11 is a perspective view schematically showing an example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment (No. 11). FIGS. 8-1 is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic device by this Embodiment 2 (the 1). FIG. 8-2 is a sectional view schematically showing an example of a processing procedure of the manufacturing method of the photovoltaic device according to the second embodiment (No. 2). FIG. 8-3 is a sectional view schematically showing an example of a processing procedure of the manufacturing method of the photovoltaic apparatus according to the second embodiment (No. 3). FIG. 8-4 is a sectional view schematically showing an example of a processing procedure of the manufacturing method of the photovoltaic apparatus according to the second embodiment (part 4). FIG. 8-5 is a sectional view schematically showing an example of a processing procedure of the manufacturing method of the photovoltaic apparatus according to the second embodiment (No. 5). FIGS. 8-6 is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic device by this Embodiment 2 (the 6). FIGS. 8-7 is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic device by this Embodiment 2 (the 7). FIGS. 8-8 is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic device by this Embodiment 2 (the 8). FIGS. 8-9 is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic device by this Embodiment 2 (the 9). FIGS. 8-10 is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic device by this Embodiment 2 (the 10). FIG. 8-11 is a sectional view schematically showing an example of a processing procedure of the manufacturing method of the photovoltaic device according to the second embodiment (No. 11).

Explanation of symbols

100 Photovoltaic device 101 P-type silicon substrate 102 N-type diffusion layer 102a Outermost surface portion 102H High-concentration N-type diffusion layer 102L Low-concentration N-type diffusion layer 103 Silicon oxide film 109 Antireflection film 110 P + layer 111 Surface electrode 112 Grid electrode 113 Bus electrode 120 Back surface electrode 121 Back side extraction electrode 122 Back side current collecting electrode 131 Etching-resistant film 140a Texture structure formation region 140b Electrode formation region 141 Opening 142 Recess

DETAILED DESCRIPTION Exemplary embodiments of a method for producing a photovoltaic device according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments. In addition, cross-sectional views of photoelectric conversion devices used in the following embodiments are schematic, and the relationship between layer thickness and width, the ratio of the thickness of each layer, and the like are different from actual ones.

Embodiment 1 FIG.
First, before describing the manufacturing method of the photovoltaic device according to the first embodiment of the present invention, an outline of the general configuration of a general photovoltaic device will be described. FIGS. 1-1 to 1-3 are diagrams schematically showing an example of the overall configuration of the photovoltaic device, FIG. 1-1 is a top view of the photovoltaic device, and FIG. FIG. 1 is a back view of the electromotive force device, and FIG. 1-3 is a cross-sectional view taken along the line AA of FIG. The photovoltaic device 100 includes a P-type silicon substrate (hereinafter also simply referred to as a silicon substrate) 101 as a semiconductor substrate, and an N-type impurity on one main surface (light-receiving surface) side of the P-type silicon substrate 101. And a P + layer 110 containing P-type impurities at a higher concentration than the silicon substrate 101 on the surface on the other main surface (back surface) side.

Further, the photovoltaic device 100 includes an antireflection film 109 that prevents reflection of incident light on the light receiving surface of the photoelectric conversion layer, and a light receiving surface for locally collecting electricity generated by the photoelectric conversion layer. The grid electrode 112 made of silver or the like provided, the bus electrode 113 made of silver or the like provided almost orthogonally to the grid electrode 112 for taking out the electricity collected by the grid electrode 112, and the photoelectric conversion layer A back side extraction electrode 121 made of aluminum or the like provided on almost the entire back surface of the P-type silicon substrate 101 for the purpose of taking out electricity and reflecting incident light transmitted through the photoelectric conversion layer, and electricity generated in the back side extraction electrode 121 And a back side collecting electrode 122 made of silver or the like for collecting current. In addition, the grid electrode 112 and the bus electrode 113 on the light receiving surface side (front surface side) are combined, hereinafter, also referred to as the surface electrode 111, and the back side extraction electrode 121 and the back side collector electrode 122 on the back side are combined. Then, it is also referred to as a back electrode 120.

In the photovoltaic device 100 configured in this way, sunlight is applied to the PN junction surface (the junction surface between the P-type silicon substrate 101 and the N-type diffusion layer 102) from the light-receiving surface side of the photovoltaic device 100. And holes and electrons are generated. Due to the electric field in the vicinity of the PN junction surface, the generated electrons move toward the N-type diffusion layer 102 and the holes move toward the P + layer 110. As a result, electrons are excessive in the N-type diffusion layer 102 and holes are excessive in the P + layer 110. As a result, photovoltaic power is generated. This photovoltaic power is generated in a direction in which the PN junction is biased in the forward direction, the front electrode 111 connected to the N-type diffusion layer 102 becomes a negative pole, and the back electrode 120 connected to the P + layer 110 becomes a positive pole. Current flows in the external circuit that does not.

Next, a method for manufacturing the photovoltaic device 100 having such a structure will be described. FIGS. 2-1 to 2-6 are perspective views schematically showing an example of the processing procedure of the manufacturing method of the photovoltaic device according to the first embodiment. FIGS. 3-1 to 3-6 are It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1. FIG. In these FIGS. 2-1 to 3-6, a part of the periphery of one grid electrode 112 of the photovoltaic device 100 is shown enlarged.

First, a silicon substrate 101 is prepared (FIGS. 2-1 and 3-1). Here, it is assumed that a P-type polycrystalline silicon substrate that is most frequently used for consumer photovoltaic devices is used. The silicon substrate 101 is manufactured by slicing a polycrystalline silicon ingot with a multi-wire saw and removing damage during slicing by wet etching using an acid or alkali solution. The thickness of the silicon substrate 101 after removing the damage is 200 μm, and the dimensions are 150 mm × 150 mm.

In many cases, a texture shape is formed simultaneously with or subsequent to the removal of damage. This is to provide an uneven shape on the surface of the silicon substrate 101 as a measure for efficiently absorbing light incident on the silicon substrate 101 inside.

Next, the silicon substrate 101 after removing the damage is put into a thermal oxidation furnace, heated in an atmosphere of phosphorus (P) as an N-type impurity, and phosphorus is diffused at a high concentration on the surface of the silicon substrate 101, so that N-type diffusion is performed. The layer 102 is formed (FIGS. 2-2 and 3-2). Here, phosphorus oxychloride (POCl ₃ ) is used to form a phosphorus atmosphere and diffuse at 800 to 850 ° C. The N-type diffusion layer 102 is controlled so that the sheet resistance is 30 to 80 Ω / □, preferably 40 to 60 Ω / □. Thereafter, the phosphorus glass layer formed by heating in the presence of phosphorus oxychloride vapor is removed in a hydrofluoric acid solution. Note that the outermost surface portion 102a in the thickness range of about 10 nm from the surface of the N-type diffusion layer 102 has reached the limit or close to the limit of the solid solubility of phosphorus in the silicon substrate 101, and has characteristics as a semiconductor. This is a very bad part.

Next, the silicon substrate 101 on which the N-type diffusion layer 102 is formed is put into an oxidation furnace in which a high-concentration ozone atmosphere can be introduced, and the outermost surface portion 102a of the N-type diffusion layer 102 is oxidized by taking in the phosphorus contained therein. (FIGS. 2-3 and 3-3). As a result, a silicon oxide film 103 containing phosphorus is formed on the outermost surface of the N-type diffusion layer 102, but the lower portion remains the N-type diffusion layer 102. The silicon thermal oxidation in this high-concentration ozone atmosphere is described in detail in Japanese Patent Application Laid-Open No. 2003-209108.

¡When thermal oxidation is performed in a high-concentration ozone atmosphere, the oxidation reaction can proceed at a higher speed at a lower temperature than in general thermal oxidation methods. FIG. 4 is a diagram showing the relationship between the thickness of the oxide film and the oxidation treatment time at each heat treatment temperature. As shown in FIG. 4, for example, a thermal oxide film having a thickness of 10 nm can be formed in about 14 minutes at 500 ° C. and in about 9 minutes at 590 ° C.

FIG. 5 is a diagram showing the diffusion coefficient of phosphorus in silicon, and FIG. 6 is a diagram showing the solid solubility of phosphorus in silicon. The outermost surface portion 102a of the N-type diffusion layer 102 is in a state in which phosphorus is contained up to the solid solubility limit as shown in FIG. 6 by the diffusion treatment, but as shown in FIG. The diffusion coefficient of phosphorus decreases rapidly as the temperature is low, and at a temperature of 700 ° C. or lower, preferably 600 ° C. or lower, which extends this graph, phosphorus can hardly move in the silicon crystal. Therefore, the oxidation of the silicon substrate (N-type diffusion layer 102) proceeds in such a manner that phosphorus is taken in along with the oxidation. In this way, the outermost surface portion 102a to be removed can be changed to the silicon oxide film 103 while containing phosphorus. The oxidation temperature is 300 to 700 ° C. where the diffusion coefficient of phosphorus is small and an oxidation rate of a certain level or more is obtained, preferably 400 to 600 ° C. The thickness of the silicon oxide film 103 to be formed is 5 to 20 nm, Desirable is controlled in the range of 8 to 15 nm.

Thereafter, the silicon oxide film 103 on the outermost surface after oxidation is unnecessary and is removed (FIGS. 2-4 and 3-4). Hydrofluoric acid dissolves the silicon oxide film, but does not dissolve the silicon crystal itself. Therefore, when this hydrofluoric acid is used, the dissolution reaction stops when the silicon oxide film 103 containing phosphorus on the outermost surface is removed, so that only the portion with poor crystallinity to be removed can be removed with good controllability.

Next, as the antireflection film 109, a SiN film is formed on the cell surface by plasma CVD (Chemical Vapor Deposition) method (FIGS. 2-5 and 3-5). 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 as the antireflection film 109. Moreover, you may form by different film-forming methods, such as a sputtering method.

Thereafter, a paste mixed with aluminum is formed by screen printing on the entire surface of the back surface of the silicon substrate 101 other than the position where the back side collecting electrode 122 is formed, and the paste mixed with silver is formed at a predetermined position (back side collector) on the back surface of the silicon substrate 101. The paste is mixed with silver on the surface of the silicon substrate 101 by the screen printing method. Then, the silicon substrate 101 is baked. For example, the firing process is performed at 760 ° C. in an air atmosphere, and the front electrode 111 is formed on the front surface and the back electrode 120 is formed on the back surface (FIGS. 2-6 and 3-6). At this time, the surface electrode 111 penetrates the antireflection film 109 and contacts the N-type diffusion layer 102 at the joint portion. As a result, the N-type diffusion layer 102 can obtain a good resistive junction with the surface electrode 111. In addition, aluminum diffuses from the paste mixed with aluminum formed on the back surface into the silicon substrate 101 to form the P + layer 110 having the BSF function on the back surface side of the silicon substrate 101 and used for forming the P + layer 110. The missing aluminum in the paste is formed as the back side extraction electrode 121. The photovoltaic device is manufactured through the above steps.

According to the first embodiment, after the N-type diffusion layer 102 is formed on the P-type silicon substrate 101, the heat treatment is performed in a high-concentration ozone atmosphere at a temperature of 700 ° C. or less at which phosphorus hardly diffuses. Only the outermost surface of the N-type diffusion layer 102 can be oxidized to form the silicon oxide film 103 containing phosphorus. Further, by etching this silicon oxide film 103 with hydrofluoric acid, only the silicon oxide film 103 can be etched without etching the P-type silicon substrate 101 (N-type diffusion layer 102). This has the effect that the portion of the N-type diffusion layer 102 having the highest phosphorus concentration and poor crystallinity can be removed easily and with good controllability. In addition, the photovoltaic device 100 formed in this way has improved crystallinity at the outermost surface portion 102a of the N-type diffusion layer 102, so that a high photovoltaic power can be realized. The output characteristics of the device 100 are improved, and the photovoltaic device 100 having high efficiency can be obtained.

Further, since the outermost surface portion 102a having poor crystallinity of the N-type diffusion layer 102 is removed, the efficiency is improved, and the photovoltaic device 100 to be manufactured contributes to the extension of the lifetime and the yield by the amount of addition. can do. As a result, the raw material can be reduced.

Embodiment 2. FIG.
In the first embodiment, the case where the structure of the diffusion layer is uniform is shown. However, in the second embodiment, a case where the structure of the diffusion layer differs depending on the part is shown. FIGS. 7-1 to 7-11 are perspective views schematically showing an example of the processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment. FIGS. 8-1 to 8-11 are FIGS. FIG. 5 is a cross-sectional view schematically showing an example of a processing procedure of the method for manufacturing a photovoltaic device according to the second embodiment. In FIGS. 7-1 to 8-11, for example, a part of the periphery of one grid electrode 112 of the photovoltaic device 100 of FIG. 1 is shown enlarged.

First, similarly to the case of FIGS. 2-1 and 3-1 in the case of the first embodiment, a P-type silicon substrate from which damage has been removed is prepared (FIGS. 7-1 and 8-1). Thereafter, the silicon substrate 101 after removal of the damage is put into a thermal oxidation furnace, heated in an atmosphere of phosphorus as an N-type impurity, and phosphorus is diffused at a high concentration on the surface of the silicon substrate 101, whereby a high-concentration N-type diffusion layer is formed. 102H is formed (FIGS. 7-2 and 8-2). Here, phosphorus oxychloride is used to form a phosphorus atmosphere and diffused at 800 to 850 ° C. Further, the surface sheet resistance of the high concentration N-type diffusion layer 102H is controlled to be 30 to 60Ω / □.

Thereafter, a film 131 having etching resistance (hereinafter referred to as an etching resistant film) 131 is formed on the high-concentration N-type diffusion layer 102H formed on one main surface (FIGS. 7-3 and 8-3). The etching resistant film 131 is a material having resistance when the silicon substrate 101 is textured and etched later, and is a silicon nitride film (hereinafter, referred to as a SiN film), a silicon oxide (SiO ₂ , SiO) film, a silicon oxynitride ( An SiON) film, an amorphous silicon (а-Si) film, a diamond-like carbon film, a resin film, or the like can be used. Here, an SiN film having a thickness of 80 nm formed by plasma CVD is used as the etching resistant film 131. Although the film thickness is 80 nm, an appropriate film thickness can be selected from the etching conditions at the time of texture / etching and the removability of the SiN film in the subsequent process.

Next, an opening 141 that is a fine hole is formed in the texture structure forming region 140a on the etching resistant film 131 (FIGS. 7-4 and 8-4). As a result, the surface of the underlying silicon substrate 101 (high-concentration N-type diffusion layer 102H) is exposed at the opening 141 portion. The opening 141 is not formed in the electrode forming region 140b where the light incident side electrode (surface electrode) of the photovoltaic device 100 is to be formed without forming the texture structure. The opening 141 can be formed by a laser irradiation method, a photolithography method used in a semiconductor process, or the like.

Next, the vicinity of the surface of the silicon substrate 101 including the high-concentration N-type diffusion layer 102H is etched through the opening 141 opened in the etching resistant film 131 to form the recess 142 (FIGS. 7-5 and 8-5). In this etching, since the silicon substrate 101 is etched through the fine opening 141, a concave portion 142 is formed on the surface of the silicon substrate 101 at the concentric position with the fine opening 141 as the center. When etching is performed with a mixed acid etching solution, a uniform texture is formed without being affected by the crystal plane orientation of the surface of the silicon substrate 101, and the photovoltaic device 100 with less surface reflection loss can be manufactured. Here, a mixed solution of hydrofluoric acid and nitric acid is used as an etching solution. The mixing ratio is hydrofluoric acid 1: nitric acid 20: water 10. The mixing ratio of the etching liquid can be changed to an appropriate mixing ratio depending on the desired etching rate and etching shape. Further, along with the formation of the recess 142 by this etching, the high concentration N-type diffusion layer 102H in that portion is simultaneously removed. That is, of the surface of the recess 142 formed by this etching, the high concentration N-type diffusion layer 102H is formed on the substrate surface side, but no impurity is introduced in a deeper region. On the other hand, the electrode formation region 140b where the surface electrode 111 is to be formed is in a state where the high-concentration N-type diffusion layer 102H remains. Further, as shown in FIGS. 7-5 and 8-5, the high-concentration N-type diffusion layer 102H can be left also in the portion between the adjacent recesses 142. Thus, the generated current is guided to the surface electrode 111 (grid electrode 112) through a low-resistance current path.

Next, after removing the etching resistant film 131 using hydrofluoric acid or the like (FIGS. 7-6 and 8-6), the silicon substrate 101 is again put into a thermal oxidation furnace and heated in the presence of phosphorus oxychloride vapor. Thus, a low concentration N-type diffusion layer 102L in which phosphorus is diffused at a low concentration is formed on the surface of the recess 142 (FIGS. 7-7 and 8-7). The diffusion temperature at this time is 800 to 850 ° C. Here, since the high-concentration N-type diffusion layer 102H remains in the electrode formation region 140b at the time of the etching, the high-concentration N-type diffusion layer 102H remains almost as it is even if the low-concentration diffusion is performed again. Become. On the other hand, in the vicinity of the bottom of the concave portion 142 of the texture structure forming region 140a, the high concentration N type diffusion layer 102H is removed during etching, and the low concentration N type diffusion layer 102L is formed on the surface of the concave portion 142. In this diffusion treatment, the surface sheet resistance of the low concentration N-type diffusion layer 102L is controlled to be 60 to 150Ω / □.

After forming the high-concentration N-type diffusion layer 102H and the low-concentration N-type diffusion layer 102L, the phosphorus glass layer formed by heating in the presence of phosphorus oxychloride vapor is removed in a hydrofluoric acid solution. Thereafter, in this state, ozone oxidation is performed in the same manner as in the first embodiment, and the uppermost surface portions of the high-concentration N-type diffusion layer 102H and the low-concentration N-type diffusion layer 102L are oxidized including phosphorus. As a result, a silicon oxide film 103 containing phosphorus is formed on the outermost surfaces of the high-concentration N-type diffusion layer 102H and the low-concentration N-type diffusion layer 102L (FIGS. 7-8 and 8-8).

In the structure of the diffusion layer of the second embodiment, a high concentration N-type diffusion layer 102H is mainly provided below the portion where the electrode portion is provided, and a low concentration N-type diffusion layer 102L is provided at other portions. Therefore, as compared with the first embodiment, a structure that can suppress the influence of the outermost surface portion is employed. However, as long as the thermal diffusion method is taken, even the low-concentration N-type diffusion layer 102L contains phosphorus up to the solid solubility limit at the outermost surface portion, and the effect is avoided to some extent. Absent. Therefore, the output characteristics of the photovoltaic device 100 can be sufficiently improved with respect to the photovoltaic device 100 having the structure in which the concave portion 142 is formed as the texture structure. In the second embodiment, the thickness to be oxidized may be smaller than that in the first embodiment because the structure capable of suppressing the influence of the outermost surface portion is used. Although it depends on the detailed structure including the surface electrode 111 and productivity, it is appropriate to control in the range of 5 to 15 nm.

Next, the silicon oxide film 103 containing phosphorus at the outermost surface portions of the high-concentration N-type diffusion layer 102H and the low-concentration N-type diffusion layer 102L is removed using hydrofluoric acid to expose the silicon portion (FIG. 7- 9, FIG. 8-9), a SiN film as an antireflection film 109 is formed on the surface of the diffusion layer by a film forming method such as a plasma CVD method (FIGS. 7-10 and 8-10).

Thereafter, a paste mixed with aluminum is formed by screen printing on the entire surface of the back surface of the silicon substrate 101 other than the position where the back side collecting electrode 122 is formed, and the paste mixed with silver is formed at a predetermined position (back side collector) on the back surface of the silicon substrate 101. The paste is mixed with silver on the surface of the silicon substrate 101 by the screen printing method. Then, a baking process is performed to form the back electrode 120 (the back side extraction electrode 121 and the back side current collecting electrode 122) and the front surface electrode 111 (the grid electrode 112 and the bus electrode 113). For example, the firing process is performed at 760 ° C. in an air atmosphere. At this time, the surface electrode 111 penetrates the antireflection film 109 and contacts the high-concentration N-type diffusion layer 102H at the joint portion. As a result, the high-concentration N-type diffusion layer 102H can obtain a good resistive junction with the surface electrode 111. In addition, aluminum diffuses from the paste mixed with aluminum formed on the back surface into the silicon substrate 101 to form a P + layer 110 having a BSF function on the back surface side of the silicon substrate 101 and used for forming the P + layer 110. The aluminum in the paste that did not exist becomes the back electrode 120 (FIGS. 7-11 and 8-11). The photovoltaic device 100 is manufactured through the above steps.

This second embodiment can also obtain the same effects as those of the first embodiment.

Although the silicon substrate used in the first and second embodiments is a P-type silicon substrate, other than a reverse-conductivity type photovoltaic device or silicon substrate that forms a P-type diffusion layer using an N-type silicon substrate. A photovoltaic device using this semiconductor substrate also has the same effect. Although a polycrystalline silicon substrate is used as the substrate, it goes without saying that the same effect can be obtained by using a single crystal silicon substrate. Furthermore, although the case where the thickness of the substrate is 200 μm is shown here, a substrate that can be self-supported, for example, thinned to about 50 μm can be used. Moreover, although the case where the dimension of the board | substrate was also 150 mm x 150 mm was shown, it cannot be overemphasized that the same effect is acquired even if it is larger or smaller than this.

As described above, the method for manufacturing a photovoltaic device according to the present invention is useful for a solar cell that generates power using sunlight.

Claims

A first diffusion layer forming step of diffusing impurities of a second conductivity type on the light incident surface side of the first conductivity type semiconductor substrate to form a first diffusion layer having a first concentration;
An oxide film forming step of forming an oxide film by oxidizing the second conductive type impurity while containing the second conductive type impurity diffused in the outermost surface portion of the first diffusion layer at a temperature at which the second conductive type impurity does not diffuse. When,
An oxide film removing step for removing the oxide film;
A method for manufacturing a photovoltaic device, comprising:
After the first diffusion layer forming step and before the oxide film forming step,
An etching resistant film forming step of forming an etching resistant film having etching resistance compared to the semiconductor substrate on the first diffusion layer;
Forming a microhole at a predetermined position on the etching-resistant film and exposing the first diffusion layer;
A recess forming step for forming a recess by etching the first diffusion layer and the semiconductor substrate around the exposed position of the first diffusion layer;
An etching resistant film removing step of removing the etching resistant film;
A second diffusion layer forming step of diffusing a second conductivity type impurity having a second concentration lower than the first concentration to form a second diffusion layer on the surface on which the recess is formed;
Further including
2. The light according to claim 1, wherein, in the oxide film forming step, an oxide film containing impurities of the second conductivity type diffused in the outermost surface portions of the first and second diffusion layers is formed. A method for manufacturing an electromotive force device.
The method for manufacturing a photovoltaic device according to claim 1, wherein in the oxide film forming step, the outermost surface portion of the first diffusion layer is oxidized at a temperature of 400 ° C or higher and 600 ° C or lower.
3. The photovoltaic device according to claim 2, wherein in the oxide film forming step, the outermost surface portions of the first and second diffusion layers are oxidized at a temperature of 400 ° C. or more and 600 ° C. or less. Production method.
The method for manufacturing a photovoltaic device according to claim 1, wherein in the oxide film forming step, the outermost surface portion of the first diffusion layer is oxidized in an atmosphere containing ozone.
2. The method of manufacturing a photovoltaic device according to claim 1, wherein, in the oxide film forming step, an outermost surface portion having a thickness of 5 to 20 nm is oxidized from the surface of the first diffusion layer.
3. The method of manufacturing a photovoltaic device according to claim 2, wherein in the oxide film forming step, an outermost surface portion having a thickness of 5 to 15 nm is oxidized from the surfaces of the first and second diffusion layers. .
2. The photovoltaic device according to claim 1, wherein in the first diffusion layer forming step, the first diffusion layer is formed so that a sheet resistance is 30Ω / □ or more and 80Ω / □ or less. Production method.
In the first diffusion layer forming step, the first diffusion layer is formed so that the sheet resistance is 30Ω / □ or more and 60Ω / □ or less,
3. The photovoltaic device according to claim 2, wherein in the second diffusion layer forming step, the second diffusion layer is formed so that a sheet resistance is 60 Ω / □ or more and 150 Ω / □ or less. Production method.