TWI629804B - Manufacturing method of solar cell - Google Patents

Abstract

The invention provides a method for manufacturing a solar cell, which comprises: a light-receiving surface (1A) of an n-type single-crystal silicon substrate (1) having a light-receiving surface (1A) and an inner surface (1B); A process for forming a film (2); a heat treatment process for heating an n-type single crystal silicon substrate (1), diffusing boron as a second conductivity type impurity from the BSG film (2), and forming a p-type diffusion layer (7), Before the pn separation process, a BSG film (2) is formed and heated to form a p-type diffusion layer (7), and the BSG film (2) is removed.

Description

Manufacturing method of solar cell

The present invention relates to a method for manufacturing a solar cell, and more particularly to improving photoelectric conversion efficiency.

In the past, one of the solar cells, as shown in Patent Document 1, for example, discloses a method of diffusing a diffusion source, such as a CVD (Chemical Vapor Deposition) method, for a method for diffusing impurities on a light-receiving surface as a light incident surface or as a light-receiving surface. After forming a film, a method in which a substrate and a film made of a diffusion source are heated in a nitrogen atmosphere to diffuse impurities into the substrate.

Advance technical literature Patent literature

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-247364

However, in the method for manufacturing a solar cell as shown in the above Patent Document 1, a phosphorous silicate glass (PSG: Phosphorus Silicate Glass) film or a borosilicate glass (BSG: Boron Silicate Glass) film is placed on a substrate After film formation, a heat treatment for diffusing impurities is performed in a nitrogen atmosphere. Therefore, during film formation, impurities such as phosphorus or boron infiltrate inside the substrate, and diffuse from the adhered products toward the impurities inside. When impurities are mixed in. The incorporation of impurities causes a reduction in the carrier life of the solar cell. In addition, the film-forming material is difficult to process due to reasons such as a large film thickness, and it is likely to cause problems such as electrical shorts due to the incorporation of the impurities.

The present invention has been completed in view of the foregoing, and after forming a solid-phase diffusion source into a film, and then performing impurity diffusion by heat treatment, impurities are prevented from being mixed therein, and processing obstacles caused by the film-forming substance are eliminated, and electrical insulation is improved to obtain The purpose of the solar cell is long carrier life.

The present invention solves the aforementioned problems, and in order to achieve the object, it provides a process including forming a solid-phase diffusion source and a protective film on a first main surface of a first conductive semiconductor substrate having first and second main surfaces facing each other. ; A process of removing a product formed on the second main surface in a film forming process; a process of heating a semiconductor substrate from which the product is removed, and forming a second conductive type first diffusion layer on the first main surface side from a solid-phase diffusion source; A process of forming a second diffusion layer having a first conductivity type on a second main surface of a semiconductor substrate; a process of removing a solid phase diffusion source and a protective film together; and electrically separating the second diffusion layer from the first diffusion layer Process. The process of removing the solid-phase diffusion source is performed before the process of electrically separating the second diffusion layer from the first diffusion layer.

According to the present invention, after the solid-phase diffusion source is formed into a film, and then the impurity is diffused by heat treatment, the inclusion of impurities on the second main surface inside is suppressed, and processing obstacles caused by the film-forming material are eliminated, and electrical insulation is improved. The effect of obtaining a solar cell with a long carrier life is achieved.

1‧‧‧n-type single crystal silicon substrate

1A‧‧‧ Light receiving surface

1B‧‧‧ inside

2‧‧‧BSG film

3‧‧‧ silicon oxide film

4‧‧‧ Boron-containing products

5‧‧‧ containing silicon oxide products

7‧‧‧p-type diffusion layer

8‧‧‧ silicon oxide film

14‧‧‧n-type diffusion layer

15a‧‧‧Light-receiving surface anti-reflection film

15b‧‧‧Insulation film

16‧‧‧ electrode

16a‧‧‧ light receiving electrode

16b‧‧‧ inside electrode

17‧‧‧ Diffusion source

18‧‧‧n-type diffusion layer

20‧‧‧ low concentration n-type diffusion layer

FIG. 1 is a process chart showing a method for manufacturing a solar cell according to the first embodiment.

Figures 2 (a) to 2 (d) are cross-sectional views showing the manufacturing process of the method for manufacturing a solar cell according to the first embodiment.

Figures 3 (a) to 3 (d) are cross-sectional views showing the manufacturing process of the method for manufacturing a solar cell according to the first embodiment.

FIG. 4 is a time chart showing the temperature in the furnace and the state of the environment in the heat treatment process in the manufacturing process of the solar cell according to the first embodiment.

Fig. 5 is a schematic diagram showing a main part of a manufacturing process of a solar cell according to the first embodiment.

Fig. 6 is a process chart showing a method for manufacturing a solar cell according to the second embodiment.

FIG. 7 is a process cross-sectional view showing a main part of a manufacturing process of a solar cell according to the second embodiment.

Fig. 8 is a process drawing of a method for manufacturing a solar cell according to the third embodiment.

FIG. 9 is a process cross-sectional view showing a main part of a manufacturing process of a solar cell according to the third embodiment.

Hereinafter, a method for manufacturing a solar cell and an embodiment of a solar cell according to the present invention will be described in detail based on the drawings. In addition, this embodiment is not intended to limit the present invention, and may be appropriately changed within a range not departing from the gist thereof. In addition, in the diagrams shown below, for ease of understanding, the scale of each layer or each member is different from reality, and the same is true in each diagram.

Embodiment 1

FIG. 1 is a process chart showing the manufacturing process of the first embodiment of the method for manufacturing a solar cell according to the present invention, FIGS. 2 (a) to 2 (d) and FIGS. 3 (a) to 3 (d) ) Is a cross-sectional view showing a manufacturing process of a method for manufacturing a solar cell according to the first embodiment. Figures 2 (a) to 2 (d) are sectional views showing changes in the solar cell substrate during continuous processing in the furnace shown in Figure 1 in the method for manufacturing a solar cell according to the first embodiment. Figures 3 (a) to 3 (d) show changes in the cross-section of the solar cell during the manufacturing process of the first embodiment in the subsequent process of the heat treatment shown in Figures 2 (a) to 2 (d). schematic diagram. Figure 4 is a time chart of the furnace temperature and environmental conditions.

In the method for manufacturing a solar cell according to the first embodiment, before the pn separation process for electrically separating the first diffusion layer and the second diffusion layer, a solid-phase diffusion source is formed and heated to form a first diffusion layer, and the solid phase is removed. Diffusion source. Furthermore, before the heat treatment process for forming the first diffusion layer, the solid-phase diffusion source formed on the second main surface is removed.

Since the method for manufacturing a solar cell according to the first embodiment is a method of forming a solid phase diffusion source into a film and heating it to form a diffusion layer, the solid phase diffusion source is removed, and electrical separation is performed, thereby improving the insulation performance of the processing place. In addition, since the process of removing the solid-phase diffusion source filmed on the second main surface is performed before the process of impurity diffusion from the solid-phase diffusion source by the heating process, the film is formed with the solid-phase diffusion source of the semiconductor substrate. On the surface opposite to the surface, the solid-phase diffusion material oozes and adheres. However, since the solid-phase diffusion source is removed to perform heat treatment, impurities from the adherent are prevented from diffusing to the substrate.

The solar cell system according to the first embodiment uses the n-type single crystal silicon substrate 1 as a first main surface having a light receiving surface 1A and a second surface having a back surface 1B. A semiconductor substrate of the first conductivity type on the main surface. The manufacturing method will be described using FIGS. 1, 2 (a) to 2 (d), 3 (a) to 3 (d), and 4. First, in step S101 of removing the damaged layer, pollution or damage generated during wafer slicing on the surface is removed. For example, an n-type single crystal silicon substrate 1 is immersed in an alkaline solution in which sodium hydroxide is dissolved in an amount of 1% by weight or more and less than 10% by weight to remove contamination and damage from the slice. Thereafter, the light-receiving surface 1A of the n-type single crystal silicon substrate 1 is immersed in, for example, a solution of 0.1% by weight or more and less than 10% by weight of an additive solution such as isopropyl alcohol or capric acid, to form a solution to obtain Anti-reflection structure with uneven texture. Moreover, the removal of contamination and damage of the slice can be performed simultaneously or separately with the formation of the texture. The texture is formed not only on the light receiving surface 1A but also on the back surface 1B. In FIGS. 2 and 3, for easy understanding, the texture is not shown, and the light receiving surface 1A and the inner surface 1B are both shown as flat surfaces.

Next, in the cleaning step S102 before film formation, the surface of the n-type single crystal silicon substrate 1 is cleaned. In this cleaning process, for example, RCA cleaning can be used to remove organic substances and metals combined with a mixed solution of sulfuric acid and hydrogen peroxide, an aqueous solution of hydrofluoric acid, a mixed solution of ammonia water and hydrogen peroxide, and a mixed solution of hydrochloric acid and hydrogen peroxide. And the oxide film manufacturing process, or, for example, according to the texture formation method, only the hydrofluoric acid aqueous solution removal process. In addition, as for the cleaning liquid, among the types of the cleaning liquid, one or a plurality of types may be selected, a mixed solution of hydrofluoric acid and hydrogen peroxide water, or ozone-containing water may be selected.

In addition, in order to prevent the various treatment liquids from becoming other contamination or the cause of unintended reactions, or to ensure the safety after being taken out of the device, in the middle stage or the stage before drying, etc., pure water is used. Wash with water.

Following the above cleaning process, the light receiving surface of the solid-phase diffusion source is 1A. In the film formation step S103 on the side, as shown in FIG. 2 (a), a solid-phase diffusion source is used, for example, as a boron-containing oxide film BSG (Boron Silicate Glass: Boron) on the light receiving surface 1A of the n-type single crystal silicon substrate 1. Phosphosilicate glass) film 2 was formed. For the film formation, for example, reduced pressure CVD and normal pressure CVD can be used. In addition, during the above-mentioned film formation process, the boron-containing product 4 is adhered to the back surface 1B of the n-type single crystal silicon substrate 1 due to the infiltration of the film formation gas. Next, on the upper portion of the BSG film 2, a film, such as a silicon oxide film 3, is formed as a protective cover, that is, a protective film during heat treatment. The silicon oxide film 3 is formed by a film forming process such as reduced pressure CVD and normal pressure CVD in the same manner as the BSG film 2, and it is preferable from the viewpoint of the continuity of the process. When the silicon oxide film 3 was formed, it was the same as the BSG film 2 was formed, and the silicon oxide-containing product 5 was adhered to the back surface 1B due to the film formation gas re-osmosis. The BSG film and the silicon oxide film as a protective film are continuously formed in the same device without opening the device, which can prevent pollution and improve the protection effect. It is not necessary to form them continuously in the same device, and they may be formed separately instead of continuously in the same device.

In step S104 of removing the inner product, as shown in FIG. 2 (b), the product formed on the inner 1B side is removed. Here, the product formed on the back surface 1B side of the n-type single crystal silicon substrate 1 is removed. In other words, after the BSG film 2 and the silicon oxide film 3 are formed, the boron-containing product 4 and the silicon oxide-containing product 5 on the back 1B side are removed. The removal is performed, for example, by dissolving in a hydrofluoric acid aqueous solution. Since the boron-containing product 4 and the BSG film 2 and the silicon oxide-containing product 5 and the silicon oxide film 3 are essentially the same, it is desirable to use, for example, a single-sided etching device. In the hydrofluoric acid aqueous solution, only the inside 1B side is contacted, and the boron-containing product 4 and the silicon oxide-containing product 5 are removed. As an example of the single-sided etching apparatus, a single-sided etching can be realized using a device that blows an etchant from the lower side with an etched surface downward, or an etching device having a structure in which only one side is immersed in the etchant.

Next, step S105 of performing a heat treatment is to continuously heat-treat the n-type single crystal silicon substrate 1. This heat treatment can be performed using a heat treatment furnace. First, the heat treatment furnace is preheated. As shown in FIG. 2 (c), heat treatment is performed in an inert gas ambient gas for forming a diffusion layer. By heat treatment, boron is diffused from the BSG film 2 to form a p-type diffusion layer 7.

Next, the step of continuously performing heat treatment in an ambient gas containing oxygen O ₂ is performed while supplying oxygen O ₂ . This heat treatment is performed by increasing temperature, heating, and lowering the temperature while changing the temperature and the ambient gas for film formation. The ambient gas during heating is divided into, for example, an ambient gas containing an inert gas such as nitrogen and argon, and an ambient gas containing oxygen. The heating is performed for any time in a temperature range of 800 ° C to 1100 ° C. However, heating is performed in an ambient gas system containing oxygen for a time of 1 minute to 20 minutes or less.

First, for example, in an ambient gas containing an inert gas such as nitrogen or argon, a temperature T at which impurity diffusion from the BSG film 2 can be performed reaches 800 ° C. to 1100 ° C. to form a desired p-type diffusion layer 7. After the formation of the p-type diffusion layer 7 is completed, a silicon oxide film 8 is formed on the entire surface of the n-type single crystal silicon substrate 1 on which the p-type diffusion layer 7 is formed by allowing oxygen to flow in, as shown in FIG. 2 (d). .

The temperature analysis of this heat treatment is shown as a curve a in FIG. 4. The furnace is replaced with nitrogen and preheating furnace, while becoming a nitrogen atmosphere and the temperature T = 900 ℃, at the time point t ₀₁ n-type single crystal silicon substrate 1 put into a heat treatment furnace, up to the time point t ₀₂ , The maintenance time t ₁ = 1 minute to 30 minutes. At time t ₀₂ , oxygen is supplied into the heat treatment furnace. While supplying oxygen, from the temperature T to the time point t ₀₃ , the maintenance time t ₂ = 1 minute to 20 minutes. In the above-mentioned oxidation process, the n-type single crystal silicon substrate 1 put into the heat treatment furnace is oxidized on the surface with oxygen contained in the ambient gas. Although the oxidation is selectively covered by the BSG film 2 and the silicon oxide film 3 on the light-receiving surface 1A side, the inner surface 1B side of the uncovered film is selectively carried out. However, even on the surface of the p-type diffusion layer 7, oxidation is partially performed, As shown in FIG. 2 (d), a silicon oxide film 8 is formed. At time t ₀₃ , the supply of oxygen is stopped, and a nitrogen gas is supplied for nitrogen replacement. The silicon oxide film 8 has a function of preventing partial entry of n-type impurities during formation of an n-type diffusion layer described below. The thickness is desirably 5 nm to 10 nm. If it is less than 5nm, the barrier function becomes poor in subsequent processes. If it is more than 10nm, although the barrier function becomes large, the risk that the n-type diffusion layer on the inner side cannot be formed satisfactorily increases due to the reverse phase effect.

After the above heating process, the temperature is lowered while supplying nitrogen, and the n-type single crystal silicon substrate 1 is taken out from the heat treatment furnace at a time point t ₀₄ , and if necessary, the silicon oxide film 8 on the inner side 1B is removed. After the silicon oxide film 8 is removed, the inside 1B is exposed. In addition, when the silicon oxide film 8 formed on the inner surface 1B is thin, it may not be removed and the impurity diffusion on the inner surface 1B may be continued.

Thereafter, impurity diffusion to the inside 1B is performed in step S106. Here, as an example, a phosphorus diffusion process is used for the POCl ₃ gas used to form the n-type diffusion layer, and it is explained accordingly. This process is comprehensive for the n-type single crystal silicon substrate 1. The POCl ₃ gas is thermally decomposed, and a phosphosilicate glass (PSG) film is first formed as a diffusion source. After that, in the subsequent heating process, Soak into the interior, in other words, spread it. Whereby, in an environment of POCl ₃ gas, during which diffusion in step S106, the phosphorus in the phosphorus diffusion using POCl ₃ gas in which exposed 1B rapidly diffused light receiving surface 1A is formed a p-type diffusion layer 7 Since a silicon oxide film 8, a BSG film 2, and a silicon oxide film 3 are formed as diffusion barriers on the side, the incorporation of phosphorus is prevented. At this time, the PSG film is formed into a desired thickness by arranging every two pieces on the inside 1B side so as to be directly exposed to the ambient gas in the furnace.

On the other hand, by arranging every two sheets on the light-receiving surface 1A side so as not to be directly exposed to the ambient gas of the furnace, the formation of phosphor glass is greatly restricted. Furthermore, a silicon oxide film 8, a BSG film 2, and a silicon oxide film 3 are formed on the surface. Due to these functions as a diffusion barrier, the incorporation of phosphorus into the silicon is prevented. That is, the diffusion of phosphorus is selectively performed on the inside 1B, and the n-type diffusion layer 14 is formed on the inside.

That is, as shown in FIG. 3 (a), the diffusion of phosphorus is selectively performed in the back surface 1B, and the n-type diffusion layer 14 is formed in the back surface 1B.

After the formation of the n-type diffusion layer 14, in step S107 of removing the solid phase diffusion source, as shown in FIG. 3 (b), the BSG film 2 as the solid phase diffusion source is removed. The BSG film 2 and the silicon oxide film 3 and the silicon oxide film 8 as a barrier function are removed using, for example, a 5 to 25% hydrofluoric acid aqueous solution. At this time, the oxide film formed by water washing is generally called a natural oxide film, and can be used as a passivation layer or a part thereof as described below. Alternatively, for the same purpose, an oxide film washed with ozone-containing water may be used.

Next, in the pn junction separation step S108, the p-type diffusion layer 7 on the side surface of the substrate is removed, and the p-type diffusion layer 7 and the n-type diffusion layer 14 are separated. Specifically, for example, as shown in FIG. 5, the n-type single-crystal silicon substrate 1 that has undergone the processes so far is stacked between tens to hundreds of pieces and sandwiched between the fixtures H to generate plasma by plasma discharge. The gas PG is excited, the substrate side is etched, and the end surface is etched. As the plasma excitation gas PG, a fluorine plasma gas that plasmas a stable CF ₄ gas with low toxicity and high etching rate can be used. Alternatively, it is also possible to use laser separation in which the surface of the substrate is close to the inner side end portion or the side of the substrate is irradiated with laser light. For example, it is only necessary to remove the p-type diffusion layer 7 at any position of the side surface of the substrate constituting the side surface portion of the substrate, the side end portion near the substrate surface, and the side end portion near the back surface of the substrate. FIG. 5 is a schematic diagram showing an end surface etching process of a main part of a manufacturing process of a solar cell according to the first embodiment.

Regarding electrical separation, the essence is to insulate the parts and regions that cause electrical shorts. Specifically, it means that the electrical insulation is achieved by removing a portion where the p-type diffusion layer is in contact with or close to the n-type diffusion layer in the silicon substrate, or by significantly reducing the conductivity by processing. In other words, what is necessary is just an operation including a process of electrically separating the first diffusion layer formed on the first main surface side and the opposite conductivity type region on the second main surface side of the semiconductor substrate. For example, before the process of electrically separating the second main surface side of the semiconductor substrate from the first diffusion layer, a method of removing the first diffusion layer on the substrate side portion of the semiconductor substrate may be performed.

Therefore, for the n-type single crystal silicon substrate, the premise is equivalent to removal or processing. The BSG film 2 and silicon oxide film 3 in this case are more resistant to plasma discharge processing than the others. The diffusion source of the diffusion means is also relatively thick. Therefore, if the end face is etched in such a state of remaining, it may not be processed sufficiently and cannot be separated well.

Therefore, after the end surface etching is performed after removing the BSG film 2 and the silicon oxide film 3, the entire separation can be performed by the end surface etching.

In addition, regarding the removal of the BSG film 2 and the silicon oxide film 3, the removal must be completed before the formation of the anti-reflection film or the inner insulating film as a subsequent process, so that the entire removal method of the BSG film 2 and the silicon oxide film 3 before the end surface is etched It is simple, has the effect of improving mass productivity or reducing manufacturing costs.

Cut or etch the end surface of the substrate as described above, as described in Section 3 (c) As shown in the figure, a solar cell substrate having a p-type diffusion layer 7 on the light receiving surface 1A side and an n-type diffusion layer 14 on the back surface 1B side is formed.

In addition, the state of separation depends on the magnitude of the leakage current or the arrangement within the module that becomes the final power generation product, and this separation process can be omitted.

After that, in step S109 of forming an anti-reflection film and forming an inner insulating film, in the inner surface 1B, for example, an inner insulating film 15b made of a silicon nitride film is formed using plasma CVD. In addition, a passivation layer may be formed between the silicon nitride film and the n-type diffusion layer. At this time, the passivation layer is desirably a silicon oxide film. In addition to the usual thermal oxidation, an oxide film formed by washing with water or washing with ozone-containing water as described above can also be used.

Next, similarly, on the light-receiving surface 1A side, a light-receiving surface anti-reflection film 15a is formed by, for example, a silicon nitride film using plasma CVD. A passivation layer may be formed between the silicon nitride film constituting the light-receiving surface anti-reflection film 15a and the n-type diffusion layer 14.

At this time, the passivation layer is desirably either one of a silicon oxide film and an aluminum oxide film, or a laminate of both. When a silicon oxide film is used for the passivation layer, in addition to the usual thermal oxidation, an oxide film washed with water or water containing ozone can be used as described above. When an aluminum oxide film is used, it is formed by, for example, plasma CVD or ALD (Atomic Layer Deposition). In this case, a fixed charge included during film formation is preferred because it has the effect of improving the passivation ability.

Especially after the hydrofluoric acid aqueous solution is processed in the removal process of the BSG film 2 and the silicon oxide film 3, when the end surface etching process is performed, the surface of the cleaned substrate is treated with the hydrofluoric acid aqueous solution. When the substrate surfaces are brought into contact with each other and a fluorine plasma gas is used, the surface state becomes unstable. Depending on the formation of a passivation layer in a continuous process, the passivation effect may be reduced.

In particular, a fluorine-based etching solution such as CF ₄ is used during etching, and when etching with a fluorine plasma gas, fluorine ions may be adsorbed on the surface of the silicon substrate and remain after the etching. When a silicon nitride film is formed by plasma CVD on the substrate surface, a silicon nitride film is formed on top of fluorine ions. Since fluorine atoms remain between the silicon substrate and the silicon nitride film, the surface is lowered. Passivation effect.

On the other hand, ALD introduces TMA (trimethylaluminum, trimethylaluminum) by introducing water, nitrogen and N ₂ exhaust gas. N ₂ exhaust gas is used as one cycle, and multiple cycles are repeated to form alumina on the surface of the silicon substrate. Membrane method. ALD repeats the cycle that includes N ₂ exhaust gas, and when N ₂ exhausts, it can exhaust the fluorine adsorbed on the substrate surface to form a clean surface state.

Therefore, by using ALD when forming the passivation layer, a sufficient passivation effect can be obtained even after performing a hydroplasma gas treatment after the hydrofluoric acid aqueous solution treatment.

In addition, the order of forming the light-receiving surface anti-reflection film 15a, the back surface insulating film 15b, and the passivation layers on both sides is not necessarily limited to the above-mentioned order, and the order other than the above may be appropriately selected.

After that, as shown in FIG. 3 (d), after forming the light-receiving surface antireflection film 15a and the inner insulating film 15b on the light-receiving surface 1A and the inner surface 1B, respectively, in the electrode formation step S110, the light-receiving surface 1A side and the inner 1B side are respectively formed. A light-receiving surface electrode 16a and a back surface electrode 16b are formed. As the electrode material, for example, copper, silver, aluminum, or a mixture thereof can be used. For example, metal powders of copper, silver, aluminum or mixtures thereof, powders of glass and ceramic components, mixed with organic solvents to form a paste, and formed into a desired shape pattern by, for example, screen printing, and dried and Formed by firing. In this way, the solar cell is completed.

As described above, according to the method for manufacturing a solar cell according to the first embodiment, the solid-phase diffusion source is formed into a film and heated to form a diffusion layer. After the solid-phase diffusion source is removed, the solid-phase diffusion source is electrically separated, which can improve processing Insulation performance reduces leakage current of solar cells. In addition, in addition to impurities intended for the light receiving surface and the inside, the incorporation of impurities of the opposite conductivity type or the incorporation of pollutants are suppressed, and a solar cell with a long carrier life and high photoelectric conversion efficiency can be realized.

In addition, when the BSG film 2 and the silicon oxide film 3 of the solid-phase diffusion source are formed, even if the boron-containing product is formed by re-osmosis to the inside 1B, since it is removed before the heating for diffusion, even after heating, the internal Diffusion of impurities.

Therefore, in addition to the intended impurities, the inclusion of impurities of opposite conductivity type on the light-receiving surface and the inside thereof, or the inclusion of pollutants are suppressed, and a solar cell with a long carrier life and high photoelectric conversion efficiency can be obtained.

In addition, the process of removing the slice damage, the process of forming a texture, and the process of cleaning processing are examples for explaining the process of Embodiment 1, and are not limited to these. Various processes may be used and are not limited to the above processes. Similarly, regarding the process of forming the inner n-type diffusion layer 14, the process of separating the pn junction, the process of forming the light-receiving surface anti-reflection film 15a and the inner insulating film 15b, and the process of forming the light-receiving surface electrode 16a and the inner electrode 16b, The use of various processes is not limited to the processes described above. In addition, from the process of forming the n-type diffusion layer 14 to the process of forming the electrode 16, as long as the solar cell functions, the appropriate order can be changed, and the order is not limited to the order described.

In addition, for explanation, an n-type single-crystal silicon substrate 1 is used, a BSG film 2 is used as a solid-phase diffusion source, and an n-type diffusion layer 14 made of phosphorus diffusion is used for the inner surface 1B. However, the structure is not limited to this. As long as it functions as a solar cell, For the substrate, other silicon-based crystalline substrates such as polycrystalline silicon substrates and silicon carbide can be used. For the conductive type, p-type substrates can also be used. In addition, as the solid-phase diffusion source, an impurity containing an n-type diffusion layer like a PSG film may be used. For the solid-phase diffusion source and the opposite side diffusion, impurities including a p-type diffusion layer such as boron may also be used. The substrate as described above can be appropriately selected for the diffusion layer formed on the light-receiving surface and the back surface, any of p-type and n-type formation, and impurity elements forming the diffusion layer.

Embodiment 2

The manufacturing method of a solar cell according to the second embodiment is a part of a high-concentration diffusion layer formed on one or both of a light-receiving surface side and a back surface side, compared with the manufacturing method of the solar cell described in the first embodiment. Since the process of removing the oxide film on the back side is the same as the process except the phosphorous diffusion process, detailed description is omitted with reference to the first embodiment.

FIG. 6 is a process chart showing a method for manufacturing a solar cell according to the second embodiment, from a heat treatment to a pn bonding and separation process. 7 (a) and 7 (b) are schematic diagrams showing changes in the cross section of the n-type single crystal silicon substrate 1 in the n-type impurity diffusion process. Hereinafter, it demonstrates using FIG.6 and FIG.7.

Since the method for manufacturing a solar cell according to the second embodiment is performed after performing step S105 as a heat treatment process for forming the p-type diffusion layer 7, it is continuously performed as shown in FIG. 7 (a). The film formation step S106a on the back side is used as the inner diffusion step S106b in the heat treatment process. Here, a diffusion source 17 containing impurities exhibiting n-type conductivity and having a high concentration of, for example, 1 × 10 ²⁰ phosphorus / cm ³ or more is formed on the silicon oxide film 8 on the back 1B. Thereafter, the same diffusion source 17 is formed, the above-described system in which a diffusion step S106b, the n-type single crystal of Embodiment 1 of the silicon substrate inside the diffusion step S106, a heat treatment in an environment of POCl ₃ gas. The impurity diffusion from the diffusion source 17 is performed at a temperature of, for example, 800 ° C to 1000 ° C.

Directly below the diffusion source, although there is a silicon oxide film 8 formed on the inside 1B, the thickness is about 5 nm to 10 nm, and the impurity concentration of the diffusion source 17 is high. Therefore, the formation of the n-type diffusion layer is not affected by it. influences. The diffusion source 17 in this portion is formed from a phosphosilicate glass (PSG) film formed by thermal decomposition of POCl ₃ gas, and impurities are contained in the n-type single crystal silicon substrate 1 in contact with the diffusion source 17. Diffusion to form a high-concentration n-type diffusion layer 18. An n-type diffusion layer 20 having a lower concentration than the n-type diffusion layer 18 is formed in a region not covered by the diffusion source 17.

Then, after the pn junction separation step S108, the step S109 for forming an anti-reflection film and the inner insulating film shown in FIG. 1 is performed, and the electrode step S110 is formed.

On the other hand, although the n-type single crystal silicon substrate 1 in a region other than directly below the diffusion source 17 is attached with impurities from the diffusion source 17 that are desorbed from the ambient gas, compared to the impurity concentration of the diffusion source 17 itself, the concentration or Since the total amount is low, the oxide film formed on the surface of the n-type single crystal silicon substrate 1 cannot pass.

Therefore, according to the second embodiment, a structure having a two-step concentration can be formed in the diffusion layer. When the two are appropriately distributed, a region other than directly below the diffusion source 17 can be suppressed to a lower concentration, thereby realizing a more efficient solar cell.

As described above, the process of forming a solid-phase diffusion source is selectively formed on the inside 1B as the second main surface, and an n-type diffusion as the first conductivity type is formed by diffusion from the PSG film as its diffusion source 17. Process for layer 20.

According to the second embodiment, the process of removing the oxide film on the inner surface 1B can be deleted from the manufacturing method without affecting the silicon oxide film 8 formed on the n-type single crystal silicon substrate 1 until the n-type impurity diffusion process is completed.

In addition, a process of forming an n-type diffusion layer as a first conductive type diffusion layer is to form a diffusion source containing 1 × 10 ²⁰ impurities / cm ³ or more on the back surface 1B of the n-type single crystal silicon substrate 1 as a second main surface. By this method, an impurity diffusion layer can be formed even if a silicon oxide film is present at a portion contacting the diffusion source, and a process of removing the silicon oxide film 8 on the inner surface 1B of the n-type single crystal silicon substrate 1 can be omitted. Furthermore, since the entire surface of the n-type single crystal silicon substrate 1 as a solar cell substrate is covered with a silicon oxide film 8 to perform diffusion from a diffusion source, even if impurities released from the diffusion source into the ambient gas adhere to the n-type single crystal The crystalline silicon substrate 1 does not diffuse into the substrate.

As described above, according to the manufacturing method of the solar cell according to the second embodiment, the process of removing the oxide film inside is not required, the formation of leakage paths adjacent to the p-type and n-type impurities is prevented, and the sun with excellent diode characteristics is realized. battery.

Embodiment 3

Regarding the removal of the BSG film 2 and the silicon oxide film 3, not all of them may be removed, and the BSG film 2 and the silicon oxide film 3 may be removed by using only the end surface and the vicinity thereof as objects. FIG. 8 is a process chart showing a method of manufacturing a solar cell according to the third embodiment, and FIGS. 9 (a) to 9 (d) are cross-sectional views showing processes of a main part of the manufacturing process of the solar cell according to the third embodiment.

Regarding the removal of the BSG film 2 and the silicon oxide film 3, it is necessary to remove the BSG film 2 and the silicon oxide film 3 before forming the anti-reflection film or the inner insulating film as a subsequent process. The method of removal before the separation process is the simplest, and it is easy to improve mass productivity or reduce manufacturing costs. However, the removal before the separation processing is mainly the position to be processed, and specifically, the end surface and the vicinity thereof are targeted. Light receiving surface 1A and The removal of most of the inside 1B before the separation process is not necessary.

Here, Embodiment 3 is a method in which the etching solution is dropped while rotating, and the BSG film 2 and the silicon oxide film 3 are removed for the end surface and the vicinity thereof. The other processes are the same as those in the first embodiment.

Until the inside diffusion step S106 of inside diffusion in the ambient gas of POCl ₃ gas, it is performed in the same manner as in the first embodiment, and as shown in FIG. 9 (a), an n-type diffusion layer 14 on the inside is formed. Fig. 9 (a) corresponds to Fig. 2 (d) of the first embodiment.

Thereafter, a solid phase diffusion source step S107S for removing the end surface is performed by a method such as dropping the etchant while rotating the substrate. As shown in FIG. 9 (b), only the end surface and the vicinity thereof are removed to remove the BSG film 2 And silicon oxide film 3.

Next, a pn junction separation step S108 is performed, and the end face is etched with the remaining BSG film 2 and the silicon oxide film 3 as protective films on most of the light receiving surface and the two inner surfaces. As shown in FIG. 9 (c), the substrate end surface is removed. The p-type diffusion layer 7.

Then, the remaining solid phase diffusion source step S107SS is performed, and as shown in FIG. 9 (d), the remaining BSG film 2 and the silicon oxide film 3 are removed. At this time, the silicon oxide film 8 on the surface and inside is also removed. This is equivalent to FIG. 3 (c) in Embodiment 1. As in Embodiment 1, an anti-reflection film 15a, a back insulating film 15b, a light-receiving surface electrode 16a, and a back electrode 16b are formed to complete a solar cell.

With the above-mentioned configuration, most of the BSG film 2 and the silicon oxide film 3 remaining on the light-receiving surface and the two inner surfaces can be applied as a protective film during separation processing. Thereby, the characteristics of the solar cell can be further improved. In addition, leakage current can be suppressed.

Embodiments 1 to 3 are formed and formed after the heat treatment process In the process of manufacturing a diffusion layer of a different conductivity type, a part of the silicon oxide film as a protective film is removed. Therefore, it becomes possible to use impurity diffusion with ordinary gas, and since there is a film remaining other than the oxide film removal portion, it is possible to prevent impurities from being mixed in and a leakage path to be formed.

As described above, Embodiments 1 to 3 show manufacturing as a solid-phase diffusion source. After the film containing impurities is formed, the diffusion source on the back side is removed, and then heat treatment is performed to prevent the diffusion of impurities from the products on the inside. Processer. Specifically, during the heat treatment, a general heat treatment is performed by using an inert gas such as nitrogen, argon, and the like, and a heat treatment is performed in an ambient gas in which oxygen flows, and a two-stage heat treatment is performed. The supply of oxygen is performed by diffusing impurities from the membrane from the solid-phase diffusion source and performing a heat treatment of an ambient gas containing no oxygen. That is, after being put into the furnace, an oxide film is formed as a diffusion barrier due to contact with the product of oxygen inside the substrate and the substrate. When the supply of oxygen is stopped, impurity diffusion from the film-forming substance is performed, and only on the film-forming surface. Diffusion of impurities. Then, since oxygen is allowed to flow in at the end of the heat treatment process, an oxide film is also formed on the film-forming surface of the solid-phase diffusion source, and then a function as a barrier for different types of diffusion is added. With this method, impurities can be diffused only on the film-forming surface.

In addition, the oxidation process after the diffusion process is explained by using FIG. 4 in Embodiment 1. It is also possible to implement oxygen introduction only at the last necessary time of the heat treatment process for diffusion, and the temperature reduction process after the heat treatment process may be performed only in If necessary, introduce oxygen. In addition, once the temperature of the diffusion furnace is reduced to normal temperature, an oxidation heat treatment process may be performed.

In addition, in Embodiments 1 to 3, the temperature in the heat treatment process for performing impurity diffusion is determined according to the type of impurity to be diffused, and may be appropriately change. In addition, the diffusion environment gas may be a reducing environment gas, such as a hydrogen environment gas, and may be appropriately adjusted in order to control the diffusion rate depending on the type of impurities.

In addition, although Embodiments 1 to 3 describe an example in which a second diffusion layer having the same conductivity type as that of the semiconductor substrate is formed on the second main surface of the semiconductor substrate, that is, the back side, the second diffusion may not be formed. Floor. In this case, the solid-phase diffusion source is removed before the semiconductor substrate is separated from the pn of the first diffusion layer. In addition, as the semiconductor substrate, an n-type single-crystal silicon substrate is used. However, other crystalline silicon substrates such as p-type single-crystal silicon substrates, p-type and n-type polycrystalline silicon substrates, or silicon compounds such as silicon carbide can also be used. Formation of a diffusion layer including a compound semiconductor is also applicable. Then, the first and second conductivity type impurities are determined according to the conductivity type of the semiconductor substrate. However, regarding the types of impurities, phosphorus and arsenic as n-type impurities and boron and gallium as p-type impurities are other general examples. Impurities are also applicable.

Although several embodiments of the present invention have been described, these embodiments are disclosed as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention, and are also included in the invention described in the scope of patent application and its equivalent.

Claims (6)

A method for manufacturing a solar cell includes the following processes: a process of forming a solid-phase diffusion source and a protective film on the first main surface of a semiconductor substrate of a first conductivity type having opposite first and second main surfaces; and removing; A process of forming a product formed on the second main surface in the film forming process; heating the semiconductor substrate from which the product has been removed, and forming a second conductive type from the solid phase diffusion source on the first main surface side A process of forming a first diffusion layer; a process of forming a second diffusion layer having a first conductivity type on the second main surface of the semiconductor substrate; a process of removing the solid-phase diffusion source and the protective film together; and forming the second The process of electrically separating the diffusion layer from the first diffusion layer; the process of removing the solid-phase diffusion source is performed before the process of electrically separating the second diffusion layer from the first diffusion layer. The method for manufacturing a solar cell according to item 1 of the scope of patent application, wherein the process of removing a product is performed before the process of forming the first diffusion layer. The method for manufacturing a solar cell according to item 1 or 2 of the scope of patent application, wherein the above-mentioned process for removing the solid-phase diffusion source remains on the first main surface and the second main surface, and selectively removes the semiconductor substrate and the Process for manufacturing the side surface of the first diffusion layer. The method for manufacturing a solar cell according to item 1 of the scope of patent application, wherein the process of forming the solid-phase diffusion source and the protective film includes a process of continuously forming the solid-phase diffusion source and the protective film. The method for manufacturing a solar cell according to item 1 of the scope of patent application, wherein the above-mentioned process for forming the second diffusion layer having the first conductivity type is included in a part of the second main surface, and the above-mentioned solid is selectively formed. Process of Phase Diffusion Source. A method for manufacturing a solar cell includes the following processes: a process of forming a solid-phase diffusion source and a protective film on the first main surface of a semiconductor substrate of a first conductivity type having opposite first and second main surfaces; and removing the protective film; A process of forming a product formed on the second main surface in the film forming process; heating the semiconductor substrate from which the product has been removed, heating the semiconductor substrate from the solid-phase diffusion source, and forming a first on the first main surface side (2) a process of the first conductive diffusion layer; a process of removing the solid phase diffusion source and the protective film together; a process of electrically separating the second main surface side of the semiconductor substrate from the first diffusion layer; The process of removing the solid-phase diffusion source is performed before the process of electrically separating the second main surface side of the semiconductor substrate from the first diffusion layer.