JPWO2015087472A1 - Manufacturing method of solar cell - Google Patents

Abstract

The present invention provides a step of preparing a second diffusing agent containing a second conductivity type dopant and a first diffusing agent containing a first conductivity type dopant; By applying a heat treatment to the semiconductor substrate coated with the first diffusing agent and the second diffusing agent; A method for manufacturing a solar cell, comprising: forming a second concentration diffusion layer, a second low concentration diffusion layer, and a first diffusion layer; and forming a thermal oxide film on a semiconductor substrate on which the diffusion layer is formed. Thereby, the manufacturing method of the solar cell which can eliminate the auto dope problem and can manufacture the solar cell with excellent electric characteristics while simplifying the manufacturing process is provided.

Description

  The present invention relates to a solar cell manufacturing method and a solar cell obtained by the manufacturing method.

  At present, in the production of consumer-use solar cells, high efficiency and reduction in manufacturing costs are important issues, and research on double-sided light-receiving solar cells is widely conducted. The details are as follows, for example.

First, a p-type silicon substrate obtained by slicing a single crystal silicon ingot produced by a Czochralski (CZ) method or a polycrystalline silicon ingot produced by a cast method by a multi-wire method is prepared. Next, after removing damage caused by slicing of the substrate surface with an alkaline solution, fine irregularities (textures) having a maximum height of about 10 μm are formed on both the light receiving surface and the back surface. Subsequently, a dopant having a different conductivity type is thermally diffused on both surfaces of the substrate by using a photomask method using an organic resist or the like, and an n-type phosphorous having a conductivity type opposite to that of the substrate is formed on the first main surface serving as the light receiving surface. A dopant is vapor-phase diffused using POCl ₃ gas to form an n-type diffusion layer, and a p-type boron dopant having the same conductivity type as the substrate is formed on the second main surface serving as a back surface using BBr ₃ gas. Diffusion is performed by a diffusion method so that ohmic contact with the electrode can be obtained. Next, TiO ₂ or SiNx is deposited on the light-receiving surface and the back surface, for example, with a film thickness of about 80 nm to form an antireflection film. Next, a back electrode paste mainly composed of silver is printed in a comb shape on the back surface and dried. On the other hand, the light-receiving surface electrode is formed by printing and drying a light-receiving surface electrode paste mainly composed of silver in a comb shape having a width of about 100 μm. Finally, the light-receiving surface electrode and the back-surface electrode are baked to form an ohmic contact with the electrode, thereby completing a double-sided light-receiving solar cell.

  The double-sided light-receiving solar cell made in this way can suppress surface recombination of the aluminum electrode region on the back side of the substrate, compared to crystalline silicon having a general back side aluminum electrode, and further a boron diffusion layer It has high photoelectric conversion characteristics due to the BSF (back surface field) effect. In addition, the double-sided light-receiving solar cell has less warpage of the substrate and less cracking when being modularized, compared to crystalline silicon having a general backside aluminum electrode.

  However, if a diffusion layer having a different conductivity type as described above and a diffusion layer having the same conductivity type but having a different concentration are formed by using a mask method such as a photoresist, there are many mask formation and mask removal steps. The number of times increases and the manufacturing cost increases.

  Therefore, as a method of diffusing impurities of the same conductivity type at different concentrations in a single heat treatment, a diffusing agent is partially applied by screen printing and heat-treated, so that the region immediately below the diffusing agent becomes a high-concentration diffusion layer. A technique has been reported in which a region other than the above is a low-concentration diffusion layer (eg, Patent Document 1).

  In this method, the power generation amount can be increased by using the light-receiving surface as a low-concentration diffusion layer while keeping the contact resistance low by the high-concentration diffusion layer directly under the electrode, and a solar cell with high conversion efficiency can be manufactured. .

JP 2007-235174 A

  Furthermore, simultaneous diffusion in which impurities of different conductivity types are diffused by a single heat treatment diffuses impurities of different conductivity types in the same heat treatment furnace, so the cost is reduced by shortening the process, and a highly competitive solar cell can be obtained. It can be produced.

However, when a phosphorus diffusing agent that is an n-type impurity source is partially applied to the first main surface and a boron diffusing agent that is a p-type impurity source is applied to the entire second main surface to perform simultaneous diffusion, The boron dopant out-diffused from the boron diffusing agent of the second main surface is auto-doped into the low-concentration phosphorus diffusion layer (n ⁺ layer) on the surface other than directly under the electrode on the first main surface, and contamination is caused. There was a problem that the electrical characteristics of the solar cell deteriorated.

  The present invention has been made in view of the above problems, and is a method for manufacturing a solar cell that can solve the problem of auto-doping while simplifying the manufacturing process and can manufacture a solar cell with excellent electrical characteristics. The purpose is to provide.

In order to achieve the above object, in the present invention, a high concentration second diffusion in which a dopant of a second conductivity type opposite to the first conductivity type is diffused on a first main surface of a semiconductor substrate of a first conductivity type. And a low-concentration second diffusion layer in which the dopant is diffused at a lower concentration than the high-concentration second diffusion layer, and the first conductivity type dopant is diffused on the second main surface of the semiconductor substrate. A method of manufacturing a solar cell for forming a first diffusion layer,
(A) preparing a second diffusing agent containing the second conductivity type dopant and a first diffusing agent containing the first conductivity type dopant;
(B) applying the first diffusing agent to the second main surface;
(C) partially applying the second diffusing agent to the first main surface;
(D) Forming the high-concentration second diffusion layer, the low-concentration second diffusion layer, and the first diffusion layer by heat-treating the semiconductor substrate coated with the first diffusing agent and the second diffusing agent. And a process of
And (e) providing a thermal oxide film on the semiconductor substrate on which the diffusion layer is formed.

  With such a method for manufacturing a solar cell, the manufacturing process can be simplified and the manufacturing cost can be reduced by diffusing impurities of different conductivity types by a single heat treatment. Further, the first conductivity type dopant auto-doped in the low-concentration second diffusion layer by the heat treatment performed in the step (d) can be reduced by forming the thermal oxide film in the step (e). As a result, a solar battery cell having excellent electrical characteristics can be manufactured.

  Preferably, the semiconductor substrate is a p-type silicon substrate, the second diffusing agent is a phosphorus diffusing agent that is vitrified by the heat treatment, and the first diffusing agent is a boron diffusing agent that is vitrified by the heat treatment.

  By using a diffusing agent that vitrifies by heat treatment, a high-concentration second diffusion layer can be easily formed. Further, such a diffusing agent can be easily removed.

  The steps (d) and (e) are preferably performed in the same heat treatment batch.

  If it is the manufacturing method of such a solar cell, a manufacturing process can be reduced further.

  Further, it is preferable that the method further includes (f) removing the heat-treated first diffusing agent and second diffusing agent after the step (d) and before the step (e).

  If it is the manufacturing method of such a solar cell, the photovoltaic cell with the more excellent electrical property can be manufactured.

  The thickness of the thermal oxide film formed in the step (e) is preferably 10 to 20 nm.

  With such a film thickness, it is easy to reduce the concentration of the first conductivity type dopant auto-doped in the low concentration second diffusion layer.

Moreover, it is preferable that the peak concentration of the first conductivity type dopant in the low concentration second diffusion layer is 5.0 × 10 ¹⁷ atoms / cm ³ or less.

  If it is such conditions, the sheet resistance of the solar cell obtained can be made low.

Moreover, it is preferable that the peak concentration of the second conductivity type dopant in the low concentration second diffusion layer is 1.0 × 10 ¹⁸ atoms / cm ³ or more.

  If it is such conditions, the short circuit current of the solar cell obtained will not fall easily.

  The peak concentration ratio of the second conductivity type dopant and the first conductivity type dopant in the low concentration second diffusion layer is preferably 10.0 or more.

  If it is such conditions, the conversion efficiency of the solar cell obtained can be improved more.

Further, after the step (e), (g) a step of forming a passivation film on the first main surface and the second main surface;
(H) applying an electrode material to the first main surface and the second main surface on which the passivation film is formed;
(I) It is preferable to have a step of firing the applied electrode material.

  If it is a manufacturing method of such a solar cell, a solar cell with higher conversion efficiency can be obtained.

  Furthermore, the present invention provides a solar cell manufactured by the method for manufacturing a solar cell of the present invention.

  Such a solar cell can be made inexpensive and excellent in conversion efficiency.

  If it is the manufacturing method of the solar cell of this invention, the 1st diffused layer of the same conductivity type as the semiconductor substrate of the 1st conductivity type is made into the 2nd main surface, the high concentration 2nd diffused layer and the low concentration of the opposite conductivity type When the second diffusion layer is simultaneously formed on the first main surface, the first conductivity type impurity auto-doped into the low concentration second diffusion layer can be reduced in concentration. As a result, a solar cell with excellent electrical characteristics can be manufactured with a high yield. Further, by diffusing impurities of different conductivity types by a single heat treatment, the manufacturing process can be simplified and the manufacturing cost can be reduced.

It is a flowchart which shows the manufacturing method (when performing a diffused layer formation and thermal oxide film formation in the same heat processing batch) of the solar cell of Example 1. FIG. It is a flowchart which shows the manufacturing method of the solar cell of Example 3 (when the vitrified diffusing agent is removed from the substrate surface after heat treatment, and then a thermal oxide film is formed and removed). It is a flowchart which shows the manufacturing method of the solar cell of Example 2 (when removing the vitrified diffusing agent from the substrate surface after heat treatment, and then forming a thermal oxide film). It is the schematic which shows an example of the solar cell obtained by the manufacturing method of the solar cell of this invention. It is the schematic which shows another example of the solar cell obtained by the manufacturing method of the solar cell of this invention. It is an application schematic diagram of the 1st diffusing agent and the 2nd diffusing agent before simultaneous diffusion. It is an image figure of a high concentration 2nd diffusion layer, a low concentration 2nd diffusion layer, and a 1st diffusion layer formed after dopant simultaneous diffusion. It is an image figure of the auto dope area | region of the low concentration 2nd diffused layer formed after dopant simultaneous diffusion. 5 is a flowchart of a solar cell manufacturing method of Comparative Example 1. FIG.

Hereinafter, the present invention will be described in more detail.
As described above, there is a need for a solar cell manufacturing method that can solve the auto-doping problem while simplifying the manufacturing process and that can manufacture a solar cell with excellent electrical characteristics.

As a result of intensive studies to achieve the above object, the present inventors have found that a second conductivity type dopant opposite to the first conductivity type is present on the first main surface of the first conductivity type semiconductor substrate. A diffused high-concentration second diffusion layer and a low-concentration second diffusion layer in which a dopant is diffused at a lower concentration than the high-concentration second diffusion layer are formed, and the first main surface of the semiconductor substrate is formed with the first A method for manufacturing a solar cell, which forms a first diffusion layer in which a conductive dopant is diffused,
(A) preparing a second diffusing agent containing the second conductivity type dopant and a first diffusing agent containing the first conductivity type dopant;
(B) applying the first diffusing agent to the second main surface;
(C) partially applying the second diffusing agent to the first main surface;
(D) Forming the high-concentration second diffusion layer, the low-concentration second diffusion layer, and the first diffusion layer by heat-treating the semiconductor substrate coated with the first diffusing agent and the second diffusing agent. And a process of
(E) A solar cell manufacturing method including a step of forming a thermal oxide film on a semiconductor substrate on which the diffusion layer is formed can solve the above-mentioned problems, and the present invention has been completed.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings, but the present invention is not limited thereto.

[Solar cell]
First, the solar cell obtained by the manufacturing method of the solar cell of this invention is demonstrated with reference to FIG. 4, FIG.

  FIG.4 and FIG.5 is schematic which shows an example of the solar cell obtained by the manufacturing method of the solar cell of this invention. As shown in FIG.4 and FIG.5, the solar cell obtained by the manufacturing method of the solar cell of this invention is the 2nd opposite to a 1st conductivity type on the 1st main surface of the semiconductor substrate 1 of a 1st conductivity type. A high-concentration second diffusion layer 2 in which a conductive dopant is diffused and a low-concentration second diffusion layer 3 in which the dopant is diffused at a lower concentration than the high-concentration second diffusion layer are formed, and is formed on the second main surface. A first diffusion layer 4 in which a dopant of the first conductivity type is diffused is formed, and an electrode (back comb electrode) 7 and an electrode (light receiving surface comb electrode) are formed on the first main surface and the second main surface. ) 8 is formed. Usually, a passivation film 6 is formed on the first main surface and the second main surface.

  Specific examples of the first conductivity type semiconductor substrate include a p-type substrate such as a boron-doped p-type single crystal silicon substrate. When the substrate is p-type, p-type dopants such as B (boron) and Ga (gallium) can be used as the first conductivity type dopant. As the second conductivity type dopant, n-type dopants such as P (phosphorus), Sb (antimony), and As (arsenic) can be used.

In this case, the high concentration second diffusion layer is an n ⁺⁺ layer, the low concentration second diffusion layer is an n ⁺ layer, and the first diffusion layer is a p ⁺ layer.

  Examples of the passivation film include a silicon nitride film. The passivation film may be laminated on a thermal oxide film 5 such as a silicon oxide film as shown in FIG.

[Method for manufacturing solar cell]
Hereinafter, an example of the method for manufacturing a solar cell of the present invention will be described by taking a p-type substrate as an example, but the present invention is not limited to this. Hereinafter, a case where the semiconductor substrate is a p-type silicon substrate, the first conductivity type dopant is a boron dopant, and the second conductivity type dopant is a phosphorus dopant will be described as an example. Therefore, the high-concentration second diffusion layer is also referred to as an n ⁺⁺ layer, the low-concentration second diffusion layer as an n ⁺ layer, and the first diffusion layer as a p ⁺ layer. Moreover, although the 1st main surface is described as a light-receiving surface and the 2nd main surface is described as a back surface, it is possible to receive light also from the 2nd main surface (back surface).

  First, a semiconductor substrate such as a boron-doped p-type single crystal silicon substrate is prepared. This silicon single crystal substrate can be obtained by slicing an ingot produced by a method such as the Czochralski (CZ) method or the floating zone (FZ) method. The specific resistance of the substrate is preferably, for example, 0.1 to 20 Ω · cm, and in particular, 0.5 to 2.0 Ω · cm is suitable for producing a high-performance solar cell.

  Next, the prepared substrate is immersed in an aqueous sodium hydroxide solution, and the damaged layer is removed by etching. For removing damage from the substrate, a strong alkaline aqueous solution such as potassium hydroxide may be used. The same object can be achieved with an aqueous acid solution such as hydrofluoric acid.

A random texture is formed on the substrate subjected to damage etching.
In general, a solar cell preferably has an uneven shape on the surface. The reason is that in order to reduce the reflectance in the visible light region, it is necessary to cause the light receiving surface to perform reflection at least twice as much as possible. The size of each of these peaks may be about 1 to 20 μm. Typical surface uneven structures include V-grooves and U-grooves. These can be formed using a grinding machine. In order to create a random concavo-convex structure, it is possible to use wet etching by dipping in an aqueous solution of sodium hydroxide and isopropyl alcohol, or to use acid etching or reactive ion etching. .

  Next, a second diffusing agent containing a second conductivity type dopant and a first diffusing agent containing a first conductivity type dopant are prepared. The first diffusing agent and the second diffusing agent are preferably those that vitrify by heat treatment. In particular, when a p-type silicon substrate is used, the second diffusing agent is preferably a phosphorus diffusing agent that is vitrified by heat treatment, and the first diffusing agent is preferably a boron diffusing agent that is vitrified by heat treatment.

A phosphorus diffusing agent that vitrifies by heat treatment can be obtained by mixing P ₂ O ₅ , pure water, PVA (polyvinyl alcohol), and TEOS (tetraethylorthosilicate). The boron diffusing agent that vitrifies by heat treatment can be obtained by mixing B ₂ O ₃ , pure water, and PVA (polyvinyl alcohol).

  Next, the first diffusing agent is applied to the second main surface, and the second diffusing agent is partially applied to the first main surface. The order in which the first diffusing agent and the second diffusing agent are applied to the substrate is not particularly limited. FIG. 6 is a schematic diagram of application of the first diffusing agent and the second diffusing agent before simultaneous diffusion. As shown in FIG. 6, a second diffusing agent (for example, phosphorus diffusing agent) 9 is partially applied to the first main surface of the substrate 1, and the first diffusing agent (for example, boron) is applied to the second main surface. (Diffusion agent) 10 is applied.

  As a specific example of the coating step, first, a boron diffusing agent that is a p-type impurity is applied to the entire back surface and dried. As this coating method, a spin coating method, an inkjet method, a screen printing method, or the like is appropriately used. Subsequently, a phosphorus diffusing agent which is an n-type impurity is partially applied to the light receiving surface and dried. As a method for applying the diffusing agent, screen printing, an inkjet method, a spray coating method, or the like is appropriately used.

  When the second diffusing agent is partially applied to the first main surface, it is preferably applied to the region where the electrode is formed (the region directly below the electrode).

  Next, the high-concentration second diffusion layer, the low-concentration second diffusion layer, and the first diffusion layer are formed simultaneously by heat-treating the semiconductor substrate coated with the first diffusing agent and the second diffusing agent. Specifically, the surfaces coated with the first diffusing agent such as a boron diffusing agent are placed on a quartz boat with the surfaces facing each other and heat-treated at 900 to 1000 ° C. for 10 to 60 minutes. The treatment atmosphere is performed in an inert gas such as nitrogen or argon, but oxygen may be included at a concentration of 5% or less. By this heat treatment, a high-concentration second diffusion layer and a low-concentration second diffusion layer are simultaneously formed on the light receiving surface side, and a uniform first diffusion layer is simultaneously formed on the back surface side.

  FIG. 7 is an image diagram of the high-concentration second diffusion layer, the low-concentration second diffusion layer, and the first diffusion layer formed after the dopant simultaneous diffusion. As shown in FIG. 7, the high-concentration second diffusion layer 2 is formed in the region where the second diffusing agent is applied on the first main surface of the substrate 1, and the low-concentration second diffusing layer 2 is formed in the region where the second diffusing agent is not applied. The two diffusion layers 3 are formed. The first diffusion layer 4 is formed on the second main surface. Further, the heat-treated second diffusing agent 11 is formed in the region of the first main surface where the diffusing agent is applied, and the heat-treated first diffusing agent 12 is formed on the second main surface.

  At this time, it is preferable that the first diffusing agent and the second diffusing agent be vitrified by heat treatment. In this case, the first diffusing agent and the second diffusing agent are vitrified by the heat treatment.

Here, when the conductivity type of the substrate 1 is p-type, the second diffusing agent is a phosphorus diffusing agent that vitrifies by heat treatment, and the first diffusing agent is a boron diffusing agent that vitrifies by heat treatment, The diffusion layer becomes an n-type diffusion layer. At this time, the region where the phosphorus diffusing agent is applied becomes the high concentration phosphorus diffusion layer (n ⁺⁺ layer), and the region where the phosphorus diffusion agent is not applied becomes the low concentration phosphorus diffusion layer (n ⁺⁺ layer). On the other hand, the first diffusion layer (p-type diffusion layer) becomes a boron diffusion layer (p ⁺ layer).

  In this case, the phosphorus diffusing agent and boron diffusing agent are vitrified by heat treatment. As a result, phosphorous glass 11 is formed in the region where the diffusing agent is applied on the first main surface, and boron glass 12 is formed on the second main surface.

  FIG. 8 is an image diagram of the auto-doped region of the low-concentration second diffusion layer formed after the dopant simultaneous diffusion. As shown in FIG. 8, in the region where the heat-treated second diffusing agent 11 is formed, the high-concentration second diffusion layer 2 is formed, and in the region where the heat-treated second diffusing agent 11 is not formed, A low-concentration second diffusion layer 15 is formed. Here, the low-concentration second diffusion layer 15 includes an auto-doped layer 14 having a high concentration of the first conductivity type dopant and an auto-doping layer 13 having a high concentration of the second conductivity type dopant.

  Since the first-conductivity-type dopant is auto-doped in the low-concentration second diffusion layer by the heat treatment described above, the second-conductivity-type dopant and the first-conductivity-type dopant peak in the low-concentration second diffusion layer at this point The concentration ratio (peak concentration of the second conductivity type dopant / peak concentration of the first conductivity type dopant) is small. Thereafter, by performing a step of forming a thermal oxide film, the peak concentration ratio can be increased, that is, the peak concentration of the first conductivity type dopant in the low concentration second diffusion layer can be decreased.

  Next, the pn junction is separated using a plasma etcher. In this process, the sample is stacked so that plasma and radicals do not enter the light-receiving surface and back surface, and in this state, the end surface is cut by several microns. This pn separation by plasma etching may be performed before or after the removal of boron glass and phosphorus glass. As an alternative method of pn separation, groove formation by a laser may be performed.

  Next, a thermal oxide film is formed on the semiconductor substrate on which the high concentration second diffusion layer, the low concentration second diffusion layer, and the first diffusion layer are formed. This step is a step for reducing the concentration of the first conductivity type dopant auto-doped in the low-concentration second diffusion layer by the heat treatment.

  After the heat treatment step and before the step of forming the thermal oxide film, a step of removing the heat-treated first and second diffusing agents may be performed. In this case, the heat-treated diffusing agent (phosphorus glass and boron glass attached to the substrate) can be removed with a high-concentration hydrofluoric acid solution or the like. Thereafter, the substrate is cleaned.

  Subsequently, the substrate from which the heat-treated diffusing agent (glass or the like) has been removed is heat-treated in a 100% oxygen atmosphere at 850 to 950 ° C. for a treatment time of 10 to 60 minutes to form an oxide film. If it is the manufacturing method of such a solar cell, the photovoltaic cell with the more excellent electrical property can be manufactured.

  Here, the thermal oxide film is formed after removing the heat-treated diffusing agent (phosphorus glass and boron glass), but the heat treatment step and the thermal oxide film forming step can be performed in the same heat treatment batch. . In this case, after the substrate is put into a heat treatment furnace, for example, heat treatment is performed at 900 to 1000 ° C. in an inert atmosphere to form the high concentration second diffusion layer, the low concentration second diffusion layer, and the first diffusion layer, A thermal oxide film is formed by switching to a 100% oxygen atmosphere and performing heat treatment at 850 to 950 ° C. for a treatment time of 10 to 60 minutes. If it is a manufacturing method of such a solar cell, a manufacturing process can be reduced.

In the step of forming the thermal oxide film, the thickness of the thermal oxide film to be formed is preferably 10 to 20 nm. By adjusting the oxide film thickness, the peak concentration of the first conductivity type dopant (p-type impurity) in the low-concentration second diffusion layer (n ⁺ layer) can be adjusted.
When the film thickness is 10 nm or more, it is easy to reduce the concentration of the first conductivity type dopant auto-doped in the low concentration second diffusion layer. In the case of 20 nm or less, re-diffusion of the second conductivity type dopant can be suppressed.

The peak concentration of the first conductivity type dopant (p-type impurity) in the low-concentration second diffusion layer (n ⁺ layer) is 5.0 × 10 ¹⁷ atoms / cm ³ or less, and the second conductivity type dopant (n The peak concentration of the (type impurities) is preferably 1.0 × 10 ¹⁸ atoms / cm ³ or more. If the peak concentration of the first conductivity type dopant is 5.0 × 10 ¹⁷ atoms / cm ³ or less, the sheet resistance can be lowered. If the peak concentration of the second conductivity type dopant is 1.0 × 10 ¹⁸ atoms / cm ³ or more, the short circuit current is unlikely to decrease. The upper limit of the peak concentration of the second conductivity type dopant in the low-concentration second diffusion layer is not particularly limited, and can be, for example, 1.0 × 10 ¹⁹ atoms / cm ³ . Although the minimum of the peak density | concentration of the 2nd conductivity type dopant in a high concentration 2nd diffused layer is not specifically limited, For example, it can be 1.0 * 10 < ²⁰ > atom / cm < ³ >.

  Furthermore, it is preferable that the peak concentration ratio of the second conductivity type dopant and the first conductivity type dopant in the low concentration second diffusion layer is 10.0 or more. If the peak concentration ratio is 10.0 or more, the conversion efficiency of the obtained solar cell can be improved more reliably.

  The peak concentration can be measured by SIMS (secondary ion mass spectrometry).

  Next, using a direct plasma CVD apparatus, a silicon nitride film as a passivation film is deposited on the light receiving surface and the back surface. At this time, a passivation film 6 may be deposited on the thermal oxide film 5 as shown in FIG. The thickness of the passivation film is adjusted so that the film thickness including the oxide film is 80 nm to 100 nm on each surface in order to also serve as an antireflection film. Other antireflection films include a silicon dioxide film, a titanium dioxide film, a zinc oxide film, a tin oxide film, an aluminum oxide film, and the like, which can be used as an alternative or a stack structure. In addition to the above, the film forming method includes a remote plasma CVD method, a coating method, a vacuum evaporation method, an ALD (atomic layer deposition) method, and the like, which can be used as appropriate.

  When the heat treatment step and the step of forming the thermal oxide film are performed in the same heat treatment batch, it is preferable to form the passivation film after removing the heat-treated diffusing agent (phosphorus glass and boron glass).

  Next, using a screen printing apparatus, a paste made of, for example, silver is applied to the light-receiving surface side and the back surface side in a comb-shaped electrode pattern and dried. Finally, firing is performed in a firing furnace to obtain a desired solar cell.

By producing a solar cell by the above method, resistance increase due to auto-doping of p-type impurities into the n ⁺ diffusion layer, which occurs during the simultaneous diffusion treatment, and formation of a high concentration p-type diffusion layer are suppressed, and excellent electrical characteristics are achieved A solar cell can be produced.

  As described above, the case of a p-type substrate has been described as an example, but even in the case of an n-type substrate, the above dopant material may be used in reverse, and there is no problem.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, these do not limit this invention.

[Manufacture of solar cells]
Example 1
The solar cell of FIG. 4 was manufactured by performing heat treatment by simultaneous diffusion of phosphoboron. In that case, the solar cell was manufactured according to the flowchart shown in FIG. FIG. 1 is a flow chart showing a method for manufacturing a solar cell of Example 1 (when a diffusion layer and a thermal oxide film are formed in the same heat treatment batch).

At this time, the prepared substrate is a crystal plane orientation (100), a 15.6 cm square 200 μm thickness, an as-slice specific resistance 2 Ω · cm (dopant concentration 7.2 × 10 ¹⁵ cm ⁻³ ) boron-doped p-type single crystal silicon substrate. is there. After damage etching and texture etching with an aqueous NaOH solution, the substrate surface was RCA cleaned to form a texture structure on the substrate surface. The substrate thickness was 180 μm (FIGS. 1 (1) and (2)).

Next, P ₂ O ₅ , pure water, PVA (polyvinyl alcohol), and TEOS (tetraethyl orthosilicate) are mixed to produce a phosphorus diffusing agent, and screen printing is performed on the region directly below the electrode on the light receiving surface side. The pattern was applied and dried at 100 ° C. for 20 minutes (FIG. 1 (3)).

Also, B ₂ O ₃ , pure water, and PVA (polyvinyl alcohol) are mixed to prepare a boron diffusing agent, spin-coated on the back side, and dried at 80 ° C. for 1 minute to uniformly form the boron diffusing agent film. It formed (FIG. 1 (4)).

  Next, the boron surfaces were placed facing each other on a quartz boat and heat-treated at 950 ° C. for 30 minutes. Further, after this step, a step of forming a thermal oxide film at 900 ° C. for 40 minutes was provided by switching to a 100% oxygen atmosphere, and then the temperature was lowered and the substrate was taken out from the heat treatment furnace (FIG. 1 (5)).

Next, the pn junction was separated using a plasma etching apparatus. The etching gas used was CF ₄ gas, and the samples were stacked so that plasma and radicals did not enter the light receiving surface and the back surface, and in this state, the end face was shaved by several microns (FIG. 1 (6)).

  Phosphorous glass and boron glass formed on the substrate surface by simultaneous diffusion were removed with an aqueous hydrofluoric acid solution, and cleaning was performed (FIG. 1 (7)).

  Next, a silicon nitride film as a passivation film was formed with a thickness of 85 nm on the light receiving surface and the back surface using a plasma CVD apparatus (FIG. 1 (8)).

  A silver paste was formed on each of the light-receiving surface side and the back surface side by screen printing, and dried and then baked at 800 ° C. for 20 minutes (FIGS. 1 (9), (10), and (11)).

(Example 2)
The solar cell shown in FIG. 5 was produced in which the thermal oxide film formation of Example 1 was performed after removing the phosphorus glass and boron glass. In that case, the solar cell was manufactured according to the flowchart shown in FIG. FIG. 3 is a flowchart showing a method for manufacturing the solar cell of Example 2 (in the case where the vitrified diffusing agent is removed from the substrate surface after heat treatment, and then a thermal oxide film is formed).

  Specifically, after the simultaneous diffusion of phosphorus boron in Example 1, the thermal oxide film is not formed in the same batch, and the substrate is taken out and pn-separated (FIGS. 3 (5) and (6)). After removing the boron glass by immersing it in a hydrofluoric acid aqueous solution (FIG. 3 (7)), the heat treatment was again performed at 900 ° C. for 40 minutes in a heat treatment furnace in a 100% oxygen atmosphere to form a thermal oxide film of 15 nm (FIG. 3). (8)). Further, the CVD film in the post-process was deposited to 70 nm for each of the light receiving surface and the back surface, and the total thickness of the oxide film and the nitride film on the light receiving surface and the back surface was set to 85 nm (FIG. 3 (9)). Other than that was carried out similarly to Example 1, and produced the solar cell.

(Example 3)
The solar cell shown in FIG. 4 was produced by removing the thermal oxide film after forming the thermal oxide film of Example 2. In that case, the solar cell was manufactured according to the flowchart shown in FIG. FIG. 2 is a flowchart showing a method for manufacturing the solar cell of Example 3 (when the vitrified diffusing agent is removed from the substrate surface after heat treatment, and then a thermal oxide film is formed and removed).

  Specifically, after the formation of the thermal oxide film in Example 2, the substrate was immersed in an aqueous hydrofluoric acid solution, and the thermal oxide film formed on the substrate surface was removed (FIG. 2 (9)). Further, the CVD film in the post-process was deposited on the light receiving surface and the back surface by 85 nm (FIG. 2 (10)). Other than that was carried out similarly to Example 2, and produced the solar cell.

Example 4
A solar cell having a thermal oxide film of 5 nm formed in Example 1 was produced.

  Specifically, the thermal oxide film formation step at the time of phosphorus boron simultaneous diffusion heat treatment in Example 1 was set to 850 ° C. for 40 minutes, and an oxide film was formed to 5 nm. The taken-out substrate was stacked, pn junction separation was performed by plasma etching, and boron glass and phosphorous glass were removed using hydrofluoric acid, and then a CVD film on the light-receiving surface and the back surface was deposited to 85 nm. Other than that was carried out similarly to Example 1, and produced the solar cell.

(Example 5)
A solar cell having a thermal oxide film of 25 nm formed in Example 1 was produced.

  Specifically, the thermal oxide film formation step at the time of phosphorus boron simultaneous diffusion heat treatment in Example 1 was set to 950 ° C. for 40 minutes, and an oxide film was formed to 25 nm. The taken-out substrate was stacked, pn junction separation was performed by plasma etching, and boron glass and phosphorous glass were removed using hydrofluoric acid, and then a CVD film on the light-receiving surface and the back surface was deposited to 85 nm. Other than that was carried out similarly to Example 1, and produced the solar cell.

(Example 6)
A solar cell having a thermal oxide film of 5 nm formed in Example 2 was produced.

  Specifically, the thermal oxide film formation in Example 2 was performed at 850 ° C. for 40 minutes, and a thermal oxide film was formed to 5 nm. A CVD film on each of the light receiving surface and the back surface was deposited to 80 nm. Other than that was carried out similarly to Example 2, and produced the solar cell.

(Example 7)
A solar cell having a thermal oxide film of 25 nm formed in Example 2 was produced.

  Specifically, thermal oxide film formation in Example 2 was performed at 950 ° C. for 40 minutes, and a thermal oxide film was formed to 25 nm. A CVD film on the light-receiving surface and the back surface was deposited to 60 nm. Other than that was carried out similarly to Example 2, and produced the solar cell.

(Example 8)
A solar cell having a thermal oxide film of 5 nm formed in Example 3 was produced.

  Specifically, thermal oxide film formation in Example 3 was performed at 850 ° C. for 40 minutes, and a thermal oxide film was formed to 5 nm. After being immersed in a hydrofluoric acid aqueous solution to remove the thermal oxide film, a CVD film on the light-receiving surface and the back surface was deposited to 85 nm. Other than that was carried out similarly to Example 3, and produced the solar cell.

Example 9
A solar cell having a thermal oxide film of 25 nm formed in Example 3 was produced.

  Specifically, thermal oxide film formation in Example 3 was performed at 950 ° C. for 40 minutes, and an oxide film was formed to 25 nm. After being immersed in a hydrofluoric acid aqueous solution to remove the thermal oxide film, a CVD film on the light-receiving surface and the back surface was deposited to 85 nm. Other than that was carried out similarly to Example 3, and produced the solar cell.

(Comparative Example 1)
For comparison, a solar cell in which no thermal oxide film was formed in Example 1 was produced. In that case, the solar cell was manufactured according to the flowchart shown in FIG. FIG. 9 is a flowchart of the solar cell manufacturing method of Comparative Example 1.

  Specifically, a thermal oxide film formation step is not provided at the time of phosphorus boron simultaneous diffusion heat treatment (FIG. 9 (5)), the taken out substrate is stacked, and pn junction separation is performed by plasma etching (FIG. 9 (6)). After removing boron glass and phosphorus glass using hydrofluoric acid (FIG. 9 (7)), a CVD film on the light-receiving surface and the back surface was deposited by 85 nm (FIG. 9 (8)). Other than that was carried out similarly to Example 1, and produced the solar cell.

  Table 1 shows a condition table for the examples and comparative examples.

[Peak concentration ratio]
The peak concentration of the boron dopant and phosphorus dopant in the n ⁺ layer was measured by SIMS on the substrate before the CVD film formation under each condition, and the peak concentration ratio was calculated. The results are shown in Table 2.

[Sheet resistance measurement]
Furthermore, the sheet resistance of the n ⁺ layer was measured using a four-point probe sheet resistance measuring machine. The results are shown in Table 2.

[Current-voltage characteristics]
As a result of measuring the current-voltage characteristics of the solar cell produced under each condition in a 25 ° C. atmosphere under a solar simulator (light intensity: 1 kW / m ² , spectrum: AM1.5 global), as shown in Table 2. As a result. In addition, the conversion efficiency in a table | surface is an average value of 50 cells made as an experiment in an Example and a comparative example.

As shown in Table 2, in Examples 1 to 3 in which high conversion efficiency is obtained, the peak concentration of boron dopant in the n ⁺ layer is 5.0 × 10 ¹⁷ atoms / cm ³ or less and the peak concentration of phosphorus dopant is 1. 0 is a × ¹⁰ 18 atoms / cm ³ or more, the phosphorus and the peak concentration ratio of boron dopant in the ^{n +} layer (phosphorus / boron) is in the above 10.0. It can be seen that these conditions are favorable conditions for obtaining high conversion efficiency.

This is due to the effect of reducing the concentration of the boron dopant auto-doped in the n ⁺ diffusion layer by forming the thermal oxide film, reducing the sheet resistance of the n ⁺ layer, and reducing the lateral flow resistance.

Further, Examples 1 to 3 have a lower boron dopant concentration and lower n ⁺ layer sheet resistance than Examples 4, 6, and 8 where the thickness of the thermal oxide film is small. High conversion efficiency.

Further, compared to the fifth, seventh, and ninth embodiments in which the thermal oxide film is thickened, since the thermal oxide film is not excessively formed in the n ⁺ layer, the boron dopant is reduced in concentration and the phosphorus dopant is re-diffused. Can be prevented. As a result, the peak concentration of the phosphorus dopant in the n ⁺ layer does not decrease and the diffusion depth does not increase, so that the recombination rate in the vicinity of the light receiving surface decreases.

  In addition, Examples 4, 6, and 8 are cases where the thickness of the thermal oxide film is smaller than that of Example 1, but even in this case, a solar cell having higher conversion efficiency than that of Comparative Example 1 could be obtained. .

  On the other hand, in Examples 5, 7, and 9 in which the thermal oxide film was thickened, the short-circuit current was slightly reduced as compared with Examples 1 to 3, but even in this case, the conversion efficiency was higher than that in Comparative Example 1. A solar cell could be obtained.

On the other hand, in Comparative Example 1, since the thermal oxide film formation for reducing the boron dopant concentration is not performed, the peak concentration ratio (phosphorus / boron) of phosphorus and boron dopant in the n ⁺ layer becomes small, and the conversion efficiency becomes low. It was.

If it is the manufacturing method of the solar cell of this invention, a boron diffusion layer (1st diffusion layer) and a phosphorus diffusion layer (high concentration 2nd diffusion layer, low concentration 2nd diffusion layer) from which density | concentration differs are formed simultaneously by one heat processing. In this case, boron dopant (first conductivity type dopant) and phosphorus dopant (second conductivity type dopant) auto-doped in the n ⁺ diffusion layer (low concentration second diffusion layer) by forming a thermal oxide film. It can be seen that a solar cell having a high conversion efficiency can be produced.

  Furthermore, the present invention is not limited to the above embodiment. For example, in this embodiment, a p-type substrate solar cell is shown. However, the above effect can be implemented even when phosphoboron simultaneous diffusion using an n-type substrate is performed, and a solar cell having high conversion efficiency is manufactured. Is possible. The above-described embodiment is an exemplification, and the present invention has any configuration substantially the same as the technical idea described in the claims of the present invention and exhibits the same function and effect. It is included in the technical scope.

Claims (10)

A high-concentration second diffusion layer in which a dopant of the second conductivity type opposite to the first conductivity type is diffused on the first main surface of the semiconductor substrate of the first conductivity type and lower than the high-concentration second diffusion layer. A method for manufacturing a solar cell, wherein a low-concentration second diffusion layer in which a dopant is diffused in a concentration is formed, and a first diffusion layer in which the first conductivity type dopant is diffused is formed on a second main surface of the semiconductor substrate. Because
(A) preparing a second diffusing agent containing the second conductivity type dopant and a first diffusing agent containing the first conductivity type dopant;
(B) applying the first diffusing agent to the second main surface;
(C) partially applying the second diffusing agent to the first main surface;
(D) Forming the high-concentration second diffusion layer, the low-concentration second diffusion layer, and the first diffusion layer by heat-treating the semiconductor substrate coated with the first diffusing agent and the second diffusing agent. And a process of
And (e) forming a thermal oxide film on the semiconductor substrate on which the diffusion layer is formed.   The semiconductor substrate is a p-type silicon substrate, the second diffusing agent is a phosphorus diffusing agent that is vitrified by the heat treatment, and the first diffusing agent is a boron diffusing agent that is vitrified by the heat treatment. Item 2. A method for producing a solar cell according to Item 1.   The method for manufacturing a solar cell according to claim 1 or 2, wherein the steps (d) and (e) are performed in the same heat treatment batch.   2. The method according to claim 1, further comprising: (f) removing the heat-treated first diffusing agent and second diffusing agent after the step (d) and before the step (e). The manufacturing method of the solar cell of Claim 2.   The method for manufacturing a solar cell according to any one of claims 1 to 4, wherein the thermal oxide film formed in the step (e) has a thickness of 10 to 20 nm. The peak concentration of the first conductivity type dopant in the low-concentration second diffusion layer is set to 5.0 × 10 ¹⁷ atoms / cm ³ or less. 6. The manufacturing method of the solar cell of description. The peak concentration of the second conductivity type dopant in the low-concentration second diffusion layer is 1.0 × 10 ¹⁸ atoms / cm ³ or more. 7. The manufacturing method of the solar cell of description.   8. The peak concentration ratio between the second conductivity type dopant and the first conductivity type dopant in the low concentration second diffusion layer is set to 10.0 or more, 8. The manufacturing method of the solar cell of description. After the step (e), (g) a step of forming a passivation film on the first main surface and the second main surface;
(H) applying an electrode material to the first main surface and the second main surface on which the passivation film is formed;
(I) It has the process of baking the apply | coated electrode material, The manufacturing method of the solar cell of any one of Claims 1-8 characterized by the above-mentioned.   A solar cell manufactured by the method for manufacturing a solar cell according to any one of claims 1 to 9.

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