JP2018174293A - Method for manufacturing semiconductor substrate, semiconductor substrate, solar battery device, and method for manufacturing solar battery device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a simple and convenient method for manufacturing a semiconductor substrate; a semiconductor substrate manufactured by the manufacturing method; a solar battery device arranged by use of the semiconductor substrate, and having an excellent power generation efficiency; and a method for manufacturing the solar battery device.SOLUTION: A method for manufacturing a selective n-type diffusion layer-attached semiconductor substrate comprises: a step of forming a p-type diffusion layer 11 on a front principal face of a semiconductor substrate 10; a step of etching a rear principal face of the semiconductor substrate 10 after the step of forming the p-type diffusion layer 11; and an n-type diffusion layer-forming step after the etching step, which includes the steps of partially applying an n-type diffusion layer-forming composition to the rear principal face of the semiconductor substrate 10 to form a first n-type diffusion layer 13, and forming, on the rear principal face of the semiconductor substrate 10, a second n-type diffusion layer 14 having a donor element concentration lower than a donor element concentration of the first n-type diffusion layer 13.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a semiconductor substrate manufacturing method, a semiconductor substrate, a solar cell element, and a solar cell element manufacturing method.

First, an example of a manufacturing process of a conventional solar cell element will be described.
Concavities and convexities (texture structure) are formed on the surface of a semiconductor substrate cut out to a thickness of about several hundred μm from a crystal ingot such as a p-type silicon crystal widely used as a substrate for solar cells. By forming the texture structure, the obtained solar cell element can absorb light efficiently. Subsequently, several tens of minutes of heat treatment is performed at 700 ° C. to 900 ° C. in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen to form an n-type diffusion layer uniformly on the surface of the p-type semiconductor substrate. . Thereby, a pn junction is formed in the p-type semiconductor substrate. After diffusion of phosphorus using a mixed gas, an excess n-type diffusion layer formed on the back surface of the p-type semiconductor substrate is etched. A film of SiO ₂ , Al ₂ O ₃ , silicon nitride (SiN _x ) or the like is formed as a passivation layer in the phosphorous diffusion layer on the light receiving surface in order to prevent recombination (also referred to as surface recombination) on the surface of the generated carriers. To do. This passivation layer may function as an antireflection film for increasing the light collection rate. Finally, an electrode composition mainly composed of Ag is applied to the light receiving surface, and an electrode composition mainly composed of Al is applied to the back surface, and this is heat-treated (fired) to obtain an ohmic contact. At this time, a high-concentration p-type diffusion layer is formed of Al on the back surface of the p-type semiconductor substrate. This high-concentration p-type diffusion layer has the effect of improving the solar cell characteristics.

It is known that a solar cell element using an n-type semiconductor substrate has higher power generation efficiency than a solar cell element using a p-type semiconductor substrate. This is because an n-type semiconductor substrate has a longer carrier lifetime and fewer oxygen defects than a p-type semiconductor substrate, making it easy to obtain high power generation efficiency. When a solar cell element is manufactured using an n-type semiconductor substrate, a step of diffusing an acceptor element such as boron may be included in order to form a pn junction. Known diffusion methods using boron as an acceptor element include a method using boron tribromide (BBr ₃ ) gas, a method using a coating material containing boron, and an ion implantation method.

A double-sided light receiving solar cell element is known as a solar cell element using an n-type semiconductor substrate. In a double-sided solar cell element, a p-type diffusion layer is generally formed on one surface of a substrate using an acceptor element, and a donor element such as phosphorus is used on the other surface, and the concentration is higher than that of the substrate. A mold diffusion layer is formed. And an electrode is formed using the electrode composition which has Ag as a main component so that light may be absorbed efficiently on both surfaces, and electricity may be passed efficiently. Currently, a double-sided light-receiving solar cell element is required to form a p-type diffusion layer as uniformly as possible on the entire surface of one surface of a substrate. Therefore, when a p-type diffusion layer is formed using boron as an acceptor element, BBr ₃ gas or a coating material is often used. On the other hand, when an n-type diffusion layer is formed using a donor element such as phosphorus, a gas containing POCl _3, which has a proven record in manufacturing a solar cell element using a p-type silicon semiconductor substrate, is often used.

  On the other hand, as a method for increasing the power generation efficiency of the double-sided light-receiving solar cell element, there is known a method for suppressing surface recombination by reducing the concentration of the donor element in the n-type diffusion layer as much as possible. If the concentration of the donor element is too low, the resistance of the electrode portion becomes high and electricity cannot be extracted efficiently. Therefore, the concentration of the donor element in the substrate is increased in the region where the electrode is formed, so-called selective back surface field (hereinafter referred to as S-BSF). The power generation efficiency can be increased by having a structure. For example, Patent Document 1 shows that a solar cell element having an S-BSF structure has high photoelectric conversion efficiency.

As a method of forming S-BSF, an etch-back method in which a phosphorus diffusion layer having a high phosphorus concentration is formed once with a gas containing POCl ₃ and partially etched, and a phosphorous silicate glass with a gas containing POCl ₃ (Hereinafter referred to as PSG) to form a phosphorus diffusion layer having a low phosphorus concentration, and then a laser method in which a phosphorus diffusion layer having a high phosphorus concentration is formed by locally heating the PSG with a laser. After the coating type diffusion material contained is printed on a part of the semiconductor substrate to form a phosphorus diffusion layer having a high phosphorus concentration, the phosphorous concentration with a gas containing POCl ₃ is applied to the portion where the coating type diffusion material is not applied. And a printing method for forming a low phosphorus diffusion layer.

Japanese Patent No. 58858891

As described above, when a p-type diffusion layer is formed using a gas containing an acceptor element such as BBr ₃ gas, boron is diffused over the entire outer periphery of the semiconductor substrate. Diffuses. Even when a coating material containing an acceptor element is used, the acceptor element scatters on the surface where the donor element is diffused during the diffusion process, and diffuses outside the region to which the coating material is applied (referred to as out-diffusion). If the acceptor element is present on the surface where the donor element is diffused, it becomes a factor that greatly reduces the solar cell characteristics.

  Further, when the S-BSF is formed by the etch back method, there is a problem that mask formation, partial etching, and mask removal are necessary, and the process becomes complicated. The laser method has a problem that it is difficult to adjust the concentration when forming a high concentration n-type diffusion layer. In the case of the printing method, in order to form a high concentration n-type diffusion layer, it is necessary to perform diffusion treatment at a high temperature. Therefore, there is a problem that the acceptor element is likely to be mixed on the surface of the semiconductor substrate where the n-type diffusion layer is formed, and the power generation efficiency is easily affected. In order to increase the power generation efficiency by partially reducing the donor element concentration of the n-type diffusion layer of the semiconductor substrate having the S-BSF structure, the surface on the n-type diffusion layer side of the substrate is not contaminated by an acceptor element such as boron. It is required to be controlled as follows.

  In Patent Document 1, first, a silicon substrate having a pn junction is formed, and a passivation layer made of a silicon oxide film and a silicon nitride film is formed as a protective film on the surface of the n-type layer. Thereafter, the passivation layer is partially opened by etching using an etching paste or the like, and the donor element is diffused into the opening region, thereby forming a high-concentration n-type diffusion region at a selective position. This method has complicated steps such as formation of a protective film and opening by partial etching in the process of forming a high concentration n-type diffusion layer at a selective position.

  In view of the above, it is an object of the present disclosure to provide a simple method for manufacturing a semiconductor substrate, a semiconductor substrate manufactured by the manufacturing method, a solar cell element excellent in power generation efficiency using the same, and a method for manufacturing the solar cell element. To do.

Means for solving the above problems are as follows.
<1> A step of forming a p-type diffusion layer on a front main surface of a semiconductor substrate, a step of etching a back main surface of the semiconductor substrate after the step of forming the p-type diffusion layer, and the etching step A step of forming a first n-type diffusion layer by partially applying an n-type diffusion layer forming composition to the back main surface of the semiconductor substrate, and the first on the back main surface of the semiconductor substrate. A step of forming an n-type diffusion layer including a step of forming a second n-type diffusion layer having a donor element concentration lower than that of the n-type diffusion layer of the n-type diffusion layer, with a selective n-type diffusion layer A method for manufacturing a semiconductor substrate.
<2> When the n-type diffusion layer forming composition is expressed as an oxide, at least one donor element-containing material selected from P ₂ O ₃ , P ₂ O ₅ and Sb ₂ O ₃ , and SiO ₂ At least one glass selected from K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO ₃ The method for producing a semiconductor substrate with a selective n-type diffusion layer according to <1>, comprising glass particles containing a component substance.
<3> When the n-type diffusion layer forming composition is expressed as an oxide, it contains glass particles containing P ₂ O ₅ , SiO ₂ and CaO, and a dispersion medium <1> or <2> The manufacturing method of the semiconductor substrate with a selective n type diffused layer of description.
<4> The method for producing a semiconductor substrate with a selective n-type diffusion layer according to any one of <1> to <3>, wherein an etching solution used for the etching includes an acid solution or an alkali solution.
<5> The method for producing a semiconductor substrate with a selective n-type diffusion layer according to <4>, wherein the etching solution contains a mixed solution of a hydrofluoric acid solution and a nitric acid solution.
<6> The method for producing a semiconductor substrate with a selective n-type diffusion layer according to <4>, wherein the etching solution contains an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution.
<7> The method for producing a semiconductor substrate with a selective n-type diffusion layer according to any one of <1> to <6>, wherein the second n-type diffusion layer is formed using a gas containing POCl _3. Method.
<8> A semiconductor substrate with a selective n-type diffusion layer manufactured by the manufacturing method according to any one of <1> to <7>.
<9> A solar cell element comprising: the semiconductor substrate with a selective n-type diffusion layer according to <8>; and an electrode provided on the semiconductor substrate with the selective n-type diffusion layer.
<10> A step of manufacturing a semiconductor substrate with a selective n-type diffusion layer having a selective n-type diffusion layer by the manufacturing method according to any one of <1> to <7>, and the selective n-type diffusion And a step of forming an electrode on the layer.

  According to the present disclosure, a simple semiconductor substrate manufacturing method, a semiconductor substrate manufactured by the manufacturing method, a solar cell element excellent in power generation efficiency using the semiconductor substrate, and a solar cell element manufacturing method are provided.

It is sectional drawing which shows notionally an example of the manufacturing process of the solar cell element which concerns on 1st embodiment of this indication. It is sectional drawing which shows notionally an example of the manufacturing process of the solar cell element which concerns on 2nd embodiment of this indication. It is the top view which looked at the solar cell element from the light-receiving surface. It is a perspective view which expands and shows a part of Drawing 3A.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless explicitly specified, unless otherwise clearly considered essential in principle. The same applies to numerical values and ranges thereof, and the present invention is not limited thereto.

In the present disclosure, the term “process” includes a process independent of another process and the process if the purpose of the process is achieved even when it cannot be clearly distinguished from the other process.
In the present disclosure, numerical ranges indicated using “to” indicate ranges including numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical description. . Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.
In the present disclosure, each component may contain a plurality of corresponding substances. When multiple types of substances corresponding to each component are present in the composition, the content or content of each component is the total content or content of the multiple types of substances present in the composition unless otherwise specified. Means quantity.
In the present disclosure, a plurality of particles corresponding to each component may be included. When a plurality of particles corresponding to each component are present in the composition, the particle diameter of each component means a value for a mixture of the plurality of particles present in the composition unless otherwise specified.
In the present disclosure, the “content ratio” of a component represents mass% of the component when the total amount of the composition containing the component is 100 mass% unless otherwise specified.
In the present disclosure, the term “layer” or “film” refers to a part of the region in addition to a case where the layer or the film is formed over the entire surface of the region when the region where the layer or the film exists is observed as a plan view. The case where it is formed is also included.
In the present disclosure, the term “lamination” indicates that layers are stacked, and two or more layers may be combined, or two or more layers may be detachable.
In the present disclosure, the “glass particle” means a glass (amorphous solid exhibiting a glass transition phenomenon) in the form of particles.
Embodiments of the present invention may be practiced without utilizing some or all of the specific and detailed content of the present disclosure.
In addition, in order to avoid obscuring the concept of the present invention, detailed description or illustration may be omitted for known points.
In the present disclosure, the average particle diameter is obtained as a volume average particle diameter at which the volume accumulation from the small particle diameter side becomes 50% in the particle size distribution measured using the laser diffraction scattering method.
In the present disclosure, “(meth) acryl” means at least one of acryl and methacryl, and “(meth) acrylate” means at least one of acrylate and methacrylate.

<< Semiconductor Substrate Manufacturing Method and Semiconductor Substrate According to First Embodiment >>
The method for manufacturing a semiconductor substrate according to the first embodiment includes a step of forming a p-type diffusion layer on the main surface of the semiconductor substrate (p-type diffusion layer formation step) and a step of forming the p-type diffusion layer. The step of etching the back main surface of the semiconductor substrate (etching step) and the step of forming an n-type diffusion layer on the back main surface of the semiconductor substrate after the etching step (in the first embodiment) N-type diffusion layer forming step). The method for manufacturing a semiconductor substrate according to the first embodiment may include other steps as necessary.
The semiconductor substrate according to the first embodiment is manufactured by the above manufacturing method.

According to the above manufacturing method, the acceptor element can be removed in the region where the n-type diffusion layer is to be formed by a simple method by etching, and the n-type diffusion layer can be formed. For this reason, a semiconductor substrate with an n-type diffusion layer can be obtained by a simple method, and a solar cell element excellent in power generation efficiency can be obtained using this. The manufacturing method of the present disclosure, boron tribromide (BBr ₃₎ Gas diffusion method using a gas such as, whether the method of forming the p-type diffusion layer such as a coating method is applicable.
<P-type diffusion layer forming step>
In the p-type diffusion layer forming step, a p-type diffusion layer is formed on the front main surface of the semiconductor substrate.
In the method for manufacturing a semiconductor substrate according to the first embodiment of the present disclosure, the p-type diffusion layer is formed before the n-type diffusion layer is formed. In general, the formation of the p-type diffusion layer is often accompanied by a heat treatment at a higher temperature than the formation of the n-type diffusion layer in order to sufficiently diffuse the acceptor element. If high-temperature heat treatment is performed to form a p-type diffusion layer after forming an n-type diffusion layer, it becomes difficult to adjust the donor element concentration in the n-type diffusion layer. On the other hand, by forming the p-type diffusion layer prior to the formation of the n-type diffusion layer, both the donor concentration in the n-type diffusion layer and the acceptor concentration in the p-type diffusion layer tend to be easily controlled. is there.

  The kind in particular of a semiconductor substrate is not restrict | limited, The semiconductor substrate which can be used as a board | substrate of a solar cell element is applicable. For example, silicon substrate, gallium phosphide substrate, gallium nitride substrate, diamond substrate, aluminum nitride substrate, indium nitride substrate, gallium arsenide substrate, germanium substrate, zinc selenide substrate, zinc telluride substrate, cadmium telluride substrate, cadmium sulfide Examples include a substrate, an indium phosphide substrate, a silicon carbide substrate, a silicon germanium substrate, and a copper indium selenium substrate. Examples of the silicon substrate include a crystalline silicon substrate. The semiconductor substrate may be an n-type semiconductor substrate or a p-type semiconductor substrate.

  In the present disclosure, the front main surface refers to one surface of the semiconductor substrate. The back main surface described later refers to the other of the two main surfaces.

A p-type diffusion layer refers to a region where an acceptor element is diffused in a semiconductor substrate.
An acceptor element means an element that can diffuse into a semiconductor substrate to form a p-type diffusion layer. Examples of the acceptor element include Group 13 elements such as boron (B), aluminum (Al), and gallium (Ga) indium (In).

  The method for forming the p-type diffusion layer is not particularly limited, and examples thereof include a method using a gas containing an acceptor element and a method using a composition containing an acceptor element. From the viewpoint of simplification of the process, a method using a gas containing an acceptor element is preferable.

Examples of the gas containing an acceptor element include boron tribromide (BBr ₃ ) and boron trichloride (BCl ₃ ). Examples of a method for forming a p-type diffusion layer using a gas containing an acceptor element include a method in which boron silicate glass (BSG) is formed on a semiconductor substrate using BBr ₃ gas and a thermal diffusion treatment is performed.

  From the viewpoint of obtaining high power generation efficiency, the temperature of the atmosphere of the thermal diffusion treatment when using a gas containing an acceptor element is preferably 800 ° C. to 1050 ° C., more preferably 800 ° C. to 1000 ° C., The temperature is more preferably 850 ° C to 1000 ° C, particularly preferably 900 ° C to 1000 ° C, and extremely preferably 900 ° C to 970 ° C. The thermal diffusion treatment time is preferably 5 minutes to 90 minutes, more preferably 10 minutes to 90 minutes, further preferably 10 minutes to 60 minutes, and 10 minutes in consideration of process shortening. It is particularly preferred that it is ˜30 minutes. In the present disclosure, the thermal diffusion treatment time refers to the holding time at the maximum temperature. If the thermal diffusion treatment time is 5 minutes or more, the acceptor element tends to be sufficiently diffused into the semiconductor substrate, and if it is 90 minutes or less, the manufacturing cost tends to be suppressed. A known continuous furnace, batch furnace, or the like can be applied to the heat treatment.

  Examples of the composition containing an acceptor element include a composition containing boron. As the boron-containing composition, a boron-containing compound is contained, and the boron in the boron-containing compound is diffused by heat treatment after being applied to the semiconductor substrate, thereby forming a p-type diffusion layer forming composition for the semiconductor substrate. A composition capable of forming a p-type diffusion layer, which is an impurity diffusion layer, in the region provided with (hereinafter also referred to as a p-type diffusion layer forming composition) can be used.

  Examples of the compound containing boron include inorganic boron compounds such as boron oxide, boron oxoacid, calcium borate, boron nitride, and boric acid; borate ester compounds; glass compounds containing boron (hereinafter also referred to as “boron-containing glass compounds”). ); Boron-doped silicon particles; boron-containing silicon oxide compound; boron alkoxide; Or the like).

  Among these, it is preferable to use at least one selected from the group consisting of boron oxide, boric acid, borate ester compounds, boron-containing glass compounds, boron nitride, boron-containing silicon oxide compounds, and boron oxide precursors. From the viewpoint of suppressing out diffusion, it is preferably at least one selected from the group consisting of boron nitride, boron-containing glass compounds, and boron-containing silicon oxide compounds, and is selected from boron nitride and boron-containing glass compounds. One or more types are more preferable, and a boron-containing glass compound is further preferable.

  The p-type diffusion layer forming composition may further contain a dispersion medium in order to adjust the viscosity of the composition. Examples of the dispersion medium include a solvent and water. The content of the dispersion medium in the p-type diffusion layer forming composition can be determined in consideration of the imparting property and the viscosity.

Examples of a method for forming a p-type diffusion layer using a composition containing an acceptor element include a method in which a composition containing an acceptor element is applied to a semiconductor substrate and a thermal diffusion process is performed.
The method for applying the composition containing the acceptor element to the semiconductor substrate is not particularly limited. For example, the printing method, the spin coating method, the brush coating, the spray method, the doctor blade method, the roll coating method, APCVD (atmospheric pressure CVD), and An ink jet method is exemplified.
The temperature of the atmosphere of the thermal diffusion treatment after applying the composition containing the acceptor element is preferably 800 ° C to 1050 ° C, more preferably 800 ° C to 1000 ° C, and 850 ° C to 1000 ° C. More preferably, it is particularly preferably 900 ° C to 1000 ° C, and very preferably 900 ° C to 970 ° C. The thermal diffusion treatment time is preferably 5 minutes to 90 minutes, more preferably 10 minutes to 90 minutes, further preferably 10 minutes to 60 minutes, and 10 minutes in consideration of process shortening. It is particularly preferred that it is ˜30 minutes. A known continuous furnace, batch furnace, or the like can be applied to the heat treatment. If the thermal diffusion treatment time is 5 minutes or more, the acceptor element tends to be sufficiently diffused into the semiconductor substrate, and if it is 90 minutes or less, the manufacturing cost tends to be suppressed.

  When performing a thermal diffusion process for diffusing the acceptor element, two semiconductor substrates may be placed in the furnace so that the back main surfaces face each other, and the thermal diffusion process may be performed. Thereby, it can suppress that an acceptor element wraps around to a back main surface.

<Etching process>
In the etching step, the back main surface of the semiconductor substrate is etched after the step of forming the p-type diffusion layer. By the etching process, the acceptor element attached to the back main surface or the p-type diffusion layer formed on the surface of the back main surface is removed.
Examples of the etching method include a method using an etching solution. Examples of the etching solution include an acid solution and an alkali solution. The acid solution preferably contains hydrofluoric acid. Hydrofluoric acid may be used alone or in combination with other acid solutions. Among these, it is more preferable to use a mixed solution of a hydrofluoric acid solution and a nitric acid solution. The mixing ratio of hydrofluoric acid and nitric acid in the mixed solution of hydrofluoric acid solution and nitric acid solution may be appropriately adjusted depending on the desired degree of etching. As the alkaline solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous tetramethylammonium hydroxide solution or the like may be used.

  When etching is performed using an etchant, the time for immersing the etchant in the semiconductor substrate is not particularly limited, and may be 0.5 minutes to 30 minutes, and is preferably 0.5 minutes to 10 minutes.

  In the etching process of the present disclosure, the back main surface is etched and the front main surface is not etched. For this reason, it is preferable to use the single side etching method which immerses the back main surface of a semiconductor substrate in etching liquid.

<N-type diffusion layer forming step according to the first embodiment>
In the n-type diffusion layer forming step according to the first embodiment, the n-type diffusion layer is formed on the back main surface of the semiconductor substrate after the etching step. An n-type diffusion layer refers to a region where a donor element of a semiconductor substrate is diffused.

  There is no restriction | limiting in particular as a method of forming an n type diffused layer in a semiconductor substrate. Examples thereof include a method using a gas containing a donor element and a method using a composition containing a donor element. From the viewpoint of simplification of the process, a method using a gas containing a donor element is preferable.

Examples of the gas containing a donor element include POCl ₃ . Examples of a method for forming an n-type diffusion layer using a gas containing a donor element include a method of performing a thermal diffusion process using a gas containing a donor element such as POCl ₃ .
The temperature of the atmosphere in the thermal diffusion treatment using a gas containing a donor element is preferably 700 ° C. to 900 ° C., and more preferably 750 ° C. to 850 ° C. A known continuous furnace, batch furnace, or the like can be applied to the heat treatment.
The thermal diffusion treatment time is preferably from 5 minutes to 90 minutes, more preferably from 10 minutes to 90 minutes, further preferably from 10 minutes to 60 minutes. It is particularly preferable that the period is from 30 minutes to 30 minutes. When the thermal diffusion treatment time is 5 minutes or more, the acceptor element tends to be sufficiently diffused into the semiconductor substrate, and when it is 90 minutes or less, the production cost can be suppressed.

  As a composition containing a donor element, for example, an n-type diffusion layer forming composition described later can be used. As a method for forming an n-type diffusion layer using a composition containing a donor element, a method described as a first n-type diffusion layer formation method in an n-type diffusion layer forming step according to a second embodiment described later Can be applied.

As a method for forming the n-type diffusion layer, an example in the case of using a gas containing POCl ₃ will be described.
In a thermal diffusion facility provided with a semiconductor substrate, the atmosphere temperature is set to 700 ° C. to 900 ° C., and a gas containing POCl ₃ is injected. The thermal diffusion treatment includes a deposition (hereinafter also referred to as “depo”) step of diffusing phosphorus while injecting a gas containing POCl ₃ to form PSG, and diffusing phosphorus by stopping the injection of the gas containing POCl ₃ . You may perform a Drive-in process. Alternatively, only the Depo process may be performed and the Drive-in process may not be performed. The temperature of the atmosphere in the Depo process and the Drive-in process may be the same temperature or different temperatures. From the viewpoint of forming the n-type diffusion layer at an appropriate concentration, the temperature of the atmosphere during the thermal diffusion treatment is preferably 750 ° C. to 850 ° C. The thermal diffusion treatment time may be 5 minutes to 90 minutes, or 10 minutes to 60 minutes, including the Depo step and the Drive-in step, from the viewpoint of balance between diffusibility into the semiconductor substrate and reduction of the process time. Is preferred. A similar thermal diffusion treatment time can be applied when the Drive-in process is not performed.

<Other processes>
The method for manufacturing a semiconductor substrate according to the first embodiment may include other steps as necessary. As other steps, for example, a step of performing a pretreatment on the semiconductor substrate before forming the diffusion layer can be cited. An example of the preprocessing includes processing for forming a texture structure. The process for forming the texture structure may be performed as follows, for example.
An alkali solution is applied to the semiconductor substrate to remove the damaged layer, and a texture structure is obtained by etching. Specifically, the damaged layer on the surface of the semiconductor substrate generated when slicing from the ingot is removed with a 20% by mass aqueous sodium hydroxide solution. Next, etching is performed with a mixed solution of 1% by mass caustic soda and 10% by mass isopropyl alcohol to form a texture structure. In the solar cell element, by forming a texture structure on the light receiving surface side, a light confinement effect is promoted and high efficiency is achieved.

  Further, a step of removing BSG, thermal oxide film, PSG, and the like on the semiconductor substrate formed by the thermal diffusion treatment with an etching solution may be performed. There is no restriction | limiting in particular in the kind of etching liquid, An aqueous solution, such as hydrogen fluoride, ammonium fluoride, ammonium hydrogen fluoride, aqueous solution of sodium hydroxide, etc. are mentioned. As the etching treatment, a known method such as a method of immersing a semiconductor substrate in an etching solution can be applied.

<< Semiconductor substrate with selective n-type diffusion layer and semiconductor substrate with selective n-type diffusion layer according to the second embodiment >>
The manufacturing method of the semiconductor substrate with a selective n-type diffusion layer according to the second embodiment further includes a step of forming n-type diffusion layers having different donor element concentrations on the back surface in the first embodiment. The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to the second embodiment includes a step of forming a p-type diffusion layer on the front main surface of the semiconductor substrate (p-type diffusion layer forming step), and the p-type diffusion. Etching the back main surface of the semiconductor substrate after the step of forming a layer (etching step), and forming the n-type diffusion layer forming composition on the back main surface of the semiconductor substrate after the etching step A step of partially applying to form a first n-type diffusion layer, and a second n having a donor element concentration lower than the donor element concentration of the first n-type diffusion layer on the back main surface of the semiconductor substrate And a step of forming an n-type diffusion layer (an n-type diffusion layer forming step according to the second embodiment) including a step of forming a mold diffusion layer. The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to the second embodiment may further include other steps as necessary.
The semiconductor substrate with a selective n-type diffusion layer according to the second embodiment is manufactured by the above manufacturing method.

In the above manufacturing method, the acceptor element is removed in the region where the n-type diffusion layer is formed by a simple method by etching without going through complicated processes such as mask formation and mask removal in the region where the n-type diffusion layer is formed. A selective n-type diffusion layer can be formed. In addition, by selectively adjusting the concentration of the donor element contained in the n-type diffusion layer forming composition, it is possible to easily adjust the concentration of the donor element in the n-type diffusion layer to produce a selective n-type diffusion layer. For this reason, a semiconductor substrate with a selective n-type diffusion layer can be obtained by a simple method, and a solar cell element excellent in power generation efficiency can be obtained using this. The manufacturing method of the present disclosure, boron tribromide (BBr ₃₎ Gas diffusion method using a gas such as, whether the method of forming the p-type diffusion layer such as a coating method is applicable.

  In this disclosure, the selective n-type diffusion layer refers to an n-type diffusion layer in which an n-type diffusion layer having a high donor element concentration is formed in a limited region. A case where a diffusion region of a donor element of a different type from that of another region is formed in the limited region is also included in the selective n-type diffusion layer.

  Hereinafter, a method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to the second embodiment will be described step by step.

<P-type diffusion layer forming step and etching step>
The details of the p-type diffusion layer forming step and the etching step are the same as the details of the p-type diffusion layer forming step and the etching step in the first embodiment.

<N-type diffusion layer forming step according to the second embodiment>
In the n-type diffusion layer forming step according to the second embodiment, after the etching step, the n-type diffusion layer forming composition is partially applied to the back main surface of the semiconductor substrate to form the first n-type diffusion layer. A step of forming (first n-type diffusion layer forming step), and a second n-type diffusion layer having a donor element concentration lower than the donor element concentration of the first n-type diffusion layer on the back main surface of the semiconductor substrate A step of forming an n-type diffusion layer, including a step of forming (second n-type diffusion layer formation step).

Either the first n-type diffusion layer forming step or the second n-type diffusion layer forming step may be first. Further, the first n-type diffusion layer forming step and the second n-type diffusion layer forming step may be a series of steps.
When the first n-type diffusion layer having a high donor element concentration is formed first by high-temperature heat treatment, and the second n-type diffusion layer having a low donor element concentration is formed by low-temperature heat treatment, the first n-type diffusion layer is formed. The donor element concentration in the diffusion layer and the second n-type diffusion layer can be easily adjusted. From the above viewpoint, it is preferable to form the first n-type diffusion layer first. From the viewpoint of simplifying the process, it is preferable to perform both processes simultaneously.
Hereinafter, each of the first n-type diffusion layer forming step and the second n-type diffusion layer forming step will be described.

[First n-type diffusion layer forming step]
In the first n-type diffusion layer forming step, the n-type diffusion layer forming composition is partially applied to the back main surface of the semiconductor substrate to form the first n-type diffusion layer. First, the n-type diffusion layer forming composition used in this step will be described. The n-type diffusion layer forming composition is used for forming at least the first n-type diffusion layer. The second n-type diffusion layer may be formed by applying an n-type diffusion layer forming composition to a semiconductor substrate, or may be formed by other methods.

-N-type diffusion layer forming composition-
In the present disclosure, the n-type diffusion layer forming composition refers to a composition capable of forming an n-type diffusion layer by being applied to a semiconductor substrate and diffusing. The n-type diffusion layer forming composition is not particularly limited as long as it contains a donor element and can form an n-type diffusion layer by being applied and diffused in a semiconductor substrate. The n-type diffusion layer forming composition may be, for example, a composition containing a compound containing a donor element and a dispersion medium, and may contain other components as necessary.

(Compound containing donor element)
A donor element is an element that can form an n-type diffusion layer by diffusing into a semiconductor substrate. Examples of the donor element include Group 15 elements such as P (phosphorus), Sb (antimony), and As (arsenic). From the viewpoint of safety and the like, P (phosphorus) is preferable.
There is no restriction | limiting in particular as a compound containing a donor element. For example, oxides such as P ₂ O ₅ and P ₂ O ₃ ; inorganic phosphorus compounds such as phosphorus silicide, silicon particles doped with phosphorus, calcium phosphate, phosphoric acid, glass particles containing phosphorus; and phosphonic acid and phosphonous Examples thereof include organic phosphorus compounds such as acid, phosphinic acid, phosphinic acid, phosphine, phosphine oxide, phosphate ester, and phosphite ester.

Among these, P ₂ O ₃ , P ₂ O ₅ , and a compound (phosphoric acid) that can be changed to a compound containing P ₂ O ₅ at a heat treatment temperature (for example, 800 ° C. or more) when diffusing a donor element into a semiconductor substrate. It is preferable to use one or more selected from the group consisting of ammonium dihydrogen, phosphoric acid, phosphonous acid, phosphinic acid, phosphinic acid, phosphine, phosphine oxide, phosphate ester, phosphite ester, etc. Among them, it is more preferable to use a compound having a melting point of 1000 ° C. or lower. This is because the compound containing the donor element is likely to be in a molten state when thermally diffusing into the semiconductor substrate, and the donor element is easily diffused uniformly into the semiconductor substrate. Specifically, it is preferable to use at least one selected from the group consisting of glass particles containing P ₂ O ₅ and phosphorus as such a compound. Further, when the melting point of the compound containing the donor element exceeds 1000 ° C., the compound having the melting point of less than 1000 ° C. is further added to the compound containing the donor element from the compound having the melting point of less than 1000 ° C. The donor element may be diffused into the semiconductor substrate.

The form of the compound containing a donor element in the n-type diffusion layer forming composition is that the compound containing the donor element is dispersed in the dispersion medium even if the compound containing the particulate donor element is dispersed in the dispersion medium. It may be in a dissolved state.
Examples of the shape when the compound containing the donor element is in the form of solid particles include a substantially spherical shape, a flat shape, a block shape, a plate shape, and a scale shape. From the viewpoints of imparting the n-type diffusion layer forming composition to the substrate, uniform diffusibility, etc., the shape of the compound particles containing the donor element is preferably substantially spherical, flat or plate-like.

When the compound containing a donor element is solid particles, the particle diameter of the particles is preferably 100 μm or less. When particles having a particle diameter of 100 μm or less are applied to a semiconductor substrate, a smooth n-type diffusion layer forming composition layer is easily obtained. Furthermore, when the compound containing the donor element is in the form of solid particles, the particle diameter of the particles is more preferably 50 μm or less. The lower limit is not particularly limited, but is preferably 0.01 μm or more, and more preferably 0.05 μm or more.
Here, the particle diameter of the particles in the case where the compound containing the donor element is in the form of solid particles represents the volume average particle diameter, and can be measured by a laser diffraction scattering method particle size distribution measuring apparatus or the like. The volume average particle diameter can be calculated based on the Mie scattering theory by detecting the relationship between the scattered light intensity and the angle of the laser light applied to the particles. Although there is no restriction | limiting in particular in the dispersion medium at the time of measuring, It is preferable to use the dispersion medium in which the particle | grains made into a measurement object do not melt | dissolve. Moreover, in the case of the particle | grains which are not secondary-aggregating, you may calculate by measuring the particle diameter using a scanning electron microscope.
When the n-type diffusion layer forming composition is in a state where the compound containing the donor element is dissolved in the dispersion medium, the shape of the compound containing the donor element used for preparing the n-type diffusion layer forming composition is not particularly limited.

  The content rate of the compound containing the donor element in the n-type diffusion layer forming composition is determined in consideration of the impartability of the n-type diffusion layer forming composition, the diffusibility of the donor element, and the like. The content of the compound containing a donor element in the n-type diffusion layer forming composition is preferably 0.1% by mass or more and 95% by mass or less, and more preferably 1% by mass or more and 90% by mass or less. It is more preferably 1% by mass or more and 80% by mass or less, particularly preferably 2% by mass or more and 80% by mass or less, and particularly preferably 5% by mass or more and 20% by mass or less. When the content of the compound containing a donor element is 0.1% by mass or more, the n-type diffusion layer tends to be sufficiently formed. When the content is 95% by mass or less, the dispersibility of the compound containing the donor element in the n-type diffusion layer forming composition is improved, and the impartability to the semiconductor substrate tends to be improved.

(Glass particles containing donor element)
The compound containing a donor element is preferably glass particles containing a donor element (hereinafter also simply referred to as glass particles). By using the glass particles containing the donor element, the diffusion of the donor element to the region other than the region to which the n-type diffusion layer forming composition is applied (referred to as out-diffusion) tends to be more effectively suppressed. Can suppress the formation of an unnecessary n-type diffusion layer. That is, an n-type diffusion layer can be formed more selectively by containing glass particles containing a donor element.

The glass particles containing a donor element may be formed, for example, containing a donor element-containing substance and a glass component substance. The donor element-containing material is not particularly limited as long as it contains a donor element. As the glass ingredient material is not particularly limited, when viewed as an oxide, it is preferably containing at least SiO ₂ and CaO.

For example, when the glass particles containing a donor element are displayed as oxides (hereinafter, the donor element-containing material and the glass component material are similarly displayed), from P ₂ O ₃ , P ₂ O ₅ and Sb ₂ O ₃ At least one kind of donor element-containing material selected, and SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO And at least one glass component substance selected from ZrO ₂ and MoO ₃ .

Among them, glass particles containing the donor element, when viewed as an _oxide, preferably contains P ₂ O 5, SiO ₂ and CaO. By combining P ₂ O ₅ which is a donor element-containing material and SiO ₂ and CaO which are glass component materials, glass particles having low hygroscopicity and excellent storage stability can be obtained. Therefore, even after long-term storage, the donor component in the glass particles is less likely to be volatilized during firing, so that not only the region to which the n-type diffusion layer forming composition is applied by the generation of the volatilizing gas, but also the opposite side, side surface, etc. The formation of the n-type diffusion layer is suppressed.

The content of the donor element-containing material and the glass component material in the glass particles is desirably set appropriately in consideration of the melting temperature, softening temperature, glass transition temperature, chemical durability, etching characteristics, and the like. For example, when the glass particles contain P ₂ O ₅ as the donor element-containing substance, the molar fraction of P ₂ O ₅ contained in the glass particles is 20 mol from the viewpoint of water resistance, melting temperature, and diffusion capacity. % To 50 mol% is preferable, and 25 mol% to 45 mol% is more preferable. When the glass particles contain SiO ₂ as a glass component, the molar fraction of SiO ₂ is preferably 30 mol% to 70 mol% from the viewpoint of water resistance, melting temperature, and etching characteristics, and is 35 mol%. More preferably, it is -65 mol%. When the glass particles contain CaO as a glass component, the molar fraction of CaO is preferably 2 mol% to 30 mol% from the viewpoint of water resistance, melting temperature, and etching characteristics, and is preferably 5 mol% to 25 mol%. It is preferable that it is mol%.

Glass particles of the present disclosure, water resistance, melting temperature, the etching characteristic, from the standpoint of a diffusing capacity, and _P 2 _{O 5} 20 mole% to 50 mole%, and SiO ₂ of 30 mol% to 70 mol%, It may contain 5 mol% to 25 mol% of CaO, and the volume average particle diameter may be 0.01 μm to 2 μm. Further, it contains 20 mol% to 50 mol% of P ₂ O ₅ , 35 mol% to 65 mol% of SiO ₂ , and 2 mol% to 30 mol% of CaO, and has a volume average particle diameter of 0.01 μm. It may be ˜2 μm. Water resistance, melting temperature, etch characteristics, and in terms of diffusing capacity, and _P 2 _{O 5} of 25 mol% to 45 mol%, and SiO ₂ of 30 mol% to 70 mol%, 2 mol% to 30 mol% The volume average particle diameter may be 0.01 μm to 2 μm.
Glass particles of the present disclosure, water resistance, melting temperature, the etching characteristic, from the standpoint of a diffusing capacity, and _P 2 _{O 5} of 25 mol% to 45 mol%, and SiO ₂ of 35 mol% to 65 mol%, It contains 5 mol% to 25 mol% CaO, and preferably has a volume average particle size of 0.01 μm to 2 μm.

Furthermore, the glass particles may have a composition in which P ₂ O ₅ , SiO _2, and CaO are combined to give a molar fraction of 100%, and in addition to these, the following glass component substances may be contained. Good. Examples of glass component materials that can be added include K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , MoO ₃ , and La _2. Examples include O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , Y ₂ O ₃ , TiO ₂ , ZrO ₂ , GeO ₂ , Al ₂ O ₃ , TeO ₂ , and Lu ₂ O ₃ . Glass component materials other than SiO ₂ and CaO can control the melting temperature, softening temperature, glass transition temperature, chemical durability, and the like by adjusting the component ratio as necessary. When glass particles contain glass component substances other than SiO ₂ and CaO, from the viewpoint of water resistance, melting temperature, etching characteristics, diffusion capacity, etc., the molar fraction in the glass particles of glass component substances other than SiO ₂ and CaO is 0.01 mol% to 10 mol%, preferably 0.1 mol% to 5 mol%.

The softening temperature of the glass particles is preferably 300 ° C. to 1000 ° C., more preferably 400 ° C. to 900 ° C., from the viewpoints of diffusibility in diffusion treatment, suppression of dripping, and the like. When the softening temperature is 300 ° C. or higher, the viscosity of the glass does not become too low in the diffusion treatment, and the occurrence of dripping is suppressed and the formation of the n-type diffusion layer other than the specific portion is easily suppressed. Tend. Moreover, when it is 1000 degrees C or less, there exists a tendency which becomes easy to suppress that a glass particle cannot fully fuse | melt and a uniform n type diffused layer is not formed.
By making the softening temperature of the glass particles within the range of 300 ° C. to 1000 ° C., as described above, it becomes easy to suppress the occurrence of dripping, and therefore, after the diffusion treatment, the n-type diffusion layer is formed into a desired shape in a specific region. It becomes easy to form. For example, when the n-type diffusion layer forming composition is applied in a linear pattern having an a μm width, the line width b after the diffusion treatment tends to be able to hold a linear pattern in the range of b <1.5 a μm.
The softening temperature of the glass particles can be obtained from a differential heat (DTA) curve or the like using a DTG-60H type differential heat / thermogravimetric simultaneous measuring device manufactured by Shimadzu Corporation.

The shape of the glass particles is not particularly limited, and examples thereof include a substantially spherical shape, a flat shape, a block shape, a plate shape, and a scale shape. From the viewpoints of suitability for application to the substrate (coating property), uniform diffusibility, and the like in the case of an n-type diffusion layer forming composition, the composition is preferably substantially spherical, flat, or plate-shaped.
The glass particles preferably have a volume average particle diameter of 10 μm or less. When glass particles having a volume average particle diameter of 10 μm or less are used, a smooth coating film is easily obtained. The volume average particle diameter of the glass particles is more preferably 5 μm or less, further preferably 2 μm or less, and particularly preferably 1 μm or less. In addition, the minimum in particular of the volume average particle diameter of a glass particle is not restrict | limited, It is preferable that it is 0.01 micrometer or more, and it is more preferable that it is 0.05 micrometer or more.

  The content of the glass particles in the n-type diffusion layer forming composition is determined in consideration of the suitability for application, the diffusibility of the donor element, and the like. For example, the content rate mentioned above can be applied as the content rate of the compound containing the donor element in the n-type diffusion layer forming composition. In general, the content of the glass particles in the n-type diffusion layer forming composition is preferably 1% by mass to 30% by mass, more preferably 5% by mass to 25% by mass, and 8% by mass. It is more preferable that it is% -20 mass%.

The glass particle of this indication can be produced in the following procedures, for example.
First, weigh the ingredients and fill the crucible. Examples of the crucible material include platinum, platinum-rhodium, gold, iridium, alumina, zirconia, quartz, carbon, boron carbide, boron nitride, and silicon nitride. The material of the crucible may be appropriately selected in consideration of the melting temperature, atmosphere, reactivity with the molten material, and the like.
Next, the raw material is heated at a temperature corresponding to the glass composition in an electric furnace to obtain a melt. At this time, it is desirable to stir the melt uniformly.
Subsequently, the obtained melt is poured onto a zirconia substrate, a carbon substrate, or the like to vitrify the melt.
Finally, the glass is crushed into particles. A known method such as a stamp mill, a jet mill, a bead mill, or a ball mill can be applied to the pulverization.

(Dispersion medium)
The n-type diffusion layer forming composition may contain a dispersion medium. The dispersion medium is a medium in which the glass particles are dispersed in the composition. Specifically, at least one selected from the group consisting of a binder and a solvent may be employed as the dispersion medium.

  The content of the dispersion medium in the n-type diffusion layer forming composition is not particularly limited, and is determined in consideration of application suitability, donor element concentration, and the like.

  When the n-type diffusion layer forming composition contains a binder, the type of the binder is not particularly limited. Examples of the binder include polyvinyl alcohol, polyacrylamide resin, polyvinyl amide resin, polyvinyl pyrrolidone, polyethylene oxide resin, polysulfonic acid, acrylamide alkyl sulfonic acid, cellulose ether resin, cellulose derivative, carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, gelatin, starch And starch derivatives, sodium alginates and sodium alginate derivatives, xanthan and xanthan derivatives, guar gum and guar gum derivatives, scleroglucan and scleroglucan derivatives, tragacanth and tragacanth derivatives, dextrin and dextrin derivatives, (meth) acrylic acid resin, (meta) ) Acrylic ester resin (eg, alkyl (meth) acrylate Resin, dimethylaminoethyl (meth) acrylate resin, etc.), butadiene resins, styrene resins, and copolymers thereof. In addition, a siloxane resin or the like can be appropriately selected. These may be used alone or in combination of two or more. Of these, ethylcellulose is preferred as the binder from the viewpoint of viscosity characteristics.

  The weight average molecular weight of the binder is not particularly limited, and it is desirable to adjust appropriately in view of the desired viscosity as the composition.

The content of the binder in the n-type diffusion layer forming composition is not particularly limited, and may be, for example, an amount that achieves the following viscosity. For example, it may be 0.5% by mass to 30% by mass, 2% by mass to 25% by mass, or 3% by mass to 20% by mass in the n-type diffusion layer forming composition.
The viscosity of the n-type diffusion layer forming composition is preferably in the range of 1 Pa · s to 500 Pa · s, more preferably in the range of 10 Pa · s to 100 Pa · s in consideration of the imparting characteristics in printing. The viscosity is measured using a Tokyo Keiki E-type viscometer EHD type under the conditions of a sample amount of 0.4 ml and a rotational speed of 5 revolutions / minute (rpm).

  When the n-type diffusion layer forming composition contains a solvent, the type of the solvent is not particularly limited. Examples of the solvent include acetone, methyl ethyl ketone, methyl n-propyl ketone, methyl isopropyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, methyl n-pentyl ketone, methyl n-hexyl ketone, diethyl ketone, and dipropyl. Ketone solvents such as ketone, diisobutylketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, acetonylacetone; diethyl ether, methyl ethyl ether, methyl-n-propyl ether, diisopropyl ether, Tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol -N-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl n-propyl ether, diethylene glycol methyl n-butyl ether, diethylene glycol di-n-propyl ether, diethylene glycol Di-n-butyl ether, diethylene glycol methyl-n-hexyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol methyl-n-butyl ether, triethylene glycol di-n-butyl ether, Triethylene glycol Cyl-n-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol methyl-n-butyl ether, tetraethylene glycol di-n-butyl ether, tetraethylene glycol methyl-n- Hexyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol di-n-butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ethyl ether, dipropylene glycol Methyl-n-butyl ether, dipropylene glycol Recall di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol methyl-n-hexyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol methyl ethyl ether, tripropylene glycol methyl-n -Butyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol methyl-n-hexyl ether, tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl ether, tetrapropylene glycol methyl ethyl ether, tetrapropylene glycol methyl-n-butyl ether, tetra Propylene glycol di-n-butyl ether, tetrapro Ether solvents such as lenglycol methyl-n-hexyl ether; methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2-butoxyethoxy) ethyl acetate, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, acetoacetic acid Ethyl acetate diethylene glycol methyl ether, acetic acid diethylene glycol monoethyl ether, acetic acid diethylene glycol monobutyl ether, acetic acid dipropylene glycol methyl ether, acetic acid dipropylene glycol ethyl ether, di Acid glycol, methoxytriethylene glycol acetate, ethyl propionate, n-butyl propionate, isoamyl propionate, diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, n-butyl lactate, n-amyl lactate , Ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, γ-butyrolactone Ester solvents such as γ-valerolactone; acetonitrile, N-methylpyrrolidinone, N-ethylpyrrolidinone, N-propyl Aprotic polar solvents such as pyrpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide; methanol, ethanol, n-propanol, Isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol, n-pentanol, isopentanol, 2-methylbutanol, sec-pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol, sec-heptanol, n-octanol, 2-ethylhexanol, sec-octanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol, phenol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol , Alcohol solvents such as diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n- Butyl ether, diethylene glycol mono-n-he Glycol monoether solvents such as sil ether, ethoxy triglycol, tetraethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether; α-terpinene, Examples include terpene solvents such as terpineol, myrcene, alloocimene, limonene, dipentene, pinene, carvone, ocimene, and ferrandrene; water and the like. These solvents may be used alone or in combination of two or more.

  In the n-type diffusion layer forming composition, the solvent is preferably at least one selected from terpineol and butyl carbitol acetate (diethylene glycol mono-n-butyl ether acetate) from the viewpoint of suitability for application to the substrate.

  The content of the solvent in the n-type diffusion layer forming composition is not particularly limited, and is determined in consideration of suitability for application, donor element concentration, and the like.

(Other additives)
The n-type diffusion layer forming composition may contain other additives as necessary. Examples of other additives include organic fillers, inorganic fillers, thixotropic agents such as organic acid salts, wettability improvers, leveling agents, surfactants, plasticizers, fillers, antifoaming agents, stabilizers, Examples thereof include metals that easily react with antioxidants, perfumes, and glass particles. Other additives may be used alone or in combination of two or more.

  Examples of the metal that easily reacts with the glass particles include Ag (silver) and Si (silicon). By making the n-type diffusion layer forming composition contain a metal that easily reacts with glass particles, when the glass is formed on the surface of the n-type diffusion layer, the formed glass is washed with acid such as hydrofluoric acid. Tends to be easily removed. Among these, Ag (silver) is preferably used as the metal that easily reacts with the glass particles.

  The method for preparing the n-type diffusion layer forming composition is not particularly limited. For example, it can be obtained by mixing a compound containing a donor element, a dispersion medium or the like using a blender, a mixer, a mortar, a rotor, or the like. Moreover, when mixing, you may heat as needed. In the case of heating at the time of mixing, the heating temperature can be, for example, 30 ° C to 100 ° C.

  There is no restriction | limiting in the method of providing an n type diffused layer formation composition to a semiconductor substrate, A printing method, an inkjet method, etc. are mentioned, Printing method, especially screen printing method are suitable.

There is no restriction | limiting in particular in the application amount of an n type diffused layer formation composition. For example, when a compound containing a donor element is glass particles containing donor element may be 0.01g ^{/ m 2} ~100g ^/ m 2 as the amount of glass ^{particles, 0.1g / m 2 ~10g / m} 2 It is preferable that

  Depending on the composition of the n-type diffusion layer forming composition, the substrate after applying the n-type diffusion layer forming composition to remove at least a part of the solvent contained in the composition before the thermal diffusion treatment May include a step of heat-treating. In this case, the heat treatment is performed at a temperature of 80 ° C. to 300 ° C. for 1 minute to 10 minutes when a hot plate is used, and for about 10 minutes to 30 minutes when a dryer or the like is used. The heat treatment conditions depend on the solvent composition of the n-type diffusion layer forming composition and are not particularly limited to the above conditions. By this heat treatment step, the n-type diffusion layer forming composition applied on the substrate can be dried.

In addition, depending on the composition of the n-type diffusion layer forming composition, in order to volatilize and remove at least a part of the dispersion medium contained in the composition, particularly the binder (resin component), before the thermal diffusion treatment A step of heat-treating the substrate after applying the n-type diffusion layer forming composition may be included. For the heat treatment in this case, for example, a condition of processing at a temperature of 300 ° C. to 800 ° C. for 1 minute to 10 minutes can be applied. A known continuous furnace, batch furnace or the like can be applied to this heat treatment.
When performing the heat treatment, depending on the composition of the n-type diffusion layer forming composition, the heat treatment at a temperature of 80 to 300 ° C. for removing the solvent and the heat treatment at a temperature of more than 300 ° C. and not more than 800 ° C. Both may be performed (that is, the heat treatment may be performed twice under different temperature conditions), or only the heat treatment at one of the temperatures may be performed.

  Next, the semiconductor substrate provided with the n-type diffusion layer forming composition is subjected to thermal diffusion treatment. The treatment temperature is preferably 800 ° C to 1000 ° C, more preferably 830 ° C to 950 ° C. The treatment time is preferably 5 minutes to 60 minutes. By this thermal diffusion treatment, the donor element diffuses into the semiconductor substrate, and an n-type diffusion layer is formed. A known continuous furnace, batch furnace, or the like can be applied to the thermal diffusion treatment. The furnace atmosphere in the thermal diffusion treatment may be appropriately adjusted to air, oxygen, nitrogen or the like.

  The region where the n-type diffusion layer forming composition is partially applied is preferably a region where an electrode is formed. Thereby, the resistance of the electrode part in the produced solar cell element can be reduced, and electricity can be taken out more efficiently.

[Second n-type diffusion layer forming step]
In the second n-type diffusion layer forming step, a second n-type diffusion layer having a donor element concentration lower than the donor element concentration of the first n-type diffusion layer is formed on the back main surface of the semiconductor substrate.
In the present disclosure, the donor element concentration of the n-type diffusion layer refers to the concentration expressed by the number of donor elements per unit volume of the n-type diffusion layer, and is measured by secondary ion mass spectrometry (SIMS). Can do. Moreover, you may confirm the relative density | concentration of the donor element density | concentration in a 1st n type diffused layer and a 2nd n type diffused layer by measuring sheet resistance.
The second n-type diffusion layer formed by this step only needs to have a donor element concentration lower than the donor element concentration of the first n-type diffusion layer, and is different in type from the first n-type diffusion layer. The donor may be diffusing.

  The method for forming the second n-type diffusion layer is not particularly limited as long as the second n-type diffusion layer is formed so that the donor element concentration is lower than that of the first n-type diffusion layer. Examples thereof include a method using a gas containing a donor element and a method using a composition containing a donor element.

Examples of the gas containing a donor element include POCl ₃ . Examples of a method for forming the second n-type diffusion layer using a gas containing a donor element include a method of performing a thermal diffusion treatment using a gas containing a donor element such as POCl ₃ .
The temperature of the atmosphere in the thermal diffusion treatment using a gas containing a donor element is preferably 700 ° C. to 900 ° C., and more preferably 750 ° C. to 850 ° C. A known continuous furnace, batch furnace, or the like can be applied to the heat treatment.
The thermal diffusion treatment time is preferably from 5 minutes to 90 minutes, more preferably from 10 minutes to 90 minutes, further preferably from 10 minutes to 60 minutes. More preferably, it is for 30 minutes. When the thermal diffusion treatment time is 5 minutes or more, the acceptor element tends to be sufficiently diffused into the semiconductor substrate, and when it is 90 minutes or less, the production cost can be suppressed.

  As the composition containing a donor element, the above-described n-type diffusion layer forming composition can be used. As a method for forming the second n-type diffusion layer using the composition containing the donor element, the method described in the first n-type diffusion layer forming step can be applied.

  The equipment for thermal diffusion treatment may be different from that used in the thermal diffusion treatment in the first n-type diffusion layer forming step, or the same equipment may be used. From the viewpoint of simplifying the process, it is preferable to use the same equipment.

  In the thermal diffusion treatment of the donor element, the two semiconductor substrates on which the p-type diffusion layer is formed may be placed in a furnace so that the surfaces of the p-type diffusion layer face each other, and the thermal diffusion treatment may be performed. . Thereby, it can suppress that a donor element is spread | diffused by the front main surface.

  The method for forming the second n-type diffusion layer so that the donor element concentration is lower than the donor element concentration in the first n-type diffusion layer is not particularly limited, and adjustment of the concentration of the n-type diffusion layer forming composition, n You may carry out by adjustment of the provision amount of a type | mold diffusion layer forming composition, adjustment of the temperature in a thermal diffusion process, etc. For example, the second n-type diffusion layer may be formed using an n-type diffusion layer forming composition having a lower donor element concentration than the n-type diffusion layer forming composition used for forming the first n-type diffusion layer, The second n-type diffusion layer may be formed by applying the n-type diffusion layer forming composition with an application amount smaller than the application amount for the first n-type diffusion layer. In addition, by forming the second n-type diffusion layer using a gas containing a donor element, a second n-type diffusion layer having a donor element concentration lower than the donor element concentration of the first n-type diffusion layer can be obtained. It tends to be easily formed.

  When the second n-type diffusion layer is formed using the n-type diffusion layer forming composition, the donor element is contained in the region where the second n-type diffusion layer is formed after the first n-type diffusion layer is formed. The composition may be applied to perform thermal diffusion treatment, and the n-type diffusion layer forming composition is applied to each of the region for forming the first n-type diffusion layer and the region for forming the second n-type diffusion layer. Then, the thermal diffusion treatment may be performed collectively.

As a method for forming the second n-type diffusion layer using a gas containing a donor element, an example in the case of using a gas containing POCl ₃ will be described.
After the thermal diffusion treatment for forming the first n-type diffusion layer is completed, the temperature of the atmosphere is lowered to 700 ° C. to 900 ° C., and a gas containing POCl ₃ is injected. The thermal diffusion treatment includes a deposition (hereinafter also referred to as “depo”) step of diffusing phosphorus while injecting a gas containing POCl ₃ to form PSG, and diffusing phosphorus by stopping the injection of the gas containing POCl ₃ . You may perform a Drive-in process. Alternatively, only the Depo process may be performed and the Drive-in process may not be performed. The temperature of the atmosphere in the Depo process and the Drive-in process may be the same temperature or different temperatures. From the viewpoint of forming the n-type diffusion layer at an appropriate concentration, the temperature of the atmosphere during the thermal diffusion treatment is preferably 750 ° C. to 850 ° C. The thermal diffusion treatment time may be 5 minutes to 90 minutes, or 10 minutes to 60 minutes, including the Depo step and the Drive-in step, from the viewpoint of balance between diffusibility into the semiconductor substrate and reduction of the process time. Is preferred. A similar thermal diffusion treatment time can be applied when the Drive-in process is not performed.

<Other processes>
The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to the second embodiment may include other steps as necessary. For example, you may have the process described as "the other process" in 1st embodiment.

  Note that, in the method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to the second embodiment, when etching for removing PSG formed by thermal diffusion treatment is performed, the first n-type diffusion layer region is formed. The formed PSG and the PSG formed in the second n-type diffusion layer region may be simultaneously removed by etching, and the formed PSG may be removed by etching after each n-type diffusion layer forming step. .

≪Solar cell element according to first embodiment and method for manufacturing solar cell element≫
The solar cell element according to the first embodiment includes the semiconductor substrate according to the first embodiment and an electrode provided on the semiconductor substrate.
The method for manufacturing a solar cell element according to the first embodiment includes a step of manufacturing a semiconductor substrate by the method of manufacturing a semiconductor substrate according to the first embodiment, and a step of forming an electrode (electrode formation step). .

  Hereinafter, an example of the manufacturing method of the solar cell element according to the first embodiment will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view conceptually showing an example of a manufacturing process of a solar cell element. In addition, the magnitude | size of the member in each figure is notional, The relative relationship of the magnitude | size between members is not limited to this. Hereinafter, an example in which a silicon substrate is used as the n-type semiconductor substrate will be described. However, in the present disclosure, the semiconductor substrate is not limited to the silicon substrate.

  In FIG. 1A, an alkaline solution is applied to a silicon substrate which is an n-type semiconductor substrate 110 to remove a damaged layer, and a texture structure is obtained by etching.

In FIG. 1 (2), thermal diffusion using a BBr ₃ gas is performed on the light-receiving surface of the n-type semiconductor substrate 110, or a p-type diffusion layer forming composition containing boron element is applied to perform thermal diffusion. Processing is performed to form a p-type diffusion layer 111. At this time, the p-type diffusion layer 111 is also formed on the opposite surface of the light receiving surface due to the scattering of boron. Further, BSG 122 is formed on the surface of the p-type diffusion layer.

  In FIG. 1C, the surface opposite to the light receiving surface is etched using an alkaline solution or an acid solution to remove boron and the like.

In FIG. 1 (4), n-type semiconductor substrate 110 is exposed to a surface opposite to the light-receiving surface by a heat treatment diffusion method using POCl ₃ gas, or by a heat treatment diffusion method by applying a material containing phosphorus element. A mold diffusion layer 113 is formed. At this time, a plurality of n-type semiconductor substrates 110 are stacked and placed in the thermal diffusion facility so that the surfaces of the p-type diffusion layers face each other so that the donor element does not enter the p-type diffusion layer on the front main surface. It is preferable.

  BSG 122, a thermal oxide film, and the like remain on the surface of the p-type diffusion layer 111 formed on the light-receiving surface of the n-type semiconductor substrate 110, and the donor element diffuses on the surface of the n-type diffusion layer 113 on the back main surface. The formed PSG 124 remains. In FIG. 1 (5), these residues are removed by etching. As the etching solution, any of known methods such as a method of immersing in an acid such as hydrofluoric acid and a method of immersing in an alkali such as caustic soda can be applied. In terms of etching ability, an etching treatment with hydrofluoric acid is preferable. Examples of the etching treatment with hydrofluoric acid include a method of immersing the n-type semiconductor substrate 110 in hydrofluoric acid. When the n-type semiconductor substrate 110 is immersed in hydrofluoric acid, the immersion time is not particularly limited. Generally, it may be 0.5 minutes to 30 minutes, and preferably 1 minute to 10 minutes. The surface of the semiconductor substrate after the residue is removed by this cleaning method exhibits hydrophobicity.

In FIG. 1 (6), an antireflection film 115 is formed on the p-type diffusion layer 111, and an antireflection film 116 is formed on the n-type diffusion layer 113. The antireflection films 115 and 116 are formed by applying a known technique. For example, when the antireflection films 115 and 116 are silicon nitride films, they are formed by a plasma CVD (PECVD; Plasma-enhanced Chemical Vapor Deposition) method using a mixed gas of SiH ₄ and NH ₃ as a raw material. At this time, hydrogen diffuses into the crystal, and orbitals that do not contribute to the bonding of silicon atoms, that is, dangling bonds and hydrogen are bonded to inactivate defects (hydrogen passivation).

More specifically, in the antireflection films 115 and 116, for example, the flow rate ratio (NH ₃ / SiH ₄ ) of the mixed gas is 0.05 to 1.0, and the pressure in the reaction chamber is 13.3 Pa (0.1 Torr). ) To 266.6 Pa (2 Torr), the film forming temperature is 300 ° C. to 550 ° C., and the frequency for plasma discharge is 100 kHz or more.

A passivation layer may be formed on the p-type diffusion layer. For example, an Al ₂ O ₃ layer may be laminated by an ALD (atomic layer deposition) method, or an SiO ₂ layer may be formed by thermal oxidation or the like. In this case, the above-described antireflection film is formed on the passivation layer.

  In FIG. 1 (7), a light receiving surface electrode metal paste is applied by screen printing on the antireflection film 115 on the front main surface and dried to form a light receiving surface electrode metal paste layer 117. As a metal paste for light-receiving surface electrodes, for example, a paste containing metal particles and glass particles, and containing a resin binder and other additives as required can be used.

  Next, a metal paste layer 119 for the back electrode on the back main surface is formed. The material and forming method of the back electrode metal paste layer 119 are not particularly limited. For example, the back electrode metal paste layer 119 may be formed by applying and drying a back electrode metal paste containing a metal such as aluminum, silver, or copper. At this time, a silver paste for forming a silver electrode may be partially provided on the back surface for connection between solar cell elements in the module process.

  In FIG. 1 (8), the metal paste layer 117 for light-receiving surface electrodes is baked to complete the solar cell element. When baked in the range of 600 ° C. to 900 ° C. for several seconds to several minutes, the antireflection film 115 which is an insulating film is melted by the glass particles contained in the metal paste for the light receiving surface electrode on the light receiving surface side, and further the n-type semiconductor substrate 110. A part of the surface is also melted, and metal particles (for example, silver particles) in the paste are solidified by forming contact portions with the n-type semiconductor substrate 110. Thereby, the formed light-receiving surface electrode 118 and the n-type semiconductor substrate 110 are electrically connected. This is called fire-through. Similarly, on the back side, the back electrode metal paste of the back electrode metal paste layer 119 is baked to form the back electrode 120.

  An example of the shape of the light-receiving surface electrode 118 will be described with reference to FIGS. 3A and 3B. The light receiving surface electrode 118 includes a bus bar electrode 30 and a finger electrode 32 intersecting with the bus bar electrode 30. FIG. 3A is a plan view of a solar cell element in which the light receiving surface electrode 118 includes a bus bar electrode 30 and a finger electrode 32 intersecting with the bus bar electrode 30 as viewed from the light receiving surface. It is a perspective view which expands and shows some 3A.

  Such a light-receiving surface electrode 118 can be formed by means such as screen printing of the above-described metal paste for light-receiving surface electrode, plating of electrode material, vapor deposition of electrode material by electron beam heating in high vacuum. The light receiving surface electrode 118 having the bus bar electrode 30 and the finger electrode 32 is generally used as the electrode on the light receiving surface side and is well known, and a known forming means for the bus bar electrode and the finger electrode on the light receiving surface side is applied. Can do.

≪Solar cell element according to second embodiment and method for manufacturing solar cell element≫
The solar cell element according to the second embodiment includes a semiconductor substrate with a selective n-type diffusion layer according to the second embodiment, and an electrode provided on the semiconductor substrate with a selective n-type diffusion layer.
Moreover, the manufacturing method of a solar cell element manufactures the semiconductor substrate with a selective n type diffused layer which has a selective n type diffused layer by the manufacturing method of the semiconductor substrate with a selective n type diffused layer which concerns on 2nd embodiment. And a step of forming an electrode on the selective n-type diffusion layer (electrode formation step).

  Hereinafter, an example of a method for manufacturing a solar cell element will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view conceptually showing an example of the manufacturing process of the solar cell element. In addition, the magnitude | size of the member in each figure is notional, The relative relationship of the magnitude | size between members is not limited to this. Hereinafter, an example in which a silicon substrate is used as the n-type semiconductor substrate will be described. However, in the present disclosure, the semiconductor substrate is not limited to the silicon substrate.

  In FIG. 2A, an alkaline solution is applied to the silicon substrate that is the n-type semiconductor substrate 10 to remove the damaged layer, and a texture structure is obtained by etching.

In FIG. 2 (2), thermal diffusion using a BBr ₃ gas is performed on the surface to be the light-receiving surface of the n-type semiconductor substrate 10 or a p-type diffusion layer forming composition containing boron element is applied to perform thermal diffusion. Processing is performed to form the p-type diffusion layer 11. At this time, the p-type diffusion layer 11 is formed on the opposite surface of the light receiving surface due to the scattering of boron. Furthermore, BSG22 is formed on the surface of the p-type diffusion layer.

  In FIG. 2 (3), the surface opposite to the light receiving surface is etched using an alkaline solution or an acid solution to remove boron and the like.

In FIG. 2 (4), the n-type diffusion layer forming composition layer 12 is formed in a region opposite to the light-receiving surface of the n-type semiconductor substrate 10 where an electrode is to be formed so as to have a shape substantially the same as the electrode pattern. Give. The n-type diffusion layer forming composition layer 12 may be applied so as to be 1.0 to 3.0 times as wide as the electrode width. From the viewpoint of suppressing the recombination of carriers, it is preferable to apply so as to be 1.5 to 2.5 times.
After the application of the n-type diffusion layer forming composition, the composition is dried and the n-type semiconductor substrate 10 is put into a thermal diffusion facility. At this time, a plurality of n-type semiconductor substrates 10 are overlapped so that the surfaces of the p-type diffusion layers face each other so that the donor element is not mixed into the p-type diffusion layer on the front main surface. It is preferable. The temperature of the atmosphere in the thermal diffusion treatment is preferably 830 ° C to 950 ° C. The furnace atmosphere for the thermal diffusion treatment can be selected according to desired conditions from an inert gas such as air, oxygen, nitrogen, and a mixed gas thereof, and a mixed gas of oxygen and nitrogen is preferable. As a result, the first n-type diffusion layer 13 shown in FIG. 2 (5) is formed.

Next, the temperature is lowered to 700 ° C. to 900 ° C. from the thermal diffusion treatment, a gas containing POCl ₃ is injected into the furnace, and the donor element concentration as shown in FIG. A second n-type diffusion layer 14 lower than the diffusion layer is formed. At this time, PSG 24 is formed on the surfaces of the first n-type diffusion layer 13 and the second n-type diffusion layer 14. In order to form a phosphorus diffusion layer at an appropriate concentration, the diffusion temperature is preferably 750 ° C. to 850 ° C., and the diffusion time is preferably 10 minutes to 60 minutes in total of the Depo step and the Drive-in step. . At this time, in the method using the gas atmosphere containing POCl ₃ , the gas containing POCl ₃ reaches the front main surface of the semiconductor substrate, but the BSG and thermal oxidation obtained when forming the p-type diffusion layer are used. The film is used as a barrier layer, and is placed in the furnace so that the surfaces of the p-type diffusion layers of the semiconductor substrate face each other, thereby preventing phosphorus diffusion to the front main surface.

On the surface of the p-type diffusion layer 11 formed on the light-receiving surface of the n-type semiconductor substrate 10, BSG22, a thermal oxide film, etc. remain, and the first n-type diffusion layer 13 and the second n-type on the back main surface. PSG 24 formed by diffusion of a donor element using a gas containing an n-type diffusion layer forming composition and POCl ₃ remains on the surface of diffusion layer 14. In FIG. 2 (6), these residues are removed by etching. As the etching solution, any of known methods such as a method of immersing in an acid such as hydrofluoric acid and a method of immersing in an alkali such as caustic soda can be applied. In terms of etching ability, an etching treatment with hydrofluoric acid is preferable. Examples of the etching treatment using hydrofluoric acid include a method of immersing the n-type semiconductor substrate 10 in hydrofluoric acid. When the n-type semiconductor substrate 10 is immersed in hydrofluoric acid, the immersion time is not particularly limited. Generally, it may be 0.5 minutes to 30 minutes, and preferably 1 minute to 10 minutes. The surface of the semiconductor substrate after the residue is removed by this cleaning method exhibits hydrophobicity.

In FIG. 2 (7), an antireflection film 15 is formed on the p-type diffusion layer 11, and an antireflection film 16 is formed on the first n-type diffusion layer 13 and the second n-type diffusion layer 14. . The antireflection films 15 and 16 are formed by applying a known technique. For example, when the antireflection films 15 and 16 are silicon nitride films, they are formed by PECVD using a mixed gas of SiH ₄ and NH ₃ as a raw material. At this time, hydrogen diffuses into the crystal, and orbitals that do not contribute to the bonding of silicon atoms, that is, dangling bonds and hydrogen are bonded to inactivate defects (hydrogen passivation).

More specifically, the antireflection films 15 and 16 have, for example, a flow rate ratio (NH ₃ / SiH ₄ ) of the above mixed gas of 0.05 to 1.0 and a reaction chamber pressure of 13.3 Pa (0.1 Torr). ) To 266.6 Pa (2 Torr), the film forming temperature is 300 ° C. to 550 ° C., and the frequency for plasma discharge is 100 kHz or more.

A passivation layer may be formed on the p-type diffusion layer. For example, an Al ₂ O ₃ layer may be laminated by an ALD (atomic layer deposition) method, or an SiO ₂ layer may be formed by thermal oxidation or the like. In this case, the above-described antireflection film is formed on the passivation layer.

  In FIG. 2 (8), the light receiving surface electrode metal paste is printed on the antireflection film 15 on the front main surface by screen printing and dried to form the light receiving surface electrode metal paste layer 17. As a metal paste for light-receiving surface electrodes, for example, a paste containing metal particles and glass particles, and containing a resin binder and other additives as required can be used.

  Next, the back electrode metal paste layer 19 for the back main surface is formed. The material and forming method of the back electrode metal paste layer 19 are not particularly limited. For example, the back electrode metal paste layer 19 may be formed by applying a metal paste for the back electrode containing a metal such as aluminum, silver, or copper and drying the paste. At this time, a silver paste for forming a silver electrode may be partially provided on the back surface for connection between solar cell elements in the module process.

  In FIG. 2 (9), the light-receiving surface electrode metal paste layer 17 is fired to complete the solar cell element. When baked in the range of 600 ° C. to 900 ° C. for several seconds to several minutes, the antireflection film 15 that is an insulating film is melted by the glass particles contained in the metal paste for the light receiving surface electrode on the light receiving surface side, and the n-type semiconductor substrate 10 A part of the surface is also melted, and metal particles (for example, silver particles) in the paste are solidified by forming contact portions with the n-type semiconductor substrate 10. Thereby, the formed light-receiving surface electrode 18 and the n-type semiconductor substrate 10 are electrically connected. This is called fire-through. Similarly, on the back side, the back electrode metal paste of the back electrode metal paste layer 19 is baked to form the back electrode 20.

  An example of the shape of the light-receiving surface electrode 18 will be described with reference to FIGS. 3A and 3B as in the first embodiment. The light-receiving surface electrode 18 includes a bus bar electrode 30 and a finger electrode 32 that intersects the bus bar electrode 30. FIG. 3A is a plan view of a solar cell element in which the light-receiving surface electrode 18 includes a bus bar electrode 30 and a finger electrode 32 intersecting with the bus bar electrode 30 as viewed from the light-receiving surface. It is a perspective view which expands and shows some 3A. Note that the n-type semiconductor substrate 110 and the antireflection film 115 in FIG. 3B are replaced with the n-type semiconductor substrate 10 and the antireflection film 15, respectively.

  Such a light-receiving surface electrode 18 can be formed by means such as screen printing of the above-described metal paste for light-receiving surface electrode, plating of electrode material, vapor deposition of electrode material by electron beam heating in high vacuum. The light-receiving surface electrode 18 having the bus bar electrode 30 and the finger electrode 32 is generally used as an electrode on the light-receiving surface side, and is well-known, and known forming means for the bus bar electrode and finger electrode on the light-receiving surface side are applied. Can do.

  In the above description, the solar cell element in which the p-type diffusion layer is formed on the light-receiving surface, the n-type diffusion layer is formed on the back surface, and the light-receiving surface electrode and the back electrode are provided on the respective layers has been described. If the composition for forming an n-type diffusion layer is used, a back contact type solar cell element can be produced. The back contact type solar cell element has an electrode on the back surface to increase the area of the light receiving surface. That is, in the back contact solar cell element, both the p-type diffusion region and the n-type diffusion region are formed on the back surface to form a pn junction structure. The n-type diffusion layer forming composition of the second embodiment can form an n-type diffusion site at a specific site, and thus can be suitably applied to the production of a back contact type solar cell element. .

  Hereinafter, embodiments of the present disclosure will be specifically described by way of examples, but the embodiments of the present disclosure are not limited to these examples.

<< Examples according to the first embodiment >>
[Example 1]
(Formation of p-type diffusion layer)
First, a boat in which a semiconductor substrate with a textured structure was placed at 700 ° C. in a diffusion furnace (Koyo Thermo System Co., Ltd., “206A-M100”) in which N ₂ : 10 L / min was flowed was introduced. At this time, two semiconductor substrates were prepared, and the two substrates were stacked and installed. By superimposing the two sheets, it is possible to suppress the BBr ₃ gas from flowing into the inner surface. This inner surface is used as a back main surface, and a surface on which an n-type diffusion layer is formed in a later step. Thereafter, the temperature is increased to 925 ° C. at a temperature increase rate of 15 ° C./min, a mixed gas of O ₂ , N ₂ , and BBr ₃ is injected into the furnace and heat-treated at 925 ° C. for 50 minutes, and boron is contained in the semiconductor substrate. Was diffused (thermally diffused) to form a p-type diffusion layer. Thereafter, the atmosphere in the diffusion furnace was changed to N ₂ : 7 L / min and O ₂ : 3 L / min, the temperature was lowered to 700 ° C. over 85 minutes, and the semiconductor substrate was taken out at 700 ° C.

(Evaluation of sheet resistance)
The sheet resistance of the diffusion part was measured using a low resistivity meter (“Loresta MCP-T360” manufactured by Mitsubishi Chemical Corporation). The sheet resistance of the diffusion portion is 70Ω / sq. It was found that a p-type diffusion layer was formed.

(etching)
Next, the back main surface of the semiconductor substrate was etched using a mixed solution of hydrofluoric acid and nitric acid to remove the boron layer formed on the back main surface. A liquid in which a 49% by mass hydrofluoric acid solution and a 70% by mass nitric acid solution were mixed at a volume ratio of 1: 100 was used. The back main surface of the semiconductor substrate was immersed in the mixed solution for 60 seconds and removed by etching. The thickness of the semiconductor substrate after the etching was measured using a micrometer (manufactured by Mitutoyo Corporation: MDC-25MX), and it was found that the semiconductor substrate was etched by a thickness of 3 μm compared with that before the etching.

(Formation of n-type diffusion layer)
Next, two semiconductor substrates on which the p-type diffusion layer is formed as described above are placed on a boat so that the surfaces of the p-type diffusion layer face each other, and N ₂ : 9 L / min, O ₂ : 1L. / Min flowed into a diffusion furnace (Koyo Thermo System Co., Ltd., “206A-M100”) at a temperature of 700 ° C. Thereafter, the temperature is raised to 850 ° C. over 15 minutes, a mixed gas of O ₂ , N ₂ , and POCl ₃ is introduced, thermal diffusion treatment is performed at 850 ° C. for 20 minutes, and the back main surface of the n-type semiconductor substrate An n-type diffusion layer was formed. Thereafter, the inside of the furnace was changed to a nitrogen atmosphere, the temperature was lowered to 700 ° C., and the semiconductor substrate was taken out. The glass component remaining on the semiconductor substrate was removed by immersion in 8% by mass hydrofluoric acid for 5 minutes.

  The n-type semiconductor substrate on which the p-type diffusion layer and the n-type diffusion layer were formed as described above was treated at 780 ° C. for 20 minutes in a thermal oxidation furnace in which oxygen was supplied at 5 L / min to form passivation layers on both sides. Thereafter, silicon nitride films were formed on both sides by PECVD. Next, silver paste is applied to both sides of the n-type semiconductor substrate by screen printing in the form of an electrode pattern with a width of 55 μm and fire-through at 800 ° C. to ensure electrical contact with the p-type diffusion layer and the n-type diffusion layer. Thus, a double-sided light receiving solar cell element was produced.

(IV measurement)
The power generation efficiency on the p-type diffusion layer side of the solar cell element was measured using an IV tracer (MP-180 manufactured by Eihiro Seiki Co., Ltd.) under a light source set to AM1.5G. As a result, the power generation efficiency was as high as 20.5%.

[Example 2]
In the boron diffusion step in Example 1, except that the p-type diffusion layer forming composition containing the boron-containing glass compound was applied to the substrate by screen printing and subjected to thermal diffusion treatment so that the sheet resistance was 70 Ω / sq. A solar cell element was prototyped and evaluated in the same manner as in Example 1. As a result, the power generation efficiency was as high as 20.3%.

[Comparative Example 1]
A solar cell element was prototyped and evaluated in the same manner as in Example 1 except that the etching process after forming the p-type diffusion layer in Example 1 was omitted. As a result, the power generation efficiency was as low as 19.2%.

<< Example according to the second embodiment >>
[Example 3]
(Preparation of n-type diffusion layer forming composition)
P ₂ O ₅ —SiO ₂ —CaO-based glass having a block shape and a volume average particle size of 0.89 μm (P ₂ O ₅ : 30 mol%, SiO ₂ : 60 mol%, CaO: 10 mol%) 10 g of particles, 5 g of ethyl cellulose, and 85 g of terpineol were mixed using an automatic mortar kneader to make a paste, thereby preparing an n-type diffusion layer forming composition. The viscosity of the obtained n-type diffusion layer forming composition was 61 Pa · s.

  The shape of the glass particles was determined by observing with a scanning electron microscope (Hitachi High-Technologies Corporation, “TM-1000 type”). The average particle size of the glass was calculated using a laser diffraction / scattering particle size distribution analyzer (Beckman Coulter, Inc., “LS 13 320 type”, measurement wavelength: 632 nm).

(Formation of p-type diffusion layer)
First, a boat in which a semiconductor substrate with a textured structure was placed at 700 ° C. in a diffusion furnace (Koyo Thermo System Co., Ltd., “206A-M100”) in which N ₂ : 10 L / min was flowed was introduced. At this time, two semiconductor substrates were prepared, and the two substrates were stacked and installed. By superimposing the two sheets, it is possible to suppress the BBr ₃ gas from flowing into the inner surface. This inner surface is used as a back main surface, and a surface on which an n-type diffusion layer is formed in a later step. Thereafter, the temperature is increased to 925 ° C. at a temperature increase rate of 15 ° C./min, a mixed gas of O ₂ , N ₂ , and BBr ₃ is injected into the furnace and heat-treated at 925 ° C. for 50 minutes, and boron is contained in the semiconductor substrate. Was diffused (thermally diffused) to form a p-type diffusion layer. Thereafter, the atmosphere in the diffusion furnace was changed to N ₂ : 7 L / min and O ₂ : 3 L / min, the temperature was lowered to 700 ° C. over 85 minutes, and the semiconductor substrate was taken out at 700 ° C.

(Evaluation of sheet resistance)
The sheet resistance of the diffusion part was measured using a low resistivity meter (“Loresta MCP-T360” manufactured by Mitsubishi Chemical Corporation). The sheet resistance of the diffusion portion is 70Ω / sq. It was found that a p-type diffusion layer was formed.

(etching)
Next, the back main surface of the semiconductor substrate was etched using a mixed solution of hydrofluoric acid and nitric acid to remove the boron layer formed on the back main surface. A liquid in which a 49% by mass hydrofluoric acid solution and a 70% by mass nitric acid solution were mixed at a volume ratio of 1: 100 was used. The back main surface of the semiconductor substrate was immersed in the mixed solution for 60 seconds and removed by etching.

(Formation of n-type diffusion layer)
Next, on the semiconductor substrate on which the p-type diffusion layer is formed as described above, the prepared n-type diffusion layer forming composition is printed with a line width of 100 μm so as to match the electrode pattern by screen printing, and on a hot plate at 150 ° C. It was dried for 5 minutes to form an n-type diffusion layer forming composition layer. Two semiconductor substrates are placed on a boat so that the surfaces of the p-type diffusion layers face each other, and a diffusion furnace (Koyo) with a temperature of N ₂ : 9 L / min and O ₂ : 1 L / min is supplied. Thermosystem Co., Ltd., “206A-M100”). Thereafter, the temperature is increased to 930 ° C. at a rate of temperature increase of 15 ° C./min, and heat treatment is performed at 930 ° C. for 10 minutes to diffuse phosphorus (thermal diffusion) into the semiconductor substrate, and to form an n-type diffusion layer having high phosphorus concentration (first N-type diffusion layer). The temperature was lowered to 800 ° C. over 15 minutes, a mixed gas of O ₂ , N ₂ , and POCl ₃ was introduced, and thermal diffusion treatment was performed at 800 ° C. for 20 minutes (Depo time 20 minutes, Drive-in time 0 minutes). An n-type diffusion layer (second n-type diffusion layer) having a low phosphorus concentration was formed on the back main surface of the n-type semiconductor substrate. Thereafter, the inside of the furnace was changed to a nitrogen atmosphere, the temperature was lowered to 700 ° C., and the semiconductor substrate was taken out. The glass component remaining on the semiconductor substrate was removed by immersion in 8% by mass hydrofluoric acid for 10 minutes.

  The n-type semiconductor substrate on which the p-type diffusion layer and the n-type diffusion layer were formed as described above was treated at 700 ° C. for 20 minutes in a thermal oxidation furnace in which oxygen was flowed at 5 L / min to form passivation layers on both surfaces. Thereafter, silicon nitride films were formed on both sides by PECVD. Next, silver paste is applied to both sides of the n-type semiconductor substrate by screen printing in the form of an electrode pattern with a width of 55 μm and fire-through at 800 ° C. to ensure electrical contact with the p-type diffusion layer and the n-type diffusion layer. Thus, a double-sided light receiving solar cell element was produced.

(IV measurement)
The power generation efficiency on the p-type diffusion layer side of the solar cell element was measured using an IV tracer (MP-180 manufactured by Eihiro Seiki Co., Ltd.) under a light source set to AM1.5G. As a result, the power generation efficiency was as high as 20.2%.

[Example 4]
In the boron diffusion step in Example 3, a spin coating material containing boron element was applied to the substrate, and the sheet resistance was 70 Ω / sq. As a result of trial evaluation of the solar cell element in the same manner as in Example 3 except that the heat diffusion treatment was performed, the power generation efficiency was as high as 20.1%.

[Example 5]
A solar cell as in Example 3, except that the back main surface was etched by immersing the back main surface for 60 minutes in an etching solution used in the etching process of the back main surface after forming the p-type diffusion layer in Example 3. The device was experimentally evaluated. As a result, the power generation efficiency was as high as 20.1%.

[Comparative Example 2]
A solar cell element was prototyped and evaluated in the same manner as in Example 3 except that the etching step after forming the p-type diffusion layer in Example 3 was omitted. As a result, the power generation efficiency was as low as 18.2%.

[Comparative Example 3]
The solar cell element was prototyped and evaluated in the same manner as in Example 4 except that the etching process after forming the p-type diffusion layer in Example 4 was omitted and the solar cell element was prototyped and evaluated. As a result, the power generation efficiency was as low as 18.5%.

(Appendix)
Means for solving the problems of the present disclosure include the following.
APPENDIX 1 A step of forming a p-type diffusion layer on a front main surface of a semiconductor substrate, a step of etching a back main surface of the semiconductor substrate after the step of forming the p-type diffusion layer, and a step of etching. And forming a n-type diffusion layer on the back main surface of the semiconductor substrate later.
Appendix 2 The method for manufacturing a semiconductor substrate according to Appendix 1, wherein the etching solution used for the etching is an acid solution or an alkali solution.
APPENDIX 3 The method for manufacturing a semiconductor substrate according to Appendix 2, wherein the etching solution includes a mixed solution of a hydrofluoric acid solution and a nitric acid solution.
Appendix 4. The method for manufacturing a semiconductor substrate according to Appendix 2, wherein the etching solution includes an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution.
APPENDIX 5 A semiconductor substrate manufactured by the manufacturing method according to any one of appendix 1 to appendix 4.
APPENDIX 6 A solar cell element comprising the semiconductor substrate according to appendix 5 and an electrode provided on the semiconductor substrate.
APPENDIX 7 A method for manufacturing a solar cell element, comprising: a step of manufacturing a semiconductor substrate by the manufacturing method according to any one of appendix 1 to appendix 4, and a step of forming an electrode.

110 n-type semiconductor substrate (silicon substrate)
111 p-type diffusion layer 113 n-type diffusion layer 115 antireflection film 116 antireflection film 117 light receiving surface electrode metal paste layer 118 light receiving surface electrode 119 back electrode metal paste layer 120 back electrode 122 BSG
124 PSG
10 n-type semiconductor substrate (silicon substrate)
11 p-type diffusion layer 12 n-type diffusion layer forming composition layer 13 first n-type diffusion layer 14 second n-type diffusion layer 15 antireflection film 16 antireflection film 17 metal paste layer 18 for light receiving surface electrode light receiving surface electrode 19 Back surface electrode metal paste layer 20 Back surface electrode 22 BSG
24 PSG
30 Busbar electrode 32 Finger electrode

Claims (10)

Forming a p-type diffusion layer on the front main surface of the semiconductor substrate;
Etching the back main surface of the semiconductor substrate after the step of forming the p-type diffusion layer;
A step of forming a first n-type diffusion layer by partially applying an n-type diffusion layer forming composition to the back main surface of the semiconductor substrate after the etching step; and a back main surface of the semiconductor substrate Forming an n-type diffusion layer, including forming a second n-type diffusion layer having a donor element concentration lower than the donor element concentration of the first n-type diffusion layer;
The manufacturing method of the semiconductor substrate with a selective n type diffused layer which has these. When the n-type diffusion layer forming composition is expressed as an oxide, at least one donor element-containing material selected from P ₂ O ₃ , P ₂ O ₅ and Sb ₂ O ₃ , SiO ₂ , K ₂ At least one glass component material selected from O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO ₃ ; The manufacturing method of the semiconductor substrate with a selective n type diffused layer of Claim 1 containing the glass particle containing these. The n-type diffusion layer forming composition, when displayed as an oxide, according to claim 1 or claim 2 containing glass particles containing P 2 _{O 5,} SiO ₂ and CaO, a dispersion medium, the A method for manufacturing a semiconductor substrate with a selective n-type diffusion layer.   The manufacturing method of the semiconductor substrate with a selective n-type diffused layer of any one of Claims 1-3 with which the etching liquid used for the said etching contains an acid solution or an alkaline solution.   The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to claim 4, wherein the etching solution contains a mixed solution of a hydrofluoric acid solution and a nitric acid solution.   The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to claim 4, wherein the etching solution contains an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution. The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to claim 1, wherein the second n-type diffusion layer is formed using a gas containing POCl ₃ .   The semiconductor substrate with a selective n type diffused layer manufactured by the manufacturing method of any one of Claims 1-7.   A solar cell element comprising: the semiconductor substrate with a selective n-type diffusion layer according to claim 8; and an electrode provided on the semiconductor substrate with the selective n-type diffusion layer.   A step of manufacturing a semiconductor substrate with a selective n-type diffusion layer having a selective n-type diffusion layer by the manufacturing method according to any one of claims 1 to 7, and on the selective n-type diffusion layer And a step of forming an electrode.