JP2018186177A - SEMICONDUCTOR SUBSTRATE WITH SELECTIVE n-TYPE DIFFUSION LAYER, SOLAR CELL ELEMENT, MANUFACTURING METHOD OF SEMICONDUCTOR SUBSTRATE WITH SELECTIVE n-TYPE DIFFUSION LAYER, AND MANUFACTURING METHOD OF SOLAR CELL ELEMENT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a semiconductor substrate with a selective n-type diffusion layer, capable of manufacturing a solar cell element excellent in power generation efficiency; a solar cell element using the semiconductor substrate with a selective n-type diffusion layer; a manufacturing method of a semiconductor substrate with a selective n-type diffusion layer; and a solar cell element manufactured by the manufacturing method.SOLUTION: A semiconductor substrate with a selective n-type diffusion layer includes: a p-type diffusion layer provided on a front main surface of a semiconductor substrate and containing boron as an acceptor element; a first n-type diffusion layer provided in a selective region on a back main surface of the semiconductor substrate and containing a donor element; a second n-type diffusion layer provided on a back main surface of the semiconductor substrate, and containing a donor element whose concentration is lower than the concentration of a donor element in the first n-type diffusion layer. The first n-type diffusion layer and the second n-type diffusion layer have a boron concentration of 3.0×10atoms/cmor less.SELECTED DRAWING: None

Description

  The present invention relates to a semiconductor substrate with a selective n-type diffusion layer, a solar cell element, a method for manufacturing a semiconductor substrate with a selective n-type diffusion layer, and a method for manufacturing a solar cell element.

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.

  As a method for increasing the power generation efficiency of the double-sided light-receiving solar cell element, there is 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.

Japanese Patent No. 58858891

In general, the S-BSF first forms a p-type diffusion layer by diffusing an acceptor element such as boron on the front main surface, and then a donor element such as phosphorus on the back main surface using POCl ₃ gas or the like. Diffusion is performed to form an n-type diffusion layer. However, when the acceptor element is diffused to the front main surface, the acceptor element may wrap around the back main surface and diffuse (also referred to as out diffusion). Therefore, even if a low-concentration n-type diffusion layer is formed on the back main surface after the p-type diffusion layer is formed, carrier recombination cannot be sufficiently suppressed in the low-concentration n-type diffusion layer. In addition, since the acceptor element is mixed in the n-type diffusion layer, it is difficult to adjust the donor element concentration in a region having a high donor element concentration and a region having a low donor element concentration. As a result, there is a problem that even if it is a solar cell element having an S-BSF structure, it is difficult to sufficiently improve the power generation efficiency.

  The present disclosure relates to a semiconductor substrate with a selective n-type diffusion layer capable of manufacturing a solar cell element having excellent power generation efficiency, a solar cell element using the semiconductor substrate with a selective n-type diffusion layer, and a semiconductor with a selective n-type diffusion layer It aims at providing the manufacturing method of a board | substrate, and the solar cell element manufactured by this manufacturing method.

Means for solving the above problems are as follows.
<1> A first n layer provided on a front main surface of a semiconductor substrate and provided in a selective region of a p-type diffusion layer containing boron as an acceptor element and a back main surface of the semiconductor substrate and containing a donor element And a second n-type diffusion layer provided on the back main surface of the semiconductor substrate and containing a donor element and having a donor element concentration lower than that of the first n-type diffusion layer, A semiconductor substrate with a selective n-type diffusion layer, wherein both of the first n-type diffusion layer and the second n-type diffusion layer have a boron concentration of 3.0 × 10 ¹⁷ atoms / cm ³ or less.
<2> The sheet resistance of the second n-type diffusion layer is 90Ω / sq. ~ 300Ω / sq. The semiconductor substrate with a selective n-type diffusion layer according to <1>.
<3> The sheet resistance of the first n-type diffusion layer is 10Ω / sq. ~ 85Ω / sq. The semiconductor substrate with a selective n-type diffusion layer according to <1> or <2>.
<4> A p-type diffusion layer on the front main surface, and a first n-type diffusion layer and a second n-type diffusion layer having a lower donor element concentration than the first n-type diffusion layer on the back main surface A solar cell comprising: the semiconductor substrate with a selective n-type diffusion layer according to any one of <1> to <3>, and an electrode provided on the first n-type diffusion layer. element.
<5> Forming a p-type diffusion layer containing boron as an acceptor element on the front main surface of the semiconductor substrate, and applying an n-type diffusion layer forming composition to a selective region on the back main surface of the semiconductor substrate A step of forming a first n-type diffusion layer containing a donor element, and a concentration of a donor element containing a donor element on the back main surface of the semiconductor substrate rather than the first n-type diffusion layer A step of forming an n-type diffusion layer, including a step of forming a second n-type diffusion layer having a low thickness, and a concentration of boron in the n-type diffusion layer being 3.0 × 10 ¹⁷ atoms / cm ³ or less. The method for producing a semiconductor substrate with a selective n-type diffusion layer according to any one of <1> to <3>, comprising
<6> The step of controlling the concentration of boron in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less is the step of forming the p-type diffusion layer before the step of forming the p-type diffusion layer. A step of forming a barrier layer on the surface, and a step of removing the barrier layer after the step of forming the p-type diffusion layer and before the step of forming the n-type diffusion layer. > The manufacturing method of the semiconductor substrate with a selective n-type diffused layer as described in>.
<7> The step of controlling the boron concentration in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less is after the step of forming the p-type diffusion layer and the n-type diffusion. The method for producing a semiconductor substrate with a selective n-type diffusion layer according to <5> or <6>, comprising a step of etching the back main surface of the semiconductor substrate before the step of forming the layer.
<8> In the step of controlling the concentration of boron in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less, the volatilization of boron is suppressed in the step of forming the p-type diffusion layer. The selective n-type diffusion layer according to any one of <5> to <7>, comprising applying a p-type diffusion layer forming composition containing a boron-containing compound to form a p-type diffusion layer Method for manufacturing a semiconductor substrate with a pad.
<9> The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to any one of <5> to <8>, wherein the second n-type diffusion layer is formed by diffusion of POCl ₃ gas.
<10> 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 any one of <5> to <9>, comprising glass particles containing a component substance.
<11> 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 <5> to <10>, and the selective n-type diffusion And a step of forming an electrode on the layer.

  According to the present disclosure, a semiconductor substrate with a selective n-type diffusion layer capable of producing a solar cell element with excellent power generation efficiency, a solar cell element using the semiconductor substrate with a selective n-type diffusion layer, and a selective n-type diffusion layer A method for manufacturing a semiconductor substrate with a semiconductor chip and a solar cell element manufactured by the manufacturing method are provided.

It is sectional drawing which shows notionally an example of the manufacturing process of the solar cell element 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 FIG. 2A.

  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) acrylic acid” means at least one of acrylic acid and methacrylic acid, and “(meth) acrylate” means at least one of acrylate and methacrylate.

≪Semiconductor substrate with selective n-type diffusion layer≫
A semiconductor substrate with a selective n-type diffusion layer of the present disclosure is provided on a front main surface of a semiconductor substrate and provided in a selective region of a p-type diffusion layer containing boron as an acceptor element and a back main surface of the semiconductor substrate. A first n-type diffusion layer containing a donor element and a second n provided on the back main surface of the semiconductor substrate and containing a donor element and having a donor element concentration lower than that of the first n-type diffusion layer And the boron concentration of each of the first n-type diffusion layer and the second n-type diffusion layer is 3.0 × 10 ¹⁷ atoms / cm ³ or less. The semiconductor substrate with a selective n-type diffusion layer of the present disclosure may have other configurations as necessary.

According to the semiconductor substrate with a selective n-type diffusion layer of the present disclosure, it is possible to manufacture a solar cell that is excellent in power generation efficiency. The reason for this is not clear, but can be considered as follows.
When a p-type diffusion layer is formed on the front main surface of a semiconductor substrate using boron as an acceptor element, boron may be volatilized to the back main surface of the semiconductor substrate. At this time, when an n-type diffusion layer is formed on the back main surface of the semiconductor substrate, boron diffuses also into the back main surface, and recombination of carriers is sufficiently suppressed, particularly in the region of the n-type diffusion layer having a low donor element concentration. I can't. However, in the semiconductor substrate with a selective n-type diffusion layer of the present disclosure, the boron concentration is set to 3.0 × 10 ¹⁷ atoms in both the first n-type diffusion layer and the second n-type diffusion layer on the back main surface. / Cm ³ or less can suppress the effect of carrier recombination due to the incorporation of boron, and further enhance the effect of suppressing the carrier recombination particularly in the region of the n-type diffusion layer having a low donor element concentration. It is considered possible. As a result, it is considered that the power generation efficiency when the solar cell element is manufactured can be further improved.

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, the semiconductor substrate with a selective n-type diffusion layer will be described for each configuration.

<P-type diffusion layer>
A p-type diffusion layer refers to a region where an acceptor element is diffused in a semiconductor substrate. The p-type diffusion layer of the present disclosure contains boron as an acceptor element and is formed on the front main surface of the semiconductor substrate. An acceptor element means an element that can diffuse into a semiconductor substrate to form a p-type diffusion layer. The p-type diffusion layer of the present disclosure may further contain a Group 13 element such as aluminum (Al) or gallium (Ga) indium (In) in addition to boron (B) as an acceptor element.

  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 substrates, indium phosphide substrates, silicon carbide, silicon germanium substrates, and copper indium selenium substrates. 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 of the semiconductor substrate refers to one surface of the semiconductor substrate. The back main surface described later refers to the other of the two main surfaces.

  A method for forming the p-type diffusion layer is not particularly limited, and examples thereof include a method using a gas containing boron and a method using a composition containing boron. A specific example of the method for forming the p-type diffusion layer will be described later.

<First n-type diffusion layer>
The first n-type diffusion layer is provided in a selective region on the back main surface of the semiconductor substrate and contains a donor element. In the present disclosure, an n-type diffusion layer refers to a region where a donor element of a semiconductor substrate is diffused.

  A donor element is an element that can form an n-type diffusion layer by diffusing into a semiconductor. 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.

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

  The sheet resistance of the first n-type diffusion layer is 10 Ω / sq. From the viewpoint of efficiently extracting electricity at the electrode forming portion. ~ 85Ω / sq. Is preferably 10Ω / sq. ~ 80Ω / sq. It is more preferable that

  The method for adjusting the sheet resistance of the first n-type diffusion layer and the second n-type diffusion layer described later is not particularly limited. For example, a method of adjusting the amount of diffusion by adjusting the temperature of the atmosphere in the step of diffusing the donor element can be mentioned. In addition, when the first n-type diffusion layer or the second n-type diffusion layer is formed using a composition containing a donor element, the donor element concentration or application amount of the composition containing the donor element is adjusted. And the like.

<Second n-type diffusion layer>
The second n-type diffusion layer is provided on the back main surface of the semiconductor substrate, contains a donor element, and has a lower donor element concentration than the first n-type diffusion layer.

  The method for forming the second n-type diffusion layer is not particularly limited as long as the concentration of the donor element is lower than that of the first n-type diffusion layer. Examples of the method for forming the second n-type diffusion layer include a method for forming a second n-type diffusion layer described later.

  The sheet resistance of the second n-type diffusion layer is 90 Ω / sq. From the viewpoint of efficiently suppressing surface recombination of carriers. ~ 300Ω / sq. And preferably 100 Ω / sq. ~ 250Ω / sq. It is more preferable that

<Concentration of boron in the first n-type diffusion layer and the second n-type diffusion layer>
In the semiconductor substrate with a selective n-type diffusion layer of the present disclosure, the boron concentration in each of the first n-type diffusion layer and the second n-type diffusion layer is 3.0 × 10 ¹⁷ atoms / cm ³ or less. (Hereinafter, the first n-type diffusion layer and the second n-type diffusion layer are also simply referred to as “n-type diffusion layer”). The boron concentration in the n-type diffusion layer is preferably 2.0 × 10 ¹⁷ atoms / cm ³ or less, and more preferably 1.0 × 10 ¹⁷ atoms / cm ³ or less. There is no particular limitation on the lower limit value of the boron concentration in the n-type diffusion layer, and the n-type diffusion layer preferably does not contain boron.

  In the present disclosure, the concentration of boron in the n-type diffusion layer refers to the concentration represented by the number of boron atoms per unit volume of the n-type diffusion layer, and can be measured by secondary ion mass spectrometry (SIMS). it can.

A method for controlling the boron concentration in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less is not particularly limited. For example, (1) before the step of forming the p-type diffusion layer, the barrier layer is formed on the back main surface of the semiconductor substrate to form the p-type diffusion layer, and then the step of forming the n-type diffusion layer. A method of removing the barrier layer, (2) a method of etching the back main surface of the semiconductor substrate after the step of forming the p-type diffusion layer and before the step of forming the n-type diffusion layer, (3) p-type diffusion In the step of forming a layer, a method of forming a p-type diffusion layer by applying a p-type diffusion layer-forming composition containing a boron-containing compound in which volatilization of boron is suppressed may be mentioned. A specific method for controlling the boron concentration in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less will be described later.

≪Method for manufacturing semiconductor substrate with selective n-type diffusion layer≫
In the method of manufacturing a semiconductor substrate with a selective n-type diffusion layer of the present disclosure, a step of forming a p-type diffusion layer containing boron as an acceptor element on the main surface of the semiconductor substrate (also referred to as a “p-type diffusion layer formation step”). And forming a first n-type diffusion layer containing a donor element by applying an n-type diffusion layer forming composition to a selective region on the back main surface of the semiconductor substrate, and the semiconductor substrate Forming a n-type diffusion layer including a step of forming a second n-type diffusion layer containing a donor element and having a donor element concentration lower than that of the first n-type diffusion layer ( Also referred to as “n-type diffusion layer forming step” and a step of controlling the boron concentration in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less (also referred to as “boron concentration control step”). ) And. The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer may further include other steps as necessary.

  Any of the p-type diffusion layer forming step and the n-type diffusion layer forming step may be performed first. From the viewpoint of easy adjustment of the boron concentration in the p-type diffusion layer and the donor element concentration in the n-type diffusion layer, the n-type diffusion layer formation step may be performed after the p-type diffusion layer formation step. preferable. 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.

  As the boron concentration control step, for example, (1) a step of forming a barrier layer on the back main surface of the semiconductor substrate before the step of forming the p-type diffusion layer (also referred to as “barrier layer forming step”), and p-type After the step of forming the diffusion layer and before the step of forming the n-type diffusion layer, the step of removing the barrier layer (also referred to as “barrier layer removal step”), (2) after the step of forming the p-type diffusion layer And, before the step of forming the n-type diffusion layer, in the step of etching the back main surface of the semiconductor substrate (also referred to as “etching step”) and (3) the p-type diffusion layer forming step, volatilization of boron is suppressed. In addition, a p-type diffusion layer-forming composition containing a boron-containing compound is applied to form a p-type diffusion layer, and the like may be combined. The specific method for controlling the boron concentration in the n-type diffusion layer is not limited to these. The timing for performing the boron concentration control step is not particularly limited, and may be performed before the p-type diffusion layer formation step, may be performed after the p-type diffusion layer formation step and before the n-type diffusion layer formation step, In at least one of the p-type diffusion layer forming step and the n-type diffusion layer forming step, the diffusion layer forming method may be adjusted.

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

<Barrier layer forming step and barrier layer removing step>
The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer of the present disclosure may include a barrier layer formation step before the p-type diffusion layer formation step as the boron concentration control step. In the present disclosure, the barrier layer has a function of preventing boron from scattering and reaching the back main surface of the semiconductor substrate in the p-type diffusion layer forming step.
The type of the barrier layer is not particularly limited as long as it has the above function, and may be a silicon oxide film (SiO ₂ or the like), a silicon nitride film (SiN _x ), or the like. From the viewpoint of easy removal of the barrier layer, the barrier layer preferably contains SiO ₂ as a main component.

  The average thickness of the barrier layer to be formed is not particularly limited, and may be several tens nm to several hundreds nm. From the viewpoint of barrier performance and ease of removal, it is preferably 50 nm to 500 nm, and more preferably 100 nm to 300 nm. The average thickness of the barrier layer is an arithmetic average value of five thicknesses measured using an interference type film thickness meter.

  As a method for forming the barrier layer, a thermal oxidation furnace, a steam thermal oxidation furnace, a PECVD (plasma CVD) apparatus, an APCVD (atmospheric-pressure chemical vapor deposition) apparatus, or the like is used. The method of forming is mentioned. From the viewpoint of high versatility, the barrier layer is preferably formed by PECVD or using a steam thermal oxidation furnace.

After forming the barrier layer, a part of the excessively formed barrier layer may be removed if necessary. For example, when using a thermal oxidation furnace or steam thermal oxidation furnace to form an SiO ₂ layer, after the formation of the SiO ₂ layer, prior to the diffusion of the p-type impurity, the front main surface with an etching solution such as hydrofluoric acid aqueous solution The SiO ₂ layer formed in (1) may be removed. Also, when forming the SiO ₂ in PECVD, there is a possibility that the SiO ₂ layer is formed on the front main surface end portion or the like may be removed. In order to remove the SiO ₂ layer on the front main surface, a floating single side etching method or the like in which the front main surface is immersed in the etchant surface can be applied.

When the barrier layer forming step is performed before the p-type diffusion layer forming step, the barrier layer removing step is performed to remove the barrier layer after the p-type diffusion layer forming step described later and before the n-type diffusion layer forming step. Do.
A method for removing the barrier layer is not particularly limited, and examples thereof include a method using a hydrofluoric acid aqueous solution. For example, when the barrier layer is formed of a SiO ₂ layer, the barrier layer can be removed by using a hydrofluoric acid aqueous solution.

  Further, for example, when BSG is formed in the formation of the p-type diffusion layer, it is possible to remove BSG at once by removing the barrier layer using a hydrofluoric acid aqueous solution. In this case, the entire semiconductor substrate is immersed in a hydrofluoric acid aqueous solution, and the BSG and the barrier layer are removed together. Further, BSG may be utilized as a barrier layer in the n-type impurity diffusion step, and in this case, only the barrier layer may be removed by single-side etching in this step.

<P-type diffusion layer forming step>
In the p-type diffusion layer forming step, a p-type diffusion layer containing boron as an acceptor element is formed on the main surface of the semiconductor substrate.

  A method for forming the p-type diffusion layer is not particularly limited, and examples thereof include a method using a gas containing boron and a method using a composition containing boron.

Examples of the gas containing boron 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 boron include a method of performing thermal diffusion treatment by forming boron silicate glass (BSG) on a semiconductor substrate using BBr ₃ gas.
When the gas containing boron is used, the temperature of the atmosphere of the thermal diffusion treatment is preferably 800 ° C. to 1050 ° C., more preferably 850 ° C. to 1000 ° C., and 900 ° C. to 970 ° C. Further preferred. The thermal diffusion treatment time is preferably 5 minutes to 90 minutes, and more preferably 10 minutes to 60 minutes. In the present disclosure, the thermal diffusion treatment time refers to the holding time at the maximum temperature. When the thermal diffusion treatment time is 5 minutes or longer, boron tends to be sufficiently diffused into the semiconductor substrate, and when it is 90 minutes or shorter, 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 a method for forming a p-type diffusion layer using a composition containing boron include a method in which a composition containing boron is applied to a semiconductor substrate and a thermal diffusion treatment is performed.

The method for applying the boron-containing composition to the semiconductor substrate is not particularly limited. For example, a printing method, a spin coating method, a brush coating, a spray method, a doctor blade method, a roll coating method, APCVD (atmospheric pressure CVD), and an inkjet Law.
The temperature of the atmosphere of the thermal diffusion treatment after applying the boron-containing composition is preferably 800 ° C to 1050 ° C, more preferably 850 ° C to 1000 ° C, and 900 ° C to 970 ° C. More preferably. The thermal diffusion treatment time is preferably 5 minutes to 90 minutes, and more preferably 10 minutes to 60 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 heat treatment is performed to diffuse boron, two semiconductor substrates may be stacked in a furnace so that the back main surfaces of the semiconductor substrates face each other, and the heat treatment may be performed. Thereby, it can suppress that boron wraps around a back main surface.

  In the method for manufacturing a semiconductor substrate with a selective n-type diffusion layer of the present disclosure, as a boron concentration control step, p-type diffusion layer formation containing a specific boron-containing compound in which volatilization of boron is suppressed in the p-type diffusion layer formation step Applying the composition to form a p-type diffusion layer may be included. Examples of the specific boron-containing compound include glass particles containing boron and a boron-containing silicon oxide compound.

When a composition containing glass particles containing boron is used as the p-type diffusion layer forming composition, the presence of boron in the glass particles tends to suppress boron from being volatilized outside during the thermal diffusion treatment. It is in. For this reason, for example, boron is bonded to an element in the glass particle or is taken into the glass, so that it is considered that it is difficult to volatilize. For this reason, it tends to be suppressed that boron is volatilized during the thermal diffusion treatment.
When a boron-containing silicon oxide compound is used as the p-type diffusion layer forming composition, the boron-containing silicon oxide compound can be obtained by a sol-gel reaction between a silicon oxide precursor and a boron compound. The boron-containing silicon oxide compound thus obtained is considered to be difficult to volatilize because the boron compound has a structure in which the boron compound is dispersed in a network formed by chemical bonding of silicon oxide (siloxane).

<Etching process>
In the method for manufacturing a semiconductor substrate with a selective n-type diffusion layer of the present disclosure, the boron concentration control step is performed after the step of forming the p-type diffusion layer and before the step of forming the n-type diffusion layer. You may have the process (etching process) of etching a back main surface. Even if boron is out-diffused on the back main surface of the semiconductor substrate in the p-type diffusion layer forming step, the acceptor element attached to the back main surface or the p-type formed on the surface of the back main surface by the etching step The diffusion layer can be 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. 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 embodiment, 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>
In the n-type diffusion layer forming step, the n-type diffusion layer forming composition is applied to a selective region on the back main surface of the semiconductor substrate to form a first n-type diffusion layer containing a donor element (“ First n-type diffusion layer forming step) and second n-type diffusion containing a donor element on the back main surface of the semiconductor substrate and having a lower donor element concentration than the first n-type diffusion layer. A step of forming a layer (also referred to as a “second n-type diffusion layer forming 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 steps, it is preferable to perform both steps in a series of steps.
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, an n-type diffusion layer forming composition is applied to a selective region on the back main surface of the semiconductor substrate to form a first n-type diffusion layer containing a donor element. . First, the n-type diffusion layer forming composition used in this step will be described. In the present embodiment, 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)
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 in the n-type diffusion layer forming composition, and preferably 1% by mass or more and 90% by mass. More preferably, 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 more preferably 5% by mass or more and 20% by mass or less. It is very preferable. When the content of the compound containing the donor element is 0.1% by mass or more, the n-type diffusion layer can 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 is 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, preferably contains SiO ₂ and alkaline earth metals (CaO, MgO, etc.) at least.

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 alkaline earth metals (CaO, MgO, etc.). By combining P ₂ O ₅ that is a donor element-containing material, SiO ₂ that is a glass component material, and an alkaline earth metal, 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 surface 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 glass particles contain an alkaline earth metal as a glass component, the molar fraction of the alkaline earth metal is preferably 2 mol% to 30 mol% from the viewpoint of water resistance, melting temperature, and etching characteristics. It is preferable that it is 5 mol%-25 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.
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 first n-type diffusion layer forming step is performed to remove at least part of the solvent contained in the composition before the thermal diffusion treatment. You may include the process of heat-processing the board | substrate after providing a diffused layer formation composition. 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.

Further, depending on the composition of the n-type diffusion layer forming composition, the first n-type diffusion layer forming step may include at least a part of the dispersion medium contained in the composition, particularly a binder (before the thermal diffusion treatment). In order to volatilize and remove the resin component), a step of heat-treating the substrate after applying the n-type diffusion layer forming composition may be included. In this case, the heat treatment can be performed under the conditions of treatment at a temperature exceeding 300 ° C. and not more than 800 ° C. for 1 minute to 10 minutes. 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 containing a donor element and having a lower donor element concentration than the first n-type diffusion layer is formed on the back main surface of the semiconductor substrate. .
In the present disclosure, the concentration of the donor element in the n-type diffusion layer refers to the concentration represented by the number of atoms of the donor element per unit volume of the n-type diffusion layer, and is measured by secondary ion mass spectrometry (SIMS). be able to. 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 element may be diffused.

  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 more preferably 10 minutes to 60 minutes. If the thermal diffusion treatment time is 10 minutes or more, the acceptor element tends to be sufficiently diffused into the semiconductor substrate, and if it is 60 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, two semiconductor substrates may be placed in the furnace with the p-type diffusion layer being overlapped, 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 (phosphorus silicate glass), and the injection of the gas containing POCl ₃ is stopped. Then, a drive-in step of diffusing phosphorus may be performed. 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 manufacturing method of the semiconductor substrate with a selective n-type diffusion layer of this indication may have other processes if needed. Examples of the other steps include a step of performing pretreatment on the semiconductor substrate before forming the diffusion layer. 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. When performing etching to remove PSG, PSG formed in the first n-type diffusion layer region and PSG formed in the second n-type diffusion layer region may be collectively removed by etching, After each n-type diffusion layer forming step, the formed PSG may be removed by etching.

  Each configuration of the semiconductor substrate with a selective n-type diffusion layer manufactured by the method for manufacturing a semiconductor substrate with a selective n-type diffusion layer of the present disclosure has been described as each configuration of the semiconductor substrate with a selective n-type diffusion layer described above. It is the same as that.

≪Solar cell element and manufacturing method of solar cell element≫
The solar cell element has a p-type diffusion layer on the front main surface, and a first n-type diffusion layer and a second n-type diffusion layer having a lower donor element concentration than the first n-type diffusion layer. A semiconductor substrate with a selective n-type diffusion layer of the present disclosure on the main surface; and an electrode provided on the first n-type diffusion layer.
Further, a method for manufacturing a solar cell element includes a step of manufacturing a semiconductor substrate with a selective n-type diffusion layer having a selective n-type diffusion layer by the method for manufacturing a semiconductor substrate with a selective n-type diffusion layer of the present disclosure, and a selection Forming an electrode on the target n-type diffusion layer.

  Hereinafter, an embodiment of a method for manufacturing a solar cell element 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 that is an n-type semiconductor substrate 10 to remove a damaged layer, and a texture structure is obtained by etching.

In FIG. 1 (2), a barrier layer 21 (SiO ₂ layer) is formed to a thickness of 100 nm to 300 nm on the back main surface using PECVD or a steam thermal oxidation furnace. In the case of forming the SiO ₂ layer by using a steam thermal oxidation furnace, the SiO ₂ layer formed on the front main surface is removed by etching. Also, when SiO ₂ is formed by PECVD, there is a possibility that an SiO ₂ layer is formed at the edge of the front main surface, etc., so it is preferable to remove this. As an etchant used for removing the SiO ₂ layer, a hydrofluoric acid aqueous solution obtained by diluting hydrofluoric acid with water is preferably used. The concentration of the hydrofluoric acid aqueous solution is preferably 2% by mass to 10% by mass, and more preferably 3% by mass to 8% by mass.

In FIG. 1 (3), thermal diffusion treatment is performed using BBr ₃ gas 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 and heated. A p-type diffusion layer 11 is formed by performing a diffusion process. At this time, BSG22 is formed on the surface of the p-type diffusion layer.

  In FIG. 1 (4), the back main surface opposite to the surface on which the p-type diffusion layer 11 is formed is treated with a hydrofluoric acid aqueous solution to remove the barrier layer 21.

In FIG. 1 (5), an 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, it is preferable to install a plurality of n-type semiconductor substrates 10 in a thermal diffusion facility so that the p-type diffusion layers face each other so that donor elements are not mixed into the p-type diffusion layer on the front main surface. 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 and nitrogen, a mixed gas thereof, and the like, and a mixed gas of oxygen and nitrogen is preferable. As a result, the first n-type diffusion layer 13 of FIG. 1 (6) 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 22 and the thermal oxidation obtained when forming the p-type diffusion layer are used. The film is used as a barrier layer, and the p-type diffusion layer of the semiconductor substrate is superposed so as to face each other, so that phosphorus diffusion to the front main surface is prevented.

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. In the diffusion layer 14, PSG 24 formed by donor element diffusion using a gas containing an n-type diffusion layer forming composition and POCl ₃ remains. In FIG. 1 (7), 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. 1 (8), 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 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, 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. 1 (9), a 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 a 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 on the first n-type diffusion layer. 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, by applying a metal paste for the back electrode to the region where the first n-type diffusion layer having a high donor element concentration is formed, the contact resistance between the electrode and the semiconductor substrate is suppressed when baked in a subsequent process. be able to. As a result, the characteristics when a solar cell element is obtained can be further improved. When the back electrode metal paste is printed and applied, alignment is performed using an LED and a CCD camera in the region where the first n-type diffusion layer is formed. At this time, a silver paste for forming a silver electrode may be partially provided on the back main surface for connection between solar cell elements in the module process.

  In FIG. 1 (10), the metal paste layer 17 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 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 and the back surface electrode 20 will be described with reference to FIGS. 2A and 2B. The light-receiving surface electrode 18 or the back surface electrode 20 includes a bus bar electrode 30 and a finger electrode 32 that intersects the bus bar electrode 30. FIG. 2A is a plan view of a solar cell element in which the light-receiving surface electrode 18 or the back-surface electrode 20 includes a bus bar electrode 30 and a finger electrode 32 intersecting the bus bar electrode 30 as viewed from the light receiving surface. 2B is an enlarged perspective view showing a part of FIG. 2A.

  Such light receiving surface electrode 18 or back surface electrode 20 may 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. it can. The light receiving surface electrode 18 or the back surface electrode 20 having the bus bar electrode 30 and the finger electrode 32 is generally used as an electrode 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.

  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. By using the mold diffusion layer forming composition, it is possible to produce a back contact type solar cell element. 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 present 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, the present embodiment will be specifically described by way of examples, but the present embodiment is not limited to these examples. “%” Means “% by mass” unless otherwise specified.

[Example 1]
(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 barrier layer)
After forming a SiO ₂ layer having a thickness of about 200 nm on the back main surface of the semiconductor substrate using a PECVD apparatus, only the front main surface is immersed in a 5% by mass hydrofluoric acid aqueous solution for 2 minutes at the end of the front main surface. to remove some excess SiO ₂ layer.

(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 950 ° C. at a temperature increase rate of 15 ° C./min, a mixed gas of oxygen, nitrogen and BBr ₃ is injected into the furnace and heat-treated at 950 ° C. for 50 minutes to diffuse boron into the semiconductor substrate ( Thermal diffusion) 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.

(Removal of barrier layer)
After boron diffusion, the barrier layer on the back main surface was removed by dipping in 5% by mass hydrofluoric acid for 2 minutes. At this time, only the back main surface was soaked in 5% by mass hydrofluoric acid to leave BSG on the front main surface.

(Measurement of boron concentration on the back main surface)
The boron concentration on the surface opposite to the surface on which the p-type diffusion layer was formed (back main surface) was measured by secondary ion mass spectrometry (SIMS). The boron concentration was 1.0 × 10 ¹⁷ atoms / cm ³ at the highest concentration.

(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 with the p-type diffusion layers facing each other, placed in a boat, and a diffusion furnace at a temperature of 700 ° C. with N ₂ : 9 L / min and O ₂ : 1 L / min (Koyo Thermo System Co., Ltd.) Company, “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 (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 30 minutes (Depo time 30 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 a 5% by mass hydrofluoric acid aqueous solution 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, a silver paste was applied in a pattern of electrodes having a width of 55 μm by screen printing on both surfaces of the n-type semiconductor substrate. At this time, on the back main surface, the back electrode silver paste was formed in the region where the first n-type diffusion layer having a high donor element concentration was formed. The formed silver paste was fired through at 800 ° C. to form an electrode in which electrical contact with the p-type diffusion layer and the n-type diffusion layer was ensured, thereby producing a double-sided light receiving solar cell element.

(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 2]
In Example 1, the barrier layer forming step was omitted, and after forming the p-type diffusion layer, only the back main surface was immersed in hydrofluoric acid (mixed liquid of hydrofluoric acid and nitric acid), and the thickness of 1 μm from the outermost surface of the back main surface An n-type semiconductor substrate on which a p-type diffusion layer and an n-type diffusion layer are formed is obtained by the same method as in Example 1 except that the etching is performed, and the boron concentration on the back main surface is measured by the same method as in Example 1. As a result, it was 5.0 × 10 ¹⁶ atoms / cm ³ at the highest concentration. Using this substrate, solar cell elements were prototyped and evaluated in the same manner as in Example 1. As a result, the power generation efficiency was as high as 20.5%.

[Comparative Example 1]
In Example 1, except that the barrier layer forming step was omitted, an n-type semiconductor substrate having a p-type diffusion layer and an n-type diffusion layer formed by the same method as in Example 1 was obtained, and the boron concentration on the back main surface was changed. When measured by the same method as in Example 1, it was 1.0 × 10 ¹⁸ atoms / cm ³ at the highest concentration. Using this substrate, solar cell elements were prototyped and evaluated in the same manner as in Example 1. As a result, the power generation efficiency was as low as 18.8%.

[Comparative Example 2]
In Example 2, an n-type semiconductor substrate on which a p-type diffusion layer and an n-type diffusion layer were formed was obtained in the same manner as in Example 2 except that the back main surface was not etched after forming the p-type diffusion layer. When the boron concentration on the back main surface was measured in the same manner as in Example 2, it was 1.0 × 10 ¹⁸ atoms / cm ³ at the highest concentration. Using this substrate, solar cell elements were prototyped and evaluated in the same manner as in Example 2. As a result, the power generation efficiency was as low as 19.0%.

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 21 Barrier layer (SiO ₂ layer)
22 BSG
24 PSG
30 Busbar electrode 32 Finger electrode

Claims (11)

A p-type diffusion layer provided on the main surface of the semiconductor substrate and containing boron as an acceptor element;
A first n-type diffusion layer provided in a selective region on the back main surface of the semiconductor substrate and containing a donor element;
A second n-type diffusion layer provided on the back main surface of the semiconductor substrate, containing a donor element and having a donor element concentration lower than that of the first n-type diffusion layer;
The semiconductor substrate with a selective n-type diffusion layer, wherein both of the first n-type diffusion layer and the second n-type diffusion layer have a boron concentration of 3.0 × 10 ¹⁷ atoms / cm ³ or less.   The sheet resistance of the second n-type diffusion layer is 90Ω / sq. ~ 300Ω / sq. The semiconductor substrate with a selective n-type diffusion layer according to claim 1, wherein   The sheet resistance of the first n-type diffusion layer is 10Ω / sq. ~ 85Ω / sq. The semiconductor substrate with a selective n-type diffusion layer according to claim 1 or 2. Claims having a p-type diffusion layer on the front main surface, and a first n-type diffusion layer and a second n-type diffusion layer having a donor element concentration lower than that of the first n-type diffusion layer on the back main surface. The semiconductor substrate with a selective n-type diffusion layer according to any one of claims 1 to 3,
An electrode provided on the first n-type diffusion layer;
A solar cell element. Forming a p-type diffusion layer containing boron as an acceptor element on the front main surface of the semiconductor substrate;
Applying an n-type diffusion layer forming composition to a selective region of the back main surface of the semiconductor substrate to form a first n-type diffusion layer containing a donor element; and the back surface of the semiconductor substrate Forming an n-type diffusion layer on the surface, including a step of forming a second n-type diffusion layer containing a donor element and having a lower donor element concentration than the first n-type diffusion layer;
Controlling the boron concentration in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less;
The manufacturing method of the semiconductor substrate with a selective n type diffused layer of any one of Claims 1-3 containing this. The step of controlling the boron concentration in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less is a barrier on the back main surface of the semiconductor substrate before the step of forming the p-type diffusion layer. 6. The method of claim 5, comprising: forming a layer; and removing the barrier layer after the step of forming the p-type diffusion layer and before the step of forming the n-type diffusion layer. A method for manufacturing a semiconductor substrate with a selective n-type diffusion layer. The step of controlling the boron concentration in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less is after the step of forming the p-type diffusion layer and the formation of the n-type diffusion layer. The method for manufacturing a semiconductor substrate with a selective n-type diffusion layer according to claim 5 or 6, comprising a step of etching a back main surface of the semiconductor substrate before the step of performing. The step of controlling the boron concentration in the n-type diffusion layer to be 3.0 × 10 ¹⁷ atoms / cm ³ or less is the step of forming the p-type diffusion layer, and the boron content in which volatilization of boron is suppressed The semiconductor substrate with a selective n-type diffusion layer according to any one of claims 5 to 7, comprising applying a p-type diffusion layer forming composition containing a compound to form a p-type diffusion layer. Manufacturing method. The method of manufacturing a semiconductor substrate with a selective n-type diffusion layer according to claim 5, wherein the second n-type diffusion layer is formed by diffusion of POCl ₃ gas. 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 any one of Claims 5-9 containing the glass particle containing these.   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 5 to 10, and on the selective n-type diffusion layer And a step of forming an electrode.