JP2013041864A - Solar battery, method of manufacturing semiconductor device, and transcription mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a solar battery having a low optical reflectance and high-performance characteristics.SOLUTION: By making an Si substrate contact in processing liquid for oxidation and dissolution for a short time in a state that a mold having a catalyst material scattered in a two-dimensional distribution is contacted, point-like fine concavities are formed on the Si substrate surface in such a configuration that point-like portions of the catalyst material of the mold are transcribed. Next, when chemical etching is performed from the whole surface of the Si substrate, an uneven surface comprising bowl-like concave surface parts extended using the fine concavities of the two-dimensional distribution as start points and a convex rising part formed by the rest of the substrate surface is formed on the Si substrate surface. Then, an impurity source is introduced from the surface to form PN junction, and thereby, the PN junction surface becomes a stable bonding structure along the uneven surface. A solar battery obtained by this way can achieve a low optical reflectance and high-performance characteristics.

Description

  The present invention relates to a solar cell, a semiconductor device, a manufacturing method thereof, and a transfer template that have a fine ridge-shaped recess on a surface of a semiconductor substrate in a two-dimensional distribution.

  2. Description of the Related Art Conventionally, in a crystalline solar cell, for example, an energy conversion efficiency utilizing a so-called “light confinement effect” has been improved by deforming a planar surface of a silicon substrate into an uneven shape. Compared to the case where the substrate surface is flat, the light reflected once by the uneven slope is received and taken in by the adjacent uneven slope, thereby substantially reducing the reflectance from the surface. This is because it becomes possible. As a result, since the total amount of incident light increases, an increase in photoelectric effect is realized.

  As a chemical treatment method using a room temperature solution when forming the above concavo-convex structure, for example, there is a method of immersing a silicon substrate in a mixed aqueous solution of an oxidizer and a solubilizer for silicon containing metal ions. It has been proposed (Patent Document 1). According to this, a porous silicon layer having a large number of micropores, which is considered to be due to the penetration of metal ions, is formed on the surface of the substrate, so-called porous layer, and the reflectance of light on the surface can be reduced. Yes.

Japanese Patent Laying-Open No. 2005-183505

  However, the above-described method for forming a concavo-convex structure using a so-called porous layer does not have sufficient controllability regarding the formation of the concavo-convex shape. Specifically, in the above method, first, metal precipitates on the surface of the silicon substrate from metal ions in the mixed aqueous solution, so that the metal functions as a reduction catalyst. Since it depends on the function of the solution and the reaction cannot be freely controlled, it is very difficult to ensure the size and distribution of the irregularities that are formed, and their reproducibility. As a reflection of this, the density and depth of the micropores in the so-called porous layer are not stable.

  Further, if there is a so-called porous layer on the surface of the Si substrate, the surface reflectance can be reduced. On the other hand, for example, the N-type is formed on the same surface of the P-type substrate via the so-called porous layer. It has been found that there is an empirical difficulty in the process of introducing impurities when forming a solar cell by uniformly forming a PN junction by introducing impurities.

The present invention is to solve the above-described problem. First, a template having a catalyst material scattered in a two-dimensional distribution is brought into contact with or close to the surface of a semiconductor substrate to be processed. The treated semiconductor substrate is treated for a short time in a mixed aqueous solution containing an oxidizing agent and a solubilizing agent, for example, a (HF + H ₂ O ₂ ) mixed aqueous solution containing hydrogen fluoride (HF) and hydrogen peroxide (H ₂ O ₂ ). As a result, fine concave portions depending on the surface shape of the scattered catalyst material are formed on the surface of the semiconductor substrate at the position of the two-dimensional distribution in such a manner that the portion of the catalyst material of the template is inverted and transferred. The porous layer described above is formed at the transfer site at the same time. Then, when the entire surface of the semiconductor substrate is treated with an oxidizing etchant, etching occurs from the recessed portion where the porous layer is formed, and the fine concave portion is expanded to become a substantially bowl-shaped concave surface. As a result, a concavo-convex surface is formed on the surface of the Si substrate. Therefore, even if an impurity source is introduced for forming a PN junction from the surface, the tip surface (joint surface) of the PN junction becomes a stable joint surface along the uneven surface. That is, according to the present invention, the Si substrate has an uneven surface distributed two-dimensionally on the surface, and has a stable PN junction structure along the uneven surface inside, and by using this semiconductor substrate, Various semiconductor devices, such as solar cells, for which surface light reflection suppression is desired, can greatly contribute to the realization of stable high performance and high functionality.

  One solar cell of the present invention is arranged such that a transfer template on which a catalyst material is scattered is opposed to a plane of a semiconductor substrate so that the catalyst material is in contact with the above-described plane, The semiconductor substrate is treated with a mixed aqueous solution containing the above-described oxidizing agent and solubilizing agent, and fine concave portions depending on the surface shape of the dotted catalyst material are formed on the surface of the semiconductor substrate. In the form of reverse transfer corresponding to the parts of the catalyst material, it is formed by being scattered at the position of the two-dimensional distribution, and then the entire surface of the semiconductor substrate is treated with an oxidizing etchant to obtain the fineness described above. The concave portion has a shape expanded into a roughly concave surface. That is, by this, the fine concave portions are etched away at a high speed, so that the ridge-shaped concave portions are formed at the transfer sites scattered at the positions of the two-dimensional distribution, and the entire surface becomes an uneven surface. Therefore, when an impurity source is introduced from the surface of the semiconductor substrate to the inside, a PN junction surface structure along the surface of the semiconductor substrate having the uneven surface can be formed. In this way, a stable and reproducible solar cell having an uneven shape on the surface and a uniform PN junction surface along the uneven surface inside can be realized.

  The template for transfer used in the production of the solar cell of the present invention is a template on a predetermined surface so that the shape of the catalyst material scattered in the two-dimensional distribution is reflected on the surface of the semiconductor substrate to be processed. The catalyst materials are arranged in a two-dimensional distribution. That is, the transfer template is formed by arranging catalyst materials on the surface in a two-dimensional distribution with an appropriate high surface density, and the transfer template is opposed to the surface of the semiconductor substrate to be processed. Then, in a state where the catalyst material is disposed so as to contact the surface of the semiconductor substrate, the semiconductor substrate is treated in a mixed aqueous solution containing the oxidizing agent and the dissolving agent to form the surface of the semiconductor substrate. In order to stably manufacture fine concave portions scattered in a two-dimensional distribution in which the surface shape of the catalyst material of the template for transfer is inverted corresponding to the same position. One of the points of interest for this transfer template is that, unlike the above-described conventional technique, a transfer template having a predetermined shape is used as a manufacturing jig for a semiconductor device, and a two-dimensional distribution is provided on the surface of the semiconductor substrate. The porous layer is removed utilizing the fact that the fine concave portions are scattered and the concave portions are easily etched by chemical etching. To form a concavo-convex surface having a low reflection characteristic on the entire surface of the substrate, and to allow a PN junction surface along the concavo-convex surface of the surface to be formed inside the semiconductor substrate. It exists in the place which can manufacture the solar cell of stable various electrical characteristics.

  Also, the manufacturing method of one semiconductor device according to the present invention is based on the actual surface shape of the catalyst material scattered in the two-dimensional distribution provided on the surface of the transfer mold, and the above-described oxidation and solubility properties. The catalyst material is disposed in such a manner that the catalyst material faces the surface of the semiconductor substrate and the dotted surface portion of the catalyst material is in contact with the surface of the semiconductor substrate. A fine concave portion scattered in a two-dimensional distribution reflecting the point-like surface portion is formed, and the entire surface is further chemically etched with an oxidizing etching solution, and the concave portion is substantially a bowl-like deep concave shape. The surface of the semiconductor substrate has an uneven surface, and a PN junction surface along the uneven surface of the semiconductor substrate is formed inside the semiconductor substrate so that it has low optical reflection characteristics and stable electrical characteristics. This means that a semiconductor device can be realized.

  According to this method for manufacturing a semiconductor device, a desired concave shape is formed on the surface of the semiconductor substrate to be processed based on the shape of the catalyst material provided on the transfer template, and reflects the shape of the transfer template. In addition, a PN junction semiconductor device having stable electrical characteristics can be obtained by forming a PN junction surface along the semiconductor substrate surface of the concave shape or the bowl-shaped portion. Can be manufactured. In other words, if the catalyst material is formed on the surface of the transfer substrate in an appropriate fine shape and scattered with a high surface density with a two-dimensional distribution, a treatment having oxidizing properties and solubility can be used. A stable PN junction semiconductor device can be manufactured through the treatment of the semiconductor substrate in the liquid, the etching treatment of the surface for forming the recesses, and the PN junction formation step.

In addition, one transfer template according to the present invention has a catalyst material scattered at a high surface density with a two-dimensional distribution on the surface, or a catalyst material at the top of the projections scattered in a two-dimensional distribution on the surface. Using this transfer template, a treatment liquid having oxidizing and dissolving properties is placed in the gap in a state where it is placed facing the surface of the semiconductor substrate so that the catalyst material comes into contact therewith. By introducing and processing, fine concave portions having a porous layer reflecting the catalyst material on the transfer template are scattered on the surface of the semiconductor substrate, and are scattered in a two-dimensional distribution, Next, the porous substrate region is completely removed by chemical treatment such as low-temperature and short-time oxidative etching at room temperature, and the semiconductor substrate is formed into a substantially bowl-like deep concave portion without the porous layer. In addition, a PN junction surface along the semiconductor substrate surface is formed. In the semiconductor substrate surface, the optically low reflectivity characteristic is realized by having a substantially bowl-shaped deep concave portion, and the PN junction surface is formed on a surface of uniform depth along the surface shape, thereby being stable. A semiconductor device having electrical characteristics can be obtained.

  The advantage of the transfer template is that the transfer template is provided on the semiconductor substrate to be processed on the basis of the surface shape of the catalyst material scattered in the two-dimensional distribution with high surface density. It is possible to stably manufacture a semiconductor substrate having a high-density uneven surface by obtaining a concave shape scattered in a two-dimensional distribution with a high surface density, reflecting the surface shape of the catalyst material on the surface, In addition, the uneven shape on the semiconductor substrate can be directly reflected in the formation of the internal PN junction surface. The focus of this transfer template is different from the above-mentioned conventional technology, and a transfer template having a high surface density and a surface shape of a catalyst material scattered in a two-dimensional distribution is used as a semiconductor device manufacturing jig. Utilizing this, it is possible to realize a semiconductor device having a low electrical reflectance characteristic and having a stable electrical characteristic by forming a PN junction surface on a surface having a uniform depth.

  In each of the above-described inventions, the template for transfer includes a catalyst material, during the treatment with a treatment liquid having oxidation property and solubility with respect to the semiconductor substrate to be treated, and in the etching treatment process on the semiconductor, A material which supplies such a treatment liquid and is resistant to the solution, specifically, an etching resistant or insoluble material is preferable. The material of the transfer template is not particularly limited, but for example, a resistant material mesh such as SUS plated with platinum or a mesh made of platinum can be used.

  Furthermore, the unevenness of the transfer template is not limited to the case where it is formed using wet chemical etching as described above. For example, isotropic or anisotropic dry etching using semiconductor technology or MEMS technology, or fine uneven shapes formed by imprinting can be applied.

  The formation mechanism of the concave shape of the semiconductor substrate can be assumed as follows. First, when a catalyst material existing on an irregular surface such as a texture structure on the surface of a transfer template is brought into contact with the semiconductor substrate surface, the catalyst material acts as a reduction catalyst for the oxidizing agent in the processing solution on the semiconductor substrate surface. Thus, the oxidizing species generated from the oxidizing material oxidizes the surface of the semiconductor substrate. Then, the oxidation site is dissolved by the above-described dissolving agent in the processing liquid. By repeating the oxidation and dissolution of the surface of the semiconductor substrate, the shape of the surface of the transfer template is generally reflected, in other words, the surface shape of the transfer template, especially the surface shape of the catalyst material. Etching of the substrate surface occurs. Therefore, in each of the above-described inventions, the catalyst material is not particularly limited as long as it functions as an oxidation catalyst in the above-described processing liquid. Suitable representative examples of the catalyst material are selected from the group of platinum (Pt), silver (Ag), copper (Cu), nickel (Ni), palladium (Pd), gold (Au), and alloys thereof. These suitable materials may be formed by a film formed by a known sputtering method, a deposited film by CVD or the like, or a metal film formed by reduction from a coating film of a metal compound of the above group, etc. A shape that is actually scattered in a two-dimensional distribution is preferable.

  Fine concave portions placed on the surface of the Si substrate in a technique similar to transfer from the template by contacting a plate with a two-dimensional distribution of point-like catalyst metal on the surface of the semiconductor substrate. Then, the entire surface of the semiconductor substrate is chemically etched, so that the semiconductor substrate has a substantially bowl-shaped deep concave portion with a two-dimensional distribution starting from the concave portions arranged in a dot shape. An undulating surface is formed. At this time, the porous layer formed by the influence of the catalytic metal on the surface of the semiconductor substrate at the first point-like recess is removed by chemical etching, and the recess is expanded as a deep recess having a substantially bowl shape. It becomes. Therefore, by performing an impurity introduction process for forming a PN junction on the same surface, a PN junction surface along the uneven surface can be stably formed.

It is an optical microscope photograph after the transfer process of the Si substrate surface in 1st Embodiment. It is an optical microscope photograph of the expanded substantially bowl-shaped deep concave part of the Si substrate surface in 1st Embodiment.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this description, common parts are denoted by common reference symbols throughout the drawings unless otherwise specified. In the drawings, elements of the present embodiment are not necessarily described with each other kept to scale.

A stencil plated stencil was previously formed, and this stencil surface was a few seconds in a mixed aqueous solution of HF (12.35 mol)) and H ₂ O ₂ (4.9 mol) (HF + H ₂ O ₂ ). By making contact at room temperature for a short time, fine spot-like concave portions are formed in a two-dimensional distribution on the surface of the Si substrate as shown in the optical micrograph (FIG. 1) after transfer in FIG.
Although not shown, in this process, a porous layer is formed on the surface portion of the Si substrate in the fine dot-like recesses described above.

Next, the surface of the Si substrate having the above-described fine dot-like recesses is mixed with nitric acid (HNO ₃ : 11.3 mol): hydrofluoric acid (HF: 0.6 mol): acetic acid (CH ₃ COOH: 1.44). 2) By performing chemical etching for 3 to 5 minutes at room temperature with an acid etching aqueous solution having a composition, the surface portion of the Si substrate is the same as the dot-like fine recesses shown in FIG. 1 as shown in FIG. However, a bowl-shaped concave portion could be formed. The saddle-like concave portion is a substantially bowl-like deep concave portion that is expanded and generated starting from the fine spot-like concave portion shown in FIG. 1 during chemical etching. The actual state of this phenomenon is understood as an extended surface region due to the etching rate difference in which the porous layer formed in the fine concave portion formed at the beginning of the base part of the Si substrate is etched and removed at a high speed on the entire surface. The

  After that, for example, by performing an impurity introduction process for forming a normal PN junction such as an ion implantation method on the same surface, the surface has the above-described deep concave shape or bowl-shaped concave portion at a predetermined depth. A bowl-shaped PN junction surface along the uneven surface could be formed stably. In a solar cell having such a PN junction, low reflectivity characteristics can be realized on the surface by the concave / convex surface having the above-described deep concave shape or bowl-shaped concave portion formed at an optimal high surface density, and a PN junction surface along the concave / convex surface It is preferably stable and has good bonding characteristics.

In the present embodiment, hydrofluoric acid is used as a treatment liquid having oxidation and solubility properties when forming fine dot-like recesses by transfer from a template on which a two-dimensional distribution of dot-like catalyst metal is arranged. A mixed aqueous solution of (HF) and hydrogen peroxide solution (H ₂ O ₂ ) was used. This treatment solution was a mixed aqueous solution of hydrofluoric acid (HF) and hydrogen peroxide solution (H ₂ O ₂ ). It is not limited to. For example, instead of hydrofluoric acid (HF) and hydrogen peroxide (H ₂ O ₂ ), an oxidizing solution such as nitric acid and sulfuric acid, and a solution in which oxygen or ozone is added and dissolved as appropriate are used. Is also possible.

In addition, the composition of the acid etching used for forming the bowl-shaped concave portion starting from the fine point-shaped concave portion is not limited to a mixed aqueous solution of nitric acid, hydrofluoric acid, and acetic acid, but also a normal nitric acid / hydrofluoric acid aqueous solution. It is possible to use alkaline etching instead of acid etching.

  In the above-described embodiment, it is another preferable aspect that the Si substrate to be processed is applied not only to a single crystal silicon substrate but also to a polycrystalline silicon substrate, an amorphous silicon substrate, or the like. In addition, although a solar cell is illustrated as a semiconductor device, the example of the semiconductor device is not limited to the solar cell. For example, also in a semiconductor device such as an optical device such as a light receiving element, the formation of the concavo-convex shape using the transfer template according to the above-described embodiment can greatly contribute to the improvement of the performance of various devices.

  Note that the disclosure of the above-described embodiments is described for explaining the embodiments, and the present invention is not limited to the conditions described in the examples. In addition, modifications within the scope of the present invention including other combinations of the embodiments are also included in the scope of the claims.

  INDUSTRIAL APPLICABILITY The present invention can greatly contribute to the improvement in performance and high functionality of a substrate to be processed using a template for transfer, and thus a solar cell manufactured using the substrate to be processed. Therefore, it can be widely used in the field of devices typified by optical devices such as semiconductor devices and light receiving elements.

Claims (5)

  A solar cell comprising a two-dimensionally distributed bowl-shaped concave portion disposed on a surface of a semiconductor substrate and a bowl-shaped PN junction surface along the bowl-shaped concave portion inside the semiconductor substrate.   A process of processing a semiconductor substrate in a processing solution having an oxidant and a solubilizing agent in a state where the catalyst material surface of the template on which the catalyst material is arranged in a two-dimensional distribution of dots is in contact, etching the entire surface of the semiconductor substrate A method for manufacturing a semiconductor device, comprising the steps of:   Using a template for transfer in which the catalyst material is arranged in a two-dimensional distribution on the surface, the surface of the catalyst material is in contact with the semiconductor substrate to be processed in a processing solution containing an oxidizing agent and a dissolving agent. And the manufacturing method of the semiconductor device which forms an uneven surface on the said semiconductor substrate.   The catalyst material is at least one selected from the group consisting of platinum (Pt), silver (Ag), copper (Cu), nickel (Ni), palladium (Pd), and gold (Au). 4. A method for manufacturing a semiconductor device according to 3.   A transfer template having catalyst materials for semiconductor etching arranged in a two-dimensional distribution in a dot pattern on a predetermined mold.