JP2017017064A - Solar cell element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell element provided with a protective film capable of sufficiently obtaining a passivation effect and a manufacturing method thereof.SOLUTION: The solar cell element 10 comprises a silicon substrate 1 having a p-type semiconductor region on one main surface thereof, a passivation film 9 containing aluminum oxide disposed on the p-type semiconductor region, a first protective film 11 having a mixture of silicon oxide and aluminum oxide disposed on the passivation film 9, and a plurality of conductor contact portions 8a penetrating the passivation film 9 and the first protective film 11 and connecting to the p-type semiconductor region of the silicon substrate 1.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a solar cell element and a manufacturing method thereof.

  A general crystalline solar cell element uses a semiconductor substrate made of silicon. A passivation film is provided on the surface of the semiconductor substrate in order to reduce minority carrier recombination loss that causes a decrease in photoelectric conversion efficiency of the solar cell element. Aluminum oxide having a negative fixed charge is used as a material for the passivation film provided on the p-type region of the semiconductor substrate. Thereby, it is known that recombination loss of minority carriers can be reduced and good photoelectric conversion efficiency can be realized (for example, refer to Patent Documents 1 to 3 below).

  However, aluminum oxide is easily altered by the penetration of moisture, and the passivation effect may be reduced. For this reason, a protective film such as silicon oxide is formed on the passivation film by a plasma enhanced CVD (PECVD) method or the like (for example, see Patent Documents 4 to 5 below).

JP 2004-193350 A JP 2009-164544 A Special table 2012-530361 gazette JP 2012-253356 A International Publication No. 2011/033826

  However, the protective film made of silicon oxide or the like has a positive fixed charge. For this reason, a protective film may weaken the effect of the negative fixed charge of aluminum oxide, and a sufficient passivation effect may not be obtained.

  Therefore, an object of the present invention is to provide a solar cell element excellent in the passivation effect and a method for manufacturing the solar cell element.

  In order to solve the above problems, a solar cell element according to one embodiment of the present invention includes a silicon substrate having a p-type semiconductor region on one main surface, and aluminum oxide disposed on the p-type semiconductor region. A passivation film, a first protective film having a mixture of silicon oxide and aluminum oxide disposed on the passivation film, and passing through each of the passivation film and the first protective film, the silicon substrate And a plurality of conductors connected to the p-type semiconductor region (which may be “conductor contact portions”).

Moreover, the manufacturing method of the solar cell element which concerns on 1 aspect of this invention is a manufacturing method of the solar cell element provided with the silicon substrate which has a p-type semiconductor area | region in one main surface, Comprising: The said p-type of the said silicon substrate A step of disposing a passivation film containing aluminum oxide on the semiconductor region; and in an atmosphere containing oxygen, irradiating a plurality of portions of the passivation film with a laser beam reaching the surface of the silicon substrate, Forming a plurality of holes in the passivation film, and disposing a first protective film having a mixture of silicon oxide and aluminum oxide on the passivation film; irradiating the holes in the passivation film and the laser beam; And disposing a conductor on the surface of the semiconductor substrate exposed in step (b).

  According to said solar cell element and its manufacturing method, the solar cell element excellent in the passivation effect of the passivation film can be provided.

FIG. 1 is a plan view showing an external appearance of a first main surface side of a solar cell element according to an embodiment of the present invention. FIG. 2 is a plan view showing the appearance of the second principal surface side of the solar cell element according to one embodiment of the present invention. FIG. 3 is a cross-sectional view showing a cross section taken along line III-III in FIG. FIG. 4 is an enlarged cross-sectional view of a portion M1 in FIG. FIG. 5 is a cross-sectional view schematically showing the state of the protective film in the vicinity of the contact portion of the solar cell element according to one embodiment of the present invention. 6 (a) to 6 (e) are cross-sectional views schematically showing an example of steps of a method for manufacturing a solar cell element according to an embodiment of the present invention. FIGS. 7A to 7C are cross-sectional views schematically showing an example of steps of a method for manufacturing a solar cell element according to an embodiment of the present invention. FIG. 8 is an enlarged cross-sectional view of a solar cell element according to another embodiment at a portion M2 in FIG.

  Hereinafter, embodiments of a solar cell element and a manufacturing method thereof according to the present invention will be described in detail with reference to the drawings. The drawings are schematically shown.

<Solar cell element>
A solar cell element 10 according to this embodiment is shown in FIGS. As shown in FIG. 3, the solar cell element 10 includes a first main surface 10a that is a light receiving surface on which light is mainly incident, and a main surface (back surface) that is located on the opposite side of the first main surface 10a. It has two main surfaces 10b and side surfaces 10c. Moreover, the solar cell element 10 includes a silicon substrate 1 as a semiconductor substrate, and the silicon substrate 1 also includes a first main surface 1a and a second main surface 1b located on the opposite side of the first main surface 1a, And a side surface 1c. The silicon substrate 1 includes a first semiconductor layer 2 that is a one-conductivity type (for example, p-type) semiconductor region, and a reverse conductivity type (for example, n-type) semiconductor region that is provided on the first main surface 10a side of the first semiconductor layer 2. And the second semiconductor layer 3. Further, the solar cell element 10 includes a BSF (Back Surface Field) layer 4 formed on the semiconductor substrate 1, an antireflection film 5, a first electrode 6, a second electrode 7, a third electrode 8, a contact portion 8a, and a passivation film. 9 and the first protective film 11. Here, the contact portion 8 a is a conductor that passes through each of the passivation film 9 and the first protective film 11 and is connected to the silicon substrate 1.

  The silicon substrate 1 is a monocrystalline or polycrystalline silicon substrate, for example. The silicon substrate 1 includes a first semiconductor layer 2 and a second semiconductor layer 3 provided on the first main surface 1a side of the first semiconductor layer 2.

Hereinafter, an example in which a p-type polycrystalline or single-crystal silicon substrate is used as the silicon substrate 1 and a p-type semiconductor is used as the first semiconductor layer 2 will be described. The thickness of the silicon substrate 1 is, for example, about 100 to 250 μm. The shape of the silicon substrate 1 is not particularly limited, but when the solar cell module is manufactured from the solar cell element 10 as long as it is a substantially square shape in plan view, the gap between the elements may be reduced. When the first semiconductor layer 2 made of the polycrystalline silicon substrate 1 is made p-type, an impurity such as boron or gallium is contained as a dopant element.

  The second semiconductor layer 3 is stacked on the first semiconductor layer 2. As a result, the second semiconductor layer 3 has a pn junction formed at the interface with the first semiconductor layer 2. The second semiconductor layer 3 is a semiconductor layer having a conductivity type opposite to that of the first semiconductor layer 2 (n-type in this embodiment), and is provided on the first main surface 1 a side of the first semiconductor layer 2. . When the first semiconductor layer 2 is a p-type conductive silicon substrate 1, for example, the second semiconductor layer 3 can be formed by diffusing an impurity such as phosphorus as a dopant on the first main surface 1a side.

  As shown in FIG. 3, a fine concavo-convex structure (texture) for reducing the reflectance of irradiated light may be provided on the first main surface 1 a side of the silicon substrate 1. The height of the convex portions of the texture is about 0.1 to 10 μm, and the interval between the adjacent convex portions is about 0.1 to 20 μm. For example, the concave portion may have a substantially spherical shape, or the convex portion may have a pyramid shape. The above-mentioned “height of the convex portion” is, for example, a straight line passing through the bottom surface of the concave portion in FIG. 3 as a reference line, and from the reference line to the top surface of the convex portion in a direction perpendicular to the reference line. It is distance. Further, the “interval between convex portions” is a distance between the centers of the top surfaces of adjacent convex portions in a direction parallel to the reference line.

  The antireflection film 5 has a function of reducing the reflectance of light irradiated on the first main surface 10 a of the solar cell element 10. The antireflection film 5 is made of, for example, silicon oxide, aluminum oxide, or a silicon nitride layer. The refractive index and thickness of the antireflection film 5 are appropriately adopted as the refractive index and thickness capable of realizing low reflection conditions for light in a wavelength range that can be absorbed by the silicon substrate 1 and contribute to power generation in sunlight. That's fine. For example, the antireflective film 5 can have a refractive index of about 1.8 to 2.5 and a thickness of about 20 to 120 nm.

The BSF layer 4 is disposed on the second main surface 1b side of the silicon substrate 1 and may have the same conductivity type as the first semiconductor layer 2 (p-type in this embodiment). The concentration of the dopant contained in the BSF layer 4 is higher than the concentration of the dopant contained in the first semiconductor layer 2. The BSF layer 4 forms an internal electric field on the second main surface 1 b side of the silicon substrate 1. Thereby, recombination of minority carriers hardly occurs near the surface of the second main surface 1b in the silicon substrate 1, and the photoelectric conversion efficiency of the solar cell element 10 is unlikely to decrease. The BSF layer 4 can be formed, for example, by diffusing a dopant element such as boron or aluminum on the second main surface 1b side of the silicon substrate 1. The concentrations of the dopant elements contained in the first semiconductor layer 2 and the BSF layer 4 are about 5 × 10 ¹⁵ to 1 × 10 ¹⁷ atoms / cm ³ and 1 × 10 ^{18 to} 5 × 10 ²¹ atoms / cm ³ , respectively. The BSF layer 4 is preferably present at a contact portion between a contact portion 8a, which will be described later, and the silicon substrate 1.

  The first electrode 6 is an electrode provided on the first main surface 1 a side of the silicon substrate 1. As shown in FIG. 1, the first electrode 6 includes a first output extraction electrode 6a and a plurality of linear first current collecting electrodes 6b. The first output extraction electrode 6a is an electrode for extracting electricity obtained by power generation to the outside. For example, the length in the short-side direction (hereinafter referred to as width) is about 0.5 to 2.5 mm. At least a part of the first output extraction electrode 6a intersects the first current collecting electrode 6b and is electrically connected. The first current collecting electrode 6 b is an electrode for collecting electricity generated from the silicon substrate 1. Moreover, the 1st current collection electrode 6b is a some linear form, Comprising: These widths are about 50-200 micrometers, for example. Thus, the width of the first collector electrode 6b is smaller than the width of the first output extraction electrode 6a. Moreover, the 1st current collection electrode 6b is provided with two or more at intervals of about 1-3 mm mutually. The thickness of the first electrode 6 is about 10 to 40 μm. Such a first electrode 6 can be formed, for example, by applying a first metal paste containing silver as a main component into a desired shape by screen printing or the like and then baking it. In addition, in this embodiment, a main component shows that the containing mass with respect to the whole component is 50 mass% or more.

  As shown in FIGS. 2 and 3, the second electrode 7 and the third electrode 8 are electrodes provided on the second main surface 1 b side of the silicon substrate 1. The second electrode 7 is an electrode for taking out the electricity obtained by the power generation by the solar cell element 10 to the outside. The second electrode 7 is formed on the silicon substrate 1 through the passivation film 9 or the first protective film 11, or through the passivation film 9 and the first protective film 11. The shape of the second electrode 7 may be arranged linearly in a dot shape (or island shape) as shown in FIG. 2, or may be a belt shape (or a line shape). The thickness of the 2nd electrode 7 is about 10-30 micrometers, and the width | variety is about 1.3-7 mm. The second electrode 7 contains silver as a main component. Such a second electrode 7 can be formed, for example, by applying a metal paste containing silver as a main component into a desired shape by screen printing or the like and then baking it.

  As shown in FIGS. 2 and 3, the third electrode 8 is an electrode for collecting electricity generated from the silicon substrate 1 on the second main surface 1 b of the silicon substrate 1, and is electrically connected to the second electrode 7. It is provided to connect to. At this time, at least a part of the second electrode 7 may be connected to the third electrode 8. Further, a part of the third electrode 8 is filled with a large number of through holes 12 penetrating the passivation film 9 and the first protective film 11 to form a contact portion 8 a, and is formed on the first semiconductor layer 2 of the silicon substrate 1. It is connected. The third electrode 8 is formed so as to cover substantially the entire surface of the first protective film 11 except for the outer peripheral portion of about 0.3 to 2 mm from the end portion of the silicon substrate 1. The thickness of the third electrode 8 is about 15 to 50 μm, and the third electrode 8 and the contact portion 8a contain aluminum as a main component. For example, a metal paste mainly containing aluminum is screen-printed into a desired shape by screen printing. It can be formed by baking after coating.

  The passivation film 9 is formed on almost the entire surface of at least the first semiconductor layer 2 which is the p-type semiconductor region of the silicon substrate 1 and has a function of reducing minority carrier recombination. As the passivation film 9, for example, a film containing aluminum oxide formed by an ALD (Atomic Layer Deposition) method or the like is preferably used. The thickness of the passivation film 9 is about 10 to 200 nm. By using a film having a strong negative fixed charge such as aluminum oxide as the passivation film 9, minority carriers (electrons in this case) are moved away from the interface between the silicon substrate 1 and the passivation film 9 by the field effect. Thereby, recombination of minority carriers can be further reduced.

The through hole 12 is a hole for penetrating the passivation film 9 and exposing the first semiconductor layer 2 of the silicon substrate 1 during the production. A contact portion 8 a is disposed in the through hole 12. The through-holes 12 are formed in a cylindrical shape with a diameter of about 30 to 150 μm, for example, by laser beam irradiation so that about 100 to 500 per cm ² are uniformly distributed.

The first protective film 11 is disposed on the passivation film 9 containing aluminum oxide in order to obtain the solar cell element 1 having excellent reliability such as moisture resistance. Furthermore, the first protective film 11 of the present embodiment includes a mixture having silicon oxide and aluminum oxide. Here, the first protective film 11 is a single layer film and does not include, for example, a laminated structure of a silicon oxide film and an aluminum oxide film. Further, it is desirable that the first protective film 11 has aluminum oxide uniformly in the matrix phase of silicon oxide. Here, “uniform” excludes the case where aluminum oxide is biased to the passivation film 9 side of the first protective film 11 due to diffusion of aluminum oxide from the passivation film 9 side. Further, even when almost no aluminum oxide is present on the side of the first protective film 11 where the passivation film 9 is not present, it cannot be said to be “uniform”. Since silicon oxide has a positive fixed charge, when only the silicon oxide film is disposed on the passivation film 9 containing aluminum oxide, the negative fixed charge of the aluminum oxide is weakened to reduce the passivation effect of the passivation film 9. . On the other hand, in the present embodiment, the first protective film 11 has a mixture containing silicon oxide and aluminum oxide, so that the aluminum oxide having a negative fixed charge on the first protective film 11 is a positive electrode of silicon oxide. The fixed charge can be weakened and the passivation effect of the passivation film 9 can be enhanced. Furthermore, since the first protective film 11 contains aluminum oxide, the thermal expansion coefficient of the first protective film 11 can be brought close to the thermal expansion coefficient of the silicon substrate 1. Thereby, the adhesiveness between the passivation film 9 and the first protective film 11 can be improved. The thermal expansion coefficient of aluminum oxide is about 7 to 8 × 10 ⁻⁶ / ° C., the thermal expansion coefficient of silicon is about 3.9 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of silicon oxide is 0.3 to 0.00. It is about 6 × 10 ⁻⁶ / ° C.

  The first protective film 11 preferably contains more silicon oxide than aluminum oxide in order to improve reliability such as moisture resistance. The fact that the first protective film 11 contains a mixture of silicon oxide and aluminum oxide can be confirmed by, for example, secondary ion mass spectrometry (SIMS).

  The formation of the first protective film 11 containing a mixture of silicon oxide and aluminum oxide is performed as follows. As shown in FIGS. 3 and 4, a through hole 12 is formed in the passivation film 9 by irradiating the passivation film 9 with a laser beam that reaches the surface of the silicon substrate 1 in an oxygen-containing atmosphere (for example, air). . At the same time, a part of the first semiconductor layer 2 of the silicon substrate 1 is also removed by laser beam irradiation, so that a part of the surface of the silicon substrate 1 in contact with the contact part 8a becomes a concave part. With the heat of laser beam irradiation, aluminum oxide of the passivation film 9 is vaporized and part of the first semiconductor layer 2 of the silicon substrate 1 is also vaporized, and the vaporized silicon is oxidized in an oxygen atmosphere to become silicon oxide. Note that the output of the laser beam and the like may be adjusted as appropriate so that aluminum oxide and silicon are vaporized. Aluminum oxide and silicon oxide obtained by oxidizing silicon are deposited on the passivation film 9 on the second main surface 1b side, and the first protective film 11 having at least a mixture of aluminum oxide and silicon oxide is formed on the passivation film 9. A film is formed. The thickness of the first protective film 11 is about 1 to 10 nm. The first protective film 11 may be formed between the passivation film 9 and the contact portion 8a. By forming the first protective film 11 also on the side surface of the passivation film 9, it is possible to obtain the solar cell element 1 further excellent in reliability such as moisture resistance. By using the same method as described above, the first protective film 11 made of a mixture of aluminum oxide and silicon oxide is also formed on the side surface of the passivation film 9.

  Furthermore, the contact part 8a is formed even inside the silicon substrate 1 by making the surface of the silicon substrate 1 with which the contact part 8a abuts into a concave part. As a result, the contact area between the contact portion 8a and the silicon substrate 1 increases, and the contact resistance between the two decreases, so that the photoelectric conversion efficiency of the solar cell element can be improved.

  In addition, the depth d of the concave portion of the silicon substrate 1 shown in FIG. 4 is preferably about 3 to 10 μm in the results of tests repeatedly performed by the inventors. When the depth d of the concave portion of the silicon substrate 1 is 3 to 10 μm, the first protective film 11 does not become too thin and can sufficiently function as a protective film. Further, when the concave portion is manufactured, the intensity of the laser beam does not become too strong, and microcracks or the like are not easily generated in the portion of the silicon substrate 1 located around the through hole 12, and the strength of the completed solar cell element 10 is increased. It is hard to decline.

Further, as described above, the first protective film 11 can be formed by removing the part of the first semiconductor layer 2 of the silicon substrate 1 at the same time as forming the through hole 12 in the passivation film 9 using laser beam irradiation. A mixture containing at least aluminum oxide and silicon oxide is easily deposited on the periphery of the contact portion 8a. As shown in FIG. 5, between the two adjacent contact portions 8a, the first region 14 around the two contact portions 8a of the first protective film 11 is located at the center between the contact portions 8a. It can be thicker than the second region 15. For example, the first region 14 is higher than the second region 15 by about 1 to 2 μm at the maximum. The length of the first region 14 is about 10% (3 to 15 μm) of the diameter of the through hole 12. According to this structure, when the contact portion 8a is formed in the through hole 12 by screen printing with a metal paste mainly composed of aluminum, the metal paste is easily filled into the through hole 12. This point will be described in detail. By increasing the thickness of the periphery of the through hole 12, the shape of the upper part of the through hole 12 and the through hole 12 becomes a funnel shape. When the third electrode 8 is formed, a metal paste mainly composed of aluminum is screen-printed. In this case, the metal paste is pressed against the silicon substrate 1 with a print squeegee or the like through screen plate making. Since the shape of the upper portion of the through hole 12 and the through hole 12 is funnel-shaped, the pressure applied to the metal paste on the upper portion of the through hole 12 is amplified in the through hole 12 portion, and the metal paste is placed in the through hole 12. Easy to fill. For this reason, it is difficult for the void portion to remain in the through hole 12, and the electrical resistance of the contact portion 8a is unlikely to increase. As a result, the bad influence to the photoelectric conversion efficiency of the solar cell element 10 can be reduced.

<Method for producing solar cell element>
Next, each process of the manufacturing method of the solar cell element 10 is demonstrated.

  First, a silicon substrate 1 is prepared as shown in FIG. The silicon substrate 1 may be single crystal silicon or polycrystalline silicon. The silicon substrate 1 can be produced by, for example, an existing CZ (Czochralski) method or a casting method. Hereinafter, an example in which a p-type polycrystalline silicon substrate is used as the silicon substrate 1 will be described. For example, a polycrystalline silicon ingot is produced by a casting method. For example, the electrical resistivity of the ingot may be set to about 1 to 5 Ω · cm by adding boron as a dopant element. Next, the silicon substrate 1 is manufactured by slicing the ingot into a square shape having a side of about 150 to 160 mm square and a thickness of about 100 to 200 μm. Thereafter, in order to remove the mechanical damage layer and the contamination layer on the cut surface of the silicon substrate 1, the surface of the silicon substrate 1 may be etched by a very small amount with an aqueous solution of NaOH or KOH or a mixed solution of hydrofluoric acid and nitric acid. .

  Further, as shown in FIG. 6B, a texture may be formed on the first main surface 1a of the silicon substrate 1 in order to reduce reflection of light on the surface. As a texture forming method, a wet etching method using an alkaline solution such as NaOH or a mixed solution of hydrofluoric acid and nitric acid, or a dry etching method using an RIE (Reactive Ion Etching) method or the like can be used.

Next, as illustrated in FIG. 6C, the n-type second semiconductor layer 3 is formed on the first main surface 1 a of the textured silicon substrate 1. The second semiconductor layer 3 is a coating thermal diffusion method in which paste-like P ₂ O ₅ is applied to the surface of the silicon substrate 1 and thermally diffused, and gas-like POCl ₃ (phosphorus oxychloride) is used as a diffusion source. It is formed by a phase thermal diffusion method or the like. The second semiconductor layer 3 is formed to have a thickness of about 0.1 to 2 μm and a sheet resistance value of about 40 to 200Ω / □. For example, in the vapor phase thermal diffusion method, the substrate 1 is heat-treated for about 5 to 30 minutes at a temperature of about 600 to 800 ° C. in an atmosphere having a diffusion gas composed of POCl ₃ or the like to convert phosphosilicate glass (PSG) into silicon. It is formed on the surface of the substrate 1. Thereafter, the silicon substrate 1 is heat-treated for about 10 to 40 minutes at a high temperature of about 800 to 900 ° C. in an inert gas atmosphere such as argon or nitrogen. Thereby, phosphorus diffuses from PSG to the silicon substrate 1, and the second semiconductor layer 3 is formed on the first main surface 1 a side of the silicon substrate 1.

  In the step of forming the second semiconductor layer 3 described above, when the second semiconductor layer 3 is also formed on the second main surface 1b side, only the second semiconductor layer 3 formed on the second main surface 1b side is used. Etch away. Thus, the p-type first semiconductor layer 2 is exposed on the second main surface 1b side. For example, the second semiconductor layer 3 formed on the second main surface 1b side is removed by immersing only the second main surface 1b side of the silicon substrate 1 in a mixed solution of hydrofluoric acid and nitric acid. Thereafter, PSG adhering to the first main surface 1a side of the silicon substrate 1 when the second semiconductor layer 3 is formed is removed by etching with hydrofluoric acid. At this time, the second semiconductor layer 3 formed on the side surface 1c of the silicon substrate 1 may also be removed.

  As described above, the polycrystalline silicon substrate 1 in which the second semiconductor layer 3 as the n-type semiconductor layer is disposed on the first main surface 1a side and the texture is formed on the surface can be prepared.

  Next, a passivation film 9 is formed. As shown in FIG. 6 (d), a passivation film 9 made of aluminum oxide is formed on the second main surface 1 b of the first semiconductor layer 2. As a method for forming the passivation film 9, for example, an ALD method, a PECVD method, or the like can be used. In particular, the ALD method may be excellent in covering the surface of the silicon substrate 1. For this reason, the passivation film 9 manufactured by the ALD method can further increase the passivation effect.

  In forming the passivation film 9 by the ALD method, first, the silicon substrate 1 on which the second semiconductor layer 3 is formed is placed in the chamber of the film forming apparatus. And the process AD shown below is repeated in multiple times in the state which heated the silicon substrate 1 at the temperature range of 100-250 degreeC. As a result, a passivation film 9 made of aluminum oxide and having a desired thickness is formed on the silicon substrate 1. The contents of steps A to D are as follows.

  [Step A] An aluminum material such as trimethylaluminum (TMA) for forming aluminum oxide is supplied onto the silicon substrate 1 together with a carrier gas such as Ar gas or nitrogen gas. As a result, the aluminum material is adsorbed around the entire periphery of the silicon substrate 1. The time for which TMA is supplied may be about 15 to 3000 milliseconds, for example.

  At the start of step A, the surface of the silicon substrate 1 is preferably terminated with an OH group. By making the surface of the silicon substrate 1 have a Si—O—H structure, a covalent bond is easily formed at the interface between the surface of the silicon substrate 1 and the formed aluminum oxide film. Thereby, the joint strength between the surface of the silicon substrate 1 and the aluminum oxide film can be improved, and the reliability of the solar cell element 10 can be further improved. This Si—O—H structure can be formed, for example, by treating the silicon substrate 1 with dilute hydrofluoric acid and then washing with pure water.

  [Step B] Purification of the inside of the chamber of the film forming apparatus is performed by nitrogen gas, and the aluminum raw material in the chamber is removed. Furthermore, aluminum materials other than components chemically adsorbed at the atomic layer level are removed from the aluminum materials physically and chemically adsorbed on the silicon substrate 1. The time for purifying the inside of the chamber with nitrogen gas may be about 1 to several tens of seconds, for example.

  [Step C] By supplying an oxidizing agent such as water or ozone gas into the chamber of the film forming apparatus, the alkyl group contained in TMA is removed and replaced with an OH group. Thereby, an atomic layer of aluminum oxide is formed on the silicon substrate 1. The time for supplying the oxidizing agent into the chamber is preferably about 500 to 1500 milliseconds. Further, by supplying H together with the oxidizing agent into the chamber, hydrogen atoms are more easily contained in the formed aluminum oxide film.

  [Step D] The inside of the chamber of the film forming apparatus is cleaned with nitrogen gas, and the oxidizing agent in the chamber is removed. At this time, for example, the oxidizing agent that did not contribute to the reaction during the formation of atomic layer level aluminum oxide on the silicon substrate 1 is removed. In addition, the time for purifying the inside of the chamber with nitrogen gas may be about 1 to several tens of seconds, for example.

  Thereafter, an aluminum oxide film having a desired thickness (for example, about 10 to 200 nm) is formed by repeating a series of steps A to D a plurality of times.

  Here, the case where aluminum oxide is formed using TMA as the aluminum material is shown, but it goes without saying that other materials may be used as the aluminum material. For example, a material that has an appropriate vapor pressure (for example, 100 Pa or more) as a gas supply source at a raw material supply temperature (within a range of -20 to 120 ° C.) and can be supplied in a gaseous state in the chamber. That's fine. As the aluminum raw material, for example, triethylaluminum (TEA) can be used. The material that can be supplied in a gaseous state may be supplied after being diluted with nitrogen gas, carbon dioxide gas or the like as a carrier gas. By adjusting the gas species of the source gas and the carrier gas and the mixing ratio thereof, the content of the constituent elements in the formed film can be adjusted optimally. In addition, the passivation film 9 can be formed all around the substrate 1 including the side surface 1c of the substrate 1 by using the ALD method. In this case, after applying an acid resistant resist to the passivation film 9 on the second main surface 1b of the substrate 1, the unnecessary passivation film 9 may be removed by etching with hydrofluoric acid or the like.

Next, as shown in FIG. 6E, an antireflection film 5 made of a silicon nitride film is formed on the first main surface 1 a side of the substrate 1. The antireflection film 5 is formed using, for example, PECVD method or sputtering method. If the PECVD method is used, the silicon substrate 1 is heated in advance at a temperature higher than the temperature during film formation. Thereafter, a mixed gas of silane (SiH ₄ ) and ammonia (NH ₃ ) is diluted with nitrogen (N ₂ ), the reaction pressure is set to about 50 to 200 Pa, plasma is formed by glow discharge decomposition, and the heated silicon substrate 1 is deposited with a silicon nitride film. Thereby, the antireflection film 5 is formed on the silicon substrate 1. The film forming temperature at this time is about 350 to 650 ° C. Further, a frequency of 10 to 500 kHz is used as the frequency of the high frequency power source necessary for glow discharge. The gas flow rate is appropriately determined depending on the size of the reaction chamber. For example, the gas flow rate may be in the range of 150 to 6000 ml / min (sccm), and the flow rate ratio F2 / F1 between the silane flow rate F1 and the ammonia flow rate F2 may be 0.5 to 15.

  Next, as shown in FIG. 7A, in an atmosphere containing oxygen, for example, a laser beam reaching the surface (second main surface 1b) of the silicon substrate 1 is irradiated to a plurality of portions of the passivation film 9, A plurality of through holes 12 are formed in the passivation film 9. At this time, the through hole 12 forms a concave portion on the surface (second main surface 1 b) of the silicon substrate 1. Use Nd: YAG (neodymium-doped yttrium, aluminum, garnet) laser beam (wavelength 1064 nm) with a Q switch or the second harmonic (SHG, wavelength 532 nm) of an Nd: YAG laser. Can do.

For example, when the second harmonic of an Nd: YAG laser with a Q switch is used, conditions of an oscillation frequency of 10 kHz, an output of 8 to 11 W, and a beam diameter of about 100 μm are preferable. As a result, the through hole 12 is formed in the passivation film 9 and at the same time a part of the first semiconductor layer 2 of the silicon substrate 1 is also removed, so that the surface shape of the silicon substrate 1 can be made concave. Become. Further, due to the heat of the laser beam irradiation, the aluminum oxide of the passivation film 9 is vaporized, and at the same time, the silicon vaporized in a part of the first semiconductor layer 2 of the silicon substrate 1 is oxidized into silicon oxide. A first protective film 11 having at least a mixture of aluminum oxide and silicon oxide is formed by being deposited on the passivation film 9 on the second main surface 1b side.

The slut holes 12 are provided in a circular shape or a straight shape in a plan view. When the slut holes 12 are provided in a circular shape, the diameter is about 30 to 150 [mu] m, and about 100 to 500 holes per 1 cm < ² > are uniformly distributed. To do.

  Next, as shown in FIGS. 7B and 7C, an electrode forming step is performed. The first electrode 6 (first output extraction electrode 6a, first current collecting electrode 6b), the second electrode 7 and the third electrode 8 are formed as follows.

  First, as shown in FIG. 7B, the first electrode 6 is formed using the first paste 17. The first paste 17 includes, for example, at least one of silver and copper as a main component of the conductive component. In this case, a metal powder such as silver (for example, a powder having a particle size of about 0.05 to 20 μm, preferably about 0.1 to 5 μm) is added to the conductive paste in an amount of 70 to 85 mass% of the total mass of the conductive paste. To be included. As the conductive paste, a kneaded glass frit and an organic vehicle is used. The organic vehicle is obtained, for example, by adding a resin component used as a binder to an organic solvent. As the binder, an acrylic resin or an alkyd resin can be used in addition to a cellulose resin such as ethyl cellulose. As the organic solvent, for example, diethylene glycol monobutyl ether acetate, terpineol or diethylene glycol monobutyl ether can be used. The content of the organic vehicle may be about 5 to 20% by mass of the total mass of the conductive paste. The glass frit component may be, for example, lead glass as a glass material. What is necessary is just to contain about 2-15 mass% of glass frit with respect to the electroconductive paste total mass. First, the first paste 17 is applied to the first main surface 1a of the substrate 1 using screen printing. After this application, the solvent is evaporated and dried at a predetermined temperature.

  The second electrode 7 which is the second main surface 10b side electrode is a conductive paste (second paste 18) containing metal powder, organic vehicle, glass frit and the like composed of silver (or silver and copper) as a main component. It is produced using. The component of the second paste 18 may be the same as that of the first paste 17. As a method for applying the second paste 18, for example, a screen printing method or the like can be used. After this application, the solvent is evaporated and dried at a predetermined temperature.

  Further, as shown in FIG. 7C, the third electrode 8 and the contact portion 8 a are formed using a third paste 19. The 3rd paste 19 uses what contains aluminum as a main component. In this case, the conductive paste contains aluminum powder (for example, a particle size of about 0.05 to 20 μm, preferably about 0.1 to 5 μm) about 65 to 80% by mass of the total mass of the conductive paste, A kneaded glass frit and an organic vehicle are used. The organic vehicle is obtained, for example, by adding a resin component used as a binder to an organic solvent. As the binder, an acrylic resin or an alkyd resin is used in addition to a cellulose-based resin such as ethyl cellulose. As the organic solvent, for example, diethylene glycol monobutyl ether acetate, terpineol or diethylene glycol monobutyl ether is used. The organic vehicle should just contain about 0.05-10 mass% of electroconductive paste total mass. As the glass frit, for example, lead-free glass can also be used. What is necessary is just to make glass frit contain about 2-15 mass% in an electrically conductive paste. This third paste 19 is superimposed on the outer periphery of the already applied second paste 18 and is substantially the same as the first protective film 11 except for the outer periphery of about 0.3 to 2 mm from the end of the silicon substrate 1. Apply over the entire surface. As a coating method, a screen printing method or the like can be used. By applying the third paste 19, the third paste 19 is also filled into the through hole 12. After this application, the solvent may be evaporated and dried at a predetermined temperature.

  Thereafter, the substrate 1 on which the first paste 17, the second paste 18, and the third paste 19 are applied has a maximum temperature of about 700 to 900 ° C. in the baking furnace, and the maximum temperature is about 0.1 seconds to several tens of seconds. Maintain and fire. As a result, each conductive paste is sintered to form the first electrode 6, the second electrode 7, the third electrode 8, and the contact portion 8a as shown in FIG. By this firing, the first paste 17 fires through the antireflection film 5 and is connected to the n-type second semiconductor layer 3 on the first main surface 1a of the silicon substrate 1, so that the first electrode 6 is formed. The third paste 19 is also connected to the p-type first semiconductor layer 2 on the second main surface 1 b at the end of the through hole 12, and the third electrode 8 is formed. Along with the formation of the contact portion 8a, the BSF layer 4 is also formed. Further, the second paste 18 is also baked to form the second electrode 7. However, since the second paste 18 and the third paste 19 on the first protective film 11 are blocked by the first protective film 11, there is almost no influence on the passivation film 9.

  In addition, this embodiment is not limited to the content mentioned above. For example, the formation of the passivation film 9 may be performed after the formation of the antireflection film 5, and the passivation film 9 may be provided on or below the antireflection film 5. The passivation film 9 only needs to contain at least aluminum oxide, and may be a laminated film of aluminum oxide and silicon oxide, for example. Further, the electrode forming step is performed by baking the first paste and the second paste for forming the first electrode 6 and the second electrode 7 having similar components, and then forming the third electrode 8. The third paste may be fired separately.

<Other embodiments>
Next, another embodiment will be described. A description of portions common to the above-described embodiment is omitted.

As shown in FIG. 8, the solar cell element 10 in the present embodiment further includes a second protective film 20 disposed between the passivation film 9 and the first protective film 11. By further providing the second protective film 20, the passivation film 9 can be more reliably protected. In this case, after forming the second protective film 20 on the passivation film 9, the first protective film 11 may be formed by forming the through hole 12 described in the above embodiment. The second protective film 20 preferably includes at least one of silicon nitride and silicon oxide. Silicon nitride and silicon oxide can be formed by a method different from the first protective film 11 such as a sputtering method, an ALD method, or a PECVD method. For this reason, even when a pinhole or a thin portion is formed in the first protective film 11, the second protective film 20 compensates for this portion, and the passivation film 9 can be more reliably protected. In particular, when the second protective film 20 is made of silicon nitride, the thermal expansion coefficient can be made close to that of the silicon substrate 1, so that the adhesion with the passivation film 9 can be improved. Note that the thermal expansion coefficient of silicon nitride is about 2.6 × 10 ⁻⁶ / ° C.

In addition, when the 2nd protective film 20 consists of silicon oxides, it is good to form using the ALD method excellent in the coverage, for example. If the second protective film 20 is manufactured by the ALD method, the passivation film 9 may be easily manufactured using the same chamber after the passivation film 9 is manufactured by the ALD method. As a raw material gas by the ALD method, for example, a silicon raw material such as bisdiethylaminosilane (BDEAS) or N, N, N ′, N ′, tetraethylsilanediamine gas, and ozone (O ₃ ) or water vapor is used. I can make a film.

  Here, when the second protective film 20 is made of silicon nitride or silicon oxide, the film thickness of the second protective film 20 is preferably thinner than that of the passivation film 9. As a result, the negative fixed charge of aluminum oxide forming the passivation film 9 becomes more dominant than the positive fixed charge of silicon nitride and silicon oxide, so that the passivation effect of the passivation film 9 is hardly lowered. In this case, the thickness of the second protective film 20 may be about 8 to 190 nm.

1: Silicon substrate 1a: First main surface 1b: Second main surface 1c: Side surface 2: First semiconductor layer (p-type semiconductor region)
3: Second semiconductor layer (n-type semiconductor region)
4: BSF layer 5: Antireflection film 6: 1st electrode 6a: 1st output extraction electrode 6b: 1st current collection electrode 7: 2nd electrode 8: 3rd electrode 8a: Contact part 9: Passivation film 10: Solar cell Element 10a: First main surface 10b: Second main surface 10c: Side surface 11: First protective film 12: Through hole 14: Peripheral portion 15: Center portion 17: First paste 18: Second paste 19: Third paste 20 : Second protective film

Claims (9)

On the other hand, a silicon substrate having a p-type semiconductor region on the main surface;
A passivation film comprising aluminum oxide disposed on the p-type semiconductor region;
A first protective film having a mixture of silicon oxide and aluminum oxide disposed on the passivation film;
A solar cell element comprising: a plurality of conductor contact portions that penetrate each of the passivation film and the first protective film and connect to the silicon substrate.   2. The solar cell element according to claim 1, wherein the first protective film has aluminum oxide uniformly in a matrix phase of silicon oxide.   The solar cell element according to claim 1 or 2, wherein one end portion of the contact portion is disposed in a concave portion provided in the silicon substrate.   The solar cell element according to any one of claims 1 to 3, wherein a second protective film is disposed between the passivation film and the first protective film.   The solar cell element according to claim 1, wherein the second protective film includes at least one of silicon nitride and silicon oxide.   The first protective film is thicker between the two adjacent contact portions than the second region located in the center between the two adjacent contact portions, rather than the first region located around each contact portion. The solar cell element according to any one of claims 1 to 5. On the other hand, a method for producing a solar cell element comprising a silicon substrate having a p-type semiconductor region on the main surface,
Disposing a passivation film containing aluminum oxide on the p-type semiconductor region of the silicon substrate;
A plurality of holes are formed in the passivation film by irradiating a plurality of portions of the passivation film with a laser beam reaching the surface of the silicon substrate in an atmosphere containing oxygen, and a silicon oxide film is formed on the passivation film. And disposing a first protective film having a mixture of aluminum oxide;
Disposing a contact portion of a conductor in the hole of the passivation film and on the surface of the semiconductor substrate exposed by irradiation with the laser beam.   The method for manufacturing a solar cell element according to claim 7, wherein the step of forming the first protective film forms a plurality of concave portions in the silicon substrate by irradiation with the laser beam.   The method of manufacturing a solar cell element according to claim 8, wherein the step of arranging the contact portion includes arranging one end portion of the contact portion in the concave portion of the silicon substrate.