WO2012032743A1 - Photoelectric conversion element and solar cell - Google Patents

Photoelectric conversion element and solar cell Download PDF

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Publication number
WO2012032743A1
WO2012032743A1 PCT/JP2011/004903 JP2011004903W WO2012032743A1 WO 2012032743 A1 WO2012032743 A1 WO 2012032743A1 JP 2011004903 W JP2011004903 W JP 2011004903W WO 2012032743 A1 WO2012032743 A1 WO 2012032743A1
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photoelectric conversion
particles
conversion element
concavo
main surface
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PCT/JP2011/004903
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French (fr)
Japanese (ja)
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小林　信行
紀美雄 市川
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富士フィルム株式会社
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022466—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
    • H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention relates to a crystalline silicon photoelectric conversion element and a solar cell using the same.
  • Crystalline Si solar cells using a single crystal Si or polycrystalline Si substrate as a photoelectric conversion layer have been put into practical use.
  • the surface of the Si substrate on the sunlight receiving side is uneven, which is called a textured structure, in order to efficiently reflect sunlight into the photoelectric conversion layer by suppressing the reflection of sunlight on the substrate surface.
  • a structure is formed.
  • the wet etching method using a sodium hydroxide aqueous solution is used for monocrystalline Si and the wet etching method using a mixed solution of hydrofluoric acid and nitric acid is used for polycrystalline Si for forming a texture structure.
  • FIG. 8A shows a surface SEM image of a single crystal Si texture structure used in a commercially available photoelectric conversion cell
  • FIG. 8B shows a surface SEM image of a polycrystalline Si texture structure used in a commercially available photoelectric conversion cell.
  • FIG. 9 shows the result of measurement by the inventor of the wavelength dependence of the reflectance of the photoelectric conversion cell of FIG. As shown in the figure, it is difficult to obtain a texture structure with good in-plane uniformity and reproducibility due to the dependency of wet etching on the crystal orientation, especially in the case of polycrystal.
  • Patent Document 4 discloses dry etching conditions capable of forming a texture structure with a high yield.
  • the surface electrode needs to be an electrode locally removed from the antireflection film and electrically connected to the photoelectric conversion layer.
  • the resistance between the photoelectric conversion layer and the electrode increases. Therefore, even if the incident efficiency is increased by inserting an antireflection film, it is difficult to obtain a high photoelectric conversion efficiency due to a decrease in photoelectric conversion efficiency accompanying an increase in resistance value.
  • a conductive paste having a fire-through property is used to penetrate the antireflection film by high-temperature baking. Therefore, there is a problem that thermal deformation of the substrate is likely to occur and yield is likely to be reduced.
  • the present invention has been made in view of the above circumstances, and an object thereof is to provide a photoelectric conversion element that has high incidence efficiency of sunlight and photoelectric conversion into a photoelectric conversion layer and can be manufactured with high yield. It is.
  • the photoelectric conversion element of the present invention comprises a photoelectric conversion layer formed by diffusing other conductivity type impurities on one main surface side of one conductivity type crystalline silicon substrate to form a pn junction, and a transparent layer formed on the one main surface.
  • a photoelectric conversion element comprising a photoconductive layer and a back electrode layer formed on a main surface opposite to the one main surface of the photoelectric conversion layer,
  • the one main surface of the photoelectric conversion layer is a textured structure surface having a concavo-convex structure having a large number of needle-like convex portions that suppress reflection of sunlight on the main surface,
  • the translucent conductive layer is formed directly on the textured structure surface.
  • the term “needle-shaped convex portion” means that the ratio of the cross-sectional area of the tip portion to the bottom portion of the convex portion on a surface substantially parallel to the main surface opposite to the texture structure surface of the substrate is 20% or less. It means a convex part. Moreover, the bottom part of a convex part shall mean the part located in the same height as the lowest part of the recessed part near the front-end
  • the reflectance of sunlight on the texture structure surface is preferably 5% or less, and more preferably 3% or less.
  • the sunlight means light having a wavelength of 400 nm to 1200 nm, which is an absorption wavelength band of Si.
  • the reflectance of sunlight is defined as the average integrating sphere reflectance of light in the above wavelength region.
  • the arithmetic average surface roughness Ra of the texture structure surface is preferably 100 nm or more.
  • the convex portion preferably has an average height of 1 ⁇ m or more.
  • the “average height of the convex portions” means the arithmetic average height of the convex portions.
  • a convex portion higher than the arithmetic average height may be included within a range of 40% or less.
  • the measurement of the height of a convex part shall be measured by AFM.
  • the texture structure surface includes, as a mask material, first particles having resistance to dry etching that forms the concavo-convex structure, second particles having a lower resistance than the first particles, and the first particles.
  • a step of arranging a mask material on one main surface of the silicon substrate a step of forming the concavo-convex structure by dry etching on the main surface on which the mask material is arranged,
  • the concavo-convex structure can be formed by performing a cleaning step including a treatment of immersing microbubbles and ultrasonic waves in dilute hydrofluoric acid supplied intermittently or continuously.
  • the microbubble generally means a fine bubble having a diameter of the order of microns (for example, Hirofumi Taisei "All about microbubbles", Nihon Jitsugyo Publishing Co., Ltd. (2006), Satoshi Kamiyama, Makoto Miyamoto. (See “Microbubble World” Industrial Research Committee (2006)).
  • the first particles are preferably inorganic particles, and more preferably particles containing SiO 2 as a main component.
  • the second particles are preferably resin particles, and are preferably particles mainly composed of an acrylic resin. It is preferable that the binder is mainly composed of a water-soluble polymer or a water-dispersible polymer.
  • the one conductivity type crystalline silicon substrate is made of polycrystalline silicon (may contain inevitable impurities).
  • the solar cell of the present invention comprises the above-described photoelectric conversion element of the present invention.
  • the main surface on the light receiving side of the photoelectric conversion layer is a texture structure surface having a large number of needle-like convex portions that suppress reflection of sunlight
  • a translucent conductive layer is directly formed on the texture structure surface.
  • the texture structure surface having a large number of needle-like convex portions can suppress the reflection of sunlight with high efficiency, so that almost the entire texture structure surface of the photoelectric conversion layer is provided without providing an antireflection film.
  • a surface electrode translucent conductive layer
  • sunlight that is incident on the texture structure surface with high incidence efficiency can be used with high photoelectric conversion efficiency, and charges can be taken out from almost the entire texture structure surface.
  • the resistance between the photoelectric conversion layer and the electrode is remarkably reduced as compared with a configuration in which electric charges are extracted by the electrode. Furthermore, since local electrode formation is unnecessary, there is no need for high-temperature firing. Therefore, according to the present invention, it is possible to provide a photoelectric conversion element that has high incident light utilization efficiency and photoelectric conversion efficiency and can be manufactured with a high yield.
  • FIG. 1 Thickness direction sectional drawing which shows the structure of the photoelectric conversion element of one Embodiment concerning this invention
  • (b) is the figure which expanded the uneven structure of the texture structure surface
  • (A)-(h) is the figure which showed typically the flow of the manufacturing method of the photoelectric conversion element of this invention shown by FIG.
  • (A) is a surface SEM photograph of the texture structure after performing ultrasonic cleaning in pure water after forming irregularities by dry etching, and (b) is when the ultrasonic cleaning time of (a) is extended by XX.
  • Surface SEM photo of the texture structure (c) is a surface SEM photo of the texture structure when the ultrasonic cleaning time is further extended for XX minutes.
  • (A) And (b) is the surface SEM image at the time of wash
  • (A) is 5000 times magnification
  • (b) is 10,000 times magnification.
  • (A) shows the wavelength dependence of the reflectance of the cut surface of the polycrystalline silicon substrate obtained by wire saw cutting from the polycrystalline silicon ingot, and (b) shows the wavelength dependence of the reflectance of the texture structure of Example 1. Illustration The figure which shows the wavelength dependence of the reflectance of the texture structure surface at the time of using a single-crystal Si substrate (when it is unprocessed, a cut surface).
  • (A) is a cut surface of a single crystal silicon substrate obtained by wire saw cutting from a single crystal silicon ingot
  • (b) is a textured structure surface when alkali etching cleaning is performed on the surface of (a)
  • (c) is ( (b) a structure provided with a SiN antireflection film on the surface
  • (d) is a textured structure surface in which a concavo-convex structure is formed by dry etching using a mask material in the present invention, and immersion treatment in diluted hydrofluoric acid is performed
  • e) is the texture structure surface of Example 3
  • (f) is the texture structure surface of Example 4.
  • (A) And (b) is a figure which shows the relationship between the reflectance of a texture structure with respect to the light of wavelength 1000nm, and surface roughness.
  • (A) is a single crystal Si system
  • (b) is a polycrystal Si system.
  • FIG. 1A is a schematic cross-sectional view in the thickness direction showing the configuration of the photoelectric conversion element of this embodiment
  • FIG. 1B is an enlarged schematic view of a part of the concavo-convex structure in FIG.
  • the scales of the respective parts are shown as being appropriately changed.
  • the photoelectric conversion element 1 is composed of a crystalline Si substrate 10 having a textured structure surface 10t (surface 10s) having a concavo-convex structure 10t having a large number of needle-like convex portions 101.
  • a layer 10 a translucent conductive layer 30 formed directly on the front surface 10s, and a back electrode layer 20 formed on the back surface 10r of the photoelectric conversion layer 10 (a main surface 10r opposite to the one main surface 10s); , And a takeout electrode 40 formed on the translucent conductive layer (surface electrode) 30.
  • a large number of needle-like convex portions 101 forming the concavo-convex structure 10t have a cross-sectional area sb at the bottom of the convex portion 101 on a surface substantially parallel to the back surface 10r of the photoelectric conversion layer 10.
  • tip part of the convex part 101 with respect to the convex part is 20% or less.
  • the bottom portion of the convex portion 101 means a portion located at the same height as the lowermost portion of the concave portion 102 closer to the tip portion among the adjacent concave portions 102. .
  • the cross-sectional area st at the tip means the remaining part protected by the mask during etching.
  • the photoelectric conversion layer 10 has a two-layer structure of a first conductivity type (p-type) Si layer 11 and a second conductivity type (n-type) Si layer 12, and a pn junction is formed in the photoelectric conversion layer 10.
  • p-type first conductivity type
  • n-type second conductivity type
  • the photoelectric conversion layer 10 may be crystalline Si, and may be single crystal or polycrystalline.
  • the reflectance of sunlight in the texture structure of a crystalline Si photoelectric conversion element by conventional wet etching is as high as about 10% for a single crystal and about 25% for a polycrystal, and is also dry etching. He stated that the reflectance of sunlight could not be reduced sufficiently even in the texture structure formed by the above. In addition, it was described that it is difficult to obtain a texture structure with good in-plane uniformity and reproducibility in the case of polycrystal due to the crystal orientation dependence of wet etching.
  • the photoelectric conversion element 1 has a texture structure surface with a very low reflectivity with single-digit reflectivity in the case of either single crystal or polycrystal as shown in Examples 5 and 6 to be described later. For this reason, in particular, when applied to polycrystalline Si having problems in low reflectance and in-plane uniformity reproducibility, a greater effect can be obtained.
  • the photoelectric conversion layer 10 has a two-layer structure of a first conductivity type (p-type) Si layer 11 and a second conductivity type (n-type) Si layer 12. It does not restrict
  • p-type dopant boron, which is a group III element, and phosphorus, which is a group V element, are preferably used as the n-type dopant.
  • the back electrode layer 20 is not particularly limited, and any metal electrode can be used, but it is preferable to use highly conductive aluminum, silver, or the like.
  • the translucent conductive layer 30 (front surface electrode) is a layer that captures light and functions as an electrode through which the charge generated in the photoelectric conversion layer 10 flows, paired with the back electrode layer 20. The film is directly formed on the textured structure surface of the uneven structure 10t.
  • the light-transmitting conductive layer 30 is not particularly limited, but ITO (indium tin oxide), metal-doped zinc oxide (n-ZnO such as ZnO: Al), and the like are preferable.
  • the film thickness of the translucent conductive layer 30 is not particularly limited, and is preferably 50 nm to 2 ⁇ m.
  • the electrode in which the coating film-forming of silver, aluminum, etc. is possible is preferable.
  • the film thickness of the extraction electrode 40 is not particularly limited and is preferably 0.1 to 3 ⁇ m.
  • the texture structure surface uneven structure 10t includes a large number of needle-like convex portions 101 at a fine pitch.
  • sunlight is well confined in the photoelectric conversion layer 10
  • the reflectance of the light on the texture structure surface is significantly reduced as compared with the conventional texture structure, and is incident on the texture structure surface.
  • Light can be incident on the photoelectric conversion layer 10 with high efficiency.
  • a reflectance of 5% or less is achieved, and 1% is realized in the lowest reflectance (see Examples described later, FIGS. 5 and 6).
  • FIG. 4 is a surface SEM image of the textured surface uneven structure 10t obtained in the examples described later, and shows the magnifications changed between (a) and (b). From the SEM image shown in FIG. 4, it is confirmed that the pitch of the convex portions 101 of the concavo-convex structure 10t is 100 to 500 nm or less, but it is recognized that there is variation in the plane.
  • the average height of the convex portions 101 is preferably higher because a large light confinement effect can be obtained. However, a longer formation time is required to increase the height of the convex portions 101.
  • the processing time (tact time) of the formation process of the convex portion 101 is preferably short from the viewpoint of running cost. Therefore, it is preferable that the average height is low as long as a desired reflectance can be realized.
  • the concavo-convex structure 10t of the present embodiment can be configured to include a large number of needle-like convex portions 101 at a fine pitch, so if the average height of the convex portions 101 is about 1 ⁇ m, A large light confinement effect is obtained, and the concavo-convex structure 10t having a sufficiently low reflectance can be obtained.
  • the individual heights h of the large number of convex portions 101 have variations similar to the pitch.
  • the maximum height roughness Rz is preferably in the range of 0.9 ⁇ m to 3.0 ⁇ m.
  • the features of the concavo-convex structure 10t including variations in pitch and height of the large number of convex portions 101 are peculiar to the structure obtained by the method for forming the concavo-convex structure 10t found by the present inventors. Below, the manufacturing method of the photoelectric conversion element 1 is demonstrated.
  • FIGS. 2A to 2H are schematic cross-sectional views showing a flow of a method for manufacturing the photoelectric conversion element 1.
  • FIG. 1 a p-type crystalline silicon substrate (wafer) 10 having a smooth surface on one principal surface (surface 10s) is prepared (FIG. 2A).
  • the silicon substrate 10 is single crystal silicon
  • an ingot formed by a pulling method or the like and in the case of polycrystalline silicon, an ingot obtained by melting and solidifying the raw material in a crucible with a wire saw or the like has a desired thickness (for example, about 300 ⁇ m).
  • the method obtained by slicing into two In addition, in the case of polycrystalline silicon, it can be obtained by pulling up from the melt into a plate shape.
  • the smoothness of the surface 10s which is the formation surface of the concavo-convex structure 10t, is preferably good because it affects the in-plane uniformity of the depth of the concavo-convex when the concavo-convex structure 10t, which is a subsequent process, is formed.
  • pn junction formation described later is generally performed by a technique in which a dopant of the other conductivity type is diffused from above the substrate of one conductivity type. Therefore, the thickness of the conductive layer on the lower layer side is on the order of microns, whereas the thickness of the conductive layer on the upper layer side is a very thin layer on the order of several hundred nm.
  • a technique for cutting out an ingot using a wire saw is generally used for a silicon substrate.
  • a wire saw is used for cutting, a micron order damage is generally left on the cut surface. .
  • the concavo-convex structure 10t which is a subsequent process, is formed by dry etching while leaving these damages, the damaged portion is more fragile than the undamaged silicon substrate portion.
  • the removal process becomes dominant, and an uneven structure is formed after removing the damage. Therefore, it is difficult to form the concavo-convex structure 10t with a good pattern when forming the concavo-convex structure 10t, and the in-plane uniformity of the concavo-convex shape and depth depends on the in-plane distribution of damage existing on the surface. The variation of the is large.
  • the crystalline silicon substrate 10 used for the manufacture of the photoelectric conversion element 1 is a single crystal or polycrystal, and the substrate cut out by the wire saw is not used as it is, and the wire saw damage is removed. There is a need to.
  • the surface smoothness is good, and there is no damage or unevenness that affects the unevenness forming process by dry etching, such as wire saw damage, it is used without performing the above damage removal treatment. be able to.
  • the uneven structure 10 t includes a plurality of first particles 51 having resistance to dry etching that forms the uneven structure 10 t on one main surface 10 s (surface 10 s) of the crystalline Si substrate 10. Then, a mask material 50 including a plurality of second particles 52 having lower dry etching resistance than the first particles 51 is provided, and irregularities are formed by dry etching using the plurality of first particles as a mask. To be formed.
  • the method for forming the mask material 50 on the surface 10s is not particularly limited, and a sheet-shaped mask material 50 prepared in advance may be used, or the first particles 51 having resistance to the dry etching and the first A liquid composition containing a second particle 52 having a dry etching resistance lower than that of the particle 51 and a binder having a lower dry etching resistance than that of the first particle 51 is prepared, and the liquid composition is applied to the surface 10s. It may be formed by coating.
  • a first particle 51 having resistance to the dry etching which is a raw material liquid for the mask material 50, and a second particle 52 having lower dry etching resistance than the first particle 51
  • a liquid composition containing a plurality of particle groups each including a binder and a binder (binder) having lower dry etching resistance than the first particles 51 is prepared.
  • the particle group is not limited to the above two types of particles, and may include other types of particles.
  • the first particles have resistance to etching and are difficult to be etched by the etching process, whereas the second particles are easily etched by the dry etching process.
  • the etching rate for example, when the etching rate ER is “second particle etching rate / first particle etching rate”, it is preferable that ER> 5, and further ER> 10.
  • the first particles are not particularly limited as long as they have etching resistance, and examples thereof include inorganic particles, organic dye / pigment particles containing inorganic elements, latex particles and capsule particles containing inorganic elements, and the like. Among these, as the first particles, inorganic particles are preferable from the viewpoints of etching resistance, availability, and handleability.
  • the inorganic particles include non-metallic materials such as titanium oxide, silica (SiO2), calcium carbonate, and strontium carbonate, metals, and semiconductor materials.
  • the metal includes Cu, Au, Ag, Sn, Pt, Pd, Ni, Co, Rh, Ir, Al, Fe, Ru, Os, Mn, Mo, W, Nb, Ta, Bi, Sb, and Pb.
  • Examples thereof include a single metal selected from the group or an alloy material composed of one or more of the metals selected from the group.
  • the semiconductor examples include Si, Ge, AlSb, InP, GaAs, GaP, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, PbS, PbSe, PbTe, SeTe, and CuCl.
  • the microcapsule etc. which included these inorganic particles and used silica as the wall membrane material are mentioned.
  • organic dye / pigment particles containing inorganic elements examples include metal element-containing azo dye particles and metal element-containing phthalocyanine dye particles.
  • latex particles and capsule particles containing inorganic elements include particles in which acrylic latex is coated with colloidal silica, particles in which acrylic latex is coated in silicate, particles in which polystyrene latex particles are coated with silica, and the like. Is not particularly limited as long as it has a difference in etching resistance with the first particles described above, but resin particles can be preferably used because of low etching resistance and easy handling.
  • the resin particles are preferably thermoplastic resin particles, and examples thereof include acrylic resin particles, polyethylene resin particles, polypropylene resin particles, polyamide particles, polyimide particles, polyethylene terephthalate resin particles, polystyrene particles, and silicone resins.
  • the average particle size of the first particles and the second particles may be the same, but the average particle size of the second particles is preferably larger than the first particles. Thereby, it becomes easy to ensure the particle
  • the average particle size of the first particles and the second particles is 0.05 ⁇ m to 1 ⁇ m from the viewpoint of thinning the particle layer to be formed and obtaining the concavo-convex structure 10 t that satisfactorily reduces the reflectance of sunlight.
  • 0.2 ⁇ m to 0.5 ⁇ m is more preferable.
  • the average particle diameter of a particle means the particle diameter obtained by a dynamic light scattering method
  • the measuring method is as follows.
  • the dynamic light scattering method it is possible to measure the particle size and particle size distribution in the submicron range or less, and the particles to be measured or dispersions thereof are dispersed by a known method such as ultrasonic irradiation in a medium. Then, after diluting it appropriately, a measurement sample is obtained.
  • the cumulative frequency curve of the particle size obtained by the dynamic light scattering method the particle size having a cumulative frequency of 50% is defined as the average particle size, and the ratio of the 10% cumulative particle size to the 90% particle size is similarly determined.
  • An example of a measuring apparatus that employs such a principle, which can be used as a distribution index, is LB-500 manufactured by Horiba, Ltd.
  • the particle size distribution of the first particles and the second particles is preferably 2 to 50, more preferably 2 to 10.
  • the maximum average particle size does not become too large, a flat particle layer is easily obtained, and uniform surface treatment is easily realized.
  • the blending amount of the first particles and the second particles is preferably about the same or more of the second particles.
  • the coverage of the first particles on the film-formed surface of the liquid composition is 30% or more and 70%.
  • the following is preferable. Therefore, the blending amount, blending ratio, and average particle size of the first particles and the second particles in the liquid composition are designed so that such a coverage can be achieved.
  • the coverage is the ratio of the first particles covering the substrate to be processed when the particle layer is formed on the substrate to be processed, that is, the area of the first particle projected onto the substrate when viewed from the etching direction. Indicates the percentage. This coverage is measured as follows. After bonding to the substrate to be processed, the surface can be observed using a scanning electron microscope or an optical microscope, and can be calculated from the projected area.
  • binder 53 Although it does not restrict
  • the binder 53 is composed of a polymerizable monomer capable of forming the above polymer material and other components constituting the particle layer to form a liquid composition for surface treatment, and is polymerized by light or heat after coating.
  • a film may be formed by reaction, that is, a particle layer may be formed.
  • Examples of the polymerizable monomer include a (meth) acrylic monomer, a (meth) acrylic acid C1-C12 alkyl ester, and a compound known as a new acrylic modifier with these. it can.
  • Examples of the acrylic modifier include carboxy-containing monomers and acid anhydride-containing monomers.
  • These polymerizable monomer monomers can be polymerized by a known polymerization method, and can be appropriately selected from known materials such as an initiator, a chain transfer agent, an oligomer material, and a surfactant necessary for the polymerization.
  • Examples of the polymerizable monomer include known epoxy monomers and isocyanate monomers.
  • those having a glass transition temperature of ⁇ 100 to 50 ° C., a number average molecular weight of 1,000 to 200,000, preferably 5,000 to 100,000, and a degree of polymerization of about 50 to 1000 are preferable.
  • examples of such include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal,
  • More preferable binders include polyvinyl alcohol or derivatives thereof, cellulose derivatives (polyvinyl pyrrolidone, carboxymethyl cellulose, hydroxyethyl cellulose, etc.), natural polysaccharides or derivatives thereof (starch, xanthan gum, alginsan, etc.) that are readily water-soluble.
  • cellulose derivatives polyvinyl pyrrolidone, carboxymethyl cellulose, hydroxyethyl cellulose, etc.
  • natural polysaccharides or derivatives thereof starch, xanthan gum, alginsan, etc.
  • Gelatin water-dispersible urethane, acrylic polymer latex and the like are also included.
  • the blending amount of the binder is appropriately set according to the dispersibility of the particle group. For example, it is preferably 5% by weight to 50% by weight, more preferably 10% by weight to 30% by weight with respect to the particle group. is there.
  • the liquid composition contains a dispersant that can stably disperse the particle group, and, for example, a surfactant and a solvent that adjust the viscosity and surface tension of the coating liquid during production. Also good.
  • phenylphosphonic acid specifically “PPA” manufactured by Nissan Chemical Co., Ltd., ⁇ -naphthyl phosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones, various Silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof can be used.
  • nonionic surfactants such as alkylene oxide, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocyclics, phosphonium or sulfoniums, etc.
  • Cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphate ester group, amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohol, alkyl Bedin type amphoteric surfactants and the like can also be used.
  • polyoxyethylene alkylphenyl ether polyoxyalkylene block copolymer, polyoxyethylene alkylphenyl ether having a polymerizable unsaturated bond such as an allyl group, or the like may be selected.
  • These dispersants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.).
  • These dispersants and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, side reaction products, decomposition products, and oxides in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.
  • the solvent constituting the liquid composition is selected from solvents that dissolve the binder according to the binder type. Specifically, for example, when applying a water-soluble binder as a binder, it is preferable to apply an aqueous solvent as a solvent from the viewpoint of environmental load and simplification of equipment.
  • aqueous solvent examples include water and lower alcohols (methanol, ethanol, butanol, isopropyl alcohol, etc.).
  • solvent water is most preferable.
  • a liquid composition is obtained by stirring and mixing so that the particle group is dispersed in a substantially uniform manner.
  • a method of stirring and mixing a method of mixing and dispersing with a stirring blade such as a dissolver that gives high-speed shearing, a dispersing device such as an ultrasonic disperser It is preferable to use a method of preparing by mixing and dispersing with the method described above.
  • the liquid composition prepared as described above is applied and formed on the surface of the crystalline Si substrate 10 where the concavo-convex structure 10t is formed, as shown in FIG.
  • the film forming method is not particularly limited, and examples of the coating method include spray method, spin coating method, dip method, roll coating method, plate coating method, doctor blade method, and screen printing method. The method and the spray method are preferable.
  • the coating thickness is preferably 100 nm to 1000 nm, more preferably 300 nm to 600 nm.
  • the spin coating method it is preferable to make the sample stage the same as the crystalline Si substrate so that the mask material does not go around the back surface of the wafer. Moreover, when it wraps around the back surface, it is preferable to wash.
  • a polymerizable monomer capable of forming the polymer material may be used as the binder 53.
  • a liquid composition is mixed in the binder 53 with other components constituting the particle layer excluding the solvent described later, and this liquid composition is applied to the film formation surface 10s and then polymerized by light or heat.
  • the mask material 50 can be formed.
  • polymerizable monomers examples include (meth) acrylic monomers used in combination with (meth) acrylic acid C1 to C12 alkyl esters, and compounds known as acrylic modifiers that are compatible with these. it can.
  • acrylic modifier examples include carboxy-containing monomers and acid anhydride-containing monomers.
  • These polymerizable monomer monomers can be polymerized by a known polymerization method, and can be appropriately selected from known materials such as an initiator, a chain transfer agent, an oligomer material, and a surfactant necessary for the polymerization.
  • the polymerizable monomer examples include known epoxy monomers and isocyanate monomers.
  • a dry etching process is performed on the mask material 50 to form the concavo-convex structure 10t.
  • the dry etching method is not particularly limited, but reactive ion etching (RIE) in which etching is performed by ionizing / radicalizing the reactive gas with plasma is preferable because the etching gas is highly straight and fine patterning is possible.
  • RIE reactive ion etching
  • ICP which is inductive coupling type reactive ion etching is preferable.
  • etching gas chlorine-based gas, fluorine-based gas, and bromine-based gas are preferable, and sulfur hexafluoride (SF 6 ) gas is more preferable.
  • SF 6 sulfur hexafluoride
  • a mixed gas of sulfur hexafluoride gas and oxygen gas is used, a finer gas is used. Since an uneven structure can be obtained, it is more preferable.
  • the binder 53 constituting the mask material 50 excluding the region covered with the first particles 51 is etched and the second particles 52 is also etched.
  • the etched region becomes a concave portion
  • the non-etched region becomes a convex portion
  • the concavo-convex structure 10 t is formed on the surface of the crystalline Si substrate 10.
  • the mask material 50 is etched in the region to be etched.
  • Conditions for performing the dry etching process are appropriately set according to the thickness and type of the mask material 50 (type of binder 53, type of particle group, etc.). For example, in the dry etching process using the mask material 50 used in Example 1 to be described later, as a result of examining the relationship between the processing time and the reflectance, the reflectance of 6% was achieved in the processing time of 6 minutes, and the processing time of 9 minutes. Then, a reflectance of 3% was achieved. Further, the reflectance was about 3% even at a processing time of 10 minutes. From these results, it was confirmed that the dry etching processing time determined to be able to achieve a reflectance of about 5% was about 8 minutes.
  • the dry etching treatment time is preferably 8 minutes or more, more preferably 8 to 10 minutes, and further preferably 8 to 9 minutes (dry etching apparatus and other devices). See Example 1 for conditions). However, the time can be shortened by increasing the power during etching.
  • FIG. 3 (a) shows a surface SEM photograph after the formation of irregularities by dry etching (about 9 minutes), followed by ultrasonic cleaning (pure water, 5 minutes).
  • the silica residue is clearly confirmed in the upper right part.
  • the thermal diffusion of the dopant gas for example, phosphoric acid gas
  • the n-type dopant for example, phosphorus
  • the etching residue and plasma damage are removed before the diffusion of the n-type dopant.
  • the etching residue is mainly the second particles (particles having high etching resistance), and other reactants (such as sulfur and fluorine compounds) with the etching gas. These residues are mainly on the convex portions 101 of the concavo-convex structure 10t, but may also remain in the concave portions 102.
  • the present inventor has earnestly studied to achieve both a cleaning effect and damage reduction. As a result, the inventors have found two cleaning methods that can satisfactorily remove the etching residue and plasma damage and achieve high photoelectric conversion efficiency. The cleaning method will be described below.
  • First cleaning method dry etching using hydrogen gas
  • dry etching with hydrogen gas is performed from above the uneven structure 10t by dry etching (arrow ⁇ in the figure).
  • the dry etching with hydrogen gas (hereinafter referred to as “hydrogen etching”) is different from the hydrogen reduction treatment for removing the natural oxide film on the surface of the silicon substrate by hydrogen reduction. And a process for removing plasma damage.
  • hydrogen etching since hydrogen is applied to the silicon substrate surface, removal of the oxide film on the surface may be performed during the same process.
  • the method of dry etching is not particularly limited, and it is preferable to select a method that can be carried out in the same apparatus as that for forming the concavo-convex that is the previous step because of ease of process.
  • the conditions for hydrogen etching are not particularly limited. It is preferable that the etching residue and plasma damage be removed well and the etching can be performed with high running cost and high reliability. Examples of such etching conditions include a hydrogen flow rate of 100 sccm, a gas pressure of 3 Pa, a high frequency output (power) of 100 W, and an etching time of 5 minutes.
  • the etching resistance is in the order of etching residue (for example, silica) ⁇ plasma damage portion ⁇ crystal Si. Therefore, even if the etching residue is sufficiently removed, the projection 101 of the concavo-convex structure 10t is not likely to be etched and adversely affect the reflectance.
  • etching residue for example, silica
  • the stain layer which is plasma damage can also be satisfactorily removed by the dry etching.
  • an alkali solution such as an aqueous sodium hydroxide solution after hydrogen dry etching.
  • a preferable concentration of the alkaline solution is 0.1 to 10 wt%. In such a concentration range, the stain layer can be removed satisfactorily by setting the etching time to 10 seconds to 2 minutes.
  • the surface of the silicon crystal substrate that has been subjected to unevenness formation and surface cleaning is very easily oxidized, and generally an oxide film of SiO 2 is formed.
  • Such an oxide film can be removed by hydrogen dry etching, but in order to further increase the removal rate, it is preferable to immerse in an acid solution such as dilute hydrofluoric acid following hydrogen dry etching.
  • the present inventor performs hydrogen etching for about 3 to 15 minutes after the formation of irregularities by dry etching using the mask material 50, and performs immersion treatment in dilute hydrofluoric acid.
  • the solar reflectance of the concavo-convex structure 10t was successfully reduced to 1%. It has been confirmed that such an effect can be obtained similarly when the Si substrate 10 is single crystal or polycrystalline.
  • second cleaning method ultrasonic cleaning containing microbubbles in dilute hydrofluoric acid
  • an ultrasonic cleaning process is performed in dilute hydrofluoric acid containing microbubbles.
  • the technique of ultrasonically cleaning the etching residue by immersing the concavo-convex structure in dilute hydrofluoric acid is a known technique, and the effect is promoted by dissolving the etching residue with dilute hydrofluoric acid and finely vibrating with ultrasonic waves. .
  • cleaning alone cannot sufficiently and efficiently remove the etching residue and plasma damage existing on the surface of the concavo-convex structure 10t of the present embodiment.
  • the present inventor In order to remove etching residues and plasma damage scattered in the fine concavo-convex structure on the order of submicron, such as the concavo-convex structure 10t of this embodiment, the present inventor not only uses ultrasonic vibration, Considering that it is necessary to apply a physical force to the object to be removed and its surroundings, cleaning is performed while simultaneously supplying microbubbles in a dilute hydrofluoric acid solution in which ultrasonic waves are generated. It has been found that etching residues and plasma damage can be satisfactorily removed in substantially the same manner as in the above cleaning method.
  • the concentration of dilute hydrofluoric acid is preferably 0.5 to 5 wt%.
  • the cleaning time can be shortened as the concentration of dilute hydrofluoric acid is increased, but a lower concentration is preferable from the viewpoint of handleability.
  • a sufficient cleaning effect can be obtained even if the concentration of dilute hydrofluoric acid is relatively low.
  • the diameter of the microbubbles is not particularly limited, but is preferably in the range of 10 to several hundred ⁇ m.
  • the degree of bubble size distribution is not particularly limited. Also included are fine bubbles having a substantially single distribution and fine bubbles having a plurality of distributions of various sizes. It also includes the case where the bubble size varies during the processing step.
  • the component gas in the microbubbles is not particularly limited, and the component gas may be a single component or a mixed component gas, and can be appropriately selected.
  • the component gas of the microbubble includes at least one selected from the group consisting of hydrogen, oxygen, nitrogen, carbon dioxide, ozone, fluorine, chlorine, bromine, iodine, argon, helium, Nitrogen and argon are preferred.
  • the size of the microbubbles is not particularly limited, but a good cleaning effect can be obtained when the bubble diameter is 10 to 100 ⁇ m.
  • the natural oxide film described in the first cleaning method it is necessary to further remove the natural oxide film described in the first cleaning method.
  • the natural oxide film may be removed by immersion in diluted hydrofluoric acid, but cleaning in diluted hydrofluoric acid is performed.
  • the cleaning time is shortened, and the natural oxide film can be removed simultaneously with the cleaning, thereby simplifying the process.
  • the method described in the first cleaning method may be used.
  • both the first cleaning method and the second cleaning method can perform good and highly efficient cleaning, and further, the concavo-convex structure by dry etching using the mask material 50.
  • the formation of 10t it is possible to form a textured structure surface having a large number of needle-like convex portions and capable of suppressing reflection of sunlight with high efficiency regardless of single crystal or polycrystal.
  • neutralization is performed when an alkaline or acidic aqueous solution adheres to the texture structure surface (uneven structure 10t) after cleaning. It is preferable. Furthermore, it is preferable to sufficiently dry the texture structure surface 10s when forming the pn junction in the next step.
  • an n layer is formed by diffusing an n-type dopant (phosphorus or the like) from the textured surface (uneven structure 10t) of the p-type silicon wafer after cleaning, and pn Form a bond.
  • n-type dopant phosphorus
  • phosphorus is thermally diffused by, for example, a gas diffusion method using phosphoryl chloride (POCl 3 ) as a diffusion source to form a pn junction (diffusion temperature is 800 ° C.).
  • pn separation is performed by cutting off the excess p layer and n layer that wrap around the side surface and the back surface.
  • the separation method is not particularly limited, and wet etching or plasma etching with dilute hydrofluoric acid may be employed. Further, when phosphorus is diffused, phosphate glass is generated on the texture structure surface 10s, and therefore, it is preferably removed by immersion in dilute hydrofluoric acid.
  • FIGS. 4A and 4B are surface SEM images of the texture structure 10s obtained by an electron microscope. The magnification is set to 5000 times and 10,000 times. As shown in the figure, neither etching residue nor plasma damage is observed in any of the photographs.
  • the photoelectric conversion element 1 since the etching residue and the plasma damage which become the inhibition factor of pn formation are very few in the texture structure surface 10s, a favorable and substantially uniform pn junction can be formed. Partial loss of the pn junction and in-plane non-uniformity greatly affect the photoelectric conversion efficiency of the photoelectric conversion element. Since the photoelectric conversion element 1 can form a good and substantially uniform pn junction as described above, the sunlight that has entered the photoelectric conversion layer 10 with high efficiency by the texture structure surface 10s has high efficiency. Photoelectric conversion can be performed.
  • the back electrode 20 is formed on the back surface 10r, and then the translucent light that covers the surface substantially uniformly on the textured surface 10s on which the pn junction is formed.
  • the conductive conductive layer 30 is directly formed (FIG. 2G).
  • a method for forming the back electrode 20 and the translucent conductive layer 30 is not particularly limited, but may be a vapor phase method such as a sputtering method, a CVD method, an MOCVD method, an MBE method, or a liquid phase method.
  • the back electrode 20 may be formed by applying a silver paste or an Al paste by a screen printing method or the like and then baking.
  • the translucent conductive layer 30 formed directly on the texture structure surface 10 s can be used as a surface electrode in this way.
  • the surface electrode is translucent, the power generation area can be increased as compared with the conventional comb electrode.
  • the electrode can be formed immediately above the pn junction, the path to the electrode is shortened, so that the series resistance can be reduced. Therefore, highly efficient power generation efficiency can be achieved by these synergistic effects.
  • high-temperature firing can provide a photoelectric conversion element that has high incident light utilization efficiency and high photoelectric conversion efficiency and can be manufactured with high yield.
  • the photoelectric conversion element 1 of this embodiment although it is preferable not to form an antireflection film, it is good also as a structure provided with the antireflection film.
  • the extraction electrode 40 is formed on the surface of the translucent conductive layer 30 to obtain the photoelectric conversion element 1 (FIG. 2 (h)).
  • the extraction electrode 40 is formed by applying and baking after screen printing using Al or silver paste.
  • the mode in which the back electrode 20 is formed first has been described.
  • the back electrode 20 may be formed after the light-transmitting conductive layer 30 is formed or after the extraction electrode 40 is formed. May be.
  • the photoelectric conversion element 1 can be manufactured.
  • the surface electrode (translucent conductive layer) 30 can be formed on substantially the entire textured surface of the photoelectric conversion layer 10 without providing an antireflection film such as SiN.
  • the photoelectric conversion element 1 has high incident light utilization efficiency and photoelectric conversion efficiency, and can be manufactured with a high yield.
  • the photoelectric conversion element 1 can be preferably used for a solar cell or the like. If necessary, a cover glass, a protective film, or the like can be attached to the photoelectric conversion element 1 to form a solar cell.
  • Example 1 a coating liquid for the mask material was prepared. First, a PVA liquid (aqueous solvent) containing 3% by weight of polyvinyl alcohol (PVA) as a binder was prepared. Next, 6 parts by weight of silica (SiO 2 ) particles (SP-03F manufactured by Fuso Chemical Co., Ltd., average particle size: 0.3 ⁇ m) are used as the first particles, and acrylic resin particles are used as the second particles with respect to 100 parts by weight of the PVA liquid.
  • PVA liquid aqueous solvent
  • PVA polyvinyl alcohol
  • a P-type polycrystalline silicon wafer (156 mm square) from which wire saw damage has been removed is coated with a mask material coating solution with a spin coater (1H-360s made by Mikasa) and dried to obtain a mask with a thickness of 0.5 ⁇ m. A material was deposited.
  • a concavo-convex structure was formed with an RIE apparatus (reactive ion etching apparatus: EXAM manufactured by Shinko Seiki Co., Ltd.).
  • RIE apparatus reactive ion etching apparatus: EXAM manufactured by Shinko Seiki Co., Ltd.
  • the etching gas is replaced with H 2 gas, dry etching is performed for 5 minutes at a hydrogen flow rate of 100 sccm, a gas pressure of 3 Pa, and a high-frequency output of 100 W, and then immersed in a 1% sodium hydroxide solution and further diluted with hydrofluoric acid. After dipping in a 10% solution, it was rinsed with pure water to obtain an uneven shape with a height of about 1 ⁇ m on the surface.
  • phosphoryl chloride (POCl 3 ) is gas diffused at a diffusion temperature of 800 ° C. to form an n-type layer on the surface, and pn separation is performed by plasma etching the wafer side and back surface with a mixed gas of CF 4 and O 2. Went.
  • an ITO transparent conductive film is formed on the surface with a plasma CVD device, and silver paste is elongated on the ITO surface for screen printing. Further, an Al paste was formed on the back surface by screen printing and then baked at a temperature of 860 ° C. to produce a photoelectric conversion element.
  • Example 2 A photoelectric conversion element was obtained in the same manner as in Example 1 except that the cleaning method for etching residue and plasma damage was changed.
  • the etching residue and plasma damage cleaning method is performed by using a microbubble generator and an ultrasonic generator in a 10% dilute hydrofluoric acid solution to which microbubbles and ultrasonic waves are continuously supplied. This was performed by immersing in pure water and then immersing in pure water. As a result, as in Example 1, an uneven shape having a height of about 1 ⁇ m was obtained on the surface.
  • Example 3 A photoelectric conversion element was obtained in the same manner as in Example 1 except that the silicon wafer was changed to a P-type single crystal wafer.
  • Example 4 A photoelectric conversion element was obtained in the same manner as in Example 2 except that the silicon wafer was changed to a P-type single crystal wafer.
  • Example 1 After carrying out to the phosphate glass removal step, the same procedure as in Example 1 was conducted, except that a SiN antireflection film was formed to a thickness of about 50 nm by plasma CVD and no translucent conductive layer was formed. Thus, a photoelectric conversion element was obtained.
  • Example 2 The same procedure as in Example 3 was performed except that one surface of a p-type polycrystalline silicon wafer was immersed in a mixed solution of hydrogen fluoride and nitric acid (mixing ratio 50:50 (volume ratio)) to form a texture structure on the surface. Thus, a photoelectric conversion element was produced.
  • Example 3 A photoelectric conversion element was produced in the same manner as in Example 1 except that ultrasonic cleaning was performed in pure water for 5 minutes instead of dry etching with hydrogen and immersion in a sodium hydroxide aqueous solution.
  • the comparative example 1 it is set as the structure which put the antireflection film in the photoelectric conversion element of this invention.
  • the reflectance was the same as in Examples 1 to 3, but it was also confirmed that power generation efficiency was reduced due to the insertion of SiN as an insulating film and the locality of the surface electrode.
  • Comparative Example 2 is a configuration of a conventional polycrystalline silicon solar cell
  • Comparative Example 3 is an example in which the etching residue cleaning step in Example 1 is a conventional ultrasonic cleaning in pure water.
  • FIG. 5 shows the reflectance spectra of the polycrystalline silicon wafer surface (a) before application of the mask material and the textured structure surface (b) before n-type dopant diffusion in Example 1.
  • the reflectance before the texture structure formation was 20% or more in the Si absorption wavelength band of 400 nm to 1200 nm, whereas the texture structure It was confirmed that the reflectance after formation was 1 to 2%.
  • FIG. 6 shows a surface of a single crystal silicon wafer (a) before application of a mask material and a texture structure surface before n-type dopant diffusion ((e): Examples 3 and (f) in Example 3 and Example 4.
  • the reflectance spectrum of Example 4) is shown.
  • FIG. 6 also shows the reflectance spectrum of the texture structure surface obtained by the conventional texture structure forming method by alkali treatment ((b) the texture structure surface of alkali treatment, (c) is (b). The surface where the SiN antireflection film is provided on the texture structure surface))).
  • FIG. 6D shows the reflectance spectrum of the concavo-convex structure surface before dry etching using hydrogen in Example 3.
  • the reflectance before the texture structure formation is 20% or more in the Si absorption wavelength band of 400 nm to 1200 nm, and the conventional alkali treatment is performed. It was confirmed that the reflectance on the texture structure surface was about 10%. Further, in the configuration in which the SiN film is provided on the texture structure surface by the conventional alkali treatment, the reflectance is 6% or less in the wavelength region shorter than 400 nm to 600 nm, but shorter on the longer wavelength side than 600 nm. It was higher than the wavelength side, and it was confirmed that the wavelength dependency of the reflectance was high. On the other hand, on the texture structure surface using the mask material, it was confirmed that the reflectance of 1 to 2% was achieved regardless of the cleaning process.
  • FIG. 7 is a graph showing the results of investigation by the inventor of the relationship between the surface roughness (1.5 ⁇ m square) of the Si substrate surface and the integrating sphere reflectance for light having a wavelength of 1 ⁇ m.
  • FIG. 7A shows the relationship between Ra (arithmetic mean surface roughness) and Rq (root mean square roughness) and reflectance
  • FIG. 7B shows Rz (maximum height roughness) and Rzjis (10-point average). The relationship between the roughness, Rp (maximum peak), and Rv (maximum valley) and the reflectance is shown.
  • the surface roughness of the texture structure surfaces of Examples 1 to 4 and Comparative Examples 1 and 2 can be estimated.
  • the arithmetic average surface roughness Ra is 122 nm or more.
  • the pitch (fineness) of the concavo-convex structure can be adjusted by the design of the first particles and the second particles included in the mask material. It is also confirmed that the maximum height roughness Rz is 1151 nm (1.151 ⁇ m) or more.
  • the present invention succeeded in producing a texture structure having a low reflectance of 6% or less in a crystalline Si solar cell, and for the first time in the crystalline Si solar cell, translucency was achieved for the first time.
  • the structure provided with the surface electrode which consists of a conductive layer (transparent electrode layer) was implement
  • solar light is confined in the photoelectric conversion layer with high efficiency, and furthermore, it has succeeded in generating power in a greatly widened power generation region, and the resistance when taking out the generated charge is minimized.
  • the photoelectric conversion element of this invention is preferably applicable to uses, such as a photoelectric conversion element used for a solar cell, an infrared sensor, etc.

Abstract

[Problem] To provide a photoelectric conversion element that has high sunlight incidence efficiency and photoelectric conversion efficiency for the photoelectric conversion layer and is capable of being produced with good yields. [Solution] The photoelectric conversion element (1) comprises: a photoelectric conversion layer (10) formed from a crystal (Si) substrate (10) having a textured structure surface provided with a textured structure (10t) having a plurality of needle shaped protrusions (101) on one main surface (10s (surface 10s)); a light-transmissive conductive layer (30) formed from direct film growth on the surface (10s); a back surface electrode layer (20) formed on the back surface (10r) (main surface (10r) on the opposite side from the one main surface (10s)) of the photoelectric conversion layer (10); and an extraction electrode (40) formed on the light-transmissive conductive layer (surface electrode) (30).

Description

光電変換素子及び太陽電池Photoelectric conversion element and solar cell
 
本発明は、結晶シリコン系光電変換素子及びこれを用いた太陽電池に関するものである。
The present invention relates to a crystalline silicon photoelectric conversion element and a solar cell using the same.
 
単結晶Ｓｉ又は多結晶Ｓｉ基板を光電変換層として利用する結晶Ｓｉ系太陽電池が実用化されている。結晶Ｓｉ系太陽電池において、太陽光の受光側のＳｉ基板面には、基板面における太陽光の反射を抑制して効率良く光電変換層内に太陽光を入射させるために、テクスチャ構造と呼ばれる凹凸構造が形成されている。
Crystalline Si solar cells using a single crystal Si or polycrystalline Si substrate as a photoelectric conversion layer have been put into practical use. In crystalline Si solar cells, the surface of the Si substrate on the sunlight receiving side is uneven, which is called a textured structure, in order to efficiently reflect sunlight into the photoelectric conversion layer by suppressing the reflection of sunlight on the substrate surface. A structure is formed.
 
一般に、テクスチャ構造の形成には、単結晶Ｓｉでは水酸化ナトリウム水溶液を用いたウエットエッチング法、多結晶Ｓｉではフッ酸と硝酸の混合溶液を用いたウエットエッチング法が用いられている。
In general, the wet etching method using a sodium hydroxide aqueous solution is used for monocrystalline Si and the wet etching method using a mixed solution of hydrofluoric acid and nitric acid is used for polycrystalline Si for forming a texture structure.
 
しかしながら、これらの方法で形成されるテクスチャ構造の太陽光の反射率は、単結晶で１０％程度、多結晶では２５％程度と、反射率を良好に低下させる構造を得ることが難しい。図８（ａ）は、市販の光電変換セルに用いられている単結晶Ｓｉテクスチャ構造の表面ＳＥＭ像、（ｂ）は市販の光電変換セルに用いられている多結晶Ｓｉテクスチャ構造の表面ＳＥＭ像である。また、図９は、図８の光電変換セルの反射率の波長依存性を、本発明者が測定した結果を示したものである。図示されるように、特に多結晶では、ウエットエッチングの結晶の面方位依存性により、面内均一性及び再現性の良いテクスチャ構造を得ることが難しい。
However, the reflectance of sunlight with a texture structure formed by these methods is about 10% for a single crystal and about 25% for a polycrystal, making it difficult to obtain a structure that reduces the reflectance satisfactorily. FIG. 8A shows a surface SEM image of a single crystal Si texture structure used in a commercially available photoelectric conversion cell, and FIG. 8B shows a surface SEM image of a polycrystalline Si texture structure used in a commercially available photoelectric conversion cell. It is. FIG. 9 shows the result of measurement by the inventor of the wavelength dependence of the reflectance of the photoelectric conversion cell of FIG. As shown in the figure, it is difficult to obtain a texture structure with good in-plane uniformity and reproducibility due to the dependency of wet etching on the crystal orientation, especially in the case of polycrystal.
 
単結晶、多結晶によらず、面内均一性及び再現性の良好なテクスチャ構造を形成する方法として、指向性の強い反応性イオンエッチング等のドライエッチングを用いることが検討されている（特許文献１～特許文献４等）。特許文献４では、歩留まり良くテクスチャ構造を形成可能なドライエッチング条件を開示している。
Regardless of single crystal or polycrystal, the use of dry etching such as reactive ion etching with strong directivity is being studied as a method for forming a texture structure with good in-plane uniformity and reproducibility (patent document) 1 to Patent Document 4). Patent Document 4 discloses dry etching conditions capable of forming a texture structure with a high yield.
 
特開昭６０－２７１９５号公報 特開平５－７５１５２号公報 特開平９－１０２６２５号公報 特開２００３－１９７９４０号公報
JP-A-60-27195 JP-A-5-75152 JP-A-9-102625 JP 2003-197940 A
 
特許文献１～４等による検討により、ドライエッチングによるテクスチャ構造の形成にて面内均一性や再現性についてはある程度向上されたが、光電変換層への太陽光の入射効率は未だ不十分であり、現在のＳｉ系光電変換素子では、テクスチャ構造上に更に反射防止膜を設けることが必須となっている。
Although the in-plane uniformity and reproducibility have been improved to some extent by the formation of the texture structure by dry etching as studied by Patent Documents 1 to 4, etc., the incident efficiency of sunlight on the photoelectric conversion layer is still insufficient. In the current Si-based photoelectric conversion element, it is essential to further provide an antireflection film on the texture structure.
 
反射防止膜は絶縁性であるため、反射防止膜を設けた構成では、その表面電極は反射防止膜の一部を除去して局所的に光電変換層と導通させた電極とする必要があり、光電変換層と電極との間の抵抗が大きくなる。従って、反射防止膜の挿入により入射効率を高めても、抵抗値の増加に伴う光電変換効率の低下により、高い光電変換効率を得ることが難しい。
Since the antireflection film is insulative, in the configuration provided with the antireflection film, the surface electrode needs to be an electrode locally removed from the antireflection film and electrically connected to the photoelectric conversion layer. The resistance between the photoelectric conversion layer and the electrode increases. Therefore, even if the incident efficiency is increased by inserting an antireflection film, it is difficult to obtain a high photoelectric conversion efficiency due to a decrease in photoelectric conversion efficiency accompanying an increase in resistance value.
 
更に、上記したような反射防止膜を貫通して局所的に光電変換半導体層と導通させた電極の形成には、ファイヤースルー性を有する導電性ペーストを用いて、高温焼成により反射防止膜を貫通させるため、基板の熱変形が発生しやすく歩留まり低下を引き起こしやすいという問題がある。
Furthermore, to form an electrode that penetrates the antireflection film as described above and is locally connected to the photoelectric conversion semiconductor layer, a conductive paste having a fire-through property is used to penetrate the antireflection film by high-temperature baking. Therefore, there is a problem that thermal deformation of the substrate is likely to occur and yield is likely to be reduced.
 
本発明は上記事情に鑑みてなされたものであり、光電変換層への太陽光の入射効率及び光電変換効率が高く、歩留まりのよい製造が可能な光電変換素子を提供することを目的とするものである。
The present invention has been made in view of the above circumstances, and an object thereof is to provide a photoelectric conversion element that has high incidence efficiency of sunlight and photoelectric conversion into a photoelectric conversion layer and can be manufactured with high yield. It is.
 
本発明の光電変換素子は、一導電型結晶シリコン基板の一主面側に他の導電型不純物を拡散させてｐｎ接合が形成されてなる光電変換層と、前記一主面に形成された透光性導電層と、前記光電変換層の前記一主面の反対側の主面に形成された裏面電極層とを備えた光電変換素子であって、
前記光電変換層の前記一主面は、該主面における太陽光の反射を抑制する多数の針状の凸部を有する凹凸構造を備えたテクスチャ構造面であり、
前記透光性導電層は該テクスチャ構造面上に直接成膜されてなることを特徴とするものである。
The photoelectric conversion element of the present invention comprises a photoelectric conversion layer formed by diffusing other conductivity type impurities on one main surface side of one conductivity type crystalline silicon substrate to form a pn junction, and a transparent layer formed on the one main surface. A photoelectric conversion element comprising a photoconductive layer and a back electrode layer formed on a main surface opposite to the one main surface of the photoelectric conversion layer,
The one main surface of the photoelectric conversion layer is a textured structure surface having a concavo-convex structure having a large number of needle-like convex portions that suppress reflection of sunlight on the main surface,
The translucent conductive layer is formed directly on the textured structure surface.
 
ここで、「針状の凸部」とは、基板のテクスチャ構造面の反対側の主面と略平行な面における、凸部の底部に対する先端部の断面積の比が、２０％以下である凸部を意味する。また、凸部の底部とは、隣接する凹部のうち先端部に近い方の凹部の最下部と同じ高さに位置する部分を意味するものとする。本明細書において「高さ」とは、基板のテクスチャ構造面の反対側の主面に対して略垂直方向の、底部から先端部までの距離を意味するものとする。
Here, the term “needle-shaped convex portion” means that the ratio of the cross-sectional area of the tip portion to the bottom portion of the convex portion on a surface substantially parallel to the main surface opposite to the texture structure surface of the substrate is 20% or less. It means a convex part. Moreover, the bottom part of a convex part shall mean the part located in the same height as the lowest part of the recessed part near the front-end | tip part among adjacent recessed parts. In the present specification, the “height” means a distance from the bottom portion to the tip portion in a direction substantially perpendicular to the main surface opposite to the texture structure surface of the substrate.
 
本発明の光電変換素子において、前記テクスチャ構造面の太陽光の反射率は、５％以下であることが好ましく、３％以下であることがより好ましい。本明細書において、太陽光とは、Ｓｉの吸収波長帯とされている波長４００ｎｍ～１２００ｎｍの光を意味することとする。また、太陽光の反射率とは、上記波長領域の光の平均積分球反射率と定義する。
In the photoelectric conversion element of the present invention, the reflectance of sunlight on the texture structure surface is preferably 5% or less, and more preferably 3% or less. In this specification, the sunlight means light having a wavelength of 400 nm to 1200 nm, which is an absorption wavelength band of Si. Further, the reflectance of sunlight is defined as the average integrating sphere reflectance of light in the above wavelength region.
 
前記テクスチャ構造面の算術平均表面粗さＲａは、１００ｎｍ以上であることが好ましい。
The arithmetic average surface roughness Ra of the texture structure surface is preferably 100 nm or more.
 
前記凸部は、平均高さが１μm以上であることが好ましい。ここで、「凸部の平均高さ」は、凸部の算術平均高さを意味する。また、ここで、算術平均高さより高い凸部を４０％以下の範囲内で含んでもよいものとする。なお、凸部の高さの測定は、ＡＦＭにより測定するものとする。
The convex portion preferably has an average height of 1 μm or more. Here, the “average height of the convex portions” means the arithmetic average height of the convex portions. Here, it is assumed that a convex portion higher than the arithmetic average height may be included within a range of 40% or less. In addition, the measurement of the height of a convex part shall be measured by AFM.
 
前記テクスチャ構造面は、マスク材として、前記凹凸構造を形成するドライエッチングに対して耐性を有する第１粒子と、該第１粒子よりも前記耐性が低い第２粒子と、前記第１粒子よりも前記耐性が低い結着剤とを含む液状組成物を前記シリコン基板の一主面に塗布成膜して得られるものを用い、
前記シリコン基板の一主面にマスク材を配する工程と、該マスク材が配された前記主面にドライエッチングにより前記凹凸構造を形成する工程と、前記凹凸構造に、水素ガスによるドライエッチング処理と、希フッ酸中に浸漬させる処理とを順次実施する洗浄工程とを施すことにより形成することができる。
The texture structure surface includes, as a mask material, first particles having resistance to dry etching that forms the concavo-convex structure, second particles having a lower resistance than the first particles, and the first particles. Using a liquid composition containing a binder having low resistance and obtained by coating a main surface of the silicon substrate,
A step of providing a mask material on one main surface of the silicon substrate; a step of forming the concavo-convex structure by dry etching on the main surface provided with the mask material; and a dry etching process using hydrogen gas on the concavo-convex structure. And a cleaning step of sequentially performing a treatment of immersing in dilute hydrofluoric acid.
 
また、上記と同様のマスク材を用い、前記シリコン基板の一主面にマスク材を配する工程と、該マスク材が配された前記主面にドライエッチングにより前記凹凸構造を形成する工程と、前記凹凸構造に、マイクロバブル及び超音波が断続的に、又は、連続的に供給されている希フッ酸中に浸漬させる処理を含む洗浄工程とを施すことにより形成することができる。
Further, using the same mask material as described above, a step of arranging a mask material on one main surface of the silicon substrate, a step of forming the concavo-convex structure by dry etching on the main surface on which the mask material is arranged, The concavo-convex structure can be formed by performing a cleaning step including a treatment of immersing microbubbles and ultrasonic waves in dilute hydrofluoric acid supplied intermittently or continuously.
 
ここでマイクロバブルとは一般的に、直径がミクロンのオーダーである微細な泡を意味する（例えば、大成博文著「マイクロバブルのすべて」日本実業出版社（２００６）、或いは、上山智嗣、宮本誠著「マイクロバブルの世界」工業調査会（２００６）参照）。
Here, the microbubble generally means a fine bubble having a diameter of the order of microns (for example, Hirofumi Taisei "All about microbubbles", Nihon Jitsugyo Publishing Co., Ltd. (2006), Satoshi Kamiyama, Makoto Miyamoto. (See "Microbubble World" Industrial Research Committee (2006)).
 
前記第１粒子は無機粒子であることが好ましく、ＳｉＯ２を主成分とする粒子であることがより好ましい。また、前記第２粒子は樹脂粒子であることが好ましく、アクリル樹脂を主成分とする粒子であることが好ましい。前記結着剤は、水溶性高分子又は水分散性高分子を主成分とするものであることが好ましい。
The first particles are preferably inorganic particles, and more preferably particles containing SiO 2 as a main component. The second particles are preferably resin particles, and are preferably particles mainly composed of an acrylic resin. It is preferable that the binder is mainly composed of a water-soluble polymer or a water-dispersible polymer.
 
本発明の光電変換素子において、前記一導電型結晶シリコン基板が多結晶シリコンからなる（不可避不純物を含んでもよい）ことが好ましい。
In the photoelectric conversion element of the present invention, it is preferable that the one conductivity type crystalline silicon substrate is made of polycrystalline silicon (may contain inevitable impurities).
 
本発明の太陽電池は、上記本発明の光電変換素子を備えたことを特徴とするものである。
The solar cell of the present invention comprises the above-described photoelectric conversion element of the present invention.
 
本発明の光電変換素子は、結晶Ｓｉ系光電変換素子において、光電変換層の受光側の主面が、太陽光の反射を抑制する多数の針状の凸部を有するテクスチャ構造面であり、該テクスチャ構造面上に透光性導電層が直接成膜されてなるものである。かかる構成では、多数の針状の凸部を有するテクスチャ構造面が、太陽光の反射を高効率に抑制することができるので、反射防止膜を設けることなく光電変換層のテクスチャ構造面の略全面に表面電極（透光性導電層）を形成することができる。そのため、テクスチャ構造面により高い入射効率で入射された太陽光を、高い光電変換効率にて利用することができる上、テクスチャ構造面の略全面から電荷を取り出すことができるため、局所的に設けられた電極により電荷を取り出す構成に比して光電変換層と電極との間の抵抗が格段に小さくなる。更に、局所的な電極形成が不要であるために高温焼成の必要もない。従って、本発明によれば、入射光の利用効率及び光電変換効率が高く、歩留まりの良い製造が可能な光電変換素子を提供することができる。
The photoelectric conversion element of the present invention, in the crystalline Si photoelectric conversion element, the main surface on the light receiving side of the photoelectric conversion layer is a texture structure surface having a large number of needle-like convex portions that suppress reflection of sunlight, A translucent conductive layer is directly formed on the texture structure surface. In such a configuration, the texture structure surface having a large number of needle-like convex portions can suppress the reflection of sunlight with high efficiency, so that almost the entire texture structure surface of the photoelectric conversion layer is provided without providing an antireflection film. A surface electrode (translucent conductive layer) can be formed on the substrate. For this reason, sunlight that is incident on the texture structure surface with high incidence efficiency can be used with high photoelectric conversion efficiency, and charges can be taken out from almost the entire texture structure surface. The resistance between the photoelectric conversion layer and the electrode is remarkably reduced as compared with a configuration in which electric charges are extracted by the electrode. Furthermore, since local electrode formation is unnecessary, there is no need for high-temperature firing. Therefore, according to the present invention, it is possible to provide a photoelectric conversion element that has high incident light utilization efficiency and photoelectric conversion efficiency and can be manufactured with a high yield.
 
（ａ）は本発明にかかる一実施形態の光電変換素子の構成を示す厚み方向断面図、（ｂ）はテクスチャ構造面の凹凸構造を拡大した図 （ａ）～（ｈ）は図１に示される本発明の光電変換素子の製造方法のフローを模式的に示した図 （ａ）はドライエッチングによる凹凸形成後純水中での超音波洗浄を行った後のテクスチャ構造の表面ＳＥＭ写真、（ｂ）は（ａ）の超音波洗浄時間を○○分延長した際のテクスチャ構造の表面ＳＥＭ写真、（ｃ）は更に○○分超音波洗浄時間を延長した際のテクスチャ構造の表面ＳＥＭ写真 （ａ）及び（ｂ）は実施例１において、水素ガスによるドライエッチング処理によりテクスチャ構造面を洗浄した場合の表面ＳＥＭ像。（ａ）は倍率５０００倍、（ｂ）は倍率１００００倍。 （ａ）は多結晶シリコンインゴットからワイヤーソーカットされて得られた多結晶シリコン基板の切断面の反射率の波長依存性、（ｂ）は実施例１のテクスチャ構造の反射率の波長依存性を示す図 単結晶Ｓｉ基板を用いた場合のテクスチャ構造面（未処理の場合は切断面）の反射率の波長依存性を示す図。（ａ）は単結晶シリコンインゴットからワイヤーソーカットされて得られた単結晶シリコン基板の切断面、（ｂ）は（ａ）の表面にアルカリエッチング洗浄した場合のテクスチャ構造面、（ｃ）は（ｂ）の表面にＳｉＮ反射防止膜を備えた構成、（ｄ）は本発明におけるマスク材を用いたドライエッチングにより凹凸構造を形成し、希フッ酸への浸漬処理を施したテクスチャ構造面、（ｅ）は実施例３のテクスチャ構造面、（ｆ）は実施例４のテクスチャ構造面。 （ａ）及び（ｂ）は、波長１０００ｎｍの光に対するテクスチャ構造の反射率と表面粗さとの関係を示す図 市販のＳｉ系光電変換セルのテクスチャ構造の表面ＳＥＭ像。（ａ）は単結晶Ｓｉ系、（ｂ）は多結晶Ｓｉ系。 図８に対応する市販のＳｉ系光電変換セルのテクスチャ構造面の反射率の波長依存性を示す図
(A) Thickness direction sectional drawing which shows the structure of the photoelectric conversion element of one Embodiment concerning this invention, (b) is the figure which expanded the uneven structure of the texture structure surface (A)-(h) is the figure which showed typically the flow of the manufacturing method of the photoelectric conversion element of this invention shown by FIG. (A) is a surface SEM photograph of the texture structure after performing ultrasonic cleaning in pure water after forming irregularities by dry etching, and (b) is when the ultrasonic cleaning time of (a) is extended by XX. Surface SEM photo of the texture structure, (c) is a surface SEM photo of the texture structure when the ultrasonic cleaning time is further extended for XX minutes. (A) And (b) is the surface SEM image at the time of wash | cleaning a texture structure surface in Example 1 by the dry etching process by hydrogen gas. (A) is 5000 times magnification, (b) is 10,000 times magnification. (A) shows the wavelength dependence of the reflectance of the cut surface of the polycrystalline silicon substrate obtained by wire saw cutting from the polycrystalline silicon ingot, and (b) shows the wavelength dependence of the reflectance of the texture structure of Example 1. Illustration The figure which shows the wavelength dependence of the reflectance of the texture structure surface at the time of using a single-crystal Si substrate (when it is unprocessed, a cut surface). (A) is a cut surface of a single crystal silicon substrate obtained by wire saw cutting from a single crystal silicon ingot, (b) is a textured structure surface when alkali etching cleaning is performed on the surface of (a), and (c) is ( (b) a structure provided with a SiN antireflection film on the surface, (d) is a textured structure surface in which a concavo-convex structure is formed by dry etching using a mask material in the present invention, and immersion treatment in diluted hydrofluoric acid is performed, e) is the texture structure surface of Example 3, and (f) is the texture structure surface of Example 4. (A) And (b) is a figure which shows the relationship between the reflectance of a texture structure with respect to the light of wavelength 1000nm, and surface roughness. The surface SEM image of the texture structure of a commercially available Si type photoelectric conversion cell. (A) is a single crystal Si system, (b) is a polycrystal Si system. The figure which shows the wavelength dependence of the reflectance of the texture structure surface of the commercially available Si type photoelectric conversion cell corresponding to FIG.
 
「光電変換半導体素子（太陽電池）及びその製造方法」
＜光電変換半導体素子＞
図面を参照して本発明にかかる一実施形態の光電変換半導体素子（以下、光電変換素子と略記する）について説明する。図１（ａ）は、本実施形態の光電変換素子の構成を示す厚み方向模式断面図、図１（ｂ）は、図１（ａ）の凹凸構造の一部を拡大した模式図である。視認しやすくするため各部の縮尺は適宜異ならせて示してある。
"Photoelectric conversion semiconductor element (solar cell) and manufacturing method thereof"
<Photoelectric conversion semiconductor element>
A photoelectric conversion semiconductor element (hereinafter abbreviated as a photoelectric conversion element) according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1A is a schematic cross-sectional view in the thickness direction showing the configuration of the photoelectric conversion element of this embodiment, and FIG. 1B is an enlarged schematic view of a part of the concavo-convex structure in FIG. In order to facilitate visual recognition, the scales of the respective parts are shown as being appropriately changed.
 
図示されるように、光電変換素子１は、一主面１０ｓ（表面１０ｓ）が多数の針状の凸部１０１を有する凹凸構造１０ｔを備えたテクスチャ構造面である結晶Ｓｉ基板１０からなる光電変換層１０と、表面１０ｓに直接成膜されてなる透光性導電層３０と、光電変換層１０の裏面１０ｒ（一主面１０ｓと反対側の主面１０ｒ）に形成された裏面電極層２０と、透光性導電層（表面電極）３０上に形成された取り出し電極４０とを備えた構成としている。
As shown in the figure, the photoelectric conversion element 1 is composed of a crystalline Si substrate 10 having a textured structure surface 10t (surface 10s) having a concavo-convex structure 10t having a large number of needle-like convex portions 101. A layer 10, a translucent conductive layer 30 formed directly on the front surface 10s, and a back electrode layer 20 formed on the back surface 10r of the photoelectric conversion layer 10 (a main surface 10r opposite to the one main surface 10s); , And a takeout electrode 40 formed on the translucent conductive layer (surface electrode) 30.
 
図１（ｂ）に示されるように、凹凸構造１０ｔを形成する多数の針状の凸部１０１は、光電変換層１０の裏面１０ｒと略平行な面における、凸部１０１の底部の断面積ｓｂに対する凸部１０１の先端部の断面積ｓｔの比が、２０％以下である凸部を意味する。図１（ｂ）に示されるように、凸部１０１の底部とは、隣接する凹部１０２のうち先端部に近い方の凹部１０２の最下部と同じ高さに位置する部分を意味するものである。先端部の断面積ｓｔはエッチング時にマスクによって保護され、残った部分を意味する。
As shown in FIG. 1B, a large number of needle-like convex portions 101 forming the concavo-convex structure 10t have a cross-sectional area sb at the bottom of the convex portion 101 on a surface substantially parallel to the back surface 10r of the photoelectric conversion layer 10. The ratio of the cross-sectional area st of the front-end | tip part of the convex part 101 with respect to the convex part is 20% or less. As shown in FIG. 1B, the bottom portion of the convex portion 101 means a portion located at the same height as the lowermost portion of the concave portion 102 closer to the tip portion among the adjacent concave portions 102. . The cross-sectional area st at the tip means the remaining part protected by the mask during etching.
 
光電変換層１０は、第一導電型（ｐ型）Ｓｉ層１１と第二導電型（ｎ型）Ｓｉ層１２との二層構造となっており、光電変換層１０内にてｐｎ接合が形成されている。本実施形態では第一導電型Ｓｉ層１１がｐ型層、第二導電型Ｓｉ層１２がｎ型層である場合を例に説明するが、それぞれの導電型が逆の構成となっていてもよい。
The photoelectric conversion layer 10 has a two-layer structure of a first conductivity type (p-type) Si layer 11 and a second conductivity type (n-type) Si layer 12, and a pn junction is formed in the photoelectric conversion layer 10. Has been. In the present embodiment, the case where the first conductivity type Si layer 11 is a p-type layer and the second conductivity type Si layer 12 is an n-type layer will be described as an example. Good.
 
光電変換素子１において、光電変換層１０は結晶性Ｓｉであればよく、単結晶でも多結晶でもよい。
In the photoelectric conversion element 1, the photoelectric conversion layer 10 may be crystalline Si, and may be single crystal or polycrystalline.
 
「背景技術」の項目において、従来のウエットエッチングによる結晶Ｓｉ系光電変換素子のテクスチャ構造の太陽光の反射率は、単結晶で１０％程度、多結晶では２５％程度と高く、また、ドライエッチングにより形成されたテクスチャ構造においても、太陽光の反射率を充分に低下させることができていないことを述べた。また、多結晶では、ウエットエッチングの結晶の面方位依存性により、面内均一性及び再現性の良いテクスチャ構造を得ることが難しいことを述べた。
In the section of “Background Art”, the reflectance of sunlight in the texture structure of a crystalline Si photoelectric conversion element by conventional wet etching is as high as about 10% for a single crystal and about 25% for a polycrystal, and is also dry etching. He stated that the reflectance of sunlight could not be reduced sufficiently even in the texture structure formed by the above. In addition, it was described that it is difficult to obtain a texture structure with good in-plane uniformity and reproducibility in the case of polycrystal due to the crystal orientation dependence of wet etching.
 
光電変換素子１は、後記実施例図５、図６に示されるように単結晶、多結晶のいずれの場合においても同様に反射率が一桁台の非常に低反射率のテクスチャ構造面を有するため、特に、低反射率、及び面内均一性再現性に課題を有する多結晶Ｓｉに適用する場合により大きな効果を得ることができる。
The photoelectric conversion element 1 has a texture structure surface with a very low reflectivity with single-digit reflectivity in the case of either single crystal or polycrystal as shown in Examples 5 and 6 to be described later. For this reason, in particular, when applied to polycrystalline Si having problems in low reflectance and in-plane uniformity reproducibility, a greater effect can be obtained.
 
光電変換層１０は、第一導電型（ｐ型）Ｓｉ層１１と第二導電型（ｎ型）Ｓｉ層１２との二層構造となっている。ｐ型ドーパント及びｎ型ドーパントとしては特に制限されず、一般に結晶Ｓｉのドーパントとして用いられているドーパントイオンであればよい。ｐ型ドーパントとしてはＩＩＩ族元素であるホウ素、ｎ型ドーパントとしてはＶ族元素であるリンが好適に用いられる。
The photoelectric conversion layer 10 has a two-layer structure of a first conductivity type (p-type) Si layer 11 and a second conductivity type (n-type) Si layer 12. It does not restrict | limit especially as a p-type dopant and an n-type dopant, What is necessary is just a dopant ion generally used as a dopant of crystalline Si. As the p-type dopant, boron, which is a group III element, and phosphorus, which is a group V element, are preferably used as the n-type dopant.
 
裏面電極層２０としては特に制限されず、任意の金属電極を用いることができるが、導電性の高いアルミニウムや銀等を用いることが好ましい。◎
透光性導電層３０（表面電極）は、光を取り込むと共に、裏面電極層２０と対になって、光電変換層１０で生成された電荷が流れる電極として機能する層であり、光電変換層１０の凹凸構造１０ｔからなるテクスチャ構造面上に直接成膜されてなるものである。透光性導電層３０としては特に制限されないが、ＩＴＯ（酸化インジウム錫）や金属ドープ酸化亜鉛（ＺｎＯ：Ａｌ等のｎ－ＺｎＯ）等が好ましい。透光性導電層３０の膜厚は特に制限されず、５０ｎｍ～２μｍが好ましい。
The back electrode layer 20 is not particularly limited, and any metal electrode can be used, but it is preferable to use highly conductive aluminum, silver, or the like. ◎
The translucent conductive layer 30 (front surface electrode) is a layer that captures light and functions as an electrode through which the charge generated in the photoelectric conversion layer 10 flows, paired with the back electrode layer 20. The film is directly formed on the textured structure surface of the uneven structure 10t. The light-transmitting conductive layer 30 is not particularly limited, but ITO (indium tin oxide), metal-doped zinc oxide (n-ZnO such as ZnO: Al), and the like are preferable. The film thickness of the translucent conductive layer 30 is not particularly limited, and is preferably 50 nm to 2 μm.
 
取り出し電極４０としては特に制限されないが、銀やアルミニウム等の塗布成膜が可能な電極が好ましい。取り出し電極４０の膜厚は特に制限されず、０．１～３μｍが好ましい。
Although it does not restrict | limit especially as the extraction electrode 40, The electrode in which the coating film-forming of silver, aluminum, etc. is possible is preferable. The film thickness of the extraction electrode 40 is not particularly limited and is preferably 0.1 to 3 μm.
 
テクスチャ構造面の凹凸構造１０ｔは、図１（ａ）に示されるように、多数の針状の凸部１０１を細かいピッチで備えた構成としている。かかる凹凸構造１０ｔでは、太陽光を良好に光電変換層１０内に閉じ込めて、テクスチャ構造面における該光の反射率を、従来のテクスチャ構造に比して格段に低下させ、テクスチャ構造面に入射した光を高効率に光電変換層１０に入射させることができる。後記実施例では、反射率５％以下を達成しており、最も低い反射率では１％を実現している（後記実施例、図５，図６を参照）。
As shown in FIG. 1 (a), the texture structure surface uneven structure 10t includes a large number of needle-like convex portions 101 at a fine pitch. In such a concavo-convex structure 10t, sunlight is well confined in the photoelectric conversion layer 10, and the reflectance of the light on the texture structure surface is significantly reduced as compared with the conventional texture structure, and is incident on the texture structure surface. Light can be incident on the photoelectric conversion layer 10 with high efficiency. In the examples described later, a reflectance of 5% or less is achieved, and 1% is realized in the lowest reflectance (see Examples described later, FIGS. 5 and 6).
 
図４は、後記する実施例において得られたテクスチャ構造面の凹凸構造１０ｔの表面ＳＥＭ像であり、（ａ）と（ｂ）とで倍率を変えたものを示してある。図４に示されるＳＥＭ像からは、凹凸構造１０ｔの凸部１０１のピッチは、１００～５００ｎｍ若しくはそれ以下となっていることが確認されるが、面内においてばらつきがあることも認められる。
FIG. 4 is a surface SEM image of the textured surface uneven structure 10t obtained in the examples described later, and shows the magnifications changed between (a) and (b). From the SEM image shown in FIG. 4, it is confirmed that the pitch of the convex portions 101 of the concavo-convex structure 10t is 100 to 500 nm or less, but it is recognized that there is variation in the plane.
 
また、凸部１０１の平均高さは、大きな光閉じ込め効果が得られることから、高い方が好ましいが、凸部１０１の高さを高くするにはより長い形成時間を要することになる。凸部１０１の形成工程の処理時間（タクトタイム）は、ランニングコストの観点から短いことが好ましく、従って、所望の反射率を実現可能な範囲で平均高さは低いことが好ましい。上記のように、本実施形態の凹凸構造１０ｔは、多数の針状の凸部１０１を細かいピッチで備えた構成とすることができるので、凸部１０１の平均高さが１μm程度であれば、大きな光閉じ込め効果が得られ、充分に低い反射率の凹凸構造１０ｔとすることができる。
The average height of the convex portions 101 is preferably higher because a large light confinement effect can be obtained. However, a longer formation time is required to increase the height of the convex portions 101. The processing time (tact time) of the formation process of the convex portion 101 is preferably short from the viewpoint of running cost. Therefore, it is preferable that the average height is low as long as a desired reflectance can be realized. As described above, the concavo-convex structure 10t of the present embodiment can be configured to include a large number of needle-like convex portions 101 at a fine pitch, so if the average height of the convex portions 101 is about 1 μm, A large light confinement effect is obtained, and the concavo-convex structure 10t having a sufficiently low reflectance can be obtained.
 
一方で、多数の凸部１０１の個々の高さｈについても、ピッチと同様ばらつきがあることが、図４のＳＥＭ像から確認することができる。凹凸構造１０ｔにおいて、最大高さ粗さＲｚとしては、０．９μｍ～３．０μｍの範囲であることが好ましい。この多数の凸部１０１のピッチ及び高さのばらつきを含む上記の凹凸構造１０ｔの特徴は、本発明者が見出した凹凸構造１０ｔの形成方法によって得られる構造に特有のものである。以下に、光電変換素子１の製造方法について説明する。
On the other hand, it can be confirmed from the SEM image of FIG. 4 that the individual heights h of the large number of convex portions 101 have variations similar to the pitch. In the concavo-convex structure 10t, the maximum height roughness Rz is preferably in the range of 0.9 μm to 3.0 μm. The features of the concavo-convex structure 10t including variations in pitch and height of the large number of convex portions 101 are peculiar to the structure obtained by the method for forming the concavo-convex structure 10t found by the present inventors. Below, the manufacturing method of the photoelectric conversion element 1 is demonstrated.
 
＜光電変換素子の製造方法＞
図２（ａ）～（ｈ）を参照して、光電変換素子１の製造方法について説明する。図２（ａ）～（ｈ）は、光電変換素子１の製造方法のフローを示す概略断面図である。まず、一主面（表面１０ｓ）の平滑性の良好なｐ型結晶シリコン基板（ウエハ）１０を用意する（図２（ａ））。
<Method for producing photoelectric conversion element>
With reference to FIGS. 2A to 2H, a method of manufacturing the photoelectric conversion element 1 will be described. 2A to 2H are schematic cross-sectional views showing a flow of a method for manufacturing the photoelectric conversion element 1. FIG. First, a p-type crystalline silicon substrate (wafer) 10 having a smooth surface on one principal surface (surface 10s) is prepared (FIG. 2A).
 
シリコン基板１０が単結晶シリコンの場合は引き上げ法等により形成されたインゴット、多結晶シリコンの場合は、原材料を坩堝内で溶解・凝固させたインゴットをワイヤーソーなどにより所望の厚み（例えば３００μｍ程度）にスライスして得る方法が一般的である。その他、多結晶シリコンの場合は、融液から板状に引き上げる方法により得ることができる。
In the case where the silicon substrate 10 is single crystal silicon, an ingot formed by a pulling method or the like, and in the case of polycrystalline silicon, an ingot obtained by melting and solidifying the raw material in a crucible with a wire saw or the like has a desired thickness (for example, about 300 μm). In general, the method obtained by slicing into two. In addition, in the case of polycrystalline silicon, it can be obtained by pulling up from the melt into a plate shape.
 
凹凸構造１０ｔの形成面である表面１０ｓの平滑性は、後工程である凹凸構造１０ｔの形成時に、その凹凸の深さの面内均一性に影響を及ぼすことから、良好であることが好ましい。
The smoothness of the surface 10s, which is the formation surface of the concavo-convex structure 10t, is preferably good because it affects the in-plane uniformity of the depth of the concavo-convex when the concavo-convex structure 10t, which is a subsequent process, is formed.
 
結晶シリコン系光電変換素子は、後に示すｐｎ接合形成を、一方の導電型の基板の上方から他方の導電型のドーパントを拡散させる手法により行うことが一般的である。従って、下層側の導電型層の厚みがミクロンオーダであるのに対し、上層側の導電型層の厚みは数百ｎｍオーダと非常に薄い層となる。
In a crystalline silicon-based photoelectric conversion element, pn junction formation described later is generally performed by a technique in which a dopant of the other conductivity type is diffused from above the substrate of one conductivity type. Therefore, the thickness of the conductive layer on the lower layer side is on the order of microns, whereas the thickness of the conductive layer on the upper layer side is a very thin layer on the order of several hundred nm.
 
一方、上記したように、シリコン基板は、インゴットを、ワイヤーソーを用いて切り出す手法が一般的であり、ワイヤーソーによる切り出しでは、その切り出し面にはミクロンオーダのダメージが残ることが一般的である。
On the other hand, as described above, a technique for cutting out an ingot using a wire saw is generally used for a silicon substrate. When a wire saw is used for cutting, a micron order damage is generally left on the cut surface. .
 
これらのダメージを残したまま後工程である凹凸構造１０ｔをドライエッチングにより形成する場合、ダメージ部分はダメージを受けていないシリコン基板部分に比して脆いため、ドライエッチング時には凹凸形成よりもダメージ部分の除去プロセスが支配的となり、ダメージ除去後に凹凸構造の形成がなされる形となる。そのため、凹凸構造１０ｔの形成時に良好なパターンでの凹凸構造１０ｔを形成することが難しく、また、表面に存在するダメージの面内分布に依存してその凹凸の形状や深さの面内均一性のばらつきが大きいものとなる。
When the concavo-convex structure 10t, which is a subsequent process, is formed by dry etching while leaving these damages, the damaged portion is more fragile than the undamaged silicon substrate portion. The removal process becomes dominant, and an uneven structure is formed after removing the damage. Therefore, it is difficult to form the concavo-convex structure 10t with a good pattern when forming the concavo-convex structure 10t, and the in-plane uniformity of the concavo-convex shape and depth depends on the in-plane distribution of damage existing on the surface. The variation of the is large.
 
従って、光電変換素子１の製造に用いる結晶シリコン基板１０は、単結晶、多結晶にかかわらず、ワイヤーソーにより切り出された基板は、そのまま使用せず、ワイヤーソーダメージが除去された状態のものとする必要がある。
Therefore, the crystalline silicon substrate 10 used for the manufacture of the photoelectric conversion element 1 is a single crystal or polycrystal, and the substrate cut out by the wire saw is not used as it is, and the wire saw damage is removed. There is a need to.
 
一方、表面の平滑性が良好で、ワイヤーソーダメージのように、ドライエッチングによる凹凸形成工程に影響を及ぼすダメージや凹凸等がないものであれば、上記のようなダメージ除去処理をすることなく用いることができる。
On the other hand, if the surface smoothness is good, and there is no damage or unevenness that affects the unevenness forming process by dry etching, such as wire saw damage, it is used without performing the above damage removal treatment. be able to.
 
光電変換素子１の製造方法において、凹凸構造１０ｔは、結晶Ｓｉ基板１０の一主面１０ｓ（表面１０ｓ）に、凹凸構造１０ｔを形成するドライエッチングに対して耐性を有する複数の第１粒子５１と、第１粒子５１よりもドライエッチング耐性が低い複数の第２粒子５２とを含むマスク材５０を配し、複数の第１粒子をマスクとしたドライエッチングにより凹凸を形成した後、マスク残渣の洗浄を行って形成される。
In the method for manufacturing the photoelectric conversion element 1, the uneven structure 10 t includes a plurality of first particles 51 having resistance to dry etching that forms the uneven structure 10 t on one main surface 10 s (surface 10 s) of the crystalline Si substrate 10. Then, a mask material 50 including a plurality of second particles 52 having lower dry etching resistance than the first particles 51 is provided, and irregularities are formed by dry etching using the plurality of first particles as a mask. To be formed.
 
マスク材５０の表面１０ｓへの形成方法は特に制限されず、あらかじめ作製されたシート状のマスク材５０を用いてもよいし、上記ドライエッチングに対して耐性を有する第１粒子５１と、第１粒子５１よりもドライエッチング耐性が低い第２粒子５２と、第１粒子５１よりもドライエッチング耐性が低い結着剤（バインダ）とを含む液状組成物を調製し、該液状組成物を表面１０ｓに塗布成膜して形成してもよい。
The method for forming the mask material 50 on the surface 10s is not particularly limited, and a sheet-shaped mask material 50 prepared in advance may be used, or the first particles 51 having resistance to the dry etching and the first A liquid composition containing a second particle 52 having a dry etching resistance lower than that of the particle 51 and a binder having a lower dry etching resistance than that of the first particle 51 is prepared, and the liquid composition is applied to the surface 10s. It may be formed by coating.
 
本実施形態では、後者である塗布成膜によりマスク材５０を形成する態様について説明する。
In the present embodiment, a mode in which the mask material 50 is formed by coating film formation, which is the latter, will be described.
 
（塗布液（液状組成物）の調製）
まず、凹凸構造１０ｔの形成に先立ち、マスク材５０の原料液となる、上記ドライエッチングに対して耐性を有する第１粒子５１と、第１粒子５１よりもドライエッチング耐性が低い第２粒子５２とをそれぞれ複数含む粒子群と、第１粒子５１よりもドライエッチング耐性が低い結着剤（バインダ）とを含む液状組成物を調製する。粒子群には、上記２種の粒子に限られず、他種の粒子を含んでもよい。
(Preparation of coating solution (liquid composition))
First, prior to the formation of the concavo-convex structure 10t, a first particle 51 having resistance to the dry etching, which is a raw material liquid for the mask material 50, and a second particle 52 having lower dry etching resistance than the first particle 51, A liquid composition containing a plurality of particle groups each including a binder and a binder (binder) having lower dry etching resistance than the first particles 51 is prepared. The particle group is not limited to the above two types of particles, and may include other types of particles.
 
ここで、ドライエッチングに対して、第１粒子はエッチング耐性を有し、エッチング処理によりエッチングされにくい粒子であるのに対し、第２粒子はドライエッチング処理によりエッチングされやすい粒子である。具体的には、エッチングレートに関して、例えば、エッチングレートＥＲを「第２粒子のエッチング速度／第１粒子のエッチング速度」としたとき、ＥＲ＞５、さらには、ＥＲ＞１０であることが好ましい。
Here, the first particles have resistance to etching and are difficult to be etched by the etching process, whereas the second particles are easily etched by the dry etching process. Specifically, regarding the etching rate, for example, when the etching rate ER is “second particle etching rate / first particle etching rate”, it is preferable that ER> 5, and further ER> 10.
 
第１粒子としては、エッチング耐性を持つものであれば、特に制限はなく、例えば、無機粒子、無機元素を含有する有機染顔料粒子、無機元素を有するラテックス粒子やカプセル粒子等が挙げられる。これらの中でも、第１粒子としては、エッチング耐性、入手容易性、及び取り扱い性の観点から、無機粒子が好ましい。
The first particles are not particularly limited as long as they have etching resistance, and examples thereof include inorganic particles, organic dye / pigment particles containing inorganic elements, latex particles and capsule particles containing inorganic elements, and the like. Among these, as the first particles, inorganic particles are preferable from the viewpoints of etching resistance, availability, and handleability.
 
無機粒子としては、酸化チタンやシリカ（ＳｉＯ２）、炭酸カルシウム、炭酸ストロンチウムなどの非金属材料、金属又は半導体材料が挙げられる。例えば金属としては、Ｃｕ、Ａｕ、Ａｇ、Ｓｎ、Ｐｔ、Ｐｄ、Ｎｉ、Ｃｏ、Ｒｈ、Ｉｒ、Ａｌ、Ｆｅ、Ｒｕ、Ｏｓ、Ｍｎ、Ｍｏ、Ｗ、Ｎｂ、Ｔａ、Ｂｉ、Ｓｂ及びＰｂからなる群より選ばれた金属単体又は前記群より選ばれた金属の１種もしくは複数種からなる合金材料が挙げられる。また、半導体としては、Ｓｉ、Ｇｅ、ＡｌＳｂ、ＩｎＰ、ＧａＡｓ、ＧａＰ、ＺｎＳ、ＺｎＳｅ、ＺｎＴｅ、ＣｄＳ、ＣｄＳｅ、ＣｄＴｅ、ＰｂＳ、ＰｂＳｅ、ＰｂＴｅ、ＳｅＴｅ、ＣｕＣｌ、などが挙げられる。また、これらの無機粒子を内包しシリカを壁膜材料としたマイクロカプセルなどが挙げられる。
Examples of the inorganic particles include non-metallic materials such as titanium oxide, silica (SiO2), calcium carbonate, and strontium carbonate, metals, and semiconductor materials. For example, the metal includes Cu, Au, Ag, Sn, Pt, Pd, Ni, Co, Rh, Ir, Al, Fe, Ru, Os, Mn, Mo, W, Nb, Ta, Bi, Sb, and Pb. Examples thereof include a single metal selected from the group or an alloy material composed of one or more of the metals selected from the group. Examples of the semiconductor include Si, Ge, AlSb, InP, GaAs, GaP, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, PbS, PbSe, PbTe, SeTe, and CuCl. Moreover, the microcapsule etc. which included these inorganic particles and used silica as the wall membrane material are mentioned.
 
無機元素を含有する有機染顔料粒子としては、金属元素含有アゾ系色素粒子や金属元素含有フタロシアニン系色素粒子などが挙げられる。
Examples of organic dye / pigment particles containing inorganic elements include metal element-containing azo dye particles and metal element-containing phthalocyanine dye particles.
 
無機元素を有するラテックス粒子やカプセル粒子としては、アクリルラテックスをコロイダルシリカで被覆した粒子、アクリルラテックスをケイ酸塩で被覆した粒子、ポリスチレンラテックス粒子をシリカで被覆した粒子などが挙げられる
第２粒子としては、上記した第１粒子とのエッチング耐性の差を有するものであれば特に制限はないが、エッチング耐性が低く、取り扱いが容易であることから、樹脂粒子を好ましく用いることができる。樹脂粒子としては、熱可塑性樹脂粒子が好ましく、例えば、アクリル樹脂粒子、ポリエチレン樹脂粒子、ポリプロピレン樹脂粒子、ポリアミド粒子、ポリイミド粒子、ポリエチレンテレフタレート樹脂粒子、ポリスチレン粒子、シリコーン樹脂等が挙げられる。
Examples of latex particles and capsule particles containing inorganic elements include particles in which acrylic latex is coated with colloidal silica, particles in which acrylic latex is coated in silicate, particles in which polystyrene latex particles are coated with silica, and the like. Is not particularly limited as long as it has a difference in etching resistance with the first particles described above, but resin particles can be preferably used because of low etching resistance and easy handling. The resin particles are preferably thermoplastic resin particles, and examples thereof include acrylic resin particles, polyethylene resin particles, polypropylene resin particles, polyamide particles, polyimide particles, polyethylene terephthalate resin particles, polystyrene particles, and silicone resins.
 
第１粒子及び第２粒子の平均粒径は、同じであってもよいが、第１粒子よりも前記第２粒子の平均粒径が大きいことが好ましい。これにより、第２粒子のエッチングにより生じる第１粒子の粒子間隙が確保され易くなる。
The average particle size of the first particles and the second particles may be the same, but the average particle size of the second particles is preferably larger than the first particles. Thereby, it becomes easy to ensure the particle | grain space | interval of the 1st particle | grains produced by the etching of 2nd particle | grains.
 
第１粒子及び第２粒子の平均粒径としては、形成する粒子層を薄膜化する観点及び太陽光の反射率を良好に低下させる凹凸構造１０ｔを得る観点から、0.05μm～1μmであることが好ましく、0.2μm～0.5μmがより好ましい。
The average particle size of the first particles and the second particles is 0.05 μm to 1 μm from the viewpoint of thinning the particle layer to be formed and obtaining the concavo-convex structure 10 t that satisfactorily reduces the reflectance of sunlight. Preferably, 0.2 μm to 0.5 μm is more preferable.
 
ここで、粒子の平均粒径は、動的光散乱法で得られる粒子径を意味し、その測定方法は以下の通りである。動的光散乱法では、サブミクロン域以下の粒子径・粒子径分布の測定が可能であり、測定しようとする粒子もしくはその分散液を媒体中で超音波照射するなどの公知の方法で分散し、これを適宜希釈したうえで測定試料とする。動的光散乱法で得られる粒子径の累積度数曲線において累積度数が５０％の粒子径を平均粒径とし、同様にして累積度数１０％の粒子径の９０％の粒子径に対する比率を粒径分布の指標とすることができる、このような原理を採用している測定装置としては、例えば堀場製作所製のＬＢ－５００等が挙げられる。
Here, the average particle diameter of a particle means the particle diameter obtained by a dynamic light scattering method, and the measuring method is as follows. In the dynamic light scattering method, it is possible to measure the particle size and particle size distribution in the submicron range or less, and the particles to be measured or dispersions thereof are dispersed by a known method such as ultrasonic irradiation in a medium. Then, after diluting it appropriately, a measurement sample is obtained. In the cumulative frequency curve of the particle size obtained by the dynamic light scattering method, the particle size having a cumulative frequency of 50% is defined as the average particle size, and the ratio of the 10% cumulative particle size to the 90% particle size is similarly determined. An example of a measuring apparatus that employs such a principle, which can be used as a distribution index, is LB-500 manufactured by Horiba, Ltd.
 
また、第１粒子及び第２粒子の粒度分布は、２～５０であることが好ましく、より好ましくは２～１０である。この粒度分布を上記範囲とすることで、最大平均粒径が大きくなりすぎず、平坦な粒子層が得られ易く、均一な表面処理が実現され易くなる。
The particle size distribution of the first particles and the second particles is preferably 2 to 50, more preferably 2 to 10. By setting the particle size distribution in the above range, the maximum average particle size does not become too large, a flat particle layer is easily obtained, and uniform surface treatment is easily realized.
 
第１粒子と第２粒子との配合量は、同程度か、第２粒子が多い方が好ましい。
The blending amount of the first particles and the second particles is preferably about the same or more of the second particles.
 
太陽光を良好に閉じ込め、上記した低い反射率のテクスチャ構造面を実現可能な凹凸構造１０ｔを得る為には、液状組成物の成膜面における上記第１粒子の被覆率が３０％以上　　７０％以下であることが好ましい。従って、かかる被覆率を実現可能な範囲となるように、液状組成物中の第１粒子及び第２粒子の配合量、配合比率、及び平均粒径を設計する。
In order to obtain a concavo-convex structure 10t capable of confining sunlight well and realizing the texture structure surface having the low reflectance described above, the coverage of the first particles on the film-formed surface of the liquid composition is 30% or more and 70%. The following is preferable. Therefore, the blending amount, blending ratio, and average particle size of the first particles and the second particles in the liquid composition are designed so that such a coverage can be achieved.
 
この被覆率とは、粒子層を被処理基板に形成したとき、第１粒子が被処理基板を覆う割合、即ち、エッチング方向から見たとき、当該第１粒子が被覆基板に投影される面積の割合を示す。この被覆率は、次のようにして測定される。被処理基板に貼り合わせた後に走査型電子顕微鏡や光学顕微鏡を使いその表面を観察し、投影面積から算出することができる。
The coverage is the ratio of the first particles covering the substrate to be processed when the particle layer is formed on the substrate to be processed, that is, the area of the first particle projected onto the substrate when viewed from the etching direction. Indicates the percentage. This coverage is measured as follows. After bonding to the substrate to be processed, the surface can be observed using a scanning electron microscope or an optical microscope, and can be calculated from the projected area.
 
結着剤５３としては、特に制限されないが、例えば、水溶性の高分子材料や有機溶媒可溶性高分子材料が挙げられる。特に、環境負荷、設備の簡略化の観点から、水溶性のものが好適である。
Although it does not restrict | limit especially as the binder 53, For example, a water-soluble polymeric material and an organic-solvent soluble polymeric material are mentioned. In particular, water-soluble ones are preferable from the viewpoint of environmental load and facility simplification.
 
また、結着剤５３は、上記高分子材料を形成し得る重合性モノマーを、粒子層を構成するその他の成分と混合し、表面処理用液状組成物を構成し、塗布後に光や熱による重合反応により成膜化、つまり粒子層を形成するようにしてもよい。
In addition, the binder 53 is composed of a polymerizable monomer capable of forming the above polymer material and other components constituting the particle layer to form a liquid composition for surface treatment, and is polymerized by light or heat after coating. A film may be formed by reaction, that is, a particle layer may be formed.
 
その重合性モノマーの例としては、（メタ）アクリル系モノマーとして、（メタ）アクリル酸Ｃ１～Ｃ１２アルキルエステルや、これらと新和性のあるアクリル系改質剤として公知の化合物を併用することができる。アクリル系改質剤としては、例えばカルボキシ含有モノマーや酸無水物含有モノマーが挙げられる。これらの重合性モノマノマーは公知の重合方法で重合させることができ、重合に必要な開始剤や連鎖移動剤、オリゴマー材料や界面活性剤など、公知の材料から適宜選択できる。また、重合性モノマーの例としては、公知のエポキシ系モノマーやイソシアネート系モノマーが挙げられる。
Examples of the polymerizable monomer include a (meth) acrylic monomer, a (meth) acrylic acid C1-C12 alkyl ester, and a compound known as a new acrylic modifier with these. it can. Examples of the acrylic modifier include carboxy-containing monomers and acid anhydride-containing monomers. These polymerizable monomer monomers can be polymerized by a known polymerization method, and can be appropriately selected from known materials such as an initiator, a chain transfer agent, an oligomer material, and a surfactant necessary for the polymerization. Examples of the polymerizable monomer include known epoxy monomers and isocyanate monomers.
 
より具体的には、例えば、ガラス転移温度が－１００～５０℃、数平均分子量が１，０００～２００，０００、好ましくは５，０００～１００，０００、重合度が約５０～１０００程度のものが好適に挙げられる。このような例としては、塩化ビニル、酢酸ビニル、ビニルアルコール、マレイン酸、アクリル酸、アクリル酸エステル、塩化ビニリデン、アクリロニトリル、メタクリル酸、メタクリル酸エステル、スチレン、ブタジエン、エチレン、ビニルブチラール、ビニルアセタール、ビニルエ－テル、等を構成単位として含む重合体又は共重合体、ポリウレタン樹脂、各種ゴム系樹脂、重量平均分子量が１０００００以下のポリビニルアルコール変性体などがある。
More specifically, for example, those having a glass transition temperature of −100 to 50 ° C., a number average molecular weight of 1,000 to 200,000, preferably 5,000 to 100,000, and a degree of polymerization of about 50 to 1000 Are preferable. Examples of such include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, Examples include polymers or copolymers containing vinyl ether as a constituent unit, polyurethane resins, various rubber resins, and modified polyvinyl alcohol having a weight average molecular weight of 100,000 or less.
 
より好ましい結着剤としては、易水溶性である、ポリビニルアルコールもしくはその誘導体、セルロース系誘導体（ポリビニルピロリドン、カルボシキメチルセルロース、ヒドロキシエチルセルロース等）、天然多糖類もしくはその誘導体（デンプン、キサンタンガムやアルギンサン等）、ゼラチン、水分散可能なウレタン、アクリル系高分子ラテックスなども挙げられる。
More preferable binders include polyvinyl alcohol or derivatives thereof, cellulose derivatives (polyvinyl pyrrolidone, carboxymethyl cellulose, hydroxyethyl cellulose, etc.), natural polysaccharides or derivatives thereof (starch, xanthan gum, alginsan, etc.) that are readily water-soluble. Gelatin, water-dispersible urethane, acrylic polymer latex and the like are also included.
 
結着剤の配合量は、粒子群の分散性に応じて適宜設定されるが、例えば、粒子群に対して５重量％～５０重量％が好ましく、より好ましくは１０重量％～３０重量％である。
The blending amount of the binder is appropriately set according to the dispersibility of the particle group. For example, it is preferably 5% by weight to 50% by weight, more preferably 10% by weight to 30% by weight with respect to the particle group. is there.
 
上記液状組成物には、上記した以外、粒子群を安定に分散させることができる分散剤や、例えば、製造時における塗布液の粘度や表面張力を調整する界面活性剤及び溶媒などを含んでいてもよい。
In addition to the above, the liquid composition contains a dispersant that can stably disperse the particle group, and, for example, a surfactant and a solvent that adjust the viscosity and surface tension of the coating liquid during production. Also good.
 
特に分散剤としては、フェニルホスホン酸、具体的には日産化学（株）社の「ＰＰＡ」など、αナフチル燐酸、フェニル燐酸、ジフェニル燐酸、ｐ－エチルベンゼンホスホン酸、フェニルホスフィン酸、アミノキノン類、各種シランカップリング剤、チタンカップリング剤、フッ素含有アルキル硫酸エステル及びそのアルカリ金属塩、などが使用できる。また、アルキレンオキサイド系、グリセリン系、グリシドール系、アルキルフェノールエチレンオキサイド付加体、等のノニオン界面活性剤、環状アミン、エステルアミド、第四級アンモニウム塩類、ヒダントイン誘導体、複素環類、ホスホニウム又はスルホニウム類等のカチオン系界面活性剤、カルボン酸、スルフォン酸、燐酸、硫酸エステル基、燐酸エステル基、などの酸性基を含むアニオン界面活性剤、アミノ酸類、アミノスルホン酸類、アミノアルコールの硫酸又は燐酸エステル類、アルキルベダイン型、等の両性界面活性剤等も使用できる。また、分散剤としては、ポリオキシエチレンアルキルフェニルエーテル、ポリオキシアルキレンブロック共重合体、アリル基などの重合性不飽和結合を有するポリオキシエチレンアルキルフェニルエーテル等を選択してもよい。これらの分散剤（界面活性剤）については、「界面活性剤便覧」（産業図書株式会社発行）に詳細に記載されている。これらの分散剤等は必ずしも１００％純粋ではなく、主成分以外に異性体、未反応物、副反応物、分解物、酸化物等の不純分が含まれてもかまわない。これらの不純分は３０％以下が好ましく、さらに好ましくは１０％以下である。本発明は脂肪酸エステルとしてＷＯ９８／３５３４５号パンフレットに記載のようにモノエステルとジエステルを組み合わせて使用することも好ましい。
In particular, as the dispersant, phenylphosphonic acid, specifically “PPA” manufactured by Nissan Chemical Co., Ltd., α-naphthyl phosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones, various Silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof can be used. In addition, nonionic surfactants such as alkylene oxide, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocyclics, phosphonium or sulfoniums, etc. Cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphate ester group, amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohol, alkyl Bedin type amphoteric surfactants and the like can also be used. As the dispersant, polyoxyethylene alkylphenyl ether, polyoxyalkylene block copolymer, polyoxyethylene alkylphenyl ether having a polymerizable unsaturated bond such as an allyl group, or the like may be selected. These dispersants (surfactants) are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.). These dispersants and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, side reaction products, decomposition products, and oxides in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. In the present invention, it is also preferable to use a combination of a monoester and a diester as described in the pamphlet of WO 98/35345 as a fatty acid ester.
 
液状組成物を構成する溶媒としては、結着剤種に合わせて、当該結着剤を溶解する溶媒から選択される。具体的には、例えば、結着剤として水溶性のものを適用する場合、溶媒として水系溶媒を適用することが、環境負荷、設備の簡略化の観点からよい。
The solvent constituting the liquid composition is selected from solvents that dissolve the binder according to the binder type. Specifically, for example, when applying a water-soluble binder as a binder, it is preferable to apply an aqueous solvent as a solvent from the viewpoint of environmental load and simplification of equipment.
 
水系溶媒としては、例えば、水、低級アルコ－ル（メタノ－ル、エタノ－ル、ブタノ－ル、イソプロピルアルコ－ル等）が挙げられる。溶媒としては、水が最も好ましい。
Examples of the aqueous solvent include water and lower alcohols (methanol, ethanol, butanol, isopropyl alcohol, etc.). As the solvent, water is most preferable.
 
上記した複数の第１粒子５１と複数の第２粒子５２とを含む粒子群、結着剤５３、及びその他の添加物を含む場合はそれらを溶媒中に添加し、結着剤５３が溶解された溶媒中に上記粒子群が略均一に分散されて含まれるように攪拌混合して液状組成物を得る。分散性良く粒子群が含まれる液状組成物とするには、攪拌混合の方法として、高速剪断を与えるディゾルバなどのような攪拌羽根で混合分散させて調製する方法、超音波分散機等の分散装置で混合分散させて調製する方法などを用いることが好ましい。
When the particle group including the plurality of first particles 51 and the plurality of second particles 52, the binder 53, and other additives are included, they are added to the solvent, and the binder 53 is dissolved. A liquid composition is obtained by stirring and mixing so that the particle group is dispersed in a substantially uniform manner. In order to obtain a liquid composition containing a group of particles with good dispersibility, as a method of stirring and mixing, a method of mixing and dispersing with a stirring blade such as a dissolver that gives high-speed shearing, a dispersing device such as an ultrasonic disperser It is preferable to use a method of preparing by mixing and dispersing with the method described above.
 
（液状組成物の塗布成膜）
上記のようにして調製された液状組成物を、図２（ｂ）に示されるように、結晶Ｓｉ基板１０の凹凸構造１０ｔ形成面に塗布成膜する。成膜方法は特に制限されず、塗布方法はスプレー法、スピンコート法、ディップ法、ロールコート法、プレートコート法、ドクターブレード法、スクリーン印刷法等が挙げられるが、生産性を考慮するとスピンコート法やスプレー法が好ましい。
(Liquid composition coating)
The liquid composition prepared as described above is applied and formed on the surface of the crystalline Si substrate 10 where the concavo-convex structure 10t is formed, as shown in FIG. The film forming method is not particularly limited, and examples of the coating method include spray method, spin coating method, dip method, roll coating method, plate coating method, doctor blade method, and screen printing method. The method and the spray method are preferable.
 
塗布厚みは100nmから1000nmが好ましく、さらには300nm～600nmが好ましい。スピンコート法の場合はウェハーの裏面にマスク材料が回り込まないように試料台を結晶Ｓｉ基板と同じにすることが好ましい。また裏面に回りこんだ場合は洗浄することが好ましい。
The coating thickness is preferably 100 nm to 1000 nm, more preferably 300 nm to 600 nm. In the case of the spin coating method, it is preferable to make the sample stage the same as the crystalline Si substrate so that the mask material does not go around the back surface of the wafer. Moreover, when it wraps around the back surface, it is preferable to wash.
 
また、結着剤５３としては、上記した以外に、上記高分子材料を形成し得る重合性モノマーを用いてもよい。かかる構成では、結着剤５３中に、後記する溶媒を除く粒子層を構成するその他の成分と混合した液状組成物とし、この液状組成物を成膜面１０ｓに塗布後、光や熱により重合させることにマスク材５０を成膜することができる。
Moreover, as the binder 53, in addition to the above, a polymerizable monomer capable of forming the polymer material may be used. In such a configuration, a liquid composition is mixed in the binder 53 with other components constituting the particle layer excluding the solvent described later, and this liquid composition is applied to the film formation surface 10s and then polymerized by light or heat. Thus, the mask material 50 can be formed.
 
かかる重合性モノマーの例としては、（メタ）アクリル系モノマーとして、（メタ）アクリル酸Ｃ１～Ｃ１２アルキルエステルや、これらと新和性のあるアクリル系改質剤として公知の化合物を併用することができる。アクリル系改質剤としては、例えばカルボキシ含有モノマーや酸無水物含有モノマーが挙げられる。これらの重合性モノマノマーは公知の重合方法で重合させることができ、重合に必要な開始剤や連鎖移動剤、オリゴマー材料や界面活性剤など、公知の材料から適宜選択できる。また、重合性モノマーの例としては、公知のエポキシ系モノマーやイソシアネート系モノマーが挙げられる。
Examples of such polymerizable monomers include (meth) acrylic monomers used in combination with (meth) acrylic acid C1 to C12 alkyl esters, and compounds known as acrylic modifiers that are compatible with these. it can. Examples of the acrylic modifier include carboxy-containing monomers and acid anhydride-containing monomers. These polymerizable monomer monomers can be polymerized by a known polymerization method, and can be appropriately selected from known materials such as an initiator, a chain transfer agent, an oligomer material, and a surfactant necessary for the polymerization. Examples of the polymerizable monomer include known epoxy monomers and isocyanate monomers.
 
（ドライエッチング処理）
次に、図２（ｃ）に示されるように、マスク材５０上からドライエッチング処理を施し、凹凸構造１０ｔを形成する。ドライエッチングの方法は特に制限されないが、エッチングガスの直進性が高く、微細なパターニングが可能であることから、反応ガスをプラズマによりイオン化・ラジカル化してエッチングを施す反応性イオンエッチング（ＲＩＥ）が好ましく、中でも誘導結合方式の反応性イオンエッチングであるＩＣＰが好ましい。
(Dry etching process)
Next, as shown in FIG. 2C, a dry etching process is performed on the mask material 50 to form the concavo-convex structure 10t. The dry etching method is not particularly limited, but reactive ion etching (RIE) in which etching is performed by ionizing / radicalizing the reactive gas with plasma is preferable because the etching gas is highly straight and fine patterning is possible. In particular, ICP which is inductive coupling type reactive ion etching is preferable.
 
エッチングガスとしては塩素系ガス、フッ素系ガス、臭素系ガスが好ましく、中でも六フッ化硫黄（ＳＦ６）ガスがより好ましい。また、これらのガス中に酸素ガスを混合させた混合ガスを用いることが、よりエッチング特性が良好となるため好ましく、中でも六フッ化硫黄ガスと酸素ガスの混合ガスを用いる場合は、より微細な凹凸構造を得ることができるためより好ましい。
As the etching gas, chlorine-based gas, fluorine-based gas, and bromine-based gas are preferable, and sulfur hexafluoride (SF 6 ) gas is more preferable. In addition, it is preferable to use a mixed gas in which oxygen gas is mixed in these gases because etching characteristics become better. In particular, when a mixed gas of sulfur hexafluoride gas and oxygen gas is used, a finer gas is used. Since an uneven structure can be obtained, it is more preferable.
 
エッチング処理が施されると、図２（ｄ）に示されるように、第１粒子５１で被覆された領域を除く、マスク材５０を構成する結着剤５３がエッチングされると共に、第２粒子５２もエッチングされる。
When the etching process is performed, as shown in FIG. 2D, the binder 53 constituting the mask material 50 excluding the region covered with the first particles 51 is etched and the second particles 52 is also etched.
 
これにより、エッチングされた領域が凹部となり、エッチングされない領域が凸部となり、結晶Ｓｉ基板１０の表面に凹凸構造１０ｔが形成される。なお、当該エッチングされる領域では、マスク材５０ごとエッチングされる。
Thereby, the etched region becomes a concave portion, and the non-etched region becomes a convex portion, and the concavo-convex structure 10 t is formed on the surface of the crystalline Si substrate 10. Note that the mask material 50 is etched in the region to be etched.
 
ドライエッチング処理を施すための条件は、マスク材５０の厚み・種類（結着剤５３の種類や粒子群の種類など）に応じて、適宜設定される。例えば、後記実施例１にて使用したマスク材５０を用いたドライエッチング処理において、処理時間と反射率の関係について調べた結果、処理時間６分で反射率６％を達成し、処理時間9分では反射率３％を達成した。また、処理時間１０分においても反射率は３％程度であった。これらの結果から、反射率５％程度を実現し得ると判断されるドライエッチング処理時間は約８分間の処理であることが確認された。従って、本実施形態において、ドライエッチング処理時間は８分以上であることが好ましく、８～１０分であることがより好ましく、８～９分であることが更に好ましい（ドライエッチングの装置及びその他の条件は実施例１を参照）。ただしエッチング時のパワー等を上げることにより時間短縮は可能である。
Conditions for performing the dry etching process are appropriately set according to the thickness and type of the mask material 50 (type of binder 53, type of particle group, etc.). For example, in the dry etching process using the mask material 50 used in Example 1 to be described later, as a result of examining the relationship between the processing time and the reflectance, the reflectance of 6% was achieved in the processing time of 6 minutes, and the processing time of 9 minutes. Then, a reflectance of 3% was achieved. Further, the reflectance was about 3% even at a processing time of 10 minutes. From these results, it was confirmed that the dry etching processing time determined to be able to achieve a reflectance of about 5% was about 8 minutes. Therefore, in the present embodiment, the dry etching treatment time is preferably 8 minutes or more, more preferably 8 to 10 minutes, and further preferably 8 to 9 minutes (dry etching apparatus and other devices). See Example 1 for conditions). However, the time can be shortened by increasing the power during etching.
 
（洗浄処理）
ドライエッチング後の凹凸構造１０ｔの表面１０ｓには、第１粒子５１や第２粒子５２、結着剤５３及び、エッチングガスの構成元素を含むエッチング残渣、更にプラズマダメージが存在している。図３（ａ）に、ドライエッチングによる凹凸形成（約９分）後、超音波洗浄（純水中、５分）洗浄を行った後の表面ＳＥＭ写真を示す。図３（ａ）には、右上部にシリカ残渣がはっきりと確認される。また、ＳＥＭ写真では確認することが難しいが、Ｓｉ基板をドライエッチング処理すると、その加工表面にステイン層と呼ばれる極微細な凹凸ができることが知られており、この層の存在により表面物性に影響を及ぼすことから、かかるステイン層をプラズマダメージと称している。
(Cleaning process)
On the surface 10 s of the concavo-convex structure 10 t after dry etching, there are etching residues including the first particles 51 and the second particles 52, the binder 53, and constituent elements of the etching gas, and further plasma damage. FIG. 3 (a) shows a surface SEM photograph after the formation of irregularities by dry etching (about 9 minutes), followed by ultrasonic cleaning (pure water, 5 minutes). In FIG. 3A, the silica residue is clearly confirmed in the upper right part. Although it is difficult to confirm with an SEM photograph, it is known that when a Si substrate is subjected to dry etching, extremely fine irregularities called a stain layer are formed on the processed surface, and the presence of this layer affects the surface physical properties. Therefore, this stain layer is called plasma damage.
 
上記エッチング残渣及びプラズマダメージの存在により、後工程のｐｎ接合形成において、ｎ型ドーパント（例えばリン）の拡散の際、ドーパントガス(例えば燐酸ガス)の熱拡散を行うが、エッチング残渣やプラズマダメージの存在により、その拡散が阻害されるため、良好なｐｎ接合を形成することができなくなる。従って、本実施形態では、ｎ型ドーパントの拡散前に、エッチング残渣及びプラズマダメージの除去を行う。
Due to the presence of the etching residue and plasma damage, the thermal diffusion of the dopant gas (for example, phosphoric acid gas) is performed when the n-type dopant (for example, phosphorus) is diffused in the subsequent pn junction formation. Due to the presence, the diffusion is inhibited, so that a good pn junction cannot be formed. Therefore, in this embodiment, the etching residue and plasma damage are removed before the diffusion of the n-type dopant.
 
エッチング残渣は、主に上記第２粒子（エッチング耐性の高い粒子）であり、その他、エッチングガスとの反応物（硫黄やフッ素の化合物）などがある。これらの残渣は主に、凹凸構造１０ｔの凸部１０１上であるが、凹部１０２にも残っている場合もある。
The etching residue is mainly the second particles (particles having high etching resistance), and other reactants (such as sulfur and fluorine compounds) with the etching gas. These residues are mainly on the convex portions 101 of the concavo-convex structure 10t, but may also remain in the concave portions 102.
 
これらの洗浄方法としては、これまで超音波洗浄や溶剤のスピン洗浄等様々な方法が採用できるが完全に表面付着物を除去できるまでには長時間かかる。また強い洗浄条件で行うと形成された凹凸形状が崩れ、反射率が逆に上がってしまうという問題があった（図３（ｂ）→（ｃ））を参照。
As these cleaning methods, various methods such as ultrasonic cleaning and solvent spin cleaning can be adopted so far, but it takes a long time to completely remove surface deposits. In addition, there is a problem that the formed uneven shape is broken when the cleaning conditions are strong, and the reflectance is increased (see FIGS. 3B to 3C).
 
そこで本発明者は、洗浄効果とダメージ低減の両立を鋭意検討した。その結果、上記エッチング残渣及びプラズマダメージを良好に取り除き、高い光電変換効率を達成可能とする２種類の洗浄方法を見出した。以下にその洗浄方法を説明する。
Therefore, the present inventor has earnestly studied to achieve both a cleaning effect and damage reduction. As a result, the inventors have found two cleaning methods that can satisfactorily remove the etching residue and plasma damage and achieve high photoelectric conversion efficiency. The cleaning method will be described below.
 
＜＜第１の洗浄方法：水素ガスを用いたドライエッチング＞＞
第１の洗浄方法では、まず、図２（ｃ）に示されるように、ドライエッチングによる凹凸構造１０ｔの上方より、水素ガスによるドライエッチングを実施する（図中矢印↓）。ここで、水素ガスによるドライエッチング（以下、「水素エッチング」とする）は、シリコン基板表面の自然酸化膜を水素還元により除去することを目的としている水素還元処理とは異なるものであり、エッチング残渣とプラズマダメージを除去するための処理である。しかしながら、シリコン基板表面に対して水素が施されるため、表面の酸化膜の除去も同じプロセス中に実施されることもある。
<< First cleaning method: dry etching using hydrogen gas >>
In the first cleaning method, first, as shown in FIG. 2C, dry etching with hydrogen gas is performed from above the uneven structure 10t by dry etching (arrow ↓ in the figure). Here, the dry etching with hydrogen gas (hereinafter referred to as “hydrogen etching”) is different from the hydrogen reduction treatment for removing the natural oxide film on the surface of the silicon substrate by hydrogen reduction. And a process for removing plasma damage. However, since hydrogen is applied to the silicon substrate surface, removal of the oxide film on the surface may be performed during the same process.
 
ドライエッチングの方法は特に制限されず、プロセスの容易性から前工程である凹凸形成と同様の装置にて実施できる方法を選択することが好ましい。
The method of dry etching is not particularly limited, and it is preferable to select a method that can be carried out in the same apparatus as that for forming the concavo-convex that is the previous step because of ease of process.
 
水素エッチングの条件は特に制限されない。良好にエッチング残渣及びプラズマダメージが除去され、且つ、ランニングコスト及び信頼性の高いエッチングが可能な範囲とすることが好ましい。かかるエッチング条件としては、例えば、水素流量１００ｓｃｃｍ、ガス圧３Ｐａ,高周波出力（パワー）１００Ｗ,エッチング時間５分等が挙げられる。
The conditions for hydrogen etching are not particularly limited. It is preferable that the etching residue and plasma damage be removed well and the etching can be performed with high running cost and high reliability. Examples of such etching conditions include a hydrogen flow rate of 100 sccm, a gas pressure of 3 Pa, a high frequency output (power) of 100 W, and an etching time of 5 minutes.
 
水素エッチングでは、エッチング耐性がエッチング残渣（例えばシリカ）＜プラズマダメージ部＜＜結晶Ｓｉ、の順であると考えられる。従って、エッチング残渣除去を充分に実施しても、凹凸構造１０ｔの凸部１０１がエッチングされて反射率に悪影響を及ぼす恐れはあまりないと考えられる。
In hydrogen etching, it is considered that the etching resistance is in the order of etching residue (for example, silica) <plasma damage portion << crystal Si. Therefore, even if the etching residue is sufficiently removed, the projection 101 of the concavo-convex structure 10t is not likely to be etched and adversely affect the reflectance.
 
プラズマダメージであるステイン層についても、上記ドライエッチングにより良好に除去することができる。しかしながら、より効率良くステイン層を除去するためには、水素ドライエッチングの後、水酸化ナトリウム水溶液等のアルカリ液によるウエットエッチングを実施することが好ましい。アルカリ液の好ましい濃度としては、０．１～１０ｗｔ％が挙げられ、かかる濃度範囲の場合、エッチング時間を１０秒～２分とすることにより良好にステイン層を除去することができる。
The stain layer which is plasma damage can also be satisfactorily removed by the dry etching. However, in order to remove the stain layer more efficiently, it is preferable to perform wet etching with an alkali solution such as an aqueous sodium hydroxide solution after hydrogen dry etching. A preferable concentration of the alkaline solution is 0.1 to 10 wt%. In such a concentration range, the stain layer can be removed satisfactorily by setting the etching time to 10 seconds to 2 minutes.
 
凹凸形成及び表面洗浄を施したシリコン結晶基板の表面は、非常に酸化されやすく、一般に、ＳｉＯ２の酸化皮膜が形成される。かかる酸化皮膜は、水素ドライエッチングにより除去することができるが、より除去率を高くするためには、水素ドライエッチングに引き続き、希フッ酸等の酸溶液に浸漬させることが好ましい。
The surface of the silicon crystal substrate that has been subjected to unevenness formation and surface cleaning is very easily oxidized, and generally an oxide film of SiO 2 is formed. Such an oxide film can be removed by hydrogen dry etching, but in order to further increase the removal rate, it is preferable to immerse in an acid solution such as dilute hydrofluoric acid following hydrogen dry etching.
 
本発明者は、後記実施例に示されるように、マスク材５０を用いたドライエッチングによる凹凸形成後、水素エッチングを３分～１５分程度実施し、希フッ酸中への浸漬処理を施すことにより、凹凸構造１０ｔの太陽光の反射率を１％まで低減させることに成功した。かかる効果は、Ｓｉ基板１０が単結晶である場合も、多結晶である場合も同様に得ることができるがこと確認されている。
As shown in the examples described later, the present inventor performs hydrogen etching for about 3 to 15 minutes after the formation of irregularities by dry etching using the mask material 50, and performs immersion treatment in dilute hydrofluoric acid. Thus, the solar reflectance of the concavo-convex structure 10t was successfully reduced to 1%. It has been confirmed that such an effect can be obtained similarly when the Si substrate 10 is single crystal or polycrystalline.
 
＜＜第２の洗浄方法：希フッ酸中でのマイクロバブル含有超音波洗浄＞＞
第２の洗浄方法では、マイクロバブルを含ませた希フッ酸中での超音波洗浄処理を実施する。希フッ酸中に凹凸構造を浸漬させてエッチング残渣を超音波洗浄する技術は公知技術であり、エッチング残渣を希フッ酸で溶解させ、超音波による微細な振動によりその効果を促進するものである。しかしながら、かかる洗浄だけでは、上記した本実施形態の凹凸構造１０ｔ表面に存在するエッチング残渣及びプラズマダメージの除去を充分に、また効率的に行うことができない。
<< second cleaning method: ultrasonic cleaning containing microbubbles in dilute hydrofluoric acid >>
In the second cleaning method, an ultrasonic cleaning process is performed in dilute hydrofluoric acid containing microbubbles. The technique of ultrasonically cleaning the etching residue by immersing the concavo-convex structure in dilute hydrofluoric acid is a known technique, and the effect is promoted by dissolving the etching residue with dilute hydrofluoric acid and finely vibrating with ultrasonic waves. . However, such cleaning alone cannot sufficiently and efficiently remove the etching residue and plasma damage existing on the surface of the concavo-convex structure 10t of the present embodiment.
 
本発明者は、本実施形態の凹凸構造１０ｔのように、サブミクロンオーダの微細凹凸構造中に点在するエッチング残渣やプラズマダメージを溶解により除去するには、超音波の振動だけではなく、更に物理的な力を除去対象物及びその周辺に加える必要があると考え、超音波の発生している希フッ酸溶液中に、更にマイクロバブルを同時に供給しながら洗浄することにより、上記した第１の洗浄方法とほぼ同等に、エッチング残渣やプラズマダメージを良好に除去できることを見出した。
In order to remove etching residues and plasma damage scattered in the fine concavo-convex structure on the order of submicron, such as the concavo-convex structure 10t of this embodiment, the present inventor not only uses ultrasonic vibration, Considering that it is necessary to apply a physical force to the object to be removed and its surroundings, cleaning is performed while simultaneously supplying microbubbles in a dilute hydrofluoric acid solution in which ultrasonic waves are generated. It has been found that etching residues and plasma damage can be satisfactorily removed in substantially the same manner as in the above cleaning method.
 
希フッ酸の濃度としては０．５～５ｗｔ％であることが好ましい。希フッ酸濃度が濃いほど洗浄時間を短縮することができるが、取り扱い性の観点から、濃度は薄い方が好ましい。本実施形態のように、超音波とマイクロバブルを含ませた洗浄を行う場合は、希フッ酸の濃度は比較的低濃度でも充分に洗浄効果を得ることができる。
The concentration of dilute hydrofluoric acid is preferably 0.5 to 5 wt%. The cleaning time can be shortened as the concentration of dilute hydrofluoric acid is increased, but a lower concentration is preferable from the viewpoint of handleability. When cleaning is performed with ultrasonic waves and microbubbles as in the present embodiment, a sufficient cleaning effect can be obtained even if the concentration of dilute hydrofluoric acid is relatively low.
 
また、マイクロバブルとしては、特にその直径は制限されないが、１０～数百μｍの範囲であることが好ましい。また、本発明は泡のサイズの分布の程度は特に限定されない。ほぼ単一の分布を有する微細な泡、種々のサイズの複数の分布を有する微細な泡をも含む。また処理工程の間に泡のサイズが変動する場合も含む。
The diameter of the microbubbles is not particularly limited, but is preferably in the range of 10 to several hundred μm. In the present invention, the degree of bubble size distribution is not particularly limited. Also included are fine bubbles having a substantially single distribution and fine bubbles having a plurality of distributions of various sizes. It also includes the case where the bubble size varies during the processing step.
 
また、マイクロバブル中の成分気体は特に制限されず、成分気体は単一の成分でも混合成分の気体でもよく、適宜選択することができる。具体的には、マイクロバブルの成分気体としては、水素、酸素、窒素、二酸化炭素、オゾン、フッ素、塩素、臭素、ヨウ素、アルゴン、ヘリウムからなる群より選ばれる少なくとも１種が挙げられ、特に、窒素、アルゴンが好ましい。
The component gas in the microbubbles is not particularly limited, and the component gas may be a single component or a mixed component gas, and can be appropriately selected. Specifically, the component gas of the microbubble includes at least one selected from the group consisting of hydrogen, oxygen, nitrogen, carbon dioxide, ozone, fluorine, chlorine, bromine, iodine, argon, helium, Nitrogen and argon are preferred.
 
また、マイクロバブルの大きさは特に制限されないが、バブルの直径が、１０～１００μｍである場合に良好な洗浄効果を得ることができる。
The size of the microbubbles is not particularly limited, but a good cleaning effect can be obtained when the bubble diameter is 10 to 100 μm.
 
このようにマイクロバブルと超音波の発生下での洗浄の場合、これらの物理的な力のみでエッチング残渣及びプラズマダメージをある程度除去することが可能である。特にこれらの除去対象物が少ない場合は純水中での洗浄で充分である。
Thus, in the case of cleaning under the generation of microbubbles and ultrasonic waves, it is possible to remove etching residues and plasma damage to some extent only by these physical forces. In particular, when there are few objects to be removed, washing in pure water is sufficient.
 
しかしながら、純水による洗浄では、第１の洗浄方法において述べた、自然酸化膜の除去を更に実施する必要がある。このように、マイクロバブルと超音波発生下での純水による洗浄を行った後に、希フッ酸に浸漬させて自然酸化膜の除去を行ってもよいが、希フッ酸中での洗浄とすることにより、洗浄時間も短縮される上、自然酸化膜の除去も洗浄と同時に実施することができ、プロセスも簡易になる。
However, in cleaning with pure water, it is necessary to further remove the natural oxide film described in the first cleaning method. In this way, after cleaning with pure water under the generation of microbubbles and ultrasonic waves, the natural oxide film may be removed by immersion in diluted hydrofluoric acid, but cleaning in diluted hydrofluoric acid is performed. As a result, the cleaning time is shortened, and the natural oxide film can be removed simultaneously with the cleaning, thereby simplifying the process.
 
プラズマダメージであるステイン層の除去については、上記第１の洗浄方法で述べたとおりの方法を用いればよい。
For removal of the stain layer that is plasma damage, the method described in the first cleaning method may be used.
 
既に述べたように、従来のウエットエッチング及びドライエッチングによるテクスチャ構造の形成では、多結晶Ｓｉ基板の場合は、多結晶の結晶粒の面方位の非一様性により、反射率を低下させることが難しく、２０％台と高いものであり、単結晶の場合でも１０％前後であった。これに比して、上記第１の洗浄方法及び第２の洗浄方法いずれの場合にも、良好で高効率な洗浄を行うことができ、更に、上記マスク材５０を用いたドライエッチングによる凹凸構造１０ｔの形成を組み合わせた態様では、単結晶、多結晶にかかわらず、多数の針状の凸部を有する、太陽光の反射を高効率に抑制できるテクスチャ構造面を形成することができる。
As described above, in the formation of a texture structure by conventional wet etching and dry etching, in the case of a polycrystalline Si substrate, the reflectance may be reduced due to non-uniformity of the plane orientation of the polycrystalline crystal grains. It is difficult and is as high as 20%. Even in the case of a single crystal, it was around 10%. Compared to this, both the first cleaning method and the second cleaning method can perform good and highly efficient cleaning, and further, the concavo-convex structure by dry etching using the mask material 50. In an aspect in which the formation of 10t is combined, it is possible to form a textured structure surface having a large number of needle-like convex portions and capable of suppressing reflection of sunlight with high efficiency regardless of single crystal or polycrystal.
 
なお、第１の洗浄方法、第２の洗浄方法のいずれにおいても、洗浄後のテクスチャ構造面（凹凸構造１０ｔ）にアルカリ性又は酸性の水溶液が付着している場合には、中和をしておくことが好ましい。更に、次工程のｐｎ接合形成時には、テクスチャ構造面１０ｓを充分に乾燥させておくことが好ましい。
In either the first cleaning method or the second cleaning method, neutralization is performed when an alkaline or acidic aqueous solution adheres to the texture structure surface (uneven structure 10t) after cleaning. It is preferable. Furthermore, it is preferable to sufficiently dry the texture structure surface 10s when forming the pn junction in the next step.
 
（ｐｎ形成）
次に、図２（ｅ）に示されるように、洗浄後のｐ型シリコンウエハのテクスチャ構造面（凹凸構造１０ｔ）から、ｎ型ドーパント（リン等）を拡散させてｎ層を形成し、ｐｎ接合を形成する。ｎ型ドーパントがリンである場合は、例えば、塩化ホスホリル（ＰＯＣｌ３）を拡散源としたガス拡散法等により、リンを熱拡散させてｐｎ接合の形成を行う（拡散温度は８００℃。）。
(Pn formation)
Next, as shown in FIG. 2E, an n layer is formed by diffusing an n-type dopant (phosphorus or the like) from the textured surface (uneven structure 10t) of the p-type silicon wafer after cleaning, and pn Form a bond. When the n-type dopant is phosphorus, phosphorus is thermally diffused by, for example, a gas diffusion method using phosphoryl chloride (POCl 3 ) as a diffusion source to form a pn junction (diffusion temperature is 800 ° C.).
 
次に側面や裏面に回りこんだ余分なｐ層やｎ層を削ってｐｎ分離を行う。分離方法は特に制限されず、希フッ酸でのウエットエッチングやプラズマエッチング等を採用してよい。また、リンを拡散させた場合は、テクスチャ構造面１０ｓにリン酸ガラスが生成されるので、希フッ酸での浸漬で除去することが好ましい。
Next, pn separation is performed by cutting off the excess p layer and n layer that wrap around the side surface and the back surface. The separation method is not particularly limited, and wet etching or plasma etching with dilute hydrofluoric acid may be employed. Further, when phosphorus is diffused, phosphate glass is generated on the texture structure surface 10s, and therefore, it is preferably removed by immersion in dilute hydrofluoric acid.
 
既に述べたように、本実施形態の光電変換素子１では、テクスチャ構造面１０ｓ（凹凸構造１０ｔ）が、エッチング残渣及びプラズマダメージが良好に除去されている。このことは、後記実施例図４（ａ），（ｂ）から確認することができる。図４（ａ），（ｂ）は、電子顕微鏡によるテクスチャ構造１０ｓの表面ＳＥＭ像であり、倍率を５０００倍、１００００倍としたものである。図示されるように、いずれの写真においてもエッチング残渣及びプラズマダメージは観察されない。
As already described, in the photoelectric conversion element 1 of the present embodiment, the etching residue and plasma damage are satisfactorily removed from the texture structure surface 10s (uneven structure 10t). This can be confirmed from the examples shown in FIGS. 4 (a) and 4 (b). FIGS. 4A and 4B are surface SEM images of the texture structure 10s obtained by an electron microscope. The magnification is set to 5000 times and 10,000 times. As shown in the figure, neither etching residue nor plasma damage is observed in any of the photographs.
 
従って、光電変換素子１では、テクスチャ構造面１０ｓにおいて、ｐｎ形成の阻害要因となるエッチング残渣やプラズマダメージが非常に少ないため、良好且つ略一様なｐｎ接合を形成することができる。ｐｎ接合の部分的な欠損や、面内不均一性は、光電変換素子の光電変換効率に大きな影響を及ぼす。光電変換素子１では、上記のように、良好且つ略一様なｐｎ接合を形成することができるため、テクスチャ構造面１０ｓにより高効率に光電変換層１０内に入射された太陽光を高効率に光電変換することができる。
Therefore, in the photoelectric conversion element 1, since the etching residue and the plasma damage which become the inhibition factor of pn formation are very few in the texture structure surface 10s, a favorable and substantially uniform pn junction can be formed. Partial loss of the pn junction and in-plane non-uniformity greatly affect the photoelectric conversion efficiency of the photoelectric conversion element. Since the photoelectric conversion element 1 can form a good and substantially uniform pn junction as described above, the sunlight that has entered the photoelectric conversion layer 10 with high efficiency by the texture structure surface 10s has high efficiency. Photoelectric conversion can be performed.
 
（電極形成）
次に、図２（ｆ）に示されるように、裏面１０ｒに裏面電極２０を形成し、次いで、ｐｎ接合が形成されたテクスチャ構造面１０ｓ上に、該面を略一様に被覆する透光性導電層３０を直接成膜する（図２（ｇ））。
(Electrode formation)
Next, as shown in FIG. 2 (f), the back electrode 20 is formed on the back surface 10r, and then the translucent light that covers the surface substantially uniformly on the textured surface 10s on which the pn junction is formed. The conductive conductive layer 30 is directly formed (FIG. 2G).
 
裏面電極２０及び透光性導電層３０の成膜方法としては特に制限されないが、スパッタ法、ＣＶＤ法、ＭＯＣＶＤ法、ＭＢＥ法等の気相法でもよいし、液相法により形成してもよい。裏面電極２０は銀ペーストやＡｌペーストをスクリーン印刷法等により塗布した後焼成して形成してもよい。
A method for forming the back electrode 20 and the translucent conductive layer 30 is not particularly limited, but may be a vapor phase method such as a sputtering method, a CVD method, an MOCVD method, an MBE method, or a liquid phase method. . The back electrode 20 may be formed by applying a silver paste or an Al paste by a screen printing method or the like and then baking.
 
光電変換素子１では、このように、テクスチャ構造面１０ｓ上に直接成膜された、透光性導電層３０を表面電極とすることができる。かかる構成では、表面電極が透光性であるため、従来の櫛形電極に比して発電面積を広くすることできる。またｐｎ接合のすぐ上に電極が形成できるため電極までの経路が短縮されるので直列抵抗を低減できる。従って、これらの相乗効果により高効率な発電効率を達成することができる。
In the photoelectric conversion element 1, the translucent conductive layer 30 formed directly on the texture structure surface 10 s can be used as a surface electrode in this way. In such a configuration, since the surface electrode is translucent, the power generation area can be increased as compared with the conventional comb electrode. Further, since the electrode can be formed immediately above the pn junction, the path to the electrode is shortened, so that the series resistance can be reduced. Therefore, highly efficient power generation efficiency can be achieved by these synergistic effects.
 
更に、従来の櫛形電極のように局所的な電極形成が不要であるために高温焼成の必要がない。高温焼成は、従って、本発明によれば、入射光の利用効率及び光電変換効率が高く、歩留まりの良い製造が可能な光電変換素子を提供することができる。
Furthermore, since local electrode formation is not required unlike conventional comb electrodes, high temperature firing is not necessary. Therefore, according to the present invention, high-temperature firing can provide a photoelectric conversion element that has high incident light utilization efficiency and high photoelectric conversion efficiency and can be manufactured with high yield.
 
なお、本実施形態の光電変換素子１では、反射防止膜は成膜しない方が好ましいが、反射防止膜を備えた構成としてもよい。
In addition, in the photoelectric conversion element 1 of this embodiment, although it is preferable not to form an antireflection film, it is good also as a structure provided with the antireflection film.
 
最後に、透光性導電層３０の表面に取り出し電極４０を形成して光電変換素子１を得る（図２（ｈ））。
Finally, the extraction electrode 40 is formed on the surface of the translucent conductive layer 30 to obtain the photoelectric conversion element 1 (FIG. 2 (h)).
 
取り出し電極４０は、Ａｌや銀ペーストを用いたスクリーン印刷法により塗布した後焼成して形成される。なお、本実施形態では、裏面電極２０を最初に形成した態様について説明したが、裏面電極２０は、透光性導電層３０形成後に成膜されてもよいし、取り出し電極４０の形成後に形成されてもよい。
以上のようにして、光電変換素子１は製造することができる。
The extraction electrode 40 is formed by applying and baking after screen printing using Al or silver paste. In the present embodiment, the mode in which the back electrode 20 is formed first has been described. However, the back electrode 20 may be formed after the light-transmitting conductive layer 30 is formed or after the extraction electrode 40 is formed. May be.
As described above, the photoelectric conversion element 1 can be manufactured.
 
上記したように、光電変換素子１では、テクスチャ構造面に入射した太陽光の反射を高効率に抑制し、高効率に光電変換層１０内に入射させることができるので、従来必須とされていたＳｉＮ等の反射防止膜を設けることなく、光電変換層１０のテクスチャ構造面の略全面に表面電極（透光性導電層）３０を形成することができる。
As described above, in the photoelectric conversion element 1, since reflection of sunlight incident on the texture structure surface can be suppressed with high efficiency and can be incident into the photoelectric conversion layer 10 with high efficiency, it has been conventionally required. The surface electrode (translucent conductive layer) 30 can be formed on substantially the entire textured surface of the photoelectric conversion layer 10 without providing an antireflection film such as SiN.
 
そのため、テクスチャ構造面により高い入射効率で入射された太陽光を、高い光電変換効率にて利用することができる上、テクスチャ構造面の略全面から電荷を取り出すことができるため、局所的に設けられた電極により電荷を取り出す構成に比して光電変換層と電極との間の抵抗が格段に小さくなる。更に、局所的な電極形成が不要であるために高温焼成の必要がなく、基板の変形等による歩留まりの低下も抑制される。従って、光電変換素子１は、入射光の利用効率及び光電変換効率が高く、歩留まりの良い製造が可能なものとなる。
For this reason, sunlight that is incident on the texture structure surface with high incidence efficiency can be used with high photoelectric conversion efficiency, and charges can be taken out from almost the entire texture structure surface. The resistance between the photoelectric conversion layer and the electrode is remarkably reduced as compared with a configuration in which electric charges are extracted by the electrode. Furthermore, since local electrode formation is unnecessary, there is no need for high-temperature firing, and a decrease in yield due to substrate deformation or the like is also suppressed. Therefore, the photoelectric conversion element 1 has high incident light utilization efficiency and photoelectric conversion efficiency, and can be manufactured with a high yield.
 
光電変換素子１は、太陽電池等に好ましく使用することができる。光電変換素子１に対して必要に応じて、カバーガラス、保護フィルム等を取り付けて、太陽電池とすることができる。
The photoelectric conversion element 1 can be preferably used for a solar cell or the like. If necessary, a cover glass, a protective film, or the like can be attached to the photoelectric conversion element 1 to form a solar cell.
 
（設計変更）
本発明は上記実施形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲内において、適宜設計変更可能である。
(Design changes)
The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate without departing from the spirit of the present invention.
 
本発明に係る実施例及び比較例について説明する。
（実施例１）
まず、マスク材の塗布液の調製を行った。まず結合剤としてポリビニルアルコール（ＰＶＡ）を３重量％含んだＰＶＡ液（水溶媒）を用意した。次に、該ＰＶＡ液１０　　　０重量部に対して第１粒子としてシリカ（ＳｉＯ２）粒子(扶桑化学社製SP-03F、平均粒径0.3μm)を６重量部、第２粒子としてアクリル樹脂粒子(綜研化学社製MP1000、平均粒径0.4μm)を４重量部、分散剤として(2-エチルヘキシルスルホコハク酸Na)を０．５重量部添加してディゾルバにて分散させてマスク材塗布液を得た。
Examples and comparative examples according to the present invention will be described.
Example 1
First, a coating liquid for the mask material was prepared. First, a PVA liquid (aqueous solvent) containing 3% by weight of polyvinyl alcohol (PVA) as a binder was prepared. Next, 6 parts by weight of silica (SiO 2 ) particles (SP-03F manufactured by Fuso Chemical Co., Ltd., average particle size: 0.3 μm) are used as the first particles, and acrylic resin particles are used as the second particles with respect to 100 parts by weight of the PVA liquid. 4 parts by weight (MP1000 manufactured by Soken Chemical Co., Ltd., average particle size 0.4 μm) and 0.5 parts by weight of (2-ethylhexylsulfosuccinate Na) as a dispersant are added and dispersed in a dissolver to obtain a mask material coating solution It was.
 
Ｐ型でワイヤソーダメージが除去された多結晶シリコンウエハ(１５６ｍｍ角)の一表面に、スピンコータ(ミカサ製1H-360s)により、マスク材塗布液を塗布して乾燥させ、膜厚０．５μｍのマスク材を成膜した。
A P-type polycrystalline silicon wafer (156 mm square) from which wire saw damage has been removed is coated with a mask material coating solution with a spin coater (1H-360s made by Mikasa) and dried to obtain a mask with a thickness of 0.5 μm. A material was deposited.
 
次に、ＲＩＥ装置（リアクティブイオンエッチング装置：神港精機社製ＥＸＡＭ）にて凹凸構造の形成を行った。
Next, a concavo-convex structure was formed with an RIE apparatus (reactive ion etching apparatus: EXAM manufactured by Shinko Seiki Co., Ltd.).
 
ＳＦ６とＯ２の混合ガス（ＳＦ６：Ｏ２＝１：０．５）を用いて、ガス圧２０Ｐａ、高周波出力１５０Ｗで８分間ドライエッチング処理をした。
Using a mixed gas of SF 6 and O 2 (SF 6 : O 2 = 1: 0.5), dry etching was performed for 8 minutes at a gas pressure of 20 Pa and a high frequency output of 150 W.
 
次いで、ＲＩＥ装置においてエッチングガスをＨ２ガスに入れ替え、水素流量１００ｓｃｃｍ、ガス圧３Ｐａ、高周波出力１００Ｗで５分間ドライエッチング処理を行い、次に水酸化ナトリウム１%溶液に浸漬し、さらに希フッ酸１０%溶液に浸漬した後、純水リンス洗浄して、表面に高さ約1μmの凹凸形状を得た。
Next, in the RIE apparatus, the etching gas is replaced with H 2 gas, dry etching is performed for 5 minutes at a hydrogen flow rate of 100 sccm, a gas pressure of 3 Pa, and a high-frequency output of 100 W, and then immersed in a 1% sodium hydroxide solution and further diluted with hydrofluoric acid. After dipping in a 10% solution, it was rinsed with pure water to obtain an uneven shape with a height of about 1 μm on the surface.
 
次に塩化ホスホリル（ＰＯＣｌ３）を、拡散温度８００℃にてガス拡散して表面にｎ型層を形成し、ウエハ側面と裏面をＣＦ4とＯ2の混合ガスによりプラズマエッチングをしてｐｎ分離を行った。
Next, phosphoryl chloride (POCl 3 ) is gas diffused at a diffusion temperature of 800 ° C. to form an n-type layer on the surface, and pn separation is performed by plasma etching the wafer side and back surface with a mixed gas of CF 4 and O 2. Went.
 
次に希フッ酸１０%溶液に浸漬させ、表面にあるリン酸ガラスを除去した後、表面にＩＴＯの透明導電膜をプラズマＣＶＤ装置にて成膜し、ＩＴＯ表面に銀ペーストを細長くスクリーン印刷にて形成し、更に、裏面にはＡｌペーストをスクリーン印刷にて形成した後温度８６０℃にて焼成し、光電変換素子を作製した。
Next, after dipping in a 10% solution of dilute hydrofluoric acid to remove the phosphate glass on the surface, an ITO transparent conductive film is formed on the surface with a plasma CVD device, and silver paste is elongated on the ITO surface for screen printing. Further, an Al paste was formed on the back surface by screen printing and then baked at a temperature of 860 ° C. to produce a photoelectric conversion element.
 
（実施例２）
エッチング残渣及びプラズマダメージの洗浄方法を異ならせた以外は実施例１と同様にして光電変換素子を得た。本実施例において、エッチング残渣及びプラズマダメージの洗浄方法は、マイクロバブル生成装置及び超音波生成装置を用いて、マイクロバブル及び超音波が連続的に供給されている希フッ酸１０%溶液中に１分間浸漬させた後、純水リンス洗浄をすることにより行った。その結果、実施例１と同様に、表面に高さ約1μmの凹凸形状を得た。
(Example 2)
A photoelectric conversion element was obtained in the same manner as in Example 1 except that the cleaning method for etching residue and plasma damage was changed. In this embodiment, the etching residue and plasma damage cleaning method is performed by using a microbubble generator and an ultrasonic generator in a 10% dilute hydrofluoric acid solution to which microbubbles and ultrasonic waves are continuously supplied. This was performed by immersing in pure water and then immersing in pure water. As a result, as in Example 1, an uneven shape having a height of about 1 μm was obtained on the surface.
 
（実施例３）
シリコンウエハをＰ型単結晶ウエハとした以外は実施例１と同様にして光電変換素子を得た。
(Example 3)
A photoelectric conversion element was obtained in the same manner as in Example 1 except that the silicon wafer was changed to a P-type single crystal wafer.
 
（実施例４）
シリコンウエハをＰ型単結晶ウエハとした以外は実施例２と同様にして光電変換素子を得た。
Example 4
A photoelectric conversion element was obtained in the same manner as in Example 2 except that the silicon wafer was changed to a P-type single crystal wafer.
 
（比較例１）
リン酸ガラスの除去工程まで実施した後、プラズマＣＶＤ法にてＳｉＮの反射防止膜を膜厚約５０ｎｍで成膜し、透光性導電層を成膜しなかった以外は実施例１と同様にして光電変換素子を得た。
(Comparative Example 1)
After carrying out to the phosphate glass removal step, the same procedure as in Example 1 was conducted, except that a SiN antireflection film was formed to a thickness of about 50 nm by plasma CVD and no translucent conductive layer was formed. Thus, a photoelectric conversion element was obtained.
 
（比較例２）
ｐ型多結晶シリコンウエハの一表面をフッ化水素と硝酸の混合溶液（配合比率５０：５０（体積比率））に浸漬させて、該表面にテクスチャ構造を形成した以外は実施例３と同様にして光電変換素子を作製した。
(Comparative Example 2)
The same procedure as in Example 3 was performed except that one surface of a p-type polycrystalline silicon wafer was immersed in a mixed solution of hydrogen fluoride and nitric acid (mixing ratio 50:50 (volume ratio)) to form a texture structure on the surface. Thus, a photoelectric conversion element was produced.
 
（比較例３）
水素によるドライエッチングから水酸化ナトリウム水溶液への浸漬工程の代わりに、純水中において超音波洗浄を５分実施した以外は実施例１と同様にして光電変換素子を作製した。
(Comparative Example 3)
A photoelectric conversion element was produced in the same manner as in Example 1 except that ultrasonic cleaning was performed in pure water for 5 minutes instead of dry etching with hydrogen and immersion in a sodium hydroxide aqueous solution.
 
（評価）
上記実施例１～３及び比較例１～３にて得られた光電変換素子の表面反射率及び発電効率を測定した。その結果を表１に示す。表１において、発電効率が◎のものは発電効率１７％以上、○は１６％～１４％、△は１３％～１１％であることを意味する。
(Evaluation)
The surface reflectance and power generation efficiency of the photoelectric conversion elements obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were measured. The results are shown in Table 1. In Table 1, when the power generation efficiency is ◎, it means that the power generation efficiency is 17% or more, ◯ is 16% to 14%, and Δ is 13% to 11%.
 
表１に示されるように、本発明の光電変換素子では、多結晶、単結晶にかかわらず、表面反射率１％、発電効率も良好であることが確認された。
As shown in Table 1, in the photoelectric conversion element of the present invention, it was confirmed that the surface reflectance was 1% and the power generation efficiency was good regardless of whether it was polycrystalline or single crystal.
 
また、比較例１では、本発明の光電変換素子に反射防止膜を入れた構成としている。比較例１では、反射率は実施例１～３と同等であるのに対し、絶縁膜であるＳｉＮの挿入、及び表面電極の局所性による発電効率の低下も確認された。
Moreover, in the comparative example 1, it is set as the structure which put the antireflection film in the photoelectric conversion element of this invention. In Comparative Example 1, the reflectance was the same as in Examples 1 to 3, but it was also confirmed that power generation efficiency was reduced due to the insertion of SiN as an insulating film and the locality of the surface electrode.
 
また、比較例２は従来の多結晶シリコン太陽電池の構成であり、比較例３は、実施例１においてエッチング残渣の洗浄工程を従来の純水中での超音波洗浄とした例である。
Comparative Example 2 is a configuration of a conventional polycrystalline silicon solar cell, and Comparative Example 3 is an example in which the etching residue cleaning step in Example 1 is a conventional ultrasonic cleaning in pure water.
実施例１～３の結果、及び比較例１～比較例３とにより、本発明の有効性を確認することができた。 From the results of Examples 1 to 3 and Comparative Examples 1 to 3, the effectiveness of the present invention could be confirmed.
 
図５は実施例１において、マスク材の塗布前の多結晶シリコンウエハ表面（ａ）と、ｎ型ドーパント拡散前のテクスチャ構造面（ｂ）の反射率のスペクトルを示したものである。図５に示されるように、多結晶Ｓｉ基板を用いた場合において、Ｓｉの吸収波長帯である４００ｎｍ～１２００ｎｍにおいて、テクスチャ構造形成前の反射率が２０％以上であったのに対し、テクスチャ構造形成後の反射率が１～２％を達成されていることが確認された。
FIG. 5 shows the reflectance spectra of the polycrystalline silicon wafer surface (a) before application of the mask material and the textured structure surface (b) before n-type dopant diffusion in Example 1. As shown in FIG. 5, when a polycrystalline Si substrate was used, the reflectance before the texture structure formation was 20% or more in the Si absorption wavelength band of 400 nm to 1200 nm, whereas the texture structure It was confirmed that the reflectance after formation was 1 to 2%.
 
図６は実施例３及び実施例４において、マスク材の塗布前の単結晶シリコンウエハ表面（ａ）と、ｎ型ドーパント拡散前のテクスチャ構造面（（ｅ）：実施例３，（ｆ）：実施例４）の反射率のスペクトルを示したものである。また、図６では、従来のアルカリ処理によるテクスチャ構造形成方法により得られたテクスチャ構造面の反射率のスペクトルも併せて示してある（（ｂ）アルカリ処理のテクスチャ構造面、（ｃ）は（ｂ）のテクスチャ構造面上にＳｉＮ反射防止膜を設けた面））。また、図６（ｄ）は、実施例３において、水素を用いたドライエッチング処理前の凹凸構造面の反射率スペクトルを示したものである。
FIG. 6 shows a surface of a single crystal silicon wafer (a) before application of a mask material and a texture structure surface before n-type dopant diffusion ((e): Examples 3 and (f) in Example 3 and Example 4. The reflectance spectrum of Example 4) is shown. FIG. 6 also shows the reflectance spectrum of the texture structure surface obtained by the conventional texture structure forming method by alkali treatment ((b) the texture structure surface of alkali treatment, (c) is (b). The surface where the SiN antireflection film is provided on the texture structure surface))). FIG. 6D shows the reflectance spectrum of the concavo-convex structure surface before dry etching using hydrogen in Example 3.
 
図６に示されるように、単結晶Ｓｉ基板を用いた場合は、Ｓｉの吸収波長帯である４００ｎｍ～１２００ｎｍにおいて、テクスチャ構造形成前の反射率が２０％以上であり、また、従来のアルカリ処理によるテクスチャ構造面における反射率１０％前後であることが確認された。また、従来のアルカリ処理によるテクスチャ構造面に、ＳｉＮ膜を設けた構成では、４００ｎｍより短波長領域から６００ｎｍの波長域において反射率は６％以下となっているが、６００ｎｍより長波長側では短波長側に比して高くなっており、反射率の波長依存性が高いことが確認された。一方、マスク材を用いたテクスチャ構造面では、洗浄工程に関わらず反射率が１～２％を達成されていることが確認された。
As shown in FIG. 6, when a single crystal Si substrate is used, the reflectance before the texture structure formation is 20% or more in the Si absorption wavelength band of 400 nm to 1200 nm, and the conventional alkali treatment is performed. It was confirmed that the reflectance on the texture structure surface was about 10%. Further, in the configuration in which the SiN film is provided on the texture structure surface by the conventional alkali treatment, the reflectance is 6% or less in the wavelength region shorter than 400 nm to 600 nm, but shorter on the longer wavelength side than 600 nm. It was higher than the wavelength side, and it was confirmed that the wavelength dependency of the reflectance was high. On the other hand, on the texture structure surface using the mask material, it was confirmed that the reflectance of 1 to 2% was achieved regardless of the cleaning process.
 
図７は、本発明者が、Ｓｉ基板面の表面粗さ（１．５μｍ角）と波長１μｍの光に対する積分球反射率との関係を調べた結果をグラフに示したものである。図７（ａ）にはＲａ（算術平均表面粗さ）及びＲｑ（二乗平均平方根粗さ）と反射率との関係、（ｂ）にはＲｚ（最大高さ粗さ），Ｒｚｊｉｓ（１０点平均粗さ），Ｒｐ（最大山），及びＲｖ（最大谷）と、反射率との関係を示してある。
FIG. 7 is a graph showing the results of investigation by the inventor of the relationship between the surface roughness (1.5 μm square) of the Si substrate surface and the integrating sphere reflectance for light having a wavelength of 1 μm. FIG. 7A shows the relationship between Ra (arithmetic mean surface roughness) and Rq (root mean square roughness) and reflectance, and FIG. 7B shows Rz (maximum height roughness) and Rzjis (10-point average). The relationship between the roughness, Rp (maximum peak), and Rv (maximum valley) and the reflectance is shown.
 
図７（ａ），（ｂ）より、上記実施例１～４及び比較例１、２のテクスチャ構造面の表面粗さを見積もることができる。実施例１～４では、反射率が１～３％であるので、これらの算術平均表面粗さＲａは１２２ｎｍ以上であることが確認される。上記実施形態において説明したように、凹凸構造のピッチ（細かさ）は、マスク材に含まれる第１粒子及び第２粒子の設計により調整することができる。また、最大高さ粗さＲｚは１１５１ｎｍ（１．１５１μｍ）以上であることも確認される。
7A and 7B, the surface roughness of the texture structure surfaces of Examples 1 to 4 and Comparative Examples 1 and 2 can be estimated. In Examples 1 to 4, since the reflectance is 1 to 3%, it is confirmed that the arithmetic average surface roughness Ra is 122 nm or more. As described in the above embodiment, the pitch (fineness) of the concavo-convex structure can be adjusted by the design of the first particles and the second particles included in the mask material. It is also confirmed that the maximum height roughness Rz is 1151 nm (1.151 μm) or more.
 
実施例１～３に示されるように、本発明により、結晶Ｓｉ系太陽電池において、６％以下の低反射率のテクスチャ構造の作製に成功し、これにより結晶Ｓｉ太陽電池において初めて、透光性導電層（透明電極層）からなる表面電極を備えた構成を実現した。かかる電極層の実現により、高効率に光電変換層中に太陽光を閉じ込め、更に、大幅に広くなった発電領域にて発電させることに成功し、発電された電荷を取り出す際の抵抗も最小限にすることを可能にした。従って、本発明によれば、太陽光の利用効率、光電変換効率、及び装置内のロスが少ない、優れた光電変換性能を有する結晶Ｓｉ系太陽電池を初めて実現することができた。
As shown in Examples 1 to 3, the present invention succeeded in producing a texture structure having a low reflectance of 6% or less in a crystalline Si solar cell, and for the first time in the crystalline Si solar cell, translucency was achieved for the first time. The structure provided with the surface electrode which consists of a conductive layer (transparent electrode layer) was implement | achieved. By realizing such an electrode layer, solar light is confined in the photoelectric conversion layer with high efficiency, and furthermore, it has succeeded in generating power in a greatly widened power generation region, and the resistance when taking out the generated charge is minimized. Made it possible to Therefore, according to the present invention, it has been possible to realize for the first time a crystalline Si-based solar cell having excellent photoelectric conversion performance with less utilization efficiency of sunlight, photoelectric conversion efficiency, and loss in the apparatus.
 
Figure JPOXMLDOC01-appb-T000001
  
Figure JPOXMLDOC01-appb-T000001
 
本発明の光電変換素子は、太陽電池、及び赤外センサ等に使用される光電変換素子等の用途に好ましく適用できる。
The photoelectric conversion element of this invention is preferably applicable to uses, such as a photoelectric conversion element used for a solar cell, an infrared sensor, etc.

Claims (13)

  1. 一導電型結晶シリコン基板の一主面側に他の導電型不純物を拡散させてｐｎ接合が形成されてなる光電変換層と、前記一主面に形成された透光性導電層と、前記光電変換層の前記一主面の反対側の主面に形成された裏面電極層とを備えた光電変換素子であって、
    前記光電変換層の前記一主面は、該主面における太陽光の反射を抑制する多数の針状の凸部を有する凹凸構造を備えたテクスチャ構造面であり、
    前記透光性導電層は該テクスチャ構造面上に直接成膜されてなることを特徴とする光電変換素子。     A photoelectric conversion layer in which a pn junction is formed by diffusing another conductivity type impurity on one principal surface side of the one conductivity type crystalline silicon substrate; a translucent conductive layer formed on the one principal surface; A photoelectric conversion element comprising a back electrode layer formed on a main surface opposite to the one main surface of the conversion layer,
    The one main surface of the photoelectric conversion layer is a textured structure surface having a concavo-convex structure having a large number of needle-like convex portions that suppress reflection of sunlight on the main surface,
    The translucent conductive layer is formed directly on the textured structure surface, and is a photoelectric conversion element.
  2. 前記テクスチャ構造面の太陽光の反射率が６％以下であることを特徴とする請求項１に記載の光電変換素子。 The photoelectric conversion element according to claim 1, wherein the reflectance of sunlight on the texture structure surface is 6% or less.
  3. 前記反射率が３％以下であることを特徴とする請求項２に記載の光電変換素子。 The photoelectric conversion element according to claim 2, wherein the reflectance is 3% or less.
  4. 前記テクスチャ構造面の算術平均表面粗さＲａが１００ｎｍ以上であることを特徴とする請求項１～３に記載の光電変換素子。 4. The photoelectric conversion element according to claim 1, wherein an arithmetic average surface roughness Ra of the texture structure surface is 100 nm or more.
  5. 前記凸部の平均高さが１μm以上であることを特徴とする請求項１～４のいずれかに記載の光電変換素子。 5. The photoelectric conversion element according to claim 1, wherein an average height of the convex portions is 1 μm or more.
  6. 前記テクスチャ構造面が、
    前記シリコン基板の一主面に、前記凹凸構造を形成するドライエッチングに対して耐性を有する第１粒子と、該第１粒子よりも前記耐性が低い第２粒子と、前記第１粒子よりも前記耐性が低い結着剤とを含む液状組成物を前記シリコン基板の一主面に塗布成膜して得られるマスク材を配する工程と、
    該マスク材が配された前記主面にドライエッチングにより前記凹凸構造を形成する工程と、
    前記凹凸構造に、水素ガスによるドライエッチング処理と、希フッ酸中に浸漬させる処理とを順次実施する洗浄工程とを施すことにより製造されたものであることを特徴とする請求項１～５のいずれかに記載の光電変換素子。     The texture structure surface is
    On one main surface of the silicon substrate, a first particle having resistance to dry etching that forms the concavo-convex structure, a second particle having a lower resistance than the first particle, and the first particle having the resistance higher than that of the first particle A step of arranging a mask material obtained by coating a liquid composition containing a binder having low resistance on one main surface of the silicon substrate;
    Forming the concavo-convex structure by dry etching on the main surface on which the mask material is disposed;
    6. The structure according to claim 1, wherein the concavo-convex structure is manufactured by subjecting a dry etching treatment with hydrogen gas and a cleaning step of sequentially immersing in the dilute hydrofluoric acid. The photoelectric conversion element in any one.
  7. 前記テクスチャ構造面が、
    前記シリコン基板の一主面に前記凹凸構造を形成するドライエッチングに対して耐性を有する第１粒子と、該第１粒子よりも前記耐性が低い第２粒子と、前記第１粒子よりも前記耐性が低い結着剤とを含む液状組成物を前記シリコン基板の一主面に塗布成膜して得られるマスク材を配する工程と、
    該マスク材が配された前記主面にドライエッチングにより前記凹凸構造を形成する工程と、
    前記凹凸構造に、マイクロバブル及び超音波が断続的に、又は、連続的に供給されている希フッ酸中に浸漬させる処理とを順次実施する洗浄工程とを施すことにより製造されたものであることを特徴とする請求項１～５のいずれかに記載の光電変換素子。     The texture structure surface is
    First particles having resistance to dry etching that forms the uneven structure on one main surface of the silicon substrate, second particles having lower resistance than the first particles, and the resistance higher than the first particles A step of disposing a mask material obtained by coating a liquid composition containing a low binder on one main surface of the silicon substrate;
    Forming the concavo-convex structure by dry etching on the main surface on which the mask material is disposed;
    The concavo-convex structure is manufactured by subjecting a washing process to sequentially perform a treatment of immersing in a dilute hydrofluoric acid to which microbubbles and ultrasonic waves are intermittently or continuously supplied. 6. The photoelectric conversion element according to claim 1, wherein
  8. 　前記第１粒子が無機粒子であり、前記第２粒子が樹脂粒子であることを特徴とする請求項６または７に記載の光電変換素子。 The photoelectric conversion element according to claim 6 or 7, wherein the first particles are inorganic particles and the second particles are resin particles.
  9. 　前記第１粒子がＳｉＯ２を主成分とする粒子であることを特徴とする請求項８に記載の光電変換素子。 The photoelectric conversion element according to claim 8, wherein the first particles are particles containing SiO 2 as a main component.
  10. 前記第２粒子がアクリル樹脂を主成分とする粒子であることを特徴とする請求項８又は９に記載の光電変換素子。 The photoelectric conversion element according to claim 8 or 9, wherein the second particles are particles mainly composed of an acrylic resin.
  11. 　前記結着剤が、水溶性高分子又は水分散性高分子を主成分とするものであることを特徴とする請求項６～１０のいずれかに記載の光電変換素子。 11. The photoelectric conversion element according to claim 6, wherein the binder is mainly composed of a water-soluble polymer or a water-dispersible polymer.
  12. 　前記一導電型結晶シリコン基板が多結晶シリコンからなる（不可避不純物を含んでもよい）ことを特徴とする請求項１～１１のいずれかに記載の光電変換素子。 12. The photoelectric conversion element according to claim 1, wherein the one-conductivity-type crystalline silicon substrate is made of polycrystalline silicon (may contain inevitable impurities).
  13. 請求項１～１２のいずれかに記載の光電変換素子を備えたことを特徴とする太陽電池。 A solar cell comprising the photoelectric conversion element according to any one of claims 1 to 12.
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