WO2018109878A1 - Solar battery and method for manufacturing solar battery - Google Patents

Solar battery and method for manufacturing solar battery Download PDF

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Publication number
WO2018109878A1
WO2018109878A1 PCT/JP2016/087274 JP2016087274W WO2018109878A1 WO 2018109878 A1 WO2018109878 A1 WO 2018109878A1 JP 2016087274 W JP2016087274 W JP 2016087274W WO 2018109878 A1 WO2018109878 A1 WO 2018109878A1
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film
solar cell
silicon substrate
diffusion layer
diffusion
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PCT/JP2016/087274
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French (fr)
Japanese (ja)
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陽一郎 西本
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三菱電機株式会社
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Priority to JP2018556100A priority Critical patent/JP6647425B2/en
Priority to PCT/JP2016/087274 priority patent/WO2018109878A1/en
Publication of WO2018109878A1 publication Critical patent/WO2018109878A1/en

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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
    • H01L31/0216—Coatings
    • 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
    • H01L31/04—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 adapted as photovoltaic [PV] conversion devices
    • H01L31/06—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 adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—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 adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • 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
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • 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
    • Y02E10/547—Monocrystalline silicon PV cells
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a solar cell using crystalline silicon and a method for manufacturing the solar cell.
  • One structure of a solar cell has a conductivity opposite to the conductivity type of the crystalline silicon substrate on the light receiving surface, which is the surface on which the sunlight of a crystalline silicon (Si) substrate including single crystal or polycrystal is incident.
  • a pn junction is formed on the light receiving surface side by diffusing impurities to be a mold.
  • a high-concentration diffusion layer having the same conductivity type as that of the substrate is provided on the back surface, and recombination of minority carriers is suppressed by the back surface field effect to achieve high output.
  • This high-concentration diffusion layer on the back surface is called a BSF (Back Surface Field) layer.
  • the BSF layer is formed by combining a baking process of aluminum (Al) paste with the formation of the back electrode and forming a high-concentration diffusion layer by diffusion of aluminum during baking. Formation is realized.
  • the crystalline silicon substrate may be referred to as a silicon substrate or a substrate, and the solar battery cell as a cell.
  • the silicon substrate occupies most of the material cost, thinning the substrate is effective in reducing the cost.
  • the formation of the BSF layer at the time of forming the back electrode by firing the aluminum paste causes a large warp in the substrate after firing, and the substrate can be thinned with the current cell structure. Is difficult.
  • a PERC (Passive Emitter and Rear Cell) cell which has been known as a high conversion efficiency cell, has not warped even if the substrate is thin.
  • the passivation film is disposed on the back surface of the substrate, the back electrode is connected to the substrate through a contact hole, and the substrate is made of Al (Al) formed by contact with silicon. This is because the area of the Si alloy portion is reduced.
  • the high conversion efficiency of the PERC cell is due to the passivation film disposed on the back surface, but a passivation film suitable for the p-type surface has not been found for a while.
  • an aluminum oxide (Al 2 O 3 ) film is suitable as a passivation film on the back surface, and PERC cells using the Al 2 O 3 film are being mass-produced.
  • TMA Trimethyl Aluminum
  • Al 2 O 3 film which is a raw material for forming the Al 2 O 3 film
  • TMA has a problem that it is a substance that is difficult to use in the production of solar cells.
  • a solar cell that achieves a thin substrate has a BSF layer (B-BSF) made of a boron diffusion layer by diffusing boron (B) on the back surface as shown in Patent Document 1.
  • B-BSF BSF layer
  • Formed solar cells have also been proposed. This is because, since boron does not form an alloy with silicon, it is considered that a solar cell with B-BSF formed is less likely to warp the substrate than an Al-BSF cell with an Al-Si alloy formed on the back surface.
  • solar cells formed with B-BSF have not been put into practical use. The reason why the solar battery cell formed with B-BSF is not put into practical use is the diffusion method of boron and the passivation film on the back surface.
  • Patent Document 1 boron is diffused by vapor phase diffusion.
  • BSG Boron Silicate Glass
  • the substrate surface is clean. There is no hydrophobic surface as a proof of the surface.
  • the reason why the substrate surface after the removal of the BSG film does not become a hydrophobic surface is that a boron silicide layer is formed on the substrate surface. If there is a boron silicide layer on the substrate surface, recombination of hole electron pairs is likely to occur, and a cell having high conversion characteristics cannot be produced.
  • the boron silicide layer generated at the interface between the BSG film and the substrate is a silicon layer with a high boron content and is also called a boron rich layer. Therefore, it is necessary to remove this boron silicide layer, and generally, a process of thermally oxidizing the substrate and removing the oxide film again is performed. However, it is also known that impurities gettered in the boron silicide layer are re-emitted during thermal oxidation, which degrades the crystal quality of the substrate.
  • Patent Document 2 discloses a technique of forming a laminated film of a BSG film and an NSG (Non Doped Silicate Glass) film on a substrate surface and forming a p-type diffusion layer by heat treatment. Is presented.
  • An object of the present invention is to obtain a solar cell that can be thinned, is easy to manufacture, and has high conversion efficiency.
  • a solar cell of the present invention includes a silicon substrate, a diffusion layer provided on the first surface of the silicon substrate, and containing a first conductivity type element, A first glass layer including a first conductivity type element and silicon (hereinafter also referred to as silicon); and a first conductivity type element stacked on the first glass layer. And a passivation film having a second glass layer containing silicon.
  • the present invention it is possible to obtain a solar cell that can be thinned, can be easily manufactured, and has high conversion efficiency.
  • FIG. 1 It is sectional drawing which shows the solar cell of Embodiment 1 typically, and is II sectional drawing of FIG. Top view of solar cell of Embodiment 1
  • Process sectional drawing which shows the manufacturing process of the solar cell of Embodiment 1 Flowchart showing the manufacturing process of the solar cell of the first embodiment.
  • Comparison diagram of open-circuit voltage Voc and short-circuit photocurrent density Jsc of the solar battery of the first embodiment and the solar battery of the comparative example The figure which shows the relationship between the internal quantum efficiency of the solar cell of Embodiment 1, and a wavelength.
  • FIG. 1 is a cross-sectional view schematically showing the solar cell of Embodiment 1, and FIG. 2 is a top view thereof.
  • FIG. 1 is a sectional view taken along line II of FIG.
  • the solar cell 10 of Embodiment 1 includes a BSG film 12 used as a diffusion source for forming a p + -type diffusion layer 14 which is a BSF layer on the back surface 11B side of the p-type single crystal silicon substrate 11 and a cap layer.
  • the used laminated film with the NSG film 13 is left as it is to form a passivation film Pa.
  • the solar cell 10 has a concavo-convex structure having a texture that reduces light reflection on a light receiving surface 11A that is a first main surface of a p-type single crystal silicon substrate 11 that is a first conductivity type semiconductor substrate. Is formed. No texture is formed on the back surface 11B which is the second main surface facing the light receiving surface 11A of the p-type single crystal silicon substrate 11, and a p + -type diffusion layer 14 which is a first conductivity type semiconductor layer is provided. . Then, the BSG film 12 which is the first glass layer used as the diffusion source for forming the p + -type diffusion layer 14 and the NSG film 13 which is the second glass layer used for the cap layer are left, and the passivation is performed.
  • a film Pa is formed.
  • an n-type diffusion layer 15 that is a second conductivity type semiconductor layer is formed on a textured uneven structure, and an antireflection film 16 is formed on the n-type diffusion layer 15 by being laminated.
  • a light receiving surface grid electrode 17G and a light receiving surface bus electrode 17B which are first current collecting electrodes on the light receiving surface 11A side, are formed on the antireflection film 16, and the light receiving surface grid electrode 17G and the light receiving surface bus electrode 17B are formed. Is in contact with the n-type diffusion layer 15 through the antireflection film 16.
  • the back surface grid electrode is formed so as to be orthogonal to the back surface bus electrode, and the back surface electrode 18 is configured to penetrate the passivation film Pa.
  • the present inventor has obtained a laminated film of the BSG film 12 formed as a diffusion source and the NSG film 13 formed on the cap layer. It has been found that it is suitable for the passivation film Pa of the p-type diffusion layer by boron diffusion.
  • a laminated film of the BSG film 12 and the NSG film 13 is used as the passivation film Pa. For this reason, since it is not necessary to form the passivation film Pa newly, a solar cell with high conversion efficiency can be manufactured, simplifying a manufacturing process.
  • the Al—Si alloy layer is not formed as in the case of the Al—BSF cell, the occurrence of warpage of the substrate due to the formation of the Al—Si alloy layer can be suppressed, and a thin silicon substrate can be used. Moreover, since the price of material gases such as diborane (B 2 H 6 ) and silane (SiH 4 ) as film forming materials is lower than that of TMA, it can contribute to reduction of power generation cost.
  • material gases such as diborane (B 2 H 6 ) and silane (SiH 4 ) as film forming materials is lower than that of TMA, it can contribute to reduction of power generation cost.
  • the concentration of boron which is the first conductivity type element, continuously changes at the interface between the BSG film 12 and the p + -type diffusion layer 14. For this reason, recombination of electrons and holes hardly occurs, and good interface characteristics can be obtained.
  • the atomic density of the interface and the periphery of the interface can be measured by various measuring apparatuses such as secondary ion mass spectrometry (SIMS).
  • FIG. 3 is a process cross-sectional view illustrating the manufacturing process of the solar cell of the first embodiment.
  • FIG. 4 is a flowchart showing manufacturing steps of the solar cell of the first embodiment.
  • a p-type single crystal silicon substrate 11 is prepared. Regardless of whether it is polycrystalline silicon or single crystal silicon, the substrate for the solar cell is delivered in an as-sliced state, so that damage during slicing remains on the substrate surface. Therefore, first, in the damaged layer removing step S101 shown in FIG. 4, the damaged layer on the surface of the p-type single crystal silicon substrate 11 is removed by etching.
  • etching an alkaline chemical solution is often used from the viewpoint of cost, but there is no problem even if a hydrofluoric acid mixed acid is used.
  • this operation is merely an operation for removing the damaged layer, and it is not necessary to form a minute uneven structure for reducing the reflectance called texture. If the texture is formed at this time, the texture is also formed on the back surface 11B of the p-type single crystal silicon substrate 11, and the characteristics of the solar cell 10 may be deteriorated instead. This point will be described later.
  • a BSG film 12 serving as a diffusion source and an NSG film serving as a cap layer on the back surface 11B side of the p-type single crystal silicon substrate 11 13 are laminated.
  • the p-type single crystal silicon substrate 11 is annealed to diffuse boron in the BSG film 12 into the p-type single crystal silicon substrate 11, and the back surface 11B side A p + -type diffusion layer 14 is formed on the surface layer.
  • the NSG film 13 is not present, boron is also released into the annealing atmosphere, so that the boron concentration in the BSG film 12 is lowered and boron is not effectively diffused into the p-type single crystal silicon substrate 11. Therefore, in order to prevent boron from being released into the annealing atmosphere, an NSG film 13 is formed on the BSG film 12 as a cap layer.
  • the boron concentration in the BSG film 12 is 1.18 wt%
  • the film thicknesses of the BSG film 12 and the NSG film 13 are 70 nm and 300 nm, respectively, and annealing is performed in a nitrogen (N 2 ) atmosphere at 1000 ° C.-60 min. went.
  • the substrate temperature may be 900 ° C. to 1100 ° C. If the substrate temperature is less than 900 ° C., sufficient diffusion cannot be achieved. On the other hand, there is no problem even if the substrate temperature exceeds 1100 ° C. However, since sufficient diffusion is possible at 1000 ° C., the merit of further increasing the temperature is small considering the cost.
  • annealing was performed in an N 2 atmosphere, but a small amount of phosphorus oxychloride (POCl 3 ) and oxygen (O 2 ) may be flowed during annealing or cooling.
  • the contamination source may be diffused from the surface of the p-type single crystal silicon substrate 11 into the p-type single crystal silicon substrate 11 to deteriorate the crystal quality.
  • POCl 3 and O 2 By flowing POCl 3 and O 2 during annealing or cooling, a phosphorus diffusion layer is formed on the surface of the p-type single crystal silicon substrate 11, and the gettering effect by this phosphorus diffusion layer reduces the influence of contamination from the apparatus. Can be expected to do.
  • this phosphorus diffusion layer is removed by etching in the next texture forming step, it does not affect the subsequent steps. Since phosphorus is more easily diffused than boron, this phosphorus diffusion layer is likely to be thick, but if the phosphorus diffusion layer becomes too thick, it will be difficult to remove in the texture forming process, so that the phosphorus diffusion layer will not be too thick. It is necessary to keep in mind.
  • This diffusion method is solid phase diffusion using the BSG film 12 as a diffusion source.
  • Boron such as boron bromide (BBr 3 ) and boron chloride (BCl 3 ) in addition to solid phase diffusion is used for boron diffusion.
  • a cell using boron diffusion by vapor phase diffusion for example, a cell in which boron diffusion is performed by vapor phase diffusion on an n-type single crystal silicon substrate and a pn junction is formed uses a film formed by a CVD method. The conversion efficiency and other characteristics are lower than those of a cell in which a pn junction is formed by the diffusion method described above. This is due to the difference in the surface state of the n-type single crystal silicon substrate after diffusion.
  • a boron silicide layer which is a boron-rich layer, is formed even if the BSG film formed during diffusion is removed, and carriers are recombined in this boron silicide layer. End up. Therefore, it is necessary to remove this boron silicide layer, and generally, a process of thermally oxidizing the substrate and removing the oxide film again is performed. However, during thermal oxidation, impurities gettered to the boron silicide layer are re-emitted and the crystal quality is degraded. For this reason, it is difficult to obtain high cell characteristics by boron vapor phase diffusion.
  • the boron concentration in the BSG film can be controlled at the time of film formation. Therefore, the formation of a boron silicide layer can be suppressed by selecting an appropriate concentration. it can.
  • the presence or absence of the boron silicide layer can be determined by removing the BSG film with hydrofluoric acid (HF) after diffusion. If a boron silicide layer is formed, a hydrophilic surface appears, and if a boron silicide layer is not formed, a hydrophobic surface appears.
  • formation of a boron silicide layer can be prevented by selecting an appropriate boron concentration in the BSG film.
  • boron diffusion it is desirable to perform boron diffusion using a laminated film of a BSG film and an NSG film obtained by CVD film formation rather than vapor phase diffusion.
  • vapor phase diffusion it is difficult to control the concentration of the BSG film, and a boron-rich layer is easily formed.
  • adjust the supply timing such as supplying a boron-containing gas for diffusion when the temperature rises to an appropriate temperature in the step of heating the substrate. It is necessary to devise measures such as increasing the boron concentration in the gas or lightly oxidizing the surface by adding a small amount of oxygen.
  • the boron concentration in the CVD BSG film 12 is 0.5 wt% to 3 wt%. If the boron concentration in the BSG film 12 exceeds 3 wt%, the surface of the p-type single crystal silicon substrate 11 becomes a hydrophilic surface, and good cell characteristics cannot be obtained. On the other hand, unless the boron concentration in the BSG film 12 is less than 0.5 wt%, desired boron diffusion cannot be performed on the surface of the p-type single crystal silicon substrate 11.
  • the boron concentration of the vapor phase diffusion BSG film is generally 5 wt% or more.
  • the BSG film 12 and the NSG film 13 also circulate around the film formation surface, so that boron is also diffused to the portion where the BSG film 12 has circulated.
  • the wraparound film and the boron diffusion layer formed by the wrapping BSG film 12 are removed by etching when the texture 11T is formed.
  • stage S5 in FIG. 3 and step S105 in FIG. 4 in order to form a pn junction, phosphorus (P) is diffused by vapor phase diffusion on the texture 11T surface on the light receiving surface 11A side to form an n-type diffusion layer. 15 is formed.
  • the BSG film 12 and the NSG film 13 exhibit the function of a diffusion mask.
  • the PSG (Phospho Silicate Glass) film formed on the light receiving surface 11A side in the diffusion step is removed.
  • the BSG film 12 and the NSG film 13 can withstand the PSG film removal after the diffusion.
  • a BSG film and an NSG film which are oxide films formed by a CVD method, have a higher etching rate than a thermal oxide film formed by thermal oxidation, but BSG formed by the manufacturing process of the solar cell of the first embodiment. Since the film 12 and the NSG film 13 have undergone an annealing process at the time of boron diffusion, the etching rate becomes comparable to that of the thermal oxide film, and remains without being removed even after the PSG film is removed.
  • an antireflection film 16 made of a silicon nitride film is formed on the light receiving surface 11A side by CVD.
  • the light receiving surface electrode 17 and the back electrode 18 are formed on the light receiving surface 11A and the back surface 11B by printing.
  • step S108 in FIG. 4 After printing the light-receiving surface electrode 17 and the back surface electrode 18, heat treatment is performed, and as shown in step S108 in FIG. 4, the light-receiving surface electrode 17 contacts the n-type diffusion layer 15 and the back surface electrode 18 is p + type by fire-through. A contact is formed in contact with the diffusion layer 14 to complete the solar cell shown in FIGS.
  • the shape of the back electrode 18 is not particularly specified, and may be determined according to the thicknesses of the BSG film 12 and the NSG film 13. If thinly fabricating the NSG film 13, the back electrode 18, after printing form with silver aluminum (AgAl) paste, fire-through that is, through the BSG film 12 and the NSG film 13 by heat treatment, p + -type The diffusion layer 14 can be contacted.
  • FIG. 5 is a diagram showing a modification of the solar cell of the first embodiment. If the NSG film 13 is thick and difficult to fire through, the modified solar cell 20 is opened in the BSG film 12 and the NSG film 13 with a laser as shown in FIG.
  • the back electrode 18 is formed by printing in the same manner as the solar cell 10 of the first embodiment.
  • FIG. 6 is a comparison diagram of the open circuit voltage Voc and the short-circuit photocurrent density Jsc of the cells of the solar battery of the first embodiment and the solar battery of the comparative example.
  • the open circuit voltage Voc is a voltage when the current flowing to the outside is 0 A
  • the short-circuit photocurrent density Jsc is a current when the voltage applied to the outside is 0 V.
  • FIG. 6 compares the presence or absence of the texture on the back surface and the difference in the passivation film on the back surface.
  • PECVD-SiN which is a silicon nitride film formed by plasma CVD (Plasma Enhanced Chemical Vapor Deposition: PECVD)
  • PECVD Plasma Enhanced Chemical Vapor Deposition
  • FIG. 7 is a diagram showing the internal quantum efficiency (Internal Quantum Efficiency) of the solar cell of the first embodiment.
  • FIG. 8 is a diagram showing the internal quantum of the solar cell using the current plasma CVD silicon nitride for the passivation film on the back surface. It is a figure which shows efficiency. 7 and 8 both show the internal quantum efficiency of the Al-BSF cell as a comparison object.
  • the internal quantum efficiency is the ratio between the carriers generated by light irradiation and the extracted current, and can be regarded as the sensitivity of the solar cell.
  • FIG. 8 is a diagram showing the internal quantum efficiency (Internal Quantum Efficiency) of the solar cell of the first embodiment.
  • FIG. 8 is a diagram showing the internal quantum of the solar cell using the current plasma CVD silicon nitride for the passivation film on the back surface. It is a figure which shows efficiency. 7 and 8 both show the internal quantum efficiency of the Al-BSF cell as a comparison object.
  • the internal quantum efficiency is the ratio between the carriers generated
  • curve A1 indicates that there is no back surface texture when the laminated film of the BSG film 12 and NSG film 13 of Embodiment 1 is used as a passivation film
  • curve A2 indicates that there is a back surface texture
  • curve P1 indicates a comparison.
  • curve P2 indicates that there is a back surface texture
  • curve B indicates a case where Al-BSF is used for the back surface passivation film Pa.
  • the short wavelength sensitivity is lower than that of the Al-BSF cell, but this is influenced by the phosphorus diffusion on the light receiving surface 11A side.
  • the sheet resistance tends to be lower in the case where there is a laminated film of BSG film 12 and NSG film 13 or PECVD-SiN on the back surface 11B than in the case where there is no film.
  • phosphorus diffusion was performed on the bare p-type single crystal silicon substrate 11 on which no film was formed under the condition that the sheet resistance was 65 ⁇ / ⁇ . The sheet resistance was about. The cause is unknown, but the short wavelength sensitivity can be dealt with by adjusting the diffusion condition and is irrelevant to the passivation characteristics of the back surface 11B. The short wavelength sensitivity can be improved by selecting an appropriate value for the sheet resistance.
  • the BSG film and the NSG film are stacked on at least a part of the first surface which is one surface of the p-type single crystal silicon substrate, and heat treatment is performed.
  • a comb electrode or a point contact structure in which contact is made by forming a contact hole can be used as the back electrode.
  • a comb electrode using a silver aluminum (AgAl) paste it is difficult to form an Al—Si alloy, and warpage can be suppressed. For this reason, it is possible to reduce the thickness of the substrate.
  • the point contact structure the area of the Al—Si alloy is reduced, so that the thickness of the substrate can be reduced.
  • FIG. 9 is a cross-sectional view showing solar cell 30 of the second embodiment.
  • FIG. 10 is a process cross-sectional view illustrating the manufacturing process of the solar cell of the second embodiment.
  • FIG. 11 is a flowchart showing manufacturing steps of the solar cell of the second embodiment.
  • the solar cell using the p-type single crystal silicon substrate 11 in which the pn junction is arranged on the light receiving surface 11A side has been described, but in the second embodiment, the p-type single crystal silicon substrate 11 is used, A solar cell 30 having a pn junction on the back surface 11B side will be described.
  • the BSG film 12 and the NSG film 13 are on the light receiving surface 11A side, the BSG film 12 and the NSG film 13 must have a role as the antireflection film 16, and the BSG film 12 and the NSG film 13 It is necessary to adjust the film thickness. More specifically, it is necessary to adjust the film thickness including the film thickness ratio of the BSG film 12 and the NSG film 13 and the total film thickness so that the reflectance at 600 nm at which the sunlight spectrum is maximized is minimized.
  • the composition of the antireflection film and the passivation film 16P on the light receiving surface 11A side and the back surface 11B side is different from that of the diffusion layer on the light receiving surface 11A side and the back surface 11B side. Is substantially the same as the method for manufacturing the solar cell of the first embodiment except that is reversed.
  • the antireflection film is composed of a laminated film of the BSG film 12 and the NSG film 13.
  • a p-type single crystal silicon substrate 11 is prepared as shown in stage S1 of FIG. 10, and a p-type single crystal silicon substrate is etched by etching in a damaged layer removing step S101 shown in FIG. 11 Remove the damage layer on the surface.
  • a BSG film 12 serving as a diffusion source and a cap layer are formed on the light receiving surface 11A side of the p-type single crystal silicon substrate 11.
  • the NSG film 13 is laminated and formed.
  • the p-type single crystal silicon substrate 11 is annealed to diffuse boron in the BSG film 12 into the p-type single crystal silicon substrate 11, and to receive the light receiving surface.
  • a p + -type diffusion layer 14 is formed on the surface layer on the 11A side.
  • a small amount of POCl 3 and O 2 may be allowed to flow during annealing or cooling.
  • stage S5 in FIG. 10 and step S105S in FIG. 11 in order to form a pn junction, P (phosphorus) is diffused by vapor phase diffusion into the textured surface on the back surface 11B side to form the n-type diffusion layer 15 Form.
  • the BSG film 12 and the NSG film 13 exhibit the function of a diffusion mask.
  • the PSG film formed on the back surface 11B side in the diffusion step is removed.
  • the BSG film 12 and the NSG film 13 can withstand the PSG film removal after the diffusion.
  • a passivation film 16P made of a silicon nitride film is formed by CVD.
  • the light receiving surface electrode 17 and the back surface electrode 18 are formed by printing.
  • step S108 of FIG. 11 after the light-receiving surface electrode 17 and the back surface electrode 18 are printed, heat treatment is performed, and contacts are formed by fire-through to complete the solar cell 30 of the second embodiment shown in FIG. To do.
  • the process is started from the removal of the damaged layer as in FIG. 3, but the damaged layer may be removed by texture etching. In this case, there is no change in the other processes except that the texture 11T is formed on the light receiving surface 11A. As shown in FIG. 10, when the damaged layer is simply removed, the texture 11T is not formed on the light receiving surface 11A side. In that case, an alternative technique for preventing reflection, such as using an antireflection film, is used.
  • solar cell 30 of Embodiment 2 it goes without saying that manufacturing workability is good, and a laminated film having high passivation properties is used as an antireflection film and a passivation film on the light receiving surface side, and NSG.
  • the interface between the film 13 and the BSG film 12 is also reflective and scattering. Therefore, according to the solar cell 30 of Embodiment 2, the light collection rate and the internal quantum efficiency are improved, and a solar cell with high conversion efficiency can be obtained.
  • a thin solar cell without warping can be obtained. In the case of a thin solar cell, whether or not the interface between the passivation film and the semiconductor substrate or the semiconductor layer is clean often affects the characteristics. Since one surface of the single crystal silicon substrate 11 is covered, a clean interface can be maintained.
  • Embodiment 3 FIG.
  • the cells using the p-type single crystal silicon substrate 11 have been described. However, these cells are naturally applicable to cells using an n-type silicon substrate.
  • boron diffusion is performed using a laminated film of a BSG film and an NSG film, and the BSG film used as the diffusion source is used as a passivation film for the boron diffusion layer.
  • the BSG film and the NSG film are on the light receiving surface side, it is necessary that the BSG film and the NSG film have a role of an antireflection film. It is necessary to adjust the film thickness, surface state, and film quality of the NSG film.
  • Embodiment 4 FIG. Next, the solar cell of Embodiment 4 is demonstrated.
  • the light receiving surface side electrode and the back surface electrode are respectively disposed on the light receiving surface that is the first main surface and the back surface that is the second main surface of the substrate constituting the solar battery cell.
  • the lamination of the BSG film and the NSG film is also applied to boron diffusion in a so-called IBC (Interdigitated Back Contact) cell in which electrodes of both electrodes are arranged on the second surface 11b which is the back surface of the solar cell.
  • IBC Interdigitated Back Contact
  • a membrane can be applied.
  • 12 is a cross-sectional view showing the solar cell of the fourth embodiment using the IBC cell structure, FIG.
  • FIG. 13 is a process cross-sectional view showing the manufacturing process of the solar cell of the fourth embodiment
  • FIG. 14 is the fourth embodiment. It is a flowchart which shows the manufacturing process of this solar cell.
  • an n-type single crystal silicon substrate 11n is used, an n-type diffusion layer 15 is formed on part of the first surface 11a side and the second surface 11b side, and the first A p + -type diffusion layer 14 is formed on a part of the second surface 11b.
  • a first electrode 17R and a second electrode 18S are formed on the back surface 11B of the solar cell.
  • the laminated film of the BSG film 12 and the NSG film 13 is formed on the surface excluding the light receiving portion. That is, a part of the back surface 11 ⁇ / b> B also forms a pn junction with the n-type diffusion layer 15 to form a light receiving portion.
  • a feature of solar cell 40 of the fourth embodiment is that p + -type diffusion layer 14, that is, a laminated film of BSG film 12 and NSG film 13 used for forming the boron diffusion layer is used as a passivation film for the boron diffusion layer.
  • an n-type single crystal silicon substrate 11n is prepared as shown in the stage S1 of FIG. 13, and the n-type single crystal silicon substrate is etched by etching in the damage layer removing step S101 shown in FIG. The damage layer on the 11n surface is removed.
  • a BSG film 12 serving as a diffusion source is formed on a part on the second surface 11b side of the n-type single crystal silicon substrate 11n by the CVD apparatus.
  • the NSG film 13 as a cap layer is formed by being laminated.
  • a mask is formed on a part of the second surface 11b side so that the BSG film 12 and the NSG film 13 are not formed.
  • n-type single crystal silicon substrate 11n is annealed, and boron in BSG film 12 is changed to n-type single crystal silicon substrate 11n.
  • a p + -type diffusion layer 14 is selectively formed on a part of the second surface 11b side by diffusion.
  • the entire surface on the first surface 11a side and the second surface are formed using the BSG film 12 and NSG film 13 on the first surface 11a side as an etching mask.
  • the texture 11T is formed on a part of the surface 11b side.
  • stage S5 in FIG. 13 and step S105SS in FIG. 14 in order to form a pn junction, phosphorus is diffused in the texture surfaces on both sides to form the n-type diffusion layer 15.
  • the BSG film 12 and the NSG film 13 function as a diffusion mask.
  • the PSG film formed on the second surface 11b side in the diffusion step is removed.
  • the BSG film 12 and the NSG film 13 can withstand the PSG film removal after the diffusion.
  • an antireflection film 16 made of a silicon nitride film is formed by CVD.
  • the first electrode 17R and the second electrode 18S are formed by printing as shown in the stage S7 in FIG. 13 and the step S107S in FIG.
  • the NSG film 13 or the antireflection film 16 is thickly stacked on both the first surface 11a side and the second surface 11b side, the film remaining on the second surface 11b until the time of electrode formation is thick. Difficult to fire through.
  • the BSG film 12 and the NSG film 13 are opened with a laser, the contact hole h is formed, the point contact is formed, and then the same as in the solar cell of the first embodiment.
  • the first electrode 17R is formed by printing.
  • FIGS. 12 and 13 are schematic views assuming the use of the n-type single crystal silicon substrate 11n, but a substrate such as a p-type single crystal silicon substrate may be used. In that case, as shown in the first to third embodiments, some process adjustment is required.
  • a p-type single crystal silicon substrate is used as the substrate constituting the solar cell.
  • p-type silicon tends to have a reduced lifetime due to metal impurities, and thus special attention must be paid to contamination. Therefore, the process of removing the laminated film of the BSG film and NSG film used as the diffusion source and forming another passivation film again makes the process complicated and may contaminate the substrate. It leads to increase in sex. Therefore, using the laminated film of the BSG film and the NSG film used as the diffusion source is also effective in reducing the possibility of substrate contamination.
  • boron is used as the first conductivity type element used as the impurity.
  • the present invention is not limited to boron, and n-type impurities such as phosphorus are used as the first conductivity type element. It is also possible to apply.
  • a phosphorus-containing film such as a PSG film formed by a CVD method is used, but a coating film may be used when the impurity concentration can be controlled.
  • the configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

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Abstract

A solar battery is provided with a passivation film (Pa) that comprises a laminated film provided with: a p+-type diffusion layer (14) that is provided on a rear surface (11B) of a p-type single crystal silicon substrate (11), and contains boron at a higher concentration than the impurity concentration of the p-type single crystal silicon substrate (11), boron being an element of a first electroconduction type; a BSG film (12), which is a first glass layer that is laminated on the rear surface (11B) in contact with the p+-type diffusion layer (14), and contains boron and silicon; and an NSG film (13), which is a second glass layer that is laminated on the BSG film (12) and contains silicon but not boron. Also, an n-type diffusion layer (15) is provided on the back surface (11B) or on a light-receiving surface (11A).

Description

太陽電池および太陽電池の製造方法Solar cell and method for manufacturing solar cell
　本発明は、結晶系シリコンを用いた太陽電池および太陽電池の製造方法に関する。 The present invention relates to a solar cell using crystalline silicon and a method for manufacturing the solar cell.
　太陽電池セルの一つの構造に、単結晶または多結晶をはじめとする結晶系シリコン（Ｓｉ）基板の太陽光が入射する側の表面である受光面に結晶系シリコン基板の導電型と反対の導電型となる不純物を拡散することによって受光面側にｐｎ接合を形成したものがある。上記構造の太陽電池では、裏面には基板の導電型と同一導電型の高濃度拡散層を設け、裏面電界効果により少数キャリアの再結合を抑制し、高出力化が図られている。この裏面の高濃度拡散層をＢＳＦ（Ｂａｃｋ　Ｓｕｒｆａｃｅ　Ｆｉｅｌｄ）層と呼ぶ。ｐ型の結晶系シリコン基板を用いた場合には、裏面電極の形成にアルミニウム（Ａｌ）ペーストの焼成工程を組み合わせ、焼成時のアルミニウムの拡散により高濃度拡散層を形成することで、ＢＳＦ層の形成を、実現させている。以下、結晶系シリコン基板をシリコン基板または基板、太陽電池セルをセルということもある。 One structure of a solar cell has a conductivity opposite to the conductivity type of the crystalline silicon substrate on the light receiving surface, which is the surface on which the sunlight of a crystalline silicon (Si) substrate including single crystal or polycrystal is incident. There is one in which a pn junction is formed on the light receiving surface side by diffusing impurities to be a mold. In the solar cell having the above-described structure, a high-concentration diffusion layer having the same conductivity type as that of the substrate is provided on the back surface, and recombination of minority carriers is suppressed by the back surface field effect to achieve high output. This high-concentration diffusion layer on the back surface is called a BSF (Back Surface Field) layer. When a p-type crystalline silicon substrate is used, the BSF layer is formed by combining a baking process of aluminum (Al) paste with the formation of the back electrode and forming a high-concentration diffusion layer by diffusion of aluminum during baking. Formation is realized. Hereinafter, the crystalline silicon substrate may be referred to as a silicon substrate or a substrate, and the solar battery cell as a cell.
　現在、太陽電池セルを用いて光エネルギーを電気エネルギーに変換する太陽光発電システムは普及が進んでいるが、更なる普及には発電コストの低減が必要である。発電コストを低減するには、材料コストを削減しつつ、太陽電池の高効率化を図る必要がある。 Currently, solar power generation systems that use solar cells to convert light energy into electrical energy are becoming more widespread, but it is necessary to reduce power generation costs for further spread. In order to reduce the power generation cost, it is necessary to increase the efficiency of the solar cell while reducing the material cost.
　材料コストの大部分を占めるのはシリコン基板であるため、基板の薄型化はコスト低減には効果的ではある。しかしながら、基板を薄型化した場合、アルミニウムペーストの焼成による裏面電極形成時のＢＳＦ層の形成では、焼成後に基板に大きな反りが生じてしまい、現状のセル構造のままでは基板の薄型化を実現するのは難しい。 Since the silicon substrate occupies most of the material cost, thinning the substrate is effective in reducing the cost. However, when the substrate is thinned, the formation of the BSF layer at the time of forming the back electrode by firing the aluminum paste causes a large warp in the substrate after firing, and the substrate can be thinned with the current cell structure. Is difficult.
　以前より、高変換効率のセルとして知られているＰＥＲＣ（Ｐａｓｓｉｖａｔｅｄ　Ｅｍｉｔｔｅｒ　ａｎｄ　Ｒｅａｒ　Ｃｅｌｌ）セルは、基板を薄くしても反りにくい。基板が反りにくい理由は、ＰＥＲＣセルでは、パッシベーション膜が基板の裏面に配され、裏面電極はコンタクトホールを介して基板と接続されており、アルミニウム（Ａｌ）とシリコンとの接触により形成されたＡｌ－Ｓｉ合金部の面積が少なくなるためである。ＰＥＲＣセルの高い変換効率は、裏面に配したパッシベーション膜によるものであるが、しばらくの間、ｐ型の面に適したパッシベーション膜は発見されていなかった。ところが近年、酸化アルミニウム（Ａｌ2Ｏ3）膜が裏面のパッシベーション膜として適していることが発見され、Ａｌ2Ｏ3膜を使用したＰＥＲＣセルが量産されつつある。 A PERC (Passive Emitter and Rear Cell) cell, which has been known as a high conversion efficiency cell, has not warped even if the substrate is thin. In the PERC cell, the passivation film is disposed on the back surface of the substrate, the back electrode is connected to the substrate through a contact hole, and the substrate is made of Al (Al) formed by contact with silicon. This is because the area of the Si alloy portion is reduced. The high conversion efficiency of the PERC cell is due to the passivation film disposed on the back surface, but a passivation film suitable for the p-type surface has not been found for a while. However, in recent years, it has been discovered that an aluminum oxide (Al 2 O 3 ) film is suitable as a passivation film on the back surface, and PERC cells using the Al 2 O 3 film are being mass-produced.
　しかしながら、Ａｌ2Ｏ3膜の成膜原料であるＴＭＡ(Ｔｒｉｍｅｔｈｙｌ　Ａｌｕｍｉｎｕｍ：トリメチルアルミニウム)は、取り扱いに注意が必要であるとともにコストが高い材料である。このため、ＴＭＡは、太陽電池の生産には使いにくい物質であるという問題がある。 However, TMA (Trimethyl Aluminum), which is a raw material for forming the Al 2 O 3 film, is a material that requires care and is expensive. For this reason, TMA has a problem that it is a substance that is difficult to use in the production of solar cells.
　基板の薄型化を実現する太陽電池としては、ＰＥＲＣセル以外に、特許文献１に示されているような、裏面にボロン（Ｂ）を拡散しボロン拡散層からなるＢＳＦ層（Ｂ－ＢＳＦ）を形成した太陽電池セルも提案されている。ボロンはシリコンと合金を形成しないため、Ｂ－ＢＳＦを形成した太陽電池セルは、裏面にＡｌ－Ｓｉ合金を形成するＡｌ－ＢＳＦセルと比較して、基板が反りにくいと考えられるからである。しかしながら、Ｂ－ＢＳＦを形成した太陽電池セルは、実用化には至っていない。Ｂ－ＢＳＦを形成した太陽電池セルが、実用化に至らない原因は、ボロンの拡散方法と裏面のパッシベーション膜にある。 In addition to PERC cells, a solar cell that achieves a thin substrate has a BSF layer (B-BSF) made of a boron diffusion layer by diffusing boron (B) on the back surface as shown in Patent Document 1. Formed solar cells have also been proposed. This is because, since boron does not form an alloy with silicon, it is considered that a solar cell with B-BSF formed is less likely to warp the substrate than an Al-BSF cell with an Al-Si alloy formed on the back surface. However, solar cells formed with B-BSF have not been put into practical use. The reason why the solar battery cell formed with B-BSF is not put into practical use is the diffusion method of boron and the passivation film on the back surface.
　特許文献１では、気相拡散によってボロンを拡散しているが、気相拡散では、通常の場合、拡散時に形成されたＢＳＧ（Ｂｏｒｏｎ　Ｓｉｌｉｃａｔｅ　Ｇｌａｓｓ）膜を除去しても、基板表面には、清浄面の証である疎水面は出ない。後述するが、ＢＳＧ膜除去後の基板表面が疎水面とならない理由は基板表面にボロンシリサイド層が形成されるためである。基板表面にボロンシリサイド層があるとホール電子対の再結合が生じ易く、変換特性の高いセルが作成できない。ＢＳＧ膜と基板との界面に生成されるボロンシリサイド層は、ボロン含有量の多いシリコン層であり、ボロンリッチ層ともよばれる。よって、このボロンシリサイド層を除去する必要があり、一般的には、基板を熱酸化し、再度、酸化膜を除去するといったプロセスが行われる。ところがボロンシリサイド層にゲッタリングされた不純物が、熱酸化の際に再放出され、基板の結晶品質を落とすことも知られている。 In Patent Document 1, boron is diffused by vapor phase diffusion. However, in vapor phase diffusion, even if the BSG (Boron Silicate Glass) film formed during the diffusion is removed, the substrate surface is clean. There is no hydrophobic surface as a proof of the surface. As will be described later, the reason why the substrate surface after the removal of the BSG film does not become a hydrophobic surface is that a boron silicide layer is formed on the substrate surface. If there is a boron silicide layer on the substrate surface, recombination of hole electron pairs is likely to occur, and a cell having high conversion characteristics cannot be produced. The boron silicide layer generated at the interface between the BSG film and the substrate is a silicon layer with a high boron content and is also called a boron rich layer. Therefore, it is necessary to remove this boron silicide layer, and generally, a process of thermally oxidizing the substrate and removing the oxide film again is performed. However, it is also known that impurities gettered in the boron silicide layer are re-emitted during thermal oxidation, which degrades the crystal quality of the substrate.
　裏面にＢ－ＢＳＦ層を形成したとしても、特許文献１に記載されているように、裏面のパッシベーション膜は必要である。特許文献１の太陽電池セルの場合、ｐ型の面に適したパッシベーション膜である酸化アルミニウム膜の使用を避けることはできず、ＰＥＲＣセルと比べて、ボロン拡散を行う分だけ、製造プロセスは煩雑になる。 Even if a B-BSF layer is formed on the back surface, as described in Patent Document 1, a passivation film on the back surface is necessary. In the case of the solar cell of Patent Document 1, the use of an aluminum oxide film that is a passivation film suitable for a p-type surface cannot be avoided, and the manufacturing process is complicated by the amount of boron diffusion compared to the PERC cell. become.
　Ｂ－ＢＳＦ層形成のための新しい拡散方法として、特許文献２に、ＢＳＧ膜とＮＳＧ（Ｎｏｎ　ｄｏｐｅｄ　Ｓｉｌｉｃａｔｅ　Ｇｌａｓｓ）膜との積層膜を基板表面に形成し、熱処理によってｐ型拡散層を形成する技術が提示されている。 As a new diffusion method for forming a B-BSF layer, Patent Document 2 discloses a technique of forming a laminated film of a BSG film and an NSG (Non Doped Silicate Glass) film on a substrate surface and forming a p-type diffusion layer by heat treatment. Is presented.
特開２００９－１４７０７０号公報JP 2009-147070 A 特開２０１４－０４５０３６号公報JP 2014-045036 A
　しかしながら、上記特許文献２の技術によれば、拡散源として成膜したＢＳＧ膜、およびキャップ層としてのＮＳＧ膜の積層膜を、ボロンの拡散後にエッチング除去した後、再度、ボロン拡散面に適したパッシベーション膜を成膜している。そのため、プロセスが煩雑となり材料コストが増える、という問題があった。 However, according to the technique of the above-mentioned Patent Document 2, the laminated film of the BSG film formed as the diffusion source and the NSG film as the cap layer is removed by etching after the diffusion of boron, and again suitable for the boron diffusion surface. A passivation film is formed. Therefore, there is a problem that the process becomes complicated and the material cost increases.
　本発明は、基板の薄型化が可能で、製造が容易でかつ変換効率の高い太陽電池を得ることを目的としている。 An object of the present invention is to obtain a solar cell that can be thinned, is easy to manufacture, and has high conversion efficiency.
　上述した課題を解決し、目的を達成するために、本発明の太陽電池は、シリコン基板と、シリコン基板の第１の表面に設けられ、第１の導電型の元素を含む拡散層と、拡散層に積層され、第１の導電型の元素とケイ素（Ｓｉ：以下シリコンということもある）とを含む第１のガラス層と、第１のガラス層に積層され、第１の導電型の元素を含まずケイ素を含む第２のガラス層とを有するパッシベーション膜とを備える。 In order to solve the above-described problems and achieve the object, a solar cell of the present invention includes a silicon substrate, a diffusion layer provided on the first surface of the silicon substrate, and containing a first conductivity type element, A first glass layer including a first conductivity type element and silicon (hereinafter also referred to as silicon); and a first conductivity type element stacked on the first glass layer. And a passivation film having a second glass layer containing silicon.
　本発明によれば、基板の薄型化が可能で、製造が容易でかつ変換効率の高い太陽電池を得ることができるという効果を奏する。 According to the present invention, it is possible to obtain a solar cell that can be thinned, can be easily manufactured, and has high conversion efficiency.
実施の形態１の太陽電池を模式的に示す断面図であり、図２のI-I断面図It is sectional drawing which shows the solar cell of Embodiment 1 typically, and is II sectional drawing of FIG. 実施の形態１の太陽電池の上面図Top view of solar cell of Embodiment 1 実施の形態１の太陽電池の製造工程を示す工程断面図Process sectional drawing which shows the manufacturing process of the solar cell of Embodiment 1 実施の形態１の太陽電池の製造工程を示すフローチャートFlowchart showing the manufacturing process of the solar cell of the first embodiment. 実施の形態１の太陽電池の変形例を示す図The figure which shows the modification of the solar cell of Embodiment 1. 実施の形態１の太陽電池および比較例の太陽電池のセルの開放電圧Ｖoc、短絡光電流密度Ｊscの比較図Comparison diagram of open-circuit voltage Voc and short-circuit photocurrent density Jsc of the solar battery of the first embodiment and the solar battery of the comparative example 実施の形態１の太陽電池の内部量子効率と波長との関係を示す図The figure which shows the relationship between the internal quantum efficiency of the solar cell of Embodiment 1, and a wavelength. 裏面のパッシベーション膜に現行のプラズマＣＶＤ（Ｃｈｅｍｉｃａｌ　Ｖａｐｏｕｒ　Ｄｅｐｏｓｉｔｉｏｎ）による窒化シリコン（ＳｉＮ）を用いたＡｌ－ＢＳＦを用いた太陽電池の内部量子効率を示す図The figure which shows the internal quantum efficiency of the solar cell which uses Al-BSF which used silicon nitride (SiN) by the present plasma CVD (Chemical Vapor Deposition) for the passivation film on the back 実施の形態２の太陽電池を示す断面図Sectional drawing which shows the solar cell of Embodiment 2. 実施の形態２の太陽電池の製造工程を示す工程断面図Process sectional drawing which shows the manufacturing process of the solar cell of Embodiment 2 実施の形態２の太陽電池の製造工程を示すフローチャートThe flowchart which shows the manufacturing process of the solar cell of Embodiment 2. 実施の形態４の太陽電池を示す断面図Sectional drawing which shows the solar cell of Embodiment 4. 実施の形態４の太陽電池の製造工程を示す工程断面図Process sectional drawing which shows the manufacturing process of the solar cell of Embodiment 4 実施の形態４の太陽電池の製造工程を示すフローチャートThe flowchart which shows the manufacturing process of the solar cell of Embodiment 4.
　以下に、本発明にかかる太陽電池および太陽電池の製造方法の実施の形態を図面に基づいて詳細に説明する。なお、この実施の形態によりこの発明が限定されるものではなく、本発明の要旨を逸脱しない範囲において適宜変更可能である。また、以下に示す図面においては、理解の容易のため、各部材の縮尺が実際とは異なる場合がある。各図面間においても同様である。 Hereinafter, embodiments of a solar cell and a method for manufacturing a solar cell according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.
実施の形態１．
　図１は、実施の形態１の太陽電池を模式的に示す断面図、図２は、同上面図である。図１は図２のI-I断面図である。実施の形態１の太陽電池１０は、ｐ型単結晶シリコン基板１１の裏面１１Ｂ側に、ＢＳＦ層であるｐ+型拡散層１４を形成するための拡散源に用いたＢＳＧ膜１２とキャップ層に用いたＮＳＧ膜１３との積層膜を、そのまま残してパッシベーション膜Ｐａとしたものである。 Embodiment 1 FIG.
FIG. 1 is a cross-sectional view schematically showing the solar cell of Embodiment 1, and FIG. 2 is a top view thereof. FIG. 1 is a sectional view taken along line II of FIG. The solar cell 10 of Embodiment 1 includes a BSG film 12 used as a diffusion source for forming a p + -type diffusion layer 14 which is a BSF layer on the back surface 11B side of the p-type single crystal silicon substrate 11 and a cap layer. The used laminated film with the NSG film 13 is left as it is to form a passivation film Pa.
　実施の形態１にかかる太陽電池１０は、第１導電型の半導体基板であるｐ型単結晶シリコン基板１１の第１の主面である受光面１１Ａに光反射を低減するテクスチャーを有する凹凸構造が形成されている。ｐ型単結晶シリコン基板１１の受光面１１Ａと対向する第２の主面である裏面１１Ｂにはテクスチャーは形成されず、第１導電型半導体層であるｐ+型拡散層１４が設けられている。そしてｐ+型拡散層１４を形成するための拡散源に用いられた第１のガラス層であるＢＳＧ膜１２およびキャップ層に用いられた第２のガラス層であるＮＳＧ膜１３が残され、パッシベーション膜Ｐａを構成している。受光面１１Ａ側には、テクスチャーを有する凹凸構造上に第２導電型半導体層であるｎ型拡散層１５が形成され、ｎ型拡散層１５上に、反射防止膜１６が積層して形成されている。そして、反射防止膜１６の上層に受光面１１Ａ側の第１の集電電極である受光面グリッド電極１７Ｇと受光面バス電極１７Ｂとが形成され、受光面グリッド電極１７Ｇと受光面バス電極１７Ｂとが反射防止膜１６を貫通してｎ型拡散層１５に接触したものである。ここで、図１では図示しないが裏面バス電極に直交するように裏面グリッド電極が形成されて、パッシベーション膜Ｐａを貫通して裏面電極１８を構成している。 The solar cell 10 according to the first embodiment has a concavo-convex structure having a texture that reduces light reflection on a light receiving surface 11A that is a first main surface of a p-type single crystal silicon substrate 11 that is a first conductivity type semiconductor substrate. Is formed. No texture is formed on the back surface 11B which is the second main surface facing the light receiving surface 11A of the p-type single crystal silicon substrate 11, and a p + -type diffusion layer 14 which is a first conductivity type semiconductor layer is provided. . Then, the BSG film 12 which is the first glass layer used as the diffusion source for forming the p + -type diffusion layer 14 and the NSG film 13 which is the second glass layer used for the cap layer are left, and the passivation is performed. A film Pa is formed. On the light receiving surface 11A side, an n-type diffusion layer 15 that is a second conductivity type semiconductor layer is formed on a textured uneven structure, and an antireflection film 16 is formed on the n-type diffusion layer 15 by being laminated. Yes. Then, a light receiving surface grid electrode 17G and a light receiving surface bus electrode 17B, which are first current collecting electrodes on the light receiving surface 11A side, are formed on the antireflection film 16, and the light receiving surface grid electrode 17G and the light receiving surface bus electrode 17B are formed. Is in contact with the n-type diffusion layer 15 through the antireflection film 16. Here, although not shown in FIG. 1, the back surface grid electrode is formed so as to be orthogonal to the back surface bus electrode, and the back surface electrode 18 is configured to penetrate the passivation film Pa.
　本発明者は、パッシベーション性の向上と基板の反りの問題とを解決すべく検討を進めた結果、拡散源として成膜したＢＳＧ膜１２とキャップ層に成膜したＮＳＧ膜１３との積層膜がボロン拡散によるｐ型拡散層のパッシベーション膜Ｐａに適していることを見出した。実施の形態１の太陽電池では、ＢＳＧ膜１２とＮＳＧ膜１３との積層膜をパッシベーション膜Ｐａとして使用する。このため、新たにパッシベーション膜Ｐａを形成する必要がないため、製造プロセスを簡略しつつ、変換効率の高い太陽電池が製造できる。また、Ａｌ－ＢＳＦセルの場合のように、Ａｌ－Ｓｉ合金層が形成されないため、Ａｌ－Ｓｉ合金層の形成による基板の反りの発生も抑制可能であり、薄いシリコン基板を用いることができる。また、成膜材料のジボラン(Ｂ2Ｈ6)、シラン(ＳｉＨ4)等の材料ガスの価格は、ＴＭＡよりも安いため、発電コストの低減に寄与することができる。 As a result of investigations to improve the passivation property and the problem of warping of the substrate, the present inventor has obtained a laminated film of the BSG film 12 formed as a diffusion source and the NSG film 13 formed on the cap layer. It has been found that it is suitable for the passivation film Pa of the p-type diffusion layer by boron diffusion. In the solar cell of the first embodiment, a laminated film of the BSG film 12 and the NSG film 13 is used as the passivation film Pa. For this reason, since it is not necessary to form the passivation film Pa newly, a solar cell with high conversion efficiency can be manufactured, simplifying a manufacturing process. Further, since the Al—Si alloy layer is not formed as in the case of the Al—BSF cell, the occurrence of warpage of the substrate due to the formation of the Al—Si alloy layer can be suppressed, and a thin silicon substrate can be used. Moreover, since the price of material gases such as diborane (B 2 H 6 ) and silane (SiH 4 ) as film forming materials is lower than that of TMA, it can contribute to reduction of power generation cost.
　また、実施の形態１の太陽電池では、ＢＳＧ膜１２とｐ+型拡散層１４との界面で、第１の導電型の元素であるボロンの濃度が連続的に変化している。このため、電子とホールとの再結合が生じにくく、良好な界面特性を得ることができる。なお界面および界面周辺の原子密度は二次イオン質量分析法（ＳＩＭＳ：　Ｓｅｃｏｎｄａｒｙ　Ｉｏｎ　Ｍａｓｓ　Ｓｐｅｃｔｒｏｍｅｔｒｙ）をはじめとする種々の測定装置で測定可能である。 In the solar cell of the first embodiment, the concentration of boron, which is the first conductivity type element, continuously changes at the interface between the BSG film 12 and the p + -type diffusion layer 14. For this reason, recombination of electrons and holes hardly occurs, and good interface characteristics can be obtained. Note that the atomic density of the interface and the periphery of the interface can be measured by various measuring apparatuses such as secondary ion mass spectrometry (SIMS).
　次に、実施の形態１の太陽電池の製造方法について説明する。図３は、実施の形態１の太陽電池の製造工程を示す工程断面図である。図４は、実施の形態１の太陽電池の製造工程を示すフローチャートである。まず、図３のステージＳ１に示すように、ｐ型単結晶シリコン基板１１を用意する。多結晶シリコン、単結晶シリコンにかかわらず、太陽電池用の基板はアズスライスの状態で納入されるため、基板表面にスライス時のダメージが残っている。そこでまず、図４に示すダメージ層の除去ステップＳ１０１で、エッチングによりｐ型単結晶シリコン基板１１表面のダメージ層を除去する。エッチングにはコストの観点からアルカリ薬液が用いられることが多いが、フッ硝酸系の混酸を用いても問題ない。但し、この作業はあくまでもダメージ層除去のための作業であって、テクスチャーと呼ばれる反射率を低減させるための微小凹凸構造を形成する必要はない。この時点でテクスチャーを形成すると、ｐ型単結晶シリコン基板１１の裏面１１Ｂにもテクスチャーが形成されてしまい、却って、太陽電池１０の特性低下を招く場合がある。この点については後述する。 Next, a method for manufacturing the solar cell according to Embodiment 1 will be described. FIG. 3 is a process cross-sectional view illustrating the manufacturing process of the solar cell of the first embodiment. FIG. 4 is a flowchart showing manufacturing steps of the solar cell of the first embodiment. First, as shown in stage S1 of FIG. 3, a p-type single crystal silicon substrate 11 is prepared. Regardless of whether it is polycrystalline silicon or single crystal silicon, the substrate for the solar cell is delivered in an as-sliced state, so that damage during slicing remains on the substrate surface. Therefore, first, in the damaged layer removing step S101 shown in FIG. 4, the damaged layer on the surface of the p-type single crystal silicon substrate 11 is removed by etching. In etching, an alkaline chemical solution is often used from the viewpoint of cost, but there is no problem even if a hydrofluoric acid mixed acid is used. However, this operation is merely an operation for removing the damaged layer, and it is not necessary to form a minute uneven structure for reducing the reflectance called texture. If the texture is formed at this time, the texture is also formed on the back surface 11B of the p-type single crystal silicon substrate 11, and the characteristics of the solar cell 10 may be deteriorated instead. This point will be described later.
　次に、ＣＶＤ装置にて、図３のステージＳ２および図４のステップＳ１０２に示すように、ｐ型単結晶シリコン基板１１の裏面１１Ｂ側に拡散源となるＢＳＧ膜１２とキャップ層としてのＮＳＧ膜１３とを積層して形成する。 Next, with a CVD apparatus, as shown in stage S2 in FIG. 3 and step S102 in FIG. 4, a BSG film 12 serving as a diffusion source and an NSG film serving as a cap layer on the back surface 11B side of the p-type single crystal silicon substrate 11 13 are laminated.
　その後、図３のステージＳ３および図４のステップＳ１０３に示すように、ｐ型単結晶シリコン基板１１をアニールしてＢＳＧ膜１２中のボロンをｐ型単結晶シリコン基板１１に拡散させ、裏面１１Ｂ側の表層にｐ+型拡散層１４を形成する。ＮＳＧ膜１３が存在しないとボロンはアニール雰囲気中にも放出されてしまうため、ＢＳＧ膜１２中のボロンの濃度が下がり、ｐ型単結晶シリコン基板１１内にボロンが効果的に拡散されない。そこでアニール雰囲気中へのボロンの放出を防ぐため、キャップ層としてＮＳＧ膜１３をＢＳＧ膜１２の上に成膜する。ここでは、ＢＳＧ膜１２中のボロン濃度を１．１８ｗｔ％、ＢＳＧ膜１２およびＮＳＧ膜１３の膜厚はそれぞれ７０ｎｍおよび３００ｎｍとし、窒素（Ｎ2）雰囲気中、１０００℃－６０ｍｉｎの条件でアニールを行った。 Thereafter, as shown in stage S3 in FIG. 3 and step S103 in FIG. 4, the p-type single crystal silicon substrate 11 is annealed to diffuse boron in the BSG film 12 into the p-type single crystal silicon substrate 11, and the back surface 11B side A p + -type diffusion layer 14 is formed on the surface layer. If the NSG film 13 is not present, boron is also released into the annealing atmosphere, so that the boron concentration in the BSG film 12 is lowered and boron is not effectively diffused into the p-type single crystal silicon substrate 11. Therefore, in order to prevent boron from being released into the annealing atmosphere, an NSG film 13 is formed on the BSG film 12 as a cap layer. Here, the boron concentration in the BSG film 12 is 1.18 wt%, the film thicknesses of the BSG film 12 and the NSG film 13 are 70 nm and 300 nm, respectively, and annealing is performed in a nitrogen (N 2 ) atmosphere at 1000 ° C.-60 min. went.
　上記拡散工程は、基板温度が９００℃から１１００℃であればよい。基板温度が９００℃に満たないと、十分な拡散ができない。一方、基板温度が１１００℃を超えても問題はないが、１０００℃で十分拡散が可能であるため、コスト面も含めて考えると、更に温度を上げるメリットは小さい。 In the diffusion step, the substrate temperature may be 900 ° C. to 1100 ° C. If the substrate temperature is less than 900 ° C., sufficient diffusion cannot be achieved. On the other hand, there is no problem even if the substrate temperature exceeds 1100 ° C. However, since sufficient diffusion is possible at 1000 ° C., the merit of further increasing the temperature is small considering the cost.
　上記工程では、Ｎ2雰囲気中でアニールを行ったが、アニール中もしくは降温中に微量のオキシ塩化リン（ＰＯＣｌ3）と酸素（Ｏ2）とを流しても良い。アニール装置が汚染されている場合、汚染源がｐ型単結晶シリコン基板１１の表面からｐ型単結晶シリコン基板１１の内部に拡散されて結晶品質が低下する場合がある。アニール中もしくは降温中にＰＯＣｌ3とＯ2とを流すことでｐ型単結晶シリコン基板１１の表面にリン拡散層を形成し、このリン拡散層によるゲッタリング効果により装置からの汚染の影響を少なくすることが期待できる。このリン拡散層は、次のテクスチャー形成工程でエッチング除去されるので、後の工程に影響を与えない。なお、リンはボロンよりも拡散され易いため、このリン拡散層は厚くなり易いが、リン拡散層が厚くなり過ぎるとテクスチャー形成工程で除去されにくくなるため、リン拡散層が厚くなり過ぎないように留意する必要がある。 In the above process, annealing was performed in an N 2 atmosphere, but a small amount of phosphorus oxychloride (POCl 3 ) and oxygen (O 2 ) may be flowed during annealing or cooling. When the annealing apparatus is contaminated, the contamination source may be diffused from the surface of the p-type single crystal silicon substrate 11 into the p-type single crystal silicon substrate 11 to deteriorate the crystal quality. By flowing POCl 3 and O 2 during annealing or cooling, a phosphorus diffusion layer is formed on the surface of the p-type single crystal silicon substrate 11, and the gettering effect by this phosphorus diffusion layer reduces the influence of contamination from the apparatus. Can be expected to do. Since this phosphorus diffusion layer is removed by etching in the next texture forming step, it does not affect the subsequent steps. Since phosphorus is more easily diffused than boron, this phosphorus diffusion layer is likely to be thick, but if the phosphorus diffusion layer becomes too thick, it will be difficult to remove in the texture forming process, so that the phosphorus diffusion layer will not be too thick. It is necessary to keep in mind.
　この拡散方法はＢＳＧ膜１２を拡散源とした固相拡散であるが、ボロンの拡散には、固相拡散の他に臭化ボロン（ＢＢｒ3）、塩化ボロン（ＢＣｌ3）をはじめとするボロン含有ガスを用いた気相拡散がある。しかしながら、気相拡散によるボロン拡散を用いたセル、例えば、ｎ型単結晶シリコン基板に気相拡散でボロン拡散を行い、ｐｎ接合を形成したセルの特性は、ＣＶＤ法により成膜した膜を利用した拡散方法によりｐｎ接合を形成したセルよりも変換効率をはじめとする特性が低い。これは、拡散後のｎ型単結晶シリコン基板の表面状態の差に起因している。 This diffusion method is solid phase diffusion using the BSG film 12 as a diffusion source. Boron such as boron bromide (BBr 3 ) and boron chloride (BCl 3 ) in addition to solid phase diffusion is used for boron diffusion. There is a gas phase diffusion using a contained gas. However, a cell using boron diffusion by vapor phase diffusion, for example, a cell in which boron diffusion is performed by vapor phase diffusion on an n-type single crystal silicon substrate and a pn junction is formed uses a film formed by a CVD method. The conversion efficiency and other characteristics are lower than those of a cell in which a pn junction is formed by the diffusion method described above. This is due to the difference in the surface state of the n-type single crystal silicon substrate after diffusion.
　上述したように、気相拡散では、通常の場合、拡散時に形成されたＢＳＧ膜を除去しても、ボロンリッチ層である、ボロンシリサイド層が形成され、このボロンシリサイド層でキャリアが再結合してしまう。よって、このボロンシリサイド層を除去する必要があり、一般的には、基板を熱酸化し、再度、酸化膜を除去するといったプロセスが行われる。ところが熱酸化の際、ボロンシリサイド層にゲッタリングされた不純物が再放出され、結晶品質を落とすことがしられている。このため、ボロンの気相拡散では高いセル特性が得られにくい。 As described above, in vapor phase diffusion, a boron silicide layer, which is a boron-rich layer, is formed even if the BSG film formed during diffusion is removed, and carriers are recombined in this boron silicide layer. End up. Therefore, it is necessary to remove this boron silicide layer, and generally, a process of thermally oxidizing the substrate and removing the oxide film again is performed. However, during thermal oxidation, impurities gettered to the boron silicide layer are re-emitted and the crystal quality is degraded. For this reason, it is difficult to obtain high cell characteristics by boron vapor phase diffusion.
　一方、ＣＶＤ法により成膜したＢＳＧ膜を拡散源とした拡散では、成膜時にＢＳＧ膜中のボロン濃度をコントロールできるため、適切な濃度を選ぶことにより、ボロンシリサイド層の形成を抑制することができる。ボロンシリサイド層の有無は、拡散後にＢＳＧ膜をフッ酸（ＨＦ）で除去することで判断できる。ボロンシリサイド層が形成されていれば親水面が現れ、ボロンシリサイド層が形成されていなければ、疎水面が現れる。ＣＶＤ成膜のＢＳＧ膜を拡散源とした拡散では、適切なＢＳＧ膜中のボロン濃度を選ぶことによって、ボロンシリサイド層の形成を防ぐことができる。 On the other hand, in diffusion using a BSG film formed by CVD as a diffusion source, the boron concentration in the BSG film can be controlled at the time of film formation. Therefore, the formation of a boron silicide layer can be suppressed by selecting an appropriate concentration. it can. The presence or absence of the boron silicide layer can be determined by removing the BSG film with hydrofluoric acid (HF) after diffusion. If a boron silicide layer is formed, a hydrophilic surface appears, and if a boron silicide layer is not formed, a hydrophobic surface appears. In diffusion using a BSG film formed by CVD as a diffusion source, formation of a boron silicide layer can be prevented by selecting an appropriate boron concentration in the BSG film.
　従って、拡散には、気相拡散よりもＣＶＤ成膜で得られたＢＳＧ膜とＮＳＧ膜との積層膜を用いてボロン拡散を行うのが望ましい。気相拡散を用いる場合には、ＢＳＧ膜の濃度制御が困難であり、ボロンリッチ層が形成され易い。このため、ボロンリッチ層の生成を抑制すべく、基板を昇温する工程で適切な温度になったときに拡散用のボロン含有ガスを供給するなど供給のタイミングを調整する、拡散開始時にボロン含有ガス中のボロン濃度を高める、あるいは少量の酸素を添加し軽く表面酸化を行うなど、工夫が必要である。 Therefore, for diffusion, it is desirable to perform boron diffusion using a laminated film of a BSG film and an NSG film obtained by CVD film formation rather than vapor phase diffusion. When vapor phase diffusion is used, it is difficult to control the concentration of the BSG film, and a boron-rich layer is easily formed. For this reason, in order to suppress the formation of a boron-rich layer, adjust the supply timing such as supplying a boron-containing gas for diffusion when the temperature rises to an appropriate temperature in the step of heating the substrate. It is necessary to devise measures such as increasing the boron concentration in the gas or lightly oxidizing the surface by adding a small amount of oxygen.
　ＣＶＤ成膜のＢＳＧ膜１２中のボロン濃度は０．５ｗｔ％から３ｗｔ％とするのが適切である。ＢＳＧ膜１２中のボロン濃度が、３ｗｔ％を超えると、ｐ型単結晶シリコン基板１１表面が親水面となり、良好なセル特性を得ることができない。一方、ＢＳＧ膜１２中のボロン濃度が、０．５ｗｔ％に満たないと、ｐ型単結晶シリコン基板１１表面に所望のボロン拡散を行うことができない。気相拡散のＢＳＧ膜のボロン濃度は、一般的には５ｗｔ％以上となる。 It is appropriate that the boron concentration in the CVD BSG film 12 is 0.5 wt% to 3 wt%. If the boron concentration in the BSG film 12 exceeds 3 wt%, the surface of the p-type single crystal silicon substrate 11 becomes a hydrophilic surface, and good cell characteristics cannot be obtained. On the other hand, unless the boron concentration in the BSG film 12 is less than 0.5 wt%, desired boron diffusion cannot be performed on the surface of the p-type single crystal silicon substrate 11. The boron concentration of the vapor phase diffusion BSG film is generally 5 wt% or more.
　次に、図３のステージＳ４および図４のステップＳ１０４に示すように、裏面１１Ｂ側のＢＳＧ膜１２およびＮＳＧ膜１３をエッチングマスクとして、ｐ型単結晶シリコン基板１１の片面、つまり受光面１１Ａ側にのみテクスチャー１１Ｔの形成を行う。なお、ステージＳ２におけるＣＶＤ法による成膜時、被成膜面の周囲にもＢＳＧ膜１２およびＮＳＧ膜１３が回り込むのでＢＳＧ膜１２が回り込んだ箇所にもボロンは拡散される。しかしながらボロンが回り込んだ箇所に形成されるＢＳＧ膜１２の膜厚は薄いため、テクスチャー１１Ｔ形成の際、回り込んだ膜、および回り込んだＢＳＧ膜１２によって形成されたボロン拡散層はエッチング除去される。 Next, as shown in stage S4 in FIG. 3 and step S104 in FIG. 4, one side of p-type single crystal silicon substrate 11, that is, light receiving surface 11A side, using BSG film 12 and NSG film 13 on the back surface 11B side as an etching mask. Only texture 11T is formed. Note that, when the film is formed by the CVD method in the stage S2, the BSG film 12 and the NSG film 13 also circulate around the film formation surface, so that boron is also diffused to the portion where the BSG film 12 has circulated. However, since the film thickness of the BSG film 12 formed in the portion where the boron wraps around is thin, the wraparound film and the boron diffusion layer formed by the wrapping BSG film 12 are removed by etching when the texture 11T is formed. The
　その後、図３のステージＳ５および図４のステップＳ１０５に示すように、ｐｎ接合を形成するため、受光面１１Ａ側のテクスチャー１１Ｔ面に気相拡散によりリン（Ｐ）を拡散してｎ型拡散層１５を形成する。ここではＢＳＧ膜１２およびＮＳＧ膜１３は拡散マスクの機能を発揮する。拡散工程後、拡散工程で受光面１１Ａ側に形成されたＰＳＧ（Ｐｈｏｓｐｈｏ　Ｓｉｌｉｃａｔｅ　Ｇａｌａｓｓ）膜を除去するが、このときもＢＳＧ膜１２およびＮＳＧ膜１３は拡散後のＰＳＧ膜除去にも耐え得る。一般にＣＶＤ法で成膜した酸化膜であるＢＳＧ膜、ＮＳＧ膜は熱酸化で形成した熱酸化膜と比較してエッチングレートが高いが、実施の形態１の太陽電池の製造プロセスで形成されたＢＳＧ膜１２、ＮＳＧ膜１３はボロン拡散時のアニール工程を経ているため、エッチングレートが熱酸化膜と同等程度になり、ＰＳＧ膜除去後でも除去されずに残っている。 Thereafter, as shown in stage S5 in FIG. 3 and step S105 in FIG. 4, in order to form a pn junction, phosphorus (P) is diffused by vapor phase diffusion on the texture 11T surface on the light receiving surface 11A side to form an n-type diffusion layer. 15 is formed. Here, the BSG film 12 and the NSG film 13 exhibit the function of a diffusion mask. After the diffusion step, the PSG (Phospho Silicate Glass) film formed on the light receiving surface 11A side in the diffusion step is removed. At this time, the BSG film 12 and the NSG film 13 can withstand the PSG film removal after the diffusion. In general, a BSG film and an NSG film, which are oxide films formed by a CVD method, have a higher etching rate than a thermal oxide film formed by thermal oxidation, but BSG formed by the manufacturing process of the solar cell of the first embodiment. Since the film 12 and the NSG film 13 have undergone an annealing process at the time of boron diffusion, the etching rate becomes comparable to that of the thermal oxide film, and remains without being removed even after the PSG film is removed.
　ＰＳＧ膜を除去した後、図３のステージＳ６および図４のステップＳ１０６に示すように、ＣＶＤ法により窒化シリコン膜からなる反射防止膜１６を受光面１１Ａ側に形成する。 After removing the PSG film, as shown in stage S6 in FIG. 3 and step S106 in FIG. 4, an antireflection film 16 made of a silicon nitride film is formed on the light receiving surface 11A side by CVD.
　反射防止膜１６を形成した後、図３のステージＳ７および図４のステップＳ１０７に示すように、受光面１１Ａおよび裏面１１Ｂに受光面電極１７および裏面電極１８を印刷により形成する。 After forming the antireflection film 16, as shown in the stage S7 in FIG. 3 and the step S107 in FIG. 4, the light receiving surface electrode 17 and the back electrode 18 are formed on the light receiving surface 11A and the back surface 11B by printing.
　受光面電極１７および裏面電極１８を印刷後、熱処理を行い、図４のステップＳ１０８に示すようにファイヤスルーにより、受光面電極１７はｎ型拡散層１５に当接するとともに裏面電極１８はｐ+型拡散層１４に当接して、それぞれコンタクトを形成し、図１および２に示した太陽電池の完成となる。 After printing the light-receiving surface electrode 17 and the back surface electrode 18, heat treatment is performed, and as shown in step S108 in FIG. 4, the light-receiving surface electrode 17 contacts the n-type diffusion layer 15 and the back surface electrode 18 is p + type by fire-through. A contact is formed in contact with the diffusion layer 14 to complete the solar cell shown in FIGS.
　裏面電極１８の形状は特に指定はなく、ＢＳＧ膜１２およびＮＳＧ膜１３の厚さに応じて決めれば良い。ＮＳＧ膜１３を薄く成膜した場合は、裏面電極１８は、銀アルミニウム（ＡｇＡｌ）ペーストを用いて印刷形成後、ファイヤスルーつまり、熱処理によりＢＳＧ膜１２およびＮＳＧ膜１３を貫通して、ｐ+型拡散層１４にコンタクトすることができる。 The shape of the back electrode 18 is not particularly specified, and may be determined according to the thicknesses of the BSG film 12 and the NSG film 13. If thinly fabricating the NSG film 13, the back electrode 18, after printing form with silver aluminum (AgAl) paste, fire-through that is, through the BSG film 12 and the NSG film 13 by heat treatment, p + -type The diffusion layer 14 can be contacted.
　また、ＮＳＧ膜１３を厚く成膜した場合、電極形成時まで裏面に残っている膜は厚く、ファイヤスルーしにくい。図５は、実施の形態１の太陽電池の変形例を示す図である。ＮＳＧ膜１３が厚くファイヤスルーしにくい場合は、変形例の太陽電池２０を図５に示すように、レーザで、ＢＳＧ膜１２およびＮＳＧ膜１３に開口し、コンタクトホールｈを形成したのち、実施の形態１の太陽電池１０と同様に印刷により裏面電極１８を形成する。 Further, when the NSG film 13 is formed thick, the film remaining on the back surface until the electrode is formed is thick and difficult to fire through. FIG. 5 is a diagram showing a modification of the solar cell of the first embodiment. If the NSG film 13 is thick and difficult to fire through, the modified solar cell 20 is opened in the BSG film 12 and the NSG film 13 with a laser as shown in FIG. The back electrode 18 is formed by printing in the same manner as the solar cell 10 of the first embodiment.
　図６は、実施の形態１の太陽電池および比較例の太陽電池のセルの開放電圧Ｖoc、短絡光電流密度Ｊscの比較図である。開放電圧Ｖocは、外部に流す電流が０Ａの時の電圧であり、短絡光電流密度Ｊscは、外部にかかる電圧が０Ｖの時の電流である。なお、図６では裏面のテクスチャーの有無、裏面のパッシベーション膜の差について比較している。プラズマＣＶＤ（Ｐｌａｚｍａ　Ｅｎｈａｎｃｅｄ　Ｃｈｅｍｉｃａｌ　Ｖａｐｏｕｒ　Ｄｅｐｏｓｉｔｉｏｎ：ＰＥＣＶＤ）法で形成した窒化シリコン膜であるＰＥＣＶＤ－ＳｉＮを裏面のパッシベーション膜としたセルでは、テクスチャー形成後にＢＳＧ膜１２およびＮＳＧ膜１３を完全除去し、再度、裏面にＰＥＣＶＤ－ＳｉＮを成膜した後に、受光面１１Ａ側にリンを拡散している。図６に示した表からも明らかなように、裏面のパッシベーション膜としてのＢＳＧ膜１２とＮＳＧ膜１３とを用いた場合との電気的特性の優位性がよく分かる結果となっている。 FIG. 6 is a comparison diagram of the open circuit voltage Voc and the short-circuit photocurrent density Jsc of the cells of the solar battery of the first embodiment and the solar battery of the comparative example. The open circuit voltage Voc is a voltage when the current flowing to the outside is 0 A, and the short-circuit photocurrent density Jsc is a current when the voltage applied to the outside is 0 V. FIG. 6 compares the presence or absence of the texture on the back surface and the difference in the passivation film on the back surface. In a cell using PECVD-SiN, which is a silicon nitride film formed by plasma CVD (Plasma Enhanced Chemical Vapor Deposition: PECVD), as a passivation film on the back surface, the BSG film 12 and the NSG film 13 are completely removed after texture formation, After forming PECVD-SiN on the back surface, phosphorus is diffused on the light receiving surface 11A side. As is apparent from the table shown in FIG. 6, the superiority of the electrical characteristics when using the BSG film 12 and the NSG film 13 as the passivation film on the back surface is well understood.
　図７は、実施の形態１の太陽電池の内部量子効率(Ｉｎｔｅｒｎａｌ　Ｑｕａｎｔｕｍ　Ｅｆｆｉｃｉｅｎｃｙ)を示す図であり、図８は、裏面のパッシベーション膜に現行のプラズマＣＶＤによる窒化シリコンを用いた太陽電池の内部量子効率を示す図である。図７および図８には、ともに比較対象としてＡｌ－ＢＳＦセルの内部量子効率を示している。内部量子効率は光照射で発生したキャリアと、取り出された電流との割合であり、太陽電池の感度とみなすこともできる。図７において、曲線Ａ１は実施の形態１のＢＳＧ膜１２およびＮＳＧ膜１３の積層膜をパッシベーション膜として用いた場合の裏面テクスチャー無、曲線Ａ２は裏面テクスチャー有を、図８において、曲線Ｐ１は比較例のＰＥＣＶＤ－ＳｉＮをパッシベーション膜として用いた場合の裏面テクスチャー無、曲線Ｐ２は裏面テクスチャー有を、図７および図８において、曲線Ｂは裏面のパッシベーション膜ＰａにＡｌ－ＢＳＦを用いた場合を示す。注目すべきは９００ｎｍ以降の長波長域の感度の差である。曲線Ａ１，Ａ２と曲線Ｐ１，Ｐ２との比較から、裏面１１Ｂにテクスチャーが無い方が感度が高く、裏面１１Ｂのパッシベーション膜ＰａにＢＳＧ膜１２およびＮＳＧ膜１３を用いた、裏面テクスチャー無、ＢＳＧ膜１２およびＮＳＧ膜１３のセルに至っては、Ａｌ－ＢＳＦセルよりも感度が高い。従って、実施の形態１のＢＳＧ膜１２およびＮＳＧ膜１３の積層膜をパッシベーション膜Ｐａとして用いた太陽電池セルは、Ａｌ－ＢＳＦセルよりも、良好な裏面パッシベーション特性を有していることを示している。 FIG. 7 is a diagram showing the internal quantum efficiency (Internal Quantum Efficiency) of the solar cell of the first embodiment. FIG. 8 is a diagram showing the internal quantum of the solar cell using the current plasma CVD silicon nitride for the passivation film on the back surface. It is a figure which shows efficiency. 7 and 8 both show the internal quantum efficiency of the Al-BSF cell as a comparison object. The internal quantum efficiency is the ratio between the carriers generated by light irradiation and the extracted current, and can be regarded as the sensitivity of the solar cell. In FIG. 7, curve A1 indicates that there is no back surface texture when the laminated film of the BSG film 12 and NSG film 13 of Embodiment 1 is used as a passivation film, curve A2 indicates that there is a back surface texture, and in FIG. 8, curve P1 indicates a comparison. When the example PECVD-SiN is used as a passivation film, no back surface texture, curve P2 indicates that there is a back surface texture, and in FIGS. 7 and 8, curve B indicates a case where Al-BSF is used for the back surface passivation film Pa. . What should be noted is the difference in sensitivity in the long wavelength region after 900 nm. From the comparison between the curves A1 and A2 and the curves P1 and P2, it is more sensitive that there is no texture on the back surface 11B, and the BSG film 12 and the NSG film 13 are used for the passivation film Pa on the back surface 11B. The cell of 12 and NSG film 13 is more sensitive than the Al-BSF cell. Therefore, it is shown that the solar battery cell using the laminated film of the BSG film 12 and the NSG film 13 of Embodiment 1 as the passivation film Pa has better back surface passivation characteristics than the Al-BSF cell. Yes.
　実施の形態１の太陽電池では、短波長感度がＡｌ－ＢＳＦセルよりも低いが、これは受光面１１Ａ側のリン拡散が影響している。同一バッチで拡散しているにも関わらず、裏面１１Ｂに、ＢＳＧ膜１２およびＮＳＧ膜１３の積層膜もしくはＰＥＣＶＤ－ＳｉＮがある場合では、無い場合と比較してシート抵抗が低くなる傾向がある。実験では、いかなる被膜も形成していない裸のｐ型単結晶シリコン基板１１内に対してシート抵抗６５Ω/□となる条件でリン拡散を行ったが、裏面１１Ｂに膜がある状態では４５Ω/□程度のシート抵抗となった。原因は不明であるが、短波長感度については、拡散条件の調整で対応可能であり、裏面１１Ｂのパッシベーション特性とは無関係である。シート抵抗を適切な値に選ぶことで短波長感度は向上させることが可能である。 In the solar cell of Embodiment 1, the short wavelength sensitivity is lower than that of the Al-BSF cell, but this is influenced by the phosphorus diffusion on the light receiving surface 11A side. In spite of diffusing in the same batch, the sheet resistance tends to be lower in the case where there is a laminated film of BSG film 12 and NSG film 13 or PECVD-SiN on the back surface 11B than in the case where there is no film. In the experiment, phosphorus diffusion was performed on the bare p-type single crystal silicon substrate 11 on which no film was formed under the condition that the sheet resistance was 65Ω / □. The sheet resistance was about. The cause is unknown, but the short wavelength sensitivity can be dealt with by adjusting the diffusion condition and is irrelevant to the passivation characteristics of the back surface 11B. The short wavelength sensitivity can be improved by selecting an appropriate value for the sheet resistance.
　以上説明したように、実施の形態１の太陽電池は、ｐ型単結晶シリコン基板の一方の表面となる第１の表面の少なくとも一部に、ＢＳＧ膜とＮＳＧ膜とを積層し、熱処理することによってＢＳＧ膜のボロンをシリコン基板に拡散させ高濃度ｐ型不純物拡散層を設け、且つ、拡散に使用したＢＳＧ膜およびＮＳＧ膜の積層膜をボロン拡散によるｐ型拡散層表面のパッシベーション膜Ｐａとして使用する。従って、製造が容易で、パッシベーション性が高く、低コストの太陽電池を実現することができる。また、ダメージ層の除去工程後、一貫して積層膜でｐ型単結晶シリコン基板の片面を被覆しているため、汚染の可能性を低減することができるとともに良好な製造作業性が得られる。実施の形態１の太陽電池では、裏面電極として、櫛型電極、もしくはコンタクトホールを形成してコンタクトをとるポイントコンタクト構造が使用できる。銀アルミニウム（ＡｇＡｌ）ペーストを用いた櫛形電極では、Ａｌ－Ｓｉ合金を形成しにくく反りを抑制する事ができる。このため、基板の薄型化をはかることができる。またポイントコンタクト構造の場合は、Ａｌ-Ｓｉ合金面積が少なくなるため、基板の薄型化をはかることができる。 As described above, in the solar cell of the first embodiment, the BSG film and the NSG film are stacked on at least a part of the first surface which is one surface of the p-type single crystal silicon substrate, and heat treatment is performed. Provides a high-concentration p-type impurity diffusion layer by diffusing boron of the BSG film into the silicon substrate, and uses the laminated film of the BSG film and NSG film used for the diffusion as the passivation film Pa on the surface of the p-type diffusion layer by boron diffusion To do. Therefore, it is possible to realize a solar cell that is easy to manufacture, highly passivatable, and low in cost. In addition, after the damaged layer removal step, one side of the p-type single crystal silicon substrate is consistently covered with the laminated film, so that the possibility of contamination can be reduced and good manufacturing workability can be obtained. In the solar cell of the first embodiment, a comb electrode or a point contact structure in which contact is made by forming a contact hole can be used as the back electrode. In a comb electrode using a silver aluminum (AgAl) paste, it is difficult to form an Al—Si alloy, and warpage can be suppressed. For this reason, it is possible to reduce the thickness of the substrate. In the case of the point contact structure, the area of the Al—Si alloy is reduced, so that the thickness of the substrate can be reduced.
実施の形態２．
　次に実施の形態２の太陽電池について説明する。図９は、実施の形態２の太陽電池３０を示す断面図である。図１０は、実施の形態２の太陽電池の製造工程を示す工程断面図である。図１１は、実施の形態２の太陽電池の製造工程を示すフローチャートである。実施の形態１では、受光面１１Ａ側にｐｎ接合を配したｐ型単結晶シリコン基板１１を用いた太陽電池セルについて説明したが、実施の形態２では、ｐ型単結晶シリコン基板１１を用い、裏面１１Ｂ側にｐｎ接合を配した太陽電池３０について説明する。この場合、ＢＳＧ膜１２およびＮＳＧ膜１３が受光面１１Ａ側になるため、ＢＳＧ膜１２およびＮＳＧ膜１３には反射防止膜１６としての役割を持たせる必要があり、ＢＳＧ膜１２およびＮＳＧ膜１３の膜厚調整が必要となる。さらに詳しく述べると、太陽光スペクトルが最大となる６００ｎｍでの反射率が最小になるよう、ＢＳＧ膜１２およびＮＳＧ膜１３の膜厚比および合計膜厚を含めて膜厚調整を行う必要がある。 Embodiment 2. FIG.
Next, the solar cell of Embodiment 2 is demonstrated. FIG. 9 is a cross-sectional view showing solar cell 30 of the second embodiment. FIG. 10 is a process cross-sectional view illustrating the manufacturing process of the solar cell of the second embodiment. FIG. 11 is a flowchart showing manufacturing steps of the solar cell of the second embodiment. In the first embodiment, the solar cell using the p-type single crystal silicon substrate 11 in which the pn junction is arranged on the light receiving surface 11A side has been described, but in the second embodiment, the p-type single crystal silicon substrate 11 is used, A solar cell 30 having a pn junction on the back surface 11B side will be described. In this case, since the BSG film 12 and the NSG film 13 are on the light receiving surface 11A side, the BSG film 12 and the NSG film 13 must have a role as the antireflection film 16, and the BSG film 12 and the NSG film 13 It is necessary to adjust the film thickness. More specifically, it is necessary to adjust the film thickness including the film thickness ratio of the BSG film 12 and the NSG film 13 and the total film thickness so that the reflectance at 600 nm at which the sunlight spectrum is maximized is minimized.
　実施の形態２の太陽電池の製造方法は、受光面１１Ａ側と裏面１１Ｂ側との拡散層の導電型が異なるのと、受光面１１Ａ側および裏面１１Ｂ側の反射防止膜およびパッシベーション膜１６Ｐの組成が逆となっている以外は実施の形態１の太陽電池の製造方法とほぼ同様である。実施の形態２では反射防止膜はＢＳＧ膜１２とＮＳＧ膜１３との積層膜で構成される。 In the method of manufacturing the solar cell of the second embodiment, the composition of the antireflection film and the passivation film 16P on the light receiving surface 11A side and the back surface 11B side is different from that of the diffusion layer on the light receiving surface 11A side and the back surface 11B side. Is substantially the same as the method for manufacturing the solar cell of the first embodiment except that is reversed. In the second embodiment, the antireflection film is composed of a laminated film of the BSG film 12 and the NSG film 13.
　まず、実施の形態１と同様、図１０のステージＳ１に示すように、ｐ型単結晶シリコン基板１１を用意し、図１１に示すダメージ層の除去ステップＳ１０１で、エッチングによりｐ型単結晶シリコン基板１１表面のダメージ層を除去する。 First, as in the first embodiment, a p-type single crystal silicon substrate 11 is prepared as shown in stage S1 of FIG. 10, and a p-type single crystal silicon substrate is etched by etching in a damaged layer removing step S101 shown in FIG. 11 Remove the damage layer on the surface.
　次に、ＣＶＤ装置にて、図１０のステージＳ２および、図１１のステップＳ１０２Ｓに示すように、ｐ型単結晶シリコン基板１１の受光面１１Ａ側に拡散源となるＢＳＧ膜１２とキャップ層となるＮＳＧ膜１３とを積層して形成する。 Next, in the CVD apparatus, as shown in stage S2 in FIG. 10 and step S102S in FIG. 11, a BSG film 12 serving as a diffusion source and a cap layer are formed on the light receiving surface 11A side of the p-type single crystal silicon substrate 11. The NSG film 13 is laminated and formed.
　その後、図１０のステージＳ３および、図１１のステップＳ１０３Ｓに示すように、ｐ型単結晶シリコン基板１１をアニールしてＢＳＧ膜１２中のボロンをｐ型単結晶シリコン基板１１に拡散させ、受光面１１Ａ側の表層にｐ+型拡散層１４を形成する。実施の形態２においても実施の形態１と同様、アニール中もしくは降温中に微量のＰＯＣｌ3とＯ2とを流してもよい。 Thereafter, as shown in stage S3 in FIG. 10 and step S103S in FIG. 11, the p-type single crystal silicon substrate 11 is annealed to diffuse boron in the BSG film 12 into the p-type single crystal silicon substrate 11, and to receive the light receiving surface. A p + -type diffusion layer 14 is formed on the surface layer on the 11A side. In the second embodiment, as in the first embodiment, a small amount of POCl 3 and O 2 may be allowed to flow during annealing or cooling.
　次に、図１０のステージＳ４および、図１１のステップＳ１０４Ｓに示すように、受光面１１Ａ側のＢＳＧ膜１２およびＮＳＧ膜１３をエッチングマスクとして、ｐ型単結晶シリコン基板１１の片面つまり裏面１１Ｂ側にのみテクスチャー１１Ｔの形成を行う。 Next, as shown in the stage S4 in FIG. 10 and the step S104S in FIG. 11, using the BSG film 12 and the NSG film 13 on the light receiving surface 11A side as an etching mask, one side of the p-type single crystal silicon substrate 11, that is, the back surface 11B side Only texture 11T is formed.
　その後、図１０のステージＳ５、および図１１のステップＳ１０５Ｓに示すように、ｐｎ接合を形成するため、裏面１１Ｂ側のテクスチャー面に気相拡散によりＰ（リン）を拡散してｎ型拡散層１５を形成する。ここではＢＳＧ膜１２およびＮＳＧ膜１３は拡散マスクの機能を発揮する。拡散工程後、拡散工程で裏面１１Ｂ側に形成されたＰＳＧ膜を除去するが、このときもＢＳＧ膜１２およびＮＳＧ膜１３は拡散後のＰＳＧ膜除去にも耐え得る。 Thereafter, as shown in stage S5 in FIG. 10 and step S105S in FIG. 11, in order to form a pn junction, P (phosphorus) is diffused by vapor phase diffusion into the textured surface on the back surface 11B side to form the n-type diffusion layer 15 Form. Here, the BSG film 12 and the NSG film 13 exhibit the function of a diffusion mask. After the diffusion step, the PSG film formed on the back surface 11B side in the diffusion step is removed. At this time, the BSG film 12 and the NSG film 13 can withstand the PSG film removal after the diffusion.
　ＰＳＧ膜を除去した後、図１０のステージＳ６および図１１のステップＳ１０６Ｓに示すように、ＣＶＤ法により窒化シリコン膜からなるパッシベーション膜１６Ｐを形成する。 After removing the PSG film, as shown in stage S6 in FIG. 10 and step S106S in FIG. 11, a passivation film 16P made of a silicon nitride film is formed by CVD.
　パッシベーション膜１６Ｐを形成した後、図１０のステージＳ７および図１１のステップＳ１０７に示すように、受光面電極１７および裏面電極１８を印刷により形成する。 After forming the passivation film 16P, as shown in the stage S7 in FIG. 10 and the step S107 in FIG. 11, the light receiving surface electrode 17 and the back surface electrode 18 are formed by printing.
　図１１のステップＳ１０８に示すように、受光面電極１７および裏面電極１８を印刷後、熱処理を行い、ファイヤスルーにより、コンタクトを形成し、図９に示した実施の形態２の太陽電池３０が完成する。 As shown in step S108 of FIG. 11, after the light-receiving surface electrode 17 and the back surface electrode 18 are printed, heat treatment is performed, and contacts are formed by fire-through to complete the solar cell 30 of the second embodiment shown in FIG. To do.
　図１０に示した製造工程では、図３と同様、ダメージ層の除去からプロセスを始めているが、テクスチャーエッチングでダメージ層を除去しても良い。この場合、受光面１１Ａにもテクスチャー１１Ｔが形成されている点が異なるだけで、他のプロセスについては、何ら変わりは無い。図１０のように、単にダメージ層を除去する場合には、受光面１１Ａ側にテクスチャー１１Ｔが形成されないことになる。その場合は、反射防止フィルムを用いるなど、反射防止のための代替技術を用いることになる。 In the manufacturing process shown in FIG. 10, the process is started from the removal of the damaged layer as in FIG. 3, but the damaged layer may be removed by texture etching. In this case, there is no change in the other processes except that the texture 11T is formed on the light receiving surface 11A. As shown in FIG. 10, when the damaged layer is simply removed, the texture 11T is not formed on the light receiving surface 11A side. In that case, an alternative technique for preventing reflection, such as using an antireflection film, is used.
　実施の形態２の太陽電池３０によれば、製造作業性が良好であることはいうまでもなく、パッシベーション性が高い積層膜を受光面側の反射防止膜およびパッシベーション膜として用いており、かつＮＳＧ膜１３とＢＳＧ膜１２との界面も反射性および散乱性を有している。従って、実施の形態２の太陽電池３０によれば、集光率および内部量子効率が向上し、変換効率の高い太陽電池を得ることができる。また、実施の形態２の太陽電池３０によれば、薄型でかつ反りのない太陽電池を得ることができる。薄型の太陽電池の場合、パッシベーション膜と、半導体基板あるいは半導体層との界面が清浄か否かが特性に影響を与えることが多いが、ダメージ層の除去工程後、一貫して積層膜でｐ型単結晶シリコン基板１１の片面を被覆しているため、清浄な界面を維持することが可能となっている。 According to solar cell 30 of Embodiment 2, it goes without saying that manufacturing workability is good, and a laminated film having high passivation properties is used as an antireflection film and a passivation film on the light receiving surface side, and NSG. The interface between the film 13 and the BSG film 12 is also reflective and scattering. Therefore, according to the solar cell 30 of Embodiment 2, the light collection rate and the internal quantum efficiency are improved, and a solar cell with high conversion efficiency can be obtained. Moreover, according to the solar cell 30 of Embodiment 2, a thin solar cell without warping can be obtained. In the case of a thin solar cell, whether or not the interface between the passivation film and the semiconductor substrate or the semiconductor layer is clean often affects the characteristics. Since one surface of the single crystal silicon substrate 11 is covered, a clean interface can be maintained.
実施の形態３．
　実施の形態１および２では、ｐ型単結晶シリコン基板１１を用いたセルについて説明したが、これらのセルは当然のことながら、ｎ型のシリコン基板を用いたセルでも適用可能である。 Embodiment 3 FIG.
In the first and second embodiments, the cells using the p-type single crystal silicon substrate 11 have been described. However, these cells are naturally applicable to cells using an n-type silicon substrate.
　この場合も、ＢＳＧ膜およびＮＳＧ膜の積層膜を用いてボロン拡散を行い、拡散源に用いたＢＳＧ膜をボロン拡散層のパッシベーション膜に用いる。 Also in this case, boron diffusion is performed using a laminated film of a BSG film and an NSG film, and the BSG film used as the diffusion source is used as a passivation film for the boron diffusion layer.
　但し、受光面側にボロン拡散層を配した太陽電池では、ＢＳＧ膜およびＮＳＧ膜が受光面側になるため、ＢＳＧ膜およびＮＳＧ膜は反射防止膜の役割を持たせる必要があり、ＢＳＧ膜およびＮＳＧ膜の膜厚、表面状態および膜質の調整が必要となる。 However, in the solar cell in which the boron diffusion layer is arranged on the light receiving surface side, since the BSG film and the NSG film are on the light receiving surface side, it is necessary that the BSG film and the NSG film have a role of an antireflection film. It is necessary to adjust the film thickness, surface state, and film quality of the NSG film.
実施の形態４．
　次に実施の形態４の太陽電池について説明する。実施の形態１から３では、太陽電池セルを構成する基板の第１の主面である受光面、および第２の主面である裏面に、それぞれ受光面側電極および裏面電極を配置した構造であったが、太陽電池の裏面である第２の面１１ｂに双方の極の電極を配置した、所謂、ＩＢＣ（Ｉｎｔｅｒｄｉｇｉｔａｔｅｄ　Ｂａｃｋ　Ｃｏｎｔａｃｔ）セルのボロン拡散に対しても、ＢＳＧ膜とＮＳＧ膜との積層膜を適用可能である。図１２は、ＩＢＣセル構造を用いた実施の形態４の太陽電池を示す断面図、図１３は、実施の形態４の太陽電池の製造工程を示す工程断面図、図１４は、実施の形態４の太陽電池の製造工程を示すフローチャートである。実施の形態４では、図１２に示すように、ｎ型単結晶シリコン基板１１ｎを用い、第１の面１１ａ側および第２の面１１ｂ側の一部にｎ型拡散層１５を形成すると共に第２の面１１ｂの一部にｐ+型拡散層１４を形成している。太陽電池の裏面１１Ｂに第１の電極１７Ｒおよび第２の電極１８Ｓを形成している。ＢＳＧ膜１２とＮＳＧ膜１３との積層膜は受光部を除く表面に形成されている。つまり裏面１１Ｂの一部もｎ型拡散層１５との間にｐｎ接合を形成し受光部を構成している。 Embodiment 4 FIG.
Next, the solar cell of Embodiment 4 is demonstrated. In Embodiments 1 to 3, the light receiving surface side electrode and the back surface electrode are respectively disposed on the light receiving surface that is the first main surface and the back surface that is the second main surface of the substrate constituting the solar battery cell. However, the lamination of the BSG film and the NSG film is also applied to boron diffusion in a so-called IBC (Interdigitated Back Contact) cell in which electrodes of both electrodes are arranged on the second surface 11b which is the back surface of the solar cell. A membrane can be applied. 12 is a cross-sectional view showing the solar cell of the fourth embodiment using the IBC cell structure, FIG. 13 is a process cross-sectional view showing the manufacturing process of the solar cell of the fourth embodiment, and FIG. 14 is the fourth embodiment. It is a flowchart which shows the manufacturing process of this solar cell. In the fourth embodiment, as shown in FIG. 12, an n-type single crystal silicon substrate 11n is used, an n-type diffusion layer 15 is formed on part of the first surface 11a side and the second surface 11b side, and the first A p + -type diffusion layer 14 is formed on a part of the second surface 11b. A first electrode 17R and a second electrode 18S are formed on the back surface 11B of the solar cell. The laminated film of the BSG film 12 and the NSG film 13 is formed on the surface excluding the light receiving portion. That is, a part of the back surface 11 </ b> B also forms a pn junction with the n-type diffusion layer 15 to form a light receiving portion.
　実施の形態４の太陽電池４０の特徴も、ｐ+型拡散層１４つまりボロン拡散層形成に用いたＢＳＧ膜１２とＮＳＧ膜１３との積層膜をボロン拡散層のパッシベーション膜として用いることにある。 A feature of solar cell 40 of the fourth embodiment is that p + -type diffusion layer 14, that is, a laminated film of BSG film 12 and NSG film 13 used for forming the boron diffusion layer is used as a passivation film for the boron diffusion layer.
　まず、実施の形態１と同様、図１３のステージＳ１に示すように、ｎ型単結晶シリコン基板１１ｎを用意し、図１４に示すダメージ層の除去ステップＳ１０１で、エッチングによりｎ型単結晶シリコン基板１１ｎ表面のダメージ層を除去する。 First, as in the first embodiment, an n-type single crystal silicon substrate 11n is prepared as shown in the stage S1 of FIG. 13, and the n-type single crystal silicon substrate is etched by etching in the damage layer removing step S101 shown in FIG. The damage layer on the 11n surface is removed.
　次に、ＣＶＤ装置によって、図１３のステージＳ２および、図１４のステップＳ１０２ＳＳに示すように、ｎ型単結晶シリコン基板１１ｎの第２の面１１ｂ側の一部に拡散源となるＢＳＧ膜１２とキャップ層としてのＮＳＧ膜１３を積層して形成する。この時、第２の面１１ｂ側の一部にはマスクを形成し、ＢＳＧ膜１２とＮＳＧ膜１３とが形成されないようにする。 Next, as shown in the stage S2 in FIG. 13 and the step S102SS in FIG. 14, a BSG film 12 serving as a diffusion source is formed on a part on the second surface 11b side of the n-type single crystal silicon substrate 11n by the CVD apparatus. The NSG film 13 as a cap layer is formed by being laminated. At this time, a mask is formed on a part of the second surface 11b side so that the BSG film 12 and the NSG film 13 are not formed.
　その後、マスクを除去し、図１３のステージＳ３および、図１４のステップＳ１０３Ｓに示すように、ｎ型単結晶シリコン基板１１ｎをアニールしてＢＳＧ膜１２中のボロンをｎ型単結晶シリコン基板１１ｎに拡散させ、第２の面１１ｂ側の一部に選択的にｐ+型拡散層１４を形成する。 Thereafter, the mask is removed, and as shown in stage S3 in FIG. 13 and step S103S in FIG. 14, n-type single crystal silicon substrate 11n is annealed, and boron in BSG film 12 is changed to n-type single crystal silicon substrate 11n. A p + -type diffusion layer 14 is selectively formed on a part of the second surface 11b side by diffusion.
　次に、図１３のステージＳ４および図１４のステップＳ１０４Ｓに示すように、第１の面１１ａ側のＢＳＧ膜１２およびＮＳＧ膜１３をエッチングマスクとして、第１の面１１ａ側の全面および第２の面１１ｂ側の一部にテクスチャー１１Ｔの形成を行う。 Next, as shown in stage S4 in FIG. 13 and step S104S in FIG. 14, the entire surface on the first surface 11a side and the second surface are formed using the BSG film 12 and NSG film 13 on the first surface 11a side as an etching mask. The texture 11T is formed on a part of the surface 11b side.
　その後、図１３のステージＳ５および図１４のステップＳ１０５ＳＳに示すように、ｐｎ接合を形成するため、両面のテクスチャー面にリンを拡散してｎ型拡散層１５を形成する。ここでもＢＳＧ膜１２およびＮＳＧ膜１３は拡散マスクとして機能する。拡散工程後、拡散工程で第２の面１１ｂ側に形成されたＰＳＧ膜を除去するが、このときもＢＳＧ膜１２およびＮＳＧ膜１３は拡散後のＰＳＧ膜除去にも耐え得る。 Then, as shown in stage S5 in FIG. 13 and step S105SS in FIG. 14, in order to form a pn junction, phosphorus is diffused in the texture surfaces on both sides to form the n-type diffusion layer 15. Again, the BSG film 12 and the NSG film 13 function as a diffusion mask. After the diffusion step, the PSG film formed on the second surface 11b side in the diffusion step is removed. At this time, the BSG film 12 and the NSG film 13 can withstand the PSG film removal after the diffusion.
　ＰＳＧ膜を除去した後、図１３のステージＳ６および図１４のステップＳ１０６ＳＳに示すように、ＣＶＤ法により窒化シリコン膜からなる反射防止膜１６を形成する。 After removing the PSG film, as shown in stage S6 in FIG. 13 and step S106SS in FIG. 14, an antireflection film 16 made of a silicon nitride film is formed by CVD.
　反射防止膜１６を形成した後、図１３のステージＳ７および、図１４のステップＳ１０７Ｓに示すように、第１の電極１７Ｒおよび第２の電極１８Ｓを印刷により形成する。 After forming the antireflection film 16, the first electrode 17R and the second electrode 18S are formed by printing as shown in the stage S7 in FIG. 13 and the step S107S in FIG.
　第１の電極１７Ｒおよび第２の電極１８Ｓを印刷後、熱処理を行い、図１４のステップＳ１０８に示すようにファイヤスルーにより、コンタクトを形成し、図１２に示した実施の形態４の太陽電池４０が完成する。 After printing the first electrode 17R and the second electrode 18S, heat treatment is performed to form a contact by fire-through as shown in step S108 of FIG. 14, and the solar cell 40 of the fourth embodiment shown in FIG. Is completed.
　また、第１の面１１ａ側、第２の面１１ｂ側共に、ＮＳＧ膜１３あるいは反射防止膜１６を厚く積んだのであれば、電極形成時まで第２の面１１ｂに残っている膜は厚く、ファイヤスルーしにくい。この場合は図５に示した変形例と同様、レーザで、ＢＳＧ膜１２およびＮＳＧ膜１３を開口し、コンタクトホールｈを形成し、ポイントコンタクトを構成したのち、実施の形態１の太陽電池と同様に印刷により第１の電極１７Ｒを形成する。 Also, if the NSG film 13 or the antireflection film 16 is thickly stacked on both the first surface 11a side and the second surface 11b side, the film remaining on the second surface 11b until the time of electrode formation is thick. Difficult to fire through. In this case, similarly to the modification shown in FIG. 5, the BSG film 12 and the NSG film 13 are opened with a laser, the contact hole h is formed, the point contact is formed, and then the same as in the solar cell of the first embodiment. The first electrode 17R is formed by printing.
　図１２および図１３は、ｎ型単結晶シリコン基板１１ｎの使用を想定した模式図を示しているが、ｐ型単結晶シリコン基板をはじめとする基板を使用しても構わない。その場合は、実施の形態１から３に示したように、多少のプロセスの調整は必要となる。 12 and 13 are schematic views assuming the use of the n-type single crystal silicon substrate 11n, but a substrate such as a p-type single crystal silicon substrate may be used. In that case, as shown in the first to third embodiments, some process adjustment is required.
　なお、実施の形態１および２では、太陽電池を構成する基板としてｐ型単結晶シリコン基板が用いられている。ｎ型シリコンに比べ、ｐ型シリコンは、金属不純物に起因するライフタイムが低下し易いため、汚染には特に注意を払う必要がある。このため、拡散源として用いたＢＳＧ膜およびＮＳＧ膜の積層膜を除去して、再度、何等かのパッシベーション膜を成膜するというプロセスはプロセスが煩雑になるのに加えて、基板を汚染させる可能性が増えることにつながる。よって、拡散源として用いたＢＳＧ膜およびＮＳＧ膜の積層膜をパッシベーション膜として用いるということは、基板汚染の可能性を下げるという点でも有効である。 In the first and second embodiments, a p-type single crystal silicon substrate is used as the substrate constituting the solar cell. Compared to n-type silicon, p-type silicon tends to have a reduced lifetime due to metal impurities, and thus special attention must be paid to contamination. Therefore, the process of removing the laminated film of the BSG film and NSG film used as the diffusion source and forming another passivation film again makes the process complicated and may contaminate the substrate. It leads to increase in sex. Therefore, using the laminated film of the BSG film and the NSG film used as the diffusion source is also effective in reducing the possibility of substrate contamination.
　また、実施の形態１から４では、不純物として用いる第１導電型の元素としてボロンを用いたが、ボロンに限定されることなく、第１導電型の元素としてリンをはじめとするｎ型不純物を適用することも可能である。例えばリンを用いる場合はＣＶＤ法で形成したＰＳＧ膜をはじめとするリン含有膜が用いられるが、不純物濃度の制御が可能な場合は塗布膜を用いてもよい。 In the first to fourth embodiments, boron is used as the first conductivity type element used as the impurity. However, the present invention is not limited to boron, and n-type impurities such as phosphorus are used as the first conductivity type element. It is also possible to apply. For example, when phosphorus is used, a phosphorus-containing film such as a PSG film formed by a CVD method is used, but a coating film may be used when the impurity concentration can be controlled.
　以上の実施の形態に示した構成は、本発明の内容の一例を示すものであり、別の公知の技術と組み合わせることも可能であるし、本発明の要旨を逸脱しない範囲で、構成の一部を省略、変更することも可能である。 The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.
　１０，２０，３０，４０　太陽電池、１１　ｐ型単結晶シリコン基板、１１ｎ　ｎ型単結晶シリコン基板、１１Ａ　受光面、１１Ｂ　裏面、１１ａ　第１の面、１１ｂ　第２の面、１２　ＢＳＧ膜、１３　ＮＳＧ膜、１４　ｐ+型拡散層、１５　ｎ型拡散層、１６　反射防止膜、１６Ｐ　パッシベーション膜、１７　受光面電極、１７Ｇ　受光面グリッド電極、１７Ｂ　受光面バス電極、１７Ｒ　第１の電極、１８　裏面電極、１８Ｓ　第２の電極、Ｐａ　パッシベーション膜。 10, 20, 30, 40 Solar cell, 11 p-type single crystal silicon substrate, 11n n-type single crystal silicon substrate, 11A light-receiving surface, 11B back surface, 11a first surface, 11b second surface, 12 BSG film, 13 NSG film, 14 p + type diffusion layer, 15 n type diffusion layer, 16 antireflection film, 16P passivation film, 17 light receiving surface electrode, 17G light receiving surface grid electrode, 17B light receiving surface bus electrode, 17R first electrode, 18 back surface Electrode, 18S second electrode, Pa passivation film.

Claims (13)

  1. 　シリコン基板と、
    　前記シリコン基板の第１の主面に設けられ、第１の導電型の元素を含む拡散層と、
    　前記シリコン基板の前記第１の主面に、前記拡散層に当接して積層され、前記第１の導電型の元素とケイ素とを含む第１のガラス層と、前記第１のガラス層に積層され、前記第１の導電型の元素を含まずケイ素を含む第２のガラス層とを有するパッシベーション膜と、
    　を備えたことを特徴とする太陽電池。     A silicon substrate;
    A diffusion layer provided on the first main surface of the silicon substrate and containing an element of the first conductivity type;
    A first glass layer including the first conductivity type element and silicon laminated on the first main surface of the silicon substrate in contact with the diffusion layer, and laminated on the first glass layer. A passivation film having a second glass layer containing silicon and not containing the first conductivity type element;
    A solar cell comprising:
  2. 　前記第１の導電型の元素は、ボロンであり、前記第１のガラス層がＢＳＧ膜であることを特徴とする請求項１に記載の太陽電池。 The solar cell according to claim 1, wherein the first conductivity type element is boron, and the first glass layer is a BSG film.
  3. 　前記第１のガラス層は、第１の導電型の元素を０．５ｗｔ％から３ｗｔ％含むことを特徴とする請求項１または２に記載の太陽電池。 3. The solar cell according to claim 1, wherein the first glass layer contains 0.5 wt% to 3 wt% of an element of the first conductivity type.
  4. 　前記第２のガラス層は、ＮＳＧ膜であることを特徴とする請求項２または３に記載の太陽電池。 The solar cell according to claim 2 or 3, wherein the second glass layer is an NSG film.
  5. 　前記パッシベーション膜は、反射防止膜を構成することを特徴とする請求項１から４のいずれか１項に記載の太陽電池。 The solar cell according to any one of claims 1 to 4, wherein the passivation film constitutes an antireflection film.
  6. 　前記パッシベーション膜は、前記第１の主面および第２の主面のうち裏面側に位置する面に設けられたことを特徴とする請求項１から５のいずれか１項に記載の太陽電池。 The solar cell according to any one of claims 1 to 5, wherein the passivation film is provided on a surface located on a back surface side of the first main surface and the second main surface.
  7. 　前記パッシベーション膜は、前記第１の主面および第２の主面のうち受光面側に位置する面に設けられたことを特徴とする請求項１から５のいずれか１項に記載の太陽電池。 6. The solar cell according to claim 1, wherein the passivation film is provided on a surface located on a light receiving surface side of the first main surface and the second main surface. 7. .
  8. 　前記第１のガラス層と前記拡散層の界面で、前記第１の導電型の元素の濃度が連続的に変化していることを特徴とする請求項２から７のいずれか１項に記載の太陽電池。 The density | concentration of the said 1st conductivity type element is changing continuously in the interface of a said 1st glass layer and the said diffusion layer, The any one of Claim 2 to 7 characterized by the above-mentioned. Solar cell.
  9. 　シリコン基板の第１の主面に、第１の導電型の元素とケイ素とを含む第１のガラス層と、前記第１の導電型の元素を含まずケイ素を含む第２のガラス層との積層膜を形成する工程と、
    　前記シリコン基板を熱処理して、前記シリコン基板の前記第１の主面に拡散層を形成する工程と、
    　前記積層膜を貫通して、前記拡散層にコンタクトする集電電極を形成する工程とを含み、
    　前記積層膜からなるパッシベーション膜を備えたことを特徴とする太陽電池の製造方法。     A first glass layer containing a first conductivity type element and silicon on a first main surface of the silicon substrate, and a second glass layer containing silicon without containing the first conductivity type element. Forming a laminated film; and
    Heat-treating the silicon substrate to form a diffusion layer on the first main surface of the silicon substrate;
    Forming a collector electrode that penetrates the laminated film and contacts the diffusion layer,
    A method for producing a solar cell, comprising a passivation film comprising the laminated film.
  10. 　シリコン基板の第１の主面に、第１の導電型の元素とケイ素とを含む第１のガラス層と、前記第１の導電型の元素を含まずケイ素を含む第２のガラス層との積層膜を形成する工程と、
    　前記シリコン基板を熱処理して、前記シリコン基板の前記第１の主面に第１の拡散層を形成する工程と、
    　前記シリコン基板の第１の主面または第２の主面に、第２の導電型の元素を含む第２の拡散層を形成する工程と、
    　前記第１の拡散層および前記第２の拡散層に第１および第２の集電電極を形成する工程とを含み、
    　前記第１および第２の集電電極のうちの少なくとも一方は、前記積層膜を貫通して前記第１の拡散層または前記第２の拡散層に接続して形成されることを特徴とする太陽電池の製造方法。     A first glass layer containing a first conductivity type element and silicon on a first main surface of the silicon substrate, and a second glass layer containing silicon without containing the first conductivity type element. Forming a laminated film; and
    Heat-treating the silicon substrate to form a first diffusion layer on the first main surface of the silicon substrate;
    Forming a second diffusion layer containing an element of the second conductivity type on the first main surface or the second main surface of the silicon substrate;
    Forming first and second current collecting electrodes on the first diffusion layer and the second diffusion layer,
    At least one of the first and second current collecting electrodes is formed through the laminated film and connected to the first diffusion layer or the second diffusion layer. Battery manufacturing method.
  11. 　前記第１のガラス層を形成する工程は、ＣＶＤ法によって前記第１のガラス層を形成する工程であることを特徴とする請求項１０に記載の太陽電池の製造方法。 The method for manufacturing a solar cell according to claim 10, wherein the step of forming the first glass layer is a step of forming the first glass layer by a CVD method.
  12. 　前記第１の拡散層を形成する工程は、９００℃から１１００℃で加熱する熱処理工程であることを特徴とする請求項１０または１１に記載の太陽電池の製造方法。 The method for manufacturing a solar cell according to claim 10 or 11, wherein the step of forming the first diffusion layer is a heat treatment step of heating at 900 to 1100 ° C.
  13. 　前記第１の拡散層を形成する工程の後であって前記第２の拡散層を形成する工程の前に、
    　前記積層膜をマスクとして前記シリコン基板の第２の主面に凹凸構造を形成する工程を備えたことを特徴とする請求項１０から１２のいずれか１項に記載の太陽電池の製造方法。     After the step of forming the first diffusion layer and before the step of forming the second diffusion layer,
    13. The method of manufacturing a solar cell according to claim 10, further comprising a step of forming a concavo-convex structure on the second main surface of the silicon substrate using the laminated film as a mask.
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