JP5058184B2 - Method for manufacturing photovoltaic device - Google Patents

Description

  The present invention relates to a method for manufacturing a photovoltaic device such as a solar cell.

  Currently, silicon solar cells that are widely used generally have a surface texture, an N-type diffusion layer, an antireflection film, and a surface electrode (for example, comb-shaped) that increase the light absorption rate on the light-receiving surface side of a P-type silicon substrate. (Ag electrodes) are sequentially formed, and a back electrode (for example, an Al electrode) is formed on the back surface (non-light-receiving surface) side of a P-type silicon substrate by screen printing, and then these are fired. . In such firing, the solvent component of the front electrode and the back electrode volatilizes, and the comb Ag electrode breaks through the antireflection film on the surface side of the silicon substrate and is connected to the N-type diffusion layer. A part of the Al of the electrode diffuses into the silicon substrate to form a back surface field (BSF) layer. This BSF layer has the role of forming an internal electric field at the bonding surface with the silicon substrate to push back minority carriers generated in the vicinity of the BSF layer into the silicon substrate and suppressing carrier recombination in the vicinity of the Al electrode. The voltage can be increased.

  In addition, a solar cell having a passivation film (insulating film) capable of reducing the recombination rate as compared with a solar cell in which a BSF layer is formed on the majority of the back surface of the silicon substrate (for example, Patent Document 1). Non-Patent Document 1) and a solar cell having a structure in which an amorphous mixed microcrystalline silicon hydride film with a small number of defects is formed by a plasma CVD method as a BSF layer (for example, see Patent Document 2) has been proposed. Yes.

In the solar cell described in Patent Document 1, a passivation layer made of a silicon oxide (SiO ₂ ) film is formed by thermal oxidation on the back side of a silicon substrate, and point-like or stripe-like windows are formed on the passivation film at predetermined intervals. It is obtained by forming, forming a back electrode on the passivation film, and baking it. As a result, the BSF layer is formed at the portion where the back electrode embedded in the window is in contact with the silicon substrate, thereby reducing the area of the back electrode on the back surface of the silicon substrate, and carrier recombination as the entire back surface of the silicon substrate. Suppress. Non-Patent Document 1 shows a case where a silicon nitride film formed by plasma CVD (Chemical Vapor Deposition) is used as a passivation film. Since this passivation film can further suppress carrier recombination compared to the BSF layer, the open-circuit voltage of the solar cell can be increased and the photoelectric conversion efficiency can be increased.

JP-A-6-169096 Japanese Patent Laid-Open No. 10-190033 G. Agostinelli, et al., “Screen Printed Large Area Crystalline Silicon Solar Cells on Thin Substrates”, IMEC 20th European Photovoltaic Solar Energy Conference, 6-10 June 2005, p.647-650

  In the solar cell described in Patent Document 1, a high quality but high cost single crystal silicon substrate is used, and a window is formed at a predetermined interval in a passivation film formed by thermal oxidation. Complex and expensive processes are used. Therefore, the solar cell manufactured in this way is expensive and has been mainly used for special applications such as space solar cells. Actually, the passivation film in such a solar cell shows an effective recombination suppressing effect for a single crystal silicon substrate with few impurities and defects. Further, since the passivation film is formed by high-temperature heat treatment in an oxygen atmosphere, a high-temperature process such as an impurity diffusion process for forming a BSF layer or an electrode formation process by screen printing is applied after the formation of the passivation film. The passivation effect can be maintained.

  By the way, it is desirable that a solar cell on the premise of mass production is manufactured using a low-quality but low-cost polycrystalline substrate instead of using the high-cost single crystal substrate as described above. However, even if a polycrystalline silicon solar cell is manufactured by applying the method described in Patent Document 1 to such a polycrystalline silicon substrate, there is a problem that a good passivation effect cannot be obtained for the passivation film. It was. The polycrystalline silicon substrate usually contains a large amount of impurities and has crystal defects and grain boundaries. Therefore, in a high temperature process of 800 to 900 ° C. or higher such as a thermal oxidation process at a high temperature or an electrode formation process after screen printing. This is because the impurities move to the grain boundaries and the interface with the passivation film, or the atmospheric gas such as oxygen forms crystal defects.

  Further, there is a problem that the thermal resistance of a passivation film such as a silicon nitride film formed by the plasma CVD method described in Non-Patent Document 1 is not sufficient. In particular, if a high temperature process such as an impurity diffusion process for forming a BSF layer or an electrode formation process by screen printing is applied after the formation of the passivation film, the passivation characteristics have been lowered. Furthermore, there is a similar problem with respect to the heat resistance of the BSF layer such as the amorphous mixed microcrystalline silicon hydride film formed by the plasma CVD method described in Patent Document 2.

  The present invention has been made in view of the above. Even in the case where a polycrystalline semiconductor substrate is used in a photovoltaic device, recombination of minority carriers in the vicinity of the back electrode is suppressed as compared with a conventional photovoltaic device. At the same time, it is an object of the present invention to obtain a method for manufacturing a photovoltaic device that can provide a back electrode structure with improved heat resistance.

  In order to achieve the above object, a method for manufacturing a photovoltaic device according to the present invention forms a second conductive type diffusion layer on the first main surface side of a polycrystalline first conductive type semiconductor substrate. A diffusion layer forming step, an antireflection film forming step of forming an antireflection film on the diffusion layer, and a conductive paste having a surface electrode shape formed on the antireflection film, and the conductive paste is formed at a temperature of 800 ° C. or more. In a method for manufacturing a photovoltaic device, comprising: a baking step of baking a conductive paste; and a back electrode structure forming step of forming a back electrode structure on the second main surface side of the semiconductor substrate, before the baking step A plasma CVD film forming step of forming a first hydrogen-containing plasma CVD film containing hydrogen on the second main surface of the semiconductor substrate by plasma CVD, and the back electrode structure forming step after the baking step Before the first water A plasma CVD film removing step for removing the contained plasma CVD film, wherein in the back electrode structure forming step, a second hydrogen-containing plasma CVD film containing hydrogen formed by plasma CVD is formed on the semiconductor substrate. It is formed on 2 main surfaces.

  According to this invention, after forming the first hydrogen-containing plasma CVD film on the back surface side of the semiconductor substrate by plasma CVD, the surface electrode is baked, and then the first hydrogen-containing plasma CVD film is removed. Since the back electrode structure including the second hydrogen-containing plasma CVD film formed again by the plasma CVD method is formed, the semiconductor substrate is subjected to bulk passivation by the first hydrogen-containing plasma CVD film at the time of firing the surface electrode, and then The second hydrogen-containing plasma CVD film provides the best interface passivation for the semiconductor substrate. As a result, recombination of minority carriers in the vicinity of the back electrode of the semiconductor substrate can be suppressed as compared with a conventional photovoltaic device using a polycrystalline semiconductor substrate, and the conventional polycrystalline silicon cell process by screen printing is followed. However, it has an effect that a photovoltaic device having good passivation characteristics can be obtained.

  Embodiments of a method for manufacturing a photovoltaic device according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments. Moreover, sectional views of the photovoltaic devices used in the following embodiments are schematic, and the relationship between the thickness and width of the layers, the ratio of the thicknesses of the layers, and the like are different from the actual ones.

Embodiment 1 FIG.
First, the configuration of the photovoltaic device used in the first embodiment will be described. FIGS. 1-1 to 1-3 are diagrams schematically showing an example of the overall configuration of the photovoltaic device according to Embodiment 1 of the present invention, and FIG. 1-1 is a top view of the photovoltaic device. FIG. 1-2 is a back view of the photovoltaic device, and FIG. 1-3 is a cross-sectional view taken along line AA of FIG. 1-2. FIG. 2 is an enlarged sectional view schematically showing a part of the configuration of the photovoltaic device, and is a sectional view taken along the line BB in FIG. 1-1. Although the opening of the through hole 130 in FIG. 2 is small, it is not shown in FIG. 1-3, but actually, as shown in FIG. 2, the passivation film 104 in FIG. 130 (opening) is formed.

  In this photovoltaic device 100, a texture structure having fine irregularities (not shown) is formed on the light receiving surface side (hereinafter also referred to as a surface side) of a P-type polycrystalline silicon substrate 101 as a semiconductor substrate. The structure has an N-type diffusion layer 102 in which an N-type impurity is diffused within a predetermined depth from the formed surface. As a result, a PN junction is formed on the surface of the silicon substrate 101. Further, an antireflection film 103 for preventing the reflection of incident light on the light receiving surface of the silicon substrate 101 is formed on the upper surface of the N-type diffusion layer 102. On this antireflection film 103, a grid electrode 111 made of Ag (silver) or the like provided in a comb-teeth shape for locally collecting current (electrons) generated in the PN junction, and the grid electrode 111 collects current. In order to take out the electric current, a bus electrode 112 made of Ag or the like provided so as to connect the grid electrodes 111 substantially orthogonal to the grid electrodes 111, and a surface electrode (light receiving surface side electrode) 110 made of Ag or the like is formed. Has been. Note that the lower portion of the surface electrode 110 is in a state of passing through the antireflection film 103 and connected to the upper surface of the N-type diffusion layer 102.

  On the other hand, on the surface opposite to the light receiving surface of the P-type silicon substrate 101 (hereinafter referred to as the back surface), a hydrogen-containing silicon oxide film 105 and a silicon carbonitride film (hereinafter referred to as SiCN) as a second hydrogen-containing plasma CVD film. A passivation film 104 having a plurality of through-holes 130 is formed. Further, on the passivation film 104, a back surface electric field layer 107 made of a microcrystalline silicon film containing a P-type impurity at a higher concentration than the silicon substrate 101 so as to fill the through hole 130 and a PN junction are generated. In addition, a back surface collecting electrode 121 made of Al (aluminum) or the like is formed in order for taking out the current (hole) and reflecting the incident light. Further, a back surface extraction electrode 122 made of Ag or the like for extracting current to the outside is provided at a predetermined position in the back surface current collection electrode 121.

  Here, the SiCN film 106 is made of a film having a higher density (dense) than the hydrogen-containing silicon oxide film 105 and having a higher chemical resistance to a chemical used for etching the silicon substrate 101 than the hydrogen-containing silicon oxide film 105. Become. The through holes 130 have a point shape or a stripe shape, and are formed in the passivation film 104 at a predetermined interval. Further, hereinafter, the back surface collecting electrode 121 and the back surface extraction electrode 122 are collectively referred to as a back surface electrode 120. Further, the passivation film 104, the back surface electric field layer 107, and the back surface collecting electrode 121 (back surface electrode 120) form a back surface electrode structure.

  In the photovoltaic device 100 configured in this way, sunlight is applied to the PN junction surface (the junction surface between the P-type silicon substrate 101 and the N-type diffusion layer 102) from the light-receiving surface side of the photovoltaic device 100. And holes and electrons are generated. Due to the electric field near the PN junction surface, the generated electrons move toward the N-type diffusion layer 102, and the holes move toward the back surface field layer 107. As a result, an excess of electrons in the N-type diffusion layer 102 and an excess of holes in the back surface field layer 107 result in generation of photovoltaic power. This photovoltaic power is generated in a direction in which the PN junction is biased in the forward direction, the front electrode 110 connected to the N-type diffusion layer 102 becomes a negative pole, and the rear electrode 120 connected to the back surface electric field layer 107 becomes a positive pole. Current flows in the external circuit.

  Further, on the back side of the silicon substrate 101, the hydrogen-containing silicon oxide film 105 inactivates dangling bonds (recombination centers) of silicon atoms and forms a potential barrier having a wider forbidden band than the silicon substrate 101. Is done. As a result, electrons which are minority carriers generated in the vicinity of the back surface side of the silicon substrate 101 are not captured by the dangling bonds of silicon atoms on the surface layer portion on the back surface side of the silicon substrate 101, and the hydrogen-containing silicon oxide is oxidized by the potential barrier. Further, it does not flow into the film 105 but is pushed back into the silicon substrate 101 by an internal electric field formed at the bonding surface between the silicon substrate 101 and the back surface electric field layer 107. This suppresses recombination of electrons, which are minority carriers generated on the back surface side of the silicon substrate 101, on the back surface side of the silicon substrate 101, thereby contributing to the generation of the above-described photovoltaic power.

  Next, a method for manufacturing the photovoltaic device 100 having such a structure will be described. FIG. 3 is a flowchart showing an example of a processing procedure of the method for manufacturing the photovoltaic device according to the first embodiment. FIGS. 4-1 to 4-10 are diagrams of the photovoltaic device according to the first embodiment. It is sectional drawing which shows an example of the process sequence of a manufacturing method typically. Note that the sizes and film forming conditions shown below are examples.

  First, a polycrystalline silicon substrate (hereinafter sometimes simply referred to as a silicon substrate) 101 is prepared (FIG. 4A). Here, a P-type polycrystalline silicon substrate having a resistivity of 1 Ωcm is used. The silicon substrate 101 is manufactured by slicing a polycrystalline silicon ingot with a multi-wire saw and removing damage during slicing by wet etching using an alkaline solution. The thickness of the silicon substrate 101 after removing the damage is 200 μm, and the dimensions are 3 cm × 3 cm. Next, the texture structure as an antireflection structure is formed on one main surface of the silicon substrate 101 by anisotropic etching using a solution obtained by adding IPA (isopropyl alcohol) to an alkaline solution such as an aqueous potassium hydroxide solution or an aqueous sodium hydroxide solution. (Step S11). Here, the texture structure is not shown.

Next, the silicon substrate 101 after the formation of the texture structure is put into a thermal diffusion furnace and heated in an atmosphere of P (phosphorus) as an N-type impurity to diffuse P on the surface of the silicon substrate 101 to a predetermined concentration. Thus, the N-type diffusion layer 102 is formed (step S12, FIG. 4-2). Here, phosphorus oxychloride (POCl ₃ ) is used as a P diffusion source. Thereby, the N-type diffusion layer 102 is formed on the upper surface, the lower surface and the side surface of the silicon substrate 101. Subsequently, the phosphorus glass layer formed on the surface of the silicon substrate 101 is removed with hydrofluoric acid.

  Thereafter, an antireflection film 103 composed of a silicon nitride (SiN) film was formed on the light-receiving surface side, that is, the main surface on the texture structure forming side, using a plasma CVD method using silane gas and ammonia gas as source gases. It is formed on the N-type diffusion layer 102 (step S13, FIG. 4-3). The film thickness and refractive index of the antireflection film 103 are set to values that most suppress light reflection. Note that two or more layers having different refractive indexes may be stacked.

  Next, hydrogen is contained as a first hydrogen-containing plasma CVD film on the N-type diffusion layer 102 formed on the back surface of the silicon substrate 101 by a plasma CVD method using a source gas composed of silane gas, hydrogen gas, and ammonia gas. A silicon nitride film (hereinafter referred to as a hydrogen-containing SiN film) 131 is formed (step S14, FIG. 4-4). At this time, it is desirable to apply power having a frequency of 400 kHz or less for plasma generation. This is because when electric power having a frequency of 400 kHz or less is applied, hydrogen easily diffuses into the silicon substrate 101 during film formation and in the subsequent baking process of the surface electrode 110. Here, the hydrogen-containing SiN film 131 is produced using a 400 kHz plasma CVD method under conditions of a substrate temperature of 450 ° C. and a gas pressure of 0.5 Torr. The thickness is preferably about 100 nm.

  Next, Ag paste is printed in the shape of a comb-shaped grid electrode on the antireflection film 103 on the light receiving surface side. Although not shown, the Ag paste is formed in a bus electrode shape so as to connect a plurality of grid electrodes. After printing, the surface electrode 110 including the grid electrode 111 and the bus electrode is formed by baking at 850 ° C. (step S15, FIG. 4-5).

Thereafter, the hydrogen-containing SiN film 131 on the back surface side and the N-type diffusion layers 102 on the back surface side and side surfaces are removed by plasma etching using hydrogen gas (step S16, FIGS. 4-6). The removal process of the hydrogen-containing SiN film 131 using the hydrogen gas can remove the hydrogen-containing SiN film 131 and the N-type diffusion layer 102 without affecting the surface structure on which the surface electrode 110 is formed, and low-frequency plasma. The active hydrogen species generated therein has the effect of terminating and repairing defects in the silicon substrate 101 through the film. Note that the hydrogen-containing SiN film 131 may be removed by RIE (Reactive Ion Etching) using a fluorine-based gas such as SF ₆ instead of plasma etching using hydrogen gas. Alternatively, the hydrogen-containing SiN film 131 may be removed by a one-side wet etching process using concentrated hydrofluoric acid. However, in the case of one-side treatment with concentrated hydrofluoric acid, it is also necessary to remove the hydrogen-containing SiN film 131 and then remove the N-type diffusion layer 102 on the back and side surfaces with an alkali solution or a mixture of hydrofluoric acid and nitric acid. There is. The removal of the N-type diffusion layer 102 on the back surface and the side surface may be performed in advance by a similar method before forming the hydrogen-containing SiN film 131 in step S14.

  Next, a hydrogen-containing silicon oxide film 105 as a second hydrogen-containing plasma CVD film is formed on the entire back surface of the silicon substrate 101 by plasma CVD using a source gas consisting of silane gas and carbon dioxide gas (step S17). 4-7). This hydrogen-containing silicon oxide film 105 is produced using a 60 MHz VHF (Very High Frequency) plasma CVD method under conditions of a substrate temperature of 170 ° C. and a gas pressure of 0.5 Torr. The thickness is preferably about 60 nm.

  As a material constituting the second hydrogen-containing plasma CVD film, when the semiconductor substrate is P-type, in addition to silicon oxide having a small positive fixed charge, it has a negative fixed charge exhibiting an effective passivation effect. Aluminum oxide or the like can be used. These films have poor heat resistance, and if formed before firing electrodes that require high-temperature firing, they do not show good passivation properties due to firing, but they are formed after printing firing, and the subsequent processes can be performed only by low-temperature processes. By forming, good heat resistance can be given. As a result, by using the second hydrogen-containing plasma CVD film made of these materials, it becomes possible to form a back surface structure having good passivation characteristics combined with the hydrogen passivation effect of the first hydrogen-containing plasma CVD film. .

  Subsequently, a silicon-based film (SiCN film) 106 containing carbon and nitrogen is formed on the hydrogen-containing silicon oxide film 105 by using a hot wire CVD method (step S18, FIG. 4-8). Here, the hot wire CVD method refers to a film deposition method in which active species formed by bringing a source gas containing silicon into contact with a metal heated to a high temperature are deposited on a substrate to form a film. A film formed by this hot wire CVD method is generally a film having a higher density and a dense structure than a film formed by the plasma CVD method. Here, for example, rhenium wire is used as the hot wire filament, the temperature is set to 1400 ° C., the substrate temperature is set to 150 ° C., and the gas pressure is set to 0.75 Torr, and hexamethyldisilazane is supplied at a flow rate of 1.75 sccm. Then, a 60 nm SiCN film 106 is formed by flowing hydrogen at a flow rate of 100 sccm. As a result, a SiCN film 106 having a denser structure than the hydrogen-containing silicon oxide film 105 is formed on the hydrogen-containing silicon oxide film 105. Thus, the passivation film 104 made of a stacked body of the hydrogen-containing silicon oxide film 105 and the SiCN film 106 is formed.

  Note that the silicon compound formed by the hot wire CVD method can be formed by introducing a gas containing carbon or nitrogen and hydrogen into a silane-based material, but a disilazane having a Si—N or Si—C bond. By using a system material as a raw material, a dense film can be formed as compared with a case where a material using carbon or nitrogen as a material is separately introduced into a silane material.

  Next, a YAG (Yttrium Aluminum Garnet) laser beam having a wavelength of 355 nm with a beam diameter reduced to a size of 100 μm × 100 μm is irradiated on the passivation film 104 (SiCN film 106) at intervals of 500 μm, penetrating the passivation film 104, A through hole 130 is formed so as to expose the upper surface on the back surface side of the silicon substrate 101 (step S19, FIG. 4-9). The portion of the silicon substrate 101 exposed at the bottom of the through hole 130 becomes a contact portion with the back surface electric field layer 107 to be formed later. Here, the damage caused by the laser generated at the laser irradiation portion on the silicon substrate 101 and the surface contamination of the silicon substrate 101 at the removed portion are mixed using a hydrofluoric acid solution mixed with a ratio of hydrofluoric acid: nitric acid = 1: 10. Remove (step S20). As a result, the region exposed at the position where the through hole 130 is formed on the silicon substrate 101 has a good surface without damage. In addition, since the SiCN film 106 in the passivation film 104 has a dense structure, it is not removed during this cleaning.

  Next, a back surface electric field layer 107 made of a microcrystalline silicon film having a P-type impurity concentration higher than the P-type impurity concentration of the silicon substrate 101 is formed on the SiCN film 106 in which the through hole 130 is formed by using a plasma CVD method. (Step S21, FIG. 4-10). Here, using a 60 MHz VHF plasma CVD method, under conditions where the substrate temperature is 200 ° C. and the gas pressure is 0.3 Torr, silane gas is 1.0 sccm, hydrogen gas is 30 sccm, carbon dioxide gas is 0.5 sccm, Then, diborane gas diluted with hydrogen is supplied at a flow rate of 1.5 sccm to form a microcrystalline silicon oxide film having a B concentration higher than the P-type impurity concentration of the silicon substrate 101 on the SiCN film 106 on the back surface side of the silicon substrate 101. To do. At this time, a microcrystalline silicon oxide film is also formed in the through hole 130 formed in the previous step.

  Thereafter, a back surface collecting electrode 121 made of Al or the like is formed on the entire surface of the back surface field layer 107 by vacuum deposition or the like, and is formed at 275 ° C. for 30 minutes in a forming gas (for example, Ar gas containing 5% hydrogen) atmosphere. Annealing is performed to form the back electrode 120 (step S22). The annealing process performed at this time is performed at a temperature (a temperature lower than 800 ° C.) that does not deteriorate the passivation effect of the hydrogen-containing silicon oxide film 105, so that the hydrogen-containing silicon oxide film 105 is formed even after the back electrode 120 is formed. Has a passivation effect. As described above, the photovoltaic device as shown in FIGS.

  As described in the above manufacturing process procedure, the first hydrogen-containing plasma CVD film is formed on the back surface of the silicon substrate 101 by the plasma CVD method before the surface electrode 110 is fired. Deterioration of the substrate 101 is suppressed. Further, by optimizing the hydrogen content of the first hydrogen-containing plasma CVD film, the first hydrogen-containing plasma CVD film is formed during the process of forming the first hydrogen-containing plasma CVD film or during firing of the surface electrode after the formation. This diffuses hydrogen into the silicon substrate 101, repairs defects in the silicon substrate 101, and provides a bulk passivation effect in which deterioration of the silicon substrate 101 (decrease in crystal quality) is suppressed.

  In addition, after firing the front surface electrode 110, the first hydrogen-containing plasma CVD film on the back side is removed, and then the passivation film 104 including the second hydrogen-containing plasma CVD film is formed by the plasma CVD method. Defects in the vicinity of the surface layer of the back surface are terminated by hydrogen active species decomposed by plasma generated in the plasma CVD process. As a result, it is possible to suppress the formation of defects near the back surface layer of the silicon substrate 101 during the baking of the back electrode 120.

  Furthermore, since the second hydrogen-containing plasma CVD film has a wider forbidden band than the silicon substrate 101, a small number of occurrences occur in the vicinity of the back side of the silicon substrate 101 by forming a potential barrier with the silicon substrate 101. Electrons that are carriers do not flow into the second hydrogen-containing plasma CVD film. Thus, the second hydrogen-containing plasma CVD film exhibits an interfacial passivation effect.

  The back electrode 120 is annealed after the second hydrogen-containing plasma CVD film is formed. The annealing temperature at this time is a temperature at which the interface passivation effect of the second hydrogen-containing plasma CVD film is not lowered (800 ° C. Therefore, the second hydrogen-containing plasma CVD film has an interface passivation effect even after the annealing treatment of the back electrode 120.

The photovoltaic device 100 manufactured as described above was evaluated for current and voltage characteristics while irradiating pseudo solar light of AM (Air Mass) 1.5. The open circuit voltage is improved by 5 mV and the short-circuit current is improved by 1 mA / cm ² with respect to the conventional photovoltaic device using the entire back surface screen printing.

  Further, in the above description, the case where silicon oxide formed by the plasma CVD method is used as the second hydrogen-containing plasma CVD film is shown, but aluminum oxide formed by the plasma CVD method is used as the second hydrogen-containing plasma CVD film. Even when used, the same improvement in characteristics can be seen.

  According to the first embodiment, since the first hydrogen-containing plasma CVD film is formed on the back surface side of the silicon substrate 101 and the surface electrode 110 is baked, the first hydrogen is added during the baking process. Hydrogen in the contained plasma CVD film diffuses into the silicon substrate 101, repairs the defects, and obtains a bulk passivation effect that suppresses deterioration of the crystal quality on the back side (deterioration of the silicon substrate 101).

  Further, since the first hydrogen-containing plasma CVD film on the back surface side of the silicon substrate 101 is removed and the passivation film 104 including the second hydrogen-containing plasma CVD film is formed before the back electrode 120 is formed, the silicon substrate In addition to repairing defects on the surface layer on the back surface side of 101, electrons which are minority carriers do not flow into the second hydrogen-containing plasma CVD film due to a potential barrier formed between the silicon substrate 101 and recombination loss. The interface passivation effect to suppress can be acquired. Further, since the first hydrogen-containing plasma CVD film exposed to a high-temperature process and having a reduced passivation effect is removed without being used as a passivation film, a second hydrogen-containing plasma CVD film is newly used as the passivation film 104. Even after the surface electrode 110 is formed, an effective interface passivation effect can be obtained.

Embodiment 2. FIG.
FIG. 5 is an enlarged cross-sectional view schematically showing a part of the configuration of the photovoltaic device. FIG. 5 is a diagram corresponding to the BB cross-sectional view of FIG. 1-1 of the first embodiment. The structure on the surface side of the photovoltaic device 100A has the same structure as that described in the first embodiment. On the other hand, on the entire surface on the back surface of the P-type silicon substrate 101, a back surface field layer 107 as a second hydrogen-containing plasma CVD film made of a microcrystalline silicon film containing P-type impurities in a higher concentration than the silicon substrate 101 In addition to taking out the current (hole) generated in the PN junction, a back surface collecting electrode 121 made of Al or the like is sequentially laminated for the purpose of reflecting incident light. Here, the back surface electric field layer 107 made of a microcrystalline silicon film is a film formed by a plasma CVD method and having a function of suppressing recombination loss in the surface layer portion on the back surface side of the silicon substrate 101. In addition, the same code | symbol is attached | subjected to the component same as Embodiment 1, and the description is abbreviate | omitted. Moreover, the back surface electric field layer 107 and the back surface current collection electrode 121 (back surface electrode 120) form the back surface electrode structure.

  Next, a manufacturing method of the photovoltaic device 100A having such a structure will be described. FIG. 6 is a flowchart showing an example of the processing procedure of the manufacturing method of the photovoltaic device according to the second embodiment, and FIGS. 7-1 to 7-2 show the photovoltaic device according to the second embodiment. It is sectional drawing which shows an example of the process sequence of a manufacturing method typically. Note that the sizes and film forming conditions shown below are examples.

  First, processing similar to that shown in steps S11 to S16 of FIG. 3 and FIGS. 4-1 to 4-6 of the first embodiment is performed. That is, a texture structure is formed on the light-receiving surface side surface of the P-type polycrystalline silicon substrate 101 cut out to a predetermined size, and after forming the N-type diffusion layer 102 on the surface of the silicon substrate 101, plasma CVD is performed on the surface side. An antireflection film 103 made of a SiN film is formed by the method, and a hydrogen-containing SiN film 131 which is a first hydrogen-containing plasma CVD film is formed by a plasma CVD method on the back side. Next, Ag paste is printed on the shape of the grid electrode 111 and the bus electrode 112 (comb shape) on the antireflection film 103 on the front surface side, and the surface electrode 110 is formed by baking at 850 ° C. Then, the hydrogen content on the back surface The SiN film 131 and the N-type diffusion layer 102 are removed by plasma etching using, for example, hydrogen gas (Steps S31 to S36).

  Thereafter, the plasma CVD method using a source gas composed of silane gas, hydrogen gas, carbon dioxide gas and hydrogen-diluted diborane gas has a P-type impurity concentration higher than the P-type impurity concentration of the silicon substrate 101 and contains hydrogen. A back surface electric field layer 107 as a second hydrogen-containing plasma CVD film made of a microcrystalline silicon oxide film is formed on the entire back surface of the silicon substrate 101 (step S37, FIG. 7-1). Here, silane gas is 1.0 sccm, hydrogen gas is 30 sccm, carbon dioxide gas is 0.5 sccm, using a 60 MHz VHF plasma CVD method under conditions where the substrate temperature is 200 ° C. and the gas pressure is 0.3 Torr. Then, diborane gas diluted with hydrogen is supplied at a flow rate of 1.5 sccm to form the back surface electric field layer 107 on the entire back surface of the silicon substrate 101. Since the back surface electric field layer 107 made of this microcrystalline silicon oxide film is low in stress, the silicon substrate 101 is not warped and exhibits a good back surface BSF effect.

  Next, a back surface collecting electrode 121 made of Al or the like is formed on the entire surface of the back surface electric field layer 107 by vacuum deposition or the like, and is formed at 275 ° C. for 30 minutes in a forming gas (eg, Ar gas containing 5% hydrogen) atmosphere. Annealing is performed to form the back electrode 120 (step S38, FIG. 7-2). As described above, a photovoltaic device 100A as shown in FIG. 5 is obtained.

  As explained in the above manufacturing process procedure, after firing the front surface electrode 110, after removing the hydrogen-containing SiN film 131 which is the first hydrogen-containing plasma CVD film on the back surface side, the second hydrogen-containing film is formed by plasma CVD. Since the back surface field layer 107, which is a microcrystalline silicon oxide film, is formed as the plasma CVD film, defects near the back surface layer of the silicon substrate 101 are terminated by hydrogen active species decomposed by plasma generated in the plasma CVD process. Is done. As a result, it is possible to suppress the formation of defects near the back surface layer of the silicon substrate 101 during the baking of the back electrode 120. In addition, deterioration of the crystal quality of the silicon substrate 101 can be prevented.

  Further, the back surface electric field layer 107 which is the second hydrogen-containing plasma CVD film has a higher P-type impurity concentration than the silicon substrate 101 and a forbidden band width wider than that of the P-type silicon substrate 101. An internal electric field is formed between the two. Due to this internal electric field, electrons that are minority carriers that are generated near the back surface side of the silicon substrate 101 and are about to flow to the back electrode 120 side are pushed back into the P-type silicon substrate 101. This makes it possible to suppress recombination near the back electrode.

The photovoltaic device 100A thus manufactured was evaluated for current and voltage characteristics while irradiating AM1.5 pseudo-sunlight. Conventionally, the same substrate was used for the entire surface of the back surface of the back surface of Al. The open circuit voltage is improved by 3 mV and the short-circuit current is improved by 0.7 mA / cm ² with respect to the type photovoltaic device.

  According to the second embodiment, after the first hydrogen-containing plasma CVD film is formed on the back surface side of the silicon substrate 101, the surface electrode 110 is baked, so that the first hydrogen is baked during the baking process. Hydrogen in the contained plasma CVD film diffuses into the silicon substrate 101 to repair defects and obtain a bulk passivation effect that suppresses deterioration of crystal quality on the back surface side.

  Further, before the back electrode 120 is formed, the first hydrogen-containing plasma CVD film on the back surface side of the silicon substrate 101 is removed, and the back surface electric field layer 107 which is the second hydrogen-containing plasma CVD film is formed by plasma CVD. Since the silicon substrate 101 is formed, the defects on the surface layer on the back surface side of the silicon substrate 101 are repaired, and the electrons that are minority carriers are pushed back into the silicon substrate 101 by the internal electric field formed between the silicon substrate 101 and the back surface. Recombination loss at the side surface layer can be suppressed. Further, the second hydrogen-containing plasma newly formed after removing the first hydrogen-containing plasma CVD film without using the first hydrogen-containing plasma CVD film exposed to a high temperature process and having a reduced passivation effect as the passivation film. Since the microcrystalline silicon oxide film is used as the back surface electric field layer 107 as the CVD film, an effective recombination suppressing effect can be obtained even after the surface electrode 110 is formed.

  Furthermore, the annealing temperature of the back surface electrode 120 is lower than 800 ° C. (275 ° C.), which does not require an impurity diffusion process at a high temperature for forming the back surface electric field layer 107. Does not deteriorate, and as a result, the recombination suppressing effect does not decrease. As described above, a hydrogen passivation effect is obtained by the first hydrogen-containing plasma CVD film formed on the back surface side of the silicon substrate 101 before the printing and baking of the front electrode 110, and as a subsequent second hydrogen-containing plasma CVD film. By substituting with the back surface electric field layer 107, it becomes possible to form a back surface structure having a good BSF effect.

  In the above description, the case where the N-type diffusion layer is formed on the light-receiving surface side of the P-type polycrystalline silicon substrate has been described, but the case where the P-type diffusion layer is formed on the light-receiving surface side of the N-type polycrystalline silicon substrate. The same effect can be obtained. The same effect can be obtained for a polycrystalline silicon substrate using a semiconductor material other than the silicon substrate.

  As described above, the method for manufacturing a photovoltaic device according to the present invention is useful when manufacturing a photovoltaic device using a polycrystalline silicon substrate.

It is a top view which shows typically an example of the whole structure of the photovoltaic apparatus by Embodiment 1 of this invention. It is a reverse view of a photovoltaic apparatus. It is AA sectional drawing of FIGS. 1-2. It is an expanded sectional view showing a part of composition of a photovoltaic device typically, and is a BB sectional view of Drawing 1-1. It is a flowchart which shows an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1. It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 1). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 2). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 3). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 4). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 5). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 6). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 7). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 8). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 9). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 1 (the 10). It is an expanded sectional view showing typically a part of composition of a photovoltaic device. It is a flowchart which shows an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 2. It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 2 (the 1). It is sectional drawing which shows typically an example of the process sequence of the manufacturing method of the photovoltaic apparatus by this Embodiment 2 (the 2).

100, 100A Photovoltaic device 101 P-type polycrystalline silicon substrate 102 N-type diffusion layer 103 Antireflection film 104 Passivation film 105 Hydrogen-containing silicon oxide film 106 SiCN film 107 Back surface electric field layer 110 Surface electrode 111 Grid electrode 112 Bus electrode 120 Back surface Electrode 121 Back surface collecting electrode 122 Back surface extraction electrode 130 Through hole 131 Hydrogen-containing SiN film

Claims (6)

A diffusion layer forming step of forming a second conductivity type diffusion layer on the first main surface side of the polycrystalline first conductivity type semiconductor substrate;
An antireflection film forming step of forming an antireflection film on the diffusion layer;
A baking step of forming a conductive paste in the shape of a surface electrode on the antireflection film and baking the conductive paste at a temperature of 800 ° C. or higher;
A back electrode structure forming step of forming a back electrode structure on the second main surface side of the semiconductor substrate;
In a method of manufacturing a photovoltaic device including:
Before the firing step, a plasma CVD film forming step of forming a first hydrogen-containing plasma CVD film containing hydrogen on the second main surface of the semiconductor substrate by plasma CVD,
A plasma CVD film removing step for removing the first hydrogen-containing plasma CVD film after the baking step and before the back electrode structure forming step;
Including
In the back electrode structure forming step, a second hydrogen-containing plasma CVD film containing hydrogen formed by a plasma CVD method is formed on the second main surface of the semiconductor substrate. Device manufacturing method. The back electrode structure forming step includes
A passivation film forming step of forming a passivation film including the second hydrogen-containing plasma CVD film having a passivation effect, formed by a plasma CVD method, on the second main surface of the semiconductor substrate;
A through hole forming step of periodically forming a plurality of through holes in the passivation film;
A back surface field layer forming step of forming a back surface field layer made of a semiconductor film having a higher impurity concentration of the first conductivity type than the semiconductor substrate on the passivation film so as to fill the through hole;
A back electrode forming step of forming a conductive material film to be a back electrode on the back surface field layer;
The method for manufacturing a photovoltaic device according to claim 1, comprising: The back electrode structure forming step includes
A back surface electric field layer made of a semiconductor film having a higher impurity concentration of the first conductivity type than the semiconductor substrate is used as the second hydrogen-containing plasma CVD film, and plasma CVD is performed on the second main surface of the semiconductor substrate. A back surface field layer forming step formed by:
A back electrode forming step of forming a conductive material film to be a back electrode on the back surface field layer;
The method for manufacturing a photovoltaic device according to claim 1, comprising:   In the plasma CVD film forming step, the first hydrogen-containing plasma CVD film is a silicon nitride film formed by a plasma CVD method in which a frequency of power applied during film formation is 400 kHz or less. The manufacturing method of the photovoltaic apparatus as described in any one of Claims 1-3.   5. The method of manufacturing a photovoltaic device according to claim 1, wherein, in the plasma CVD film removing step, the first hydrogen-containing plasma CVD film is removed by plasma etching.   The method for manufacturing a photovoltaic device according to claim 5, wherein plasma etching using hydrogen gas is performed in the first hydrogen-containing plasma CVD film removal step.

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