WO2016111132A1

WO2016111132A1 - Method for manufacturing solar cell

Info

Publication number: WO2016111132A1
Application number: PCT/JP2015/085296
Authority: WO
Inventors: 邦彦西村
Original assignee: 三菱電機株式会社
Priority date: 2015-01-07
Filing date: 2015-12-16
Publication date: 2016-07-14
Also published as: TW201637232A; JPWO2016111132A1

Abstract

This method for manufacturing a solar cell comprises: a first step wherein a first oxide film having a film thickness of more than 50 nm but 200 nm or less is formed on a first surface of a semiconductor substrate of a first conductivity type; a second step wherein a first diffusion source that contains a first dopant is selectively formed on the first oxide film; a third step wherein the semiconductor substrate, on which the first diffusion source has been formed, is subjected to a heat treatment, thereby forming a first dopant diffused layer, in which the first dopant is diffused, in a region of the superficial layer of the first surface, said region being immediately below the first diffusion source; and a fourth step wherein an electrode is formed on the first dopant diffused layer.

Description

Manufacturing method of solar cell

The present invention relates to a method for manufacturing a solar cell using a semiconductor substrate.

In solar cells, a selective emitter structure in which a high-concentration doping layer is formed below the electrode and a low-concentration doping layer is formed in a region other than the high-concentration doping layer on the light-receiving surface side is used for high efficiency. ing. The low-concentration doping layer can suppress the absorption of incident light and obtain a good short-circuit current, and can further suppress the recombination loss of photogenerated carriers. Contribute to realization. On the other hand, the high-concentration doping layer can reduce the contact resistance between the electrode and the semiconductor substrate, and thus contributes to the realization of a good curve factor in the solar cell.

As a method for forming a selective emitter structure, Patent Document 1 discloses that a semiconductor substrate is heat-treated after a dopant paste is printed and formed in a comb shape on the light receiving surface side of the semiconductor substrate. By performing the heat treatment, the dopant in the dopant paste is thermally diffused into the semiconductor substrate to form a first diffusion region which is a high concentration dopant diffusion layer having a high dopant concentration. At the same time, after the dopant component volatilized from the dopant paste in the gas phase adheres to the surface of the semiconductor substrate, it is thermally diffused into the semiconductor substrate and is a low-concentration dopant diffusion layer having a dopant concentration lower than that of the first diffusion region. The diffusion region is formed. Thus, a first diffusion region having a high dopant concentration and a second diffusion region having a lower dopant concentration than the first diffusion region are formed by a single heat treatment.

JP 2007-235174 A

However, in the technique of Patent Document 1, since a low concentration dopant diffusion layer is formed by diffusing volatile components from the dopant paste into the semiconductor substrate, a low concentration dopant diffusion layer having a uniform dopant concentration cannot be formed. There is a problem. In this case, due to the non-uniformity of the dopant concentration in the low concentration dopant diffusion layer, the power generation characteristics vary in the plane of the solar cell.

The present invention has been made in view of the above, and an object of the present invention is to obtain a solar cell manufacturing method capable of forming a dopant diffusion layer by preventing diffusion of a volatile component from a dopant paste to a substrate.

In order to solve the above-described problems and achieve the object, the present invention provides a first oxide film having a thickness of greater than 50 nm and less than or equal to 200 nm on a first surface of a first conductivity type semiconductor substrate. A first step, a second step of selectively forming a first diffusion source containing a first dopant on the first oxide film, and a heat treatment of the semiconductor substrate on which the first diffusion source is formed, A third step of forming a first dopant diffusion layer in which the first dopant is diffused in a region immediately below the first diffusion source on the surface layer of the first surface; and a step of forming an electrode on the first dopant diffusion layer. And 4 steps.

According to the present invention, it is possible to prevent the diffusion of the volatile component from the dopant paste to the substrate and form the dopant diffusion layer.

Schematic top view showing the solar battery cell according to the first embodiment. FIG. 3 is a schematic cross-sectional view of a relevant part showing the solar battery cell according to the first embodiment. A flowchart which shows the manufacturing method of the photovoltaic cell concerning Embodiment 1. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the first embodiment. The characteristic view which shows the relationship between the film thickness of the protective oxide film in Embodiment 1, and the sheet resistance of a pad part and a blank part A flowchart which shows the manufacturing method of the photovoltaic cell concerning Embodiment 2. FIG. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the second embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the second embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the second embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the second embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the second embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the second embodiment. A flowchart which shows the manufacturing method of the photovoltaic cell concerning Embodiment 3. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the third embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the third embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the third embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the third embodiment. A flowchart which shows the manufacturing method of the photovoltaic cell concerning Embodiment 4. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fourth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fourth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fourth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fourth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fourth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fourth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fourth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fourth embodiment. Schematic top view showing the solar cell according to the fifth embodiment. Schematic diagram showing the bottom surface of the solar cell according to the fifth embodiment. Cross-sectional schematic diagram of relevant parts showing a solar cell according to a fifth embodiment. A flowchart which shows the manufacturing method of the photovoltaic cell concerning Embodiment 5. FIG. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the fifth embodiment. Cross-sectional schematic diagram of relevant parts showing a solar battery cell according to a sixth embodiment. A flowchart which shows the manufacturing method of the photovoltaic cell concerning Embodiment 6. FIG. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the sixth embodiment. A flowchart which shows the manufacturing method of the photovoltaic cell concerning Embodiment 7. FIG. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the seventh embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the seventh embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the seventh embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the seventh embodiment. Cross-sectional view of relevant parts for explaining the manufacturing process of the solar battery cell according to the seventh embodiment.

Hereinafter, a method for manufacturing a solar cell according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. 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.

Embodiment 1 FIG.
FIG. 1 is a schematic top view showing a solar battery cell 1 according to Embodiment 1 of the present invention. FIG. 2 is a schematic cross-sectional view of the relevant part showing the solar battery cell 1 according to the first embodiment of the present invention, and is a relevant part cross-sectional view taken along line AA in FIG.

In the solar cell 1 according to the first embodiment, the n-type light-receiving surface side dopant diffusion layer 3 in which phosphorus which is a p-type dopant is diffused as the first dopant is the light-receiving surface side of the p-type semiconductor substrate 2. A semiconductor substrate 11 having a pn junction is formed. An antireflection film 4 made of an insulating film is formed on the light receiving surface side dopant diffusion layer 3.

As the semiconductor substrate 2, a p-type single crystal silicon substrate is used. Hereinafter, the semiconductor substrate 2 made of a p-type single crystal silicon substrate may be referred to as a p-type silicon substrate 2. The semiconductor substrate 2 is not limited to a p-type single crystal silicon substrate, and a p-type polycrystalline silicon substrate may be used.

On the light receiving surface side of the semiconductor substrate 11, that is, the light receiving surface side of the n-type light receiving surface side dopant diffusion layer 3, a texture structure for confining light is formed. The texture structure is formed by minute irregularities called textures. The minute unevenness increases the area of the light receiving surface that absorbs light from the outside, suppresses the reflectance on the light receiving surface, and efficiently confines the light in the solar battery cell 1. For example, a pyramidal protrusion is formed. Is done. The dimension of the minute irregularities is very small with one side of one protrusion being about 0.1 μm to 10 μm, and is not shown as an irregular shape in FIG. 2 and the following drawings.

The antireflection film 4 is composed of a silicon nitride film (SiN) that is an insulating film. The antireflection film 4 is not limited to a silicon nitride film, and may be formed of an insulating film such as a silicon oxide film (SiO ₂ ) or a titanium oxide film (TiO ₂ ).

In addition, a plurality of elongated light receiving surface side grid electrodes 5a are provided side by side on the light receiving surface side of the semiconductor substrate 11, and the light receiving surface side bus electrode 5b that is electrically connected to the light receiving surface side grid electrode 5a is provided on the light receiving surface side grid electrode. 5a, and is electrically connected to the light-receiving surface side high-concentration dopant diffusion layer 3a of the n-type light-receiving surface side dopant diffusion layer 3 at the bottom surface portion. The light receiving surface side grid electrode 5a and the light receiving surface side bus electrode 5b are made of a silver material.

The light-receiving surface side grid electrode 5a collects electricity generated inside the semiconductor substrate 11 in which linear patterns having a line width of about 50 μm are arranged in parallel at intervals of about 2 mm. The light-receiving surface side bus electrode 5b has a width of about 1 mm to 3 mm, and two to four are arranged in parallel per solar cell, and electricity collected by the light-receiving surface side grid electrode 5a is externally supplied. Take out. The light-receiving surface side grid electrode 5a and the light-receiving surface-side bus electrode 5b constitute the light-receiving surface-side electrode 5, which is a first electrode having a comb shape.

As the electrode material of the light-receiving surface side electrode of the silicon solar cell, a silver paste is usually used and a frit-shaped lead boron glass is added. Lead boron glass has a property of being melted by heating at, for example, about 750 ° C. to 850 ° C. and corroding silicon nitride. In general, in a method for manufacturing a crystalline silicon solar cell, a method of obtaining electrical contact between a silicon substrate and a silver paste using the characteristics of glass frit is used.

On the other hand, the back surface side electrode 6 containing an aluminum material is provided on the entire back surface of the semiconductor substrate 11 which is the surface facing the light receiving surface. Further, a back side BSF (Back Surface Field) layer 7, which is a p + layer containing a p-type dopant in a higher concentration than the p-type silicon substrate 2, is formed on the surface layer portion of the back surface of the semiconductor substrate 11. The back side BSF layer 7 is provided in order to obtain the BSF effect, and the electron concentration of the semiconductor substrate 2 is increased by an electric field having a band structure so that the electrons in the semiconductor substrate 2 do not disappear.

In the solar cell 1, two types of layers are formed as the n-type light-receiving surface side dopant diffusion layer 3 to form a selective emitter structure. In the surface layer portion of the p-type silicon substrate 2 on the light-receiving surface side, light-receiving surface-side high-concentration dopant diffusion in which the n-type dopant is diffused at a relatively high concentration in the lower region of the light-receiving surface-side electrode 5 and its peripheral region Layer 3a is formed. Further, in the surface layer portion of the p-type silicon substrate 2 on the light-receiving surface side, the light-receiving surface in which the n-type dopant is diffused at a relatively low concentration in the region where the light-receiving surface-side high-concentration dopant diffusion layer 3a is not formed. A side low-concentration dopant diffusion layer 3b is formed. That is, the solar cell 1 has a selective emitter structure including the light receiving surface side high concentration dopant diffusion layer 3a and the light receiving surface side low concentration dopant diffusion layer 3b. The light receiving surface side high concentration dopant diffusion layer 3a is a low resistance diffusion layer having a lower electrical resistance than the light receiving surface side low concentration dopant diffusion layer 3b. The light receiving surface side low concentration dopant diffusion layer 3b is a high resistance diffusion layer having a higher electric resistance than the light receiving surface side high concentration dopant diffusion layer 3a.

Therefore, if the dopant diffusion concentration of the light receiving surface side high concentration dopant diffusion layer 3a is the first diffusion concentration and the dopant diffusion concentration of the light receiving surface side low concentration dopant diffusion layer 3b is the second diffusion concentration, the second diffusion concentration is It becomes lower than 1 diffusion concentration. Further, when the electric resistance value of the light receiving surface side high concentration dopant diffusion layer 3a is the first electric resistance value and the electric resistance value of the light receiving surface side low concentration dopant diffusion layer 3b is the second electric resistance value, the second electric resistance value is obtained. Becomes larger than the first electric resistance value.

The light receiving surface side electrode 5 described above is formed on the light receiving surface side high concentration dopant diffusion layer 3a. In the light receiving surface side high-concentration dopant diffusion layer 3a, light is incident on the solar cell 1 in the region where the light receiving surface side electrode 5 is not formed and the region where the light receiving surface side low concentration dopant diffusion layer 3b is formed. It becomes the light receiving surface. In the solar battery cell 1, a light receiving surface side high-concentration dopant diffusion layer 3 a having a low electric resistance is formed below the light receiving surface side electrode 5, and the contact resistance between the semiconductor substrate 11 and the light receiving surface side electrode 5. Is made smaller. Further, in the region other than the light receiving surface side high concentration dopant diffusion layer 3a on the light receiving surface side of the semiconductor substrate 11, a light receiving surface side low concentration dopant diffusion layer 3b having a low dopant concentration is formed to reduce the carrier recombination rate. .

Next, a method for manufacturing the solar cell 1 according to the first embodiment will be described with reference to FIGS. FIG. 3 is a flowchart showing a process flow of the method for manufacturing the solar battery cell 1 according to the first embodiment of the present invention. 4 to 13 are cross-sectional views of relevant parts for explaining the manufacturing steps of the solar battery cell 1 according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of steps S101 and S102 of FIG. In step S 101, a p-type silicon substrate 2 is prepared as the semiconductor substrate 2. The p-type silicon substrate 2 is manufactured by cutting and slicing a single crystal silicon ingot obtained by pulling a single crystal into a desired size and thickness using a cutting machine such as a band saw or a multi-wire saw. The damage layer of time remains. Accordingly, the damage layer is also removed, and the surface of the p-type silicon substrate 2 is etched to remove the damage layer that occurs when the silicon substrate is cut out and exists near the surface of the p-type silicon substrate 2.

Step S102 forms a texture structure by forming minute irregularities on the surface of the p-type silicon substrate 2. Since the minute unevenness is very fine, it is not expressed as an uneven shape in FIGS. For the formation of the texture structure, a chemical solution obtained by mixing 10% isopropyl alcohol with 6% sodium hydroxide (NaOH) aqueous solution is used. The surface of the p-type silicon substrate 2 is etched by immersing the p-type silicon substrate 2 sliced into a plate shape in a chemical solution set at 80 ° C. for 10 minutes, and the entire surface of the p-type silicon substrate 2 is textured. A structure is obtained.

Since the surface of the p-type silicon substrate 2 is etched at a depth of about 10 μm under the above etching conditions, the damage layer formed on the surface of the p-type silicon substrate 2 at the time of slicing can be removed at the same time. Therefore, the removal of the damaged layer in step S101 may be performed in step S102. Here, the case where a chemical solution in which isopropyl alcohol is mixed in an NaOH aqueous solution is used, but a chemical solution obtained by adding a commercially available texture etching additive to an alkaline aqueous solution such as an NaOH aqueous solution or a potassium hydroxide (KOH) aqueous solution may be used. It doesn't matter. In addition, when the p-type silicon substrate 2 is a polycrystalline silicon substrate, a mixed solution of hydrofluoric acid and nitric acid can be used.

FIG. 5 is an explanatory diagram of step S105 in FIG. In step S105, the protective oxide film 13 is formed as a first oxide film on both the first surface serving as the light receiving surface of the solar cell 1 and the second surface serving as the back surface of the solar cell 1 in the p-type silicon substrate 2. Is a step of forming. The formation of the protective oxide film 13 is realized by performing dry oxidation or wet oxidation. Specifically, for example, a quartz glass boat on which 300 p-type silicon substrates 2 are placed at intervals of 3.5 mm is inserted into a quartz tube of a horizontal furnace heated to about 700 ° C. to 800 ° C. Is done. While introducing 10 SLM nitrogen, the temperature in the quartz tube is raised to 1100 ° C., and when the temperature in the quartz tube reaches 1100 ° C., oxygen is allowed to flow into the quartz tube for 30 minutes. After 30 minutes, the introduction of oxygen is stopped and the gas introduced into the quartz tube is switched to nitrogen. Then, after the temperature in the quartz tube is lowered again to about 700 ° C. to 800 ° C., the boat is taken out from the quartz tube. At this time, an oxide film is formed with a film thickness of about 60 nm on the front and back surfaces of the p-type silicon substrate 2. Here, dry oxidation in which oxygen is introduced into the quartz tube at a high temperature is used for forming the protective oxide film 13, but wet oxidation in which water vapor is introduced into the quartz tube may be used. Wet oxidation is a method in which pure water is bubbled with oxygen and oxygen containing water vapor is introduced into the furnace. When wet oxidation is used, for example, by introducing oxygen containing water vapor into the quartz tube for 15 minutes in a state where the temperature in the quartz tube is 930 ° C., an oxide film of about 60 nm can be obtained. .

FIG. 6 is an explanatory diagram of step S106 in FIG. Step S 106 is a step of printing a dopant paste as a first diffusion source on the protective oxide film 13. Here, as the dopant paste, a phosphorus-containing dopant paste 14 which is a resin paste containing a phosphorus oxide is selectively printed on the protective oxide film 13 using a screen printing method. The printing pattern of the phosphorus-containing dopant paste 14 is a comb shape composed of a pattern in which linear patterns having a line width of 150 μm are arranged in parallel at intervals of 2 mm and a pattern in which four linear patterns having a line width of 1.2 mm are arranged in parallel. The pattern is After printing, the phosphorus-containing dopant paste 14 is dried at 250 ° C. for 5 minutes. In addition, the printing method of the phosphorus containing dopant paste 14 is not restricted to the screen printing method, The inkjet method or the method of discharging directly from a nozzle can be used.

FIG. 7 is an explanatory diagram of step S107 in FIG. Step S107 is a process of heat-treating the p-type silicon substrate 2 on which the phosphorus-containing dopant paste 14 is printed. A boat on which the p-type silicon substrate 2 is placed is placed in a horizontal furnace, and the p-type silicon substrate 2 is heat-treated at about 960 ° C. for 10 minutes. By this heat treatment, phosphorus, which is a dopant component in the phosphorus-containing dopant paste 14, penetrates the protective oxide film 13 and is thermally diffused into the p-type silicon substrate 2 immediately below the phosphorus-containing dopant paste 14, thereby providing the first dopant. A light receiving surface side high concentration dopant diffusion layer 3a which is a diffusion layer and has a sheet resistance of about 25Ω / □ is formed. That is, phosphorus in the phosphorus-containing dopant paste 14 penetrates the protective oxide film 13 and diffuses into the p-type silicon substrate 2 in the region immediately below the phosphorus-containing dopant paste 14 to form the light-receiving surface side high-concentration dopant diffusion layer 3a. The Since phosphorus in the phosphorus-containing dopant paste 14 is thermally diffused into the p-type silicon substrate 2 immediately below the phosphorus-containing dopant paste 14, the light-receiving surface side high-concentration dopant diffusion layer 3 a is the same as the printing pattern of the phosphorus-containing dopant paste 14. It is formed in a comb-shaped pattern. Note that phosphorus, which is a dopant component in the phosphorus-containing dopant paste 14, penetrates the protective oxide film 13 and is adjacent to the region immediately below the phosphorus-containing dopant paste 14 and the region immediately below in the plane direction of the p-type silicon substrate 2. It spreads slightly in the area and diffuses. In the present specification, the region including the adjacent region is referred to as a region immediately below.

On the other hand, the protective oxide film 13 prevents the dopant component volatilized from the phosphorus-containing dopant paste 14 during the heat treatment from diffusing into the p-type silicon substrate 2 other than the region immediately below. Hereinafter, the function and effect of the protective oxide film 13 formed in step S105 will be described. In the course of the heat treatment in step S107, the dopant component is volatilized from the surface of the phosphorus-containing dopant paste 14 into the atmosphere. Here, the inventor's experiment indicates that the dopant component volatilized in the process of the heat treatment in step S107 is inhibited by the protective oxide film 13 and does not diffuse into the p-type silicon substrate 2 under the protective oxide film 13. It became clear.

The degree of inhibition by which the protective oxide film 13 inhibits the stripped dopant component depends on the thickness of the protective oxide film 13. Therefore, hereinafter, the relationship between the thickness of the protective oxide film 13 and the degree of inhibition will be described with reference to the results of basic experiments. The inventors prepared a plurality of 156 mm square p-type silicon substrates having a texture structure for basic experiments. Thereafter, protective oxide films having various thicknesses were formed on the surface of the p-type silicon substrate by a method similar to step S105 in FIG. The thickness range of the protective oxide film was set to 0 nm to 230 nm corresponding to the absence of the oxide film. Thereafter, a phosphorus-containing dopant paste was printed and formed on the surface of one surface of the p-type silicon substrate by a method similar to step S106 in FIG. Thereafter, a heat treatment was performed on the p-type silicon substrate by a method similar to step S107 in FIG.

Here, a special test pattern was used as the printing pattern of the phosphorus-containing dopant paste. The test pattern is formed on the substantially entire surface of both sides of a 156 mm square p-type silicon substrate with the comb pattern described in step S106 of FIG. 3, and a 10 mm square partially filled with a dopant paste, and This is a pattern in which a blank portion is formed in which a dopant paste is not formed at all on a 10 mm square. Hereinafter, a portion partially filled with 10 mm square with a dopant paste is referred to as a pad portion. A blank part where no dopant paste is partially formed on a 10 mm square is called a blank part. The pad portion is provided in order to confirm a change in sheet resistance in a region where the dopant paste is formed in the p-type silicon substrate in a later step. Moreover, the blank part is provided in order to confirm the change of the sheet resistance by the volatile component from a dopant paste in the area | region in which the dopant paste is not formed in a p-type silicon substrate. Evaluation of sheet resistance requires an evaluation area of about 10 mm square in order to measure four terminals by contacting four probes in a row at 1 mm intervals.

After the heat treatment, the protective oxide film and the phosphorus-containing dopant paste were removed by a method similar to step S108 in FIG. FIG. 14 shows the results of measuring the sheet resistance of the pad portion and the blank portion after removal of the protective oxide film and phosphorus-containing dopant paste. FIG. 14 is a characteristic diagram showing the relationship between the thickness of the protective oxide film and the sheet resistance of the pad portion and blank portion in the first embodiment. When there is no protective oxide film on the surface of the p-type silicon substrate, that is, when the thickness of the protective oxide film is 0 nm, a sheet resistance of about 100 Ω / □ is exhibited even in a blank portion where no dopant paste is formed, It was found that phosphorus was diffused by volatile components from the adjacent dopant paste.

On the other hand, when a protective oxide film was formed on the surface of the p-type silicon substrate and the protective oxide film was thickened, the sheet resistance of the blank portion increased rapidly. And when the film thickness of the protective oxide film was larger than 50 nm, it was found that the sheet resistance of the blank portion was about 300Ω / □ or more, and the value hardly functioned as the diffusion layer. This indicates that phosphorus has a slower diffusion rate in the oxide film than that in silicon, and the oxide film functions as a diffusion protective film.

On the other hand, even when the protective oxide film was formed on the pad portion, the sheet resistance increased slowly with respect to the increase in the protective oxide film thickness. However, it was found that when the thickness of the protective oxide film exceeds 200 nm, the sheet resistance of the pad portion exceeds 300 Ω / □ and does not function as a diffusion layer.

From the above, by forming the protective oxide film with a film thickness between 50 nm and 200 nm, the protective oxide film prevents the diffusion of volatile components from the dopant paste to the surface of the p-type silicon substrate. It was found that phosphorus was diffused from the dopant paste immediately below the dopant paste. Here, even if the film thickness of the protective oxide film is set to 200 nm or less, the sheet resistance of the p-type silicon substrate immediately below the dopant paste tends to gradually increase according to the film thickness. In this case, in order to obtain a p-type silicon substrate having a desired sheet resistance, the heat treatment conditions may be changed according to the thickness of the protective oxide film.

FIG. 8 is an explanatory diagram of step S108 in FIG. Step S108 is a step of removing the protective oxide film 13 and the phosphorus-containing dopant paste 14. The protective oxide film 13 and the phosphorus-containing dopant paste 14 can be removed by immersing the p-type silicon substrate 2 in a 10% hydrofluoric acid aqueous solution for about 240 seconds.

FIG. 9 is an explanatory diagram of step S103 in FIG. In step S103, the light receiving surface side low-concentration dopant diffusion layer 3b is formed on each of the first surface serving as the light receiving surface of the solar cell 1 and the second surface serving as the back surface of the solar cell 1 in the p-type silicon substrate 2. Or it is the process of performing the thermal diffusion which forms the low concentration dopant diffusion layer 3c. The light-receiving surface side low-concentration dopant diffusion layer 3b and low-concentration dopant diffusion layer 3c are formed by inserting the p-type silicon substrate 2 having a textured structure into a thermal diffusion furnace and presenting phosphorus oxychloride (POCl ₃ ) vapor. Realized by heat treatment below. Specifically, for example, a quartz glass boat on which 300 p-type silicon substrates 2 are placed at an interval of 3.5 mm is inserted into a quartz tube of a horizontal furnace heated to about 750 ° C. While introducing 10 SLM of nitrogen, the temperature in the quartz tube is raised to 820 ° C., and a material gas is allowed to flow into the quartz tube for 10 minutes. The material gas is a POCl ₃ vapor obtained by bubbling nitrogen gas through POCl ₃ sealed in a glass container. After 10 minutes, the introduction of the material gas is stopped, and the inside of the quartz tube is maintained at 820 ° C. for another 10 minutes.

At this time, the surface layer on the surface of the p-type silicon substrate 2, that is, the surface layer on the light-receiving surface side of the p-type silicon substrate 2, is a second dopant diffusion layer having a uniform concentration of phosphorus lower than that of the first dopant diffusion layer. The light-receiving surface-side low-concentration dopant diffusion layer 3b diffused in (1) is formed in a region where the light-receiving surface-side high-concentration dopant diffusion layer 3a is not formed. Further, a phosphorus-containing glass layer 12 which is an oxide-containing glass layer containing phosphorus and is formed on the light-receiving surface side high-concentration dopant diffusion layer 3a and the light-receiving surface-side low concentration dopant diffusion layer 3b. Also, a low concentration dopant diffusion layer 3c in which phosphorus is diffused at a uniform concentration is formed on the surface layer on the back surface of the p-type silicon substrate 2. Further, a phosphorus-containing glass layer 12 that is an oxide-containing glass layer containing impurities and containing phosphorus is formed on the low-concentration dopant diffusion layer 3c.

The region where the light-receiving surface side high-concentration dopant diffusion layer 3a is already formed before the thermal diffusion of step S103 is present on the light-receiving surface side of the p-type silicon substrate 2, but the light-receiving surface side formed in step S103 The dopant concentration of the low-concentration dopant diffusion layer 3b is relatively lower than the dopant concentration of the light-receiving surface side high-concentration dopant diffusion layer 3a. For this reason, even after the step S103, the light-receiving surface side high-concentration dopant diffusion layer 3a remains on the light-receiving surface side of the p-type silicon substrate 2 with a high concentration. Therefore, the light-receiving surface side high-concentration dopant diffusion layer 3a partially exists on the light-receiving surface side of the p-type silicon substrate 2 after step S103, and fills the space between the light-receiving surface-side high-concentration dopant diffusion layers 3a. There is a light-receiving surface side low-concentration dopant diffusion layer 3b.

The low-concentration dopant diffusion layer 3c obtained as described above has a sheet resistance of about 100Ω / □ measured by the four-terminal method. The sheet resistance measurement cannot be accurately performed on the light receiving surface side because it is affected by the light receiving surface side high-concentration dopant diffusion layer 3a. Therefore, the inventor evaluates the low-concentration dopant diffusion layer 3c on the back surface of the p-type silicon substrate 2 without the light-receiving surface side high-concentration dopant diffusion layer 3a.

A vertical furnace may be used instead of the horizontal furnace. A material other than POCl ₃ can be used as the material gas. In addition, the dopant for forming the n-type light-receiving surface side low-concentration dopant diffusion layer 3b and the n-type low-concentration dopant diffusion layer 3c in step S103 is an n-type dopant that can be used for the formation of solar cells. Good.

FIG. 10 is an explanatory diagram of step S104 in FIG. Step S104 is a step of removing the phosphorus-containing glass layer 12. The phosphorus-containing glass layer 12 can be removed by immersing the p-type silicon substrate 2 in a 10% hydrofluoric acid aqueous solution for about 60 seconds.

FIG. 11 is an explanatory diagram of step S109 in FIG. Step S109 is a process of forming the antireflection film 4. The antireflection film 4 is formed by forming a silicon nitride film having a refractive index of 2.1 and a film thickness of 80 nm on the light-receiving surface side dopant diffusion layer 3, that is, on the light-receiving surface side high-concentration dopant diffusion layer 3a and on the light-receiving surface side. A film is formed on the low-concentration dopant diffusion layer 3b. The silicon nitride film functions not only as the antireflection film 4 but also as a passivation film for suppressing surface recombination on the light receiving surface side of the p-type silicon substrate 2.

FIG. 12 is an explanatory diagram of step S110 in FIG. Step S110 is a process of printing an electrode. On the back surface of the p-type silicon substrate 2, an aluminum (Al) -containing paste 15 for forming a back-side electrode containing aluminum (Al) is screen-printed on the entire surface of the low-concentration dopant diffusion layer 3c, and the back surface side before firing. An electrode is formed. After the Al-containing paste 15 is dried at 250 ° C. for 5 minutes, on the light-receiving surface side of the p-type silicon substrate 2, the silver (Ag) -containing paste 16 for forming the light-receiving surface side electrode containing silver (Ag) is antireflective. Screen printing is performed on the film 4 to form the light-receiving surface side electrode 5 before firing.

The printing pattern of the Ag-containing paste 16 has the same comb shape as the light-receiving surface side high-concentration dopant diffusion layer 3a, and a pattern in which linear patterns with a line width of 50 μm are arranged in parallel at intervals of 2 mm, and four lines with a line width of 1 mm. It is a comb-shaped pattern which consists of the pattern which arranged the parallel pattern in parallel. Further, the Ag-containing paste 16 is printed at a position included in a region having a width of 150 μm and a region having a width of 1.2 mm of the pattern of the phosphorus-containing dopant paste 14 formed in Step S106. That is, the Ag-containing paste 16 is printed at a position included in a 150 μm wide region and a 1.2 mm wide region of the pattern of the light receiving surface side high concentration dopant diffusion layer 3a.

The printing position of the Ag-containing paste 16 needs to be aligned with the pattern of the light receiving surface side high concentration dopant diffusion layer 3a. The region of the light receiving surface side high-concentration dopant diffusion layer 3a is image-recognized using an infrared camera, and the printing position of the Ag-containing paste 16 is determined. In addition to image recognition using an infrared camera, a cross mark for alignment is printed on the outer peripheral edge of the p-type silicon substrate 2 by a laser processing machine at the time of step S101, and the phosphorus-containing dopant paste printing step of step S106 In the printing process of the Ag-containing paste 16 in step S110, the cross mark may be used as a reference. Further, the printing position of the Ag-containing paste 16 may be determined by recognizing three points on the outer shape of the p-type silicon substrate 2 in Step S106 and Step S110. If the printing position of the Ag-containing paste 16 is shifted, the light receiving surface side electrode 5 is formed on the light receiving surface side low-concentration dopant diffusion layer 3b, and the light receiving surface side dopant diffusion layer 3 and the light receiving surface side electrode 5 are formed. As a result, the fill factor deteriorates due to the increase in contact resistance, and the open circuit voltage deteriorates due to increased surface recombination. For this reason, it is important to align the printing position of the Ag-containing paste 16 with the pattern of the light-receiving surface side high-concentration dopant diffusion layer 3a.

FIG. 13 is an explanatory diagram of step S111 in FIG. Step S111 is a step of performing a heat treatment to form an electrode by firing a paste for forming an electrode. The p-type silicon substrate 2 on which the electrode forming paste is formed is placed in a tunnel furnace and heat-treated at a peak temperature of 800 ° C. for 3 seconds for a short time. As a result, the resin component in the paste disappears, and in the Ag-containing paste 16, the contained glass particles penetrate the silicon nitride film of the antireflection film 4, and the Ag particles contact the light-receiving surface side high-concentration dopant diffusion layer 3a. And electrical continuity is obtained. Thereby, the light-receiving surface side electrode 5 is obtained.

Further, Al contained in the Al-containing paste 15 reacts with silicon on the back surface of the p-type silicon substrate 2 to form an aluminum-silicon (Al—Si) alloy, and low-concentration dopant diffusion on the back surface of the p-type silicon substrate 2. The layer 3c is penetrated by an Al—Si alloy, and Al is diffused into the silicon on the back surface of the p-type silicon substrate 2 to form the back surface side BSF layer 7. Thereby, the back surface side electrode 6 is obtained.

By performing the above steps, it is possible to obtain the solar battery cell 1 in which the light-receiving surface side low-concentration dopant diffusion layer 3b has a uniform dopant concentration in the surface direction of the p-type silicon substrate 2 shown in FIGS. it can.

The semiconductor substrate 2 may be an n-type single crystal silicon substrate or an n-type polycrystalline silicon substrate. In this case, the conductivity type of each member in the first embodiment may be reversed. Also in this case, a p-type light-receiving surface side low-concentration dopant diffusion layer having the structure shown in FIGS. 1 and 2 and having a uniform dopant concentration in the surface direction of the n-type silicon substrate is obtained by performing the above-described steps. A solar battery cell provided can be obtained.

As described above, in the method for manufacturing a solar cell according to the first embodiment, the protective oxide film 13 having a thickness of 50 nm to 200 nm is formed on the p-type silicon substrate 2. Then, a phosphorus-containing dopant paste 14 is printed in a predetermined pattern on the protective oxide film 13 and heat treatment is performed. For this reason, the p-type silicon substrate 2 covered with the protective oxide film 13 is not diffused by the dopant component volatilized from the phosphorus-containing dopant paste 14, and the dopant in the low-concentration dopant diffusion layer 3c formed in a later step. Inhomogeneity of the diffusion concentration of the components can be eliminated.

Thus, according to the first embodiment, the solar cell 1 having the selective emitter structure including the light-receiving surface side high-concentration dopant diffusion layer 3a and the light-receiving surface-side low concentration dopant diffusion layer 3b is replaced with the phosphorus-containing dopant paste 14 The volatilization component from can be easily obtained by preventing diffusion of the volatilization component into the p-type silicon substrate 2. That is, a photovoltaic cell having uniform power generation characteristics in the plane direction in which variations in power generation characteristics due to non-uniformity of the dopant concentration of the light-receiving surface side low-concentration dopant diffusion layer 3b in the plane direction of the p-type silicon substrate 2 are prevented. 1 can be easily obtained.

Embodiment 2. FIG.
In the second embodiment, a modification of the solar cell manufacturing method according to the first embodiment will be described with reference to FIGS. FIG. 15: is the flowchart which showed the process flow of the manufacturing method of the photovoltaic cell concerning Embodiment 2 of this invention. 16 to 21 are cross-sectional views of relevant parts for explaining the manufacturing process of the solar battery cell according to the second embodiment of the present invention.

In the method of manufacturing a solar cell according to the second embodiment, before the protective oxide film is formed in step S105 in the flowchart of FIG. 3 in the first embodiment, thermal diffusion in step S103 and phosphorus-containing glass in step S104. Perform layer removal. Thus, no heat treatment exceeding 800 ° C. is performed after the formation of the light receiving surface side high concentration dopant diffusion layer 3a. For this reason, the dopant on the surface of the light receiving surface side high concentration dopant diffusion layer 3a is not diffused into the light receiving surface side high concentration dopant diffusion layer 3a by the heat treatment exceeding 800 ° C. Therefore, a good electrode contact can be maintained without reducing the surface dopant concentration of the light-receiving surface side high-concentration dopant diffusion layer 3a due to heat treatment exceeding 800 ° C.

In Embodiment 2 of the present invention, first, Step S101 and Step S102 are performed in the same manner as in Embodiment 1.

FIG. 16 is an explanatory diagram of step S103 in FIG. Step S103 is a heat for forming the low-concentration dopant diffusion layer 3c on both sides of the first surface serving as the light receiving surface of the solar cell 1 and the second surface serving as the back surface of the solar cell 1 in the p-type silicon substrate 2. This is a step of performing diffusion. Formation of the low-concentration dopant diffusion layer 3c is realized by placing the p-type silicon substrate 2 on which the texture structure is formed in a thermal diffusion furnace and heat-treating it in the presence of phosphorus oxychloride (POCl ₃ ) vapor. Specifically, for example, a quartz glass boat on which 300 p-type silicon substrates 2 are placed at intervals of 3.5 mm is loaded into a quartz tube of a horizontal furnace heated to 750 ° C. While introducing 10 SLM of nitrogen, the temperature in the quartz tube is raised to 820 ° C., and a material gas is allowed to flow into the quartz tube for 10 minutes. The material gas is a POCl ₃ vapor obtained by bubbling nitrogen gas through POCl ₃ sealed in a glass container. After 10 minutes, the introduction of the material gas is stopped, the inside of the quartz tube is maintained at 820 ° C. for another 10 minutes, the temperature is lowered to 750 ° C., and the boat is taken out of the quartz tube. At this time, on the front and back surfaces of the p-type silicon substrate 2, a low-concentration dopant which is a second dopant diffusion layer in which phosphorus is diffused at a uniform concentration lower than that of the first dopant diffusion layer in the plane direction of the p-type silicon substrate 2. The diffusion layer 3c and the phosphorus-containing glass layer 12 that is an impurity-containing glass layer that is an oxide film and contains phosphorus are formed in this order. Further, the low-concentration dopant diffusion layer 3c thus obtained has a sheet resistance measured by the four-terminal method of about 100Ω / □. A vertical furnace may be used instead of the horizontal furnace. A material other than POCl ₃ can be used as the material gas. The dopant for forming the n-type low-concentration dopant diffusion layer 3c may be any n-type dopant that can be used for forming the solar battery cell.

FIG. 17 is an explanatory diagram of step S104 in FIG. Step S104 is a step of removing the phosphorus-containing glass layer 12. The phosphorus-containing glass layer 12 can be removed by immersing the p-type silicon substrate 2 in a 10% hydrofluoric acid aqueous solution for about 60 seconds.

FIG. 18 is an explanatory diagram of step S105 of FIG. Step S105 is a step of forming the protective oxide film 13 as a first oxide film on the low-concentration dopant diffusion layer 3c on the first surface side which becomes the light receiving surface in the p-type silicon substrate 2. As the protective oxide film 13, a silicon oxide film is formed by a chemical vapor deposition (CVD) method using silane (SiH ₄ ) as a material gas. Specifically, a silicon oxide film having a thickness of 120 nm is formed by exposing the p-type silicon substrate 2 heated to 500 ° C. in a mixed atmosphere of silane and oxygen (O ₂ ) at atmospheric pressure. The atmospheric pressure CVD method is employed because it can be formed at a low temperature and a high film formation rate, but a thermal oxide film formed by wet oxidation or dry oxidation can also be used as the protective oxide film 13. However, since wet oxidation and dry oxidation have a high process temperature of about 900 ° C. to 1000 ° C., it should be noted that the dopant concentration profile in the low-concentration dopant diffusion layer 3 c formed earlier changes. In wet oxidation and dry oxidation, it is preferable to take into account changes due to the process temperature in the dopant concentration profile in the low-concentration dopant diffusion layer 3c previously formed.

FIG. 19 is an explanatory diagram of step S106 in FIG. Step S 106 is a step of printing a dopant paste as a first diffusion source on the protective oxide film 13. Here, as the dopant paste, a phosphorus-containing dopant paste 14 which is a resin paste containing a phosphorus oxide is selectively printed on the protective oxide film 13 using a screen printing method. The printing pattern of the phosphorus-containing dopant paste 14 is a comb shape composed of a pattern in which linear patterns having a line width of 150 μm are arranged in parallel at intervals of 2 mm and a pattern in which four linear patterns having a line width of 1.2 mm are arranged in parallel. The pattern is After printing, the phosphorus-containing dopant paste 14 is dried at 250 ° C. for 5 minutes. In addition, the printing method of the phosphorus containing dopant paste 14 is not restricted to the screen printing method, The inkjet method or the method of discharging directly from a nozzle can be used.

FIG. 20 is an explanatory diagram of step S107 of FIG. Step S107 is a process of heat-treating the p-type silicon substrate 2 on which the phosphorus-containing dopant paste 14 is printed. A boat on which the p-type silicon substrate 2 is placed is loaded into a horizontal furnace similar to step S103, and the p-type silicon substrate 2 is heat-treated at 960 ° C. for 10 minutes. By this heat treatment, phosphorus, which is a dopant component in the phosphorus-containing dopant paste 14, penetrates the protective oxide film 13 and is thermally diffused into the p-type silicon substrate 2 immediately below the phosphorus-containing dopant paste 14, thereby providing the first dopant. A light receiving surface side high concentration dopant diffusion layer 3a which is a diffusion layer and has a sheet resistance of about 25Ω / □ is formed. That is, phosphorus in the phosphorus-containing dopant paste 14 penetrates the protective oxide film 13 and diffuses into the low-concentration dopant diffusion layer 3c and the p-type silicon substrate 2 in the region immediately below the phosphorus-containing dopant paste 14 to increase the light receiving surface side height. A concentration dopant diffusion layer 3a is formed. Since phosphorus in the phosphorus-containing dopant paste 14 is thermally diffused into the p-type silicon substrate 2 immediately below the phosphorus-containing dopant paste 14, the light-receiving surface side high-concentration dopant diffusion layer 3 a is the same as the printing pattern of the phosphorus-containing dopant paste 14. It is formed in a comb-shaped pattern. Note that phosphorus, which is a dopant component in the phosphorus-containing dopant paste 14, penetrates the protective oxide film 13 and is adjacent to the region immediately below the phosphorus-containing dopant paste 14 and the region immediately below in the plane direction of the p-type silicon substrate 2. It spreads slightly in the area and diffuses.

On the other hand, as described in the first embodiment, the protective oxide film 13 prevents the diffusion of the dopant component volatilized from the phosphorus-containing dopant paste 14 during the heat treatment into the low-concentration dopant diffusion layer 3c. That is, in the low-concentration dopant diffusion layer 3c on the light-receiving surface side, phosphorus other than the region immediately below the phosphorus-containing dopant paste 14 does not diffuse phosphorus as a dopant component from the phosphorus-containing dopant paste 14, and the sheet resistance is 100Ω / □ It remains about the same level. Therefore, among the low-concentration dopant diffusion layer 3c on the light-receiving surface side of the p-type silicon substrate 2, the light-receiving surface-side high-concentration dopant diffusion layer 3a is formed in the region immediately below the phosphorus-containing dopant paste 14, and the light-receiving surface-side high-concentration dopant diffusion is formed. The region where the layer 3a is not formed becomes the light receiving surface side low-concentration dopant diffusion layer 3b. Thereby, the light-receiving surface side dopant diffusion layer 3 is formed, and the semiconductor substrate 11 is obtained.

Therefore, as described in the first embodiment, by setting the thickness of the protective oxide film 13 to be greater than 50 nm and equal to or less than 200 nm, the dopant component volatilized during the heat treatment in Step S107 is inhibited by the protective oxide film 13. The light-receiving surface side high-concentration dopant is diffused by diffusing the dopant component from the phosphorus-containing dopant paste 14 into the p-type silicon substrate 2 in the region immediately below the phosphorus-containing dopant paste 14 without diffusing into the p-type silicon substrate 2. Layer 3a can be formed. That is, in the present second embodiment, the film thickness that can penetrate the protective oxide film 13 differs between the diffusion of the dopant component volatilized during the heat treatment in step S107 and the direct diffusion from the phosphorus-containing dopant paste 14. Is used to eliminate non-uniformity of the dopant concentration due to diffusion of the volatilized dopant component. As a result, when the light-receiving surface side high-concentration dopant diffusion layer 3a is formed by thermal diffusion using the phosphorus-containing dopant paste 14, the concentration of the low-concentration dopant diffusion layer 3c previously formed is that of the p-type silicon substrate 2. It is possible to prevent non-uniformity in the plane.

FIG. 21 is an explanatory diagram of step S108 in FIG. Step S108 is a step of removing the protective oxide film 13 and the phosphorus-containing dopant paste 14. The protective oxide film 13 and the phosphorus-containing dopant paste 14 can be removed by immersing the p-type silicon substrate 2 in a 10% hydrofluoric acid aqueous solution for about 240 seconds.

Thereafter, as in the case of the first embodiment, by performing steps S109 to S111, the light receiving surface side low-concentration dopant diffusion layer 3b in the surface direction of the p-type silicon substrate 2 shown in FIGS. Can obtain a solar battery cell 1 having a uniform dopant concentration.

Thus, according to the second embodiment, the solar cell 1 having the selective emitter structure including the light-receiving surface side high-concentration dopant diffusion layer 3a and the light-receiving surface-side low concentration dopant diffusion layer 3b is converted into the phosphorus-containing dopant paste 14 The volatilization component from can be easily obtained by preventing diffusion of the volatilization component into the p-type silicon substrate 2. That is, a photovoltaic cell having uniform power generation characteristics in the plane direction in which variations in power generation characteristics due to non-uniformity of the dopant concentration of the light-receiving surface side low-concentration dopant diffusion layer 3b in the plane direction of the p-type silicon substrate 2 are prevented. 1 can be easily obtained. Further, according to the second embodiment, since the heat treatment is not performed at a temperature exceeding 800 ° C. after the formation of the light receiving surface side high concentration dopant diffusion layer 3a, the surface dopant concentration of the light receiving surface side high concentration dopant diffusion layer 3a. It is possible to maintain a good electrode contact without lowering.

Embodiment 3 FIG.
In the third embodiment, a modification of the method for manufacturing a solar cell according to the second embodiment will be described with reference to FIGS. FIG. 22 is a flowchart showing a process flow of the method for manufacturing a solar battery cell according to the third embodiment of the present invention. 23 to 26 are cross-sectional views of relevant parts for explaining the manufacturing process of the solar battery cell according to the third embodiment of the present invention. In FIG. 22, the same steps as those in FIGS. 3 and 15 are denoted by the same reference numerals. In FIGS. 23 to 26, the same members as those in the above-described embodiment are denoted by the same reference numerals.

In the solar cell manufacturing method according to the third embodiment, the step of removing the phosphorus-containing glass layer in step S104 and the step of forming the protective oxide film in step S105 in the flowchart of FIG. 15 in the second embodiment. In addition, the protective oxide film is formed during the thermal diffusion process in step S103. In step S103 in the second embodiment, the phosphorus-containing glass layer 12 that is an oxide film is formed to have a thickness of about 20 nm. At this film thickness, diffusion from the volatilized component of the dopant paste is inhibited in the heat treatment process of the dopant paste in step S107. Not enough to Therefore, in the third embodiment, a dry oxidation process at 1100 ° C. for 30 minutes or a wet oxidation process at 930 ° C. for 15 minutes is inserted in the latter half of the thermal diffusion process in step S103 of the second embodiment.

In Embodiment 3 of the present invention, first, Step S101 and Step S102 are performed in the same manner as in Embodiment 1.

FIG. 23 is an explanatory diagram of step S201 in FIG. In step S201, thermal diffusion is performed to form the low-concentration dopant diffusion layer 3c on the surface of the p-type silicon substrate 2, and the phosphorus-containing glass layer 12 formed by thermal diffusion remains on the p-type silicon substrate 2. In this step, the protective oxide film 13 is formed. The thermal diffusion for forming the low-concentration dopant diffusion layer 3c is performed in the same manner as in the second embodiment. At this time, on the front and back surfaces of the p-type silicon substrate 2, a low-concentration dopant diffusion layer 3c in which phosphorus is diffused at a uniform concentration in the surface direction of the p-type silicon substrate 2, and an impurity-containing glass layer that is an oxide film and contains phosphorus And the phosphorus-containing glass layer 12 are formed in this order.

Then, after thermal diffusion, a dry oxidation process at 1100 ° C. for 30 minutes or a wet oxidation process at 930 ° C. for 15 minutes is performed. In the dry oxidation process, after thermal diffusion, the quartz tube is heated to about 1000 ° C. to 1100 ° C. while introducing 10 SLM nitrogen without taking out the boat, and the material gas is allowed to flow into the quartz tube for 10 minutes. The material gas is an oxygen gas that does not contain water vapor. In the wet oxidation process, after the thermal diffusion, the quartz tube is heated to about 930 ° C. to 1030 ° C. while introducing 10 SLM nitrogen without taking out the boat, and the material gas is allowed to flow into the quartz tube for 15 minutes. . The material gas is an oxygen gas containing water vapor. Thereby, the protective oxide film 13 is formed on the phosphorus-containing glass layers 12 on the front and back surfaces of the p-type silicon substrate 2.

FIG. 24 is an explanatory diagram of step S202 of FIG. Step S202 is a step of selectively printing the phosphorus-containing dopant paste 14 on the protective oxide film 13 on the light receiving surface side. The phosphorus-containing dopant paste 14 is printed in the same manner as in the second embodiment.

FIG. 25 is an explanatory diagram of step S203 of FIG. Step S203 is a process of heat-treating the p-type silicon substrate 2 on which the phosphorus-containing dopant paste 14 is printed. The p-type silicon substrate 2 is heat-treated at 960 ° C. for 10 minutes in the same manner as in step S107 of the first embodiment. By this heat treatment, as in step S107, phosphorus in the phosphorus-containing dopant paste 14 thermally diffuses into the p-type silicon substrate 2 directly below the phosphorus-containing dopant paste 14 through the protective oxide film 13, and step S107. Similarly to the above, the light receiving surface side high concentration dopant diffusion layer 3a is formed. That is, the phosphorus in the phosphorus-containing dopant paste 14 penetrates the protective oxide film 13 and the phosphorus-containing glass layer 12, and the low-concentration dopant diffusion layer 3c and the p-type silicon substrate 2 in the region immediately below the phosphorus-containing dopant paste 14 The light receiving surface side high-concentration dopant diffusion layer 3a is formed.

FIG. 26 is an explanatory diagram of step S204 of FIG. Step S204 is a step of removing the protective oxide film 13, the phosphorus-containing glass layer 12, and the phosphorus-containing dopant paste 14. The protective oxide film 13, the phosphorus-containing glass layer 12 and the phosphorus-containing dopant paste 14 can be removed by immersing the p-type silicon substrate 2 in a 10% hydrofluoric acid aqueous solution, as in the second embodiment. . The state of p-type silicon substrate 2 after step S204 is the same as that after step S108 of the first embodiment.

Thereafter, similarly to the second embodiment, by performing steps S109 to S111, the light receiving surface side low-concentration dopant diffusion layer 3b in the surface direction of the p-type silicon substrate 2 shown in FIGS. Can obtain a solar battery cell 1 having a uniform dopant concentration.

The semiconductor substrate 2 may be an n-type single crystal silicon substrate or an n-type polycrystalline silicon substrate. In this case, the conductivity type of each member in the third embodiment may be reversed. Also in this case, a p-type light-receiving surface side low-concentration dopant diffusion layer having the structure shown in FIGS. 1 and 2 and having a uniform dopant concentration in the surface direction of the n-type silicon substrate is obtained by performing the above-described steps. The solar cell 1 provided can be easily obtained by preventing the volatilization component from the phosphorus-containing dopant paste 14 from diffusing into the p-type silicon substrate 2.

What should be noted in the third embodiment is that the protective oxide film 13 is formed in the state in which the phosphorus-containing glass layer 12 formed in the thermal diffusion process of step S201 remains on the low-concentration dopant diffusion layer 3c. Heating at about 1100 ° C. or about 930 ° C. and heating at about 960 ° C. as a heat treatment in step S203. By applying these heats, phosphorus is further diffused from the phosphorus-containing glass layer 12 into the p-type silicon substrate 2. For this reason, it is necessary to adjust the phosphorus content in the phosphorus-containing glass layer 12.

According to the above-described third embodiment, the light receiving surface-side low-concentration dopant diffusion layer 3b has a uniform dopant concentration in the plane direction of the p-type silicon substrate 2 as compared with the case of the first embodiment. It can be obtained by the number of steps. Therefore, a solar cell in which the dopant concentration in the low concentration diffusion region is uniform in the plane of the semiconductor substrate can be manufactured by a simpler method.

Embodiment 4 FIG.
A method for manufacturing a solar battery cell according to the fourth embodiment will be described with reference to FIGS. FIG. 27 is a flowchart showing a process flow of the method for manufacturing a solar battery cell according to the fourth embodiment of the present invention. 28 to 35 are cross-sectional views of relevant parts for explaining the manufacturing process of the solar battery cell according to the fourth embodiment of the present invention. In FIGS. 28 to 35, the same members as those in the above-described embodiment are denoted by the same reference numerals.

FIG. 28 is an explanatory diagram of steps S301 and S302 of FIG. In step S301 and step S302, the same processing as in step S101 and step S102 of the first embodiment is performed.

FIG. 29 is an explanatory diagram of step S303 in FIG. In step S303, a phosphorus-containing oxide film 31 and a protective oxide film 32 are formed as oxide films on the light-receiving surface side of the p-type silicon substrate 2. Here, a silicon oxide film is formed by an atmospheric pressure CVD method using silane (SiH ₄ ), oxygen (O ₂ ), and phosphine (PH ₃ ) as material gases. Specifically, the p-type silicon substrate 2 heated to 500 ° C. is exposed to a mixed atmosphere of silane, oxygen and phosphine at atmospheric pressure, so that phosphorus is first contained on the light-receiving surface side of the p-type silicon substrate 2. A phosphorus-containing oxide film 31 that is a first lower oxide film having a thickness of 30 nm is formed. Thereafter, mixing of phosphine is stopped, and the p-type silicon substrate 2 is exposed in a mixed atmosphere of silane and oxygen, so that a protective oxide film that is a 120 nm-thickness first oxide film not containing phosphorus is formed. 32 is formed on the phosphorus-containing oxide film 31. The phosphorus concentration in the phosphorus-containing oxide film 31 is lower than that of the phosphorus-containing dopant paste 14.

FIG. 30 is an explanatory diagram of step S304 of FIG. Step S304 is a step of selectively printing the phosphorus-containing dopant paste 14 on the protective oxide film 32. Printing of the phosphorus-containing dopant paste 14 is performed in the same manner as in step S106 of the first embodiment. The printing pattern of the phosphorus-containing dopant paste 14 is a comb shape composed of a pattern in which linear patterns having a line width of 150 μm are arranged in parallel at intervals of 2 mm and a pattern in which four linear patterns having a line width of 1.2 mm are arranged in parallel. Pattern. After printing, the phosphorus-containing dopant paste 14 is dried at 250 ° C. for 5 minutes.

FIG. 31 is an explanatory diagram of step S305 in FIG. Step S305 is a process of heat-treating the p-type silicon substrate 2 on which the phosphorus-containing dopant paste 14 is printed. Specifically, a boat on which the p-type silicon substrate 2 is placed is placed in a horizontal furnace, and the p-type silicon substrate 2 is heat-treated at 960 ° C. for 15 minutes. By this heat treatment, phosphorus, which is a dopant component in the phosphorus-containing dopant paste 14, penetrates the protective oxide film 32 and the phosphorus-containing oxide film 31 and thermally diffuses into the p-type silicon substrate 2 immediately below the phosphorus-containing dopant paste 14. In addition, phosphorus in the phosphorus-containing oxide film 31 is thermally diffused into the p-type silicon substrate 2 immediately below the phosphorus-containing dopant paste 14, and the light-receiving surface side high-concentration dopant diffusion layer 3a having a sheet resistance of about 20Ω / □ is formed. It is formed. The light receiving surface side high-concentration dopant diffusion layer 3 a is formed in the same comb-shaped pattern as the printing pattern of the phosphorus-containing dopant paste 14.

On the other hand, in the surface layer on the light-receiving surface side of the p-type silicon substrate 2, the dopant component of the phosphorus-containing dopant paste 14 does not diffuse in the region other than the region immediately below the phosphorus-containing dopant paste 14. However, phosphorus in the phosphorus-containing oxide film 31 is thermally diffused into the surface layer on the light-receiving surface side of the p-type silicon substrate 2 in a region other than the region immediately below the phosphorus-containing dopant paste 14. Then, a light-receiving surface side low concentration dopant diffusion layer 3b having a sheet resistance of about 100Ω / □ is formed as a third dopant diffusion layer in which phosphorus is diffused at a uniform concentration in the surface direction of the p-type silicon substrate 2. Thereby, the light receiving surface side dopant diffusion layer 3 having the light receiving surface side high concentration dopant diffusion layer 3a and the light receiving surface side low concentration dopant diffusion layer 3b is formed.

By performing the above steps, the light receiving surface side dopant diffusion layer 3a and the light receiving surface side low concentration dopant diffusion layer 3b in the surface direction of the p-type silicon substrate 2 have a uniform dopant concentration. It is possible to form the layer 3 with fewer steps than in the first embodiment.

Here, in the fourth embodiment, the laminated film of the phosphorus-containing oxide film 31 and the protective oxide film 32 which are oxide films is formed on the p-type silicon substrate 2 because the phosphorus-containing oxide film 31 contains phosphorus. Is a second diffusion source serving as a diffusion source. In addition, this laminated film plays a role of preventing the dopant component volatilized from the phosphorus-containing dopant paste 14 from diffusing into the light receiving surface side low-concentration dopant diffusion layer 3b. Also in this case, if the thickness of the laminated film as an oxide film is up to 200 nm, the dopant can be diffused from the phosphorus-containing dopant paste 14 to the p-type silicon substrate 2 through the laminated film. Since the phosphorus-containing oxide film 31 is protected by the protective oxide film 32, it is possible to prevent phosphorus in the phosphorus-containing oxide film 31 from volatilizing in the atmosphere during the heat treatment. It is possible to efficiently diffuse phosphorus into the substrate 2.

On the other hand, since the dopant component volatilized from the phosphorus-containing dopant paste 14 cannot penetrate the oxide film having a film thickness larger than 50 nm, the protective oxide film 32 functions as a protective film. Therefore, the light-receiving surface side low-concentration dopant diffusion layer 3b in which phosphorus is diffused at a uniform concentration that is not affected by the volatilization component from the phosphorus-containing dopant paste 14 is obtained.

Here, in order to prevent phosphorus from being volatilized from the phosphorus-containing oxide film 31 in the subsequent heat treatment process, a protective oxide film 32 having a thickness of 120 nm is deposited on the phosphorus-containing oxide film 31 as a capping film. The oxide film 31 may be 150 nm and the protective oxide film 32 may not be formed. Even when only the phosphorus-containing oxide film 31 is provided with a film thickness of 50 nm or more and 200 nm or less without forming the protective oxide film 32, the dopant component volatilized from the phosphorus-containing dopant paste 14 is received by the phosphorus-containing oxide film 31. It plays a role of preventing diffusion to the surface-side low-concentration dopant diffusion layer 3b.

FIG. 32 is an explanatory diagram of step S306 in FIG. Step S306 is a step of removing the protective oxide film 32 and the phosphorus-containing oxide film 31, which are oxide films, and the phosphorus-containing dopant paste 14. The removal of the oxide film and the phosphorus-containing dopant paste 14 can be performed by immersing the p-type silicon substrate 2 in a 10% hydrofluoric acid aqueous solution for about 360 seconds.

FIG. 33 is an explanatory diagram of step S307 in FIG. Step S307 is a step of forming the antireflection film 4. The formation of the antireflection film 4 is performed in the same manner as in step S109 of the first embodiment.

FIG. 34 is an explanatory diagram of step S308 in FIG. Step S308 is a step of printing an electrode. The electrodes are printed in the same manner as in step S110 of the first embodiment by printing the Al-containing paste 15 and the Ag-containing paste 16. In this case, the Al-containing paste 15 is printed on the silicon surface on the back surface of the p-type silicon substrate 2.

FIG. 35 is an explanatory diagram of step S309 in FIG. Step S309 is a step of performing a heat treatment to form an electrode by firing an electrode forming paste. The electrode heat treatment is performed in the same manner as in step S111 of the first embodiment.

The semiconductor substrate 2 may be an n-type single crystal silicon substrate or an n-type polycrystalline silicon substrate. In this case, the conductivity type of each member in the fourth embodiment may be reversed. Also in this case, a p-type light-receiving surface side low-concentration dopant diffusion layer having the structure shown in FIGS. 1 and 2 and having a uniform dopant concentration in the surface direction of the n-type silicon substrate is obtained by performing the above-described steps. A solar battery cell provided can be obtained.

According to the fourth embodiment described above, the laminated film of the phosphorus-containing oxide film 31 that is an oxide film and the protective oxide film 32 prevents diffusion of the volatile component of the dopant paste into the low-concentration dopant diffusion layer during heat treatment. In addition, this laminated film is used as a dopant diffusion source. Thereby, the solar cell 1 having a selective emitter structure including the light receiving surface side high concentration dopant diffusion layer 3a and the light receiving surface side low concentration dopant diffusion layer 3b having a uniform dopant concentration in the surface direction of the p-type silicon substrate 2 is obtained. Thus, it can be efficiently obtained with a smaller number of steps than in the first embodiment.

Embodiment 5 FIG.
FIG. 36 is a schematic top view showing the solar battery cell 41 according to the fifth embodiment of the present invention. FIG. 37 is a schematic bottom view showing the solar battery cell 41 according to the fifth embodiment of the present invention. FIG. 38 is a schematic cross-sectional view of the relevant part showing a solar battery cell 41 according to the fifth embodiment of the present invention, and is a relevant part cross-sectional view taken along line BB in FIGS. 36 and 37.

In the solar cell 41 according to the fifth embodiment, a p-type light-receiving surface side dopant diffusion layer 43 in which boron (B) is diffused is formed on the entire light-receiving surface of the n-type semiconductor substrate 42, and a pn junction is formed. A semiconductor substrate 51 is formed. An antireflection film 4 made of an insulating film is formed on the light receiving surface side dopant diffusion layer 43.

As the semiconductor substrate 42, an n-type single crystal silicon substrate is used. Hereinafter, the semiconductor substrate 42 made of an n-type single crystal silicon substrate may be referred to as an n-type silicon substrate 42. The semiconductor substrate 42 is not limited to an n-type single crystal silicon substrate, and an n-type polycrystalline silicon substrate may be used.

A texture structure is formed on the light receiving surface side of the n-type silicon substrate 42, that is, on the light receiving surface side of the p-type light receiving surface side dopant diffusion layer 43. Since the fine unevenness of the texture structure is very fine, it is not shown as an uneven shape in FIG. 38 and the following drawings.

A plurality of elongated light receiving surface side grid electrodes 45a are arranged side by side on the light receiving surface side of the semiconductor substrate 42, and a light receiving surface side bus electrode 45b that is electrically connected to the light receiving surface side grid electrode 45a is connected to the light receiving surface side grid electrode 45a. They are provided so as to be orthogonal to each other, and are electrically connected to the p-type light-receiving surface side dopant diffusion layer 43 at the bottom surface portion. The light receiving surface side grid electrode 45a and the light receiving surface side bus electrode 45b are made of a silver material. The light-receiving surface-side grid electrode 45a and the light-receiving-surface-side bus electrode 45b are electrically connected to the p-type light-receiving-surface-side dopant diffusion layer 43, except that the light-receiving-surface-side grid electrode 5a and the light-receiving-surface-side bus electrode 5b described above. It is formed with the same composition. The light-receiving surface side grid electrode 45a and the light-receiving surface-side bus electrode 45b constitute a light-receiving surface-side electrode 45 that is a first electrode having a comb shape.

On the other hand, a plurality of elongated backside grid electrodes 46a are arranged side by side on the backside that is the surface facing the light receiving surface in the semiconductor substrate 42, and the backside bus electrode 46b that is electrically connected to the backside grid electrode 46a is provided on the backside. It is provided so as to be orthogonal to the side grid electrode 46a, and is electrically connected to the back-side high-concentration dopant diffusion layer 47a of the n-type back-side dopant diffusion layer 47 at the bottom part. The back side grid electrode 46a and the back side bus electrode 46b are made of a silver material. The back-side grid electrode 46a and the back-side bus electrode 46b constitute a back-side electrode 46 that is a second electrode having a comb shape. Further, on the backside dopant diffusion layer 47, a backside passivation film 48 made of an insulating film is formed.

The n-type backside dopant diffusion layer 47 is an n-type dopant diffusion layer in which phosphorus is diffused as an n-type dopant in the surface layer on the backside of the semiconductor substrate 42. In the solar battery cell 41, two types of layers are formed as the n-type backside dopant diffusion layer 47 to form a selective diffusion structure. That is, in the surface layer portion on the back surface side of the n-type silicon substrate 42, the back-side high-concentration dopant diffusion layer in which the n-type dopant is relatively diffused in the lower region of the back-side electrode 46 and its peripheral region. 47a is formed. Further, in the surface layer portion on the back surface side of the n-type silicon substrate 42, the back surface side in which the n-type dopant is uniformly diffused at a relatively low concentration in a region where the back surface high-concentration dopant diffusion layer 47a is not formed. A low-concentration dopant diffusion layer 47b is formed. The back side high concentration dopant diffusion layer 47a is a low resistance diffusion layer having a lower electrical resistance than the back side low concentration dopant diffusion layer 47b. The back side low concentration dopant diffusion layer 47b is a high resistance diffusion layer having a higher electrical resistance than the back side high concentration dopant diffusion layer 47a. The back side dopant diffusion layer 47 is configured by the back side high concentration dopant diffusion layer 47a and the back side low concentration dopant diffusion layer 47b.

Therefore, if the dopant diffusion concentration of the back-side high-concentration dopant diffusion layer 47a is the third diffusion concentration and the dopant diffusion concentration of the back-side low-concentration dopant diffusion layer 47b is the fourth diffusion concentration, the fourth diffusion concentration is the third diffusion concentration. It becomes lower than the concentration. Further, when the electrical resistance value of the back-side high-concentration dopant diffusion layer 47a is the third electrical resistance value and the electrical resistance value of the back-side low-concentration dopant diffusion layer 47b is the fourth electrical resistance value, the fourth electrical resistance value is It becomes larger than the third electric resistance value.

In the solar cell 41 according to the fifth embodiment configured as described above, the back side low-concentration dopant diffusion layer 47b suppresses carrier recombination on the back side of the n-type silicon substrate 42 as a BSF layer. Therefore, a good open circuit voltage can be obtained. Moreover, since the back surface side high concentration dopant diffusion layer 47a reduces the contact resistance of the back surface side dopant diffusion layer 47 and the back surface side electrode 46, a favorable curve factor can be obtained.

Next, a method for manufacturing the solar battery cell 41 according to the fifth embodiment will be described with reference to FIGS. FIG. 39 is a flowchart showing a process flow of the method for manufacturing the solar battery cell 41 according to the fifth embodiment of the present invention. 40 to 49 are cross-sectional views of relevant parts for explaining manufacturing steps of the solar battery cell 41 according to the fifth embodiment of the present invention.

FIG. 40 is an explanatory diagram of step S401 and step S402 of FIG. In steps S401 and S402, the same processes as those in steps S101 and S102 of the first embodiment are performed except that the n-type silicon substrate 2 is used as the semiconductor substrate 42.

FIG. 41 is an explanatory diagram of step S403 in FIG. Step S403 is a process of performing thermal diffusion for forming a p-type dopant diffusion layer 43a on the surface of the n-type silicon substrate. Formation of the dopant diffusion layer 43a is realized by placing the n-type silicon substrate 42 on which the texture structure is formed in a thermal diffusion furnace and heat-treating it in the presence of boron tribromide (BBr ₃ ) vapor. Specifically, for example, a quartz glass boat on which 300 n-type silicon substrates 42 are placed at intervals of 3.5 mm is loaded into a quartz tube of a horizontal furnace heated to 750 ° C. While introducing 10 SLM of nitrogen, the temperature in the quartz tube is raised to 940 ° C., and the material gas is allowed to flow into the quartz tube for 10 minutes. The material gas is BBr ₃ vapor obtained by bubbling nitrogen gas through BBr ₃ sealed in a glass container.

After 10 minutes, the introduction of the material gas is stopped, the inside of the quartz tube is maintained at 940 ° C. for another 10 minutes, the temperature inside the quartz tube is lowered to 750 ° C., and the boat is taken out from the quartz tube. At this time, on the front and back surfaces of the n-type silicon substrate 42, a p-type dopant diffusion layer 43a in which boron is diffused at a uniform concentration in the surface direction of the n-type silicon substrate 42, and an impurity-containing glass containing an oxide film containing boron. A boron-containing glass layer 52 as a layer is formed in this order. In addition, the p-type dopant diffusion layer 43a thus obtained has a sheet resistance of about 90Ω / □ measured by the four-terminal method. A vertical furnace may be used instead of the horizontal furnace. In addition, a material other than BBr ₃ can be used as long as it is a p-type dopant. Note that the material gas, it is also possible to use materials other than BBr _3. Moreover, the dopant for forming the p-type dopant diffusion layer 43a may be any p-type dopant that can be used for forming the solar battery cell.

FIG. 42 is an explanatory diagram of step S404 of FIG. Step S404 is a step of removing the p-type dopant diffusion layer 43a and the boron-containing glass layer 52, which are dopant-containing layers formed on the back surface opposite to the light receiving surface in the n-type silicon substrate 42. Using a commercially available edge isolation device, the liquid level of the chemical solution stored in the chemical solution tank and mixed at a volume ratio of hydrofluoric acid: nitric acid: pure water = 1: 7: 3 is applied only to the back surface of the n-type silicon substrate 42. Wet the liquid and transport it with a roller. As a result, only the silicon on the back surface of the n-type silicon substrate 42 can be shaved to a depth of 2 μm.

By keeping the temperature of the chemical solution at 15 ° C. and providing an exhaust port above the n-type silicon substrate 42 to exhaust the generated gas, the chemical solution does not enter the surface of the n-type silicon substrate 42 and the dopant on the back surface. Only the containing layer can be removed. The n-type silicon substrate 42 that has passed through the chemical bath is washed with shower rinse, the surface alteration layer is removed with a 10% aqueous KOH solution at room temperature, further washed with shower rinse, and dried with an air knife. As a result, the p-type dopant diffusion layer 43a which is the dopant diffusion layer on the back surface of the n-type silicon substrate 42 is removed, and the p-type dopant diffusion layer 43a remaining on the surface of the n-type silicon substrate 42 becomes the p-type light-receiving surface. The side dopant diffusion layer 43 is formed.

FIG. 43 is an explanatory diagram of step S405 of FIG. Step S405 is a step of forming a phosphorus-containing oxide film 53 and a protective oxide film 54, which are back-surface oxide films, as second oxide films on the back-surface side of the n-type silicon substrate 42. Here, in the same manner as in step S303 in the fourth embodiment, a phosphorus-containing oxide film 53 that is a second lower oxide film having a thickness of 30 nm and a protective oxide film that is a second upper oxide film having a thickness of 120 nm are used. 54 are formed on the back surface side of the n-type silicon substrate 42 in this order. The phosphorus concentration in the phosphorus-containing oxide film 53 is lower than that of the phosphorus-containing dopant paste 14.

FIG. 44 is an explanatory diagram of step S406 of FIG. Step S406 is a step of selectively printing the phosphorus-containing dopant paste 14 as the backside dopant paste as the third diffusion source on the protective oxide film 54 on the backside of the n-type silicon substrate 42. Printing of the phosphorus-containing dopant paste 14 is performed in the same manner as in step S106 of the first embodiment. The printing pattern of the phosphorus-containing dopant paste 14 is a comb shape composed of a pattern in which linear patterns having a line width of 150 μm are arranged in parallel at intervals of 2 mm and a pattern in which four linear patterns having a line width of 1.2 mm are arranged in parallel. Pattern. After printing, the phosphorus-containing dopant paste 14 is dried at 250 ° C. for 5 minutes.

FIG. 45 is an explanatory diagram of step S407 of FIG. Step S407 is a process of heat-treating the n-type silicon substrate 42 on which the phosphorus-containing dopant paste 14 is printed. Specifically, a boat on which an n-type silicon substrate 42 is placed is placed in a horizontal furnace, and the n-type silicon substrate 42 is heat-treated at 960 ° C. for 15 minutes. By this heat treatment, phosphorus as a dopant component in the phosphorus-containing dopant paste 14 penetrates the protective oxide film 54 and the phosphorus-containing oxide film 53 and is thermally diffused into the n-type silicon substrate 42 immediately below the phosphorus-containing dopant paste 14. . Further, phosphorus in the phosphorus-containing oxide film 53 immediately below the phosphorus-containing dopant paste 14 is thermally diffused into the n-type silicon substrate 42 immediately below the phosphorus-containing dopant paste 14. As a result, on the surface layer of the n-type silicon substrate 42 immediately below the phosphorus-containing dopant paste 14, a back-side high-concentration dopant diffusion layer 47a that is a fourth dopant diffusion layer and has a sheet resistance of about 20Ω / □ is formed. The back-side high-concentration dopant diffusion layer 47 a is formed in the same comb-shaped pattern as the printing pattern of the phosphorus-containing dopant paste 14.

On the other hand, in the surface layer on the back surface side of the n-type silicon substrate 42, the dopant component of the phosphorus-containing dopant paste 14 does not diffuse in the region other than the region immediately below the phosphorus-containing dopant paste 14. However, phosphorus in the phosphorus-containing oxide film 53 is thermally diffused to the surface layer on the back surface side of the n-type silicon substrate 42 in a region other than the region immediately below the phosphorus-containing dopant paste 14. Then, a back side low-concentration dopant diffusion layer 47b having a sheet resistance of about 100Ω / □ is formed as a fifth dopant diffusion layer in which phosphorus is diffused at a uniform concentration in the surface direction of the n-type silicon substrate. Thereby, the back surface side dopant diffusion layer 47 which has the back surface side high concentration dopant diffusion layer 47a and the back surface side low concentration dopant diffusion layer 47b is formed.

In the fifth embodiment, the laminated film of the phosphorus-containing oxide film 53 that is an oxide film and the protective oxide film 54 is a diffusion source of phosphorus to the n-type silicon substrate 42 because the phosphorus-containing oxide film 53 contains phosphorus. Is the fourth diffusion source. In addition, this laminated film plays a role of preventing the dopant component volatilized from the phosphorus-containing dopant paste 14 from diffusing into the backside low-concentration dopant diffusion layer 47b. Also in this case, if the thickness of the laminated film is up to 200 nm, it is possible to diffuse the dopant from the phosphorus-containing dopant paste 14 to the n-type silicon substrate 42 through the laminated film. Since the phosphorus-containing oxide film 53 is protected by the protective oxide film 54, the phosphorus in the phosphorus-containing oxide film 53 can be prevented from volatilizing in the atmosphere during the heat treatment. It is possible to efficiently diffuse phosphorus into the substrate 42.

On the other hand, since the dopant component volatilized from the phosphorus-containing dopant paste 14 cannot penetrate the oxide film having a thickness of more than 50 nm, the protective oxide film 54 functions as a protective film. Therefore, the back-side low-concentration dopant diffusion layer 47b in which phosphorus is diffused at a uniform concentration that is not affected by the volatilization component from the phosphorus-containing dopant paste 14 is obtained.

Here, a protective oxide film 54 having a thickness of 120 nm is formed on the phosphorus-containing oxide film 53 as a capping film so that phosphorus is not volatilized from the phosphorus-containing oxide film 53 in the heat treatment process. The protective oxide film 54 may be formed to have a thickness of 150 nm. Even when only the phosphorus-containing oxide film 53 is provided with a thickness of 50 nm or more and 200 nm or less without forming the protective oxide film 54, the phosphorus-containing oxide film 53 has a dopant component volatilized from the phosphorus-containing dopant paste 14 on the back surface. It plays a role of preventing diffusion to the side low-concentration dopant diffusion layer 47b.

FIG. 46 is an explanatory diagram of step S408 of FIG. Step S408 is a step of removing the boron-containing glass layer 52, the protective oxide film 54, the phosphorus-containing oxide film 53, and the phosphorus-containing dopant paste 14 that are oxide films. The removal of the oxide film and the phosphorus-containing dopant paste 14 can be performed by immersing the n-type silicon substrate 42 in a 10% hydrofluoric acid aqueous solution for about 360 seconds.

FIG. 47 is an explanatory diagram of steps S409 and S410 of FIG. Step S409 is a process of forming the antireflection film 4. The antireflection film 4 is formed by forming a silicon nitride film having a refractive index of 2.1 and a film thickness of 80 nm on the light receiving surface side dopant diffusion layer 43 by the same method as in step S109 of the first embodiment. In the fifth embodiment, since the p-type light-receiving surface side dopant diffusion layer 43 is a p-type layer in which boron is diffused, an alumina film having a negative fixed charge is used to obtain good passivation performance. You can also Further, by forming the antireflection film 4 with a two-layer film in which an alumina film is laminated on the n-type silicon substrate 42 side and a silicon nitride film is laminated on the upper layer, both the field effect and the hydrogen termination effect can be obtained. it can. Step S 410 is a step of forming the back surface side passivation film 48. As the back surface side passivation film 48, a silicon nitride film is formed on the back surface side dopant diffusion layer 47 in the same manner as the antireflection film 4.

FIG. 48 is an explanatory diagram of step S411 in FIG. Step S411 is a process of printing an electrode. The electrodes are printed by the same method as in step S110 of the first embodiment, and the silver-containing paste 55 and the silver-aluminum-containing paste 56 containing Ag and Al are printed. In the fifth embodiment, the light-receiving surface side of the n-type silicon substrate 42 is a p-type light-receiving surface-side dopant diffusion layer 43 in which boron is diffused. Therefore, the light-receiving surface-side electrode 45 and the light-receiving surface-side dopant diffusion layer In order to maintain sufficient electrical continuity with 43, an Ag paste containing about 3% by weight of Al is used. The silver-containing paste 55 is printed on the back surface side passivation film 48 on the back surface of the n-type silicon substrate 42. The silver-aluminum-containing paste 56 is printed on the antireflection film 4 in the same comb-shaped pattern as in the first embodiment.

The printed pattern of the silver-containing paste 55 has the same comb shape as the back-side high-concentration dopant diffusion layer 47a, a pattern in which linear patterns with a line width of 50 μm are arranged in parallel at intervals of 2 mm, and four linear shapes with a line width of 1 mm. It is a comb-shaped pattern composed of patterns in which patterns are arranged in parallel. Further, the silver-containing paste 55 is printed at a position included in a region having a width of 150 μm and a region having a width of 1.2 mm of the pattern of the phosphorus-containing dopant paste 14 formed in step S406. That is, the silver-containing paste 55 is printed at a position included in a 150 μm wide region and a 1.2 mm wide region of the pattern of the back side high-concentration dopant diffusion layer 47a.

The printing position of the silver-containing paste 55 needs to be aligned with the pattern of the back side high-concentration dopant diffusion layer 47a. The printing position of the silver-containing paste 55 can be aligned by the method described in step S110 in the first embodiment. If the printing position of the silver-containing paste 55 is shifted, the back-side electrode 46 is formed on the back-side low-concentration dopant diffusion layer 47b, and the contact resistance between the back-side dopant diffusion layer 47 and the back-side electrode 46. As a result, the fill factor deteriorates, and the open circuit voltage deteriorates due to increased surface recombination of carriers. For this reason, it is important to align the printing position of the silver-containing paste 55 with the pattern of the back-side high-concentration dopant diffusion layer 47a.

FIG. 49 is an explanatory diagram of step S412 of FIG. Step S412 is a step of performing a heat treatment to form an electrode by baking a paste for forming an electrode. The electrode heat treatment is performed in the same manner as in step S111 of the first embodiment. Thereby, the resin component in a paste lose | disappears. Then, on the light receiving surface side, the glass particles contained in the silver-aluminum-containing paste 56 penetrate the silicon nitride film, and the Ag particles come into contact with the light receiving surface side dopant diffusion layer 43 to obtain electrical conduction. Thereby, the light-receiving surface side electrode 45 is obtained. On the back side, Ag particles contained in the silver-containing paste 55 come into contact with the back side high-concentration dopant diffusion layer 47a to obtain electrical conduction. Thereby, the back surface side electrode 46 is obtained.

By performing the above steps, a solar battery cell 41 having a uniform dopant concentration in the back-side low-concentration dopant diffusion layer 47b in the surface direction of the n-type silicon substrate 42 shown in FIGS. 36 to 38 can be obtained. .

The semiconductor substrate 42 may be a p-type single crystal silicon substrate or a p-type polycrystalline silicon substrate. In this case, the conductivity type of each member in the fifth embodiment may be reversed. Also in this case, by performing the above-described steps, a p-type backside low-concentration dopant diffusion layer having the configuration shown in FIGS. 36 to 38 and having a uniform dopant concentration in the plane direction of the p-type silicon substrate is provided. A solar battery cell can be obtained.

As described above, in the method for manufacturing a solar cell according to the fifth embodiment, a laminated film of the phosphorus-containing oxide film 53 and the protective oxide film 54 as an oxide film is formed on the back surface of the n-type silicon substrate 42 by 50 nm. A film thickness of 200 nm or less is formed. Then, the phosphorus-containing dopant paste 14 is printed in a predetermined pattern on the protective oxide film 54 and heat treatment is performed. Therefore, the back surface of the n-type silicon substrate 42 covered with the protective oxide film 54 is not diffused by the dopant component volatilized from the phosphorus-containing dopant paste 14, and the diffusion of the dopant component in the back-side low-concentration dopant diffusion layer 47 b. Concentration non-uniformity can be eliminated.

Thereby, according to the fifth embodiment, diffusion of the volatile component from the phosphorus-containing dopant paste 14 to the n-type silicon substrate 42 is prevented, and the back-side high-concentration dopant diffusion layer 47a and the n-type silicon substrate 42 are prevented. The solar battery cell 41 having a selective diffusion structure including the back-side low-concentration dopant diffusion layer 47b having a uniform dopant concentration in the surface direction can be efficiently obtained with a small number of steps. That is, variation in suppression of carrier recombination on the back surface of the n-type silicon substrate 42 as the BSF layer due to non-uniformity of the dopant concentration of the back-side low-concentration dopant diffusion layer 47b in the surface direction of the n-type silicon substrate 42 is prevented. Thus, the solar battery cell 41 having uniform power generation characteristics in the plane direction can be easily obtained.

Embodiment 6 FIG.
FIG. 50 is a schematic cross-sectional view of the relevant part showing a solar battery cell 61 according to the sixth embodiment of the present invention, and is a relevant part cross-sectional view corresponding to FIG. In addition, the same code | symbol is attached | subjected about the same member as the photovoltaic cell 41 concerning 5 embodiment. Moreover, since the structure seen from the upper surface and lower surface of the photovoltaic cell 61 is the same as the photovoltaic cell 41 concerning Embodiment 5, description is abbreviate | omitted with reference to FIG. 36 and FIG. The difference between the solar battery cell 61 and the solar battery cell 41 according to the fifth embodiment is the configuration of the light-receiving surface side dopant diffusion layer. Therefore, below, the light-receiving surface side dopant diffusion layer different from the photovoltaic cell 41 is demonstrated.

In the solar cell 61 according to the sixth embodiment, a p-type light-receiving surface side dopant diffusion layer 63 in which boron (B) is diffused is formed on the entire light-receiving surface of the n-type semiconductor substrate 42, and a pn junction is formed. A semiconductor substrate 71 is formed. An antireflection film 4 made of an insulating film is formed on the light receiving surface side dopant diffusion layer 63.

In the solar battery cell 61, two types of layers are formed as the p-type light-receiving surface side dopant diffusion layer 63 to form a selective emitter structure. That is, in the surface layer portion on the light receiving surface side of the n-type silicon substrate 42, the light receiving surface side high concentration in which the p-type dopant is relatively diffused in the lower region of the light receiving surface side electrode 45 and its peripheral region. A dopant diffusion layer 63a is formed. In the surface layer portion of the n-type silicon substrate 42 on the light-receiving surface side, a light-receiving surface in which the p-type dopant is diffused at a relatively low concentration in a region where the light-receiving surface-side high-concentration dopant diffusion layer 63a is not formed. A side low-concentration dopant diffusion layer 63b is formed. The light receiving surface side high concentration dopant diffusion layer 63a is a low resistance diffusion layer having a lower electrical resistance than the light receiving surface side low concentration dopant diffusion layer 63b. The light receiving surface side low concentration dopant diffusion layer 63b is a high resistance diffusion layer having a higher electrical resistance than the light receiving surface side high concentration dopant diffusion layer 63a.

Therefore, if the dopant diffusion concentration of the light receiving surface side high concentration dopant diffusion layer 63a is the fifth diffusion concentration and the dopant diffusion concentration of the light receiving surface side low concentration dopant diffusion layer 63b is the sixth diffusion concentration, the sixth diffusion concentration is It becomes lower than 5 diffusion density. Further, if the electric resistance value of the light receiving surface side high concentration dopant diffusion layer 63a is the fifth electric resistance value and the electric resistance value of the light receiving surface side low concentration dopant diffusion layer 63b is the sixth electric resistance value, the sixth electric resistance value is obtained. Becomes larger than the fifth electric resistance value.

In the solar battery cell 61 according to the sixth embodiment configured as described above, the light receiving surface side high-concentration dopant diffusion layer 63a has a contact resistance between the light receiving surface side dopant diffusion layer 63 and the light receiving surface side electrode 45. Since it reduces, a favorable fill factor can be obtained. In addition, the light receiving surface side low-concentration dopant diffusion layer 63b reduces the recombination rate of carriers on the light receiving surface side of the n-type silicon substrate.

Next, a method for manufacturing the solar battery cell 61 according to the sixth embodiment will be described with reference to FIGS. FIG. 51 is a flowchart showing a process flow of the method for manufacturing the solar battery cell 61 according to the sixth embodiment of the present invention. 52 to 61 are cross-sectional views of relevant parts for explaining the manufacturing steps of the solar battery cell 61 according to the sixth embodiment of the present invention.

FIG. 52 is an explanatory diagram of steps S501 and S502 of FIG. In steps S501 and S502, the same processes as those in steps S101 and S102 of the first embodiment are performed except that the n-type silicon substrate 42 is prepared as a semiconductor substrate.

FIG. 53 is an explanatory diagram of step S503 in FIG. In step S503, a boron-containing oxide film 64 and a protective oxide film 65 are formed on the light receiving surface side of the n-type silicon substrate 42 as the light receiving surface side oxide film. Here, a silicon oxide film is formed by an atmospheric pressure CVD method using silane, oxygen, and diborane (B ₂ H ₆ ) as material gases. Specifically, the n-type silicon substrate 42 heated to about 450 ° C. to 550 ° C. is exposed to a mixed atmosphere of silane, oxygen, and diborane at atmospheric pressure, so that the n-type silicon substrate 42 first has a light-receiving surface side. Then, a boron-containing oxide film 64 having a thickness of 30 nm containing boron is formed. Thereafter, the mixing of diborane is stopped, and the n-type silicon substrate 42 is exposed in a mixed atmosphere of silane and oxygen, so that the protective oxide film 65 having a thickness of 120 nm not containing boron is changed to a boron-containing oxide film 64. Form on top. The boron-containing concentration in the boron-containing oxide film 64 is lower than that of the boron-containing dopant paste 66.

Here, a protective oxide film 65 having a thickness of 120 nm is formed on the boron-containing oxide film 64 as a capping film so that boron is not volatilized from the boron-containing oxide film 64 in the atmosphere in the heat treatment process. The protective oxide film 65 may not be formed with a thickness of 150 nm. Even when only the boron-containing oxide film 64 is provided with a film thickness of 50 nm or more and 200 nm or less without forming the protective oxide film 65, the boron-containing oxide film 64 is a dopant component volatilized from a boron-containing dopant paste 66 described later. Plays a role of preventing diffusion to the light receiving surface side low concentration dopant diffusion layer 63b.

FIG. 54 is an explanatory diagram of step S504 in FIG. Step S504 is a step of forming a phosphorus-containing oxide film 53 and a protective oxide film 54, which are back-surface oxide films, on the back surface side of the n-type silicon substrate 42. Here, the phosphorous-containing oxide film 53 having a thickness of 30 nm and the protective oxide film 54 having a thickness of 120 nm are formed in this order in the same manner as in step S303 in FIG. 27 in the fourth embodiment. It is formed on the back side. Here, in order to prevent boron from being volatilized in the atmosphere in the subsequent heat treatment process, a protective oxide film 54 having a thickness of 120 nm is deposited on the phosphorus-containing oxide film 53 as a capping film. The protective oxide film 54 may not be formed by setting 53 to 150 nm.

FIG. 55 is an explanatory diagram of step S505 of FIG. Step S505 is a step of selectively printing a boron-containing dopant paste 66 as a light-receiving surface side dopant paste on the protective oxide film 65 on the light-receiving surface side of the n-type silicon substrate 42. Here, as the boron-containing dopant paste 66, a resin paste containing boron oxide is printed on the protective oxide film 65 using a screen printing method. The printed pattern of the boron-containing dopant paste 66 is a comb-shaped pattern composed of a pattern in which linear patterns with a line width of 150 μm are arranged in parallel at intervals of 2 mm and a pattern in which four linear patterns with a line width of 1.2 mm are arranged in parallel. Pattern. After printing, the boron-containing dopant paste 66 is dried at 250 ° C. for 5 minutes. The printing method of the boron-containing dopant paste 66 is not limited to the screen printing method, and an ink jet method or a method of directly discharging from a nozzle can be used.

FIG. 56 is an explanatory diagram of step S506 in FIG. Step S506 is a step of selectively printing the phosphorus-containing dopant paste 14 as the backside dopant paste on the protective oxide film 54 on the backside of the n-type silicon substrate 42. The phosphorus-containing dopant paste 14 is printed by the same method as in the first embodiment. The printing pattern of the phosphorus-containing dopant paste 14 is a comb shape composed of a pattern in which linear patterns having a line width of 150 μm are arranged in parallel at intervals of 2 mm and a pattern in which four linear patterns having a line width of 1.2 mm are arranged in parallel. Pattern. After printing, the phosphorus-containing dopant paste 14 is dried at 250 ° C. for 5 minutes.

FIG. 57 is an explanatory diagram of step S507 in FIG. Step S507 is a process of heat-treating the n-type silicon substrate 42 on which the boron-containing dopant paste 66 and the phosphorus-containing dopant paste 14 are printed. Specifically, a boat on which an n-type silicon substrate 42 is placed is placed in a horizontal furnace, and the n-type silicon substrate 42 is heat-treated at 960 ° C. for 15 minutes.

By this heat treatment, boron, which is a dopant component in the boron-containing dopant paste 66, penetrates the protective oxide film 65 and the boron-containing oxide film 64 directly below the boron-containing dopant paste 66 on the light-receiving surface side of the n-type silicon substrate 42. The n-type silicon substrate 42 is thermally diffused. Further, boron in the boron-containing oxide film 64 immediately below the boron-containing dopant paste 66 is thermally diffused into the n-type silicon substrate 42 immediately below the boron-containing dopant paste 66. As a result, a light-receiving surface side high-concentration dopant diffusion layer 63 a having a sheet resistance of about 30 Ω / □ is formed on the surface layer of the n-type silicon substrate 42 immediately below the boron-containing dopant paste 66. The light-receiving surface side high-concentration dopant diffusion layer 63 a is formed in the same comb-shaped pattern as the printing pattern of the boron-containing dopant paste 66.

On the other hand, in the surface layer on the light-receiving surface side of the n-type silicon substrate 42, the dopant component of the boron-containing dopant paste 66 does not diffuse in the region other than the region immediately below the boron-containing dopant paste 66. However, the boron in the boron-containing oxide film 64 is thermally diffused into the surface layer on the back surface side of the n-type silicon substrate 42 in the region other than the region immediately below the boron-containing dopant paste 66. Then, a light-receiving surface side low-concentration dopant diffusion layer 63b having a sheet resistance of about 90Ω / □ is formed in which boron is diffused at a uniform concentration in the surface direction of the n-type silicon substrate. As a result, the light receiving surface side dopant diffusion layer 63 of the selective emitter structure having the light receiving surface side high concentration dopant diffusion layer 63a and the light receiving surface side low concentration dopant diffusion layer 63b is formed.

In the sixth embodiment, the boron-containing oxide film 64 that is an oxide film and the protective oxide film 65 are formed of a boron diffusion source to the n-type silicon substrate 42 because the boron-containing oxide film 64 contains boron. It becomes. In addition, this laminated film plays a role of preventing the dopant component volatilized from the boron-containing dopant paste 66 from diffusing into the light receiving surface side low-concentration dopant diffusion layer 63b. Also in this case, if the thickness of the laminated film is up to 200 nm, the dopant can be diffused from the boron-containing dopant paste 66 to the n-type silicon substrate 42 through the laminated film. Since the boron-containing oxide film 64 is protected by the protective oxide film 65, the boron in the boron-containing oxide film 64 can be prevented from volatilizing in the atmosphere during the heat treatment. Boron can be efficiently diffused into the substrate 42.

Further, on the back surface side of the n-type silicon substrate 42, in the surface direction of the n-type silicon substrate 42 and the back-side high-concentration dopant diffusion layer 47a having a sheet resistance of about 20Ω / □, as in step S407 of the fifth embodiment. A back-side low-concentration dopant diffusion layer 47b having a sheet resistance of about 100Ω / □ in which phosphorus is diffused at a uniform concentration is formed. Thereby, the back surface selective diffusion BSF layer which consists of the back surface side dopant diffusion layer 47 which has the back surface side high concentration dopant diffusion layer 47a and the back surface side low concentration dopant diffusion layer 47b is formed. Accordingly, the selective emitter structure on the light receiving surface side and the back surface selective diffusion BSF layer can be formed simultaneously by one heat treatment.

FIG. 58 is an explanatory diagram of step S508 of FIG. Step S508 is a process of removing the dopant paste and the oxide film. In this step, the phosphorus-containing dopant paste 14 and the boron-containing dopant paste 66 are removed. Further, the protective oxide film 65, the boron-containing oxide film 64, the protective oxide film 54, and the phosphorus-containing oxide film 53, which are oxide films, are removed. The removal of the oxide film and the phosphorus-containing dopant paste 14 can be performed by immersing the n-type silicon substrate 42 in a 10% hydrofluoric acid aqueous solution for about 360 seconds.

FIG. 59 is an explanatory diagram of steps S509 and S510 of FIG. Step S509 is a step of forming the antireflection film 4 on the light receiving surface side dopant diffusion layer 63. The formation of the antireflection film 4 is performed in the same manner as in step S409 of the fifth embodiment. Step S 510 is a step of forming the back surface side passivation film 48. As the back surface side passivation film 48, a silicon nitride film is formed on the back surface side dopant diffusion layer 47 in the same manner as the antireflection film 4.

FIG. 60 is an explanatory diagram of step S511 of FIG. Step S511 is a process of printing an electrode. The electrode printing is performed in the same manner as step S411 in the fifth embodiment. The printed pattern of the silver-aluminum-containing paste 56 has the same comb shape as the light-receiving surface side high-concentration dopant diffusion layer 63a, and a pattern in which linear patterns with a line width of 50 μm are arranged in parallel at intervals of 2 mm and 4 with a line width of 1 mm. This is a comb-shaped pattern composed of a pattern in which linear patterns of books are arranged in parallel. Further, the silver-aluminum-containing paste 56 is printed at a position included in a region having a width of 150 μm and a region having a width of 1.2 mm of the pattern of the boron-containing dopant paste 66 formed in step S505. That is, the silver-aluminum-containing paste 56 is printed at a position included in a 150 μm wide region and a 1.2 mm wide region of the pattern of the light receiving surface side high concentration dopant diffusion layer 63a.

The printing position of the silver-aluminum-containing paste 56 needs to be aligned with the pattern of the light receiving surface side high-concentration dopant diffusion layer 63a. The alignment of the printing position of the silver-aluminum-containing paste 56 can be performed by the method described in the description of step S110 in the first embodiment.

FIG. 61 is an explanatory diagram of step S512 of FIG. Step S512 is a step of performing a heat treatment to form an electrode by firing an electrode forming paste. The electrode heat treatment is performed in the same manner as in step S111 of the first embodiment. Thereby, the resin component in a paste lose | disappears. On the light receiving surface side, the glass particles contained in the silver-aluminum-containing paste 56 penetrate the silicon nitride film, and the Ag particles come into contact with the light receiving surface side high-concentration dopant diffusion layer 63a to obtain electrical conduction. Thereby, the light-receiving surface side electrode 45 is obtained. On the back side, Ag particles contained in the silver-containing paste 55 come into contact with the back side high-concentration dopant diffusion layer 47a to obtain electrical conduction. Thereby, the back surface side electrode 46 is obtained.

By performing the above steps, the p-type light-receiving surface side low-concentration dopant diffusion layer 63b having a uniform dopant concentration in the surface direction of the n-type silicon substrate 42 and the surface of the n-type silicon substrate 42 shown in FIG. A solar cell 61 having a p-type back-side low-concentration dopant diffusion layer 47b having a uniform dopant concentration in the direction can be obtained.

The semiconductor substrate 42 may be a p-type single crystal silicon substrate or a p-type polycrystalline silicon substrate. In this case, the conductivity type of each member in the sixth embodiment may be reversed. Also in this case, an n-type light-receiving surface side low-concentration dopant diffusion layer having a configuration shown in FIG. 50 and having a uniform dopant concentration in the surface direction of the p-type silicon substrate by performing the above-described steps, and p-type A p-type back-side low-concentration dopant diffusion layer having a uniform dopant concentration in the surface direction of the silicon substrate can be obtained. That is, a light-receiving surface side selective emitter layer including a low-concentration dopant diffusion layer having a uniform dopant concentration in the plane direction of the p-type silicon substrate, and a low-concentration dopant diffusion layer having a uniform dopant concentration in the plane direction of the p-type silicon substrate. The selective diffusion BSF structure on the back side can be formed simultaneously by one heat treatment.

In the above-described sixth embodiment, diffusion of the volatile component of the dopant paste during the heat treatment to the low-concentration dopant diffusion layer is prevented, and low-concentration dopant diffusion with a uniform dopant concentration in the plane direction of the n-type silicon substrate 42 is performed. The selective emitter structure including the layers and the selective diffusion BSF layer including the low-concentration dopant diffusion layer having a uniform dopant concentration in the plane direction of the n-type silicon substrate 42 can be simultaneously formed by one heat treatment. Therefore, according to the sixth embodiment, the solar battery cell 61 having the light receiving surface side selective emitter structure and the back surface side selective diffusion BSF layer can be efficiently formed with a small number of steps.

Embodiment 7 FIG.
In the seventh embodiment, a modification of the solar cell manufacturing method according to the third embodiment will be described with reference to FIGS. FIG. 62 is a flowchart showing a process flow of a method for manufacturing a solar battery cell according to the seventh embodiment of the present invention. 63 to 67 are cross-sectional views of relevant parts for explaining the manufacturing process of the solar cell according to the seventh embodiment of the present invention. 62, the same steps as those in FIGS. 3 and 22 are denoted by the same reference numerals. In FIGS. 63 to 67, the same members as those in the above-described embodiment are denoted by the same reference numerals.

In the solar cell manufacturing method according to the seventh embodiment, in the flowchart of FIG. 22 in the third embodiment, instead of performing the thermal diffusion and the protective oxide film formation in step S201, the ion implantation in step S701 is performed. In step S702, thermal diffusion and protective oxide film formation are performed.

In Embodiment 7 of the present invention, first, Step S101 and Step S102 are performed in the same manner as in Embodiment 1.

FIG. 63 is an explanatory diagram of step S701 in FIG. Step S701 is a step of forming an ion implantation layer 81 by implanting phosphorus ions, which are the first dopant, by ion implantation on one surface of the p-type silicon substrate 2 on the light receiving surface side. In phosphorus implantation by the ion implantation method, the material gas is PH ₃ gas, the implantation energy is 6.5 keV, and the ion dose is 5 × 10 ¹⁵ (atoms / cm ² ).

FIG. 64 is an explanatory diagram of step S702 of FIG. Step S702 heat-treats the p-type silicon substrate 2 in which phosphorus has been implanted into one surface by an ion implantation method, so that phosphorus implanted into the ion implanted layer 81 at a higher concentration than the light receiving surface side low-concentration dopant diffusion layer 3b. This is a step of diffusing from the surface layer of the p-type silicon substrate 2 in the depth direction of the p-type silicon substrate 2, that is, in the inner direction of the p-type silicon substrate 2. Specifically, for example, a quartz glass boat on which 300 p-type silicon substrates 2 are placed at intervals of 3.5 mm is loaded into a quartz tube of a horizontal furnace heated to 750 ° C. The temperature inside the quartz tube is raised to 900 ° C. while introducing nitrogen, and when the temperature in the quartz tube reaches 900 ° C., oxygen is allowed to flow into the quartz tube for 30 minutes and held for 30 minutes. Thereafter, the inside of the quartz tube is heated to 1050 ° C. while introducing oxygen, and is further maintained for 70 minutes. Thereafter, the introduction of oxygen is stopped, and the gas introduced into the quartz tube is switched to nitrogen. Then, after the temperature in the quartz tube is lowered to 750 ° C., the boat is taken out from the quartz tube.

At this time, phosphorus is diffused at a uniform concentration in the surface layer on the surface of the p-type silicon substrate 2, that is, on the light-receiving surface side of the p-type silicon substrate 2, for example, low-concentration dopant diffusion with a sheet resistance of 90Ω / □. Layer 82 is formed. Further, a protective oxide film 83 is formed on the low concentration dopant diffusion layer 82. A protective oxide film 83 is formed on the back surface of the p-type silicon substrate 2. Thereby, for example, a protective oxide film 83 having a film thickness of 65 nm can be obtained.

FIG. 65 is an explanatory diagram of step S202 of FIG. Step S202 is a step of selectively printing the phosphorus-containing dopant paste 14 on the protective oxide film 83 on the light receiving surface side. The phosphorus-containing dopant paste 14 is printed in the same manner as in the third embodiment.

FIG. 66 is an explanatory diagram of step S203 of FIG. Step S203 is a process of heat-treating the p-type silicon substrate 2 on which the phosphorus-containing dopant paste 14 is printed. The p-type silicon substrate 2 is heat-treated at about 960 ° C. for 10 minutes as in step S203 of the third embodiment. By this heat treatment, phosphorus in the phosphorus-containing dopant paste 14 is thermally diffused into the p-type silicon substrate 2 directly below the phosphorus-containing dopant paste 14 through the protective oxide film 83, and the light-receiving surface side high-concentration dopant diffusion layer 3a is formed. That is, phosphorus in the phosphorus-containing dopant paste 14 penetrates the protective oxide film 83 and diffuses into the low-concentration dopant diffusion layer 82 and the p-type silicon substrate 2 in the region immediately below the phosphorus-containing dopant paste 14 to receive the light receiving surface. A high concentration dopant diffusion layer 3a is formed.

On the other hand, the protective oxide film 83 prevents the diffusion of the dopant component volatilized from the phosphorus-containing dopant paste 14 during the heat treatment into the low-concentration dopant diffusion layer 82. That is, in the low-concentration dopant diffusion layer 82 on the light-receiving surface side, the region other than the region immediately below the phosphorus-containing dopant paste 14 does not diffuse phosphorus as a dopant component from the phosphorus-containing dopant paste 14, and the sheet resistance is 90Ω / □ It remains about the same level. Therefore, in the low concentration dopant diffusion layer 82 on the light receiving surface side of the p-type silicon substrate 2, the light receiving surface side high concentration dopant diffusion layer 3 a is formed immediately below the phosphorus-containing dopant paste 14, and the light receiving surface side high concentration dopant diffusion is formed. The region where the layer 3a is not formed becomes the light receiving surface side low-concentration dopant diffusion layer 3b.

FIG. 67 is an explanatory diagram of step S703 in FIG. Step S204 is a process of removing the protective oxide film 83 and the phosphorus-containing dopant paste 14. The protective oxide film 83 and the phosphorus-containing dopant paste 14 can be removed by immersing the p-type silicon substrate 2 in a 10% hydrofluoric acid aqueous solution, as in the third embodiment. The state of the p-type silicon substrate 2 after step S204 is such that there is no low-concentration dopant diffusion layer 3c on the back side of the p-type silicon substrate 2 after step S204 of the third embodiment. That is, the light-receiving surface side high-concentration dopant diffusion layer 3a and the light-receiving surface-side high concentration dopant diffusion layer 3a are formed on the surface layer of the surface of the p-type silicon substrate 2, that is, the surface layer on the light-receiving surface side of the p-type silicon substrate 2. A light-receiving surface side low-concentration dopant diffusion layer 3b, which is a second dopant diffusion layer formed in a region not formed and phosphorous is diffused at a uniform concentration lower than that of the first dopant diffusion layer, is formed.

Thereafter, as in the case of the third embodiment, by performing steps S109 to S111, the light receiving surface side low-concentration dopant diffusion layer 3b in the surface direction of the p-type silicon substrate 2 shown in FIGS. Can obtain a solar battery cell 1 having a uniform dopant concentration.

According to the above-described seventh embodiment, the light-receiving surface with higher in-plane dopant concentration uniformity in the plane direction of the p-type silicon substrate 2 by combining ion implantation and heat treatment for forming the low-concentration dopant diffusion layer 82. The side low concentration dopant diffusion layer 3b can be obtained. Therefore, it is possible to manufacture a solar cell in which the in-plane uniformity of the dopant concentration in the low concentration diffusion region is more uniform in the plane of the semiconductor substrate.

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, or can be combined with the technique of the above embodiment. In addition, a part of the configuration can be omitted or changed without departing from the gist of the present invention.

1 solar cell, 2 semiconductor substrate, 3 light receiving surface side dopant diffusion layer, 3a light receiving surface side high concentration dopant diffusion layer, 3b light receiving surface side low concentration dopant diffusion layer, 3c, 82 low concentration dopant diffusion layer, 4 antireflection film 5, 5 light receiving surface side electrode, 5a light receiving surface side grid electrode, 5b light receiving surface side bus electrode, 6 back surface side electrode, 7 back surface side BSF layer, 11 semiconductor substrate, 12 phosphorus-containing glass layer, 13, 83 protective oxide film, 14 phosphorus-containing dopant paste, 15 aluminum-containing paste, 16 silver-containing paste, 31 phosphorus-containing oxide film, 32 protective oxide film, 41 solar cell, 42 semiconductor substrate, 43 light-receiving surface side dopant diffusion layer, 43a dopant diffusion layer, 45 Light receiving surface side electrode, 45a Light receiving surface side grid electrode, 45b Light receiving surface side bus power , 46 Back side electrode, 46a Back side grid electrode, 46b Back side bus electrode, 47 Back side dopant diffusion layer, 47a Back side high concentration dopant diffusion layer, 47b Back side low concentration dopant diffusion layer, 48 Back side passivation film, 51 Semiconductor substrate, 52 boron-containing glass layer, 53 phosphorus-containing oxide film, 54 protective oxide film, 55 Ag-containing paste, 56 silver-aluminum-containing paste, 61 solar cell, 63 light-receiving surface side dopant diffusion layer, 63a light-receiving surface side high Concentration dopant diffusion layer, 63b light-receiving surface side low concentration dopant diffusion layer, 64 boron-containing oxide film, 65 protective oxide film, 66 boron-containing dopant paste, 71 semiconductor substrate, 81 ion implantation layer.

Claims

A first step of forming a first oxide film having a thickness of more than 50 nm and not more than 200 nm on a first surface of a first conductivity type semiconductor substrate;
A second step of selectively forming a first diffusion source containing a first dopant on the first oxide film;
Heat-treating the semiconductor substrate on which the first diffusion source is formed to form a first dopant diffusion layer in which the first dopant is diffused in a region immediately below the first diffusion source in the surface layer of the first surface; 3 steps,
A fourth step of forming an electrode on the first dopant diffusion layer;
The manufacturing method of the solar cell characterized by including.
After the third step, a second dopant diffusion layer in which the first dopant is diffused in a region other than the first dopant diffusion layer in the surface layer of the first surface at a concentration lower than that of the first dopant diffusion layer. Including a fifth step of forming
The manufacturing method of the solar cell of Claim 1 characterized by these.
Before the first step, including a sixth step of forming a second dopant diffusion layer in which the first dopant is diffused at a lower concentration than the first dopant diffusion layer on the surface layer of the first surface,
In the first step, the first oxide film is formed on the second dopant diffusion layer,
Forming the first dopant diffusion layer in a region immediately below the first diffusion source in the second dopant diffusion layer in the third step;
The manufacturing method of the solar cell of Claim 1 characterized by these.
The first step is performed continuously after the sixth step by changing the heat treatment conditions in one heat treatment step;
The manufacturing method of the solar cell of Claim 3 characterized by these.
In the sixth step, the second dopant diffusion layer is formed by implanting ions of the first dopant into the surface layer of the first surface and then heat-treating the semiconductor substrate.
The manufacturing method of the solar cell of Claim 3 characterized by these.
The first oxide film is a second diffusion source containing the first dopant at a lower concentration than the first diffusion source,
In the third step, the first layer at a lower concentration than the first dopant diffusion layer in a region immediately below the second diffusion source in the surface layer of the first surface and in a region other than the first dopant diffusion layer. Forming a third dopant diffusion layer in which the dopant is diffused;
The manufacturing method of the solar cell of Claim 1 characterized by these.
In the first step, a step of forming a first lower oxide film containing the first dopant at a concentration lower than that of the first diffusion source on the first surface, and a surface layer of the first oxide film and including the dopant Forming a non-first upper oxide film on the upper layer of the first lower oxide film,
The method for producing a solar cell according to claim 6.
The first dopant is a dopant of a second conductivity type;
The method for producing a solar cell according to claim 6 or 7, wherein:
The first dopant is a first conductivity type dopant;
The method for producing a solar cell according to claim 6 or 7, wherein:
Before the third step, including a seventh step of forming a second oxide film having a thickness of greater than 50 nm and less than or equal to 200 nm on the second surface of the semiconductor substrate facing the first surface;
The method for manufacturing a solar cell according to claim 1, wherein:
An eighth step of selectively forming a third diffusion source containing a second dopant on the second oxide film between the seventh step and the third step;
Forming a fourth dopant diffusion layer in which the second dopant is diffused in a region immediately below the third diffusion source in the surface layer of the second surface in the third step;
The method for manufacturing a solar cell according to claim 10.
The second oxide film is a fourth diffusion source containing the second dopant at a lower concentration than the third diffusion source;
In the third step, the second dopant is lower than the fourth dopant diffusion layer in a region immediately below the fourth diffusion source in the surface layer of the second surface and other than the fourth dopant diffusion layer. Forming a fifth dopant diffusion layer diffused in concentration;
The method for manufacturing a solar cell according to claim 11.
In the seventh step, a step of forming a second lower oxide film containing the second dopant at a lower concentration than the third diffusion source on the second surface, and a surface layer of the second oxide film and including the dopant Forming a non-second upper oxide film on the upper layer of the second lower oxide film,
The method for producing a solar cell according to claim 12.
The first dopant is a second conductivity type dopant, and the second dopant is a first conductivity type dopant;
The method for manufacturing a solar cell according to claim 12 or 13, wherein:
The first dopant is a first conductivity type dopant, and the second dopant is a second conductivity type dopant;
The method for manufacturing a solar cell according to claim 12 or 13, wherein: