JP2003158277A - Method for manufacturing solar cell - Google Patents

Abstract

(57) [Abstract] [Problem] To uniformize the characteristics of solar cells,
Provided is a method for manufacturing a solar battery cell having a small leak current and a large output power. SOLUTION: In a furnace in which an inert gas flows, a plurality of P
The mold silicon wafer is heated. By causing the inert gas to flow down, the phosphorus vaporized from the diffusion processing film can be discharged out of the furnace. This prevents the vaporized phosphorus from remaining in the furnace and reduces the phosphorus concentration in the furnace. This prevents the vaporized phosphorus from diffusing to the surface of the P-type silicon wafer other than on one side in the thickness direction, makes it possible to form a good PN junction, and reduces the increase in leakage current. it can.
Further, by supplying an inert gas having a maximum flow rate within a predetermined temperature range, it is possible to prevent the temperature unevenness in the furnace from increasing, and to make the characteristics of the manufactured solar cell uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solar battery cell in which an impurity semiconductor layer is formed on a semiconductor substrate. In addition, in the present specification, the “inert gas” includes a gas including nitrogen, an element belonging to Group 0 of the periodic table, which is argon, neon, helium, krypton, xenon, and radon.

[0002]

2. Description of the Related Art In a solar cell, a second semiconductor layer is formed on a surface portion of a first conductivity type semiconductor substrate, and a PN junction portion is formed. In the conventional solar cell manufacturing method, in order to form a PN junction portion on a P-type conductive semiconductor substrate (hereinafter referred to as a P-type semiconductor substrate), an N-type surface is formed on one surface of the P-type semiconductor substrate. A type semiconductor layer is formed. N
The type semiconductor layer is formed by a method of thermally diffusing N-type conductivity type impurities such as a vapor phase diffusion method using POCl ₃ or a coating diffusion method using P ₂ O ₅ and ionizing the N-type conductivity type impurities. Then, an ion implantation method or the like that accelerates and implants into the P-type semiconductor substrate is used. Among them, the thermal diffusion method has the features that the structure of the device is simple, the handling is easy, and the cost is low.

A first conventional solar cell manufacturing method using such a thermal diffusion method includes a coating step and a thermal diffusion step. In the coating step, a diffusion treatment agent containing P ₂ O ₅ which is an N-type conductivity type impurity as a main component is formed on one surface in the thickness direction of the P-type silicon wafer, which is a light receiving surface when configured as a solar cell. This is the step of applying. The thermal diffusion step is a step of heating the P-type silicon wafer after being coated with the diffusion treatment agent in a diffusion furnace for a certain period of time. The thermal diffusion step may be performed in an atmosphere in which a small amount of nitrogen is flowed in order to make the diffusion temperature condition in the furnace uniform.

In the thermal diffusion process, phosphorus contained in the diffusion treatment agent permeates from the surface on one side in the thickness direction of the P-type silicon wafer into the inside of the P-type silicon wafer, and the N-type semiconductor is formed on one side in the thickness direction of the P-type silicon wafer. Form the layers. As a result, a PN junction portion where the P-type semiconductor portion of the P-type semiconductor substrate and the N-type semiconductor layer are adjacent to each other is formed.

During the heating step, a part of phosphorus contained in the diffusion treatment agent is vaporized by heating. The vaporized phosphorus wraps around and adheres to the other surface of the P-type silicon wafer in the thickness direction, and an out diffusion phenomenon occurs in which the phosphorus diffuses on the other surface side in the thickness direction. Due to the out diffusion, phosphorus permeates inward from the other side in the thickness direction of the P-type silicon wafer and reaches the PN junction. The semiconductor portion containing phosphorus becomes an N-type semiconductor. Therefore PN
The N-type semiconductor portion is formed on the P-type semiconductor layer formation side of the junction portion, the ratio of the P-type semiconductor portion decreases, and the PN junction portion cannot be formed well.

As described above, in the first conventional manufacturing method, the ratio of the P-type semiconductor portion on the P-type semiconductor layer forming side in the PN junction portion decreases. In the solar cell manufactured by this, the output current decreases as the leak current increases, and the characteristics of the solar cell deteriorate significantly.

As a second conventional method of manufacturing a solar battery cell, a technique of performing the thermal diffusion step in an atmosphere containing hydrogen chloride is disclosed in, for example, Japanese Patent Laid-Open No. 54-64985. The phosphorus vaporized from the diffusion treatment agent reacts with chlorine in the atmosphere to form a compound of phosphorus and chlorine, which traps the vaporized phosphorus. This prevents phosphorus from wrapping around to the other side in the thickness direction of the P-type silicon wafer.

As a third prior art method of manufacturing a solar battery cell, there is a method of applying a diffusion inhibitor containing titanium to the surface of the P-type silicon wafer opposite to the light receiving surface. By heating the silicon wafer to which the diffusion preventing agent is attached, a diffusion preventing film of a TiO ₂ film containing titanium is formed at the diffusion preventing agent coated portion of the silicon wafer. The diffusion prevention film serves as a mask for preventing diffusion. The phosphorus vaporized in the thermal diffusion process adheres to the diffusion barrier film. This prevents phosphorus from directly adhering to the diffusion prevention film adhesion portion of the P-type silicon wafer, and prevents diffusion from occurring in the diffusion prevention film adhesion portion of the P-type silicon wafer.
Such a conventional technique is disclosed, for example, in JP-A-59-182.
No. 577, and the applicant of the present application also discloses, for example, Japanese Patent Application No. 63-184396 and Japanese Patent Application No. 3-17.
The technology disclosed in Japanese Patent No. 703 has already been proposed and implemented.

[0009]

In the second conventional method for manufacturing a solar cell, hydrogen chloride is an active element and chemically reacts with impurities vaporized from the diffusion treatment agent. A compound is produced by such a chemical reaction. Therefore, chlorine and chlorine compounds may adhere to the semiconductor substrate after the thermal diffusion process. Therefore, it is necessary to perform a step of removing chlorine and chlorine compounds as the next step, which causes a problem that the number of steps is increased. Further, chlorine or a chlorine compound remaining on the semiconductor substrate adversely affects the manufacturing process of the solar battery cell after the thermal diffusion process, and there is a problem that the performance of the solar battery cell deteriorates.

In order to improve the productivity of solar cells,
The thermal diffusion process may be performed with a plurality of semiconductor substrates housed in a diffusion furnace. For example, in the thermal diffusion process that the applicant of the present invention has already implemented, 200 to 3
One hundred semiconductor substrates are stored. When a plurality of semiconductor substrates are accommodated in a diffusion furnace, impurities are vaporized from the respective diffusion-treated films attached to each semiconductor substrate, and the concentration of impurities filling the furnace is increased.

In the third conventional solar cell manufacturing method, when the concentration of the vaporized impurities is high as described above, the vaporized impurities pass through the diffusion prevention film to form the PN junction of the semiconductor substrate. Reach the part. When the impurities reach the PN junction portion, the PN junction portion cannot be formed satisfactorily, the leak current of the manufactured solar cell increases, and the quality deteriorates.

Therefore, an object of the present invention is to make the characteristics of the solar battery cells to be manufactured uniform, prevent the formation of an impurity semiconductor layer in a portion other than a desired portion of each semiconductor substrate, and reduce the leakage current. A method of manufacturing a cell is provided.

[0013]

According to the present invention, a diffusion treatment agent is attached to a first predetermined portion of a surface of a semiconductor substrate, and a diffusion preventing agent is attached to a second predetermined portion, and an inside of a furnace. The diffusion treatment agent and the diffusion preventive agent were attached in the furnace in which the atmospheric gas flows down so that the flow rate of the atmospheric gas flowing down is the maximum flow rate that can maintain the temperature in the furnace within a predetermined temperature range. And a thermal diffusion step of heating a plurality of semiconductor substrates.

According to the invention, the second surface of the semiconductor substrate is
To prevent the impurities vaporized from the diffusion treatment agent in the furnace from adhering to the diffusion preventing agent and diffusing at the second predetermined portion on the surface of the semiconductor substrate. You can

Further, a plurality of semiconductor substrates are heated in the furnace in which the atmospheric gas flows down. The impurities vaporized from the diffusion treatment agent by heating can be carried to the downstream side in the flow-down direction of the atmospheric gas by the atmospheric gas. This can prevent vaporized impurities from staying in the furnace and reduce the impurity concentration in the furnace. This can prevent vaporized impurities from adhering to portions other than the first predetermined portion of the surface of the semiconductor substrate, and prevent diffusion of impurities in portions other than the first predetermined portion of the surface of the semiconductor substrate. can do.

Further, by increasing the flow rate of the atmospheric gas flowing down in the furnace, it is possible to increase the transport amount of the vaporized impurities from the diffusion treatment agent, and the vaporized impurities are diffused except in the first predetermined portion. This can be prevented more reliably. However, as the flow rate of the atmospheric gas increases, temperature unevenness occurs in the furnace, and the temperature unevenness affects diffusion of the plurality of semiconductor substrates arranged in the furnace. Therefore, set a predetermined furnace temperature range that is a temperature range that does not affect the diffusion of all semiconductor substrates placed in the furnace, and set the maximum flow rate within this predetermined temperature range. By flowing down the atmospheric gas, it is possible to reduce the deviation of the quality of the solar cell due to the temperature unevenness of the diffusion furnace, and to prevent the vaporized impurities from diffusing outside the first predetermined portion.

Further, according to the present invention, in the predetermined temperature range, the deviation from the optimum temperature at which the growth efficiency of the impurity semiconductor layer formed on the semiconductor substrate is the highest is 0.8 of the optimum temperature.
It is characterized in that the range is 0% or less.

According to the present invention, the atmospheric gas is allowed to flow down at the maximum flow rate that is maintained within the temperature range in which the deviation from the optimum temperature at which the growth efficiency is highest becomes 0.80% or less of the optimum temperature. As a result, it is possible to preferably realize the prevention of the variation in the quality of the solar battery cells due to the influence of the temperature unevenness in the furnace, and the prevention of the diffusion to other than the first predetermined portion. When the atmospheric gas flows down at a flow rate such that the deviation from the optimum temperature exceeds 0.80% of the optimum temperature,
The flow rate becomes excessive, the temperature unevenness in the furnace becomes large, and the deviation of the quality of the manufactured solar cells becomes large.

Further, according to the present invention, a diffusion treatment agent is attached to the first predetermined portion of the surface of the semiconductor substrate, and a diffusion inhibitor is attached to the second predetermined portion, and an atmosphere gas flowing down in the furnace. The atmospheric gas is flowed so that the flow rate is 4 times or more and 8 times or less than the flow rate at which the temperature in the furnace can be maintained at the optimum temperature at which the growth efficiency of the impurity semiconductor layer formed on the semiconductor substrate is highest. And a thermal diffusion step of heating a plurality of semiconductor substrates to which a diffusion treatment agent and a diffusion inhibitor are attached in a furnace.

According to the invention, the second surface of the semiconductor substrate is
To prevent the impurities vaporized from the diffusion treatment agent in the furnace from adhering to the diffusion preventing agent and diffusing at the second predetermined portion on the surface of the semiconductor substrate. You can

Further, a plurality of semiconductor substrates are heated in the furnace in which the atmospheric gas flows down. The impurities vaporized from the diffusion treatment agent by heating can be carried to the downstream side in the flow-down direction of the atmospheric gas by the atmospheric gas. This can prevent vaporized impurities from staying in the furnace and reduce the impurity concentration in the furnace. This can prevent vaporized impurities from adhering to portions other than the first predetermined portion of the surface of the semiconductor substrate, and prevent diffusion of impurities in portions other than the first predetermined portion of the surface of the semiconductor substrate. can do.

Further, by increasing the flow rate of the atmospheric gas flowing down in the furnace, the transport amount of the vaporized impurities from the diffusion treatment agent can be increased, and the vaporized impurities are diffused except the first predetermined portion. This can be prevented more reliably. However, as the flow rate of the atmospheric gas increases, temperature unevenness occurs in the furnace, and the temperature unevenness affects diffusion of the plurality of semiconductor substrates arranged in the furnace. By flowing the atmosphere gas so that the flow rate is 4 times or more and 8 times or less than the flow rate that can be maintained at the optimum temperature at which the growth efficiency of the impurity semiconductor layer is maximized, the surface of each semiconductor substrate due to temperature unevenness is removed. The diffusion unevenness of the first predetermined portion can be set within a predetermined allowable range. It is possible to prevent impurities from diffusing into a portion other than the first predetermined portion. If the flow rate is less than 4 times the flow rate that can be maintained at the optimum temperature, the leak current of the manufactured solar battery cell increases and the output power decreases. Further, when the flow rate exceeds eight times the flow rate that can be maintained at the optimum temperature, the temperature unevenness in the furnace becomes large, and the deviation in the quality of the solar battery cells becomes large.

The present invention is also characterized in that the flow rate of the atmospheric gas is 6.5 times or more and 8 times or less than the flow rate capable of maintaining the optimum temperature.

According to the present invention, the atmosphere gas is flowed down so that the growth rate of the impurity semiconductor layer is 6.5 times or more and 8 times or less of the flow rate that can be maintained at the optimum temperature that maximizes the growth efficiency. It is possible to more reliably realize the prevention of diffusion to a portion other than the desired portion which is the predetermined portion of No. 1 and the prevention of diffusion failure due to the influence of temperature unevenness in the furnace.

Further, according to the present invention, the diffusion treatment agent is adhered to the first predetermined portion of the surface of the semiconductor substrate, and the diffusion preventing agent is adhered to the second predetermined portion, and the atmosphere gas flowing down in the furnace. Of the ambient gas can maintain the temperature in the furnace within a predetermined temperature range, and the flow rate of 0.195 liters / minute · cm ² or more in a standard state, that is, the volume of the atmosphere gas passing per minute per square centimeter is 0.
And a thermal diffusion step of heating a plurality of semiconductor substrates to which a diffusion treatment agent and a diffusion inhibitor are attached in a furnace in which an atmospheric gas is flowed down so as to have 195 liters or more. Is a manufacturing method.

According to the invention, the second surface of the semiconductor substrate is
To prevent the impurities vaporized from the diffusion treatment agent in the furnace from adhering to the diffusion preventing agent and diffusing at the second predetermined portion on the surface of the semiconductor substrate. You can

Further, a plurality of semiconductor substrates are heated in the furnace in which the atmospheric gas flows down. The impurities vaporized from the diffusion treatment agent by heating can be carried to the downstream side in the flow-down direction of the atmospheric gas by the atmospheric gas. This can prevent vaporized impurities from staying in the furnace and reduce the impurity concentration in the furnace. This can prevent vaporized impurities from adhering to portions other than the first predetermined portion of the surface of the semiconductor substrate, and prevent diffusion of impurities in portions other than the first predetermined portion of the surface of the semiconductor substrate. can do.

Further, by increasing the flow rate of the atmospheric gas flowing down in the furnace, the transport amount of the vaporized impurities from the diffusion treatment agent can be increased, and the vaporized impurities diffuse outside the first predetermined portion. This can be prevented more reliably. However, as the flow rate of the atmospheric gas increases, temperature unevenness occurs in the furnace, and the temperature unevenness affects diffusion of the plurality of semiconductor substrates arranged in the furnace. By keeping the temperature in the furnace within a predetermined temperature range, and by flowing the atmospheric gas so that the flow rate is 0.195 liter / min · cm ² or more in the standard state,
It is possible to prevent the diffusion failure of the first predetermined portion of the surface of the semiconductor substrate due to the temperature unevenness, and to prevent the impurities from diffusing to other portions.

According to the present invention, the diffusion treatment agent is attached to one surface of the semiconductor substrate in the thickness direction, and the diffusion inhibitor is attached to the other surface of the semiconductor substrate in the thickness direction. Is arranged so that the other surface in the thickness direction faces.

According to the invention, since the surface of the semiconductor substrate on the other side in the thickness direction to which the diffusion preventing agent is attached faces the upstream side in the flowing direction of the atmospheric gas, the thickness to which the diffusion treating agent is attached. The surface on one side in the direction is arranged on the downstream side in the flowing direction of the atmospheric gas. Impurities vaporized from the diffusion treatment agent attached to the semiconductor substrate are transported to the downstream side in the downflow direction by the atmospheric gas, so that they can be prevented from attaching to the diffusion inhibitor on the upstream side in the downflow direction of the semiconductor substrate. . In this way, it is possible to more reliably prevent impurities vaporized on one side in the thickness direction of the semiconductor substrate from advancing around the semiconductor substrate and adhering to the other side in the thickness direction.

Further, the present invention is characterized in that the atmospheric gas is a gas which does not chemically react with the diffusion treatment agent and the diffusion inhibitor attached to the semiconductor substrate.

According to the present invention, since the atmospheric gas is a gas that does not chemically react with the diffusion treatment agent and the diffusion inhibitor, for example, an inert gas, the vaporized impurities and the diffusion inhibitor do not chemically react with the atmospheric gas. Therefore, it is possible to prevent the formation of reaction products in the furnace. This prevents reaction products from adhering to the semiconductor substrate, so in the next step,
It need not be removed from the semiconductor substrate. Therefore, it is possible to prevent the reaction product from affecting the treatment in the process after the thermal diffusion process and prevent the characteristics of the manufactured solar cell from being deteriorated.

Further, the present invention is characterized in that the diffusion inhibitor comprises at least one of titanium, titanium oxide and glass.

According to the invention, the diffusion inhibitor is titanium,
Since at least one of titanium oxide and glass is contained, it is possible to favorably prevent the diffusion of the vaporized impurities from the diffusion treatment agent.

Further, according to the present invention, after the impurity semiconductor layer is formed at the first predetermined position on the surface of the semiconductor substrate in the thermal diffusion step,
The present invention is characterized by including an inhibitor removal step of eluting a diffusion inhibitor attached to a second predetermined position on the surface of the semiconductor substrate with a hydrogen fluoride solution to remove the diffusion inhibitor.

According to the present invention, after the impurity semiconductor layer is formed at the first predetermined position in the thermal diffusion step, an inhibitor removal step of removing the diffusion inhibitor with a hydrogen fluoride solution is included. By using the hydrogen fluoride aqueous solution, the diffusion inhibitor can be easily eluted in the hydrogen fluoride solution and removed.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION A solar cell comprises a P-type semiconductor layer in which positively charged holes serve as carriers in a semiconductor substrate.
A PN junction portion is formed adjacent to the N-type semiconductor layer in which electrons having negative charges serve as carriers.

When the PN junction portion is irradiated with sunlight, the light is absorbed and electrons and holes are generated. Electrons and holes generated by light irradiation are generated by the potential barrier at the PN junction.
Separated into N-type and P-type sides, respectively. Holes are excessively accumulated in the P-type region and electrons are excessively accumulated in the N-type region, so that a potential difference occurs between both ends of the PN junction. By electrically connecting both ends of the PN junction, current flows,
It can be taken out as electric power.

FIG. 1 is a flow chart showing a step of forming a PN junction part which is a part of a method for manufacturing a solar cell according to an embodiment of the present invention. In a solar cell, for example, a PN junction portion is formed on a polycrystalline silicon wafer. When the preparation of the P-type silicon wafer to which the P-type conductivity type impurity is added for the PN junction is completed in step s0, the process proceeds to step s1 and the PN junction part forming process is started. A P-type silicon wafer has, for example, 125 sides.
It is formed into a square plate with a thickness of 0.2 mm.
It is above and 0.4 mm or less.

In step s1, phosphorus pentoxide (chemical formula: P ₂ O ₅ ) is contained as a main component on the surface on one side in the thickness direction, which is the light receiving surface when the P-type silicon wafer is configured as a solar cell. A liquid diffusion treatment agent is spin-coated with a coating device, and tetraisopropoxy titanium (chemical formula: [(CH ₃ ) ₂ CHO] _{4 is formed on} at least a part of the surface on the other side in the thickness direction, which is the surface opposite to the light-receiving surface. A coating process is performed in which a liquid diffusion inhibitor containing Ti) as a main component is spin coated by a coating device. The diffusion treatment agent and the diffusion prevention agent are attached to the P-type silicon wafer to a predetermined thickness by spin coating. Next, the diffusion treatment agent and diffusion prevention agent applied to the P-type silicon wafer are dried to remove the organic component. A plurality of P-type silicon wafers coated with a diffusion treatment agent and a diffusion prevention agent are placed in a damper boat, which is a container for storing a large number of P-type silicon wafers.
For example, 200 to 300 sheets are stored and dried in a furnace at about 100 degrees for 30 minutes. Upon drying, the diffusion treating agent and the diffusion preventing agent become a solid state and form a film. When the diffusion treatment agent dries, the diffusion treatment film with a thickness of 300 nm becomes P, for example.
The diffusion preventing agent is formed on the surface of the p-type silicon wafer on one side in the thickness direction, and the diffusion preventing film is dried to form a diffusion preventing film having a thickness of 300 nm on the other side of the p-type silicon wafer in the thickness direction. When each film is formed in this way, the adhesion process is completed, and the process proceeds to step s2.

In step s2, a thermal diffusion process is performed. A plurality of P-type silicon wafers accommodated in the damper boat are filled with an inert gas at a flow rate of 0.32 liter / min · cm.
Heat in the diffusion furnace that flows down in ² . For example, while flowing down an inert gas, it is heated at about 900 degrees for about 30 minutes. The heating for forming the diffusion treatment film and the diffusion prevention treatment film shown in step s1 may be performed in the diffusion furnace.

By heating the P-type silicon wafer, phosphorus contained in the diffusion-treated film is diffused at the surface portion on one side in the thickness direction where the diffusion-treated film is in contact with the P-type semiconductor,
Phosphorus permeates to the surface portion on one side in the thickness direction of the P-type silicon wafer. As a result, an N-type semiconductor layer, which is an impurity semiconductor layer, is formed on the surface of the P-type silicon wafer on one side in the thickness direction. As a result, a PN junction is formed at the boundary between the N-type semiconductor layer and the P-type semiconductor portion of the P-type silicon wafer. When the heating by the diffusion furnace is completed, the process proceeds to step s3. For example, the thickness of the N-type semiconductor layer is several μm.

At step s3, the diffusion prevention film is removed. Specifically, after the thermal diffusion process is completed, the diffusion prevention film, which is a mixture containing titanium, titanium oxide, and glass, is etched with a hydrogen fluoride solution. As a result, the diffusion barrier film can be eluted into the hydrogen fluoride solution to easily remove the diffusion barrier film from the P-type silicon wafer. When the removal of the diffusion barrier film is completed, the process proceeds to step s4. In step s4, formation of the PN junction portion is completed. After the PN junction portion forming step, an electric field layer and an electrode forming step are performed.

FIG. 2 is a cross-sectional view showing the manufacturing process of the solar battery cell. As the process proceeds to FIGS. 2 (1) to 2 (8),
The manufacturing process progresses. FIG. 3 is a flowchart showing a manufacturing process including a PN junction forming process of a solar battery cell. At step a0, a P-type silicon wafer is formed as a P-type semiconductor substrate. The P-type silicon wafer 1 is formed by cutting the polycrystalline silicon manufactured by the casting method into a plate shape. P-type conductive impurities are added to polycrystalline silicon to become a P-type semiconductor. When the P-type silicon wafer 1 to be such a semiconductor substrate is prepared, the process proceeds to step a1.

At step a1, a defect layer removing process for removing the defect layer 2 is performed. As shown in FIG. 2A, the prepared P-type silicon wafer 1 is formed with a defect layer 2 to which deposits and oxides are attached. The P-type silicon wafer 1 is immersed in an alkaline solution such as sodium hydroxide (chemical formula: NAOH) and potassium hydroxide (chemical formula: KOH) to carry out wear etching, and as shown in FIG. The defect layer 2 formed on the wafer 1 is removed. When the defective layer 2 of the P-type silicon wafer 1 is thus removed, the process proceeds to step a2.

At step a2, a PN junction portion forming step of forming a PN junction portion is performed. As shown in FIG. 2C, the N-type semiconductor layer 3 is formed on the surface of the P-type silicon wafer 1 on one side in the thickness direction by using a thermal diffusion method. Specifically, the steps s1 to s4 shown in FIG. 1 are performed to form a PN junction part. When the formation of the PN junction portion is completed, the process proceeds to step a3.

In step a3, as shown in FIG. 2 (4), a back surface electric field layer forming step for forming a back surface electric field layer 4 opposite to the light receiving surface of the solar battery cell is performed. By forming the back surface electric field layer 4, the P-type silicon wafer 1 is formed.
It is possible to prevent carrier recombination in the vicinity of the back surface of the device and prevent a decrease in output. In the electric field layer, for example, aluminum is diffused to the back surface side of the P-type silicon wafer 1 to form the back surface electric field layer 4 serving as a P ⁺ -type semiconductor portion on the back surface portion of the P-type silicon wafer. When the back surface field layer 4 is formed in this way, the process proceeds to step a4.

In step s3 shown in FIG. 1, since the diffusion prevention film is removed by the aqueous solution of fluoride, diffusion failure due to aluminum is prevented, and in the step a3,
It is possible to easily dope the P ⁺ aluminum for forming the back surface electric field layer formed on the surface of the P-type silicon wafer 1 on the other side in the thickness direction. Here, P ⁺ means a semiconductor layer containing more P-type conductivity type impurities than the P-type silicon wafer.

At step a4, as shown in FIG. 2 (5), an antireflection film forming step of forming an antireflection film 5 for preventing reflection of light on the light receiving surface is performed. The antireflection film 5 is
For example, titanium dioxide (chemical formula: TiO ₂ ), silicon nitride (chemical formula: Si _x N _y , where “x” and “y” are arbitrary natural numbers), tin dioxide (chemical formula: SnO ₂ ), or the like. The antireflection film 5 is formed on the surface on the light receiving surface side. By forming the antireflection film 5, it is possible to prevent light from being reflected on the light receiving surface and prevent a decrease in output as a solar cell. After forming the antireflection film 5 as described above, the process proceeds to step a5.

At step a5, an electrode forming process is performed. As shown in FIG. 2 (6), the front electrode paste 6 is printed on the antireflection layer 5, and the paste application step of printing the back electrode paste 7 on the back surface electric field layer 4 is performed. Next, a pre-drying step of pre-drying the pastes 6 and 7 is performed, and when the pre-drying is completed, the electrode pastes 6 and 7 are fired at a high temperature while supplying nitrogen or air. As a result, as shown in FIG. 2 (7), front and back electrodes are formed on the substrate. The formed front side electrode 8 is inserted through the antireflection film 5 and electrically connected to the N-type semiconductor layer 3,
The back electrode 9 is electrically connected to the back surface field layer 4. When the electrodes 8 and 9 are formed, the process proceeds to step a6. At step a6, as shown in FIG. 2 (8), the electrodes 8 and 9 are
Solder 10 is piled up, proceed to step a7, and step a
At 7, the manufacturing process of the solar battery cell is completed.

FIG. 4 is a block diagram showing the main structure of the diffusion furnace 20 used in the method for manufacturing a solar cell of the present invention. The diffusion furnace 20 is a diffusion furnace main body 2 that accommodates a plurality of P-type silicon wafers 1 accommodated in a damper boat 21.
2 and heating means 23 for heating the P-type silicon wafer 1.
A gas inserting means 24 for supplying an inert gas to the diffusion furnace main body 22, a gas discharging means 25 for discharging the inert gas passing through the diffusion furnace main body to the outside of the diffusion furnace main body; And a temperature detecting means 26 for detecting the temperature. Further, based on the temperature in the furnace detected by the temperature detecting means 26,
It may have a control means 27 for giving a command for adjusting the heating amount to the heating means 23 and for giving a command for adjusting the flow rate of the inert gas to the gas inserting means 24.

The damper boat 21 holds 250 P-type silicon wafers in an upright position and, while being accommodated in the diffusion furnace main body 22, arranges them in the gas flow-down direction X and accommodates the P-type silicon wafers in a line. The P-type silicon wafers are arranged with a space L therebetween.

The diffusion furnace body 22 has, for example, an inner diameter D of 20.
It is formed to have a size of 0 mm and has an axial dimension H of 100 cm. Further, since the P-type silicon wafers are housed in the diffusion furnace main body 22 and arranged side by side with an interval therebetween, an inert gas can be formed between two adjacent P-type silicon wafers. As a result, the impurities vaporized from the diffusion-treated film are not retained near the diffusion-treated film but are carried by the inert gas. The inert gas flows from one end in the axial direction of the diffusion furnace main body 22 toward the other end in the axial direction.

It is desirable that the heating means 23 is constructed so that the set temperature can be varied, and that the heating means 23 can partially heat the furnace so that the temperature distribution in the furnace is uniform. Further, the gas inserting means 24 supplies the inert gas from one end side in the axial direction in the furnace. Further, the gas discharge means 25 or the gas insertion means 24 causes the inert gas to flow down into the furnace. For example, the gas discharging means 25 is composed of a vacuum pump or the like.

By controlling the heating time, the heating temperature, and the flow rate of the inert gas, the conditions under which the diffusion of the P-type silicon wafer is optimized so that the manufactured solar cells have few deviations and have high quality characteristics. In addition, a thermal diffusion process is performed. For example, the flow rate of the inert gas is maximized within a range in which the deviation from the optimum temperature at which the growth efficiency of the N-type semiconductor layer, which is an impurity semiconductor layer caused by diffusion, is highest is 0.80% or less of the optimum temperature. Or the flow rate that keeps the optimum temperature.
Adjust the flow rate to 0 times or more and 8.0 times or less. Preferably, the flow rate is at least 6.5 times the flow rate at which the optimum temperature can be maintained, and 8.
Adjust the flow rate to 0 times or less. Or standard condition, that is, 0.195 liters / minute at a temperature of 0 degree and a pressure of 1 atmosphere.
The flow rate is adjusted to be equal to or higher than the flow rate of ² cm ² and the temperature inside the diffusion furnace body is within a predetermined range. Further, the adjustment of the flow rate of the inert gas, the temperature of the diffusion furnace main body, and the diffusion time based on such conditions may be performed manually, and the control means 2
7 may be used.

The growth efficiency is the rate at which diffusion grows favorably for given energy. For example, in the present embodiment, the optimum temperature at which the growth efficiency is highest is in the temperature range of 868 ° C. or higher and 872 ° C. or lower, and the flow rate of the inert gas that can maintain the optimum temperature is 0.041 liter / min. cm ² .

FIG. 5 is a side view showing the P-type silicon wafer 1 in a state where the diffusion treatment film 41 and the diffusion prevention film 40 are formed by the diffusion treatment agent and the diffusion prevention agent. Figure 6
Is a P-type silicon wafer 1 on which the diffusion prevention film 41 is formed.
FIG. 6 is a plan view showing the surface on the other side in the thickness direction of FIG. FIG. 7 is a plan view showing a surface on one side in the thickness direction of the P-type silicon wafer 1 on which the diffusion treatment film 40 is formed.

A diffusion treatment agent is attached to the center of one side surface in the thickness direction of the P-type silicon wafer, and the P-type silicon wafer 1 is rotated, whereby the diffusion treatment agent is evenly distributed over the entire surface on one side in the thickness direction by centrifugal force. spread. Similarly, a diffusion preventive agent is attached to the center of the other surface in the thickness direction of the P-type silicon wafer 1 and the P-type silicon wafer 1 is rotated, so that the diffusion prevention treatment agent is applied to the surface on the other side in the thickness direction by centrifugal force. Spread evenly over at least a portion of the. Next, the P-type silicon wafer 1 on which the diffusion treatment agent and the diffusion prevention agent have spread is
By heating at about 100 degrees for 30 minutes, the organic components are removed, the diffusion treatment film 41 is formed on the surface of the P-type silicon wafer 1 on one side in the thickness direction, and the diffusion treatment film 41 on the other side in the thickness direction of the P-type silicon wafer 1 is formed. Diffusion prevention film 40 on a part of the surface
Is formed.

As shown in FIG. 6, the diffusion preventive film 40 is formed.
Is formed in a circle centered on the center position of the surface on the other side in the thickness direction. Therefore, the diffusion prevention film 40 is not formed on the edge portion on the other side in the thickness direction of the P-type silicon wafer. The circular shape allows the diffusion preventing film to be easily formed by spin coating.

As shown in FIG. 7, the diffusion treatment film 41 is formed on almost the entire surface on one side in the thickness direction. The N-type semiconductor layer can be formed on the entire surface on one side in the thickness direction of the P-type silicon wafer by being formed on almost the entire surface on the one side in the thickness direction which becomes the light receiving surface of the solar cell, It is possible to maximize the ratio of the N-type semiconductor layer to the light-receiving surface portion and improve the output power of the solar battery cell.

The P-type silicon wafer 1 has a diffusion preventive film 40.
In the state where the surface on the side where the is formed is arranged on the upstream side in the downward direction X of the inert gas, and the surface on the side where the diffusion treatment film 41 is formed is arranged on the downstream side in the downward direction X of the inert gas, It is housed in the diffusion furnace main body 22.

The step of drying the diffusion treatment agent and the diffusion inhibitor may be carried out in a diffusion furnace in which an inert gas flows down. Since the diffusion treatment agent is attached to the surface facing the downstream side in the downflow direction X, oxygen vaporized from the diffusion treatment agent is carried by the inert gas to the downstream side in the downflow direction and prevented from adhering to the diffusion prevention agent. can do. As a result, the composition of the diffusion prevention film 41 can reduce the titanium dioxide TiO ₂ component and increase the proportion of the titanium Ti component. Since titanium Ti is more easily removed by hydrogen fluoride than titanium dioxide TiO ₂ , the diffusion barrier film can be easily removed by an aqueous solution of hydrogen fluoride.

FIG. 8 is a graph showing the temperature distribution in the diffusion furnace main body 22 when the flow rate of the inert gas is changed. In FIG. 8, the solid line A shows the temperature change in the furnace when the flow rate of the inert gas is 0.041 liters / minute · cm ² , and when the flow rate is 0.13 liters / minute · cm ² . The temperature change in the furnace is shown by the one-dot chain line B, and the flow rate is 0.195.
The broken line C shows the temperature change in the furnace in the case of liter / min · cm ^2.
And a flow rate of 0.3249 liter / min · cm ² is indicated by a broken line D.

The optimum temperature inside the furnace was set at 870 ° C.
The greater the flow rate of active gas, the greater the temperature unevenness in the furnace.
Become Inert gas flow rate is 0.041 l / min.
cm ²In case A, the temperature is in the axial direction of the diffusion furnace body.
In the range L1 where the distribution is 868 degrees or more and 872 degrees or less
Yes, the flow rate of inert gas is 0.13 liters / min.c
m²In the case of B, the temperature component along the axial direction of the diffusion furnace body
The cloth is in the range of 866 degrees or more and 874 degrees or less,
Deviation from the set temperature of 870 degrees is 0.46% or less
The range is L2. The flow rate of the inert gas is 0.3249.
Liter / minute / cm²In case of, D is the direction of the axis of the diffusion station body
The temperature distribution across the direction is above 864 degrees and below 877 degrees.
The deviation from the set temperature of 870 degrees in the range L3 is
The maximum flow rate is in the range of 0.80% or less.

The inert gas is supplied from the gas inserting means 24 into the furnace at the atmospheric temperature, and the temperature thereof is raised by the heating means 23 as it flows downstream in the downward direction X. The P-type silicon wafer 1 is heated by heat radiation from the heating means 23. The inert gas is also heated by the heat radiation from the heating means 23. When the flow rate of the inert gas flowing down the furnace is large, the P-type silicon wafer 1 is heated by the heating means 2.
It is heated by the heat radiation from 3 and is affected by the heat transfer from the inert gas. As a result of the inert gas flowing down, the temperature of the P-type silicon wafers 1 housed in the diffusion furnace body 22 on the upstream side in the downflow direction X becomes lower, and the temperature of the wafers on the downstream side in the downflow direction X becomes lower. Becomes higher.

FIG. 9 is a graph showing the performance of the solar battery cells manufactured by changing the flow rate of the inert gas.
In (1) and FIG. 9 (2), the flow rate of the inert gas is high,
That is, the performance of the solar battery cell when manufactured at 0.3249 liters / minute · cm ² is shown. FIGS. 9 (3) and 9 (4) show that the flow rate of the inert gas is as shown in FIG. 9 (1) and FIG.
(2) shows the performance of solar cells when manufactured at less than 0.1950 liters / minute · cm ² ,
9 (5) and 9 (6) shows that the flow rate of the inert gas is smaller than that in FIGS. 9 (3) and 9 (4), that is, 0.0.
The performance of the solar cell when manufactured at 406 liters / minute · cm ² is shown.

9 (1), 9 (3) and 9
(5) shows the deviation of the output power Pm of the solar cell,
9 (2), 9 (4) and 9 (6) show the relationship between the leak current Id of the solar battery cell and the output power Pm.

As shown in FIGS. 9 (2), 9 (4) and 9 (6), by increasing the flow rate of the inert gas,
The variation in the leak current Id for each manufactured solar cell is reduced, and uniform quality can be obtained. Further, the leak current Id of the solar battery cell is reduced. Also in FIG.
As shown in (1), FIG. 9 (3) and FIG. 9 (5), the proportion of solar cells with high output power Pm among the solar cells manufactured by increasing the flow rate of the inert gas. Will increase. By increasing the flow rate of the atmospheric gas, phosphorus vaporized from the diffusion treatment film during the thermal diffusion is carried by the atmospheric gas. Therefore, the concentration of vaporized phosphorus in the diffusion furnace main body 22 can be reduced, and vaporized phosphorus can be prevented from adhering to the other side in the thickness direction of the P-type silicon wafer. As described above, since phosphorus does not diffuse on the other side in the thickness direction, P at the PN junction portion
To prevent the N-type semiconductor portion from being formed on the type semiconductor side,
The PN junction portion can be kept good. In particular, by flowing down the maximum flow rate of the inert gas while maintaining the temperature range of the deviation within 0.80% of the optimum temperature, the leak current is reduced, and a solar cell with high maximum output can be manufactured. it can. When an inert gas having a flow rate maintained in a temperature range where the deviation from the optimum temperature is small is flown down, the flow rate becomes too small, the leak current increases, and the output voltage decreases. When a maximum flow rate of an inert gas that falls within the temperature range with a deviation of more than 0.80% from the optimum temperature is flowed down, the flow rate becomes excessive and temperature unevenness in the furnace increases, resulting in variations in the quality of solar cells. May occur.

FIG. 10 is a graph showing the performance of solar cells manufactured when the flow rate of the inert gas is changed. In FIG. 10, points a to f indicate points at which the flow rate of the inert gas is changed, a is 0.0406 liter / min · cm ² , b is 0.0975 liter / min · cm ² , c.
Is 0.1950 liter / min · cm ² , d is 0.260
The characteristics of the leak current and the output voltage when an inert gas at a flow rate of 0 liter / min · cm ² , e is 0.3249 liter / min · cm ² , and f is 0.3899 liter / min · cm ² are shown. Show. Table 1 is a graph showing the performance of the solar cells manufactured when the flow rate of the inert gas is changed.

[0070]

[Table 1]

As shown in FIG. 10 and Table 1, the leak current Id decreases as the flow rate of the inert gas increases from the point a to the point d, that is, the output power P increases.
m increases. Further, as it goes from the point d to the point e,
The leakage current Id decreases with the output power Pm kept substantially constant. Further, the output power Pm decreases from point e to point f.

Further, from the point c to the point a, that is, the flow rate of the inert gas flowing down is 0.195 liter /
When the value is smaller than the minute · cm ² , the leak current Id increases dramatically and the output power Pm decreases. This is because when the flow rate of the inert gas into the diffusion furnace main body 22 is reduced, the vaporized phosphorus serving as the N + diffusion source is out-diffused to the other surface in the thickness direction, which is the side opposite to the light receiving surface.

Further, from the point e to the point f, that is, the flow rate of the inert gas is 0.3249 liter / min.cm.
^When it becomes larger than ² , the output power Pm becomes smaller. This is because when the flow rate of the inert gas supplied into the diffusion furnace main body 22 becomes excessively large, the temperature unevenness in the diffusion furnace main body 22 becomes large, which largely deviates from the diffusion temperature condition of the P-type silicon wafer. is there. The inert gas flow rate is
When it is larger than 0.3249 liter / min · cm ² , the temperature deviation in the diffusion furnace main body 22 becomes large and the quality of the manufactured solar battery cell is not uniform.

Therefore, 0.195 l / min · cm
By flowing an inert gas of ² or more, that is, 4 times or more of the flow rate capable of maintaining the optimum temperature, the leak current Id of the manufactured solar cell is reduced, the decrease of the output power Pm is prevented, and the quality is made uniform. Can be kept.

Point e and point d at which the output power Pm further increases
Between points, that is, 0.2600 liters / min · cm ²
High output power is achieved by flowing the inert gas in the range L5 which is not less than 0.3249 liters / minute · cm ^{2 and not} less than 6.5 times and not more than 8 times the flow rate at which the optimum temperature can be maintained. It is possible to manufacture a solar cell capable of obtaining

As described above, according to the embodiment of the present invention, in the thermal diffusion step, vaporized phosphorus is prevented from adhering to the surface on the other side in the thickness direction of the P-type silicon wafer, and the diffusion temperature range is widened. The quality of the solar cells is made uniform and the leak current is reduced by performing the diffusion within the temperature range where the diffusion failure of the diffusion furnace main body 22 does not occur without deviating, and the solar cells with large output power are manufactured. be able to.

Specifically, as shown in FIGS. 9 and 10, the flow rate is 4 times or more and 8 times or less, preferably 6.5 times or more and 8 times or less of the flow rate at which the optimum temperature can be maintained. Flow down the active gas. In this embodiment, a flow rate of 0.195, which is 4 to 8 times the flow rate of 0.04 liter / min · cm ² , which keeps the range of 868 degrees or more and 872 degrees or less substantially constant.
An inert gas having a flow rate of not less than liter / minute · cm ^{2 and not} more than 0.320 liter / minute · cm ² is flowed down.
If the flow rate is less than 4 times the flow rate that can keep the diffusion temperature condition almost constant, that is, less than 0.16 liter / min · cm ² , the leak current Id increases and the output power Pm decreases. In addition, the flow rate exceeds 8 times the flow rate that can keep the diffusion temperature condition almost constant, that is, the flow rate is 0.32 liter / min.
When it exceeds cm ² , temperature unevenness occurs in the diffusion furnace main body, and the quality of the solar battery cell deteriorates depending on the storage location.

In particular, by setting the flow rate range of 6.5 times or more and 8.0 times or less of the flow rate that can keep the diffusion temperature condition almost constant, the output power is further improved and the solar battery cell with less leak current is manufactured. can do.

Further, the flow rate of the inert gas is maximized with the temperature range of the entire diffusion furnace main body maintained at a diffusion temperature deviation of 0.80% or less, for example, at which diffusion efficiency is good, for example, 864 degrees or more and 877 degrees or less. By doing so, a solar cell with a small leak current can be manufactured.

Since the surface on the one side in the thickness direction to which the diffusion-treated film is attached is arranged on the downstream side X in the inflow direction of the inert gas, the phosphorus vaporized from the diffusion-treated film is in the down-flow direction by the inert gas. Since it is transported to the downstream side of X, it can be prevented from adhering to the diffusion prevention film. As a result, it is possible to more reliably prevent the impurities vaporized on one side in the thickness direction of the P-type semiconductor wafer from going around the semiconductor substrate and scattering to the other side in the thickness direction.

Further, as the atmosphere gas flowing down in the furnace, a gas which does not chemically react with the diffusion treatment film and the diffusion prevention film, for example, an inert gas is used, so that the atmosphere gas does not chemically react and the reaction product in the furnace. Can be prevented from being formed. This eliminates the need to remove the atmospheric gas and its reaction product in the next step. Further, the influence of the atmospheric gas used in the thermal diffusion step on the steps after the thermal heating step can be reduced, and the characteristics of the manufactured solar battery cell can be prevented from being deteriorated.

Since the diffusion prevention film contains at least one of titanium, titanium oxide and glass, it is possible to prevent vaporized phosphorus from diffusing on the other side in the thickness direction of the P-type silicon wafer. You can In addition, after the N-type semiconductor layer is formed in the thermal diffusion step, the diffusion inhibitor is removed using an aqueous solution of hydrogen fluoride, whereby the diffusion inhibitor can be easily eluted in the hydrogen fluoride solution and removed. .

The above description is merely one example of the present invention, and the configuration can be changed within the scope of the invention.
For example, in the embodiment, the N-type semiconductor layer is formed on the P-type silicon wafer, but the second-conductivity-type semiconductor layer different from the first-conductivity-type may be formed on the first-conductivity-type semiconductor substrate.
For example, the P-type semiconductor layer may be formed on the N-type semiconductor substrate by changing the diffusion treatment agent. BSF type (Back Surfa
It can also be applied to a ce Field) type n ⁺ / P / P ⁺ solar cell. Further, in the present embodiment, the diffusion inhibitor and the diffusion treatment agent are liquid, and it is assumed that the diffusion prevention film and the diffusion treatment film are solid by heating and drying, but the diffusion prevention agent and the diffusion treatment agent are solid. Alternatively, they may be directly formed into a film shape.

[0084]

As described above, according to the present invention, the variation in the quality of the solar cell due to the temperature unevenness of the diffusion furnace is reduced, and the impurities are introduced into a portion other than the first predetermined portion of the surface of the semiconductor substrate. It is possible to prevent the diffusion.
For example, in a solar cell in which an N-type semiconductor layer is formed by diffusing on one surface in the thickness direction of a P-type semiconductor substrate to form a PN junction portion, impurities are introduced from the other surface in the thickness direction of the semiconductor substrate. Can be prevented from penetrating into. This prevents formation of the N-type semiconductor portion on the P-type semiconductor layer side of the PN junction portion, and P
The ratio of the type semiconductors can be improved, and the defective bonding at the PN junction portion can be reduced. As a result, it is possible to manufacture solar cells with little leakage current and improved power characteristics, to improve the yield of the solar cells, and to reduce the production cost.

Further, according to the present invention, the predetermined temperature range is within a range in which the deviation from the optimum temperature at which the growth efficiency is the highest is 0.80% or less of the optimum temperature and the maximum flow rate is the atmospheric gas. By flowing down the flow rate of, it is possible to reduce the deviation of the quality of the solar battery cells due to the influence of temperature unevenness in the furnace, and to prevent the diffusion to other than the first predetermined portion. As a result, high-quality solar cells can be manufactured evenly.

Further, according to the present invention, by flowing the atmospheric gas so that the growth efficiency of the impurity semiconductor layer is 4 times or more and 8 times or less of the flow rate that can be maintained at the optimum temperature that maximizes the growth efficiency, Can be prevented from diffusing to a portion other than a predetermined portion, and the quality deviation due to the influence of temperature unevenness in the furnace can be reduced. This makes it possible to manufacture high quality solar cells.

Further, according to the present invention, the flow rate of 6. which can be maintained at the optimum temperature that maximizes the growth efficiency of the impurity semiconductor layer.
By flowing the atmospheric gas so as to be not less than 5 times and not more than 8 times, it is possible to prevent diffusion to a portion other than a desired portion which is the first predetermined portion, and to prevent diffusion failure due to the influence of temperature unevenness in the furnace. The prevention can be realized more reliably.

Further, according to the present invention, the temperature in the furnace can be maintained within a predetermined temperature range, and it is 0.195 in the standard state.
By flowing down the atmospheric gas so that the flow rate is at least 1 liter / min · cm ² , it is possible to prevent diffusion to other than the first predetermined portion and to prevent defective diffusion due to the influence of temperature unevenness in the furnace. It can be realized suitably.

Further, according to the present invention, since the surface of the semiconductor substrate on the other side in the thickness direction to which the diffusion preventive agent is attached faces the upstream side in the flowing direction of the atmospheric gas, one side in the thickness direction of the semiconductor substrate. It is possible to more reliably prevent the impurities vaporized on the side from going around the semiconductor substrate and scattering to the other side in the thickness direction. This can prevent diffusion from occurring on the other side in the thickness direction of the semiconductor substrate, and further reduce the leak current of the manufactured solar cell.

Further, according to the present invention, since the atmospheric gas is a gas that does not chemically react with the diffusion treating agent and the diffusion preventing agent, for example, an inert gas, the reaction product due to the atmospheric gas is removed after the thermal diffusion step. There is no need to do so, the influence on the next process can be reduced, and the characteristics of the manufactured solar battery cell can be prevented from deteriorating.

According to the invention, the diffusion inhibitor is titanium,
Since it contains at least one of titanium oxide and glass, it is possible to favorably prevent the impurities vaporized from the diffusion treatment agent from diffusing in the second predetermined portion.

Further, according to the present invention, after the impurity semiconductor layer is formed at the first predetermined position in the thermal diffusion step, an inhibitor removing step of removing the diffusion inhibitor with a hydrogen fluoride solution is included, and the hydrogen fluoride aqueous solution is included. By removing the diffusion inhibitor by using, the diffusion inhibitor can be easily eluted in the hydrogen fluoride solution and removed.

[Brief description of drawings]

FIG. 1 is a flowchart showing a step of forming a PN junction part which is a part of a method for manufacturing a solar cell according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process of a solar battery cell.

FIG. 3 is a flowchart showing a manufacturing process including a PN junction forming process of a solar cell.

FIG. 4 is a block diagram showing a main configuration of a diffusion furnace 20 used in the method for manufacturing a solar cell of the present invention.

FIG. 5 is a side view showing the P-type silicon wafer 1 in a state where the diffusion treatment film 41 and the diffusion prevention film 40 are formed by the diffusion treatment agent and the diffusion prevention agent.

FIG. 6 is a plan view showing the other surface in the thickness direction of the P-type silicon wafer 1 on which the diffusion prevention film 41 is formed.

FIG. 7 is a plan view showing a surface on one side in the thickness direction of the P-type silicon wafer 1 on which the diffusion treatment film 40 is formed.

FIG. 8 is a graph showing a temperature distribution in the diffusion furnace main body 22 when the flow rate of the inert gas is changed.

FIG. 9 is a graph showing the performance of solar cells manufactured by changing the flow rate of an inert gas.

FIG. 10 is a graph showing the performance of solar cells manufactured when the flow rate of the inert gas is changed.

[Explanation of symbols]

1 P-type silicon wafer 3 N-type semiconductor layer 4 Back surface electric field layer 5 Antireflection layer 8 Front electrode 9 Back electrode 10 Solder 20 diffusion furnace 21 damper boat 22 Main body of diffusion furnace 23 Heating means 40 Diffusion prevention film 41 Diffusion treated film X downflow direction

Claims (9)

[Claims] 1. A step of adhering a diffusion treatment agent to a first predetermined portion of a surface of a semiconductor substrate and a diffusion preventive agent to a second predetermined portion of the semiconductor substrate, and a flow rate of an atmospheric gas flowing down in the furnace. In order to keep the temperature inside the furnace at the maximum flow rate that can be maintained within the predetermined temperature range,
And a thermal diffusion step of heating a plurality of semiconductor substrates to which a diffusion treatment agent and a diffusion inhibitor are adhered in a furnace in which an atmospheric gas is flown down. 2. The predetermined temperature range is a range in which the deviation from the optimum temperature at which the growth efficiency of the impurity semiconductor layer formed on the semiconductor substrate is highest is 0.80% or less of the optimum temperature. The method for manufacturing a solar cell according to claim 1. 3. A step of adhering a diffusion treatment agent to a first predetermined portion of a surface of a semiconductor substrate and a diffusion preventive agent to a second predetermined portion of the semiconductor substrate, and a flow rate of an atmospheric gas flowing down in the furnace. In the furnace in which the atmospheric gas is flowed so that the temperature in the furnace is 4 times or more and 8 times or less than the flow rate that can be maintained at the optimum temperature at which the growth efficiency of the impurity semiconductor layer formed on the semiconductor substrate is highest. And a thermal diffusion step of heating a plurality of semiconductor substrates having a diffusion treatment agent and a diffusion prevention agent attached thereto, the method for producing a solar cell. 4. The method for manufacturing a solar battery cell according to claim 3, wherein the flow rate of the atmospheric gas is 6.5 times or more and 8 times or less the flow rate capable of maintaining the optimum temperature. 5. A step of adhering a diffusion treatment agent to a first predetermined portion of a surface of a semiconductor substrate and a diffusion preventive agent to a second predetermined portion of the semiconductor substrate, and a flow rate of an atmospheric gas flowing down in the furnace. The temperature inside the furnace can be kept within a predetermined temperature range, and it is 0.19 in the standard state.
And a thermal diffusion step of heating a plurality of semiconductor substrates to which a diffusion treatment agent and a diffusion inhibitor are attached in a furnace in which an atmospheric gas is flown so that the flow rate is 5 liters / minute · cm ² or more. A method for manufacturing a solar cell, comprising: 6. A diffusion treatment agent is adhered to one surface of the semiconductor substrate in the thickness direction, and a diffusion inhibitor is adhered to the other surface of the semiconductor substrate in the thickness direction. It arrange | positions so that the other surface may be faced and the manufacturing method of the photovoltaic cell in any one of the Claims 1-5 characterized by the above-mentioned. 7. The manufacturing of a solar cell according to claim 1, wherein the atmospheric gas is a gas that does not chemically react with the diffusion treatment agent and the diffusion inhibitor attached to the semiconductor substrate. Method. 8. The method for manufacturing a solar battery cell according to claim 1, wherein the diffusion inhibitor contains at least one of titanium, titanium oxide and glass. 9. An impurity semiconductor layer is formed at a first predetermined position on the surface of the semiconductor substrate by a thermal diffusion process, and then a diffusion inhibitor attached at a second predetermined position on the surface of the semiconductor substrate is treated with hydrogen fluoride. The method for producing a solar battery cell according to any one of claims 1 to 8, further comprising a step of removing the inhibitor by eluting it into a solution and removing it.