JP2006013258A - Manufacturing method of solar battery element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a solar battery element which suppresses internal stresses imparted to the solar battery element by the heating at baking of electrodes and alleviates warpage of a semiconductor substrate. <P>SOLUTION: This manufacturing method of the solar battery includes the semiconductor substrate, having front and rear surfaces, a front surface electrode provided on the front surface, and a rear surface electrode provided on the rear surface. The method comprises an electrode-forming process for forming the front surface electrode and/or the rear surface electrode by applying an electrode material onto the semiconductor substrate, and baking this semiconductor substrate. The electrode-forming process comprises a first baking step of nearly horizontally disposing and baking the semiconductor substrate, and a second baking step of baking the semiconductor substrate, in a state where the semiconductor substrate is turned by nearly by 90° about the vertical direction as the axis. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a solar cell element, and more particularly to a method for manufacturing a solar cell element in which a front electrode and a back electrode are formed in a state where the influence of thermal stress on a semiconductor substrate is reduced in an electrode firing step of a semiconductor substrate.

The structure of a general solar cell element is shown in FIG. A reverse conductivity type region 2 exhibiting n-type is provided by diffusing an n-type impurity of reverse conductivity type (for example, P) to a certain depth in the vicinity of the light-receiving surface side surface of a p-type semiconductor substrate 1 such as polycrystalline silicon. A pn junction is formed with the p-type semiconductor substrate 1. An antireflection film 3 made of a silicon nitride film or the like is provided on the reverse conductivity type region 2. A surface electrode 4 is provided on the front surface on the light receiving surface side, and a back electrode 5 is provided on the back surface. . Simultaneously with the formation of the collecting electrode 5, aluminum is diffused on the back surface of the semiconductor substrate 1 to form a back surface electric field region (high concentration p ⁺ region) 6.

  The surface electrode 4 and the back electrode 5 of these solar cell elements can be obtained by applying, drying, and baking an electrode material mainly composed of metal.

  For example, as a method of forming the front electrode 4 and the back electrode 5, the following method is described in Patent Document 1 and the like.

(1) In order to form the collector electrode 5a, an electrode material mainly composed of aluminum or the like is applied to most of the semiconductor substrate 1 except for a part of the back surface and dried. (2) The output extraction electrode 5b is formed. In order to form the electrode, the electrode material mainly composed of silver or the like is applied to the part where the electrode material is not applied in (1) and the peripheral part of the aluminum and dried. (3) To form the surface electrode 4 The electrode material mainly composed of silver or the like is applied to the surface of the semiconductor substrate 1 and dried. (4) The electrode material applied to the front surface and the back surface is simultaneously fired to obtain the front electrode 4 and the back electrode 5. The method is a method in which the front electrode 4 and the back electrode 5 are fired simultaneously (simultaneous firing method), but may be fired separately. (For example, see Patent Document 2)
Also, the front electrode 4 and the back electrode 5 with silver as the main component and with good solder wettability (the current collecting electrode 5a with aluminum as the main component and the output extraction electrode 5b with silver as the main component and good solder wettability). Is formed. At this time, the collector electrode 5a formed on substantially the entire back surface is mainly composed of aluminum that acts as a p-type impurity element with respect to the silicon semiconductor substrate 1, and therefore is not in contact with the collector electrode 5a. A back surface electric field region (high concentration p ⁺ region) 6 is formed. This back surface electric field region 6 has an effect of improving the solar cell characteristics.

  As described above, the electrode material is applied to the semiconductor substrate and then baked. In general, a continuous baking furnace is used for this baking. By using a continuous firing furnace, many semiconductor substrates can be continuously fired, and productivity is extremely high.

  An example of such a continuous firing furnace is a belt-type continuous firing furnace. In this belt-type continuous firing furnace, a semiconductor substrate is placed on a conveyor belt that penetrates the heating section of the firing furnace, and the conveyor belt is rotated endlessly, thereby passing through the heating section of the firing furnace. , Firing. FIG. 3 is a view for explaining the structure of a belt-type continuous firing furnace, wherein 8 is a conveying belt, 9 is an upper heater, 10 is a lower heater, 11 is a cover, and 12 is a roller. The firing furnace for processing the semiconductor substrate 1 includes an upper heater 9 (9a to 9c) and a lower heater 10 (10a to 10c) in a cover 11 provided for heat insulation and safety, and to cut off the atmosphere from outside air. ) Is installed. The upper heater 9 and the lower heater 10 are heaters such as far infrared and near infrared, and are composed of resistance coils, lamps, and the like. A conveyor belt 8 is provided through the furnace in the longitudinal direction of the firing furnace, and this conveyor belt 8 is circulated endlessly by the roller 12 being rotationally driven, and thus is placed on the conveyor belt 8. The semiconductor substrate 1 spends a predetermined time and passes through the baking furnace, and baking is performed during that time.

  Usually, the conveying belt 8 is made of a metal material from the viewpoint of heat resistance and strength. However, when the semiconductor substrate 1 on which the paste-like electrode material is applied on the conveying belt side is directly placed on the conveying belt 8, the unsintered electrode material is transferred to the conveying belt 8 by heating during firing. It will be alloyed with other metals. For this reason, there is a problem that the semiconductor substrate 1 is stuck to the conveyor belt 8. In such a case, forcibly peeling off may damage the semiconductor substrate 1 and shorten the life of the conveyor belt 8.

As an example of means for solving this problem, the belt shape described in Patent Document 3 is shown in FIGS. FIG. 4 shows the positional relationship between the semiconductor substrate and the transport belt at this time. In FIG. 4, the semiconductor substrate shows a cross section perpendicular to the traveling direction of the transport belt 8. FIG. 5 shows an enlarged view of a portion Z in FIG. In this document, in order to reduce the contact area between the semiconductor substrate 1 and the conveyor belt, two opposing sides of the semiconductor substrate 1 are supported and a space region is formed between the semiconductor substrate 1 and the conveyor belt 8. It is described that the problem is solved by forming. As shown in FIG. 5, the semiconductor substrate 1 is held by a step portion of a substantially convex protruding portion of the support member 13 provided on the conveying belt 8. Therefore, as shown in FIG. 4, by supporting two opposing sides of the semiconductor substrate 1 and forming a space region between the semiconductor substrate 1 and the transport belt 8, the semiconductor substrate 1 and the transport belt 8. The contact area with is reduced. Therefore, since the entire surface of the semiconductor substrate 1 is not in contact with the transport belt 8, the electrode material is baked without sticking to the transport belt 8 due to heating during firing.
JP 10-335267 A Japanese Patent Laid-Open No. 10-144543 No. 4-8092

  When the semiconductor substrate is baked, the thermal history is locally different, so that internal stress is generated in the substrate and causes warping. In recent years, a semiconductor substrate for forming a solar cell element has been increasing in size, and generally has a size of about 10 cm × 10 cm to 15 cm × 15 cm. Furthermore, from the viewpoint of cost reduction, the thickness of the semiconductor substrate has been reduced in order to reduce the amount of semiconductor material used. A thin semiconductor substrate that is enlarged in this manner may have a difference in formation state due to a difference in thermal history in the semiconductor substrate when an electrode or the like is formed by baking. Moreover, since it is easy to warp and is vulnerable to impacts and stress, problems such as cracking and chipping and a decrease in yield may occur.

  The present invention has been made in view of these problems of the prior art, and suppresses internal stress applied to the semiconductor substrate constituting the solar cell element by heating at the time of firing the electrode, thereby mitigating warpage of the semiconductor substrate. It aims at providing the manufacturing method of the solar cell element which can do.

  In order to achieve the above object, a method for manufacturing a solar cell element according to claim 1 of the present invention includes a semiconductor substrate having a front surface and a back surface, a front surface electrode provided on the front surface side, and a back surface side. A back surface electrode, comprising: an electrode forming step of firing the electrode material applied to the semiconductor substrate to form the front surface electrode and / or the back surface electrode; and The forming step includes a first baking step in which the semiconductor substrate is disposed substantially horizontally and is fired, and the semiconductor substrate is rotated by approximately 90 ° from the direction fired in the first firing step with the vertical direction as an axis. And a second firing step for firing.

  Here, the method for manufacturing a solar cell element according to claim 2 of the present invention is the solar cell element according to claim 1, wherein the back electrode is a collector electrode formed on substantially the entire back surface of the semiconductor substrate. And an output extraction electrode connected to the current collecting electrode.

  Moreover, the manufacturing method of the solar cell element which concerns on Claim 3 of this invention is a manufacturing method of the solar cell element of Claim 1 or 2, In the said collector electrode, said 1st baking process and said 2nd baking It is formed through a process.

  And the manufacturing method of the solar cell element which concerns on Claim 4 of this invention WHEREIN: The semiconductor substrate of Claim 3 WHEREIN: Between the said collector electrodes, it is the same conductivity type as this semiconductor substrate, and is a higher concentration impurity. And this region is formed by the first firing step and the second firing step.

  The method for manufacturing a solar cell element according to claim 5 of the present invention is the method for manufacturing a solar cell element according to claim 4, wherein the semiconductor substrate is a p-type silicon semiconductor, and the current collecting electrode is It is formed with aluminum as the main component.

  Furthermore, the manufacturing method of the solar cell element concerning Claim 6 of this invention is a manufacturing method of the solar cell element as described in any one of Claim 1-5, Said 1st baking process and said 2nd. A step of turning the semiconductor substrate upside down was provided between the firing step.

  Furthermore, the manufacturing method of the solar cell element concerning Claim 7 of this invention is a manufacturing method of the solar cell element as described in any one of Claims 1-6, Said 1st baking process and said 2nd. The firing step is performed using a belt-type continuous firing furnace having a transport belt that rotates endlessly, and the semiconductor substrate is disposed on the transport belt.

  Moreover, the manufacturing method of the solar cell element according to claim 8 of the present invention is the method for manufacturing the solar cell element according to claim 7, wherein the belt-type continuous firing furnace is disposed above the transport belt. An upper heater and a lower heater are provided below.

  And the manufacturing method of the solar cell element which concerns on Claim 9 of this invention is a manufacturing method of the solar cell element of Claim 6. WHEREIN: The said semiconductor substrate is from the calorie | heat amount received from the said lower heater in the said electrode formation process. Also, the amount of heat received from the upper heater was made larger.

  As described above, the present invention is a method of manufacturing a solar cell element including a semiconductor substrate having a front surface and a back surface, a front surface electrode provided on the front surface, and a back electrode provided on the back surface, The electrode forming step includes applying an electrode material to a semiconductor substrate and firing the semiconductor substrate to form the front surface electrode and / or the back electrode, and the electrode forming step includes disposing the semiconductor substrate substantially horizontally. A first baking step of baking and a second baking step of baking the semiconductor substrate in a state where the semiconductor substrate is rotated by about 90 ° from the direction of baking in the first baking step with the vertical direction as an axis. It is possible to prevent a large amount of heat from being concentrated on a part of the substrate. As a result, a solar cell element in which the internal stress accumulated in the semiconductor substrate due to the difference in thermal history is suppressed and the formation state is made uniform can be obtained.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing an example of the structure of a solar cell element according to the method for manufacturing a solar cell element of the present invention, and FIG. 2 (a) is a top view showing a surface electrode of the solar cell element shown in FIG. FIG. 2B is a bottom view showing the back electrode of the solar cell element shown in FIG. In the figure, 1 is a semiconductor substrate, 2 is a reverse conductivity type region, 3 is an antireflection film, 4 is a surface electrode, 5 is a back electrode, 5a is a current collecting electrode, 5b is an output extraction electrode, and 6 is a back surface electric field region. Indicates.

  Here, the effect | action of the solar cell element shown in FIG. 1 is demonstrated easily.

  When light is incident from the side of the antireflection film 3 that is the light receiving surface side of the solar cell element, it is absorbed and photoelectrically converted in the bulk region of the semiconductor substrate 1 that is mainly a p-type semiconductor, and electron-hole pairs (electron carriers and Hole carriers) are generated. Photoelectron-generated electron carriers and hole carriers (photogenerated carriers) generate a photovoltaic force between the front electrode 4 provided on the front side of the solar cell element and the back electrode 5 provided on the back side. The antireflection film 3 plays the role of increasing the amount of photogenerated carriers by reducing the reflectance in a desired light wavelength region depending on the refractive index and the film thickness of the film to be the antireflection film, and thus the light of the solar cell element. The current density Jsc is improved.

Further, since the current collecting electrode 5a of the back electrode 5 is usually formed using aluminum which acts as a p-type impurity element with respect to silicon as a semiconductor substrate, a p ⁺ region is formed on the back surface side surface portion of the silicon substrate. The back surface electric field region 6 is formed. The back surface field region 6 is also called a BSF (Back Surface Field) region, and prevents a decrease in efficiency due to recombination due to photogenerated carriers near the back surface of the semiconductor substrate 1. For this reason, photogenerated carriers generated near the back surface of the semiconductor substrate 1 are accelerated by this electric field, so that electric power is effectively extracted, and in particular, photosensitivity of a long wavelength is increased. As a result, the photocurrent density Jsc is improved, and since the minority carrier (electron) density is reduced in the back surface electric field region 6, the diode current amount (dark current amount) in the region in contact with the back electrode 5 is reduced. As a result, the open circuit voltage Voc is improved.

Next, the manufacturing process of the solar cell element having the above structure will be described. The semiconductor substrate 1 is made of single crystal or polycrystalline silicon. When semiconductor silicon is used as the semiconductor substrate 1, it contains about 1 × 10 ¹⁶ to 10 ¹⁸ atoms / cm ^{3 of} semiconductor impurities exhibiting p-type conductivity such as boron (B) and gallium (Ga), and has a specific resistance of 1 A substrate of about 0.0 to 2.0 Ω · cm is preferably used. A single crystal silicon substrate is formed by a pulling method or the like, and a polycrystalline silicon substrate is formed by a casting method or the like. Since a polycrystalline silicon substrate can be mass-produced and is more advantageous than a single crystal silicon substrate in terms of manufacturing cost, an example using polycrystalline silicon will be described here.

  The polycrystalline silicon ingot is formed by, for example, a casting method, sliced to a thickness of about 300 μm, and cut into a size of about 10 cm × 10 cm or 15 cm × 15 cm to form the semiconductor substrate 1. In order to clean the cut surface of the substrate, it is desirable that the surface be etched by a very small amount with hydrofluoric acid or hydrofluoric acid.

  Thereafter, it is desirable to form minute protrusions on the surface of the silicon substrate using a dry etching method or a wet etching method.

Next, the semiconductor substrate 1 is placed in a diffusion furnace and heat-treated in a gas containing an impurity element such as phosphorus oxychloride (POCl ₃ ) to diffuse phosphorus atoms in the outer surface portion of the semiconductor substrate 1. A reverse conductivity type region 2 having an n-type conductivity type with a sheet resistance of about 30 to 300 Ω / □ is formed.

  And after removing other portions on the surface side of the semiconductor substrate 1, which is the light receiving surface side of the solar cell element, leaving the reverse conductivity type region 2, it is washed with pure water. As this removal method, for example, a resist film resistant to hydrofluoric acid is applied to the surface side of the semiconductor substrate 1, and a reverse conductivity type region other than the surface side of the semiconductor substrate 1 is used by using a mixed solution of hydrofluoric acid and nitric acid. After etching away, the resist film may be removed.

Next, an antireflection film 3 is formed on the surface side of the semiconductor substrate 1. The antireflection film 3 is made of, for example, a silicon nitride film, and is formed by, for example, a plasma CVD method in which a mixed gas of silane (SiH ₄ ) and ammonia (NH ₃ ) is plasmatized by glow discharge decomposition and deposited. The antireflection film 3 is formed so as to have a refractive index of about 1.8 to 2.3 in consideration of a refractive index difference with the semiconductor substrate 1 and is formed to a thickness of about 500 to 1000 mm. . When the silicon nitride film is formed in the presence of hydrogen plasma in this way, it has a passivation effect at the same time, so that it has an effect of improving the electric characteristics of the solar cell in addition to the antireflection function.

  And by the electrode formation process which concerns on this invention, the back surface electrode 5 containing the surface electrode 4, the current collection electrode 5a, and the output extraction electrode 5b is formed as follows.

  The collector electrode 5a constituting the back electrode 5 is made by adding 10 to 30 parts by weight and 0.1 to 5 parts by weight, for example, of 100 parts by weight of aluminum, metal, organic vehicle, and glass frit made of aluminum powder. An electrode material made into a paste is used. As a specific shape, for example, as shown in FIG. 2 (b), the collecting electrode 5a is formed on almost the entire back surface excluding a portion where the output extraction electrode 5b described later is formed. As a coating method, a known method such as a screen printing method can be used, and after coating, the solvent is evaporated at a predetermined temperature and dried.

  The output extraction electrode 5b and the front electrode 4 constituting the back electrode 5 are made of a metal material having good solder wettability, such as silver powder, an organic vehicle, and a glass frit, 10 to 30 parts by weight with respect to 100 parts by weight of silver. 0.1 to 5 parts by weight of an electrode material made into a paste is used. As a specific shape, for example, as shown in FIGS. 2A and 2B, the surface electrode 4 is formed in a lattice shape, and the output extraction electrode 5b is mainly composed of the above-described aluminum. It is provided at a site where the current collecting electrode 5a is not applied, and the peripheral edge is formed so as to overlap the current collecting electrode 5a. As a coating method, a known method such as a screen printing method can be used, and after coating, the solvent is evaporated at a predetermined temperature and dried.

  The front electrode 4 and the back electrode 5 applied and dried as described above can be formed by baking the electrodes on the semiconductor substrate by performing the first baking process and the second baking process of the present invention described later. it can.

  The firing method described below will be described using the structure of a belt-type continuous firing furnace shown in FIG. In FIG. 3, 8 is a conveyance belt, 9 (9a, 9b, 9c) is an upper heater, 10 (10a, 10b, 10c) is a lower heater, 11 is a cover, and 12 is a roller.

  The belt-type continuous firing furnace for processing the semiconductor substrate 1 includes a plurality of upper heaters 9 (9a, 9b, 9c) in a cover 11 provided for heat insulation and safety, and for shielding the atmosphere from outside air. The lower heater 10 (10a, 10b, 10c) is mounted. The upper heater 9 and the lower heater 10 are heaters such as far infrared and near infrared, and are composed of resistance coils, lamps, and the like.

  A conveyor belt 8 is provided through the furnace in the longitudinal direction of the belt-type continuous firing furnace, and this conveyor belt 8 circulates when the roller 12 is driven to rotate, and is thus placed on the conveyor belt 8. The semiconductor substrate 1 passes through the firing furnace.

  When the electrode material applied to the semiconductor substrate 1 is baked by such a belt-type continuous baking furnace, the temperature usually rises suddenly from the vicinity of the entrance and rises to a maximum temperature of 600 to 800 ° C., and reaches the maximum temperature. After reaching the temperature distribution, the temperature distribution gradually decreases. This is to prevent cracking of the solar cell element due to stress due to rapid cooling after the temperature necessary for sintering of the electrode material is first reached. Specifically, the upper heater 9a and the lower heater 10a on the inlet side of the belt-type continuous firing furnace are set to a temperature higher than the maximum temperature in consideration of the outflow of heat, and the upper heaters 9b and 9c and the lower heaters 10b and 10c are set. May be set such that the temperature gradually decreases as the semiconductor substrate 1 moves downstream.

  Hereinafter, an embodiment of each firing step of the first firing step and the second firing step according to the solar cell manufacturing method of the present invention will be described with reference to FIG. FIG. 2A is a diagram viewed from the surface direction of the semiconductor substrate 1. On the surface of the semiconductor substrate 1, one side is A, and one side that is parallel to A is A '. The remaining B and B 'are opposed to each other and are in a parallel positional relationship. Here, the direction parallel to the sides A and A ′ is defined as the Y direction, and the direction parallel to the sides B and B ′ is defined as the X direction.

  In the electrode forming step according to the present invention, an electrode material is applied to the semiconductor substrate, and the semiconductor substrate is baked to form the front electrode and / or the back electrode. Then, a first baking step in which the semiconductor substrate 1 is disposed substantially horizontally and is fired, and the semiconductor substrate 1 is fired in a state where the semiconductor substrate 1 is rotated by approximately 90 ° from the direction of firing in the first firing step with the vertical direction as an axis. And a second firing step. In this process, when the traveling direction of the semiconductor substrate 1 held on the belt is the X direction and the side A enters the firing furnace first, there is a time difference until the side A ′ facing A enters the firing furnace. is there. At this time, the sides B and B 'are heated almost simultaneously at both sides, so that there is little time difference in the thermal history.

  And in the 2nd baking process, since it rotated 90 degrees from the direction in a 1st baking process, the semiconductor substrate 1 advances to a Y direction. Conversely, in the second firing step, the sides A and A 'are heated at the same time, so there is little difference in the thermal history. Further, there is a time difference between sides B and B ′ before entering the firing furnace. Therefore, since the semiconductor substrate 1 can balance the thermal history generated in the first baking step and the thermal history generated in the second baking step to make the internal stress uniform, the warpage of the semiconductor substrate 1 is alleviated. can do.

  Next, it is desirable that the collecting electrode 5a is formed through the first firing step and the second firing step. The reason is as follows. First, the current collecting electrode 5a has a large area and a large amount of electrode material is used. Therefore, since it is greatly affected by the difference in thermal expansion coefficient between the semiconductor substrate 1 and the electrode material, the influence on the warp of the semiconductor substrate 1 is large. Here, for each of the firing steps of the first firing step and the second firing step according to the present invention, the heat history for the substrate can be made more uniform for the reasons described above, so that the substrate does not greatly warp in one direction, It will bend evenly in both directions. As a result, since large warpage can be suppressed, cracking of the semiconductor substrate 1 due to warpage can be reduced. Furthermore, the ohmic contact between the semiconductor substrate 1 and the collector electrode 5a is more stable after the first firing step and the second firing step.

  Further, the current collecting electrode 5a is made of an electrode material containing a semiconductor impurity having the same conductivity type as that of the semiconductor substrate 1, and the semiconductor substrate 1 and the current collecting electrode 5a are separated by passing through a first firing step and a second firing step. Further, a back surface electric field region 6 having the same conductivity type as the semiconductor substrate 1 and containing a higher concentration of impurities is formed on substantially the entire surface. The back surface electric field region 6 serves to reduce the rate at which photogenerated electron carriers reach the back electrode 5 from the semiconductor substrate 1 and recombine, thereby improving the photocurrent density Jsc. Further, since the minority carrier (electron) density is reduced in the back surface electric field region 6, it functions to reduce the amount of diode current (dark current amount) in this region and the region in contact with the back electrode 5, and the open circuit voltage Voc is improved. The effect that it does is acquired, and the characteristic of a solar cell element can be improved.

Here, when a p-type silicon semiconductor is used as the semiconductor substrate 1, it is desirable to use a material containing aluminum as a main component as the electrode material of the current collecting electrode 5a. As described above, by firing the collector electrode 5a mainly composed of aluminum as the electrode material, aluminum is thermally diffused into the silicon substrate at the junction between the collector electrode 6 and the silicon substrate, and the silicon substrate is p-type. A back surface electric field region (high concentration p ⁺ region) 6 containing a large amount of aluminum as an impurity can be formed.

  And it is desirable to provide the front-back inversion process which reverses the semiconductor substrate 1 between the 1st baking process and the 2nd baking process. As described above, the semiconductor substrate 1 is reversed between the first firing step and the second firing step from the state fired in the first firing step, whereby the influence of the heat that the semiconductor substrate 1 receives from the inside of the firing furnace is affected. It can be dispersed to make the internal stress uniform.

Furthermore, when a front / back reversal step is included between the first firing step and the second firing step,
(1) During the first firing step, the semiconductor substrate 1 is placed on the transport belt 8 in a state where nothing is present on the surface on the light receiving surface side, and the back side electrode is fired.

(2) The surface electrode 4 is applied and dried on the light-receiving surface side of the semiconductor substrate 1 (3) After the front and back reversing step, such a procedure of firing the surface electrode 4 side of the semiconductor substrate 1 in the second firing step If firing is performed, contact between the surface electrode 4 and the conveyor belt 8 can be prevented, contamination on the light receiving surface side of the semiconductor substrate 1 can be prevented, and reduction in the amount of received light can be prevented.

  Further, in the first firing step and the second firing step, a belt-type continuous firing furnace having a transport belt that rotates endlessly is used, and the semiconductor substrate 1 is disposed on the transport belt 8. It is desirable to do.

  This is because mass production is possible by using a belt-type continuous firing furnace provided with an endlessly rotating conveyor belt, which is very useful in terms of cost.

  The firing furnace including the conveyor belt 8 is preferably provided with an upper heater 9 and a lower heater 10 above and below, respectively, with the conveyor belt 8 interposed therebetween. This is because, in the case of a belt-type firing furnace including the upper heater 9 and the lower heater 10, it is possible to simultaneously fire the front electrode 4 and the back electrode 5 in the electrode formation.

  Here, when such a belt-type continuous firing furnace using the upper heater 9 and the lower heater 10 is used, the amount of heat received by the semiconductor substrate 1 in each firing step is larger when received from the upper heater 9 than the lower heater 10. It is desirable to be With such a configuration, the heating state from above and below becomes asymmetric, and the symmetry of the temperature distribution inside the semiconductor substrate 1 in each baking step can be broken. As a result, the effect in the embodiment of the present invention can be made more reliable, the thermal history inside the semiconductor substrate can be more dispersed, and the formation state can be made uniform.

  The reason is that the lower heater 10 is opposed to the lower surface of the semiconductor substrate 1 (the surface in contact with the conveying belt 8) with the conveying belt 8 interposed therebetween, and directly contacts the upper heater 9 facing the upper surface of the semiconductor substrate 1. In comparison, it is difficult to supply a high amount of heat to the semiconductor substrate 1. Of course, it is possible by increasing the electric power, but the conveyor belt 8 is heated more, and it is natural to increase the amount of heat from the upper heater 9 from the viewpoint of efficient use of energy. Yes, more preferred.

  Moreover, in the 1st baking process which provided the front-and-back inversion process of the semiconductor substrate 1 before the 2nd baking process, or the 2nd baking process, the surface side of the semiconductor substrate 1 is surely directed toward the lower heater 10 with less received heat. Will be fired. Therefore, since the amount of heat is not applied to the surface side of the semiconductor substrate 1 more than necessary, damage to the reverse conductivity type region 2 can be reduced, and a solar cell element with excellent output characteristics can be obtained.

  As described above, when the belt-type continuous firing furnace using the upper heater 9 and the lower heater 10 is used, whether the amount of heat received by the semiconductor substrate 1 in each firing step is greater from the upper heater 9 than the lower heater 10. Can be confirmed as follows.

(A) A thermocouple is attached to a plurality of locations (symmetric locations on the front and back sides) of the front and back surfaces of the dummy semiconductor substrate. (B) The upper heater 9 and the lower heater 10 are set to predetermined temperature conditions. (C) (a) A dummy semiconductor substrate is placed on the conveyor belt 8 and sent at a predetermined belt speed. (D) The temperature of the front and back surfaces of the dummy semiconductor substrate is measured by a thermocouple, and a temperature profile is created (e) ( Compare the temperature profile created in d) integrated over time on the front and back surfaces, and compare the amount of heat applied (take an average value for multiple locations)
In Patent Document 3, in order to prevent unsintered electrode material from alloying with the metal of the conveyor belt 8 due to heating during firing, two opposing sides of the semiconductor substrate 1 are supported, It is described that a space region is formed between 1 and the conveying belt 8. FIG. 4 shows the positional relationship between the semiconductor substrate and the transport belt at this time. In FIG. 4, the semiconductor substrate shows a cross section perpendicular to the traveling direction of the transport belt 8. FIG. 5 shows an enlarged view of a portion Z in FIG. As shown in FIG. 5, the semiconductor substrate 1 is held by a step portion of a substantially convex protruding portion of the support member 13 provided on the conveying belt 8. Therefore, as shown in FIG. 4, by supporting two opposing sides of the semiconductor substrate 1 and forming a space region between the semiconductor substrate 1 and the transport belt 8, the semiconductor substrate 1 and the transport belt 8. The contact area with is reduced. Therefore, since the entire surface of the semiconductor substrate 1 is not in contact with the transport belt 8, the electrode material is baked without sticking to the transport belt 8 due to heating during firing.

  When the electrodes are formed by firing while supporting the two opposing sides of the semiconductor substrate 1 as described above, the conveying belt 8 and the support member 13 are also heated simultaneously with heating the semiconductor substrate. When the semiconductor substrate 1 constituting the solar cell element is placed on the conveyor belt 8, two opposing sides (for example, A and A ′ shown in FIG. 2) of the semiconductor substrate 1 are held by the support member 13. Therefore, the temperature rising speed differs between the portions A and A ′ that are in direct contact with the support member 13 and the portions B and B ′ that are not in contact with each other in the semiconductor substrate. The difference in thermal history occurs between the A ′ side and the B, B ′ side, and the substrate is warped due to internal stress due to the difference in thermal history.

  However, in the embodiment of the present invention, when the semiconductor substrate 1 is baked as the baking step, in the first baking step, the semiconductor substrate 1 shown in FIG. The A and A ′ sides are placed on the support member 13 of the conveyor belt 8 and fired in a state of being arranged substantially horizontally. In the second firing step, the semiconductor substrate 1 is placed in the first direction with the vertical direction as the axis. The semiconductor substrate 1 is rotated about 90 ° from the firing direction in the firing step, and the direction of entry of the semiconductor substrate 1 is the Y direction, and the B and B ′ sides of the semiconductor substrate 1 shown in FIG. Place and fire. As a result, a thermal history different from the thermal history applied to the semiconductor substrate 1 in the first firing step is applied in the second firing step, and therefore in a wider region, in particular, on the A, A ′ side and B, B Heat is uniformly applied on the 'side. And since the heat quantity more than necessary is not applied to one part, the solar cell element by which internal stress was relieve | moderated and the curvature of the board | substrate was relieve | moderated can be obtained.

  It should be noted that the embodiment of the present invention is not limited to the above-described example, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  For example, in the above description, the belt-type firing furnace has been described using an example in which mass production is possible. However, the present invention is not limited to this, and the batch firing furnace also includes the first firing step as described above, It is also effective to include a step of rotating the direction of the semiconductor substrate by 90 ° between the second baking step and / or a front / back reversing step of reversing the semiconductor substrate in the vertical direction.

  The reason for this is that the firing temperature in the batch-type firing furnace is non-uniform, and the heat received by the semiconductor substrate 1 is partially due to the step of rotating the semiconductor substrate 1 by 90 ° in the vertical direction in the second firing step. To avoid concentrating on. As a result, it becomes possible to disperse the internal stress of the semiconductor substrate, and a semiconductor substrate having a uniform formation state can be obtained.

  The surface electrode 4 is etched in advance at a portion corresponding to the surface electrode 4 of the antireflection film 3, and an electrode material (silver paste or the like) is applied to the portion and baked to establish conduction with the reverse conductivity type region 2. You may do it. Further, an electrode material (silver paste or the like) is directly applied on the antireflection film 3 and baked, and the antireflection film 3 is penetrated by a so-called fire-through method so as to be electrically connected to the reverse conductivity type region 2. Good.

  Next, from the viewpoint of the electrode firing order, the surface electrode 4 is provided on the surface of the semiconductor substrate 1 and the back electrode 5 is provided on the back surface, but the back electrode 5 is formed on substantially the entire surface. Current collecting electrode 5a and an output extraction electrode 5b connected to the current collecting electrode 5a. The order and combination of firing for forming these electrodes may be other than the methods described above. For example, the back electrode 5 (the collector electrode 5a and the output extraction electrode 5b) may be formed in the first baking process, the surface electrode 4 may be formed in the second baking process, or the output extraction electrode 5b in the first baking process. The collector electrode 5a and the surface electrode 4 may be formed in the second firing step, but the collector electrode 5a is desirably formed through the first firing step and the second firing step. . Moreover, the surface electrode 4 may be formed through a 1st baking process and a 2nd baking process.

  A loader (not shown) for continuously disposing the semiconductor substrate 1 before firing on the transport belt 8 is provided on the entrance side of the transport belt 8, and further, firing is performed on the exit side of the transport belt 8. You may provide the unloader (not shown) which can pick up the subsequent semiconductor substrate 1 from the conveyance belt 8 continuously.

Furthermore, if the first baking step and the second baking step are processed using different baking furnaces, preferably belt type continuous baking furnaces, a large amount of semiconductor substrates can be processed with high productivity. So desirable. In this case, it is desirable to provide a mechanism for rotating the surface of the semiconductor substrate after the first baking step by approximately 90 ° about the vertical direction or reversing the front and back. For example, after a semiconductor substrate is aggregated into a cassette by an unloader, a mechanism is provided to rotate the cassette itself about 90 ° about the vertical direction or to reverse the front and back, and then a firing furnace used for the second firing step What is necessary is just to set this cassette to a loader and to supply a semiconductor substrate in a predetermined state. Needless to say, the loader is previously structured so that the cassette can be set in a predetermined state.

  Furthermore, in the belt-type continuous firing furnace, both the upper heater 9 and the lower heater 10 are shown in FIG. 3, but the present invention is not limited to this, and a structure having only the upper heater 9 or only the lower heater 10 may be used. However, when the electrode material is applied to both surfaces of the semiconductor substrate 1, it is more desirable that both the upper heater 9 and the lower heater 10 are provided, because using them can perform firing simultaneously. This is because the front electrode 4 and the back electrode 5 of the semiconductor substrate 1 can be heated and fired simultaneously.

  In FIG. 3, each of the upper heater 9 and the lower heater 10 is divided into three parts. However, the upper heater 9 and the lower heater 10 are not limited to this and may be more or less than this. However, in order to freely set the heating profile of the semiconductor substrate 1, it is desirable to divide into three or more.

  In the above description, the semiconductor substrate 1 has been described as an example in which the upper heater 9 receives a larger amount of heat than the lower heater 10. Usually, the lower heater 10 is opposed to the semiconductor substrate 1 with the conveying belt 8 interposed therebetween as compared with the upper heater 9. Therefore, it is easier to increase the amount of heat from the upper heater 9. There is no problem even if the heater is installed only at the top or the bottom. If the method for manufacturing a solar cell element according to the present invention is used regardless of how the heater is attached, the thermal history to the semiconductor substrate is made uniform, the warp of the semiconductor substrate is suppressed, and the damage to the reverse conductivity type region 2 is reduced. be able to.

  Similarly, in the above description, the example in which two firing steps are provided as the firing step, such as the first firing step and the second firing step, has been described. You may provide the baking process.

  Moreover, in each baking process including the first baking process, the semiconductor substrate is disposed substantially horizontally, but it is not necessarily required to be strictly horizontal. For example, in the case of a belt-type continuous firing furnace, the conveyor belt may have an inclination to improve exhaust, but such an inclination is sufficient if the semiconductor substrate does not slide off the conveyor belt. You may arrange | position in the state which has. In this case, in the second baking step, the direction orthogonal to the semiconductor substrate surface may be regarded as the vertical direction and rotated by 90 ° for baking.

  The material of the semiconductor substrate may be a known compound semiconductor other than silicon. Further, the electrode material to be fired, the electrode shape to be applied, or the application method are not limited to the above-described examples, and any combination of materials and shapes that can exhibit the characteristics as a solar cell element can be used according to the configuration of the present invention. Needless to say, the advantages of the present invention can be obtained.

It is a schematic sectional drawing which shows the structure of a solar cell element. (A) is the top view which looked at the solar cell element of FIG. 1 from the surface side, (b) is the bottom view which looked at the solar cell element of FIG. 1 from the back surface side. It is a schematic structure figure of a belt type continuous firing furnace. It is a figure for demonstrating a belt type continuous baking furnace. It is a figure for demonstrating a belt-type continuous baking furnace, and is an enlarged view of the Z section of FIG.

Explanation of symbols

1: Semiconductor substrate 2: Reverse conductivity type region 3: Antireflection film 4: Front electrode 5: Back electrode 5a: Current collecting electrode 5b: Output extraction electrode 6: Back surface electric field region 8: Conveying belt 9: Upper heaters 9, 9a 9b, 9c: Upper heater 10, 10a, 10b, 10c: Lower heater 11: Cover 12: Roller 13: Support member

Claims (9)

A method for manufacturing a solar cell element, comprising a semiconductor substrate having a front surface and a back surface, a front surface electrode provided on the front surface, and a back electrode provided on the back surface,
Including an electrode forming step of applying an electrode material to the semiconductor substrate and firing the semiconductor substrate to form the front electrode and / or the back electrode;
The electrode forming step includes a first firing step in which the semiconductor substrate is disposed substantially horizontally and fired;
A second baking step of baking the semiconductor substrate in a state where the semiconductor substrate is rotated by approximately 90 ° from the direction of baking in the first baking step with the vertical direction as an axis;
The manufacturing method of the solar cell element containing this. 2. The method for manufacturing a solar cell element according to claim 1, wherein the back electrode includes a collector electrode formed on substantially the entire back surface, and an output extraction electrode connected to the collector electrode. The said current collection electrode is a manufacturing method of the solar cell element of Claim 1 or 2 formed through said 1st baking process and a 2nd baking process. The semiconductor substrate has a back surface electric field region that has the same conductivity type as the semiconductor substrate and contains a higher concentration of impurities between the collecting electrode and the back surface electric field region. The manufacturing method of the solar cell element according to claim 3 formed by said 2nd baking process. The method for manufacturing a solar cell element according to claim 4, wherein the semiconductor substrate is a p-type silicon substrate, and the collecting electrode is mainly composed of aluminum. The manufacturing method of the solar cell element as described in any one of Claims 1-5 which provided the front-back inversion process which reverses the said semiconductor substrate between the said 1st baking process and said 2nd baking process. The first firing step and the second firing step are performed using a belt-type continuous firing furnace provided with a transport belt that rotates endlessly, and the semiconductor substrate is disposed on the transport belt. The manufacturing method of the solar cell element as described in any one of Claim 6 from. The said belt-type continuous baking furnace is a manufacturing method of the solar cell element of Claim 7 provided with the upper heater and the lower heater in the upper direction and the downward direction on both sides of the said belt for conveyance. 9. The solar cell element according to claim 8, wherein the amount of heat received from the upper heater is larger than the amount of heat received from the lower heater in the first baking step and the second baking step. Production method.

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