JP2006310792A - Heating furnace and manufacturing method of solar cell element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating furnace or the like capable of reducing variations in the temperature received by a workpiece. <P>SOLUTION: A heating furnace 1 heating a workpiece 5 inside comprises a conveying means 2 for mounting the workpiece 5 for conveying it in the heating furnace 1, a heating means 3 arranged inside the heating furnace 1 for heating the workpiece 5, and a heat control means 6 for indirectly transmitting the heat obtained by the heating means 3 to the workpiece 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heating furnace and a method for manufacturing a solar cell element using the same.

  In general solar cell elements, a pn junction is formed on a semiconductor substrate such as single crystalline silicon or polycrystalline silicon having semiconductivity, and silver or aluminum is used so that power can be taken out when irradiated with light. Electrodes as main components are formed on the front and back surfaces of the semiconductor substrate.

  For example, as described in Patent Document 1, the electrode of such a solar cell element is obtained by applying a paste mainly composed of aluminum or the like to most of the semiconductor substrate excluding a part on the non-light-receiving surface side. After drying, after applying and drying a paste mainly composed of silver or the like so as to cover the portion not coated with the paste mainly composed of aluminum or the like and its peripheral part, the light receiving surface of the semiconductor substrate is finally provided. A co-firing method is often used in which a paste mainly composed of silver or the like is applied to the side, dried, and simultaneously fired.

  In general, a continuous heating furnace (firing furnace) is used for firing such an electrode. By using a continuous heating furnace, a large amount of a semiconductor substrate coated with a paste for forming an electrode can be processed, and the productivity is extremely high.

As an example of such a continuous heating furnace, there is a belt-type continuous heating furnace as shown in FIG. This is because the object to be processed is loaded on a conveying means such as an endless belt made of a heat-resistant metal mesh or the like passing through the heating part of the heating furnace, and the endless belt is rotated. It is passed through and fired. In addition, in order to improve the heat insulation of a heating furnace, the space in a heating furnace is enclosed with the heat insulating material, and the heater is provided up and down centering on the endless belt with which a to-be-processed object is loaded.
JP 10-335267 A

  In the heating furnace, the heat generated by the heater directly reaches the object to be processed, and there is an influence of reflection and radiation from the side wall inside the heating furnace made of heat insulating material. There is a problem that the variation becomes large. Furthermore, heaters that emit mid-infrared rays or near-infrared rays can be rapidly heated, but unlike far-infrared heaters, it is difficult to divide them into small sizes in a heating furnace. There is a disadvantage that the temperature variation of the is large and difficult to control.

  As described above, due to the difference in the firing temperature in the heating furnace, the object to be treated may not be fired at the optimum firing temperature at one or both of the end part and the center part of the heating furnace. Thus, the electrical characteristics of the solar cell element and the adhesive strength of the electrodes on both the front and back surfaces with the semiconductor substrate are greatly affected, and the quality of the solar cell element is significantly reduced. In order to avoid the problem, there is a method of supplying the object to be processed only to the central portion in the furnace, but this method is not preferable because the production amount is greatly reduced.

  The present invention has been made in view of such conventional problems, and a heating furnace capable of reducing variations in temperature experienced by an object to be processed, and a method for manufacturing a solar cell element using the heating furnace. The purpose is to provide.

  The present invention is a heating furnace that heat-treats an object to be processed therein, a conveying unit that places and conveys the object to be processed, and a heating unit that is disposed inside the heating furnace and heats the object to be processed And heat control means for indirectly transferring the heat obtained from the heating means to the object to be processed.

  It is preferable that the heat control means is disposed between the conveying means and the inner wall of the heating furnace.

  In addition, the transport unit is configured to place a plurality of the objects to be processed in a plurality of rows and transport in the row direction. Or it is preferable to arrange | position between the said row | line | column and the said heating furnace inner wall.

  Further, the conveying means is constituted by a mesh belt, the heating means is arranged above and below the conveying means, and the heat control means is arranged above and / or below the conveying means. preferable.

  Here, it is preferable that the heat control means is a heat reflection suppressing member that has less heat reflection than the inner wall of the heating furnace. In this case, it is particularly preferable that the heating means is disposed closer to the inner wall of the heating furnace than the object to be processed located at the end.

  The heat control unit may be a heat reflecting member having a heat reflecting surface that reflects heat in a predetermined direction. In this case, the heating unit heats more than the object to be processed located at an end. It is particularly preferable that it is arranged on the furnace center side.

  Moreover, this invention is a manufacturing method of the solar cell element which has the process of baking the metal paste formed in the surface of the semiconductor substrate using the said heating furnace.

  The heating furnace of the present invention heats an object to be processed therein, and is disposed inside the heating furnace for placing and transferring the object to be processed and heating the object to be processed. Since the heating means and the heat control means for indirectly transferring the heat obtained from the heating means to the object to be processed are provided, the center and the end of the conveying means It is possible to effectively suppress variation in the firing temperature of the treatment body and to perform uniform firing.

  It is preferable that the heat control means is disposed between the conveying means and the inner wall of the heating furnace. Thereby, especially at the end of the conveying means, when the influence of heat reflection by the inner wall of the heating furnace is strong or when the heat reflection is very little and the heating becomes insufficient, at the center and the end of the conveying means, It is possible to effectively suppress variation in the firing temperature of the object to be processed.

  In addition, the transport unit is configured to place a plurality of the objects to be processed in a plurality of rows and transport in the row direction. Or it is preferable to arrange | position between the said row | line | column and the said heating furnace inner wall. Thereby, it is possible to suppress the firing temperature of the object to be processed from being varied for each column.

  Further, the conveying means is constituted by a mesh belt, the heating means is arranged above and below the conveying means, and the heat control means is arranged above and / or below the conveying means. preferable. Thereby, when simultaneously heating both surfaces of the object to be processed, variation in the firing temperature of the object to be processed can be effectively suppressed on both surfaces.

  Here, it is preferable that the heat control means is a heat reflection suppressing member that has less heat reflection than the inner wall of the heating furnace. In this case, it is particularly preferable that the heating means is disposed closer to the inner wall of the heating furnace than the object to be processed located at the end. This can reduce the influence of heat reflection from the inner wall of the heating furnace made of a heat insulating material or the like on the object to be processed which is strongly affected by heat reflection in the heating furnace. As a result, it is possible to suppress the firing temperature of the object to be processed from being varied between the central portion and the end portion of the conveying means.

  The heat control unit may be a heat reflecting member having a heat reflecting surface that reflects heat in a predetermined direction. In this case, the heating unit heats more than the object to be processed located at an end. It is particularly preferable that it is arranged on the furnace center side. By doing in this way, the heat generated by the heating means is reflected by the heat reflecting member and can efficiently reach the object to be processed, and as a result, the firing temperature of the object to be processed becomes the center of the conveying means. It is possible to suppress variation at the end.

  In addition, the method for manufacturing a solar cell element of the present invention includes a step of firing a metal paste formed on the surface of a semiconductor substrate using the heating furnace. Thus, variation in the firing temperature can be effectively suppressed. As a result, the fired state of the fired electrode of the solar cell element becomes uniform, and variations in the electrical characteristics of the solar cell element and the adhesive strength between the semiconductor substrate and the electrode can be reduced and the quality can be improved.

  Hereinafter, the heating furnace of this invention and the manufacturing method of the solar cell element of this invention are demonstrated in detail using figures.

--heating furnace--
≪First embodiment≫
1 and 2 are views for explaining the structure of the first embodiment of the heating furnace according to the present invention. FIG. 1 (a) is a sectional view in the furnace length direction of the heating furnace, and FIG. The cross section of the furnace width direction of the heating furnace is shown. FIG. 2 is a partial cross-sectional view of the heating furnace shown in FIG. 1 as viewed from above.

  In the figure, 1 is a heating furnace, 2 is a conveying means (2a is a belt, 2b is a support, 2c is a roller), 3 is a heating means (3a is an upper heater, 3b is a lower heater), 5 is an object to be processed, 6 (60) is a heat reflection suppressing member, and 8 is a processing space.

  The heating furnace 1 heats the object to be processed 5 in its interior, and has heat insulation and safety, and a cover provided to block the atmosphere from outside air, and heat insulation for heat insulation and safety. It has the furnace body comprised with the material 1a. Inside the furnace body, there is a processing space 8 for processing the workpiece 5.

  The conveying means 2 is disposed so as to penetrate the processing space 8 inside the furnace body in the furnace length direction. For example, an endless belt made of a heat-resistant alloy such as stainless steel is used, and a roller By rotating 2c, it circulates endlessly and moves the object 5 loaded on the conveying means 2 in the conveying direction (furnace length direction). In addition, when using the belt 2a as the conveyance means 2, you may make it support with the support body 2b so that it may not sag during rotation. A large number of objects to be processed 5 can be processed simultaneously by arranging the objects to be processed 5 in a plurality of rows on the conveying means 2.

  The heater 3 is disposed inside the processing space 8 and heats the workpiece 5 placed on the transport means 2. The heater 3 may be, for example, a far-infrared heater, a lamp, resistance heating, or the like, but a heater that emits mid-infrared rays or near-infrared rays (middle / near-infrared heater) is used from the viewpoint of rapid temperature rise characteristics. For example, a lamp heater can be used. In the present specification, the mid-infrared ray or near-infrared ray refers to an infrared ray having a wavelength of 0.7 μm to 3 μm. In general, the mid-infrared rays may be classified as 1.5 to 3 μm, and the near-infrared rays may be classified as 0.7 to 1.5 μm, but they are not strictly distinguished here.

  In the example shown in FIG. 1, an upper heater 3a and a lower heater 3b are arranged with the conveying means 2 as a boundary. In particular, when a mesh belt 2a (mesh belt) conveyed endlessly is used as the conveying means 2, the heat radiated from the lower heater 3b places the object 5 on the belt 2a through the mesh belt. Since it reaches the surface, the workpiece 5 can be processed from both the upper surface side and the lower surface side. However, the present invention is not limited to this, and only one of the upper heater 3a and the lower heater 3b may be used.

  Further, in the example shown in FIG. 1A, the upper heater 3a and the lower heater 3b are divided into three parts in the transport direction. In this way, it is desirable to divide the plurality of parts into a plurality of pieces in the transport direction and provide the heaters independently, so that it becomes easy to change the firing profile for the object 5 to be processed. However, the present invention is not limited to this structure. Furthermore, in FIG. 2, although it described by the example in which the clearance gap exists between the divided | segmented upper heaters 3a and the to-be-processed object 5 is visible through this clearance gap, it is not restrict | limited also about this.

  In addition, when processing the to-be-processed object 5 with the heating furnace 1, the coating agent is normally apply | coated to the to-be-processed object 5. FIG. For example, in the case of a solar cell element, as will be described later, a metal paste containing a predetermined metal powder, a binder, an organic solvent, and the like is applied in a predetermined shape. Components such as a binder contained in such a coating agent are vaporized or burned from the object to be processed 5 in the heating furnace 1 during the baking process, and are gasified. When this gas fills the heating furnace 1, the product characteristics are adversely affected during the firing process. Therefore, the heating furnace 1 is supplied with an exhaust device (not shown) for exhausting exhaust gas to the outside or supplying air to the furnace. A device (not shown) is provided.

  Next, the heat reflection suppressing member 60 will be described in detail.

  In the present invention, as shown by the double-headed arrow in FIG. 1 (b) and the dotted line region in FIG. 2, the heat reflection suppressing member 60 starts from the end of the conveying means 2 where the influence of reflection in the furnace is strong, from the heating furnace inner wall 1b. Up to the processing space 8. In other words, it is only necessary that the heat reflection suppressing member 60 is positioned between the conveying means 2 and the heating furnace inner wall 1b when viewed in plan. As a result, the influence of reflection from the heating furnace inner wall 1b and the like can be suppressed at the end of the conveying means 2 where the influence of reflection in the furnace is strong. It is possible to prevent variation between the part and the end part.

  The material of the heat reflection suppressing member 60 is preferably a material that reflects less heat from the heater, particularly radiant energy in the wavelength range of the infrared region than the inner wall of the processing space 8, and the heat insulating material 1 a that is the inner wall of the processing space 8. Instead, a material having a low reflectance of electromagnetic waves (infrared region) having a wavelength that contributes to firing of the object to be processed 5 may be selected. In particular, those having a reflectivity of 0.3 or less, preferably 0.2 or less in the wavelength range of the infrared region, particularly 0.7 to 3 μm are preferable. In order to reduce the reflectance, it is more preferable to use a black member or roughen the surface of the member. The reflectance can be measured using an arbitrary spectral reflectance measuring device, and for example, measured using a reflectance measuring device MSR7000 manufactured by Opto Research Co., Ltd. Furthermore, it is necessary to select a material that has thermal strength in the operating temperature range of the heating furnace 1 and that does not deform or deteriorate. Moreover, it is necessary to select a member that is not eroded by the binder or the like contained in the paste when the object 5 is fired. As the heat reflection suppressing member 60 satisfying such a condition, a graphite material that is a substance close to a pure black body (an object that completely absorbs radiation energy of all wavelengths) is suitable.

  The specific arrangement of the heat reflection suppressing member 60 is, for example, the conveying means 2 between the upper heat insulating material inside the upper heater 3a (the heat reflection suppressing member 60a), the upper heater 3a and the support 2b. Perpendicular to (heat reflection suppressing member 60b), parallel to the conveying means 2 between the upper heater 3a and the support 2b (heat reflection suppressing member 60c), the lower heat insulating material located below the lower heater 3b The inner side (heat reflection suppressing member 60d) is preferable.

  Further, in the example shown in the figure, the heat reflection suppressing members (60a, 60b, 60c, 60d) are described so as to have the same structure at symmetrical positions when viewed from the center of the conveying means 2. Not all are necessary. Of these heat reflection suppression members (60a, 60b, 60c, 60d), only the necessary heat reflection suppression member is selected and arranged so that the firing temperature of the object 5 on the conveying means 2 is uniform. Just do it. Further, the size, shape, and material of the heat reflection suppressing member (60a, 60b, 60c, 60d) may be changed according to the respective baking conditions so that the baking temperature of the object 5 on the conveying means 2 is uniform. good.

  Further, these heat reflection suppressing members 60 are not only installed in parallel and perpendicular to the conveying means 2 like the heat reflection suppressing members (60a, 60b, 60c), but also like the heat reflection suppressing member 60d. It can also be installed at an angle. However, in this case, it is desirable to fix so that it does not drop or change its inclination due to vibration of conveyance or the like.

  In addition, when the heat reflection suppression member 60 with a low reflectance is provided, when the absorption rate of the radiant energy from the heater 3 increases and the temperature of the heat reflection suppression member 60 rises, The radiation is generated based on the emissivity, which is the ratio of the radiant divergence of the black body thermal radiation at the same temperature. Therefore, there is a possibility that the end of the conveying means 2 is affected by the radiation from the heat reflection suppressing member 60.

  Therefore, in order to suppress the radiation from the heat reflection suppressing member 60, the temperature of the heat reflection suppressing member 60 may be controlled so that the temperature of the heat reflection suppressing member 60 does not become too high. Since the wavelength at which the radiant energy density is maximum is inversely proportional to the temperature of the member, the radiant energy in the wavelength range in the infrared region can be suppressed by controlling the temperature of the heat reflection suppressing member 60. For example, the heat conductivity of the heat insulating material 1a is reduced by increasing the heat conductivity of the heat reflection suppressing member 60, further increasing the heat conductivity of the heat insulating material 1a, or reducing the thickness of the heat insulating material 1a. By controlling the temperature rise of the heat reflection suppressing member 60, the radiation of the heat reflection suppressing member 60 may be suppressed. Alternatively, as shown in FIG. 12, a heat exchanger may be incorporated in the heat reflection suppression member 60 as the radiation suppression mechanism 7, and a medium such as air is flowed to control the temperature of the heat reflection suppression member 60. Also good. However, the thermal conductivity of the heat reflection suppressing member, the thermal conductivity or thickness of the heat insulating material, the temperature of the air in the heat exchanger, the flow rate, etc. are appropriately adjusted so as to suppress the influence of the ambient temperature in the heating furnace 1. Is preferred.

<< Second Embodiment >>
Next, the structure of the second embodiment of the heating furnace according to the present invention will be described with reference to FIGS. 3 and 4.

  3 and 4 are views for explaining the structure of the second embodiment of the heating furnace according to the present invention. FIG. 3 (a) is a sectional view in the furnace length direction of the heating furnace, and FIG. 3 (b). Shows an example of a cross section in the furnace width direction of the heating furnace, and FIG. 3C shows still another example of a cross section in the furnace width direction of the heating furnace. FIG. 4 is a partial cross-sectional view of the heating furnace as viewed from above.

  In addition, since the structure of the basic heating furnace 1 is the same as that of 1st embodiment, only the feature point in 2nd embodiment is demonstrated below.

  In the present embodiment, the objects to be processed 5 are stacked on the conveying means 2 in a plurality of rows in the furnace width direction. And when seen in a plan view, the heat reflection suppressing member 60 (60e) is between one row of the object to be processed 5 and another row adjacent thereto (corresponding to a double arrow B portion in FIG. 3B), And / or it was made to be located between the row | line | column of the edge of the to-be-processed object 5, and the inner wall 1b of the processing space 8 (corresponding to the double-headed arrow A part in FIG. 3B).

  By arranging the heat reflection suppressing member 60 (60e) in this way, the influence of the reflection of the radiant energy of the heater from the inner wall of the processing space 8 constituted by the heat insulating material 1a is mitigated, and the object to be processed 5 receives. The heat is mainly limited to the heat from the heater 3. As a result, it is possible to prevent the firing temperature of the object to be processed 5 from varying from column to column.

  In the example shown in FIG. 3 (b), between the end row of the object to be processed 5 and the inner wall 1b of the processing space 8 (the double arrow A part in FIG. 3 (b)), one row of the object to be processed 5 By disposing the heat reflection suppressing member 60e between both adjacent rows (part B in FIG. 3B), variation in temperature for each row can be more sufficiently suppressed. .

  However, since the influence of the reflection from the inner wall 1b of the processing space 8 is small in the center of the furnace, as in the example shown in FIG. 3C, if the temperature can be sufficiently suppressed, In the central part of the furnace, the heat reflection suppressing member 60e is not necessarily installed.

≪Third embodiment≫
In the third embodiment of the present invention, a heat reflecting member 61 is installed as the heat control means 6 instead of the above-described heat reflection suppressing member 60.

  The structure of the third embodiment of the heating furnace according to the present invention will be described with reference to FIGS. 10 and 11.

  In addition, since the structure of the basic heating furnace 1 is the same as that of 1st embodiment, only the feature point in 3rd embodiment is demonstrated below.

  The heat reflecting member 61 preferably has a heat reflecting surface that reflects heat. For example, as shown in FIG. 10, the heat reflecting surface 62a in the upper heat reflecting member 61a and the heat reflecting in the lower heat reflecting member 61b. Like the surface 62b, the heat reflecting surfaces 62a and 62b are provided so as to be substantially in the same direction with respect to the conveying direction of the object 5 to be processed. Due to such an arrangement, the near infrared rays radiated from the heater 3 are reflected by the heat reflecting surfaces 62a and 62b and spread more uniformly in the processing space 8, and as a result, on the conveying means 2 It is possible to make the heating state of the object 5 being conveyed more uniform.

  As shown in FIG. 10B, it is desirable that the heat reflecting member 61 is arranged in the processing space 8 so that the heat reflecting surface is in a substantially vertical direction. Furthermore, as shown in the figure, by using a heat reflection member 61 having a shape like an upper heat reflection member 61a having a plate shape, both main surfaces thereof can be used as heat reflection surfaces 62a. It is desirable because it can be done. Usually, since the conveying means 2 is provided substantially horizontally, the heat reflecting surface 62 is conveyed if the flat heat reflecting member 61 is disposed so that the heat reflecting surfaces which are both main surfaces are in a substantially vertical direction. It becomes perpendicular to the means 2, and the object to be processed 5 on the transport means 2 can be heated more uniformly. If a plurality of the plate-like heat reflecting members 61 are arranged so as to surround the upper heater 3a, it is desirable because the influence of reflection from other regions in the processing space 8 can be reduced.

  Further, for the same reason, it is desirable that the lower heat reflecting member 61b is also arranged so as to be perpendicular to the conveying means 2 in the same manner as the upper heat reflecting member 61a. In addition, it is desirable to arrange so as to surround the lower heater 3b.

  By disposing the heat reflecting member 61 in this way, the heat generated by the heater 3 passes through the space surrounded by the heat reflecting member 61 and reaches the target object 5 on the conveying means 2 without waste.

  Further, as described above, the objects to be processed 5 are stacked on the conveying means 2 in a plurality of rows in the conveying direction. However, when viewed in plan, the heat reflecting member 61 is attached to the objects to be processed 5. It is desirable to provide it between one row and another adjacent row and / or between the row at the end of the object to be processed 5 and the inner wall 1b of the treatment space 8. By arrange | positioning in this way, the heat | fever reflection member 61 will be arrange | positioned by the fixed space | interval (it depends on the period of the row | line | column of the to-be-processed object 5). Therefore, the space surrounded by the heat reflecting member 61 is placed in mutually similar thermal environments (effects of radiation, conduction, convection, etc.), and the object to be processed 5 passes through the processing space 8 of the heating furnace 1. When this is done, variation in the amount of heat received by each object 5 is reduced.

  Moreover, as shown in FIG. 11, it is preferable to further provide side wall heat reflecting members 61c arranged on the side walls of the processing space 8 on both sides of the conveying means 2 with the heat reflecting surface 62c facing inward. By reflecting the heat by the side wall heat reflecting member 61c, the influence of the reflection in the heating furnace 1 can be made constant, and the heat generated by the heater 3 can be efficiently given to the object 5 to be processed. The variation in the firing temperature can be reduced, and the firing temperature of the object to be treated 5 can be prevented from varying between the central portion and the end portion in the furnace.

  Next, as the material of the heat reflecting member 61, a material having a reflectance of 0.7 or more, preferably 0.8 or more in the wavelength range of the infrared region, particularly 0.7 μm to 3 μm is preferable. Among the reactive metals and quartz glass, those having a high reflectance with respect to near infrared rays can be selected. The reflectance can be measured using an arbitrary spectral reflectance measuring device, and for example, measured using a reflectance measuring device MSR7000 manufactured by Opto Research Co., Ltd. Furthermore, in order to increase the reflectance, it is more preferable to use a white member or to polish the surface of the member and apply a mirror finish. In particular, by using a highly reflective member in the above range, the heat generated by the heater 3 can be more efficiently applied to the object 5 to be processed, and the temperature increase rate of the object 5 can be further increased. . However, quartz glass not only has the effect of accelerating the influence of reflection in the heating furnace 1 but also needs to select a material that can maintain sufficient thermal strength and that does not undergo deformation or alteration. Is suitable. Moreover, you may use what performed metal film-forming to heat insulation members, such as graphite and ceramics.

  In the present invention, the heat reflecting member 61 is used so that the heat from the heater 3 is appropriately reflected and scattered to make the thermal environment in the heating furnace 1 uniform. The material is not limited to those described above. For example, even if the same member as the inner side wall of the heating furnace 1 is used as the material of the heat reflecting member 61, the effect of reflection in the heating furnace 1 is uniformized when arranged at the predetermined position described above, and the heating furnace When the temperature variation within 1 is reduced, it can be regarded as the heat reflecting member of the present invention. Alternatively, the heat reflecting member mentioned above may be used as the side wall member.

≪Other variations etc.≫
The above is the basic description of the heating furnace according to the present invention, but the present invention is not limited to the above-described embodiment. For example, as described below, many modifications and changes are made within the scope of the present invention. Can be added.

  First, in the above embodiment, the belt-type continuous heating furnace using the belt 2a as the conveying means 2 has been described. However, the belt-type continuous heating furnace is not particularly limited thereto. For example, a walking beam type continuous heating furnace or a roller conveyance body is used. Even if it is a continuous heating furnace, the effect of this invention is fully acquired.

  Moreover, in the example shown in FIG.1, FIG3, FIG.10, the upper heater 3a and the lower heater 3b are arrange | positioned by the conveyance means 2 as a boundary. In particular, when a mesh belt conveyed endlessly is used as the conveying means 2, the heat radiated from the lower heater 3b reaches the surface on which the object to be processed 5 is loaded on the belt 2a through the mesh belt. The body 5 can be processed from both the upper surface side and the lower surface side. At this time, the heat reflection suppressing member 60 or the heat reflecting member 61 is located above and / or below the conveying means 2 so as to satisfy the conditions of the first embodiment, the second embodiment, and the third embodiment. If it is arranged at the position, the effect of the invention will be sufficiently exerted. For example, in FIG. 3B, the heat reflection suppressing member 60e is installed only at the upper part of the conveying means 2. However, by providing it at the lower part of the conveying means 2, the influence of reflection in the furnace is further alleviated. And good results can be obtained.

  Further, the arrangement position of the heat reflection suppressing member 60 may be anywhere as long as the effect of the present invention is obtained. For example, as shown in FIG. 9, the heat reflection suppressing member 60 may be provided as a side wall member.

  Furthermore, the heat reflection suppressing member 60 or the heat reflection member 61 is preferably provided in the entire longitudinal direction of the heating furnace 1, but is not particularly required to be provided in the entire region. For example, the temperature rises rapidly or reaches a maximum temperature. You may provide only in the range.

  Furthermore, it is desirable that the heat reflection suppressing member 60 or the heat reflecting member 61 be arranged symmetrically in the vertical direction and in the horizontal direction with the conveying means 2 as the center. However, when it is desired to make a difference in temperature within the heating furnace 1, the heat reflection suppressing member 60 or the heat reflecting member 61 can be freely changed without being vertically or horizontally symmetrical. Further, it is not necessary to provide the heat reflection suppressing member 60 or the heat reflecting member 61 at all. For example, when there is no variation in temperature at the central portion of the conveying means 2, the heat reflection suppressing member 60 or the heat reflecting member 61 can be removed. Therefore, only the required heat reflection suppressing member 60 or heat reflection member 61 may be selected. The shape, size and material of the heat reflection suppressing member 60 or the heat reflecting member 61 may be changed so that the firing temperature is uniform.

--Method of manufacturing solar cell elements--
Next, as one example of the optimum application of the heating furnace of the present invention, a method for manufacturing a solar cell element will be taken as an example and briefly described with reference to FIGS.

  FIG. 6 shows a cross-sectional structure of a general solar cell element.

  7A and 7B are views of a general solar cell element as viewed from the light receiving surface side and the non-light receiving surface side. FIG. 7A shows the light receiving surface side, and FIG. 7B shows the non-light receiving surface side.

  FIG. 8A to FIG. 8D are diagrams showing a process of forming the general solar cell element shown in FIG.

  In the figure, 11 is a semiconductor substrate, 12 is a diffusion region, 13 is an antireflection film, 14 is a front electrode (14a is a bus bar electrode, 14b is a finger electrode), 15 and 16 are back electrodes (15 is a collector electrode, 16 is a collector electrode) An output extraction electrode 17) is a BSF layer.

The semiconductor substrate 11 often used as the solar cell element 10 is made of single crystal silicon, polycrystalline silicon, or the like. The semiconductor substrate 11 contains about 1 × 10 ¹⁶ atoms · cm ⁻³ of one conductivity type semiconductor impurity such as boron (B) and has a specific resistance of about 1 to 5 Ω · cm. In the case of a single crystal semiconductor substrate, it is formed by a pulling method or the like, and in the case of a polycrystalline semiconductor substrate, it is formed by a casting method or the like. Since a polycrystalline semiconductor substrate can be mass-produced and is more advantageous than a single crystal semiconductor substrate in terms of casting cost, an example using a polycrystalline semiconductor substrate will be described here.

  For example, a polycrystalline silicon ingot formed by a casting method is cut into an appropriate size such as 10 cm × 10 cm or 15 cm × 15 cm, and sliced to a thickness of 500 μm or less, more preferably 300 μm or less, and the semiconductor substrate 11 To do. In order to clean the mechanically damaged layer and the contaminated layer on the cut surface of the semiconductor substrate 11, it is desirable to slightly etch the surface of the semiconductor substrate with NaOH, KOH, hydrofluoric acid, or hydrofluoric acid.

Next, the semiconductor substrate 11 is placed in a diffusion furnace, and heat treatment is performed in a gas containing an impurity element such as phosphorus oxychloride (POCl ₃ ), whereby 1 × 10 ¹⁶ phosphorus atoms are formed on the surface portion of the semiconductor substrate 11. ~10 ¹⁸ atoms · ^{cm -3} approximately is diffused to form a diffusion region 12 having a thickness of approximately 0.3 to 0.5 [mu] m.

Then, an antireflection film 13 is formed on the surface side of the semiconductor substrate 11. The antireflection film 13 is made of, for example, a silicon nitride film (SiN _x ) or the like, and has a thickness of 500 to 1000 nm by a plasma CVD method using a mixed gas of silane (SiH ₄ ) and ammonia (NH ₃ ). It is formed in about 90-2.30. The antireflection film 13 is provided in order to prevent light from being reflected from the surface of the semiconductor substrate 11 and to effectively take light into the semiconductor substrate 11.

  Next, the surface electrode 14 is formed on the light receiving surface side of the semiconductor substrate 11, and the back electrodes 15 and 16 are formed on the non-light receiving surface side of the semiconductor substrate 11. Each of the front electrode 14 and the back electrodes 15 and 16 is a fired electrode mainly composed of a metal, and these fired electrodes are formed of a semiconductor substrate 11 coated with a metal paste such as a silver paste or an aluminum paste in a predetermined shape. The object 5 is obtained by firing using the heating furnace of the present invention. Specifically, it is as follows.

  Here, the surface electrode 14 is formed of a bus bar electrode 14a and finger electrodes 14b. One or a plurality of bus bar electrodes 14a are formed in parallel over the entire length of the semiconductor substrate 11, and a plurality of finger electrodes 14b are formed over the entire length of the semiconductor substrate 11 so as to intersect with the bus bar electrodes 14a. The surface electrode 14 is formed by applying a silver paste mainly made of silver powder, a binder, glass frit or the like to the surface of the semiconductor substrate 11 by a screen printing method or the like.

  The back electrodes 15 and 16 are mainly made of aluminum powder and binder after a silver paste mainly composed of silver powder, binder, glass frit and the like is applied to the formation position of the output extraction electrode 16 by a screen printing method and dried. Then, an aluminum paste made of glass frit or the like is formed by applying the current collecting electrode 15 at a position where the collector electrode 15 is to be formed by a screen printing method or the like. The order in which the back electrodes 15 and 16 are formed is not particularly limited. That is, the output electrode 16 may be formed by screen-printing an aluminum paste to form the collecting electrode 15 and then screen-printing the silver paste. .

  The semiconductor substrate 11 formed as described above and coated with a metal paste on both sides in a predetermined shape is dried, and then, for example, as described above, for example, FIG. 1 to FIG. 4, FIG. Using the heating furnace of the present invention provided with the heat control means 6 (heat reflection suppressing member 60 or heat reflection member 61) shown in FIG. 4, the surface is baked at 600 to 800 ° C. for about 1 to 30 minutes by the method described above. Electrode 14 and backside electrodes 15 and 16 are formed. As described above, by performing the baking treatment using the semiconductor substrate 11 coated with the metal paste in a predetermined shape as the object 5 to be processed, the baking state of the baking electrode of the solar cell element 10 becomes uniform, and the electrical characteristics of the solar cell element 10 and Thus, the adhesive strength between the semiconductor substrate and the electrode is less affected, and the variation in the adhesive strength between the front and back electrodes of the semiconductor substrate 11 is small and the quality is excellent.

  Note that the BSF layer 17 is formed on the non-light-receiving surface side of the semiconductor substrate 11 by baking the aluminum paste that is the current collecting electrode 15 of the back surface electrodes 15 and 16. The BSF layer 17 forms an internal electric field on the non-light-receiving surface side of the semiconductor substrate 11 and can prevent a reduction in efficiency due to carrier recombination in the vicinity of the back surface of the semiconductor substrate 11. That is, carriers generated in the vicinity of the back surface of the semiconductor substrate 11 are accelerated by this electric field, so that electric power can be taken out effectively. This is particularly preferable because the photosensitivity at a long wavelength increases.

  In addition, since the metal paste is applied to both surfaces of the semiconductor substrate 11, it is desirable to use the heating furnace 1 of a type in which the heaters 3 are provided above and below the conveying means 2, so that the front and back sides can be simultaneously applied. It can be fired.

  The heating furnace 1 provided with the middle / near infrared heater has the disadvantages that the temperature variation in the heating furnace 1 is large and difficult to control, but the variation in the firing state is reduced, and the end and center in the heating furnace 1 are reduced. Even if the solar cell elements 10 are supplied to any row of the parts, the same firing state can be obtained.

  In the above embodiment, the method for firing the electrodes of the solar cell element 10 has been described by taking the simultaneous firing method as an example. However, the present invention is not limited to this, and the effect is effectively exhibited even when firing multiple times. To do. That is, even if the heating furnace 1 according to the present invention is used after baking the back electrode material, the influence given by re-sintering of the back electrode material can be suppressed.

  Moreover, although the solar cell element 10 comprised as the back surface electrodes 15 and 16 by the current collection electrode 15 which consists of aluminum, and the output extraction electrode 16 which consists of silver was demonstrated as an example, this is not restrict | limited.

It is a schematic diagram which shows 1st embodiment of the heating furnace of this invention, (a) is a cross-sectional schematic diagram of a furnace length direction, (b) is a cross-sectional schematic diagram of a furnace width direction. It is a mimetic diagram showing a first embodiment of a heating furnace of the present invention, and is a partial sectional view seen in plan view. It is a schematic diagram which shows 2nd embodiment of the heating furnace of this invention, (a) is a cross-sectional schematic diagram of a furnace length direction, (b), (c) is a cross-sectional schematic diagram of a furnace width direction. It is a schematic diagram which shows 2nd embodiment of the heating furnace of this invention, and is the fragmentary sectional view seen from the top. It is a schematic diagram which shows embodiment of a general heating furnace, (a) is a cross-sectional schematic diagram of a furnace length direction, (b) is a cross-sectional schematic diagram of a furnace width direction. It is a figure for demonstrating the structure of a solar cell element. It is a figure for demonstrating the structure of a solar cell element, (a) is the top view seen from the surface side, (b) is the bottom view seen from the back surface side. (A)-(d) is a figure for demonstrating the manufacturing method of the electrode of a solar cell element. It is a schematic diagram which shows other embodiment of the heating furnace of this invention, (a) is a cross-sectional schematic diagram of a furnace length direction, (b) is a cross-sectional schematic diagram of a furnace width direction. It is a schematic diagram which shows 3rd embodiment of the heating furnace in this invention, (a) is a cross-sectional schematic diagram of a furnace length direction, (b) is a cross-sectional schematic diagram of a furnace width direction, (c) is a cross-sectional schematic diagram from the upper part FIG. It is a cross-sectional schematic diagram of the furnace width direction which shows the modification of 3rd embodiment of the heating furnace in this invention. It is a cross-sectional schematic diagram of the furnace width direction which shows the modification of 2nd embodiment of the heating furnace in this invention.

Explanation of symbols

1: Heating furnace 1a: Heat insulating material 1b: Heating furnace inner wall (inner wall of processing space)
2: Conveying means 2a: Belt 2b: Support 2c: Roller 3: Heating means (heater)
3a: Upper heater 3b: Lower heater 5: Object to be treated (solar cell element)
6: Heat control means 60 (60a, 60b, 60c, 60d, 60e): Heat reflection suppression member 61 (61a, 61b, 61c): Heat reflection member 62 (62a, 62b, 62c): Heat reflection surface 7: Radiation suppression Mechanism 8: Processing space 10: Solar cell element 11: Semiconductor substrate 12: Diffusion region 13: Antireflection film 14: Surface electrode 14a: Bus bar electrode 14b: Finger electrode 15: Current collecting electrode 16: Output extraction electrode 17: BSF layer

Claims (9)

A heating furnace for heat-treating an object to be processed inside;
Conveying means for placing the object to be processed and conveying the inside of the heating furnace;
A heating means disposed inside the heating furnace for heating the object to be processed;
And a heat control means for indirectly transferring the heat obtained from the heating means to the object to be processed.   The heating furnace according to claim 1, wherein the heat control means is disposed between the conveying means and the inner wall of the heating furnace. The conveying means is configured to place a plurality of the objects to be processed so as to form a plurality of rows, and to convey in the row direction,
The heating furnace according to claim 1, wherein the thermal control means is disposed between the adjacent rows and / or between the rows and the inner wall of the heating furnace. The conveying means is composed of a mesh belt, and the heating means is arranged above and below the conveying means,
The heating furnace according to any one of claims 1 to 3, wherein the heat control means is arranged above and / or below the conveying means.   The heating furnace according to any one of claims 1 to 4, wherein the heat control means is a heat reflection suppressing member having less heat reflection than the inner wall of the heating furnace.   The heating furnace according to claim 5, wherein the heating unit is disposed closer to the inner wall side of the heating furnace than the object to be processed located at an end.   The heating furnace according to any one of claims 1 to 4, wherein the heat control means is a heat reflecting member having a heat reflecting surface that reflects heat in a predetermined direction.   The heating furnace according to claim 7, wherein the heating means is disposed closer to the center of the heating furnace than the object to be processed located at an end. A method for producing a solar cell element, comprising a step of firing a metal paste formed on a surface of a semiconductor substrate using the heating furnace according to any one of claims 1 to 8.

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