JP2004123433A - Silicon sheet,its manufacturing process, substrate for manufacturing the same and solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost solar battery, especially by inhibiting warpage in a low-cost silicon sheet with an improved yield which requires no slicing step and applying the silicon sheet to the solar battery. <P>SOLUTION: The silicon sheet has a first plane, another plane continuously formed from the first plane and, around the first plane, a thickness-reinforcing part which is thicker than the average thickness of the first plane. The inexpensive solar battery is obtained by using the silicon. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to plate silicon, a method of manufacturing plate silicon, a substrate for manufacturing plate silicon, and a solar cell using the plate silicon. The plate-like silicon of the present invention has a first surface and a plate-like silicon having another surface formed continuously with the first surface, and a portion different from a continuous portion of the first surface and the other surface. A plate-shaped silicon, a plate-shaped silicon production method, a plate-shaped silicon production substrate, and a plate-shaped silicon, characterized in that there is a plate thickness reinforcing portion thicker than the average plate thickness of the first surface. The present invention relates to a solar cell using silicon.
[0002]
[Prior art]
Conventionally, since polycrystalline silicon has been manufactured by pouring a silicon melt into a mold and gradually cooling it, and then slicing the obtained polycrystalline ingot, there has been a problem that silicon loss due to slicing is large. The present inventors have developed a plate-like silicon manufacturing method capable of mass production at low cost without a slicing step as a method capable of eliminating this slice loss and mass production of polycrystalline silicon wafers at low cost. (See Patent Document 1). In this manufacturing method, a substrate is immersed in a melt of a raw material to grow plate-like silicon on the substrate.
[0003]
[Patent Document 1]
JP 2001-247396 A
[0004]
[Problems to be solved by the invention]
When plate silicon is manufactured by the above-described plate silicon manufacturing method, there is a problem that the plate silicon falls into or out of the crucible. Further, since the plate-like silicon grows not only on the growth surface of the plate-like silicon on the substrate but also on the front and rear surfaces and the lateral surface of the growth substrate, the expansion coefficient of the plate-like silicon and the material of the growth substrate during the temperature decrease after the growth of the plate-like silicon. There is a problem that residual stress remains in the surface of the plate-like silicon or cracks occur in the plate-like silicon due to the stress due to the difference in temperature and the time delay of the temperature change. Further, there is a problem that the plate-like silicon may be warped in a direction to eliminate the residual stress.
[0005]
The present invention aims to solve these problems.
[0006]
[Means for Solving the Problems]
As a result of intensive studies, the present inventor has found that the above problem can be solved by making the plate-like silicon formed into a special shape, and has completed the present invention.
[0007]
The plate-shaped silicon of the present invention has a first surface, and a plate-shaped silicon having another surface formed continuously with the first surface, in a peripheral portion of the first surface, the average thickness of the first surface. It is characterized by having a thick plate thickness reinforcing portion.
[0008]
The plate-like silicon according to the present invention is characterized in that the plate-thickness reinforcing portion of the plate-like silicon exists at a position opposite to a continuous portion between the first surface and the other surface.
[0009]
The plate-shaped silicon of the present invention is characterized in that the plate-shaped reinforcing portions of the plate-shaped silicon are present at all positions including a continuous portion between the first surface and another surface.
[0010]
The plate-like silicon of the present invention is characterized in that the plate-thickness reinforcing portion of the plate-like silicon is 105% or more and 170% or less of the average plate thickness of the first surface.
[0011]
The plate-like silicon of the present invention is characterized in that the width of the plate thickness reinforcing portion of the plate-like silicon is 10% or less of the length of the longer side of the plate-like silicon.
[0012]
The plate-shaped silicon of the present invention is characterized in that the area of the plate thickness reinforcing portion of the plate-shaped silicon is 35% or less of the area of the first surface.
[0013]
The method for producing plate-like silicon according to the present invention includes a step of bringing a substrate into contact with a silicon melt, growing plate-like silicon on the surface of the substrate, and then separating the substrate from the melt.
[0014]
The manufacturing method of the plate-like silicon of the present invention is characterized in that another surface continuous with the first surface of the plate-like silicon is formed from a front part in a traveling direction of the substrate.
[0015]
In the method for producing plate-like silicon according to the present invention, the plate-thickness reinforcing portion of the plate-like silicon is formed at a rear portion in a traveling direction of the substrate.
[0016]
In the method for producing plate-like silicon according to the present invention, the plate-thickness control portion of the substrate on which the plate-thickness reinforcing portion of the plate-like silicon grows has a periodic protrusion, and the protrusion at the closest position of the protrusion is provided. The distance to the part is 0.1 mm or more and 2 mm or less.
[0017]
The substrate for producing plate-like silicon according to the present invention is characterized in that the plate-thickness control section of the substrate on which the plate-thickness reinforcing section of plate-like silicon grows contains any one of silicon carbide, pyrolytic carbon, and graphite. I do.
[0018]
The plate-like silicon manufacturing substrate according to the present invention is characterized in that the plate thickness control section of the substrate on which the plate-like silicon thickness reinforcing section grows is lower than the plane on which the first surface of the plate-like silicon grows.
[0019]
A solar cell using plate silicon of the present invention is characterized by being manufactured from another surface continuous with the first surface of the plate silicon and the first surface from which the plate thickness reinforcing portion is removed.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention relates to plate silicon, a method of manufacturing plate silicon, a solar cell using the plate silicon, and a substrate for manufacturing plate silicon.
[0021]
(Plate silicon)
The plate-shaped silicon of the present invention has a first surface and another surface continuously formed on the first surface, and a peripheral portion of the first surface has a thickness larger than an average thickness of the first surface. It is characterized by having a thick reinforcing portion.
[0022]
The features of the plate-like silicon according to the present invention will be described with reference to FIG. FIG. 1A is a schematic perspective view of a plate-like silicon according to the present invention, and FIG. 1B is a cross-sectional view of the plate-like silicon when cut along 1B-1B in FIG. The plate-shaped silicon S1 according to the present invention has a first surface S1A and another surface via a continuous portion S1D continuous with the first surface S1A, that is, a second surface S1B. Has a plate thickness reinforcing portion S1E in which the average plate thickness H1 in the peripheral portion is larger than the average plate thickness h1 in the central portion of the first surface. Further, in the plate-shaped silicon S1 of the present invention, the angle α formed between the normal vector V1A of the first surface S1A and the other surface, that is, the normal vector V1B of the second surface S1B forms an obtuse angle. The normal vector at this time is defined on a continuous surface. That is, when defining the vector, if the plane is in contact with the substrate when manufacturing the plate-like silicon, both vectors select the normal vector from the plane in contact with the substrate. This makes it possible to define the angle between the normal vectors V1A and V1B. This angle α preferably satisfies 90 ° <α <180 °, and more preferably 120 ° <α <180 °. When the angle α is 180 °, that is, when the vector is in the opposite direction, excessive stress is applied when only the plate-like silicon is removed from the substrate on which the plate-like silicon is grown, and the plate-like silicon is damaged. 120 ° <α <180 °, which is not so preferable and can be easily detached from the substrate, because there is a possibility that the substrate may be broken or the substrate may be damaged. As will be described later, even the shapes shown in FIGS. 2 to 4 correspond to the plate-shaped silicon of the present invention.
[0023]
In the following description, the plate silicon is represented by S, the normal vector on the plate silicon is V, the substrate on which the plate silicon is grown is acronym C, and the subsequent numbers are represented by the plate silicon number or the substrate number. I do. The last letter is A for the first surface, B for the second surface constituting the other surface, C for the third surface constituting the other surface, and is thicker than the average plate thickness of the first surface of the plate-like silicon. The thickness reinforcing portion is denoted as E. Also in the substrate, the surfaces on which the first surface, the second surface, and the third surface of the plate-like silicon grow are referred to as the first surface, the second surface, and the third surface of the substrate.
[0024]
1B, the average thickness H1 of the thickness reinforcing portion S1E is larger than the average thickness h1 of the central portion of the first surface S1A. However, in this drawing, the plate thicknesses h1 and H1 are indicated by the plate thickness at a specific place, but in the present invention, indicate the average plate thickness. That is, there may be a portion extremely thinner than the average plate thickness H1 in the plate thickness reinforcing portion S1E, and the plate thickness may be changed stepwise. The average thickness H1 of the thickness reinforcing portion S1E existing in the peripheral portion of the first surface is not less than 105% and not more than 170% of the average thickness h1 of the central portion of the first surface S1A. When the average thickness is 105% or less, it is difficult to sufficiently fulfill the role of the thickness reinforcing portion. When the average thickness is 170% or more, it is possible to suppress warpage of the plate-like silicon. It is not very desirable because the utilization efficiency is low.
[0025]
The role of the sheet thickness reinforcing portion is that the presence of the sheet thickness reinforcing portion S1E that is thicker than the average sheet thickness h1 of the first surface S1A in the plane of the sheet silicon S1 significantly reduces the warpage of the sheet silicon S1. You can do it. This is a state in which the second surface S1B of the plate-like silicon is hooked to the substrate on which the plate-like silicon is grown and is fixed to the substrate. However, the plate thickness reinforcing portion S1E is fixed to the substrate. Not. Therefore, the plate-like silicon grown on the substrate may be warped by the influence of heat shrinkage or gravity. However, in the plate-like silicon of the present invention, since the plate-thickness reinforcing portion S1E having a plate thickness larger than the average plate thickness h1 exists, the plate-like silicon is less likely to be warped. This is because the plate thickness reinforcing portion S1E, which is thicker than the average plate thickness h1 of the first surface S1A of the plate silicon, serves as a beam of the plate silicon. Such plate-like silicon with less warpage can be easily provided to a solar cell manufacturing process, and the plate-like silicon can be obtained at a high yield because the strength of the obtained plate-like silicon is not reduced. Will be able to Further, it is possible to produce plate-like silicon having a thickness smaller than that of a 350 μm wafer usually used for a solar cell.
[0026]
In the plate-like silicon having the plate-thickness reinforcing portion, the width W1 of the plate-thickness reinforcing portion S1E is preferably 20% or less of the length of the long side of the plate-like silicon. For example, when the size of the obtained silicon plate is a square having a length of 155 mm and a width of 155 mm, the size is preferably 31.1 mm or less. This is because, as the width of the thicker portion becomes wider, the warpage of the plate-like silicon can be suppressed, but the raw material use efficiency is greatly reduced, and the price of the obtained plate-like silicon is reduced. This is because it becomes difficult to suppress
[0027]
Further, in the plate-like silicon having the plate-thickness reinforcing portion, the area of the plate-thickness reinforcing portion S1E having a plate thickness is preferably 35% or less of the area of the plate-like silicon S1. This is also because the larger the area of the plate thickness reinforcing portion, the lower the raw material utilization efficiency and the more difficult it is to suppress the price of the obtained plate-like silicon.
[0028]
Next, the shape of the plate-shaped silicon of the present invention will be described with reference to FIGS. 2 to 4 are schematic perspective views of plate-like silicon according to the present invention. In FIG. 2, the portion different from FIG. 1A is the shape of the second surface (S1B and S2B) of the plate-like silicon. The second surface S1B of the plate-shaped silicon S1 in FIG. 1 has a planar structure, whereas the second surface S2B of the plate-shaped silicon S2 in FIG. 2 has a curved surface. In the silicon plate S2, the normal vector V2A of the first surface and the normal vector V2B of the second surface form an obtuse angle. However, when the normal vector V2B of the second surface is near the boundary with the first surface S2A of the plate-like silicon, the angle between the normal vectors becomes an acute angle because of the curved surface shape. There is. However, in the present invention, it is sufficient that there is at least one portion where the angle between the normal vectors is obtuse. The angle formed by the normal vector may include an acute angle. In other words, it suffices if there is another surface where the angle between the normal vectors is obtuse. In this example, the plate thickness reinforcing portion S2E is formed on the side opposite to the second surface S2B.
[0029]
In FIG. 3, the plate-shaped silicon S3 includes a first surface S3A and other surfaces, that is, a second surface S3B and a third surface S3C, and has a total of three surfaces, and has normal vectors V3A, V3B, and V3C, respectively. . Although the plate-like silicon (S1 and S2) described so far has a two-sided structure, in the present invention, the function is achieved if the first and second surfaces are present in the plate-like silicon. Has more than two surfaces, the effect is more exhibited. That is, the plate-shaped silicon S3 has a portion having a U-shaped cross-sectional shape at the end, and the normal vector V3A of the first surface and the normal vector V3B of the second surface form an obtuse angle. . By adopting such a three-sided structure, when the substrate is immersed in the melt to produce the plate-like silicon, the drop rate of the plate-like silicon is greatly improved.
[0030]
Further, in FIG. 3, the plate thickness reinforcing portion S <b> 3 </ b> E of the plate-like silicon has a structure having a convex portion on the lower side. In the present invention, a plate thickness reinforcing portion of the plate-like silicon exists, and it is sufficient to suppress the warpage of the plate-like silicon, and the shape as shown in FIG. 3 may be used.
[0031]
In FIG. 4, the plate-shaped silicon S4 includes three surfaces, a first surface S4A, a second surface S4B, and a third surface S4C, and has normal vectors V4A, V4B, and V4C, respectively. Even with such a three-sided structure, falling of the plate-like silicon can be suppressed. Further, in this figure, the plate thickness reinforcing portion S4E of the plate-like silicon has convex portions on both the upper side and the lower side. The plate thickness reinforcing portion S4E having such a shape is more preferable because it is possible to further suppress the warpage of the obtained plate-like silicon.
[0032]
As described above, the plate thickness reinforcing portion (S1E, S2E, S3E, S4E) thicker than the average plate thickness of the first surface has a convex portion on the lower side or a convex portion on the upper side. , The upper and lower portions may have convex portions.
[0033]
Next, the shape of the plate-like silicon of the present invention will be described with reference to FIG. FIG. 5A is a schematic perspective view of the plate-like silicon of the present invention, and FIG. 5B is a view showing the thick portion around the plate-like silicon in FIG. FIG. 4 is a perspective view of the plate-like silicon when removed by removal. In FIG. 5 (A), the first surface S5A is hardly warped because the plate thickness reinforcing portion S5E is present in the entire peripheral portion of the first surface S5A. This means that the peripheral thickness reinforcing portion S5E forms a strong frame, and the first surface S5A does not warp. With such a plate-like silicon, by removing the plate-thickness reinforcing portion S5E, the obtained plate-like silicon S5A hardly includes warpage, and a solar cell is manufactured using an inexpensive process. Will be able to do it. However, with such a shape, the area of the thickness reinforcing portion S5E becomes large. Therefore, it is preferable to reduce the width of the thickness reinforcing portion S5E as much as possible. More preferably, it is 10 mm or less. By adopting such a shape, plate-shaped silicon with good yield and without warpage can be obtained. In FIG. 5, the first surface S5A, the second surface S5B, and the third surface S5C have normal vectors V4A, V4B, and V4C, respectively.
[0034]
(substrate)
Next, a substrate for manufacturing the plate silicon of the present invention will be described with reference to FIG. FIG. 6A is a schematic perspective view of a substrate for manufacturing the plate-like silicon of the present invention, and FIG. 6B is a cross-sectional view of the substrate taken along line 6B-6B in FIG. (C) is a cross-sectional view of the substrate when cut along 6C-6C in (A). By using such a substrate C6, the plate-shaped silicon of the present invention can be manufactured. In the substrate of the present invention, the first surface C6A of the substrate on which the first surface of the plate silicon is grown, the second surface C6B of the substrate on which the second surface of the plate silicon is grown, and the third surface of the plate silicon are grown. The third surface C6C of the substrate is provided, and further, there is a thickness control portion C6E in which the thickness of the plate-like silicon is large and the thickness reinforcing portion grows. Further, the first surface C6A of the substrate has a structure that can be separated from the substrate edge C6G by a moat structure C6F. By adopting such a shape, even if silicon adheres to the side surface of the substrate C6, the silicon is separated by the moat structure C6F. Becomes possible.
[0035]
At this time, the width W6G of the substrate edge is preferably 1 mm or more and 10 mm or less. When the width W6G of the substrate edge is 1 mm or less, the width of the substrate edge is small, and the strength of the substrate edge is reduced due to thermal influence. This is not preferable because the heat loss is large when heating or cooling the substrate due to the increase.
[0036]
The width W6F of the moat structure C6F for separating the substrate edge C6G and the first surface C6A is preferably 1 mm or more and 7 mm or less. 1.5 mm or more and 5 mm or less are more preferable. When the width W6F of the moat structure is 1 mm or less, the substrate edge C6G and the first surface C6A are connected due to the surface tension of the silicon melt, which is not preferable. When the width W6F is 7 mm or more, the width W6F of the moat structure is reversed. This is not desirable because the possibility that the silicon melt will penetrate into the concave portions increases, and the possibility that the plate-like silicon cracks from that portion increases. The depth D6F of the moat structure C6F is preferably 1 mm or more and 8 mm or less. 2 mm or more and 5 mm or less are more preferable. When the depth D6F of the moat structure C6F is 1 mm or less, the substrate edge C6G and the first surface C6A are connected due to the surface tension of the silicon melt, which is not preferable. When the depth D6F is 8 mm or more, the substrate strength cannot be secured. , Not very good.
[0037]
Further, the second surface C6B of the substrate intersects the first surface C6A of the substrate at an angle β. If the angle β is large, the obtained plate-like silicon is likely to fall, and conversely, if the angle β is small, it will not fall. That is, the angle β is preferably an acute angle, and more preferably 60 ° or less.
[0038]
In the present invention, the portion where the thick portion of the plate-like silicon grows, that is, the thickness control portion C6E preferably has a shape having regular irregularities. That is, it is possible to control the thickness of the obtained plate-like silicon by increasing the density at which the crystal nuclei are generated in the thickness control unit C6E to be greater than the density of the crystal nuclei generated at the first surface C6A of the substrate. It becomes. For example, if the surface of the first surface C6A of the substrate is machine-finished by a lathe or a milling machine, it is preferable to mechanically form irregularities on the surface of the plate thickness control unit C6E. At this time, it is preferable that the pitch of the protrusions is 0.1 mm or more and 2 mm or less. 0.5 mm or more and 1 mm or less are more preferable. As described above, by forming the concavities and convexities in the plate thickness control section C6E, it is possible to easily increase the thickness of the plate-like silicon plate. In particular, the surface shape of the plate thickness control portion C6E is preferably a shape having a dot-like protrusion 13A shown in FIG. 13A or a shape having a linear protrusion 13B as shown in FIG. 13B. . This makes it possible to control the generation position of silicon crystal nuclei, and is particularly preferable when forming the plate thickness reinforcing portion uniformly.
[0039]
Furthermore, it is preferable that the surface of the first surface C6A of the substrate also has an uneven shape. This is because by providing the first surface C6A of the substrate with a concavo-convex structure in advance, the generation site of the crystal nucleus can be limited, and not only the homogeneity of the obtained plate-like silicon can be improved, but also the obtained plate-like silicon can be improved. It greatly improves the releasability of silicon in shape. The pitch of the projections of the surface irregularities on the first surface C6A of the substrate is preferably 0.5 mm or more and 2.5 mm or less. When the pitch is 0.5 mm or less, the semiconductor properties of the obtained plate-like silicon are slightly inferior, and the conversion efficiency of the obtained solar cell is slightly inferior. If the pitch is 2.5 mm or more, the surface irregularities of the obtained plate-like silicon become large, and it becomes difficult to pass through a printing process suitable for mass production.
[0040]
For example, when the pitch of the convex portions of the surface irregularities of the first surface C6A of the substrate and the pitch of the convex portions of the surface irregularities of the plate thickness control portion C6E are both set to 1 mm, the pitch of the convex portions and the concave portions of the plate thickness control portion C6E. By reducing the height difference, the plate thickness can be increased. Reducing the height difference between the projections and the recesses changes the way the silicon melt enters the recesses of the substrate, and the location where crystal nuclei are generated only on the projections is increased. become. As a result, the crystal nuclei are also generated around the convex portions, the thickness of the plate-like silicon can be increased, and the plate thickness reinforcing portion can be formed.
[0041]
Further, the thickness reinforcing portion may be manufactured by coating a tip portion of the convex portion of the thickness control portion C6E with a material having high wettability with respect to a silicon melt, such as silicon carbide or pyrolytic carbon. Becomes possible. This is because, when a material having high wettability with respect to the silicon melt is present on the substrate surface, the amount of crystal nuclei generated at the convex portion of the substrate can be increased, and the thickness of the plate-like silicon can be increased, A plate thickness reinforcing portion can be formed.
[0042]
As described above, controlling the contact portion between the silicon melt and the substrate surface is a very important factor in producing the plate thickness reinforcing portion, and in particular, controlling the density of the protrusions and the material of the protrusions. Is preferred.
[0043]
FIG. 6 shows a case where the first surface C6A of the substrate and the projections of the thickness control unit C6E are formed on substantially the same surface. In FIG. 7, however, FIG. This is a case where the thickness control unit C7E exists on the lower side.
[0044]
FIG. 7A is a schematic perspective view of a substrate for manufacturing the plate-like silicon of the present invention, and FIG. 7B is a cross-sectional view of the substrate taken along line 7B-7B in FIG. (C) is a cross-sectional view of the substrate when cut along 7C-7C in (A). In this drawing, a thickness control unit C7E exists below the first surface C7A. When the thickness control unit C7E exists below the first surface C7A, the thickness can be more easily increased. Even if the plate thickness control unit C7E is present at a position lower than the first surface C7A, the melt can enter, so that the plate thickness reinforcement unit can be manufactured. As described above, by providing the uneven shape, the generation site of the crystal nucleus can be limited, and the plate thickness reinforcing portion can be more easily obtained. 7, the second surface C7B, the third surface C7C, the depth D7F of the digging structure C7F, the width W7F of the moat structure C7F, and the width W7G of the substrate edge C7G have substantially the same structure as the embodiment of FIG. it can.
[0045]
Next, the substrate of the present invention will be described with reference to FIG. FIG. 8A is a schematic perspective view of a substrate for manufacturing the plate-like silicon of the present invention, and FIG. 8B is a cross-sectional view of the substrate taken along line 8B-8B in FIG. (C) is a cross-sectional view of the substrate when cut along 8C-8C in (A). In this figure, it is the case where two substrates C7 shown in FIG. 7 are connected. That is, two plate-like silicon grown from the first surface (C8LA and C8RA) of one substrate C8 are obtained. Also in this substrate C8, since the digging structure (C8LF and C8RF) exists between the first surface (C8LA and C8RA) of the substrate and the edge C8G of the substrate, the obtained plate-like silicon is formed via the digging structure. It is not connected continuously. In this figure, the first surface (C8LA and C8RA) of the substrate is separated by two digging structures (C8LF and C8RF). In this figure, the moats are separated by two moats (C8LF and C8RF), but they may have a common moat at the center of the substrate. When the first surface of the substrate is separated by such a single moat structure, it is preferable to increase the width of the moat structure. This is because the growth rate of the plate-like silicon increases at the center of the substrate due to the influence of heat. The width of the moat structure at the central portion of the substrate is preferably at least 1 and at most 3 times the width of the moat structure at the peripheral portion of the substrate. The second surface C8LB and the third surface (C8RC, C8LC) have the same shape as the embodiment of FIG.
[0046]
When the substrate is formed in such a manner that two plate-like silicon can be obtained from one substrate, the productivity is good, and as a result, inexpensive plate-like silicon can be provided.
[0047]
Next, the substrate of the present invention will be described with reference to FIG. FIG. 9A is a schematic perspective view of a substrate for manufacturing the plate-like silicon of the present invention, and FIG. 9B is a cross-sectional view of the substrate when cut along 9B-9B in FIG. (C) is a cross-sectional view of the substrate when cut along 9C-9C in (A). In this substrate, the thickness control units (C9RE and C9LE; hatched portions) are provided on the left and right sides of the first surface C9A of the substrate, and the projections are formed in those portions. At this time, it is preferable that the pitch of the protrusions is 0.1 mm or more and 2 mm or less. 0.5 mm or more and 1 mm or less are more preferable. As described above, by forming the concavities and convexities in the plate thickness control unit C9LE, it is possible to easily increase the plate thickness of the plate-like silicon. The presence of the thickness control units (C9RE and C9LE) at the parallel positions makes it possible to more easily suppress the warpage.
[0048]
The second surface C9B, the third surface C9C, the groove structure C9F, and the substrate edge portion C9G can adopt a structure according to the embodiment of FIG.
[0049]
Next, the substrate of the present invention will be described with reference to FIG. FIG. 10A is a schematic perspective view of a substrate for manufacturing the plate-like silicon of the present invention, and FIG. 10B is a cross-sectional view of the substrate taken along line 10B-10B in FIG. (C) is a sectional view of the substrate when cut at 10C-10C in (A). In this drawing, the substrate C10 has regions having different surface shapes. That is, the first surface C10A is adjacent to the thickness control unit C10E, and the growth suppression unit C10H is adjacent to the thickness control unit C10E. The growth suppressing portion C10H has the same effect as the moat structure of the substrate shown in FIGS. That is, as the purpose of the moat structure was to separate the silicon grown on the first surface and the silicon grown on the edge of the substrate, this growth suppressing portion C10H is also provided by the thickness controlling portion C10E. This is to prevent silicon from growing on the periphery. At this time, it is preferable to form irregularities on the surface of the growth suppressing portion C10H. That is, it is preferable to form a surface shape that can be easily formed by machining as shown in FIGS. 13A and 13B on the growth suppressing portion C10H. FIG. 13A is an enlarged schematic diagram of a substrate surface having a dot-shaped convex portion 13A, and FIG. 13B is an enlarged schematic diagram of a substrate surface having a linear convex portion 13B.
[0050]
In this figure, the pitch P13A or P13B of the dot-like protrusions 13A or the linear protrusions 13B is preferably 0.5 mm or more and 3 mm or less, and the tip angle thereof is particularly preferably 30 ° or more and 120 ° or less. If the pitch of the projections is smaller than 0.5 mm, crystals will grow on the growth suppressing portion C10H, which is not preferable. When the pitch is 3 mm or more, silicon grows also in the concave portion existing between the convex portion and the adjacent convex portion, which is not preferable. On the other hand, if the tip angle is smaller than 30 °, the strength of the tip portion of the projection cannot be secured, which is not preferable. On the other hand, when the angle is 120 ° or more, silicon grows also around the protrusion, which is not preferable. The growth suppressing portion C10H only needs to be formed as long as the plate-like silicon is not formed, and may have a shape in which the silicon grown on the convex portion is not continuous.
[0051]
Further, when the pitch of the convex portions of the growth suppressing portion C10H is the same as the pitch of the convex portions formed in the thickness control portion C10E, the angle of the convex portion of the growth suppressing portion C10H is set to be steep. There is a need. That is, as shown in FIG. 13B, the vertex angle γ of the substrate having a triangular cross section is reduced. With such a shape, the starting point of silicon crystal growth is only the linear convex portion 13B on the substrate surface, and only silicon crystal nuclei are generated at the convex portion. Will not do.
[0052]
Further, it may have a substrate surface structure as shown in FIG. FIG. 14 is an enlarged schematic view of the substrate surface having the linear projections 14. 13B is different from FIG. 13B in that the concave portion 15 of the substrate has a flat portion. The existence of such a flat portion makes it possible to delay the time until the crystals generated from the adjacent convex portions 14 are connected. That is, the silicon crystal grows only on the linear protrusions 14. With such a substrate surface structure, the vertex angle δ can be freely adjusted even at the same pitch, and the growth suppressing portion can be formed with good control. In this figure, the cross-sectional shape of the concave portion is a trapezoid having a flat portion, but it may be U-shaped. The essence of this shape is to provide a structure that can simultaneously control the vertex angle δ and the pitch P14 of the convex portions. A suitable shape of the growth suppressing portion is such that the pitch P14 of the convex portions is 0.5 mm or more and 3 mm or less, the vertex angle δ is 30 ° or more and 120 ° or less, and the length of the concave portions is 0.5 mm or more and 3 mm or less.
[0053]
In FIG. 10, the second surface C10B and the third surface C10C are formed to be perpendicular or parallel to the first surface C10A. The width W10E of the thickness control unit C10E is preferably set in a range of 5 to 15 mm. Further, the height D10H and the width W10H of the growth suppressing portion C10H are preferably set in the ranges of 5 to 25 mm and 5 to 20 mm, respectively.
[0054]
As described above, by providing the growth suppressing portion C10H around the thickness control portion C10E, a desired plate-like silicon can be obtained.
[0055]
(Plate manufacturing equipment)
Next, a method for producing plate-like silicon using the substrate of the present invention will be described. The apparatus for obtaining plate silicon of the present invention is particularly effective when the apparatus shown in FIG. 11 is used. However, the device for implementing the present invention is not limited to this. FIG. 11 is a schematic cross-sectional view of the inside of a manufacturing apparatus for manufacturing the plate-shaped silicon of the present invention.
[0056]
The apparatus for manufacturing plate silicon shown in FIG. 11 includes the obtained plate silicon S, substrate C, crucible 61, heating heater 62, silicon melt 63, crucible base 64, heat insulating material 65, crucible elevating base 66, substrate And a fixing table 68 for holding the substrate C. As shown in FIG. 11, the substrate C having a temperature equal to or lower than the raw material melt temperature is immersed in the silicon melt 63 in the crucible 61 while drawing the trajectory of the arrow Z from the left side in the figure. At this time, the silicon melt 63 is kept at a temperature equal to or higher than the melting point by the heater 62 for heating. In order to obtain stable plate-shaped silicon S, it is necessary to adjust the temperature of the melt, and to configure the apparatus so that the temperature of the atmosphere in the chamber and the temperature of the substrate C can be strictly controlled.
[0057]
It is preferable to provide the substrate C with a structure that can easily control the temperature. The material of the substrate is not particularly limited, but is preferably a material having good thermal conductivity or a material having excellent heat resistance. For example, high-purity graphite, silicon carbide, quartz, boron nitride, alumina, zirconium oxide, aluminum nitride, metal, and the like can be used, but an optimal material may be selected according to the purpose. High-purity graphite is more preferable because it is relatively inexpensive and is a material with high workability. The material of the substrate can be appropriately selected in consideration of various characteristics such as industrial low cost and the quality of the obtained plate-like silicon substrate. Further, when a metal is used for the substrate, there is no particular problem as long as the metal is used at a temperature equal to or lower than the melting point of the substrate, such as constantly cooling, and does not significantly affect the characteristics of the obtained plate-like silicon.
[0058]
In order to facilitate temperature control, it is convenient to use a fixing table 68 for holding a copper substrate. The fixing table 68 indicates a portion connecting the shaft 67 and the substrate C. The fixing table 68 and the substrate C are preferably connected to a cooling means. This is because the temperature of the substrate C can be more easily adjusted by being connected to the cooling mechanism. Further, it is preferable to have a heating mechanism for heating the substrate C. That is, it is preferable that the substrate be provided not only with a cooling mechanism but also with a heating mechanism. In the substrate C that has entered the silicon melt, plate-like silicon S grows on the surface of the substrate. Thereafter, the substrate escapes from the silicon melt, but the substrate side receives heat from the silicon melt, and the temperature of the substrate tends to increase. However, if the same substrate is subsequently immersed in the silicon melt at the same temperature, a cooling mechanism for lowering the temperature of the substrate is required. That is, it is better to control the temperature of the growth substrate using the heating mechanism before the substrate once escaped from the silicon melt is cooled by the cooling mechanism and before being immersed in the silicon melt. The heating mechanism may be a high-frequency induction heating system, a resistance heating system, or a lamp heating system.
[0059]
As described above, by using the cooling mechanism and the heating mechanism together, the stability of the plate-like silicon is significantly improved.
[0060]
What is important together with the temperature control of the substrate is the temperature control of the silicon melt. If the temperature of the melt is set near the melting point, the surface of the silicon melt may solidify due to the substrate coming into contact with the melt. preferable. This can be strictly controlled using a plurality of thermocouples or a radiation thermometer.
[0061]
To strictly control the temperature of the melt, it is directly preferable that the thermocouple be immersed in the melt. However, since impurities from the thermocouple protection tube etc. may be mixed into the melt, contamination may occur. It is necessary to have a structure that prevents The control method is preferably indirectly controlled, for example, by inserting a thermocouple into a crucible or the like, or has a structure in which the temperature of the silicon melt can be measured by a radiation thermometer.
[0062]
The crucible 61 containing the melt is placed on a heat insulating material 65 via a crucible base 64. This is used to keep the melt temperature uniform and to minimize heat removal from the crucible bottom. On the heat insulating material 65, a crucible base 64 is installed, a crucible elevating shaft 66 is connected, and an elevating mechanism is provided. This is because the plate-like silicon grows on the substrate C, so that the substrate C is always moved up and down so that it can be immersed at the same depth from the surface of the silicon melt. The method for enabling the immersion at the same depth from the molten metal surface is not limited to this. It is also possible to apply a method in which the position of the molten metal surface is kept constant, that is, a method of replenishing raw materials taken out as plate-like silicon. For this, it is possible to use a method in which a polycrystalline material (lump) as a raw material is melted and charged, a method of sequentially charging a melt as it is, a method of sequentially charging powder, and the like. However, it is preferable not to disturb the surface of the silicon melt as much as possible. If the melt surface is disturbed, the wave shape generated at that time is reflected on the melt surface side of the obtained plate-like silicon, which may impair the uniformity of the obtained plate-like silicon and impair the stability of quality. Because there is.
[0063]
Next, another plate-like silicon manufacturing apparatus will be described with reference to FIG. In FIG. 12, a heat shield plate 82 is provided on a crucible 71, and a fixed base 78 and a substrate C capable of moving through an opening 83 thereof are connected to a fixed leg 77. It is connected to the. On the heat insulating material 75, a crucible base 74 is installed, a crucible elevating shaft 76 is connected, and an elevating mechanism is provided. The cooler 79 is connected to an arm 81 having a joint 80 whose angle can be changed. However, in this drawing, devices such as a means for moving an arm or a joint and a chamber capable of evacuating are not shown. In the present apparatus, a heat shield plate 82 is opened on the crucible 71, and the substrate C is configured to draw an arbitrary trajectory. The crystal grows on the substrate C, and the plate-like silicon S is formed. At this time, by controlling the temperature of the substrate C, the temperature of the silicon melt 73, and the like, it becomes possible to control the thickness of the formed plate-like silicon. In this device, the substrate C is moved by the arm 81 having the joint portion 80, but may be moved by the arm 81. In this way, by providing a mechanism for moving the entire arm, the substrate C can be immersed at the same depth from the surface of the silicon melt.
[0064]
(Production method of plate-like silicon)
Next, a method for manufacturing plate silicon using the apparatus for manufacturing plate silicon shown in FIG. 11 will be described.
[0065]
First, a silicon lump (raw material) in which the concentration of boron is adjusted so that the specific resistance of the obtained plate-like silicon is 0.5 to 5 Ω · cm is filled into the high-purity graphite crucible 61 until it becomes full. The crucible is set in an apparatus as shown in FIG. Next, the chamber is evacuated to reduce the pressure in the chamber to a predetermined pressure. Thereafter, Ar gas is introduced into the chamber, and Ar gas is kept flowing from the upper portion of the chamber at a flow rate of 10 L / min. The reason why the gas is continuously supplied is to obtain a clean silicon surface.
[0066]
Next, the temperature of the heater 62 for melting silicon is set to 1500 ° C., which is equal to or higher than the melting point, and the silicon lump in the crucible 61 is completely melted. At this time, since the silicon raw material is melted to lower the liquid level, new silicon powder is introduced so that the molten metal surface of the silicon melt is at a position 1 cm below the upper surface of the crucible 61. It is preferable that the heater for melting silicon is not heated up to 1500 ° C. at a time, but is heated up to about 1300 ° C. at a rate of 5 to 50 ° C./min and then raised to a predetermined temperature. This is because when the temperature is rapidly increased, thermal stress is intensively applied to the corners of the crucible, which leads to breakage of the crucible.
[0067]
Thereafter, after confirming that the silicon has completely melted, the temperature of the silicon melt is set at 1410 ° C. and maintained for 30 minutes to stabilize the melt temperature. Next, the crucible 61 is moved to a predetermined position using the crucible lifting mechanism 66. The temperature of the silicon melt at this time is preferably from 1400 ° C to 1500 ° C. This is because the melting point of silicon is around 1410 ° C., and if the temperature is set to 1400 ° C. or less, the molten metal surface gradually solidifies from the crucible wall. On the other hand, if the temperature is set to 1500 ° C. or higher, the growth rate of the obtained plate-like silicon is reduced, and the productivity is deteriorated.
[0068]
Next, plate-like silicon is grown, and a substrate as shown in FIGS. 6 to 10 is advanced from the left side to the right side in FIG. At this time, the surface of the substrate, for example, the first surface C6A of FIG. 6 is brought into contact with the silicon melt, and the substrate C6 is moved so that the second surface C6B of the substrate and the third surface C6C of the substrate are on the traveling direction side. Let it. As described above, by bringing the first surface C6A of the substrate into contact with the silicon melt, plate-like silicon is formed on the first surface C6A. The trajectory for growing the plate-like silicon on the substrate is not particularly limited. For example, it is preferable to have a structure that can realize an arbitrary orbit, such as a circular orbit, an elliptical orbit, or a combination thereof.
[0069]
6 to 10, the shape of the second surface or the third surface of the substrate located at the front part in the traveling direction of the substrate C is not particularly limited. More preferably, the shape is such that the plate-like silicon grown on the first surface does not fall.
[0070]
The surface temperature of the substrate when entering the silicon melt needs to be lower than the freezing point of the silicon melt. More preferably, it is 100 ° C. or higher and 1100 ° C. or lower. If the temperature of the substrate is 100 ° C. or less, stable control becomes difficult. That is, in the case of continuous production, the substrate waiting to be immersed in the chamber receives radiant heat from the silicon melt, and it is difficult to maintain the substrate at 100 ° C. at all times. It is because it leads to. On the other hand, if the temperature of the substrate is 1100 ° C. or higher, not only is it necessary to heat the substrate to 1100 ° C., but also the growth rate of the plate-like silicon becomes slow, which is not preferable because the productivity is deteriorated. In order to adjust the temperature of the substrate, since both the cooling mechanism and the heating mechanism are provided, not only the productivity can be improved, but also the yield of the product can be improved and the quality can be stabilized.
[0071]
In addition, as a method of controlling the surface temperature of the substrate with good reproducibility, mount the substrate on the fixed base at a position where the radiant heat from the silicon melt does not reach or is less affected, and then immediately By adopting a method of entering the substrate, a device configuration in which the temperature of the substrate is not controlled is also possible.
[0072]
Further, here, since the description is made using the manufacturing apparatus shown in FIG. 11, the plate-shaped silicon S grows below the substrate C. However, by using a device configuration different from that in FIG. 11 and turning the substrate upside down, it is also possible to produce plate-like silicon on the upper side of the substrate C.
[0073]
Next, a method for manufacturing plate silicon according to the present invention using the plate silicon manufacturing apparatus shown in FIG. 12 will be described. Here, an example of a method of manufacturing plate silicon using the plate silicon manufacturing apparatus of FIG. 12 is described. However, the present invention is not limited to the manufacturing apparatus, and the substrate devised by the present invention is brought into contact with a silicon melt. Is essential, and the plate-shaped silicon of the present invention can be easily obtained.
[0074]
A silicon raw material in which the concentration of boron is adjusted so that the specific resistance of the obtained plate-like silicon becomes 1 Ω · cm is charged into a quartz crucible 71 protected by a high-purity carbon crucible, and an apparatus as shown in FIG. Install inside. Thereafter, evacuation is performed using a rotary pump until the pressure in the main chamber becomes 300 Pa, and further evacuation is performed using a mechanical booster pump until the pressure in the main chamber becomes 6 Pa.
[0075]
Next, the crucible is heated to 500 ° C. at a rate of 4 ° C./min using an inverter having a frequency of 4 kHz and a power of 80 kW as a heater 72 for crucible heating. Moisture contained in the carbon crucible is removed by maintaining the pressure in the main chamber at 6 Pa and the crucible temperature at 500 ° C. for 90 minutes. Further, the reason why the temperature is not raised at once is to prevent the crucible from being damaged due to concentrated thermal stress applied to the corners of the crucible.
[0076]
After such baking, the output of the inverter is temporarily stopped, and the heating of the crucible is stopped. In this state, Ar gas is filled until the pressure of the main chamber becomes 800 hPa. When the inside of the main chamber reaches 800 hPa, the crucible is heated again at a heating rate of 10 ° C./min, and the temperature is raised until the crucible temperature reaches 1550 ° C. By stabilizing the temperature of the crucible at 1550 ° C., all of the silicon lump in the crucible eventually melts to become a silicon melt. After confirming that the silicon lump is completely dissolved, the silicon lump or the silicon powder is additionally introduced so that the height of the silicon molten metal surface becomes 15 mm from the upper end of the crucible. After confirming that all the added silicon lump has melted, the set temperature of the crucible is lowered to 1430 ° C., and the state is maintained for 30 minutes to stabilize the temperature of the silicon melt.
[0077]
Next, plate-like silicon is grown on the substrate C, and the first surface of the substrate is moved so as to contact the silicon melt. As described above, the plate-shaped silicon S grows on the surface of the substrate when the first surface of the substrate comes into contact with the silicon melt. The orbit for producing the plate-shaped silicon S on the substrate C may be a circular orbit or an elliptical orbit. In particular, by adopting an apparatus structure as shown in FIG. 12 that can realize an arbitrary track, the yield of the obtained plate-like silicon S can be improved.
[0078]
As shown in FIG. 12, the substrate C and the plate-shaped silicon S may be separated in the chamber or may be carried out of the chamber. In particular, if the production speed is to be increased, it is preferable to peel off the substrate C in the chamber and carry out only the plate silicon S to the outside of the chamber. By doing so, not only is it unnecessary to carry out the substrate C out of the chamber, but also the consumption of Ar gas can be significantly reduced, and a more inexpensive plate-like silicon can be provided. Become.
[0079]
【Example】
(Example 1)
(Production of plate-shaped silicon)
A silicon raw material whose boron concentration was adjusted so that the specific resistance of the obtained plate-like silicon became 2 Ω · cm was put in a quartz crucible protected by a high-purity carbon crucible, and mounted in a chamber shown in FIG. .
[0080]
First, the inside of the chamber is evacuated to about 3 Pa and replaced with Ar gas at normal pressure. Thereafter, Ar gas is introduced into the chamber and returned to normal pressure, and then Ar gas is constantly supplied to the upper part of the chamber at 5 L / min. And leave it flowing. Next, the silicon raw material is melted by a heater. The temperature of the silicon melting heater is raised to 1500 ° C. at a heating rate of 8 ° C./min to confirm that the silicon raw material is completely melted. ° C, 1450 ° C, and 1425 ° C to reduce the temperature step by step.
[0081]
Next, the substrate having the shape shown in FIG. 6 was immersed in a silicon melt at a depth of 10 mm with the second surface side of the substrate as the front side in the traveling direction, to grow 100 sheet silicon. The temperature at which the substrate entered the silicon melt was set at 600 ° C. The size of the substrate used was 150 mm in length, 150 mm in width, and 30 mm in thickness, and the angle between the first surface and the second surface of the substrate was 40 °. Further, the width and depth of the moat structure were 3 mm, and the width of the edge of the substrate was 2 mm. The width of the plate thickness control unit is 5 mm, and the surface thereof has a pyramid-shaped uneven shape as shown in FIG. 13A, the pitch of the protrusions is 0.5 mm, and the height is 0 mm. 0.2 mm. The thickness of the obtained plate-shaped silicon reinforcing portion was about 400 μm.
[0082]
The second surface and the thickness reinforcing portion of the obtained plate-like silicon were removed by laser cutting, and plate-like silicon having a length of 125 mm, a width of 125 mm and a thickness of about 330 μm was cut out from the first surface of the plate-like silicon. Next, the shape of the plate-like silicon surface was measured with a displacement meter using a laser, and the amount of warpage was measured. The amount of warpage of the obtained plate-like silicon was about 0.5 mm on average.
[0083]
(Production of solar cell)
Next, a solar cell was manufactured using the obtained plate-like silicon. Next, etching and cleaning were performed with a mixed solution of nitric acid and hydrofluoric acid, and then alkali etching was performed using sodium hydroxide. Then, POCl ₃ N to p-type substrate by diffusion ⁺ A layer was formed. After removing the PSG film formed on the surface of the plate-like silicon with hydrofluoric acid, n ⁺ A silicon nitride film was formed on the layer using a plasma CVD device. Next, n which is also formed on the surface which is to be the back surface of the solar cell ⁺ The layer is removed by etching with a mixed solution of nitric acid and hydrofluoric acid to expose the p substrate, on which a back electrode and a p ⁺ Layers were formed simultaneously. Next, the electrode on the light receiving surface side was formed by a screen printing method. Thereafter, a solder dip was performed on the silver electrode portion to produce a solar cell.
[0084]
The obtained solar cell has an AM of 1.5 and 100 mW / cm. ² , The cell characteristics were evaluated in accordance with the “Method for Measuring the Output of Crystalline Solar Cell (JIS C 8913 (1988))”.
[0085]
The measurement results show that the average short-circuit current of the completed cell was 30.3 (mA / cm). ² ), Open voltage 587 (mV), fill factor 0.745, and efficiency 13.3 (%). From the obtained plate-like silicon, the number of cells whose cell characteristics were finally evaluated was 95.
[0086]
(Example 2)
A plate-like silicon was produced in the same manner as in Example 1 except that the substrate shown in FIG. 7 was used and the surface temperature of the substrate when it entered the melt was 300 ° C.
[0087]
The size of the substrate used was 150 mm in length, 150 mm in width, and 20 mm in thickness, and the angle between the first surface and the second surface of the substrate was 20 °. Further, the width and depth of the moat structure were 3 mm, and the width of the edge of the substrate was 2 mm. The width of the plate thickness control unit is 5 mm, and the surface thereof has a pyramid-shaped uneven shape as shown in FIG. 13A, the pitch of the protrusions is 0.5 mm, and the height is 0 mm. .1 mm. The surface of the first surface of the substrate used has a pyramid-shaped uneven shape as shown in FIG. 13A, the pitch of the convex portions is 1.0 mm, and the height is 0.1 mm. 2 mm. The thickness of the obtained plate-shaped silicon reinforcing portion was about 420 μm.
[0088]
The second surface of the obtained plate-like silicon and the plate thickness reinforcing portion were removed by laser cutting, and plate-like silicon having a length of 125 mm, a width of 125 mm and a thickness of about 350 μm was cut out from the first surface of the plate-like silicon. Next, the shape of the plate-like silicon surface was measured with a displacement meter using a laser, and the amount of warpage was measured. The amount of warpage of the obtained plate-like silicon was about 0.3 mm on average.
[0089]
A solar cell was also manufactured using the obtained plate-like silicon. The obtained solar cell has an AM of 1.5 and 100 mW / cm. ² , The cell characteristics were evaluated in accordance with the “Method for Measuring the Output of Crystalline Solar Cell (JIS C 8913 (1988))”. The measurement result of the manufactured solar cell is an average value, and the short-circuit current is 31.2 (mA / cm). ² ), Open circuit voltage 595 (mV), fill factor 0.747, and efficiency 13.8 (%). From the obtained plate-like silicon, 94 sheets were finally evaluated for cell characteristics.
[0090]
(Example 3)
Plate-like silicon was produced in the same manner as in Example 1 except that the growth substrate shown in FIG. 8 was used and the temperature at which the substrate entered the melt was 450 ° C.
[0091]
The size of the substrate used was 150 mm in length, 300 mm in width, and 40 mm in thickness, and the angle between the first surface and the second surface of the substrate was 30 °. Further, the width and depth of the moat structure were 4 mm, and the width of the substrate edge was 1 mm. The width of the plate thickness control unit is 7 mm, and the surface thereof has a pyramid-like uneven shape as shown in FIG. 13A, the pitch of the protrusions is 0.8 mm, and the height is 0 mm. .15 mm. The thickness of the obtained plate-shaped silicon reinforcing portion was about 400 μm.
[0092]
The second surface of the obtained plate-like silicon and the plate thickness reinforcing portion were removed by laser cutting, and plate-like silicon having a length of 125 mm, a width of 125 mm and a thickness of about 320 µm was cut out from the first surface of the plate-like silicon. Next, the shape of the plate-like silicon surface was measured with a displacement meter using a laser, and the amount of warpage was measured. The average warpage of the obtained plate-like silicon was about 0.32 mm.
[0093]
A solar cell was also manufactured using the obtained plate-like silicon. The obtained solar cell has an AM of 1.5 and 100 mW / cm. ² , The cell characteristics were evaluated in accordance with the “Method for Measuring the Output of Crystalline Solar Cell (JIS C 8913 (1988))”. The measurement result of the manufactured solar cell is an average value, and the short-circuit current is 30.8 (mA / cm). ² ), Open-circuit voltage 591 (mV), fill factor 0.743, and efficiency 13.5 (%). From the obtained plate-like silicon, the number of cells whose cell characteristics were finally evaluated was 96.
[0094]
(Comparative Example 1)
A plate-like silicon was produced in the same manner as in Example 1 except that the substrate shown in FIG. 7 without a thickness control unit was used.
[0095]
The size of the substrate used was 150 mm in length, 150 mm in width, and 30 mm in thickness, and the angle between the first surface and the second surface of the substrate was 40 °. Further, the width and depth of the moat structure were 3 mm, and the width of the edge of the substrate was 2 mm.
[0096]
The peripheral portions of the second surface and the first surface of the obtained silicon plate were removed by laser cutting, and a silicon plate having a length of 125 mm, a width of 125 mm and a thickness of about 30 μm was cut out from the first surface of the silicon plate. Next, the shape of the plate-like silicon surface was measured with a displacement meter using a laser, and the amount of warpage was measured. The amount of warpage of the obtained plate-like silicon was about 1.5 mm on average.
[0097]
A solar cell was also manufactured using the obtained plate-like silicon. The obtained solar cell has an AM of 1.5 and 100 mW / cm. ² , The cell characteristics were evaluated in accordance with the “Method for Measuring the Output of Crystalline Solar Cell (JIS C 8913 (1988))”. The measurement result of the manufactured solar cell is an average value, and the short-circuit current is 28.8 (mA / cm). ² ), Open-circuit voltage 588 (mV), fill factor 0.713, and efficiency 12.1 (%). From the obtained plate-like silicon, the number of cells whose cell characteristics were finally evaluated was 80. It is considered that such a result is that the plate-shaped silicon is warped due to the use of the substrate having no plate thickness control unit, and as a result, a problem has occurred in the manufacturing process of the solar cell. Specifically, it is considered that the short-circuit current and the fill factor were reduced due to the occurrence of cracks due to the printing pressure at the time of forming the light receiving surface electrode and the narrowing of the light receiving surface electrode.
[0098]
(Example 4)
(Production of plate-shaped silicon)
A silicon raw material in which the concentration of boron is adjusted so that the specific resistance of the obtained plate-like silicon becomes 2 Ω · cm is charged into a quartz crucible protected by a high-purity carbon crucible, and is placed in an apparatus as shown in FIG. It was installed in. Thereafter, evacuation was performed using a rotary pump until the pressure in the main chamber reached 350 Pa. Thereafter, exhaust was further performed using a mechanical booster pump until the pressure became 3 Pa.
[0099]
Next, the crucible is heated to 700 ° C. at a rate of 10 ° C./min. The water contained in the carbon crucible is removed by maintaining the pressure in the main body chamber at 6 Pa and the crucible temperature at 700 ° C. for 60 minutes. After such baking, the output of the inverter is temporarily stopped, and the heating of the crucible is stopped. In this state, argon gas is filled at a flow rate of 50 L / min until the pressure of the main chamber becomes 800 hPa.
[0100]
When the inside of the main chamber reaches 800 hPa, the flow rate of the argon gas is increased to 10 L / min, and the crucible is heated again at a rate of 10 ° C./min, until the temperature of the crucible reaches 1500 ° C. By keeping the temperature of the crucible at 1500 ° C. for 1 hour and stabilizing, all the silicon lump in the crucible eventually melts to become a silicon melt. After confirming that the silicon lump has completely dissolved, the silicon lump is additionally introduced so that the height of the silicon molten metal surface is 10 mm from the upper end of the crucible. After confirming that all the added silicon chunks were melted, the set temperature of the crucible was dropped through 1480 ° C., 1450 ° C., and 1420 ° C., and the temperature was further lowered for 30 minutes to stabilize the temperature of the silicon melt. Keep state. At this time, it was confirmed that the solidification of silicon did not progress from around the crucible wall of the silicon melt.
[0101]
Next, the substrate having the shape shown in FIG. 9 was immersed in a silicon melt at 10 mm with the second surface side of the substrate as the front side in the traveling direction, to grow 100 sheet silicon. The temperature at which the substrate entered the silicon melt was 200 ° C. The size of the substrate used was 150 mm in length, 150 mm in width, and 30 mm in thickness, and the angle between the first surface and the second surface of the substrate was 40 °. Further, the width and depth of the moat structure were 3 mm, and the width of the edge of the substrate was 2 mm. The width of the thickness control sections provided on the left and right sides in the traveling direction of the substrate is 5 mm, and the surface thereof has a pyramid-like uneven shape as shown in FIG. Was 0.5 mm and the height was 0.2 mm. The thickness of the obtained plate-shaped silicon reinforcing portion was about 410 μm.
[0102]
The second surface and the left and right plate thickness reinforcing portions of the obtained plate-like silicon were removed by laser cutting, and plate-like silicon having a length of 125 mm, a width of 125 mm, and a thickness of about 330 μm was cut out from the first surface of the plate-like silicon. Next, the shape of the plate-like silicon surface was measured with a displacement meter using a laser, and the amount of warpage was measured. The average warpage of the obtained plate-like silicon was about 0.2 mm.
[0103]
(Production of solar cell)
Next, a solar cell was manufactured using the obtained plate-like silicon. Next, alkali etching was performed using sodium hydroxide while also cleaning the silicon plate. Thereafter, PSG (phosphorus-containing silicate glass) is applied by a spin coating method, and then dried, and n is applied to the p-type substrate by thermal diffusion. ⁺ A layer was formed. Then, after removing the PSG film formed on the surface of the plate-like silicon with hydrofluoric acid, n ⁺ A silicon nitride film was formed on the layer using a plasma CVD device.
[0104]
Next, an aluminum paste is printed and baked on the surface to be the back surface side of the solar cell, so that the back surface electrode and p ⁺ Layers were formed simultaneously. Next, the electrode on the light receiving surface side was formed by printing and baking the silver paste. Thereafter, a solder dip was performed on the silver electrode portion to produce a solar cell.
[0105]
The obtained solar cell has an AM of 1.5 and 100 mW / cm. ² , The cell characteristics were evaluated in accordance with the “Method for Measuring the Output of Crystalline Solar Cell (JIS C 8913 (1988))”.
[0106]
The measurement results show that the average short-circuit current of the completed cells was 31.1 (mA / cm). ² ), Open-circuit voltage 583 (mV), fill factor 0.745, and efficiency 13.5 (%). From the obtained sheet silicon, 98 sheets were finally evaluated for cell characteristics.
[0107]
(Example 5)
Plate silicon was produced in the same manner as in Example 1 except that the substrate shown in FIG. 10 was used and the surface temperature of the substrate when it entered the melt was 300 ° C.
[0108]
The size of the substrate used was 150 mm in length, 150 mm in width, and 20 mm in thickness, and the angle between the first surface and the second surface of the substrate was 30 °. Further, the width of the plate thickness control section is 5 mm, and the surface thereof has a pyramid-like uneven shape as shown in FIG. 13A, the pitch of the protrusions is 0.5 mm, and the height is Was 0.1 mm. Further, the width of the growth suppressing portion existing in the peripheral portion is 5 mm, and the surface thereof has a pyramid-shaped uneven shape as shown in FIG. 13A, and the pitch of the convex portion is 1. The height was 5 mm and the height was 1 mm. The thickness of the obtained plate-shaped silicon reinforcing portion was 420 μm.
[0109]
The second surface of the obtained plate-like silicon and the plate thickness reinforcing portion were removed by laser cutting, and plate-like silicon having a length of 125 mm, a width of 125 mm and a thickness of about 350 μm was cut out from the first surface of the plate-like silicon. Next, the shape of the plate-like silicon surface was measured with a displacement meter using a laser, and the amount of warpage was measured. The amount of warpage of the obtained plate-like silicon was about 0.3 mm on average.
[0110]
A solar cell was also manufactured using the obtained plate-like silicon. The obtained solar cell has an AM of 1.5 and 100 mW / cm. ² , The cell characteristics were evaluated in accordance with the “Method for Measuring the Output of Crystalline Solar Cell (JIS C 8913 (1988))”. The measurement result of the manufactured solar cell is an average value, and the short-circuit current is 30.9 (mA / cm). ² ), Open circuit voltage 593 (mV), fill factor 0.742, and efficiency 13.6 (%). From the obtained plate-like silicon, the number of cells whose cell characteristics were finally evaluated was 95.
[0111]
It should be noted that the embodiments and examples disclosed this time are examples of all points and are not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0112]
【The invention's effect】
As described above, by adopting the shape of the plate-like silicon according to the present invention, the problem of warpage of the plate-like silicon can be avoided, and the plate-like silicon can be supplied stably at a low cost. become. In addition, by manufacturing a solar cell using this plate-like silicon, the solar cell can be supplied at a low price.
[Brief description of the drawings]
1A is a schematic perspective view of a plate-like silicon of the present invention, and FIG. 1B is a cross-sectional view of the plate-like silicon cut along 1B-1B in FIG. 1A.
FIG. 2 is a schematic perspective view of the plate-shaped silicon of the present invention.
FIG. 3 is a schematic perspective view of the plate-shaped silicon of the present invention.
FIG. 4 is a schematic perspective view of the plate-shaped silicon of the present invention.
FIG. 5A is a schematic perspective view of a plate-like silicon of the present invention, and FIG. 5B is a schematic perspective view of the plate-like silicon of FIG.
6A is a schematic perspective view of a substrate for producing the plate-like silicon of the present invention, FIG. 6B is a cross-sectional view of the substrate cut along 6B-6B in FIG. 6A, and FIG. It is sectional drawing of the board | substrate cut | disconnected along 6C-6C in (A).
7A is a schematic perspective view of a substrate for producing the plate-like silicon of the present invention, FIG. 7B is a cross-sectional view of the substrate cut along 7B-7B in FIG. 7A, and FIG. It is sectional drawing of the board | substrate cut | disconnected along 7C-7C in (A).
8A is a schematic perspective view of a substrate for manufacturing the plate-like silicon of the present invention, FIG. 8B is a cross-sectional view of the substrate taken along 8B-8B in FIG. 8A, and FIG. It is sectional drawing of the board | substrate cut | disconnected along 8C-8C in (A).
9A is a schematic perspective view of a substrate for producing the plate-like silicon of the present invention, FIG. 9B is a cross-sectional view of the substrate taken along 9B-9B in FIG. 9A, and FIG. It is sectional drawing of the board | substrate cut | disconnected along 9C-9C in (A).
10A is a schematic perspective view of a substrate for producing the plate-like silicon of the present invention, FIG. 10B is a cross-sectional view of the substrate cut along 10B-10B in FIG. 10A, and FIG. It is sectional drawing of the board | substrate cut | disconnected along 10C-10C in (A).
FIG. 11 is a schematic sectional view of a manufacturing apparatus for manufacturing the plate-like silicon of the present invention.
FIG. 12 is a schematic cross-sectional view of a manufacturing apparatus for manufacturing plate silicon of the present invention.
FIG. 13A is a schematic perspective view of irregularities formed on a substrate for producing the plate silicon of the present invention, and FIG. 13B is formed on a substrate for producing the plate silicon of the present invention. It is a schematic perspective view of the uneven | corrugated which is.
FIG. 14 is a schematic perspective view of concaves and convexes formed on a substrate for producing plate silicon of the present invention.
[Explanation of symbols]
S, S1, S2, S3, S4, S5 Plate silicon, S1A, S2A, S3A, S4A, S5A First surface of plate silicon, S1B, S2B, S3B, S4B, S5B Second surface of plate silicon, S1C , S2C, S3C, S4C, S5C Third surface of plate silicon, S1D continuous portion, S1E, S2E, S3E, S4E, S5E Plate thickness reinforcing portion of plate silicon, C, C6, C7, C8, C9, C10 Substrate , C6A, C7A, C8RA, C8LA, C9A, C10A The first surface of the substrate, the C6B, C7B, C8RB, C8LB, C9B, the second surface of the C10B substrate, the third surface of the C6C, C7C, C8LC, C8RC, C9C, C10C substrate Surface, C6E, C7E, C8LE, C9RE, C9LE, C10E thickness control part, C6F, C7F, C8RF, C8LF, C9F moat structure, 6G, C7G, C8G, C9G substrate edge, C10H growth suppression unit.

Claims (13)

A first surface, and a plate-like silicon having another surface continuously formed on the first surface, in a peripheral portion of the first surface, having a thickness reinforcing portion thicker than the average thickness of the first surface. Plate-like silicon characterized by the above-mentioned. The plate-like silicon according to claim 1, wherein the plate-thickness reinforcing portion of the plate-like silicon exists at a position opposite to a portion where the first surface and the other surface are continuous with each other. The plate-shaped silicon according to claim 1, wherein the plate-shaped reinforcing portions of the plate-shaped silicon are present at all positions including a continuous portion between the first surface and another surface. The plate-like silicon according to claim 1, wherein the plate-thickness reinforcing portion of the plate-like silicon is at least 105% and at most 170% of the average plate thickness of the first surface. 2. The silicon plate according to claim 1, wherein the width of the plate thickness reinforcing portion of the silicon plate is 10% or less of the length of the long side of the silicon plate. The plate-like silicon according to claim 1, wherein the area of the plate thickness reinforcing portion of the plate-like silicon is 35% or less of the area of the first surface. The method for producing plate-like silicon according to any one of claims 1 to 6, wherein the substrate is brought into contact with a silicon melt, the plate-like silicon is grown on the substrate surface, and then the substrate is separated from the melt. A method for producing plate-like silicon, comprising the steps of: 8. The method for manufacturing plate silicon according to claim 7, wherein the other surface continuous with the first surface of the plate silicon is formed from a front portion in a traveling direction of the substrate. 9. The method for manufacturing plate silicon according to claim 8, wherein the plate thickness reinforcing portion of the plate silicon is formed at a rear portion in a traveling direction of the substrate. The thickness control part of the substrate on which the thickness reinforcement part of the plate-shaped silicon grows has a periodic protrusion, and the distance to the protrusion closest to the protrusion is 0.1 mm or more, The substrate for producing plate-like silicon according to claim 8, wherein the thickness is 2 mm or less. 9. The manufacturing method according to claim 8, wherein the thickness control unit of the substrate on which the thickness reinforcing portion of the silicon plate grows includes one of silicon carbide, pyrolytic carbon, and graphite. Substrate. 9. The plate-like silicon according to claim 8, wherein the thickness control unit of the substrate on which the plate-thickness reinforcing portion of the plate-like silicon grows is formed lower than the surface on which the first surface of the plate-like silicon grows. Manufacturing substrate. A solar cell manufactured from the other surface continuous with the first surface of the plate-shaped silicon according to claim 1 and the first surface from which a thickness reinforcing portion is removed.

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