WO2002020882A1

WO2002020882A1 - Silicon sheet producing apparatus and solar cell comprising silicon sheet produced by the same

Info

Publication number: WO2002020882A1
Application number: PCT/JP2001/007001
Authority: WO
Inventors: Shuji Goma; Kazuto Igarashi; Kohzaburoh Yano; Hiroshi Taniguchi
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2000-09-08
Filing date: 2001-08-13
Publication date: 2002-03-14
Also published as: JP4451556B2; AU2001277784A1; JP2002080295A; TWI251627B

Abstract

A silicon sheet producing apparatus comprising a crucible (14) containing fused silicon and a rotating cooling body (11) rotatably disposed above the crucible (14) and having at least one flat surface (1) for growing a solid silicon sheet (12) on the surface is characterized by comprising a separating/transfer out mechanism for separating a silicon sheet (12) formed on the flat surface (1) of the rotating cooling body (11) by dipping it in a fused silicon (13) by the rotation and then lifting it up from the fused silicon (13) and transferring the separated silicon sheet (12) by the inertia force by the rotation of the rotating cooling body (11) and/or the fall by the gravity out of the apparatus before the silicon sheet (12)is dipped again in the fused silicon (13). With this, a planar silicon sheet free of internal stress can be produced and the silicon sheet can be taken out continuously and stably.

Description

Specification

TECHNICAL FIELD The present invention relates to a silicon sheet manufacturing apparatus and a solar cell using the silicon sheet.

The present invention relates to an apparatus for manufacturing a silicon sheet which can be mainly used for a solar cell and the like, and a solar cell using the silicon sheet. Background art

Conventionally, as a method of immersing a rotary cooling body in a molten metal to take out silicon generated on the cooling body surface, for example, there is a silicon purification method disclosed in US Pat. No. 4,231,755. .

According to this method, a part of the cylindrical surface of the rotary cooling body is immersed in the melt, and while the rotary cooling body is rotating, a silicon solidified shell is grown on the cylindrical surface, which is then redissolved to take out liquid silicon. Thereby, the silicon melt from which impurities have been removed can be taken out.

Further, as a device for immersing a rotary cooling body in molten silicon to directly take out a silicon sheet generated on the surface of the rotary cooling body, a silicon ribbon disclosed in Japanese Patent Application Laid-Open No. 10-28995 is disclosed. There are manufacturing equipment.

The main part of the silicon ribbon manufacturing apparatus is composed of a heating and melting section for silicon and a cooling section including a rotary cooling body.

FIG. 6 shows a method of pulling out a silicon ribbon by this manufacturing apparatus. That is, a part of the cylindrical surface of the rotary cooling body 61 made of a heat-resistant material is immersed in the molten silicon 63 in the vertically movable crucible 64, and the rotary cooling body 61 is not rotated. At first, the silicon ribbon 62 is continuously taken out by using the carbon net 65 to draw it out. According to this method, both the process cost and the raw material cost can be reduced as compared with the conventional silicon wafer manufacturing method in which a silicon ingot is sliced with a wire and the like to obtain a wafer.

As an invention in which this method is improved, there is a crystal sheet manufacturing apparatus disclosed in Japanese Patent Application Laid-Open No. 2001-19595.

FIG. 7 shows a method of drawing a crystal sheet by this manufacturing apparatus.

The rotary cooling body 71 has a concavo-convex structure composed of annular convex portions 77 and concave portions 78 alternately formed on the peripheral surface in the direction of the rotation axis.

Only the protrusions 77 are immersed in the metal or non-ferrous metal melt 73 so that the melt 73 does not adhere to the bottom of the recesses 78. As a result, a crystal nucleus is generated and grown in the convex portion 77, and a crystal sheet 72 is formed in contact with the crystal grown from the adjacent convex portion 77.

According to this method, since the concave portions 7 8 are not immersed in the melt 73, the adhesive strength between the rotary cooling body 71 and the crystal sheet 72 is reduced, and the crystal sheet 72 is easily separated from the rotary cooling body 71. Can be peeled. In addition, the crystal nuclei can be controlled so as to be generated only in the convex portions 77, and relatively large crystal grains can be obtained. Further, the crystal sheet having the tip portion inserted into the concave portion 78 of the rotary cooling body 71 With the provision of the take-out portion 75, the crystal sheet 72 is easily and continuously brought into contact with the rotary cooling body 71 and peeled off.

In the method disclosed in the above-mentioned US Pat. No. 4,231,755, it is necessary to re-melt the metal and take it out in a liquid state. In other words, it is impossible to directly extract the plate-like metal, and it is necessary to recrystallize the re-melted metal. Therefore, when this method is applied to the production of silicon ribbons, many processes such as melting, solidification shell formation, remelting and recrystallization are required, and the production power, time, and cost increase. Also, continuous production of silicon ribbons is not possible.

In the crystal sheet manufacturing apparatus disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2001-195595, the silicon solidified shell formed on the cylindrical rotary cooling body 71 is removed. With this configuration, it is impossible to directly pull out a flat silicon sheet. In addition, since the silicon sheet to be taken out is not flat, it is difficult to continuously withdraw it.

In addition, even when the flat portion is extended and the flat crystal sheet 72 along the contact portion is drawn out, the crystal growth is performed on the cylindrical rotary cooling body 71, so that the crystal along the cylinder is formed. This is a method of stretching the sheet 72 to a flat surface. Therefore, when the crystal sheet 72 cannot be completely stretched, the crystal sheet 72 remains curved, and continuous extraction is impossible. Further, the crystal sheet 72 taken out does not become flat.

Furthermore, even if the crystal sheet 72 is completely stretched by optimizing the conditions, the internal stress remains in the crystal sheet 72, so that the strength of the crystal sheet 72 is reduced, and the drawing process and the slow cooling process are performed. In such a case, the crystal sheet 72 may be damaged, and stable continuous production of the crystal sheet 72 is difficult.

Due to these problems, it is difficult to continuously and stably produce a large amount of planar silicon sheets at low cost with the above-described conventional techniques. In the silicon ribbon manufacturing apparatus disclosed in the above-mentioned Japanese Patent Application Publication No. Hei 10-299895, the silicon solidified shell formed on the cylindrical rotary cooling body 61 is drawn with a force sheet at the initial stage of drawing. By pulling and stretching, the grown flat silicon ribbon 62 is continuously pulled out following the force—bonnet 65.

However, when the continuous drawing is performed, the subsequent silicon ribbon 62 is always pulled by the silicon ribbon 62 itself, and a large load is applied. Therefore, the silicon ribbon 62 is easily broken. In this case, since a rubber sheet or the like is used at the initial stage of the drawing, it is impossible to immediately resume the drawing of the silicon ribbon 62, and it is difficult to perform a stable continuous drawing. In addition, since the silicon ribbon 62 is pulled out in a plane by pulling the crystal grown on the rotary cooling body 61, internal stress remains in the silicon ribbon 62, and the strength of the silicon ribbon 62 is reduced. Therefore, the withdrawal process or In the slow cooling process, the silicon ribbon 62 may be damaged, and stable continuous production is difficult. The semiconductor characteristics of the semiconductor device manufactured from the silicon ribbon 62 are degraded by internal stress.

Further, when the silicon ribbon 62 cannot be completely stretched, the silicon ribbon 62 remains curved, cannot be continuously taken out, and the taken-out silicon ribbon 62 does not become flat.

The present invention has been made in view of such circumstances, and uses a silicon sheet manufacturing apparatus capable of continuously producing a large amount of a planar silicon sheet stably at a low cost and a silicon sheet produced thereby. The purpose is to provide solar cells that have been used. Disclosure of the invention

According to the present invention, a molten silicon storage portion for storing molten silicon, and at least one flat surface rotatably disposed above the molten silicon storage portion and for solidifying and growing the silicon sheet on the surface. A rotary cooling body having a rotating cooling body having a rotating surface, the silicon being formed on the flat surface of the rotating cooling body once immersed in the molten silicon by rotation and then pulled up from the molten silicon before being immersed again in the molten silicon. A peeling / unloading mechanism is provided to peel off the silicon sheet and take it out of the device by using the inertia and / or gravity of the rotating cooling body to drop it. An apparatus for manufacturing a silicon sheet is provided.

According to the present invention, since the rotary cooling body solidifies and grows the silicon crystal ribbon on a flat surface, that is, a flat surface having no curvature, a mechanism for extending the curved silicon sheet into a planar shape becomes unnecessary, and no internal stress remains. Silicon sheets can be continuously manufactured in large quantities and stably.

The silicon sheet manufactured by the silicon sheet manufacturing apparatus of the present invention does not need to be sliced separately, and a flat silicon sheet can be directly obtained. Further, since there is no loss due to slicing, it contributes to cost reduction. The silicon sheet in the present invention means a square or rectangular plate-like silicon whose size and shape are defined by the size and shape of the flat surface of the rotary cooling body. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram illustrating a configuration of a silicon sheet manufacturing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a silicon sheet manufacturing apparatus according to another embodiment of the present invention.

FIG. 3 is a diagram illustrating a first step of a method of peeling a silicon sheet using the peeling member of FIG.

FIG. 4 is a diagram illustrating a second step of the method of peeling the silicon sheet using the peeling member of FIG.

FIG. 5 is a diagram illustrating a configuration of a carry-out auxiliary member included in the silicon sheet manufacturing apparatus of FIGS. 1 and 2.

FIG. 6 is a diagram illustrating the configuration of a conventional silicon sheet manufacturing apparatus. Figure 7 is a best mode for carrying out the _c invention is a diagram illustrating another structure of a conventional silicon sheet manufacturing apparatus

The present invention will be described in more detail with reference to the accompanying drawings. The present invention is not limited by these.

FIG. 1 shows a first example of the configuration of the silicon sheet manufacturing apparatus of the present invention. In the silicon sheet manufacturing apparatus of the present invention, for example, a heat insulating material is stretched inside an outer wall of the apparatus made of stainless steel or the like, and, for example, a heater disposed oppositely and a central portion of these heaters And a rotary cooling body 11 disposed above the crucible 14 and supported by a shaft.

On the peripheral surface of the rotary cooling body 11, there are a plurality of The flat surface 1 is formed, and when the flat surface 1 is immersed in the molten silicon 13, a silicon sheet 12 is formed on the surface of the flat surface 1.

Observation of the peeled surface of the silicon sheet 12 formed on the flat surface 1 by a scanning electron microscope showed that the area fixed to the surface of the flat surface 1 was 5 to 5% of the area of the generated silicon sheet. It is known to be 10%. In other words, since the entire silicon sheet 1 2 is not fixed to the surface of the flat surface 1, if an appropriate impact is given after the crystal growth, the silicon sheet 1 2 can be easily separated from the flat surface 1. Is possible.

In addition, even if no external impact is applied, there is a silicon sheet that separates from the rotary cooling body 11 and falls under the influence of micro-vibration or gravity caused by the rotation of the rotary cooling body 11.

The action of gravity when the silicon sheet 12 is separated from the rotary cooling body 11 will be described.

First, when the flat surface 1 on which silicon is to be grown is set at the lowest point, and the flat surface 1 is immersed in molten silicon 13, the silicon sheet 12 grows on the surface of the flat surface 1.

Here, assuming that the position of the flat surface 1 immersed in the molten silicon 13 at the lowest point of the rotary cooling body 11 is 0 degree, the rotary cooling body 11 rotates from the 0 degree position, The silicon sheet 12 rotates together with the rotary cooling body 11. When the rotating cooling body 11 rotates 360 degrees, the flat surface 1 at the lowest point is immersed in the molten silicon 13 again. It is necessary to take out the silicon sheet 12 from it.

As described above, when the silicon sheet 12 is peeled off by the minute vibration caused by the rotation of the rotary cooling body 11, the silicon sheet 12 is positioned at 0 to 90 degrees (the rotation of the rotary cooling body 11 takes four minutes). (One round or less), the silicon sheet 12 falls immediately below the flat surface 1 because of the gravity. A gutter member 17 must be provided as a means for collecting the silicon sheet 12. In addition, the silicon sheet 12 that does not fall at a position within 0 to 180 degrees rotates while being placed on the flat surface 1. In particular, as described above, the silicon sheet 12 that does not peel off from the rotary cooling body 11 only by minute vibration caused by the rotation of the rotary cooling body 11 needs to be peeled off by applying an impact from the impact generating member 15 as described above. In order to peel and remove the silicon sheet 12 using the inertial force due to rotation and the drop due to gravity, after the silicon sheet 12 is peeled, it is necessary to reach the position where the gutter member 16 for carrying out the equipment is installed. However, it is necessary to move the silicon sheet 12 with the silicon sheet 12 resting on the rotary cooling body 11.

When the silicon sheet 12 is peeled off at a position within 0 to 90 degrees using the impact generating member 15, the silicon sheet 12 is located below the flat surface 1 which is the silicon sheet generating portion. As it is located, the silicon sheet 12 falls immediately. Therefore, the silicon sheet 12 can be taken out by using the gutter member 17. In this case, the gutter member 17 and the impact generating member 15 have a structure in which they approach each other.

When the silicon sheet 12 is peeled at a position between 90 degrees and 180 degrees, the silicon sheet 12 is on the flat surface 1, and the direction of the gravitational force due to rotation and the direction of gravity are Is reversed, so that the silicon sheet 1 2 does not fall from the flat surface 1 and moves to the uppermost point while remaining on the flat surface 1. In other words, in this case, the result is equivalent to the case where the peeling is performed at the position of 180 degrees which is the highest point.

When the silicon sheet 12 peels at a position between 180 degrees and 270 degrees, if the inertia force or gravity is larger than the static friction force between the silicon sheet 12 and the surface of the flat surface 1, At this point, the silicon sheet 1 2 falls off the flat surface 1. On the other hand, if the static friction force is larger than the inertial force or gravity, the silicon sheet 12 moves on the rotating cooling body 11 to a position of up to 270 degrees, When it reaches the position, it falls directly below regardless of the magnitude of the static friction coefficient.

That is, when the silicon sheet 12 is peeled off by applying an impact in the position range of 90 degrees to 270 degrees, regardless of the relationship between the static friction force and the inertia force or gravity, The silicon sheet 12 falls apart from the rotary cooling body 11 in a position range of 180 degrees to 270 degrees.

When the silicon sheet 12 peels off at a position between 270 ° and 360 °, the silicon sheet 12 becomes flat as well as when the silicon sheet 12 peels off at a position between 0 ° and 90 °. Since it is located below surface 1, silicon sheet

1 2 falls instantly. Therefore, in this case, the gutter member 16 needs to be installed immediately below the peeling position, and the gutter member 16 and the impact generating member 15 are arranged close to each other.

Due to the configuration of the device, it is difficult to bring the impact generator 15 that gives an impact for peeling off and the gutter member 16 that carries out the dropped silicon sheet close to each other. It is desirable that the position at which the film is peeled off be set in the range of 90 to 270 degrees.

For the above reason, it is desirable that the gutter member 16 be installed below the track on which the silicon sheet 12 separates from the flat surface 1 moved to the position range of 180 to 270 degrees and falls. .

In Fig. 1, one gutter member 17 is installed at a position of 60 degrees close to the rotating cooling body 11, and the impact generating member 15 is given a shock perpendicular to the silicon sheet surface. In this case, the gutter member 16 is installed at an upper position of 180 degrees, which is the highest point, and the other gutter member 16 is installed close to the rotary cooling body 11 at a position of 270 degrees.

The configuration of the impact generating member 15 is not particularly limited, but a physical impact generating means for pressing a solid substance against the surface of the silicon sheet 12 with an appropriate force is the simplest and preferable.

On the other hand, the method of peeling the silicon sheet 12 by bringing the peeling member into contact with one side of the front end side in the traveling direction of the silicon sheet 12 (the end on the upstream side in the rotation direction) is also effective because there is no movable part. It is considered to be an effective means.

When an impact is applied to the edge of the silicon sheet 12 in a direction parallel to the silicon sheet surface, the impact force is perpendicular to the silicon sheet surface. It is easy to expect that much less force is required for the impact force. In addition, the upper limit of the impact force at which the silicon sheet 12 is broken is much larger. However, when an impact is applied in the parallel direction, it is necessary to apply an impact only to the silicon sheet 12 without contacting the rotating cooling body 11. That is, it is necessary to apply an impact only to the side surface portion constituting the thickness of the silicon sheet 12. FIG. 2 shows a second example of the configuration of the silicon sheet manufacturing apparatus of the present invention. The silicon sheet manufacturing apparatus of this example uses the rotation of the rotary cooling body 21 to apply an impact in a parallel direction using a peeling member.

Since the flat surface 1 is composed of a flat surface without a curve, the silicon sheet 12 is formed on the surface of the flat surface 1 and the silicon sheet 12 has a flat surface without the curve, and the silicon sheet 2 2 on the flat surface 1 is formed. The sides 22 a and 22 b of the front end (front end) and the rear end (end) in the traveling direction have a larger turning radius than other parts of the silicon sheet 12. Therefore, the acute-angled peeling member 25 for promoting the peeling of the silicon sheet 22 is provided at the front end of the silicon sheet 22 in the traveling direction without contacting the edge of the flat surface 1 of the rotary cooling body 21 as the base. If it is fixed so as to be in contact with only one side 22 a on the side (upstream in the rotational direction), the peeling member 25 effectively separates the silicon sheet 22. In other words, the peeling tip of the peeling member 25 is formed by a circular orbit having a maximum radius of rotation passing through a corner on the front end side in the traveling direction on the flat surface 1 of the rotary cooling body 21 that generates the silicon sheet 22, It is necessary to install between the circular orbit located outside by the thickness of the sheet 22.

FIG. 3 shows a state immediately before the peeling member 25 and the silicon sheet 22 come into contact with each other. The exfoliation tip of the exfoliation member 25 is located slightly outside the circular orbit 31 with the maximum turning radius through which the corner (ridge) 30 on the front end side in the traveling direction of the flat surface 1 that forms the silicon sheet 22 2 passes. Have been.

As shown in FIG. 3, it can be seen that portions other than the side 22 a on the front end side in the traveling direction of the silicon sheet 22 pass inside the orbit 31.

FIG. 4 shows a state immediately after the rotary cooling body 21 further rotates from the state shown in FIG. 3 and the peeling member 25 comes into contact with the silicon sheet 22. In FIG. 4, the rotary cooling body 21 does not contact the peeling member 25 at all. The silicon sheet 22 has a structure in which only one side 22 a on the front end side in the traveling direction comes into contact with the peeling member 25, peels off from the flat surface 1, slides down to the gutter member 26, and is carried out. ing.

The thickness of the silicon sheet 22 in FIG. 2 varies depending on the temperature conditions of the molten silicon 23 and the like, the number of revolutions and cooling conditions of the rotary cooling body 21, and the like. Since it is 0 m, the peeling member 25 can be installed with an accuracy of several 100 m.

Further, the position at which the peeling member 25 is installed can be set based on substantially the same concept as in the case where an impact is applied to the surface of the silicon sheet 22 described above. As in the above case, assuming that the position of the flat surface 1 at the lowest point of the rotary cooling body 11 and immersed in the molten silicon 13 is 0 degrees, the rotary cooling body 11 rotates 360 degrees. It is necessary to take out the silicon sheet 22 before immersing it in the molten silicon 23 again.

The difference between the peeling member 25 and the impact generating member 15 is that the silicon sheet 22 peeled off from the flat surface 1 by the peeling member 25 does not move while remaining on the rotary cooling body 21 and the peeling member 2 Regardless of the installation position of 5, the separation member 25 can be immediately separated from the flat surface 1 at the installation position.

When the peeling member 25 is set at a position of 0 to 180 degrees, the silicon sheet 22 is separated from the rotating cooling body 21 while reversing the rotating direction of the rotating cooling body 21. Will fall. Therefore, the silicon sheet 22 slides down the gutter member 28 and can be taken out. However, the greater the distance between the separation position and the gutter member 28, the greater the impact due to the drop.

In order to alleviate the impact due to the drop and simplify the apparatus, it is desirable that the separation member 25 and the gutter member 26 be close to each other or integrated. When the peeling member 25 is installed at a position of 180 degrees to 270 degrees, especially in a structure in which the peeling member 25 and the gutter member 26 are integrally installed, the silicon sheet 22 is peeled off after the peeling. Separate from the rotating cooling body 2 1 and smoothly slide down to the gutter member 26 Will be. In addition, no special movable member other than the rotation of the rotary cooling body 21 is required to give an impact for peeling, which contributes to simplification of the apparatus, and improves durability and maintainability of the apparatus. .

In both the first and second examples, it is desirable that the gutter member has a structure capable of being carried out by utilizing the weight of the silicon sheet in order to simplify the device configuration. In other words, instead of forced conveyance by a rotating power mechanism, etc., the silicon sheet is piled up due to friction with the gutter member and the gutter member is inclined at an angle greater than the angle at which the silicon sheet falls under its own weight. It is desirable to adopt a structure to be carried out.

Further, by adding a carry-out assisting member such as a roller, it is possible to carry out the silicon sheet more efficiently.

Hereinafter, examples based on the embodiments of the present invention will be described. The invention is not limited by these.

Example 1

Embodiment 1 is an example in which a method is used in which a flat surface and a planar silicon sheet of a rotary cooling body for producing a silicon sheet are subjected to impact from a vertical direction to peel off the silicon sheet from the flat surface. .

As shown in FIG. 1, the silicon sheet manufacturing apparatus according to the first embodiment includes a square crucible 14, a heating crucible for melting silicon supplied to the crucible 14, and a silicon sheet generating unit. A rotating cooling body 11 having a plurality of flat surfaces 1 formed thereon, a rotating shaft (not shown) rotatably supporting the rotating cooling body 11, and an impact giving an impact to peel off the silicon sheet 12. It consists of a generating member 15 and two gutter members 16 and 17 for carrying the peeled silicon sheet 12 out of the apparatus.

These components are housed in a rectangular parallelepiped device main body having an outer wall having a heat insulating material (not shown). The device main body is sealed so that the inside can be maintained in an atmosphere of, for example, argon gas.

Rotary cooling of the silicon sheet 1 2 generated on the surface of the rotating cooling body 1 1 What peels off due to minute vibrations caused by the rotation of the body 11 is carried out by one of the gutter members 17.

The rotary cooling body 11 has a hollow structure, and performs cooling by passing a gas or liquid cooling medium inside.

The method of applying a shock to peel off the silicon sheet 12 that does not peel due to minute vibrations caused by the rotation of the rotating cooling body 11 is to apply a specified impact force while synchronizing with the rotation of the rotating cooling body 11 The mechanism is not particularly limited as long as it can be given to the silicon sheet 12 on the surface 1.

In the present embodiment, a striking member such as a rod made of a carbon material is hung directly above the rotary cooling body 11 with a string or the like, and the silicon sheet 12 is moved upward in synchronization with the rotation of the rotary cooling body 11. Upon reaching the point, the impact member was dropped to make an impact generating member 15 that impacts the entire silicon sheet 12 on the flat surface 1. The position at which the impact due to the falling weight of the striking member is given is 180 ° (the highest point) when the lowest point of the rotating cooling body 11 is 0 °, and the surface of the silicon sheet 12 is located at this position. Is subjected to a vertical shock.

In the present invention, by using the pulse motor for the rotary drive source of the rotary cooling body 11, the rotation state (rotation angle) of the rotary cooling body 11 is read by the pulse mode. Therefore, it is possible to drive the impact generating member 15 by grasping the timing when each flat surface 1 reaches the position of 180 degrees (the highest point).

Specifically, the other end of the string connected to the striking member is fixed to a reel attached to the rotating shaft of the motor, and the reel is wound up and released by the reel by rotating the rotating shaft forward and backward. I do. The forward and reverse rotation of the rotating shaft is synchronized with the rotation of the rotary cooling body 11. That is, when each flat surface 1 reaches the position of 180 degrees (the highest point), the string wound on the reel is released, and the striking member falls on the silicon sheet 12 on the flat surface 1 by its own weight. Let it.

The impact generating member 15 is not limited to the configuration in which the impact member is dropped by its own weight as described above. By performing the conversion, it is possible to synchronize almost completely, and it is possible to arbitrarily set the position on the silicon sheet 12 to give an impact and the hitting angle.

In the present embodiment, the material of the impact member is a carbon rod. However, the material is not particularly limited as long as it can withstand the temperature in the apparatus and has little influence on contamination of silicon.

In particular, it is effective to improve the durability by using a member harder than silicon, such as a member coated with SiC or the like, or by coating a material harder than silicon. Yes, it also has the effect of preventing pollution by carbon powder.

The shape of the striking member is not particularly limited as long as it can apply a specified impact force, but the striking surface of the striking member has a large radius of curvature in order to prevent a single point of impact force. Alternatively, it preferably has a flat surface shape.

Further, a plurality of striking members may be provided so that the impacts of these striking members are simultaneously applied to a plurality of locations on the silicon sheet surface. In this case, the concentration of impact force can be reduced.

Peeled gutter member 1 6, 1 7 for unloading the silicon sheet 1 2, as shown in the structure is preferably _c Figure 5 having a plate-like running surface for silicon sheet 1 2 slides down by its own weight, the silicon sheet 1 2 gutter In order to prevent them from falling off the members 16 and 17 and dropping in the horizontal direction, a fall prevention guide 54 is installed on the side of the gutter members 16 and 17 as a carry-out auxiliary member. Is preferred.

Further, as shown in FIG. 5, in order to further promote the sliding of the silicon sheet 12 by its own weight, it is preferable to install a roller 53 as a carry-out assisting member on the sliding surface.

In the present embodiment, the gutter member 51 provided with such a guide 54 and a roller 53 as a carry-out auxiliary member is installed at both the positions of 60 degrees and 270 degrees. The installation angle (inclination angle) of the gutter member 51 is inclined 30 degrees downward with respect to the horizontal, The structure is such that the silicon sheet 12 is carried out of the apparatus by its own weight.

Regarding the installation position of the gutter member 51, it is necessary to consider the configuration of the apparatus and the position where the silicon sheet 12 separates from the rotary cooling body 11 and falls. The installation angle must be set so that the silicon sheet 12 slides down by its own weight due to friction between the material of the gutter member 51 and the silicon sheet 12.

Regarding the surface configuration of the gutter member 51 (16, 17), it is preferable to select a surface having as smooth a surface as possible in order to reduce the frictional force with the silicon sheet 12.

If, for example, a material that is softer than the silicon sheet 12 is selected as such a material, the impact when the silicon sheet 12 slides down on the gutter members 16 and 17 can be reduced. Although the silicon sheet 12 can be prevented from being broken, the durability is reduced. Even when a hard material such as a SiC coat is selected, it is possible to provide a structure in which the silicon sheet 12 is not broken by considering the installation angle and the installation position.

The rotary cooling body 11 preferably has a structure that is not immersed in the molten silicon 23 except for the flat surface 1 that generates the silicon sheet. Note that the simplest structure of a rotary cooling body is a structure in which the cross-sectional shape is a polygonal column. In this case, since the adjacent flat surfaces 1 are continuous with each other via the sides, the adjacent silicon sheets 1 There is a risk that the two will be integrated.

Therefore, in the present invention, as shown in FIG. 1, a gear-type rotary cooling body 11 in which vertices of a polygonal column are cut inward is applied. In this structure, since the flat surface 1 is formed on the side surface of the polygonal prism, the flat surfaces 1 can be a simple structure that gives continuous shocks at a fixed time interval even for discontinuous shocks. An example of a method for manufacturing the silicon sheet 12 using the above-described apparatus will be described.

First, a crucible 14 filled with solid silicon was heated all day long to melt the silicon. Next, raise the crucible 14 and rotate it as shown in Figure 1. The flat surface 1 of the subcooler 11 was immersed in molten silicon 13 and the rotary cooler 11 was rotated.

As a result, substantially the same silicon sheet 12 was formed on all the flat surfaces 1 of the gear-type rotary cooling body 11. The impact generating member 15 is applied for a certain period of time so that when the flat silicon sheet 12 becomes horizontal on the flat surface 1 at the highest point, the silicon sheet 12 falls vertically and gives an impact to the silicon sheet 12. Control was performed so that falling and rising were repeated at intervals.

When the silicon sheet 12 was grown in this way and checked through the drilled holes of the device, about 30% of the silicon sheet fell from the flat surface 1 due to vibration at the position of 0 to 180 degrees. However, one of the gutter members 17 was slid down and carried out of the apparatus and collected.

The remaining about 70% of the silicon sheet is peeled off from the flat surface 1 at the highest point (at the position of 180 degrees), then separated from the flat surface 1 and slid down to the other gutter member 16. It was carried out of the equipment and collected.

The recovered silicon sheet 12 had a smooth surface and a uniform thickness (average thickness of about 270 m), and became a columnar silicon sheet formed by stable and continuous crystal growth.

Example 2

Example 2 is an example in which a method is used in which a silicon sheet is peeled off from a flat surface by applying an impact from a direction parallel to the flat surface and the planar silicon sheet of the rotary cooling body that generates the silicon sheet.

As shown in FIG. 2, the silicon sheet manufacturing apparatus according to the second embodiment has substantially the same configuration as that of the first embodiment, but differs from the first embodiment in that an impact is applied to the surface of the planar silicon sheet 22. The impact-generating member 15 has been removed, and the acute-angle peeling member 25 for peeling off the silicon sheet 22 at a position of 270 ° with respect to the lowest point 0 ° of the rotary cooling body 21 This is that the peeling member 25 is formed integrally with the gutter member 26 for carrying out the silicon sheet. The peeling member 25 will be described with reference to FIG.

As the peeling member 25, carbon whose tip was sharpened was used. The peeling member 25 is formed by a tangent to the circular orbit 31 formed by the corner 30 of the flat surface 1 at a position that is 27 ° from the 0 ° position that is the lowest point of the rotary cooling body 21. It was installed in parallel and at a distance of 100 / / 1 from the circular orbit 31 outside. Thereby, the silicon sheet 22 having a thickness of 10 O ^ m or more can be separated from the flat surface 1.

The peeling member 25 was integrated with the tip of the gutter member 26 inclined 30 degrees with respect to the horizontal, thereby simplifying the device members.

The gutter members 26 and 28 for carrying out the peeled silicon sheet 22 shown in FIG. 2 were members provided with guides 54 and rollers 53 as in the first embodiment. The installation positions, angles, surface forms, materials, and the like of the gutter members 26 and 28 can be set in the same manner as in the first embodiment.

As in the case of the first embodiment, the rotary cooling body 21 used was a gear-type cooling body in which the vertices of a polygonal prism were pressed inward. In particular, when the peeling member 25 is used, when the adjacent silicon sheets 22 are integrated, the peeling member 25 is brought into contact with one side 22 a of the front end side in the traveling direction of the silicon sheet 22. However, since it becomes difficult to apply an impact in a direction parallel to the planar silicon sheet 22, a gear-type structure such as the rotary cooling body 21 is desirable.

In the device configuration in this example, since there is no member such as the shock generating member 15 that moves in synchronization with the rotary cooling body 21, the flat surface 1 formed on the rotary cooling body 21 is periodically continuous. It does not need to be a structure, and the interval between adjacent flat surfaces 1 and the size of each flat surface 1 may be different.

An example of a method for manufacturing a silicon sheet 22 using the above-described apparatus will be described. First, a crucible 24 filled with solid silicon was heated by a heater to melt the silicon. Next, the crucible 24 was raised, and as shown in FIG. 2, the flat surface 1 of the gear-type rotary cooling body 21 was immersed in molten silicon 23, and the rotary cooling body 21 was rotated. As a result, the gear type rotary cooling body 21 Approximately the same silicon sheet 22 was formed on all the flat surfaces 1.

When the silicon sheet 22 was grown in this way and confirmed through the holes in the device, about 30% of the silicon sheet 22 was flat at a position between 0 ° and 180 ° due to vibration. , And slipped down one of the gutter members 28 to be carried out of the device and collected.

The remaining about 70% of the silicon sheet comes into contact with the peeling member 25 and peels off from the flat surface 1, then separates from the rotary cooling body 21 and slides down to the other gutter member 26. It was carried out of the device and collected.

The recovered silicon sheet 12 has a smooth surface and a uniform thickness (average thickness of about 270 m), as in Example 1, and is formed by stable and continuous crystal growth. It became a columnar silicon sheet.

Comparative Example 1

Comparative Example 1 compares a silicon sheet manufactured by the conventional technique with a silicon sheet manufactured by using the silicon sheet manufacturing apparatus of the present invention.

Manufacturing of a silicon sheet according to the prior art is performed using a silicon sheet manufacturing apparatus having a rotary cooling body having an uneven structure on the peripheral surface as shown in FIG.

The silicon sheet manufacturing apparatus shown in FIG. 7 has almost the same configuration as that of the first embodiment, but differs from the apparatus of the first embodiment in that the rotary cooling body 71 is a cylindrical type, It is provided with a convex portion 77 and a concave portion 78, and is provided with a silicon sheet removing portion 75 in which the tip is inserted into the concave portion 78. (The convex portion 77 and the concave portion 78 are On the peripheral surface of the rotary cooling body 71, they are formed alternately and parallel to a direction orthogonal to the rotation axis.

An example of a method for manufacturing a silicon sheet using the above apparatus will be described. First, a crucible 74 filled with solid silicon was heated by a heater to melt the silicon. Next, the crucible 74 is raised, and as shown in FIG. 7, only the projections 77 of the rotary cooling body 71 are immersed in the molten silicon 73, and the rotary cooling is performed. Body 7 1 was rotated. As a result, in the silicon sheet 72, a crystal nucleus was generated only at the convex portion 77 of the cylindrical cooling body 71, and the crystal grew from the nucleus as a starting point.

Further, the silicon melt 73 comes into contact with the crystal growing from the adjacent convex portion 77, so that it does not contact the concave portion 78, but has a cavity between the rotary cooling body 71 and the silicon sheet. 7 2 was generated. In addition, the silicon sheet 72 with the tip inserted therein is installed in the recess 78, that is, in the cavity between the silicon sheet 72 and the rotary cooling body 71, so that the silicon sheet 72 is It was forcibly deformed from a cylindrical shape to a planar shape, and was carried out of the apparatus along the silicon sheet take-out part 75.

When the process of growing the silicon sheet 72 was confirmed from the hole II, the silicon sheet 72 was broken once every few minutes in the area along the cut-out part 75. This is because there was a portion in the silicon sheet 72 where the curve could not be completely stretched, which prevented the silicon sheet 72 from being carried out linearly.

The unloaded silicon sheet 72 grew thick at the portion corresponding to the convex portion 77, and grew thinly at the portion corresponding to the concave portion 78. Further, the average thickness of the silicon sheet 72 was about 250 m at the convex portion 77 and about 200 m at the concave portion 78.

Example 3

Using the silicon sheets produced in Examples 1 and 2 and Comparative Example 1, solar cells were produced.

The procedure for fabricating a solar cell is a known method consisting of the steps of cleaning a silicon sheet sample, texture etching, forming a diffusion layer, removing an oxide film, forming an antireflection film, back etching, forming a back electrode, and forming a light receiving surface electrode. It is. The delivery of the above samples between each process was basically performed by an automatic transport mechanism. Although the silicon sheets according to Example 1 and Example 2 were able to perform all automatic conveyance between the above-described steps, the silicon sheet according to Comparative Example 1 had a curvature in the generated silicon sheet. Remains and irregularities on the surface As a result, there was a silicon sheet that could not be transferred to the next step using the automatic transfer mechanism.

Next, Table 1 shows the results of measuring the characteristics of the solar cells manufactured in Examples 1 and 2 and Comparative Example 1 using a solar simulator. table 1

As is clear from Table 1, the short-circuit current densities of the solar cells according to Example 1 and Example 2 are both 27 mA / cm ^2, which is larger than 25 mAZ cm ² of Comparative Example 1. This is thought to be due to a defect due to distortion due to internal stress remaining in the silicon sheet.

Regarding the fill factor, in Comparative Example 1, the internal stress was significantly reduced due to the influence of defects due to distortion due to remaining in the silicon sheet.

The conversion efficiency (%) was 10% in Comparative Example 1, whereas it was significantly improved to 12% in Examples 1 and 2.

As is clear from the above description, according to the silicon sheet manufacturing apparatus according to the first embodiment, by growing silicon on the flat surface 1 of the rotary cooling body 11, a planar silicon sheet having no internal stress is obtained. In addition, the silicon sheet can be taken out continuously and stably.

The removed silicon sheet has a smooth surface and a uniform thickness, so that a silicon wafer can be formed without a polishing step or a slicing step.

Also, since there is no slice loss, a low-cost silicon wafer can be provided. According to the silicon sheet manufacturing apparatus according to the second embodiment, a planar silicon sheet having no internal stress can be obtained, and the silicon sheet can be continuously and stably taken out.

In the second embodiment, since the mechanically movable part (impact generating member 15) for peeling the silicon sheet in the first embodiment is not provided, the peeling operation is synchronized with the rotary cooling body 21. There is no need to perform this, and the device can be simplified. Therefore, it is possible to reduce the cost, improve the durability and maintainability of the device. According to the present invention, since the rotary cooling body solidifies and grows the silicon crystal ribbon on a flat surface, that is, a flat surface having no curvature, a mechanism for extending the curved silicon sheet into a planar shape becomes unnecessary, and no internal stress remains. Silicon sheets can be continuously produced in large quantities and stably at low cost.

Since the manufactured silicon sheet has a smooth surface and a uniform thickness, a silicon wafer can be formed without a polishing step or a slicing step, thus providing a low-cost silicon wafer. Can be.

Peeling-Since the unloading mechanism has an impact generating member, the silicon sheet can be easily peeled from the surface of the rotary cooling body.

Since the peeling / unloading mechanism has an acute-angled peeling member, there is no mechanically movable part in the peeling member, so a mechanism for synchronizing the peeling operation with the rotation of the rotary cooling body is omitted. Therefore, simplification and cost reduction of the device can be achieved, and durability and maintainability are improved.

The peeling / carrying-out mechanism peels the silicon sheet in the position range from 90 degrees to 270 degrees, so that the silicon sheet can be reliably carried out of the apparatus. Since the peeling and unloading mechanism has an unloading gutter member, the silicon sheet can be unloaded out of the apparatus with a simple configuration.

The gutter member is disposed at an angle such that the silicon sheet peeled off from the flat surface is piled up by the frictional force with the gutter member and can slide down by its own weight. Unloading is possible. Therefore, there is no need for forced conveyance means that requires complicated mechanisms such as a rotary power mechanism. Therefore, the device configuration can be simplified.

Separation · Since the unloading mechanism has an unloading auxiliary member in addition to the gutter member, it is possible to further promote the sliding of the silicon sheet due to its own weight.

Since the gutter member is integrated with the peeling member, the device members can be further simplified.

Using the gutter member integrated with the peeling member, the silicon sheet is peeled by contacting the end of the silicon sheet on the upstream side in the rotation direction within a position range of 180 ° to 270 °, so the rotation The silicon sheet separated from the cooling body can be smoothly slid down to the discharge gutter member.

In addition, no special movable member other than the rotation of the rotary cooling body is required to give an impact for peeling, which contributes to simplification of the device and improves durability and maintainability of the device. .

The solar cell manufactured by using the silicon sheet manufacturing apparatus of the present invention has a higher short-circuit current density and a larger fill factor than the solar cell using the silicon sheet manufactured by the conventional silicon sheet manufacturing apparatus. The manufacturing cost can be reduced while improving the manufacturing cost.

Claims

The scope of the claims

1. Rotary cooling having a molten silicon storage section for storing molten silicon, and at least one flat surface rotatably disposed above the molten silicon storage section for solidifying and growing a silicon sheet on the surface. After being once immersed in the molten silicon by rotation, the flat surface of the rotating cooling body pulled up from the molten silicon is peeled off before the flat surface of the rotating cooling body is immersed in the molten silicon again A silicon sheet manufacturing apparatus characterized in that a peeling / unloading mechanism is provided to carry the peeled silicon sheet out of the apparatus by utilizing the inertial force and / or the gravity force caused by the rotation of the rotary cooling body. .

2. The silicon sheet manufacturing apparatus according to claim 1, wherein the peeling / unloading mechanism includes an impact generating member for peeling the silicon sheet by applying a physical impact to the rotary cooling body. .

3. Peeling-off mechanism is equipped with an acute angle peeling member for peeling off the silicon sheet by contacting the end of the silicon sheet generated on the flat surface of the rotary cooling body on the upstream side in the rotation direction. The silicon sheet manufacturing apparatus according to claim 1 or 2, wherein:

4. The peeling and unloading mechanism sets the position of the flat surface at the lowest point of the rotary cooling body, which is immersed in the molten silicon, at 0 °, and the position at which the rotary cooling body makes one rotation from 0 ° is 360 ° The silicon sheet manufacturing apparatus according to any one of claims 1 to 3, wherein the silicon sheet is peeled in a position range from 90 to 270 degrees when the temperature is set to degrees.

5. The peeling / unloading mechanism is provided with an unloading gutter member for receiving the silicon sheet separated from the flat surface and unloading the silicon sheet outside the apparatus. 2. The silicon sheet manufacturing apparatus according to claim 1.

6. The gutter member has a silicon sheet that has been peeled off from a flat surface. 6. The silicon sheet manufacturing apparatus according to claim 5, wherein the silicon sheet manufacturing apparatus is arranged at an angle at which the pile can slide down by its own weight by being piled with frictional force.

7. The silicon sheet manufacturing apparatus according to claim 5, wherein the peeling-out mechanism has a carry-out assisting member for assisting carry-out of the silicon sheet, in addition to the gutter member.

8. The silicon sheet manufacturing apparatus according to any one of claims 5 to 7, wherein the gutter member is integrated with the acute-angled stripping member according to claim 3.

9. The position of the flat surface that is at the lowest point of the rotary cooling body and immersed in the molten silicon is 0 °, and the position where the rotary cooling body makes one rotation from the 0 ° position is 360 °. Wherein the silicon sheet is peeled off by contacting the end of the silicon sheet on the upstream side in the rotation direction in a position range from 180 degrees to 270 degrees. Silicon sheet manufacturing equipment.

10. The silicon sheet manufacturing apparatus according to claim 1, wherein the rotary cooling body comprises a gear-type rotary body in which the vertices of the polygonal column are cut inward, and a flat surface is formed on a side surface of the polygonal column.

11. A solar cell manufactured using the silicon sheet by the silicon sheet manufacturing apparatus according to any one of claims 1 to 10.