WO2003002457A1

WO2003002457A1 - Thin sheet producing method, and solar cell

Info

Publication number: WO2003002457A1
Application number: PCT/JP2002/006189
Authority: WO
Inventors: Shuji Goma; Yoshihiro Tsukuda; Koji Yoshida
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2001-06-29
Filing date: 2002-06-20
Publication date: 2003-01-09
Also published as: TW546848B; JP2003081690A; JP4132786B2

Abstract

A shin sheet producing method for obtaining a thin sheet of metallic material or semiconductor material in that a substrate having a growth surface is contacted with a melt of the above-mentioned material to grow crystals of the material on the substrate, wherein as seen from the thin sheet growth surface side of the substrate, the substrate and/or the melt is moved so that the melt moves toward the thin sheet growth surface side of the substrate. For example, by moving a movable body of substrate having a growth surface (5a), the growth surface (5a) is brought into contact with a melt (3), and then the growth surface (5a) is separated from the melt (3), such series of moving operations causing crystals of the material to grow on the growth surface (5a); in such thin sheet producing method, the orbit of the substrate leaving the melt (3) is circular, and the distance between the front end of the growth surface (5a) as seen in the movement direction and the center of rotation along the circular orbit is set at a value smaller than the distance between the terminal end of the growth surface (5a) as seen in the movement direction and the center of rotation along the circular orbit.

Description

Thin plate manufacturing method and solar cell

The present invention relates to a thin plate manufacturing method that can be mainly used for solar cells and the like, and a solar cell using a thin plate obtained by the thin plate manufacturing method. Background art

As an apparatus for directly extracting a silicon thin plate from molten silicon, there is a silicon-dendritic web crystal growth apparatus disclosed in Japanese Patent No. 2575838. The main part of this dendrite web crystal growth apparatus is composed of a susceptor for accommodating a crucible containing a silicon melt, a susceptor lid having a slot, and a heating element such as a Koinole induction heater. Using this apparatus, it is possible to pull out thin, thin plate-like dendrite webs grown continuously in the (111) crystal direction from the susceptor lid slot car.

According to this method, the dendrite web is thin and thin, and requires little secondary processing such as slicing prior to device manufacturing. Therefore, conventional silicon wafers are obtained by slicing an ingot with a wire saw or the like to obtain a wafer. It is said that both process costs and raw material costs can be reduced compared to manufacturing methods. In addition, generally, in order to obtain a silicon thin plate of 150 / zm, it is possible to grow the silicon thin plate at a drawing speed of about 1.3 to 1.4 cm / min.

On the other hand, a method for immersing a rotary cooling body in molten silicon to obtain a low-cost silicon thin plate which solidifies on the cooling body surface is disclosed in Japanese Patent Application Laid-Open No. 10-28995. There is a disclosed apparatus for manufacturing a silicon thin plate.

The main part of the silicon thin plate manufacturing apparatus is composed of a heating and melting section for silicon and a cooling section including a rotary cooling body. As shown in FIG. 22, a part of the cylindrical surface of the rotary cooling body 81 made of a heat-resistant material is immersed in molten silicon in a vertically movable crucible 84, and the rotary cooling body 81 is rotated. While pulling out the carbon net 8 8 Thus, the silicon thin plate 82 solidified and grown on the carbon net is continuously taken 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 an ingot is sliced with a wire saw or the like to obtain a wafer. In addition, since the rotary cooling body cools, pulls out, and supports silicon, the pulling out speed can be greatly improved. The drawing speed can be controlled depending on the size and the number of rotations of the rotary cooling body, but it is generally possible to pull out at 10 cm / min or more.

In a silicon dendrite web crystal growth apparatus, the growth rate is as low as about 1.3 cm / min. Therefore, it is difficult to improve productivity. On the other hand, in the method of manufacturing a silicon thin plate disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 10-28995, high-speed drawing of usually 10 cmZ or more is possible. In order to increase the immersion depth of the rotating cooling body, in order to support and rotate the rotating cooling body while rotating, and to prevent the rotating shaft that guides and discharges the cooling medium from immersing in the silicon melt in the P direction. Requires larger equipment. In this method, when the silicon thin plate solidified and grown from the melt is separated from the melt, the angle between the growth surface and the melt surface is small, so that it is difficult to smooth the thin plate surface.

Here, a conventional method for manufacturing a silicon thin plate will be described in detail. In FIG. 22, the crucible 84 is filled with the melt 83. A carbon net 88 follows the rotary cooling body 81, and the silicon melt creeps up on the carbon net 88. The crawled silicon melt 82a is cooled and then turns into a liquid pool 82b. According to this method, the silicon melt creeps up to a height of about 2 O mm from the melt surface due to surface tension, and as the rotation further advances, the silicon melt crawling up to the surface becomes 8 2 a. The remaining silicon melt is solidified and grows in the melt, and remains on the thin plate.Since the remaining silicon melt has a large surface tension, the solution is not uniformly distributed but localized, and a liquid having a zero-like shape is formed. Dummy 8 2 b remains. As this gradually solidifies, the surface undulation of the silicon thin plate increases. Also, small protrusions are formed on the surface of the undulation.

Also, when the cross section of the removed silicon thin plate was checked, On the grown columnar crystal having a uniform thickness, a random orientation region having a thickness of 50 to 500 / xm and a particle size of 50 to: L00 μm was confirmed. This is due to the solidification of the liquid pool crawling on the uniform columnar crystal, which is smaller in particle size than the columnar crystal and has more grain boundaries in the thickness direction of the silicon thin plate. When used, it can be seen that the grain boundaries in this area become defects that cause the carriers to recombine. Similarly, as shown in FIG. 8, a case where a polygonal column type rotary cooling body having a flat or a plane processed surface (hereinafter referred to as a substantially flat surface) growth surface on the surface of the rotary cooling body 21 is used. However, it is difficult to increase the angle between the growth surface and the melt surface when the growth surface separates from the melt, and the silicon melt crawling on the surface solidifies and grows in the melt. The liquid will remain on the thin plate, and since the surface tension of the silicon melt is large, the liquid will not be evenly distributed but will be localized. When this solidifies, the surface undulation of the silicon thin plate increases.

In this way, the method of immersing the rotating cooling body in the silicon melt and solidifying and growing a silicon thin plate on the surface can be performed at high speed, but the silicon melt crawls on the surface, and the surface smoothness and This causes the crystallinity to decrease. The growth surface moves away from the melt in order to reduce the amount of melt crawling on the surface of the thin plate in order to continuously pull out a smooth thin plate at a high speed while preventing crawling and liquid pooling. At this time, the angle between the growth surface and the melt surface must be close to vertical.

If solar cells are manufactured using such thin silicon plates, smoothing such as mechanical polishing must be newly performed, which is a factor that hinders cost reduction. That is, in such a situation, of course, stable continuous growth is also difficult. Disclosure of the invention

The present invention has been made to solve the above-described problems, and suppresses the occurrence of small projections on the surface of a silicon thin plate, obtains a thin plate having a flat surface, and stably and continuously obtains the thin plate at low cost. The purpose is to grow.

In the method for producing a thin plate according to the present invention, a substrate having a thin plate growth surface is brought into contact with a melt of a material containing at least one of a metal material and a semiconductor material, and the thin plate of the material is grown on the substrate. To obtain a thin plate formed of the material. A method for producing a thin plate, wherein the substrate and the Z or the melt move such that the melt moves toward the thin plate growth surface side of the substrate when viewed from the thin plate growth surface side of the substrate. .

Another manufacturing method of a thin plate according to the present invention includes: moving a moving body on which a substrate having a thin plate growth surface is disposed, thereby causing the thin plate growth surface of the substrate to be at least one of a metal material and a semiconductor material. Is contacted with a melt of a material containing, and thereafter, a thin plate of the material is grown on the substrate by a series of moving operations for separating a thin plate growth surface of the substrate from the melt, thereby forming the substrate. A sheet manufacturing method for obtaining a thin sheet, wherein the substrate and the Z or the melt are moved such that the melt moves toward the thin plate growth side of the substrate when viewed from the thin plate growth side of the substrate. It is a manufacturing method.

Further, in the method of manufacturing a thin plate according to the present invention, the moving body on which the substrate having the thin plate growth surface is arranged may move the thin plate growth surface of the substrate to at least one of a metal material and a semiconductor material. A crystal of the material is grown on the substrate by a series of moving operations of bringing the thin plate growth surface of the substrate away from the melt by contact with the melt of the material to be contained. A trajectory when the substrate separates from the melt is a circular orbit, and a distance 1 ^ between a tip of the growth surface in the moving direction and the center of the rotation axis of the circular orbit is determined by the growth a thin plate manufacturing method characterized by the moving direction end face smaller than the distance R ₂ between the rotation center of the circular path.

Further, the angle between the thin-plate growth surface and the melt surface at the time when the tip of the thin-plate growth surface in the moving direction separates from the melt is 20 degrees to 60 degrees, and the end of the thin-plate growth surface in the moving direction. It is preferable that the angle formed by the thin plate growth surface and the melt surface at the time when the portion separates from the melt is 60 degrees to 100 degrees. Preferably, the semiconductor material is a silicon material.

Further, a solar cell according to the present invention is a solar cell manufactured using a thin plate manufactured by the thin plate manufacturing method according to the present invention.

The manufacturing method according to the present invention is obtained by clarifying the relationship between the moving direction and the moving speed of the melt and the moving direction and the moving speed of the substrate when growing a thin plate on the substrate. It is intended to reduce the number of small protrusions on the surface of the thin plate and improve the flatness of the thin plate.

When a thin plate is grown on a substrate, there are two cases, in which the substrate moves and the melt moves. The present invention is characterized in that the substrate and the Z or the melt move such that the melt moves toward the thin plate growth surface side of the substrate when viewed from the thin plate growth surface side of the substrate. That is, it can be realized by defining the relative speed.

FIG. 1A to FIG. 1D and FIG. 2A to FIG. 2D illustrate the case where the moving direction and the moving speed of the substrate and the moving direction and the moving speed of the melt are changed. In the figure, substrates 200 and 210 are immersed in the melt to form melt surfaces 201 and 211. In this figure, for example, the surface formed by the acute angle between the melt surface 201 and the substrate 200 is the growth surface of the thin plate. In the figure, only the simplified substrate and the melt surface are shown, and the arrows in the figure show the direction and size of the movement of the substrate and the melt. The arrows in the figure show only the horizontal components of the moving directions of the substrate and the melt. That is, the vertical component may be arbitrary.

In the present invention, the magnitude of the moving speed of the substrate and the magnitude of the moving speed of the melt will be described separately. First, the case where the moving speed of the substrate is faster than the moving speed of the melt in Fig. L A to Fig. 1D (moving speed of the substrate> moving speed of the melt) will be described. Fig. 1A shows the case where the substrate movement direction A1 and the melt movement direction a1 are opposite, Fig. 1B shows the case where the substrate movement direction B1 and the melt movement direction b1 are the same, and Fig. 1C If the substrate movement direction C1 is the same as the melt movement direction c1, but the direction is opposite to that in Figure IB, the figure ID shows that the substrate movement direction D1 is opposite to the melt movement direction d1. This is the case in the opposite direction from FIG. 1A. In FIG. 1A to FIG. 1D, the case where there is an effect of suppressing small projections present on the obtained thin plate is when the state shown in FIG. 1A and FIG. 1B is reached.

Next, the case where the moving speed of the substrate shown in FIGS. 2A to 2D is lower than the moving speed of the melt (the moving speed of the substrate <the moving speed of the melt) will be described. Figure 2A shows the case where the moving direction A2 of the substrate and the moving direction a2 of the melt are opposite.Figure 2B shows the case where the moving direction B2 of the substrate and the moving direction b2 of the melt are the same. In the case where the moving direction C 2 of the substrate and the moving direction c 2 of the melt are the same but opposite to the direction of FIG. 2B, FIG. 2D shows that the moving direction D 2 of the substrate and the moving direction d 2 of the melt are opposite. However, this is the case in the opposite direction from that of Fig. 2A. In these figures, if there is an effect of suppressing the small protrusions present on the obtained thin plate, see Fig. 2A and Fig. It is time to come to state 2B.

In FIGS. 1A to 1D and FIGS. 2A to 2D, when the states shown in FIGS. 1A, 1B, 2A, and 2B are respectively obtained, there is an effect of suppressing small protrusions. This can be said to be a state in which the melt comes toward the thin-plate growth side of the substrate when viewed from the thin-plate growth side of the substrate. Conversely, the effect of suppressing the small protrusions is small because the melt moves away from the thin-plate growth side of the substrate when viewed from the thin-plate growth side of the substrate.

In other words, the present invention makes it possible to suppress small projections when the melt is continuously supplied to the substrate when the melt is grown on the substrate surface. This state is due to the shape of the meshes formed at the interface between the substrate and the melt surface.

Figures 3A and 3B show schematic diagrams of the mescus shape formed at the interface between the substrate and the melt. FIG. 3A shows a state in which a convex meniscus 220 is formed at the interface between the substrate 22 1 and the melt surface 22 2, and FIG. 3B shows a state at the interface between the substrate 22 1 and the melt surface 22 2. This shows a state in which mescuses 223 are formed. In this figure, the surface on which the meniscus is formed is shown only on the growth surface of the thin plate (the right side of the substrate 221), and is not shown on the surface where the thin plate does not grow (the left side of the substrate 221). In FIGS. 3A and 3B, when the melt solidifies on the substrate surface to form a thin plate, in FIG. 3A, the meniscus shape is always maintained due to the continuous supply of the melt. While the convex shape can be maintained, in FIG. 3B, the amount of the melt becomes insufficient and the meniscus shape becomes concave.

In the case where small projections can be suppressed, that is, in the case of FIGS. 1A and 1B, FIGS. 2A and 2B, the state in which the meniscus shape can maintain a convex shape can be maintained for a long time. On the other hand, in the case of FIG. 1C and FIG. 1D, FIG. 2C and FIG. 2D, the probability that the mescus shape becomes concave becomes high, and it becomes difficult to completely suppress the protrusion, and the thin plate Loss of uniformity. This is due to the phenomenon that the meniscus breaks when the meniscus shape changes from convex to concave. The moving speed of the substrate ゃ the moving speed of the melt ゃ Depending on the surface tension of the melt material, small protrusions and thin plates on the surface of the obtained thin plate due to waving of the melt surface caused by the breakage of the meniscus Bring swell. In the present invention, in particular, by defining a relative velocity component in the horizontal direction in the movement of the melt with respect to the substrate, it is possible to achieve both suppression of small protrusions and improvement of flatness. Next, the moving direction of the substrate and the moving direction of the melt will be described. The moving direction of the substrate includes a linear trajectory, a circular trajectory, an elliptical trajectory, and the like. However, there is no particular problem as long as the trajectory can maintain the relationship with the moving direction of the melt described above. That is, it may have a complex trajectory including a linear trajectory and a circular trajectory. Particularly preferred is a substrate having a circular orbit when the substrate escapes. The circular orbit not only facilitates the thin-plate recovery mechanism, but also facilitates the relationship between the moving direction and the moving speed of the substrate and the moving direction and the moving speed of the melt. In other words, the trajectory when the substrate separates from the melt is a circular orbit, and the distance 1 ^ between the tip of the growth surface of the substrate in the moving direction and the center of the rotation axis of the circular orbit is equal to the end of the growth surface of the substrate in the moving direction. This can be realized by making the distance from the center of the rotation axis of the circular orbit smaller than R ₂ . This, means that R ₂ two distances are the same, it means that depicts the circular path.

The substrate, the melt surface, and the trajectory of the movement of the substrate will be described based on the schematic cross-sectional view of the thin plate manufacturing apparatus in FIG. The thin plate manufacturing equipment has a sloped substrate 230, a fixed base 2 '31 capable of mounting the substrate, a fixed base and a rotating shaft 2 32 mounted on the center of the rotating shaft, and a crucible 2 3 4 melt. When the substrate 230 is immersed in the substrate 233, a trajectory 235 in which the leading end of the substrate in the moving direction moves and a trajectory 236 in which the end of the substrate in the moving direction moves are shown. Also, the moving body (assembly) combining the substrate 230, the fixed base 231, and the shaft 2332 is shown before entering the melt, during immersion in the melt, and immediately before exiting from the melt. In this figure, the rotation is counterclockwise. With such a manufacturing apparatus, it is possible to easily realize the conditions specified in the present invention only by controlling the moving speed of the substrate 230, in other words, the rotational speed. The moving speed and moving direction of the substrate can be controlled by the rotating speed and the direction of the rotating shaft.

On the other hand, the moving speed and moving direction of the melt are determined by the convection of the melt caused by heat. Generally, the convection of the melt caused by heat flows from a high temperature part to a low temperature part, but the manner of convection of the melt differs depending on the crucible shape, heating method or heat removal method. With the structure shown in Fig. 4, the force varies depending on the control temperature of the melt.Since the outermost surface of the melt is not heated, heat removal from the melt surface increases and the direction of melt movement becomes complicated. Tend to be. Therefore, it is preferable to keep the melt temperature higher than the melting point in consideration of the amount of heat removed from the melt surface. In order to obtain a thin plate having high uniformity and few small protrusions, it is preferable to adopt a configuration in which the temperature of the substrate can be precisely controlled. That is, by passing a cooling medium such as a cooling gas or cooling water through the inside of the fixed base 231 or the rotating shaft 232, it is possible to control the temperature of the substrate 230 having the growth surface to a low temperature. However, in order to control the quality of the obtained thin plate, it is possible to adopt a structure that can heat the substrate. In this case, it is preferable to control the temperature with a heater before immersion. In order to obtain a more stable thin plate, it is more preferable to provide both a cooling mechanism and a heating mechanism.

In the present invention, the moving speed of the substrate is preferably 1 cm / sec or more. If it is 1 cm / sec or more, the movement of the melt can be performed without much consideration because the substrate is inclined. On the other hand, if it is 1 cm / sec or less, it is necessary to strictly consider the moving speed and directionality of the melt. Considering the simplification of the apparatus, it is preferable to adopt a configuration that can be controlled only by the moving speed of the substrate. The method for manufacturing a thin plate according to the present invention can also be implemented by moving only the melt when both the movement of the substrate and the movement of the melt move.

FIG. 5 is a partial schematic perspective view of the thin film manufacturing apparatus when the melt moves. This apparatus is composed of a substrate 240 having a growth surface, a fixed substrate 2441 to which the substrate 240 can be attached and detached, a shaft 2442 that can move up and down, and an inclined table 24 that supplies the melt to the substrate. 3. Equipped with a crucible 2 4 4 for holding the melt. For simplicity, FIG. 5 does not show a motor for vertical movement or a heater for holding the melt. The melt held in the crucible 244 is supplied to the inclined table 243 in a molten state. .

Next, in this state, the substrate 240 is brought into contact with the melt, and thereafter, the substrate 240 is moved upward, whereby the substrate 240 can be separated from the melt. In this way, a thin plate can be grown on the substrate 240. At this time, since the melt flows down the inclined table, the substrate 240 only moves up and down, and when viewed from the thin plate growth surface side of the substrate of the present invention, the melt moves toward the thin plate growth surface side of the substrate. It is possible to realize that it will come. At this time, since the moving speed of the melt can be adjusted by the inclination of the tilting table, it is possible to realize a state in which the melt comes toward the growth surface side of the substrate only by moving the substrate up and down. . At this time, the structure of the board 240, the fixed board 241, and the movable shaft 242 can be moved not only up and down, but also along the inclination of the inclined base 243. It may be.

With the above structure, it is possible to control the moving speed of the moving body (assembly) in the direction in which the melt falls, and it is possible to suppress small projections on the thin plate and undulation on the surface. In this figure, it is preferable that the fixed substrate 24 1 and the substrate 240 have a removable structure. This is because the production speed can be significantly improved by adopting a structure in which the thin plate obtained as the substrate 240 can be taken out of the system as it is. Further, it is preferable that the inclined table 243 is heated by a heater or the like so that the melt does not solidify on the inclined table. In addition, by connecting a plurality of moving bodies (assemblies) in series, the production speed can be further improved, and as a result, an inexpensive thin plate can be provided.

Next, a method of manufacturing a thin plate will be described with reference to FIG. 6 which shows a cross-sectional view of a thin plate manufacturing apparatus. This manufacturing apparatus was housed in a substrate 250 having an inclination, a thin plate 25 1 formed on the substrate, a fixed base 25 2 on which the substrate can be detached, and a crucible 25 5 4 on a crucible base 255. Equipped with melt 2 5 3, heater 2 5 6 for heating the melt, elevating platform 2 57, elevating shaft 2 58, additional charging pipe 2 59, hermetically sealable chamber 2 60 and take-out mechanism 2 61 ing. In this figure, the moving body (assembly) including the substrate 250 and the fixed base 255 has a structure in which rotation can be controlled by a motor or the like provided outside the chamber.

In addition, the lifting shaft 258 also has a structure that can be controlled to move in the vertical direction by a motor or the like provided outside the chamber. Further, the substrate 250 and the obtained thin plate 25 1 are structured so that the substrate can be carried out of the chamber. When continuity is considered, productivity is further improved by separating the carry-in route and the carry-out route of the substrate 250.

Next, a method for manufacturing a silicon thin plate will be described with reference to FIG. The manufacturing equipment consists of a chamber with good airtightness. Raw materials for the obtained sheet are prepared in a crucible, and high-purity silicon or lower-grade metal-grade silicon can be used as raw materials. Preferably, a raw material in which metal-grade silicon is purified and the amount of metal impurities is reduced is used. The crucible can be made of graphite or silica. However, when silica is used, the crucible silica Since the oxygen component contained in the steel is transferred to the silicon thin plate to be manufactured, a graphite crucible is more preferable.

Next, the inside of the apparatus is evacuated to reduce the pressure inside the champer. After the pressure reduction, Ar gas, which is an inert gas, is introduced into the chamber. In addition to Ar gas, He gas, N ₂ gas, and the like can be considered, but Ar gas is more preferable. Further, Ar gas introduced into the chamber is preferably introduced from the upper part of the chamber and exhausted from the lower part. This is because the silicon oxide is quickly discharged out of the chamber due to the reaction of a small amount of oxygen component generated from the furnace material in the chamber with the silicon melt.

Next, the temperature is increased while adjusting the pressure in the chamber. In particular, silicon oxide is generated in a relatively large amount at the initial stage of the temperature rise and the initial stage of the dissolution of silicon. The melting point of silicon is about 140 ° C, but it is raised to about 150 ° C above the melting point until complete dissolution, and after confirming complete dissolution, the substrate is immersed Cool down to the temperature at which At this time, the melt temperature at the time of immersion is preferably near the melting point, but if it is too close to the melting point, the solidification of the molten metal surface may start immediately after the immersion of the substrate, so that it is slightly higher than the melting point in consideration of productivity. More preferably, the temperature is set.

Also, since silicon has a larger solid volume than a liquid, its complete dissolution reduces the bulk of the melt. Because of this, the height of the molten metal surface becomes low, and it is necessary to add silicon chunks or silicon in a molten state. In consideration of continuous productivity, it is preferable to perform additional charging for adjusting the molten metal level in a molten state. This is because the molten metal shakes when it is put in a solid state, and it is necessary to stop the movement of the substrate and wait for it to completely dissolve. After the molten metal surface has been adjusted to the desired position, raise the crucible to a predetermined position. Next, the first substrate is loaded into the champer.

After that, the shaft is rotated 120 ° and the next substrate is loaded. In this state, the first substrate is located just above the melt, that is, just before immersion. At this position, a mechanism for adjusting the temperature of the substrate is preferably present. That is, the substrate temperature is a factor that affects the characteristics of the obtained silicon thin plate. The temperature of the substrate immediately before being immersed in the melt is preferably 200 ° C. or more and 130 ° C. or less. This is because it is difficult to adjust the temperature below 200 ° C. That is, considering serial production, In order to keep the incoming substrates one after another at 200 ° C, it is necessary to further cool the fixed base.

For this purpose, a large amount of cooling gas and cooling water must flow, which makes it difficult not only to keep the temperature inside the chamber constant at all times, but also lowers the thermal efficiency, resulting in low-cost substrates. Will be difficult to provide. On the other hand, it is also difficult to maintain the substrate temperature at more than 130 ° C. This is because maintaining the substrate at a temperature of more than 1300 ° C. immediately before immersion requires a considerable amount of time, resulting in poor productivity. In order to adjust the substrate temperature, it is preferable to control the temperature by using a cooling mechanism and a heating mechanism together. This is necessary in order to always immerse the substrate at a constant temperature. In this apparatus, the substrate controlled to a predetermined temperature is immersed in a circular orbit. However, since the substrate is inclined, the effects of the present invention can be obtained, and a silicon thin plate having excellent surface smoothness can be obtained. The immersed substrate and the silicon thin plate adhered to the substrate are removed from the rotating shaft having a rotating mechanism at the upper part of the chamber, and are carried out of the system. Through this series of operations, it is possible to obtain a silicon thin plate.

In another thin plate manufacturing method according to the present invention, as shown in FIG. 4, the orbit when the substrate separates from the melt is a circular orbit, and the distance between the tip of the growth surface in the moving direction and the center of the circular orbit is the growth surface. to be smaller than the distance R ₂ between the moving direction end and the circular orbit center, provided by inclining the growth surface, when the silicon thin plate grown on the growth surface and the growth surface is away from the melt, the melt surface By making the angle closer to vertical, the silicon melt is removed.

In the present invention, a completely smooth plane and a plane whose surface is processed to have a specific shape in order to control the state of fine growth are collectively referred to as a substantially plane. Here, a description will be given assuming that the plane including the above is simply smooth.

Further, in the present invention, the solid state growth from the melt causes the crystal state to be a single crystal or polycrystal, amorphous, or a thin plate of a mixture of crystalline and amorphous depending on conditions such as temperature. Sometimes it becomes.

The melt contains semiconductor materials such as silicon, germanium, gallium, arsenic, indium, phosphorus, boron, antimony, zinc, and tin. Or aluminum, two A melt containing a metallic material such as nickel or iron can be used. As an example, a case where a polycrystalline silicon thin plate is manufactured from a silicon melt will be described.

It is desired that the substrate constituting the growth surface has excellent heat resistance and does not contaminate the silicon thin plate 2, and is preferably made of carbon, SiC, a high melting point metal, or the like, and a material obtained by coating these materials with another substance.

According to the present invention, a substantially planar substrate is immersed in a melt of a substance containing at least one of a metal material and a semiconductor material, and then separated from the melt, whereby substantially flat growth is achieved. A method for producing a thin plate by solidifying and growing a melt on a surface, wherein the orbit when the substrate is separated from the melt is a circular orbit. Therefore, a case where a substrate mounted on the rotary cooling body makes a circular motion with the rotation axis using a polygonal-column type rotary cooling body will be described below with reference to FIG.

In the thin plate manufacturing equipment, when the growth surface of the substrate on the rotary cooling body is separated from the silicon melt, the angle between the growth surface and the melt surface depends on the shape and size of the rotary cooling body and the substrate, and on the growth surface. Determined from three factors: size and immersion depth. As shown in Fig. 22 showing the conventional manufacturing method, in the case of a growth surface along a rotating arc such as a cylindrical rotating cooling body 81, the growth surface and the melt when the curved surface separates from the melt surface The angle a with the surface is constant. In the manufacturing apparatus of the present invention shown in FIG. 7, when the growth surface on the substrate placed on the polygonal rotary cooling body 1 is rotated, each part of the growth surface moves from the center of the rotation axis. Since the distance (rotation diameter) of the growth surface differs from the silicon melt, the angle between the growth surface and the melt surface when the growth surface separates from the silicon melt differs depending on each part of the growth surface.

In FIG. 8 showing a side view of the thin plate manufacturing apparatus, a substrate 50 having a uniform thickness is placed on a polygonal column-shaped rotary cooling body 21 so as to be parallel to each surface of the polygonal column. The case where a silicon thin plate is grown on 25a will be described.

Assuming that the growth surface 25 a of the substrate 50 formed on the polygonal rotary cooling body 21 is a square of 20 O mm square, the height of the rotary cooling body including the rotary cooling body 21 and the substrate 50 is The height (the distance between the opposing surfaces is the same as the diameter of rotation at the center of each growth surface) is about 74 O mm. When the substrate is immersed in the silicon melt 23 by 20 mm on the basis of the position where the center of each growth surface 25a of the substrate 50 is located at the lowest position to grow the silicon thin plate 22 on the growth surface, 25 d in the moving direction of each surface (first move away from the melt within the growth surface The angle between the growth surface and the melt surface when the part moves away from the melt is about 9 degrees, which is almost horizontal.

As the rotation progresses, the angle] 32 between the growth surface and the melt surface increases. The angle j32 between the growth surface and the melt surface when the end portion 25 e in the moving direction (the part that separates from the melt last in the growth surface) separates from the melt is about 40 degrees.

On the other hand, in the manufacturing apparatus shown in FIG. 7, the distance between the tip 5 d in the moving direction of the growth surface 5 a and the center of the rotation axis (the tip 5 d in the moving direction) The thickness of the substrate is increased toward the terminal end so that the rotational radius is smaller than the distance between the terminal end 5 e of the growth surface in the moving direction and the center of the rotation axis (the turning radius of the terminal end 5 e in the moving direction). A substrate with an inclined growth surface (tilted growth surface substrate 5) is installed. Therefore, a case where the silicon thin plate 2 is grown on the growth surface 5a of the inclined growth surface substrate 5 will be described.

First, a method of designing an inclined growth surface substrate will be described with reference to FIGS. In the present invention, in order to systematically evaluate the results, the growth surface was inclined so that the growth surface area was constant. That is, in FIG. 12, in the moving direction front end 5 d and the virtual moving direction end 5 f (that is, the end in the moving direction when the angle-tilt angle between the surface of the polygonal rotary cooling body and the growth surface is 0 °). ) Is 20 O mm, and this surface is inclined at an arbitrary inclination angle 5 a with respect to the straight line 5 d-5 f. That is, the distance between the tip 5d in the moving direction and the end 5f in the moving direction is also 20 mm. In other words, the shape is such that an isosceles triangle having three points 5d, 5e, and 5f as vertices is placed on a substrate with a tilt angle of 0 °. As a result, the size of the growth surface 5a does not change.

When designed by the above method, the inclined growth surface substrate set at various inclination angles is designed into the shape shown in FIG. In FIG. 13, as an example, five inclination angles of 0 degree, 30 degrees, 45 degrees, and 60 degrees are shown. When the inclination angle 5 ο; is 0 degrees, the entire substrate surface is covered with the growth surface 5 a. As the inclination angle 5a increases, the non-growth surface (the surface that does not grow) _5g increases. When the inclined growth angle is 60 degrees, the isosceles triangle becomes a regular triangle, so that the growth surface 5a and the non-growth surface 5g have the same size. When the inclination angle 5α exceeds 60 degrees, the non-growth surface becomes larger than the growth surface.

When a thin plate grows on 5 g of the non-growth surface, when the non-growth surface separates from the melt Since the angle between the non-growth surface and the melt surface is extremely small, a thin plate with extremely poor smoothness is obtained. Therefore, the thin plate grown in this area causes material loss, so that the non-grown surface is covered with silicon nitride / silicon boride, which has poor wettability with the melt, so that the thin plate does not grow on the non-growth surface, or It is desirable to adopt a growth prevention structure such as forming a groove with a pitch exceeding the tension of the melt.

If provided the inclination angle 5 _alpha is inclined in the range of ◦ degree to 7 5 °, when the moving direction tip 5 d and the moving direction ends 5 e is separated from the silicon melt, the growth surface and the melt surface As shown in Fig. 16, it can be seen that the tapping angle, which is the angle made, increases both. Here, the angle formed between the growth surface and the melt surface] is 31. The angle 90 ° is completely perpendicular, and when it exceeds 90 °, the growth surface 5a is in the opposite direction to the silicon melt 3 (melt). (Upward as viewed from above) and away from the melt.

By tilting the growth surface 5a, the angle 131 between the growth surface and the melt surface can be controlled, but the difference in the rotation diameter between the tip 5d in the moving direction of the growth surface and the end 5e in the moving direction 5e of the growth surface. Therefore, as shown in Fig. 17, there is a difference in the immersion depth. The difference in immersion depth at an inclination angle of 40 degrees at which the angle between the growth surface and the melt surface at the end 5 e in the moving direction reaches about 90 degrees is about 12 Omm. If the difference in immersion depth is large, not only can the size of the crucible holding the silicon melt not be reduced, but also the thickness of the silicon thin plate becomes uneven due to the influence of the melt temperature distribution and the difference in immersion time. The tilt angle 5a needs to be optimized while taking into account the effect of the immersion depth.

The method described above reduces the amount of melt creeping over the uniform columnar crystal, thereby smoothing the silicon thin plate and eliminating the need for secondary processing such as polishing, thus providing a low-cost wafer. It is possible to In addition, since the liquid pool region having a smaller grain size than the columnar crystal and having more crystal grain boundaries in the thickness direction of the thin plate is reduced, for example, when used as a solar cell, defects that cause recombination of the carrier are reduced. However, it is possible to improve the characteristics of the solar cell.

FIG. 10A and FIG. 10B show a front view and a side view of the fixed base 1 and the oblique growth substrate 5 around the same time, respectively. In the figure, when the growth surface of the substrate is tilted (tilt angle> 0 degree), in order to change the tilt angle 5a in various ways, the tilted growth surface substrate 5 is screwed to the screw hole 5b and the screw hole 5c of the fixing base 1 Attach the inclined growth substrate 5 to the fixed base 1 with the corresponding screws. Structure. Thereby, it is possible to manufacture the silicon thin plate 2 and compare the evaluation with the case where the inclination angle is changed variously. FIGS. 11A and 1IB show a front view and a side view, respectively, of a state in which the inclined growth substrate 5 is mounted on the fixed base 1.

Next, FIG. 9 shows a state in which the inclined growth surface substrate 5 is attached to a dodecahedral-type rotating cooling body via a fixed base. By rotating the rotating shaft 8 at a constant speed, the growth surface of the substrate can be immersed in the melt. BRIEF DESCRIPTION OF THE FIGURES

1A to 1D are schematic views illustrating the principle of the thin plate manufacturing method according to the present invention. 2A to 2D are schematic views illustrating the principle of the thin plate manufacturing method according to the present invention. 3A and 3B are schematic diagrams illustrating the principle of the thin plate manufacturing method according to the present invention. FIG. 4 is a schematic sectional view of a manufacturing apparatus used in the thin plate manufacturing method of the present invention.

FIG. 5 is a schematic perspective view of a manufacturing apparatus used in the thin plate manufacturing method of the present invention.

FIG. 6 is a sectional view of a manufacturing apparatus used in the thin plate manufacturing method of the present invention.

FIG. 7 is a schematic view of an apparatus used in the method for producing a thin plate according to the present invention.

FIG. 8 is a side view of the thin plate manufacturing apparatus in which the substrates are set so as to be parallel to each surface of the polygonal prism.

FIG. 9 is a schematic view of a polygonal column type rotary cooling body.

FIG. 10A and FIG. 1OB are a front view and a side view of the oblique growth surface substrate and the fixing table. FIG. 11A and FIG. 11B are a front view and a side view in a state where the inclined growth surface substrate is mounted on a fixed base.

FIG. 12 is a schematic view of an inclined growth surface substrate.

FIG. 13 is a schematic view showing a state in which the inclined growth surface substrate is arranged with a different inclination angle. FIG. 14 is a schematic view of a manufacturing apparatus used in the thin plate manufacturing method of the present invention.

FIG. 15 is a schematic view of a manufacturing apparatus used in the thin plate manufacturing method of the present invention.

Figure 16 is a diagram showing the relationship between the oblique angle and the tapping angle.

FIG. 17 is a diagram showing the relationship between the inclination angle and the maximum difference in the immersion depth of the inclined growth surface. FIG. 18 is a diagram showing the relationship between the inclination angle and the maximum undulation of the silicon thin plate.

FIG. 19 is a diagram showing the relationship between the tilt angle and the maximum undulation of the silicon thin plate. FIG. 20 is a diagram showing the relationship between the inclination angle and the maximum undulation of the silicon thin plate. FIG. 21 is a schematic side view of a manufacturing apparatus used in the thin plate manufacturing method of the present invention. FIG. 22 is a schematic view of a manufacturing apparatus used in a conventional thin plate manufacturing method. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described based on embodiments.

In the present embodiment, a polycrystalline silicon thin plate was manufactured by solidifying a silicon melt. The material of the substrate, rotating shaft and rotating cooling body was graphite. The substrate surface (growth surface) was a smooth plane. In the case of using a substrate connecting mechanism for connecting the substrates, the material was graphite and the surface was coated with silicon carbide.

(Embodiment 1)

Embodiment 1 is directed to a case where a silicon thin plate is grown on a growth surface of a substrate by immersing in a melt while moving in a circular motion along a circular orbit, and subsequently moving away from the melt. Is a method in which the growth surface is inclined.

FIG. 7 shows a silicon thin plate manufacturing apparatus according to the first embodiment. The silicon thin plate manufacturing equipment consists of a rectangular crucible 4, a heating heater that melts the silicon 3 supplied to the crucible 4, a rotating shaft that supports the rotating cooling body 1, a 1-sided prismatic rotating cooling body 1, The dodecahedron prism-shaped rotary cooling body 1 is composed of a substrate 5 that can be attached to each surface. These are housed in a rectangular parallelepiped outer wall and heat insulation. The inside of the device is surrounded by heat insulating material and sealed so that the inside can be held under an argon gas atmosphere.

When the growth surface of the substrate 5 is not tilted (tilt angle = 0 degree), the growth surface 25a of the substrate has a structure in which 12 prisms are formed as shown in FIG. These 12 substrates 50 were configured to be attachable with screws 26. 1 Assuming that the substrate growth surface 25 a on the rotary cooling body 2 1 of a dihedral prismatic type 2 1 is a square of 20 O mm square, the height of the rotary cooling body 2 1 The surface-to-surface distance = the rotation diameter at the center of each growth surface) is about 74 O mm.

When changing the inclination angle of the 12 inclined growth surface substrates 5, all the 12 inclined growth surface substrates were replaced. The inclined growth surface substrate 5 is pressed against each surface of the rotary cooling body 1 as shown in FIG. 11A and FIG. 1IB, and screw holes 5 b at both ends of the inclined growth surface substrate 5 are formed. The inclined growth surface substrate 5 was fixed to the rotary cooling body 1 by tightening the screw 6 into the screw hole of the rotary cooling body 1 corresponding to the screw hole 5 b. '

In the present embodiment, an inclined growth surface substrate 5 having an inclination angle 5α of 0 ° to 75 ° was prepared, and the silicon thin plate 2 was manufactured using these. For each inclined growth surface substrate 5, first, the rotary cooling body 1 is rotated to make the inclined growth surface substrate 5 circularly move, and then the crucible 4 is raised, and the growth surface 5a is melted by silicon. By immersing in the silicon melt 3 and then separating from the silicon melt 3, the silicon thin plate 2 grows on the growth surface. In this embodiment, the growth surface is immersed in the silicon melt 3 for 2 O mm with reference to the position where the center of the growth surface when the substrate with a tilt angle of 0 ° is mounted is located at the lowest position. Silicon thin plate 2 was grown on the surface. Thereafter, the silicon thin plate 2 was taken out of the apparatus, and its surface undulation and plate thickness were evaluated. The surface undulation was evaluated using the maximum undulation defined by JISBO 61-1994.

When the surface undulation of the removed silicon thin plate 2 was measured, the maximum undulation (W _CM ) was about 400 μππ at a tilt angle of 5α of 0 ° as shown in Fig. 18, but the tilt angle of 5 It is less than 200 in the range of 15 to 50 degrees, which indicates that the smoothness can be greatly improved in this range.

This is because the amount of the silicon melt crawling on the surface of the silicon thin plate decreases as the angle β1 formed between the growth surface and the melt surface when the growth surface moves away from the melt increases. Above 40 °, the maximum swell began to increase again.

It was thought that the average value of the angle formed by the growth surface and the melt surface when the tip and the end portions left the melt climbed at 90 degrees, and the amount of silicon melt was minimized. When the inclination angle exceeds 40 degrees, the growth surface on the end 5 e side in the moving direction moves away from the melt while facing upward against the gravity, so that the melt becomes more silicon than when moving downward and away from the melt. Since it easily remains on the thin plate, it crawls on the lower tilt angle side than the tilt angle of 60 degrees (the angle between the growth surface and the melt surface is about 90 degrees), and the amount of silicon melt becomes the minimum, and the silicon thin plate It was also found that the maximum swell of the sample became smaller at an inclination angle of 15 to 50 degrees.

In the present embodiment, in order to obtain a planar silicon thin plate, a silicon substrate is placed on the growth surface of the rotary cooling body in which the inclined growth surface substrate 5 is installed on each surface of the polygonal rotary cooling body 1. When this method is used, the depth of immersion in the silicon melt differs depending on each part of the growth surface as compared with the case where a cylindrical rotary cooling body is used. The difference in the immersion depth may cause unevenness in the thickness of the silicon thin plate due to the influence of the melting temperature distribution at night and the difference in the immersion time. Therefore, the thicknesses of various parts of the removed silicon thin plate were measured.

When the inclination angle 5α was close to 0 degrees, the plate thickness tended to be thinnest at the center and thickest at the tip 5d in the moving direction and the end 5e in the moving direction. In addition, as the inclination angle 5α was increased, the thickness of the portion closer to the end 5e in the movement direction became larger. In other words, when the tilt angle is 0 degree, the distance between the center of the growth surface and the center of the rotation axis (immersion volatilization at the center of the growth surface) is the smallest, and when the tilt angle increases, the end in the moving direction and the center of the rotation axis This is because the distance (the immersion depth at the end in the moving direction) increases, and the plate thickness increases as the immersion time increases as the immersion depth increases.

The difference between the maximum and minimum values of the thickness of each part of the silicon thin plate (thickness difference) affects the process of manufacturing devices such as solar cells using silicon thin plates. Distribution is small).

As shown in Fig. 18, when the inclination angle is less than 50 degrees, the thickness difference is less than 150 / zm, but when it exceeds 50 degrees, the thickness difference increases, It turned out to be more than / zm. In the solar cell fabrication process, if the plate thickness difference exceeds 150 m, unevenness will occur in the electrode printing and anti-reflection film formation on the silicon thin plate, so the plate thickness difference must be less than 15 O / xm. However, it is desirable to set the inclination angle 5a to 50 degrees or less.

In particular, in order to realize smoothness of the silicon thin plate and not to be greatly affected by the difference in the plate thickness, it is desirable that the inclination angle is set to 15 to 50 degrees in the configuration of the present apparatus.

In the present embodiment, the inclination angle 5α of 15 ° to 50 ° means, as can be converted from the graph of FIG. 16, that the growth surface moves with the growth surface when the front end moves away from the melt. The angle between the liquid surface is 20 degrees to 60 degrees, and the angle between the growth surface and the melt surface when the end is away from the melt is 60 degrees to 100 degrees. Equivalent to. In the present embodiment, the angle formed between the growth surface and the melt surface was controlled only by simply tilting the growth surface, but for example, changing the size of the rotating cooling body ', changing the area of the growth surface The tip of the growth surface in the direction of movement away from the melt by a method including at least one of the following steps: changing the immersion depth, and / or tilting the growth surface. The angle between the surface and the growth surface should be controlled within the range of 2.0 to 60 degrees, and the angle between the growth surface and the melt surface when the end is separated from the melt should be within the range of 60 to 100 degrees. Thus, it is possible to obtain a low-cost crystal sheet having a flat surface.

In particular, the case where a rotating cooling body is used has been described.However, when a substrate having a substantially flat growth surface is movable, and when the growth surface moves by an operation that does not rotate, the growth surface is melted. It is possible to take a method of growing a crystal thin plate on the growth surface by immersing in a melt and then separating from the melt. In this case as well, the angle between the growth surface and the melt surface when the tip part moves away from the melt in the direction of movement of the growth surface is 20 to 60 degrees, and the growth surface when the end part moves away from the melt. By controlling the angle between the liquid surface and the liquid surface in the range of 60 degrees to 100 degrees, it is possible to obtain a low-cost crystal thin plate having a flat surface.

(Embodiment 2)

In the second embodiment, although the substrate makes a non-circular orbital motion, the silicon thin plate surface is smoothed in contrast to a case where the substrate makes a circular motion along the circular orbit at least from the infiltration into the melt until it leaves the melt. This is a method for improving the crystallinity of a silicon thin plate.

FIG. 14 shows a silicon thin plate manufacturing apparatus according to the second embodiment. The silicon thin plate manufacturing equipment consists of a rectangular crucible 34, a heating heater that melts the silicon supplied to the crucible 34, a rotating shaft that supports the rotating cooling body 31, a 1-sided prismatic rotating cooling body 31. Each of the substrates is composed of inclined growth surface substrates 35 connected at regular intervals. These are housed in a rectangular parallelepiped outer wall and heat insulator. The inside of the device is surrounded by a heat insulating material and sealed so that the inside can be held under an argon gas atmosphere.

When the growth surface of the substrate was not inclined (the inclination angle was 0 degree), a substrate 50 as shown in FIG. 8 was used. When the growth surface of the substrate was inclined, as shown in FIG. 14, an inclined substrate in which the growth surface was inclined at an arbitrary angle with respect to the case where the substrate was not inclined was used. Each board is continuously connected by the coupler 9, and the boards are connected continuously from outside the system. It is possible to discharge the substrate together with the grown silicon thin plate 32 outside the system. A board introduction port and a discharge port are provided on the outer wall of the equipment where the connector is introduced from the outside of the equipment and the outer wall of the equipment where it is discharged. I'm preventing. Atmospheric gases exhausted from the system are immediately sent to the exhaust gas treatment facility by the exhaust ducts located close to the substrate inlet and outlet.

This method makes it possible to continuously produce and remove silicon thin plates. Outside the system, the process of peeling and collecting the silicon thin plate from the substrate, cleaning and adjusting the substrate (especially the growth surface), and replacing the substrate can be performed while the continuous operation is in progress. Further, by controlling the tension of the connected substrate outside the system, the substrate can be pressed against the rotary cooling body 31 at an arbitrary pressure. Between the time when the substrate comes into contact with the rotary cooling body 31 and the time when the substrate separates from the rotary cooling body 31, as in the first embodiment, the substrate is integrated with the rotary cooling body. In other words, the silicon thin plate performs a circular motion until it is immersed in the melt and separates from the melt, so that it is possible to grow a silicon thin plate as in the first embodiment.

1 If the growth surface of the substrate on the dihedral prismatic rotary cooling body that is not tilted is a square of 20 O mm square, the height of the rotating cooling body including the rotating cooling body and the substrate (distance between the facing surface and the surface The rotation diameter at the center of the growth surface is about 74 O mm.

In the present embodiment, an inclined growth surface substrate 35 having an inclination angle 5α of 0 ° to 75 ° was prepared, and a silicon thin plate 32 was manufactured using these substrates. For each inclined growth surface substrate 35, first, the rotating cooling body 31 is rotated to continuously introduce and discharge the inclined growth surface substrate 35, and then the crucible 34 is raised to grow. The surface 35a is immersed in the silicon melt 33, and then separated from the silicon melt 33, so that the silicon thin plate 32 grows on the growth surface. The grown silicon thin plate 32 is discharged outside the system while being integrated with the substrate.

In the present embodiment, the growth surface is immersed in the silicon melt 33 at 2 O mm with reference to the position where the center of the growth surface when the substrate having the inclination angle of 0 ° is mounted is located at the lowest position. A silicon thin plate 32 was grown on the growth surface. Thereafter, the silicon thin plate 32 was taken out of the apparatus, and the surface undulation and the plate thickness were evaluated. When the surface undulation of the removed silicon thin plate 32 was measured, the maximum undulation (WCM) was about 400 μπα at a tilt angle of 0 ° as shown in Fig. 19, but the tilt angle was 15 It is less than 200 μm at degrees to 55 degrees, and it was found that the smoothness can be greatly improved in this range. This is the same result as in the first embodiment. Growth surface 35a (and substrate) Force S Even if there is no circular motion, if the growth surface circularly moves from at least when it enters the melt to when it separates from the melt, the same as in the first embodiment. A similar effect can be obtained.

Next, the thickness of the removed silicon thin plate at various sites was measured. As in Embodiment 1, as shown in Fig. 19, when the inclination angle 5α is within 50 degrees, the thickness difference is less than 150 m, but 50 degrees. It was found that the difference in plate thickness increased when the ratio exceeded 15 O / i Hi or more. It is desirable to set the inclination angle to 5 or 55 degrees or less so that the sheet thickness difference is less than 15 O / zm.

From the above, it is desirable to set the inclination angle to 15 to 50 degrees in the present apparatus configuration because the silicon thin plate is smoothed and is not greatly affected by the difference in thickness. In the present embodiment, the inclination angle of 15 degrees to 50 degrees means, as can be converted in the graph of FIG. 16, the inclination angle between the growth surface and the growth surface when the tip of the growth surface moves away from the melt. The angle between the melt surface is 20 degrees to 60 degrees, and the angle between the growth surface and the melt surface when the end is separated from the melt is 60 degrees to 100 degrees. Is equivalent to In other words, the angle between the growth surface and the melt surface when the tip of the growth surface moves away from the melt is 20 degrees to 60 degrees, and the growth surface and the melt surface when the ends are away from the melt. By controlling the angle between 60 ° and 100 °, it is possible to obtain a low-cost crystal sheet having a flat surface.

(Embodiment 3)

In the third embodiment, although the substrate does not move in a circular orbit while the substrate is immersed in the melt, at least at a point away from the melt, the substrate makes a circular motion along the circular orbit. This is a method for smoothing silicon and improving the crystallinity of a silicon thin plate.

FIG. 15 shows a silicon thin plate manufacturing apparatus according to the third embodiment. The silicon thin plate manufacturing equipment consists of a square crucible 44 and a heating unit that melts the silicon supplied to the crucible 44. Heaters, two 12-hedral prismatic rotary cooling bodies 12 and 13 having the same size and arranged in parallel to the silicon melt 4 3 and a rotating shaft supporting them are connected at regular intervals. It consists of a substrate. These are housed in a rectangular parallelepiped device outer wall and heat insulating material. The inside of the device is surrounded by heat insulating material, and the inside of the device is sealed so that it can be held under an argon gas atmosphere.

When the growth surface of the substrate was not inclined (the inclination angle was 0 degree), a substrate 50 as shown in FIG. 8 was used. When the growth surface of the substrate was tilted, as shown in Fig. 15, an inclined substrate whose growth surface was tilted at an arbitrary angle with respect to the case where the substrate was not tilted was used. The substrates 45 are continuously connected by a coupler 19, and the substrates are continuously introduced from outside the system, pressed against the first rotary cooling body 12 and immersed in the silicon melt 43. Pickled. Subsequently, the rotary cooling body 12 is separated from the silicon melt and moves toward the second rotary cooling body 13 while being immersed in the silicon melt. Since the substrate 45 pressed against the rotating cooling body 13 is separated from the silicon melt while being fixed to the rotating cooling body 13, the movement of the substrate when the growth surface is separated from the silicon melt is a rotation cooling. As in the case of reject 13, the orbit is circular. After the substrate is separated from the silicon melt 43, it is also separated from the rotary cooling body 13 and the substrate together with the grown silicon thin plate 42 can be discharged out of the system.

As in the second embodiment, a substrate introduction port and a discharge port are provided on the outer wall of the apparatus, and the atmospheric pressure in the apparatus system is set to be equal to or higher than the atmospheric pressure, thereby preventing entry into the atmosphere. Atmospheric gas discharged from the system is sent to an exhaust gas treatment facility by an exhaust duct.

This method makes it possible to continuously produce and remove silicon thin plates. In addition, since the time for immersion in the melt (the distance that the growth surface moves in the melt) is long, when the rotation speed of the rotary cooling body (the moving speed of the substrate) is increased, the immersion time is insufficient. It is possible to eliminate the shortage of growth on the growing surface, and as a result, it is possible to shorten the manufacturing time of silicon thin plates and reduce costs.

As in Embodiment 2, the process of peeling and collecting the silicon thin plate from the substrate, collecting and cleaning the substrate (especially the growth surface), replacing the substrate, etc. can be performed while the system is running outside the system. is there. In addition, the connected substrate controls the tension outside the system By doing so, it becomes possible to press the substrate against the rotary cooling bodies 12 and 13 at an arbitrary pressure.

1 Assuming that the growth surface of the substrate not tilted on the dihedral prismatic rotary cooling body 1 2, 1 3 is a square of 20 O mm square, the rotation cooling body 12 or 13 and the combined rotary cooling body including the substrate The height (distance between opposing surfaces = rotation diameter at the center of each growth surface) is approximately 74 O mm.

In the present embodiment, a non-tilted substrate or an inclined substrate similar to that of the second embodiment is used. An inclined growth surface substrate 45 having an inclination angle 5α of 0 ° to 75 ° was prepared, and a silicon thin plate 42 was manufactured using these substrates. For each inclined growth surface substrate 45, first, the rotating cooling bodies 12 and 13 are rotated to continuously introduce and discharge the inclined growth surface substrate 45, and then raise the crucible 44. Then, the growth surface 45a is immersed in the silicon melt 43, and then separated from the silicon melt 43, whereby the silicon thin plate 42 grows on the growth surface. The grown silicon thin plate 42 is discharged outside the system while being integrated with the substrate.

In the present embodiment, the growth surface is immersed in the silicon melt 43 by 20 mm with reference to the position where the center of the growth surface when the substrate having the inclination angle of 0 ° is attached is located at the lowest position. A silicon thin plate 42 was grown on the growth surface. Thereafter, the silicon thin plate 42 was taken out of the apparatus, and the surface undulation and the thickness were evaluated.

When the surface undulation of the removed silicon thin plate 42 was measured, the maximum undulation (WCM) was about 400 μππ at an inclination angle of ◦ degrees as shown in Fig. 20, but the inclination angle was 15 It is less than 15 Ομπι at degrees to 50 degrees, and it was found that the smoothness can be greatly improved in this range. This is the same result as in the first and second embodiments.

Even if the growth surface 45a (and the base surface) does not make a circular motion, the same effect as in Embodiments 1 and 2 can be obtained if the growth surface makes a circular motion at least when it separates from the melt. It is.

Next, the thickness of the removed silicon thin plate at various sites was measured. As shown in Fig. 20, the sheet thickness difference is less than 15 when the inclination angle is less than 50 degrees, as in the first and second embodiments. If it exceeds, the thickness difference increases and becomes 150 / xm or more. Inclination angle 5 or 50 degrees or less so that the thickness difference is less than 15 O / xm It is desirable to set below.

From the above, it is desirable to set the inclination angle to 15 to 50 degrees in the present apparatus configuration because the silicon thin plate is smoothed and is not greatly affected by the difference in thickness. In the present embodiment, the inclination angle of 15 degrees to 50 degrees means that, as can be converted from the graph of FIG. 16, the growth surface moves in the direction of movement away from the melt. The angle between the liquid surface is 20 to 60 degrees, and the angle between the growth surface and the melt surface when the end is separated from the melt is 60 to 100 degrees. Equivalent to. In other words, the angle between the growth surface and the melt surface when the tip of the growth surface moves away from the melt is 20 degrees to 60 degrees, and the growth surface and the melt surface when the ends are away from the melt. By controlling the angle between 60 ° and 100 °, it is possible to obtain a low-cost crystal sheet having a flat surface.

(Comparative Example 1)

Comparative Example 1 is an example of simulating a conventional method using a cylindrical rotary cooling body without tilting the growth surface.

FIG. 22 shows a silicon thin plate manufacturing apparatus according to Comparative Example 1. In the apparatus configuration, a cylindrical rotary cooling body 81 having a diameter of 74 O mm is used instead of the dodecahedral polygonal column type rotary cooling body 1 and the inclined growth surface substrate 5 in the first embodiment.

First, the crucible 84 is raised, and the rotating cooling body 81 around which the carbon net 88 is wound is immersed in the silicon melt 83 for 2 mm, and the rotating cooling body 81 is rotated while the carbon net 88 is rotated. By pulling out, the silicon thin plate 82 grown on the surface of the T-rotating cooling body was pulled out. Since a cylindrical rotary cooling body is used, the immersion depth and the angle between the growth surface and the melt surface when moving away from the melt are constant at each part of the growth surface. In the present comparative example, the angle formed by the growth surface and the melt surface when leaving the melt is about 20 degrees. The silicon melt 82a crawled up on the surface was localized and remained on the surface of the silicon thin plate, and a liquid pool 82b was locally generated on the surface. At the position where the rotation further advanced, a large swell was formed on the surface of the silicon thin plate due to the liquid pool 82 b gradually solidifying.

Measurement of the surface waviness of the extracted silicon thin, the maximum waviness (W _CM) was about 4 5 0 μ πι. Compared to Embodiments 1-3, silicon with a flat surface The force that can satisfy the angle between the growth surface and the melt surface when the tip of the growth surface separates from the melt, which is the condition for obtaining a thin plate, is between 20 and 60 degrees. Since the angle between the growth surface and the melt surface at the time of separation cannot satisfy the range of 60 degrees to 100 degrees, as in the case of the planar growth surface, the growth surface is The maximum waviness increased compared to the case where a flat growth surface was used, because the melt rising on the silicon thin plate was not reduced by increasing the angle formed with the melt surface.

The difference between the maximum value and the minimum value (thickness difference) at each part of the silicon thin plate was small, because there was no difference in the immersion depth at each part, and was about 45 / im.

(Embodiment 4)

A solar cell was manufactured using the silicon thin plates manufactured according to Embodiments 1 to 3 and Comparative Example 1. An example of a manufacturing procedure is a sequence of cleaning, texture etching, formation of a diffusion layer, removal of an oxide film, formation of an antireflection film, back etching, formation of a back surface electrode, and formation of a light receiving surface electrode, which are general methods. Delivery between each process was basically performed by an automatic transport mechanism.

Regarding the silicon thin plates according to the first and second embodiments, all the silicon thin plates using the inclined growth surface substrate having an inclination angle of 15 to 50 degrees could be automatically transported, but for the other silicon thin plates, In some cases, the automatic transport mechanism could not be used due to unevenness due to liquid pools. With respect to the silicon thin plate according to Comparative Example 1, the automatic transfer mechanism could not be used because of the remaining curvature and the convexity due to the liquid pool.

Next, the results of measuring the characteristics of a solar cell manufactured from a silicon thin plate using an inclined growth surface substrate with a tilt angle of 0 ° and 40 ° in Comparative Example 1 and Embodiments 1 to 3 using a solar simulator are shown. It is shown in Table 1 below. Fiber Electricity β Degree w ≡ Maximum ^

Fill factor

MnA / cm ² ) (mV) (mW / cm ² ) (%) Comparative example 1 25 570 10 0.702 10 i angle o degree 26 575 11 0.736 11 diagonal angle 40 degree 28 575 12 0.739 12 Angle of inclination 0 degree 26 575 11 0.736 11 Angle of inclination 40 degree 28 575 12 0.739 12 银 Angle of inclination 0 degree 26 575 11 0.736 11 俱 Angle of inclination 40 degree 27 575 12 0.773 12 embodiment 1, both embodiment 3 embodiment 2 and embodiment, the short circuit current density of the solar cell that by the inclination angle 4 0 degree is ^{2 7~ 2 8 mA / cm 2} , 2 5 m Bruno 0 of Comparative example 1 111 ² , tilt angle 0 degree 2 6 1 ₁ 1 1 8 _/ ^/ 0 111 ² bigger ぃ. This is presumably because the defects in the fine particle size region due to the liquid pool were removed by texture etching. The fill factor is also improved to reduce defects, and the conversion efficiency is 10% in Comparative Example 1, 11% in Embodiments 1 to 3 at an inclination angle of 0 °, and 12% at an inclination angle of 40 °. And could be greatly improved.

(Embodiment 5)

A silicon raw material whose boron concentration was adjusted so that the specific resistance of the obtained plate-like silicon was 2 Ω mcm was put into a high-purity graphite crucible, and the crucible was set in the apparatus shown in FIG. Next, the inside of the chamber is evacuated and the pressure is once reduced to 5 Pa or less. Thereafter, Ar gas is introduced into the chamber, and while maintaining 700 hPa, the Ar gas always flows from the upper part of the chamber at SL / min.

Next, the temperature of the silicon melting heater is set at 148 ° C., and the silicon is completely melted. At this time, the liquid level is lowered by dissolving the silicon raw material. Therefore, by adding new silicon raw material, the molten metal surface position is adjusted to a predetermined position. After that, set the temperature of the silicon melt to 142 ° C and hold it for 30 minutes. Stabilize the liquid temperature. At this time, it was confirmed that there was no solidification of the molten metal surface.

Next, the substrate whose temperature is controlled using both the cooling mechanism and the heating mechanism is immersed in the silicon melt. At this time, the control temperature of the substrate was three conditions of 300 ° C., 600 ° C., and 900 ° C.

After that, the crucible was gradually raised, and the base was immersed in the silicon melt when the inclined substrate was raised to a position where it could be completely immersed. At this time, the tilt angle of the tilted substrate was 10 °. At this time, the moving speed of the substrate was 300 cm / min. At this time, the obtained plate-like silicon could be easily peeled off from the substrate, and its size was 75 mm × 75 mm. 100 sheets of such square thin plate silicon were produced, and the plate thickness was converted from the weight. Table 2 shows the average values of the obtained sheet thicknesses.

Next, a solar cell was manufactured using the obtained plate-like silicon. The obtained plate-like silicon was etched and washed with a mixed solution of nitric acid and hydrofluoric acid, and then alkali-etched with sodium hydroxide. Thereafter, an n layer was formed on p-type substrate by POC 1 ₃ diffusion. After removing the PSG film formed on the plate-like silicon surface with hydrofluoric acid, a silicon nitride film was formed using plasma CVD on the n-layer on the light-receiving surface side of the solar cell. Next, the n-layer formed on the back side of the solar cell is etched away with a mixed solution of nitric acid and hydrofluoric acid, exposing the p-substrate, and simultaneously forming the back electrode and p + layer on it. did. Next, the electrode on the light receiving surface side was formed using a screen printing method. Thereafter, solder coating was performed to produce a solar cell.

The cell characteristics of the manufactured solar cell were measured under irradiation of AM I.5, 10 OmW / cm ² . Table 2 shows the average values of the obtained characteristics.

By changing the angle of the substrate even in a circular orbit, it is possible to create an oncoming flow.

Table 2

Substrate temperature Weight equivalent plate thickness Short-circuit current Open-circuit voltage Fill factor Conversion efficiency

(° C) (m) (mA / cm ² ) (mV) (-) (%)

300 550 29.5 593 0.75 13.1

600 480 28.9 590 0.75 12.8

900 350 28.5 589 0.73 12.3 (Embodiment 6)

A silicon raw material whose boron concentration has been adjusted so that the specific resistance of the obtained plate-like silicon is 0.5 Ωcm is placed in a high-purity graphite crucible, and the crucible is set up in the device shown in Fig. 21 did. In the figure, the manufacturing equipment consists of a substrate 26 2, a fixed base 26 3, a variable-length shaft 26 4 connected to the rotating shaft, a melt 26 5, a heater 26 6, and a crucible 26 2 7. It has a crucible elevating shaft 2 6 8. The variable length shaft 264 is structured so that the distance from the substrate to the center of the rotating shaft can be increased when the substrate escapes from the melt. Next, the inside of the chamber is evacuated, and the pressure is reduced to 10 Pa or less. After that, Ar gas is introduced into the chamber, and Ar gas is always kept flowing from the upper part of the chamber at 10 LZmin while maintaining 700 hPa.

Next, the temperature of the heater for melting silicon is set to 1500 ° C., and silicon is completely melted. At this time, the liquid level is lowered by dissolving the silicon raw material, so that the silicon surface is adjusted to a predetermined position by newly adding the silicon raw material. Thereafter, the temperature of the silicon melt is set at 140 ° C., and the temperature is maintained for 30 minutes to stabilize the melt temperature. At this time, it was confirmed that there was no solidification of the molten metal surface.

Next, the substrate whose temperature is controlled using both the cooling mechanism and the heating mechanism is immersed in the silicon melt. The control temperature of the substrate at this time was 400 ° C.

Then, the crucible was gradually raised, and when the substrate was raised to a position where the substrate could be completely immersed, the substrate was immersed in a silicon melt. At this time, the moving speed of the substrate was 400 cm / min.

At this time, the obtained plate-like silicon could be easily peeled from the substrate, and its size was 10 Omm X 10 Omm. Ten such square silicon thin plates were prepared, and the thickness was converted from the weight. Table 3 shows the average values of the obtained plate thicknesses. Table 3 shows the number of small protrusions on the surface per silicon thin plate.

(Comparative Example 2)

A silicon thin plate was manufactured in exactly the same manner as in Embodiment 6 except that the distance from the center of the substrate and the rotation axis was kept constant without using a variable length axis. The plate thickness was converted. Table 3 shows the average values of the obtained plate thicknesses. Table 3 shows the number of small protrusions on the surface per silicon thin plate.

Table 3

(The invention's effect)

In the method for producing a thin plate according to the present invention, a substrate having a growth surface is brought into contact with a melt of a material containing at least one of a metal material and a semiconductor material, and the material is grown on the substrate. In the method of manufacturing a thin plate for obtaining a thin plate formed of the above material, the melt is directed toward (approached to) the thin plate growth surface of the substrate when viewed from the thin plate growth surface of the substrate, By controlling the meniscus shape of the melt, it was possible to stably and continuously grow a thin plate having a flat surface with few small protrusions at low cost.

Further, by moving a moving body on which a substrate having a growth surface is disposed, the surface of the substrate is brought into contact with a melt of a material containing at least one of a metal material and a semiconductor material, and thereafter, In a sheet manufacturing method for obtaining a thin plate formed of the material by growing the material on the surface of the substrate by a series of moving operations for separating the surface of the substrate from the melt, the method includes the steps of: By adopting a configuration in which the melt comes to (approaches) the growth side of the substrate when the substrate is thin, a thin plate with few flat protrusions and a flat surface can be stably manufactured at low cost.

In the method for producing a thin plate according to the present invention, the distance between the tip of the growth surface in the movement direction and the center of the circular orbital rotation axis is smaller than the distance between the end of the growth surface in the movement direction and the center of the circular orbital rotation shaft. By inclining the growth surface, it is possible to increase the angle between the growth surface and the melt surface when the growth surface separates from the melt, and to reduce the amount of melt crawling on the growth surface. As a result, a thin plate with a flat surface could be stably and continuously grown at low cost.

Also, tilt the growth surface, change the size of the rotating cooling body, and increase the area of the growth surface. By changing the immersion depth, the angle between the growth surface and the melt surface when the tip of the growth surface in the moving direction moves away from the melt is from 20 degrees to 60 degrees. By setting the angle between the growth surface and the melt surface when the end in the moving direction of the melt separates from the melt in the range of 60 ° to 100 °, the amount of the melt crawling on the growth surface and It was possible to optimize the thickness of the crystal thin plate, and to obtain a smooth and thin crystal thin plate.

In addition, by using a silicon material as the material, a low-cost silicon wafer serving as a material of a semiconductor device, particularly, a solar cell could be obtained.

Furthermore, by using the thin plate obtained by the thin plate manufacturing method according to the present invention, it is possible to reduce the cost of the material, to reduce the fine particle size region due to the rise of the melt, and to reduce the crystallinity. To improve the performance, a solar cell with improved conversion efficiency was obtained using a general solar cell manufacturing method.

As mentioned above, the growth surface when the growth surface separates from the melt by inclining the growth surface, changing the size of the rotating cooling body, changing the area of the growth surface, changing the immersion depth, etc. Increases the angle between the silicon melt and the melt surface, thereby reducing the crawling of the silicon melt and the accumulation of liquid, making the surface of the silicon thin plate smooth and forming a silicon wafer regardless of the polishing and slicing processes. did it.

Industrial applicability

According to the manufacturing method of the present invention, the rotary cooling body is replaced with a cylindrical type, and a substrate or a structure having a planar growth surface such as a polyhedron can be applied, so that a flat and smooth silicon wafer can be formed. It is. In addition, since the fine grain size region is reduced and the crystallinity is improved, the conversion efficiency can be improved by using a general solar cell manufacturing method. As a result, a silicon wafer can be provided at lower cost. be able to.

Claims

The scope of the claims

1. A substrate having a thin plate growth surface is brought into contact with a melt of a material containing at least one of a metal material and a semiconductor material, and a thin plate of the material is grown on the substrate, thereby forming the substrate. A method for producing a thin sheet, characterized in that the substrate and / or the melt move so that the melt moves toward the sheet growth side of the substrate when viewed from the sheet growth side of the substrate. Thin plate manufacturing method.

2. The angle between the thin-plate growth surface and the melt surface at the time when the leading end in the moving direction of the thin-plate growth surface separates from the melt is 20 degrees to 60 degrees, and

2 .The thin plate according to claim 1, wherein an angle formed by the thin plate growth surface and the melt surface at a point in time when an end portion in the moving direction of the thin plate growth surface is separated from the melt is 60 degrees to 100 degrees. Construction method.

3. The method according to claim 1, wherein the semiconductor material is a silicon material.

4. A solar cell using a thin plate manufactured by the thin plate manufacturing method according to claim 1.

5. Move the moving body on which the substrate having the thin plate growth surface is arranged to bring the thin plate growth surface of the substrate into contact with a melt of a material containing at least one of a metal material and a semiconductor material. A method for producing a thin plate made of the material by growing a thin plate of the material on the substrate by a series of moving operations for separating a surface of the substrate from the melt; A method for manufacturing a thin plate, comprising: moving a substrate and Z or a melt so that the melt moves toward a thin plate growth surface side of the substrate when viewed from a surface side.

6. By moving a moving body on which a substrate having a thin plate growth surface is arranged, the thin plate surface of the substrate is brought into contact with a melt of a material containing at least one of a metal material and a semiconductor material, Then, by a series of moving operations for separating the thin plate growth surface of the substrate from the melt, a crystal of the material is grown on the substrate, thereby obtaining a thin plate formed of the material.

The orbit when the substrate separates from the melt is a circular orbit,

The distance 1 ^ between the tip of the growth surface in the moving direction and the center of the rotation axis of the circular orbit is Sheet production process, characterized in that the moving direction end of the growth surface smaller than the distance R ₂ between the rotation center of the circular path.