JP2006093434A - Manufacturing method of crystal sheet and solar battery cell manufactured by using crystal sheet manufactured by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely collect a crystal sheet by preventing the crystal sheet formed on a substrate from falling, and to provide a method for producing a thin crystal sheet which is excellent in flatness in large quantities at a low cost. <P>SOLUTION: In the manufacturing method of the crystal sheet, the crystal sheet is manufactured by bringing one side or both sides of a major surface of a cooled substrate into contact with a melt of a sheet material and forming crystal of the sheet material on the substrate. The sheet material comprises a metallic material and/or a semiconductor material, the substrate has a matrix formed of a sheet material and a film covering a part or an entire surface of the matrix, and the film is formed of a material which is different from the sheet material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a crystal sheet from a melt containing a metal material or a semiconductor material. In particular, the present invention relates to a method for producing a low-cost solar cell, and a method for producing a silicon sheet for a solar cell directly from a silicon melt.

  Conventionally, as a method for producing a polycrystalline silicon sheet used in a solar cell, for example, a high-purity silicon material to which a dopant such as phosphorus or boron is added is heated and melted in a crucible in an inert atmosphere. There is a method in which a liquid is poured into a mold and slowly cooled to obtain a polycrystalline ingot (see Patent Document 1). In order to produce a polycrystalline silicon sheet for a solar cell from the thus obtained polycrystalline ingot, the ingot is sliced using a wire saw or an inner peripheral blade method. Therefore, since a slicing step of the polycrystalline silicon ingot is required, a slice loss is generated by the thickness of the wire or the inner peripheral blade. For this reason, the overall yield is deteriorated, and as a result, it is difficult to provide a low-priced sheet.

  As a method for producing a silicon sheet without a slicing step, there is a silicon plate continuous casting method (see Patent Document 2). In this method, molten silicon is supplied to a horizontal heating mold, a dummy graphite plate is inserted in the horizontal direction, and the tip of the graphite plate is brought into direct contact with the silicon melt under the thickness control plate. Then, when the silicon melt is fixed to the tip of the graphite plate, the silicon plate is pulled out by using a roller. Further, the silicon plate is continuously manufactured by cooling with the gas from the gas blowing pipe of the cooling device. Therefore, since the thickness of the silicon plate is controlled by pulling out the silicon plate from under the thickness control plate, it is difficult to control the thickness of 600 μm or less as used in solar cells.

  As another silicon sheet manufacturing method, there is a silicon ribbon manufacturing method (see Patent Document 3). The manufacturing apparatus used in this method is roughly composed of a silicon heating and melting part and a rotary cooling body made of a heat-resistant material. A silicon ribbon is formed on the surface of the rotating cooling body by bringing the rotating cooling body, in which one end of the carbon net is wound in advance, into direct contact with the silicon melt. When the formed silicon ribbon is taken out, the silicon ribbon following the silicon fixed to the carbon net is taken out continuously by rotating the rotating cooling body and pulling out the wound carbon net. Therefore, when the thickness of the grown silicon is very thin, the silicon ribbon reacts with the carbon net and the silicon ribbon becomes brittle. It must be stopped and productivity is reduced.

  In addition, there is a mechanism to pressurize and supply the silicon melt to the outer peripheral surface of the rotary cooling body by the pressure of the jet, but since the pressure is applied by stirring the silicon melt, the pressure is applied to the grown silicon. In addition, defects may be introduced. The growth rate of silicon includes the heater temperature for maintaining the silicon in a molten state, the immersion depth, the type and flow rate of the cooling gas circulating in the rotating cooling body, and the rotating speed of the rotating cooling body. It is controlled by a number of factors. Therefore, it is technically difficult to pull out the silicon ribbon stably while controlling the growth rate. Furthermore, a wedge body is provided to scrape the silicon chips remaining on the surface of the rotary cooling body. However, the surface of the rotary cooling body may be damaged by the wedge body that is in direct contact with the surface of the rotary cooling body that is the growth surface. There is a problem that the uniformity of the growing silicon ribbon is impaired by removing the applied release material.

Therefore, in order to solve these problems and to provide a sheet that can be mass-produced at low cost, is thin, and has excellent flatness, the substrate having the uneven portions as shown in FIGS. 2 and 3 is cooled, A method for producing a sheet, wherein the surface of a concavo-convex portion of a cooled substrate is brought into contact with a melt of a material containing at least one of a metal material and a semiconductor material, and crystals of the melted material are grown on the surface of the concavo-convex portion. Has been proposed (see Patent Document 4). Moreover, as shown in FIG. 4, a sheet manufacturing apparatus is proposed that forms a sheet on the surface of a substrate by holding the substrate in a substrate transport mechanism and immersing the substrate in a melt (Patent Document 5 and Patent Document). 6). A sheet having a good columnar crystal structure can be produced by the production apparatus and the production method.
Japanese Unexamined Patent Publication No. 6-64913 JP-A-7-256624 Japanese Patent Laid-Open No. 10-29895 JP 2001-223172 A JP 2003-59849 A JP 2003-183015 A

  The manufacturing method proposed in Patent Document 4 uses graphite, silicon nitride, and silicon carbide as a substrate, particularly when manufacturing a polycrystalline sheet of silicon, and the substrate has a thermal expansion coefficient different from that of silicon. The polycrystalline sheet is peeled off from the substrate by actively using it. However, in the manufacturing apparatus proposed in Patent Document 5 and Patent Document 6, since the polycrystalline sheet is manufactured under the substrate, there is a possibility that the polycrystalline sheet falls due to gravity.

  The subject of this invention is preventing the fall of the crystal sheet formed on the board | substrate, and recovering a crystal sheet reliably. Another object of the present invention is to provide a method for mass-producing a thin crystal sheet having excellent flatness at low cost. Furthermore, it is to provide a large amount of inexpensive solar cells by reliably recovering the crystal sheet to reduce raw material loss.

The method for producing a crystal sheet of the present invention is a method for producing a crystal sheet by bringing one or both surfaces of a principal surface of a cooled substrate into contact with a melt of the sheet material and growing crystals of the sheet material on the substrate. And
The sheet material contains a metal material and / or a semiconductor material,
The substrate is characterized in that it has a base material made of a sheet material and a film covering a part or the entire surface of the base material, and the film is made of a material different from the sheet material. It is preferable that the substrate to be used has an uneven surface having a convex pitch of 0.05 mm or more and 5 mm or less on one side or both sides of the main surface.

  Preferably, the sheet material is silicon, the entire surface of the base material is covered with a silicon oxide film, and the polycrystalline silicon sheet grown on the substrate is removed by removing the silicon oxide film. A thermal oxide film is suitable for the silicon oxide film. The silicon oxide film can be removed with a hydrogen fluoride solution.

  On the other hand, it is preferable that the sheet material is silicon, one side of the main surface of the base material is covered with a silicon oxide film, and the polycrystalline silicon sheet grown on the substrate is removed by removing the silicon oxide film. . A thermal oxide film is suitable for the silicon oxide film, and a film formed by an atmospheric pressure CVD method or a low pressure CVD method can be preferably used. The silicon oxide film can be removed with a hydrogen fluoride solution.

  The silicon oxide film to be formed preferably has a thickness of 0.01 mm or more and 1 mm or less. In addition, the polycrystalline silicon solar battery cell of the present invention is manufactured using a crystal sheet manufactured by such a method.

  According to the present invention, the crystal sheet formed on the substrate can be prevented from falling and the crystal sheet can be reliably recovered.

  The method for producing a crystal sheet of the present invention is illustrated in FIG. First, the surface of a base material 52 as shown in FIG. 5A is covered with a film 53 to form a substrate 51 (FIG. 5B). Next, one or both surfaces of the principal surfaces 51a and 51b of the cooled substrate 51 are brought into contact with the melt 54 of the sheet material, and the crystal of the sheet material is grown on the substrate 51 to produce the crystal sheet 55 (FIG. 5 (c)). The crystal sheet 55 can be removed by removing the film 53 (FIG. 5D).

  The sheet material used contains a metal material and / or a semiconductor material. For example, a semiconductor material such as silicon, germanium, gallium, arsenic, indium, phosphorus, boron, antimony, zinc, or tin can be used, and a metal material such as aluminum, nickel, or iron can be included. If the temperature of the melt of the sheet material is in the vicinity of the melting point of the material to be used, the surface of the molten metal may be solidified when the substrate being cooled comes into contact with the melt. preferable. For example, when the sheet material is silicon, the temperature of the melt is desirably adjusted to 1430 ° C. or higher, which is higher than the melting point 1420 ° C. of silicon.

  The substrate to be used has a base material made of a sheet material and a film covering a part or the entire surface of the base material. In FIG. 1, the example of the board | substrate 1 which the film | membrane 3 covers the whole surface of the base material 2 is shown. FIG. 6B shows an example of a substrate 61 in which a part of the base material 62 is covered with a film 63. This film is made of a material different from the sheet material.

  In the present invention, in order to eliminate the difference in thermal expansion coefficient between the base material of the substrate and the crystal sheet to be manufactured, the same material is selected for the base material of the substrate and the crystal sheet. For example, when the crystal sheet to be manufactured is made of silicon, the base material of the substrate is also made of silicon. Thus, by making the base material and the crystal sheet have the same coefficient of thermal expansion, when the melt of the sheet material cools down and crystallizes on the substrate, the sheet material is peeled from the substrate due to thermal stress, Cracking and falling off can be effectively prevented. Accordingly, the crystal sheet can be reliably recovered, the raw material loss is reduced, and a large amount of crystal sheets can be supplied at low cost, so that an inexpensive polycrystalline silicon solar cell can be provided.

  The film on the substrate surface is formed of a material different from the sheet material, that is, a material different from the base material from the viewpoint of facilitating the recovery of the crystal sheet. As a material for the film, silicon oxide, silicon carbide, silicon nitride, pyrolytic carbon, or the like can be used.

  The substrate preferably has irregularities on one or both sides of the main surface. When the cooled substrate is immersed in the melt of the sheet material, a crystal nucleus of the sheet material is generated at the tip of the convex portion on the substrate, and the crystal grown from the adjacent tip contacts the concave portion, and the crystal sheet Can be grown stably. The convex portion is effective as a line as shown in FIG. 2, and is also effective as a dot as shown in FIG. The pitch of the convex portions is preferably 0.05 mm or more from the viewpoint of increasing the grain size of the growing crystal. Moreover, the pitch of a convex part is 5 mm or less at the point which raises the growth rate of a crystal sheet by increasing a contact with a melt. Therefore, the thickness of the crystal sheet can be adjusted by the pitch of the convex portions. The recess can be a V-shaped groove or a U-shaped groove. The depth of the groove is preferably 0.05 mm or more. If the depth of the groove is shallower than 0.05 mm, the melt reaches the bottom of the groove, and the contact area becomes large and adheres, so that it is difficult to peel off the crystal sheet. The substrate is used after cooling in order to increase crystal growth. Cooling includes direct cooling or indirect cooling. The refrigerant is preferably an inert gas such as nitrogen or argon from the viewpoint of preventing oxidation of the crystal sheet.

  The polycrystalline silicon sheet is grown by removing the silicon oxide film by growing the polycrystalline silicon sheet on the substrate in which the sheet material is silicon and the entire surface of the base material made of silicon or one surface of the main surface is covered with the silicon oxide film. By removing, a polycrystalline silicon sheet having a thickness of 0.1 mm or more and 1 mm or less can be collected. In addition, this method makes it possible to recycle the used substrate at the same time. A method for producing a polycrystalline silicon sheet is illustrated in FIG. First, one of the main surfaces 62a and 62b of the silicon base material 62 as shown in FIG. 6A is covered with the silicon oxide film 63 to form the substrate 61 (FIG. 6B). Next, the cooled substrate 61 is brought into contact with the silicon melt 64, which is a sheet material, and a crystal of the sheet material is grown on the substrate 61 to produce a crystal sheet 65 (FIG. 6C). The crystal sheet 65 can be removed and collected by removing the silicon oxide film 63 (FIG. 6D).

  The silicon oxide film is preferably formed to a thickness of 0.01 mm or more and 1 mm or less in order to separate the polycrystalline silicon sheet and the substrate. The silicon oxide film can be formed by thermally oxidizing the surface of silicon as a base material. In addition, after the entire surface of silicon is thermally oxidized, a photoresist is applied to one surface, and the surface not coated with the photoresist is treated with a hydrogen fluoride solution to remove the thermal oxide film on the surface. A silicon oxide film can be formed on one side. In addition, there is a method of depositing silicon oxide on the surface of the base material by an atmospheric pressure CVD method or a low pressure CVD method. On the other hand, the removal of the silicon oxide film can be easily performed with a hydrogen fluoride solution.

Example 1
In this example, a crystal sheet was manufactured using an apparatus 40 as shown in FIG. The apparatus 40 includes a substrate transfer mechanism 41. The substrate transfer mechanism 41 has a horizontal movement motor 41b. The substrate transfer mechanism 41 and the substrate 46 held by the substrate transfer mechanism 41 are moved by the horizontal movement motor 41b. It is possible to move freely in the horizontal direction 42.

  The horizontal movement shaft 42a is connected to a vertical movement motor 43b, and the horizontal movement shaft 42a is movable along the vertical movement shaft 43a. That is, the vertical movement shaft 43a is a linear rail with teeth, and the vertical movement motor 43b is operated to move the horizontal movement shaft 42a, the substrate transport mechanism 41, and the substrate 46 in the vertical direction 43. It is possible to move freely. Therefore, the substrate 46 can freely move in the horizontal direction 42 and the vertical direction 43. Below the horizontal moving shaft 42a, a crucible 44 for holding the melt 45 and a heating mechanism 44a for heating the melt 45 are arranged. Above the melt 45, a heat shielding mechanism 44b is arranged.

  Using the apparatus 40 having such a structure, first, silicon mixed with boron was used as a sheet material so as to have a specific resistance of 2 Ω · cm, and heated to prepare a melt at 1430 ° C. Next, as shown in FIG. 4, after mounting the substrate 46 on the substrate transport mechanism 41 at a position A away from the melt 45, the substrate 46 was cooled by blowing nitrogen gas at 600 L / min (not shown). Absent.). Next, after the horizontal movement motor 41b is driven and the substrate 46 is transported to the position just above the melt 45, the horizontal movement motor 41b and the vertical movement motor 43b are driven independently, whereby the substrate is moved. The substrate 46 was immersed in the silicon melt 45 while giving an arbitrary trajectory to 46. Subsequently, a polycrystalline silicon sheet was grown on the substrate 46 by taking out the substrate 46 from the melt 45. Finally, after the substrate 46 is transported to the position B away from the melt 45 by the horizontal direction moving motor 41b and the vertical direction moving motor 43b, the substrate 46 is detached from the substrate transporting mechanism 41, and then the polycrystal. The characteristic silicon sheet was collected.

  The manufacturing process of this polycrystalline silicon sheet is shown in FIG. First, the surface of the base material 52 as shown in FIG. 5A was covered with a film 53 to form a substrate 51 (FIG. 5B). The base material 52 was made of silicon containing boron, which is the above-described sheet material, and the base material was thermally oxidized to form a silicon oxide film having a thickness of 0.1 mm on the entire surface. Next, one of the principal surfaces 51a and 51b of the cooled substrate 51 is brought into contact with the silicon melt 54, and polycrystalline silicon is grown on the substrate 51 to form a crystal sheet 55 (FIG. 5 ( c)) Subsequently, the crystal sheet 55 was removed by immersing in a hydrogen fluoride solution and dissolving the film 53 (FIG. 5D). The thickness of the obtained crystal sheet was 0.5 mm at the thick part and 0.3 mm at the thin part. In addition, as shown in FIG. 2, the board | substrate has a linear convex part, the pitch of a convex part is 1 mm, and the thing which has a V-shaped groove | channel in the recessed part was used. There is no peeling or falling of the crystal sheet between the immersion of the substrate 51 in the silicon melt 54 and the removal of the crystal sheet 55, and no cracks are observed in the collected polycrystalline silicon sheet. It was.

Example 2
Example 1 except that the substrate has a dot-like convex portion as shown in FIG. 3, the pitch of the convex portion is 1 mm, and the concave portion has a V-shaped groove. A crystal sheet was produced in the same manner. The thickness of the obtained crystal sheet was 0.6 mm at the thick part and 0.4 mm at the thin part. There was no peeling or falling of the crystal sheet between the immersion of the substrate in the silicon melt and the removal of the crystal sheet, and no cracks were observed in the collected polycrystalline silicon sheet.

Example 3
A silicon oxide film having a thickness of 0.1 mm is formed on one side of the main surface of the base material by atmospheric pressure CVD as a substrate, and the surface on which the silicon oxide film is formed is brought into contact with a silicon melt. A crystal sheet was produced in the same manner as in Example 1 except that crystalline silicon was grown on the substrate. The thickness of the manufactured crystal sheet was 0.6 mm at the thick part and 0.3 mm at the thin part. There was no peeling or falling of the crystal sheet between the immersion of the substrate in the silicon melt and the removal of the crystal sheet, and no cracks were observed in the collected polycrystalline silicon sheet.

Example 4
Using the polycrystalline silicon sheet produced in Example 1, a solar cell was produced. First, the polycrystalline silicon sheet was etched with a mixed solution of nitric acid and hydrofluoric acid, washed, and then alkali-etched with a sodium hydroxide solution. Next, POCl ₃ was diffused to form an n layer on the p-type substrate. After the PSG film formed on the sheet surface was removed with hydrofluoric acid, a silicon nitride film was formed on the n layer on the light-receiving surface side of the solar cell using plasma CVD.

Subsequently, the n layer formed on the back surface side of the solar cell is etched and removed with a mixed solution of nitric acid and hydrofluoric acid, the p substrate is exposed, and the back electrode and the p ⁺ layer are formed thereon. Formed simultaneously. Next, the electrode on the light receiving surface side was formed by a screen printing method. Thereafter, solder dipping was performed to manufacture a solar cell.

About the manufactured solar cell, the cell characteristic was measured under irradiation of AM1.5 and 100 mW / cm < ² >. The measurement results were a short-circuit current of 31 mA / cm ² , an open-circuit voltage of 590 mV, a fill factor of 0.70, and an efficiency of 12.3%.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  A method for mass-producing a thin crystal sheet having excellent flatness at low cost can be provided.

It is sectional drawing which shows the structure of the board | substrate preferably used in this invention. It is a perspective view which shows the shape of the board | substrate preferably used in this invention. It is a perspective view which shows the shape of the board | substrate preferably used in this invention. It is a schematic diagram which shows the example of the manufacturing apparatus used in this invention. It is process drawing which shows the manufacturing method of this invention. It is process drawing which shows the other manufacturing method of this invention.

Explanation of symbols

  1, 51, 61 Substrate, 2, 52, 62 Base material, 3, 53, 63 Film, 54, 64 Melt, 55, 65 Crystal sheet.

Claims (11)

A method for producing a crystal sheet by contacting one or both surfaces of a principal surface of a cooled substrate with a melt of the sheet material and growing crystals of the sheet material on the substrate,
The sheet material contains a metal material and / or a semiconductor material,
The method for producing a crystal sheet, wherein the substrate has a base material made of the sheet material and a coating covering a part or the entire surface of the base material, and the coating is made of a material different from the sheet material.   2. The method for producing a crystal sheet according to claim 1, wherein the substrate has irregularities having a convex pitch of 0.05 mm or more and 5 mm or less on one side or both sides of the main surface.   The sheet material is silicon, the entire surface of the base material is covered with a silicon oxide film, and the polycrystalline silicon sheet grown on the substrate is removed by removing the silicon oxide film. Item 3. A method for producing a crystal sheet according to Item 1 or 2.   The method for manufacturing a crystal sheet according to claim 3, wherein the silicon oxide film is a thermal oxide film.   The method for producing a crystal sheet according to claim 3 or 4, wherein the silicon oxide film is removed by a hydrogen fluoride solution.   The sheet material is silicon, one side of the main surface of the base material is covered with a silicon oxide film, and the polycrystalline silicon sheet grown on the substrate is removed by removing the silicon oxide film. The method for producing a crystal sheet according to claim 1 or 2.   The method for manufacturing a crystal sheet according to claim 6, wherein the silicon oxide film is a thermal oxide film.   The method for producing a crystal sheet according to claim 6, wherein the silicon oxide film is formed by an atmospheric pressure CVD method or a low pressure CVD method.   The method for producing a crystal sheet according to claim 6, wherein the silicon oxide film is removed with a hydrogen fluoride solution.   The method for manufacturing a crystal sheet according to claim 3, wherein the silicon oxide film has a thickness of 0.01 mm or more and 1 mm or less.   A polycrystalline silicon solar cell manufactured using the crystal sheet manufactured by the method according to claim 3.

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