JP5057770B2 - Method for producing solid phase sheet - Google Patents

Description

  The present invention relates to a method for producing a solid phase sheet in which a semiconductor material melt is solidified and grown on a substrate surface, and more particularly to a method for producing a polycrystalline silicon sheet for solar cells. Moreover, it is related with the radiation reflecting plate used for the manufacturing method of the solid-phase sheet | seat.

  Conventionally, a solid phase sheet of polycrystalline silicon is manufactured by gradually cooling a silicon melt contained in a mold over time, cutting the resulting polycrystalline ingot on a block, and then slicing the block. Therefore, the cost increase due to slicing and the loss of silicon are large.

  As a method for solving such a problem and manufacturing a solid phase sheet of polycrystalline silicon in a large amount at a low cost, a method that does not require a slicing step is known (see Patent Document 1). In this method, a plurality of carbon (graphite) substrates are swirled in a sealed processing chamber, the carbon substrate is immersed in a silicon melt held in a crucible, a crystal sheet is deposited on the substrate, and a solid phase sheet is produced. (See Patent Document 1). By this manufacturing method, the waiting time in the post-process can be shortened, and damage and defects of the semiconductor substrate can be prevented.

  On the other hand, as an apparatus for producing a silicon solid-phase sheet using a square crucible, an example in which a heat insulating material is installed on the upper surface of the square crucible is known (see Patent Document 2). By installing a heat insulating material on the upper surface of the square crucible, the variation in temperature distribution in the horizontal direction of the crucible is reduced, and problems such as furnace material damage, material melt supercooling, solidification and crucible cracking are avoided. be able to.

  Further, it is a method related to a single crystal pulling method by the Czochralski (CZ) method, and by suppressing the solidification growth of the melt in the vicinity of the crucible wall, the surface temperature of the melt is kept as low as possible and the pulling of the crystal is made fast. A method intended to do this has been introduced (see Patent Document 3). This method is intended to suppress solidification growth by increasing the melt temperature in the vicinity of the crucible wall by installing a radiation reflecting plate suspended by a wire in the vicinity of the crucible wall.

Furthermore, as in Patent Document 2, a solid-phase sheet manufacturing apparatus in which heat insulating means is provided on the upper surface of the crucible and the heat insulating means is movable is introduced (see Patent Document 4). In this solid-phase sheet manufacturing apparatus, by making the heat insulating means movable, the horizontal temperature distribution of the molten silicon in a square crucible or the like can be more evenly distributed and the melt can be covered. Examples of heat insulation materials are illustrated.
JP 2002-289544 A JP 2005-29405 A JP-A-5-43383 JP 2006-182626 A

  The melt temperature for producing the solid-phase sheet is around 1430 ° C. and is close to the melting point of silicon, so that the melt may start to solidify due to the temperature distribution. In particular, the melt in the vicinity of the crucible wall is a region where the inner wall of the crucible escapes radiant heat, and crystal nuclei are likely to be generated.

  In the method for producing a solid phase sheet described in Patent Document 1, since the crucible for containing the silicon melt is small and a circular crucible, there is little variation in the temperature distribution of the melt, and the solidification growth of the melt. Was not a problem. However, if the crucible is changed to a rectangular shape in order to increase the immersion efficiency, the variation in temperature distribution will increase, especially the temperature drop on the long side will be seen, and the melt will solidify and grow from the long side, and the substrate will be immersed. Inhibits.

  Moreover, although the solid-phase sheet manufacturing apparatus described in Patent Document 2 uses a rectangular crucible, the size of the square crucible is relatively small, and the melt retention time is on the order of several days. . Further, the dispersion of the temperature distribution in the horizontal direction of the melt is small, and the solidification that grows from the long side of the square crucible is about 10 mm. However, when the square crucible becomes large and the holding days are on the order of several weeks, solidification generated on the long side of the square crucible gradually grows and inhibits immersion of the substrate.

  On the other hand, in the single crystal pulling method introduced in Patent Document 3, the radiation reflector is installed on the melt surface in the form of being hung by a wire, and therefore the radiation reflector is heated only by radiant heat from the silicon melt. Is done. Therefore, the radiation reflecting plate itself does not reach a high temperature, and the radiation reflecting plate itself does not radiate heat enough to suppress solidification of the melt.

  Moreover, although the example which installs a heat insulating material on a melt is also shown in the Example for the manufacturing apparatus described in patent document 4, although a heat insulating material is in contact with the crucible upper surface, it is movable. Therefore, the degree of contact with the crucible is small and the amount of heat conducted from the crucible itself is not large. Therefore, as in the example of Patent Document 3, since the heat insulating material is heated only by the radiant heat from the silicon melt, the heat insulating material itself does not become a high temperature, and the crucible is enlarged and the melt is held for a long time. Suppression of solidification growth near the crucible wall is difficult.

  An object of the present invention is a method for continuously producing a solid-phase sheet by immersing a substrate in a semiconductor material melt, which suppresses solidification occurring near the interface between the inner wall of the crucible and the semiconductor material melt. Another object of the present invention is to provide a method for producing a solid phase sheet capable of continuous production. Another object of the present invention is to provide a radiation reflector used in such a manufacturing method.

  The present invention relates to a method for manufacturing a solid phase sheet in which a semiconductor material melt is accommodated in a crucible and a substrate is immersed in the semiconductor material melt to produce a solid phase sheet on the surface of the substrate. A radiation reflector is provided in contact with both sides of the outer surface, and the radiation reflector is provided with a radiation reflector capable of reflecting radiation from the semiconductor material melt, and the radiation reflector is disposed immediately above the semiconductor material melt. It is characterized by that. When the upper surface of the crucible has a substantially rectangular shape, a mode in which a radiation reflector is provided on the long side of the rectangle is preferable. Moreover, the aspect in which the radiation reflection part of a radiation reflection plate has a part which cross | intersects the plane which a crucible upper surface and a radiation reflection plate contact | connect is suitable.

  The radiation reflector of the present invention contains a semiconductor material melt in a crucible and radiates the solid phase sheet for use in a method for producing a solid phase sheet by immersing the substrate in the semiconductor material melt. Reflecting plate, an outer surface contact portion that can contact the outer surface of the crucible, an upper surface contact portion that can contact the upper surface of the crucible, and toward the crucible melt storage portion when installed on the crucible And a radiation reflecting portion capable of reflecting radiation from the melt. It is preferable that the radiation reflecting portion of the radiation reflecting plate has a portion located below the surface where the radiation reflecting plate and the upper surface of the crucible are in contact.

  According to the present invention, it is possible to suppress the growth of solidification generated from the vicinity of the boundary between the melt of the semiconductor material and the inner wall of the crucible, so that the number of days that can be continuously produced can be extended.

  The method for producing a solid phase sheet of the present invention includes, for example, immersing a substrate for solid phase sheet growth in a melt of a semiconductor material such as silicon held in a graphite crucible heated by induction heating. This is a method for producing a solid-phase sheet by crystal growth of a melt on a substrate surface. Further, a radiation reflecting plate in contact with both the upper surface of the crucible and the outer surface of the crucible is provided. The radiation reflecting plate includes a radiation reflecting portion capable of reflecting radiation from the semiconductor material melt, and the radiation reflecting portion is disposed immediately above the semiconductor material melt. Therefore, radiant heat from the semiconductor material melt can be reflected by the radiation reflecting portion. Furthermore, the radiation reflector itself becomes high temperature by the conduction heat from the crucible, and heat can be radiated from the radiation reflector itself to the vicinity of the tangent line between the molten metal surface of the semiconductor melt and the crucible. For this reason, the effect of suppressing solidification growth near the crucible wall is great.

  When the upper surface of the crucible has a substantially rectangular shape, the radiation reflector is preferably provided on the long side of the rectangle. Normally, when a rectangular crucible is used, solidification growth occurs preferentially from the vicinity of the crucible wall on the long side, but the solidification growth on the long side is suppressed by installing a radiation reflector on the long side. can do. Moreover, the aspect in which the radiation reflection part of a radiation reflection plate has a part which cross | intersects the plane which a crucible upper surface and a radiation reflection plate contact | connect is preferable. If the radiation reflector has a portion that intersects the flat surface where the upper surface of the crucible and the radiation reflector are in contact, the radiation reflector receives the radiation heat from the inner wall of the crucible, which is stronger than the radiation from the silicon melt, and emits this radiation heat. As a result, solidification growth near the crucible wall can be more effectively suppressed.

  In FIG. 1, the perspective view of the crucible used when implementing the manufacturing method of the solid-phase sheet | seat of this invention is illustrated. When a crucible 105 having a substantially rectangular crucible upper surface 101 as shown in FIG. 1 is heated by induction heating, the magnetic flux density is highest at the corners and lower in the order of the short side and the long side, and the respective temperatures are also the same. The corner is the highest and the long side is the lowest. When producing a solid phase sheet from the semiconductor material melt 104, the temperature of the semiconductor material melt 104 is set near the melting point in order to increase the growth rate of the solid phase sheet on the substrate. As a result, solidification growth from the vicinity of the long side increases.

Further, once solidified, solidification does not melt by itself in a steady state. For example, in the case of silicon melt, the emissivity of silicon melt is about 0.27, whereas the emissivity of solid silicon is about 0.55. The outflow energy E of heat due to radiation is expressed by E = εδT ⁴ . Here, ε is the emissivity, δ is the Stefan-Boltzmann coefficient, and T is the temperature. Therefore, in the case of silicon at the same temperature, the solid has an energy outflow about twice that of the melt. For this reason, the solidification generated in the vicinity of the inner wall of the crucible is not melted by itself and the outflow of energy is large, so that the solidification growth is promoted.

  Therefore, as shown in FIG. 1, the radiation reflector 103 is installed so as to cover the vicinity of the interface between the inner wall of the crucible 105 and the semiconductor material melt 104. Here, when the interface between the inner wall of the crucible 105 and the semiconductor material melt 104 is heated, not only the radiation heat from the semiconductor material melt 104 is reflected by the radiation reflector 103, but also the radiation reflector 103 itself is heated to a high temperature. Thus, it is more effective to add heat radiation from the radiation reflector 103 itself. In order to increase the temperature of the radiation reflecting plate 103, it is preferable that the radiation reflecting plate 103 has a structure in contact with both the crucible upper surface 101 and the crucible outer surface 102 and receives heat from the crucible 105. According to such an embodiment, heating can be performed more effectively than in the case of heating only by radiant heat from the semiconductor material melt 104.

  The radiation reflecting plate 103 includes a portion heated only by radiation from the semiconductor material melt 104 and a portion heated directly from the crucible 105, so that a large temperature distribution occurs in the plane of the radiation reflecting plate. For this reason, when ceramic or graphite such as alumina is used as the material of the radiation reflector 103, it cannot withstand the large internal stress due to the temperature distribution described above and is easily destroyed. Therefore, the material of the radiation reflector 103 is preferably a carbon fiber reinforced carbon material (composite carbon) that has heat resistance and is resistant to thermal stress. Further, it is preferable to use a refractory metal such as tantalum or molybdenum.

  In FIG. 1, the heat insulating material is not shown in order to show the contact relationship between the radiation reflector 103 and the crucible outer surface 102. FIG. 2 is a cross-sectional view of a crucible used when the method for producing a solid phase sheet of the present invention illustrated in FIG. 1 is cut along a plane including II-II. As shown in FIG. 2, when heating the crucible 205 for holding the semiconductor material melt 204, normally, the insulating material 206 surrounds the crucible 205 to save heating energy and protect the induction heating coil 207. Cover. The heat insulating material 206 used at this time is preferably a heat-resistant, high heat-insulating alumina felt or carbon fiber felt. Further, as a method for fixing the radiation reflecting plate 203, a mode in which the crucible 205 and the heat insulating material 206 are sandwiched is desirable.

  FIG. 3 is a cross-sectional view of the crucible used in carrying out the method for producing a solid phase sheet of the present invention illustrated in FIG. 1 in the same manner as in FIG. 2, and is a more effective radiation reflector. The heating method is shown. The radiation reflector 303 is heated by heat conduction from the crucible 305 and radiant heat from the semiconductor material melt 304. By using the radiant heat from the crucible inner wall 305a, the radiation reflector 303 is more effectively heated. It becomes possible.

  For example, when the material of the crucible 305 is graphite, the emissivity of graphite is approximately 1.0, so that a very large energy is radiated as compared with the emissivity 0.27 from the silicon melt. Therefore, in order to effectively receive the radiant heat from the crucible inner wall 305a by the radiation reflector 303, the radiation reflector of the radiation reflector 303 is a surface where the upper surface of the crucible 305 and the radiation reflector 303 are in contact as shown in FIG. A shape that intersects 308 is preferred. In other words, the radiation reflector includes an outer surface contact portion that can contact the crucible outer surface, an upper surface contact portion that can contact the upper surface of the crucible, and a crucible melt container when installed on the crucible. A radiation reflection part capable of reflecting radiation from the melt toward the part, and the radiation reflection part is a surface where the crucible upper surface and the radiation reflection plate are in contact with each other when the radiation reflection plate is installed in the crucible. An embodiment having a portion located on the lower side is preferable. When the radiation reflecting plate 303 has such a radiation reflecting portion, the crucible inner wall receives radiation heat from both the melt 304 and the crucible inner wall 305a and radiates radiation heat toward the melt near the crucible inner wall. The effect of suppressing the coagulation growth of the nearby melt can be enhanced.

  FIG. 4 is also a cross-sectional view of the crucible used when the method for producing the solid phase sheet of the present invention illustrated in FIG. 1 is cut in the same manner as in FIG. The heating method is shown. 3 exemplifies a mode in which the cross-sectional shape of the radiation reflector is “U” -shaped, but in addition, as shown in FIG. 4, the radiation reflector has a surface 408 where the crucible upper surface and the radiation reflector are in contact with each other. Similarly, the radiation reflecting plate 403 can effectively use the radiation from the crucible inner wall, and the temperature of the radiation reflecting plate 403 can be increased. Although the aspect which a radiation reflection part cross | intersects the surface which a crucible upper surface and a radiation reflecting plate contact | connect is illustrated in FIG. 3 and FIG. 4, this is an example and is not limited to these examples. Moreover, although the crucible whose crucible upper surface is substantially rectangular shape was demonstrated, application of this invention is not limited to a substantially rectangular crucible. For example, when the upper surface of the crucible is circular, the variation in temperature distribution in the horizontal direction of the crucible is smaller than that of a rectangular crucible, but as the semiconductor material melt temperature is lowered, the melting of the semiconductor material is reduced. The problem that solidification occurs and grows from the boundary between the liquid and the inner wall of the crucible is inevitable. Therefore, the problem of crystal solidification growth can be avoided by installing a radiation reflector on the entire circumference of the upper surface of the circular crucible.

  An example of a method for producing a solid phase sheet is shown, but the present invention is not limited to this example.

Example 1
FIG. 5 illustrates a production apparatus used when the solid phase sheet production method of the present invention is carried out. A silicon raw material whose boron concentration was adjusted so that the specific resistance of the produced solid phase sheet was 2 Ω · cm was placed in a high-purity graphite crucible 505 and installed in the apparatus as shown in FIG. The upper surface of the crucible 505 used at this time was rectangular, and the size of the inner diameter was 600 mm × 400 mm. A radiation reflector 503 was installed on each of the two long sides of the crucible 505. The radiation reflector 503 has a width of 400 mm in the long side direction, a contact length of 30 mm with the upper surface of the crucible, a projecting length of 60 mm on the melt surface, and a contact length of 60 mm with the outer surface of the crucible. What consists of material (composite carbon) was used. The radiation reflecting plate 503 is disposed so as to be sandwiched between the heat insulating material 506 made of alumina felt and the crucible 505. As a result, the radiation reflecting portion capable of reflecting the radiation from the melt of the semiconductor material has a melting point of the crucible. It was arrange | positioned just above the liquid storage part.

  Next, the inside of the chamber 502 was evacuated, and then Ar gas was introduced. Ar gas was always introduced from the upper part of the chamber at 100 L / min while maintaining 800 hPa. Next, the set temperature of the control thermocouple of the induction heating coil 507 around the crucible 505 is set to 1500 ° C. and heated to completely melt the silicon. Since the initially charged silicon becomes low in volume when dissolved, an additional silicon raw material is added to make the silicon hot water surface a predetermined height. Thereafter, the control temperature was set to 1430 ° C. and held for 30 minutes to stabilize the melt temperature.

  Thereafter, a substrate 513 of 200 mm × 200 mm size made of graphite was set at the tip of the immersion mechanism 512. Next, the substrate 513 was immersed in the silicon melt 504 at an immersion depth of 10 mm, and a solid phase sheet 511 was grown on the surface of the substrate. Thereafter, the substrate is transferred to the apparatus sub chamber 509 by the transfer conveyor 508, the gate valve 510 that partitions the sub chamber and the apparatus main body is closed, the sub chamber is evacuated by a rotary pump, replaced with the atmosphere, and then the solid phase sheet. The substrate in a state in which was formed was taken out of the sub chamber. In this way, continuous production for 14 days was performed. Thereafter, the induction heating coil was turned off to rapidly reduce the temperature, the crucible was taken out of the apparatus, and the radiation reflector was removed. Since the solidified 514 grown during the continuous production grows gradually, the crystal grains are fine. On the other hand, after the production is completed, the solidification that grows when the induction heating coil is turned off and the temperature is suddenly lowered is mainly acicular crystals, and can be clearly distinguished from the fine solidification 514 grown during continuous production. Therefore, it is possible to measure the amount of solidified 514 grown during continuous production. When the length from the inner wall of the crucible was measured for the silicon solidified 514 near the center of the long side grown during continuous production, it was about 25 mm.

  As a comparative example, continuous production was carried out for 14 days in the same manner as in the example except that the radiation reflector 503 was omitted, and then the distance from the inner wall of the crucible was measured for silicon solidification near the center of the long side of the crucible. As a result, it was about 75 mm. Since the distance between the crucible 505 and the substrate 513 is (400−200) / 2 = 100 mm, the distance between the inner wall of the crucible and the substrate when the substrate is immersed after continuous operation for 14 days is the case where the radiation reflector 503 is provided. Was 100−25 = 75 mm, and 100−75 = 25 mm when no radiation reflector was provided. If there is no gap between the inner wall of the crucible and the substrate, the substrate 513 and the silicon solidified 514 collide with each other, and there is a risk of causing damage to the apparatus. On the other hand, the growth rate of the silicon solidified 514 is 25 mm ÷ 14 days≈1.8 mm / day when the radiation reflector is provided, whereas it is 75 mm ÷ 14 days when the radiation reflector is not provided. ≈5.4 mm / day. Therefore, the possible number of days for continuous production is 100 mm ÷ 1.8 mm / day = 55.6 days when the radiation reflector is provided, whereas 100 mm ÷ 5 when the radiation reflector is not provided. 4 mm / day = 18.5 days. Therefore, it was found that the number of days that can be continuously produced is greatly increased by installing the radiation reflector 503.

  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.

  Since the solidification growth of crystals on the inner wall of the crucible can be suppressed, the number of days that can be continuously produced can be extended.

It is a perspective view of a crucible used when implementing the manufacturing method of the solid phase sheet of the present invention. It is sectional drawing of the crucible used when implementing the manufacturing method of the solid-phase sheet | seat of this invention. It is sectional drawing of the crucible used when implementing the manufacturing method of the solid-phase sheet | seat of this invention, and is a figure which shows the heating method of a more effective radiation reflecting plate. It is sectional drawing of the crucible used when implementing the manufacturing method of the solid-phase sheet | seat of this invention, and is a figure which shows the heating method of a more effective radiation reflecting plate. It is a figure which illustrates the apparatus used when implementing the manufacturing method of the solid-phase sheet | seat of this invention.

Explanation of symbols

  101 crucible upper surface, 102 crucible outer surface, 103, 203, 303, 403, 503 radiation reflector, 104, 204, 304 semiconductor material melt, 105, 205, 305, 505 crucible, 206, 506 heat insulating material, 207, 507 Induction heating coil, 305a crucible inner wall, 308, 408 surface where crucible upper surface and radiation reflector come into contact, 502 chamber, 504 silicon melt, 508 conveyor for conveyance, 509 equipment subchamber, 510 gate valve, 511 solid phase sheet, 512 Immersion mechanism, 513 substrate, 514 solidification.

Claims (2)

A method for producing a solid phase sheet in which a semiconductor material melt is accommodated in a crucible and a substrate is immersed in the semiconductor material melt to produce a solid phase sheet on the surface of the substrate,
The upper surface of the crucible has a substantially rectangular shape, and a radiation reflecting plate having an upper surface contact portion in contact with the upper surface of the crucible and an outer surface contact portion in contact with the outer surface of the crucible is arranged on both long sides of the rectangle on the upper surface of the crucible. The radiation reflector is provided with a radiation reflection portion capable of reflecting radiation from the semiconductor material melt so as to extend from the upper surface contact portion to the opposite side of the outer surface contact portion , and the radiation reflection portion is provided. A method for producing a solid phase sheet, which is disposed immediately above a melt of a semiconductor material and uses a carbon fiber reinforced carbon material, tantalum or molybdenum as a material of the radiation reflector. 2. The method for producing a solid phase sheet according to claim 1, wherein the radiation reflecting plate has a portion where a radiation reflecting portion is located below a lower surface of the upper surface contact portion .

Images