Single-Crystal Production Equipment and Single-Crystal Production Method

Abstract

Produced is a large single crystal with no crystal grain boundary, which is a high-quality single crystal that has a uniform composition in both the vertical and horizontal directions at an optimum dopant concentration. Provided is a single-crystal production equipment including, at least: a granular raw material supply apparatus which supplies a certain amount of a granular raw material downward; a granular raw material melting apparatus which heats and melts the granular raw material and supplies the thus obtained raw material melt downward; and a crystallization apparatus which allows a single crystal to precipitate out of a mixed melt that is formed upon receiving a melt formed by irradiating an infrared ray from a first infrared ray irradiation equipment to the upper surface of a seed single crystal and the raw material melt supplied from the granular raw material melting apparatus.

Claims

1. A single-crystal production equipment for producing a large single crystal by melting a granular raw material using a granular raw material melting apparatus, supplying the thus obtained raw material melt into a melt formed on the upper surface of a seed single crystal below to generate a mixed melt, and then allowing a solid to precipitate out of said mixed melt as a single crystal, wherein said single-crystal production equipment comprises, at least: a granular raw material supply apparatus which supplies a certain amount of said granular raw material downward; said granular raw material melting apparatus which heats and melts said granular raw material supplied from said granular raw material supply apparatus and supplies the thus obtained raw material melt downward; and a crystallization apparatus which allows a single crystal to precipitate out of said mixed melt that is formed upon receiving a melt formed by irradiating an infrared ray from a first infrared ray irradiation equipment to the upper surface of said seed single crystal and said raw material melt supplied from said granular raw material melting apparatus.

2. The single-crystal production equipment according to claim 1, wherein said granular raw material supply apparatus comprises: a hopper which stores said granular raw material; and a granular raw material quantitative supply equipment which controls said granular raw material in said hopper to be supplied at a prescribed rate and supplies a certain amount of said granular raw material downward.

3. The single-crystal production equipment according to claim 1, wherein said granular raw material supply apparatus comprises a granular raw material scraping equipment which scrapes said granular raw material out of said hopper and supplies said granular raw material downward.

4. The single-crystal production equipment according to claim 2, wherein said granular raw material supply apparatus comprises a supply pipe through which said granular raw material supplied from said granular raw material quantitative supply equipment is supplied to a prescribed position of said granular raw material melting apparatus below.

5. The single-crystal production equipment according to claim 4, wherein a material of said supply pipe is quartz.

6. The single-crystal production equipment according to claim 2, wherein said hopper comprises an attachment-detachment mechanism for attaching and detaching a storage container storing said granular raw material.

7. The single-crystal production equipment according to claim 6, wherein said attachment-detachment mechanism has an atmosphere controlling function of arbitrarily controlling the atmosphere inside said attachment-detachment mechanism and said storage container.

8. The single-crystal production equipment according to claim 1, wherein said granular raw material melting apparatus and said crystallization apparatus are arranged inside a single-crystal production chamber.

9. The single-crystal production equipment according to claim 2, wherein said granular raw material supply apparatus is arranged inside said single-crystal production chamber.

10. The single-crystal production equipment according to claim 9, comprising an atmosphere control equipment which connects the inside of said hopper with said single-crystal production chamber, or controls the inside of said hopper and said single-crystal production chamber to have the same atmosphere.

11. The single-crystal production equipment according to claim 2, wherein said hopper is constituted by plural hoppers in which granular raw materials having different compositions are each stored.

12. The single-crystal production equipment according to claim 1, wherein said granular raw material melting apparatus comprises: a granular raw material melting vessel which receives said granular raw material; and a vessel heating equipment which heats said granular raw material melting vessel and thereby melts said granular raw material in said granular raw material melting vessel.

13. The single-crystal production equipment according to claim 12, wherein said granular raw material melting vessel comprises: a melting section where said granular raw material is heated and melted; and a melt retaining section where only a melt generated in said melting section is retained.

14. The single-crystal production equipment according to claim 13, wherein said granular raw material melting vessel is constituted by: a boat-shaped vessel; and a separation plate which divides said boat-shaped vessel into said melting section and said melt retaining section and comprises a groove on a lower part.

15. The single-crystal production equipment according to claim 14, wherein a raw material melt guiding apparatus, which supplies said raw material melt discharged from said granular raw material melting vessel onto said melt formed on the upper surface of said seed single crystal below, is arranged at a lower end of said granular raw material melting vessel.

16. The single-crystal production equipment according to claim 13, wherein said granular raw material melting vessel is constituted by: a melting dish; and a separation dish which is arranged inside said melting dish, has an inverted V-shaped cross-section and comprises a groove on a lower part, and said granular raw material melting vessel is configured such that it is divided into said melting section and said melt retaining section between said melting dish and said separation dish.

17. The single-crystal production equipment according to claim 16, wherein a raw material melt guiding apparatus, which supplies said raw material melt discharged from said granular raw material melting vessel onto said melt formed on the upper surface of said seed single crystal below, is arranged at a lower end of said granular raw material melting vessel.

18. The single-crystal production equipment according to claim 13, wherein said granular raw material melting vessel is constituted by: a cylindrical section; and a funnel-shaped section which is arranged inside said cylindrical section and has an opening at a lower end, and the inner side of said cylindrical section constitutes said melting section and a space between the outer side of said cylindrical section and said funnel-shaped section constitutes said melt retaining section.

19. The single-crystal production equipment according to claim 12, wherein said vessel heating equipment is a second infrared ray irradiation equipment.

20. The single-crystal production equipment according to claim 12, wherein said vessel heating equipment is a high-frequency induction heating equipment.

21. The single-crystal production equipment according to claim 12, wherein said vessel heating equipment is a resistance heating equipment.

22. The single-crystal production equipment according to claim 16, wherein said granular raw material melting vessel comprises a melting vessel rotating mechanism which rotates in the horizontal direction.

23. The single-crystal production equipment according to claim 12, wherein a part or the entirety of said granular raw material melting vessel is composed of platinum, iridium, quartz, silicon carbide, carbon, graphite, a carbon or graphite material whose surface has been converted to silicon carbide, or a carbon or graphite material whose surface has been coated with silicon carbide in advance.

24. The single-crystal production equipment according to claim 1, comprising said granular raw material supply apparatus in a plural number.

25. The single-crystal production equipment according to claim 24, comprising said granular raw material melting apparatus in a plural number.

26. The single-crystal production equipment according to claim 8, wherein a single-crystal holding table, on which said seed single crystal is placed, is arranged on the bottom of said single-crystal production chamber.

27. The single-crystal production equipment according to claim 26, wherein said single-crystal holding table comprises a holding table rotating mechanism which rotates in the horizontal direction.

28. The single-crystal production equipment according to claim 26, wherein said single-crystal holding table comprises an elevator apparatus which moves in the vertical direction at a prescribed speed.

29. The single-crystal production equipment according to claim 1, wherein an auxiliary heating equipment is arranged on the outer side of said seed single crystal.

30. A single-crystal production method of producing a high-quality single-crystal product having a uniform composition by melting a granular raw material, which has an optimum dopant composition of a single-crystal material to be produced, in a single-crystal production chamber, adding dropwise the thus obtained raw material melt into a melt formed on the upper surface of a seed single crystal arranged therebelow so as to generate a mixed melt, and then allowing a single crystal to precipitate out of said mixed melt as a solid, wherein said single-crystal production method comprises, at least, the steps of: supplying a required amount of said granular raw material to a granular raw material melting apparatus via a granular raw material supply apparatus arranged above said single-crystal production chamber; preparing a raw material melt by melting said granular raw material thus supplied to said granular raw material melting apparatus using said granular raw material melting apparatus; supplying the thus obtained raw material melt into a melt formed on said seed single crystal below; and irradiating the upper surface of said seed single crystal with an infrared ray to form a melt, subsequently generating a mixed melt phase by adding dropwise said raw material melt to the thus formed melt from said granular raw material melting apparatus, and then allowing a single crystal to precipitate as a solid on said seed single crystal from the lower side of said mixed melt phase.

31. The single-crystal production method according to claim 30, wherein said granular raw material is composed of a granular crystal base material and a granular dopant material.

32. The single-crystal production method according to claim 30, wherein, during production of a dopant-doped single crystal, the intensity and the distribution of said infrared ray irradiated to the upper surface of said seed single crystal are controlled such that said mixed melt formed on said seed single crystal uniformly has a prescribed thickness at all times.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0178] FIG. 1 is a schematic view showing a single-crystal production equipment according to one embodiment of the present invention.

[0179] FIG. 2 is a schematic view showing a single-crystal production equipment according to another embodiment of the present invention.

[0180] FIG. 3 is a schematic view showing a boat-type granular raw material melting vessel according to one embodiment of the present invention.

[0181] FIG. 4 is a schematic view showing a granular raw material melting vessel having a two-layer structure (umbrella-like structure) according to another embodiment of the present invention.

[0182] FIG. 5 is a schematic view showing a simple-type granular raw material melting vessel according to yet another embodiment of the present invention.

[0183] FIG. 6 is a set of drawings showing the production steps of a single crystal using the single-crystal production equipment of the present invention.

DESCRIPTION OF EMBODIMENTS

[0184] Embodiments (examples) of the present invention will now be described in more detail based on the drawings.

[0185] The single-crystal production equipment and single-crystal production method according to the present invention are used for highly efficiently producing a large single crystal of, for example, 100 to 300 mm or larger in diameter, while homogenizing its composition to be optimum.

[0186] The term “seed single crystal” used herein refers to an initial form of a crystal in the production of a large-diameter single crystal using a single-crystal production equipment. A crystal which is grown from this seed single crystal and maintains the same orientation in its entirety is referred to as “single crystal”. In contrast, an aggregate of single crystals each having a different orientation is referred to as “polycrystal”.

[0187] In the case of a polycrystal, individual single crystals have different crystal orientations at their boundaries, and this leads to disadvantages such as reduction in the power generation efficiency. Therefore, a high-performance silicon substrate is desired to be a single crystal which entirely has the same orientation and thus does not contain such crystal grain boundaries.

[0188] Further, the term “granular raw material” used herein refers to a powderized (granulated) raw material from which a single crystal is produced. It is noted here that the term “granular raw material” encompasses granular crystal base materials and granular dopants.

[0189] In the production of a dopant-containing single crystal, the dopant concentration in the resulting crystal does not agree with the composition of a melt from which the crystal (solid) having this concentration precipitates. The ratio between the dopant concentration in a solution and that in a solid precipitating from the solution is referred to as “distribution coefficient”, and the solution used in this case is referred to as “solvent” in the discipline of crystal growth.

[0190] Theoretically, a solid having the same composition as a raw material should precipitate out of a solvent defined by the composition of the raw material and the distribution coefficient; however, strictly speaking, the composition of a mixed melt formed by a melt formed on the resulting single crystal and a raw material melt dropped thereto is actually different between a part where the raw material melt is dropped and a part away therefrom. Therefore, in the present specification, the term “solvent” is not used, and the term “mixed melt” is used instead.

[0191] Further, in the drawings, the size and the shape of the particles representing the granular raw material are not particularly restricted.

[0192] <Single-Crystal Production Equipment 10>

[0193] As shown in FIG. 1, a single-crystal production equipment 10 of the present Example assumes a case of producing a silicon single crystal having an optimum dopant composition.

[0194] In the single-crystal production equipment 10, a single-crystal holding table 18, a holding table rotating mechanism 20 and an elevator apparatus 22 are arranged on the bottom of a single-crystal production chamber 11 which can be vacuum-evacuated and retain an inert gas atmosphere such as argon gas, and a seed single crystal 12 having a substantially circular cross-sectional shape is placed on the single-crystal holding table 18.

[0195] Further, on the outer side of the single-crystal holding table 18, an auxiliary heating equipment 86 which heats the seed single crystal 12 placed on the single-crystal holding table 18 is arranged, and an insulating material 87 is arranged on the outer side of the auxiliary heating equipment 86. The single-crystal production chamber 11 is a water-cooling structure which is capable of efficiently controlling the inner atmosphere.

[0196] Meanwhile, in the upper part of the single-crystal production chamber 11, a hopper 33 which stores a granular raw material 52 is arranged. The hopper 33 has an opening on its lower part, and a spiral rod (not shown), which is equipped with a rotating mechanism and coated with polypropylene, is arranged inside the hopper 33 and rotated at all times during use. By rotating this spiral rod, the occurrence of a so-called cavitation phenomenon where a cavity is created in the granular raw material 52 stored in the hopper 33 and stable supply of the granular raw material 52 is thereby made no longer possible can be inhibited.

[0197] The opening on the lower part of the hopper 33 is directly connected to the single-crystal production chamber 11, and the hopper 33 and the single-crystal production chamber 11 are configured in such a manner to have the same internal atmosphere at all times.

[0198] Moreover, on a lateral side of the opening of the hopper 33, a granular raw material scraping equipment (hereinafter, also simply referred to as “scraping equipment”) 48 is arranged. This scraping equipment 48 includes a propylene-coated receptacle having a spoon-like shape that is attached to a tip of a rod, and it is configured such that, by inserting this rod to the opening of the hopper 33 and then pulling out and half-rotating the rod with the granular raw material 52 being placed in the receptacle, the granular raw material 52 in the receptacle can be supplied onto a granular raw material quantitative supply equipment (hereinafter, also simply referred to as “quantitative supply equipment”) 50 positioned underneath the hopper 33.

[0199] The quantitative supply equipment 50 adjusts the amount of the granular raw material 52 to be supplied while measuring the weight thereof and supplies a prescribed amount of the granular raw material 52 to a supply pipe 51 therebelow which has a supply position adjusting function. In the drawing, a symbol 60 represents a position adjusting mechanism.

[0200] The hopper 33 in this embodiment stores a granular mixture obtained by mixing dopant-free granular silicon and a granular raw material doped with a dopant at a high concentration such that the granular mixture has an optimum composition, and this enables to surely maintain the composition ratio of the granular raw material 52 constant.

[0201] In this embodiment, the hopper 33 is used singly; however, the configuration is not restricted to this mode and, for example, a hopper for storing the dopant-free granular silicon and a hopper for storing the granular raw material doped with a dopant at a high concentration may be separately arranged.

[0202] At the upper end of such hopper 33, a known attachment-detachment mechanism 46 is arranged such that a storage container 47 which stores the granular raw material 52 can be attached and detached as desired. The attachment-detachment mechanism 46 includes an atmosphere controlling function for arbitrarily controlling the atmospheres inside the attachment-detachment mechanism 46 and the storage container 47. FIG. 1 shows a state where the storage container 47 is detached from the hopper 33.

[0203] By using the storage container 47 that can be attached to and detached from the hopper 33 in this manner, the granular raw material 52 can be supplied to the hopper 33 at any time as required even in the midst of operating the single-crystal production equipment 10 to produce a single crystal. Therefore, it is not necessary to use a large hopper 33, and a reduction in the size of the single-crystal production equipment 10 can be realized.

[0204] The granular raw material 52 supplied from the scraping equipment 48 is supplied to a prescribed position of a granular raw material melting vessel (hereinafter, also referred to as “melting vessel”) 56 of a granular raw material melting apparatus through the supply pipe 51 in a prescribed amount using the quantitative supply equipment 50 which has a function of adjusting the supply amount while measuring the weight.

[0205] To the supply pipe 51, the position adjusting mechanism 60, which adjusts the position of an outlet at the lower end of the supply pipe 51, is attached.

[0206] It is preferred that the melting vessel 56, which melts the granular raw material 52, have a multi-section structure divided into a “melting section” where the granular raw material 52 is melted and a “melt retaining section” where the resulting melt is retained; and that the melting vessel 56 have a function of preventing unmelted granular raw material 52 from being supplied downward along with the raw material melt 67.

[0207] As for the shape of the melting vessel 56, for example, such a boat-type melting vessel 56 as shown in FIGS. 1 and 3 or such a melting vessel 56 having a two-layer structure (umbrella-like structure) as shown in FIGS. 2 and 4 can be utilized. Further, in the case of producing a silicon single crystal, such a simple-type melting vessel 56 as shown in FIG. 5 can be utilized as well.

[0208] First, in the boat-type melting vessel 56, as shown in FIG. 3, a boat-shaped vessel 61 which receives the granular raw material 52 supplied from the supply pipe 51 is fitted inside a high-frequency induction heating equipment 55. A separation plate 63 having a groove 66 on a lower part is arranged inside the boat-shaped vessel 61, and the boat-shaped vessel 61 is divided by the separation plate 63 into the “melting section” and the “melt retaining section”.

[0209] The granular raw material 52 to be supplied to the boat-shaped vessel 61 through the supply pipe 51 may be directly supplied into the boat-shaped vessel 61; however, it is preferred to supply the granular raw material 52 into the boat-shaped vessel 61 using a funnel for granular raw material 53 since this makes it easier to supply the granular raw material 52 at a prescribed position.

[0210] By induction heating performed by the high-frequency induction heating equipment 55, the temperature of the boat-shaped vessel 61 is increased, and the granular raw material 52 is thereby heated and melted, as a result of which only the thus formed raw material melt 67 moves to an adjacent section (the section on the right in FIG. 3) through the groove 66 on the lower part of the separation plate 63 and is retained therein.

[0211] At this point, when the granular raw material 52 has a lower specific gravity than the raw material melt 67, since the granular raw material 52 floats on the raw material melt 67, the granular raw material 52 is prevented from passing through the groove 66 below. On the other hand, when the specific gravity of the granular raw material 52 is higher than that of the raw material melt 67, the granular raw material 52 stays in a lower part of the raw material melt 67.

[0212] Once the raw material melt 67 retained in the boat-shaped vessel 61 has reached the height of an outlet 68 arranged on the boat-shaped vessel 61, the raw material melt 67 flows to the outside through the outlet 68 and is thereby supplied onto the seed single crystal below. The raw material melt 67 discharged from the outlet 68 is preferably supplied onto the seed single crystal 12 below through a tubular or rod-shaped (not shown) raw material melt guiding apparatus 54 which, as shown in FIG. 3, extends from the lower end of the boat-shaped vessel 61 to immediately above the seed single crystal 12. By this, the occurrence of liquid surface fluctuations caused by addition of droplets can be inhibited, so that a stable liquid surface can be maintained.

[0213] In this case, in the boat-type melting vessel 56, the unmelted granular raw material 52 can be prevented from being supplied downward along with the raw material melt 67.

[0214] Meanwhile, as shown in FIG. 4, the melting vessel 56 having a two-layer structure (umbrella-like structure) is constituted by a melting dish 62 and a separation dish 64 which is disposed thereon in such a manner to have an inverted V-shaped cross-section, and this melting vessel 56 is configured in such a manner to be divided between the melting dish 62 and the separation dish 64 into a melting section where the granular raw material 52 is melted and a melt retaining section where the resulting raw material melt 67 is retained.

[0215] As vessel heating equipments for heating the granular raw material 52 supplied to the melting dish 62, as shown in FIG. 2, second infrared ray irradiation equipments 72 and 82 are used, and infrared rays 74 and 85 are irradiated to the melting vessel 56 from these second infrared ray irradiation equipments 72 and 82.

[0216] It is preferred that the second infrared ray irradiation equipments 72 and 82 be arranged above and on a side of the melting vessel 56 as shown in FIG. 2, respectively; however, they may both be arranged either above or on a side of the melting vessel 56. As the second infrared ray irradiation equipments 72 and 82, laser irradiation equipments are preferably used; however, other than laser irradiation equipments, the second infrared ray irradiation equipments 72 and 82 may also be resistance heating equipments (particularly, carbon resistance heating equipments in the case of producing a silicon single crystal), or irradiation apparatuses configured such that, for example, an infrared ray emitted from an infrared lamp is reflected by the inner surface of an elliptical reflector. In this case, as the infrared lamp, a halogen lamp, a xenon lamp or the like can be used.

[0217] In the melting vessel 56 having a two-layer structure (umbrella-like structure), by the infrared rays irradiated from the second infrared ray irradiation equipments 72 and 82, the granular raw material 52 is heated and melted, and only the resulting raw material melt 67 moves to the central part through a groove 66 arranged at the lower end of the separation dish 64 and is retained in the separation dish 64.

[0218] At this point, when the granular raw material 52 has a lower specific gravity than the raw material melt 67, since the granular raw material 52 floats on the raw material melt 67, the granular raw material 52 is prevented from passing through the groove 66 below.

[0219] On the other hand, when the specific gravity of the granular raw material 52 is higher than that of the raw material melt 67, the granular raw material 52 stays in a lower part of the raw material melt 67.

[0220] The raw material melt 67 retained in the separation dish 64 remains in the central part and, once the raw material melt 67 has reached the height of an outlet 68 arranged on a pipe 59 in the central part, the raw material melt 67 flows into the pipe 59 through the outlet 68 and is thereby supplied onto the upper surface of the seed single crystal below. By this, the unmelted granular raw material 52 can be prevented from dripping down along with the raw material melt 67.

[0221] The pipe 59 arranged in the central part extends to immediately above the seed single crystal 12 and functions as the raw material melt guiding apparatus 54. By this, the occurrence of liquid surface fluctuations caused by addition of droplets can be inhibited, so that a stable liquid surface can be maintained.

[0222] Further, as shown in FIG. 5, the simple-type melting vessel 56 stores the granular raw material 52 supplied from the upper end and is constituted by a cylindrical section 57, whose lower end is inserted into an optimum melt 91 on the upper surface of the seed single crystal 12, and a funnel-shaped section 58, which is arranged inside the cylindrical section 57 and has an opening at the lower end.

[0223] In this simple-type melting vessel 56, particularly as in the case of silicon, when the specific gravity of the granular raw material 52 is lower than that of the raw material melt 67, since the unmelted granular raw material 52 floats on the melt in the cylindrical section 57, hardly any granular raw material 52 is let out of the melting vessel 56.

[0224] Even if the granular raw material 52 is let out, since the granular raw material 52 floats on the melt, it is unlikely that the granular raw material 52 is heated and melted by an infrared ray irradiated from above, adheres to the interface of the growing crystal and is thereby incorporated into the product.

[0225] As vessel heating equipments for heating this melting vessel 56, the second infrared ray irradiation equipments 72 and 82 may be used as in the case of the melting vessel 56 having a two-layer structure (umbrella-like structure) shown in FIG. 2.

[0226] As the material of the above-described boat-type melting vessel 56, melting vessel 56 having a two-layer structure (umbrella-like structure) and simple-type melting vessel 56, for example, platinum, iridium, quartz, silicon carbide, carbon, graphite, a carbon or graphite material whose surface has been converted to silicon carbide, or a carbon or graphite material whose surface has been coated with silicon carbide in advance, is selected in accordance with the raw material.

[0227] The melting vessel 56 having a two-layer structure (umbrella-like structure) has a function of being rotated in the horizontal direction by a melting vessel rotating mechanism 70. By rotating the melting vessel 56 having a two-layer structure (umbrella-like structure) in this manner, the granular raw material 52 is evenly supplied from the supply pipe 51 into the melting vessel 56, so that the granular raw material 52 can be surely melted.

[0228] Meanwhile, a seed single crystal holding table (hereinafter, also simply referred to as “holding table”) 18 is arranged in the lower part of the single-crystal production chamber 11.

[0229] Further, the auxiliary heating equipment 86 is arranged on the outer side of the holding table 18, and the periphery of the auxiliary heating equipment 86 is constituted by the insulating material 87.

[0230] The seed single crystal 12 is placed on the holding table 18, and the holding table 18 is rotated at a prescribed speed by the holding table rotating mechanism 20, whereby uneven irradiation of the upper surface of the seed single crystal 12 with the infrared ray (laser light) is reduced, and the resulting melt phase is thus allowed to have uniform temperature.

[0231] Further, the elevator apparatus 22 is attached to the holding table 18. This provides a configuration in which the height position of the melt phase formed on the upper surface of the seed single crystal 12 can be controlled to be optimal at all times.

[0232] Moreover, infrared ray transmitting windows 27, 73 and 84 are each arranged between the seed single crystal 12 and a first infrared ray irradiation equipment 26 for heating the seed single crystal 12 and between the melting vessel 56 and the respective second infrared ray irradiation equipments 72 and 82. The material of these infrared ray transmitting windows 27, 73 and 84 is not particularly restricted as long as it can transmit infrared rays; however, the infrared ray transmitting windows 27, 73 and 84 are preferably made of, for example, quartz.

[0233] The single-crystal production equipment 10 according to one embodiment of the present invention is configured as described above, particularly in such a manner that the granular raw material 52 is converted into the raw material melt 67 using the boat-type melting vessel 56, the melting vessel 56 having a two-layer structure (umbrella-like structure) or the simple-type melting vessel 56 and only the raw material melt 67 is supplied to the upper surface of the seed single crystal 12; therefore, the single-crystal production equipment 10 is capable of producing a high-quality large single crystal with no negative crystal or crystal grain boundary, which has a uniform composition in both the vertical and horizontal directions at an optimum dopant concentration.

[0234] Furthermore, since the single-crystal production equipment 10 of the present invention includes no crucible, it is capable of producing a high-quality single crystal with no contamination from a crucible and without the generation of exsolution lamellae, which is one of the most serious defects in the case of, for example, using silicon.

[0235] <Single-Crystal Production Method>

[0236] A single-crystal production method using the single-crystal production equipment 10 will now be described.

[0237] As shown in FIG. 6(a), the seed single crystal 12 is placed on the holding table 18 in the single-crystal production chamber 11.

[0238] Next, a granular raw material pellet for optimum melt 90, which is prepared estimating the composition and the amount of an optimum melt phase to be formed, is placed on the upper surface of the seed single crystal 12. The single-crystal production chamber 11 is hermetically sealed, and the atmosphere inside the single-crystal production chamber 11 is vacuum-evacuated by a gas evacuation unit (not shown), followed by introduction of an inert atmosphere, such as argon gas, into the single-crystal production chamber 11.

[0239] Further, as shown in FIG. 6(b), an optimum melt phase composed of the optimum melt 91 is formed by irradiating an infrared ray 28 to the upper surface of the seed single crystal 12 from the first infrared ray irradiation equipment 26.

[0240] Subsequently, as shown in FIG. 6(c), the scraping equipment 48, the quantitative supply equipment 50 and the vessel heating equipment, which are positioned above the seed single crystal 12, are put into operation so as to scrape the granular raw material 52 having an optimum composition out of the hopper 33, feed the granular raw material 52 into the melting vessel 56 through the supply pipe 51 at a prescribed rate, and supply the resulting raw material melt 67 into the optimum melt 91 on the upper surface of the seed single crystal 12.

[0241] As the thickness of a mixed melt formed by the supply of the raw material melt 67 to the optimum melt 91 on the upper surface of the seed single crystal 12 increases, the infrared ray 28 becomes less likely to reach therebelow and, therefore, the temperature in the vicinity of a solid-liquid interface underneath the optimum melt 91 is lowered, as a result of which a solid phase starts to precipitate on the seed single crystal 12 as shown in FIG. 6(d).

[0242] The operation of feeding the granular raw material 52 having an optimum dopant composition to the melting vessel 56 is continuously performed. As shown in FIG. 6(e), the solid phase continues to precipitate in the lower part of the optimum melt phase of the seed single crystal 12, whereby a single crystal 92 continues to grow.

[0243] Once the prescribed supply of the granular raw material 52 is completed, the output of the first infrared ray irradiation equipment 26 is slowly lowered.

[0244] Then, as shown in FIG. 6(f), a complete single crystal 92 is formed as a whole.

[0245] After the completion of the single crystal 92, the temperature is slowly lowered, and the single-crystal production chamber 11 is cooled to room temperature and then opened, after which the single crystal 92 on the holding table 18 is taken out as a product.

[0246] It is noted here that, in this embodiment, the irradiation dose distribution of the infrared ray 28 is designed such that the surface of the single crystal 92 can be maintained as flat as possible throughout the production process.

[0247] In the single-crystal production equipment 10 and the single-crystal production method according to the present invention, a granular raw material obtained by mixing the granular raw material 52 composed of a granular crystal base material (granular silicon) and a granular dopant material at an optimum composition is used. This mixed granular raw material 52 having an optimum composition is stored in the hopper 33 and, using the scraping equipment 48 and the quantitative supply equipment 50, the granular raw material 52 is dropped therefrom through the supply pipe 51 into the melting vessel 56, and only the resulting raw material melt 67 is supplied to the upper surface of the seed single crystal 12 below, whereby the processes from the supplying and the melting of the granular raw material 52 to the solidification of the single crystal 92 are continuously performed.

[0248] In other words, in a steady state, the granular raw material 52, which is continuously supplied into the melting vessel 56, is heated and melted to obtain the raw material melt 67, and the single crystal 92 is precipitated by supplying the thus obtained raw material melt 67 to the upper surface of the seed single crystal 12; therefore, the resulting single crystal 92 has the same composition as that of the granular raw material 52 having an optimum composition.

[0249] Accordingly, the crystal being produced is allowed to uniformly have an optimum composition.

[0250] This enables to produce, for example, a high-quality single crystal having a uniform composition at a dopant concentration that allows the single crystal to realize a high conversion efficiency when used for photovoltaic power generation. A single crystal having an optimum composition can thus be produced with good yield, and this consequently contributes to a reduction of the production cost.

[0251] The single-crystal production equipment 10 of the present invention and a single-crystal production method using the single-crystal production equipment 10 have been described thus far; however, the present invention is not restricted to the above-described embodiments.

[0252] In the above-described embodiments, for the production of an N-type semiconductor, a mixed granular raw material, which is obtained by mixing a dopant-free high-purity silicon granular raw material and a granular raw material doped with phosphorus at a high concentration such that the resultant has a prescribed optimum composition, is used.

[0253] For the production of a P-type semiconductor, similarly, a mixed granular raw material, which is obtained by mixing a dopant-free high-purity silicon granular raw material and a granular raw material doped with boron at a high concentration such that the resultant has a prescribed optimum composition, is used.

[0254] When a dopant-free high-purity granular silicon and a granular raw material doped with phosphorus, boron or the like at a high concentration are separately supplied, there is an advantage that the dopant concentration in the product can be changed as appropriate. However, in most cases, since the optimum concentration is known, it is efficient to prepare a granular raw material (granular silicon material+granular dopant material) 52 that has a composition ratio conforming to the optimum concentration and to supply this granular raw material 52 at once.

[0255] Further, in the above-described embodiments, no particular mention is made on the particle size of the granular raw material 52 and the like; however, when the particle size of the granular raw material 52 is excessively large, it may take time to melt the granular raw material 52. On the other hand, an excessively small particle size is likely to cause inconvenience such as scattering of the granular raw material 52 during the supply.

[0256] Therefore, the particles of the granular raw material 52 preferably have a size of approximately 0.1 to 0.5 mm in diameter.

[0257] Moreover, in the above-described embodiments, a case where a dopant-free high-purity silicon granular raw material 52 is used as the granular crystal base material was described as an example, the granular crystal base material is not restricted thereto, and any granular raw material 52 prepared in accordance with the substance to be produced can be used.

[0258] Furthermore, in the above-described embodiments, plural first infrared ray irradiation equipments 26 each of which irradiates an infrared ray may be arranged, and the scraping equipment, the quantitative supply equipment, the supply pipe, the melting vessel and the vessel heating equipment may also each be arranged in a plural number. Defining the scraping equipment, the quantitative supply equipment, the supply pipe, the melting vessel and the vessel heating equipment as a single set, it is preferred to arrange the set in a plural number.

[0259] In the above-described manner, a variety of modifications can be made in the single-crystal production equipment 10 of the present invention within the scope of the objects of the present invention.

REFERENCE SIGNS LIST

[0260] 10: single-crystal production equipment [0261] 11: single-crystal production chamber [0262] 12: seed single crystal [0263] 18: single-crystal holding table [0264] 20: holding table rotating mechanism [0265] 22: elevator apparatus [0266] 26: first infrared ray irradiation equipment [0267] 27: infrared ray transmitting window [0268] 28: infrared ray [0269] 33: hopper [0270] 46: attachment-detachment mechanism [0271] 47: storage container [0272] 48: granular raw material scraping equipment [0273] 50: granular raw material quantitative supply equipment [0274] 51: supply pipe [0275] 52: granular raw material [0276] 53: funnel for granular raw material [0277] 54: raw material melt guiding apparatus [0278] 55: high-frequency induction heating equipment [0279] 56: melting vessel [0280] 57: cylindrical section [0281] 58: funnel-shaped section [0282] 59: pipe [0283] 60: position adjusting mechanism [0284] 61: boat-shaped vessel [0285] 62: melting dish [0286] 63: separation plate [0287] 64: separation dish [0288] 66: groove [0289] 67: raw material melt [0290] 68: outlet [0291] 70: melting vessel rotating mechanism [0292] 72: second infrared ray irradiation equipment [0293] 73: infrared ray transmitting window [0294] 74: infrared ray [0295] 82: second infrared ray irradiation equipment [0296] 84: infrared ray transmitting window [0297] 85: infrared ray [0298] 86: auxiliary heating equipment [0299] 87: insulating material [0300] 90: granular raw material pellet for optimum melt [0301] 91: optimum melt [0302] 92: single crystal