Method of Producing a Single-Crystal

Abstract

A method for producing a single crystal having a diameter of 200 mm or greater in which: (1) a seed crystal is provided; (2) an upper surface of the seed crystal is melted with an infrared ray supplied obliquely from above to create a melt covering the upper surface of the seed crystal; and (3) a powder raw material is supplied from above the seed crystal onto an area of the melt that is 90% or less of a diameter of the seed crystal, and the powder raw material supplied onto the melt is melted with the infrared ray supplied obliquely from above to melt the powder raw material while, simultaneously, a lower surface of the melt is solidified on the seed crystal. The infrared ray is applied to an area of the melt that is within 90% of the diameter of the seed crystal.

Claims

1. A method for producing a single crystal having a diameter of 200 mm or greater, the method comprising: providing a seed crystal; melting an upper surface of the seed crystal with an infrared ray supplied obliquely from above to create a melt covering the upper surface of the seed crystal; and simultaneously, a) supplying a powder raw material from above the seed crystal onto an area of the melt that is 90% or less of a diameter of the seed crystal, and melting the powder raw material supplied onto the melt with the infrared ray supplied obliquely from above to melt the powder raw material, wherein the infrared ray is applied to an area of the melt that is within 90% of the diameter of the seed crystal; and b) solidifying a lower surface of the melt on the seed crystal.

2. The method of claim 1, further comprising heating an outer side surface of the seed crystal while the raw material powder is supplied onto the melt and melted and the lower surface of the melt is solidified.

3. The method of claim 1, further comprising rotating the seed crystal while the raw material powder is supplied onto the melt and melted and the lower surface of the melt is solidified.

4. The method of claim 1, further comprising lowering the seed crystal as new melt is created by the melting of the powder raw material and a portion of the melt is solidified thereby adding to a length of the seed crystal.

5. The method of claim 1, wherein the powder raw material floats on a surface of the melt until it is melted by the infrared ray.

6. The method of claim 1, wherein the powder raw material is melted in a center portion of the upper surface of the seed crystal and the resulting melt flows to an outer part of the upper surface of the seed crystal.

7. The method of claim 1, wherein a prescribed amount of the powder raw material is supplied from a hopper through a supply pipe arranged above the seed crystal.

8. The method of claim 1, wherein a rate at which the powder raw material is supplied is adjustable.

9. The method of claim 1, wherein the powder raw material is supplied through a supply pipe and the supply pipe is moved laterally from a central position above the seed crystal to a position above the seed crystal that is within 90% of a diameter of the seed crystal.

10. The method of claim 1, wherein the powder raw material comprises a crystal base material powder and a dopant powder.

11. The method of claim 10, wherein the crystal base material powder comprises silicon.

12. The method of claim 10, wherein the dopant powder comprises boron or phosphorous.

13. The method of claim 1, wherein the powder raw material is supplied through a supply pipe and a crystal base material powder is supplied to the supply pipe from a first hopper and a dopant powder is supplied to the supply pipe from a second hopper.

14. The method of claim 1, wherein the powder raw material is supplied through a supply pipe and a mixture of a crystal base material powder and a dopant powder is supplied to the supply pipe from a hopper.

15. The method of claim 1, wherein the infrared ray is supplied by the combination of an elliptical reflector whose inner surface is used as a reflection surface and an infrared lamp which is arranged at a first focal point on a bottom side of the elliptical reflector or the infrared ray is supplied by a semiconductor laser module.

16. The method of claim 15, wherein the infrared ray is supplied by a plurality of elliptical reflectors and infrared lamps or a plurality of semiconductor laser modules.

17. The method of claim 1, wherein the seed crystal is contained in a transparent quartz tube, the powder raw material is supplied into the quartz tube, and the heat for heating the outer side surface of the seed crystal and the infrared ray applied to the upper surface of the seed crystal and powder raw material are generated outside of the quartz tube.

18. The method of claim 17, wherein the atmosphere in the transparent quartz tube is a vacuum or an inert gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0139] FIG. 1 is a schematic view showing a single-crystal production equipment according to one embodiment of the present invention.

[0140] FIG. 2 is a drawing of the single-crystal production equipment shown in FIG. 1 as viewed from the above and is used for explaining the supply range of a powder raw material.

[0141] FIGS. 3(a)-(c) depict a process diagram showing the production steps of a single crystal using the single-crystal production equipment of the present invention, wherein FIG. 3(a) depicts a state where a seed crystal is placed on a table, FIG. 3(b) depicts a state where a transparent quartz tube is arranged around the seed crystal, and FIG. 3(c) depicts a state of infrared irradiation carried out by infrared heating apparatuses and auxiliary heating apparatuses.

[0142] FIGS. 4(a)-(c) depict a process diagram showing the production steps of a single crystal using the single-crystal production equipment of the present invention, wherein FIG. 4(a) depicts a state where a powder raw material is supplied onto the seed crystal, FIG. 4(b) depicts a state of growing a single crystal while lowering the table using an elevator apparatus, and FIG. 4(c) depicts a state where the production of the single crystal has been completed with termination of the infrared irradiation by the infrared heating apparatuses and auxiliary heating apparatuses.

DESCRIPTION OF THE INVENTION

[0143] Embodiments of the present invention will now be described in more detail based on the drawings.

[0144] The single-crystal production equipment of the present invention is used for highly efficiently producing a large single crystal of, for example, 200 to 300 mm or larger in diameter, while avoiding contamination by impurities and homogenizing its composition to be optimum at a high purity.

[0145] The term “seed crystal” used herein refers to an initial form of a crystal in the production of a large single crystal using a single-crystal production equipment. A crystal which is grown from the seed crystal and maintains the same orientation in its entirety is referred to as “single crystal”.

<Single-Crystal Production Equipment 10>

[0146] As shown in FIG. 1, a single-crystal production equipment 10 of the present Example comprises: a transparent quartz tube 12, in which a seed crystal 30 is placed; a powder raw material supply apparatus 14, which is arranged above the transparent quartz tube 12 and above the seed crystal 30 and supplies a powder raw material 24, which is composed of a silicon powder and a dopant doped powder, directly onto the seed crystal 30 placed in the transparent quartz tube 12; and an infrared ray irradiation apparatus 16, which is arranged outside the transparent quartz tube 12 and irradiates an infrared ray 18 to the powder raw material 24, which is supplied into the transparent quartz tube 12 by the powder raw material supply apparatus 14, from obliquely above in the downward direction.

[0147] In addition, in the single-crystal production equipment 10 of the present invention, an auxiliary heating apparatus 32, which heats the outer side part of the seed crystal 30, is arranged outside the transparent quartz tube 12.

[0148] The auxiliary heating apparatus 32 is used for heating an outer part 60 of the seed crystal 30 in advance and, when the powder raw material 24 is melted by irradiating thereto the infrared ray 18 from the infrared ray irradiation apparatus 16 in a state where the outer part 60 of the seed crystal 30 has been heated in this manner, the irradiation dose of the infrared ray 18 can be reduced and the controllability can be improved.

[0149] As the infrared ray irradiation apparatus 16 used for irradiating the infrared ray 18 to the powder raw material 24 and the auxiliary heating apparatus 32 used for heating the outer part 60 of the seed crystal 30, for example, those which are configured such that the infrared ray 18 emitted from an infrared lamp 20 or 46 is reflected by the inner surface of an elliptical reflector 22 or 48 can be used.

[0150] As the infrared lamps 20 and 46, for example, a halogen lamp or a xenon lamp can be used. Since a halogen lamp or a xenon lamp can be obtained inexpensively, the production cost of the single-crystal production equipment 10 can be reduced. The number of the infrared ray irradiation apparatuses 16 and that of the auxiliary heating apparatuses 32 are not restricted to one, and a plurality of these apparatuses may be arranged. In cases where a plurality of these apparatuses are arranged, it is preferred to circumferentially arrange them at regular intervals around the seed crystal 30 since this enables to achieve uniform heating.

[0151] Alternatively to the case where the infrared ray irradiation apparatus 16 and the auxiliary heating apparatus 32 are constituted by the infrared lamps 20 and 46 and the elliptical reflectors 22 and 48, respectively, these apparatuses may be semiconductor laser modules (not shown). By using semiconductor laser modules (not shown), the infrared ray irradiation apparatus 16 and the auxiliary heating apparatus 32 can be reduced in size, which contributes to downsizing of the single-crystal production equipment 10.

[0152] In the single-crystal production equipment 10 of the present invention, the transparent quartz tube 12 is arranged in a closed chamber 26, and the infrared ray irradiation apparatus 16 and the auxiliary heating apparatus 32 are arranged externally to the transparent quartz tube 12 in the closed chamber 26. It is noted here, however, that the arrangement of the auxiliary heating apparatus 32 is not restricted thereto, and the auxiliary heating apparatus 32 may be a cylindrical resistance heating-type electric furnace (not shown) arranged externally to the seed crystal 30 but inside the transparent quartz tube 12.

[0153] Further, the transparent quartz tube 12 is configured such that it can be vacuum-evacuated by an atmosphere control apparatus (not shown) and retain an inert gas atmosphere such as argon gas inside. By vacuum-evacuating the atmosphere in the transparent quartz tube 12 and replacing the atmosphere with an inert gas atmosphere, even when an oxidizable material is used, oxidation thereof through reaction with the air can be inhibited.

[0154] Meanwhile, the seed crystal 30 is placed on a table 50 arranged in a lower part of the transparent quartz tube 12, and this table 50 is configured to be rotated by a rotary drive apparatus 52. By rotating the table 50 in this manner, the infrared ray 18 can be uniformly irradiated to the powder raw material 24 from the infrared ray irradiation apparatus 16, so that the powder raw material 24 can be evenly heated.

[0155] Further, the table 50 is also configured to be movable in the vertical direction as desired using an elevator apparatus 54 and, as described below, by lowering the table 50 as the growth of a single crystal proceeds, the size of the single crystal can be increased.

[0156] Meanwhile, above the transparent quartz tube 12, the powder raw material supply apparatus 14 is arranged, and this powder raw material supply apparatus 14 comprises: a hopper 40, which stores a powder raw material 24; a supply adjustment unit 42, which supplies a prescribed amount of the powder raw material 24 stored in the hopper 40 to a prescribed position of the transparent quartz tube 12; and a supply pipe 44, which is arranged on the lower end of the supply adjustment unit 42 and through which the powder raw material 24 is supplied into the transparent quartz tube 12.

[0157] The supply adjustment unit 42 comprises: a supply rate adjustment apparatus 34 which adjusts the rate at which the powder raw material 24 is supplied into the transparent quartz tube 12; and a supply position adjustment apparatus 36 which adjusts the supply position, and this configuration enables to adjust the supply of the powder raw material 24 in accordance with the growth state of a single crystal.

[0158] The hopper 40 in this embodiment is a hopper for mixed powder, which stores a mixed powder obtained by mixing a silicon powder and a dopant doped powder, and this enables to surely maintain the composition ratio of the powder raw material 24 constant.

[0159] In this case, however, the dopant concentration of a melt phase initially formed on the seed crystal 30 is required to be higher than that of the powder raw material 24 at a ratio defined by distribution coefficient. Therefore, a solid in an amount corresponding to the required amount of a solvent phase is separately prepared at a high concentration and placed on the seed crystal 30 in advance, and this solid is melted first to form a solvent phase and the powder raw material 24 starts to be supplied thereafter, whereby a single crystal 30a having a uniform composition in its entirety can be produced.

[0160] In this embodiment, a hopper for mixed powder is used as the hopper 40; however, the hopper 40 is not restricted thereto and, for example, the hopper 40 may be constituted by both a hopper for silicon powder which stores a silicon powder and a hopper for dopant doped powder which stores a dopant doped powder.

[0161] By using both a hopper for silicon powder and a hopper for dopant doped powder in this manner, a desired composition ratio can be easily achieved in the supply adjustment unit 42.

[0162] For example, when growing a phosphorus-doped N-type silicon single crystal, the powder raw material 24 to be supplied first is adjusted to have a phosphorus concentration that is three times higher than that of an optimum-concentration composition, and this powder raw material 24 is supplied in the same amount as that of a melt phase formed in a steady state, after which the powder raw material 24 having the optimum-concentration composition is supplied in an amount controlled to be the same as that of the material being solidified, whereby the resulting single crystal 30a is allowed to have a composition that roughly conforms to the optimum-concentration composition from the beginning, so that the good-quality product yield as a whole can be improved.

[0163] As an alternative to the above-described combination of a hopper for silicon powder and a hopper for dopant doped powder, a combination of a hopper for silicon powder and a hopper for mixed powder, which stores a mixed powder obtained by mixing a silicon powder and a dopant doped powder, may be used as well.

[0164] The upper end of such a hopper 40 is configured such that a powder raw material container 56, which stores the powder raw material 24, can be attached to and detached from as desired (FIG. 1 shows a state where the powder raw material container 56 is detached).

[0165] By using such a powder raw material container 56, the powder raw material 24 can be freshly supplied even in the midst of operating the single-crystal production equipment 10 to produce a single crystal, and this enables to continuously supply a required amount of the powder raw material 24 into the transparent quartz tube 12 at all times without having to hold an extremely large powder raw material container 56 over the hopper 40, so that an increase in the size of the single crystal production equipment 10 can be avoided.

[0166] The powder raw material container 56 is preferably configured in conformity with the specifications of the hopper 40. For example, as in this embodiment, when the hopper 40 is a hopper for mixed powder which stores a mixed powder obtained by mixing a silicon powder and a dopant doped powder, it is preferred that the powder raw material container 56 be configured to store the mixed powder.

[0167] Meanwhile, when the hopper 40 is constituted by a combination of a hopper for silicon powder and a hopper for dopant doped powder, the powder raw material container 56 may be a combination of a container for silicon powder and a container for dopant doped powder.

[0168] Further, the supply pipe 44 of the powder raw material 24 is configured such that, by the supply adjustment unit 42 arranged above the supply pipe 44, a prescribed amount of the powder raw material 24 is supplied therethrough to a prescribed position on the seed crystal 30 placed in the transparent quartz tube 12.

[0169] As shown in FIG. 2, the supply pipe 44 is arranged above the seed crystal 30 placed in the transparent quartz tube 12 and configured such that it can be moved laterally between a central position above the seed crystal 30 and a position of the outer part 60.

[0170] It is preferred that the powder raw material 24 be supplied from the supply pipe 44 to an area A which corresponds to 90% or less of the diameter of the seed crystal 30. In this manner, by supplying the powder raw material 24 such that the supply stops before reaching the outer part 60 of the seed crystal 30, the powder raw material 24 can be safely melted and the resulting melt can be stably maintained, so that the single crystal 30a that has a uniform composition in both the vertical and horizontal directions at an optimum dopant concentration can be produced.

[0171] As for the position and amount at which the powder raw material 24 is supplied from the supply pipe 44, they are desirably determined using the supply position adjustment apparatus 36 and the supply rate adjustment apparatus 34 of the supply adjustment unit 42, respectively.

[0172] For example, by reducing the supply amount of the powder raw material 24 in the vicinity of the center of the seed crystal 30 and increasing the supply amount toward the outer part 60 of the seed crystal 30, the powder raw material 24 is evenly supplied anywhere on the seed crystal 30 and can thus be surely melted, and the single crystal 30a that has a uniform composition in both the vertical and horizontal directions at an optimum dopant concentration can be produced.

[0173] The material of such a supply pipe 44 is preferably quartz. Since quartz does not absorb the infrared ray 18, it does not cause a temperature increase by absorbing stray light from the infrared source and, since quartz has a smooth surface, the amount of the powder raw material 24 retained thereon can be reduced, which are preferred.

[0174] Moreover, in the single-crystal production equipment 10 of the present invention, when heating the powder raw material 24 using the infrared ray irradiation apparatus 16, it is preferred to irradiate the infrared ray 18 to within 90% of the diameter of the seed crystal 30.

[0175] In this process as well, in the same manner as for the position at which the powder raw material 24 is supplied from the supply pipe 44, by heating the powder raw material 24 such that the heating stops before reaching the outer part 60 of the seed crystal 30, not only the surface of the growing single crystal can be maintained flat but also the powder raw material 24 can be safely melted and the resulting melt can be stably maintained, so that the single crystal 30a that has a uniform composition in both the vertical and horizontal directions at an optimum dopant concentration can be produced.

[0176] The single-crystal production equipment 10 according to one Example of the present invention is configured in the above-described manner, and a single-crystal production method using the single-crystal production equipment 10 will now be described.

<Single-Crystal Production Method>

[0177] First, as shown in FIG. 3(a), the seed crystal 30 is placed on the table 50 in the closed chamber 26.

[0178] Next, as shown in FIG. 3(b), the transparent quartz tube 12 is arranged externally to the seed crystal 30 in such a manner to surround the seed crystal 30 and, using an atmosphere control apparatus (not shown), the atmosphere inside the transparent quartz tube 12 is vacuum-evacuated, and an inert gas (e.g., argon gas) or an atmosphere gas (e.g., oxygen) is introduced to the transparent quartz tube 12 in accordance with the type of the single crystal to be grown.

[0179] In this state, as shown in FIG. 3(c), the seed crystal 30 is subsequently heated by irradiating its upper part and side surface simultaneously with the infrared ray 18 emitted from the infrared ray irradiation apparatus 16 arranged obliquely above the seed crystal 30 and the infrared ray 18 emitted from the auxiliary heating apparatus 32 arranged laterally to the seed crystal 30, respectively. In this process, the table 50 on which the seed crystal 30 is rotated in the circumferential direction.

[0180] Then, as shown in FIG. 4(a), once the upper part of the seed crystal 30 is melted, a small amount of the powder raw material 24 is supplied thereto from the supply pipe 44. In this state, the supply and melting of the powder raw material 24 as well as solidification on the seed crystal 30 in the lower part are continuously carried out to allow a single crystal to grow continuously. Thereafter, as shown in FIG. 4(b), the single crystal is allowed to increase its size by lowering the table 50 in accordance with the growth rate of the single crystal.

[0181] Once the single crystal has grown to a prescribed size, as shown in FIG. 4(c), the irradiation of the infrared ray 18 from the infrared ray irradiation apparatus 16 and the auxiliary heating apparatus 32 is gradually reduced and eventually terminated completely.

[0182] After solidification of the entire material is finished and the temperature is decreased to room temperature, the closed chamber 26 is opened and the single crystal (solidified product) 30a is taken out of the transparent quartz tube 12, whereby the production of the single crystal 30a is completed.

[0183] As described above, in the single-crystal production equipment 10 of the present invention, since the process of supplying the powder raw material 24 into the transparent quartz tube 12 as well as the melting and subsequent solidification processes are continuously carried out and a single crystal is produced while continuously supplying the powder raw material 24 into the transparent quartz tube 12 in the same amount as that of the material being solidified, the composition of the resulting crystal can be made uniform.

[0184] 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.

[0185] For instance, in the above-described embodiment, a case where a silicon powder is used as the crystal base material powder was described as an example; however, the crystal base material powder is not restricted thereto, and any powder prepared in accordance with the substance desired to be produced can be used.

[0186] Further, no particular mention is made above with regard to the particle size of the powder raw material (silicon powder+dopant doped powder) 24; however, when the particle size is excessively large, it takes time to melt the particles, and the particles, upon falling into the transparent quartz tube 12, may sink through the melt phase and reach the surface of the solidified product below.

[0187] If the powder raw material 24 reaches the surface of the solidified product, the powder raw material 24 is incorporated into the solidified product, and the growth of other crystals tends to start therefrom.

[0188] Meanwhile, if the powder raw material 24 has an excessively small particle size, since the particles thereof are scattered in the surrounding when they are allowed to fall toward the transparent quartz tube 12, the controllability is impaired. Accordingly, the particles of the powder raw material 24 preferably have a size of about 0.5 mm in diameter.

[0189] 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.

DESCRIPTION OF SYMBOLS

[0190] 10: single-crystal production equipment [0191] 12: transparent quartz tube [0192] 14: powder raw material supply apparatus [0193] 16: infrared ray irradiation apparatus [0194] 18: infrared ray [0195] 20: infrared lamp [0196] 22: elliptical reflector [0197] 24: powder raw material [0198] 26: closed chamber [0199] 30: seed crystal [0200] 30a: single crystal [0201] 32: auxiliary heating apparatus [0202] 34: supply rate adjustment apparatus [0203] 36: supply position adjustment apparatus [0204] 40: hopper [0205] 42: supply adjustment unit [0206] 44: supply pipe [0207] 46: infrared lamp [0208] 48: elliptical reflector [0209] 50: table [0210] 52: rotary drive apparatus [0211] 54: elevator apparatus [0212] 56: powder raw material container [0213] 60: outer part [0214] A: area