JP4214618B2 - Method for producing crucible for melting silicon - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crucible for melting silicon used for producing a silicon single crystal by the Czochralski method (CZ method) and a method for producing the same.
[0002]
[Prior art]
Conventionally, the CZ method is known as one of methods for growing a semiconductor single crystal such as silicon or gallium arsenide. This CZ method is characterized by the fact that a single crystal having a large diameter and high purity can be easily obtained with no dislocations or very few lattice defects. is there.
[0003]
An apparatus for producing a silicon single crystal by the CZ method is known as shown in FIG.
In this figure, reference numeral 21 is a chamber filled with an inert gas, 22 is a crucible disposed in the chamber, 23 is a heating element disposed around the crucible 22, and 24 is disposed above the crucible 22. This is a silicon single crystal pulling device which can be rotated up and down.
[0004]
The crucible 22 includes a quartz inner crucible 33 in which molten silicon 32 is accommodated, and a carbon outer crucible 34 fitted to the outer surface of the inner crucible 33. The lower surface of the crucible 22 is attached to the upper side of the shaft 30.
[0005]
The silicon single crystal pulling device 24 includes a shaft that is disposed above the crucible 22 and that can freely move up and down. A chuck 39 is attached to the lower end of the shaft. The chuck 39 holds a silicon seed crystal 40.
[0006]
When a silicon single crystal is manufactured using the silicon single crystal growth apparatus having such a configuration, first, solid silicon is accommodated in the crucible 22. Then, an inert gas flows into the chamber 21 from the upper part of the chamber, and the crucible 22 in the chamber 21 is heated by the heating element 23. In this way, after the solid silicon in the crucible 22 is made into the molten silicon 32, the silicon single crystal pulling device 24 is lowered and the seed crystal 40 is immersed in the molten silicon 32. In this state, the silicon single crystal pulling device 24 and the crucible 23 are rotated in opposite directions, and the silicon single crystal pulling device 24 is slowly raised. In this way, the seed crystal 40 grows, and a large rod-shaped silicon single crystal 41 is grown below the seed crystal 40.
[0007]
In such a method for producing a silicon single crystal by the CZ method, a crucible made of quartz is conventionally used as a crucible for melting the raw material solid silicon. This quartz crucible is amorphous, and its structure is not stable compared to crystals, so it is easy to soften at high temperatures. Therefore, the quartz crucible is usually fitted with a carbon outer crucible to maintain its shape.
[0008]
[Problems to be solved by the invention]
However, when silicon is melted using such a crucible, the quartz crucible and the carbon outer crucible react to generate carbon monoxide gas, and the carbon monoxide gas is taken into the molten silicon. There have been problems such as an increase in the concentration of carbon in the silicon ingot.
[0009]
The present invention has been made in view of the above-described circumstances. In a crucible that contains solid silicon when melting solid silicon, deformation during the melting of silicon is small, and the use of an outer crucible made of carbon is omitted. An object of the present invention is to provide a crucible for melting silicon and a method for producing the same.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, in the method for producing a crucible for melting silicon according to the present invention, a slurry in which colloidal silica and amorphous silica powder are mixed is attached to a bowl-shaped surface having the same shape as the inner space of a desired crucible. Thereafter, the operation of forming the stucco layer by spraying amorphous silica sand on the surface of the slurry layer is repeated an arbitrary number of times to form a crucible shell in which the slurry layer and the stucco layer are alternately laminated, and then The mold is melted and removed, and the crucible shell is heated and calcined at 800 to 1200 ° C. for 1 to 8 hours and fired to form a molded body in which crystalline silicas are diffusion-bonded by sintering. In this case, the crucible for melting silicon has a structure in which the solvent is volatilized from the slurry layer, and a binder layer mainly composed of silica powder and a stucco layer composed of silica sand are alternately laminated.
[0011]
In addition, this silicon melting crucible is a molded body in which crystalline silica particles having a stable structure are diffusion-bonded by firing, so that it has higher strength than an amorphous quartz crucible and contains molten silicon. However, high temperature softening is suppressed. Therefore, it becomes possible to abolish the use of the carbon outer crucible.
[0012]
The crucible shell is composed of an inner layer portion and an outer layer portion in which the slurry layer and the stucco layer are alternately laminated, and the silica sand of the outer layer portion has a larger average particle diameter than the silica sand of the inner layer portion. May be.
[0013]
For example, the average particle size of the silica sand in the inner layer portion may be 100 μm or more and 1000 μm or less, and the average particle size of silica sand in the outer layer portion may be more than 100 μm and 2000 μm or less.
In this case, the silicon melting crucible can be uniformly finished with the silica sand having a small average particle diameter in addition to the suppression of softening even at a high temperature as described above, and the inner surface of the inner layer portion containing silicon. .
Moreover, since the outer surface of the outer layer portion has irregularities due to rough silica sand, even if a carbon outer crucible is used, the outer crucible is in point contact with the carbon outer crucible, the reaction therebetween is suppressed, and the silicon ingot The generation of carbon monoxide, which causes the impurities, can be reduced.
[0014]
In the case of a silicon single crystal pulling apparatus comprising a silicon melting crucible and a carbon member that supports the bottom surface of the crucible in a radially open state, the carbon member is placed on the side surface of the silicon melting crucible. Since it does not face the arranged heating element, heating by the heating element is suppressed, and the outer surface of the silicon melting crucible has irregularities due to rough silica sand, so that the irregularities and the carbon member are in a point contact state. Therefore, the reaction between the silicon melting crucible and the carbon member is suppressed, and the generation of carbon monoxide that causes impurities in the silicon ingot can be reduced. The generated carbon monoxide gas is also flowed downward by the argon gas flowing from the upper part of the single crystal pulling apparatus, so that the amount taken into the molten silicon in the crucible is small.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
First, a preferred embodiment of a method for producing a silicon melting crucible according to the present invention will be described in detail with reference to the flowchart of FIG.
[0016]
First, in step S01, a bowl having a bowl having the same shape as the inner space of a desired crucible is prepared. Next, in step S02, this saddle shape is immersed in a slurry obtained by mixing silica powder and colloidal silica, and then pulled up to form a slurry layer on the surface of the saddle shape. Next, in step S03, silica sand is sprayed on the surface of the slurry layer to form a stucco layer. Next, the steps S02 and S03 are repeated any number of times to form a dense inner layer portion in which slurry layers and stucco layers are alternately laminated.
[0017]
Next, in step S04, the saddle mold on which the inner layer portion is formed is dipped in the slurry and then pulled up to form a slurry layer on the surface of the inner layer portion. Next, in step S05, silica sand having an average particle size larger than that of the silica sand of the inner layer portion is dispersed on the slurry layer to form a stucco layer. Steps S04 and S05 are repeated an arbitrary number of times to alternately stack slurry layers and stucco layers, and finally form a slurry layer to form an outer layer portion. Thus, an inner layer portion made of fine silica sand and an outer layer portion made of coarse silica sand are formed on the bowl-shaped surface.
[0018]
In step S06, the saddle mold having the inner layer portion and the outer layer portion formed on the surface in this manner is heated and melted at a temperature of 70 to 200 ° C. to be removed. In this last step S07, the crucible shell made of the silica laminate thus obtained is heated and held at 800 to 1200 ° C. for 1 to 8 hours and fired, so that the inner layer portion 3 and the outer layer portion as shown in FIG. The silicon melting crucible 1 having 4 is completed.
Since the silicon melting crucible produced in this manner is made of crystalline silica particles having a stable structure, the strength is high, and high-temperature softening is suppressed even when molten silicon is accommodated.
[0019]
Here, although the case where the inner layer part by fine silica sand and the outer layer part by coarse silica sand were laminated | stacked was demonstrated, the fine silica sand may osmose | permeate the layer of coarse silica sand. At this time, a silicon melting crucible made mainly of fine silica sand and an outer surface mainly made of coarse silica sand is suitable.
[0020]
FIG. 3 is an enlarged schematic view of a part of the obtained silicon melting crucible. In an actual silicon melting crucible, usually a large number of layers are laminated, but in this schematic diagram, the inner layer portion 3 has two binder layers 5 and a stucco layer 6a, and the outer layer portion 4 has three binder layers 5. Only two stucco layers 6b are drawn.
Since the inner layer portion 3 is made of silica sand 7 having a small average particle diameter, it is easy to form a flat surface by heating and melting the inner side surface 3a containing silicon with a burner.
[0021]
In this case, if the silica sand 8 of the outer layer portion 4 has an average particle diameter larger than the depth of the unevenness on the surface of the carbon member, the unevenness 9 due to the silica sand 8 on the outer surface of the silicon melting crucible and the carbon sand It is in a point contact state with the member and is more effective in reducing the reaction during that time. Or conversely, as the carbon member, a member having a surface with an uneven depth smaller than the average particle diameter of the silica sand of the outer layer portion may be used.
[0022]
FIG. 4 is a schematic view of the vicinity of a silicon melting crucible and a carbon member of the silicon single crystal pulling apparatus according to the present invention.
In this figure, reference numeral 15 is a silicon melting crucible disposed in a chamber (not shown), 16 is a carbon member for fixing and supporting the silicon melting crucible, 18 is a shaft to which the carbon member is attached, Reference numeral 17 denotes a heating element for melting the solid silicon in the silicon melting crucible.
[0023]
The carbon member 16 has the radially outer side of the silicon melting crucible 15 open and faces the bottom surface portion 15 a to support the silicon melting crucible 15 and is disposed on the side surface portion 15 b of the silicon melting crucible 15. Since it does not face the heating element 17, the heating by the heating element 17 is suppressed, and the outer surface of the silicon melting crucible 15 has irregularities due to rough silica sand, so that it is in point contact with the carbon member 16. Therefore, the reaction between the silicon melting crucible 15 and the carbon member 16 is suppressed, and the generation of carbon monoxide that causes impurities in the silicon ingot can be reduced. Further, the generated carbon monoxide gas (arrow A in the figure) is also caused to flow downward by argon gas (arrow B in the figure) flowing from the upper part of the silicon single crystal pulling apparatus (not shown). The amount taken into the molten silicon 32 accommodated in the crucible 15 is small.
[0024]
【Example】
Regarding the carbon concentration contained in the silicon ingot produced by the CZ method, the case where the silicon melting crucible produced by the method of the present invention as described above is used without being fitted with the carbon outer crucible, and the conventional quartz A comparison was made between the case where a crucible made of carbon was fitted with an external crucible made of carbon.
[0025]
In producing the crucible for melting silicon according to the present invention, a saddle type having an outer shape of φ500 mm and a height of 300 mm was used. The slurry was prepared by mixing silica powder having an average particle size of about 30 μm and colloidal silica at a weight ratio of about 65:35. A silica sand having an average particle diameter of about 200 μm was used as the silica sand of the stucco layer in the inner layer portion, and five slurry layers and stucco layers were alternately laminated to form an inner layer portion having a total thickness of 3 mm. Furthermore, silica sand with an average particle diameter of about 1000 μm was used as the silica sand of the stucco layer in the outer layer portion, and five slurry layers and stucco layers were alternately laminated to form an outer layer portion having a total thickness of 7 mm.
[0026]
Thus, the saddle type having the inner layer portion and the outer layer portion of the silica layer formed on the surface was heated and melted at a temperature of about 100 ° C. to be removed. The crucible shell made of the silica laminate obtained in this way was heated and held at 800 ° C. for 8 hours, and fired to prepare a silicon melting crucible.
[0027]
A silicon single crystal ingot of φ3 in. × 150 mm was actually obtained by the CZ method using the silicon melting crucible manufactured in this manner and without using a carbon outer crucible, and the carbon in the ingot was obtained. The concentration was about 5 × 10 ¹⁴ atoms / cm ³ . On the other hand, the carbon concentration in the case of a silicon single crystal manufactured by using a quartz crucible fitted to a carbon outer crucible as in the prior art and manufactured under the same pulling conditions was about 1 × 10 ¹⁶ atoms / cm ^3. It was. That is, the carbon concentration in the silicon single crystal is such that when the crystalline silica particle-dispersed silicon melting crucible according to the present invention which does not require the carbon outer crucible is used, the conventional carbon outer crucible is required. Compared to the case where a crucible is used, it is reduced to 1/20.
Thus, it was confirmed that the silicon melting crucible which does not require the carbon outer crucible of the present invention is effective in reducing the carbon concentration in the silicon single crystal.
[0028]
【The invention's effect】
As described above in detail, according to the method for producing a crucible for melting silicon according to the present invention, the following effects can be obtained.
[0029]
The crucible for melting silicon manufactured by the manufacturing method of the present invention is a molded body in which crystalline silica particles having a stable structure dispersed in the crucible are diffusion-bonded by firing, so that the strength is high and the molten silicon is Even if accommodated, high temperature softening is suppressed. Therefore, it is possible to abolish the use of the carbon outer crucible.
[0030]
A silicon melting crucible consists of an inner layer portion and an outer layer portion in which arbitrary layers of a binder layer and a stucco layer are alternately laminated, and when the silica sand of the outer layer portion has a larger average particle size than the silica sand of the inner layer portion, the silicon melting The inner surface of the crucible can be easily formed into a flat surface by heating and melting with a burner and is suitable for producing a high-quality silicon ingot, and the outer surface is made of silica sand having a large average particle diameter. Since it has irregularities, it is in a point contact state with the carbon member, so that the reaction between the silicon melting crucible and the carbon member is suppressed, and the generation of carbon monoxide that causes impurities in the silicon ingot can be reduced. .
[0031]
In the case of the silicon single crystal pulling apparatus equipped with the silicon melting crucible of the present invention, the silicon melting crucible is supported in a point contact state with the carbon outer crucible, so that the reaction between them is suppressed, and carbon monoxide is generated. Therefore, it becomes possible to manufacture a silicon ingot having a low carbon concentration. Moreover, it becomes possible to abolish the use of the outer crucible made of carbon, and in that case, it becomes possible to produce a silicon ingot having a low carbon concentration.
[0032]
In the case of a silicon single crystal pulling apparatus comprising the silicon melting crucible of the present invention and a carbon member supporting the bottom surface of the crucible in a radially open state, the silicon melting crucible and the carbon member This can suppress the generation of carbon monoxide which causes impurities in the silicon ingot.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an embodiment according to a manufacturing method of the present invention.
FIG. 2 is a cross-sectional view of an example of a silicon melting crucible of the present invention.
FIG. 3 is an enlarged view of a part of FIG. 2;
FIG. 4 is a view showing an embodiment of a silicon melting crucible and a carbon member according to the present invention.
FIG. 5 is a diagram showing an embodiment of a conventional silicon single crystal pulling apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Silicon melting crucible 3 Inner layer part 3a Inner side surface 4 Outer layer part 4a Outer side surface 5 Binder layer 6a Stucco layer 6b Stucco layer 7 Silica sand 8 Silica sand 9 Concavity and convexity 15 Silicon melting crucible 15a Bottom surface part 15b Side part 16 Carbon member 17 Heating element 18 Shaft 21 Chamber 22 Crucible 23 Heating element 24 Silicon single crystal pulling device 30 Shaft 32 Molten silicon 40 Seed crystal 41 Silicon single crystal A Flow of carbon monoxide gas B Flow of argon gas

Claims (2)

  In a method for producing a silicon melting crucible, after a slurry mixed with colloidal silica and amorphous silica powder is attached to a bowl-shaped surface having the same shape as the inner space of a desired crucible, the surface of the slurry layer is amorphous. The operation of forming a stucco layer by spraying quality silica sand is repeated an arbitrary number of times to form a crucible shell in which a slurry layer and a stucco layer are alternately stacked, and then the crucible is melted and removed. A method for producing a crucible for melting silicon, characterized in that a shell is heated and calcined at 800 to 1200 ° C. for 1 to 8 hours and fired to form a molded body in which crystalline silicas are diffusion-bonded by sintering.   The crucible shell is composed of an inner layer portion and an outer layer portion in which the slurry layer and the stucco layer are alternately laminated, and the silica sand of the outer layer portion has a larger average particle diameter than the silica sand of the inner layer portion. The method for producing a crucible for melting silicon according to claim 1.

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