JP4411889B2 - Crucible - Google Patents

Description

  The present invention relates to a crucible for growing calcium fluoride to a single crystal by cooling.

  Conventionally, as a crucible for growing calcium fluoride into a single crystal by cooling and cooling, one configured to grow calcium fluoride into a single crystal along the crystal plane of a seed (seed crystal) It is known (see, for example, Patent Document 1).

On the inner surface of this type of crucible, a large-diameter raw material storage portion into which calcium fluoride raw material is introduced and a small-diameter seed storage portion into which calcium fluoride seeds (seed crystals) are stored are continuously formed. Both are continuous via a tapered cone surface.
Japanese Patent Laid-Open No. 10-265296

  By the way, in the conventional example of this kind of crucible described above, when the calcium fluoride melted in the crucible is crystallized along the crystal plane of the seed by cooling, the wall surface and the cone surface of the raw material container on the inner surface of the crucible Polycrystals (heterogeneous phases) are likely to be generated with the corners of the boundary and the corners of the boundary between the cone surface and the wall surface of the seed accommodating portion as nuclei. In addition, when calcium fluoride shrinks by cooling, calcium fluoride adheres to the corners of the inner surface of these crucibles, generating residual stress and strain in the crystal, which tends to cause grain boundaries. Therefore, polycrystal (heterogeneous phase) is likely to occur. As a result, there is a problem that a single crystal of calcium fluoride cannot be easily grown.

  Then, this invention makes it a subject to provide the crucible which can prevent the polycrystallization and can grow the single crystal of calcium fluoride easily.

A crucible according to the present invention is a crucible for growing a calcium fluoride into a single crystal along a seed crystal surface by melting and cooling, and a raw material container containing a calcium fluoride raw material. In addition, a tapered cone surface is formed between the seed accommodating portion and the seed accommodating portion, and the wall surface and the cone surface of the raw material accommodating portion are 1/10 or more of the inner diameter between the wall surfaces of the raw material accommodating portion. The cone surface and the wall surface of the seed storage part are set to a curvature radius that is 1/10 or more of the inner diameter between the wall surfaces of the raw material storage part. smoothly continuous through the convex curved surface which has a surface roughness of the inner surface of the crucible by the maximum height method is equal to or less than Rmax6.4S.

  In the crucible according to the present invention, the wall surface and the cone surface of the raw material storage portion are smoothly continuous via the concave curved surface, and the cone surface and the wall surface of the seed storage portion are smoothly continuous via the convex curved surface. Therefore, when calcium fluoride melted in the crucible is crystallized along the crystal plane of the seed by cooling, generation of nuclei that cause polycrystals on the inner surface of the crucible is suppressed. Further, since the calcium fluoride is easily separated from the inner surface of the crucible when shrinking by cooling, the occurrence of residual stress and strain in the crystal of calcium fluoride is suppressed. As a result, a single crystal of calcium fluoride is easily grown.

  In the crucible of the present invention, the curvature radius of the curved surface continuously connecting the wall surface of the raw material container, the cone surface and the seed container wall on the inner surface of the crucible is 1/10 or more of the inner diameter between the wall surfaces of the raw material container, preferably 1/6 or more, more preferably 1/4 or more.

  In the crucible according to the present invention, the wall surface and the cone surface of the raw material storage portion are smoothly continuous via the concave curved surface, and the cone surface and the wall surface of the seed storage portion are smoothly continuous via the convex curved surface. Therefore, when calcium fluoride melted in the crucible is crystallized along the crystal plane of the seed by cooling, generation of nuclei that cause polycrystals on the inner surface of the crucible is suppressed. Further, since the calcium fluoride is easily separated from the inner surface of the crucible when shrinking by cooling, the occurrence of residual stress and strain in the calcium fluoride crystal is suppressed. Therefore, according to the present invention, a single crystal of calcium fluoride can be easily grown.

  Hereinafter, embodiments of a crucible according to the present invention will be described with reference to the drawings. In the drawings to be referred to, FIG. 1 is a schematic diagram showing a schematic structure of a vacuum VB furnace provided with a crucible according to an embodiment, and FIG. 2 is a cross-sectional view showing a structure of the crucible according to the embodiment shown in FIG. .

As shown in FIG. 1, a crucible 1 according to an embodiment is disposed inside a heater 2A in a vacuum VB furnace 2 as a single crystal growth apparatus by a vertical Bridgman (hereinafter abbreviated as VB) method, The calcium fluoride (CaF ₂ ) raw material M is melted and cooled by being moved up and down at a very low speed through the shaft 2B, and the seed is made of a single crystal of calcium fluoride (CaF ₂ ). For example, S is grown into a single crystal along a crystal plane of (1,1,1) orientation.

The inside of the vacuum VB furnace 2 is depressurized to 10 ⁻⁴ Pa or less by a vacuum pump 2C, and heated to, for example, about 1400 to 1500 ° C. by a heater 2A. In order to prevent the seed S from melting by the heating of the heater 2A, the shaft 2B of the vacuum VB furnace 2 is configured to constitute a cooling water circulation path.

  That is, the shaft 2B is formed of a double tube in which the upper end of the inner tube 2B1 is retracted from the upper end of the outer tube 2B2, and a cap-like heat transfer member 2D is fitted and fixed to the upper end portion. And this heat-transfer member 2D is comprised so that the lower part of the seed S may be forcedly cooled by connecting to the center part of the bottom member 1C of the crucible 1 mentioned later.

  Here, as shown in FIG. 2, the crucible 1 of one embodiment includes a crucible body 1A, a lid member 1B that covers the opening of the crucible body 1A, and a bottom member 1C that is fixed to the lower portion of the crucible body 1B. It is prepared for. The crucible body 1A is made of a high-purity carbon material as a material that has heat resistance and can improve the smoothness of the inner surface, and the inner surface is coated with glossy glassy carbon (GC). .

The crucible body 1A is formed with a large-diameter raw material storage portion 1D for storing a raw material M (see FIG. 1) of calcium fluoride (CaF ₂ ). A small-diameter seed accommodating portion 1E that accommodates, for example, a cylindrical seed S (see FIG. 1) is formed as a straight circular hole at the center of the crucible main body 1A to the bottom member 1C. And between the raw material accommodating part 1D and the seed accommodating part 1E, the taper-shaped (funnel-shaped) cone surface 1F which comprises the bottom of the raw material accommodating part 1D is formed.

  On the other hand, the lid member 1B and the bottom member 1C are also made of a heat-resistant high-purity carbon material. A connecting cylinder portion 1C1 for fitting and fixing a heat transfer member 2D (see FIG. 1) fixed to the upper end portion of the shaft 2B of the vacuum VB furnace 2 projects from the center portion of the bottom surface of the bottom member 1C. ing.

  Here, a concave curved surface 1J is formed at a boundary portion between the wall surface 1H of the raw material storage portion 1D and the cone surface 1F, and the wall surface 1H of the raw material storage portion 1D and the cone surface 1F continue smoothly through the concave curved surface 1J. is doing. Further, a convex curved surface 1L is formed at the boundary portion between the cone surface 1F and the wall surface 1K of the seed accommodating portion 1E, and the cone surface 1F and the wall surface 1K of the seed accommodating portion 1E are smoothly continuous via the convex curved surface 1L. ing.

  The wall surface 1H of the raw material container 1D is formed straight, and the inner diameter between the wall surfaces 1H is set to 250 mm, for example. Moreover, the internal diameter of the seed accommodating part 1E is set to 20 mm, for example.

Here, if the cone angle θ of the cone surface 1F is too small, residual stress and strain are generated in the crystal of calcium fluoride (CaF ₂ ) grown in the raw material container 1D, resulting in polycrystal. (Different phase) is likely to occur. On the other hand, if the cone angle θ of the cone surface 1F is too large, the growth of a single crystal of calcium fluoride (CaF ₂ ) is likely to be hindered. Therefore, the cone angle θ of the cone surface 1F is set to the range of 120 ° to 130 ° as the most preferable range among the range of 95 ° to 150 °.

Further, when the concave curved surface 1J and the convex curved surface 1L are angular because the radius of curvature is too small, when the calcium fluoride (CaF ₂ ) melted in the raw material container 1D is crystallized by cooling, the concave concave curved surface is formed. Polycrystals (heterogeneous phases) are likely to occur with 1J and the convex curved surface 1L as nuclei. In addition, when calcium fluoride (CaF ₂ ) contracts due to cooling, calcium fluoride (CaF ₂ ) adheres to these angular concave curved surface 1J and convex curved surface 1L, and residual stress and strain are generated in the crystal. Due to this, polycrystal (heterogeneous phase) is likely to occur.

  Therefore, in the crucible 1 of one embodiment, the curvature radii of the concave curved surface 1J and the convex curved surface 1L are set to a large curvature radius that is 1/10 or more of the inner diameter (for example, 250 mm) between the wall surfaces 1H of the raw material container 1D. . For example, the radius of curvature of the concave curved surface 1J is set to about 60 mm, and the radius of curvature of the convex curved surface 1L is set to about 50 mm.

Further, when the surface roughness of the wall surface 1H and the cone surface 1F of the raw material container 1D is rough, when the calcium fluoride (CaF ₂ ) melted in the raw material container 1D is crystallized by cooling, the wall surface 1H and the cone Polycrystals (heterogeneous phases) are likely to be generated with minute irregularities such as the surface 1F serving as nuclei. In addition, when calcium fluoride (CaF ₂ ) contracts due to cooling, calcium fluoride (CaF ₂ ) adheres to the wall surface 1H and the cone surface 1F, resulting in residual stress and distortion in the crystal. Therefore, polycrystal (heterogeneous phase) is easily generated.

  Accordingly, the inner surface of the crucible extending from the wall surface 1H of the raw material container 1D of the crucible body 1A to the wall surface 1K of the seed container 1E through the concave curved surface 1J, the cone surface 1F, and the convex curved surface 1L has a surface roughness of at least Rmax6. .4 s or less, for example, Rmax of about 3.2 s.

  Since the inner surface of the crucible body 1A is finished to about Rmax 3.2 s, the contact angle between the inner surface of the crucible and the water droplet is at least 100 ° or less, for example 90 °.

The crucible 1 of one embodiment configured as described above is a vacuum VB furnace 2 (FIG. 1) that is decompressed to 10 ⁻⁴ Pa or less in order to melt the raw material M of calcium fluoride (CaF ₂ ) shown in FIG. In the reference), the inside of the heater 2A heated to around 1400 ° C. is raised by the shaft 2B at a slow speed of about 10 mm / h and held at the raised position for about 10 hours. At that time, the lower part of the seed S is forcibly cooled via the heat transfer member 2D by the cooling water circulating in the shaft 2B from the inner pipe 2B1 to the outer pipe 2B2, thereby preventing melting of the portion other than the upper part of the seed S. Is done.

The crucible 1 cools the molten calcium fluoride (CaF ₂ ) raw material M and grows it into a single crystal along the crystal plane of the seed (seed crystal) S, for example, in the (1,1,1) orientation. Therefore, the shaft 2B is lowered at a very low speed of, for example, about 1.0 mm / h, which is 1.5 mm / h or less, and is held at the lowered position in the vacuum VB furnace 2 for about 5 hours.

Thereafter, the molten calcium fluoride (CaF ₂ ) in the crucible 1 is controlled at 70 ° C./h or less by controlling on / off of the heater 2A of the vacuum VB furnace 2 in order to prevent quenching (cracking due to thermal shock). For example, it is cooled at a cooling rate of about 30 ° C./h.

  Here, in the crucible 1 of the embodiment, the wall surface 1H of the raw material container 1D of the crucible body 1A and the cone surface 1F are smoothly continuous via the concave curved surface 1J having a large curvature radius of about 60 mm, and the cone surface 1F. And the wall surface 1K of the seed accommodating portion 1E are smoothly continuous via a convex curved surface 1L having a large curvature radius of about 50 mm. That is, there is no place where the crucible inner surface extending from the wall surface 1H of the raw material container 1D through the concave curved surface 1J, the cone surface 1F, and the convex curved surface 1L to the wall surface 1K of the seed container 1E is smoothly and continuously squared.

Therefore, in the crucible 1 of one embodiment, the calcium fluoride (CaF ₂ ) melted in the raw material container 1D is crystallized along the (1,1,1) -oriented crystal plane of the seed S by cooling. In this case, the generation of nuclei that cause polycrystals on the inner surface of the crucible is suppressed. Further, since calcium fluoride (CaF ₂ ) is easily separated from the inner surface of the crucible when shrinking by cooling, the occurrence of residual stress and distortion in the calcium fluoride (CaF ₂ ) crystal is suppressed. As a result, a single crystal of calcium fluoride (CaF ₂ ) is reliably grown.

Moreover, since the molten calcium fluoride (CaF ₂ ) in the crucible 1 is cooled at a cooling rate of 70 ° C./h or less, for example, about 30 ° C./h, quenching (cracking due to thermal shock) is prevented and good. Grown into a single crystal.

In addition, in order to cool the molten calcium fluoride (CaF ₂ ) and grow it into a single crystal, the speed at which the crucible 1 is lowered at a very low speed, that is, the growth speed is 1.5 mm / h or less, for example 1.0 mm / h. Therefore, the crystal orientation of the grown single crystal is stable as shown in FIG. It was found that when the growth rate was 1.5 mm / h or more and 2 mm / h, the crystal orientation was dispersed and not stable as shown in FIG.

It is a mimetic diagram showing a schematic structure of a vacuum VB furnace provided with a crucible concerning one embodiment of the present invention. It is sectional drawing which shows the structure of the crucible which concerns on one Embodiment shown in FIG. It is a figure which shows the distribution condition of the crystal orientation in the crystal | crystallization obtained when the growth speed | rate which lowers the crucible shown in FIG. 1 in the vacuum VB furnace 2 at very low speed was 1.0 mm / h. It is a figure which shows the distribution condition of the crystal orientation in the crystal | crystallization obtained when the growth speed | rate which lowers the crucible shown in FIG. 1 in the vacuum VB furnace 2 at very low speed was 2.0 mm / h.

Explanation of symbols

1 crucible 1A crucible body 1B lid member 1C bottom member 1D raw material container 1E seed container 1F cone surface 1H raw material container wall 1J concave curved surface 1K seed container wall 1L convex curved surface 2 vacuum VB furnace 2A heater 2B shaft 2C vacuum pump 2D heat transfer member M calcium fluoride raw material S calcium fluoride (CaF ₂₎ seed (CaF ₂₎ (seed crystal)

Claims (1)

A crucible for growing a single crystal along the crystal plane of the seed by melting and cooling calcium fluoride,
A tapered cone surface is formed between a raw material storage part that stores the raw material of calcium fluoride and a seed storage part that stores the seed,
The wall surface and the cone surface of the raw material container are smoothly and continuously connected through a concave curved surface set to a curvature radius of 1/10 or more of the inner diameter between the wall surfaces of the raw material container .
And, the cone surface and the wall surface of the seed housing part are smoothly continuous via a convex curved surface set to a curvature radius of 1/10 or more of the inner diameter between the wall surfaces of the raw material housing part ,
A crucible characterized in that the surface roughness of the inner surface of the crucible by the maximum height method is Rmax 6.4 s or less .

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