JP2006176358A - Apparatus and method for manufacturing single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for obtaining a single crystal of high quality, as an apparatus and a method for manufacturing an oxide single crystal. <P>SOLUTION: The apparatus for manufacturing the single crystal has: a crucible 3 into which a raw material is filled; a high frequency induction heating coil 10 for forming a melt 2 by heating/melting the raw material in the crucible 3 by using high frequency induction heating; a pulling shaft 6 for pulling the single crystal 1 from the melt 2; and a ceramic refractory material 4 which has a low emissivity ceiling surface 4b with a Pt disk 11 arranged thereon, the surface 4b covering an upper part of the crucible 3 and being disposed opposite to the surface 2a of the melt 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a single crystal manufacturing apparatus and manufacturing method, and more particularly to an oxide single crystal manufacturing apparatus and manufacturing method.

Currently, oxide single crystals that are industrially applied as optical devices and acoustic devices are mainly manufactured using a method called a Cz (Czochralski) method (a pulling method). The Cz method is used to produce a single crystal such as Si, LiNbO ₃ , LiTaO _3, etc., with a material having almost the same composition of the melt and the crystal precipitated from the melt, thereby producing a large and high-quality bulk single crystal. This is a method that can be obtained at low cost and is extremely important industrially.

  By the way, when manufacturing industrially useful oxide single crystals, cracks and the like are likely to occur due to internal thermal stress caused by temperature distribution, and heat is transferred from the solidification latent heat and melt generated at the crystal growth interface. There was a problem that the crystal was twisted and bent without being able to dissipate heat. In order to solve these problems, efforts have been made to optimize the geometry of the structure around the crucible for each material.

  In the course of conducting research on the production of various oxide single crystals using the Cz method, it has been found that there are almost common problems with materials having a high melting point and little absorption of visible light and infrared light. That is, when producing a single crystal from these materials, there is a problem that the allowable range of the temperature at which the seed crystal is brought into contact with the melt (seeding temperature) is narrow and the seed crystal melts, and the crystal diameter starts to expand. Since it expands rapidly, the narrow diameter of the neck portion cannot be maintained, and there is a problem that it is difficult to suppress crystal defects.

Japanese Patent Publication No. 56-27476 JP-A-8-175896

  The objective of this invention is providing the manufacturing apparatus and manufacturing method of a single crystal which can obtain a high quality single crystal.

  The purpose is to provide a crucible filled with the raw material, a heating part for heating and melting the raw material in the crucible using high frequency induction heating to generate a melt, a pulling shaft for pulling a single crystal from the melt, This is achieved by a single crystal manufacturing apparatus comprising a structural material that covers an upper portion of the crucible and has a surface having a low emissivity relative to the liquid surface of the melt.

  In the above-described single crystal manufacturing apparatus of the present invention, the surface is formed substantially smoothly using a forming material having a low emissivity.

  In the apparatus for producing a single crystal of the present invention, the forming material is a platinum group metal simple substance or an alloy thereof.

  The object is to produce a melt by heating and melting the raw material in the crucible using high-frequency induction heating, and in the method for producing a single crystal in which the single crystal is pulled up from the melt, a surface having a low emissivity is formed on the surface of the melt. This is achieved by a method for producing a single crystal characterized by being disposed relative to the liquid surface.

  In the method for producing a single crystal of the present invention, the surface is formed substantially smoothly using a forming material having a low emissivity.

  In the method for producing a single crystal according to the present invention, the forming material is a platinum group metal simple substance or an alloy thereof.

  In the method for producing a single crystal according to the present invention, the raw material has a melting point of 1700 ° C. or higher.

A single crystal production method of the present invention, the melt and the single crystal expressed by a composition formula _{Gd 3-x Ca x Mg y} Zr z Ga 5-y-z O 12 (0.30 <x <0 .34, 0.30 <y <0.34, 0.60 <z <0.68).

  According to the present invention, it is possible to produce a high quality single crystal even for a material having a high melting point and little absorption of visible light and infrared light.

A single crystal manufacturing apparatus and manufacturing method according to an embodiment of the present invention will be described with reference to FIGS. First, the principle of this embodiment will be described. The amount of radiation heat q per unit area between parallel infinite plane A, B to each other, planar A, respectively T _A the absolute temperature of the _B, and T _B, the plane A, B are both black body (epsilon (emissivity) = 1), it is represented by the formula (1).
^{_{q = σ (T A 4 -T}} B 4) ··· (1)
σ: Stefan-Boltzmann constant

As in equation (1), the amount of radiant heat transfer is proportional to the difference between the absolute temperature and the fourth power. Therefore, even if the difference between the absolute temperatures T _A and T _B is the same, the radiation is increased when the absolute temperatures T _A and T _B increase. The amount of heat exchange due to heat transfer increases rapidly. Therefore, radiant heat transfer is dominant in heat transfer when a single crystal is manufactured using a material having a high melting point. The materials that are difficult to seed have a common point that the melting point is 1700 ° C. or higher. For this reason, it has been speculated that the problem of radiant heat transfer is inherent in the cause of difficulty in seeding.

Here, it expands about the radiation heat transfer between the surfaces of a general structure instead of infinite planes. In the case of the surfaces of structures, unlike the case of infinite planes, the thermal energy radiated from one does not all reach the other. Therefore, in order to discuss heat exchange between the surfaces by radiant heat transfer, the angular relationship between the surfaces (view factor) is used. FIG. 1 is a diagram for explaining the angular relationship. When the surface i and the surface j are arranged as shown in FIG. 1, the angular relationship F _ij of the surface j with respect to the surface i can be expressed by an equation ( It is expressed as 2). The areas of the surfaces i and j are A _i and A _j , respectively, and the angles formed between the straight lines connecting the surfaces i and j and the normal vectors n _i and n _j of the surfaces i and j are β _i and β _j , respectively. To do.
_{F ij = (1 / πA i} ) ∫ Ai ∫ Aj cosβ i cosβ j (1 / r 2) dA i dA j
... (2)

Using the angular relationship F _ij , the thermal energy Q radiated from the surface i and reaching the surface j is expressed by the equation (3), where the emissivity of the surface i is ε _i and the absolute temperature of the surface i is T _i. The
Q = A _i ε _i σ T _i ⁴ · F _ij (3)

Of the energy Q that has reached the surface j, the thermal energy Q ′ that is actually absorbed by the surface j is expressed by the equation (4), and the thermal energy Q ″ that is re-radiated without being absorbed by the surface j is expressed by the equation (4). 5). Let the emissivity of surface j be ε _j .
Q ′ = A _i ε _i σ T _i ⁴ · F _ij ε _j (4)
Q ″ = A _i ε _i σT _i ⁴ · F _ij (1−ε _j ) (5)

That is, when the surface j is not a black body (ε _j <1), it is necessary to consider the thermal energy Q ″ that reaches the surface j and is radiated again. Here, the rate at which the thermal energy radiated from the surface i reaches the surface j and is absorbed is introduced as G _ij (Gebhart's Absorption factor (Gebhart absorption coefficient)). The radiant heat balance Q _j of the surface j is expressed by Expression (6) with the side from which the surface j is emitted being positive. Let T _j be the absolute temperature of surface j.

... (6)

The Gebhart absorption coefficient G _ij is obtained by dividing the thermal energy Q ″ ′ emitted from the surface i and absorbed by reaching the surface j by the total thermal energy A _i ε _i σT _i ⁴ radiated from the surface i. Is required. The thermal energy Q ″ ′ is expressed by equation (7), and the Gebhart absorption coefficient G _ij is expressed by equation (8). Here, it is assumed that ρ _i = 1−ε _i .
Q ′ ″ = A _i ε _i σ T _i ⁴ (F _ij ε _j + (F _i1 ρ ₁ G _1j +... + F _ii ρ _i G _ij +... + F _iN ρ _N G _Nj )) (7)
_{G ij = F ij ε j +} F i1 ρ 1 G 1j + ··· + F ii ρ i G ij + ··· + F iN ρ N G Nj
... (8)

Therefore, the Gebhart absorption coefficient G _ij can be obtained by solving the simultaneous equations of Expression (9).
AG _i = b _i (9)
here,
G _i ^T = [G _1i , G _2i ,..., G _Ni ]
b _i = [− F _1i ε _i , −F _2i ε _i ,..., −F _Ni ε _i ]
It is. When all the surfaces are black bodies (ε = 1, ρ = 0), it can be easily derived that G _ij = F _ij from Equation (8).

  Here, the radiation heat transfer around the growing single crystal will be verified. FIG. 2 schematically shows a cross-sectional configuration of a general single crystal manufacturing apparatus. As shown in FIG. 2, the single crystal manufacturing apparatus includes a crucible 3 for storing the melt 2 and a heat insulating material 7 provided around the crucible 3. A vertically upper portion of the crucible 3 is covered with a ceramic refractory structure (structural material) 4 while ensuring a space 8 in which the single crystal 1 having a required length can be kept warm. In the center of the top wall 4a of the ceramic refractory structure 4, an opening 4d is provided. A lifting shaft 6 having a seed crystal (not shown) attached to the lower end is provided through the opening 4d.

  The main targets for heat exchange with the growing single crystal 1 by radiant heat transfer are the liquid surface 2a of the melt 2, the side wall surface 3a of the crucible 3, the side wall surface 4c and the ceiling surface 4b of the ceramic refractory structure 4. You can think of it. FIG. 3 schematically shows the surface 1a of the single crystal 1 and the target surface for radiation heat transfer. FIG. 3A shows a state where the single crystal 1 is grown with the same crystal diameter (θ = 90 °, where θ is an angle between the surface 1a and the liquid surface 2a), and FIG. FIG. 3C shows a state where the diameter is increasing (θ> 90 °), and FIG. 3C shows a state where the crystal diameter is decreasing (θ <90 °). In FIG. 3, the normal vector of the surface 1a is indicated by an arrow.

  FIG. 4 is a graph qualitatively showing the relationship between the angle θ and the angular relationship F with respect to each surface of the surface 1a. The horizontal axis represents the angle θ (°), and the vertical axis represents the angular relationship F. A line a in the graph indicates an angular relationship F with respect to the liquid surface 2a, a line b indicates an angular relationship F with respect to the side wall surface 3a, a line c indicates an angular relationship F with respect to the side wall surface 4c, and a line d indicates an angle with respect to the ceiling surface 4b. Relationship F is shown.

  FIG. 5 is a graph qualitatively showing the relationship between the angle θ and the Gebhart absorption coefficient G for each surface of the surface 1a. The horizontal axis represents the angle θ (°), and the vertical axis represents the absorption coefficient G. The line e in the graph indicates the absorption coefficient G for the surface 1a itself, the line f indicates the absorption coefficient G for the liquid surface 2a, and the line g indicates the absorption coefficient G for the side wall surface 3a. Line h indicates the absorption coefficient G for the side wall surface 4c, and line i indicates the absorption coefficient G for the ceiling surface 4b.

As shown in FIGS. 3 to 5, when the crystal diameter of the single crystal 1 is reduced (θ <90 °), the surface 1a in the vicinity of the liquid surface 2a is subject to radiant heat exchange mainly for the melt. 2 and the side wall surface 3a of the crucible 3. On the other hand, when the crystal diameter of the single crystal 1 is increased (θ> 90 °), the ratio of performing radiant heat exchange with the liquid surface 2a and the side wall surface 3a is reduced, and the ceramic refractory structure 4 side is reduced. The ratio of performing radiant heat exchange with the wall surface 4c and the ceiling surface 4b increases. The temperature of the surface 1a of the single crystal 1 and T _1, the temperature of the melt 2 liquid level 2a and T _2, the temperature of the side wall surfaces 3a of the crucible 3 and T _3, the side wall surface 4c of the ceramic refractory structure 4 Is T ₄ and the temperature of the ceiling surface 4 b is T ₅ , T ₃ > T ₂ > T ₁ > T ₄ > T _{5 under} appropriate growth conditions. In the radiant heat exchange between the liquid surface 2a and the side wall surface 3a having a higher temperature than the surface 1a and the surface 1a, the thermal energy absorbed by the surface 1a tends to be larger than the thermal energy radiated from the surface 1a. On the other hand, in the radiant heat exchange between the side wall surface 4c and the ceiling surface 4b having a lower temperature than the surface 1a and the surface 1a, the thermal energy radiated from the surface 1a tends to be larger than the thermal energy absorbed by the surface 1a. . If ε = 1 simply, then G _ij = F _ij , so that G _ij in the equation (6) is replaced with the angular relationship F shown qualitatively in FIG. You can think about the balance. That is, it can be seen that the radiant heat balance changes from negative to positive as the angle θ increases.

  Since the amount of radiant heat transfer between the two surfaces is proportional to the difference of the fourth power of the absolute temperature of each surface (see equation (1)), when the melting point of the raw material is high (that is, the temperature of the liquid surface 2a is high) The change of radiant heat balance becomes very large. Therefore, it is considered that when the surface 1a whose normal direction is vertically upward from the horizontal direction is formed (θ> 90 °), the single crystal 1 is rapidly cooled and the crystal diameter rapidly expands.

In order to improve the crystal growth angle dependency of radiant heat transfer, it is effective to lower the Gebhart absorption coefficient dependency on the crystal growth angle. Specifically, by reducing the Gebhart absorption coefficient G of the side wall surface 4c and the ceiling surface 4b of the ceramic refractory structure 4 having a low temperature, the crystal growth angle dependency of radiant heat transfer is improved. As can be seen from Equation (9), the emissivity ε may be lowered in order to reduce the Gebhart absorption coefficient G. That is, it is effective to reduce the emissivity ε of the side wall surface 4c or the ceiling surface 4b of the ceramic refractory structure 4. For example, Patent Document 1 discloses a technique for changing the emissivity ε of both the side wall surface 4c and the ceiling surface 4b using a radiant heat reflector. However, the composition formula _{Gd 3-x Ca x Mg y} Zr z Ga 5-y-z O 12 (0.30 <x <0.34,0.30 <y <0.34,0.60 <z <0 When the radiant heat reflector as described above was used when growing the single crystal represented by .68), the heat radiation amount of the entire system was reduced, and the temperature gradient necessary for crystal growth could not be obtained. . From the above, it was found that in order to dissipate the latent heat of solidification necessary for crystallization, it is necessary to lower the emissivity of only one of the side wall surface 4c side and the ceiling surface 4b side.

In order to make the single crystal have a desired diameter, a portion having a plane oblique to the crystal growth direction, usually called a shoulder, is formed. In many cases, the angle θ of the shoulder portion when the diameter is normally expanded is set to 120 ° to 150 °. On the other hand, the angle θ when the diameter is abnormally increased is often 160 ° or more. From the relationship between the angle θ and the angular relationship F _1i shown in FIG. 4, when it is desired to selectively suppress the formation of a shoulder that causes abnormal growth (the angle θ is large), the ceiling surface 4 b of the ceramic refractory structure 4 is used. It is clearly effective to reduce the emissivity ε on the side.

  Examples of the material having a low emissivity include platinum group metals such as platinum (Pt), iridium (Ir), and rhodium (Rh). For example, there is a report example that the emissivity of Pt is 0.15 to 0.2 and the emissivity of Ir is 0.35. The effective emissivity of a certain surface is determined by the emissivity and surface shape of the material forming the surface. By making the surface mirror-like, the emissivity of the surface is lowered and approaches the emissivity of the material forming the surface. The emissivity of rough surfaces such as ceramic compacts that are not dense is generally 0.5 or more. Therefore, the emissivity of the ceiling surface 4b of the conventional ceramic refractory structure 4 is considered to be 0.5 or more, and the ceiling surface 4b is formed of a platinum group metal such as Pt or Ir or an alloy thereof and the surface is made into a mirror surface. By doing so, the emissivity can be lowered. For example, the emissivity of the ceiling surface 4b is approximately 0.15 to 0.2 by forming the ceiling surface 4b with Pt and making the surface a mirror surface. In simple terms, the emissivity of the ceiling surface 4b can be lowered by installing a plate or foil formed of a platinum group metal or an alloy thereof and having a substantially smooth surface on the ceiling surface 4b.

Patent Document 2 discloses a technique using a radiant heat reflector fixed to a lifting shaft. In the above technique, for the installation position of the radiant heat reflector is close to a single crystal and the melt surface, the composition formula _{Gd 3-x Ca x Mg y} Zr z Ga 5-y-z O 12 (0.30 <x < 0.34, 0.30 <y <0.34, 0.60 <z <0.68) When a material having a high melting point and a low absorption of visible light and infrared light is used. In addition, it is difficult to obtain a temperature gradient necessary for single crystal growth. In addition, it is necessary to secure a visual field from the observation window for the seeding operation, but it is difficult to secure the visual field because the radiant heat reflector is present near the surface of the single crystal and the melt.

When Pt and Ir are compared among platinum group metals, a higher effect can be obtained by using Pt having a lower emissivity. However, since Pt is softened at about 1500 ° C., for example, the composition formula Gd _3−x Ca _x Mg _y Zr _z Ga _5−yz O ₁₂ (0.30 <x <0.34, 0.30 < When growing a single crystal having a melting point of 1700 ° C. or higher, such as a single crystal represented by y <0.34, 0.60 <z <0.68), a Pt plate or the like is melted in the crucible 3. It is desirable to arrange at a position away from the liquid 2. Therefore, the ceiling surface 4b, which is opposite to the liquid surface 2a of the melt 2 and is further away from the melt 2 than the side wall surface 4c, is optimal as an arrangement position of the Pt plate or the like.
Hereinafter, the single crystal manufacturing apparatus and manufacturing method according to the present embodiment will be described more specifically with reference to examples.

(Example)
An apparatus for producing a single crystal according to an example of the present embodiment will be described. FIG. 6 schematically shows a cross-sectional configuration of the single crystal manufacturing apparatus according to this embodiment. As shown in FIG. 6, the single crystal manufacturing apparatus includes a ceramic refractory housing 9 and an Ir crucible which is disposed in the center of the ceramic refractory housing 9 and contains a melt 2 in which a filled raw material is melted. 3. The diameter of the crucible 3 was 150 mm, the height (depth) was 150 mm, and the thickness was 2.5 mm. A heat insulating material 7 is provided around the crucible 3. A vertically upper portion of the crucible 3 is covered with a ceramic refractory structure 4 while ensuring a space 8 where the single crystal 1 having a required length can be kept warm. Openings 9b and 4d are provided in the centers of the top wall 9a of the ceramic refractory housing 9 and the top wall 4a of the ceramic refractory structure 4, respectively. A lifting shaft 6 penetrating the openings 9b and 4d and extending vertically downward from a power source (not shown) is provided. The lower end of the pulling shaft 6 can hold the seed crystal 5. A high frequency induction coil 10 (heating unit) is wound around the outside of the ceramic refractory housing 9. A high-frequency current is passed through the high-frequency induction coil 10 to induce and heat the inside of the crucible 3, thereby melting a raw material having a desired crystal composition filled in the crucible 3 to generate a melt 2. The melt 2 is heated to a predetermined temperature. It is supposed to keep on. In addition, the ceiling surface 4b facing the melt 2 of the inner wall surface of the ceramic refractory structure 4 has a thickness of 0. 0 mm made of Pt and smoothed to reduce the emissivity of the ceiling surface 4b. A 2 mm Pt disk 11 is installed.

Next, a method for producing a single crystal according to this example will be described. The crucible 3 is filled with about 13000 g of raw material powder represented by the composition formula Gd _2.68 Ca _0.32 Mg _0.32 Zr _0.64 Ga _4.04 O ₁₂ , and a high frequency current is passed through the high frequency induction coil 10 to supply the raw material. The powder was melted to produce melt 2. A single crystal having a [111] orientation represented by the composition formula Gd _2.68 Ca _0.32 Mg _0.32 Zr _0.64 Ga _4.04 O ₁₂ was used as the seed crystal 5 and attached to the lower end of the pulling shaft 6. The seed crystal 5 was brought into contact with the melt 2 in an atmosphere in which 0.5 volume% O ₂ was mixed with N ₂ , and the pulling shaft 6 was pulled vertically upward at a speed of 2.0 mm / h to grow a single crystal. . FIG. 7 shows a single crystal 1 manufactured using the method for manufacturing a single crystal according to this example. As shown in FIG. 7, by using the method for producing a single crystal according to the present embodiment, a neck portion having a diameter (neck diameter) of 3 mm and a length of about 15 mm and a straight body portion having a diameter of 80 mm and a length of about 50 mm are provided. A transparent single crystal 1 was obtained. The angle θ of the shoulder portion between the neck portion and the straight body portion of the single crystal 1 was about 120 °.

  As a comparative example for this, crystal growth was performed under exactly the same conditions except that the Pt disk 11 was not installed on the ceiling surface 4b. As a result, the thin neck diameter could not be maintained, and crystal defects occurred.

  As described above, according to the present embodiment, since a temperature gradient necessary for crystal growth can be obtained even when a material having a high melting point and little absorption of visible light and infrared light is used, the seed crystal Therefore, the problem of melting may not occur, a long neck portion can be formed while maintaining a narrow neck diameter, and a high-quality single crystal can be manufactured. In this embodiment, since the Pt disk 11 and the like are installed only on the ceiling surface 4b, it is easy to secure a visual field from the observation window.

It is a figure explaining the angular relationship between surfaces. It is a figure which shows typically the cross-sectional structure of the manufacturing apparatus of a common single crystal. It is a figure which shows typically the surface of a single crystal, and the symmetrical surface of radiation heat transfer. It is a graph which shows qualitatively the relationship between angle (theta) and the angular relationship F with respect to each surface of the surface 1a. It is a graph which shows qualitatively the relationship between angle (theta) and the Gebhart absorption coefficient G with respect to each surface of the surface 1a. It is sectional drawing which shows typically the structure of the manufacturing apparatus of the single crystal by the Example of one embodiment of this invention. It is a figure which shows the single crystal produced using the manufacturing method of the single crystal by the Example of one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single crystal 1a Surface 2 Melt 2a Liquid surface 3 Crucible 3a Side wall surface 4 Ceramic refractory structure 4a, 9a Top wall 4b Ceiling surface 4c Side wall surface 4d, 9b Opening 5 Seed crystal 6 Lifting shaft 7 Heat insulating material 8 Space 9 Ceramic Refractory housing 10 High frequency induction coil 11 Pt disk

Claims (8)

A crucible filled with raw materials;
A heating unit that heat-melts the raw material in the crucible using high-frequency induction heating to generate a melt;
A pulling shaft for pulling up the single crystal from the melt;
And a structural material that covers the upper portion of the crucible and has a surface with a low emissivity facing the liquid surface of the melt. An apparatus for producing a single crystal according to claim 1,
The apparatus for producing a single crystal, wherein the surface is formed substantially smoothly using a forming material having a low emissivity. An apparatus for producing a single crystal according to claim 2,
The apparatus for producing a single crystal, wherein the forming material is a platinum group metal simple substance or an alloy thereof. In the method for producing a single crystal in which the raw material in the crucible is heated and melted using high frequency induction heating to produce a melt, and the single crystal is pulled up from the melt,
A method for producing a single crystal, wherein a surface having a low emissivity is disposed relative to the liquid surface of the melt. A method for producing a single crystal according to claim 4,
The method for producing a single crystal, wherein the surface is formed substantially smoothly using a forming material having a low emissivity. A method for producing a single crystal according to claim 5,
The method for producing a single crystal, wherein the forming material is a platinum group metal simple substance or an alloy thereof. A method for producing a single crystal according to any one of claims 4 to 6,
The raw material has a melting point of 1700 ° C. or higher. A method for producing a single crystal according to claim 7,
The melt and the single crystal expressed by a composition formula _{Gd 3-x Ca x Mg y} Zr z Ga 5-y-z O 12 (0.30 <x <0.34,0.30 <y <0.34, 0.60 <z <0.68). A method for producing a single crystal, wherein