JP2006176359A - 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 having a large size, 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 coil 10 for forming a melt 2 by heating/melting the raw material in the crucible 3; a pulling shaft 6 for pulling the single crystal 1 from the melt 2; and a plate-like convection-suppressing structure 12 having a surface 12a arranged close to the liquid surface 2a of the melt 2 and suppressing the occurrence of convection of the melt 2 in the vicinity of the liquid surface 2a. <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, single crystals mainly used for industrial use are manufactured by using a method called Cz (Czochralski) method (pull-up method). The Cz method is used to manufacture a single crystal such as Si, GaAs, LiTaO _3, etc., which is a material having substantially the same composition as the melt and crystals deposited from the melt. This is a single crystal production method which is obtained at low cost and is extremely important industrially.

However, some oxide single crystals such as rutile (TiO ₂ ), for example, have been difficult to produce using the Cz method even for very small crystals. For rutile single crystals, the melt composition and the crystal composition match, but due to the instability of convection in the melt, a diameter of 1 inch can be obtained even by using a magnetic field application Cz method that has the effect of suppressing convection. There were only examples of growing the following small crystals.

On the other hand, it is known that a rutile single crystal can be grown relatively easily by the Bernoulli method or the FZ (Floating Zone) method. Actually, single crystals having a diameter of about 1 inch manufactured using the Bernoulli method or the FZ method are commercially available. A rutile single crystal produced by using the EFG method is also sold. FIG. 6 is a diagram for explaining the EFG method. As shown in FIG. 6, in the EFG method, a die 104 having a slit 105 is provided in a crucible 103. The TiO ₂ melt 102 is sucked up to the upper surface of the mold 104 above the liquid surface by capillary action due to surface tension. The shape of the crystal growth interface of the single crystal 101 pulled up from the melt 102 is controlled by the mold 104. In the EFG method, there is an example of growing a small cylindrical single crystal, but a flat single crystal 101 is mainly grown. However, since there is no effective means for controlling the shape of the crystal growth interface when growing a cylindrical bulk single crystal, there is no example of growing a large and cylindrical bulk single crystal. As described above, there is a problem that it is difficult to produce a large oxide single crystal such as columnar rutile.

JP-A-5-97586

  The objective of this invention is providing the manufacturing apparatus and manufacturing method of a single crystal from which a large sized single crystal is obtained.

  The object is to provide a crucible filled with the raw material, a heating unit for heating and melting the raw material in the crucible to generate a melt, a pulling shaft for pulling up the single crystal from the melt, and a liquid in the melt. This is achieved by an apparatus for producing a single crystal comprising a convection suppressing structure that includes a surface disposed in the vicinity of a surface and suppresses convection of the melt in the vicinity of the liquid surface.

  In the single crystal manufacturing apparatus of the present invention, the convection suppressing structure is manufactured using the same material as the crucible.

  In the apparatus for producing a single crystal according to the present invention, the convection suppressing structure has a plate shape.

  In the apparatus for producing a single crystal according to the present invention, the convection suppressing structure has a hole at substantially the center.

  The apparatus for producing a single crystal according to the present invention is characterized in that the convection suppressing structure is movable substantially perpendicular to the liquid surface.

  The apparatus for producing a single crystal according to the present invention is characterized in that the surface is substantially planar.

  The apparatus for producing a single crystal according to the present invention is characterized in that the surface is substantially parallel to the liquid surface.

  Another object of the present invention is to produce a melt by heating and melting the raw material in the crucible and pulling the single crystal from the melt while suppressing convection in the vicinity of the liquid surface of the melt. This is achieved by the manufacturing method.

  In the method for producing a single crystal of the present invention, the surface of the convection suppressing structure that suppresses the flow of the melt is disposed in the vicinity of the liquid surface in the melt.

  In the method for producing a single crystal according to the present invention, the surface is arranged substantially parallel to the liquid surface.

  The method for producing a single crystal according to the present invention is characterized in that the distance between the surface and the liquid surface is kept substantially constant.

In the method for producing a single crystal according to the present invention, the melt and the single crystal are TiO ₂ .

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing apparatus and manufacturing method of a single crystal which can obtain a large-sized single crystal are realizable.

  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 Cz method and the FZ method are essentially the same in the sense that a solid is obtained as a single crystal when the melt is solidified. However, the Cz method and the FZ method may have different levels of difficulty in growing a single crystal, as represented by a rutile single crystal. Consider the cause of this.

  FIG. 1 is a diagram illustrating the comparison between the FZ method and the conventional Cz method. FIG. 1A shows the FZ method, and FIG. 1B shows the conventional Cz method. As shown in FIG. 1A, in the FZ method, a part of the raw material rod 20 is melted by infrared rays or the like to generate the melt 22, and the raw material rod 20 is moved in the direction of arrow a to set the infrared irradiation position. Move relatively upward in the figure. The single crystal 21 is obtained by the solidification of the melt 22 sequentially from the bottom in the figure. On the other hand, in the Cz method, as shown in FIG. 1 (b), the raw material filled in the crucible 3 is heated and melted to produce the melt 2, and the seed crystal 5 attached to the pulling shaft is melted into the melt 2. The single crystal 1 is obtained by pulling up the seed crystal 5. In the FZ method, since the crystal growth interface A and the gas-liquid interface (melt free surface) B exist in different planes, unstable convection in the vicinity of the gas-liquid interface B of the melt 22 directly affects the crystal growth. Not give. On the other hand, in the Cz method, since the crystal growth interface A and the gas-liquid interface B exist in the same plane, unstable convection in the vicinity of the gas-liquid interface B of the melt 2 directly affects the crystal growth. It is considered that the difference in the difficulty of single crystal growth between the FZ method and the conventional Cz method is caused by this difference. If it is a small single crystal, the FZ method may be easier to grow than the conventional Cz method.

  Another method is to grow a single crystal from the lower side of the crucible (pulling down method). FIG. 2 is a diagram for explaining the lowering method. As shown in FIG. 2, in the pulling-down method, a crucible 13 having a small hole 13a at the bottom is used. A raw material rod 17 is disposed vertically above the crucible 13. An SiC heater 14 is disposed around the raw material rod 17 to heat and melt the raw material rod 17 and drop the melt 2 into the crucible 13, and an SiC heater 15 that maintains the melt 2 at a predetermined temperature around the crucible 13. Is arranged. The crucible 13 and the SiC heaters 14 and 15 are surrounded by the ceramic refractory structure 4. A heater 19 for obtaining a temperature gradient necessary for crystal growth is disposed below the ceramic refractory structure 4. In the pulling method, a single crystal 1 is obtained by pulling a seed crystal (not shown) attached to the pulling shaft 16 in contact with the melt 2 leaking from the small hole 13a.

  In the pulling-down method, thermal equilibrium for solidifying the single crystal 1, material balance for solidifying the melt 2 leaking from the small hole 13 a as the single crystal 1, and an appropriate crystal growth environment are all realized simultaneously. Is difficult. In addition, in order to improve the quality of the single crystal 1, it is common to form a neck portion having a small diameter, but the straight body portion having a diameter larger than the neck portion and heavy in weight is held on the neck portion. Have difficulty. In addition, when vibration is applied to the apparatus, the vibration is naturally damped by the Cz method, whereas there is a risk that the apparatus is broken or falls by the pulling-down method. Thus, the pulling-down method has an essential problem with respect to the enlargement of the single crystal 1.

As a result of considering the disadvantages of various single crystal growth methods, it is concluded that the Cz method is superior if the convection stability in the vicinity of the free surface of the melt 2 is improved particularly for the growth of large-sized rutile single crystals. was gotten. When producing a rutile single crystal using the Cz method, the material for forming the crucible 3 is not platinum (Pt) having a melting point lower than that of TiO ₂ (about 1850 ° C.) but higher than that of TiO _2. Iridium (Ir) is generally used. Since Ir is easily oxidized, the single crystal is grown in a state where the oxygen concentration is low. Therefore, the following reduction reaction tends to occur on the free surface of the TiO ₂ melt 2.
TiO ₂ → 1 / 2Ti ₂ O ₃ + 1 / 2O ₂

The unstable convection in the vicinity of the free surface of the melt 2 is considered to be Marangoni convection caused by a difference in surface tension between TiO ₂ and Ti ₂ O ₃ . A similar phenomenon has been observed in a melt containing a transition metal element such as Fe ₂ O ₃ as a main component, and is not a special phenomenon limited to TiO ₂ . Since it is difficult to eliminate surface tension imbalance on the free surface of the melt 2, it is most effective to suppress the flow of the melt 2 in the vicinity of the free surface in order to suppress Marangoni convection. it is conceivable that.

  Therefore, in the present embodiment, as a method for improving the convection stability of the free surface of the melt and avoiding the adverse effect on the crystal growth interface due to unstable convection, the melt 2 is grown during the single crystal growth using the Cz method. A convection suppressing structure that suppresses the flow in the vicinity of the surface is installed in the melt 2. In addition, the single crystal 1 is grown while keeping the distance between the melt surface and the surface of the structure for suppressing convection at a distance necessary for suppressing Marangoni convection. In the present embodiment, it is used that the fluid velocity is 0 on the solid surface, and the flow of the thin fluid layer existing on the solid is suppressed by its viscosity.

  FIG. 3 schematically shows a cross-sectional configuration of the single crystal manufacturing apparatus according to the present embodiment. As shown in FIG. 3, the single crystal manufacturing apparatus is disposed in a ceramic refractory housing 9 and a central portion of the ceramic refractory housing 9, and contains, for example, an Ir-made melt 2 containing a melted raw material 2. It has a crucible 3. 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 4b are provided at 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 4b 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. Further, for example, three openings 9c and 4c are provided in the top wall 9a of the ceramic refractory housing 9 and the top wall 4a of the ceramic refractory structure 4, respectively (only one is shown in FIG. 3). . Drive shafts 11 are provided that extend through the openings 9c and 4c and extend vertically downward from a power source (not shown). A convection suppressing structure 12 made of, for example, Ir is connected to the lower end of the drive shaft 11 via a mounting rod 23. The upper surface 12a of the convection suppressing structure 12 is substantially horizontal and substantially parallel to the liquid surface (gas-liquid interface) 2a of the melt 2. The convection suppressing structure 12 can be moved in a vertical direction substantially perpendicular to the liquid level 2a by a power source, for example.

  For example, 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. After generating the melt 2, the convection suppressing structure 12 is submerged in the melt 2 so that the surface 12a is disposed in the vicinity of the liquid surface 2a. During the growth of the single crystal 1, for example, the distance between the surface 12a and the liquid surface 2a is kept substantially constant. That is, since the melt 2 is crystallized, the height of the liquid surface 2a is lowered. Therefore, the position of the convection suppressing structure 12 is moved vertically downward in accordance with the drop in the height of the liquid surface 2a. In the case of using the continuous raw material charge Cz method in which a raw material having the same weight as the weight of the melt crystallized per unit time is used, the height of the liquid surface 2a is almost constant, so that convection is suppressed. There is no need to move the structural body 12. Therefore, in that case, a power source for driving the drive shaft 11 is not necessarily required, and the convection suppressing structure 12 may be simply fixed at a predetermined position.

  FIG. 4 is a perspective view showing the configuration of the convection suppressing structure 12. As shown in FIG. 4, the convection suppressing structure 12 has, for example, a disk shape having a substantially planar surface 12a. Three attachment rods 23 made of the same material as the convection control structure 12 and extending perpendicularly to the surface 12a and attached to each drive shaft 11 are fixed to the surface 12a. The structure 12 for suppressing convection needs to satisfy the conditions that it is chemically stable in the high-temperature melt 2 and that the shape change in the high-temperature melt 2 is small. Since these conditions are the same as the conditions to be satisfied by the crucible 3, the convection suppressing structure 12 is manufactured using, for example, the same material (Ir in this example) as the crucible 3. Further, the surface 12a is preferably substantially planar or curved with an inclination at least near the region necessary for crystal growth in order to suppress unstable convection of the melt 2 in the vicinity of the crystal growth interface.

When the distance between the liquid surface 2a of the TiO ₂ melt 2 and the surface 12a of the convection suppressing structure 12 was set to 3 mm or less, the flow pattern of the liquid surface 2a that was normally observed disappeared. From this, the convection in the vicinity of the liquid surface 2a of the melt 2 can be suppressed to a desired level by changing the holding height of the convection suppressing structure 12 and adjusting the distance between the liquid surface 2a and the surface 12a. It was confirmed that convection could be suppressed almost completely.

  When the disc-shaped convection suppressing structure 12 as shown in FIG. 4 is used, it is difficult for natural convection to flow downward from the convection suppressing structure 12 in the melt 2. In some cases, the axial symmetry of the temperature distribution is impaired, and the high-quality single crystal 1 cannot be obtained. FIG. 5 is a perspective view showing a modified example of the configuration of the convection suppressing structure 12. As shown in FIG. 5, the convection suppressing structure 12 has a hole 18 substantially at the center. By doing so, it was found that the axially symmetric natural convection of the melt 2 can be selectively generated through the hole 18 and a high-quality single crystal 1 can be obtained.

(Example)
A single crystal manufacturing apparatus and manufacturing method according to an example of the present embodiment will be described. First, about 1900 g of rutile TiO ₂ was filled in an Ir crucible 3. The diameter of the crucible 3 was 100 mm, the height (depth) was 100 mm, and the thickness was 2.5 mm. A high frequency current of 70 kHz was passed through the high frequency induction coil 10 by a high frequency oscillator, and the raw material in the crucible 3 was heated and melted to produce a TiO ₂ melt 2. After that, an Ir convection suppressing structure 12 having a hole 18 as shown in FIG. 5 was submerged in the melt 2 and arranged so that the distance between the liquid surface 2a and the surface 12a was about 6 mm. A Bernoulli TiO ₂ single crystal of [001] orientation was used as the seed crystal 5 and attached to the lower end of the pulling shaft 6. The seed crystal 5 is brought into contact with the melt 2 in an atmosphere in which 1% by volume of O ₂ is mixed with N ₂ , and the convection in the vicinity of the liquid surface 2a of the melt 2 is kept constant with the distance between the liquid surface 2a and the surface 12a kept constant. The single crystal 1 was grown by pulling the pulling shaft 6 vertically upward at a speed of 1.0 mm / h. As a result, a columnar and high-quality rutile single crystal having a diameter of 50 mm and a length of 40 mm was obtained.

  As described above, in the present embodiment, the convection suppressing structure 12 that suppresses the convection in the vicinity of the liquid surface 2a of the melt 2 is used, and the single crystal is maintained while keeping the distance between the liquid surface 2a and the surface 12a substantially constant. Cultivate As a result, it is possible to grow oxide single crystals such as rutile which have not been grown by the conventional Cz method, and it is possible to obtain large, high-quality single crystals with high industrial productivity.

It is a figure which compares and demonstrates FZ method and the conventional Cz method. It is a figure explaining the pulling-down method. It is sectional drawing which shows typically the structure of the manufacturing apparatus of the single crystal by one embodiment of this invention. It is a perspective view which shows the structure of the structure for convection suppression. It is a perspective view which shows the modification of a structure of the structure for convection suppression. It is a figure explaining the EFG method.

Explanation of symbols

1, 21 Single crystal 2, 22 Melt 2a Liquid surface 3, 13 Crucible 4 Ceramic refractory structure 4a, 9a Top wall 4b, 4c, 9b, 9c Opening 5 Seed crystal 6 Lifting shaft 7 Heat insulating material 8 Space 9 Ceramic refractory Object housing 10 high frequency induction coil 11 drive shaft 12 convection suppressing structure 12a surface 13a small hole 14, 15 SiC heater 16 pulling shaft 17, 20 raw material rod 18 hole 19 heater 23 mounting rod

Claims (12)

A crucible filled with raw materials;
A heating unit for heating and melting the raw material in the crucible to generate a melt;
A pulling shaft for pulling up the single crystal from the melt;
An apparatus for producing a single crystal, comprising: a convection suppressing structure that includes a surface disposed near a liquid surface in the melt and suppresses convection of the melt near the liquid surface. An apparatus for producing a single crystal according to claim 1,
The convection suppressing structure is manufactured using the same material as that of the crucible. An apparatus for producing a single crystal according to claim 1 or 2,
The convection suppressing structure has a plate-like shape. An apparatus for producing a single crystal according to any one of claims 1 to 3,
The apparatus for producing a single crystal, wherein the convection suppressing structure has a hole at substantially the center. An apparatus for producing a single crystal according to any one of claims 1 to 4,
The apparatus for producing a single crystal, wherein the structure for suppressing convection is movable substantially perpendicular to the liquid surface. An apparatus for producing a single crystal according to any one of claims 1 to 5,
The apparatus for producing a single crystal, wherein the surface is substantially planar. An apparatus for producing a single crystal according to any one of claims 1 to 6,
The apparatus for producing a single crystal, wherein the surface is substantially parallel to the liquid surface. The raw material in the crucible is heated and melted to produce a melt,
A method for producing a single crystal, wherein the single crystal is pulled up from the melt while suppressing convection near the liquid surface of the melt. A method for producing a single crystal according to claim 8,
A method for producing a single crystal, comprising disposing a surface of a convection suppressing structure for suppressing flow of the melt in the vicinity of the liquid surface in the melt. A method for producing a single crystal according to claim 9,
The method for producing a single crystal, wherein the surface is disposed substantially parallel to the liquid surface. A method for producing a single crystal according to claim 9 or 10,
A method for producing a single crystal, characterized in that the distance between the surface and the liquid surface is kept substantially constant. A method for producing a single crystal according to any one of claims 8 to 11,
The method for producing a single crystal, wherein the melt and the single crystal are TiO ₂ .

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