JP2018039694A - Single crystal growing apparatus and single crystal manufacturing method - Google Patents

Abstract

The present invention provides a single crystal growing apparatus in which a flow of a melt is stably directed toward the center, and seeds can be reliably seeded in the same state and a crystal having a good shape can be stably grown. A crucible 20 for storing a melt 21 obtained by melting a raw material of an oxide single crystal, a heater 30 disposed around the crucible 20 for heating the raw material of an oxide single crystal, and an axis of the crucible 20 are provided. And a pulling shaft 50 to which a seed crystal 51 of an oxide single crystal is attached. On the melt surface of the crucible 20, a plurality of rectifying plates 22b extending radially from the outer periphery of the circular ring 22a are provided. The rectifying member 22 to be provided is arranged. [Selection] Figure 2

Description

  The present invention relates to a single crystal growth apparatus and a method for producing a single crystal, and is particularly suitable for a sapphire single crystal.

  A sapphire single crystal is a crystal having a corundum structure of aluminum oxide, and has already been used in many fields because it has excellent mechanical and thermal properties, chemical stability, and light transmittance. In particular, sapphire single crystals are used as substrates for silicon-on-sapphire (SOS) devices in the optical field, and the demand for these sapphire is growing dramatically as the importance of these applications increases.

  Conventionally, as a method for producing a sapphire single crystal, various crystal production methods (EFG method, Ky method, VHGH method, HEM method, arc energy method, CZ method, etc.) have been studied. Among them, the Czochralski method (CZ method) is a typical method for producing a single crystal that is effective in terms of quality and cost by processing a single crystal on a substrate and polishing the surface. is there. The CZ method is a method for growing a single crystal by melting a sapphire raw material in a crucible, bringing a seed crystal into contact with a melt surface obtained by melting the raw material, and gradually pulling it up.

  For example, Patent Document 1 describes a sapphire single crystal manufacturing apparatus that includes a chamber using a carbon heater and a molybdenum crucible installed in the chamber in order to grow a sapphire single crystal.

JP 2011-195423 A

  In the single crystal manufacturing apparatus, natural convection causes a flow from the periphery of the crucible toward the center of the melt surface, and since the center of the melt surface is the lowest temperature position, seeding is required at this center. However, since the melting point of the sapphire single crystal raw material exceeds 2000 ° C. in the single crystal manufacturing apparatus, the flow of the melt can be very unstable. There is a possibility that the position of the lowest temperature on the liquid surface is shifted from the center, seeding is not successful, and the yield of the single crystal is deteriorated.

  Therefore, the present invention solves the above-mentioned conventional problems, and makes it possible to perform stable seeding by making sure that the lowest temperature position on the melt surface is at the center. It aims at providing the manufacturing method of a crystal | crystallization.

  That is, the single crystal growth apparatus according to one aspect of the present invention is a single crystal growth apparatus for manufacturing an oxide single crystal by the Czochralski method, and a melt obtained by melting the raw material of the oxide single crystal. A crucible to be stored; a heater that is disposed around the crucible and that heats the raw material of the oxide single crystal; and a pulling shaft on which a seed crystal of the oxide single crystal is attached above an axis of the crucible. A rectifying member provided with a plurality of rectifying plates extending radially from the outer periphery of the circular ring is disposed on the melt surface of the crucible.

  In the single crystal growing apparatus according to one aspect of the present invention, it is preferable that an inner diameter of the circular ring is larger than a diameter of the seed crystal.

  In the single crystal growing apparatus according to one embodiment of the present invention, it is preferable that the inner diameter of the circular ring is twice or more than the diameter of the seed crystal.

  In the single crystal growing apparatus according to one aspect of the present invention, it is preferable that six or eight rectifying plates of the rectifying member are attached at equal intervals.

  Moreover, in the single crystal growing apparatus which concerns on 1 aspect of this invention, it is preferable that the immersion rate of the said baffle plate is 0.4-0.8.

  In the single crystal growth apparatus according to one embodiment of the present invention, when the diameter of the crucible is 350 mm or more and 450 mm or less, the height of the crucible is preferably 400 mm or more and 800 mm or less.

  In the single crystal growing apparatus according to one embodiment of the present invention, the oxide single crystal is preferably a sapphire single crystal.

  A method for producing a single crystal according to another embodiment of the present invention is a method for producing an oxide single crystal by producing an oxide single crystal by the Czochralski method, wherein the raw material for the oxide single crystal is used as the raw material. A heating step for maintaining the melted state in the crucible at a temperature exceeding the melting point of the crucible, and an installation step for arranging a rectifying member provided with a plurality of rectifying plates extending radially from the outer periphery of the circular ring; A pulling shaft to which the seed crystal of the oxide single crystal is attached is disposed above the crucible axis, and the oxide single crystal is brought into contact with the center of the melt surface by bringing the seed crystal into contact with the center of the melt surface. A growing step for growing, a removing step for removing the rectifying member, and a pulling step for lifting the pulling shaft that supports the oxide single crystal. In the setting step, the melt surface of the crucible is placed on the melt surface. By arranging the rectifying member The melt toward the center of the melting liquid level and controls so that convection.

  In the method for producing a single crystal according to another aspect of the present invention, it is preferable that an inspection step for inspecting the growth of the oxide single crystal is further provided after the growth step.

  According to the present invention, the flow of the melt is stably directed toward the center, so that seeding can be reliably performed in the same state, and crystals having a good shape can be stably grown.

It is a schematic sectional drawing which shows the conventional single crystal growth apparatus. (A) is a schematic sectional view showing a single crystal growing apparatus according to an embodiment of the present invention, and (B) is a schematic sectional view showing a crucible provided in the single crystal growing apparatus according to an embodiment of the present invention. . (A) is a perspective view which shows the rectifying member of the single crystal growing apparatus which concerns on one Embodiment of this invention, (B) is a perspective view which shows the rectifying member of the single crystal growing apparatus which concerns on one Embodiment of this invention. . It is a figure which shows the velocity distribution of the melt stored in the crucible with which the single crystal growth apparatus which concerns on one Embodiment of this invention is equipped, and shows the positional relationship of the flow of a melt and a baffle plate. It is a flowchart which shows the outline of the manufacturing method of the single crystal which concerns on one Embodiment of this invention. (A) is a figure which shows the temperature distribution on the melt surface in Example 1, (B) is an enlarged view which shows the temperature distribution in the center part on the melt surface in Example 1. FIG. (A) is a figure which shows the temperature distribution on the melt surface in the comparative example 1, (B) is an enlarged view which shows the temperature distribution in the center part on the melt surface in the comparative example 1.

  Hereinafter, preferred embodiments of the present invention will be described in detail. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and all the configurations described in the present embodiment are essential as means for solving the present invention. Not necessarily.

[1. Overview]
Conventionally, to produce a sapphire single crystal from a sapphire raw material melt by the Czochralski method, a sapphire single crystal growing apparatus 100 as shown in FIG. 1 is used.

  In this single crystal growing apparatus 100, a crucible 140 for filling a sapphire material in a space surrounded by a heat insulating material 120 and a heater 130 installed in a chamber 110 is installed. In order to maintain the surface of the raw material melt at a fixed position, the crucible 140 is supported by the crucible base 150 and the crucible shaft 160, and the upper surface of the melt 141 is passed from the upper part of the chamber 110 through the opening on the upper surface of the heat insulating material 120. A seed crystal 171 is brought into contact with each other via a crystal axis 170, and the crystal axis 170 and the seed crystal 171 are pulled up to grow a sapphire single crystal.

  In the growth of this single crystal, first, the seed crystal 171 is placed at the center of the melt surface, the crystal is deposited on the tip of the seed crystal 171, and then the seed crystal 171 is pulled up while rotating to grow the crystal.

  If the flow of the melt is unstable, the position of the lowest temperature on the melt surface is shifted from the center, the seeding is not successful, and the yield of the single crystal is deteriorated. When the position of the lowest temperature on the melt surface deviates from the center, the crystal grows at a position deviated from the center of the seed crystal, so that a twisted crystal is formed and the yield of the crystal is deteriorated. Further, when a crystal deviating from the central axis grows, the rotation of the rotating crystal axis increases and the crystal axis is damaged.

  Thus, in the case of a sapphire single crystal, since the melting point is very high, 2040 ° C., the seed crystal can be brought into contact with the lowest temperature position on the melt surface while constantly monitoring the furnace environment. is important. However, control of the contact position of the seed crystal in such an extremely high temperature environment is an extremely difficult task.

  In order to solve this problem, the inventors have intensively studied, and as a result, controlling the convection of the melt in the crucible so that the lowest temperature position of the melt surface in the crucible becomes the center position of the crucible, In order to achieve this, a rectifying member having a plurality of rectifying plates facing the center of the crucible is immersed in the melt surface, and the melt near the melt surface in the crucible is immersed in the crucible. We found that this is possible by forcibly inducing convection in the direction of the center position.

  By the above method, convection of the crucible surface of the aluminum oxide raw material melt is caused, the melt is convected downward in the center of the crucible, and the central portion that convects downward is the lowest temperature position on the melt surface. Since the seed crystal can be easily seeded by contacting the seed crystal at the position, and the single crystal can be pulled uniformly at the center position of the crucible, the temperature gradient can be adjusted to an appropriate gradient. A single crystal without (void, polycrystallization) can be obtained in high yield. Hereinafter, the single crystal growth apparatus and the single crystal manufacturing method according to the present embodiment will be described.

[2-1. Single crystal growth equipment]
First, the single crystal growth apparatus according to the present embodiment will be described. The single crystal growing apparatus according to the present embodiment is an apparatus for producing an oxide single crystal such as a sapphire single crystal from a melt obtained by heating and melting a raw material in a crucible by a CZ method.

  FIG. 2A is a schematic cross-sectional view showing a single crystal growth apparatus according to an embodiment of the present invention, and FIG. 2B is a schematic view showing a crucible provided in the single crystal growth apparatus according to an embodiment of the present invention. It is sectional drawing. As shown in FIG. 2A, the single crystal growing apparatus 1 according to the present embodiment includes a chamber 10, a crucible 20, a heater 30, a heat insulating material 40, a pulling shaft 50, and a support shaft 60. It is a thing.

  The chamber 10 has a substantially cylindrical shape. The chamber 10 has a gas introduction pipe (not shown) and a gas discharge pipe (not shown). For example, above a pull chamber (not shown) attached to the upper part of the chamber 10 at the normal time such as during single crystal growth. Then, an inert gas or the like can be introduced into the furnace through a gas introduction pipe, and the introduced gas can be discharged out of the furnace from a gas discharge pipe at the bottom of the chamber by a vacuum pump (not shown) or the like. On the other hand, when charging the raw material, the gate valve (not shown) is closed and the raw material is charged in the pull chamber. After that, the pull chamber uses a gas exhaust pipe and a gas introduction pipe for the pull chamber. Gas replacement. Note that a viewing window (not shown) may be provided in the chamber 10 so as to penetrate the heat insulating material 40, and the state of pulling up the oxide single crystal can be confirmed. Further, the chamber 10 is also provided with various temperature measuring means.

  The crucible 20 is disposed inside the chamber 10. The crucible 20 stores a melt 21 obtained by melting a raw material of an oxide single crystal. The crucible 20 has a substantially cylindrical shape. The size of the crucible 20 is not particularly limited. For example, when the diameter of the crucible 20 is 350 mm or more and 450 mm or less, the height of the crucible 20 is preferably 400 mm or more and 800 mm or less. Such a size is structurally suitable for convection of the melt 21 to the center of the melt surface in the crucible 20.

  When the sapphire single crystal is grown by the CZ method, since the melting point of the sapphire single crystal is 2040 ° C., the growth environment of the single crystal is a high temperature of 2000 ° C. or higher. In such a high temperature environment, materials that can be used for the crucible 20 are sapphire single crystal raw materials such as tungsten (W), iridium (Ir), molybdenum (Mo), tantalum (Ta), carbon, and alloys thereof. It is limited to a high melting point material having heat resistance equal to or higher than the melting point, and tungsten or molybdenum which is smaller than the thermal expansion coefficient of sapphire is particularly preferable.

  As shown in FIG. 2 (B), a rectifying member 22 is arranged on the melt surface along the axis of the crucible 10 in the crucible 10. The rectifying member 22 is provided with a plurality of rectifying plates 22b extending radially from the outer periphery of the circular ring 22a. In the present embodiment, by arranging the rectifying member 22 on the melt surface, the plurality of rectifying plates 22b provided on the rectifying member 22 stabilizes the convection of the melt toward the center of the melt surface. . In order to pull up the rectifying member 22 after the growth of the single crystal is finished, the rectifying member pulling shaft 23 extends vertically upward from the circular ring 22a.

  It is preferable that a part of the current plate 22b is immersed in the melt 21, and the immersion rate of the current plate 22b is 0.4 or more and 0.8 or less. Since the rectifying plate 22b that is not immersed is exposed outside the melt, the convection of the melt is more stably directed toward the center of the melt surface. The immersion rate is an index indicating the ratio of the height of the rectifying plate immersed in the melt to the height of the rectifying plate. Further, a clearance of about 0.1 mm to 1.0 mm is provided between the front edge of the current plate and the inner peripheral surface of the crucible facing the front edge so that the current member can be easily removed.

  The inner diameter of the circular ring 22 a is preferably larger than the diameter of the seed crystal 51, and more preferably twice or more than the diameter of the seed crystal 51. The upper limit value can be appropriately selected from the inner diameters of the circular ring 22a and the crucible 20, and the inner diameter of the circular ring 22a may be four times or less than the diameter of the seed crystal. The circular ring 22a provided on the rectifying member 22 can secure a wide area for immersing the seed crystal 51, and the area where the minimum temperature in the melt is widened can be more reliably seeded in the same state. Can do.

  FIG. 3A is a perspective view showing a rectifying member of a single crystal growing apparatus according to an embodiment of the present invention, and FIG. 3B shows a rectifying member of a single crystal growing apparatus according to an embodiment of the present invention. It is a perspective view. The rectifying member 22 shown in FIG. 3 (A) extends radially from the outer periphery of the circular ring 22a, and six rectifying plates 22b are provided at equal intervals. The cross section of the circular ring 22a may be circular, elliptical, or square. 3B extends radially from the outer periphery of the circular ring 22a and the holding member 22c, and six current plates 22b are provided at equal intervals. The holding member 22c has a circular shape. The ring 22a extends vertically downward in a cylindrical shape, and is cut out in a substantially U shape in a region where the rectifying plate 22b is not provided.

  That is, the rectifying plate 22b of the rectifying member 22 is not limited as long as a plurality of rectifying plates 22b are attached, but it is preferable that six (see FIGS. 3A and 3B) or eight are attached at equal intervals. This makes it possible to control the flow in the vicinity of the melt surface divided at equal intervals at a depth of about 50 mm from the melt surface, so that the flow of the melt 21 is more stably directed toward the center. The seeds can be more reliably seeded in the same state, and crystals having good shapes can be stably grown.

  Next, FIG. 4 is a diagram showing the velocity distribution of the melt stored in the crucible provided in the single crystal growth apparatus according to one embodiment of the present invention, and shows the positional relationship between the flow of the melt and the current plate. is there. According to FIG. 4, the flow of the melt 21 is at a constant speed from the side surface in the crucible 20 to the center of the melt surface in the direction of the arrow through both ends of the melt surface. The flow of the melt is controlled so as to be directed toward the center of the melt surface by the rectifying plate 22b. Next, the flow of the melt 21 becomes very fast from the vicinity of the center of the melt surface, and becomes faster than other regions. Since the flow of the melt 21 is fast to the bottom of the crucible 20 and the flow of the melt 21 hits the bottom of the crucible 20, the flow of the melt 21 gradually reaches both ends of the bottom of the crucible 20. To be late. Thus, the melt 21 convects in the crucible 20 inwardly according to the velocity distribution. In addition, since the melt 21 convects inward, there is no melt flow in the inner periphery.

  As described above, the flow in the melt is in the center direction, and the depth of the flow toward the center in the vicinity of the melt surface is about 50 mm. The current plate 22b needs to be 10 mm or more. Even if the rectifying plate 22b deeper than 50 mm is inserted, the effect does not change. Therefore, the width of the rectifying plate 22b is preferably 10 mm or more and 50 mm or less. The thickness of the rectifying plate 22b is not particularly limited, but is preferably 1 mm or more and 5 mm or less. In order not to obstruct the flow of the melt 21, the thickness is set to 5 mm or less. If it is too thick, the flow toward the center at the end face of the current plate 22b changes. Moreover, in order to perform stable rectification in strength, the thickness is set to 1 mm or more.

  The material of the rectifying member 22 is not particularly limited, but when the sapphire single crystal is grown by the CZ method, the heat resistance is higher than the melting point of the raw material for sapphire single crystal such as tungsten, iridium, molybdenum, tantalum, and alloys thereof. Among them, tungsten and molybdenum are preferred, which are smaller than the thermal expansion coefficient of sapphire.

  The heater 30 is provided around the crucible 20 in order to melt the single crystal raw material filled in the crucible 20. The heater 30 is not particularly limited, but a resistance heater is preferable. As an alternative to the heater 30, a heating coil may be installed in the crucible and subjected to high frequency induction heating.

  The heat insulating material 40 is provided outside the heater 30 and along the inner surface of the chamber 10. Although the melting point of the sapphire single crystal is very high, since the heat insulating material 40 is provided not only on the side of the heater 30 but also on the upper side and the lower side, sufficient heat retention can be secured, and the sapphire in the crucible 20 The raw material can be efficiently heated.

  The pulling shaft 50 is disposed above the axis of the crucible 20. A pulling shaft 50 is attached with a seed crystal 51 of an oxide single crystal. Further, the pulling shaft 50 may be provided with a weight measuring unit (not shown) in order to measure the crystal weight of the grown single crystal.

  The support shaft 60 is disposed along the axial center of the chamber 10 in order to support the crucible 20 so that it can be placed via the support base 61. The support shaft 60 can move up and down. In addition, the support base 61 is disk shape. The support base 61 is made of heat-resistant metal, graphite, or the like.

  In order to move the straightening member pulling shaft 23, the pulling shaft 50, and the support shaft 60 up and down, drive motors (not shown) can be arranged respectively. The driving motor and the weight measuring unit can be connected to a control unit (not shown).

[2-2. Single crystal manufacturing method]
Next, a method for producing a single crystal will be described. FIG. 5 is a flowchart showing an outline of a method for producing a single crystal according to an embodiment of the present invention. As shown in FIG. 5, the method for producing a single crystal according to the present embodiment includes a heating step (hereinafter, also referred to as “heating step S <b> 1”) in which a raw material for an oxide single crystal is held in a melt 21 state. The step of arranging the rectifying member 22 (hereinafter also referred to as “installation step S2”), the step of growing the oxide single crystal (hereinafter also referred to as “growing step S3”), and the rectifying member 22 are arranged. A removal step (hereinafter also referred to as “removal step S5”) to be removed and a pulling step (hereinafter also referred to as “lifting step S6”) for raising the pulling shaft 50 are included. Moreover, in this embodiment, you may further provide inspection process S4 after growing process S3. Hereinafter, each process S1-S6 is demonstrated, respectively.

  The heating step S1 is a step of holding the raw material of the oxide single crystal in the state of the melt 21 melted in the crucible 20 at a temperature exceeding the melting point of the raw material.

  Moreover, in the manufacturing method of the oxide single crystal of this embodiment, a sapphire single crystal can be manufactured more suitably among oxide single crystals. For this reason, aluminum oxide powder can be used more suitably as a raw material for single crystals.

The aluminum oxide powder is aluminum oxide substantially composed of two elements of Al and O. Α-alumina (Al ₂ O ₃ ) having a material purity of about 99.95 to 99.998% is preferable. In addition to Al and O, Ti, Cr, Si, Ca, Mg, and the like may be included in accordance with the type of target sapphire single crystal. Among these, Si, Ca, Mg and the like can be inevitably contained as components of the sintering aid, but the content is desirably as small as possible. Moreover, when using an aluminum oxide powder, the particle size and density are not particularly limited, but for handling, for example, the particle size is preferably 10 mm or less, more preferably 5 mm or less. The density of the aluminum oxide powder is close to the theoretical density of 4 g / cm ³ of α-alumina when the raw material is filled. Therefore, the density of the aluminum oxide powder to be used is preferably 2 g / cm ³ or more, and more preferably 3 g / cm ³ or more. In the present embodiment, the average particle size means a particle size having an integrated value of 50%, and can be measured by a particle size distribution measuring device such as SALD-7000 (Shimadzu Corporation).

After putting the raw material of the oxide single crystal in the crucible 20, after removing the air while reducing the pressure with a vacuum pump, the raw material is melted in the crucible 20 while flowing an inert gas (N ₂ gas or Ar gas). .

  In heating process S1, the raw material for single crystals can be put into the crucible 20, and the raw material for single crystals can be fuse | melted by heating the crucible 20 with the heater 30. FIG. The heating speed until the single crystal raw material reaches the melting point is not particularly limited. However, in order to suppress the occurrence of bumping phenomenon that occurs when the raw material melts non-uniformly, the heating speed is not increased rapidly. It is better to heat gradually over time. For this reason, it is desirable to gradually heat, for example, over 10 hours, particularly over 12 hours.

  Even after the single crystal raw material is melted, it is preferable to continue heating at a temperature in the furnace that is 10 ° C. to 20 ° C. higher than the melting point of the single crystal raw material. Although the time which continues heating in the temperature range which concerns is not specifically limited, For example, it is preferable to continue for 3 hours or more, and it is more preferable to continue for 5 hours or more. The temperature measurement at this time can be performed using, for example, a thermocouple (not shown) inserted into the heat insulating material 40 on the outer periphery of the heater 30.

  The installation step S2 is a step of arranging the rectifying member 22 provided with a plurality of rectifying plates 22b extending radially from the outer periphery of the circular ring 22a. And by arrange | positioning the rectification | straightening member 22 to the melt surface of the crucible 20, it controls so that the melt 21 may be convected toward the center of a melt surface. As a result, the convection of the melt 21 is stably directed toward the center of the melt surface, and the center of the melt surface is the lowest temperature position.

  In the growth step S3, a pulling shaft 50 to which a seed crystal 51 of an oxide single crystal is attached is arranged above the axis of the crucible 20, and the seed crystal 51 attached to the pulling shaft 50 is set at the center of the melt surface. This is a step of growing an oxide single crystal by contact. Specifically, the seed crystal 51 attached to the pulling shaft 50 is lowered while being rotated to the melt surface, and the seed crystal 51 is immersed at the minimum temperature position at the center of the melt surface described above.

  The inspection step S4 is a step for inspecting that the oxide single crystal has grown. From a viewing window (not shown) provided in the chamber 10, it is confirmed that the oxide single crystal has grown. If the rectifying member 22 is removed in the next removal step S5 in a state where the oxide single crystal has not grown, the convection becomes non-uniform and the center of the melt surface shifts. Therefore, even if the oxide single crystal is pulled in the pulling step S6, which is a subsequent step, the crystal grows out of the pulling axis 50, and a crystal with a shape deviating from the axial symmetry is formed, and it is necessary to remelt the crystal. Occurs.

  The removing step S5 is a step of removing the rectifying member 22. Specifically, the rectifying member 22 is removed by raising the rectifying member pulling shaft 23 that supports the rectifying member 22 in the vertical direction. Thereby, in the pulling-up process S6 which is the next process, the rectifying member 22 does not become an obstacle to producing the grown oxide single crystal. The pulling speed of the straightening member pulling shaft 23 is appropriately adjusted.

  The pulling step S6 is a step of raising the pulling shaft 50 that supports the grown oxide single crystal. Specifically, the pulling shaft 50 that supports the oxide single crystal is raised by rotating the crucible 20 and rotating the oxide single crystal in the opposite direction. Thereby, the grown oxide single crystal can be produced while maintaining the flow of the inner melt 21 in the crucible 20.

  The crystal shape of the crystal to be grown can be adjusted by measuring the weight of the crystal being grown, deriving the diameter, growth speed, and the like by calculation, and adjusting the rotation speed and pulling speed of the pulling shaft 50. For example, the seed crystal 51 may be rotated at 0.2 rpm to 20 rpm. Further, the crystal weight can be measured at appropriate time intervals, and the change can be fed back to control the melt temperature of the raw material melt 21. Note that after the single crystal is sufficiently grown in the growing step S3, the crucible 11 may be lowered by the support shaft through the removing step S5, and the pulling shaft 50 that supports the grown single crystal may be raised.

  Thus, by raising the pulling shaft 50 that supports the grown single crystal, the grown single crystal and the melt 21 are separated from each other, whereby an oxide single crystal can be produced.

[2-3. Summary]
As described above, the single crystal growing apparatus 1 according to the present embodiment is a single crystal growing apparatus 1 that produces an oxide single crystal by the Czochralski method, and is a melt 21 in which a raw material of an oxide single crystal is melted. , A crucible 20 that is stored around the crucible 20, a heater 30 that heats the raw material of the oxide single crystal, and a pullup in which a seed crystal 51 of the oxide single crystal is attached above the axis of the crucible 20. A shaft 50. Then, on the melt surface of the crucible 20, a rectifying member 22 provided with a plurality of rectifying plates 22b extending radially from the outer periphery of the circular ring 22a is disposed.

  The method for producing a single crystal according to this embodiment is a method for producing an oxide single crystal by the Czochralski method, wherein the raw material for the oxide single crystal is adjusted to the melting point of the raw material. An installation in which a heating step S1 for holding the melt 21 melted in the crucible 20 at a temperature exceeding the temperature, and a rectifying member 22 provided with a plurality of rectifying plates 22b extending radially from the outer periphery of the circular ring are arranged. A pulling shaft 50 to which a seed crystal 51 of an oxide single crystal is attached is disposed above the axis of the step S2 and the crucible 20, and the seed crystal 51 is brought into contact with the center of the melt surface to thereby provide a single oxide. It has a growing step S3 for growing crystals, a removing step S5 for removing the rectifying member 22, and a pulling step S6 for lifting the pulling shaft 50 that supports the oxide single crystal. And in installation process S2, by arrange | positioning the rectification | straightening member 22 in the melt surface of the crucible 20, it controls so that the melt 21 is convected toward the center of a melt surface.

  In the present embodiment, by arranging the flow regulating member 22 on the melt surface, the flow of the melt 21 is stably directed toward the center of the melt surface by the plurality of flow straightening plates 22b provided on the flow regulating member 22. Become. Since the circular ring 22a provided in the rectifying member 22 secures a region for immersing the seed crystal 51, this region becomes the lowest temperature in the melt, so that seeding can be reliably performed in the same state. As a result, in this embodiment, a crystal having a good shape can be stably grown.

  Hereinafter, the present invention will be specifically described by way of examples, but is not limited thereto.

Example 1
First, in Example 1, using the single crystal growing apparatus 1 shown in FIG. 2A, a rectifying member including eight rectifying plates 22b that cause forced convection with the crucible 20 shown in FIG. 2B. 22 and the temperature distribution at the time of seeding was obtained with the single crystal growing apparatus 1 having the following configuration.
・ Tungsten crucible: diameter 400mm x height 540mm x thickness 2mm
-Melt (aluminum oxide): height of melt surface in crucible 480 mm
-Seed crystal: □ 20mm x length 140mm
・ Round ring: Diameter 100mm x Height 5mm
・ Rectifying plate (8 sheets): length 130mm x depth 33mm x thickness 2mm

  The seed crystal 51 was seeded in a state where the rectifying plate 22b was immersed to a depth of 30 mm from the melt surface of the aluminum oxide.

  6A is a diagram showing the temperature distribution on the melt surface in Example 1, and FIG. 6B is an enlarged view showing the temperature distribution in the center on the melt surface in Example 1. FIG. According to FIG. 6 (A), the temperature distribution on the melt surface was divided into eight, and all the fractions were substantially equivalent. It was also confirmed that the convection of the melt 21 was directed to the center of the melt surface because the temperature distribution was lower in the center than the outer peripheral portion of the melt surface. Furthermore, according to FIG. 6 (B), it was confirmed that the black square overlaps with the lowest temperature portion. Note that the black squares shown in FIGS. 6A and 6B indicate the part where the seed crystal 51 is immersed.

  That is, it was confirmed that the lowest temperature portion was provided at almost the center of the end face of the seed crystal 51, and that good crystal growth was possible.

(Comparative Example 1)
Next, in the comparative example 1, it was set as the structure similar to Example 1 except not using the rectification | straightening member 22 using the single crystal growth apparatus 1 shown in FIG. 7A is a diagram showing the temperature distribution on the melt surface in Comparative Example 1, and FIG. 7B is an enlarged view showing the temperature distribution in the center portion on the melt surface in Comparative Example 1. FIG. According to FIG. 7A, the temperature distribution on the melt surface is fractionated into six, but these fractions were not equivalent. Further, according to FIG. 7B, it was confirmed that the black square was shifted from the lowest temperature portion. Note that the black squares shown in FIGS. 6A and 6B indicate the part where the seed crystal 51 is immersed.

  Therefore, when the rectifying member 22 is not inserted, the temperature distribution on the melt surface is as shown in FIGS. 7A and 7B, the temperature center is shifted from the end face of the seed crystal 51, and from the crystal axis. It was confirmed that crystals grew from the shifted position. If it continued as it was, it shifted from the rotation axis and the crystal grew, and a crystal with a shape shifted from the axial symmetry was formed. For this reason, it was necessary to redissolve the prepared crystal.

(Consideration based on Examples)
From the results of Example 1 and Comparative Example 1, by arranging the rectifying member 22 on the melt surface of the crucible 20, the convection of the melt 21 can be directed to the center of the melt surface. It was confirmed that the center was at the lowest temperature position. As a result, it can be said that the deterioration of the yield of single crystals and the decrease in yield can be eliminated, and stable seeding can be performed.

DESCRIPTION OF SYMBOLS 1 Single crystal growth apparatus, 10 chamber, 20 crucible, 21 melt, 22 rectifying member, 22a circular ring, 22b rectifying plate, 22c holding member, 23 pulling shaft for rectifying member, 30 heater, 40 heat insulating material, 50 pulling shaft, 51 seed crystal, 60 support shaft, 61 support base, 100 single crystal growth device, 110 chamber, 120 heat insulating material, 130 heater, 140 crucible, 141 melt, 150 crucible base, 160 crucible shaft, 170 crystal shaft, 171 seed crystal , S1 heating process, S2 installation process, S3 growing process, S4 inspection process, S5 removal process, S6 pulling process

Claims (9)

A single crystal growing apparatus for producing an oxide single crystal by the Czochralski method,
A crucible for storing a melt obtained by melting the raw material of the oxide single crystal;
A heater that is disposed around the crucible and heats the raw material of the oxide single crystal;
A pulling shaft on which the seed crystal of the oxide single crystal is mounted above the crucible axis;
An apparatus for growing a single crystal, wherein a rectifying member provided with a plurality of rectifying plates extending radially from an outer periphery of a circular ring is disposed on a melt surface of the crucible.   The single crystal growing apparatus according to claim 1, wherein an inner diameter of the circular ring is larger than a diameter of the seed crystal.   The single crystal growing apparatus according to claim 2, wherein an inner diameter of the circular ring is twice or more than a diameter of the seed crystal.   The single crystal growing apparatus according to any one of claims 1 to 3, wherein six or eight rectifying plates of the rectifying member are attached at equal intervals.   The single crystal growth apparatus according to any one of claims 1 to 4, wherein an immersion rate of the current plate is 0.4 or more and 0.8 or less.   The single crystal growing apparatus according to any one of claims 1 to 5, wherein when the diameter of the crucible is 350 mm or more and 450 mm or less, the height of the crucible is 400 mm or more and 800 mm or less.   The single crystal growth apparatus according to any one of claims 1 to 6, wherein the oxide single crystal is a sapphire single crystal. An oxide single crystal production method for producing an oxide single crystal by the Czochralski method,
A heating step of holding the raw material of the oxide single crystal in a melted state melted in a crucible at a temperature exceeding the melting point of the raw material;
An installation step of arranging a rectifying member provided with a plurality of rectifying plates extending radially from the outer periphery of the circular ring;
A pulling shaft to which the seed crystal of the oxide single crystal is attached is disposed above the center of the crucible, and the oxide single crystal is grown by bringing the seed crystal into contact with the center of the melt surface. A training process,
A removal step of removing the flow regulating member;
A pulling step of lifting the pulling shaft that supports the oxide single crystal,
In the installation step, a method for producing a single crystal that controls the melt to be convected toward the center of the melt surface by disposing the rectifying member on the melt surface of the crucible.   The method for producing a single crystal according to claim 8, further comprising an inspection step for inspecting that the oxide single crystal has grown after the growing step.