JP2019127428A - Crystal growth apparatus - Google Patents

Abstract

To provide a crystal growth apparatus which copes with long size of crystal growth length, with low cost while preventing defect such as crack from generating.SOLUTION: The apparatus includes: a metal crucible which pools raw material melt; an inductive coil for heating arranged around the crucible; a metal after-heater of a hollow shape arranged over the crucible; and a pull-up shaft for pulling up crystal from the raw material melt, a length of the after-heater being variable in a moving direction of the pull-up shaft.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a crystal growth apparatus.

  As a method for producing an oxide single crystal, a crucible filled with a raw material to become an oxide single crystal is heated to a high temperature to melt the raw material, and a seed crystal is brought into contact with the liquid surface of the raw material melt in the crucible from above. Thereafter, a crystal growth method by the Czochralski method is widely practiced in which an oxide single crystal having the same orientation as that of the seed crystal is grown by rotating it while rotating.

  In single crystal growth by the Czochralski method, an induction coil is disposed around the crucible, and an eddy current is generated in the crucible by supplying a high frequency current to the induction coil, which generates heat in the crucible and the raw material in the crucible is It melts.

  Also, as the pulling progresses, the upper part of the single crystal is cooled along the seed rod (pulling axis), but if the heating element is only a crucible, the temperature gradient in the growing single crystal becomes large. The idea is to keep the top of the crucible warm. For example, in order to suppress a crack due to a thermal stress caused by a temperature difference in the crystal, a cylindrical after heater, which is a heating element other than the crucible, is disposed at the top of the crucible (see, for example, Patent Document 1). In addition, a donut-shaped (annular) reflector may be arranged to keep the upper part of the crucible warm.

JP, 2014-125404, A

  By the way, in recent years, the market for oxide single crystals, particularly lithium tantalate, is expanding as a surface acoustic wave device material, and the pulling length of the single crystal is gradually increased in order to secure the production amount. Along with this lengthening, it is easy to generate cracks due to bending of the crystal, polycrystallization generated at the straight barrel, cracks due to thermal strain during cooling, solidification of raw material at the bottom of the crucible, etc. It causes the rate to decrease. In particular, it is presumed that the crack caused by the thermal strain is generated due to the temperature gradient at the upper end and the lower end of the grown crystal becoming larger since the pulling distance becomes longer.

  In order to cope with this lengthening, Patent Document 1 arranges a first induction coil arranged around the crucible and a second derivative arranged around the after heater, and each derivative is individually provided. A crystal growth apparatus has been disclosed in which a high frequency power source of the above is prepared and set so that the supplied high frequency currents are in reverse phase with each other. In the crystal growth apparatus described in Patent Document 1, since the after heater can be heated individually, it is possible to set an appropriate temperature gradient.

  However, in the configuration of the crystal growing apparatus described in Patent Document 1, two power supply facilities are required, the facility cost is high, and the installation location is also widened. Further, it is necessary to appropriately control the magnetic field caused by the first high-frequency current and the magnetic field caused by the second high-frequency current by reversing the phases of the first high-frequency current and the second high-frequency current. Advanced control is required.

  Therefore, in view of the above circumstances, an object of the present invention is to provide a crystal growth apparatus that can cope with an increase in crystal growth length at low cost without occurrence of defects such as cracks.

In order to achieve the above object, a crystal growth apparatus according to an aspect of the present invention is a metal crucible capable of storing a raw material melt;
A heating induction coil disposed around the crucible;
A metallic afterheater having a hollow shape disposed above the crucible;
And a pulling shaft capable of pulling a crystal from the raw material melt;
The after heater has a variable length in the moving direction of the pulling shaft.

  According to the present invention, it is possible to provide a single crystal growth apparatus that can cope with an increase in the crystal growth length at low cost without occurrence of defects such as cracks.

It is the schematic which showed an example of the crystal growth apparatus which concerns on the 1st Embodiment of this invention. It is the figure which showed an example of the after heater of the crystal growth apparatus which concerns on the 1st Embodiment of this invention. It is a figure showing an example of the after heater concerning a prior art. It is sectional drawing which shows the detail of the after-heater which concerns on the 1st Embodiment of this invention. It is the figure which showed the modification of FIG. It is a figure for demonstrating the attachment method of the after heater of the crystal growth apparatus which concerns on 1st Embodiment. It is the figure which showed an example of the crystal growth apparatus which concerns on the 2nd Embodiment of this invention. It is the figure which showed an example of the crystal growth apparatus which concerns on the 3rd Embodiment of this invention. It is a graph when the heat generation distribution of an example of the after heater of the crystal growing apparatus according to the present example is simulated from the center of the bottom of the crucible to the top of the after heater. It is the figure which showed the temperature distribution in the depth direction of the melt in the crucible of the growth initial stage of an example of the after heater of the crystal growth apparatus which concerns on a present Example. It is the figure which showed the temperature distribution in the radial direction of the melt surface of the initial stage of growth of the example of the after heater of the crystal growth apparatus which concerns on a present Example. It is the figure which showed the temperature distribution in the height direction in the crystal | crystallization of the latter stage of the growth of an example of the after-heater of the crystal growth apparatus concerning a present Example.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

The crystal growth apparatus using the chocoskey method of the present invention is lithium niobate LiNbO ₃ (hereinafter referred to as “LN”) grown in the air or in an inert gas atmosphere, and tantalum acid. An oxide single crystal such as lithium LiTaO ₃ (hereinafter referred to as “LT”) or yttrium aluminum garnet Y ₃ Al ₅ O ₁₂ (hereinafter referred to as “YAG”). It is a crystal growth apparatus used for manufacturing. The Czochralski method is called a seed cut out according to a certain crystal orientation, and is usually infiltrated into the melt of the same composition at the tip of a rectangular parallelepiped with a side of about several millimeters in cross-section, and is gradually pulled up while rotating. Is a method of producing a single crystal by increasing the diameter while propagating the properties of the seed crystal.

[First Embodiment]
FIG. 1 is a schematic view showing an example of a crystal growth apparatus according to a first embodiment of the present invention. As shown in FIG. 1, the crystal growth apparatus according to the first embodiment includes a crucible 10, a crucible base 20, a reflector 30, an after heater 40, a heat insulating material 50, a refractory 60, and a pull-up. A shaft 70, an induction coil 80, a power supply 90, and a control unit 100 are provided. The heating means is an induction coil 80 for heating the crucible 10 and the after heater 40. The power supply 90 is also provided to supply high frequency power to the induction coil 80.

  In the crystal growing apparatus according to this embodiment, the crucible 10 is placed on the crucible base 20. An after heater 40 is installed above the crucible 10 via a reflector 30. The after-heater 40 has a hollow shape as a whole, and the length of the after-heater 40 varies in the pulling-up axial direction according to crystal growth. In FIG. 1, the after-heater 40 is divided into three hollow members, the three hollow members having different radii (and diameters) from each other, arranged radially overlapping, and having a low overall height. The shaped after-heater 40 is shown. That is, each hollow member is disposed so as to surround the hollow member having a smaller diameter than itself and to be surrounded by the hollow member having a larger diameter than itself. The details of the after heater 40 will be described later.

  A heat insulating material 50 is provided to surround the crucible 10. A refractory 60 is provided outside the heat insulating material 50 and covers the entire periphery of the crucible 10. An induction coil 80 is disposed outside the side surface of the refractory 60.

  The refractory 60 having the induction coil 80 provided outside is placed on a support base (not shown). In addition, a chamber (not shown) covers the periphery of the induction coil 80.

  The crucible 10 and the heat insulating material 50 provided around the crucible 10 constitute a hot zone part. Further, a pulling shaft 70 is provided above the crucible 10. The pulling shaft 70 has a seed crystal holding portion 71 at its lower end, and is configured to be able to move up and down by the pulling shaft drive portion 72. The pull-up shaft 70 further includes an after / heater mounting jig 73, a jig support portion 74, and a connecting member 75. Furthermore, a power supply 90 and a control means 100 are provided outside the periphery of the chamber (not shown).

  In FIG. 1, a seed crystal 150, a crystal raw material 160, and a pulled single crystal (also referred to as a crystal) 170 are shown as related constituent elements.

  Next, individual components of the crystal growth apparatus according to the first embodiment will be described.

  The crucible 10 is a container for storing and holding the crystal raw material 160 and growing the single crystal 170. The crystal raw material 160 is held in a molten state in which a metal or the like to be crystallized is melted. The material of the crucible is made of platinum, iridium or the like having heat resistance although it depends on the crystal raw material 160.

  The crucible table 20 is provided as a mounting table for supporting the crucible 10 from below. The crucible base 20 may be made of various materials as long as it has sufficient heat resistance to withstand the heating of the induction coil 80 and durability to support the crucible 10. As shown in FIG. 1, the crucible base 20 may be configured to support a refractory 60 in addition to the crucible 10.

  The reflector 30 is a member that reflects the heat rising from the crucible 10 and returns the heat to the crucible 10 side. The reflector 30 may also be made of various materials as long as it can reflect heat and heat resistance enough to withstand the heating of the induction coil 80. For example, the reflector 30 is made of a metal material having sufficient heat resistance such as platinum and iridium. .

  The after heater 40 is a heating means for heating the single crystal 170 pulled up above the crucible 10. The single crystal 170 to be grown is moved away from the crucible 10 as the pulling of the single crystal 170 proceeds, so the temperature gradient of the single crystal 170 may be large, and problems such as cracking of the single crystal 170 may occur. In order to improve this, an after heater 40 is installed above the crucible 10 to maintain an appropriate temperature gradient.

  The after heater 40 is made of a metal material having sufficient heat resistance such as platinum or iridium, and is heated by induction heating of the induction coil 80. The after heater 40 is provided, for example, on the reflector 30. Since the after heater 40 has a sufficient weight, even if it is not fixed on the reflector 30, it can be installed in a stable state.

  In the present embodiment, the after heater 40 varies the length of the after heater in the axial direction of crystal growth, that is, the moving direction (pulling direction) of the pulling shaft 70 according to crystal growth. This is to cope with the lengthening of the single crystal 170, and the after heater 40 can be extended upward as the pulling shaft 70 moves upward and the single crystal 170 is pulled upward and moves upward. It has become. In FIG. 1, the after-heater 40 is shown contracted and lowered. The details of the after heater 40 will be described later.

  The heat insulating material 50 is provided to prevent the heat of the crucible 10 from being released to the outside. Therefore, the heat insulating material 50 is provided to surround the crucible 10. In the general crystal growing apparatus, the heat insulating material 50 is often provided around the after heater 40, but in the crystal growing apparatus according to the present embodiment, the length of the after heater 40 is variable. Therefore, the heat insulating material 50 is not provided around the after heater 40 so as not to hinder the movement of the after heater 40.

  The refractory 60 plays a role of holding heat generated by the induction coil 80 of the crucible 10 inside and preventing release to the outside. The refractory 60 is made of a material having high heat resistance. Thus, the refractory 60 is provided to surround the crucible 10. The refractory 60 may also be mounted on the crucible table 20. Further, the refractory 60 has an opening 31 on the ceiling surface, and is configured such that the lifting shaft 70 can be inserted.

  The pulling shaft 70 is a means for holding the seed crystal 150, bringing the seed crystal 150 into contact with the surface of the raw material melt 160 stored in the crucible 10, and pulling the single crystal while rotating. The pulling shaft 70 has a seed crystal holding portion 71 for holding the seed crystal 150 at the lower end portion, and also has a pulling shaft drive mechanism 72 having a motor as a rotation mechanism. The motor is a rotational drive mechanism for performing an operation of pulling up the crystal while rotating it when pulling up the crystal.

  The pull-up shaft 70 includes an after / heater mounting jig 73, a jig support portion 74, and a connecting member 75. The after-heater mounting jig 73 is means for connecting the lifting shaft 70 and the after-heater 40. That is, it is installed on the pulling shaft 70 and connected to the after heater 40 to transmit the pulling movement of the pulling shaft 70 to the after heater 40. The jig support part 74 is a member for supporting the after-heater mounting jig 73. In FIG. 1, the after heater mounting jig 73 is placed and supported from below. The jig support portion 74 is fixed to the pull-up shaft 70. The connecting member 75 is a member for connecting the after-heater mounting jig 73 and the after-heater 40, and is composed of, for example, a wire or a rod. The details of the configuration of the pulling shaft 70 will also be described later.

  The induction coil 80 is a means for inductively heating the crucible 10, and is disposed to surround the crucible 10 and the refractory 60. The induction coil 80 may be of any type or form as long as it can inductively heat the crucible 10. The induction heating coil 40 generates an eddy current in the crucible 10 with an alternating current, and heats the crucible 10 with the Joule heat.

  The induction coil 80 may or may not be provided around the after heater 40. The induction heating effect of the induction coil 80 extends to the after heater 40 even when the induction coil 80 is provided only around the crucible 10 (only in the range of the same height as the crucible 10). Thus, the induction coil 80 inductively heats the after heater 40 as well as the crucible 10.

  The induction coil 80 may have any form as long as it can inductively heat the crucible 10, the after heater 40 and the like, but is configured as, for example, a high frequency induction heating device including a high frequency heating coil. In this case, the power supply 90 is configured as a high frequency power supply that supplies high frequency power to the induction coil 80.

  The power source 90 is configured as a high frequency power source that supplies high frequency power to the induction coil 80. The power supply 80 supplies power not only to the induction coil 80 but also to the entire crystal growth apparatus.

  The control unit 100 is a means for controlling the entire crystal growth apparatus, and controls the operation of the entire crystal growth apparatus including the crystal growth process. For example, the control unit 110 includes a CPU (Central Processing Unit), a central processing unit, and a memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and may be configured by a microcomputer that operates according to a program. However, it may be composed of an electronic circuit such as an ASIC (Application Specified Integrated Circuit) developed for a specific application.

  The crystal growth apparatus according to this embodiment can be applied to various crystal raw materials 160, and the type of the crystal raw material 160 is not limited, but, for example, a lithium tantalate raw material may be used. In addition, a crystal raw material 160 for growing various oxide single crystals can be used.

  Next, the after heater, which is a feature of the present invention, will be described with reference to FIG. FIG. 2 is a view showing an example of an after heater of the crystal growing apparatus according to the first embodiment of the present invention. 2A is a diagram showing a state in which the after heater 40 is minimized, and FIG. 2B is a diagram showing a state in which the after heater 40 is maximized.

  As shown in FIGS. 2A and 2B, the after heater 40 according to the first embodiment of the present invention is disposed above the crucible 10, specifically, on the reflector 30, and In order to cope with the lengthening, the length of the after heater 40 is changed in the moving direction of the pulling shaft 70 according to the growth of the single crystal 170. In the present embodiment, an after heater 40 composed of three cylindrical members 41 to 43 is prepared, and in the initial stage of growth, as shown in FIG. 2A, the after heater 40 is installed in a state where the three cylindrical members 41 to 43 overlap. Be done. That is, in the radial direction, the cylindrical members 41, 42, 43 are arranged so as to overlap in order from the inside toward the outside. Therefore, the height of the after heater 40 is the same height as the height of one cylindrical member 41 to 43.

  At the rear stage of growth, as shown in FIG. 2B, the after heater 40 having the maximum height is installed in a state in which the upper end and the lower end of the three cylindrical members 41 to 43 are connected to each other. The after heater 40 is also inductively heated by the high frequency from the induction coil 80.

  FIG. 3 shows an after-heater according to the prior art. The after-heater according to the prior art is an integrated after-heater, which is fixed from the initial stage of growth to the completion of growth and has a certain height.

  Here, the purpose of installing the after heater and the purpose of changing the length of the after heater will be described. In single crystal growth by the Czochralski method, the seed crystal 150 is brought into contact with the melted raw material 160 in the crucible 10 and pulled up to thereby cool the crystal body 170 and grow the crystal. At this time, cracks due to thermal strain may occur. This is presumed to be caused by the fact that the temperature gradient at the upper and lower ends of the grown crystal body 170 increases as the pulling distance increases. In order to prevent this, conventionally, an after-heater is provided, and the upper portion of the crystal body 170 is heated and kept warm.

  However, if the overall length of the after heater is correspondingly increased as the crystal length becomes longer, the crystal body 170 can be kept warm in the late stage of crystal growth, but the temperature gradient in the raw material melt 160 is small in the early stage of crystal growth. In some cases, crystals can not be grown. That is, at the initial stage of crystal growth, the entire raw material melt 160 becomes high temperature, and the temperature of the surface where the temperature of the raw material melt 160 is preferably low is also high. As a result, the temperature gradient between the outer side of the raw material melt 160 (near the inner wall of the crucible 10) and the lower part (center and lower part of the crucible 10) becomes small, and the temperature range at which the crucible 10 can be heated becomes small, making temperature control difficult. Met. For this reason, the crystal length has to be set so as to have an appropriate temperature gradient according to the state of crystal growth, and lengthening is difficult.

  Therefore, the after-heater 40 of the crystal growing apparatus according to the first embodiment of the present invention varies the length of the after-heater 40 in the pulling axis direction according to the growth of the crystal. Specifically, in the initial stage of growth, the length is set shorter than the length of a conventional after heater, and when growing a straight barrel, a part of the after heater is extended according to the pulling up length of the crystal by a variable mechanism. It is a mechanism. That is, as the crystal growth proceeds, the after heater 40 is stretched, and the entire length in the pulling direction is elongated. In the initial stage of crystal growth, since the after-heater is short, the amount of heat generation is small, the temperature gradient is large, temperature control becomes easy, and it becomes easy to set an appropriate temperature condition. Further, the position of the upper end of the after heater is set at a position substantially above the upper end of the crystal except in the initial stage of pulling. Preferably, it is 30 mm to 70 mm, and more preferably 50 mm. This is because heat generation concentrates on the upper end portion of the after-heater 40 in a high frequency region where the high frequency of the induction coil 80 is high, particularly 7 kHz or more. That is, by disposing the heat generating portion at the upper end of the after heater above the upper end of the crystal, the upper portion of the upper end of the crystal can always be warmed during the pulling of the crystal. In addition, the after heater 40 can substantially cover the grown crystal body 170 and can suppress the occurrence of cracks.

  Hereinafter, an example of a method of forming the after heater 40 by a plurality of overlapping cylindrical members will be specifically described.

  FIG. 4 is a cross-sectional view showing details of the after heater according to the first embodiment of the present invention. FIG. 4A is an enlarged cross-sectional view of the after heater. FIG. 4B is a cross-sectional view at the minimum of the cross section of the after heater. FIG. 4C is a cross-sectional view at the maximum of the cross section of the after heater.

  As shown in FIG. 4 (a), each cylindrical member 41 has a protrusion 41a at the upper end facing inward and a protrusion 41b at the lower end facing outward.

  As shown in FIG. 4 (b), an after heater 40 comprising a plurality of cylindrical members 41 to 43 having different diameters is prepared, but each has a diameter that can be moved up and down and arranged close to each other. Set In FIG. 4A, the cylindrical member 41 is shown as a representative, but as shown in FIG. 4B, the cylindrical members 42 and 43 also have the same shape, with protrusions 42a on the upper end. 43a, the lower end is provided with projections 42b, 43b. The protrusions 41a and 41b may be formed on the entire circumference in the circumferential direction or may be attached to a part. When attached to a part, three or four parts are formed evenly in the circumferential direction. In addition, when it attaches to one part, a position is defined in the upper and lower protrusions 41a and 41b. When the inner cylindrical member 41 is pulled up by the protrusions 41a and 41b, the protrusions are in contact with each other and engaged, and the next cylindrical member 42 is pulled up.

  FIG. 4C shows a state in which all the cylindrical members 41 to 43 are pulled up and the height of the after heater 40 is maximized. As shown in FIGS. 4B and 4C, when the innermost cylindrical member 41 is pulled up, the protrusion 41 b at the lower end of the cylindrical member 41 and the cylindrical member 42 disposed adjacent to the outer side of the cylindrical member 41. The projection 42a at the upper end is engaged, and the cylindrical member 42 is pulled up. When the cylindrical member 42 is pulled up by the height, the projection 42b at the lower end of the cylindrical member 42 engages with the projection 43a at the upper end of the cylindrical member 43 adjacent to the outside, and the cylindrical member 43 is pulled up. In this way, the projections of the lower end of the inner cylindrical member engage with the projections of the upper end of the outer cylindrical member, whereby the cylindrical members 41 to 43 are gradually pulled up sequentially from the inside, and the entire length of the after heater 40 The length is configured to gradually increase. In the present embodiment, the protrusions 41a to 43a and 41b to 43b function as engaging portions.

  FIG. 5 is a view showing a modified example of FIG. In FIG. 5, the projections 41a, 41b, 42a, 42b, 43a, 43b are respectively formed on portions of the cylindrical members 41, 42, 43 in the circumferential direction, and the projections 41b, 42b at the lower end of the inner cylindrical members 41, 42. Is an example in which longitudinally extending grooves 41c, 42c, 43c are formed in a part of the outer peripheral surface except the lower end so as to engage with the projections 42a, 43a at the upper end of the cylindrical members 42, 43 to be pulled up next. FIG. 5 is a cross-sectional view when the groove is cut in the pulling-up axis direction. The grooves 41c, 42c, 43c are indicated by broken lines. In this case, since the protrusions 42a and 43a fit in the grooves 41c and 42c, the cylindrical members 41 to 43 can be installed without providing a gap between the respective cylindrical members 41 to 43.

  FIG. 6 is a diagram for explaining a method of attaching the after-heater 40 of the crystal growing apparatus according to the first embodiment. FIG. 6 (a) shows an example of the state of the after heater 40 at the initial stage of crystal growth, and FIG. 6 (b) shows an example of the state of the after heater 40 at the late stage of crystal growth.

  As shown in FIGS. 6A and 6B, the upper end of the innermost cylindrical member 41 is attached to the pull-up shaft 70 via an after / heater attachment jig 73. As shown in FIG. 6 (b), the positional relationship between the after heater 40 and the after heater mounting jig 73 is such that the upper end of the after heater 40 is positioned above the upper end of the crystal during crystal growth. Set Further, the after-heater mounting jig 73 is connected to the lifting shaft 70 by a jig support portion 74. The jig support portion 74 is attached and fixed to the pull-up shaft 70, and the after heater mounting jig 73 is installed in a state of being mounted on the jig support portion 74. As a result, when the pulling-up shaft 70 ascends while rotating, the jig supporting portion 74 rotates with the pulling-up shaft 70, but since the after / heater mounting jig 73 is in a free state, the jig supporting portion It becomes possible to rise without turning with 74. That is, the outer heater 40 can be pulled up without rotating.

  More specifically, the after-heater mounting jig 73 is a ring-shaped rotating tool having an inner diameter larger than that of the pulling shaft system on a stopper (jig support portion 74) fixed to the pulling shaft 70, and a small diameter wire or small diameter Attach the upper end of the innermost after heater with a thin rod etc. By using the after-heater mounting jig 73, the height of the after-heater 40 can be varied according to the pulling of the crystal without being affected by the rotation of the pulling shaft 70. The pulling shaft 70 rises as the crystal grows, and the after heater 40 rises from the innermost cylindrical member 41, and can keep the crystal substantially in the after heater 40 during crystal growth.

  Further, the outermost cylindrical member 43 may be fixed to the reflector 30 or the furnace body, a heat insulating material or the like. Thereby, the rotation of the after heater 40 can be reliably prevented.

  The connecting member 75 may be a rod or the like in addition to a wire. However, in the case of a rod, the length is constant, and the rod may be left over depending on the positional relationship (distance) between the after / heater mounting jig 73 and the cylindrical member 41. What is necessary is just to make it the structure which provides the hole which escapes and protrudes on the outer side of the after-heater 40. In the case where the connecting member 75 is a wire, the wire sags downward even in the positional relationship in which the length is excessive, so there is no need to take that point into consideration.

  Next, the shape of the outer heater 40 will be described.

  The diameter of the after heater 40 is a cylindrical shape that is larger than the diameter of the oxide single crystal 170 to be obtained and smaller than the diameter of the crucible 10. With regard to the length of the after heater 40, for example, at the start of pulling as shown in FIG. 6A, the length of the oxide single crystal 170 is half to 1/1 of the total length so that the length is minimized. Preferably up to four. At the end of the pulling, it is preferable that the length of the after heater 40 is extended and is set to 1.3 times the pulling length of the oxide single crystal 170 to the pulling length. Further, the number of divisions is appropriately determined from the minimum length and the maximum length. Preferably, it is divided into three. As a material of the after heater 40, for example, a metal such as platinum or iridium is used.

  In the first embodiment, the example where the after-heater 40 is composed of the three cylindrical members 41 to 43 has been described. However, the number of the cylindrical members 41 to 43 is changed depending on the application and the like. For example, two or four or five may be possible.

  Further, in the first embodiment, from the viewpoint of easy connection with the lifting shaft 70, the cylindrical member 41 arranged on the innermost side and the after heater mounting jig 73 are connected. It is not essential but may be connected to another cylindrical member 42, 43. For example, when the direction of the projections 41a to 43a and 41b to 43b is reversed, the outermost cylindrical member 43 and the after heater mounting jig 73 are connected, and the cylindrical member 42 is directed inward from the outer cylindrical member 43. , 41 can also be pulled up sequentially. However, since the lifting shaft 70 exists inside the after heater 40, it is more efficient as a lifting structure to be connected to the innermost cylindrical member 41.

Second Embodiment
FIG. 7 is a view showing an example of a crystal growth apparatus according to a second embodiment of the present invention. The crystal growing apparatus according to the second embodiment is different in that the after heater 140 has a tapered shape, not a cylindrical shape. For this reason, the hollow members 141 to 143 having a tapered shape constitute an after heater. The innermost hollow member 141, the middle hollow member 142, and the outermost hollow member 143 gradually increase in diameter, so that when the inner hollow member 141 is pulled up, the lower end of the hollow member 141 and the middle hollow member When the upper end of 142 is engaged and the hollow member 142 is also pulled up, the lower end of the hollow member 142 is engaged with the upper end of the hollow member 143. In this manner, the length of the after heater 140 can be gradually increased as the single crystal 170 is grown.

  The inclination angle of the after heater 140, that is, the taper angle may be varied depending on the application, and may be an appropriate taper angle. For example, the taper angle (tilt angle) of the after heater 140 may be set to a predetermined angle within a range of 0.5 degrees or more and 2 degrees or less so as to approximate a cylindrical shape.

  As described above, the after heater does not necessarily have to be in a cylindrical shape, and may have a hollow shape with a hollow center. And according to the hollow shape of after heater 140, the shape of hollow members 141-143 can be defined. Moreover, if the number of hollow members 141 to 143 is also plural, various numbers can be used according to the application.

  The method for attaching the after heater 140 can be configured in exactly the same manner as in the first embodiment, and can be connected to the lifting shaft 70 using the after heater attaching jig 73.

  Since other configurations are the same as those of the crystal growth apparatus according to the first embodiment, the description thereof is omitted.

Third Embodiment
FIG. 8 is a view showing an example of a crystal growth apparatus according to a third embodiment of the present invention. The crystal growth apparatus according to the third embodiment is different in that the after-heater 240 is not divided into a plurality of members, and the single after-heater 240 itself has a stretchable structure. Specifically, the after heater 240 has a bellows structure, and has an upper end connected to the pulling shaft 70.

  The method of attaching the after heater 140 can be configured in exactly the same manner as in the first embodiment, and can be connected to the lifting shaft 70 using the after heater attaching jig 73.

  Thus, the after heater 240 itself may be provided with a telescopic structure, and the length thereof may be variable. Since the number of parts is reduced, there is an advantage that the assembly and installation become easy.

  Since other configurations are the same as those of the crystal growth apparatus according to the first embodiment, the description thereof is omitted.

[Example]
In the embodiment, an example of performing a simulation experiment will be described.

  For example, assuming growth of an oxide single crystal with a diameter of 100 mm and a total length of 170 mm (with a pulling length of 140 mm), the after heater of this example has a cylindrical shape and three different after heaters. Place them on top of each other. The diameters are arranged in the radial direction as φ148 mm, φ144 mm, and φ140 mm. Each length is 48 mm. In this case, the after heater has a minimum length of 48 mm and a maximum length of 140 mm.

  The thickness is 1.0 mm, and protrusions and 1.0 mm are provided on the upper and lower ends of the after heater. The protrusions are set to the entire circumference of the circumference, with the upper end of the after heater inward and the lower end outward. By making the projections all around, it is possible to arrange without regard to the engagement position of the upper and lower projections.

  In addition, when a taper is attached to the after heater as shown in the second embodiment instead of the protrusion, it may be set so as not to interfere with the grown crystal. For example, it is preferable to incline by 0.5 degrees to 2 degrees with respect to the vertical direction.

  FIG. 9 is a graph when a heat generation distribution of an example of the after heater of the crystal growing apparatus according to the present embodiment is simulated from the crucible bottom center to the after heater upper end.

  In this simulation, the growth of an oxide single crystal with a diameter of φ100 mm and a total length of 170 mm (with a pull-up length of 140 mm) is assumed, and the after heater of this example has a cylindrical shape and 3 pieces in diameter. Different Φ148 mm, Φ144 mm, and Φ140 mm were arranged in an overlapping manner. Each length was 48 mm. At this time, the minimum length of the after heater was 48 mm, and the maximum length was 140 mm. The thickness was 1.0 mm, and a protrusion 1.0 mm was provided on the upper and lower ends of the after heater. The protrusions were set to the entire circumference of the circumference, with the upper end of the after-heater being inward and the lower end being outward. The diameter of the crucible was φ175 mm.

  As can be seen from FIG. 9, the heat generation distribution is such that the position of the melt interface is 170 mm from the bottom of the crucible and the position of the melt interface, compared with the conventional after heater ((fixed on graph, curve C). -In the initial stage of heater growth (movable (initial) on the graph, curve A), the amount of generated heat is suppressed. In addition, the rear stage of growth of the after heater of this example (the movable on the graph (later), curve B) is almost the same as the conventional after heater, and the upper end of the after heater has the same calorific value .

  As shown in the curve A, by suppressing the calorific value of the after heater at the initial stage of growth, it is possible to secure many ranges in which the heating amount may be increased when it is desired to adjust the heating amount. Can be made easier. Thereby, it is possible to effectively prevent polycrystallization of the crystal at the initial stage of growth.

  On the other hand, since the calorific value of the after heater at the rear stage of the growth has not been a big problem conventionally, as shown by the curves B and C, the calorific value similar to the conventional one can be secured and a sufficient calorific value can be obtained. Is shown.

  FIG. 10 is a diagram showing the temperature distribution in the depth direction of the melt in the crucible in the initial stage of growth of an example of the after-heater of the crystal growth apparatus according to this example. FIG. 10A is a graph when the temperature distribution from the bottom of the crucible to the top surface of the crucible is simulated. FIG. 10 (b) shows the simulation range of the temperature distribution of this embodiment, and FIG. 10 (c) shows the simulation range of the temperature distribution of the conventional example. In FIG. 10A, a curve D indicates the simulation result of the present embodiment, and a curve E indicates the simulation result of the conventional example.

  The simulation conditions are the same as the conditions in FIG. In the conventional after heater (in the graph (fixed), curve E), the melt top is warmed because the after heater is long, and the heat generation of the crucible required to bring the crystal-melt interface to the melting point is small Therefore, the temperature gradient in the vertical direction becomes small, and temperature control for crystal growth is difficult. In the after heater (moving on the graph, curve D) of the present embodiment, the height of the cylinders is low at the initial stage of growth, and the melt upper portion is not so much warmed as compared with the conventional after heater. For this reason, the heat generation of the crucible increases and the temperature gradient in the melt in the vertical direction becomes large, and the temperature control becomes easy.

  FIG. 11 is a view showing the temperature distribution in the radial direction of the melt surface at the initial stage of growth of an example of the after heater of the crystal growth apparatus according to the present embodiment. FIG. 11A is a graph when a simulation is performed in the crucible outer diameter direction from the center of the crucible. FIG. 11 (b) shows the simulation range of the temperature distribution of this embodiment, and FIG. 11 (c) shows the simulation range of the temperature distribution of the conventional example. In FIG. 11A, the curve F shows the simulation result of the present example, and the curve G shows the simulation result of the conventional example.

  The simulation conditions are the same as the conditions in FIG. The conventional after-heater ((fixed) on the graph, curve G) has a small temperature gradient in the horizontal direction on the melt surface as well as the temperature gradient in the vertical direction, making it difficult to control crystal growth. On the other hand, in the after heater of this example (moving on the graph, curve F), at the initial stage of growth, the cylinders overlap and the height is low, and the melt upper part is not heated so much compared to the conventional after heater. Therefore, the heat generation in the crucible increases, the temperature gradient in the horizontal direction increases, and temperature control becomes easy.

  FIG. 12 is a view showing the temperature distribution in the height direction in the crystal in the later stage of the growth of an example of the after heater of the crystal growth apparatus according to the present embodiment. FIG. 12 (a) is a graph when simulating the temperature distribution from the bottom of the crystal to the top of the crystal. FIG. 12 (b) shows the simulation range of the temperature distribution of the present embodiment, and FIG. 12 (c) shows the simulation range of the temperature distribution of the conventional example. In FIG. 12A, the curve H shows the simulation result of the present example, and the curve I shows the simulation result of the conventional example.

  The conditions for simulation are the same as the conditions in FIG. The temperature difference between the upper and lower ends in the vertical direction in the crystal is 50 ° C. in the case of the conventional after heater (the graph is (fixed), curve I), and the temperature of the after heater (movable on the graph, curve H) of this embodiment is In this case, the temperature is almost the same as 55 ° C., and it is unlikely that stress increases or cracks occur in the crystal during growth.

  From the above simulation results, it was shown that by using the after-heater of this example, the temperature gradient in the vertical and horizontal directions in the melt was increased at the initial stage of growth, and temperature control was facilitated. Thereby, there can be a margin in the setting range of the growth conditions. The latter half of the growth is almost the same as the conventional after-heater. For this reason, temperature control becomes easy at the initial stage of growth, and the conditions can be set appropriately even if the length of the crystal is increased. In the later stage of growth, the length of the crystal can be increased by setting the length of the after heater corresponding to the length of the crystal.

  The preferred embodiments and examples of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments and examples, and the above-described embodiments and examples can be performed without departing from the scope of the present invention. Various modifications and substitutions may be made to the embodiments.

10 crucible 20 crucible base 30 reflector 40, 140, 240 after heater 41, 42, 43 cylindrical member 141, 142, 143 hollow member 50 heat insulating material 60 refractory 70 pulling shaft 71 seed crystal holding portion 72 pulling shaft driving portion 73 after Heater mounting jig 74 jig supporting unit 80 induction coil 90 power supply 100 control unit 150 seed crystal 160 crystal raw material 170 single crystal (crystal)

Claims (7)

A metal crucible capable of storing the raw material melt,
A heating induction coil disposed around the crucible;
A metallic afterheater having a hollow shape disposed above the crucible;
And a pulling shaft capable of pulling a crystal from the raw material melt;
The after-heater is a crystal growth apparatus in which the length is variable in the moving direction of the pulling shaft.   The crystal growing apparatus according to claim 1, wherein the length of the after heater extends in accordance with the growth of the crystal.   The crystal growth apparatus according to claim 2, wherein the after heater is connected to the pulling shaft.   The crystal growing apparatus according to claim 3, wherein the after heater is connected to the pulling shaft via a wire or a rod.   The after-heater has a plurality of hollow members having different diameters arranged in an overlapping manner in the radial direction of the hollow shape, and when one of the adjacent hollow members is pulled up by a predetermined height, the other is engaged The crystal growing apparatus according to claim 4, wherein the crystal growing apparatus has a connected pulling structure that is pulled up.   The crystal growing apparatus according to claim 5, wherein the wire or the rod is directly connected only to the hollow member which is pulled up first among the plurality of hollow members. Bringing a raw material melt stored in a metal crucible into contact with a seed crystal held on a pulling shaft to start pulling the crystal;
Extending a metal after-heater disposed above the crucible in response to the pulling of the crystal so as to cover at least the periphery of the height of the crystal.

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