JP2018002573A - Crystal growth apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal growth apparatus capable of suppressing solidification of row material melt from a bottom surface of a crucible during crystal growth of an oxide single crystal, and thereby elongating the single crystal.SOLUTION: A crystal growth apparatus has a crucible 30 having a prescribed bottom surface 31, and a crucible stand 40 on which the crucible can be installed, the crucible stand having an installation surface 41 with a contact area ratio with the bottom surface being 10-38% with respect to the bottom surface.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a crystal growth apparatus.

  Lithium niobate and lithium tantalate oxide single crystals, which are used as materials for surface acoustic wave filters (SAW filters) for removing signal noise in communication equipment, have good crystal characteristics and are large crystals. It is common to grow by the Czochralski method that can obtain a diameter. In the Czochralski method, a raw material is melted in a precious metal crucible, and the seed crystal is brought into contact with the surface of the raw material melt and pulled up while being rotated by a crucible support rod. Is a way to grow.

  Patent Document 1 and Patent Document 2 propose an oxide single crystal growth apparatus in which an alumina crucible base is installed at the bottom of a ceramic refractory and a crucible is installed thereon.

JP-A-7-187880 JP 2003-165996 A

  However, as the crystal growth technique develops and the lengthening of the crystal proceeds, in the configuration of the growth apparatus described in Patent Document 1 and Patent Document 2, the raw material melt is solidified from the bottom of the crucible during single crystal growth. Due to the phenomenon, the tail portion of the growing crystal comes into contact with the solidified crystal at the bottom of the crucible, which makes it difficult to lengthen the crystal.

  The present invention has been made paying attention to such problems, and is capable of suppressing the solidification of the raw material melt from the bottom surface of the crucible during the crystal growth of the oxide single crystal and enabling the lengthening of the single crystal. An object is to provide a training apparatus.

To achieve the above object, a crystal growth apparatus according to an aspect of the present invention includes a crucible having a predetermined bottom surface,
The crucible can be installed, and a crucible base having an installation surface whose contact area ratio with the bottom surface is 10 to 38% with respect to the bottom surface.

  According to the present invention, solidification of the raw material melt from the bottom surface of the crucible can be suppressed by optimizing the contact area of the crucible base in contact with the bottom surface of the crucible and suppressing the heat conduction of the bottom surface of the crucible.

It is the figure which showed the crystal growth apparatus which concerns on the 1st Embodiment of this invention. It is the figure which showed an example of the crucible stand of the crystal growth apparatus which concerns on the 1st Embodiment of this invention. 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 crucible base member of the crystal growing apparatus which concerns on the 2nd Embodiment of this invention. 6 is a graph of crystal weight and crucible bottom temperature drop during crystal growth in Example 1 and Comparative Example 1.

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

[Configuration of crystal growth equipment]
FIG. 1 is a diagram showing a crystal growth apparatus according to a first embodiment of the present invention used for growing a single crystal such as an oxide single crystal.

  A general growing apparatus includes a work coil 10, a ceramic refractory 20, a crucible 30, a crucible base 40, a heat insulating material 50, a lifting shaft 60, a lid 70, a reflector 90, and a seed crystal holding treatment. The tool 120 and the after heater 130 are provided. Moreover, in FIG. 1, the seed crystal 80, the melt 100, and the single crystal 110 are shown as a related component.

  The crucible 30 is a container for holding the crystal material melt 100. Note that the crystal raw material is melted by heating to form a melt 100. The crucible 30 may be made of, for example, iridium. The crucible 30 has a bottom surface 31 and is supported by the bottom surface 31 being installed on the installation surface 41 of the crucible base 40.

  The ceramic refractory 20 is a means for enclosing the whole including the crucible 30 and has a configuration similar to a container capable of accommodating the whole including the crucible 30. The ceramic refractory 20 is literally made of ceramic.

  The crucible base 40 is installed on the bottom surface of the ceramic refractory 20, and the crucible 30 is installed on the top surface 41 of the crucible base 40. Since the upper surface 41 of the crucible base 40 is a surface on which the crucible 30 can be installed, it may be called the crucible installation surface 41. A concave portion is formed on the surface of the crucible base 40 to reduce the contact area with the bottom surface 31 of the crucible 30. This point will be described later.

  The heat insulating material 50 is installed so as to surround the crucible 30 and has a function of preventing the heat of the crucible 30 from being released to the outside.

  The reflector 90 is attached along the upper end surface of the crucible 30 and has a donut plate shape.

  The after heater 130 is attached to the reflector 90 and has a cylindrical shape.

  The pulling shaft 60 is a rotating shaft for pulling up the single crystal 110 and is provided at the center of the crucible 30.

  The lid 70 is provided so as to close the upper end portion of the after heater 130, and an opening 71 for passing the lifting shaft 60 is provided in the center.

  The seed crystal holding jig 120 is a jig for holding the seed crystal 80 and is provided on the lower side (lower end portion) of the pulling shaft 60.

  The work coil 10 is provided on the outer side of the ceramic refractory 20 so as to surround the ceramic refractory 20, inductively heats the crucible 30, melts the raw material filled therein, and forms a melt 100. Have

  FIG. 2 is a view showing an example of the crucible base 40 of the crystal growth apparatus according to the first embodiment of the present invention. A recess-shaped portion 42 is formed on the upper surface (crucible installation surface) 41 of the crucible base 40. In FIG. 2, the recessed portion 42 is configured as a plurality of concentric circular grooves. Thereby, the contact area of the upper surface 41 of the crucible base 40 and the bottom surface 31 of the crucible 30 installed on the upper surface 41 can be reduced. Then, heat is released from the bottom surface 31 of the crucible 30 through the crucible base 40, thereby suppressing the occurrence of the phenomenon that the temperature of the crucible bottom surface 31 decreases and the melt 100 near the crucible bottom surface 31 is solidified. it can.

  In the crucible base 40 according to the first embodiment of the present invention, the contact area ratio between the bottom surface 31 of the crucible 30 and the top surface 41 of the crucible base 40 on which the crucible 30 is installed is 10 to 38% with respect to the bottom surface 31 of the crucible. (Crucible base contact area / crucible bottom area × 100). As shown in FIG. 1, the upper surface 41 of the crucible base 40 has a smaller overall area than the bottom surface 31 of the crucible 30, so that all flat surfaces on which the recessed portions 42 are not formed are the same as the bottom surface 31 of the crucible 30. Contact. Therefore, if the flat surface portion of the entire upper surface 41 is set to be 10 to 38% of the bottom area of the crucible 30, the above condition is satisfied.

  Thus, if the contact area between the bottom surface 31 of the crucible 30 and the top surface 41 of the crucible base 40 is 10% or more with respect to the crucible bottom area, the crucible 30 can be stably placed on the crucible base 40 and the bottom surface of the crucible. The temperature change of 31 can be suppressed and heat retention can be ensured.

  The contact area between the bottom surface 31 of the crucible 30 and the top surface 41 of the crucible base 40 is set to 38% or less with respect to the crucible bottom area. When the contact area between the bottom surface 31 of the crucible 30 and the crucible base 40 exceeds 38%, heat is easily released from the bottom surface 31 of the crucible to the crucible base 40, and the heat retaining property of the bottom surface 31 of the crucible is reduced. The raw material melt is easily solidified. For example, the contact area ratio of the upper surface 41 of the crucible base 40 to the area of the bottom surface 31 of the crucible 30 is preferably 12 to 36%.

  In the crucible base 40 according to the first embodiment of the present invention, the crucible base 40 is stably formed by forming the recessed portion 42 on the upper surface 41 of the crucible base 40 that is a contact surface with the crucible bottom surface 31. It is possible to control the contact area with the crucible bottom surface 31 while ensuring a size that can be placed on the crucible.

  In addition, as shown in FIG. 2, the recessed portion 42 may be a concentric groove. With such a configuration, the contact area between the bottom surface 31 of the crucible 30 and the top surface 41 of the crucible base 40 can be reduced while reliably supporting the crucible 30 having the circular bottom surface 31. More specifically, since the crystal growth apparatus generally heats the surroundings of the crucible 30 to melt the raw material, the raw material melt 100 naturally convects in the crucible 30 and the temperature of the raw material melt 100 with a lowered temperature is reduced. Convection occurs toward the center of the crucible 30. Therefore, solidification of the raw material melt 30 is likely to occur from the center of the crucible 30 and it is desirable that the central portion of the crucible 30 and the central portion of the crucible base 40 are not in contact with each other. The concentric groove shown in FIG. 2 can suppress the influence of such convection, and is one of the preferable configurations of the recessed portion 42.

  However, the shape of the recessed portion 42 is not limited to a plurality of concentric grooves, and can be various recessed shape patterns depending on the application.

  The crucible base 40 may be made of various materials that can withstand high temperatures such as alumina, but is preferably made of zirconia. Since zirconia has a lower thermal conductivity than other ceramics, it is suitable for increasing the heat retention of the bottom of the crucible.

  FIG. 3 is a diagram showing an example of a crystal growth apparatus according to the second embodiment of the present invention. In FIG. 3, only the parts different from the crystal growth apparatus according to the first embodiment are shown, and the common parts are not shown, but the configuration of FIG. 1 can be applied to those parts. In FIG. 3, the same reference numerals are assigned to the same components as those of the crystal growth apparatus according to the first embodiment, and the description thereof is omitted.

  The crucible base 45 of the crystal growth apparatus according to the second embodiment is composed of a single member in that the plurality of crucible base members 46 are overlapped, and the crystal growth according to the first embodiment is configured. Different from the crucible base 40 of the apparatus. In FIG. 3, six crucible base members 46 are stacked to constitute one crucible base 45.

  FIG. 4 is a view showing an example of the crucible base member 46. As shown in FIG. 4, the crucible base member 46 is different from the crucible base member 46 in the first embodiment in that the thickness of the crucible base member 46 is reduced, but a recessed portion 48 is formed on the upper surface 47. To do. Moreover, in FIG. 4, the hollow shape part 48 is a plurality of concentric grooves, and this point is the same as that of the crucible base 40 in the first embodiment.

  In FIG. 3, if the first crucible base member 46 for installing the crucible is the first, the first crucible base member 46 may be of a size that allows the crucible 30 to be stably installed. When it is brought into contact with the heat insulating material, the heat retaining effect is further increased.

  The second and subsequent crucible base members 46 are preferably installed below the first crucible base member 46 and have a larger diameter than the first crucible base member 46. This is because, when hollow beads such as zirconia bubbles are repeatedly used as the heat insulating material 50 over a long period of time, the heat insulating material 50 undergoes a thermal change during crystal growth, resulting in the formation of lumps and cavities, so that the symmetry of the temperature gradient collapses, The yield of breeding deteriorates. Therefore, it is preferable to install the crucible base member 46 having the upper surface 47 larger than the first crucible base member 46 so that the second and subsequent crucible base members 46 can serve as an alternative to the heat insulating material 50.

  However, as shown in FIG. 3, the second and subsequent crucible base members 46 may have the same shape as the first crucible base member 46. In this case, the hollow shape part 48 may also be the same shape.

  The crucible base member 46 may also be made of various materials that can withstand high temperatures, such as alumina, but is preferably made of zirconia as in the first embodiment.

[Oxide single crystal growth procedure]
The method for growing the oxide single crystal is not particularly limited, and a known technique can be used. As an example, a procedure for growing an oxide single crystal is shown.

  The coarsely crushed raw material is filled in the crucible 30, and the crucible 30 is dielectrically heated by the work coil 10 and melted.

  Next, the single crystal 110 is grown by bringing the seed crystal 80 into contact with the melted raw material melt 100 and pulling the seed crystal 80 upward by the pulling shaft 60 while rotating the seed crystal 80. When pulling up the single crystal 110, heat radiation from the bottom of the crucible 30 through the crucible bases 40 and 45 can be suppressed, and the single crystal 110 that can be grown by one pulling can be elongated. Thereby, the productivity of crystal growth can be increased.

  Examples of the present invention will be specifically described below with reference to comparative examples, but the present invention is not limited to the following examples.

[Example 1]
1, the contact area ratio (%) of the crucible base (made of zirconia) having a diameter of 130 mm to the bottom surface of the crucible (made of iridium) having a diameter of 205 mm and a height of 180 mm (contact area of the crucible base / crucible) Grooves were formed concentrically so that the bottom area × 100) was 26% (see FIG. 2).

  In a crucible, 30 kg of a firing raw material having a composition ratio of Li / Ta = 0.944 (molar ratio) was put and melted, and then a lithium tantalate single crystal having a diameter of 6 inches was grown by the Czochralski method. .

  Table 1 shows the weight of the pulled crystal, the length of the straight body of the crystal, and the temperature drop at the bottom of the crucible.

As a result, the weight of the grown lithium tantalate single crystal was 17.4 kg, the length of the straight cylinder was 83 mm, and the temperature drop at the bottom of the crucible from the start of crystal growth to the end of growth was -13.5 ° C.

[Example 2]
In the single crystal growing apparatus shown in FIG. 1, the contact area ratio (%) of the crucible base (made of zirconia) having a diameter of 130 mm to the bottom face of the crucible (made of iridium) having a diameter of 205 mm and a height of 180 mm (contact area of the crucible base / Grooves were formed concentrically so that the crucible bottom area × 100) was 36% (see FIG. 2).

  In a crucible, 30 kg of a firing raw material having a composition ratio of Li / Ta = 0.944 (molar ratio) was put and melted, and then a lithium tantalate single crystal having a diameter of 6 inches was grown by the Czochralski method. .

  In the same manner as in Example 1, a temperature survey during the growth was performed.

  As a result, as shown in Table 1, the weight of the grown lithium tantalate single crystal was 17.3 kg, the straight body length was 83 mm, and the temperature drop at the bottom of the crucible from the start of crystal growth to the end of growth was −18 It was 3 ° C.

[Example 3]
In the single crystal growing apparatus shown in FIG. 1, the contact area ratio (%) of the crucible base (made of zirconia) having a diameter of 130 mm to the bottom face of the crucible (made of iridium) having a diameter of 205 mm and a height of 180 mm (contact area of the crucible base / Grooves were formed concentrically so that the crucible bottom area × 100) was 12% (see FIG. 2).

  In a crucible, 30 kg of a firing raw material having a composition ratio of Li / Ta = 0.944 (molar ratio) was put and melted, and then a lithium tantalate single crystal having a diameter of 6 inches was grown by the Czochralski method. .

  In the same manner as in Example 1, a temperature survey during the growth was performed.

  As a result, as shown in Table 1, the weight of the grown lithium tantalate single crystal was 17.8 kg, the straight body length was 85 mm, and the temperature drop at the bottom of the crucible from the start of crystal growth to the end of growth was −5 It was 3 ° C.

[Comparative Example 1]
In the single crystal growing apparatus shown in FIG. 1, a crucible (made of iridium) having a diameter of 205 mm was placed on a crucible base (made of zirconia) having a diameter of 130 mm and a height of 180 mm. Since no grooves are formed on the upper surface of the crucible base, the contact area ratio (%) (the contact area of the crucible base / the crucible bottom area × 100) is 40%.

  In a crucible, 30 kg of a firing raw material having a composition ratio of Li / Ta = 0.944 (molar ratio) was put and melted, and then a lithium tantalate single crystal having a diameter of 6 inches was grown by the Czochralski method. .

  In the same manner as in Example 1, a temperature survey during the growth was performed.

  As a result, as shown in Table 1, the weight of the grown lithium tantalate single crystal was 16.6 kg, the straight body length was 75 mm, and the temperature drop at the bottom of the crucible from the start of crystal growth to the end of growth was -21. It was 5 ° C.

[Consideration based on Examples]
As summarized in Table 1, it was found that adjusting the contact area ratio makes it difficult to lower the temperature at the bottom of the crucible and has a heat retaining effect. As a result, it was confirmed that the weight of the single crystal when the raw material solidified region from the bottom of the crucible and the single crystal contact each other increased, and a 6-inch lithium tantalate single crystal having a longer straight body was obtained. In particular, when the contact area between the upper surface of the crucible base and the bottom surface of the crucible is 12% or more and 36% or less with respect to the entire bottom area of the crucible, the amount of decrease in the temperature of the bottom surface of the crucible is reduced, and the length of the straight body portion It can be seen that the length can be increased.

  FIG. 5 shows a graph of crystal weight and crucible bottom temperature drop during crystal growth in Example 1 and Comparative Example 1. It is known that when crystals are formed during crystal growth, latent heat is released and the temperature of the raw material melt rises. In FIG. 5, the time (A and B in the figure) when the crucible temperature drop increases in the vicinity of the crystal weight exceeding 1000 g represents crystal formation. In Example 1 (A) and Comparative Example 1 (B), it can be seen that the release of latent heat due to crystal formation appears slower in Example 1 (A). From this, in Example 1, the heat retaining property of the crucible bottom was maintained, and solidification (crystal formation) of the raw material melt at the bottom of the crucible could be suppressed. .

  As described above, according to the crystal growing apparatus according to the present embodiment, it is possible to grow a crystal longer than the conventional one, and it is possible to improve productivity.

  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 can be made to the embodiments.

10 Work coil Coil 20 Ceramic refractory 30 Crucible 31 Bottom 40, 45 Crucible base 41, 47 Upper surface (installation surface)
42, 48 Recessed portion 46 Crucible base member 50 Insulating material 60 Lifting shaft 70 Lid 80 Seed crystal 90 Reflector 100 Melt 110 Single crystal 120 Seed crystal holding jig 130 After heater

Claims (9)

A crucible having a predetermined bottom surface;
A crystal growing apparatus comprising: a crucible base on which the crucible can be installed, and a ratio of a contact area with the bottom surface is 10 to 38% with respect to the bottom surface.   The crystal growth apparatus according to claim 1, wherein the installation surface of the crucible base has a recessed portion.   The crystal growth apparatus according to claim 2, wherein the hollow portion is a concentric groove.   The crystal growth apparatus according to claim 2 or 3, wherein the crucible base includes a plurality of crucible base members that can be stacked.   The crystal growing apparatus according to claim 4, wherein the plurality of crucible base members have the same shape.   The crystal growing device according to claim 5, wherein the hollow shape portions have the same shape.   The crystal growth apparatus according to claim 4, wherein the crucible base member that is not in contact with the crucible has a larger installation surface than the crucible base member that is in contact with the crucible among the plurality of crucible base members.   The crystal growth apparatus according to any one of claims 1 to 6, wherein the crucible base is made of zirconia.   The crystal growth apparatus according to any one of claims 1 to 7, wherein a ratio of a contact area with the bottom surface of the crucible base is 12 to 36% with respect to the bottom surface.