JP6724614B2 - Crystal growth equipment - Google Patents

Description

The present invention relates to a crystal growing device.

Oxide single crystals of lithium niobate and lithium tantalate, which are used as materials for surface acoustic wave filters (SAW filters) for removing signal noise of communication equipment, have good crystal characteristics and are large crystals. It is general to grow by the Czochralski method that can obtain the thing of a diameter. The Czochralski method melts a raw material in a precious metal crucible, brings the seed crystal into contact with the surface of the raw material melt, and pulls it while rotating it with a pulling shaft to form a cylindrical single crystal in the same direction as the seed crystal. It is a method of growing.

Patent Documents 1 and 2 propose an oxide single crystal growth device in which a crucible table made of alumina is installed at the bottom of a ceramic refractory and a crucible is installed thereon.

JP-A-7-187880 JP, 2003-165796, A

However, as the crystal growth technique has been developed and the length of the crystal has been lengthened, the raw material melt is solidified from the bottom of the crucible during the single crystal growth in the configurations of the growth devices described in Patent Documents 1 and 2. Due to the phenomenon, the tail portion of the growing crystal comes into contact with the solidified crystal of the crucible bottom, which makes it difficult to increase the length of the crystal.

The present invention has been made in view of such problems, a crystal capable of lengthening the single crystal by suppressing solidification of the raw material melt from the bottom surface of the crucible during crystal growth of the oxide single crystal. The purpose is to provide a growing device.

To achieve the above object, the crystal growing apparatus according to an embodiment of the present invention, the iridium crucible having a bottom surface,
Can be disposed the crucible, the contact area ratio of the bottom, have a, a crucible stand made of zirconia having an installation surface is 10 to 38% relative to the bottom surface,
The installation surface of the crucible base has a recess-shaped portion,
The crucible base comprises a plurality of stackable crucible base members,
Wherein the plurality of crucible base member, Ru same shape der.

According to the present invention, it is possible to suppress solidification of the raw material melt from the bottom surface of the crucible 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 stand member of the crystal growth apparatus which concerns on the 2nd Embodiment of this invention. 3 is a graph of a crystal weight and a crucible bottom temperature drop during crystal growth in Example 1 and Comparative Example 1.

Embodiments for carrying out the present invention will be described below with reference to the drawings.

[Structure of crystal growth device]
FIG. 1 is a diagram showing a crystal growing 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 stand 40, a heat insulating material 50, a pulling shaft 60, a lid 70, a reflector 90, and a seed crystal holding treatment. It has a tool 120 and an after-heater 130. Further, in FIG. 1, a seed crystal 80, a melt 100, and a single crystal 110 are shown as related components.

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

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

The crucible stand 40 is installed on the bottom surface of the ceramic refractory material 20, and the crucible 30 can be installed on the upper surface 41 thereof. Since the upper surface 41 of the crucible base 40 is a surface on which the crucible 30 can be installed, it may be referred to as a crucible installation surface 41. A depression-shaped 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. Note that 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 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 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 of the after-heater 130, and an opening 71 for allowing the pull-up shaft 60 to pass through is provided at 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 outside the ceramic refractory material 20 so as to surround the ceramic refractory material 20, induction-heats the crucible 30, and melts the raw material filled inside to form the melt 100. Have.

FIG. 2 is a diagram showing an example of the crucible table 40 of the crystal growing apparatus according to the first embodiment of the present invention. A depression-shaped portion 42 is formed on the upper surface (crucible installation surface) 41 of the crucible base 40. The recessed portion 42 is configured as a plurality of concentric circular grooves in FIG. Accordingly, the contact area between 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, by releasing heat from the bottom surface 31 of the crucible 30 via the crucible base 40, the temperature of the crucible bottom surface 31 is lowered, and the occurrence of the phenomenon that the melt 100 near the crucible bottom surface 31 is solidified can be suppressed. 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 upper 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. The contact area of the crucible base/the bottom area of the crucible×100 is set. As shown in FIG. 1, since the entire top surface 41 of the crucible base 40 has a smaller area than the bottom surface 31 of the crucible 30, all flat surfaces on which the recessed portions 42 are not formed are 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.

As described above, if the contact area between the bottom surface 31 of the crucible 30 and the upper surface 41 of the crucible base 40 is 10% or more of the crucible bottom area, the crucible 30 can be stably placed on the crucible base 40, and the crucible bottom surface can be stably placed. The temperature change of 31 can be suppressed and the heat retention can be secured.

The contact area between the bottom surface 31 of the crucible 30 and the upper surface 41 of the crucible base 40 is 38% or less of the bottom area of the crucible. 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 crucible bottom surface 31 to the crucible base 40, and the heat retention property of the crucible bottom surface 31 is reduced. The raw material melt easily solidifies. 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%.

The crucible base 40 according to the first embodiment of the present invention stably forms the crucible base 40 by forming the recessed portion 42 on the upper surface 41 of the crucible base 40 that is the 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 mounted on the crucible.

Further, as shown in FIG. 2, the recessed shape portion 42 may be a concentric groove. With this configuration, the contact area between the bottom surface 31 of the crucible 30 and the upper 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 growing apparatus generally heats the periphery of the crucible 30 to melt the raw material, the raw material melt 100 spontaneously convects in the crucible 30 and the temperature of the raw material melt 100 decreases. 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 do not contact each other. The concentric grooves shown in FIG. 2 can suppress the influence of such convection, and is one of the preferable configurations of the hollow shape portion 42.

However, the shape of the depression-shaped portion 42 is not limited to the plurality of concentric grooves, and various depression-shaped patterns can be used according to the application.

The crucible base 40 may be made of various materials such as alumina that can withstand high temperature, 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 growing apparatus according to the second embodiment of the present invention. Note that, in FIG. 3, only parts different from the crystal growth apparatus according to the first embodiment are shown and common parts are omitted, but the configuration of FIG. 1 can be applied to those parts. Further, in FIG. 3, the same components as those of the crystal growth apparatus according to the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The crucible base 45 of the crystal growing apparatus according to the second embodiment is configured by stacking a plurality of crucible base members 46, and is configured by one member. It is different from the crucible base 40 of the device. In FIG. 3, six crucible base members 46 are stacked to form one crucible base 45.

FIG. 4 is a diagram 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 40 in the first embodiment in that the crucible base member 46 is different in that the thickness is reduced, but that the upper surface 47 has a recessed portion 48. To do. Further, in FIG. 4, the recessed shape portion 48 is a plurality of concentric circular grooves, and this point is also the same as the crucible base 40 in the first embodiment.

In FIG. 3, assuming that the crucible base member 46 on which the crucible is installed is the first, the first crucible base member 46 may be of a size that allows the crucible 30 to be installed stably, and the crucible 30 and the surroundings of the crucible may be arranged. The heat retention effect is further enhanced by contacting with a heat insulating material.

The second and subsequent crucible base members 46 are preferably installed below the first crucible base member 46 and have a diameter larger than that of 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 for a long period of time, the heat insulating material 50 undergoes a thermal change during crystal growth, and lumps and cavities are formed, so that the symmetry of the temperature gradient is broken, and the crystal The yield of cultivation deteriorates. Therefore, it is preferable that the second and subsequent crucible base members 46 be provided with the crucible base member 46 having a larger upper surface 47 than that of the first crucible base member 46 so as to serve as a substitute for 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 recess-shaped portion 48 may also have the same shape.

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

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

The roughly crushed raw material is filled in the crucible 30, and the work coil 10 dielectrically heats and melts the crucible 30.

Next, the seed crystal 80 is brought into contact with the melt 100 of the melted raw material, and the single crystal 110 is grown by rotating the seed crystal 80 and pulling it upward with the pulling shaft 60. When pulling the single crystal 110, heat radiation from the bottom surface of the crucible 30 via the crucible platforms 40 and 45 can be suppressed, and the single crystal 110 that can be grown by one pull can be elongated. Thereby, the productivity of crystal growth can be improved.

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

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

30 kg of a firing material having a composition ratio of Li/Ta=0.943 (molar ratio) was placed in the crucible and melted, and then a 6-inch diameter lithium tantalate single crystal 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 amount of temperature drop in the crucible bottom.

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

[Example 2]
In the single crystal growth apparatus shown in FIG. 1, the contact area ratio (%) of the crucible table (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 table/ Grooves were formed concentrically so that the crucible bottom area×100) was 36% (see FIG. 2).

30 kg of a firing material having a composition ratio of Li/Ta=0.943 (molar ratio) was placed in the crucible and melted, and then a 6-inch diameter lithium tantalate single crystal was grown by the Czochralski method. ..

The temperature was investigated during the growth in the same manner as in Example 1.

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 amount of the crucible bottom surface from the crystal growth start to the growth end was −18. It was 0.3°C.

[Example 3]
In the single crystal growth apparatus shown in FIG. 1, the contact area ratio (%) of the crucible table (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 table/ Grooves were formed concentrically so that the crucible bottom area×100) was 12% (see FIG. 2).

30 kg of a firing material having a composition ratio of Li/Ta=0.943 (molar ratio) was placed in the crucible and melted, and then a 6-inch diameter lithium tantalate single crystal was grown by the Czochralski method. ..

The temperature was investigated during the growth in the same manner as in Example 1.

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 amount of the crucible bottom surface from the crystal growth start to the growth end was −5. It was 0.3°C.

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

30 kg of a firing material having a composition ratio of Li/Ta=0.943 (molar ratio) was placed in the crucible and melted, and then a 6-inch diameter lithium tantalate single crystal was grown by the Czochralski method. ..

The temperature was investigated during the growth in the same manner as in Example 1.

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 amount of the crucible bottom surface from the crystal growth start to the growth end was -21. It was 0.5°C.

[Consideration based on Examples]
As summarized in Table 1, it was found that by appropriately adjusting the contact area ratio, the temperature at the bottom of the crucible was less likely to decrease, and there was a heat retention effect. As a result, it was confirmed that the weight of the single crystal when the raw material solidified region from the crucible bottom comes into contact with the single crystal increased, and a 6-titanium lithium titanate single crystal having a longer straight body portion was obtained. In particular, when the contact area between the top surface of the crucible 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 is reduced. It can be seen that the length can be made longer.

Further, FIG. 5 shows a graph of the crystal weight and the crucible bottom temperature drop during the crystal growth of Example 1 and Comparative Example 1. It is known that when crystals are generated during crystal growth, latent heat is released and the temperature of the raw material melt rises. In FIG. 5, the point of time when the amount of drop in the crucible temperature rises near the point where the weight of the crystal exceeds 1000 g (A and B in the figure) represents crystal formation. It can be seen that in Example 1(A) and Comparative Example 1(B), the release of latent heat due to crystal formation appears later in Example 1(A). From this, in Example 1, since the heat-retaining property of the crucible bottom was maintained and the solidification (crystal formation) of the raw material melt of the crucible bottom could be suppressed, it was possible to grow a long crystal having a longer straight body portion than the conventional one. ..

As described above, according to the crystal growing apparatus of the present embodiment, it is possible to grow crystals with a longer length than in the conventional case, and it is possible to improve productivity.

Although the preferred embodiments and examples of the present invention have been described above in detail, the present invention is not limited to the above-described embodiments and examples, and the above-described embodiments and without departing from the scope of the present invention Various modifications and substitutions can be added to the embodiment.

10 Work Coil Coil 20 Ceramic Refractory 30 Crucible 31 Bottom 40, 45 Crucible 41, 47 Top (Installation Surface)
42, 48 Dimple-shaped portion 46 Crucible base member 50 Heat insulating material 60 Pulling shaft 70 Lid 80 Seed crystal 90 Reflector 100 Melt 110 Single crystal 120 Seed crystal holding jig 130 After heater

Claims (5)

Iridium crucible having a bottom surface,
Can be disposed the crucible, the contact area ratio of the bottom, have a, a crucible stand made of zirconia having an installation surface is 10 to 38% relative to the bottom surface,
The installation surface of the crucible base has a recess-shaped portion,
The crucible base comprises a plurality of stackable crucible base members,
Wherein the plurality of crucible base member is the same shape der Ru crystal growth apparatus. The recess-shaped portion, the crystal growing apparatus according to claim 1 have the same shape. An iridium crucible having a bottom surface,
The crucible can be installed, and the contact area ratio with the bottom surface has a crucible base made of zirconia having an installation surface that is 10 to 38% with respect to the bottom surface,
The installation surface of the crucible base has a recess-shaped portion,
The crucible base comprises a plurality of stackable crucible base members,
Wherein among the plurality of crucibles base member, said crucible base member which is not in contact with the crucible, crystal growth apparatus that having a large mounting surface than the crucible base member in contact with the crucible. The crystal growing device according to any one of claims 1 to 3 , wherein the recess-shaped portion is a concentric circular groove. The crystal growing apparatus according to any one of claims 1 to 4 , wherein a contact area ratio of the crucible table with the bottom surface is 12 to 36% with respect to the bottom surface.