JP2005015271A - Apparatus and method for manufacturing single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and method for manufacturing a single crystal which enable the single crystal to be grown efficiently with good reproducibility while avoiding the deformation of a crucible. <P>SOLUTION: The apparatus for manufacturing the single crystal by growing it by a Czochralski method using an induction heating method is characterized in that the apparatus is provided with: an electroconductive crucible for housing a crystal raw material whose weight density in a liquid state is lower than that in a solid state and melting it; an induction heater arranged so as to surround at least the side face of the crucible; and an electroconductive shielding body provided between the induction heater and the electroconductive crucible so as to surround the side face of the electroconductive crucible at least ranging from the bottom face of the electroconductive crucible to a prescribed height. Further, in the method for manufacturing the single crystal, an upper part higher than the prescribed height of the electroconductive crucible is heated by induction heating with the induction heater and a lower part lower than the prescribed height of the electroconductive crucible is heated by the electroconductive shielding body which is induction heated with the induction heater. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a single crystal manufacturing apparatus and a single crystal manufacturing method for growing a single crystal by a Czochralski method using an induction heating method.
[0002]
[Prior art]
When growing oxide single crystals such as lithium tantalate and lithium niobate and fluoride single crystals such as calcium fluoride and aluminum fluoride, the Czochralski method using an induction heating method is used.
In this method, first, a single crystal raw material is put into a conductive crucible, and a heat insulating material made of alumina or the like is arranged around and on the crucible so as to obtain an appropriate temperature gradient. Next, the crucible is heated by induction heating using a coil called a work coil, and the raw material placed in the crucible is heated and melted to obtain a melt. Next, the temperature of the melt is adjusted so as to be close to the melting point, and the seed crystal is immersed in the melt while rotating the seed crystal from above the crucible. Then, the seed crystal is pulled at a speed of several cm / h or less while adjusting the heating amount or the like so that the pulling portion has a predetermined shape, and a single crystal is grown.
[0003]
The induction heating method used as a method for heating the crucible is a method described below. First, as an induction heating body, a coil wound in multiple lengths around a crucible is arranged around the crucible, and a high-frequency current is passed through the coil. Then, a magnetic field is generated inside the coil in the coil winding direction. Since the magnetic field changes according to the change in the high-frequency current, an induced current flows on the side surface of the crucible in a direction that cancels the change in the magnetic field. Joule heat is generated by the electric resistance of the current crucible, and as a result, the crucible is heated. Therefore, the crucible that can be heated by the induction heating method needs to be made of a conductive material that can withstand high temperatures, and is generally made of a noble metal such as iridium, platinum, or platinum rhodium.
[0004]
Such a crucible is reused because it is expensive and does not necessarily need to be replaced with a new one each time a single crystal is produced. In general, the melt of the raw material remains in a solidified state in the lower part of the crucible once used for producing the single crystal.
[0005]
Since this residual material can be reused, in order to use the raw material effectively, the next time a single crystal is manufactured, a supplementary material is added on top of the residual material and the crucible is heated so that the residual material and supplement The raw material is melted.
[0006]
[Problems to be solved by the invention]
In oxides such as lithium tantalate and lithium niobate and fluorides such as calcium fluoride and aluminum fluoride, the weight density of the liquid phase is smaller than the weight density of the solid phase. Accordingly, the volume expansion pressure is generated since the volume expansion occurs when the raw material as the solid phase is melted to become the melt as the liquid phase. At this time, when the residual raw material starts to melt before the replenishing raw material, since there is a solid such as the replenishing raw material on the residual raw material, the expansion pressure of the melt is not released and pressure is applied to the side of the crucible.
[0007]
At this time, the temperature of the crucible is higher than the temperature of the residual raw material inside, and the crucible is softened, so that the side surface of the crucible lower part in particular is deformed and expands in the radial direction by the volume expansion pressure. When this deformation is repeated, the diameter of the lower crucible gradually expands. That is, the volume of the crucible gradually changes.
[0008]
FIGS. 2A to 2D are schematic views of the conventional crystal raw material melting step described above. First, the replenishing raw material 4 is put into the crucible 2 surrounded by the work coil 1 and the heat insulating material 5 of alumina and having the residual raw material 3 remaining therein. An alumina hat 6 is disposed above the crucible to maintain an appropriate temperature gradient (FIG. 2 (a)).
[0009]
When the crucible 2 is induction-heated by passing a high-frequency current through the work coil 1, the residual raw material 3 is melted and a melt 7 is generated. Since the density of the melt 7 is lower than that of the residual raw material 3, it tends to expand in volume. However, since there are solid-phase residual raw material 3 and supplementary raw material 4 that are not yet melted above, the melt 7 exerts a volume expansion pressure on the side surface of the crucible 2, and the crucible 2 is deformed to expand its diameter (FIG. 2 (b)).
[0010]
Thereafter, the upper residual raw material 3 and replenishing raw material 4 are gradually melted (FIG. 2 (c)), and all the raw materials are melted to become a melt (FIG. 2 (d)), but the crucible 2 remains deformed.
If such a crucible is used, even if the same amount of raw material is charged into the crucible, the height of the melt surface changes. As a result, the temperature gradient at the time of growing the single crystal changes for each production, and it becomes impossible to grow a single crystal with good reproducibility.
[0011]
Moreover, the crucible where such deformation is repeated may be distorted, and a part of the crucible may crack and the melt inside may ooze out. In this case, the height of the melt surface changes greatly, and the temperature gradient becomes inadequate, resulting in problems such as many defects being introduced into the grown single crystal and cracking of the single crystal. As a result, the manufacturing efficiency is reduced due to the interruption of the manufacturing process or the occurrence of defective products. Moreover, since the number of times the crucible is reused decreases, it is not preferable from the viewpoint of cost.
[0012]
Therefore, it is important to avoid deformation of the crucible and appropriately melt the raw material. In order to melt the raw material without deforming the crucible, it is desirable to melt the supplementary raw material before the residual raw material. That is, the replenishing material replenished from above the residual material melts before the residual material, melts the replenishing material while releasing the volume expansion pressure above the crucible above the crucible, and the melt contacts If the residual raw material is gradually melted, volume expansion pressure is not applied to the crucible, and deformation of the crucible can be suppressed.
[0013]
In order to melt the raw material as described above, it is important to first heat from the upper part of the crucible.
In the case of induction heating, since the side surface of the crucible is heated by supplying a high-frequency current to the work coil, the manner in which the crucible is heated differs depending on the position of the crucible with respect to the work coil, the diameter of the crucible and the like. In general, the magnetic field induced by the work coil is the strongest and the largest amount of change in the vicinity of the center axis of the work coil winding. Therefore, when the crucible is placed near the center axis of the work coil, the induced current becomes the largest and is easily heated. . In addition, the larger the crucible diameter, the larger the magnetic field inside the crucible and the greater the induced current flowing on the side of the crucible, so that it becomes easier to heat. Further, since the crucible is heated by Joule heat due to electric resistance, the amount of heating is also affected by the thickness of the crucible.
[0014]
Next, the relative position of the work coil crucible in the vertical direction will be described. First, in the step of pulling up the single crystal, the raw material is in a melt state, and it is necessary to provide a temperature gradient above the melt, that is, to lower the temperature above the crucible. It is necessary to optimize the position of the crucible relative to the work coil so as to achieve such an optimal temperature gradient.
[0015]
However, in the step of melting the raw material, it is preferable to heat and melt the raw material in the upper part of the crucible first in order to avoid deformation of the crucible as described above. It must be changed from the position. At this time, since the upper part of the crucible is spatially open, even if the upper part of the crucible is preferentially heated in the process of melting the raw material, heat is released from the open part above the crucible at the same time, so the upper part of the crucible is melted. In order to make it sufficient temperature, it must heat more than the heat radiation, and heating efficiency will become very bad.
[0016]
Therefore, as a countermeasure, it is conceivable to cover the crucible or use a long crucible to increase the distance between the heating part and the heat dissipation part. In this case, the temperature required for the process of pulling up the single crystal This is not preferable because the gradient is small.
For this reason, in the growth of single crystals using raw materials that cause volume expansion by melting, a method for avoiding crucible deformation due to volume expansion accompanying melting of the raw materials and efficiently growing high-quality single crystals is desired. It was rare.
[0017]
In view of the above problems, an object of the present invention is to provide a single crystal production apparatus that solves problems in production of a single crystal due to deformation of a crucible and enables efficient and reproducible single crystal growth. It is.
[0018]
Another object of the present invention is to provide a method for producing a single crystal that solves the problems in the production of the single crystal due to the deformation of the crucible and enables efficient and reproducible single crystal growth. .
[0019]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in a single crystal manufacturing apparatus for growing a single crystal by the Czochralski method using an induction heating method,
At least a conductive crucible for melting a crystal raw material having a weight density in a liquid phase lower than that in a solid phase; and an induction heating body arranged to surround at least a side surface of the conductive crucible; A conductive shield disposed between the induction heating body and the conductive crucible so as to surround at least a side surface of a portion from the bottom surface of the conductive crucible to a predetermined height. An apparatus for producing a single crystal is provided (claim 1).
Thus, by surrounding the portion from the bottom surface of the conductive crucible to a predetermined height with the conductive shield, the crystal material in the crucible is melted from the top, and the deformation of the crucible due to the volume expansion pressure of the melt is suppressed. be able to.
[0020]
The predetermined height is preferably the height of the upper surface of the residual crystal raw material remaining in the conductive crucible (Claim 2).
In this way, by setting the height of the conductive shield to the height of the upper surface of the residual crystal raw material, the crystal raw material in the crucible is surely melted from the replenishing raw material, and the crucible is deformed by the volume expansion pressure of the melt. Can be suppressed.
[0021]
The conductive shield may have a bottom surface.
As described above, a conductive shield having a bottom surface, for example, a commercially available crucible can be applied.
[0022]
Further, the conductive shield may have a bellows shape (claim 4).
Thus, if the conductive shield has a bellows shape, the surface area of the shield can be increased. Further, the position of the work coil and the conductive shield can be changed in the axial direction due to the bellows shape, so that the heat generation temperature distribution of the crucible can be changed. Therefore, the shielding effect at the initial stage of melting can be increased.
[0023]
Moreover, it is preferable to provide a moving mechanism for independently moving the conductive shield and the conductive crucible.
Thus, by providing a moving mechanism for independently moving the conductive shield and the conductive crucible, the relative relationship between the conductive shield, the conductive crucible, and the induction heating body according to the amount of the remaining raw material or the like. The position can be adjusted optimally.
[0024]
Further, the method of the present invention includes at least a method for producing a single crystal by growing the single crystal by the Czochralski method using an induction heating method.
A crystalline raw material whose weight density in the liquid phase is lower than the weight density in the solid phase is put into a conductive crucible,
The induction heating body arranged so as to surround the side surface of the conductive crucible, the upper portion of the conductive crucible is induction-heated above a predetermined height to melt the crystal raw material inside the upper portion of the crucible,
On the other hand, a conductive shield disposed between the induction heating body and the conductive crucible so as to surround at least a side surface of the portion from the bottom surface of the conductive crucible to a predetermined height is provided by the induction heating body. A method for producing a single crystal, comprising: induction heating, heating a lower portion of the conductive crucible from a predetermined height by the conductive shield subjected to induction heating, and melting a crystal raw material inside the lower portion of the crucible. (Claim 6).
[0025]
In this way, the induction heating body induces and heats the upper part of the conductive crucible above a predetermined height to melt the crystal material inside the crucible upper part, while the conductive shield is induced by the induction heating body. By heating, the lower part of the conductive crucible is heated by a conductive shield that is induction-heated, and by melting the crystal raw material inside the crucible lower part, the crystal raw material in the crucible is melted from the upper part, The deformation of the crucible due to the volume expansion pressure of the melt can be suppressed.
[0026]
At this time, the predetermined height is preferably set to the height of the upper surface of the residual crystal raw material remaining in the conductive crucible (Claim 7).
In this way, by setting the height of the conductive shield to the height of the upper surface of the residual crystal material, the crystal material in the crucible is reliably melted from the replenishing material, and deformation of the crucible due to the expansion pressure of the melt is suppressed. can do.
[0027]
In addition, it is preferable that the crystalline raw material inside the crucible lower part is melted by the conductive shield after the induction heating body starts melting the crystalline raw material inside the crucible upper part (Claim 8).
Thus, after the melting of the crystal raw material inside the upper part of the crucible starts, the deformation of the crucible due to the expansion pressure of the melt can be suppressed by melting the crystal raw material inside the lower part of the crucible.
[0028]
At this time, it is provided with a moving mechanism for independently moving the conductive shield and the conductive crucible, and in the step of melting the crystal raw material, the conductive shield is moved with respect to the conductive crucible by the moving mechanism. You may move relatively (Claim 9).
In this way, in the process of melting the crystal material, if the conductive shield is moved relative to the conductive crucible by the moving mechanism, for example, the process of melting the crystal material can be performed in a shorter time.
[0029]
In addition, a moving mechanism for independently moving the conductive shield and the conductive crucible is provided, and in the step of growing a single crystal, the conductive shield is moved relative to the conductive crucible by the moving mechanism. (Claim 10). As described above, in the process of growing the single crystal, if the conductive shield is moved relative to the conductive crucible by the moving mechanism, the temperature gradient necessary for growing the single crystal is changed and optimized. be able to.
[0030]
In addition, in the step of lowering the temperature of the grown single crystal, provided with a moving mechanism for independently moving the conductive shield and the conductive crucible, the grown single crystal and the grown single crystal by the moving mechanism It may be moved to the same height, and the grown single crystal may be annealed by the conductive shield (claim 11).
In this way, in the step of lowering the temperature of the grown single crystal, if annealing is performed with the conductive shield, a higher quality single crystal from which crystal distortion and defects have been removed can be obtained.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, although embodiment of this invention is described, this invention is not limited to this.
As described above, in order to avoid the deformation of the crucible, it is preferable to dissolve the raw material in the upper part of the crucible first. However, since the upper part of the crucible is spatially open, even if the top part of the crucible is preferentially heated in the process of melting the raw material, heat from the open part above the crucible occurs at the same time. In order to bring it to a temperature, it must be heated more than its heat dissipation, and the heating efficiency becomes very bad. On the other hand, if a crucible is covered or a long crucible with a long length is used, the process of growing crystals Since a necessary temperature gradient becomes small, it is not preferable in the process of growing crystals.
[0032]
In view of this, the present inventor makes use of the characteristics of induction heating so as to enclose the side surface of the portion from the bottom surface of the conductive crucible to a predetermined height between the conductive crucible and the work coil that is the induction heating body. The present invention has been completed by finding that the above-mentioned problems can be overcome by arranging a conductive shield.
[0033]
When a high-frequency current is passed through the work coil that is an induction heating body, a variable magnetic field is generated inside the work coil. Then, an induced current flows so as to cancel the fluctuation of the magnetic field, and Joule heat is generated due to the electrical resistance of the conductive shield, at least inside the work coil and located at the position closest to the work coil. As a result, induction heating is performed. Since the magnetic field fluctuation generated in the work coil due to the current induced in the conductive shield is mitigated, no induced current is generated in the side surface of the conductive crucible surrounded by the conductive shield, or at least the conductive shield is Less than if not placed. Therefore, the induction heating effect on the lower part of the conductive crucible by the work coil can be suppressed.
[0034]
The conductive crucible inside the conductive shield that is induction-heated is indirectly heated mainly by heat conduction or radiation from the conductive shield. Therefore, the temperature of the side surface of the conductive crucible surrounded by the shield is lower than that in the case where induction heating is performed directly by the work coil. The temperature of the conductive crucible can be controlled by changing the distance between the conductive shield and the thickness or type of the heat insulating material.
[0035]
The material of the conductive shield is not particularly limited as long as it is a conductor for induction heating and has an electric resistance necessary for heating. The same material as that of the conductive crucible may be used, and since the temperature is higher than that of the conductive crucible, it may be made of a material that can withstand higher temperatures and hardly deform.
[0036]
As shown in FIG. 1A, the single crystal manufacturing apparatus of the present invention includes at least a conductive crucible 12, a work coil 11 arranged so as to surround the conductive crucible 12, and a conductive crucible therebetween. The conductive shield 18 is provided so as to surround at least a portion from the bottom surface to a predetermined height. Furthermore, a heat insulating material 15 such as alumina is provided between the work coil 11 and the conductive shield 18 and between the conductive shield 18 and the conductive crucible 12, and an appropriate temperature gradient is maintained above the crucible. Therefore, a hat 16 such as alumina is provided. A crucible moving mechanism 25 is provided at the lower part of the apparatus. Further, a shield moving mechanism for moving the conductive shield may be provided.
[0037]
Regarding the shape of the conductive shield 18, for example, as shown in FIG. 3, a cylindrical body without a bottom surface (FIG. 3A), a crucible with a bottom surface (FIG. 3B), or the like can be applied. If it is a crucible shape, a commercially available crucible can be used. Moreover, if it is a bellows shape (FIG.3 (c)), even if it is the same height, a surface area can be enlarged, and it can also be expanded-contracted up and down according to the height of a residual raw material. Any cylindrical body such as a tapered shape, a wave shape, a conical shape, a dome shape, or the like can be applied as necessary as long as it is subjected to appropriate induction heating. Moreover, a part of the side surface of the conductive shield may be in contact with the inner conductive crucible (FIG. 3D).
[0038]
Hereinafter, the melting process of the crystal raw material according to the present invention will be described with reference to FIGS.
The conductive shield 18 is disposed between the work coil 11 and the conductive crucible 12 so as to surround at least the side surface 12a of the portion from the bottom surface of the conductive crucible 12 to the upper surface of the residual raw material 13 or the height in the vicinity thereof. ing. A supplementary raw material 14 is additionally charged on the residual raw material 13. (Fig. 1 (a))
[0039]
Here, when a high-frequency current is passed through the work coil 11, the side 12 a of the portion surrounded by the conductive shield 18 of the conductive crucible 12 is induction-heated rather than the induction heating from the work coil 11. Therefore, the temperature of the side surface 12a at the lower part of the conductive crucible is lower than that when the conductive shield 18 is not present.
[0040]
On the other hand, the side surface 12 b of the upper portion of the conductive crucible containing the replenishing material 14 that is not surrounded by the conductive shield 18 is directly subjected to induction heating by the work coil 11. Therefore, the temperature of the side surface 12b at the upper part of the conductive crucible becomes higher than that of the side surface 12a at the lower part of the conductive crucible containing the residual raw material 13.
[0041]
Here, a temperature difference occurs between the upper and lower portions 12b and 12a of the side surface of the conductive crucible. If the conductive crucible 12 is made of a single material and has an integrated shape, the temperature is somewhat averaged due to the movement of heat between the upper and lower parts. However, the conductive crucible 12 is always heated. Therefore, this temperature distribution does not change greatly. Therefore, the replenishment raw material 14 is first heated from the portion in contact with the side surface 12b of the upper portion of the conductive crucible and starts to melt (FIG. 1 (b)).
[0042]
At this time, since the side surface 12a under the conductive crucible is heated through the heat insulating material 15 mainly by the conductive shield 18, the residual raw material 13 has not yet melted. Therefore, the melt 17 produced by melting the replenishment material 14 descends below the crucible and accumulates on the residual material 13, and the residual material 13 in contact with the melt 17 begins to gradually melt from above (FIG. 1). (C)). At this time, since the raw material of the solid phase that has not yet been melted is below the crucible, all the volume expansion pressure generated when the raw material melts is released to the upper side of the crucible, and the crucible is not deformed by the volume expansion pressure.
[0043]
In this way, the raw material is gradually dissolved from above, and all the residual raw material 13 and the supplementary raw material 14 in the crucible can be melted without deforming the conductive crucible 12 (FIG. 1 (d)).
[0044]
In order to melt the residual raw material 13 quickly, at least after the replenishing raw material 14 starts to melt, the conductive shield 18 is moved slowly downward or the crucible is moved upward to enter the residual raw material 13 which has not yet melted. Alternatively, the side surface 12a of the lower portion of the conductive crucible 12 may be directly induction heated by the work coil 11 gradually from above.
[0045]
Next, as shown in FIG. 4 or 5, the seed crystal 20 is rotated from above the conductive crucible 12 while being immersed in the melt 17, and the heating amount and the like are adjusted so that the lifting portion 21 has a predetermined shape. However, the seed crystal 20 is pulled up at a speed of several cm / h or less, and the single crystal 22 is grown. At this time, as shown in FIG. 5, by moving the conductive shield 18 with respect to the conductive crucible 12 by the shield moving mechanism 24, the temperature gradient can be changed to some extent and optimized. In the case of a crystal that is easily cracked due to thermal strain, as shown in FIG. 6, in the process of separating the grown single crystal 22 from the melt 17 and lowering the temperature, the conductive shield 18 is moved by the moving holding wire 23. It is also possible to carry out the annealing process by moving to the height of the single crystal 22.
[0046]
【Example】
EXAMPLES Hereinafter, although an Example and comparative example of this invention are given and this invention is demonstrated concretely, this invention is not limited to these.
(Example 1)
Lithium niobate (chemical formula: LiNbO ₃ ) In the platinum crucible having a diameter of 150 mm for pulling up the single crystal, only 3,000 g of the raw material remaining after the previous single crystal pulling process remains. The height of the upper surface of this residual raw material was 40 mm from the bottom of the crucible.
[0047]
Around this crucible, an alumina heat insulating material having a thickness of 10 mm is disposed, and outside thereof, zirconia is dispersed to improve the strength (hereinafter referred to as reinforced platinum). The diameter is 170 mm, the height is 50 mm, and the thickness is 2 mm. Are arranged concentrically with a platinum crucible so that the bottom and bottom ends of the crucible are aligned.
An alumina heat insulating material having a thickness of 10 mm is further arranged outside the cylinder. A work coil of 300φ × 500 mm × 10 turns for induction heating is arranged outside the metal plate concentrically with a platinum crucible and a reinforced platinum cylinder. Above the platinum crucible, a dome-shaped alumina cylinder of 180φ × 160φ × 150 mmh is arranged. In the platinum crucible containing the residual raw material, LiNbO ₃ Of 2,000 g of 99.99% pure calcined material.
[0048]
When the platinum crucible supplemented with the raw material is heated by applying a high-frequency current to the work coil, the upper portion of the platinum crucible turns red, and the supplemented firing raw material starts to melt. At this time, when the temperature was measured with a thermocouple brought into contact with the bottom of the platinum crucible, it was 920 ° C., and it was found that the residual raw material under the crucible was not yet melted. When the high frequency current is further increased, the raw material in the crucible is further melted into a melt, and a temperature peak generated when the raw material is melted is also observed in the thermocouple in contact with the bottom of the platinum crucible, The temperature was 1,005 ° C.
[0049]
Thus, it was judged that all the raw materials in the crucible were melted, and the seed crystal was immersed in the melt surface to pull up 2,000 g of a single crystal having a diameter of 3 inches (75 mm) and a length of 100 mm. At this time, the reinforced platinum cylinder remains held in the same position. The above process was repeated 10 times, and the platinum crucible with the remaining raw material was taken out. As a result, a bulge of about 1 mm occurred in the portion where the raw material on the side of the crucible remained, but there was no significant deformation. .
LiNbO ₃ The melt and crystal densities are 3.8 and 4.7, respectively.
[0050]
(Example 2)
Lithium tantalate (chemical formula: LiTaO ₃ ) In the first iridium crucible with a diameter of 150 mm for pulling up the single crystal, only 4,000 g of the raw material remaining after the previous single crystal pulling process remains. The height of the upper surface of this residual raw material was 32 mm from the bottom of the crucible.
[0051]
Around the crucible, an alumina heat insulating material having a thickness of 10 mm is disposed, and on the outside thereof, a second iridium crucible having a diameter of 180 mm, a height of 70 mm, and a thickness of 2 mm is concentrically formed on the first iridium crucible. Place it in contact with the bottom of one crucible.
An alumina heat insulating material having a thickness of 10 mm is further arranged on the outer periphery of the second iridium crucible. On the outside, a work coil of 300φ × 500 mm × 10 turns for induction heating is arranged concentrically with the first and second iridium crucibles. A dome-shaped platinum cylinder of 180φ × 160φ × 150 mmh is disposed above the first iridium crucible. In the first iridium crucible containing this residual material, LiTaO ₃ 4,000 g of calcined raw material having a purity of 99.99% is replenished.
[0052]
When the crucible supplemented with the raw material is heated by applying a high-frequency current to the work coil, the upper part of the first iridium crucible turns red, and the supplemented firing raw material starts to melt. At this time, when the temperature was measured with a thermocouple brought into contact with the bottom of the first iridium crucible, it was found to be 1,470 ° C., and the residual raw material at the bottom of the crucible was not yet melted. When the high-frequency current is further increased, the raw material in the crucible is further melted into a melt, and even in the thermocouple that is in contact with the bottom of the first iridium crucible, a temperature peak is generated when the raw material is in the melt. Was observed, and the temperature was 1,610 ° C.
[0053]
Thus, it was judged that all the raw materials in the crucible were melted, and the seed crystal was immersed in the melt surface to pull up 4,000 g of crystals having a diameter of 3 inches (75 mm) and a length of 100 mm. At this time, the first iridium crucible was moved upward 10 hours after the single crystal growth using the first iridium crucible, but the second iridium crucible was held in the same position. . The above process was repeated 10 times, and when the first iridium crucible in which the raw material remained was taken out, a bulge of about 1 mm occurred in the portion where the raw material on the side of the crucible remained, but a large deformation There was no.
LiTaO ₃ The melt and crystal densities are 5.8 and 7.5, respectively.
[0054]
Example 3
Bismuth germanate (chemical formula: Bi ₄ Ge ₃ O ₁₂ ) In the platinum crucible having a diameter of 150 mm for pulling up the single crystal, only 3,500 g of the raw material remaining and solidified after the previous single crystal pulling process remains. The height of the upper surface of this residual raw material was 30 mm from the bottom of the crucible.
[0055]
Around this crucible, a silicate heat insulator with a thickness of 10 mm is placed. On the outside, a platinum cylinder with a diameter of 180 mm, a height of 70 mm, and a thickness of 2 mm is placed concentrically with the platinum crucible, and the bottom and bottom ends of the crucible are aligned. Arrange. The platinum cylinder at this time has a bellows shape. The bellows-shaped platinum cylinder is welded to a platinum crucible.
A silicate heat insulating material having a thickness of 10 mm is further arranged on the outer periphery of the cylinder. On the outside, a work coil of 300φ × 500 mm × 10 turns for induction heating is arranged concentrically with the platinum crucible and the platinum cylinder. Above the platinum crucible, an alumina cylinder of 180φ × 160φ × 150 mmh is arranged. In the platinum crucible containing this residual material, Bi ₄ Ge ₃ O ₁₂ 4,000 g of calcined raw material having a purity of 99.99% is replenished.
[0056]
When the platinum crucible supplemented with the raw material is heated by applying a high-frequency current to the work coil, the upper portion of the platinum crucible turns red, and the supplemented firing raw material starts to melt. At this time, when the temperature was measured with a thermocouple brought into contact with the bottom of the platinum crucible, it was 820 ° C., and it was found that the residual raw material at the bottom of the crucible was not yet melted. As the high-frequency current is further increased, the raw material in the crucible further melts into a melt, and a temperature peak that occurs when the raw material becomes a melt is observed even at the thermocouple temperature in contact with the platinum crucible bottom. The temperature was 950 ° C.
[0057]
Thus, it was judged that all the raw materials in the crucible were melted, and the seed crystal was immersed in the melt surface to pull up 4,000 g of crystals having a diameter of 3 inches (75 mm) and a length of 100 mm. At this time, since the outer bellows-shaped platinum cylinder is welded to the inner platinum crucible, the relative position thereof does not change even during crystal growth. The above process was repeated 10 times, and when the platinum crucible with the remaining raw material was taken out, a bulge of about 2 mm occurred in the portion where the raw material on the side of the crucible, including the bellows portion, remained. There was no major deformation.
Bi ₄ Ge ₃ O ₁₂ The melt and crystal densities are 6.2 and 7.1, respectively.
[0058]
(Example 4)
Lithium niobate (chemical formula: LiNbO ₃ ) In the platinum crucible having a diameter of 150 mm for pulling up the single crystal, only 3,000 g of the raw material remaining after the previous single crystal pulling process remains. The height of the upper surface of this residual raw material was 40 mm from the bottom of the crucible.
[0059]
Around this crucible, an alumina heat insulating material having a thickness of 10 mm is disposed, and outside thereof, zirconia is dispersed to improve the strength (hereinafter referred to as reinforced platinum). The diameter is 170 mm, the height is 50 mm, and the thickness is 2 mm. Are arranged concentrically with the platinum crucible, with the bottom and bottom ends of the crucible aligned.
An alumina heat insulating material having a thickness of 10 mm is further arranged outside the cylinder. A work coil of 300φ × 500 mm × 10 turns for induction heating is arranged outside the metal plate concentrically with a platinum crucible and a reinforced platinum cylinder. Above the platinum crucible, a dome-shaped alumina cylinder of 180φ × 160φ × 150 mmh is arranged. In the platinum crucible containing the residual raw material, LiNbO ₃ Of 2,000 g of 99.99% pure calcined material.
[0060]
When the platinum crucible supplemented with the raw material is heated by applying a high-frequency current to the work coil, the upper portion of the platinum crucible turns red, and the supplemented firing raw material starts to melt. At this time, when the temperature was measured with a thermocouple brought into contact with the bottom of the platinum crucible, it was 920 ° C., and it was found that the residual raw material under the crucible was not yet melted. When the high frequency current is further increased, the raw material in the crucible is further melted into a melt, and a temperature peak generated when the raw material is melted is also observed in the thermocouple in contact with the bottom of the platinum crucible, The temperature was 1,005 ° C.
[0061]
Thus, it was judged that all the raw materials in the crucible were melted, and the seed crystal was immersed in the melt surface to pull up 2,000 g of a single crystal having a diameter of 3 inches (75 mm) and a length of 100 mm. At this time, the cylinder of reinforced platinum is kept in the same position during crystal growth, but when the growth is finished and the crystal is separated and cooled, the wire holding the reinforced platinum cylinder is lifted, When the crystal was held at a certain position, the strengthened platinum cylinder was inductively heated, and the temperature could be lowered while annealing the crystal. The above process was repeated 10 times, and the platinum crucible with the remaining raw material was taken out. As a result, a bulge of about 2 mm occurred in the portion where the raw material on the side of the crucible remained, but there was no significant deformation. . In addition, defects such as coloring of the pulled crystal were reduced by about 10% compared to Example 1.
[0062]
(Comparative Example 1)
Lithium tantalate (chemical formula: LiTaO ₃ ) In the iridium crucible with a diameter of 150 mm for pulling up the single crystal, only 4,000 g of the raw material remaining after the previous single crystal pulling process remains. The height of the upper surface of this residual raw material was 32 mm from the bottom of the crucible.
[0063]
An alumina heat insulating material having a thickness of 20 mm is arranged around the crucible. On the outside, a work coil of 300φ × 500 mm × 10 turns for induction heating is arranged concentrically with the iridium crucible. Above the iridium crucible, a dome-shaped platinum cylinder of 180φ × 160φ × 150 mmh is arranged. In this iridium crucible containing the residual raw material, LiTaO ₃ 4,000 g of calcined raw material having a purity of 99.99% is replenished.
[0064]
When the crucible supplemented with the raw material is heated by applying a high-frequency current to the work coil, the upper part of the crucible turns a little red, but the supplemented firing raw material has not yet dissolved. In this state, when the temperature was measured with a thermocouple brought into contact with the bottom of the iridium crucible, a temperature peak generated when the raw material became a melt was observed at around 1,600 ° C. That is, the residual raw material in the lower part of the crucible is in a molten state. As the high-frequency current was further increased, it was observed that for a while the replenished solid-phase calcined raw material sinks into the melt of the residual raw material at the bottom of the crucible, which was measured by the previous thermocouple. The temperature dropped from the peak value to 1,580 ° C.
[0065]
Thus, it was judged that all the raw materials in the crucible were melted, and the seed crystal was immersed in the melt surface to pull up 4,000 g of crystals having a diameter of 3 inches (75 mm) and a length of 100 mm. The above process was repeated 10 times, and the iridium crucible with the remaining raw material was taken out. As a result, a large bulge of about 10 mm was formed in the portion where the raw material on the side of the crucible remained. A crack of about 1 mm occurred in the welded part.
[0066]
As is clear from the examples and comparative examples described above, according to the present invention, the conductive shield is disposed between the work coil and the crucible so as to surround the side surface of the portion from the bottom surface of the crucible to a predetermined height. By providing the body, even if the same crucible was used 10 times, the crucible was not greatly deformed or cracked, and the effect of the present invention was clarified. Therefore, the manufacturing apparatus and the manufacturing method according to the present invention avoid the deformation of the crucible, contribute to the production of a stable single crystal, and contribute to the increase in the number of times the crucible is reused.
[0067]
The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
[0068]
【The invention's effect】
As described above, in the single crystal manufacturing apparatus for growing a single crystal by the Czochralski method using the induction heating method, a predetermined distance from the bottom surface of the conductive crucible is at least between the induction heating body and the conductive crucible. It is possible to avoid deformation of the crucible caused by the volume expansion pressure caused by melting the raw material in the crucible from the lower part by including a conductive shield arranged so as to surround the side surface of the part up to the height. Become.
In addition, the upper part of the conductive crucible is induction-heated from the predetermined height by the induction heating body to melt the crystal raw material inside the upper part of the crucible and the conductive shielding body is induction-heated by the induction heating body. By heating the lower part of the crucible below a predetermined height and melting the crystal raw material inside the crucible lower part, the crystal raw material in the crucible is melted from the upper part, and the deformation of the crucible due to the volume expansion pressure of the melt is suppressed. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a melting step of a crystal raw material by a single crystal manufacturing apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic view showing a melting step of a crystal raw material by a conventional single crystal production apparatus.
FIG. 3 is a cross-sectional view showing an example of a conductive shield according to an embodiment of the present invention.
FIG. 4 is a schematic view showing a single crystal pulling process by the single crystal manufacturing apparatus according to the embodiment of the present invention.
FIG. 5 is a schematic view showing a single crystal pulling process by a single crystal manufacturing apparatus according to another embodiment of the present invention.
FIG. 6 is a schematic diagram showing annealing in a temperature drop process of a single crystal by the single crystal manufacturing apparatus according to the embodiment of the present invention.
[Explanation of symbols]
1 ... Work coil, 2 ... Crucible,
3 ... residual raw material 4 ... supplementary raw material
5 ... insulation, 6 ... hat,
7 ... melt, 11 ... work coil,
12 ... Conductive crucible,
12a ... the side of the lower part of the conductive crucible,
12b ... the side of the upper part of the conductive crucible,
13 ... residual raw material, 14 ... replenishing raw material,
15 ... insulation, 16 ... hat,
17 ... melt, 18 ... conductive shield,
20 ... Seed crystal, 21 ... Pulling part,
22 ... single crystal, 23 ... moving holding wire,
24 ... Shield moving mechanism, 25 ... Crucible moving mechanism.

Claims (11)

In a single crystal manufacturing apparatus that grows a single crystal by the Czochralski method using an induction heating method,
At least a conductive crucible for melting a crystal raw material having a weight density in a liquid phase lower than that in a solid phase; and an induction heating body arranged to surround at least a side surface of the conductive crucible; A conductive shield disposed between the induction heating body and the conductive crucible so as to surround at least a side surface of a portion from the bottom surface of the conductive crucible to a predetermined height. Single crystal manufacturing equipment. The single crystal manufacturing apparatus according to claim 1, wherein the predetermined height is a height of an upper surface of a residual crystal raw material remaining in the conductive crucible. The single crystal manufacturing apparatus according to claim 1, wherein the conductive shield has a bottom surface. The single-crystal manufacturing apparatus according to claim 1, wherein the conductive shield has a bellows shape. The apparatus for producing a single crystal according to any one of claims 1 to 4, further comprising a moving mechanism for independently moving the conductive shield and the conductive crucible. In the method for producing a single crystal that grows a single crystal by the Czochralski method using an induction heating method, at least,
A crystalline raw material whose weight density in the liquid phase is lower than the weight density in the solid phase is put into a conductive crucible,
The induction heating body arranged so as to surround the side surface of the conductive crucible, the upper portion of the conductive crucible is induction-heated above a predetermined height to melt the crystal raw material inside the upper portion of the crucible,
On the other hand, a conductive shield disposed between the induction heating body and the conductive crucible so as to surround at least a side surface of the portion from the bottom surface of the conductive crucible to a predetermined height is provided by the induction heating body. A method for producing a single crystal, comprising: induction heating, heating a lower portion of the conductive crucible from a predetermined height by the conductive shield subjected to induction heating, and melting a crystal raw material inside the lower portion of the crucible. The method for producing a single crystal according to claim 6, wherein the predetermined height is set to a height of an upper surface of a residual crystal raw material remaining in the conductive crucible. 8. The crystal material inside the crucible lower part is melted by the conductive shield after the crystal raw material inside the crucible upper part starts melting by the induction heating body. A method for producing a single crystal. A moving mechanism for independently moving the conductive shield and the conductive crucible, and in the step of melting the crystal material, the conductive shield is moved relative to the conductive crucible by the moving mechanism; The method for producing a single crystal according to any one of claims 6 to 8, wherein the single crystal is moved. A moving mechanism for independently moving the conductive shield and the conductive crucible, and in the step of growing a single crystal, the conductive shield is moved relative to the conductive crucible by the moving mechanism; The method for producing a single crystal according to claim 6, wherein the single crystal is moved. In the step of lowering the temperature of the grown single crystal, a moving mechanism for independently moving the conductive shield and the conductive crucible is provided, and the conductive shield is moved to the same height as the grown single crystal by the moving mechanism. The method for producing a single crystal according to claim 6, wherein the grown single crystal is annealed by the conductive shield.

Images