JP6759926B2 - Crystal growth device - Google Patents

Description

The present invention relates to a crystal growth device, and more particularly to a crystal growth device suitable for crystal growth by the chocolate ralsky method.

The so-called Czochralski method, in which a crucible filled with a raw material is heated to a high temperature to melt the raw material, and a seed crystal is brought into contact with the liquid surface of the raw material melt in the crucible from above and then raised to grow a single crystal. A single crystal growing method called is conventionally practiced. In the single crystal growth by the Czochralski method, a work coil that flows a high-frequency power supply is arranged around the crucible, and the crucible heats up due to the induction heating generated by passing the high-frequency power supply through this work coil, and the raw material in the crucible melts. Will be done. In the Czochralski method, as the seed crystal rises, a single crystal grows as it is pulled up from the raw material melt. Since the upper part of the single crystal moves away from the pit as it is pulled up, the heat from the pit is difficult to transfer to the distant part, and if the heating element is only the pit, the temperature difference distribution of the growing single crystal is It may become large and problems such as cracking of a single crystal may occur. In order to improve this problem, a mechanism in which an afterheater is provided in the hot zone at the upper part of the crucible is also known (see, for example, Patent Document 1).

Patent Document 1 describes a sapphire single crystal growing apparatus having a configuration in which a work coil is divided in the vertical direction so that each divided coil can be individually controlled, and a high-frequency oscillator having a phase reversed is connected to each divided coil. Is described. The sapphire single crystal growing device described in Patent Document 1 prevents a decrease in the melt in the pit, controls the high frequency current of each dividing coil according to the growth of the crystal, and is generated by the positional relationship between the liquid level and the pit. The configuration is intended to maintain the optimum heating status of the melt and after-heater.

Japanese Unexamined Patent Publication No. 2014-125404

However, in the configuration described in Patent Document 1 described above, when the upper end of the single crystal comes to a region between the divided coils or a position higher than the upper end of the upper divided coils, heat is transferred to that portion. There is a problem that it becomes difficult, the uniformity of the single crystal cannot be ensured, and a high quality single crystal may not be grown. In addition, since there is such a portion where heat is difficult to transfer, it may be difficult to lengthen the single crystal. In addition, the device is also expensive because each split coil is controlled by using high-frequency oscillation with the phase reversed.

In recent years, there is a strong demand for cost reduction of oxide single crystals, which are in great demand. Above all, there is a strong demand for a longer growth length in a single crystal, which is expected to improve productivity. In order to deal with this, various measures have been taken in the crystal growth equipment, but at the same time, there is a strong demand for cost reduction of the crystal growth equipment.

Therefore, an object of the present invention is to provide a single crystal growth apparatus capable of reliably heating the upper part of a growing single crystal and at a low cost, capable of increasing the length of the crystal growth length.

In order to achieve the above object, the crystal growing apparatus according to one aspect of the present invention includes a crucible capable of holding a raw material melt and a crucible.
A first heating means arranged around the crucible,
A first elevating mechanism for elevating and elevating the first heating means,
A second heating means arranged above the crucible,
It has a second elevating mechanism for elevating and elevating the second heating means.
The first and second heating means are composed of an induction heating coil, and the first induction heating coil, which is the first heating means, is wound more than the second induction heating coil, which is the second heating means. a lot.

According to the present invention, it is possible to provide a single crystal growing apparatus capable of reliably heating the upper part of a growing single crystal and capable of increasing the crystal growing length at low cost.

It is a schematic diagram which showed an example of the crystal growth apparatus which concerns on embodiment of this invention. It is a detailed figure which showed an example of the elevating mechanism of the work coil of the crystal growth apparatus which concerns on embodiment of this invention.

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

The chocolate-ski type crystal growing apparatus according to the embodiment of the present invention is grown in the air or an inert gas atmosphere, such as lithium niobate LiNbO ₃ (hereinafter LN), lithium tantalate LiTaO ₃ (hereinafter LT), and ittium aluminum. This is a crystal growing device used for producing oxide single crystals such as Garnet Y ₃ Al ₅ O ₁₂ (hereinafter referred to as YAG). In the Chocolalski method, the tip of a rectangular parallelepiped single crystal, which is called a seed cut out according to a certain crystal orientation and usually has a side of several mm in cross section, is infiltrated into a melt of the same composition and gradually pulled up while rotating. This is a method of producing a single crystal by increasing the diameter while propagating the properties of the seed crystal.

FIG. 1 is a schematic view showing an example of a crystal growing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the crystal growing apparatus according to the present embodiment includes a crucible 10, a crucible stand 20, a reflector 30, an afterheater 40, a heat insulating material 50, a ceramic refractory 60, and a pulling shaft. A 70, a heating means 100, a power source 130, and a control means 140 are provided. The heating means 100 has two heating means, a main work coil 80 for heating the crucible and a sub work coil 90 for heating the upper part of the crucible. Further, the power supply 130 also has two power supplies, a main power supply 110 that supplies power to the main work coil and a sub power supply 120 that supplies power to the sub work coil.

In the crystal growing apparatus according to the present embodiment, the crucible 10 is placed on the crucible stand 20. An afterheater 40 is installed above the crucible 10 via a reflector 30. A heat insulating material 50 is installed so as to surround the crucible 10. Further, a ceramic refractory 60 is provided on the outer side 50 of the heat insulating material to cover the entire circumference of the crucible 10. A heating means 100 is arranged on the outside of the side surface of the ceramic refractory 60. The main work coil 80 surrounds the crucible 10 in the horizontal direction. Further, the sub work coil 90 surrounds the after heater 40 in the horizontal direction. Further, the periphery of the heating means 100 including the main work coil 80 and the subwork coil 90 may be covered with a chamber (not shown) so that the periphery of the crucible 10 and the heating means 100 are housed in the chamber. The crucible 10 and the heat insulating material 50 provided around the crucible 10 form a hot zone portion. Further, a pulling shaft 70 is provided above the crucible 10. The pull-up shaft 70 has a seed crystal holding portion 71 at the lower end, and is configured to be able to be raised and lowered by the pull-up shaft drive portion 72. Further, a control means 140 and a power supply 130 are provided outside the periphery of the chamber (not shown). Further, in FIG. 1, a seed crystal 150, a raw material melt 160, and a single crystal 170 are shown as related components.

Next, individual components of the crystal growing apparatus according to the present embodiment will be described.

The crucible 10 is a container for holding a crystal raw material and growing crystals. The crystal raw material is held in the state of a melt in which the crystallizing metal or the like is melted. The material of the crucible is molybdenum, indium, etc., which have heat resistance, although it depends on the crystal raw material.

The crucible stand 20 is a support stand for supporting the crucible 10. The crucible stand 20 may be made of various materials and may have various shapes as long as the crucible 10 can be placed on the upper surface and supported. However, since the crucible 10 is heavy, a high-strength material is used. Used.

The reflector 30 is a reflector for reflecting the heat generated by the crucible 10 generated by the induction heating of the main work coil 80 without letting it escape upward and returning it downward. The reflector 30 is not essential and may be provided as needed, but it is preferable to provide the reflector 30 from the viewpoint of increasing the heating efficiency. In FIG. 1, an annular reflector 30 is provided so as to enter the inside from the upper end of the crucible 10, but the shape and arrangement of the reflector 30 can be variously changed depending on the application.

The afterheater 40 is a heating means or a heat retaining means for preventing the upper part of the single crystal from cooling. That is, as the pulling up of the single crystal 170 progresses, the upper part of the single crystal 170 moves away from the crucible 10, so that the temperature distribution of the single crystal 170 becomes large, and problems such as cracks may occur in the upper part of the single crystal 170. is there. In order to improve this, it is intended to install an afterheater 40 in the hot zone above the crucible to maintain an appropriate temperature distribution. The shape of the afterheater 40 is larger than the diameter of the oxide single crystal 170 to be obtained and smaller than the diameter of the crucible 10. The total length is a cylinder that is longer than half and shorter than twice the total length of the oxide single crystal 170 to be obtained. The material is made of a dielectric such as iridium. Although the name of the afterheater 40 is a heater, the afterheater 40 itself does not necessarily have to have a heating mechanism. For example, the subwork coil 90 may generate heat by induction heating and function as a heater, or when heating is performed using a normal heater such as a heating wire without using induction heating, a member having high heat retention. May be configured to effectively keep the upper part of the single crystal warm. That is, the afterheater 40 functions at least as a heat retaining member, and also functions as a heating element or a heating member when performing induction heating.

The heat insulating material 50 is installed so as to surround the crucible 10 and has a function of preventing the heat generated from the crucible 10 from being released to the outside.

The ceramic refractory 60 is a means for enclosing the entire including the crucible 10, and has a structure similar to a container capable of accommodating the entire including the crucible 10. The ceramic refractory 60 is literally made of ceramic.

The pulling shaft 70 is a means for holding the seed crystal 150, bringing the seed crystal 150 into contact with the surface of the crystal raw material (melt) 160 held in the crucible 10, and pulling the single crystal 170 while rotating. The pull-up shaft 70 has a seed crystal holding portion 71 for holding the seed crystal 150 at the lower end portion, and also includes a pull-up shaft driving portion 72 using a motor or the like which is a rotation mechanism. The motor is a rotation drive mechanism for pulling up the single crystal 170 while rotating the single crystal 170.

The heating means 100 is a means for heating the crucible 10 and the afterheater 40, and is arranged so as to surround the crucible 10 and the afterheater 40. The heating means 100 may be in any mode as long as it can heat the crucible 10 and the afterheater 40, but for example, a high frequency induction heating device including a high frequency heating coil may be used. In this case, the power source 130 is heated by using a high frequency power source. The heating means 100 has two heating means, a main work coil 80 for heating the crucible 10 and a sub work coil 90 for heating the upper portion of the crucible 10. As will be described later, the main work coil 80 and the sub work coil 90 have a mechanism for individually raising and lowering in the vertical direction.

The power supply 130 supplies power to the crystal growing apparatus including the heating means 100. There are two power supplies, a main power supply 110 that supplies power to the main work coil 80 and a sub power supply 120 that supplies power to the sub work coil 90.

A chamber (not shown) has a function of blocking the high heat of the hot zone portion, that is, the crucible 10 and the heating means 100, and accommodating them.

The control means 140 is a means for controlling the entire crystal growth apparatus, and controls the operation of the entire crystal growth apparatus including the crystal growth process. The control means may be composed of, for example, a microcomputer including a CPU (Central Processing Unit, a central processing unit, and a memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory)) and operated by a program. It may be composed of an electronic circuit such as an ASIC (Application Specific Integrated Circuit) developed for a specific application.

Next, the elevating mechanism of the main work coil 80 and the sub work coil 90 constituting the heating means 100, which is a feature of the crystal growing apparatus according to the embodiment of the present invention, will be described.

The feature of the crystal growing apparatus according to the embodiment of the present invention is that the heating means 100 has two heating means of the main work coil 80 and the sub work coil 90, and the main work coil 80 and the sub work coil 90 are individually provided. It is to go up and down.

In the process of growing the single crystal 170, the amount of the raw material melt 170 in the crucible 10 decreases as the single crystal 170 grows, and the solid-liquid interface where the crystal is grown gradually decreases. The work coil 80 is gradually lowered by automatic control as the single crystal 170 grows. As a result, the state of the solid-liquid interface is maintained optimally, and a single crystal 170 with few defects can be obtained.

Further, since the upper end of the single crystal 170 gradually rises as the single crystal 170 grows, the subwork coil 90 is gradually raised by automatic control in order to keep the heat retention of the upper part of the single crystal constant. As a result, the heat retention of the upper part of the single crystal is optimally performed, the thermal strain due to the large temperature difference between the upper part of the single crystal and the solid-liquid interface can be suppressed, and problems such as cracking of the single crystal 170 can be avoided. Therefore, the main work coil 80 and the sub work coil 90 are individually moved up and down in opposite directions (the main work coil 80 is downward and the sub work coil 90 is upward) according to the growing condition of the single crystal 170, and the speed thereof is also single crystal. It can be adjusted individually according to the temperature gradient of 170 and the like. By appropriately controlling the ascending / descending operation of the main work coil 80 and the sub work coil 90, it is possible to grow a crystal having a longer growing length than before without problems such as cracking of the single crystal 170. The means for raising and lowering the main work coil 80 and the sub work coil 90 each use a vertical raising and lowering mechanism individually connected to a motor or the like.

FIG. 2 is a detailed view showing an example of the elevating mechanisms 85 and 95 of the work coils 80 and 90 of the crystal growing device according to the embodiment of the present invention. The main work coil 80 and the sub work coil 90 are individually connected to the drive motors 82 and 92 via the main work support 81 and the sub work coil support 91. In the elevating mechanism drive 85 and 95, the rotation of the drive motors 82 and 92 is converted into a driving force in the vertical direction by using the worm gears 83 and 93 and the ball screws 84 and 94, and the work coils 80 and 90 are moved up and down.

The individual components of FIG. 2 will be described in more detail below.

The main work coil 80 and the sub work coil 90 are high frequency induction heating coils for generating an electromagnetic induction action by supplying high frequency power. The crucible 10 and the afterheater 40 generate heat due to the electromagnetic induction action. Since the main work coil 80 requires a stronger heating force than the sub work coil 90, in FIG. 2, the main work coil 80 is configured with 8 coil turns and the sub work coil 90 is configured with 3 coil turns. However, these are only examples, and may have various configurations depending on the application. Further, in the present embodiment, an example in which the heating means 100 is configured as the work coils 80 and 90 using induction heating is given, but other types of heaters can also be applied. If the heating means 100 is divided into upper and lower parts and individually provided, and each of them can be raised and lowered individually, the effect of reducing the temperature difference between the solid-liquid interface and the upper part of the single crystal can be obtained even with other heaters. Because.

The main work coil support 81 is a support means for supporting the main work coil 80. The main work coil support 81 may have various configurations as long as it can support the main work coil 80 so as to be vertically movable.

Similarly, the subwork coil support 91 is a support means for supporting the subwork coil 90. The subwork coil support 91 may also have various configurations as long as it can support the subwork coil 90 so as to be vertically movable.

The main work coil drive motor 82 is a drive means for moving the main work coil 80 up and down. The rotational driving force around the axis of the main work coil drive motor 82 having a rotating axis in the horizontal direction is converted into a driving force for rotating the ball screw 84 vertically extended by the worm gear 83. The ball screw 84 has a screw shaft 84a and a nut 84b, and the rotation of the screw shaft 84a causes the screwed nut 84b to move up and down, and the main work coil 80 can be raised and lowered via the main work coil support 81. .. The main work coil support 81, the worm gear 83, and the ball screw 84 are provided in pairs facing each other in the diameter direction of the main work coil 80, and are configured to support and raise and lower the main work coil 80 from both sides.

These configurations are the same in the elevating mechanism 95 of the sub work coil 90, and the driving force of the sub work coil drive motor 92 is used as the driving force of vertical movement by the pair of worm gears 93, the ball screw 94, and the sub work coil support 91. It is transmitted to the sub work coil 90 to raise and lower the sub work coil 90. The ball screw 94 has a screw shaft 94a and a nut 94b, and the subwork coil support 91 is moved up and down in the same manner as the elevating mechanism 85 of the main work coil 80.

The raising and lowering operation of the main work coil 80 and the sub work coil 90 during crystal growth is controlled by the control unit 140. Since the control unit 140 controls the pulling operation of the pulling shaft drive unit 72, the main work coil 80 and the sub work coil 90 are moved up and down in conjunction with this pulling operation. For example, the pulling operation of the pulling shaft 70 is started, and as the pulled single crystal 170 moves upward, the subwork coil 90 comes to a horizontal position covering the upper end of the single crystal 170. Control the ascending / descending motion. Similarly, as the liquid level of the raw material melt 160, that is, the solid-liquid interface decreases, the sub work coil 80 controls the elevating operation of the main work coil 80 so as to come to a horizontal position covering the solid-liquid interface. The elevating operation can be controlled by the control unit 140 controlling the rotational operation of the drive motors 82 and 92.

As described above, the crystal growth apparatus according to the present embodiment is provided with the elevating mechanisms 85 and 95 that independently raise and lower the main work coil 80 and the sub work coil 90, so that the crystal growth operation having a small difference in temperature distribution is provided. It is possible to prevent the occurrence of defects such as cracks.

The elevating stroke of the main work coil 80 and the elevating stroke of the sub work coil 90 can be set in various ways depending on the application. For example, the elevating stroke of the main work coil 80 is 130 to 170 mm, and the sub work. The elevating stroke of the coil 90 may be set in the range of 80 to 120 mm, and the elevating stroke of the main work coil 80 may be set to be larger than the elevating stroke of the sub work coil. Preferably, the elevating stroke of the main work coil 80 may be set to about 150 mm, and the elevating stroke of the sub work coil 90 may be set to about 100 mm.

Further, in FIG. 2, the elevating mechanisms 85 and 95 are provided below the main work coil 80 and the sub work coil 90. With such a configuration, the elevating mechanisms 85 and 95 can be housed inside a frame (not shown) on which the chamber is placed. However, the elevating mechanisms 85 and 95 may be installed in various positions depending on the application.

Further, the elevating mechanisms 85 and 95 of the main work coil 80 and the sub work coil 90 shown in FIG. 2 are merely examples, and if the main work coil 80 and the sub work coil 90 can be elevated independently, various elevating mechanisms 85 and 95 can be used. May be used.

Next, the main power supply 110 and the sub power supply 120 will be described in more detail.

The crystal growing apparatus according to the embodiment of the present invention is characterized in that the high frequency power supply 130 is provided so that the frequencies of the main power supply 110 and the sub power supply 120 have a difference of 5 times or more. Generally, when a plurality of high-frequency coils are arranged in series, the coils interfere with each other and an induced current flows from another coil. In order to sufficiently reduce the influence, the frequency ratio of the main power supply 110 and the sub power supply 120 is set to 5 times or more. Even with this setting, some interference remains, but the amount of operation of the high-frequency power supply 130 during crystal growth is sufficiently small, and even if interference is included, the power supply 130 can be controlled according to the crystal growth situation. It is possible. Since the main power supply 110 and the sub power supply 120 use different frequencies, matching of the power supply frequencies with the crucible 10 and the afterheater 40 can be performed with the respective power supplies 110 and 120, which is efficient for induction heating. It is possible to fine-tune to the frequency and reduce the power for induction heating.

The high-frequency power supplies 110 and 120 used in the crystal growing apparatus according to the embodiment of the present invention only increase the frequency ratio to 5 times or more and do not require phase control or the like, and therefore are compared with the power supplies used in Patent Document 1. It can be procured at a sufficiently small cost.

As described above, the crystal growing apparatus according to the present embodiment is provided with two heating means 80 and 90, and is provided with elevating mechanisms 85 and 95 capable of raising and lowering each individually, and the heating means 80 and 90 are provided during crystal growth. By raising and lowering, it is possible to suppress the temperature drop of the solid-liquid interface and the upper part of the single crystal, prevent the occurrence of defects such as cracks, and grow the single crystal 170 with high uniformity. Further, since the crystal can be grown in a state where the temperature state is well maintained, the oxide single crystal 170 having a long growth length can be grown.

Next, examples of the present invention will be described. For ease of understanding, the same reference numerals are given to the components corresponding to the components described so far.

The crystal growing apparatus according to the present embodiment was an apparatus for obtaining an oxide single crystal 170 having a diameter of about 200 mm by using a raw material having a melting point of about 1800 ° C. The crystal growing device covers a hot zone consisting of a pull-up shaft 70, a chamber 10, a heat insulating material 50 and a heating means 100, which suspends a seed crystal 150 and has a rotating function, and covers the hot zone to replace the internal atmosphere of the hot zone. It is composed of a chamber having a function of blocking high heat, a frame for accommodating the elevating mechanisms 85 and 95 and supporting the chamber. In addition, an afterheater 40 was installed above the crucible 10. In the heating means 100, the main work coil 80 is arranged around the crucible 10 in the horizontal direction, and the sub work coil 90 is arranged around the after heater 40 in the horizontal direction.

The elevating range of the main work coil 80 and the sub work coil 90 is set so as to be separated by at least 10 mm or more between the upper limit value of the main work coil 80 and the lower limit value of the sub work coil 90 so as not to overlap each other. The elevating stroke of the main work coil 80 was set to 150 mm. The elevating stroke of the subwork coil 90 was set to 100 mm.

Two power supplies 130 are installed: a main power supply 110 that supplies power to the main work coil 80 and a sub power supply 120 that supplies power to the sub work coil 90. The frequency of the high frequency power supplied from the main power supply 110 was 7 kHz, the frequency of the high frequency power supplied from the sub power supply 120 was 50 kHz, and the frequency was about 7 times the frequency of the high frequency power of the main power supply 110.

Using such a crystal growing device, it was possible to grow an oxide crystal having a longer growing length than before.

Although the preferred embodiments and examples of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments and examples, and does not deviate from the scope of the present invention. Various modifications and substitutions can be added to the examples.

10 坩 堝 40 Afterheater 70 Pull-up shaft 71 Seed crystal holding part 72 Pull-up shaft drive part 80 Main work coil 81 Main work coil support 82, 92 Drive motor 83, 93 Worm gear 84, 94 Ball screw 85, 95 Lifting mechanism 90 Sub work coil 91 Sub work coil support 110 Main power supply 120 Sub power supply 140 Control unit 150 Seed crystal 160 Raw material melt 170 Single crystal

Claims (7)

A crucible that can hold the raw material melt,
A first heating means arranged around the crucible,
A first elevating mechanism for elevating and elevating the first heating means,
A second heating means arranged above the crucible,
It has a second elevating mechanism for elevating and elevating the second heating means.
The first and second heating means are composed of an induction heating coil, and the first induction heating coil, which is the first heating means, is wound more than the second induction heating coil, which is the second heating means. A large number of crystal growth devices. The crystal growing device according to claim 1, wherein each of the first and second elevating mechanisms has a motor individually. An after-heater is provided above the crucible.
The crystal growing device according to claim 1 or 2, wherein the second heating means is provided around the afterheater. A crucible that can hold the raw material melt,
A first heating means arranged around the crucible,
A first elevating mechanism for elevating and elevating the first heating means,
A second heating means arranged above the crucible,
It has a second elevating mechanism for elevating and elevating the second heating means.
The first and second heating means consist of an induction heating coil.
With the first high frequency power source connected to the first heating means,
It has a second high frequency power source connected to the second heating means, and has.
A crystal growing device having a difference of 5 times or more between the frequencies of the first high-frequency power supply and the second high-frequency power supply. A pull-up shaft capable of pulling up a single crystal by holding a seed crystal at the lower end and bringing the seed crystal into contact with the liquid surface of the raw material melt held in the crucible.
Further, the pulling shaft, the first lifting mechanism, and a control means for controlling the lifting operation of the second lifting mechanism are provided.
The crystal according to any one of claims 1 to 4, wherein the control means controls the elevating operation of the first elevating mechanism and the second elevating mechanism in conjunction with the pulling operation of the pulling shaft. Training device. The crystal growing device according to claim 5, wherein the control means controls the elevating operation of the second elevating mechanism so that the second heating means surrounds the upper end of the single crystal. The crystal growth according to claim 5 or 6, wherein the control means controls the elevating operation of the first elevating mechanism so that the first heating means surrounds the liquid surface of the raw material melt. apparatus.

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