JP2018111633A - Apparatus and method for growing oxide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for growing an oxide single crystal, capable of corresponding to low cost, and a large diameter and long size of the oxide single crystal.SOLUTION: An apparatus 100 for growing an oxide single crystal comprises: a heat insulator 7 surrounding a heating space SP; a crucible 1 arranged in the heating space SP; a resistance heating type heater 4 arranged in the heating space SP; and an intermediate annular plate member 7C arranged in the heating space SP. The heating space SP is thermally separated into an upper heating space SP1 and a lower heating space SP2 by the crucible 1 and the intermediate annular plate member 7C, and the resistance heating type heater 4 includes an upper stage heater 4U arranged in the upper heating space SP1, and a middle heater 4M and lower stage heater 4L arranged in the lower heating space SP2 .SELECTED DRAWING: Figure 1

Description

  The present invention relates to an oxide single crystal growing apparatus and a growing method.

  Conventionally, lithium niobate single crystals have been widely used as materials for surface acoustic wave devices, light modulation devices, and the like. For growing a single crystal, a growing apparatus that employs a high frequency induction heating-type chockey type growing method (hereinafter referred to as “Cz method”) has been widely used. However, the high-frequency induction heating method has a problem that the manufacturing cost of the single crystal increases because water cooling of a high-frequency power source, a growth furnace, a work coil, and the like is necessary. There is also a problem that the temperature gradient in the growth furnace is steep and defects are likely to occur in the single crystal. As a means for solving these problems, a growing apparatus employing a resistance heating method is known (see Patent Document 1). Patent Document 1 shows that a single crystal of lithium niobate can be grown in the resistance heating type Cz method as well as the high frequency induction heating type Cz method.

JP 2003-221299 A

  In recent years, the market for surface acoustic wave devices has expanded. Therefore, in order to secure the production amount of a single crystal of lithium niobate that is a material for a surface acoustic wave device, the diameter of the single crystal is increased and the length thereof is increased.

  However, the increase in diameter and length of the single crystal is a cause of decreasing the yield rate of the single crystal. Specifically, increasing the diameter of a single crystal requires an increase in crucible diameter for melting the raw material. The crucible diameter is increased by gradually reducing the temperature gradient in the radial direction at the center of the melt surface, and the single crystal suddenly grows during seeding or shoulder growth (the upper end portion of the single crystal formed in a conical shape). May cause growth. In addition, the natural convection of the melt may be reduced, and the bending of the single crystal may be caused during the growth of the straight body portion (a portion of the single crystal formed in a substantially cylindrical shape). Furthermore, a large temperature difference is caused between the outer peripheral portion and the inside of the single crystal, which may cause cracks due to thermal strain during cooling. In addition, the lengthening of the single crystal causes an increase in the pulling distance, a large temperature difference between the upper end and the lower end of the single crystal, and may cause cracks due to thermal strain during cooling.

  Therefore, it is desirable to provide an apparatus for growing an oxide single crystal that employs a resistance heating method that can cope with an increase in the diameter and length of the oxide single crystal at low cost.

  An oxide single crystal growth apparatus according to an embodiment of the present invention is an oxide single crystal growth apparatus, comprising a refractory surrounding a heating space, a crucible disposed in the heating space, and the heating space. And a heat shield disposed in the heating space, and the heating space is heated to the upper heating space and the lower heating space by the crucible and the heat shielding plate. The heater includes an upper heater disposed in the upper heating space and a lower heater disposed in the lower heating space.

  By the above-mentioned means, an oxide single crystal growing apparatus employing a resistance heating method that can cope with an increase in the diameter and length of the oxide single crystal at low cost is provided.

It is a longitudinal cross-sectional view of the breeding apparatus which concerns on embodiment of this invention. It is the cross-sectional view which looked at the plane shown by the II-II line of FIG. 1 from the top. FIG. 2 is a top view of the growing apparatus of FIG. 1 in a state in which a member above the crucible is removed. It is a figure which shows the positional relationship of a crucible and an intermediate | middle annular plate member.

  A growing apparatus according to an embodiment of the present invention is a resistance heating type growing apparatus used for growing (manufacturing) an oxide single crystal using a Cz method. The oxide single crystal includes lithium niobate (hereinafter referred to as “LN”), lithium tantalate (hereinafter referred to as “LT”), gadolinium gallium garnet (hereinafter referred to as “GGG”), Including sapphire. The oxide single crystal is grown in the air or in an inert gas atmosphere.

  In the Cz method, a seed crystal cut according to a certain crystal orientation is immersed in a melt having the same composition and gradually pulled up while rotating, thereby producing a single crystal with a large diameter while propagating the properties of the seed crystal. Is the method. The seed crystal is, for example, a cuboid single crystal having a cross-sectional side of about 5 to 10 mm, and is attached to the tip of the seed bar. Then, dipping in the melt, pulling up and the like are performed by raising and lowering the seed bar.

  Here, with reference to FIGS. 1-3, the growth apparatus 100 which concerns on embodiment of this invention is demonstrated. FIG. 1 is a longitudinal sectional view of the growing apparatus 100. 2 is a cross-sectional view of the plane indicated by the line II-II in FIG. 1 as viewed from above (+ Z direction). FIG. 3 is a top view of the growing apparatus 100 in a state where a member above the crucible 1 is removed.

  The growing apparatus 100 includes a crucible 1, a crucible base 2, a crucible shaft 3, a heater 4, a heat insulating material 7, a base 13, an outer wall 15, a control device 50, a rotary lifting device 51, and a power source 52.

  The crucible 1 is a container for holding the raw material of the oxide single crystal 11. The raw material is held in the state of a melt 12 in which a metal or the like to be subjected to single crystallization is melted. The crucible 1 is made of, for example, a heat-resistant metal such as platinum or indium.

  The crucible base 2 is a base on which the crucible 1 is placed. The crucible shaft 3 is a shaft that supports the crucible base 2. The crucible shaft 3 may be rotatable to rotate the crucible 1 placed on the crucible base 2. Further, the crucible 1 placed on the crucible base 2 may be moved up and down to move up and down.

  The heater 4 is a device for heating the raw material, the crucible 1, the grown oxide single crystal 11, and the like. In the example of FIG. 1, the heater 4 is arranged to have a three-stage configuration along the vertical direction (Z-axis direction). Specifically, it includes an upper heater 4U, a middle heater 4M, and a lower heater 4L.

  The heat insulating material 7 is a refractory surrounding the heating space SP. In the example of FIG. 1, it is installed so as to surround the crucible 1 and the heater 4. The heat insulating material 7 is made of, for example, zirconia, alumina, platinum, or the like.

  Specifically, the heat insulating material 7 includes an upper annular plate member 7A, an upper cylindrical member 7B, an intermediate annular plate member 7C, a lower cylindrical member 7D, and a lower plate member 7E. At least two of the upper annular plate member 7A, the upper cylindrical member 7B, the intermediate annular plate member 7C, the lower cylindrical member 7D, and the lower plate member 7E may be integrally formed. For example, the upper cylindrical member 7B and the intermediate annular plate member 7C may be integrally formed. Alternatively, the upper annular plate member 7A, the upper cylindrical member 7B, and the intermediate annular plate member 7C may be integrally formed. Further, the lower cylindrical member 7D and the lower plate member 7E may be integrally formed.

  In the example of FIG. 1, the crucible 1, the upper annular plate member 7A, the upper cylindrical member 7B, and the intermediate annular plate member 7C define an upper heating space SP1. The crucible 1, the intermediate annular plate member 7C, the lower cylindrical member 7D, and the lower plate member 7E define a lower heating space SP2. The upper end of the crucible 1 is in contact with the lower surface (-Z side surface) of the intermediate annular plate member 7C at the inner peripheral end of the intermediate annular plate member 7C. That is, the heating space SP is thermally separated into the upper heating space SP1 and the lower heating space SP2 by the crucible 1 and the intermediate annular plate member 7C. The intermediate annular plate member 7C functions as an annular heat shield.

  The positional relationship as shown in FIG. 4 may be sufficient as the crucible 1 and the intermediate | middle annular plate member 7C. FIG. 4 is a view showing another example of the positional relationship between the crucible 1 and the intermediate annular plate member 7C, and corresponds to an enlarged view around the crucible 1 in FIG.

  Specifically, FIG. 4A shows a positional relationship when the inner diameter D1 of the intermediate annular plate member 7C is smaller than the inner diameter D2 of the crucible 1. FIG. 4B shows a positional relationship when the inner peripheral end surface of the intermediate annular plate member 7 </ b> C and the outer surface of the crucible 1 are in contact with each other at the upper end of the crucible 1. FIG. 4C shows the positional relationship when the inner peripheral end surface of the intermediate annular plate member 7 </ b> C and the outer surface of the crucible 1 are in contact with each other at the center of the crucible 1. In the example of FIG. 4C, the upper end of the crucible 1 protrudes by a distance D3 above the upper surface (+ Z side surface) of the intermediate annular plate member 7C (+ Z direction). 4D shows the positional relationship when the outer peripheral end surface of the annular projecting portion 7C1 projecting downward (in the −Z direction) at the inner peripheral end of the intermediate annular plate member 7C and the inner surface of the upper end portion of the crucible 1 are in contact with each other. Indicates. Thus, the crucible 1 and the intermediate annular plate member 7C are arranged so that the upper heating space SP1 and the lower heating space SP2 can be separated in an airtight manner.

  The grown oxide single crystal 11 moves away from the crucible 1 as the oxide single crystal 11 is pulled up. For this reason, the temperature gradient in the oxide single crystal 11 in the vertical direction is increased, and there is a possibility that problems such as cracking of the oxide single crystal 11 occur. In order to suppress the occurrence of this problem, an upper heater 4U as an upper heater is installed in the upper heating space SP1. This is to maintain an appropriate temperature distribution in the upper heating space SP1. On the other hand, a middle heater 4M and a lower heater 4L as lower heaters are arranged in the lower heating space SP2. This is because the crucible 1 is heated to melt the raw material. Moreover, it is for promoting the natural convection of the melt 12 during crystal growth. In the example of FIG. 1, the upper heater 4 </ b> U is disposed at a position higher than the crucible 1. The middle heater 4M is disposed at substantially the same height as the crucible 1. The lower heater 4L is arranged at a position lower than the crucible 1. FIG. 3 is a top view of the growing apparatus 100 in a state in which the members above the crucible 1, that is, the upper annular plate member 7A, the upper cylindrical member 7B, the intermediate annular plate member 7C, and the upper heater 4U are removed. It is.

  The gantry 13 is a support base for supporting the main body of the growing apparatus 100. On the gantry 13, the heat insulating material 7 and the outer wall 15 as the main body are placed.

  The outer wall 15 is a member that blocks heat and is disposed so as to surround the heat insulating material 7. In the example of FIG. 1, it has a cylindrical shape and blocks high heat generated by each of the crucible 1 and the heater 4 from being transmitted to the outside. The outer wall 15 can be divided in a horizontal direction or the like with a predetermined vertical cross section, and has a structure in which the inner crucible 1, the heater 4, and the like can be exposed by removing part of the outer wall 15. It may be possible to divide vertically in a predetermined horizontal section.

  The control device 50 is a means for performing overall control of the growth apparatus 100, and controls the overall operation of the growth apparatus 100 including the crystal growth process. In the example of FIG. 1, the control device 50 is a microcomputer including a CPU, a ROM, a RAM, and the like. However, it may be composed of an electronic circuit such as an ASIC. The control device 50 is provided on the outside of the outer wall 15, for example, and controls the heater 4, the rotary lifting device 51 and the like. A broken-line arrow in FIG. 1 represents a signal line that transmits a control signal.

  The rotary lifting device 51 is a device that can lift and lower the seed rod 10 while rotating it. In the example of FIG. 1, the rotary lifting device 51 is provided above the crucible 1 (+ Z direction). And the motor which functions as a rotation apparatus and a raising / lowering apparatus is included. A motor that functions as a rotating device and a motor that functions as a lifting device may be included separately. The seed bar 10 has a seed crystal holding part for holding the seed crystal 9 at the lower end.

  The rotary elevating device 51 brings the seed crystal 9 into contact with the surface of the raw material (melt 12) put in the crucible 1 and pulls up the seed crystal 9 while rotating.

  The power source 52 is a device that supplies power to the growing device 100. In the example of FIG. 1, the power source 52 is provided outside the outer wall 15 and supplies power to the heater 4, the rotary lifting device 51, and the like. A solid arrow in FIG. 1 represents a power line.

  Next, a method for growing the oxide single crystal 11 using the growth apparatus 100 will be described. First, the worker inputs a raw material of the oxide single crystal 11 such as LN, LT, GGG, sapphire, or the like into the crucible 1. Thereafter, the raw material in the crucible 1 is heated and melted by the heater 4. Thereafter, the seed crystal 9 attached to the tip of the seed rod 10 is brought into contact with the surface of the melt 12 in the crucible 1 by the rotary lifting device 51. Hereinafter, this process is referred to as seeding.

  Thereafter, the seed crystal 9 is gradually pulled upward while being rotated by the rotary elevating device 51. The shoulder temperature and the straight body of the oxide single crystal 11 are grown by controlling the heating temperature, the number of rotations, the pulling speed, and the like. Thereafter, when the oxide single crystal 11 reaches a predetermined length, the pulling rate and the like are controlled to separate the surface of the melt 12 from the grown oxide single crystal 11. Thereafter, the separated oxide single crystal 11 is cooled to complete the growth of the oxide single crystal 11.

  In the above-described growing method using the growing apparatus 100, for example, the upper heater 4U is not used in seeding and shoulder growing, and only the middle heater 4M and the lower heater 4L are used. Further, the intermediate annular plate member 7C suppresses heat from being transmitted from the lower heating space SP2 to the upper heating space SP1, and prevents the temperature of the upper heating space SP1 from becoming higher than necessary. Therefore, the vertical temperature gradient in the upper heating space SP1 tends to increase. In addition, the temperature hardly rises near the center of the surface of the melt 12.

  On the other hand, the crucible 1 is heated by the middle heater 4M and the lower heater 4L, and the temperature rises. Therefore, the temperature is likely to increase in the vicinity of the peripheral edge of the surface of the melt 12. Therefore, the temperature gradient in the radial direction on the surface of the melt 12 tends to increase. As a result, rapid growth of the oxide single crystal 11 is suppressed.

  When the growth of the straight body portion is started after the shoulder portion of the oxide single crystal 11 is formed, the upper heater 4U is used and the upper heating space SP1 is kept warm. That is, the oxide single crystal 11 pulled up from the surface of the melt 12 is kept warm.

  Therefore, the above-described growth apparatus 100 can prevent the oxide single crystal 11 from being bent during the growth even when the long oxide single crystal 11 having a large diameter is grown. In addition, it is possible to suppress the occurrence of cracks due to a temperature difference between the inside and outside of the oxide single crystal 11, cracks due to polycrystallization resulting from instability of the convection of the melt 12, cracks due to strain during cooling, and the like.

  Next, examples of the present invention will be specifically described with reference to comparative examples. In the following description, a method for growing a single crystal of lithium niobate will be described as an example.

  As shown in FIG. 1, a platinum crucible 1 is disposed on a crucible base 2 supported by a crucible shaft 3. The crucible 1 is filled with a raw material of lithium niobate. A resistance heating type heater 4 is disposed around the crucible 1. The heater 4 is made of metal and has a cylindrical shape as shown in FIGS. The heater 4 includes an upper heater 4U, a middle heater 4M, and a lower heater 4L. The middle heater 4M and the lower heater 4L may be integrated. The outside, upper side, and lower side of the heater 4 are covered with a heat insulating material 7 made of zirconia or alumina. An intermediate annular plate member 7C made of zirconia, alumina or platinum is disposed between the upper heater 4U and the middle heater 4M. The lower surface (−Z side surface) of the intermediate annular plate member 7 </ b> C is in contact with the upper end of the crucible 1. Therefore, the heating space SP surrounded by the heat insulating material 7 is thermally blocked by the upper heating space SP1 and the lower heating space SP2 by the crucible 1 and the intermediate annular plate member 7C. That is, the movement of the atmospheric gas in the lower heating space SP2 heated by the middle heater 4M and the lower heater 4L to the upper side (+ Z side) of the intermediate annular plate member 7C is suppressed or prevented. As a result, the growth apparatus 100 can efficiently melt the lithium niobate raw material by operating the middle heater 4M and the lower heater 4L with relatively little electric power to heat the crucible 1.

  After the raw material is melted, the growing apparatus 100 controls the outputs of the middle heater 4M and the lower heater 4L to adjust the melt 12 to a temperature suitable for seeding. Then, when the melt 12 reaches a temperature suitable for seeding, the platinum seed rod 10 is lowered, and the seed crystal 9 attached to the tip of the seed rod 10 is brought into contact with the melt 12. Thereafter, a lithium niobate single crystal continuously extending from the seed crystal 9 is obtained by pulling it up vertically (+ Z direction) at a speed of 2 to 5 mm / h while rotating the seed bar 10 at 1 to 20 rpm.

  At the time of seeding and shoulder growth, the temperature gradient in the radial direction on the surface of the melt 12 needs to be a certain level in order to suppress rapid growth of the lithium niobate single crystal.

  The growth apparatus 100 suppresses the increase in the temperature of the upper heating space SP1 by suppressing the transfer of heat from the lower heating space SP2 to the upper heating space SP1 by the intermediate annular plate member 7C, so that the radial direction on the surface of the melt 12 The temperature gradient can be made relatively steep. The center of the surface of the melt 12 in contact with the relatively low temperature upper heating space SP1 and the melt 12 in contact with the relatively high temperature crucible 1 heated directly by the middle heater 4M and the lower heater 4L. This is because the temperature difference from the peripheral edge of the surface can be increased.

  Thus, the growth apparatus 100 can suppress rapid growth of the lithium niobate single crystal when forming the shoulder portion of the lithium niobate single crystal.

  Further, when the straight body portion is formed after the shoulder portion of the lithium niobate single crystal is formed, the growing apparatus 100 operates the upper heater 4U to pull up the lithium niobate single crystal. It is possible to prevent the shoulder portion from being excessively cooled.

  As described above, the growth apparatus 100 appropriately operates the upper heater 4U according to the growth of the lithium niobate single crystal, so that the lithium niobate single crystal has a large diameter and a long length. A single crystal can be grown appropriately. Specifically, the temperature gradient in the radial direction on the surface of the melt 12 is appropriately maintained, and the natural convection of the melt 12 is appropriately maintained, so that the lithium niobate single crystal during the growth of the lithium niobate single crystal is obtained. Can be prevented from bending. In addition, it is possible to suppress or prevent the occurrence of cracks due to temperature difference between the inside and outside of the lithium niobate single crystal, cracks due to polycrystallization resulting from instability of the convection of the melt 12, cracks due to strain during cooling, and the like.

  As described above, the growth apparatus 100 for the oxide single crystal 11 includes the heat insulating material 7 as a refractory surrounding the heating space SP, the crucible 1 disposed in the heating space SP, and the resistance disposed in the heating space SP. The heating type heater 4 and an intermediate annular plate member 7C as a heat shield disposed in the heating space SP are provided. The heating space SP is thermally separated into an upper heating space SP1 and a lower heating space SP2 by the crucible 1 and the intermediate annular plate member 7C. The resistance heater 4 includes an upper heater 4U as an upper heater disposed in the upper heating space SP1, and a middle heater 4M and a lower heater 4L as lower heaters disposed in the lower heating space SP2.

  With this configuration, the resistance heating type growth apparatus 100 can cope with an increase in the diameter and length of the oxide single crystal 11 at a low cost. Specifically, the growth apparatus 100 can prevent the oxide single crystal 11 from being bent during the growth even when the long oxide single crystal 11 having a large diameter is grown. In addition, it is possible to suppress the occurrence of cracks due to a temperature difference between the inside and outside of the oxide single crystal 11, cracks due to polycrystallization resulting from instability of the convection of the melt 12, cracks due to strain during cooling, and the like.

  The intermediate annular plate member 7 </ b> C extends from the inner wall of the heat insulating material 7 toward the crucible 1 and is configured to contact the upper end of the crucible 1. That is, the heating space SP is divided into the upper heating space SP1 and the lower heating space SP2 by the crucible 1 and the intermediate annular plate member 7C. Therefore, the growth apparatus 100 suppresses heat from being transferred from the lower heating space SP2 to the upper heating space SP1 during seeding or shoulder growth, and the temperature of the upper heating space SP1 becomes higher than necessary. Can be prevented. As a result, the temperature gradient in the radial direction of the surface of the melt 12 can be increased, and rapid growth of the oxide single crystal 11 during seeding or shoulder growth can be suppressed. Further, the growing apparatus 100 can appropriately keep the upper heating space SP1 warm by the upper heater 4U when the straight body portion is grown. Therefore, even when the long oxide single crystal 11 having a large diameter is grown, the oxide single crystal 11 can be prevented from being bent during the growth. In addition, it is possible to suppress the occurrence of cracks due to the temperature difference between the inside and outside of the oxide single crystal 11 in the upper heating space SP1, cracks due to polycrystallization resulting from instability of convection of the melt 12, cracks due to strain during cooling, and the like.

  The upper heating space SP1 and the lower heating space SP2 may be airtightly separated. In this case, the growth apparatus 100 can prevent the atmospheric gas in the lower heating space SP2 heated by the middle heater 4M and the lower heater 4L from entering the upper heating space SP1. As a result, the growing apparatus 100 can efficiently heat the crucible 1 by operating the middle heater 4M and the lower heater 4L with relatively little electric power and efficiently melt the raw material of lithium niobate.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments. For example, improvement of each member, change of structure, and the like may be performed without departing from the scope of the present invention.

  For example, in the above-described embodiment, the upper heater 4U as the upper heater is disposed in the upper heating space SP1, and the middle heater 4M and the lower heater 4L as the lower heater are disposed in the lower heating space SP2. However, the upper heater may be composed of two or more stages of heaters. Further, the lower heater may be composed of a single stage heater, or may be composed of three or more stages of heaters.

  In the above-described embodiment, the heater 4 has a cylindrical shape, but may be configured to be separable in the circumferential direction.

  Further, the growing device 100 may raise the crucible shaft 3 to bring the upper end of the crucible 1 into contact with the lower surface (−Z side surface) of the intermediate annular plate member 7C.

  DESCRIPTION OF SYMBOLS 1 ... Crucible 2 ... Crucible base 3 ... Crucible shaft 4 ... Heater 4U ... Upper stage heater 4M ... Middle stage heater 4L ... Lower stage heater 7 ... Thermal insulation 7A ... Upper annular plate member 7B ... Upper cylindrical member 7C ... Intermediate annular plate member 7D ... Lower cylindrical member 7E ... Lower plate member 9 ... Seed crystal 10 ... Seed rod 11 ... -Oxide single crystal 12 ... Melt 13 ... Stand 15 ... Outer wall 50 ... Control device 51 ... Rotating elevator 52 ... Power supply

Claims (6)

A device for growing an oxide single crystal,
Refractories surrounding the heating space,
A crucible disposed in the heating space;
A resistance heating heater disposed in the heating space;
A heat shield disposed in the heating space,
The heating space is thermally separated into an upper heating space and a lower heating space by the crucible and the heat shield plate,
The heater includes an upper heater disposed in the upper heating space and a lower heater disposed in the lower heating space.
Training device. The heat shield plate extends from the inner wall of the refractory toward the crucible and contacts the upper end of the crucible;
The growing apparatus according to claim 1. The upper heating space and the lower heating space are hermetically separated,
The training apparatus according to claim 1 or 2. The oxide single crystal includes lithium niobate, lithium tantalate, gadolinium gallium garnet, and sapphire single crystals.
The growing device according to any one of claims 1 to 3.   A method for growing the oxide single crystal using the growth apparatus according to claim 1. Heating the crucible with the lower heater to melt the raw material;
Contacting the seed crystal attached to the tip of the seed rod with the raw material melt in the crucible;
Lifting the seed rod while rotating;
Heating the oxide single crystal formed at the tip of the seed rod with the upper heater,
The method of claim 5.