JP2003300791A - Method and apparatus for growing oxide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for growing a single crystal, by which the formation of a crack in the crystal is suppressed when the crystal is cooled after growth of the crystal. <P>SOLUTION: The contact of a vaporized substance generated from a solution with a grown crystal is inhibited and the formation of the crack is prevented at the time of cooling by allowing an atmospheric gas to flow downward when the single crystal is pulled from a raw material melt. The apparatus for growing the oxide single crystal has a crucible for holding the melt obtained by melting a raw material, a pulling system for pulling the single crystal from the crucible in a chamber, and a cylindrical member arranged so as to surrounding the pulled single crystal. The chamber is divided into two chambers at the border of the cylindrical member, and an exhaust mechanism and a suction mechanism are provided in the upper side chamber and the lower side chamber, respectively. The atmospheric gas is allowed to flow downwardly from the suction mechanism along the cylindrical inner wall so as to inhibit the single crystal from being brought into contact with the vaporized substance generated from the crucible. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for growing an oxide single crystal, and more particularly to a technique for growing a single crystal in which the lattice constant of the grown crystal is likely to change due to the evaporation of the growth solution.

[0002]

2. Description of the Related Art LN single crystals and LT having a congruent composition
Single crystals are generally grown by the batch CZ method. On the other hand, the continuous raw material supply type double crucible CZ method (hereinafter referred to as DCCZ method), which is disclosed in Japanese Patent Application Laid-Open No. 11-35393, pulls the crystal while continuously supplying the raw material having the same composition as the crystal to be pulled up, is grown. It has been attracting attention as a growth method that does not accompany changes in the environment over time, that is, melt composition and decrease in liquid volume. This DCCZ method is particularly effective for LN single crystals and LT single crystals having a stoichiometric composition, but it is said that long and highly uniform crystals can be grown even when growing LN single crystals and LT single crystals having a congruent composition. In this respect, this means is considered to be an effective means.

[0003]

When the LN single crystal or the LT single crystal is pulled up by using the conventional growing method and growing apparatus, there is a problem that the crystal is cracked during cooling after the growth is completed. . Due to this crack, the production yield of the single crystal was remarkably reduced.

[0004]

The present invention avoids the occurrence of crystal cracks in the growth of oxide single crystals having a composition deviated from the stoichiometric composition by the pulling method. By preventing the evaporated material from the growth melt (hereinafter referred to as the melt) from hitting the grown single crystal, the stress caused by the nonuniform lattice constant is prevented from occurring on the crystal surface. That is, it has a mechanism for preventing the evaporated material from coming into contact with the grown crystal.

As a result of various investigations, the present inventors have found that the problem is that the crystal is exposed to the evaporate from the melt at a high temperature. In general, in order to maintain the crystal quality, the pulling rate must be reduced as the diameter of the pulled crystal increases, and as a result, the crystal is exposed to the evaporated material for a long time. Further, when pulling a long crystal, the pulling speed is the same, but the pulling time becomes long. With the method proposed in the present invention, the time of exposure to high temperature can be significantly shortened.

(1) In the method for growing an oxide single crystal according to the present invention, a raw material is melted in a crucible to obtain a melt, and when a single crystal is pulled from the melt, an evaporation product generated from the solution is a grown crystal. By growing a single crystal while preventing contact with
Generation of single crystal cracks can be prevented.

(2) In the above (1), the evaporation gas can be prevented from coming into contact with the crystal by flowing the atmospheric gas by downflow. The term “downflow” also includes flowing an atmospheric gas in a direction opposite to the pulling direction along the growing single crystal.

(3) In the above (2), the chamber is divided into two chambers with a cylindrical wall provided in the chamber surrounding the grown single crystal as a boundary, and an exhaust mechanism is provided in the lower chamber. However, it is preferable that the downflow be performed by providing an intake mechanism in the upper chamber and flowing the atmospheric gas from the upper chamber to the lower chamber.

(4) In the above (3), by having a mechanism for heating the cylindrical wall, cracks due to heat shock to the crystal can be prevented. What is a heat shock?
It means that the temperature of the pulled single crystal drops sharply and stress is generated in the crystal.

The method for growing an oxide single crystal according to any one of the present inventions is particularly effective for lithium niobate or lithium tantalate having a deviated stoichiometric composition. When the growth from the start of crystal pulling to the end of pulling exceeds 48 hours, that is, when the diameter of the single crystal is 130 mm or more, or when the pulling crystal length (straight body length) is 10
It is also effective when it exceeds 0 mm. This is because the longer the time for pulling the single crystal, the greater the probability of attachment of the vaporized component and the greater the degree of cracking.
Therefore, if the structure of the present application is applied, a great effect can be obtained in preventing cracking of the single crystal.

The oxide single crystal growth apparatus of the present invention is an oxide single crystal growth apparatus for pulling a single crystal from a melt of a crucible, and the evaporation product generated from the melt is a single crystal pulled up. It is characterized by having a mechanism for preventing touch.

Another oxide single crystal growth apparatus of the present invention is
The chamber is equipped with a crucible for holding a melt in which the raw material is melted and a pulling device for pulling a single crystal from the crucible, and a cylindrical member arranged so as to surround the pulled single crystal. In order to prevent the vapor from the crucible from touching the single crystal, the chamber is divided into two chambers, the lower chamber has an exhaust mechanism, and the upper chamber has an intake mechanism. In the apparatus for growing an oxide single crystal, an atmospheric gas is caused to flow from the suction mechanism to the inside of a cylindrical wall by downflow.

In any one of the above-described oxide single crystal growth apparatuses of the present invention, a means for heating the pulled single crystal may be provided in order to delay the cooling rate of the pulled single crystal. Reducing the cooling rate corresponds to slow cooling.

When the atmospheric gas is downflowed, a space in which the atmospheric gas stays is generated in the middle of the flow path, and the evaporate from the melt may reach the single crystal. Therefore, if a means for heating the single crystal immediately after the pulling is provided in addition to performing the downflow, the atmospheric gas that directly or indirectly downflows is also warmed. It is also effective to warm downflow gas itself. By warming, it is possible to prevent the atmospheric gas from staying at the boundary between the melt surface and the single crystal immediately after the pulling, and to prevent the vaporized component from adhering to the single crystal.

In the above-mentioned growing method or growing apparatus, the tubular member or the tubular wall has a structure that suppresses the attachment of the vaporized component to the minimum and is suitable for gradually cooling the pulled oxide single crystal. The term tubular member refers to a tubular wall,
It is used to include plates and cylinders that function as enclosures.
It is desirable that the tubular member has a circular cross section (cylindrical portion) in order to prevent adhesion and to perform slow cooling uniformly. However, polygonal shapes can also be used as long as the uniformity of the effect is not impaired. The material of the tubular member or the tubular wall is preferably platinum (Pt) in consideration of durability and the like. However, iridium (Ir) or carbon (C) may be used,
The material can be appropriately selected depending on the heating temperature and the composition of the atmosphere.

The following structure can be used as a structure for gradually cooling the pulled single crystal, that is, for cooling while heating to prevent the occurrence of cracks. For example, (a)
(B) a structure for heating the tubular member itself, (b) a heater for slow cooling provided around the tubular member to heat the tubular member to heat the single crystal by the radiation, (c) an inert gas for downflow For example, (d) a structure in which a heater is provided before reaching between the tubular member and the single crystal, and a heater is provided not only in the tubular member but in the upper end portion of the chamber. As the heater, a high frequency coil, a carbon type heater, a heating wire or the like can be used. The effect of preventing cracks by the oxide single crystal growth apparatus of the present invention is remarkably exhibited when a large diameter or long lithium niobate single crystal or lithium tantalate single crystal is produced.

The tubular member of the present application is not intended to limit heat radiation. If positive cooling or heat shielding is performed, a large number of cracks will occur in the oxide single crystal.

The inert gas for downflowing the tubular member or the tubular wall preferably has a flow rate of 50 to 500 (cc / min) when introduced into the chamber from the valve. The distance t between the cylindrical member (cylindrical portion) and the melt surface is preferably in the range of 1 mm ≦ t ≦ 30 mm.
The flow rate of the downflowing inert gas passing through the region of the interval t is preferably 1 mm / min or more and 1000 mm / min or less. If the flow velocity is less than 1 mm / min, it will be difficult to avoid vaporized components from adhering to the single crystal. If the flow rate exceeds 1000 mm / min, the melt surface is affected and the uniformity of crystal growth is hindered. The unit mm / min represents the moving speed of the inert gas per minute. During the downflow, the rotation speed for pulling the single crystal is within the range of 2 rpm or more and 20 rpm or less, and the pulling rate is within the range of 0.5 mm / h or more and 3 mm / h or less. The unit of flow rate is (cc / mi
n) = 1.67 * 10 ⁻⁸ (m ³ / s).

An inert gas such as argon or nitrogen can be used as the atmosphere gas for the downflow. Although an inert gas having a single composition is used in the examples, it is possible to add another component gas to the inert gas and flow the gas as long as the purpose of preventing adhesion and slow cooling can be achieved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for growing an oxide single crystal will be described in detail with reference to the drawings. The present invention is not limited to these examples. (Embodiment 1) FIG. 1 is a sectional view of an oxide single crystal growing apparatus according to the present invention. First, the structure of the growing device will be described.
This growing device (also referred to as a CZ device) is a crucible 22 that holds a melt 21 in which an oxide material is melted, and a pulling device that pulls up the oxide single crystal 10 from the melt 21 by the Czochralski method. The chamber 30 is provided with the pulling device and the crucible 22, and a power source 40.

The crucible 22 is a cylindrical container made of platinum (Pt). A high frequency coil is provided as the melting heater 23 so as to surround the side surface of the crucible 22,
A predetermined current was supplied from the power source 40 to the melting heater 23 to heat the crucible 22, thereby melting the oxide material put into the crucible 22 and filling the melt 21.
The crucible rotating device 33 connected to the bottom surface side of the crucible 22 via the shaft 31 has a mechanism for rotating the crucible 22 at a desired speed and an elevating mechanism for adjusting the height of the crucible. Although detailed illustration is omitted in FIG. 1, the crucible 22 is composed of a platinum crucible and a container supporting the platinum crucible, and the container is connected to the shaft 31. When the melting heater 23 is composed of a high-frequency coil, the platinum crucible can be heated more efficiently if the container supporting the crucible is composed of a non-metal.

The pulling device includes a chamber upper end portion 19 protruding above the chamber 30, a pulling shaft 11 provided so as to pass through the chamber upper end portion 19, and a pulling shaft 11 rotating or vertically moving. The driving device 12 is provided. The cylindrical portion 1 made of platinum is provided on the inner wall side of the chamber 30 so as to correspond to the upper end portion 19 of the chamber.
4 is provided, and the heater 13 for decooling is provided so as to surround the circumference of the cylindrical portion 14. The lower end of the cylindrical portion 14 extends to near the liquid surface of the melt 21, and the distance between the lower end and the melt t is 1
It was set so as to be 0 mm.

When an experiment was performed by changing the value of t, 1
It was found that the range of mm ≦ t ≦ 30 mm is good. When t is less than 1 mm, the melt surface sways due to the effect of downflow, which is not preferable. If t exceeds 30 mm, the effect of preventing the retention of downflow is weakened and the growth of the single crystal is affected. An intake valve 16 as an intake mechanism was provided at the upper end 19 of the chamber, and an exhaust valve 26 as an exhaust mechanism was provided at the bottom of the chamber. Here, “for cooling” means that the pulled oxide single crystal 10 is heated so as not to be cooled rapidly, and the temperature is gradually lowered.

The controller 50 using a personal computer automatically controlled the following parameters to pull the single crystal. That is, the melting heater 23
Alternatively, the current supplied from the power source 40 to the slow cooling heater 13, the opening / closing / flow rate adjustment of the intake valve 16 or the exhaust valve 26, the rotation speed of the crucible, the single crystal pulling speed (growing speed) and the rotation speed, and the downflow gas flow rate. , Adjustment of the distance between the melt surface and the cylindrical portion by raising and lowering the crucible. Although not shown in FIG. 1, a thermocouple was provided in each of the crucible 22 and the cylindrical portion 14, and the measured temperature was fed back to the control device 50. Although the automatic control is performed according to the control procedure programmed in the control means, it can also be performed by the input from the input means provided in the control means, if necessary.

Although not shown, a cylinder and a flow meter for supplying an inert gas were provided at the tip of the intake valve 16, and a vacuum pump was provided at the tip of the exhaust valve. The chamber corresponds to a closed container, and a magnetic fluid bearing is used to maintain airtightness between the shaft 31 and the chamber 30.
The upper surface of the chamber upper end portion 19 that supports the pull-up shaft 11 has a sealing function that allows the pull-up shaft to move up and down and maintains an airtight state.

The pulling of a single crystal by the apparatus shown in FIG. 1 will be described. First, the seed chuck 5 provided at the tip of the pulling shaft 11 holds the seed crystal 5 of LiNbO ₃ having a congruent composition, and the crucible 22 is filled with the raw material. Purity 9
Regarding 9.99% or more of Li ₂ CO ₃ and Nb ₂ O ₃ ,
The Li and Nb atoms were mixed so that the molar ratio was 50%: 50%, rubber press molded under a hydrostatic pressure of 1 * 10 ⁻⁴ ton / m ² , and sintered in oxygen at about 1050 ° C. What was done was used as a raw material.

The air in the chamber was exhausted from the exhaust valve 26 by the vacuum pump. Then, the melting heater 23 was energized from the power source 40 to melt the raw material powder in the crucible and hold it for about 20 hours (20 hours) to obtain the melt 21. The slow cooling heater 13 was energized to heat the cylindrical portion 14. Then, the crucible rotating device 33 was activated to rotate the crucible 22, and the pulling shaft 11 was lowered by the driving device 12 to bring the lower end of the seed crystal 5 into contact with the surface of the melt 12. The crucible was rotated at 0.2 rpm in the opposite direction to the pulling shaft to homogenize the melt composition. When the seed crystal 5 reaches the cylindrical portion of the crystal when the pulling shaft is lowered, 300 cc / argon of argon gas (Ar gas) is supplied from the valve 16.
The introduction was started at min. Flow velocity is 62 mm / m
became in. The unit of flow rate is (cc / min) = 1 * 1
^{0 -3 (l / min) =} 1.67 * 10 -8 (m 3 /
s). While controlling the amount of rotation and the rising speed of the pulling shaft 11, a lithium niobate single crystal (LiNbO
₃ single crystal) was pulled up. Pulling speed is 1.0m
The crystal rotation speed was 10 rpm as m / h. In unit notation, h corresponds to 1 hour, min corresponds to 1 minute, and rpm corresponds to the number of rotations per minute. When the diameter of the conical single crystal grown into the seed crystal reached a predetermined value, the pulling conditions were kept constant and a straight body portion (a single crystal columnar region) was formed. The straight body part was gradually cooled by the radiant heat from the cylindrical part.
The length of the straight body part, that is, the straight body length was pulled up to 120 mm.

After the pulling is completed, the single crystal is separated from the melt,
The gradual cooling heater 13 was operated for a while to maintain the high temperature state of the single crystal while continuing the gradual cooling, and the energization to the melting heater 23 was stopped. After a while, the power supply to the slow cooling heater was stopped. After a while, valves 16 and 26 were stopped to stop the downflow. After waiting for the pulled oxide single crystal to cool naturally, the production of the single crystal was completed.

Ar gas introduced from the intake valve 16 is
The exhaust valve 26 passes through the upper chamber composed of the chamber upper end 19 and the cylindrical portion 14, passes through the gap (distance t) between the lower end of the cylindrical portion 14 and the melt 21, and passes through the chamber 30 corresponding to the lower chamber. Discharged from. In the first embodiment, an operation in which the inert gas (Ar gas) passes through the upper chamber and further passes through the gap to the lower chamber is referred to as downflow, and the configuration thereof is referred to as a downflow mechanism. Opening and closing of the intake valve 16 and exhaust valve 26 and flow rate adjustment were controlled by electric signals from the controller 50. The upper chamber corresponds to the upper chamber, and the lower chamber corresponds to the lower chamber.

When the CZ apparatus of the batch method having the downflow mechanism shown in FIG. 1 was used to grow at various pulling speeds, a congruent lithium niobate single crystal having a 135 mm diameter without cracks could be obtained. It was afterwards,
The obtained single crystal was heated to a temperature of abnormal Curie temperature, then a voltage of about 5 to 10 V / cm was applied from the z-axis direction of the crystal, and cooled to room temperature to perform single polarization treatment. . The single-polarized single crystal was processed to obtain an LN single crystal wafer.

Due to the structure of the cylindrical portion and the heater for decooling and the down flow, the components evaporated from the melt could be placed on the inert gas and discharged. In addition, the single crystal pulled from the melt was gradually cooled by the structure that prevents rapid cooling. It should be noted that the vaporized component of the melt blown to the lower chamber using the inert gas as a carrier touches the side of the inner wall of the chamber 30 separated from the heater and cools and solidifies, so that it should be discharged to the outside from the exhaust valve. Instead, it can be collected when cleaning the inside of the chamber.

(Comparative Example) When a similar experiment was conducted using a general CZ apparatus, cracks were generated in all the crystals. When the Curie temperature of the surface layer of this crystal was examined, it was found that the Curie temperature was significantly different from the Curie temperature of the center (center portion) of the crystal. Further, when the crystal cut out from the central part was left to stand on the growth melt, the Curie temperature was found to be higher than that of the untreated crystal. Furthermore, when left for a long time, white powder was generated on the crystal surface. When this powder was analyzed by an X-ray diffractometer, it was found that Li ₃
It was found to be the composition of Nb ₁₃ . The above results are
It shows that the lithium oxide evaporated from the melt adhered to the crystal surface and penetrated into the crystal to change the composition state of the crystal.

(Embodiment 2) Regarding the oxide single crystal growing apparatus of FIG. 1, a gas warming apparatus 17 is newly provided between the intake valve 16 and the gas cylinder to configure the growing apparatus of FIG.
A single crystal was produced under substantially the same conditions as in Example 1. However, the apparatus configuration and the growing method of Example 2 differ from Example 1 in the following two points. The first point is that the slow cooling heater 13 is not provided. The second point is that when the intake valve 16 is opened, the gas warming device is operated to heat the inert gas and then introduced into the upper chamber. Gas warm-up device 1
Reference numeral 7 denotes a coil-shaped platinum wire arranged in the gas flow passage to energize to directly warm the inert gas, and a current was supplied from the power source 50. The configuration of Example 2 in which the gas warming device is used instead of the gradual cooling heater can prevent the evaporation component from the melt surface of the crucible from adhering to the single crystal and can gradually cool the single crystal. When grown at various pulling speeds, a single crystal of lithium niobate having a congruent composition and a diameter of 135 mm could be obtained without cracking.

(Embodiment 3) Regarding the apparatus for growing an oxide single crystal shown in FIG. 1, two crucibles were used so that the double crucible method (DCCZ method) for continuously supplying the raw material and keeping the melt at a constant composition can be carried out. It was replaced with a heavy crucible and a raw material supply mechanism was provided. When the inert gas is also made to flow from the route for supplying the raw material from the raw material supply mechanism to the outer crucible of the double crucible, it is guided to the lower chamber together with the inert gas to be downflowed from the cylindrical part and exhausted from the exhaust valve Configured to. Then, a raw material with an excessive Li component composition (the molar ratio of Li: Nb was 0.58%: 0.0.
42%) was used to grow LN single crystals. As a result, similarly to Example 1, it was possible to suppress cracks in the pulled single crystal by avoiding evaporation components and by slow cooling.

(Embodiment 4) The growing apparatus of Embodiments 1 to 3 is used.
The raw material is Li with a purity of 99.99% or more._TwoCO _Threeas well as
Ta_TwoO_ThreeTo the congruent composition under the same conditions
Lithium acid single crystal or stoichiometric lithium tantalate single crystal
Trained. As a result, the evaporated single crystal was pulled up.
Can avoid cracks and suppress cracks
It was

[0036]

According to the structure of the present invention, by providing the downflow mechanism, it is possible to suppress the attachment of the evaporated material from the melt and to grow the oxide single crystal in which the cracks are suppressed. It is particularly effective for growing large diameter and long crystals.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an oxide single crystal growing device according to the present invention.

FIG. 2 is a schematic cross-sectional view of another oxide single crystal growth device according to the present invention.

[Explanation of symbols]

5 seed crystal, 10 oxide single crystal, 11 pulling shaft, 12 driving device, 13 slow cooling heater, 1
4 cylindrical part, 16 intake valve, 17 gas warming device, 19 chamber upper end part, 21 melt, 22 crucible, 23 melting heater, 26 exhaust valve,
30 chamber, 31 shaft, 33 crucible rotating device, 40 power supply, 50 control device.

Claims (11)

[Claims] 1. A single crystal is grown by melting a raw material in a crucible to obtain a melt, and preventing evaporants generated from the melt from coming into contact with the single crystal when pulling the single crystal from the melt. And a method for growing an oxide single crystal. 2. The method for growing an oxide single crystal according to claim 1, wherein the vaporized substance is prevented from coming into contact with the single crystal by causing an atmosphere gas to flow down flow. 3. The chamber is divided into two chambers with a tubular wall provided in the chamber surrounding the grown single crystal as a boundary, the lower chamber has an exhaust mechanism, and the upper chamber has intake air. The method for growing an oxide single crystal according to claim 2, wherein a mechanism is provided to allow an atmospheric gas to flow from the upper chamber to the lower chamber. 4. The method for growing an oxide single crystal according to claim 3, further comprising a mechanism for heating the cylindrical wall. 5. The method for growing an oxide single crystal according to claim 1, wherein the oxide single crystal is lithium niobate or lithium tantalate having a deviated stoichiometric composition. 6. The method for growing an oxide single crystal according to claim 1, wherein a diameter of the oxide single crystal is 130 mm or more. 7. The method for growing an oxide single crystal according to claim 1, wherein the oxide single crystal has a pull-up crystal length (straight body length) of more than 100 mm. 8. The method for growing an oxide single crystal according to claim 1, wherein the time from the start of pulling the crystal to the end of pulling exceeds 48 hours. 9. A growth apparatus for an oxide single crystal for pulling a single crystal from a melt of a crucible, comprising a mechanism for preventing an evaporated material generated from the melt from coming into contact with the pulled single crystal. Apparatus for growing an oxide single crystal. 10. A chamber is provided with a crucible for holding a melt in which a raw material is melted and a pulling device for pulling a single crystal from the crucible, and a cylindrical member arranged so as to surround the pulled single crystal, The chamber is divided into two chambers with the tubular member as a boundary, the lower chamber has an exhaust mechanism, and the upper chamber has an intake mechanism so as to prevent evaporants from the crucible from touching the single crystal. In order to achieve the above, the growth apparatus for an oxide single crystal is characterized in that an atmospheric gas is caused to flow from the suction mechanism to the inside of the cylindrical wall by downflow. 11. The apparatus for growing an oxide single crystal according to claim 9, further comprising means for heating the pulled single crystal in order to delay the cooling rate of the pulled single crystal.