JPH10265293A - Growing of single crystal and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need for forming a single crystal after growth to a single domain by growing the single crystal formed as the single domain at the time of continuously growing the single crystal by a micro-pulling down method. SOLUTION: The single crystal 14 is formed by cooling the melt of a single crystal material while this material is pulled down from a crucible 7. The single crystal 14 is provided with a temp. gradient near the Curie temp. in the cooling process of the single crystal 14, by which the single crystal is pulled down and the single domain is continuously formed. The device is provided with temp. control mechanisms 12A, 12B for providing the single crystal 14 with the temp. gradient near the Curie temp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a single crystal by a micro pull-down method and an apparatus therefor.

[0002]

2. Description of the Related Art Recently, as a method of growing an oxide single crystal, a method of forming a single crystal fiber by a so-called micro-pull-down method has attracted attention. According to this method, potassium ion, lithium lithium niobate (K ₃ Li) is described in “DENSO News”, July 1993 (No. 522), pp. 4-8, JP-A-4-280891, and JP-A-6-345588. _{2-2x Nb5 + x O15 + x} (hereinafter, referred to as KLN)) and the like are disclosed.

[0003] According to the above article of "DENSO News",
Electric power is supplied to a platinum cell or crucible for resistance heating. At the bottom of the cell, a melt outlet is formed, and a rod-shaped body called a melt feeder is inserted through the outlet, thereby supplying the melt to the outlet.
The state of the solid-liquid interface is also controlled. By adjusting the diameter of the melt outlet, the thickness of the feeder, the length of the feeder projecting from the outlet, and the like, the KLN single crystal fiber with a small diameter is continuously formed. According to this μ pull-down method, a single crystal fiber having a diameter of 1 mm or less can be formed, thermal distortion can be reduced, convection in the melt can be controlled, and the diameter of the single crystal fiber can be easily controlled. It has the feature that a small high-quality single crystal suitable for the second harmonic generation can be produced. Similarly, it is used for a blue second harmonic generation device, an optical communication waveguide device, a surface acoustic wave filter device, and the like.
It is known that LiNbO ₃ , LiTaO _{3 and the} like can be grown.

In the single crystal growth by the micro-pulling-down method, conventionally, in the process of cooling the grown crystal, in order to suppress the occurrence of cooling cracks and the like due to strain immediately after the growth, temperature control of the growth point and its vicinity (see FIG. Temperature gradient, annealing, etc.) are being studied.

[0005]

However, for example, LiN
When a single crystal fiber made of a ferroelectric compound such as bO ₃ , LiTaO ₃ , or KLN is grown, the obtained single crystal fiber may have a multi-domain structure or may have a single-domain structure by accident. As a result, it was found that a result having good reproducibility was not obtained. When a second harmonic (SHG) generating element was manufactured using such a single crystal fiber and its SHG generation efficiency and the like were evaluated, no large efficiency was obtained as a whole. For this reason, it is essential that the single crystal once grown is separately treated in a single domain.

However, in order to perform single domain processing on a ferroelectric single crystal, for example, LiNbO ₃ , LiTaO ₃ , K
It is necessary to apply a voltage through a platinum plate electrode through the LN powder. During this single domaining treatment, the crystallinity of the single crystal deteriorates. Further, depending on the conditions at the time of applying a voltage, the single crystal may be damaged such as generation of cracks or the like. Furthermore, it is necessary to perform a process for complicated single-domain processing, and the entire manufacturing apparatus is also complicated.

An object of the present invention is to make it possible to grow a single-domain single crystal when continuously growing a single crystal by a micro-pulling-down method. The elimination of the need for a single domain. It is another object of the present invention to obtain a single-domain single crystal having extremely good crystallinity.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for growing a single crystal, wherein a single crystal is melted from a crucible and cooled to form a single crystal. The present invention relates to a method for growing a single crystal, characterized in that a temperature gradient is provided in the single crystal near the Curie point, whereby the single crystal is lowered and the single domain is continuously domainized.

The present invention also provides a crucible containing a melt of a single crystal material and having a draw-out port for pulling down the melt, a heating mechanism for melting the single crystal material in the crucible, and An apparatus for growing a single crystal, comprising a driving mechanism for lowering the single crystal from the crucible, and a heating mechanism for providing a temperature gradient to the single crystal near the Curie point. , A single crystal growing apparatus.

The present inventor has proposed that L
iNbO_Three, LiTaO _ThreeKLN, etc. single crystal fiber
Experiments for cultivating cultivators, and furthermore, JP-A-8-259375
As disclosed in the report,
LiNbO_Three, LiTaO_ThreeKLN, etc. single crystal play
We have been conducting experiments to continuously grow This laboratory
In the process of research, we conducted experiments with constant manufacturing conditions
Also, the inside of the single crystal fiber and the plate is multi-domain
Or almost a single domain,
I discovered that the structure was not constant.

The present inventor has been studying to find out the cause, but the molten material pulled down from the outlet of the crucible is cooled and solidified, and passes through the Curie temperature in the process of being lowered further downward. However, the inventor has found that the cause is that the temperature around the single crystal is not constant in this temperature range. In other words, at this time, if a certain degree of temperature gradient occurs in the single crystal, the single domain progresses in accordance with the temperature gradient, and if the temperature gradient inside the single crystal is small or does not exist, it is randomly divided. It is presumed that a domain structure is generated and a multi-domain structure is generated.

On the basis of this estimation, if the heating mechanism is actually controlled at least in the vicinity of the Curie temperature under such a condition that a temperature gradient occurs in the single crystal, the single crystal always becomes constant and has a single domain. That is, the present invention has been reached.

Specifically, in order to control the temperature gradient inside the single crystal itself, the temperature difference between both surfaces of the single crystal in a lowered state is controlled to be 10 ° C. or more so that the single crystal can be stabilized. It has been found that a single crystal having a single domain structure can be grown. In other words, by controlling the temperature gradient near the Curie point so as to provide a temperature difference of 10 ° C. or more on both surfaces of the grown single crystal plate or the like, a single domain structure in which the low temperature side is a minus surface and the high temperature side is a plus surface. Was found to be obtained. From this viewpoint, it is preferable that the temperature difference be 50 ° C. or more.

On the other hand, by setting the temperature difference to 300 ° C. or less, it is possible to prevent the deterioration of crystallinity and the occurrence of cracks due to the stress inside the single crystal. From this viewpoint, in order to further improve the crystallinity of the single crystal, the temperature difference is preferably set to 200 ° C. or less.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method and apparatus of the present invention can be applied to both fiber-like single crystals and plate-like single crystals. However, rather than a fibrous single crystal,
The plate-shaped or plate-shaped single crystal was more reliably formed into a single domain. Specifically, under predetermined conditions,
It has been found that both surfaces of the grown single crystal plate have negative polarization with higher certainty and reliability.

The present invention relates to a method for producing a solid solution single crystal.
Especially suitable for As a solid solution single crystal, for example,
LiNbO_Three, LiTaO_Three, Li (Nb, Ta)
O_Three, KLN (K_ThreeLi_2-2xNb_{5 + x}O_{15 + x}), KLT
N [K_ThreeLi_2-2x(Ta _yNb_1-y)_{5 + x}O_{15 + x}], B
a_1-XSr_XNb_TwoO₆Tungsten blow centered on
Can be exemplified.

LiNbO ₃ , LiTaO ₃ , and KLN single crystals have recently attracted attention as optical materials, particularly as single crystals for blue light second harmonic generation (SHG) devices for semiconductor lasers. . Since it can generate light up to the ultraviolet region of 390 nm, by using such short wavelength light, it can be applied to a wide range of applications such as optical disk memory, medicine, photochemistry, and various types of optical measurement. is there.

The present invention can be applied to the growth of compositionally segregated oxide single crystals. For example, when neodymium forms a solid solution in LiNbO ₃ , since the segregation coefficient is not 1, only a smaller amount of neodymium than the amount of neodymium in the composition of the melt enters the single crystal. For example, even if about 1.0 mol of neodymium is contained in the melt, only about 0.3 mol is contained in the single crystal. However, by rapidly cooling the melt in the nozzle portion, a single crystal having a composition similar to that of the melt can be produced without causing segregation. this is,
The present invention can also be applied to other laser single crystals, for example, YAG substituted with Nd, Er, and Yb, and YVO ₄ substituted with Nd, Er, and Yb.

In the present invention, the method for growing a single crystal, particularly an oxide single crystal, is not particularly limited as long as it is a micro-pulling method. However, it is necessary that the growing apparatus is provided with a temperature control mechanism for providing a temperature gradient to the single crystal near the Curie point. The temperature control near the Curie point of such a single crystal is, specifically, the Curie point ±
It is necessary to carry out in the range of 150 ° C. Although the temperature control mechanism is not particularly limited, the following can be preferably exemplified from the viewpoint of mass productivity.

(1) In the cooling zone below the growth furnace, heaters are provided on the left and right sides of the single crystal plate. Each heater has a structure in which the temperature gradient of each part in the vertical direction of the heater can be freely set.

(2) In the cooling zone below the growth furnace, heaters are provided on the left and right sides of the single crystal plate. On one side of the single crystal, an auxiliary heater is provided outside the heater, and the auxiliary heater is heated to raise the temperature of one side of the single crystal to the other side of the single crystal. Increase the temperature by 10 ° C. or more.

(3) In the cooling zone below the growth furnace, heaters are provided on the left and right sides of the single crystal plate. The distance between the heater and one surface of the single crystal is made relatively small, and the heater and the single crystal are brought closer. At the same time, the distance between the heater and the other surface of the single crystal is made relatively large, and the heater is separated from the single crystal. As a result, the temperature of one surface of the single crystal is set to be higher than the temperature of the other surface by 10 ° C. or more.

In the case of a single crystal fiber, (1)
To (3).

[0024]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG. 1 is a schematic sectional view showing a manufacturing apparatus for growing a single crystal.

A crucible 7 is provided inside the furnace body. So as to surround the crucible 7 and the upper space 5 thereof,
An upper furnace 1 is installed, and a heater 2 is provided in the upper furnace 1.
Is buried. The nozzle 13 extends downward from the lower end of the crucible 7, and an outlet 13 a is formed at the lower end of the nozzle 13. The lower furnace 3 is installed so as to surround the nozzle portion 13 and the space 6 around the nozzle portion 13, and the heater 4 is embedded in the lower furnace 3. Both the crucible 7 and the nozzle portion 13 are formed of a corrosion-resistant conductive material. Needless to say, the form of the heating furnace itself can be variously changed. For example, in FIG. 1, the heating furnace is divided into two zones, but the heating furnace can be divided into three or more zones.

One electrode of the power supply 10 is connected to the position A of the crucible 7 by the electric wire 9, and the other electrode of the power supply 10 is connected to the lower end B of the crucible 7. One electrode of the power supply 10 is connected to the position C of the nozzle 13 by the electric wire 9, and the other electrode is connected to the lower end D of the nozzle 13. Each of these energizing mechanisms is separated from each other, and is configured so that its voltage can be controlled independently.

In the crucible 7, an intake pipe 11 extends upward, and an intake port 22 is provided at an upper end of the intake pipe 11. This intake 22
Slightly protrude from the bottom of the melt 8. The melt inlet may be formed at the bottom of the crucible so as not to protrude from the bottom of the crucible. In this case, the intake pipe 11 is not provided. An after heater can be provided in the space 6 at intervals so as to surround the nozzle portion 13.

The upper furnace 1, the lower furnace 3, and the after-heater are heated to appropriately determine the temperature distribution in the spaces 5 and 6, the raw material of the melt is supplied into the crucible 7, and the electric power is supplied to the crucible 7 and the nozzle unit 13. To generate heat. In this state,
In the single crystal growing portion 18 at the lower end of the nozzle portion 13, the melt slightly protrudes from the opening 13a, and is held by the surface tension to form a relatively flat surface.

As a result, the single crystal plate 14 is continuously formed on the upper side of the seed crystal 15, and is drawn downward. In this embodiment, the seed crystal 15 and the single crystal plate 14 are fed by rollers 16.

The single crystal plate 14 is cooled down from the nozzle portion 13, but in this embodiment, the heaters 12 A and 12 A are further provided on both sides of the single crystal plate 14.
12B is installed. The temperature of the single crystal plate 14 during the passage through this region is usually the Curie temperature ± 200 ° C.
, Preferably within 150 ° C. By controlling the temperatures of the heaters 12A and 12B, the temperature difference between the surfaces 14a and 14b of the single crystal 14 is adjusted as described above.

FIG. 2A is a side view of the single crystal 14, and FIG. 2B is a plan view. This plate 14
For example, it is grown in a state where it is divided into single domains in the direction of arrow E.

In FIG. 1, the single crystal fiber 20
2 is also made into a single domain in the direction of arrow E in the fiber 20 as shown in FIG.

FIG. 3 is a schematic sectional view schematically showing a manufacturing apparatus according to another embodiment. The same parts as those in the apparatus of FIG. The peripheral parts such as the upper furnace and the lower furnace shown in FIG. 1 are not shown in FIG. In the apparatus shown in FIG. 3, the electrode of the power supply 10A is connected to the upper end F and the substantially central portion G of the crucible 7, and the power supply 10B is connected to the substantially central portion G and the lower end H of the crucible 7. Are connected to the lower end H of the crucible 7 and the upper end I of the nozzle.
The 0C electrode is connected. An AC power supply 10 </ b> D is connected to the nozzle unit 13. Each of these energizing mechanisms is separated from each other, and is configured so that its voltage can be controlled independently.

The single crystal plate 14 is cooled down from the nozzle portion 13. In this embodiment, the heaters 12 A and 12 A are further provided on both sides of the single crystal plate 14.
12B is installed. The temperature of the single crystal plate 14 during the passage through this region is usually the Curie temperature ± 200 ° C.
, Preferably within 150 ° C. Further, an auxiliary heater 19 is provided outside the heater 12A. By controlling each temperature of each heater 12A, 12B, 19, one surface 14a of single crystal 14
Is adjusted as described above.

FIG. 4 is a schematic sectional view showing an apparatus according to another embodiment of the present invention. The same members as those shown in FIG. 3 are denoted by the same reference numerals. Heaters 25A and 25B are provided on both sides of the single crystal plate 14. The temperature of the single crystal plate 14 while passing through this region is set so as to be usually within the Curie temperature ± 200 ° C., preferably 150 ° C. or less. On one surface 14a side of the single crystal plate 14, the distance m between the plate 14 and the heater 25A is made relatively small, and the other surface 1
4b, the distance l between the plate 14 and the heater 25B
Are relatively large. Thereby, the surface 14a and the surface 1
4b can be adjusted to a certain range.

Next, a description will be given of a form of a nozzle portion particularly suitable for manufacturing a single crystal plate. The inventor formed a flat surface having a planar shape corresponding to the cross section of the single crystal plate at the tip of the nozzle portion in the μ reduction method,
A single crystal plate is formed by forming a plurality of rows of melt flow holes in the nozzle portion, simultaneously lowering the melt from each melt flow hole, and integrating the melt pulled down from each flow hole along a flat surface. Can be formed.

In this embodiment, the entire nozzle portion can be formed in a flat plate shape. Further, an extended portion may be provided at the distal end of the tubular nozzle portion, and the distal end surface of the extended portion may be a flat surface as described above. Alternatively, the nozzle portion may be constituted by a plurality of tubular members, and the respective tubular members may be joined to each other to be integrated, so that an integral flat surface can be formed by the distal end surface of each tubular member.

[0038]

EXAMPLES Hereinafter, more specific experimental results will be described. Using a single crystal manufacturing apparatus as shown in FIG. 1, a LiNbO ₃ single crystal plate 14 was manufactured according to the present invention. The temperature of the entire furnace was controlled by the upper furnace 1 and the lower furnace 3. The temperature gradient in the vicinity of the single crystal growing section 18 can be controlled by the power supply to the nozzle section 13 and the heat generated by the after heater. As a mechanism for lowering the single crystal plate 14, a mechanism for lowering the single crystal plate 14 while uniformly controlling the lowering speed within a range of 2 to 100 mm / hour in the vertical direction was mounted.

Lithium carbonate and niobium oxide are mixed with 50:
The raw material powder was prepared by mixing at a composition ratio of 50. About 50 g of the raw material powder was supplied into a platinum crucible 7 and the crucible 7 was set at a predetermined position. The temperature of the space 5 in the upper furnace 1 was adjusted to a range of 1250 to 1350 ° C.
The raw material in was melted. The temperature of the space 6 in the lower furnace 3 is
The temperature was controlled at 700 ° C to 1000 ° C. A predetermined power was supplied to the crucible 7, the nozzle portion 13, and the after-heater, and a single crystal was grown. At this time, the temperature of the single crystal growing section could be set at 1200 ° C. to 1300 ° C., and the temperature gradient at the single crystal growing section could be controlled at 10 to 150 ° C./mm.

The shape of the cross section outside the nozzle portion 13 was rectangular, and its size was 1.0 mm × 30 mm. The length of the nozzle 13 was 20 mm. Thirty melt flow holes were provided in the nozzle portion 13. The diameter of each melt flow hole was 0.2 mm. The planar shape of the crucible 7 was circular, its diameter was 30 mm, and its height was 30 mm.

The temperature difference between the surfaces 14a and 14b of the single crystal plate 14 was set to 50.degree. Width 50mm, thickness 1.0
mm single crystal plate was pulled down in the a-axis direction at a speed of 20 mm / hour. A cooling zone of 80 mm for cooling from around 1150 ° C. to around 1000 ° C.
It was passed through this zone at 0 mm / hour for about 4 hours.

This single crystal plate was thermally decomposed with a 3: 1 mixture of hydrofluoric acid and nitric acid at 180 ° C. for 1 hour. As a result, while the plus side was not etched at all, the minus side was etched by about 10 μm, and etch pits were observed in portions having poor crystallinity. As a result, it was confirmed that a complete single-domain crystal was obtained.

When the SHG generation efficiency of this LiNbO ₃ single crystal was measured, it was improved by about 30% as compared with the conventional single-domain-treated single crystal. The cause is related to a reduction in the distortion of the substrate, for example, an improvement in crystallinity by reducing the X-ray rocking curve by about 20% in half width.

[0044]

As described above, according to the present invention, when a single crystal is continuously grown by the micro-pulling-down method, a single crystal having a single domain can be grown. Domainization processing can be eliminated. As a result, a single-domain single crystal having extremely good crystallinity can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a manufacturing apparatus for growing a single crystal according to an embodiment of the present invention.

2A is a side view of the single crystal plate 14, FIG. 2B is a plan view of the single crystal plate 14, FIG.
(C) is a sectional view of the single crystal fiber 20.

FIG. 3 is a schematic sectional view showing a main part of a manufacturing apparatus for growing a single crystal according to another embodiment of the present invention.

FIG. 4 is a schematic sectional view showing a main part of a manufacturing apparatus for growing a single crystal according to still another embodiment of the present invention.

[Explanation of symbols]

1 upper furnace, 2 heater of upper furnace 1, 3 lower furnace, 4
Heater of lower furnace 3, 7 crucible, 10, 10A, 1
0B, 10C, 10D power supply, 12A, 12B 2-zone heater, 13 nozzle, 13a outlet, 14
Single crystal plate, 15 seed crystals, 18 single crystal growing part,
20 single crystal fiber, 19 auxiliary heater, 25,
25A heater

Claims (4)

[Claims] 1. A method for growing a single crystal, wherein a single crystal is formed by cooling a melt of a single crystal material from a crucible while cooling the single crystal, wherein the single crystal is cooled near a Curie point during the cooling of the single crystal. A method for growing a single crystal, characterized in that the temperature of the single crystal is lowered and a single domain is continuously formed by providing a temperature gradient to the single crystal. 2. The method for growing a single crystal according to claim 1, wherein a temperature difference at the same pulling position of the single crystal when the single crystal is lowered is 10 ° C. to 300 ° C. 3. The method of growing a single crystal according to claim 1, wherein said single crystal is a ferroelectric. 4. A crucible containing a melt of a single crystal material and having a draw-out port for pulling down the melt, a melting and heating mechanism for melting the single crystal material in the crucible, A single crystal growing apparatus comprising a driving mechanism for pulling down the single crystal from the crucible, comprising a temperature control mechanism for providing a temperature gradient to the single crystal near a Curie point. A single crystal growing apparatus.