JP7310339B2 - Method for growing lithium niobate single crystal - Google Patents

Description

The present invention relates to a method for growing a lithium niobate single crystal that is used as a substrate material for a surface acoustic wave device. It relates to a method of breeding.

Lithium niobate (LiNbO ₃ ; sometimes abbreviated as LN) single crystal is an artificial ferroelectric crystal with a melting point of about 1250°C and a Curie temperature of about 1140°C. LN single crystal substrates obtained by cutting out LN single crystals and polishing them are mainly used as materials for surface acoustic wave devices (SAW filters) mounted in mobile communication devices.

Industrially, LN single crystals are mainly grown by the Czochralski (sometimes abbreviated as Cz) method, and for example, a high-frequency dielectric heating type growth furnace described in Patent Document 1 is used. In general, a platinum crucible is used and grown in an air atmosphere or in a nitrogen-oxygen mixed gas atmosphere with an oxygen concentration of about 20%. The grown LN single crystal is colorless and transparent or pale yellow with high transparency. The grown LN single crystal is subjected to “annealing treatment” to remove residual strain due to thermal stress during growth and cooling, and “poling treatment” to align the electrical polarity of the entire crystal to a single polarization. After that, it is handed over to the substrate processing process.

Here, the Cz method is a method of obtaining a single crystal having the same crystal orientation as the seed crystal by bringing the seed crystal into contact with the surface of the raw material melt in the crucible and continuously pulling the seed crystal while rotating it. . After the crystal is grown to the desired size (crystal diameter x crystal length), the crystal to be grown is separated from the raw material melt by adjusting the crystal pulling speed and melt temperature, cooled to near room temperature, and removed from the growth furnace. Take out the crystal. In crystal growth by the Cz method, it is important to conduct the latent heat generated by the solidification of the raw material melt at the crystal growth interface upward through the seed crystal efficiently. is carried out under a temperature gradient adjusted to reduce the In the Cz method, a seed crystal having a diameter of about 10 mm or less is generally used, and a single crystal having a diameter several times to several tens of times larger than the diameter of the seed crystal can be grown.

By the way, when an LN single crystal is grown by the Cz method, a phenomenon of polycrystallization from the habit line part (ridge poly), especially in the early stage of growth from the start of pulling the seed crystal to the crystal diameter of about φ30 mm. often occur. In a crystal with "ridge poly", cracks occur throughout the crystal starting from the poly part, and therefore the LN single crystal substrate as a product cannot be processed. Therefore, suppression of "ridge poly" is very important for improving the productivity of LN single crystals.

"Ridge poly" is caused by abnormal growth on low index planes (facet planes) that form habit lines. A facet surface is a flat surface when viewed in atomic order, and growth on the facet surface is caused by accumulation of phenomena in which steps move parallel to the surface (lateral growth). Therefore, the atoms incorporated into the crystal phase on the facet surface have fewer bonds from the crystal phase than on the off-facet surface (rough surface with unevenness on the order of atoms) on which adhesion grows. In addition, the melt in contact with the facet surface is more supercooled than the melt in contact with the off-facet surface due to the Berg effect. For this reason, in growth on facet planes, even small fluctuations in the crystal growth rate cause atoms arriving at the growth plane to enter the crystalline phase at the wrong site or orientation before being stabilized at the original site according to the symmetry of the crystal. easy to get caught. The above-mentioned "ridge poly" is generated starting from atoms incorporated at such wrong positions.

In fact, the faster the crystal growth rate or the worse the axial symmetry of the temperature distribution in the melt with respect to the pulling axis, the higher the occurrence rate of "ridge poly". When the growth rate is high, the facet plane develops greatly, so the degree of supercooling of the melt in contact with the facet plane becomes high. If the temperature distribution in the melt has poor axial symmetry with respect to the pulling axis, the crystal rotation causes the temperature experienced by the growth interface to fluctuate within one rotation, resulting in large fluctuations in the growth rate, and the growth rate increases at low temperatures. end up In addition, the occurrence of "ridge poly" is concentrated in the period of enlarging the crystal diameter immediately after the start of pulling of the seed crystal (so-called growth of the crystal shoulder). This is because when the crystal diameter is small, crystal growth occurs in the central portion of the melt surface, and this is the time when the grown crystal is most susceptible to temperature fluctuations.

When "ridge poly" occurs, the entire crystal becomes defective as described above, resulting in a significant drop in productivity.

JP 2019-6612 (see paragraph number 0030)

The present invention has been made with a focus on such problems, and its object is to suppress the occurrence of the above-mentioned "ridge poly" and stably produce high-quality niobium with a high single crystallinity. An object of the present invention is to provide a method for growing a lithium oxide single crystal by the Czochralski method.

That is, the present invention
Using a crucible with an inner diameter d, a seed crystal is brought into contact with the raw material melt in the crucible, and the seed crystal is pulled up while rotating to grow a crystal shoulder and a subsequent crystal straight body portion with a crystal diameter D. In the method for growing a lithium niobate single crystal by the Larski method,
From the start of pulling the seed crystal until the grown crystal diameter reaches the smaller value of (1/2) D or (1/3) d, the pulling rate of the seed crystal is in the range of 0 to 1 mm/H. and the rate of increase of the crystal radius is set in the range of 5 to 20 mm / H, and after the crystal diameter exceeds the above numerical value, the pulling rate is gradually increased, and the crystal diameter D is grown in the straight body part of the crystal. is characterized by setting the pulling rate in the range of 2 to 5 mm/H.

According to the method for growing a lithium niobate single crystal according to the present invention,
From the start of pulling the seed crystal until the diameter of the grown crystal reaches (1/2) D or (1/3) d, whichever is smaller, the seed crystal pulling speed is 0 to 1 mm/H. In addition, the rate of increase of the crystal radius is set in the range of 5 to 20 mm/H to suppress the occurrence of "ridge poly". It is set in the range of H and can prevent a decrease in growth efficiency.

Therefore, a high-quality lithium niobate single crystal can be stably grown with a high single-crystallization ratio, so that the productivity of the lithium niobate single-crystal substrate can be improved and the cost can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows typically schematic structure of the single-crystal growth apparatus by the Czochralski method. Relationship between "growth crystal diameter (mm)" and "ridge/poly occurrence rate (%)" when an LN single crystal with a crystal diameter D of the crystal straight body of φ110 mm (= 4 inches) was grown by the Cz method. Graph diagram showing . When an LN single crystal having a crystal diameter D of the crystal straight body portion of φ110 mm (= 4 inches) is grown by the Cz method (however, the crystal diameter at which the slow pulling speed is terminated is specified to be 55 mm for all crystals), from the start of pulling to the above FIG. 2 is a graph showing the relationship between the "increase rate of crystal radius (mm/H)" and the "rate of occurrence of ridge poly (%)" up to a crystal diameter of 55 mm.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Overview of Single Crystal Growth Apparatus and Single Crystal Growth Method]
First, with reference to FIG. 1, a configuration example of a single crystal growth apparatus 10 by the Cz method and an outline of a single crystal growth method will be described.

FIG. 1 is a cross-sectional view schematically showing the schematic configuration of a high-frequency induction heating single crystal growth apparatus 10. A resistance heating single crystal growth apparatus is also used for growing LN single crystals. The difference between the high-frequency induction heating type single crystal growth apparatus and the resistance heating type single crystal growth apparatus is that in the case of the high-frequency induction heating type, the metal crucible set in the work coil 15 is heated by the high-frequency magnetic field formed by the work coil 15. An eddy current is generated on the side wall of the crucible 12, and the crucible 12 itself becomes a heating element due to the eddy current, forming a temperature environment necessary for melting the raw material in the crucible 12 and crystal growth. In the case of the resistance heating type, the heat generated by the resistance heater installed on the outer periphery of the crucible is used to melt the raw material and form the temperature environment necessary for crystal growth. Since the essence of the Cz method is the same regardless of which heating method is used, the method for growing a single crystal using a high-frequency induction heating single crystal growing apparatus will be described below.

As shown in FIG. 1 , a high-frequency induction heating single crystal growth apparatus 10 has a crucible 12 placed in a chamber 11 . The crucible 12 is placed on the crucible table 13 . A refractory material 14 is arranged in the chamber 11 so as to surround the crucible 12 . A work coil 15 is arranged so as to surround the crucible 12. A high-frequency magnetic field generated by the work coil 15 causes an eddy current to flow in the wall of the crucible 12, and the crucible 12 itself becomes a heating element. A pulling shaft (seed bar) 16 is provided in the upper part of the chamber 11 so as to be rotatable and vertically movable. A seed holder 17 for holding the seed crystal 1 is attached to the tip of the lower end of the pulling shaft (seed rod) 16 .

Here, the crucible 12 used in the Cz method is selected so that the inner diameter d of the crucible 12 is also changed according to the crystal diameter D to be grown, and generally D/d is about 0.5 to 0.7. be done. For example, when growing a crystal with a crystal diameter D of φ110 mm (=4 inches), a crucible with an inner diameter d of about 150 mm to 220 mm is used.

In the Cz method, a single crystal piece to be the seed crystal 1 is brought into contact with the melt surface of the single crystal raw material 18 in the crucible 12 , and the seed crystal 1 is pulled upward while being rotated by a pulling shaft (seed rod) 16 . , a cylindrical single crystal having the same orientation as the seed crystal 1 is grown.

The rotation speed and pulling speed of the seed crystal 1 depend on the type of crystal to be grown and the temperature environment during growth, and must be appropriately selected according to these conditions. Further, during crystal growth, it is necessary to release the solidification latent heat generated by the crystallization of the melt at the growth interface upward through the seed crystal. 8° C./cm). In addition, in order to prevent the shape of the grown crystal from bending or twisting, a temperature gradient (for example, 1 to 5° C./ cm), and in order to stabilize heat convection in the melt, it is preferable to conduct the growth under a temperature gradient in which the temperature increases vertically from the growth interface toward the bottom of the crucible.

When growing an LN single crystal, the melting point of the LN crystal is 1250° C., and oxygen is required in the growth atmosphere. is used. The pulling speed during growth is generally about several mm/H, and the rotation speed is about several to several tens of rpm. Further, the inside of the furnace during the growth is generally the air or a nitrogen-oxygen mixed gas atmosphere with an oxygen concentration of about 20%. After growing the crystal to a desired size under these conditions, the growing crystal is separated from the melt by changing the pulling speed or gradually increasing the melt temperature, and then placed in the growth furnace. The power of is lowered at a predetermined rate to slowly cool the crystal, and after the temperature in the furnace reaches around room temperature, the crystal is taken out from the growth furnace.

The crystal grown by such a method and removed from the furnace was subjected to annealing treatment to remove residual strain caused by temperature differences in the crystal and poling treatment to align the direction of spontaneous polarization in the crystal. Later, it is handed over to a substrate processing step that performs slicing, polishing, and the like.

[Adjustment of “Pulling speed” and “Crystal radius increase speed” to suppress ridge poly]
By the way, when an LN crystal is grown by the Cz method using the above-described growth furnace described in Patent Document 1, "ridge poly" that polycrystallizes from the habit line portion of the crystal often occurs, and the growth process is delayed. It reduces productivity. The cause of the occurrence of "ridge poly" is the misalignment of atoms on the facet surface caused by fluctuations in the growth rate as described above, and it is effective to grow at the slowest speed possible to suppress this misalignment. . For this reason, it is effective to set the pulling speed of "approximately 2 to 5 mm/H" exemplified in Patent Document 1 to a lower speed. However, even if a high-quality single crystal is grown by growing the crystal at a low speed from the start to the end of the crystal growth, the productivity per unit time is lowered, resulting in an increase in cost.

Therefore, in order to find an appropriate condition for the pulling rate that suppresses the occurrence of "ridge poly" without lowering productivity, the present inventors set the pulling rate to "3 mm /H” and using a Pt crucible with an inner diameter of 150 mm, a 128° RY-LN crystal [here, the above “128° RY" is the crystal growth orientation (the crystal orientation of the seed crystal)] was conducted, and the detailed investigation of the occurrence of the above-mentioned "ridge poly" resulted in the results shown in the graph of FIG. In addition, it was found that the occurrence rate of "ridge poly" is very high at the initial stage of growth, when the crystal diameter is small.

The reason for the above is that the smaller the crystal diameter, the more dominant the heat convection in the melt, and the crystal growth occurs near the center of the melt, where temperature fluctuations are large. As a result, fluctuations in the growth rate tend to occur. it is conceivable that. In order to suppress the occurrence of "ridge poly", it is ideal to suppress temperature fluctuations and reduce fluctuations in the growth rate. It is practically difficult due to non-uniformity, deformation, and the like. Therefore, in order to suppress the occurrence of the above-mentioned "ridge poly", it is necessary to minimize fluctuations in the growth rate even if temperature fluctuations occur, and to allow the atoms arriving at the growth interface to be taken in at stable positions. It is effective to slow down the growth rate to give sufficient margin.

Therefore, the present inventor conducted an LN crystal growth test using crucibles with different inner diameters and changing the pulling speed, and found that the crystal diameter grown from the start of pulling the seed crystal was (1/2) D Alternatively, the inventors have found that the rate of occurrence of "ridge poly" can be significantly reduced by setting the pulling speed to a low speed until the value of (1/3)d, whichever is smaller, is reached.

However, during the period from the start of pulling the seed crystal until the diameter of the grown crystal reaches the smaller value of (1/2) D or (1/3) d, even if the pulling speed is set to a low speed, It has been found that when the rate of increase in the crystal radius of is high, the rate of occurrence of "ridge poly" increases as shown in FIG. Therefore, when we analyzed the conditions for suppressing the occurrence of the above-mentioned "ridge poly" with good reproducibility, we found that the crystal diameter grown from the start of pulling the seed crystal is (1/2) D or (1/3) d, whichever is smaller. In addition to the above condition that the seed crystal pulling rate is set to a low speed until the numerical value of It was confirmed that the crystal radius increase rate must be 20 mm/H or less until the smaller numerical value is reached. As shown in FIG. 3, the slower the increase rate of the crystal radius, the higher the effect of suppressing "ridge poly". There is no difference in the suppressive effect of Furthermore, the slower the increase rate of the crystal radius, the longer the crystal growth time and the lower the productivity. Therefore, in consideration of productivity, it is necessary to set the increasing speed of the crystal radius to 5 mm/H or more and 20 mm/H or less. The increase rate of the crystal radius is controlled by adjusting the melt surface temperature by adjusting the electric power supplied to the growth furnace.

The present invention found by the above-mentioned LN crystal growth test and technical analysis,
Using a crucible with an inner diameter d, a seed crystal is brought into contact with the raw material melt in the crucible, and the seed crystal is pulled up while rotating to grow a crystal shoulder and a subsequent crystal straight body portion with a crystal diameter D. In the method for growing a lithium niobate single crystal by the Larski method, the period from the start of pulling the seed crystal until the diameter of the grown crystal reaches (1/2) D or (1/3) d, whichever is smaller. sets the seed crystal pulling rate in the range of 0 to 1 mm/H and the crystal radius increase rate in the range of 5 to 20 mm/H, and after the crystal diameter exceeds the above numerical value, the pulling rate is gradually increased. It is characterized in that the pulling speed is set in the range of 2 to 5 mm/H when the straight body portion of the crystal having the crystal diameter D is grown.

Hereinafter, the method for growing a lithium niobate single crystal by the Czochralski method of the present invention will be described in detail.

As described above, "ridge poly" tends to occur in the early stage of growth. Especially when the crystal diameter is small, crystal growth occurs in the central part of the melt surface, so the grown crystal is most susceptible to temperature fluctuations. It's an easy time. Therefore, it is necessary to set the pulling rate to a low speed when the crystal diameter is small, and to set it to "0 to 1 mm/H". In order to suppress "ridge poly", it is important to give time margin for the atoms that have reached the growth interface to be taken in at stable positions. preferable. In addition, it is necessary to set the increasing speed of the crystal radius to "5 to 20 mm/H" at this time.

The range in which the pulling speed is set to a low speed is until the diameter of the grown crystal reaches (1/2)D or (1/3)d, whichever is smaller. Even if the diameter of the grown crystal is the same, the temperature fluctuation of the melt surface during growth varies depending on the diameter of the crucible. Using crucibles with different inner diameters and changing the pulling speed, a crystal growth test was conducted. I found it necessary. For example, when the crystal diameter D to be grown is φ110 mm, it is necessary to lower the pulling speed from φ50 mm to φ55 mm. It should be noted that although it is possible to lower the pulling speed beyond the above-mentioned crystal diameter (φ50 mm to φ55 mm), in this case, even if a high-quality single crystal can be grown, the productivity per unit time is lowered. Therefore, the cost will increase. In addition, in order to suppress "ridge poly" with good reproducibility, the crystal radius until the grown crystal diameter reaches the smaller value of (1/2) D or (1/3) d should be set in the range of 5 to 20 mm/H. The rate of occurrence of "ridge poly" tends to decrease as the rate of increase in the crystal radius decreases, but in consideration of productivity, the rate should be 5 mm/H or more.

Then, after the crystal diameter to be grown exceeds the smaller numerical value of (1/2) D or (1/3) d, the pulling speed is gradually increased, and during the growth of the crystal straight body portion of the crystal diameter D requires setting the pull-up speed to 2-5 mm/H. The rate of increase in the crystal radius during the growth of the straight body of the crystal depends on the controlled shape of the straight body of the crystal, so it is appropriately set according to the shape to be controlled.

EXAMPLES Hereinafter, examples of the present invention will be specifically described with reference to comparative examples.

In the examples and comparative examples, as in the conventional crystal growth method, the temperature gradient (4° C./cm) in which the temperature decreases upward from the growth interface of the raw material melt, and the growth interface in the raw material melt The crystal is grown under a growth environment that satisfies a temperature gradient (3° C./cm) in which the temperature increases in the horizontal direction from the crucible wall.

[Example 1]
A 128° RY-LN crystal with a straight body diameter of φ110 mm (=4 inches) was grown using a Pt crucible with an inner diameter of 150 mm using the high frequency induction heating type single crystal growth apparatus shown in FIG. In addition, the diameter of the crystal grown from the start of pulling the seed crystal is φ50 mm [the smaller value of (1/2) D = 55 mm and (1/3) d = 50 mm shown in Table 1 "Low-speed growth crystal diameter A" column. ], the pulling rate was kept constant at "1.0 mm/H" and the growth rate of the crystal radius was set at "20 mm/H".

First, LN powder was charged as the raw material 18 in the Pt crucible 12, and the raw material 18 was melted. Then, the tip of the seed crystal 1 was immersed in the raw material melt in the crucible 12, and rotated at a rotation speed of 10 rpm. The pulling rate is set to "1.0 mm/H" until the diameter of the crystal to be grown is φ50 mm, and the increase rate of the crystal radius during this period is adjusted so as not to exceed "20 mm/H" at the maximum by adjusting the input power. After growing the crystal with a diameter of φ110 mm, the pulling rate is changed from “1.0 mm/H” to “3.0 mm/H” until the crystal diameter reaches φ110 mm. 128° RY-LN crystal with a straight body diameter of φ110 mm (=4 inches) and a straight body length of 100 mm was grown at a constant pulling rate of 3.0 mm/H. The grown LN crystal was separated from the raw material melt, cooled to around room temperature, and then taken out.

Then, growth was performed 50 times under the same conditions, and 49 LN crystals were obtained. The single crystallization rate was 98%.

Table 1 shows the growth conditions and results.

[Example 2]
The diameter of the crystal grown from the start of pulling the seed crystal is φ50 mm [the smaller value of (1/2) D = 55 mm and (1/3) d = 50 mm shown in Table 1 "Low-speed growth crystal diameter A"]. 128° RY-LN with a crystal straight body diameter of φ 110 mm (= 4 inches) and a crystal straight body length of 100 mm under the same conditions as in Example 1, except that the pulling speed until it becomes 0.0 mm/H. crystals were grown.

Then, growth was performed 50 times under the same conditions, and 49 LN crystals were obtained. The single crystallization rate was 98%.

Table 1 shows the growth conditions and results.

[Example 3]
Using a crucible with an inner diameter of φ180 mm, the diameter of the crystal grown from the start of pulling the seed crystal is φ55 mm [(1/2) D = 55 mm and (1/3) d = 60 mm shown in Table 1 "Low-speed growth crystal diameter A" column. [smaller numerical value]] under the same conditions as in Example 1, except that the pulling rate was set to "1.0 mm/H". A 100 mm 128° RY-LN crystal was grown.

Then, growth was performed 50 times under the same conditions, and 48 LN crystals were obtained. The single crystallization rate was 96%.

Table 1 shows the growth conditions and results.

[Example 4]
Using a crucible with an inner diameter of φ180 mm, the diameter of the crystal grown from the start of pulling the seed crystal is φ55 mm [(1/2) D = 55 mm and (1/3) d = 60 mm shown in Table 1 "Low-speed growth crystal diameter A" column. [smaller numerical value]] was set to "0.0 mm/H" under the same conditions as in Example 1. A 100 mm 128° RY-LN crystal was grown.

Then, growth was performed 50 times under the same conditions, and 49 LN crystals were obtained. The single crystallization rate was 98%.

Table 1 shows the growth conditions and results.

[Comparative Example 1]
The diameter of the crystal grown from the start of pulling the seed crystal is φ50 mm [the smaller value of (1/2) D = 55 mm and (1/3) d = 50 mm shown in Table 1 "Low-speed growth crystal diameter A"]. The conditions were the same as in Example 1, except that the pulling rate until the height was 2.0 mm/H, which exceeded the upper limit of 1.0 mm/H. A 128° RY-LN crystal with a body length of 100 mm was grown.

Then, the growth was performed 50 times under the same conditions, and 37 LN crystals were obtained. The single crystallization rate was 74%. All 13 defective crystals were "ridge poly".

Table 1 shows the growth conditions and results.

[Comparative Example 2]
The diameter of the crystal grown from the start of pulling the seed crystal is φ40 mm [Different from the smaller value of (1/2) D = 55 mm and (1/3) d = 50 mm shown in Table 1 "Low-speed growth crystal diameter A" column. The conditions were the same as in Example 1 except that the pulling rate until the crystal diameter] was set to 0.0 mm/H. °RY-LN crystals were grown.

Then, growth was performed 50 times under the same conditions, and 39 LN crystals were obtained. The single crystallization rate was 78%. All 11 defective crystals were "ridge poly".

Table 1 shows the growth conditions and results.

[Comparative Example 3]
The diameter of the crystal grown from the start of pulling the seed crystal is φ50 mm [the smaller value of (1/2) D = 55 mm and (1/3) d = 50 mm shown in Table 1 "Low-speed growth crystal diameter A"]. The conditions were the same as in Example 1, except that the rate of increase in the crystal radius was set to "30 mm/H", which exceeded the upper limit of 20 mm/H. A 128° RY-LN crystal with a length of 100 mm was grown.

Then, the growth was performed 50 times under the same conditions, and 36 LN crystals were obtained. The single crystallization rate was 72%. All 14 defective crystals were "ridge poly".

Table 1 shows the growth conditions and results.

[Comparative Example 4]
The diameter of the crystal grown from the start of pulling the seed crystal is φ50 mm [the smaller value of (1/2) D = 55 mm and (1/3) d = 50 mm shown in Table 1 "Low-speed growth crystal diameter A"]. The conditions were the same as in Example 1, except that the rate of increase in the crystal radius was set to "3 mm/H", which is less than the lower limit of 5 mm/H. A 128° RY-LN crystal with a length of 100 mm was grown.

Then, growth was performed 50 times under the same conditions, and 49 LN crystals were obtained. The single crystallinity was 98%, which is a high single crystallinity.

However, the growth time required for the grown crystal diameter to reach φ50 mm was as long as about 17 hours, resulting in a decrease in productivity.

Table 1 shows the growth conditions and results.

According to the method for growing a lithium niobate single crystal according to the present invention, the occurrence of "ridge poly" is suppressed and a high-quality lithium niobate single crystal can be stably grown. It has industrial applicability for use in the production of lithium niobate single crystals used as

Reference Signs List 1 seed crystal 10 single crystal growth apparatus 11 chamber 12 crucible 13 crucible stand 14, 19 refractory 15 work coil 16 pulling shaft (seed rod)
17 seed holder 18 single crystal growth raw material

Claims (1)

Using a crucible with an inner diameter d, a seed crystal is brought into contact with the raw material melt in the crucible, and the seed crystal is pulled up while rotating to grow a crystal shoulder and a subsequent crystal straight body portion with a crystal diameter D. In the method for growing a lithium niobate single crystal by the Larski method,
From the start of pulling the seed crystal until the grown crystal diameter reaches the smaller value of (1/2) D or (1/3) d, the pulling rate of the seed crystal is in the range of 0 to 1 mm/H. and the rate of increase of the crystal radius is set in the range of 5 to 20 mm / H, and after the crystal diameter exceeds the above numerical value, the pulling rate is gradually increased, and the crystal diameter D is grown in the straight body part of the crystal. is a method for growing a lithium niobate single crystal, characterized in that the pulling speed is set in the range of 2 to 5 mm/H.

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