JP6515853B2 - Method of manufacturing single crystal and apparatus therefor - Google Patents

Description

  The present invention is a method for producing a single crystal such as lithium niobate (LN), tantalum tantalate (LT), garnet or the like used in surface acoustic wave devices or optical communication devices using the Czochralski method (Cz method). The present invention relates to a method of manufacturing a crystal, and in particular, by preventing solidification of a raw material melt during single crystal growth, rapid drop of the melt surface due to raw material solidification and accompanying rapid growth of single crystal are generated. The present invention relates to a method and apparatus for producing a single crystal in which the quality of crystals is not deteriorated by not causing the reaction.

LT (lithium tantalate: LiTaO ₃ ), LN (lithium niobate: LiNbO ₃ ), GGG (Gd ₃ Ga ₅ O ₁₂ ), TGG (Tb ₃ Ga ₅ O ₁₂ ), GSAG (Gd ₃ Sc ₂ Al ₃ O ₁₂₎ Oxide single crystals having a high melting point, such as TSAG (Tb ₃ Sc ₂ Al ₃ O ₁₂ ), etc. are usually produced using the Czochralski method (Cz method). Further, since these materials have high melting points of 1200 ° C. to 1800 ° C., noble metal crucibles having high melting points such as platinum and iridium are used for the crucible applied to this manufacturing method.

  By the way, the rotation pulling method (Czochralski method) of the single crystal is performed using, for example, a single crystal growth apparatus as shown in FIG. That is, the single crystal growth apparatus a is a work piece for heating the raw material b by induction heating of the crucible c in which the raw material b is charged inside and a heat insulating material d for keeping the outside warmer and further outside the crucible c. The main part is constituted by a coil (high frequency coil) e and a pulling shaft g provided on the upper side of the crucible c so as to be movable up and down and holding a seed crystal f at its tip and rotating in the arrow direction. Here, the work coil e is installed around the crucible c with an appropriate number of turns, and the lower end of the work coil e is below the bottom of the crucible c in order to ensure the melting property of the raw material b in the crucible c. The upper end of the work coil e is positioned above the upper end of the crucible c.

  Then, in order to manufacture a single crystal such as lithium tantalate (LT) using this manufacturing apparatus, first, the raw material b is charged into the crucible c and filled, and then the work coil e is energized and the crucible is c is heated, and the raw material b in the crucible c is heated to a temperature above its melting point to melt it.

  Next, after adjusting the output of the high frequency supplied to the crucible c so that the melted raw material melt reaches an appropriate temperature, the pulling shaft g is lowered to move the seed crystal f to the center of the melted raw material melt. Contact single crystal pieces such as LT. Then, the output of the high frequency wave introduced into the crucible c is gradually reduced to lower the temperature of the raw material melt, and the raw material melt is gradually solidified centering on the seed crystal f, and at the same time it is raised while rotating the seed crystal f. A single crystal is produced by performing the operation of

  By the way, among the above-described series of steps of the rotational pulling method (Czochralski method), the determination of the melting end point in the raw material melting operation has conventionally been performed by a manual operation determined by the operator while observing the raw material . For this reason, the problem that the said judgment operation was mistaken had arisen.

As a method of improving such a problem, the temperature of the crucible at the time of dissolving the raw material is directly measured by a radiation thermometer provided outside the chamber. It has been proposed to correct the output of the heater so that the measured temperature matches the target temperature (see, for example, Patent Document 1).
As another improvement method, a temperature sensor for measuring the temperature of the raw material is provided at the bottom of the crucible, and the melting state of the raw material is detected from the second derivative value of the temperature measured by this temperature sensor, It has been proposed that temperature control of the raw material melt is performed with the point of time when the second derivative value changes from negative to positive as the end point of melting of the raw material (see, for example, Patent Document 2).

JP-A-9-227277 (Embodiment of the invention, FIG. 2) JP 10-338596 A (embodiment of the invention, FIG. 1)

  By the way, when heating a crucible by high frequency induction heating, the eddy current by which a high frequency is induced to a crucible is not uniform, and is especially induced near the corner of a crucible upper end or a crucible bottom. On the contrary, the induction current is weak near the center of the crucible bottom, and as a result, the temperature of the melt near the crucible bottom is lower than other regions. To raise the temperature at the bottom of the crucible, it is convenient to lower the work coil to increase the eddy current applied to the bottom of the crucible, but if the specific gravity of the high frequency output is biased to the bottom of the crucible, heating of the top of the crucible The temperature drops to cause problems such as cracking of the crystal due to temperature difference.

  Here, if the single crystal to be produced has a small diameter of, for example, 50φ or less, the diameter of the crucible used for producing the single crystal is also at most about 100φ, making it difficult to induce high frequency near the center of the bottom of the crucible. Extreme temperature decrease hardly occurs, but when the diameter of the crucible exceeds 100φ, the temperature decrease in the area near the center of the bottom of the crucible may seriously affect the crystal growth. .

First, when the temperature at the bottom of the crucible is low, in the process of lowering the temperature of the raw material melt by gradually reducing the output of high frequency in crystal growth, it was cooled on the melt surface or crystal interface by natural convection in the melt. The raw material melt flows down near the center of the upper portion of the crucible and reaches the bottom of the crucible, but if the temperature at the bottom of the crucible is not sufficiently high, the raw material melt near the bottom of the crucible may solidify rapidly. In the case of LT, since the specific gravity of the melt is 5.7 g / cm ³ and the solid is 7.5 g / cm ³ , the melt position of the raw material melt is as shown in FIG. 5 along with solidification of the raw material near the crucible bottom. Will be reduced to This is nothing but a rapid increase in the growth rate for crystals grown by the rotational pulling method. The rapid increase in growth rate leads to the induction of crystal defects and further to the generation of polycrystals. Therefore, although it is necessary to avoid solidification of the raw material during growth, the crucible is deformed each time the number of times of crystal growth is increased, and the change of convection due to it or deterioration of the refractory placed around the crucible progresses. The temperature at the bottom of the crucible tends to decrease, and the raw material solidifies.

  Furthermore, when solidification of the raw material proceeds during crystal growth, the raw material solidified at the bottom of the crucible grows upward in the crucible like a stone crucible, and the single crystal grown by the rotational pulling method collides with the solidified raw material Had a problem that

  The present invention was made in view of such problems, and the technical problem to be solved by the present invention is a method of producing a single crystal for preventing the raw material melt from solidifying in the vicinity of the bottom of a crucible and the same It is in providing an apparatus.

  According to a first technical feature of the present invention, in the method of producing a single crystal, wherein a single crystal is produced from a raw material melt accommodated in a crucible by a rotation pulling method, the crucible bottom portion is formed by a temperature sensor installed in the crucible Whether the minute fluctuation component in the unit time of the temperature exceeds a predetermined threshold based on the measurement step of measuring the temperature of the raw material melt in the vicinity and the temperature information from the temperature sensor measured in the measurement step Under the condition that the minute fluctuation component of the temperature exceeds the threshold value in the discrimination step of judging signs of solidification of the raw material melt in the vicinity of the crucible bottom depending on whether or not the minute fluctuation component of the temperature is below the threshold value And a heating step of promoting heating of the bottom of the crucible.

According to a second technical feature of the present invention, in the method for producing a single crystal having the first technical feature, the determining step calculates a minute fluctuation component of the temperature as a standard deviation, and uses this standard deviation. It is a manufacturing method of the single crystal characterized by distinguishing.
According to a third technical feature of the present invention, in the method of manufacturing a single crystal having the first technical feature, the heating step includes a high frequency coil for heating provided movably in the vertical direction around the crucible. In the method of manufacturing a single crystal, the high frequency coil is lowered at a speed of 1 mm or more and 12 mm or less per hour under the condition that the minute fluctuation component of the temperature exceeds the threshold.
A fourth technical feature of the present invention is the method for producing a single crystal according to the first technical feature, wherein the crucible is a noble metal crucible.
According to a fifth technical feature of the present invention, in the method for producing a single crystal having the first technical feature, the single crystal comprises LT (lithium tantalate: LiTaO ₃ ), LN (lithium niobate: LiNbO ₃₎ Or GGG (Gd ₃ Ga ₅ O ₁₂ ), TGG (Tb ₃ Ga ₅ O ₁₂ ), GSAG (Gd ₃ Sc ₂ Al ₃ O ₁₂ ) or TSAG (Tb ₃ Sc ₂ Al ₃ O ₁₂ ) It is a manufacturing method of the single crystal characterized by the above.

  According to a sixth technical feature of the present invention, in a single crystal manufacturing apparatus for manufacturing a single crystal from a raw material melt contained in a crucible by a rotational pulling method, the raw material melt attached to the crucible and near the bottom of the crucible The minute fluctuation component of the temperature per unit time is calculated based on temperature information from the temperature sensor for detecting the temperature of the crucible, the high frequency coil provided around the crucible and performing high frequency induction heating the crucible, and the temperature sensor And a control mechanism for generating a control signal for the high frequency coil based on the obtained calculation result, and a drive mechanism for driving the high frequency coil so as to be movable in the vertical direction, Indications of solidification of the raw material melt in the vicinity of the bottom of the crucible are determined based on whether or not the minute fluctuation component exceeds a predetermined threshold value, and the temperature exceeds the threshold value. By the drive mechanism to the small variation component below the threshold is lowered at a predetermined rate to the high frequency coil, an apparatus for producing a single crystal, characterized in that to promote the heating of the crucible bottom.

According to the invention having the first technical feature, it is possible to provide a method of manufacturing a single crystal capable of preventing the situation where the raw material melt is solidified near the bottom of the crucible.
According to the invention having the second technical feature, a minute fluctuation component in a unit time of temperature can be accurately calculated.
According to the invention having the third technical feature prevents a situation in which the raw material melt is solidified in the vicinity of Le pot bottom, moreover, it is possible to produce a less crystal defect single crystal.
According to the invention having the fourth technical feature, it is effective in producing a high melting point oxide single crystal.
According to the invention having the fifth technical feature, the raw material melt can be prevented from solidifying in the vicinity of the bottom of the crucible, and a high melting point oxide single crystal can be produced.
According to the invention having the sixth technical feature, it is possible to provide an apparatus for producing a single crystal capable of preventing the raw material melt from being solidified near the bottom of the crucible.

It is explanatory drawing which shows the outline | summary of embodiment of the manufacturing method of the single crystal to which this invention was applied. FIG. 1 is an explanatory view showing an outline of a single crystal production apparatus according to a first embodiment. FIG. 6 is a graph showing the relationship between the crystal weight and the temperature and time of the bottom of the crucible in the process of producing a single crystal by the single-crystal producing apparatus according to Embodiment 1. FIG. 7 is a graph showing the relationship between temperature oscillation of the crucible bottom and time in the process of manufacturing a single crystal by the single crystal manufacturing apparatus according to Embodiment 1. It is explanatory drawing which shows the outline of the manufacturing apparatus of the conventional single crystal.

Outline of Embodiment FIG. 1 is an explanatory view showing an outline of an embodiment of a method of manufacturing a single crystal to which the present invention is applied.
In the figure, a method of producing a single crystal is a method of producing a single crystal from a melt of a raw material M accommodated in a crucible 1 by a rotation pulling method, wherein a temperature sensor 2 installed in the crucible 1 is used. Based on the temperature information from the measurement process A for measuring the temperature of the raw material M melt near the bottom of the crucible 1 and the temperature sensor 2 measured in the measurement process A, the minute fluctuation component ΔT in the unit time of the temperature is determined in advance Under the condition that the minute fluctuation component ΔT of the temperature in the determination step B exceeds the threshold α in the determination step B for determining the sign of solidification of the raw material M melt in the vicinity of the bottom of the crucible 1 based on whether or not the threshold α is exceeded. And a heating step C for promoting the heating of the bottom of the crucible 1 so as to make the minute fluctuation component ΔT of the temperature not more than the threshold value α.
In FIG. 1, reference numeral 3 is a high frequency coil for heating provided around the crucible 1, 4 is a heat insulating material surrounding the periphery of the crucible 1, and 5 is a pulling shaft for pulling the material M melt in the crucible 1 while rotating it. It is.

In this technical means, the present embodiment focuses on the minute fluctuation component ΔT in unit time of temperature from the measurement process A by the temperature sensor 2 and the temperature information by the temperature sensor 2 and measures the raw material M melt near the bottom of the crucible 1 It may be any process as long as it includes a determination step B for determining a sign of solidification, and a heating step C for promoting heating of the bottom of the crucible 1 based on the determination result of the determination step B. Here, if the temperature of the raw material M melt near the bottom of the crucible 1 can be measured, the installation place of the temperature sensor 2 is the bottom of the crucible 1 in FIG. 1, but it is not limited to this. Also, the number of temperature sensors 2 does not matter.
In addition, “small fluctuation component ΔT in unit time of temperature” in the determination step B may be appropriately selected as long as it can be quantified. The inventors of the present invention have found that the increase in the minute fluctuation component ΔT of the temperature mentioned above is related to the fact that the raw material M melt in the vicinity of the bottom of the crucible 1 is changed to a sign of solidification. It is contemplated to heat the raw material M melt so as to prevent the solidification of the raw material M melt.
Furthermore, in the heating step C, the heating condition may be changed so as to make the minute fluctuation component ΔT of the temperature not more than the threshold value α, and the heating of the bottom of the crucible 1 may be promoted. However, if the heating temperature suddenly changes, there is a possibility of crystal defects, and in order to avoid this, it is preferable not to change the heating temperature suddenly.

Next, a typical aspect or a preferable aspect of the method for producing a single crystal according to the present embodiment will be described.
First, as a preferable embodiment of the discrimination step B, there is an embodiment in which the minute fluctuation component ΔT of the temperature is calculated as a standard deviation, and the discrimination is performed using this standard deviation. Thus, using the standard deviation is preferable in that the minute fluctuation component ΔT of the temperature can be accurately grasped.
Moreover, as a preferable mode of the heating step C, the high frequency coil 3 for heating provided so as to be vertically movable around the crucible 1 is used, and under the condition that the minute fluctuation component ΔT of the temperature exceeds the threshold α, the high frequency coil There is a mode in which 3 is lowered at a speed va of 1 mm or more and 12 mm or less per hour. In the present example, the movable high frequency coil 3 is used to lower the high frequency coil 3 at a predetermined speed in order to promote heating of the raw material M melt in the vicinity of the bottom of the crucible 1. Here, if the descending speed is less than 1 mm per hour, it takes too long for the minute fluctuation component ΔT to reach within the threshold α, and if it exceeds 12 mm per hour, the temperature change is large and the crystal defects are improved It is difficult to do.
Furthermore, in the case of producing a high melting point oxide single crystal, it is preferable to use a noble metal crucible as the crucible 1. As high melting point oxide single crystals mentioned here, LT (lithium tantalate: LiTaO ₃ ), LN (lithium niobate: LiNbO ₃ ), GGG (Gd ₃ Ga ₅ O ₁₂ ), TGG (Tb ₃ Ga ₅ O ₁₂₎ And GSAG (Gd ₃ Sc ₂ Al ₃ O ₁₂ ) or TSAG (Tb ₃ Sc ₂ Al ₃ O ₁₂ ).

Further, when the method of manufacturing a single crystal according to the present embodiment is embodied, the following single crystal manufacturing apparatus is constructed.
In this example, the apparatus for producing a single crystal is for producing a single crystal from the melt of the raw material M accommodated in the crucible 1 by a rotational pulling method, and is attached to the crucible 1 and the raw material M near the bottom of the crucible 1 Based on temperature information from the temperature sensor 2 for detecting the temperature of the melt, the high frequency coil 3 provided around the crucible 1 and performing high frequency induction heating on the crucible 1, and the minute per unit time of the temperature based on temperature information from the temperature sensor 2 A control device (not shown) that calculates fluctuation component ΔT and generates a control signal for high frequency coil 3 based on the obtained calculation result, and a drive mechanism (not shown) that drives high frequency coil 3 so as to move vertically. And the controller determines signs of solidification of the raw material M melt near the bottom of the crucible 1 based on whether or not the minute fluctuation component ΔT of the temperature exceeds a predetermined threshold α, and Article beyond (For example in a range from W) a high-frequency coil 3 is lowered at a predetermined rate va by the drive mechanism to the small variation component ΔT at temperatures below the threshold value alpha, it is intended to promote the heating of the crucible 1 bottom.

Hereinafter, the present invention will be described in more detail based on the embodiment shown in the attached drawings.
実 施 Embodiment 1
FIG. 2 is a system configuration diagram showing an outline of a single crystal manufacturing apparatus according to the first embodiment.
That is, this single crystal manufacturing apparatus has a crucible 13 whose outer side is covered with a heat insulating material 11 and the raw material 12 is charged into the inside, and a bottom of the crucible 13 is attached to monitor the raw material temperature in the crucible 13. A temperature sensor 14, a work coil (high frequency coil) 16 disposed outside the heat insulator 11 and connected to the high frequency power supply 15 and performing high frequency induction heating on the crucible 13, and a temperature sensor 14 are connected and output from the temperature sensor 14 The digital thermometer 17 which reads the temperature of the raw material 12 by the received signal and the signal output from the digital thermometer 17 connected to the digital thermometer 17 standardize the minute fluctuation component which is the minute temperature fluctuation in the unit time of temperature. A micro computer which outputs appropriate drive information of the work coil 16 based on the operation information which is calculated as deviation and obtained. And a work coil drive mechanism 19 connected to the microcomputer 18 to control the position of the work coil 16 by an information signal output from the microcomputer 18, and also connected to the microcomputer 18 and output from the microcomputer 18. The main part is constituted by the high frequency output regulator 20 which controls the high frequency output by the information signal, the pulling shaft 21 on the upper side of the crucible 13, and the crystal weight sensor 22 on the pulling shaft 21.
The type of the temperature sensor 14 is not particularly limited, and even if an R type or B type thermocouple specified in JIS C 1602: 1995 is applied, or a fiber sensor or pyrometer using light is used. You may use etc.

Here, FIG. 3 shows the temperature change and the crystal weight of the bottom of the crucible 13 read by the temperature sensor 14 (B-type thermocouple) disposed at the bottom of the crucible 13 when growing an LT single crystal using this manufacturing apparatus. It is the graph which plotted the sensor 22. FIG.
As can be seen from FIG. 3, the temperature of the bottom of the crucible 13 gradually decreases with the crystal growth, but it can be confirmed that there is a region in which minute vibrations occur in the temperature. These micro vibrations are divided into three regions.
The first region is a region where there is little temperature vibration at the bottom of the crucible 13 from 0 minutes (the start of crystal pulling) to 350 minutes. Further, the second region is a region of 350 minutes to 1150 minutes, and the amplitude of the temperature vibration is about 0.5 ° C. at maximum. The third region is a region after 1150 minutes, and is again a region where there is little temperature vibration.

  And a discontinuous rise in temperature can be confirmed between the second area and the third area. The temperature rises rapidly by 3 ° C., which is the heat of solidification due to the solidification of the raw material, and shows the result of rapid solidification of the melt of the raw material 12 near the bottom of the crucible 13. In order to observe temperature oscillations in a unit time of temperature (in this case, 30 minutes), large temperature changes are excluded and when small fluctuations in temperature are analyzed as a standard deviation, the form is as shown in the graph of FIG. The standard deviation can easily detect the sign of solidification of the raw material at the boundary of 0.06 ° C. That is, the standard deviation is less than or equal to 0.06 ° C. in the first region, but above 0.06 ° C. in the second region and again below 0.06 ° C. in the third region.

  According to the inventor's detailed investigation, in the first region, the melt of the raw material 12 is not solidified yet, so the temperature change at the bottom of the crucible 13 is smooth, but in the second region, the raw material is minute While it starts to solidify. When solidified, a heat of solidification is generated and the solidified portion is melted again, but the temperature is lowered because energy is consumed at the time of melting. In this way, the second region frequently repeats the solidification and melting of the raw material. As the temperature at the bottom of the crucible 13 is further lowered, the solidification of the melt of the raw material 12 at the bottom of the crucible 13 progresses rapidly, and the heat of solidification is generated at once. Then, in the third region, as a result of the solid raw material wall being formed at the bottom of the crucible 13 due to solidification of the raw material, it became clear that the temperature sensor 14 can hardly detect the temperature vibration occurring thereafter.

Thus, the temperature of the bottom of the crucible 13 is measured continuously and in detail in the process of preparing the crystal by adjusting the high frequency output with high precision while measuring the crystal weight with the crystal weight sensor 22, and the large temperature of the bottom of the crucible 13 The change is excluded, and after only the minute temperature vibration is analyzed to detect the time when the second region is reached, the work coil is adjusted so that the temperature vibration becomes equal to or less than a preset threshold (in this example, 0.06 ° C.) By gradually lowering 16, it becomes possible to prevent solidification of the melt of the raw material 12 in advance by heating the bottom of the crucible 13.
In this example, the work coil 16 for high frequency induction heating is installed around the crucible 13 with an appropriate number of turns, and the lower end of the work coil 16 is a crucible in order to ensure the melting property of the raw material 12 in the crucible 13. The upper end of the work coil 16 is disposed about 80 to 120 mm above the upper end of the crucible 13 and located about 60 to 100 mm below the bottom of the base 13.
Here, the descending speed of the work coil 16 for high frequency induction heating is preferably 1 mm or more and 12 mm or less per hour. If the descending speed is less than 1 mm per hour, it takes time to reduce the standard deviation to a specified value or less, and the crystal defects can not be improved. On the other hand, when the descending speed exceeds 12 mm per hour, the temperature change is large and the crystal defects can not be improved. Further, in this example, the method of moving the work coil 16 is adopted. However, if the work coil 16 is lowered in advance by a predetermined amount and fixedly arranged, heating is concentrated in the lower part of the crucible 13 and the raw material In order to bring the surface of the 12 melt close to the melting point, the lower part of the crucible 13 is heated excessively, forced convection becomes too strong, the convection on the surface of the melt of the raw material 12 is disturbed, and axial symmetry of the single crystal But it is not preferable in that the life of the crucible 13 is shortened.
Further, in the present embodiment, since the temperature distribution of the melt of the raw material 12 in the crucible 13 changes when the work coil 16 moves, the high-frequency output adjuster 20 changes the temperature distribution of the melt of the raw material 12 accompanying the movement of the work coil 16. The high frequency output is automatically adjusted to sense a change and to control a change in growth rate and a change in diameter during crystal growth accompanying the change.

Thus, based on the standard deviation of the minute fluctuation component in unit time of temperature measured by the temperature sensor 14 provided in the crucible 13, the sign of solidification of the raw material 12 melt is detected in advance, and the value of the standard deviation Control to lower the work coil 16 finely so that the value becomes less than a prescribed value (predetermined threshold value) to strengthen the heating of the bottom of the crucible 13 and solidify the raw material 12 melt generated at the bottom of the crucible 13 Can be prevented, rapid growth of crystals due to solidification of the raw material 12 melt can be prevented, and the crystal quality can be improved.
Further, in this embodiment, a control method (1 mm or more per hour or more per hour) for finely lowering the work coil 16 according to an embodiment in which the type of high melting point oxide single crystal and the size of the crucible 13 (for example, diameter 100 to 250 mm) are changed. When the method of falling at a speed of 12 mm or less was adopted, it was confirmed that a good single crystal could be obtained.
Although this embodiment is suitable for the method of producing high melting point oxide single crystals such as LN and LT, the present embodiment is not limited to the production of these high melting point oxide single crystals, and other single crystals may be used. It can be naturally applied to the production of (that is, a single crystal which can be produced without using a noble metal crucible such as platinum or iridium).

Hereafter, the Example which materialized the manufacturing apparatus of the single crystal which concerns on Embodiment 1 is described in detail.
Example 1
The growth of LT (LiTaO ₃ ) single crystal was attempted using the manufacturing apparatus shown in FIG. In addition, a crucible made of iridium having a diameter of 170 mmφ, a height of 200 mm and a thickness of 2 mm was used for growth, and about 20 kg of LT powder was filled in the crucible 13. The raw materials were heated and melted by high frequency induction heating, and the growth atmosphere was a nitrogen atmosphere to which 2% of oxygen was added.

  As a temperature sensor 14 for monitoring the temperature of the raw material 12 melt, a B-type thermocouple specified in JIS C 1602: 1995 was used. The melting point of LT is 1650 ° C., and when the thermocouple is brought into direct contact with the crucible 13, deterioration is severe. Therefore, the thermocouple was placed in the center of the bottom of the crucible 13 via a refractory. The output voltage of this thermocouple is converted into a temperature signal by the digital thermometer 17, and then taken into the microcomputer 18, and based on the read temperature, the standard deviation of the minute vibration amount (minute fluctuation component) of the temperature in 30 minutes It was calculated as.

  Further, in order to drive the work coil 16, the microcomputer 18 and the work coil drive mechanism 19 are connected by a communication line, and the movement amount of the work coil 16 can be controlled by the microcomputer 18.

Under these conditions, as described above, after the molten raw material 12 melt is adjusted by the high frequency power regulator 20 so that the melt is at an appropriate temperature, the pulling shaft 21 is lowered to melt the raw material 12 melted. The seed crystal 23 is brought into contact with the center of the solution, the output of high frequency is gradually reduced to lower the temperature of the melt of the raw material 12, and the pulling shaft 21 is raised while rotating the seed crystal 23. While measuring the crystal weight with the weight sensor 22, the high frequency output was precisely adjusted to start crystal growth. Then, in the crystal produced, where the standard deviation of the temperature oscillation is above the 0.06 ° C., it was to lower the work coil 16 43 minutes at a speed of 10mm per hour, the standard deviation of the temperature oscillations to 0.06 ° C. Since the temperature was below the level, the movement of the work coil 16 was stopped and crystal production was continued thereafter. As a result, the standard deviation of the temperature vibration was maintained at less than 0.06 ° C. until the end of the growth, and the rapid solidification of the raw material 12 melt did not occur.

Example 2
The configuration is substantially the same as that of the first embodiment, but in this embodiment, the work coil 16 is lowered at a speed of 10 mm per hour for 26 minutes.
Example 3
The configuration is substantially the same as that of the first embodiment, but in this embodiment, the work coil 16 is lowered at a speed of 5 mm per hour for 78 minutes.
Example 4
The configuration is substantially the same as that of the first embodiment, but in this embodiment, the work coil 16 is lowered at a speed of 5 mm per hour for 67 minutes.
Example 5
The configuration is substantially the same as that of the first embodiment, but in this embodiment, the work coil 16 is lowered at a speed of 2 mm per hour for 184 minutes.
Example 6
The configuration is substantially the same as that of the first embodiment, but in this embodiment, the work coil 16 is lowered at a speed of 2 mm per hour for 209 minutes.

Moreover, the following aspects were prepared as Comparative Examples 1-6.
比較 Comparative Examples 1 to 3
The configuration is substantially the same as that of the first embodiment, but in any of the embodiments, the work coil 16 is fixed.
比較 Comparative Example 4
This embodiment is configured substantially the same as the first embodiment, but is a mode in which the work coil 16 is lowered at a speed of 15 mm per hour for 34 minutes (a mode in which the movement of the work coil 16 is too fast).
Comparative Example 5
This embodiment is configured substantially the same as the first embodiment, but is a mode in which the work coil 16 is lowered at a speed of 25 mm per hour for 22 minutes (a mode in which the movement of the work coil 16 is too fast).
Comparative Example 6
The configuration is substantially the same as that of the first embodiment, but this is an embodiment in which the work coil 16 is lowered at a speed of 0.5 mm per hour for 852 minutes (a movement of the work coil 16 is too slow).

The threshold value of the standard deviation used at this time actually varies depending on the configuration of the crystal growth furnace, such as the crucible size in the manufacturing apparatus and the structure of the heat retention system. Therefore, when the configuration of the crystal growth furnace is changed, it is necessary to obtain an appropriate threshold in advance.
As in the present embodiment (Examples 1 to 6), the work coil 16 is appropriately moved with respect to the solidification of the raw material 12 melt, and the work coil 16 is subjected to the solidification of the raw material 12 melt. X-ray topographic image is taken by rounding the lower part of the crystal with the comparative examples (Comparative Examples 1 to 6) in which the movement of the work coil 16 is not fixed properly or fixed, and the amount of each crystal defect is quantified and compared investigated.
The results are shown in Table 1. Crystal defects are shown in arbitrary units (AU).

  As is apparent from Table 1, in the case of the example, it is understood that the crystal defects can be reduced by about 30 to 50% as compared with the comparative example.

DESCRIPTION OF SYMBOLS 1 crucible 2 temperature sensor 3 high frequency coil 4 heat insulating material 5 pulling axis M raw material 11 heat insulating material 12 raw material 13 crucible 14 temperature sensor 15 high frequency power supply 16 work coil 17 digital thermometer 18 microcomputer 19 work coil drive mechanism 20 high frequency output regulator 21 Pull-up shaft 22 Crystal weight sensor 23 Seed crystal

Claims (6)

In a method of producing a single crystal, wherein a single crystal is produced from a raw material melt contained in a crucible by a rotational pulling method,
Measuring the temperature of the raw material melt near the bottom of the crucible with a temperature sensor installed in the crucible;
Indication of solidification of the raw material melt in the vicinity of the bottom of the crucible depending on whether or not the minute fluctuation component in the unit time of the temperature exceeds a predetermined threshold based on the temperature information from the temperature sensor measured in the measurement step. A determining step of determining
A heating step for promoting heating of the crucible bottom so that the minute fluctuation component of the temperature is equal to or less than the threshold under the condition that the minute fluctuation component of the temperature exceeds the threshold in the determining step;
A method of producing a single crystal, comprising: In the method of producing a single crystal according to claim 1,
The method of manufacturing a single crystal according to claim 1, wherein the determining step calculates a minute fluctuation component of the temperature as a standard deviation, and determines using the standard deviation. In the method of producing a single crystal according to claim 1,
The heating step uses a high frequency coil for heating provided movably in the vertical direction around the crucible, and under the condition that the minute fluctuation component of the temperature exceeds the threshold, the high frequency coil is 1 mm or more per hour, A method for producing a single crystal, comprising lowering at a speed of 12 mm or less. In the method of producing a single crystal according to claim 1,
The method for producing a single crystal, wherein the crucible is a noble metal crucible. In the method of producing a single crystal according to claim 1,
The single crystal is made of LT (lithium tantalate: LiTaO ₃ ), LN (lithium niobate: LiNbO ₃ ), GGG (Gd ₃ Ga ₅ O ₁₂ ), TGG (Tb ₃ Ga ₅ O ₁₂ ), GSAG (Gd ₃ Sc) _A method for producing a single crystal, characterized in that it is any of ₂ Al ₃ O ₁₂ ) and TSAG (Tb ₃ Sc ₂ Al ₃ O ₁₂ ). In a single crystal production apparatus for producing a single crystal from a raw material melt contained in a crucible by a rotation pulling method,
A temperature sensor attached to the crucible to detect the temperature of the raw material melt near the bottom of the crucible;
A high frequency coil provided around the crucible and performing high frequency induction heating on the crucible;
A control device that calculates a minute fluctuation component of the temperature per unit time based on temperature information from the temperature sensor, and generates a control signal for the high frequency coil based on the obtained calculation result;
And a drive mechanism for driving the high frequency coil so as to be movable in the vertical direction.
The controller determines the sign of solidification of the raw material melt near the crucible bottom depending on whether the minute fluctuation component of the temperature exceeds a predetermined threshold, and the minute of the temperature under the condition exceeding the threshold. The apparatus for manufacturing a single crystal, wherein the high frequency coil is lowered at a predetermined speed by the driving mechanism so as to make the fluctuation component equal to or less than the threshold value, thereby promoting heating of the crucible bottom.