JP7456182B2 - Single crystal manufacturing method - Google Patents

Description

The present invention relates to a method for producing a single crystal. In particular, the present invention relates to a method for producing a single crystal by the Czochralski (hereinafter abbreviated as Cz) method using a high-frequency induction heating furnace. Further, for example, the above single crystal may be an oxide single crystal, lithium tantalate, or lithium niobate.

Oxide single crystal substrates processed from ferroelectric single crystals of lithium tantalate ( _LiTaO3 : hereafter abbreviated as "LT") or lithium niobate (LiNbO3: hereafter abbreviated as "LN") are used primarily as materials for surface acoustic wave elements (SAW filters) that remove electrical signal noise in mobile communication devices.

Industrially, LT and LN single crystals, which are the materials of SAW filters, are mainly grown by the Cz method, and for example, a high frequency dielectric heating type growth furnace described in Patent Document 1 is used. As shown in Figure 1, the Cz method is a method in which a single crystal piece serving as a seed crystal is brought into contact with the surface of a raw material melt in a crucible, and the seed crystal is pulled upward while rotating to form a cylinder in the same orientation as the seed crystal. This is a method of growing single crystals. For example, in the case of LT single crystal growth, since the melting point of LT crystal is as high as 1650°C, a crucible made of iridium (Ir), a high melting point metal, is used, filled with a specified LT raw material, and a high-frequency induction heating method is used. It is grown using an electric furnace (growth furnace). The pulling speed during growth is generally about several mm/H, and the rotational speed is about several to several tens of rpm. Furthermore, the inside of the furnace during growth is generally a nitrogen-oxygen mixed gas atmosphere with an oxygen concentration of about several percent. Under these conditions, a single-crystal ingot can be obtained by forming a cone-shaped growth part called a shoulder and then forming a cylindrical growth part (hereinafter referred to as a straight body part) to obtain a circular substrate. . After growing the straight body to the desired length, the grown crystal is separated from the melt by changing the pulling speed and gradually increasing the melt temperature, and then the power of the growth furnace is turned off. The crystals are slowly cooled by lowering the temperature at a predetermined rate, and the crystals are taken out from the growth furnace after the temperature inside the furnace reaches around room temperature. Approximately half of the LT raw material remains in the iridium crucible after crystal growth compared to when the growth was started. The LT raw material remaining in the crucible is used for the next growth, and the iridium crucible is filled with LT raw material corresponding to the weight of the pulled crystal, the raw material is melted, and crystal growth is performed. In this way, the raw material is repeatedly melted and cooled while the solidified raw material always remains at the same position in the crucible.

In the crystal growth temperature range, an iridium crucible expands by about 1 to 2 mm due to thermal expansion. During the cooling process after crystal growth, the raw material near the center of the melt surface begins to solidify while the iridium crucible is expanded. Thereafter, as the temperature inside the furnace decreases, the material solidifies from near the bottom of the crucible toward the side walls of the crucible, and finally the center of the raw material inside the crucible solidifies. The iridium crucible contracts as the temperature inside the furnace decreases, but since the thermal expansion coefficient of LT is smaller than that of iridium, outward stress is generated on the side walls of the iridium crucible near the surface of the solidified raw material. Since there is no solidified raw material on the side wall of the iridium crucible above the surface of the solidified raw material, stress is generated inward. The amount of deformation in one thermal cycle is small, but if the raw material is melted and cooled repeatedly at the same solidified surface position, the stress of plastic deformation will work, and the deformation of the iridium crucible will gradually increase. (See Patent Document 2).

In single crystal growth using the Cz method, the crystal weight is measured using a load cell placed above the pulling shaft, the crystal diameter is calculated from the weight increase per control cycle, and the high frequency output is changed based on the difference from the target diameter. Automatic Diameter Control (ADC) is used to control the diameter.

JP 2019-6612 Publication JP 2019-52067 Publication

However, there is a problem in that when the crucible is deformed, the calculated crystal diameter differs from the actual diameter. If crystal growth is performed in this deformed crucible, a single crystal will be grown with a crystal diameter that deviates from the target diameter.

For this reason, shape defects such as increases and decreases in crystal diameter due to crucible deformation, and crystal defects such as polycrystalization and crack defects are often observed, causing a decrease in productivity.

Therefore, the present invention was made with attention to such problems, and even if there is crucible deformation, automatic diameter control works accurately and effectively, and oxide single crystals can be grown with high productivity. The purpose is to provide a method for growing crystals.

In order to achieve the above object, a method for producing a single crystal according to one embodiment of the present invention heats and melts a raw material introduced into a crucible, and then brings a seed crystal into contact with the surface of the raw material melt and draws it while rotating. A method for producing a single crystal by the Cz method of growing a single crystal by raising the
A step of measuring the crystal weight with a load cell placed above the pulling shaft and calculating the crystal diameter from the amount of weight increase per control cycle;
In automatic diameter control that controls the diameter of a crystal to be grown by changing the output based on the difference from the target diameter, the amount of crucible deformation from the crucible inner diameter measured in advance is calculated, and the target diameter correction amount is calculated according to the amount of crucible deformation. and a step of calculating a correction coefficient for the pulling speed;
performing the automatic diameter control with the target diameter corrected by the target diameter correction amount and the pulling speed corrected by the pulling speed correction coefficient,
The single crystal is one selected from lithium tantalate, lithium niobate, and yttrium aluminum garnet.

According to the present invention, it is possible to suppress crystal shape defects due to crucible deformation, reduce crystal defects such as polycrystalization and crack defects, and improve productivity.

FIG. 1 is a cross-sectional view showing a schematic configuration of a high-frequency induction heating type single crystal growth apparatus. FIG. 3 is a diagram for explaining a method of calculating a crystal diameter. FIG. 3 is a diagram showing an example of the shape of a deformed crucible. FIG. 3 is a diagram for explaining an example of a method for measuring the inner diameter of a crucible. FIG. 3 is a diagram showing the pulling rate coefficient when a crucible of LT single crystal and a crucible diameter of φ210 mm is used. It is a figure showing the target diameter actual correction amount obtained from the crystal diameter Dc actually grown. FIG. 13 is a diagram for explaining a method of correcting the target value of the crystal diameter when the crucible diameter is increased. FIG. 3 is a diagram for explaining a method of correcting a target value of a crystal diameter when the crystal diameter decreases.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

First, with reference to FIG. 1, a configuration example of a single crystal growth apparatus using the Cz method and an overview of the single crystal growth method will be described. The single crystal growth apparatus using the Cz method according to the present invention uses lithium niobate LiNbO ₃ (hereinafter sometimes abbreviated as "LN"), which is grown in the air or in an oxygen-containing inert gas atmosphere. For the production of oxide single crystals such as lithium tantalate LiTaO ₃ (hereinafter sometimes abbreviated as "LT") and yttrium aluminum garnet Y ₃ Al ₅ O ₁₂ (hereinafter sometimes abbreviated as "YAG"). This is the single crystal growth equipment used.

FIG. 1 is a sectional view showing a schematic configuration of a high-frequency induction heating type single crystal growth apparatus. The high-frequency induction heating type single crystal growth apparatus includes a crucible 10, a refractory 20, a crucible stand 30, a work coil 40, a pulling shaft 50, a load cell 60, a chamber 70, a high-frequency power source 80, and a control section 90. Equipped with

A seed crystal holder 51 is provided at the lower end of the pulling shaft 50, and holds a seed crystal 110. A raw material melt 120 is stored and held within the crucible 10.

As shown in FIG. 1, the high-frequency induction heating type single crystal growth apparatus arranges a crucible 10 in a chamber 70. Crucible 10 is placed on crucible stand 30 via refractory 20 . A refractory material 20 is arranged in the chamber 70 so as to surround the crucible 10. A work coil 40 is arranged so as to surround the crucible 10, and a high frequency magnetic field generated by the work coil 40 causes an eddy current to flow in the wall of the crucible 10, so that the crucible 10 itself becomes a heating element. In this manner, in the high-frequency induction heating type single crystal growth apparatus, an eddy current is generated on the side wall of the crucible 10 installed in the work coil 40 due to the high-frequency magnetic field formed by the work coil 40, and the eddy current causes the crucible 10 to The crucible itself becomes a heating element and creates a temperature environment necessary for melting the raw material in the crucible 10 and growing crystals.

A pulling shaft (seed rod) 50 is provided in the upper part of the chamber 70 so as to be rotatable and movable in the vertical direction. The pulling shaft 50 is configured to be movable up and down by an upper pulling shaft drive motor 52. Further, a load cell 60 for measuring the weight of the crystal is attached to the tip of the upper end of the pulling shaft (seed rod) 50. A seed crystal holder 51 for holding the seed crystal 100 is attached to the lower end of the pulling shaft (seed rod) 50 . The chamber 70 covers components other than the pulling shaft 50, the pulling shaft driving motor 52, and the load cell 60.

Also, a control unit 90 for controlling the operation of the entire crystal growth apparatus, a storage unit 100 for storing automatic diameter control data being executed, and a unit for supplying power to the high frequency coil 40 and the entire single crystal growth apparatus. A power source 80 is provided outside the chamber 70.

In the Cz method, a single crystal piece serving as a seed crystal 110 is brought into contact with the surface of a single crystal raw material melt 120 in a crucible 10, and the seed crystal 110 is pulled upward while being rotated by a pulling shaft (seed rod) 50. As a result, a cylindrical single crystal having the same orientation as the seed crystal 110 is grown.

When growing an LT single crystal, the melting point of the LT crystal is 1650° C., so for example, a crucible 10 made of iridium (Ir), which is a high melting point metal, is used. Note that the crucible 10 is not limited to being made of iridium, and various high melting point metals that exceed the melting point of LT crystal, 1650° C., can be used.

The pulling speed during growth is generally approximately several mm/H, and the rotational speed is approximately several to several tens of rpm. Furthermore, the inside of the furnace during growth is generally a nitrogen-oxygen mixed gas atmosphere with an oxygen concentration of about several percent. After growing a single crystal to a desired size under such conditions, the grown crystal is separated from the raw material melt 120 by performing operations such as changing the pulling speed and gradually increasing the melt temperature. Thereafter, the power of the growth furnace is reduced at a predetermined rate to slowly cool the crystal, and after the temperature inside the furnace reaches around room temperature, the crystal is taken out from inside the growth furnace. Approximately half of the LT raw material remains in the crucible 10 after crystal growth compared to when the growth was started. The LT raw material remaining in the crucible 10 is used for the next growth, and the crucible 10 is filled with LT raw material corresponding to the weight of the pulled crystal, the raw material is melted, and crystal growth is repeated.

In single crystal growth using the Cz method, the weight of the crystal is measured by a load cell 60 placed above the pulling shaft 50, the crystal diameter is calculated from the weight increase per control cycle, and the high frequency output is changed based on the difference from the target diameter. Automatic Diameter Control (ADC) is used to control the diameter by adjusting the diameter. Note that the control period is not particularly limited, but is generally in the range of 1 minute to 5 minutes/time, and may be 2 minutes/time, for example. Specifically, from the crystal weight W measured by the load cell 60, the pulling distance dh by which the crystal was pulled at that time, the crucible diameter D _m , the crystal density ρ _c , and the melt density ρ _m , the crystal diameter is determined by formula (1). can be found. In addition, when ΔW, it is assumed that the crystal diameter Dc and the crucible diameter change Dm small.

なお、式（１）は以下のように算出される。

Note that equation (1) is calculated as follows.

As shown in FIG. 2, if the pulling distance of the single crystal 130 when growing the single crystal 130 is dh and the liquid surface drop distance of the raw material melt 120 is dH, the effective growth distance is given by formula (2).

微小時間に形成された単結晶１３０の重量と、原料融液１２０の減少重量は等しいので、式（３）が成立する。

Since the weight of the single crystal 130 formed in a minute time is equal to the reduced weight of the raw material melt 120, equation (3) holds true.

π(D _c /2) ² (dh+dH)ρ _c =π(D _m /2) ² dHρ _m (3)
Equation (4) is obtained from Equation (2) and Equation (3).

単結晶１３０が微小成長したときの重量変化量△Ｗは、単結晶１３０の微小成長により減少した原料融液１２０の重量に等しいので、式（５）が成立する。

Since the weight change amount ΔW when the single crystal 130 micro-grows is equal to the weight of the raw material melt 120 reduced due to the micro-growth of the single crystal 130, equation (5) holds true.

π(D _m /2) ² dHρ _m =△W (5)
By eliminating dH from equations (4) and (5), equation (1) is obtained.

In this way, the crystal diameter D _c is calculated from equation (1) using the weight increase amount ΔW of the single crystal 130 actually measured by the load cell 60 and the pulling distance dh.

The crystal diameter D _c calculated here is compared with the target crystal diameter, and the growth furnace heater output is adjusted and controlled so that the crystal diameter becomes a predetermined crystal diameter.

As described above, in crystal growth, approximately half of the LT raw material at the start of growth remains in the crucible 10 after crystal growth, and this LT raw material remaining in the crucible 10 is used for the next growth. The LT raw material equivalent to the pulled crystal weight W is filled into the iridium crucible, the raw material is melted, and the crystal growth is repeated. In this way, the raw material is repeatedly melted and cooled with the solidified raw material always remaining in the same position in the crucible 10, so the crucible side wall near the surface of the raw material remaining in the crucible 10 bulges outward, and the crucible side wall above the raw material surface gradually becomes constricted inward.

FIG. 3 is a diagram showing an example of the shape of such a deformed crucible 10. In FIG. 3, the region where the crucible side wall constricts inward is the region where crystal growth is performed. The crucible 10 becomes constricted and its inner diameter becomes smaller, which causes defects in crystal shape such as diameter defects and bending, polycrystalization, and cracks. Alternatively, the region expanding outward may gradually rise and the vicinity of the surface of the raw material remaining in the crucible 10 may spread. Therefore, the inventor of the present invention measured the inner diameter of the crucible 10, focused on correcting the target diameter of the ADC according to the amount of crucible deformation, and the change in the liquid level drop speed due to crucible deformation, and used a crucible with advanced deformation. As a result of conducting tests, we found that by adjusting the ADC target diameter correction amount and pulling speed according to the amount of crucible change, it was possible to suppress crystal shape defects, as well as polycrystalization and crack defects. .

In the above equation (1), the undeformed crucible diameter Dm is used as the calculated crystal diameter Dc. If the crucible is deformed, the crucible diameter Dm changes, so it is necessary to calculate the crystal diameter Dc accordingly. Furthermore, it is preferable to correct the pulling speed as well. This is because when the crucible deforms, the liquid level drop distance changes. When the crucible diameter Dm is large, the liquid level drop distance becomes small, and when the crucible diameter Dm is small, the liquid level fall distance becomes long. When the crucible diameter Dm in the region where crystal growth is performed is deformed so as to gradually become smaller, the effective growth distance gradually increases because the liquid level drop distance gradually increases during crystal growth.

Hereinafter, a method for correcting the target diameter of the ADC of the present invention will be described in detail.

FIG. 4 is a diagram for explaining a method of measuring the crucible 10. First, the crucible diameter (crucible inner diameter) Dm is measured in advance. The crucible diameter Dm is measured after the grown crystal is taken out. It is best to use a caliper gauge as a measuring device. The crucible 10 is rarely deformed while maintaining its symmetry. There are various ways of deformation, such as local swelling or constriction. For this reason, the measurement of the crucible diameter Dm approaches the true value as the number of measurement points increases, but as shown in FIG. 4(a), for each height position shown in FIG. 4(b), The diameter may be measured and the average value may be determined as the crucible diameter Dm. The crucible diameter Dm is measured in a range from the upper end of the crucible 10 to the solidified portion of the raw material in the crucible, as shown in FIG. 4(b). The measurement interval is not particularly limited, but it is preferable to measure continuously. A caliper gauge may measure, for example, at intervals of 10 mm.

Next, the initial undeformed crucible inner diameter Dm0 is subtracted from the average value of the crucible inner diameter measurements in four directions to obtain the amount of change in the crucible diameter. In addition, the crystal diameter Dc1 was determined from the crucible diameter Dm1 when the crucible was deformed using the above formula (1), and the calculated value of the crystal diameter (Dc0-Dc1) when there was no deformation was used as the target diameter calculation correction value.

Furthermore, when the crucible diameter Dm changes, the liquid level drop distance dH changes. Therefore, the liquid level drop distance dH when the crystal diameter Dc is fixed constant and the crucible diameter Dm is varied is calculated. If the liquid level drop distance when the crucible diameter Dm changes is dH', then the effective growth distance is (dG=dh+dH'). In order to match the effective growth distance (dG=dh+dH) which is the same as the crucible diameter Dm0 when new, it is sufficient to multiply it by the pulling rate coefficient a.

That is, the pulling speed coefficient a is determined from equation (6).

a(dh+dH')=(dh+dH) (6)
FIG. 5 shows the pulling rate coefficient when a LT single crystal crucible with a crucible diameter of φ210 mm is used. The liquid level drop distance dH is determined by the crystal density ρ _c , the melt density ρ _m , the crucible diameter Dm, and the crystal diameter Dc. Therefore, when the crucible diameter Dm changes, the pulling rate coefficient a also changes. The larger the crucible diameter Dm is, the smaller the slope of the pulling rate coefficient a tends to be. The relationship between the pulling rate coefficient a can be calculated for each crystal type, crucible diameter Dm, and crystal size (diameter) Dc. By adjusting the pulling speed in this way, the effective growth distance (dG = dh + dH) during crystal growth becomes the same effective growth distance (dG = dh + dH) as when using the undeformed crucible 10, and the effective growth It is possible to suppress the occurrence of crystal defects due to distance fluctuations, and reduce polycrystalization and crack defects.

Further, the target diameter correction amount may be changed from the target diameter calculation correction amount to the target diameter actual correction amount. A test was conducted using the above target diameter calculation correction amount (Dc0-Dc1) and pulling rate coefficient a, but when the amount of crucible deformation was large, the diameter dimensions of the grown crystals sometimes did not match. Therefore, when we performed the growth using the target diameter correction amount (Dc0-Dc1) and the pulling rate coefficient a and compared the grown crystal diameters, we found that the slope tended to be steeper and larger than the calculated value. Ta.

Figure 6 shows the results obtained from the actually grown crystal diameter Dc when the crucible diameter is φ210 mm and the crucible is deformed, using the target diameter calculation correction amount (Dc0-Dc1) and the pulling speed coefficient a. Indicates the target diameter actual correction amount. In FIG. 6, straight line A indicates the target diameter calculation correction amount, and straight line B indicates the target diameter actual correction amount.

In FIG. 6, when the amount of change in the crucible inner diameter is positive, the target diameter calculation correction amount A is larger than the target diameter actual correction amount B, and when the amount of change in the crucible inner diameter is negative, the target diameter actual correction amount B is larger than the target diameter calculation correction amount A.

Here, when the crucible diameter Dm is widening, it is preferable to perform control to make the target value of the crystal diameter Dc even smaller than the calculated value.

FIG. 7 is a diagram for explaining why it is preferable to perform such control. As shown in FIG. 7, when the crucible diameter Dm is widening, the weight change amount ΔW of the actual value becomes smaller than the calculated ΔW of the ADC. In this case, the ADC determines that the target diameter has not been reached and performs control to increase the crystal diameter, increasing the possibility that a single crystal 130 having a diameter larger than the target diameter will be grown. Therefore, in such a case, it is preferable to adjust the target value of the crystal diameter to be smaller than the calculated value.

On the other hand, when the crucible diameter Dm becomes narrow, it is preferable to set the target value of the crystal diameter Dc to be larger than the calculated value.

Figure 8 is a diagram to explain why it is preferable to perform such control. As shown in Figure 8, when the crucible diameter Dm becomes smaller, the weight change amount ΔW' of the actual value tends to become larger, and it is highly likely that the crystal diameter is determined to be thicker and the ADC performs control to make the crystal diameter thinner. Therefore, in this case, it is preferable to set the target value of the crystal diameter thicker than the calculated value and adjust it so that an appropriate thickness is ensured.

The difference between the actual value and the calculated value shown in FIG. 6 is considered to be because the crucible deforms in the direction of expansion at the lower part of the crucible. For this reason, the distribution of heat generation at the bottom of the crucible tends to be gentle, and it is presumed that this is the effect. Therefore, when the crucible variable is large, it is more preferable to use the actual target diameter correction amount, which corrects the slope more steeply than the calculated value, as the target diameter correction amount.

Next, the target diameter correction amount and pulling speed coefficient during growth are determined from the amount of deformation of the crucible 10 described above, the set value of automatic diameter control is corrected, and a single crystal is grown. Correction at this time can be made in accordance with the interval at which the deformation of the crucible is measured. For example, correction values may be determined and corrected at intervals of 10 mm from the start of crystal growth.

To set the correction value, for example, with reference to FIG. 6, the diameter of the crucible at the height of the raw material melt during crystal shoulder growth is 5 mm larger than when new, and the crucible diameter at the height of the raw material melt during growth of the lower part of the straight body is set. If the inner diameter is 10 mm smaller, the target diameter correction amount for the shoulder portion is -4 mm, and the target diameter correction amount for the lower part of the straight body is +8 mm. The target diameter for shoulder growth is set 4 mm smaller, and the target diameter for the lower part of the trunk is set 8 mm larger. Similarly, for the region from the shoulder to the lower part of the body, the target diameter correction amount may be determined from the measured crucible inner diameter, and the target diameter of the ADC step may be changed.

Next, the pulling speed coefficient is determined from the relationship diagram of the change in the crucible inner diameter and the pulling speed coefficient shown in Figure 5.

For example, if the inner diameter of the crucible at the height of the raw material melt during crystal shoulder growth is 5 mm larger than when new, and the inner diameter of the crucible at the height of the raw material melt during crystal shoulder growth is 10 mm smaller, the shoulder should be pulled up. The speed coefficient is 1.06, and the pulling speed coefficient of the lower part of the straight body is 0.87. The pulling speed is set to be the pulling speed during shoulder growth multiplied by 1.06, and the pulling speed is set to be the pulling speed of the lower part of the trunk multiplied by 0.87. Note that the interval at which the correction is performed is the interval at which the crucible diameter (crucible inner diameter) is measured. If there is a difference in the correction value between these intervals, the correction value may be controlled with a slope so that it changes gradually during this interval.

By correcting the automatic diameter control setting and growing the single crystal, a single crystal with a stable shape can be obtained.

These controls can be implemented by storing the contents of Figures 5 and 6 in the memory unit 100, and having the control unit 90 perform calculations and execute ADC while sequentially calculating the target diameter, target diameter calculation correction amount, target diameter actual correction amount, and lifting speed coefficient.

[Example]
Next, examples of the present invention will be specifically described.

[Example 1]
Using the high-frequency induction heating type single crystal growth apparatus shown in FIG. 1, an LT crystal with a crystal body diameter of 160 mm was grown using an iridium crucible with an inner diameter of 210 mm.

The crucible used was an iridium crucible that had been used 100 times.

First, the inner diameter of the crucible was measured using a caliper gauge. The diameters in the four directions shown in FIG. 2 were measured at 10 mm intervals from the top of the crucible. The amount of change in the inner diameter of the crucible corresponding to the surface position of the raw material melt was 10 mm from the upper end, and 20 mm was +1 mm from when it was new. The amount of change in the crucible inner diameter at the 30 mm, 40 mm, and 50 mm positions was -2 mm, the amount of change in the crucible inner diameter at the 60 mm, 70 mm, and 80 mm positions was -5 mm, and the amount of change in the crucible inner diameter at the 90 mm position was -8 mm.

From the relationship diagram between crucible inner diameter change amount and ADC target diameter correction amount shown in Fig. 3, when the target diameter correction amount is the target diameter actual correction amount, the ADC target diameter correction amount for 10 and 20 mm from the upper end is -0.8 mm, and the direct diameter correction amount is -0.8 mm. The correction amount at the 30mm, 40mm, and 50mm length positions is +1.6mm, the straight body length 60mm, 70mm, and 80mm positions is +4mm, and the straight body length 90mm position is +6.4mm, and the target diameter from the top to 20mm is 159mm. .2mm, the target diameter up to 50mm was changed to 161.6mm, the target diameter up to 80mm was changed to 164mm, and the ADC target diameter up to 90mm was changed to 166.4mm.

Next, from the relationship diagram between crucible diameter change amount and pulling speed coefficient shown in Fig. 4, the pulling speed coefficient at the position up to 20 mm from the upper end is 1.01, and the pulling speed coefficient at the position up to 50 mm is 0.98. , 0.94 for the position up to 80 mm, and 0.90 for the position up to 90 mm, and the values were changed to the respective pulling speeds multiplied by the pulling speed coefficient, and LT single crystal growth was performed.

A crack-free LT single crystal with a straight body length of 120 mm was obtained. When the diameter of the straight body was measured, the crystal diameter was 161 mm to 157 mm, and a crystal with no diameter defect was obtained.

[Example 2]
The configuration shown in FIG. 1 was constructed using an iridium crucible that had been used 150 times in a high-frequency induction heating furnace. The constructed crucible was deformed in such a way that the mouth of the crucible widened and the sides of the crucible became constricted, so it was expected that defects in crystal shape would occur. Therefore, before filling the LT raw material, the inner diameter of the crucible was measured using a caliper gauge, the ADC target diameter was corrected and the pulling speed was adjusted in advance, and then the LT single crystal was grown.

First, the diameters in the four directions shown in FIG. 2 were measured at 10 mm intervals from the upper end of the crucible. The amount of change in the inner diameter of the crucible at positions 10 mm and 20 mm from the upper end was +4 mm compared to when it was new. The crucible inner diameter change at the surface of the raw material melt with a straight body length of 30 mm is ±0 mm, the crucible inner diameter change at the 40 mm, 50 mm, and 60 mm positions is -5 mm, and the crucible inner diameter change at the 70, 80 mm, and 90 mm positions is -10 mm. there were.

Then, from the relationship diagram of crucible inner diameter change amount and ADC target diameter correction amount shown in FIG. 3, the target diameter correction amount for 10 mm and 20 mm from the upper end is -3.2 mm and 30 mm, assuming the target diameter correction amount as the target diameter actual correction amount. The position correction amount is ±0mm, 40mm, 50mm, 60mm position is +4mm, 70mm, 80mm, 90mm position is +8mm, target diameter up to 20mm from the top is 156.8mm, target diameter up to 30mm is 160mm, 60mm. The target diameter up to the 90 mm position was set to 164 mm, and the target diameter up to the 90 mm position was 168 mm.

Next, from the relationship diagram of crucible inner diameter variation and pulling speed coefficient shown in FIG. 4, the pulling speed coefficient at 10 mm and 20 mm from the upper end is 1.05, and the pulling speed coefficient at a position where the straight body length is 30 mm is 1. The pulling speed coefficient at the 00, 40 mm, 50 mm, and 60 mm positions is 0.94, and the pulling speed coefficient at the 70 mm, 80 mm, and 90 mm positions is 0.87, and the pulling speed of each ADC step is multiplied by the adjustment multiplier. Changed to numerical value.

When the LT raw material was filled and crystal growth was performed, a crack-free LT single crystal with a straight body length of 120 mm was obtained. The diameter of the straight body was 160 mm to 154 mm, and crystals without diameter defects were obtained.

[Example 3]
Using an iridium crucible that had been used 100 times, LT single crystal growth was performed 20 times by correcting the ADC target diameter and adjusting the pulling speed in accordance with the amount of change in the crucible inner diameter in the same manner as in Example 1. Note that the target diameter correction amount was the actual target diameter correction amount.

Eighteen LT single crystals with a straight body length of 120 mm and no cracks or defective diameters were obtained, and the growth yield was 90%. The breakdown of defects was one polycrystalline and one crack.

[Example 4]
Using an iridium crucible that had been used 100 times, LT single crystal growth was performed 20 times by adjusting the target diameter calculation correction amount and pulling speed according to the amount of change in crucible diameter in the same manner as in Example 1. Note that the target diameter correction amount was the target diameter calculation correction amount.

Sixteen LT single crystals with a straight body length of 120 mm without any diameter defects or cracks were obtained, and the growth yield was 80%. The breakdown of the defects was three due to polycrystalline defects and one defective due to cracking.

[Comparative example 1]
Using an iridium crucible that has been used 100 times, LT single crystal growth was performed 20 times by adjusting only the pulling speed according to the amount of change in the crucible inner diameter and without correcting the ADC target diameter. Other conditions were the same as in Example 1.

Twelve crack-free LT single crystals with a straight body length of 120 mm were obtained, and the growth yield was 60%. The breakdown of the defects was that 4 were polycrystalline and 4 were cracked. When the diameter of the straight body part was measured, the diameter of the straight body part was 163 mm to 151 mm. A portion of the straight body was less than 153 mm, resulting in a diameter defect.

As described above, according to this example, by carrying out the method for manufacturing a single crystal according to this embodiment, even if the inner diameter of the crucible 10 changes due to use, it does not affect the manufacturing of the single crystal and can be maintained at a predetermined level. It has been shown that it is possible to produce single crystals with uniform diameters within the range of .

As explained above, according to the method for growing an oxide single crystal according to the present invention, the inner diameter of the crucible is measured, and the ADC target diameter is corrected and the pulling speed is adjusted according to the amount of change in the crucible inner diameter. It becomes possible to suppress crystal defects such as polycrystalization and cracks caused by crystal shape and effective growth distance, and diameter defects, thereby improving productivity and reducing costs.

Although the preferred embodiments and examples of the present invention have been described in detail above, the present invention is not limited to the embodiments and examples described above, and can be applied to the examples described above without departing from the scope of the present invention. Various modifications and substitutions may be made.

The present invention can be used in the production of single crystals using the Cz method.

10 crucible 20 refractory 30 crucible stand 40 coil heater 50 pulling shaft 51 seed crystal holding section 52 pulling shaft driving motor 60 load cell 70 chamber 80 high frequency power supply 90 control section 100 storage section

Claims (4)

A method for producing a single crystal by the Cz method, in which a raw material put into a crucible is heated and melted, and then a seed crystal is brought into contact with the surface of the raw material melt and the single crystal is grown by pulling up while rotating, the method comprising:
a step of measuring the crystal weight with a load cell placed above the pulling shaft and calculating the crystal diameter from the amount of weight increase per control cycle;
In automatic diameter control that controls the diameter of a crystal to be grown by changing the output based on the difference from the target diameter, the amount of crucible deformation from the crucible inner diameter measured in advance is calculated, and the target diameter is corrected according to the amount of crucible deformation. a step of calculating a correction coefficient for the amount and the pulling speed;
performing the automatic diameter control with the target diameter corrected by the target diameter correction amount and the pulling speed corrected by the pulling speed correction coefficient,
A method for producing a single crystal, wherein the single crystal is one selected from lithium tantalate, lithium niobate, and yttrium aluminum garnet. 2. The method for manufacturing a single crystal according to claim 1, wherein the target diameter correction amount is an actual target diameter correction amount. 3. The single crystal manufacturing method according to claim 2, wherein the calculation of the target diameter correction amount differs depending on whether the crucible deformation amount is an increase or a decrease. 3. The method for producing a single crystal according to claim 1, wherein the step of calculating the target diameter correction amount and the pulling rate correction coefficient in accordance with the amount of crucible deformation is performed based on a predetermined conversion formula or conversion table.

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