Method and device for producing oxide single crystal

Abstract

This method for producing an oxide single crystal is characterized by comprising: a first step for heating a single crystal raw material (8) in a crucible (6) so as to melt a portion of the single crystal raw material (8); a second step for producing a raw material melt (8) by heating the single crystal raw material (8) so as to melt all of the single crystal raw material (8), and bringing the seed crystal (2) into contact with the liquid surface of the raw material melt (8); a third step in which the seed rod (3) is pulled while the weight of the seed rod (3) is measured, the output power of the heating source (7) is adjusted so that the single crystal pulling weight rate of the single crystal grown from the seed crystal (2) becomes a prescribed value, the neck portion, the tapered portion, and the straight body portion of the single crystal are formed from the seed crystal, and the single crystal in which the straight body portion has been formed is separated from the liquid surface; and a fourth step for slowly cooling the single crystal separated from the liquid surface at a predetermined output power of the heating source (7). And the first to fourth steps are automatically operated. The apparatus for producing an oxide single crystal according to the present invention is a production apparatus capable of automatically operating the first to fourth steps. According to the present invention, it is possible to provide a method for producing an oxide single crystal and a device for producing an oxide single crystal, whereby the burden on an operator is reduced, the error of the operator is eliminated, and the yield of the oxide single crystal is improved.

Description

Technical Field

[0001] The present invention relates to a method and a device for producing an oxide single crystal. Background Art

[0002] The Czochralski method is also called the Czochralski method. It is a method in which a single crystal raw material is heated and melted in a crucible to form a raw material melt, and then a seed crystal is brought into contact with the melt and pulled while rotating to grow a single crystal.

[0003] In this method, since the single crystal does not come into contact with the crucible, mechanical strain due to the crucible does not occur, and thus it has the advantage of being easy to produce a high-quality and large-diameter crystal.

[0004] Therefore, yttrium aluminum garnet (Y3Al5O 12 , YAG), sapphire (Al2O3), lithium niobate (LiNbO3, LN), lithium tantalate (LiTaO3, LT), bismuth germanate (Bi4Ge3O 12 , BGO) and other oxide single crystals are mostly produced by this method.

[0005] However, in the growth of oxide single crystals based on the Czochralski method, the optimization of the seeding operation of bringing the seed crystal into contact with the raw material melt is an important factor in determining the quality of the grown crystal. For example, when the seeding operation is performed at an appropriate time, the meniscus diameter of the crystal is stable, so high-quality single crystals can be grown.

[0006] In the past, the timing of seeding was determined by a skilled operator who observed the state of the furnace through an observation window, relying on the operator's experience and intuition. Therefore, there were sometimes differences in the timing of seeding between operators, and the success rate of single crystal growth became insufficient.

[0007] In order to solve this problem, methods for suppressing the timing deviation of seeding operation between operators have been studied. For example, in the seeding operation method described in Patent Document 1, the measured crucible bottom temperature is substituted into a prescribed relationship to calculate the crucible bottom temperature during the seeding operation, and the seeding operation is performed when the measured crucible bottom temperature reaches the calculated crucible bottom temperature.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent document 1: Japanese Patent No. 6575764. Summary of the invention

[0011] Problems to be solved by the invention

[0012] In order to find the relationship between the crucible bottom temperature when the raw material is melted and the crucible bottom temperature during the seeding operation, a skilled person must perform seeding operations on one crucible 6 to 11 times in order to accurately investigate the relationship between the crucible bottom temperature when the raw material is melted and the crucible bottom temperature during the seeding operation. Therefore, in the seeding operation method described in Patent Document 1, it is very time-consuming to find the relationship. In addition, since there will be a timing deviation in the seeding operation between operators, it is preferred that a specific skilled person find the relationship. Therefore, in the seeding operation method described in Patent Document 1, it is sometimes more time-consuming to find the relationship. In addition, usually the operator takes into account multiple seeding operations, so even if the crucible bottom temperature suitable for the seeding operation is calculated by the calculation formula, sometimes the seeding operation cannot be performed at the timing of the crucible bottom temperature. Therefore, the following problems arise: since the seeding operation is performed at a temperature higher than the appropriate temperature, the seed rod is separated from the liquid surface; or since the seeding operation is performed at a temperature lower than the appropriate temperature, the raw material melt around the seed rod solidifies, etc.

[0013] Furthermore, it is considered that if an operator performs seeding operations on multiple machines, the burden on the operator increases, and as a result, the influence of variations in operating efficiency between operators increases, which may affect variations in oxide single crystal yields between operators.

[0014] In order to solve the above-mentioned problems, an object of the present invention is to provide a method for producing an oxide single crystal and an apparatus for producing an oxide single crystal, which can reduce the burden on an operator and eliminate operator errors, thereby improving the yield of the oxide single crystal.

[0015] Means of solving problems

[0016] The present inventors have conducted intensive research and found that the above-mentioned problems can be solved by automatically operating the seeding operation, thereby completing the present invention. That is,

[0017] [1] A method for producing an oxide single crystal, comprising heating and melting a single crystal raw material put into a crucible using a heating source to prepare a raw material melt, bringing a seed crystal into contact with the raw material melt, and producing the oxide single crystal by a rotary pulling method, characterized in that it comprises the following steps:

[0018] The first step is to heat the raw material for single crystal in the crucible with the output power of the heating source that melts a part of the raw material for single crystal, or to adjust the output power of the heating source so that the temperature of the raw material for single crystal reaches a first temperature that melts a part of the raw material for single crystal, thereby heating the raw material for single crystal in the crucible;

[0019] The second step is to adjust the output power of the heating source so that the temperature of the raw material melt in the crucible reaches a second temperature at which all the raw materials for single crystals are melted, thereby heating the raw materials for single crystals to produce a raw material melt, and lowering a seed rod having a seed crystal at the front end so that the seed crystal contacts the liquid surface of the raw material melt;

[0020] A third step is to adjust the output power of the heating source so that the weight of the single crystal grown from the seed crystal reaches a predetermined value while the seed crystal rod is lifted while measuring the weight of the seed crystal rod, thereby forming a neck portion, a tapered portion, and a straight body portion of the single crystal from the seed crystal, and separating the single crystal having the straight body portion formed therein from the liquid surface; and

[0021] The fourth step is to slowly cool the single crystal separated from the liquid surface with a predetermined output power of the heating source;

[0022] The first step to the fourth step are automatically operated.

[0023] [2] A method for manufacturing an oxide single crystal according to the above-mentioned [1], wherein in the first step and the second step, the liquid surface temperature of the raw material melt in the crucible is measured using a radiation thermometer through an observation window provided so as to be able to observe the liquid surface of the raw material melt in the crucible, and the output power of the heating source is adjusted based on the measured liquid surface temperature.

[0024] [3] A method for manufacturing an oxide single crystal according to the above-mentioned [2], wherein, when the inner diameter of the crucible at the liquid surface position of the raw material melt is set to R, the distance between the position where the liquid surface temperature of the raw material melt is measured and the center position of the liquid surface of the raw material melt is less than 2 / 3R.

[0025] [4] The method for producing an oxide single crystal according to [2] above, wherein the liquid surface temperature at a seeding position with which the seed crystal contacts is measured.

[0026] [5] The method for producing an oxide single crystal according to [2] above, wherein the distance between the position where the temperature of the liquid surface of the raw material melt is measured and the position of the liquid surface of the raw material melt with which the seed crystal contacts is 15 mm or more.

[0027] [6] The method for producing an oxide single crystal according to any one of [2] to [5] above, wherein, at least in the second step, an atmospheric gas is introduced into the surface of the observation window to prevent fogging of the observation window.

[0028] [7] The method for producing an oxide single crystal according to any one of [1] to [6] above, wherein in the second step, the output power of the heating source is adjusted to an output power that is smaller than the following maximum output power and larger than the following minimum output power:

[0029] Maximum output power: the output power of the heating source that makes the temperature of the raw material melt reach the temperature for melting the seed crystal;

[0030] Minimum output power: the output power of the heating source for the heating source to generate heat corresponding to latent heat associated with melting of the raw material for single crystal.

[0031] [8] The method for producing an oxide single crystal according to any one of [1] to [7] above, wherein:

[0032] In the second step, the seed crystal rod is lowered while measuring the weight of the seed crystal rod, and when the weight of the seed crystal rod changes by 0.5 g or more, it is determined that the seed crystal is in contact with the liquid surface of the raw material melt.

[0033] In the second step, while the seed crystal is brought into contact with the liquid surface of the raw material melt, the output power of the heating source is adjusted so that the temperature of the raw material melt reaches a third temperature at which the raw material melt under the seed crystal is deprived of latent heat and solidifies, thereby heating the raw material melt, and then the seed crystal is brought into contact with the liquid surface of the raw material melt. Then, while the absolute value of the weight change after maintaining for 10 minutes is less than 1 g, transfer to the third step.

[0034] [9] An oxide single crystal manufacturing device, which uses a heating source to heat and melt a single crystal raw material put into a crucible to prepare a raw material melt, brings a seed crystal into contact with the raw material melt, and manufactures an oxide single crystal by a rotary pulling method, characterized in that it comprises:

[0035] A seed rod with a seed crystal at the front end,

[0036] a weighing sensor for measuring the weight of the seed rod,

[0037] a pulling and rotating driving mechanism for pulling up the seed crystal rod while rotating it,

[0038] a heating source for heating and melting the raw material for single crystal put into the crucible,

[0039] a thermometer for measuring the temperature of the single crystal raw material and the raw material melt in the crucible, and

[0040] A control unit for controlling the lifting and rotating driving mechanism and the heating source;

[0041] The control unit implements the following steps:

[0042] The first step is to heat the raw material for single crystal in the crucible with the output power of the heating source that melts a part of the raw material for single crystal, or to adjust the output power of the heating source so that the temperature of the raw material for single crystal reaches a first temperature that melts a part of the raw material for single crystal, thereby heating the raw material for single crystal in the crucible;

[0043] The second step is to adjust the output power of the heating source so that the temperature of the raw material melt in the crucible reaches a second temperature at which all the raw materials for single crystals are melted, thereby heating the raw materials for single crystals to produce a raw material melt, and lowering a seed rod having a seed crystal at the front end so that the seed crystal contacts the liquid surface of the raw material melt;

[0044] A third step is to adjust the output power of the heating source so that the weight of the single crystal grown from the seed crystal reaches a predetermined value while the seed crystal rod is lifted while measuring the weight of the seed crystal rod, thereby forming a neck portion, a tapered portion, and a straight body portion of the single crystal from the seed crystal, and separating the single crystal having the straight body portion formed therein from the liquid surface; and

[0045] In the fourth step, the single crystal separated from the liquid surface is slowly cooled with a predetermined output power of the heating source.

[0046]

[10] The device for producing an oxide single crystal according to [9] above, wherein:

[0047] The thermometer is a radiation thermometer,

[0048] In the first step and the second step, the control unit uses the radiation thermometer through an observation window provided to observe the liquid surface of the raw material melt in the crucible, and adjusts the output power of the heating source based on the measured liquid surface temperature of the raw material melt.

[0049]

[11] An oxide single crystal manufacturing device according to the above-mentioned

[10] , wherein, when the inner diameter of the crucible at the liquid surface position of the raw material melt is set to R, the distance between the position where the liquid surface temperature of the raw material melt is measured and the center position of the liquid surface of the raw material melt is less than 2 / 3R.

[0050]

[12] The device for producing an oxide single crystal according to

[10] above, wherein the liquid surface temperature at a seeding position with which the seed crystal contacts is measured.

[0051]

[13] An oxide single crystal manufacturing apparatus according to

[10] above, wherein the distance between the position where the liquid surface temperature of the raw material melt is measured and the position of the liquid surface of the raw material melt with which the seed crystal contacts is 15 mm or more.

[0052]

[14] The manufacturing device of an oxide single crystal according to any one of

[10] to

[13] above, wherein the manufacturing device further comprises an observation window fogging prevention device for introducing an atmospheric gas into the surface of the observation window to prevent fogging of the observation window,

[0053] The control unit prevents the observation window from fogging by using the observation window fogging prevention device at least in the second step.

[0054]

[15] According to the oxide single crystal manufacturing device described in any one of [9] to

[14] above, the control unit adjusts the output power of the heating source in the second step at an output power smaller than the following maximum output power and larger than the following minimum output power:

[0055] Maximum output power: the output power of the heating source that makes the temperature of the raw material melt reach the temperature for melting the seed crystal;

[0056] Minimum output power: the output power of the heating source for the heating source to generate heat corresponding to latent heat associated with melting of the raw material for single crystal.

[0057]

[16] The device for producing an oxide single crystal according to any one of [9] to

[15] above, wherein:

[0058] The control unit lowers the seed crystal rod while measuring the weight of the seed crystal rod in the second step, and determines that the seed crystal is in contact with the liquid surface of the raw material melt when the weight of the seed crystal rod changes by 0.5 g or more.

[0059] The control unit further adjusts the output power of the heating source in the second step, while the seed crystal is in contact with the liquid surface of the raw material melt, so that the temperature of the raw material melt reaches a third temperature at which the raw material melt under the seed crystal is deprived of latent heat and solidifies, thereby heating the raw material melt, and then brings the seed crystal into contact with the liquid surface of the raw material melt, and then, transfers to the third step while maintaining the absolute value of the weight change at 1 g or less for 10 minutes.

[0060] Effects of the Invention

[0061] According to the present invention, a method for producing an oxide single crystal and an apparatus for producing an oxide single crystal can be provided, which can reduce the burden on operators and eliminate operator errors, thereby improving the yield of oxide single crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] [ Figure 1 ] Figure 1 This is a schematic diagram of an oxide single crystal production apparatus according to one embodiment of the present invention.

[0063] [ Figure 2 ] Figure 2 (a) is a schematic diagram of an observation window of the production apparatus of the oxide single crystal used in Example 1 when observing the observation window from above, Figure 2 (b) Yes Figure 2 (a) AA cross-section view.

[0064] [ Figure 3 ] Figure 3 It is a graph showing the change in output power (power) of the heating source in the first step and the second step of Example 1, the liquid surface temperature of the raw material melt measured by a radiation thermometer, the crucible bottom temperature measured by a thermocouple, and the weight change of the seed rod measured by a weighing sensor.

[0065] [ Figure 4 ] Figure 4 This is a graph showing the heating temperature setting pattern of the single crystal raw material and the raw material melt in the crucible in the second step of Example 1. DETAILED DESCRIPTION

[0066] [Method for producing oxide single crystal]

[0067] The method for manufacturing an oxide single crystal of the present invention is to use a heating source to heat and melt a raw material for a single crystal put into a crucible to make a raw material melt, make a seed crystal contact with the raw material melt, and manufacture an oxide single crystal by a rotary pulling method. The method for manufacturing an oxide single crystal is characterized by comprising the following steps: a first step, heating the raw material for a single crystal in the crucible with an output power of the heating source that melts a portion of the raw material for a single crystal, or adjusting the output power of the heating source so that the temperature of the raw material for a single crystal reaches a first temperature that melts a portion of the raw material for a single crystal, thereby heating the raw material for a single crystal in the crucible; a second step, adjusting the output power of the heating source so that the raw material melt in the crucible The temperature reaches a second temperature at which all the raw materials for single crystals are melted, thereby heating the raw materials for single crystals to prepare a raw material melt, and lowering a seed rod having a seed crystal at the front end so that the seed crystal contacts the liquid surface of the raw material melt; in a third step, while measuring the weight of the seed rod and lifting the seed rod, the output power of the heating source is adjusted in such a way that the single crystal lifting weight speed of the single crystal grown from the seed crystal reaches a specified value, the neck, the cone and the straight body of the single crystal are formed from the seed crystal, and the single crystal with the straight body formed is separated from the liquid surface; and in a fourth step, the single crystal separated from the liquid surface is slowly cooled with a predetermined output power of the heating source; and the first to fourth steps are automatically operated. Thus, the burden on the operator can be reduced, the operator's mistakes can be eliminated, and the yield rate of the oxide single crystal can be improved.

[0068] (First process)

[0069] In the first step, the single crystal raw material in the crucible is heated with the output power of the heating source that melts a portion of the single crystal raw material, or the output power of the heating source is adjusted so that the temperature of the single crystal raw material reaches the first temperature that melts a portion of the single crystal raw material, thereby heating the single crystal raw material in the crucible.

[0070] The heating source may include, for example, a resistance heating source, a high-frequency induction heating source, etc. The high-frequency induction heating source is preferably suitable for high-melting-point oxides. The high-frequency induction heating source uses a metal crucible such as platinum or iridium as a crucible into which the single crystal raw material is put, and heats the molten single crystal raw material by induction heating the metal crucible. The output power of the heating source is controlled, for example, by a high-frequency constant current control method.

[0071] The heating time when the raw material for single crystal in the crucible is heated at an output of the heating source at which a part of the raw material for single crystal is melted is, for example, 1 to 10 hours, preferably 1 to 4 hours.

[0072] The output power of the heating source for melting a portion of the raw material for a single crystal can be obtained, for example, by heating the raw material for a single crystal while observing the condition in the crucible loaded with the raw material for a single crystal through an observation window to investigate the output power of the heating source when a portion of the raw material for a single crystal is melted.

[0073] As a thermometer for measuring the temperature of the raw material for single crystal, for example, a thermocouple in contact with the bottom of the crucible, a radiation thermometer for detecting the temperature of the crucible wall, a radiation thermometer for detecting the liquid surface temperature of the raw material melt in the crucible, etc. can be used. Since the thermocouple in contact with the bottom of the crucible will deteriorate during the repeated production of oxide single crystals, so that the temperature detection accuracy becomes poor, it is preferable to use a radiation thermometer for measurement; since the oxide single crystal is grown at the liquid surface of the raw material melt in the crucible, it is more preferable to use a radiation thermometer to detect the liquid surface temperature of the raw material melt in the crucible. For example, the temperature of the raw material melt can be measured using a radiation thermometer through an observation window, and the output power of the heating source can be adjusted based on the measured temperature.

[0074] The first temperature can be obtained, for example, by observing the condition in the crucible containing the single crystal raw material through an observation window while heating a portion of the melted single crystal raw material, and measuring the temperature when a portion of the single crystal raw material is melted. When the oxide single crystal to be produced is lithium tantalate, the first temperature is, for example, 1580°C.

[0075] (Second process)

[0076] In the second step, the output power of the heating source is adjusted so that the temperature of the raw material melt in the crucible reaches the second temperature at which all the raw materials for single crystal are melted, thereby heating the raw materials for single crystal to produce the raw material melt, and lowering the seed rod having a seed crystal at the front end so that the seed crystal contacts the liquid surface of the raw material melt. The temperature of the raw material melt in the crucible can be measured by the same method as the temperature of the single crystal raw material in the first step.

[0077] The second temperature can be obtained, for example, by observing the state of the crucible filled with the single crystal raw material through an observation window while heating the single crystal raw material, and measuring the temperature when all the single crystal raw material is melted. When the oxide single crystal to be produced is lithium tantalate, the second temperature is, for example, 1630°C.

[0078] When the seed crystal is brought into contact with the liquid surface of the raw material melt, it is preferred to adjust the output power of the heating source so that the temperature of the raw material melt reaches the third temperature at which the raw material melt under the seed crystal is deprived of latent heat and solidified, thereby heating the raw material melt. Thus, the seeding operation can be started at an appropriate time. When the seed crystal is brought into contact with the liquid surface of the raw material melt, the third temperature at which the raw material melt under the seed crystal is deprived of latent heat and solidified, specifically, is the temperature of the raw material melt when a skilled person in the seeding operation starts the seeding operation. When the oxide single crystal manufactured is lithium tantalate, the third temperature is, for example, 1639°C.

[0079] As described above, the thermocouple in contact with the bottom of the crucible will deteriorate during the repeated manufacture of oxide single crystals, so that the detection accuracy of the temperature deteriorates. Therefore, it is preferred to use a radiation thermometer to measure the liquid surface temperature of the raw material melt through an observation window to determine the temperature (the third temperature) of the raw material melt for implementing the seeding operation. Thus, regardless of the manufacturing device used, the temperature of the raw material melt at which a skilled person in the seeding operation starts the seeding operation can be directly applied as the temperature for starting the seeding operation. Then, based on the liquid surface temperature of the position of the contact seed measured by a radiation thermometer through an observation window set to be able to observe the liquid surface of the raw material melt in the crucible, the output power of the heating source is adjusted so that the liquid surface temperature reaches the third temperature, thereby even if the operator is not a skilled person in the seeding operation, the operator can start the seeding operation at the same time as the skilled person in the seeding operation.

[0080] In addition, when the inner diameter of the crucible at the liquid surface position of the raw material melt is set to R, the measurement position of the liquid surface temperature of the raw material melt can be any position within a distance of 2 / 3R or less from the center position of the liquid surface of the raw material melt. In this case, the measurement range of the liquid surface temperature of the raw material melt is within a range of about 5 to 10 mmφ centered on the measurement position. In the area at a distance of 2 / 3R or less from the center position of the liquid surface of the raw material melt, the temperature gradient of the liquid surface becomes smaller than that near the outer peripheral side of the crucible, so the repeatability of the temperature control is good. The measurement position of the liquid surface temperature of the raw material melt is preferably any position within a distance of 1 / 2R or less from the center position of the liquid surface of the raw material melt.

[0081] The position for measuring the liquid surface temperature may also be the position where the seed crystal is brought into contact. In this case, the range for measuring the liquid surface temperature of the raw material melt is within a range of about 5 to 10 mmφ centered at the measuring position. By measuring the liquid surface temperature at such a position, the raw material melt can be controlled at an appropriate temperature for seeding until just before the seed crystal is brought into contact.

[0082] In addition, the measurement position of the liquid surface temperature may also be a remote position at a distance of more than 15 mm from the seeding position. In this case, the measurement range of the liquid surface temperature of the raw material melt is within a range of about 5 to 10 mmφ centered on the measurement position. At the moment when the seed rod is lowered and the seed contacts the raw material melt, the temperature of the raw material melt around the seed sometimes drops, but by doing so, the measured value of the radiation thermometer is not easily affected by the temperature drop, and the action of excessively increasing the output power of the heating source in order to follow the decrease in the temperature measurement value of the radiation thermometer can be suppressed. The measurement position of the liquid surface temperature is preferably a remote position at a distance of more than 20 mm from the seeding position.

[0083] Before lowering the seed rod and making the seed contact the liquid surface of the raw material melt, it is preferred to keep it in a range of more than 5mm and less than 40mm from the liquid surface of the raw material melt for more than 5 minutes. Thus, the seed can be raised to a temperature close to the raw material melt by the radiant heat from the raw material melt and the crucible. By doing so, the thermal shock to the seed when the seed contacts the raw material melt can be alleviated. In addition, the temperature of the raw material melt can also be suppressed from sharply decreasing and solidifying. If the distance from the melt is closer than 5mm, the seed may contact the raw material melt. If it is farther than 40mm, the radiant heat is weak and the temperature rise of the seed is insufficient. In the case of a holding time of less than 5 minutes, the temperature rise of the seed may also be insufficient. It is further preferred to be in a range of more than 10mm and less than 30mm from the liquid surface of the raw material melt. For the distance from the seed to the liquid surface, the volume can be calculated from the weight of the raw material melt, the position of the melt interface can be calculated from the shape of the crucible, and the distance to the interface can be calculated from the moving distance of the seed rod. In addition, the distance to the interface can also be directly measured by a laser sensor or the like.

[0084] Preferably, at least in the second step, the atmospheric gas is introduced into the surface of the observation window to prevent the fogging of the observation window. Thereby, the accuracy of the temperature measured by the observation window using a radiation thermometer can be further improved. It should be noted that the evaporated melt and metal oxide solidify on the observation window with a low temperature and adhere to the observation window, which is the cause of the fogging of the observation window. In addition, the atmospheric gas is the atmospheric gas when the oxide single crystal is pulled from the raw material melt. In the case where the oxide single crystal is lithium tantalate, the atmospheric gas is, for example, a mixed gas of 1 volume % oxygen and 99 volume % nitrogen. The flow rate of the atmospheric gas when introducing the atmospheric gas is not particularly limited as long as it can prevent the fogging of the observation window, and is preferably 3 to 200 m / min, and more preferably 30 to 150 m / min. It should be noted that in the first step, when the temperature of the raw material melt is measured by a radiation thermometer through the observation window, it is also preferred to introduce the atmospheric gas to prevent the fogging of the observation window.

[0085] When the seed crystal rod is lowered so that the seed crystal contacts the liquid surface of the raw material melt, it is preferred to lower the seed crystal rod while measuring the weight of the seed crystal rod. Then, preferably, when the weight of the seed crystal rod changes by more than 0.5 g, it is determined that the seed crystal contacts the liquid surface of the raw material melt. Thus, the contact between the seed crystal and the liquid surface of the raw material melt can be determined with higher accuracy. In addition, the deviation of the contact between the seed crystal and the liquid surface of the raw material melt between operators becomes smaller.

[0086] When the seed crystal rod is lowered so that the seed crystal contacts the liquid surface of the raw material melt, the seed crystal rod is preferably lowered slowly. Specifically, the lowering speed of the seed crystal rod when the seed crystal contacts the liquid surface of the raw material melt is preferably 0.01 to 1 mm / sec, more preferably 0.05 to 0.5 mm / sec.

[0087] It is preferred that the pulling of the oxide single crystal is started when the absolute value of the weight change when the seed crystal is kept in contact with the liquid surface of the raw material melt for 10 minutes is less than 1g. Thus, the pulling of the oxide single crystal (the third process) can be started at a more appropriate time. It should be noted that when the absolute value of the weight change when the seed crystal is kept for 10 minutes is greater than 1g, the operator is notified by the device through an alarm, for example. Then, the operator performs the seeding operation again. Specifically, it is believed that because the seed crystal rod is separated from the liquid surface when the weight reduction is greater than 1g, the set temperature of the liquid surface is slightly adjusted to a lower level. On the other hand, it is believed that because solidification occurs around the seed crystal rod when the weight increase is greater than 1g, the set temperature of the liquid surface is slightly adjusted to a higher level. Through these operations, the temperature of the liquid surface can be set to the correct appropriate temperature. For whether the set temperature is an appropriate temperature, the seeding operation can be repeated again, and it can be judged by whether the absolute value of the weight reaches less than 1g. By the seeding operation again, when the temperature of the liquid surface reaches an appropriate temperature, pulling (the third process) can be started.

[0088] In the second step, the output power of the heating source is preferably adjusted to an output power smaller than the maximum output power described below and larger than the minimum output power described below. By making the output power of the heating source larger than the minimum output power described below, the output power of the heating source can be used only for the latent heat when the solid turns into a liquid, thereby suppressing the time extension for the temperature of the raw material melt to reach the desired temperature. In addition, by making the output power of the heating source smaller than the maximum output power described below, it is possible to suppress a sharp rise in the temperature of the raw material melt or melting of the seed crystal.

[0089] Maximum output power: The output power of the heating source that makes the temperature of the raw material melt reach the temperature of the molten seed crystal

[0090] Minimum output power: The output power of the heating source used to generate the latent heat associated with the melting of the single crystal raw material

[0091] It should be noted that those skilled in seeding know from experience the output of the heating source that reaches the temperature of the molten seed crystal and the output of the heating source when the temperature of the raw material melt hardly rises. Therefore, the output of these heating sources can be used as the maximum output and the minimum output, respectively.

[0092] During the period when the temperature of the raw material melt changes from the second temperature to the third temperature, the temperature of the raw material melt can be heated to a temperature higher than the second temperature and the third temperature, that is, a fourth temperature. In this way, the raw material for the single crystal can be further completely melted, and the convection of the raw material melt is increased, so that the raw material melt can be made more uniform. In the case where the oxide single crystal to be manufactured is lithium tantalate, the fourth temperature is, for example, 1665°C. It should be noted that the holding time when the temperature of the raw material melt is at the fourth temperature is not particularly limited as long as the raw material melt becomes sufficiently uniform by the convection of the raw material melt, and is preferably 1 minute to 10 hours, and more preferably 5 minutes to 1 hour.

[0093] (Third process)

[0094] In the third step, while the weight of the seed crystal rod is measured and the seed crystal rod is pulled up, the output power of the heating source is adjusted so that the single crystal pulling weight speed of the single crystal grown from the seed crystal reaches a predetermined value, the neck, the cone and the body of the single crystal are formed from the seed crystal, and the single crystal with the body formed is separated from the liquid surface. For example, the method used for automatic diameter control of oxide single crystals based on the crystal weight method in the conventional crystal automatic pulling device can be applied to the single crystal growing method in the third step.

[0095] For example, in the case of forming the neck of a single crystal, the output power of the heating source is adjusted so that the single crystal pulling weight speed gradually increases. Specifically, while the seed rod is pulled, the output power of the heating source is reduced little by little. As a result, the liquid surface temperature of the raw material melt is reduced little by little, so the single crystal pulling weight speed gradually increases, and as a result, the single crystal gradually becomes thicker. In addition, in the case of forming the body of a single crystal, the output power of the heating source is adjusted so that the single crystal pulling weight speed is constant. Specifically, while the seed rod is pulled, the output power of the heating source is kept constant. As a result, the liquid surface temperature of the raw material melt is constant, so the single crystal pulling weight speed is constant, and as a result, the thickness of the single crystal is constant. Then, the single crystal with a straight body is separated from the liquid surface. It should be noted that in the case of forming a gentle convex shape such as a tail on a single crystal, a gentle convex shape is formed on the single crystal by controlling the number of rotations of the single crystal.

[0096] (Automatic operation)

[0097] In the method for producing an oxide single crystal of the present invention, the first to fourth steps are automatically operated. Thus, when an operator performs seeding operations on multiple machines, the burden on the operator can be reduced. The first to fourth steps can be automatically operated, for example, using an oxide single crystal production device according to an embodiment of the present invention described later.

[0098] [Apparatus for producing oxide single crystal]

[0099] An oxide single crystal manufacturing apparatus according to one embodiment of the present invention is an oxide single crystal manufacturing apparatus that uses a heating source to heat and melt a single crystal raw material put into a crucible to prepare a raw material melt, brings a seed crystal into contact with the raw material melt, and manufactures an oxide single crystal by a rotary pulling method. Figure 1As shown, an oxide single crystal production device 1 according to an embodiment of the present invention includes a seed crystal rod 3 having a seed crystal 2 at the front end, a load cell 4 for measuring the weight of the seed crystal rod 3, a pull-up rotation drive mechanism 5 for pulling the seed crystal rod 3 while rotating it, a heating source 7 for heating and melting the single crystal raw material put into a crucible 6, a thermometer 9 for measuring the temperature of the single crystal raw material and the raw material melt 8 in the crucible, and a control unit 10 for controlling the pull-up rotation drive mechanism 5 and the heating source 7. The seed crystal 2 and the heating source 7 are contained in a reaction container 12. The state of the crystal raw material and the raw material melt 8 in the crucible 6 can be observed through an observation window 13. In addition, the thermometer 9 can measure the temperature of the crystal raw material and the raw material melt 8 in the crucible 6 through the observation window 13. It should be noted that the seed crystal rod 3, the load cell 4, the pull-up rotation drive mechanism 5, the heating source 7, the thermometer 9 and the pull-up rotation drive mechanism 5 can use those used in a conventional crystal automatic pulling device. The control unit 10 is connected to the load cell 4 and the thermometer 9 , and can obtain the weight information of the seed rod 3 from the load cell 4 and the temperature information of the single crystal raw material and the raw material melt 8 in the crucible from the thermometer 9 .

[0100] The control unit 10 can control the lifting and rotating drive mechanism 5 and the heating source 7 based on the weight information of the seed rod 3 from the weighing sensor 4 and the temperature information of the single crystal raw material and the raw material melt 8 in the crucible from the thermometer 9. Thus, the control unit 10 can implement the following steps: a first step, heating the single crystal raw material 8 in the crucible 6 with the output power of the heating source 7 that melts a part of the single crystal raw material 8, or adjusting the output power of the heating source 7 so that the temperature of the single crystal raw material 8 reaches the first temperature for melting a part of the single crystal raw material, thereby heating the single crystal raw material 8 in the crucible; a second step, adjusting the output power of the heating source 7 so that the temperature of the raw material melt in the crucible 6 reaches the second temperature for melting all of the single crystal raw material 8, thereby heating the single crystal raw material 8 to produce The raw material melt 8 is prepared by the following steps: a first step is to remove the raw material melt 8 from the raw material melt 8, and a seed rod 3 having a seed crystal 2 at the front end is lowered so that the seed crystal 2 contacts the liquid surface of the raw material melt 8; a third step is to adjust the output power of the heating source 7 so that the single crystal lifting weight speed of the single crystal grown from the seed crystal 2 reaches a predetermined value while the seed rod 3 is lifted while measuring the weight of the seed rod 3, so as to form the neck, the cone and the straight body of the single crystal from the seed crystal 2, and separate the single crystal with the straight body from the liquid surface; and a fourth step is to slowly cool the single crystal separated from the liquid surface with the predetermined output power of the heating source 7. It should be noted that the first to fourth steps have been described in the description unit of the method for producing the oxide single crystal of the present invention, so the description of the first to fourth steps is omitted.

[0101] like Figure 2 (a) and Figure 2As shown in (b), a slit 14 may be formed at a portion of the periphery of the observation window 13, and the atmospheric gas may be introduced from the slit 14 to the surface of the observation window, thereby preventing the observation window 13 from fogging. Figure 2 The arrows in (b) indicate the flow of the atmospheric gas.

[0102] Since it becomes the reference data of the temperature of the raw material melt 8 in the crucible 6, Figure 1 As shown, the oxide single crystal production apparatus 1 may further include a thermocouple 15 in contact with the bottom of the crucible.

[0103] The manufacturing apparatus of the oxide single crystal according to one embodiment of the present invention may further include a crucible rotation drive mechanism for rotating the crucible. In addition, in order to detect the pulling length of the seed rod, the manufacturing apparatus of the oxide single crystal according to one embodiment of the present invention may further include a position sensor such as a magnetic ruler. In addition, in order to be able to move the position of the working coil of the heating source, the manufacturing apparatus of the oxide single crystal according to one embodiment of the present invention may further include a working coil moving drive mechanism. In this case, in order to be able to detect the moving length of the working coil, the manufacturing apparatus of the oxide single crystal according to one embodiment of the present invention may further include a position sensor such as a magnetic ruler.

[0104] The oxide single crystal production apparatus 1 according to one embodiment of the present invention is merely an example of the oxide single crystal production apparatus according to the present invention, and therefore the oxide single crystal production apparatus 1 according to one embodiment of the present invention does not limit the oxide single crystal production apparatus according to the present invention.

[0105] Example

[0106] The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0107] [Example 1]

[0108] Using raw materials of the same composition, a cylindrical crucible with an inner diameter of 150 mmφ, and a high-frequency induction heating furnace, a lithium tantalate single crystal with a diameter of 4 inches is produced by the Czochralski method. A schematic diagram of a production apparatus for producing a lithium tantalate single crystal is shown in FIG. Figure 1 By using this device, the first to fourth steps described below are automatically operated. In addition, a schematic diagram of the observation window 13 of the manufacturing device for manufacturing lithium tantalate single crystal is shown in FIG. Figure 2 (a) and Figure 2 (b) A slit 14 was formed in a part of the outer periphery of the observation window 13, and 4 L of an atmospheric gas of 1 vol% oxygen and 99 vol% nitrogen was introduced therefrom. The flow rate of the atmospheric gas at this time was 40 m / min.

[0109] First, the power of the oscillator of the heating source 7 is turned on, and the temperature is raised for 2 hours at the specified output power of the heating source 7 until a portion of the single crystal raw material is melted. At this time, the crucible bottom temperature is 1350°C, the state in the crucible 6 confirmed from the observation window 13 is a solid-liquid mixed state, and the liquid surface temperature of the raw material melt measured through the observation window 13 is 1580°C.

[0110] The temperature of the crucible bottom is measured using a thermocouple 15, and a radiation thermometer is used as the thermometer 9 for measuring the liquid surface temperature from the observation window 13. The seeding position is the center of the crucible at the liquid surface, and the temperature measurement range of the radiation thermometer 9 is about 10 mm φ of the liquid surface centered on the seeding position. Figure 3 1 and 2 show the change in the output power (power) of the heating source in the first step and the second step, the liquid surface temperature of the raw material melt measured by the thermometer 9, the temperature of the bottom of the crucible measured by the thermocouple 15, and the weight change of the seed rod 3 measured by the weighing sensor 4. After 2 hours in the first step or when the liquid surface temperature of the raw material melt 8 reaches 1580°C or above, the process is transferred to the second step, and the signal of the thermometer 9 is fed back to the output power of the heating source 7 to control the temperature of the raw material for single crystal and the raw material melt 8.

[0111] exist Figure 4 FIG. 4 shows a temperature setting pattern of the single crystal raw material and the raw material melt 8 in the crucible 6 in the second step. Figure 4 As shown in FIG. 1 , the output power of the heating source 7 is controlled so that the liquid surface temperature of the raw material melt 8 rises from 1580°C to 1630°C (STP1) in 20 minutes. At this time, the maximum and minimum values ​​of the output power of the heating source 7 are set as described above, and the output power of the heating source 7 is controlled to be larger than the minimum value and smaller than the maximum value. The reason is that if the output power of the heating source 7 is greater than the maximum value, the seed rod 3 may melt. In addition, if the output power of the heating source 7 is less than the minimum value, the liquid surface temperature of the raw material melt 8 may not reach the desired temperature by using only the output power of the heating source 7 as the latent heat when the solid turns into liquid.

[0112] Then, the liquid surface temperature of the raw material melt 8 is raised from 1630°C to 1665°C at a heating rate of 3°C / min (STP2), and after being kept for 20 minutes to make the raw material melt 8 more uniform by convection of the raw material melt 8 in the crucible (STP3), the liquid temperature of the raw material melt 8 is lowered to 1639°C (optimal temperature) over 20 minutes (STP4). When it reaches 1650°C or less, the seed rod 3 is automatically lowered by 70 mm and moved to a position 30 mm above the liquid surface of the raw material melt 8. When the raw material melt reaches 1639°C (STP5), the seed rod 3 is lowered by 20 mm. After the liquid surface temperature of the raw material melt 8 is kept at 1639°C (optimal temperature) for 10 minutes, the seed rod 3 is lowered by 1 mm at a rate of 0.1 mm / sec, and when the weight of the seed rod 3 is detected by the load cell 4 to change by 0.5 g, the seed rod 3 is stopped to perform seeding. After seeding is completed, if it is determined that the weight change of the seed rod 3 detected by the load cell 4 is within ±1 g for 10 minutes, the process automatically shifts to the crystal pulling step (third step).

[0113] In the third step, the weight of the seed rod 3 detected by the weighing sensor 4 is fed back to the output power of the heating source 7, so that the neck, cone and straight body of the single crystal are formed from the crystallization, and the single crystal with the straight body is separated from the liquid surface of the raw material melt 8, thereby completing the crystallization cultivation.

[0114] In the fourth step, the single crystal separated from the liquid surface of the raw material melt 8 is cooled to room temperature over 8 hours while controlling the output of the heating source 7 .

[0115] Since the first to fourth steps can be automatically operated, even if the operator is responsible for multiple machines, the burden on the operator can be reduced, the operator's mistakes can be eliminated, and the yield rate of lithium tantalate single crystals can be improved.

[0116] The same operation was performed 10 times, and it was found that the automatic operation was possible without any problem 8 times. In 2 times, the seed crystal broke after contacting the raw material melt.

[0117] [Example 2]

[0118] Using raw materials of the same composition and a crucible with an inner diameter of 150 mmφ, a lithium tantalate single crystal with a diameter of 4 inches was manufactured by the Czochralski method using a high-frequency induction heating furnace. The seeding position was at the center of the crucible at the liquid level, and the position of the temperature measurement by the radiation thermometer 9 was set to a position 25 mmφ away from the center of the seeding position, and the range of 5 mmφ of the liquid level was measured. The other conditions were the same as those in Example 1. There were no particular problems, and the first to fourth steps could be automatically operated. The same lithium tantalate manufacturing was carried out a total of 10 times, and it was found that all 10 times could be automatically operated without problems.

[0119] [Example 3]

[0120] Using raw materials of the same composition and a crucible with an inner diameter of 150 mmφ, a lithium tantalate single crystal with a diameter of 4 inches was manufactured by the Czochralski method using a high-frequency induction heating furnace. The seeding position is the center of the crucible at the liquid surface, and the position of the temperature measurement by the radiation thermometer 9 is set to a position 90 mmφ away from the center of the seeding position, and the range of 5 mmφ of the liquid surface is measured. At this time, the control temperature of the radiation thermometer is set to 1645°C (the temperature of the part where the seed crystal contacts the raw material melt is changed to the set temperature of 1639°C). The other conditions are the same as those in Example 1. There are no particular problems, and the first to fourth processes can be automatically operated. The same lithium tantalate production was implemented a total of 10 times, and it was found that all 10 times could be automatically operated without problems.

[0121] [Example 4]

[0122] Using raw materials of the same composition and a crucible with an inner diameter of 200mmφ, a lithium tantalate single crystal with a diameter of 6 inches was manufactured by the Czochralski method using a high-frequency induction heating furnace. The seeding position is the center of the crucible at the liquid level, and the range of temperature measurement by the radiation thermometer 9 is set to a position 130mmφ from the center of the seeding position, and the range of 5mmφ of the liquid level is measured. At this time, the control temperature of the radiation thermometer is set to 1644°C (the temperature of the part where the seed crystal contacts the raw material melt is changed to the set temperature of 1639°C). The other conditions are the same as those in Example 1. There are no particular problems, and the first to fourth steps can be automatically operated. The same lithium tantalate manufacturing was implemented a total of 10 times, and it was found that all 10 times could be automatically operated without problems.

[0123] [Example 5]

[0124] Using raw materials of the same composition and a crucible with an inner diameter of 200 mmφ, a lithium tantalate single crystal with a diameter of 6 inches was manufactured by the Czochralski method using a high-frequency induction heating furnace. The range of temperature measurement by the radiation thermometer 9 is set to a position 150 mmφ away from the center of the crucible at the liquid surface, and the range of 5 mmφ of the liquid surface is measured. At this time, the control temperature of the radiation thermometer is set to 1649°C (the temperature of the part where the seed crystal contacts the raw material melt is changed to the set temperature of 1639°C). The other conditions are the same as those in Example 1. There are no particular problems, and the first to fourth steps can be automatically operated. The same lithium tantalate manufacturing was implemented a total of 10 times, and it was found that 9 times it could be automatically operated without problems. However, there was one time when the raw material melt partially solidified after the seed crystal contacted the raw material melt.

[0125] [Comparative Example 1]

[0126] The first step is carried out in the same manner as in Example 1.

[0127] In the second step, the output power (equivalent to the output power near the maximum value of the embodiment) was raised from 1580°C to 1630°C by manual operation so that the seed rod did not melt. Figure 3 The temperature setting mode shown is used to adjust the liquid surface temperature of the raw material melt by manual operation. When the liquid surface temperature of the raw material melt reaches 1639°C, the seed rod is lowered by 20 mm. After maintaining the liquid surface temperature at 1639°C (suitable temperature) for 10 minutes, the operator lowers the seed rod while observing the liquid surface of the raw material melt through the observation window, confirming that the liquid surface of the raw material melt is in contact with the seed rod to end the seeding. After the seeding is completed, the operator confirms that the weight change of the weighing sensor is within ±1g during 10 minutes. Then, press the crystal pulling start button to transfer from manual to automatic crystal cultivation process.

[0128] The third step and the fourth step are performed in the same manner as the third step and the fourth step of Example 1, respectively.

[0129] Regarding the second process, when the operator performs the seeding operation in multiple oxide single crystal manufacturing devices, it is sometimes impossible to perform the seeding operation at an appropriate temperature in several oxide single crystal manufacturing devices. For example, the temperature for the seeding operation is higher than the appropriate temperature, resulting in a simple error of no seed neck after seeding. In particular, when the operator is a novice, the frequency of simple errors as described above increases, and the production capacity decreases. It should be noted that in Examples 1 to 5, such simple errors did not occur at all.

[0130] Explanation of symbols

[0131] 1. Oxide single crystal manufacturing device,

[0132] 2 seed crystals,

[0133] 3 seed rods,

[0134] 4 load cells,

[0135] 5. Lifting and rotating drive device,

[0136] 6 Crucible,

[0137] 7. Heating source,

[0138] 8 Raw materials and raw material melts for single crystals,

[0139] 9 Thermometer,

[0140] 10. Control Department,

[0141] 12 reaction vessel,

[0142] 13 Observation window,

[0143] 14 slits,

[0144] 15 Thermocouple.

Claims

1. A method for producing an oxide single crystal, wherein a raw material for a single crystal put into a crucible is heated and melted by a heating source to prepare a raw material melt, a seed crystal is brought into contact with the raw material melt, and an oxide single crystal is produced by a rotary pulling method, wherein: Including the following processes: The first step is to heat the raw material for single crystal in the crucible with the output power of the heating source that melts a part of the raw material for single crystal, or to adjust the output power of the heating source so that the temperature of the raw material for single crystal reaches a first temperature that melts a part of the raw material for single crystal, thereby heating the raw material for single crystal in the crucible; The second step is to adjust the output power of the heating source so that the temperature of the raw material melt in the crucible reaches a second temperature at which all the raw materials for single crystals are melted, thereby heating the raw materials for single crystals to produce a raw material melt, and lowering a seed rod having a seed crystal at the front end so that the seed crystal contacts the liquid surface of the raw material melt; The third step comprises: adjusting the output power of the heating source so that the weight of the single crystal grown from the seed crystal reaches a predetermined value while the seed crystal rod is lifted while measuring the weight of the seed crystal rod, forming a neck portion, a tapered portion and a straight body portion of the single crystal from the seed crystal, and separating the single crystal having the straight body portion formed therein from the liquid surface; as well as The fourth step is to slowly cool the single crystal separated from the liquid surface with a predetermined output power of the heating source; The first step to the fourth step are automatically operated.

2. The method for producing an oxide single crystal according to claim 1, wherein: In the first step and the second step, the liquid surface temperature of the raw material melt in the crucible is measured using a radiation thermometer through an observation window provided to observe the liquid surface of the raw material melt in the crucible, and the output power of the heating source is adjusted based on the measured liquid surface temperature.

3. The method for producing an oxide single crystal according to claim 2, wherein: When the inner diameter of the crucible at the liquid surface position of the raw material melt is defined as R, the distance between the position where the liquid surface temperature of the raw material melt is measured and the center position of the liquid surface of the raw material melt is equal to or less than 2 / 3R.

4. The method for producing an oxide single crystal according to claim 2, wherein: The liquid surface temperature at the seeding position where the seed crystal contacts is measured.

5. The method for producing an oxide single crystal according to claim 2, wherein: The distance between the position where the liquid surface temperature of the raw material melt is measured and the position of the liquid surface of the raw material melt with which the seed crystal is brought into contact is 15 mm or more.

6. The method for producing an oxide single crystal according to any one of claims 2 to 5, wherein: At least in the second step, atmospheric gas is introduced to the surface of the observation window to prevent fogging of the observation window.

7. The method for producing an oxide single crystal according to any one of claims 1 to 6, wherein: In the second step, the output power of the heating source is adjusted to an output power that is smaller than the following maximum output power and larger than the following minimum output power: Maximum output power: the output power of the heating source that makes the temperature of the raw material melt reach the temperature for melting the seed crystal; Minimum output power: the output power of the heating source for the heating source to generate heat corresponding to latent heat associated with melting of the raw material for single crystal.

8. The method for producing an oxide single crystal according to any one of claims 1 to 6, wherein: In the second step, the seed crystal rod is lowered while measuring the weight of the seed crystal rod, and when the weight of the seed crystal rod changes by 0.5 g or more, it is determined that the seed crystal is in contact with the liquid surface of the raw material melt. In the second step, while the seed crystal is brought into contact with the liquid surface of the raw material melt, the output power of the heating source is adjusted so that the temperature of the raw material melt reaches a third temperature at which the raw material melt under the seed crystal is deprived of latent heat and solidifies, thereby heating the raw material melt, and then the seed crystal is brought into contact with the liquid surface of the raw material melt. Then, while the absolute value of the weight change after maintaining for 10 minutes is less than 1 g, transfer to the third step.

9. An oxide single crystal manufacturing device, which uses a heating source to heat and melt a single crystal raw material put into a crucible to make a raw material melt, makes a seed crystal contact with the raw material melt, and manufactures an oxide single crystal by a rotary pulling method, characterized in that: have: A seed rod with a seed crystal at the front end, a weighing sensor for measuring the weight of the seed rod, a pulling and rotating driving mechanism for pulling up the seed crystal rod while rotating it, a heating source for heating and melting the raw material for single crystal put into the crucible, a thermometer for measuring the temperature of the single crystal raw material and the raw material melt in the crucible, and A control unit for controlling the lifting and rotating driving mechanism and the heating source; The control unit implements the following steps: The first step is to heat the raw material for single crystal in the crucible with the output power of the heating source that melts a part of the raw material for single crystal, or to adjust the output power of the heating source so that the temperature of the raw material for single crystal reaches a first temperature that melts a part of the raw material for single crystal, thereby heating the raw material for single crystal in the crucible; The second step is to adjust the output power of the heating source so that the temperature of the raw material melt in the crucible reaches a second temperature at which all the raw materials for single crystals are melted, thereby heating the raw materials for single crystals to produce a raw material melt, and lowering a seed rod having a seed crystal at the front end so that the seed crystal contacts the liquid surface of the raw material melt; The third step comprises: adjusting the output power of the heating source so that the weight of the single crystal grown from the seed crystal reaches a predetermined value while the seed crystal rod is lifted while measuring the weight of the seed crystal rod, forming a neck portion, a tapered portion and a straight body portion of the single crystal from the seed crystal, and separating the single crystal having the straight body portion formed therein from the liquid surface; as well as In the fourth step, the single crystal separated from the liquid surface is slowly cooled with a predetermined output power of the heating source.

10. The manufacturing apparatus for oxide single crystal according to claim 9, wherein: The thermometer is a radiation thermometer, In the first step and the second step, the control unit adjusts the output of the heating source based on the liquid surface temperature of the raw material melt measured by the radiation thermometer through an observation window provided to enable observation of the liquid surface of the raw material melt in the crucible.

11. The manufacturing apparatus for oxide single crystal according to claim 10, wherein: When the inner diameter of the crucible at the liquid surface position of the raw material melt is defined as R, the distance between the position where the liquid surface temperature of the raw material melt is measured and the center position of the liquid surface of the raw material melt is equal to or less than 2 / 3R.

12. The manufacturing apparatus for an oxide single crystal according to claim 10, wherein: The liquid surface temperature at the seeding position where the seed crystal contacts is measured.

13. The manufacturing apparatus of an oxide single crystal according to claim 10, wherein: The distance between the position where the liquid surface temperature of the raw material melt is measured and the position of the liquid surface of the raw material melt with which the seed crystal is brought into contact is 15 mm or more.

14. The device for producing an oxide single crystal according to any one of claims 10 to 13, wherein: The manufacturing device further includes an observation window fogging prevention device for introducing an atmospheric gas to a surface of the observation window to prevent fogging of the observation window. The control unit prevents the observation window from fogging by using the observation window fogging prevention device at least in the second step.

15. The production apparatus for an oxide single crystal according to any one of claims 9 to 14, wherein: The control unit adjusts the output power of the heating source in the second step at an output power that is smaller than the following maximum output power and larger than the following minimum output power: Maximum output power: the output power of the heating source that makes the temperature of the raw material melt reach the temperature for melting the seed crystal; Minimum output power: the output power of the heating source for the heating source to generate heat corresponding to latent heat associated with melting of the raw material for single crystal.

16. The device for producing an oxide single crystal according to any one of claims 9 to 15, wherein: The control unit lowers the seed crystal rod while measuring the weight of the seed crystal rod in the second step, and determines that the seed crystal is in contact with the liquid surface of the raw material melt when the weight of the seed crystal rod changes by 0.5 g or more. The control unit further adjusts the output power of the heating source in the second step, while the seed crystal is in contact with the liquid surface of the raw material melt, so that the temperature of the raw material melt reaches a third temperature at which the raw material melt under the seed crystal is deprived of latent heat and solidifies, thereby heating the raw material melt, and then brings the seed crystal into contact with the liquid surface of the raw material melt, and then, transfers to the third step while maintaining the absolute value of the weight change at 1 g or less for 10 minutes.

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