JP2016130205A - Production method for sapphire single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for sapphire single crystal that has a high crystallization rate with respect to a fed raw material.SOLUTION: The production method for a sapphire single crystal by a Czochralski method is provided in which a seed crystal 20 is brought into contact with a material melt 21 in a crucible 12, which is heated and molten by a cylindrical heater 14 arranged facing a side face of an outer surface of the crucible 12 and a disk-shaped heater 13 arranged facing a bottom face of the outer surface of the crucible 12, then the seed crystal 20 and a sapphire single crystal 22 is pulled up while rotating the seed crystal 20. The production method for a sapphire single crystal performs a cylindrical heater lowering step of lowering the cylindrical heater 13 after the seed crystal 20 starts to be pulled up; and/or a disk-shaped heater moving step of elevating the disk-shaped heater 13 toward the bottom face of the outer surface of the crucible 12. The cylindrical heater lowering step and/or the disk-shaped heater moving step is performed after a shoulder part of the sapphire single crystal is formed or when the material melt has a solidification ratio of 50% or higher.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a sapphire single crystal.

  A sapphire single crystal is a crystal having a corundum structure of aluminum oxide, and has excellent mechanical and thermal properties, chemical stability, and light transmittance, and thus is used in many fields. In particular, in the semiconductor field, it is used as a substrate for growing a light emitting layer of a gallium nitride (GaN) light emitting diode or as a substrate for a silicon on sapphire (SOS) device. As importance increases, the demand is growing dramatically.

  As a main method for producing a sapphire single crystal, a Czochralski method (Cz method) or a chiloporous method in which a sapphire polycrystal raw material is melted in a crucible and a seed crystal is brought into contact with the surface of the raw material melt and gradually pulled up. (KY method) is known. The grown sapphire single crystal is processed into a disk shape and is shipped as a sapphire single crystal substrate by polishing the surface.

  For example, Patent Literature 1 discloses a crystal growth apparatus for a sapphire single crystal by the Czochralski method. In the crystal growth apparatus of Patent Document 1, a crucible for containing raw material powder is disposed on a support shaft in a chamber, and a side heater is provided on the side of the crucible, and a disc-shaped bottom heater passes through the support shaft below the crucible. Has been placed. A heat insulating material is provided around the side heater and below the bottom heater along the inner surface of the furnace body, and a gas supply pipe and a gas discharge pipe are attached to the top and bottom of the chamber. In addition, a lifting shaft that can move up and down is provided at the top of the crucible so as to penetrate the heat insulating material. In the pulling of the single crystal, the side heater and the bottom heater of the apparatus are operated to heat the raw material for single crystal to generate a raw material melt. Thereafter, the seed crystal is brought into contact with the surface of the raw material melt, and the single crystal can be grown while being pulled up.

  By the way, when a sapphire single crystal having a melting point of 2050 ° C. and a high melting point is grown by the Czochralski method, the heat insulating space surrounded by the heat insulating material becomes a high temperature environment exceeding 2000 ° C. For this reason, in the growth of a sapphire single crystal, the heat transfer in the heat insulation space is mainly radiant light, and the heat insulation space is easily soaked, and it is not easy to form a temperature gradient suitable for crystal growth. . In addition, compared with other oxide single crystal raw material melts such as lithium tantalate (LT), lithium niobate (LN), or yttrium aluminum garnet (YAG) The liquid has a very low viscosity and unstable convection. For this reason, it is difficult to optimize the temperature gradient in the raw material melt.

  When growing a sapphire single crystal by a pulling method such as the Czochralski method or the Cairo porous method, during the pulling method of the above-mentioned other oxide single crystal or a semiconductor single crystal such as silicon or gallium phosphide. Unlike this, the growth interface tends to be a conical shape extending greatly toward the lower part of the raw material melt. That is, the growth interface is convex toward the lower part of the raw material melt, and the degree of convexity tends to be very large. For this reason, in the growth of a sapphire single crystal, it is known that the growth interface shape in the raw material melt and its forward speed have an important influence on the growth yield and crystal quality. The shape of the crystal growth interface is determined mainly by the flow of latent heat generated with solidification, that is, the temperature distribution and temperature gradient of the crystal growth field.

  Therefore, in growing a sapphire single crystal by the pulling method, it is required to control the temperature and temperature gradient in the heat insulating space including the inside of the raw material melt with high accuracy.

  On the other hand, in order to improve the productivity of the sapphire single crystal and reduce the cost, it has been studied to increase the size of the grown crystal. This is because the yield per unit time can be increased and the cost can be reduced by increasing the crystal size.

  However, in order to grow a large crystal, as a matter of course, it is necessary to enlarge the crucible and the heat insulating material surrounding the crucible and increase the volume of the heat insulating space surrounded by the heat insulating material. And as the volume of the crucible, the heat insulating material, and the heat insulating space increases, their heat capacities also increase. For this reason, precise control of the melt surface temperature (seeding temperature) in the process of starting seeding called seeding in contact with the melt and the appropriate temperature gradient in the heat insulation space surrounded by the heat insulating material It becomes difficult to make it.

  If crystal growth is performed in a state where the seeding temperature and the temperature gradient in the heat insulating space are inappropriate, it becomes difficult to control the crystal growth rate and the shape of the growth interface accompanying it, and the defect occurrence rate increases. In fact, as the crystal growth size increases, the incidence of defects such as bubbles, lineage, and polycrystallization tends to increase, especially in the upper part of the grown crystal (corresponding to the initial growth). Therefore, there has been a problem that the yield improvement and cost reduction effect expected from the increase in crystal size have not been sufficiently obtained.

  Thus, various studies have been made on methods for adjusting the temperature gradient to an appropriate range in order to grow large sapphire single crystals with high quality. For example, a method of installing a heat reflecting plate in the upper space of the melt, a method of adjusting the output ratio of these heaters by dividing the heater for heating the raw material melt into two parts for crucible side surface heating and crucible bottom surface heating, etc. Has been reported.

  In addition, as a method for obtaining an appropriate timing for bringing the seed crystal into contact with the raw material melt, that is, an appropriate seeding temperature, the surface temperature of the raw material melt and the outer surface temperature of the bottom of the crucible containing the raw material melt are radiated. Methods such as measurement using a thermometer and thermocouple have been reported.

  By combining these and setting the appropriate pulling speed and crystal rotation speed corresponding to the temperature environment, the growth interface shape at the initial stage of crystal growth is controlled to an appropriate shape, and a high-quality sapphire unit with a crystal weight of 100 kg class. Crystals began to grow.

JP 2011-195423 A

  However, even in the above method, crystal growth could be continued only to less than 80% of the amount of raw material charged in the crucible. This is because when the growth is continued until the weight of the sapphire single crystal with respect to the weight of the raw material charged in the crucible becomes 80% or more, the bottom of the grown crystal adheres to the crucible bottom inner wall (with a bottom) or remains in the crucible. This is because a phenomenon in which the raw material instantly solidifies during the growth (melt solidification) occurred and the growth was stopped.

  On the other hand, market demands for increasing the diameter and cost of sapphire substrates are becoming stronger, and accordingly, the growth of growing crystals and the reduction of growing costs are required. For this reason, in order to increase the size of the grown crystal and reduce the growth cost, it has been required to further improve the crystallization rate (solidification rate) of the input raw material.

  In view of the above-described problems of the prior art, an object of one aspect of the present invention is to provide a method for producing a sapphire single crystal having a high crystallization rate with respect to an input raw material.

In order to solve the above problems, according to one aspect of the present invention, a cylindrical heater disposed to face the side surface of the outer surface of the crucible, and a disk shape disposed to face the bottom surface of the outer surface of the crucible A method for producing a sapphire single crystal by the Czochralski method in which a seed crystal is brought into contact with a raw material melt in a crucible heated and melted by a heater and then the seed crystal and the sapphire single crystal are pulled up while rotating the seed crystal. There,
After starting to raise the seed crystal,
Provided is a method for producing a sapphire single crystal, which performs a cylindrical heater lowering step for lowering the cylindrical heater and / or a disk-shaped heater moving step for raising the disk-shaped heater toward the bottom surface of the outer surface of the crucible. can do.

  According to one embodiment of the present invention, a method for producing a sapphire single crystal with a high crystallization rate relative to an input raw material can be provided.

Sectional drawing of the sapphire single crystal growth apparatus which can be used when manufacturing a sapphire single crystal in embodiment of this invention. Explanatory drawing of the sapphire single crystal at the time of sapphire single crystal growth, and its circumference | surroundings. Explanatory drawing of the sapphire single crystal at the time of sapphire single crystal growth, and its circumference | surroundings. Explanatory drawing of the name of each part of a sapphire single crystal. Explanatory drawing of a structure of the sapphire single crystal growth apparatus used when manufacturing a sapphire single crystal in Example 1 of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.

  One structural example of the manufacturing method of the sapphire single crystal of this embodiment is demonstrated.

  The method for producing a sapphire single crystal of the present embodiment includes a cylindrical heater disposed so as to face the side surface of the outer surface of the crucible, and a disk-shaped heater disposed so as to face the bottom surface of the outer surface of the crucible. It is possible to use a method for producing a sapphire single crystal by the Czochralski method of pulling up the seed crystal and the sapphire single crystal while rotating the seed crystal after bringing the seed crystal into contact with the raw material melt in the heat-melted crucible. it can.

  And the manufacturing method of the sapphire single crystal of this embodiment is a cylindrical heater descent | fall process which lowers a cylindrical heater after the pulling start of a seed crystal, and / or a disk-shaped heater toward the bottom surface among the outer surfaces of a crucible. The disk-shaped heater moving process to raise can be implemented.

  First, a configuration example of a sapphire single crystal growth apparatus that can be suitably used in the method for manufacturing a sapphire single crystal of the present embodiment will be described with reference to FIG.

  FIG. 1 schematically shows a cross-sectional view of a cross section passing through the central axis of a crucible 12 of a sapphire single crystal growing apparatus (sapphire single crystal manufacturing apparatus) 10.

  A sapphire single crystal growth apparatus 10 shown in FIG. 1 includes a crucible 12 in which a sapphire material is filled in a chamber formed by a furnace body 11, a disk-shaped heater 13 for heating the bottom surface of the crucible 12, and a crucible 12 A cylindrical heater 14 for heating the outer peripheral surface can be arranged. Furthermore, the heat insulating material 16 which comprises the heat insulation space 15 can be provided. The types of heaters of the disk heater 13 and the cylindrical heater 14 are not particularly limited, but for example, a resistance heating method is preferable. Moreover, as the heat insulating material 16, for example, a carbon heat insulating material can be suitably used.

  And it extends from the outside of the heat insulation space 15 to the inside through an opening provided in the bottom surface portion 161 of the heat insulating material 16 and is connected to each of the disk heater 13 and the cylindrical heater 14 to supply electric power. Two cylindrical heater electrodes 17a and 17b can be provided.

  A support shaft 18 that supports the crucible 12 can be provided through the bottom surface portion 161 of the heat insulating material 16 and the opening of the disk-shaped heater 13. Further, the pulling shaft 19 to which the seed crystal 20 is attached can be inserted at the tip through the holder 19a through the opening provided in the upper surface portion 162 of the heat insulating material 16. The pulling shaft 19 can move in the vertical direction in the figure, and performs seeding for bringing the seed crystal 20 into contact with the raw material melt 21 or sapphire from the raw material melt 21 in the crucible 12 by the Czochralski method at the time of growth. The single crystal 22 can be pulled up and grown.

  Further, the sapphire single crystal growing apparatus 10 shown in FIG. 1 can have a gas supply means, a gas exhaust means, etc. (not shown) in order to control the inside of the furnace to a desired atmosphere.

  In the Czochralski method, as described above, seeding is performed by bringing the seed crystal into contact with the raw material melt heated and melted by the heater, and then the sapphire single crystal is pulled up while rotating the seed crystal. Crystals can be produced. However, when the temperature gradient, temperature, and seeding temperature in the heat insulating space containing the raw material melt are not appropriate, defects such as bubbles and lineage may occur in the grown sapphire single crystal. In addition, there were cases where the breeding was canceled. This point will be described below with reference to FIG. FIG. 2 is a diagram schematically showing a state in which the seed crystal 31 is seeded in the raw material melt 33 and then the seed crystal 31 is pulled up to grow a sapphire single crystal 32. A cross-sectional view in a plane perpendicular to the surface of the raw material melt 33 is shown.

  First, when the seed crystal 31 is seeded on the raw material melt 33 with reference to FIG. 2A, and the temperature of the raw material melt in the initial growth stage is lower than the appropriate temperature range, The state of crystal growth when the gradient is smaller than the appropriate range will be described. If the temperature of the raw material melt is lower than the appropriate temperature range during seeding or at the initial stage of growth, or if the temperature gradient in the heat insulation space is smaller than the appropriate range, the crystals grow rapidly immediately after seeding. Resulting in. For this reason, as shown to Fig.2 (a), the shape of the growth interface (solid-liquid interface) 32a of the sapphire single crystal 32 in the initial stage of growth becomes concave toward the melt.

  The solubility of the impurity gas component contained in a trace amount in the raw material melt 33 is high in the raw material melt 33 which is a liquid phase, whereas the sapphire single crystal 32 which is a solid phase is low, It is different from the liquid phase. Therefore, as shown in FIG. 2A, when the shape of the growth interface 32a becomes concave toward the raw material melt 33, the solid phase of the raw material melt is solidified, that is, as the growth interface 32a advances, Due to the difference in solubility from the liquid phase, the concentration of the gas component discharged into the liquid phase increases in the vicinity of the growth interface 32a. When the concentration of the discharged gas component in the raw material melt exceeds the dissolved amount of the raw material melt 33, bubbles 34 are formed. When the growth interface 32a is concave toward the raw material melt 33, the bubbles 34 grow. It remains in the vicinity of the interface 32a. Then, the bubble 34 is taken into the sapphire single crystal 32 by the advance of the growth interface 32a, thereby generating a bubble defect.

  In addition, when the growth interface 32a has a high forward speed, the gas component of the solubility difference between the solid phase and the liquid phase cannot be completely discharged into the liquid phase, and the gas component is taken into the solid phase in a supersaturated state. In some cases, it accumulates by diffusion and manifests as microvoids.

  Further, when crystal growth proceeds in a state where the growth interface 32a is concave in this way, as shown in FIG. 2B, a crystal called lineage 35 that propagates in a direction perpendicular to the growth interface 32a of the sapphire single crystal 32 is obtained. Defect accumulation occurs. As a result, the accumulation of the lineage 35 generates a rotation region 36 of crystal orientation, which causes polycrystallization.

  On the other hand, if the temperature of the raw material melt at the time of seeding is higher than the appropriate temperature range, the seed crystal is exposed to a temperature environment higher than the melting point. The crystals melt and the growth is stopped.

  In addition, when the temperature gradient in the heat insulation space is larger than the appropriate range, the temperature difference in the grown crystal also increases, so thermal strain caused by the temperature difference is generated during crystal growth, and the grown crystal is cracked. There is a high possibility that

  As described above, when the sapphire single crystal is grown, if the shape of the growth interface is concave toward the raw material melt, defects such as bubbles, lineage, and polycrystallization are likely to occur, which is not preferable.

  Therefore, from the viewpoint of preventing entrapment of bubbles and occurrence of crystal defects, the shape of the growth interface between the sapphire single crystal and the raw material melt is convex to the raw material melt side from the time of shoulder formation, which is the initial stage of crystal growth. It is preferable that

  It is more preferable to control the tip angle θ of the convex growth interface within a desired range. This point will be described below with reference to FIG.

  FIG. 3 is a diagram schematically showing how the seed crystal 41 is pulled up by seeding the seed crystal 41 into the raw material melt 42 and growing the sapphire single crystal 43. A cross-sectional view in a plane perpendicular to the surface of the liquid 42 is shown. In FIG. 3, the growth interface 43a of the sapphire single crystal 43 is convex toward the raw material melt 42 side, and the tip angle is θ.

  When the tip angle θ is an acute angle than the desired range, the temperature gradient in the depth direction of the raw material melt 42 is not set appropriately, and the sapphire single crystal 43 moves at a high speed in the depth direction of the raw material melt 42. If you are growing in. In such a situation, the amount of the gas component discharged per unit time at the tip of the convex growth interface 43a increases, and the tip of the convex growth interface 43a is a raw material whose gas component concentration is highly supersaturated. It will grow in the melt 42. Therefore, in the vicinity of the tip of the growth interface 43a, microvoids are easily generated due to the incorporation of bubbles into the crystal and the diffusion and accumulation of supersaturated gas components incorporated into the crystal. In addition, deterioration of crystallinity due to high-speed growth, generation of dislocation due to stress due to temperature difference in the crystal, generation of lineage due to movement of the dislocation, and polycrystallization due to their accumulation are likely to occur.

  On the other hand, when the tip angle θ is an obtuse angle than the desired range, the diameter of the grown sapphire single crystal 43 is expanding at a high speed. In such a case, since bubbles are generated at a high concentration in the vicinity of the growth interface 43a of the high-speed growth part (crystal diameter expansion part) for the same reason as described above, they are generated in the sapphire single crystal 43 at the growth interface 43a. The bubble density near the crystal surface called the so-called crystal shoulder increases. In addition, as in the case described above, microvoids are generated due to accumulation of supersaturated gas components taken into the crystal after solidification. When the bubble density of the crystal shoulder increases, the radiation light is scattered there, so that the temperature difference inside the crystal becomes small, and the latent heat of solidification generated along with the growth becomes difficult to escape toward the seed crystal 41. As a result, the flow rate of heat increases from the crystal shoulder surface to the upper space. In addition, since the thermal convection of the melt flowing from the outer peripheral part of the crucible toward the central part collides with the angle close to the frontal collision directly under the growth interface of the grown crystal, the convection is disturbed immediately under the sapphire single crystal 43. Here, turbulence of convection means that an upward flow (that is, a growth interface direction) is generated by collision in addition to thermal convection. As a result, a concave growth interface is formed, and bubbles are easily taken not only in the crystal diameter enlarged portion but also in the crystal central portion. Further, polycrystallization due to lineage accumulation due to concave interface growth is likely to occur.

  For the reasons described above, in order to obtain a high-quality sapphire single crystal with good reproducibility, the shape of the growth interface is made convex toward the raw material melt side from the time of shoulder formation, which is the initial stage of sapphire single crystal growth. The tip angle at this time is preferably controlled within a desired range.

  And in order to make the shape of the growth interface convex toward the raw material melt side, and to make the tip angle at this time a desired range, the temperature gradient of the heat insulating space is set to an appropriate range when growing the sapphire single crystal, The seeding temperature is preferred.

  Therefore, the sapphire single crystal growth apparatus 10 that can be suitably used in the method of manufacturing a sapphire single crystal of the present embodiment shown in FIG. 1 includes a disk heater 13 that heats the bottom surface of the crucible 12 and the crucible 12 as described above. It is preferable to have a cylindrical heater 14 that heats the outer peripheral surface of the cylindrical member. And it is preferable to comprise so that the output ratio of the disk shaped heater 13 and the cylindrical heater 14 can be adjusted. Specifically, for example, the output ratio for both heaters can be adjusted by control means (not shown).

  In this way, the heater for heating the raw material melt is divided into two by the disc heater 13 for heating the bottom surface of the crucible 12 and the cylindrical heater 14 for heating the side surface of the crucible 12, and the output ratio of the heater is adjusted. Thus, the temperature gradient of the heat insulating space 15 including the inside of the raw material melt 21 can be precisely controlled within an appropriate range. For this reason, the introduction of bubbles and the occurrence of crystal defects are prevented, and the shape of the growth interface is made convex to the raw material melt side with an appropriate opening angle from the time of shoulder formation, which is the initial stage of crystal growth. be able to.

  In addition, when manufacturing a sapphire single crystal as described above, the tip angle θ of the convex growth interface of the sapphire single crystal is preferably within a desired range. Since the suitable range of the tip angle θ and the temperature control conditions therefor vary depending on the size of the apparatus and the like, it can be experimentally obtained by, for example, performing a preliminary test in advance.

  Moreover, in the sapphire single crystal growth apparatus 10 shown in FIG. 1, the method of setting the temperature gradient of the heat insulation space 15 including the inside of the raw material melt 21 to an appropriate range is not limited to the method described above. For example, a heat reflecting plate (not shown) is provided in the space above the raw material melt 21, the positions of the disk heater 13 and the cylindrical heater 14 and the position of the raw material melt are adjusted, and the heat insulating space 15 including the raw material melt 21 is included. The temperature gradient inside can also be appropriate. These methods (means) can also be used in combination.

  When a heat reflecting plate is provided in the sapphire single crystal growing apparatus, the form is not particularly limited, and any configuration can be adopted. For example, in a space above the crucible 12 in the heat insulating space 15 of the sapphire single crystal growing apparatus 10 shown in FIG. 1, a plurality of circles arranged at predetermined intervals in the axial direction of the pulling shaft 19 and having openings in the radial center portion. A multilayer heat reflecting plate including a ring-shaped plate-shaped body can be obtained. In this case, the size of the opening formed in the plate-like body constituting the heat reflecting plate is not particularly limited, but for example, it can be configured such that it gradually decreases from the crucible 12 side upward.

  The sapphire single crystal growth apparatus 10 shown in FIG. 1 further uses a radiation thermometer or a thermocouple to measure the temperature of the raw material melt 21 surface and the bottom outer surface temperature of the crucible 12 containing the raw material melt 21. Can be measured. Thereby, seeding temperature can be optimized.

  Specifically, for example, as shown in FIG. 1, raw material melt surface temperature measuring means 23 for measuring the temperature of the raw material melt surface through an observation window 23a can be provided. As the raw material melt surface temperature measuring means 23, for example, a radiation thermometer can be used.

  As a means for measuring the bottom outer surface temperature of the crucible 12, for example, a through hole penetrating the support shaft 18 may be provided, and the crucible bottom temperature measuring means 24 may be provided in the through hole. As the crucible bottom temperature measuring means 24, for example, a thermocouple or a radiation thermometer can be used.

  In addition to the above temperature measuring means, a crucible side surface temperature measuring means 25 for measuring the temperature of the side surface of the outer surface of the crucible 12 from a port (observation window) 25a provided on the side face of the sapphire single crystal growing apparatus 10 may be provided. it can. As the crucible side surface temperature measuring means 25, for example, a radiation thermometer or a thermocouple can be used. The crucible side surface temperature measuring means 25 can also be configured so that the position in the height direction can be changed and adjusted so that it can be measured at an arbitrary position on the side surface of the crucible 12. In this case, the port (observation window) 25a may have a slit shape that is long in the height direction, for example. Further, the cylindrical heater 14 may be provided with a slit, an opening or the like as necessary so as not to interfere with the crucible side surface temperature measuring means 25.

  As described above, defects such as bubbles, lineage, and crystallization occur in the sapphire single crystal grown by setting the temperature gradient in the heat insulating space 15 including the raw material melt 21 and the seeding temperature to an appropriate temperature. Can be suppressed.

  However, when producing a sapphire single crystal, an attempt to increase the crystallization rate causes a phenomenon called bottoming or melt solidification in the latter half of the growth of the sapphire single crystal, as described above, thereby increasing the crystallization rate. It was difficult. In addition, bottoming refers to a phenomenon in which the grown crystal bottom is fixed to the crucible bottom inner wall, and melt solidification refers to a phenomenon in which the raw material remaining in the crucible is instantaneously solidified during the growth.

  Therefore, the inventors of the present invention studied the reason why the above-mentioned bottoming or melt solidification occurred in the latter half of the growth of the sapphire single crystal, and the crystallization rate of the grown crystal was limited.

  According to the study by the inventors of the present invention, bottoming out or melt solidification occurs in the latter half of the growth of the sapphire single crystal because the growth of the sapphire single crystal progresses from the growth interface. This is thought to be due to an increase in the amount of heat flowing through the crystal.

  Crystal growth of a sapphire single crystal takes away latent heat from the raw material melt held above the melting point at the growth interface with the raw material melt, and the deprived heat does not stay near the growth interface and is below the melting point. It progresses by flowing to the low temperature part. As crystal growth progresses, the volume of the grown crystal increases, and the amount of heat released from the crystal surface increases, the heat flow in the crystal also increases. When crystal growth is proceeding in a controllable state, the amount of heat taken from the growth interface is a steady state with respect to the amount of heat supplied from the heater to the raw material melt. Moving forward in equilibrium.

  However, if this balance is lost in the direction in which the amount of heat supplied from the heater to the raw material melt is larger, the growth interface is further stopped and further retreated. That is, the growth of the grown crystal stops and further melts. On the other hand, if the balance is lost in the direction in which the amount of heat taken away from the growth interface is larger, the forward speed of the growth interface increases. Furthermore, it leads to rapid growth and solidification of the remaining raw material melt.

  In the latter half of the growth of the sapphire single crystal, the remaining amount of the raw material melt is greatly reduced compared to the initial stage of the growth, and the volume of the grown crystal existing in the space above the surface of the raw material melt is increased. Yes. In addition, the upper part of the grown crystal is drawn to a low temperature part where the temperature difference from the melting point is large. Therefore, the amount of heat released from the grown crystal surface becomes very large, and the amount of heat flowing through the grown crystal from the growth interface increases. On the other hand, in the latter half of the growth, the distance between the growth interface of the grown crystal and the side wall and bottom surface of the crucible is close, the thickness of the melt existing between the crystal side surface and the crucible side wall, the crystal bottom surface and the crucible. The depth of the melt existing between the bottom surfaces of the two is small. Therefore, as the crystal growth proceeds, the heat flow increases and the heat exchange is performed over a short distance, so that it is difficult to control the balance between the amount of heat supplied from the heater to the melt and the amount of heat taken away from the growth interface. Become.

  In crystal growth of a sapphire single crystal, the growth rate is controlled by adjusting the heater output and the pulling speed as the growth progresses. However, the heater has a heat generation distribution. In particular, a cylindrical heater that heats the side of the crucible usually has the largest amount of heat generation at the center position in the height direction of the heater, and the amount of heat generation decreases as it moves away from it in the vertical direction. As the growth progresses and the remaining amount of the raw material melt decreases, the surface position of the raw material melt moves downward with a small amount of heat generated by the side heater. In contrast, since the surface area and volume of the grown crystal increase, the amount of heat taken away from the growth interface increases. Correspondingly, even if the heater output is adjusted, etc., it is very difficult to adjust the crystal growth rate due to the influence of the heat generation distribution in the heater described above.

  In particular, when the remaining amount of the raw material melt is about 20% of the initial raw material melt amount, the amount of heat taken away from the growth interface is very large. The forward speed of the growth interface could not be controlled, and rapid growth occurred, so that bottoming and melt solidification could not be avoided.

  Therefore, in the method for producing a sapphire single crystal according to the present embodiment, as described above, after starting the pulling of the seed crystal, the cylindrical heater lowering step of lowering the cylindrical heater, and / or the disk-shaped heater on the outer surface of the crucible. Of these, the disk-shaped heater moving step of raising the bottom surface can be performed.

  As described above, by changing the relative position of the heater with respect to the crucible as the sapphire single crystal grows, it becomes possible to supply an appropriate amount of heat to the raw material melt even in the latter half of the growth. Control of the speed is facilitated, and bottoming and melt solidification during growth can be prevented.

  For this reason, according to the manufacturing method of the sapphire single crystal of this embodiment, the sapphire single crystal whose crystallization rate (solidification rate) with respect to the input raw material weight is 80% or more can be grown. In particular, in the method for producing a sapphire substrate of this embodiment, the crystallization ratio with respect to the weight of the input raw material is preferably 85% or more, and more preferably 90% or more.

In addition, the crystallization rate with respect to input raw material weight is computable with the following formula | equation (1). (Crystalization rate relative to input raw material weight) = 100 × (weight of obtained sapphire single crystal) / (input raw material weight) Formula (1)
In the cylindrical heater lowering step, for example, the cylindrical heater 14 for heating the side wall of the crucible 12 can be lowered in accordance with the lowering speed of the raw material melt surface position accompanying the progress of the growth. As described above, the cylindrical heater 14 has a peak in heat generation at or near the center position in the height direction. For this reason, by performing the cylindrical heater lowering step, it is possible to supply an appropriate amount of heat to the raw material melt 21 by lowering the cylindrical heater 14 in accordance with the lowering of the surface position of the raw material melt. .

  In the cylindrical heater lowering step, the speed of lowering the cylindrical heater is not particularly limited, and can be selected according to, for example, the calculated lowering speed of the raw material melt surface position. In particular, in the cylindrical heater lowering step, it is preferable to lower the cylindrical heater 14 so that the height of the highest temperature portion of the cylindrical heater 14 is within the surface height of the raw material melt 21 ± 30 mm.

  This is because the cylindrical heater 14 is lowered so that the height of the hottest portion of the cylindrical heater 14 is within the surface height of the raw material melt within ± 30 mm, so that the cylindrical heater 14 is in the vicinity of the surface of the raw material melt. This is because the hottest portion can be disposed, and a sufficient amount of heat can be supplied to the raw material melt 21. In particular, in the cylindrical heater lowering step, it is more preferable to lower the cylindrical heater 14 so that the highest temperature portion of the cylindrical heater 14 has a surface height of the raw material melt 21 of ± 15 mm.

  For example, the highest temperature portion of the cylindrical heater 14 is detected in advance in the height direction of the cylindrical heater 14, and the position of the highest temperature of the cylindrical heater 14 is detected. It can be the height of the part. Moreover, you may consider the center part of the height direction of the cylindrical heater 14 as the hottest part of a cylindrical heater.

  In the disk heater moving process, the disk heater 13 for heating the bottom of the crucible 12 can be raised. As shown in FIG. 1, when the raw material put in the crucible 12 is melted and seeding is performed or at the initial stage of single crystal growth, the disc-shaped heater 13 may be arranged separately from the bottom of the crucible 12. it can. In the disk heater moving step, the distance between the disk heater 13 and the crucible 12 can be reduced by raising the disk heater 13. This is because a sufficient amount of heat can be supplied to the raw material melt 21 by bringing the disc heater 13 close to the bottom surface of the crucible 12.

  In the disk-shaped heater moving process, the speed at which the disk-shaped heater 13 is moved is not particularly limited. For example, it can be arbitrarily selected according to the speed calculated by a preliminary test, the temperature in the heat insulating space 15, other control conditions, and the like. Can be selected. For example, in the disk-shaped heater moving step, the disk-shaped heater 13 can be raised at a speed of 1/20 or more and 1/5 or less of the pulling speed of the seed crystal.

  This is because if the moving speed when raising the disk-shaped heater 13 is less than 1/20 of the crystal pulling speed, there is a possibility that the amount of heat necessary for reducing the raw material melt 21 cannot be sufficiently supplied. . Further, if the moving speed when raising the disk heater 13 is faster than 1/5 of the crystal pulling speed, the amount of heat supplied to the raw material melt 21 may be excessive. In particular, in the step of moving the disc-shaped heater, it is more preferable to raise the disc-shaped heater 13 at a speed of 1/15 or more and 1/5 or less of the crystal pulling speed.

  Even if only one of the cylindrical heater lowering process and the disk heater moving process is performed, bottoming and melt solidification can be avoided, and the crystallization rate can be increased. It is preferable from the viewpoint of suppressing the occurrence of bottoming and melt solidification more reliably.

  The timing of performing the cylindrical heater lowering step and / or the disc-shaped heater moving step can be performed at any timing after the start of pulling up the seed crystal as described above. For example, the shoulder portion of the sapphire single crystal is It is preferable to carry out after the formation.

  In addition, after a shoulder part is formed, after the straight body part of a sapphire single crystal is confirmed, a cylindrical heater lowering process and / or a disk-shaped heater moving process can also be implemented. It can also be carried out when the solidification rate of the raw material melt is 50% or more.

  Here, the shoulder part and the straight body part of the sapphire single crystal will be described with reference to FIG. FIG. 4 schematically shows a cross-sectional view in a plane passing through the central axis of the obtained sapphire single crystal. The sapphire single crystal to be grown can be grown by bringing the seed crystal into contact with the raw material melt as described above and then pulling up the seed crystal while rotating it. At the beginning of pulling up the seed crystal, the sapphire single crystal grows in the width direction. Then, after the growth in the width direction is saturated, the growth in the width direction is hardly observed, and the growth occurs in the pulling direction.

  Therefore, the portion of the sapphire single crystal obtained as shown in FIG. 4 on the side of the seed crystal 51 that has grown in the width direction after the start of the pulling of the seed crystal has a substantially conical shape. A is called the shoulder.

  Then, after the growth in the width direction is saturated, the growth in the width direction is hardly seen as described above, so that it becomes a substantially columnar shape, and this portion B is called a straight body portion.

  In the description of the present embodiment, the term “shoulder” has already been used, but has the same meaning as described here.

  Therefore, when the cylindrical heater lowering step and / or the disc-like heater moving step is performed after the shoulder portion of the sapphire single crystal is formed as described above, the growth in the width direction of the growing sapphire single crystal is saturated. It means that the above-mentioned process is performed after confirming this. That is, in the method for manufacturing a sapphire single crystal according to the present embodiment, the cylindrical heater lowering step and / or the disc-shaped heater moving step can be performed at the time of growing the straight body part in the latter half of the sapphire single crystal growth.

  As described above, the cylindrical heater lowering process and / or the disk-shaped heater moving process is a process performed mainly for the purpose of preventing bottoming and melt solidification. It occurs mainly in the second half of sapphire crystal growth. For this reason, as described above, the cylindrical heater lowering step and / or the disc-like heater moving step can be suitably performed after the shoulder portion, which is the latter stage of sapphire single crystal growth, is formed.

  The method for controlling the output of each heater when performing the above-described cylindrical heater lowering step and / or disk-shaped heater moving step is not particularly limited. Can also be controlled.

  In particular, it is preferable that the output of the heater is controlled to an optimum condition in accordance with a measured value such as a temperature actually measured during the growth of the sapphire single crystal so that the crystal growth rate is a desired value so that the crystal growth rate can be precisely controlled. . In this case, the sapphire single crystal growing apparatus 10 shown in FIG. 1 that can be used in the sapphire single crystal manufacturing method of the present embodiment can have an arbitrary measuring means for detecting temperature and the like.

  Specifically, for example, the sapphire single crystal growing apparatus includes a means for measuring the shoulder surface temperature of the sapphire single crystal, a means for measuring the temperature of the side surface of the outer surface of the crucible, and the temperature of the bottom portion of the outer surface of the crucible. Means for measuring.

  In the case of the sapphire single crystal growth apparatus 10 shown in FIG. 1, for example, as a means for measuring the sapphire single crystal shoulder surface temperature, the sapphire single crystal shoulder surface measuring the sapphire single crystal shoulder surface temperature through the observation window 26a. A temperature measuring means 26 can be provided. As the sapphire single crystal shoulder surface temperature measuring means 26, for example, a radiation thermometer can be used.

  Moreover, as means for measuring the temperature of the side surface of the outer surface of the crucible 12, for example, as described above, from the port (observation window) 25a provided on the side surface of the sapphire single crystal growth apparatus 10, the outer surface of the crucible 12 A crucible side surface temperature measuring means 25 for measuring the side surface temperature can be provided. As the crucible side surface temperature measuring means 25, for example, a radiation thermometer or a thermocouple can be used.

  The crucible side surface temperature measuring means 25 can also be configured so that the temperature measurement position can be arbitrarily changed. In this case, for example, the temperature measurement position can be changed in accordance with the descending speed of the raw material melt surface position calculated in advance. Specifically, it is preferable that the temperature of the side surface portion corresponding to the raw material melt surface position can be measured.

  As a means for measuring the temperature at the bottom of the outer surface of the crucible 12, for example, a through hole penetrating the support shaft 18 can be provided as described above, and the crucible bottom temperature measuring means 24 can be provided in the through hole. . As the crucible bottom temperature measuring means 24, for example, a thermocouple or a radiation thermometer can be used.

  In addition, although the example which provided the raw material melt surface temperature measurement means 23 and the sapphire single crystal shoulder surface temperature measurement means 26 is shown in the sapphire single crystal growth apparatus 10 shown in FIG. It is not limited. For example, the surface temperature of the raw material melt 21 and the surface temperature of the shoulder portion of the sapphire single crystal 22 may be detected by one temperature measuring means.

  Then, as described above, the sapphire single crystal shoulder surface temperature measuring means 26, the crucible side surface temperature measuring means 25, the crucible bottom temperature measuring means 24, the crucible bottom surface temperature, the crucible side surface temperature, and the crucible bottom temperature Based on this, the output of the cylindrical heater 14 and / or the disk-shaped heater 13 can be controlled.

  The control parameter is not limited to the temperature detected by the various temperature measuring means described above. For example, the weight of the grown sapphire single crystal can be detected, and the weight of the grown sapphire single crystal can also be used as a parameter for controlling the heater output.

  Although only the control of the heater output has been described here, the temperature detected by the above-described various temperature measuring means is also used for the position and moving speed of each heater in the cylindrical heater lowering process and / or the disk heater moving process. It can also be configured to be controlled by.

  According to the sapphire single crystal manufacturing method of the present embodiment described above, it is possible to suppress the bottom of the grown crystal and the occurrence of melt solidification in the latter half of the crystal growth. For this reason, the crystallization rate with respect to an input raw material can be made high, and a large sapphire single crystal can be manufactured with a sufficient yield.

  Specific examples and comparative examples will be described below, but the present invention is not limited to these examples.

Here, first, an evaluation method of a sapphire single crystal grown in the following examples and comparative examples will be described.
(Polarization inspection)
Polarization inspection was performed by immersing a sapphire single crystal obtained by growth in methylene iodide and irradiating with a white light source.
(X-ray topograph)
The X-ray topograph was evaluated using a large sample Lang camera (manufactured by Rigaku Corporation, LGL-8).

Next, the growth conditions of the sapphire single crystal in each example and comparative example will be described.
[Example 1]
A sapphire single crystal growing apparatus having a configuration similar to that of the sapphire single crystal growing apparatus 10 shown in FIG. 1 except that a multilayer reflector and a weight sensor described below are further provided. Was trained.

  The structure of the multilayer reflector installed in the sapphire single crystal growing apparatus used in the present embodiment will be described with reference to FIG. FIG. 5 schematically shows the crucible 12 and its upper part in FIG. 1, and the description of the other components is omitted. The same members as those in FIG. 1 are given the same numbers.

  As shown in FIG. 5, the multilayer reflector 61 was provided above the crucible 12 and the raw material melt 21 disposed in the crucible 12. The multilayer reflecting plate 61 has a structure in which a plurality of heat reflecting plates, which are annular plates, are arranged at a predetermined interval in the axial direction of the lifting shaft 19. And in the central part of the radial direction of each heat reflecting plate, so as not to interfere with the pulling shaft 19, the seed crystal 20 attached via the holder 19a, and the sapphire single crystal 22 grown on the tip of the seed crystal 20, An opening is provided. The opening is formed so that the diameter of the opening gradually decreases from the crucible 12 side upward.

  In order to measure the weight of the sapphire single crystal being grown, a weight sensor (not shown) is provided on the pulling shaft 19. And it is comprised so that a heater output may be controlled corresponding to the weight increase speed detected with the weight sensor.

  In addition, in the sapphire single crystal growing apparatus 10 used in the present embodiment, as in the sapphire single crystal apparatus shown in FIG. 1, the surface temperature of the raw material melt 21 is measured through the observation window 23a at the top. A radiation thermometer is provided as the raw material melt surface temperature measuring means 23. In addition, a thermocouple is installed as a crucible bottom temperature measuring means 24 for measuring the bottom temperature of the crucible 12 through the support shaft 18, and the temperature of the side surface portion of the outer surface of the crucible 12 is adjusted through the observation window 25a. A radiation thermometer is installed as the crucible side surface temperature measuring means 25 for measuring. Further, a radiation thermometer is installed as the sapphire single crystal shoulder surface temperature measuring means 26 for measuring the surface temperature of the sapphire single crystal shoulder through the observation window 26a.

  In addition, the inside of the growing furnace is observed with a video camera or visually through an observation window (not shown in FIG. 1), and the video camera image can be confirmed in real time on a monitor installed outside the furnace. When performing observation in the furnace during the growth, it is performed through a light shielding filter.

  Furthermore, the sapphire single crystal growing apparatus used in this example has a gas supply means (not shown) and a gas exhaust means for controlling the inside of the furnace to a desired atmosphere.

  The procedure and conditions when a sapphire single crystal is grown in this example will be specifically described below. The growth direction of the sapphire single crystal grown in this example was the a-axis.

First, 120 kg of polycrystalline aluminum oxide (Al ₂ O ₃ ) as a raw material was filled in a crucible 12 (diameter: 400 mmφ), and this crucible 12 was placed on a support shaft 18 of a sapphire single crystal growth apparatus. The purity of the raw material was 4N. In addition, the seed crystal 20 was held at the tip of the Mo lifting shaft 19 through a Mo holder 19a.

  Thereafter, the atmosphere in the furnace was changed to an Ar gas atmosphere, and then the raw material in the crucible 12 was heated to 2050 ° C. or higher by the carbon disk heater 13 and the cylindrical heater 14 and melted.

  Video camera image taken through observation window for observation inside furnace, raw material melt surface temperature measuring means 23, crucible side surface temperature measuring means 25 radiation thermometer, crucible bottom temperature measurement It was confirmed from the temperature measurement value of the thermocouple of means 24. Next, the temperature of the surface of the raw material melt was measured using the raw material melt surface temperature measuring means 23, and the temperature was adjusted to be 2 ° C. higher than the melting point of aluminum oxide. At this time, the measured value of the thermocouple of the crucible bottom temperature measuring means 24 was 15 ° C. higher than the melting point of aluminum oxide. Furthermore, the temperature of the crucible side surface measured by the crucible side surface temperature measuring means 25 at a position corresponding to the melt surface position was a value 12 ° C. higher than the melting point of aluminum oxide. According to a preliminary test conducted in advance, each measured value becomes the above value, so that the temperature gradient in the heat insulating space 15 including the inside of the raw material melt, and the temperature of the raw material melt grows and seeds the sapphire single crystal. The temperature is suitable for.

Note that the heater output ratio (W ₂ / W ₁ ), which is the ratio of the output (W ₁ ) of the disk heater at this time and the output (W ₂ ) of the cylindrical heater 14, was 1.5.

  In this state, the seeding operation was carried out after sufficiently leaving it to stabilize the temperature at the above-mentioned temperature. After confirming that the tip of the seed crystal 20 became familiar with the raw material melt 21 with a video camera image, the seed crystal was started to be pulled at a pulling speed of 2 mm / hr. After starting the pulling, the outputs of the disk heater 13 and the cylindrical heater 14 were gradually lowered to enlarge the grown crystal diameter and form the shoulder.

  After the formation of the crystal shoulder, the pulling speed of the seed crystal and the sapphire single crystal was changed to 1 mm / hr when shifting to straight body growth. During the growth of the straight body part, the temperature of the disk-shaped heater 13 and the cylindrical heater 14 was set so that the crystal weight increase per unit time was 500 g / hr. When the growth crystal weight reached 50% of the input raw material weight, the disk heater moving process and the cylindrical heater lowering process were started simultaneously. In the disk-shaped heater moving step, the disk-shaped heater 13 was raised at a speed of 0.1 mm / hr. In the cylindrical heater lowering step, the cylindrical heater was lowered at a speed of 1 mm / hr.

  The measured value of the thermocouple of the crucible bottom temperature measuring means 24 when the disk heater moving process and the cylindrical heater lowering process were started simultaneously was 12 ° C. higher than the melting point of aluminum oxide. Moreover, the temperature of the crucible side surface measured by the crucible side surface temperature measuring means 25 at a position corresponding to the melt surface position at the start of both steps was 10 ° C. higher than the melting point of aluminum oxide. Furthermore, the sapphire single crystal shoulder surface temperature measured by the sapphire single crystal shoulder surface temperature measuring means 26 at the start of both steps was 14 ° C. lower than the melting point of aluminum oxide.

  After starting the disk-shaped heater moving step and the cylindrical heater lowering step, the heater output change rate was adjusted so that the crucible bottom temperature and the crucible side wall temperature changed in proportion to the crystal shoulder surface temperature drop rate. In the cylindrical heater lowering step, the height of the highest temperature portion of the cylindrical heater detected in advance was maintained within the surface height of the raw material melt within ± 15 mm. The surface height of the raw material melt at this time is calculated from the pulling rate of the seed crystal and the sapphire single crystal.

  As a result, a sapphire single crystal weighing 117 kg (maximum diameter: 300 mm, length 480 mm) was obtained. That is, it was confirmed that the crystallization rate relative to the input raw material weight (120 kg) reached 97.5%.

  As a result of observing the crystallinity of the obtained sapphire single crystal by polarization inspection, it is a single crystal without grain boundaries, and there are few void defects immediately after the start of growth, and there is no high quality in the straight body part Single crystal was confirmed.

  From this crystal, a sample (vertically cut sample) cut out on the c-plane parallel to the pulling axis and including the pulling axis was prepared, and the distribution of crystal defects was observed by X-ray topography. Similar to the above, it was only slightly present in the upper half of the crystal. It was also confirmed that no lineage was formed in the entire region of the longitudinally cut sample.

  Further, a crystal is grown under the same conditions as this condition, and two c-axis 6 inch φ ingots are punched from the lower half and the upper half, respectively, and each ingot is cut into a substrate shape with a wire saw and then polished. Processing was performed to obtain a c-plane sapphire single crystal substrate having a diameter of 6 inches and a thickness of 1 mm. Sampling was performed every 10 sheets from the obtained single crystal substrate, and X-ray topographic observation was performed in the same manner as the longitudinally cut sample. No lineage was observed on all the substrates.

Next, the half width (FWHM) of these c-plane sapphire single crystal substrates was measured using an X-ray diffraction apparatus. As a result, the FWHM values of all the substrates were in the range of 6 ″ ± 2 ″, and it was confirmed that the crystallinity was very excellent over the entire grown crystal.
[Example 2]
A sapphire single crystal was produced in the same manner as in Example 1 except that the disc-shaped heater moving step was not performed after the growth crystal weight reached 50% of the input raw material weight, and only the cylindrical heater lowering step was performed. .

  As a result, since it became difficult to control the growth rate when the crystal weight reached 112 kg, the growth was terminated and the sapphire single crystal was separated from the raw material melt and cooled. The obtained crystal was a sapphire single crystal weighing 112 kg (maximum diameter: 300 mm, length 465 mm). That is, it was confirmed that the crystallization rate with respect to the input raw material weight (120 kg) reached 93.3%.

  When the obtained sapphire single crystal was evaluated by polarization inspection and X-ray topography in the same manner as in Example 1, crystal defects such as grain boundaries, defective lineage, and polycrystallization were hardly found. The evaluation using the X-ray topograph was performed on the vertically cut sample and the c-plane sapphire single crystal substrate in the same manner as in Example 1.

Moreover, when the X-ray-diffraction measurement was implemented about the c-plane sapphire single crystal produced similarly to Example 1, it has also confirmed having crystallinity equivalent to Example 1. FIG.
[Example 3]
A sapphire single crystal was produced in the same manner as in Example 1 except that the cylindrical heater lowering process was not performed after the growth crystal weight reached 50% of the input raw material weight, and only the disk-shaped heater moving process was performed. .

  As a result, since it became difficult to control the growth rate when the crystal weight reached 108 kg, the growth was terminated and the sapphire single crystal was separated from the raw material melt and cooled. The obtained crystal was a sapphire single crystal weighing 108 kg (maximum diameter: 300 mm, length 452 mm). That is, it was confirmed that the crystallization rate relative to the input raw material weight (120 kg) reached 90.0%.

  When the obtained sapphire single crystal was evaluated by polarization inspection and X-ray topography in the same manner as in Example 1, crystal defects such as grain boundaries, defective lineage, and polycrystallization were hardly found. The evaluation using the X-ray topograph was performed on the vertically cut sample and the c-plane sapphire single crystal substrate in the same manner as in Example 1.

Moreover, when the X-ray-diffraction measurement was implemented about the c-plane sapphire single crystal produced similarly to Example 1, it has also confirmed having crystallinity equivalent to Example 1. FIG.
[Comparative Example 1]
A sapphire single crystal was produced in the same manner as in Example 1 except that the cylindrical heater lowering step and the disc heater moving step were not performed after the growth crystal weight reached 50% of the input raw material weight.

  As a result, since it became difficult to control the growth rate when the crystal weight reached 95 kg, the growth was terminated and the sapphire single crystal was separated from the raw material melt and cooled. The obtained crystal was a single crystal weighing 95 kg (maximum diameter: 300 mm, length 415 mm). That is, it was confirmed that the crystallization rate relative to the input raw material weight (120 kg) was as low as 79.1%.

  When the obtained sapphire single crystal was evaluated by polarization inspection and X-ray topography in the same manner as in Example 1, crystal defects such as grain boundaries, defective lineage, and polycrystallization were hardly found. The evaluation using the X-ray topograph was performed on the vertically cut sample and the c-plane sapphire single crystal substrate in the same manner as in Example 1.

Moreover, when the X-ray-diffraction measurement was implemented about the c-plane sapphire single crystal produced similarly to Example 1, it has also confirmed having crystallinity equivalent to Example 1. FIG.
[Comparative Example 2]
A sapphire single crystal was grown in the same manner as in Example 1 except that the cylindrical heater lowering step and the disc heater moving step were not performed after the grown crystal weight reached 50% of the input raw material weight. .

  When the crystal weight reached 95 kg, it became difficult to control the growth rate, but the heater output change rate and the pulling rate were readjusted to continue the growth. However, when the crystal weight reached 97 kg, the bottom of the crystal occurred and the growth had to be stopped. The pulling was stopped, the heater output was increased, and the crystal and the crucible were fixed and cooled. The obtained crystal had a weight of 89 kg (maximum diameter: 300 mm, length: 390 mm), but a crack was generated and a single crystal could not be obtained.

DESCRIPTION OF SYMBOLS 10 Sapphire single crystal growth apparatus 12 Crucible 13 Disc heater 14 Cylindrical heater 20 Seed crystal 21 Raw material melt 22 Sapphire single crystal 24 Crucible bottom temperature measuring means 25 Crucible side surface temperature measuring means 26 Sapphire single crystal shoulder surface temperature measuring means

Claims (6)

To the raw material melt in the crucible heated and melted by the cylindrical heater arranged to face the side surface of the outer surface of the crucible and the disk-shaped heater arranged to face the bottom surface of the outer surface of the crucible, A method for producing a sapphire single crystal by the Czochralski method of pulling up the seed crystal and the sapphire single crystal while rotating the seed crystal after contacting the seed crystal,
After starting to raise the seed crystal,
A method for producing a sapphire single crystal, wherein a cylindrical heater lowering step for lowering the cylindrical heater and / or a disk heater moving step for raising the disk heater toward the bottom surface of the outer surface of the crucible.   2. The method for producing a sapphire single crystal according to claim 1, wherein the cylindrical heater lowering step and / or the disk-shaped heater moving step is performed after the shoulder portion of the sapphire single crystal is formed.   The method for producing a sapphire single crystal according to claim 1 or 2, wherein the cylindrical heater lowering step and / or the disk-shaped heater moving step is performed when the solidification rate of the raw material melt is 50% or more.   The cylindrical heater lowering step lowers the cylindrical heater so that the height of the hottest portion of the cylindrical heater is within a surface height of the raw material melt within ± 30 mm. The manufacturing method of the sapphire single crystal as described in any one.   5. The sapphire single crystal according to claim 1, wherein, in the step of moving the disk-shaped heater, the disk-shaped heater is raised at a speed of 1/20 or more and 1/5 or less of a pulling speed of the seed crystal. Manufacturing method. A sapphire single crystal comprising means for measuring a sapphire single crystal shoulder surface temperature, means for measuring the temperature of the side surface of the outer surface of the crucible, and means for measuring the temperature of the bottom portion of the outer surface of the crucible. The manufacturing method of the sapphire single crystal as described in any one of Claims 1 thru | or 5 which uses a growing apparatus.

Images