JP2010265150A - Method for producing sapphire single crystal and method for producing seed crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reducing crystal distortion or cracks in a seed crystal used for the crystal growth of a sapphire single crystal and for improving the production efficiency of the sapphire single crystal. <P>SOLUTION: The method includes: a step S101 of processing a seed crystal, in which a seed crystal comprising a sapphire single crystal is processed; and a heating step S102 of the seed crystal, in which the seed crystal subjected to the process step S101 is heated to a predetermined temperature. In the heating step S102 of the seed crystal, crystal distortion or cracks in the seed crystal are removed, which prevents a sapphire ingot from dropping into a melt or generating crystal distortion in a subsequent growing step S103 of the sapphire single crystal. Then the step S103 of growing a single crystal is carried out, in which a sapphire single crystal is grown by using the seed crystal subjected to the heating step S102. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a sapphire single crystal using a melt of aluminum oxide, and a method for producing a seed crystal used for growing a sapphire single crystal.

  In recent years, a sapphire single crystal has been widely used as a substrate material for growing an epitaxial film of a group III nitride semiconductor (such as GaN) when manufacturing a blue LED, for example. In addition, sapphire single crystals are widely used as members for holding polarizers used in, for example, liquid crystal projectors.

  Such a sapphire single crystal plate or wafer is generally obtained by cutting an ingot of sapphire single crystal to a predetermined thickness. Various proposals have been made on methods for producing sapphire single crystal ingots, but they are often produced by melt-solidification methods because of their good crystal characteristics and the ease of obtaining large crystal diameters. In particular, the Czochralski method (Cz method), which is one of the melt solidification methods, is widely used for the production of sapphire single crystal ingots.

  In order to produce an ingot of a sapphire single crystal by the Czochralski method, a crucible is first filled with a raw material of aluminum oxide, and the raw material is melted by heating the crucible by a high frequency induction heating method or a resistance heating method. After the raw material is melted, the seed crystal is brought into contact with the surface of the raw material melt, and the seed crystal is pulled upward at a predetermined speed while rotating the seed crystal at a predetermined rotation speed (see, for example, Patent Document 1).

JP 2008-207992 A

  By the way, the seed crystal is cut out in a predetermined size from, for example, an ingot of a sapphire single crystal. Further, as in Patent Document 1, when a sapphire single crystal ingot is manufactured by, for example, a pulling method, the seed crystal is fixed to a seed crystal mounting jig in a single crystal pulling apparatus. In general, in order to fix the seed crystal to the mounting jig, the seed crystal is processed by cutting a part of the seed crystal.

Thus, when processing such as cutting is performed on the seed crystal, crystal distortion and cracks may occur in the seed crystal. When a sapphire single crystal is grown using a seed crystal having crystal distortion, the crystal distortion in the seed crystal is inherited, and there is a possibility that crystal distortion may occur in the obtained ingot of the sapphire single crystal.
For example, when the sapphire single crystal is grown by the pulling method, the load applied to the seed crystal gradually increases with the growth of the sapphire single crystal (sapphire ingot). At this time, if crystal distortion or cracks occur in the seed crystal, the seed crystal may break during the growth of the sapphire single crystal (sapphire ingot), and the ingot may fall into the melt.

As described above, when crystal distortion occurs in the sapphire single crystal ingot or the sapphire single crystal ingot falls into the melt, the production efficiency of the sapphire single crystal decreases.
An object of this invention is to reduce the crystal distortion and crack of a seed crystal used for crystal growth of a sapphire single crystal. Moreover, it aims at improving the manufacturing efficiency of a sapphire single crystal.

  For this purpose, a method for producing a sapphire single crystal to which the present invention is applied is a method for producing a sapphire single crystal in which a sapphire single crystal is grown on a sapphire seed crystal using a sapphire seed crystal attached to a mounting member. The sapphire seed crystal is attached to the sapphire seed crystal while the sapphire seed crystal attached to the attachment member is immersed in the sapphire melt and pulled up. A crystal growth step for growing a crystal, and the heat treatment is characterized in that the sapphire seed crystal is heat-treated at a temperature lower than a temperature at which the sapphire single crystal is grown on the sapphire seed crystal.

In such a method for producing a sapphire single crystal, the sapphire seed crystal can be characterized by being subjected to a heat treatment after being processed for attachment to the attachment member.
Further, the sapphire seed crystal can be characterized by being subjected to heat treatment at a temperature higher than 1100 ° C. and lower than 1900 ° C.
Furthermore, the sapphire seed crystal can be characterized by being subjected to a heat treatment that maintains the temperature for 0.5 hour or more.
And a sapphire seed crystal can be attached to an attachment member so that the c-axis direction in the crystal orientation of a sapphire seed crystal may become a pulling direction.

  From another viewpoint, the method for producing a seed crystal to which the present invention is applied is a method for producing a sapphire seed crystal that is attached to a mounting member and is immersed in a sapphire melt to grow a sapphire single crystal, A temperature raising step for raising the temperature of the sapphire seed crystal to a temperature lower than the temperature for growing the sapphire single crystal on the sapphire seed crystal, and a temperature holding step for keeping the sapphire seed crystal at a temperature are provided. Can do.

  Such a seed crystal manufacturing method may further include a processing step of performing processing for attaching the sapphire seed crystal to the attachment member before the temperature raising step.

The sapphire seed crystal can be characterized by being heated by being placed in a heated atmosphere.
Furthermore, the sapphire seed crystal can be characterized by being heated while being held by a member made of aluminum oxide.

  According to the present invention, crystal distortion and cracks of a seed crystal used for crystal growth of a sapphire single crystal can be reduced. In addition, the production efficiency of the sapphire single crystal can be improved.

It is a flowchart of an example of the manufacture procedure of the sapphire single crystal in this embodiment. It is a figure of an example for demonstrating the seed crystal to which this embodiment is applied. It is a figure of an example for demonstrating the whole structure of the heating apparatus in this embodiment. It is an example for demonstrating the heating process of the seed crystal in this embodiment. It is a figure of an example for demonstrating the whole structure of the single crystal pulling apparatus used for a single crystal growth process. It is a figure of an example for demonstrating the seed crystal holder in a single crystal pulling apparatus. It is a figure of an example for demonstrating the examination result about the conditions of holding temperature. It is a figure of an example for demonstrating the examination result about the conditions of holding time.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a flowchart of an example of a manufacturing procedure of a sapphire single crystal in the present embodiment. In this embodiment, the sapphire single crystal is manufactured by the Czochralski method (Cz method) which is one of the melt solidification methods. And as shown in FIG. 1, the manufacturing procedure of the sapphire single crystal of this embodiment is equipped with three processes.

First, a seed crystal processing step for processing a seed crystal (sapphire seed crystal) made of a single crystal of sapphire is performed (step 101). The processing in the processing step of the seed crystal of the present embodiment is processing for cutting out a seed crystal of a desired size from a sapphire single crystal for seed crystal, or attaching a seed crystal to a mounting jig of a single crystal pulling device 3 (described later). It is a process such as cutting a seed crystal to fix it.
Next, a seed crystal heating step of heating the seed crystal to a predetermined temperature is performed on the seed crystal that has undergone the processing step (step 102). In this seed crystal heating step, crystal distortion and cracks in the seed crystal are removed. By doing so, in the present embodiment, the sapphire ingot is prevented from falling into the melt or crystal distortion in the sapphire ingot in the subsequent growth process of the sapphire single crystal.
Then, a single crystal growth step for growing a sapphire single crystal (sapphire ingot) is performed using the seed crystal that has undergone the heating step (step 103).

<Process of processing seed crystal>
FIG. 2 is a diagram illustrating an example of the seed crystal 10 to which the present embodiment is applied. FIG. 2 is a perspective view of the seed crystal 10 of the present embodiment.
The seed crystal 10 is used for growing a sapphire single crystal. The seed crystal 10 is obtained by cutting out a predetermined crystal orientation from a sapphire single crystal prepared for a seed crystal. In the single crystal growth step of the present embodiment, pulling is performed in the c-axis direction in the sapphire crystal orientation. The seed crystal 10 is attached to a seed crystal holder 41 (see FIG. 6 described later) of the single crystal pulling apparatus 3 such that the longitudinal direction in FIG. 2 is the pulling direction. Therefore, in the seed crystal 10 of the present embodiment, the longitudinal direction shown in FIG. 2 is the c-axis direction in the crystal orientation.

  In addition, as shown in FIG. 2, the seed crystal 10 is formed with two grooves, a first groove 11 and a second groove 12. These grooves are parts used when attaching to a seed crystal holder 41 (see FIG. 6 described later) of the single crystal pulling apparatus 3 described later. The first groove 11 and the second groove 12 are formed by cutting the seed crystal 10 with, for example, a diamond file.

<Heating process of seed crystal>
FIG. 3 is a diagram illustrating an example of the overall configuration of the heating device 2 in the present embodiment.
As shown in FIG. 3, the heating device 2 includes a furnace chamber 21, a loading table 22 on which the seed crystal 10 is placed, a heater 23 that serves as a heat source, and a control unit 24 that controls the heating temperature of the heater 23. Yes.

The loading table 22 of this embodiment is a table on which the seed crystal 10 is placed. Moreover, in this embodiment, in order to heat the seed crystal 10 which consists of a sapphire single crystal, the mounting base 22 which mounts the seed crystal 10 is made from aluminum oxide. In this way, by making the mounting table 22 made of aluminum oxide, substances other than aluminum oxide are prevented from adhering to the seed crystal 10. For example, when the loading table 22 is made of a material other than sapphire and the seed crystal 10 is heated, the material constituting the loading table 22 reacts with the seed crystal 10, or the material and the atmospheric gas are mixed. By reacting, impurities may adhere to the seed crystal 10. Therefore, in the present embodiment, the loading table 22 is made of aluminum oxide having the same composition as the seed crystal 10.
Further, by using the same material as that of the seed crystal 10 for the mounting table 22, the thermal conductivity of the both becomes equal. By doing so, in this embodiment, for example, the temperature of the part of the seed crystal 10 that contacts the mounting table 22 is prevented from being locally higher or lower than the other parts.

Various heat sources can be used for the heater 23, but in this embodiment, a ceramic heater or a carbon heater is used as the heater 23. In the present embodiment, these are used as the heater 23 to prevent impurities from adhering to the seed crystal 10 due to heat generated by the heat source.
The control unit 24 accepts settings such as a holding temperature T1, a holding time t in heating, a heating rate (rising temperature per unit time), a cooling rate (falling temperature per unit time), and the like in the furnace chamber 21. The heating temperature of the heater 23 is controlled based on the temperature, the temperature of the seed crystal 10 and the like.

FIG. 4 is a diagram illustrating an example of a heating process (a heating process P1, a temperature holding process P2, and a cooling process P3) of the seed crystal 10 in the present embodiment.
First, the seed crystal 10 is placed on the loading table 22 provided in the furnace chamber 21 of the heating device 2. Then, as described below, the seed crystal 10 is subjected to a temperature raising step P1 for raising the temperature to a predetermined temperature, a temperature holding step P2 for maintaining the predetermined temperature for a predetermined time, and a temperature lowering step P3 for lowering the predetermined temperature. Is subjected to heat treatment. In the following description, the temperature held in the temperature holding step P2 is called “holding temperature T1”, and the time for maintaining the temperature of the seed crystal 10 at the holding temperature T1 is called “holding time t”.

(Temperature raising process)
In the temperature raising step P1, as shown in FIG. 4, the temperature of the seed crystal 10 is increased from the initial temperature T0 of the seed crystal 10 (for example, 25 ° C. at normal temperature) to the holding temperature T1. The holding temperature T1 is lower than the temperature at which the sapphire single crystal is grown on the seed crystal 10 in the single crystal growth step described later. In this embodiment, the holding temperature T1 is 1400 ° C. In the present embodiment, the atmospheric condition in the furnace chamber 21 is an air atmosphere (oxygen concentration: 21% by volume). Further, the time until the seed crystal 10 is raised from the initial temperature T0 to the holding temperature T1 is set based on, for example, the temperature rising rate, although it depends on the atmospheric conditions. In the present embodiment, the rate of temperature increase is 10 ° C./min.

In the present invention, the rate of temperature rise depends on the atmospheric conditions and is not particularly limited. However, it is usually arbitrarily selected within the range of 0.5 ° C./min to less than 50 ° C./min in the air atmosphere. It is preferable to set it, and it is desirable to set it in the range of 1 ° C./min or more and less than 20 ° C./min.
On the other hand, if the lower limit is set to 0.5 ° C./min or less, the time in the process becomes long, the productivity of the product is deteriorated, and the cost is not practical. When the rate exceeds 50 ° C./minute, a large temperature gradient is generated in the seed crystal 10.
As the atmospheric conditions, in addition to the air atmosphere, an environment in which the oxygen concentration is slightly increased or a rare gas atmosphere such as Ar (argon) may be employed.
Further, in the temperature raising step P1, as shown in FIG. 4, the temperature may be raised from the initial temperature T0 to the holding temperature T1 in a single step, and the temperature is held from the initial temperature T0 through a plurality of steps including a plurality of temperature raising steps. The temperature may be raised to the temperature T1.

(Temperature holding process)
In the temperature holding step P2, the temperature of the seed crystal 10 is maintained at the holding temperature T1. In this embodiment, the temperature of the seed crystal 10 is set to 1400 ° C. and is continued for 3 hours. In addition, although holding temperature T1 is somewhat dependent also on holding time t, the temperature range of 1100 degreeC or more and less than 1900 degreeC is preferable normally, 1200 to 1800 degreeC is more preferable, Furthermore, 1300 to 1700 degreeC is desirable.

The holding temperature T1 can be arbitrarily set to a higher temperature when the holding time t is shortened in the temperature range of 1100 ° C. or more and less than 1900 ° C., and when the holding time t is increased, the above temperature range. Can be arbitrarily set to a lower temperature.
Specifically, when the holding time t is set to 0.5 hours, for example, it is preferably in the range of 1300 ° C. or higher and lower than 1900 ° C. For example, when the holding time t is 3 hours, it is preferable that the holding time t be in a range of 1200 ° C. or higher and lower than 1900 ° C. Furthermore, when the holding time t is set to 20 hours, for example, it is preferable to set the temperature in the range of 1100 ° C. or higher and lower than 1800 ° C. (see FIG. 7 described later).
On the other hand, in the range where the holding temperature T1 is 1200 ° C. or higher and 1800 ° C. or lower, the holding time t is preferably set to at least 3 hours or longer. The holding time t is more preferably set to 3 hours or more (see FIG. 7 described later).

(Cooling process)
In the temperature lowering process P3, after the holding time t has elapsed in the temperature holding process P2, the temperature of the seed crystal 10 is lowered from the holding temperature T1. In this embodiment, the rate of temperature decrease is set to 5 ° C./min. In the present invention, the rate of temperature decrease is not particularly limited, but is preferably 0.5 ° C./min or more and less than 40 ° C./min, and 1 ° C./min or more and less than 15 ° C./min. It is desirable to do.
The reason for setting the magnitude relationship between the rate of temperature rise and the rate of temperature drop as described above is that if the rate is too large, cracks may occur due to thermal shock, especially when the temperature is lowered because it is more susceptible to thermal shock. It is more preferable that the temperature lowering rate is slower than the temperature rising rate. In the temperature raising step and the temperature lowering step, if the lower limit is 0.5 ° C./min or less, the time in the step becomes longer, the productivity of the product becomes worse, and the cost is not practical.

<Single crystal growth process>
Next, the single crystal growth process will be described.
FIG. 5 is a diagram illustrating an example of the overall configuration of the single crystal pulling apparatus 3 used in the single crystal growth step.
The single crystal pulling apparatus 3 of this embodiment includes a heat insulating container 31, a crucible 32, a heating coil 33, and a pulling bar 40.
The heat insulation container 31 has a columnar outer shape, and a columnar space is formed in the inside. Moreover, the heat insulation container 31 is comprised by assembling the components which consist of a heat insulating material made from zirconia. The crucible 32 is provided below the inner side of the heat insulating container 31 and accommodates the alumina melt 100 formed by melting aluminum oxide. As shown in FIG. 5, the crucible 32 is arranged to open upward in the vertical direction.

The heating coil 33 is disposed so as to face the wall surface of the crucible 32 with the heat insulating container 31 interposed therebetween. The heating coil 33 is arranged so that the upper end portion is located above the upper end of the crucible 32 so that the lower end portion is located below the lower end of the crucible 32.
The heating coil 33 generates an eddy current in the crucible 32 when a high-frequency alternating current is supplied. As a result, Joule heat is generated in the crucible 32 and the crucible 32 is heated. And when the aluminum oxide accommodated in the crucible 32 accompanying the heating of the crucible 32 is heated exceeding the melting | fusing point (about 2050 degreeC), an aluminum oxide will fuse | melt in the crucible 32 and will become the alumina melt 100.

  The pulling rod 40 extends downward from above the heat insulating container 31. The lifting rod 40 is made of, for example, a metal rod such as stainless steel, and is attached so as to be able to move in the vertical direction and rotate around the axis.

  Further, the lifting rod 40 is connected to a lifting drive portion (not shown) for lifting the lifting rod 40 vertically upward and a rotation drive portion (not shown) for rotating the lifting rod 40. The pulling drive unit is composed of a motor so that the pulling speed of the pulling rod 40 can be adjusted. Moreover, the rotational drive part is also comprised with the motor, and can adjust the rotational speed of the raising rod 40 now.

FIG. 6 is a diagram illustrating an example of the seed crystal holder 41 in the single crystal pulling apparatus 3.
A seed crystal holder 41 for mounting and holding the seed crystal 10 is provided at the end of the pulling bar 40 on the vertically lower side. As shown in FIG. 6, the seed crystal holder 41 has one end fixed to the pulling rod 40 and the seed crystal 10 attached to the other end. The seed crystal holder 41 has an opening into which a part of the seed crystal 10 is inserted. A first groove 421 and a second groove 422 are formed in the opening. The first groove 421 and the second groove 422 are grooves formed on the inner wall of the opening from the front side of FIG.

  When attaching the seed crystal 10 to the seed crystal holder 41 as an example of the attachment member, first, the seed crystal 10 is inserted into the opening on the other end side of the seed crystal holder 41. Then, the first groove 421 of the seed crystal holder 41 and the first groove 11 of the seed crystal 10 are opposed to the second groove 422 of the seed crystal holder 41 and the second groove 12 of the seed crystal 10. Align to. Further, as shown in FIG. 6, the seed crystal 10 is inserted into the seed crystal holder 41 by inserting a pin 43 into a space formed by the groove of the seed crystal holder 41 and the groove of the seed crystal 10 facing each other. Fixed.

The seed crystal 10 subjected to the heat treatment in the seed crystal heating step is attached to the seed crystal holder 41 of the single crystal pulling apparatus 3 (see FIG. 6). On the other hand, the solid aluminum oxide filled in the crucible 32 (see FIG. 5) is melted by heating. At this time, the temperature of the alumina melt 100 in the crucible 32 is about 2050 ° C. or higher.
Next, in a state where the lower end portion of the seed crystal 10 is in contact with the aluminum oxide melt, that is, the alumina melt 100, the seed crystal 10 is pulled upward while being rotated, so that a single sapphire is formed below the seed crystal 10. A crystal (sapphire ingot 200) is formed. At this time, the temperature for crystal growth on the seed crystal 10 is at least 2050 ° C. And the obtained sapphire ingot 200 is taken out outside after being cooled. As described above, a series of steps in the growth process of the sapphire single crystal is completed.

  The sapphire ingot 200 obtained in this way is molded by cutting or the like. Furthermore, the sapphire single crystal wafer is obtained by cutting the sapphire ingot 200 in a direction perpendicular to the pulling direction. At this time, since the sapphire ingot 200 of this embodiment is crystal-grown in the c-axis direction, the main surface of the obtained wafer is the c-plane ((0001) plane).

Next, preferable conditions for the holding temperature T1 and the holding time t in the above-described seed crystal heating step will be described.
The inventor used the seed crystal 10 in which cracks and crystal distortion occurred through the seed crystal processing step, and performed the seed crystal heating step at different holding temperatures T1 or holding times t. Thereby, the several seed crystal 10 produced based on each condition was obtained. Then, the state (external shape, presence or absence of cracks, degree of crystal distortion) of the obtained seed crystal 10 was examined, and four stages of evaluation (A evaluation, B evaluation, C evaluation, D evaluation) were performed.

In the A evaluation, the outer shape of the seed crystal 10 is not changed before and after the heating step, and the seed crystal 10 is not cracked. In addition, the A-evaluated seed crystal 10 has no crystal distortion.
In addition, the seed crystal 10 of A evaluation is in a state where the seed crystal 10 is not broken during the crystal growth when the single crystal growth process is performed using the seed crystal 10. Further, the seed crystal 10 of A evaluation is once used for pulling up the sapphire ingot 200 and then used for pulling up a new sapphire ingot 200 separately without going through the seed crystal heating step again (hereinafter referred to as single crystal growth step). (Referred to as reuse of the seed crystal 10).

In the B evaluation, a slight change was observed in the outer shape (appearance) of the seed crystal 10 before and after the heating step (B1 evaluation), and a slight crack was observed in the seed crystal 10 (B2 evaluation). In addition, the seed crystal 10 of B evaluation does not show crystal distortion.
In addition, the seed crystal 10 of B evaluation is in a state where the seed crystal 10 is not broken when the seed crystal 10 is used to perform a single crystal growth step. Further, the seed crystal 10 for B evaluation can be reused in the single crystal growth step, similarly to the A evaluation.

In the C evaluation, a slight change is observed in the outer shape of the seed crystal 10 before and after the heating step (C1 evaluation), and cracks are observed in the seed crystal 10 (C2 evaluation). The C-evaluated seed crystal 10 shows no crystal distortion.
The seed crystal 10 of C evaluation is in a state where the seed crystal 10 is not broken when the seed crystal 10 is used to perform a single crystal growth step. The C-evaluated seed crystal 10 cannot be reused in the single crystal growth process.

The D evaluation is one in which the outer shape of the seed crystal 10 is remarkably changed before and after the heating step (D1 evaluation), and the seed crystal 10 has many cracks (D2 evaluation). Further, when the crystal state of the seed crystal 10 of D evaluation is observed, crystal distortion is observed.
The seed crystal 10 of D evaluation may cause crystal distortion in an ingot of a sapphire single crystal due to cracks and crystal distortion in the seed crystal 10 when the single crystal is grown using the seed crystal 10. Is expensive. Further, the seed crystal 10 of D evaluation has a high possibility that the seed crystal 10 is broken when the seed crystal 10 is used to perform a single crystal growth step.

FIG. 7 is a diagram illustrating an example of the condition of the holding temperature T1.
In the seed crystal heating step, a plurality of seed crystals 10 were produced by changing the conditions of the holding temperature T1 and the holding time t. The atmospheric condition was an air atmosphere.
As shown in FIG. 7, when the holding time t was as short as 0.5 hours, the evaluation was C2 evaluation when the holding temperature T1 was set to less than 1100 ° C. (1000 ° C.). When the holding temperature T1 is set to less than 1100 ° C. (1000 ° C.), it is considered that cracks and crystal distortion in the seed crystal 10 have not been sufficiently removed.

  When the holding temperature T1 was set to 1100 ° C to 1200 ° C, the evaluation result was B2 evaluation. It was found that when the holding temperature T1 reached 1200 ° C., the crystal distortion of the seed crystal 10 began to be removed although some cracks were observed. This is considered to be because the atoms constituting the seed crystal 10 are easily moved by setting the holding temperature T1 higher than 1200 ° C., and the crystal distortion is relaxed.

  Moreover, when the holding temperature T1 was set to 1300 ° C. to 1800 ° C., the evaluation was A evaluation. When the holding temperature T1 is set within these temperature ranges, the outer shape of the seed crystal 10 before and after heating is not changed, crystal distortion and cracks are removed, and the seed crystal 10 can be reused. It became clear.

  When holding temperature T1 was set to 1900 degreeC, the evaluation became B1 evaluation. It was found that when the holding temperature T1 reached 1900 ° C., the seed crystal 10 as a whole was slightly deformed by the heating process.

  When holding temperature T1 was set to 2000 degreeC, the evaluation became D1 evaluation. Based on the relationship between the holding temperature T1 and the state of the seed crystal 10, the cracks in the seed crystal 10 tend to be removed as the holding temperature T1 increases. However, it has been found that when the holding temperature T1 is higher than 1900 ° C., the seed crystal 10 itself is deformed by heating.

Here, since the melting point of sapphire is about 2050 ° C., it is necessary to suppress the holding temperature T1 to 2000 ° C. or less.
Hereinafter, the cases where the holding time t is 3 hours and 20 hours are also shown in FIG. 7 and will not be described in detail, but the evaluation of the seed crystals differs depending on the holding temperature T1. However, in the temperature range where the holding temperature T1 is 1300 ° C. to 1700 ° C., the evaluation was A evaluation even at a holding time t of at least 0.5 hour or more.

FIG. 8 is a diagram illustrating an example of the condition for the holding time t.
A plurality of seed crystals 10 were produced using the heating device 2 with different conditions for the holding time t. The holding temperature T1 was 1200 ° C. and 1800 ° C., and the atmospheric condition was an air atmosphere.
As shown in FIG. 8, when the holding temperature T1 is 1200 ° C., when the holding time t is set to 2 hours or less, the evaluation is B2 evaluation. At this holding temperature T1, it is considered that when the holding time t is 2 hours or less, the atoms have not moved to such an extent that the cracks of the seed crystal 10 can be removed.

When the holding time t was set to 3 hours or more (or more than 2 hours), the evaluation result was A evaluation.
Here, even when the holding time t was set longer than 3 hours such as 20 hours, for example, there was no significant difference in the degree of cracking and deformation in the seed crystal 10. In view of the cost of the seed crystal heating step, the holding time t may be at least 3 hours.
Further, as shown in FIG. 8, when the holding temperature T1 is 1800 ° C., the holding time t may be 0.5 hours, and the evaluation result is A evaluation. On the other hand, at the holding time t of 1 hour or more, the evaluation was B1 evaluation, and a slight change was observed in the outer shape of the seed crystal 10.

It should be noted that the seed crystal 10 of D evaluation (D1 evaluation or D2 evaluation) has a large variation in outer shape, or when single crystal growth is performed using the seed crystal 10, cracks or crystals in the seed crystal 10 are observed. Due to the distortion, there is a high possibility that crystal distortion will occur in the sapphire single crystal ingot, which is not preferable for use in the subsequent single crystal growth step.
Furthermore, when the seed crystal 10 of C evaluation was subjected to a single crystal growth step using the seed crystal 10, the seed crystal 10 was highly likely to break and was not recommended.
In addition, A evaluation and B evaluation (B1 evaluation or B2 evaluation) could be used as a seed crystal in the subsequent single crystal growth process.

As described above, in the step of heating the seed crystal shown in FIG. 7, the holding temperature T1 is set to 1100 ° C. or higher and lower than 1900 ° C., more preferably 1200 ° C. or higher and lower than 1900 ° C., further desirably 1300. It is understood that by setting the temperature to 1 ° C. or more and less than 1800 ° C., cracks and crystal distortion in the seed crystal 10 can be removed while suppressing deformation of the seed crystal 10.
Further, from the results shown in FIG. 8, when the holding temperature T1 is in the range of 1200 ° C. or higher and 1800 ° C. or lower, when the holding time t is at least 0.5 hour or more in the seed crystal heating step, B evaluation (B1 evaluation or B2 evaluation) and A evaluation, and it can be understood that cracks and crystal distortion in the seed crystal 10 can be removed while suppressing deformation of the seed crystal 10.

  In particular, as in this embodiment, when a sapphire single crystal is grown in the c-axis direction, it is known that crystal distortion is more likely to occur than when grown in the a-axis direction, for example. . On the other hand, in this embodiment, by removing the crystal distortion in the seed crystal 10, the generation of the crystal distortion in the sapphire single crystal is suppressed when the sapphire single crystal is grown using the seed crystal 10. It becomes possible to do.

In addition, when a heating method in which the seed crystal 10 is locally heated is used in the seed crystal heating step, the seed crystal 10 may be deformed or crystal distortion may be caused by local heating. . On the other hand, in this embodiment, the seed crystal 10 is arranged in the furnace chamber 21 of the heating device 2 and the seed crystal 10 is placed in a heated atmosphere, so that the seed crystal 10 is almost uniformly distributed over the entire seed crystal 10. 10 is being heated.
Furthermore, in this embodiment, by placing the seed crystal 10 in a heated atmosphere for a predetermined time, the seed crystal 10 is sufficiently heated so that atoms of the seed crystal 10 can move. By doing so, cracks and crystal distortion in the seed crystal 10 are removed.

  In the seed crystal heating step in this embodiment, the seed crystal 10 is heated so that the holding temperature T1 is constant. Here, as described above, if the holding temperature T1 is higher than 1100 ° C., the crystal distortion and cracks of the seed crystal 10 can be removed. Therefore, in the temperature holding step P2, the holding temperature T1 may fluctuate up and down as long as the holding temperature T1 is within the temperature range of 1100 ° C. or higher and lower than 1900 ° C.

2 ... heating device, 3 ... single crystal pulling device, 10 ... seed crystal, 41 ... seed crystal holder

Claims (9)

Using a sapphire seed crystal attached to an attachment member, a sapphire single crystal manufacturing method for growing a sapphire single crystal on the sapphire seed crystal,
An attachment step of attaching the heat-treated sapphire seed crystal to the attachment member;
A step of immersing the sapphire seed crystal attached to the attachment member in a sapphire melt and pulling up the sapphire seed crystal while growing a sapphire single crystal on the sapphire seed crystal; and
In the heat treatment, the sapphire seed crystal is heat-treated at a temperature lower than a temperature at which the sapphire seed crystal is grown on the sapphire seed crystal.   The method for producing a sapphire single crystal according to claim 1, wherein the sapphire seed crystal is subjected to the heat treatment after being processed for attachment to the attachment member.   The method for producing a sapphire single crystal according to claim 1 or 2, wherein the sapphire seed crystal is subjected to heat treatment at a temperature higher than 1100 ° C and lower than 1900 ° C.   The method for producing a sapphire single crystal according to any one of claims 1 to 3, wherein the sapphire seed crystal is subjected to heat treatment for holding at the temperature for 0.5 hours or more.   5. The sapphire single crystal according to claim 1, wherein the sapphire seed crystal is attached to the attachment member such that a c-axis direction in a crystal orientation of the sapphire seed crystal is a pulling direction. Crystal production method. A method for producing a sapphire seed crystal that is attached to a mounting member and is immersed in a sapphire melt to grow a sapphire single crystal,
A temperature raising step for raising the temperature of the sapphire seed crystal to a temperature lower than the temperature at which the sapphire single crystal is grown on the sapphire seed crystal;
And a temperature holding step of holding the sapphire seed crystal at the temperature.   The method for producing a seed crystal according to claim 6, further comprising a processing step of performing processing for attaching the sapphire seed crystal to the attachment member before the temperature raising step.   The method for producing a seed crystal according to claim 6 or 7, wherein the sapphire seed crystal is heated by being placed in a heated atmosphere.   The said sapphire seed crystal is heated in the state hold | maintained at the member made from aluminum oxide, The manufacturing method of the seed crystal of Claim 8 characterized by the above-mentioned.

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