JP2010173929A - Sapphire single crystal pulling apparatus, crucible for producing sapphire single crystal, and method for producing sapphire single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deformation of a crucible accompanying solidification of alumina melt, and to obtain a continuous temperature gradient in the alumina melt. <P>SOLUTION: In a single crystal pulling apparatus, a high frequency current is supplied to a heating coil 30 to heat a crucible 20 and the alumina melt in the crucible 20 to grow a sapphire ingot made of a sapphire single crystal from the alumina melt in the crucible 20. The crucible 20 includes a bottom 21 and a wall 22, the wall rising from the periphery of the bottom 21 and having a thickness which continuously increases from the side away from the bottom 21 to the side close to the bottom. The heating coil 30 is wound around the outside of the wall 22 of the crucible 20 and arranged so that the space between the heating coil and the wall 22 on the side close to the bottom 21 is smaller than the space between the heating coil and the wall 22 on the side away from the bottom 21. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sapphire single crystal pulling apparatus using a melt of aluminum oxide, a crucible for producing a sapphire single crystal, and a method for producing 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 a holding member for a polarizer used in a liquid crystal projector, for example.

  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 for a method for producing a sapphire single crystal ingot, but it is often produced by a melt-solidification method because of its good crystal characteristics and ease of obtaining a large crystal size. 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 manufacture a sapphire single crystal ingot by the Czochralski method, first, a crucible is filled with a raw material of aluminum oxide, and the crucible is heated by an induction heating method or a resistance heating method to melt the raw material. After the raw material is melted, the seed crystal cut in a predetermined crystal orientation 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 (patent) Reference 1).

  By the way, in the production of a sapphire single crystal using the Czochralski method, in the crucible, by providing a temperature gradient that makes the temperature of the alumina melt on the lower side higher than the temperature of the alumina melt on the upper side, It is preferable from the viewpoint of obtaining a homogeneous single crystal to cause natural convection in the melt.

As a conventional technique described in the publication, a crucible for a single crystal pulling apparatus that pulls a single crystal from a melt of langasite (La ₃ Ga ₅ SiO ₁₄ ) heated by induction heating is used. There is also a technique using a thin plate thickness (see Patent Document 2).

  In addition, as a conventional technique described in other publications, as a crucible for a single crystal pulling apparatus that pulls a single crystal from a melt of langasite that is also heated by induction heating, a flange shape that protrudes outward from the lower side surface There is a technique that uses an outer peripheral portion (see Patent Document 3).

JP 2008-207992 A JP 2004-284853 A JP 2004-284854 A

  By the way, in the manufacture of a sapphire single crystal by the Czochralski method, after pulling up the sapphire single crystal, a part of the alumina melt remains in the crucible. This alumina melt is cooled by stopping induction heating to the crucible, and then solidifies on the bottom side of the crucible.

Here, when using a crucible with the lower side of the side thinner than the upper side, the thinner part of the lower side is subjected to mechanical stress by solidified alumina (aluminum oxide). The crucible is likely to be deformed.
In addition, when the flange-shaped outer peripheral portion is formed so as to protrude on the lower side of the side surface, the formation portion of the flange-shaped outer peripheral portion is heated intensively. It becomes difficult to obtain a temperature gradient.

  An object of the present invention is to suppress crucible deformation accompanying solidification of an alumina melt and to make a temperature gradient in the alumina melt continuous.

  For this purpose, a sapphire single crystal pulling apparatus to which the present invention is applied includes a crucible containing an alumina melt, induction heating means for induction heating the crucible, and a sapphire single crystal from the alumina melt contained in the crucible. The crucible has a bottom portion and a wall portion that rises from the periphery of the bottom portion and has a wall thickness that continuously increases from the side farther from the bottom portion toward the side closer to the bottom portion, and induction heating means Has a heating coil wound around the outside of the wall part of the crucible and arranged so that the distance from the wall part closer to the bottom is closer than the distance from the wall part away from the bottom. It is said.

In such a sapphire single crystal pulling apparatus, the crucible may be made of iridium, an alloy containing iridium, platinum, or an alloy containing platinum.
Further, the outer surface of the wall portion of the crucible may be characterized by having a linear cross-sectional shape from the side closer to the bottom toward the side away from the bottom.
Furthermore, the crucible can be characterized in that the outer diameter of the wall portion on the side close to the bottom is set larger than the outer diameter of the wall portion on the side far from the bottom.
Furthermore, the pulling means can be characterized by pulling up the sapphire single crystal grown in the c-axis direction from the alumina melt.

  From another point of view, the present invention is a crucible that contains alumina melt and is used for manufacturing a sapphire single crystal, and rises from the bottom and the periphery of the bottom and approaches the bottom from the side farther from the bottom. It has the wall part which thickness increases continuously toward the side, It is characterized by the above-mentioned.

In such a crucible, the bottom part and the wall part may be made of iridium, an alloy containing iridium, platinum, or an alloy containing platinum.
Moreover, the outer diameter of the wall part in the side close | similar to a bottom part can be set larger than the outer diameter of the wall part in the side far from a bottom part.
Further, the outer surface of the wall portion may have a linear cross-sectional shape from a side closer to the bottom portion to a side away from the bottom portion.

  Furthermore, from another viewpoint, the method of manufacturing a sapphire single crystal to which the present invention is applied rises from the bottom and the peripheral edge of the bottom and continuously increases in thickness from the side farther from the bottom toward the side closer to the bottom. From the distance between the charging step of adding the alumina raw material to the crucible having the increasing wall portion, and the wall portion on the side where the crucible charged with the alumina raw material is wound outside the wall portion of the crucible and away from the bottom portion A heating process in which an alternating current is supplied to a heating coil arranged so that the distance from the wall near the bottom is close, and an alumina raw material is melted to form an alumina melt, and heating. It has a growth process in which a crucible using a coil is induction-heated and a sapphire single crystal is pulled up from the alumina melt in the crucible to grow.

  Such a manufacturing method can be characterized in that the sapphire single crystal is grown in the c-axis direction in the growth step.

  ADVANTAGE OF THE INVENTION According to this invention, while suppressing the deformation | transformation of the crucible accompanying solidification of an alumina melt, the temperature gradient in an alumina melt can be made continuous.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Embodiment 1>
FIG. 1 is a diagram for explaining an example of the configuration of a single crystal pulling apparatus 1 to which the present embodiment is applied.
The single crystal pulling apparatus 1 includes a heating furnace 10 for growing a sapphire ingot 200 made of a sapphire single crystal. The heating furnace 10 includes a heat insulating container 11. Here, the heat insulation container 11 has a columnar outer shape, and a columnar space is formed in the inside. And the heat insulation container 11 is comprised by assembling the components which consist of a heat insulating material made from zirconia. The heating furnace 10 further includes a chamber 14 that houses the heat insulating container 11 in an internal space. Furthermore, the heating furnace 10 is formed to penetrate the side surface of the chamber 14, and the gas supply pipe 12 that supplies gas from the outside of the chamber 14 to the inside of the heat insulating container 11 through the chamber 14 is formed to penetrate the side surface of the chamber 14. And a gas discharge pipe 13 for discharging gas from the inside of the heat insulating container 11 to the outside through the chamber 14.

Further, a crucible 20 that accommodates an alumina melt 300 formed by melting aluminum oxide is disposed below the inner side of the heat insulating container 11 so as to open vertically upward.
Furthermore, the heating furnace 10 includes a metal heating coil 30 wound around a portion that is outside the side surface on the lower side of the heat insulating container 11 and inside the side surface on the lower side of the chamber 14. The heating coil 30 is disposed so as to face the wall surface of the crucible 20 with the heat insulating container 11 interposed therebetween.
Details of the crucible 20 and the heating coil 30 will be described later.

  Furthermore, the heating furnace 10 includes a lifting rod 40 that extends downward from above through through holes provided in the upper surfaces of the heat insulating container 11 and the chamber 14, respectively. The pulling rod 40 is attached so as to be able to move in the vertical direction and rotate around the axis. A sealing material (not shown) is provided between the through hole provided in the chamber 14 and the lifting rod 40. A holding member 41 for attaching and holding a seed crystal 210 (see FIG. 2 described later) serving as a base for growing the sapphire ingot 200 is attached to an end portion of the pulling bar 40 on the vertically lower side. Yes.

  Further, the single crystal pulling apparatus 1 includes a pulling drive unit 50 for pulling up the pulling bar 40 vertically upward and a rotation driving unit 60 for rotating the pulling bar 40. Here, the pulling drive unit 50 is configured by a motor or the like, and can adjust the pulling speed of the pulling rod 40. Moreover, the rotation drive part 60 is also comprised by the motor etc., and can adjust the rotational speed of the raising rod 40 now.

  Furthermore, the single crystal pulling apparatus 1 includes a gas supply unit 70 that supplies gas into the chamber 14 via the gas supply pipe 12. In the present embodiment, the gas supply unit 70 can supply an inert gas such as nitrogen, for example. Moreover, the gas supply part 70 can also supply oxygen in addition to inert gas, such as nitrogen, as needed. The gas supply unit 70 adjusts the concentration of oxygen in the mixed gas, for example, by changing the mixing ratio of oxygen and nitrogen, or adjusts the flow rate of the mixed gas supplied into the chamber 14. It is also possible to do.

  On the other hand, the single crystal pulling apparatus 1 includes an exhaust unit 80 that exhausts gas from the inside of the chamber 14 via the gas exhaust pipe 13. The exhaust unit 80 includes, for example, a vacuum pump or the like, and can decompress the chamber 14 and exhaust the gas supplied from the gas supply unit 70.

  Furthermore, the single crystal pulling apparatus 1 includes a coil power supply 90 that supplies an alternating current to the heating coil 30. The coil power supply 90 can set the presence / absence of supply of an alternating current to the heating coil 30 and the amount of current to be supplied, and further the frequency of the alternating current supplied to the heating coil 30.

  In addition, the single crystal pulling apparatus 1 includes a weight detection unit 110 that detects the weight of the sapphire ingot 200 that grows on the lower side of the pulling bar 40 via the pulling bar 40. The weight detection unit 110 includes, for example, a known weight sensor.

  The single crystal pulling apparatus 1 includes a control unit 100 that controls operations of the pulling drive unit 50, the rotation drive unit 60, the gas supply unit 70, the exhaust unit 80, and the coil power supply 90 described above. Further, the control unit 100 calculates the crystal diameter of the sapphire ingot 200 to be pulled up based on the weight signal output from the weight detection unit 110 and feeds it back to the coil power supply 90.

  In the present embodiment, the heating coil 30 and the coil power source 90 constitute an induction heating means. The lifting rod 40, the holding member 41, and the lifting drive unit 50 constitute a lifting means.

FIG. 2 shows an example of the configuration of a sapphire ingot 200 manufactured using the single crystal pulling apparatus 1 shown in FIG.
The sapphire ingot 200 includes a seed crystal 210 that serves as a base for growing the sapphire ingot 200, a shoulder 220 that extends under the seed crystal 210 and is integrated with the seed crystal 210, and a lower portion of the shoulder 220. A straight body portion 230 extending and integrated with the shoulder portion 220, and a tail portion 240 extending under the straight body portion 230 and integrated with the straight body portion 230 are provided. In the sapphire ingot 200, a single crystal of sapphire grows in the c-axis direction from the upper side, that is, from the seed crystal 210 side, to the lower side, that is, from the tail part 240 side.

  Here, the shoulder portion 220 has a shape in which the diameter gradually increases from the seed crystal 210 side toward the straight body portion 230 side. Further, the straight body portion 230 has such a shape that the diameters thereof are substantially the same from the upper side to the lower side. The diameter of the straight body 230 is set to a value slightly larger than the diameter of the desired sapphire single crystal wafer. And the tail part 240 has the shape which becomes convex shape from upper direction to the downward direction, when the diameter reduces gradually toward the downward direction from the upper part.

In the present embodiment, the reason why the sapphire ingot 200 having a crystal grown in the c-axis direction is manufactured is as follows.
In general, a blue LED substrate material, a polarizer holding member of a liquid crystal projector, and the like are cut out from an ingot so that the plane ((0001) plane) perpendicular to the c-axis of the sapphire single crystal is the main plane. Often wafers are used. Therefore, from the viewpoint of yield, it is preferable to use a sapphire single crystal ingot grown in the c-axis direction for cutting out the wafer. For this reason, in the present embodiment, the sapphire ingot 200 in which the crystal is grown in the c-axis direction is manufactured in consideration of the convenience in the subsequent process.

  FIG. 3 is an example of a cross-sectional view for explaining the configuration of crucible 20 and heating coil 30 and the positional relationship between them in single crystal pulling apparatus 1 shown in FIG.

First, the configuration of the crucible 20 will be described.
The crucible 20 is made of iridium and has a shape that opens vertically upward. The crucible 20 has a bottom portion 21 and a wall portion 22 that rises upward from the periphery of the bottom portion 21. The crucible 20 of the present embodiment has a shape in which the outer diameter gradually increases from vertically upward to vertically downward.

  In the following description, a surface of the bottom portion 21 that faces outward is referred to as a bottom outer surface 21a, and a surface that faces inward, that is, a surface that forms a recess, is referred to as a bottom inner surface 21b. In addition, the surface facing the outer side, that is, the surface facing the heating coil 30 in the wall portion 22 is referred to as a wall outer surface 22a, and the surface facing the inner side, that is, the surface that forms a recess together with the bottom inner surface 21b is referred to as a wall inner surface 22b.

The bottom portion 21 has a circular shape, and has a substantially uniform thickness (for example, about 2 mm to 7 mm) over the entire region.
On the other hand, the wall portion 22 has a configuration in which the thickness is increased more on the lower side than on the upper side. More specifically, in the present embodiment, the thickness of the wall portion 22 in the uppermost portion, that is, the first thickness T1 is 2 mm, whereas the thickness of the wall portion 22 in the lowermost portion, that is, the second thickness. T2 is 7 mm. The wall inner surface 22b has a linear cross section that extends substantially vertically downward from above, whereas the wall outer surface 22a has a linear cross section that obliquely extends downward from above. Thus, the wall outer surface 22a of the crucible 20 has a linear cross-sectional shape that is continuous from the top to the bottom and has no inflection point.

The height H of the crucible 20 is about 150 mm. The first outer diameter Do1 that is the diameter of the uppermost side of the crucible 20 is about 154 mm. Furthermore, the diameter of the lowermost side of the crucible 20, that is, the second outer diameter Do2 which is the diameter of the wall outer surface 22a at the bottom 21, is about 164 mm.
On the other hand, the inner diameter Di which is the diameter of the concave portion of the crucible 20 is constant at about 150 mm regardless of the position in the vertical direction.
FIG. 3 shows an example of a cross section of the crucible 20 and does not reflect the specific dimensions.

Next, the configuration of the heating coil 30 will be described.
The heating coil 30 is configured by, for example, a hollow copper tube. The heating coil 30 is wound in a spiral shape and has a cylindrical shape when viewed as a whole. That is, in the present embodiment, the inner diameter on the upper side and the inner diameter on the lower side of the heating coil 30 are substantially the same. Thereby, the space formed in the inside by the wound heating coil 30 is cylindrical. Further, the central axis of the heating coil 30 passing through the cylindrical space is substantially perpendicular to the horizontal direction.

Furthermore, the relative positional relationship between the crucible 20 and the heating coil 30 in the single crystal pulling apparatus 1 (see FIG. 1) will be described.
First, the crucible 20 is disposed inside a cylindrical space formed by the heating coil 30. Then, the crucible 20 is placed at a site that is substantially in the center of the circular region formed by the heating coil 30. The lower end of the heating coil 30 is positioned below the lower end of the crucible 20, and the upper end of the heating coil 30 is positioned above the upper end of the crucible 20.

  Thereby, the space | interval (distance) L which is the shortest distance with the wall part outer surface 22a of the inner side crucible 20 of the heating coil 30 reduces gradually from the upper direction of the crucible 20, and the heating coil 30 and the crucible 20 are made. The lower side is closer. More specifically, the lowermost side of the inner crucible 20 on the inner side of the heating coil 30 than the first distance L1 which is the shortest distance from the wall outer surface 22a on the uppermost side of the inner crucible 20 of the heating coil 30. The second distance L2, which is the shortest distance from the wall outer surface 22a, is shorter. In this example, the difference between the first interval L1 and the second interval L2 is the difference between the first thickness T1 and the second thickness T2, that is, 5 mm.

FIG. 4 is a flowchart for explaining a procedure for manufacturing the sapphire ingot 200 shown in FIG. 2 using the single crystal pulling apparatus 1 shown in FIG.
In manufacturing the sapphire ingot 200, first, a melting step is performed in which solid aluminum oxide filled in the crucible 20 in the chamber 14 is melted by heating (step 101).
Next, a seeding step is performed in which temperature adjustment is performed in a state where the lower end portion of the seed crystal 210 is in contact with the aluminum oxide melt, that is, the alumina melt 300 (step 102).
Next, the shoulder crystal forming step is performed in which the shoulder crystal 220 is formed below the seed crystal 210 by pulling upward while rotating the seed crystal 210 in contact with the alumina melt 300 (step 103).
Subsequently, a straight body part forming step is performed in which the straight body part 230 is formed below the shoulder part 220 by pulling upward through the seed crystal 210 while rotating the shoulder part 220 (step 104).
Further, the tail forming step of forming the tail 240 below the straight body 230 by pulling up and separating from the alumina melt 300 while rotating the straight body 230 through the seed crystal 210 and the shoulder 220. Is executed (step 105).
And the cooling process which stops and cools the heating of the alumina melt 300 in the crucible 20 is executed (step 106), and after the obtained sapphire ingot 200 is cooled, it is taken out of the chamber 14 and a series of manufacturing is performed. Complete the process.

  The sapphire ingot 200 thus obtained is first cut at the boundary between the shoulder 220 and the straight body 230 and at the boundary between the straight body 230 and the tail 240, and the straight body 230 is cut out. . Next, the cut out straight body portion 230 is further cut in a direction orthogonal to the longitudinal direction to form a sapphire single crystal wafer. 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). The obtained wafer is used for manufacturing blue LEDs and polarizers.

  Then, each process mentioned above is demonstrated concretely. However, here, the description will be made in order from the preparation process executed before the melting process of step 101.

(Preparation process)
In the preparation step, first, a <0001> c-axis seed crystal 210 is prepared. Next, the seed crystal 210 is attached to the holding member 41 of the pulling rod 40 and set at a predetermined position. Subsequently, the crucible 20 is filled with a raw material of aluminum oxide, that is, an alumina raw material, and the heat insulating container 11 is assembled in the chamber 14 using parts made of a heat insulating material made of zirconia.
Then, the inside of the chamber 14 is decompressed using the exhaust unit 80 in a state where the gas supply from the gas supply unit 70 is not performed. Thereafter, the gas supply unit 70 supplies a predetermined gas into the chamber 14 to bring the inside of the chamber 14 to normal pressure.

(Melting process)
In the melting step, the gas supply unit 70 supplies a predetermined gas into the chamber 14. Note that the gas supplied in the melting step may be the same as or different from that in the preparation step. At this time, the rotation driving unit 60 rotates the pulling rod 40 at the first rotation speed.
The coil power supply 90 supplies a high-frequency alternating current (referred to as a high-frequency current in the following description) to the heating coil 30. When a high frequency current is supplied from the coil power supply 90 to the heating coil 30, the magnetic flux repeatedly generates and disappears around the heating coil 30. When the magnetic flux generated by the heating coil 30 crosses the crucible 20 through the heat insulating container 11, a magnetic field is generated on the wall surface of the crucible 20 so as to prevent the change of the magnetic field, thereby eddy current in the crucible 20. Will occur. The crucible 20 generates Joule heat (W = I ² R) proportional to the skin resistance (R) of the crucible 20 due to the eddy current (I), and the crucible 20 is heated. When the crucible 20 is heated and the aluminum oxide accommodated in the crucible 20 is heated to exceed its melting point (2054 ° C.), the aluminum oxide is melted in the crucible 20 to become an alumina melt 300.

(Seeding process)
In the seeding step, the gas supply unit 70 supplies a predetermined gas into the chamber 14. Note that the gas supplied in the seeding step may be the same as or different from that in the melting step.
Then, the pulling drive unit 50 lowers the pulling rod 40 to a position where the lower end of the seed crystal 210 attached to the holding member 41 comes into contact with the alumina melt 300 in the crucible 20 to stop. In this state, the coil power supply 90 adjusts the current value of the high-frequency current supplied to the heating coil 30 based on the weight signal from the weight detection unit 110.

(Shoulder formation process)
In the shoulder forming step, the high frequency current supplied from the coil power supply 90 to the heating coil 30 is adjusted, and then held for a while until the temperature of the alumina melt 300 is stabilized, and then the lifting rod 40 is moved to the first rotational speed. Pull up at the first pulling speed while rotating.

Then, the seed crystal 210 is pulled up while being rotated with its lower end immersed in the alumina melt 300, and a shoulder 220 that expands vertically downward is formed at the lower end of the seed crystal 210. It will be done.
Note that the shoulder forming step is completed when the diameter of the shoulder 220 becomes about several mm larger than the desired diameter of the wafer.

(Straight body part forming process)
In the straight body forming step, the gas supply unit 70 supplies a predetermined gas into the chamber 14. In addition, the gas supplied in a straight body part formation process may be the same as a shoulder part formation process, and may differ.
The coil power supply 90 continues to supply a high-frequency current to the heating coil 30 to heat the alumina melt 300 through the crucible 20.
Further, the pulling drive unit 50 pulls the pulling rod 40 at the second pulling speed. Here, the second pulling speed may be the same as or different from the first pulling speed in the shoulder forming step.
Furthermore, the rotation drive unit 60 rotates the pulling rod 40 at the second rotation speed. Here, the second rotation speed may be the same speed as the first rotation speed in the shoulder forming step, or may be a different speed.

  The shoulder 220 integrated with the seed crystal 210 is pulled up while being rotated while the lower end of the shoulder 220 is immersed in the alumina melt 300. The trunk portion 230 is formed. The straight body 230 may be a body having a diameter equal to or larger than a desired wafer diameter.

(Tail formation process)
In the tail forming step, the gas supply unit 70 supplies a predetermined gas into the chamber 14. Note that the gas supplied in the tail portion forming step may be the same as or different from that in the straight body portion forming step.
The coil power supply 90 continues to supply a high-frequency current to the heating coil 30 to heat the alumina melt 300 through the crucible 20.
Further, the pulling drive unit 50 pulls the pulling rod 40 at the third pulling speed. Here, the third pulling speed may be the same as the first pulling speed in the shoulder forming process or the second pulling speed in the straight body forming process, or may be a speed different from these. Good.
Furthermore, the rotation drive unit 60 rotates the pulling rod 40 at the third rotation speed. Here, the third rotation speed may be the same as the first rotation speed in the shoulder forming process or the second rotation speed in the straight body forming process, or may be different from these. Also good.
In the early stage of the tail formation process, the lower end of the tail 240 is kept in contact with the alumina melt 300.
Then, at the end of the tail forming process after a predetermined time has elapsed, the pulling drive unit 50 increases the pulling speed of the pulling bar 40 and pulls the pulling bar 40 further upward, thereby lowering the lower end of the tail 240. Pull away from melt 300. Thereby, the sapphire ingot 200 shown in FIG. 2 is obtained.

(Cooling process)
In the cooling process, the gas supply unit 70 supplies a predetermined gas into the chamber 14. Note that the gas supplied in the cooling step may be the same as or different from the tail forming step.
Further, the coil power supply 90 stops the supply of the high-frequency current to the heating coil 30 and stops the heating of the alumina melt 300 through the crucible 20.
Further, the pulling drive unit 50 stops the pulling of the pulling rod 40 and the rotation driving unit 60 stops the rotation of the pulling rod 40.
At this time, a small amount of aluminum oxide that did not form the sapphire ingot 200 remains as the alumina melt 300 in the crucible 20. For this reason, the alumina melt 300 in the crucible 20 with the stop of heating is gradually cooled and solidified in the crucible 20 after falling below the melting point of aluminum oxide to become aluminum oxide solid.
Then, the sapphire ingot 200 is taken out from the chamber 14 with the chamber 14 sufficiently cooled.

  By the way, in the manufacture of such a sapphire ingot 200, the behavior of the alumina melt 300 in the crucible 20 greatly affects the growth of the sapphire single crystal. More specifically, it is preferable that the alumina melt circulates in the crucible 20 by natural convection. In order to realize such natural convection, it is preferable that the temperature of the lower side of the alumina melt 300 in the crucible 20 is higher than the upper side, and the temperature gradually increases from the upper side toward the lower side. It is more preferable to go.

  For this reason, it is preferable that the crucible 20 containing the alumina melt 300 has a configuration in which the lower side can be heated more than the upper side, and the crucible 20 can be gradually heated from the upper side toward the lower side. More preferably.

Here, in this embodiment, as is clear from FIGS. 1 and 3, the distance L between the heating coil 30 and the outer wall surface 22 a of the crucible 20 gradually increases from the upper side to the lower side of the crucible 20. It has become narrower.
In general, in induction heating, it is known that the shorter the distance between the heating coil and the object to be heated, the higher the density of the magnetic flux passing through the object to be heated, and as a result, the heating becomes easier and the temperature rises. .
For this reason, by adopting the configuration of the present embodiment, the lower side, that is, the side closer to the wall portion 22 is more easily heated than the upper side of the crucible 20. As a result, in the alumina melt 300 in the crucible 20, the temperature on the lower side rather than the upper side increases, and natural convection of the alumina melt 300 in the crucible 20 is promoted.

  In the present embodiment, the wall outer surface 22a has a linear cross-sectional shape that is continuous from the top to the bottom and has no inflection points. For this reason, the space | interval L with the wall part outer surface 22a of the heating coil 30 and the crucible 20 becomes narrower linearly from the upper part side of the crucible 20 toward the lower part side. Thereby, the situation where the specific part between the uppermost part and the lowermost part of the wall part 22 of the crucible 20 becomes extremely easy to be heated does not occur, and the temperature gradient of the alumina melt 300 in the crucible 20 is lowered from above. Can be continuous towards

  Further, in the present embodiment, since natural convection of the alumina melt 300 in the crucible 20 can be promoted in this way, bubbles in the alumina melt 300 can be further removed along with natural convection. Thereby, it can suppress that a bubble is taken in into the sapphire ingot 200. In particular, when manufacturing a sapphire ingot 200 crystal-grown in the c-axis direction as in the present embodiment, bubbles are easily taken into the sapphire ingot 200, but the manufacturing is performed using the method described above. By performing, the sapphire ingot 200 in which the intake of bubbles is further suppressed can be obtained.

  In the present embodiment, the alumina melt 300 is solidified in the crucible 20 to form aluminum oxide in the cooling step, and this aluminum oxide is solidified on the lower side of the crucible 20, that is, on the bottom 21 side. At this time, mechanical stress is applied to the lower side of the crucible 20 accompanying the solidification of the aluminum oxide. However, in this embodiment, the wall portion 22 is formed so as to be thicker toward the lower side. It becomes possible to suppress deformation due to mechanical stress. Therefore, the crucible 20 with little deformation can be used over a long period of time, the productivity of the sapphire ingot 200 can be improved, and the cost of the crucible 20 can be further reduced.

In the present embodiment, the cross-sectional shape of the wall outer surface 22a of the crucible 20 is linear, but the cross-sectional shape of the wall outer surface 22a is not limited to this.
That is, for example, as shown in FIG. 5A and FIG. 5B, the cross-sectional shape of the wall outer surface 22a may be a curved shape that is continuous and has no inflection points.

<Embodiment 2>
Although the present embodiment is substantially the same as the first embodiment, the cross-sectional shape of the crucible 20 and the arrangement of the heating coil 30 are different. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 6 is an example of a cross-sectional view for explaining the configuration of crucible 20 and heating coil 30 in the present embodiment and the positional relationship between crucible 20 and heating coil 30 in single crystal pulling apparatus 1 shown in FIG. .

First, the configuration of the crucible 20 will be described.
The crucible 20 is made of iridium as in the first embodiment, and has a shape that opens vertically upward. The crucible 20 has a bottom portion 21 and a wall portion 22 that rises upward from the periphery of the bottom portion 21. And the crucible 20 of this Embodiment has the shape from which the outer diameter becomes substantially constant from the vertical upper direction to the vertical downward direction.

The bottom portion 21 has a circular shape, and has a substantially uniform thickness (for example, about 2 mm to 7 mm) over the entire region.
On the other hand, the wall portion 22 has a configuration in which the thickness is increased more on the lower side than on the upper side. More specifically, also in this embodiment, the thickness of the wall portion 22 at the uppermost portion, that is, the first thickness T1 is 2 mm, whereas the thickness of the wall portion 22 at the lowermost portion, that is, the second thickness. The thickness T2 is 7 mm. However, in the present embodiment, the wall outer surface 22a has a linear cross section that extends substantially vertically downward from above, whereas the wall inner surface 22b has a linear cross section that extends obliquely downward from above. have. Thus, the wall part inner surface 22b in the crucible 20 has a cross-sectional shape which is continuous from the upper side to the lower side and has no inflection point.

The height H of the crucible 20 is about 150 mm. Further, the first inner diameter Di1 which is the diameter of the uppermost side of the concave portion of the crucible 20 is about 160 mm, and the second inner diameter Di2 which is the diameter of the lowermost side of the concave portion is about 150 mm.
On the other hand, the outer diameter Do which is the diameter of the crucible 20 is constant at about 164 mm regardless of the position in the vertical direction.

Next, the heating coil 30 will be described.
The heating coil 30 is configured by a hollow copper tube, for example, as in the first embodiment. The heating coil 30 is wound in a spiral shape. However, in the present embodiment, the inner diameter on the lower side is smaller than the inner diameter on the upper side of the heating coil 30. Thereby, the space formed in the inside by the wound heating coil 30 also has a trapezoidal cross section. Further, the central axis of the heating coil 30 passing through this space is substantially perpendicular to the horizontal direction as in the first embodiment.

Furthermore, the relative positional relationship between the crucible 20 and the heating coil 30 in the single crystal pulling apparatus 1 (see FIG. 1) will be described.
First, the crucible 20 is arranged inside a trapezoidal space formed by the heating coil 30. Then, the crucible 20 is placed at a site that is substantially in the center of the circular region formed by the heating coil 30. The lower end of the heating coil 30 is positioned below the lower end of the crucible 20, and the upper end of the heating coil 30 is positioned above the upper end of the crucible 20.

  As a result, the distance (distance) L, which is the shortest distance between the inner wall of the heating coil 30 and the outer wall surface 22a of the crucible 20, gradually decreases from the upper side to the lower side of the crucible 20, as in the first embodiment. The coil 30 and the crucible 20 are closer to the lower side. More specifically, the lowermost side of the inner crucible 20 on the inner side of the heating coil 30 than the first distance L1 which is the shortest distance from the wall outer surface 22a on the uppermost side of the inner crucible 20 of the heating coil 30. The second distance L2, which is the shortest distance from the wall outer surface 22a, becomes shorter. In this example, the difference between the first interval L1 and the second interval L2 is determined by the inclination of the heating coil 30 with respect to the wall outer surface 22a of the crucible 20, and is set to 5 mm, for example.

  Also in the present embodiment, a sapphire ingot 200 shown in FIG. 2 is obtained by executing the manufacturing procedure shown in FIG.

Also in the present embodiment, the distance L between the heating coil 30 and the wall outer surface 22a of the crucible 20 gradually decreases from the upper side to the lower side of the crucible 20, and the wall outer surface 22a. However, it has a linear cross-sectional shape that is continuous from the top to the bottom and has no inflection point.
For this reason, as in the first embodiment, natural convection of the alumina melt 300 in the crucible 20 accompanying induction heating of the crucible 20 can be promoted, and the temperature of the alumina melt 300 in the crucible 20 can be increased. The gradient can be continuous from top to bottom.

  Also in this embodiment, since the wall portion 22 of the crucible 20 is formed thicker toward the lower side, deformation due to mechanical stress received from aluminum oxide when the alumina melt 300 is solidified is suppressed. can do. Furthermore, as a material of the crucible 20, in addition to the above-mentioned iridium, an alloy containing iridium, platinum, or an alloy containing platinum can be used.

In the present embodiment, the cross-sectional shape of the wall inner surface 22b of the crucible 20 is linear, but the cross-sectional shape of the wall inner surface 22b is not limited to this.
For example, the cross-sectional shape of the wall inner surface 22b may be a curved shape that is continuous and has no inflection points.
For example, as shown in FIG. 7, both the wall outer surface 22a and the wall inner surface 22b may be formed as inclined surfaces.

It is a figure for demonstrating the structure of the single crystal pulling apparatus with which this Embodiment is applied. It is a figure which shows an example of a structure of the sapphire ingot obtained using the single crystal pulling apparatus. It is an example of sectional drawing for explaining the composition of a crucible and a heating coil in the single crystal pulling apparatus of Embodiment 1, and the positional relationship between them. It is a flowchart for demonstrating the procedure which manufactures a sapphire ingot using a single crystal pulling apparatus. FIG. 6 is a view showing a cross section of a crucible in a modification of the first embodiment. It is an example of a sectional view for explaining the configuration of the crucible and the heating coil in the second embodiment and the positional relationship between the crucible and the heating coil in the single crystal pulling apparatus. It is a figure which shows the cross section of the crucible in the modification of Embodiment 2. FIG.

DESCRIPTION OF SYMBOLS 1 ... Single crystal pulling apparatus, 10 ... Heating furnace, 11 ... Heat insulation container, 12 ... Gas supply pipe, 13 ... Gas discharge pipe, 14 ... Chamber, 20 ... Crucible, 21 ... Bottom part, 21a ... Bottom part outer surface, 21b ... Bottom part inner surface 22 ... Wall part, 22a ... Wall part outer surface, 22b ... Wall part inner surface, 30 ... Heating coil, 40 ... Lifting rod, 41 ... Holding member, 200 ... Sapphire ingot, 300 ... Alumina melt, Di ... Inner diameter, Di1 ... 1st inside diameter, Di2 ... 2nd inside diameter, Do1 ... 1st outside diameter, Do2 ... 2nd outside diameter, T1 ... 1st thickness, T2 ... 2nd thickness, H ... Height of crucible , L ... interval, L1 ... first interval, L2 ... second interval

Claims (11)

A crucible containing the alumina melt;
Induction heating means for induction heating the crucible;
A pulling means for pulling up the sapphire single crystal from the alumina melt contained in the crucible,
The crucible is
The bottom,
A wall part that rises from the periphery of the bottom part and has a wall thickness that continuously increases from the side farther from the bottom part toward the side approaching the bottom part,
The induction heating means includes
A heating coil wound around the outside of the wall portion of the crucible and disposed so that the distance from the wall portion closer to the bottom portion is closer than the distance from the wall portion away from the bottom portion; A sapphire single crystal pulling apparatus characterized by comprising:   2. The sapphire single crystal pulling apparatus according to claim 1, wherein the crucible is made of iridium, an alloy containing iridium, platinum, or an alloy containing platinum.   3. The sapphire unit according to claim 1, wherein an outer surface of the wall portion of the crucible has a linear cross-sectional shape from a side close to the bottom portion to a side away from the bottom portion. Crystal pulling device.   The crucible is set such that an outer diameter of the wall portion on a side close to the bottom portion is set larger than an outer diameter of the wall portion on a side far from the bottom portion. The sapphire single crystal pulling device described.   5. The sapphire single crystal pulling apparatus according to claim 1, wherein the pulling means pulls the sapphire single crystal grown in the c-axis direction from the alumina melt. A crucible containing alumina melt and used for the production of sapphire single crystals,
The bottom,
A crucible for producing a sapphire single crystal, comprising: a wall portion that rises from the periphery of the bottom portion and continuously increases in thickness from a side farther from the bottom portion toward a side approaching the bottom portion.   The crucible for sapphire single crystal production according to claim 6, wherein the bottom and the wall are made of iridium, an alloy containing iridium, platinum, or an alloy containing platinum.   The crucible for sapphire single crystal production according to claim 6 or 7, wherein an outer diameter of the wall portion on the side close to the bottom portion is set larger than an outer diameter of the wall portion on a side far from the bottom portion.   The surface of the outer side of the said wall part has a linear cross-sectional shape toward the side away from the said bottom part from the side close | similar to the said bottom part, The any one of Claim 6 thru | or 8 characterized by the above-mentioned. Crucible for sapphire single crystal production. An introduction step of introducing an alumina raw material into a crucible having a bottom portion and a wall portion that rises from the periphery of the bottom portion and continuously increases in thickness toward a side closer to the bottom portion from a side farther from the bottom portion;
The crucible charged with the alumina raw material is wound around the outside of the wall part of the crucible, and the distance from the wall part closer to the bottom part than the distance from the wall part on the side away from the bottom part A melting step in which the alumina raw material is melted by induction heating by supplying an alternating current to a heating coil arranged so that the alumina raw material is melted, and
A method for producing a sapphire single crystal, comprising: a step of inductively heating the crucible using the heating coil, and growing the sapphire single crystal from the alumina melt in the crucible.   The method for producing a sapphire single crystal according to claim 10, wherein, in the growth step, the sapphire single crystal is grown in a c-axis direction.

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