WO2011074533A1

WO2011074533A1 - Single crystal pulling apparatus and single crystal pulling method

Info

Publication number: WO2011074533A1
Application number: PCT/JP2010/072373
Authority: WO
Inventors: 智博庄内
Original assignee: 昭和電工株式会社
Priority date: 2009-12-17
Filing date: 2010-12-13
Publication date: 2011-06-23
Also published as: JP2011126738A; TW201129730A

Abstract

Disclosed is a single crystal pulling apparatus (1) that is provided with a heat-insulating container (11), which has a heating furnace (10) for growing a sapphire ingot (200) composed of a columnar sapphire single crystal, and which has a columnar space formed therein. A crucible (20) that contains a raw material melt is disposed at the lower section in the heat-insulating container (11). Furthermore, the apparatus is provided with a convection control plate (17), which is disposed inside of the crucible (20) but outside of the sapphire ingot (200), and is held such that one end portion of the plate is dipped in an alumina melt (300), and which suppresses heat convection on the surface of the alumina melt (300). In the single crystal pulling wherein the Czochralski (Cz) method is employed, a thermal strain of the single crystal to be grown is suppressed by making the temperature gradient of the melt on a crystal growing interface gentle by suppressing thermal convection.

Description

Single crystal pulling apparatus and single crystal pulling method

The present invention relates to a single crystal pulling apparatus and a single crystal pulling method for growing a single crystal from a melt.

In a single crystal pulling apparatus using the Czochralski method (Cz method), a single crystal of a target material is pulled from a raw material melt that is accommodated in a crucible and heated through the crucible.
In order to produce a single crystal by the Cz method, for example, a raw material is first filled in a crucible, and the raw material is melted by heating the crucible by a high-frequency heating method or a resistance heating method. When the raw material is melted to become a raw material melt, 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 determined while rotating at a predetermined rotation speed. A single crystal is grown by pulling at a high speed.

At this time, since the raw material melt is heated through the crucible, the temperature of the surface of the raw material melt (melt) is high on the crucible wall surface side, and the temperature is lowered as it approaches the center of the crucible. For this reason, the melt has a temperature gradient (temperature gradient) from the crucible wall surface side toward the center portion, and generates a flow (thermal convection).
In particular, an oxide single crystal has high viscosity and low thermal conductivity, and therefore has a large temperature gradient on the melt surface (crystal growth interface) on which the crystal grows. For this reason, defects and dislocations due to thermal stress were likely to occur in the grown single crystal.
Therefore, it has been proposed to control thermal convection.

In Patent Document 1, a plurality of plate members projecting in the radial direction are attached to the inner wall of the crucible to divide the crucible, and by controlling the movement in the circumferential direction by pressing the melt convection in the partition, A crucible for a crystal growth apparatus is described in which liquid convection is brought close to an axial object and generation of a vortex structure in the circumferential direction is prevented.
In Patent Document 2, when a single crystal is grown by the Czochralski method, a cylindrical device having slits at the periphery is made, and the suppression efficiency of the melt surface flow is changed by the aperture ratio, and at the same time, the temperature is higher than that outside the cylinder. A crystal growth method is described that adjusts the amount of a simple flow introduced into the cylinder.

Japanese Patent Laid-Open No. 6-211593 JP-A-5-105579

By the way, in the growth of a single crystal by the Cz method, it is effective to suppress the generation of defects and dislocations due to thermal strain by relaxing the temperature gradient generated by the thermal convection on the melt surface (crystal growth interface).
For this purpose, it is effective to suppress thermal convection on the melt surface. However, in Patent Document 1, the vortex structure generated in the circumferential direction of the crucible is suppressed, but the thermal convection is left as it is. On the other hand, in patent document 2, since the melt is convected through the slit, thermal convection cannot be suppressed.
The present invention suppresses thermal distortion of a single crystal to be grown by relaxing the temperature gradient at the crystal growth interface of the melt by suppressing thermal convection in single crystal pulling by the Czochralski (Cz) method. With the goal.

A single crystal pulling apparatus to which the present invention is applied has a bottom portion and a wall portion rising from a peripheral edge of the bottom portion, a crucible containing a raw material melt, a raw material melt placed above the crucible and contained in the crucible Between the pulling member for pulling up the columnar single crystal, the inner wall of the crucible, and the single crystal pulled from the raw material melt, one end side is inserted into the raw material melt from the surface of the raw material melt, and the raw material melt And a convection control member that suppresses thermal convection on the surface.
In such a single crystal pulling apparatus, the convection control member is cylindrical and is inserted so that the axis of the convection control member is perpendicular to the surface of the raw material melt, and the inner diameter D of the convection control member is For the inner diameter R and the diameter r of the single crystal to be pulled up,
r <D ≦ (R + r) / 2
It can be characterized by being.
The single crystal pulling apparatus may further include a coil that is wound around the outside of the crucible and induction-heats the crucible by supplying an alternating current.
Further, the convection control member is provided with a cut on one end side immersed in the raw material melt to suppress induction heating due to the supply of alternating current, and the convection control member is provided with an AC on the other end side where no cut is provided. It can be characterized in that it is induction heated by supplying current.

The crucible contains alumina melt as a raw material melt, and the pulling member pulls up the columnar sapphire single crystal from the alumina melt stored in the crucible.
In addition, the convection control member can be characterized by being made of iridium, molybdenum, tungsten, or an alloy thereof.

From another point of view, the single crystal pulling method to which the present invention is applied is obtained by attaching a seed crystal of the single crystal to the raw material melt in the crucible and pulling the seed crystal while rotating it. A shoulder forming step for forming a shoulder portion extending downward, and a trunk forming step for forming the trunk portion below the shoulder portion by pulling up the shoulder portion attached to the raw material melt while rotating. A convection control member, which is provided between the inner wall of the crucible and the shoulder portion or the trunk portion, and controls the thermal convection on the surface of the raw material melt in the shoulder formation step and the trunk formation step. Control is performed so that one end of the material is inserted into the raw material melt at a predetermined depth.
In such a single crystal pulling method, the convection control member is provided with a notch for suppressing induction heating by supplying an alternating current on one end portion side immersed in the raw material melt, so as to form a shoulder portion and a trunk portion. In the process, the crucible and the other end portion where the notch of the convection control member is not provided may be characterized in that induction heating is performed by supplying an alternating current.
Further, the crucible may contain an alumina melt as a raw material melt, and the single crystal may be a columnar sapphire single crystal.

According to the present invention, thermal convection can be suppressed in single crystal pulling by the Czochralski (Cz) method, so that the temperature gradient at the crystal growth interface of the melt becomes loose, and the thermal strain of the grown single crystal is reduced. Can be suppressed.

It is a figure for demonstrating an example of a structure of the single crystal pulling apparatus in this Embodiment. It is a figure which shows an example of a structure of the sapphire ingot manufactured using a single crystal pulling apparatus. It is a figure which shows an example of a structure of a crucible and a convection control board. It is a figure for demonstrating the temperature gradient of the alumina melt surface. It is a flowchart for demonstrating an example of the procedure which manufactures a sapphire ingot using a single crystal pulling apparatus. It is a figure explaining the position of the convection control board in a shoulder part formation process and a straight body part formation process.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
(Single crystal pulling device 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.
This single crystal pulling apparatus 1 has a heating furnace 10 for growing a sapphire ingot 200 made of a sapphire single crystal as an example of a columnar single crystal. The heating furnace 10 has a cylindrical outer shape, and includes a heat insulating container 11 in which a cylindrical space is formed. 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.

A crucible 20 that houses an alumina melt 300 as an example of a raw material melt obtained by melting aluminum oxide (Al ₂ O ₃ ) is disposed below the inside of the heat insulating container 11. The crucible is made of, for example, iridium (Ir).
Further, a crucible support base 15 having a disk-like outer shape is disposed below the inside of the heat insulating container 11 and below the bottom 21 (see FIG. 3) of the crucible 20. This crucible support base 15 may be made of iridium like the crucible 20. The crucible support base 15 is supported by the shaft 16 from the inner bottom surface of the heat insulating container 11. The shaft 16 may also be made of iridium like the crucible 20 and the crucible support 15. Thus, the crucible 20 is supported from the inner bottom surface of the heat insulating container 11 by the crucible support base 15 and the shaft 16.

Furthermore, the inner side of the crucible 20 and the outer side of the sapphire ingot 200, that is, between the inner wall of the crucible 20 and the sapphire ingot 200, one end is held so as to be inserted into the alumina melt 300. A convection control plate 17 is provided as an example of a convection control member that suppresses convection.
The convection control plate 17 is configured, for example, in a cylindrical shape, and one end of the convection control plate 17 is perpendicular to the surface of the alumina melt 300 at a predetermined depth (Hm in FIG. 3 described later). Has been inserted. The convection control plate 17 may be made of iridium like the crucible 20.
Further, the convection control plate 17 is held so as not to contact either the sapphire ingot 200 or the crucible 20.
The crucible 20 and the convection control plate 17 will be described in detail later.

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 side surface of the crucible 20 with the heat insulating container 11 interposed therebetween.
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, 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. The central axis of the heating coil 30 passing through the columnar space is substantially perpendicular to the horizontal direction, that is, along the vertical direction.

Furthermore, the heating furnace 10 includes a lifting rod 40 as an example of a lifting member 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.

The heating furnace 10 includes a support rod 18 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 support bar 18 supports the convection control plate 17 and is attached so as to be movable in the vertical direction. A seal material (not shown) is provided between the through hole provided in the chamber 14 and the support rod 18.

The single crystal pulling apparatus 1 includes a pulling drive unit 50 for pulling the pulling rod 40 vertically upward (in the direction of arrow A) and a rotation driving unit 60 for rotating the pulling rod 40 in the direction of arrow B. Here, the pulling drive unit 50 is composed of a motor or the like, and can adjust the pulling speed of the pulling bar 40 in the direction of arrow A. The rotation driving unit 60 is also composed of a motor or the like so that the rotation speed of the lifting rod 40 in the direction of arrow B can be adjusted.
Further, the single crystal pulling apparatus 1 includes a convection control plate driving unit 120 for pulling down the support bar 18 vertically downward (in the direction of arrow C). The convection control plate driving unit 120 is constituted by a motor or the like, and can adjust the pulling-down speed of the support rod 18 in the arrow C direction.

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.

Also, 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 conventionally known load cell.

The single crystal pulling apparatus 1 includes a control unit 100 that controls the operations of the pulling drive unit 50, the rotation drive unit 60, the gas supply unit 70, the exhaust unit 80, the coil power supply 90, and the convection control plate drive unit 120 described above. ing. 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.

(Sapphire Ingot 200)
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 230 that extends and is integrated with the shoulder 220 (it is a trunk, but is called a straight body because it is cylindrical), and a straight body 230 that extends below the straight body 230 and And an integrated tail 240. 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 sapphire ingot 200 may be called a sapphire single crystal or simply a single crystal.

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 r of the straight body 230 is set to a value slightly larger than the diameter of the desired sapphire single crystal wafer. The diameter r of the straight body 230 is the diameter of the sapphire ingot 200, but is also referred to as a single crystal diameter here.
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. FIG. 2 shows an example in which the tail 240 has a convex shape protruding below the straight body 230. However, when manufacturing conditions are varied, a broken line in FIG. As shown, it may have a concave shape that is recessed below the straight body portion 230.

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.

However, the single crystal pulling apparatus 1 shown in FIG. 1 can pull not only the sapphire ingot 200 grown in the c-axis direction but also the sapphire ingot 200 grown in the a-axis direction, for example. In addition to sapphire, it is possible to pull up various oxide single crystals, and it is also possible to pull up single crystals other than oxides.

(Crucible 20 and convection control plate 17)
FIG. 3 is a diagram showing an example of the configuration of the crucible 20 and the convection control plate 17 shown in FIG. 3A is a perspective view, and FIG. 3B is a front view. In these drawings, only the crucible 20, the alumina melt 300, the sapphire ingot 200, and the convection control plate 17 are shown, so that the structure of the crucible 20 and the convection control plate 17 can be easily understood. FIG. 3 (b) is a front view of the crucible 20 as viewed from the alumina melt 300.
Below, the structure of the crucible 20 and the convection control board 17 is demonstrated, and the positional relationship of the crucible 20 (including the sapphire ingot 200) and the convection control board 17 is demonstrated.

<Crucible 20>
First, the configuration of the crucible 20 will be described.
In the present embodiment, the crucible 20 is made of iridium. The crucible 20 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 bottom portion 21 has a circular shape and has a substantially uniform thickness (for example, about 2 mm to 7 mm) over the entire area. Further, the wall portion 22 has a cylindrical shape, and this also has a substantially uniform thickness (for example, about 2 mm to 7 mm) over the entire region.
The inner diameter R of the crucible 20 is determined by the diameter r of the sapphire ingot 200 to be grown. For example, in order to obtain a sapphire single crystal wafer having a diameter of about 150 mm (about 6 inches), the diameter r of the sapphire ingot 200 needs to be about 153 mm. An inner diameter R of the crucible 20 on which the sapphire ingot 200 is grown is about 223 mm.

The crucible 20 is not limited to iridium. It may be made of molybdenum or tungsten. In addition, it may be composed of an alloy of molybdenum and tungsten (Mo—W), and further containing other metal elements such as niobium and tantalum.
Further, the crucible support 15 and the shaft 16 are not limited to iridium, as with the crucible 20.

<Convection control plate 17>
First, the configuration of the convection control plate 17 will be described.
The convection control plate 17 has a cylindrical shape with a diameter D and a height Hs, and is held by a support bar 18 (see FIG. 1).
The convection control plate 17 is inserted into the alumina melt 300 so that one end (lower end) side is a depth Hm (Hm <Hs) and the axis of the cylinder is perpendicular to the surface of the alumina melt 300. . And the other end part (upper end part) side of the convection control board 17 is comprised so that a part of sapphire ingot 200 may be surrounded.

Further, in a region I on the lower end side of the convection control plate 17, a notch (slit) 17 a is provided from one end portion along the side surface of the cylindrical convection control plate 17. The length Hc of the notch 17a is set larger than the depth Hm inserted into the alumina melt 300 (Hm <Hc) and smaller than the height Hs of the convection control plate 17 (Hc <Hs). That is, the notch 17a starts from one end of the convection control plate 17 and ends in the middle of the side surface of the cylindrical convection control plate 17. The end point of the notch 17a is on the alumina melt 300. And in the area | region II of the upper end part side of the convection control board 17, the notch | incision 17a is not provided.
The convection control plate 17 is not limited to iridium. It may be made of molybdenum or tungsten. In addition, it may be composed of an alloy of molybdenum and tungsten (Mo—W), and further containing other metal elements such as niobium and tantalum.

Here, the reason why the cuts 17a are provided will be described.
In the present embodiment, the crucible 20 is induction-heated by supplying an alternating current to the heating coil 30.
At this time, the convection control plate 17 may also be induction-heated depending on the material of the convection control plate 17 and the magnitude of the magnetic field generated by the heating coil 30. Then, in addition to the crucible 20, the convection control plate 17 also becomes a heating element and changes the temperature of the alumina melt 300. Therefore, a notch 17a is provided in the convection control plate 17 so that a closed circuit is not formed with respect to the induced current generated in the convection control plate 17, and the convection control plate 17 is prevented from generating heat.
In the present embodiment, the induced current flows in the circumferential direction of the cylindrical convection control plate 17. Therefore, if a cut is made along the side surface direction of the convection control plate 17, a closed circuit is not configured for the induced current.

In the present embodiment, the length Hc of the notch 17a is made larger than the depth Hm inserted into the alumina melt 300. However, even if the convection control plate 17 is induction-heated, the temperature gradient of the alumina melt 300 remains. As long as it is within an allowable range, the length Hc of the notch 17a may be smaller than the depth Hm inserted into the alumina melt 300 (Hc <Hm), and the end point of the notch 17a may be within the alumina melt 300. .
Further, the notch 17a is not limited to the above shape as long as the induced current can hardly flow, and may be an opening that does not connect to the end of the convection control plate 17. A plurality of cuts 17a may be provided.
On the contrary, when the convection control plate 17 is not induction-heated, or when the temperature gradient at the crystal growth interface of the alumina melt 300 is within an allowable range even if the convection control plate 17 is induction-heated, the convection control plate 17. It is not necessary to provide the notch 17a.

Next, the reason why the notch 17a is provided in the region I of the convection control plate 17 and not provided in the region II will be described.
As described above, induction heating does not occur in the region I of the convection control plate 17 provided with the cuts 17a. However, in the region II of the convection control plate 17 where the notch 17a is not provided, induction heating occurs and the convection control plate 17 is heated. The region II of the convection control plate 17 surrounds the sapphire ingot 200 that is exposed from the surface of the alumina melt 300. Therefore, the region II of the convection control plate 17 that is induction-heated can keep the sapphire ingot 200 exposed. Thereby, it is possible to prevent the sapphire ingot 200 from being rapidly cooled and further suppress the occurrence of thermal distortion. That is, the region II of the convection control plate 17 can play a role as an after heater.

The convection control plate 17 is required not to be deformed even when inserted into the alumina melt 300. Therefore, the thickness of the convection control plate 17 is preferably 1 mm to 8 mm. If it is too thick, the cost of the convection control plate 17 itself is increased, which is not preferable. On the other hand, if the thickness is too thin, the strength of the convection control plate 17 is reduced, and the plate is easily broken. The thickness is preferably 1 mm to 5 mm. More preferably, it is 1.5 mm to 3 mm.
When the convection control plate 17 is inserted into the alumina melt 300 at a depth of about 20 mm, the surface flow becomes small. Therefore, the depth Hm for inserting the convection control plate 17 into the alumina melt 300 is selected from the range of 15 mm to 35 mm. If it is too shallow, it is not sufficient to loosen the temperature gradient generated by the thermal convection on the melt surface (crystal growth interface), and it becomes difficult to suppress the occurrence of defects and dislocations due to thermal strain. If it is too deep, the meandering of the convection passing through the lower end of the convection control plate 17 becomes large, convection is disturbed, and the temperature at the melt surface (crystal growth interface) may become unstable. Therefore, it is preferably 20 mm to 25 mm.
The length Hc of the notch 17a is preferably 20 mm to 40 mm. Whether the length Hc is too long or too short affects the effect of induction heating by the convection control plate 17 as described above. Therefore, the range of 25 mm to 35 mm is preferable.
Further, the width of the notch 17a may be 2 mm to 10 mm as long as the induced current is less likely to flow. If it is too wide, it will not be sufficient to loosen the temperature gradient by thermal convection, and if it is too narrow, discharge will occur and induced current will flow. Therefore, it is preferably 3 mm to 5 mm.

<Positional relationship between crucible 20 and convection control plate 17>
Next, the positional relationship between the crucible 20 (including the sapphire ingot 200) and the convection control plate 17 will be described.
The convection control plate 17 is inserted into the alumina melt 300 at a depth Hm between the wall portion 22 (inner wall) of the crucible 20 and the sapphire ingot 200. And the convection control board 17 is arrange | positioned so that neither the crucible 20 nor the sapphire ingot 200 may contact.
The inner diameter D of the convection control plate 17 is determined by the diameter r of the single crystal to be grown. The inner diameter D of the convection control plate 17 preferably satisfies r <D ≦ (R + r) / 2. That is, the convection control plate 17 is closer to the intermediate point with respect to the sapphire ingot 200 side or the inner side than the inner wall of the crucible 20.
For example, as described above, when obtaining a sapphire wafer having a diameter of about 150 mm (6 inches), the diameter r of the sapphire ingot 200 is about 153 mm. The inner diameter R of the crucible 20 is about 223 mm. Then, the distance between the sapphire ingot 200 and the inner wall of the crucible 20 is 35 mm. Therefore, it can be considered that the inner diameter D of the convection control plate 17 is 183 mm, and the distance between the sapphire ingot 200 and the inside of the convection control plate 17 is 15 mm. When the distance between the convection control plate 17 and the inner wall of the crucible 20 is small, there is a possibility that the temperature of the convection control plate 17 rises due to radiation from the crucible 20 and becomes a new convection generation source. For this reason, the inner diameter D of the convection control plate 17 is larger than the diameter r of the sapphire ingot 200, and is preferably a midpoint between the outer wall of the sapphire ingot 200 and the inner wall of the crucible 20 or a range set inside thereof. For example, it is preferable that r <D ≦ (R + r) / 2.
The height Hs of the convection control plate 17 may be set by the length of the portion of the sapphire ingot 200 that is intended to function as an after heater.

(Temperature distribution on the surface of the alumina melt 300)
Next, the temperature gradient of the alumina melt 300 in the present embodiment will be described.
FIG. 4 is a diagram for explaining a temperature gradient on the surface of the alumina melt 300. FIG. 4A is a diagram for explaining the thermal convection of the alumina melt 300 when this embodiment is applied, and FIG. 4B is a diagram of the surface of the alumina melt 300 in FIG. 4A. It is a figure explaining a temperature gradient. On the other hand, FIG. 4 (c) is a diagram for explaining the thermal convection of the alumina melt 300 when the present embodiment is not applied, and FIG. 4 (d) is a diagram illustrating the alumina fusion in FIG. 4 (c). It is a figure explaining the temperature distribution of the liquid 300 surface. 4A and 4C show a cross section of the crucible 20, the alumina melt 300, the sapphire ingot 200, and the convection control plate 17 cut along a plane including the pulling axis of the sapphire ingot 200. FIG. 4 (b) and 4 (d) show the temperature (vertical axis) of the alumina melt 300 at the position (horizontal axis) in the crucible 20 in the cross section shown in FIGS. 4 (a) and 4 (c). Show.

First, in FIG. 4A, thermal convection of the alumina melt 300 when the present embodiment is applied will be described.
In the present embodiment, 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 a part of the magnetic flux generated in the heating coil 30 crosses the crucible 20 through the heat insulating container 11 in this way, a magnetic field is generated on the wall surface of the crucible 20 to prevent the change of the magnetic field. As a result, an induced current is generated in the crucible 20 and the wall portion 22 of the crucible 20 generates heat. That is, the wall portion 22 of the crucible 20 is heated by the supply of alternating current to the heating coil 30.

As a result, the alumina melt 300 whose density has been lowered by heating rises at the portion of the alumina melt 300 that contacts the wall portion 22 of the crucible 20. The alumina melt 300 tends to flow toward the center of the crucible 20 having a low temperature. However, in this embodiment, since the convection control plate 17 is inserted into the surface of the alumina melt 300, the convection control plate 17 blocks the flow of the alumina melt 300.
The flow of the alumina melt 300 blocked by the convection control plate 17 moves toward the bottom of the crucible 20 along the convection control plate 17. However, after passing one end of the convection control plate 17, it goes up again toward the center of the crucible 20. Then, head to the center of the crucible 20.
The alumina melt 300 flows toward the bottom 21 of the crucible 20 at the center of the crucible 20. Thereafter, the bottom of the crucible 20 flows toward the wall 22.
As described above, the convection control plate 17 blocks the thermal convection on the surface of the alumina melt 300 and deforms the flow of the alumina melt 300.

As described above, in the present embodiment, the convection control plate 17 blocks the flow of the surface flow from the wall portion 22 of the crucible 20 toward the center portion. Thereby, as shown in FIG.4 (b), the temperature gradient is eased in the crystal growth interface (area | region shown by G in FIG. 4) which is a boundary of the alumina melt 300 and the sapphire ingot 200. FIG. That is, the convection control plate 17 prevents the alumina melt 300 heated in the vicinity of the wall portion 22 of the crucible 20 from flowing directly into the crystal growth interface (G). Thereby, the thermal strain of the grown single crystal is small, and the occurrence of defects and dislocations is suppressed.

On the other hand, in the case where the present embodiment shown in FIG. 4C is not applied, the convection control plate 17 is not used, so that the surface flow from the wall portion 22 of the crucible 20 toward the center portion directly generates the crystal growth interface (G ) Therefore, as shown in FIG. 4D, the temperature gradient at the crystal growth interface (G) becomes steep. For this reason, the center part of the sapphire ingot 200 is crystallized at a low temperature, and the peripheral part is crystallized at a high temperature. Therefore, since the peripheral portion tends to shrink with crystallization, a compressive stress is generated, and the central portion tends to stretch due to heat from the peripheral portion, thereby generating a tensile stress. As a result, residual stress is generated inside the crystal, and defects and dislocations are generated.

(Method for producing sapphire ingot 200)
FIG. 5 is a flowchart for explaining an example of 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, a shoulder forming step of forming a shoulder 220 below the seed crystal 210 is performed by pulling up the seed crystal 210 in contact with the alumina melt 300 while rotating it (in the direction of arrow A in FIG. 1). (Step 103).
Subsequently, a straight body portion that forms a straight body portion 230, which is a body portion, below the shoulder portion 220 by pulling upward through the seed crystal 210 while rotating the shoulder portion 220 (in the direction of arrow B in FIG. 1). A formation process is executed (step 104). In addition, since the straight body part forming process is a process of forming the body part, it is also referred to as a body part forming process.
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 the present 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.

FIG. 6 is a diagram for explaining the position of the convection control plate 17 in the shoulder portion forming step and the straight body portion forming step. FIG. 6A shows the position of the convection control plate 17 in the shoulder forming step, and FIGS. 6B and 6C show the position of the convection control plate 17 in the straight body forming step. FIG. 6C shows a state where the growth of the straight body portion 230 has progressed more than the state shown in FIG.

Now, each step shown in FIG. 5 described above will be specifically described with reference to FIG. However, here, the description will be made in order from the preparation step executed before the melting step of Step 101.

<Preparation process>
In the preparation step, first, a c-axis (<0001>) 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 raw material of aluminum oxide, that is, the alumina raw material is filled in the crucible 20 and disposed on the crucible support 15, and then the heat insulating container 11 is assembled in the chamber 14.
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.

Further, the coil power supply 90 supplies a high frequency current 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 a part of the magnetic flux generated in the heating coil 30 crosses the crucible 20 through the heat insulating container 11 in this way, a magnetic field is generated on the wall surface of the crucible 20 to prevent the change of the magnetic field, and as a result, the crucible. An induced current is generated in 20. Then, Joule heat (W = I ² Z) proportional to the skin resistance (Z) of the crucible 20 is generated on the wall portion 22 of the crucible 20 by the induced current (J), and the wall portion 22 of the crucible 20 generates heat. .

Further, a part of the magnetic flux generated in the heating coil 30 with the supply of the high frequency current crosses the convection control plate 17. Along with this, a magnetic field is generated in the region II where the notch 17a of the convection control plate 17 is not provided so as to prevent the change of the magnetic field, and as a result, an induced current is also generated in the region II in the convection control plate 17. In the region II in the convection control plate 17, Joule heat proportional to the skin resistance of the region II in the convection control plate 17 is generated by the induced current, and the region II in the convection control plate 17 generates heat.

In this way, when the wall portion 22 is heated and the aluminum oxide accommodated in the crucible 20 is heated beyond its melting point (2054 ° C.), the alumina raw material, that is, aluminum oxide is contained in the crucible 20. It melts to become an alumina melt 300.
At this time, one end portion of the convection control plate 17 is preferably installed at a depth Hm from the surface of the alumina melt 300 by the convection control plate driving unit 120. This is because the temperature gradient of the surface of the alumina melt 300 in the crucible 20 is set to the temperature gradient in the shoulder portion forming step and the straight body portion forming step.

<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 and stops it. 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.
Also at this time, it is preferable that one end of the convection control plate 17 is installed at a position having a depth Hm from the surface of the alumina melt 300.

<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.

In the shoulder forming process, the alumina melt 300 is consumed as the shoulder 220 grows, and the position of the surface of the alumina melt 300 gradually decreases. However, one end of the convection control plate 17 is controlled by the convection control plate driving unit 120 so as to be maintained at a position of a depth Hm from the surface of the alumina melt 300 as shown in FIG. . That is, the convection control plate 17 is driven in the direction of arrow C following the change in the surface of the alumina melt 300. Thereby, the temperature gradient of the single crystal growth interface G is gently maintained.
The change in the position of the surface of the alumina melt 300 can be predicted based on the weight signal output from the weight detector 110. Moreover, the position of the surface of the alumina melt 300 can also be measured by a non-contact liquid level gauge using ultrasonic waves or the like. The control unit 100 may set the pulling speed of the support rod 18 based on the position of the surface of the alumina melt 300 thus obtained.

Further, the region II in the convection control plate 17 generates heat due to the supply of a high-frequency current to the heating coil 30. Therefore, the shoulder 220 that is pulled up from the alumina melt 300 and has a face is kept warm by heat radiation from the region II in the convection control plate 17. Thereby, the shoulder 220 is restrained from generating thermal distortion due to rapid cooling.

<Straight body part formation 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 diameter of the straight body 230 may be equal to or larger than the desired diameter of the wafer.

Also in the straight body part forming step, the alumina melt 300 is consumed as the straight body part 230 grows, and the position of the surface of the alumina melt 300 gradually decreases. However, as shown in FIGS. 6B and 6C, even if the position of the surface of the alumina melt 300 changes, one end of the convection control plate 17 has a depth Hm from the surface of the alumina melt 300. It is controlled to be kept in position. That is, the convection control plate 17 is driven in the direction of arrow C following the change in the surface of the alumina melt 300. Thereby, the temperature gradient of the single crystal growth interface G is gently maintained.
Further, the region II in the convection control plate 17 generates heat due to the supply of the high frequency current to the heating coil 30. Therefore, the straight body 230 immediately after being pulled up from the alumina melt 300 is kept warm by heat radiation from the region II in the convection control plate 17. As a result, the straight body portion 230 is restrained from generating thermal distortion due to rapid cooling.

<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 formation 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.
In the tail formation step, the temperature gradient on the surface of the alumina melt 300 (crystal growth interface) has little effect on single crystal defects and dislocations. Therefore, the convection control plate 17 may be controlled so that one end thereof is inserted from the surface of the alumina melt 300 in the same manner as the shoulder forming process and the straight body forming process, and in the middle of the tail forming process. , It may be taken out from the surface of the alumina melt 300.

<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.

In the present embodiment, the depth Hm at which one end of the convection control plate 17 is inserted into the alumina melt 300 is the same in the shoulder forming step and the straight body forming step, but thermal distortion is further suppressed. As is done, it may be variable.
In the present embodiment, the crucible 20 is heated by the high frequency induction heating method. However, the resistance heating method of heating the crucible 20 by passing a current through a heater (resistor) provided around the crucible 20. Other methods may be used. In the resistance heating method, the convection control plate 17 may not be provided with the notch 17a for suppressing induction heating.

As described above, in the present embodiment, the convection control plate 17 blocks the flow (thermal convection) of the alumina melt 300 from the wall portion 22 of the crucible 20 toward the center on the surface of the alumina melt 300. Relax the temperature gradient at the growth interface. Thereby, the thermal strain of the grown single crystal is suppressed, and the generation of defects and dislocations in the single crystal can be suppressed.

DESCRIPTION OF SYMBOLS 1 ... Single crystal pulling apparatus, 10 ... Heating furnace, 11 ... Heat insulation container, 14 ... Chamber, 15 ... Crucible support stand, 16 ... Shaft, 17 ... Convection control board, 18 ... Support rod, 20 ... Crucible, 30 ... Heating coil , 40 ... Lifting rod, 41 ... Holding member, 50 ... Lifting drive unit, 60 ... Rotation drive unit, 70 ... Gas supply unit, 80 ... Exhaust unit, 90 ... Coil power source, 100 ... Control unit, 110 ... Weight detection unit, DESCRIPTION OF SYMBOLS 120 ... Convection control board drive part, 200 ... Sapphire ingot, 210 ... Seed crystal, 220 ... Shoulder part, 230 ... Straight trunk part, 240 ... Tail part, 300 ... Alumina melt

Claims

A crucible having a bottom portion and a wall portion rising from the periphery of the bottom portion and containing a raw material melt;

A lifting member that is disposed above the crucible and pulls up the columnar single crystal from the raw material melt contained in the crucible;

Between the inner wall of the crucible and the single crystal pulled up from the raw material melt, one end side is inserted into the raw material melt from the surface of the raw material melt, and heat convection on the surface of the raw material melt A single crystal pulling apparatus comprising: a convection control member that suppresses stagnation.
The convection control member is cylindrical and is inserted so that the axis of the convection control member is perpendicular to the surface of the raw material melt.

The inner diameter D of the convection control member is smaller than the inner diameter R of the crucible and the diameter r of the single crystal to be pulled up.

r <D ≦ (R + r) / 2
The single crystal pulling apparatus according to claim 1, wherein:
The single crystal pulling apparatus according to claim 1, further comprising a coil wound around the crucible and induction-heating the crucible by supplying an alternating current.
The convection control member is provided with a notch for suppressing induction heating due to supply of alternating current on one end side immersed in the raw material melt,

The single crystal pulling apparatus according to any one of claims 1 to 3, wherein the convection control member is induction-heated by supplying an alternating current at the other end portion where the notch is not provided.
The crucible contains an alumina melt as the raw material melt,

5. The single crystal pulling apparatus according to claim 1, wherein the pulling member pulls a columnar sapphire single crystal from the alumina melt accommodated in the crucible.
The single crystal pulling apparatus according to any one of claims 1 to 5, wherein the convection control member is made of iridium, molybdenum, tungsten, or an alloy thereof.
A shoulder forming step of attaching a seed crystal of a single crystal to a raw material melt in a crucible, and forming a shoulder extending downward of the seed crystal by pulling up the seed crystal while rotating;

Including a body part forming step of forming a body part below the shoulder part by pulling up the shoulder part attached to the raw material melt while rotating,

A convection control member that is provided between the inner wall of the crucible and the shoulder or the trunk in the shoulder formation step and the trunk formation step, and controls thermal convection on the surface of the raw material melt; And a method of pulling a single crystal, wherein the one end side of the convection control member is controlled to be inserted into the raw material melt at a predetermined depth.
The convection control member is provided with a notch for suppressing induction heating due to supply of alternating current on one end side immersed in the raw material melt,

In the shoulder forming step and the trunk forming step, the other end portion of the crucible and the convection control member where the notch is not provided is induction-heated by supplying an alternating current. The method for pulling a single crystal as described.
The crucible contains an alumina melt as the raw material melt,

The single crystal pulling method according to claim 7, wherein the single crystal is a columnar sapphire single crystal.