JP6302192B2 - Single crystal growth apparatus and method - Google Patents

Description

  The present invention relates to a single crystal growth apparatus and method.

The background art will be described taking a sapphire single crystal as an example.
The Czochralski method is known as a method for growing a single crystal. In the Czochralski method, a seed crystal is brought into contact with the surface of the raw material melt in the crucible, and then the seed crystal is gradually pulled up from the heating region of the crucible and cooled to form a single crystal below the seed crystal. It is a way to grow.

  FIG. 5 shows a general example of a pulling apparatus used in this method for growing a single crystal. This apparatus includes a chamber 11 that constitutes a crystal growth furnace. A single crystal pulling rod 12 that can be moved up and down by a drive mechanism (not shown) is suspended from an upper portion of the chamber 11 through an opening. It is installed. A seed crystal 210 is attached to the tip of the single crystal pulling rod 12 via a holding member 13, and the seed crystal 210 is disposed on the central axis of the crucible 419. Further, a load cell (not shown) for measuring the crystal weight is provided at the upper end of the single crystal pulling rod 12.

  The crucible 419 generally has a circular opening as viewed from above, a cylindrical body, and a bottom surface having a planar shape, a bowl shape, or an inverted conical shape. Also, as the material of the crucible, a material that can withstand the melting point of aluminum oxide as a raw material melt and has low reactivity with aluminum oxide is suitable, and iridium, molybdenum, tungsten, rhenium or a mixture thereof is generally used. Used.

  The crucible 419 is supported by a cylindrical support base made of a refractory material.

In the pulling of the single crystal sapphire using the single crystal pulling apparatus described above, the sapphire raw material (added with Cr ₂ O ₃ , Fe ₂ O ₃ , NO as a dopant if necessary) is put in the crucible 419, and the heating coil 20 The crucible 419 is heated by flowing an electric current to melt the sapphire raw material, kept warm by the refractory 15 (heat insulating body) 15, and while the pulling rod 12 or the crucible 419 is rotated, the pulling rod 12 This is performed by immersing the seed crystal 210 at the lower end and pulling up the pulling rod 12.
However, the single crystal growth apparatus using the above-described high frequency heating method has the following problems.

(1) In the high-frequency heating method, the crucible serves both as a container for holding the raw material melt and as a heater for melting the raw material by generating heat from the crucible itself.
For this reason, in the crucible, a portion where heat is generated and a portion where heat is not generated are mixed, the temperature gradient of the melt in the crucible becomes steep, and the grown single crystal is distorted. The problem.

(2) A crucible made of Mo or W has low heating efficiency due to high frequency, and a crucible made of Ir having better heating efficiency than them must be used. The problem of high costs.

In Patent Document 1, the crucible has a double structure including a molybdenum or tungsten crucible 76 disposed on the inner side and an iridium crucible 73 disposed on the outer side at a distance close to but not in contact with each other. The technique (1) is solved by preventing the temperature gradient of the melt in the crucible from becoming steep.
However, in Patent Document 1, an Ir crucible is used, and the problem (2) described above remains.

  In Patent Document 2, a crucible is disposed inside a heat vessel (heating chamber) by cutting, and a heating element is provided outside the crucible so as to surround the crucible wall. A shielding body is provided inside the heating element and outside the crucible so as to prevent the constituent material of the heating element 17 from being mixed into the alumina melt 300 in the crucible so as to surround the crucible wall. A crystal growth apparatus is disclosed.

  In the techniques described in Patent Document 1 and Patent Document 2, both the heating element and the melt container are separated, the heating element and the container are separated from each other, and the heat of the heating element is transmitted to the container by radiation. It is what.

JP 2008-7353 A JP 2011-105575 A

However, the techniques presented by Patent Document 1 and Patent Document 2 also have the following problems. (1) In the technique described in Patent Document 1, an Ir crucible is used, which increases costs.
(2) When a single crystal is grown using the technique described in Patent Document 2, the tail portion thereof is elongated to a length equal to or greater than the diameter of the ingot, as shown in FIG. in this way,
If only the tail is extended, the length of the effective straight body length of the diameter required for the amount of raw material filled in the crucible is shortened, and the productivity is reduced.

(3) In the technique described in Patent Document 2, inexpensive graphite is used. In order to prevent carbon gas or carbon particles generated by heating from being mixed into the melt, it is necessary to provide a shielding plate between the graphite as the heating body and the crucible as the storage body. When disposing, keep away from the crucible without contact, keep the distance from the crucible uniform all around the circumference in order to transmit heat uniformly to the crucible, the upper end of the shielding plate at the upper end of the heating element The requirement to keep higher must be met.

In order to actually arrange and assemble the shielding plate while satisfying such requirements, many ideas are required. In fact, Patent Document 2 merely conceptually arranges them.
(4) When a single crystal is actually grown by the technique of Patent Document 2, the thermal efficiency is extremely poor and the power consumption becomes large.
Further, conventional single crystals have high hardness and are difficult to process.

The present invention allows the use of a crucible made of graphite, is extremely simple to assemble and arrange, has good thermal efficiency, and can grow a single crystal having a large diameter of 8 inches or more with little distortion. An object is to provide a training apparatus and a training method.
An object of the present invention is to provide a single crystal growing apparatus and a growing method capable of growing a single crystal that has a hardness lower than that of a conventional single crystal and is easy to process.

The invention according to claim 1 includes a heating chamber formed of a heat insulating material provided in the chamber, a crucible provided in the heating chamber, and a heating coil disposed on the outer periphery of the heating chamber, In the single crystal growth apparatus for raising the seed crystal by bringing the seed crystal into contact with the raw material melt obtained by heating the crucible,
The crucible, it from a first crucible having a bottom with a carbide tungsten on the surface of the tungsten bottom outer surface, and a second crucible having a bottom made of graphite is disposed outside the first crucible Ri, which is the first of the bottom outer single crystal growing apparatus Do that by contacting the inner bottom surface of the carbide and the second crucible surface of the crucible.

  The invention according to claim 2 is the single crystal growth apparatus according to claim 1, wherein the bottomed third crucible made of molybdenum is arranged inside the first crucible via a spacer made of tungsten.

The invention according to claim 3 is the single crystal growth apparatus according to claim 1 or 2, wherein the single crystal is an oxide single crystal.
The invention according to claim ₄ is the single crystal growth apparatus according to any one of claims 1 to 3, wherein the oxide is sapphire (Al ₂ O ₃ ) or ScAlMgO ₄ .

  The invention according to claim 5 is the single crystal growing apparatus according to any one of claims 1 to 4, wherein the first crucible is arranged in contact with or apart from the second crucible.

  The invention according to claim 6 is the single crystal growing apparatus according to any one of claims 1 to 5, wherein a carbon felt is disposed on the outer periphery of the second crucible.

  The invention according to claim 7 is the sapphire single crystal growing apparatus according to any one of claims 1 to 6, wherein the tungsten carbide has a thickness of 0.5 mm to 5 mm.

  The invention according to claim 8 is the single crystal growth apparatus according to any one of claims 1 to 7, wherein the tungsten carbide is formed by thermal spraying, sputtering, or CVD.

The invention according to claim 9 is the single crystal growth apparatus according to any one of claims 1 to 8, wherein the single crystal is a single crystal having a diameter of 6 inches or more.
The invention according to claim 10 includes a heating chamber formed of a heat insulating material provided in the chamber, a crucible provided in the heating chamber, and a heating coil disposed on the outer periphery of the heating chamber, In the single crystal growth apparatus for raising the seed crystal by bringing the seed crystal into contact with the raw material melt obtained by heating the crucible,
The crucible includes a bottomed first crucible and a bottomed second crucible made of graphite disposed outside the first crucible, and an outer periphery of the first crucible and the second crucible. Is a single crystal growth apparatus in which tungsten carbide powder is charged in a space formed by the inner periphery of the steel.

The invention according to claim 11 is a method for growing a single crystal using the single crystal growth apparatus according to any one of claims 1 to 10,
The raw material powder is charged into the first crucible, the pressure in the heating chamber is subsequently reduced, and the second crucible is heated to a high temperature by supplying a high-frequency current to the heating coil, and the first crucible is heated by the heat. This is a method for growing a single crystal, in which an internal raw material is melted, a seed crystal is brought into contact with the molten melt, and the seed crystal is pulled up while rotating to grow a single crystal.

  The invention according to claim 12 is the method for growing a single crystal according to claim 11, wherein the single crystal is a sapphire single crystal, and the growth is performed while introducing argon gas into the apparatus.

  The invention according to claim 13 is the single crystal growth apparatus according to claim 12, wherein the argon gas is introduced from below the apparatus.

  The invention according to claim 14 is the method for growing a single crystal according to claim 12 or 13, wherein the second crucible is heated to 2300 ° C or lower.

The present invention has the following various effects.
A crucible made of graphite can be used, and a single crystal can be grown at a low cost.
Assembly and placement of single crystal growth equipment is extremely simple.
Thermal efficiency is good, and the generation of strain in the grown single crystal can be reduced.
It is possible to obtain a single crystal that is lower in hardness than conventional and easy to process.

It is a conceptual diagram which shows the single crystal growth apparatus which concerns on form 1. It is a conceptual diagram which shows the single crystal growth apparatus which concerns on form 2. It is a figure which shows notionally the ingot of the single crystal grown using the single crystal growth apparatus which concerns on form 1. FIG. It is a conceptual diagram which shows the single crystal growth apparatus which concerns on form 3. It is a conceptual diagram which shows the conventional single crystal growth apparatus. It is a figure which shows notionally the ingot of the single crystal grown using the single crystal growth apparatus which concerns on another prior art. It is a figure which shows the magnetic field in a circular coil periphery.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[First form of training apparatus]
FIG. 1 is a diagram for explaining a single crystal pulling apparatus according to a first embodiment for carrying out the present invention.
A heating chamber 15 formed of a heat insulating material provided in the chamber 11, a crucible provided in the heating chamber 15, and a heating coil 20 disposed on the outer periphery of the heating chamber 15, and heating the crucible In the single crystal growing apparatus for bringing the seed crystal 210 into contact with the raw material melt 300 obtained in this way and then raising the seed crystal 210 to grow the single crystal 200,
The crucible is a single crystal composed of a bottomed first crucible 18 having tungsten carbide on the surface of tungsten, and a bottomed second crucible 19 made of graphite disposed outside the first crucible 18. It is a training device.

Hereinafter, this embodiment will be described in more detail.
(First crucible)
The base (main body) of the first crucible is made of tungsten (W). It has a bottom and a sidewall that rises from the periphery of the bottom. The outer surface (including the bottom outer surface) of the base is covered with tungsten carbide (WC).
In Patent Document 2, the shielding plate made of WC is arranged so as not to contact the Mo crucible. This is because a temperature gradient is generated in the melt upon contact, which is believed to cause strain in the grown single crystal.

However, the present inventor has found that WC does not cause a temperature gradient in the melt even when it comes into contact with the crucible holding the melt. WC has a thermal conductivity much lower than that of W. Therefore, it is presumed that WC works as a heat buffer layer and uniformly transfers heat to the base body made of W and thus to the melt. WC has a low thermal emissivity, which is presumed to be the cause of poor thermal efficiency.

The coating with WC may be performed by thermal spraying, CVD, or sputtering.
The thickness of the WC coating layer is preferably 0.3 mm to 1 mm. When the thickness is 0.3 mm or more, peeling of the WC coating layer hardly occurs even when repeated use is performed. By setting the thickness to 1 mm or less, the heat from the second crucible can be more efficiently transmitted to the base of the first crucible and thus to the raw material melt. When correcting the temperature of the melt, it can be corrected more quickly, and the controllability is excellent. From this viewpoint, 0.5 mm or more and 0.8 mm or less is more preferable.

(Second crucible)
The second crucible 19 is made of graphite. Graphite is much cheaper than Ir. Moreover, the heat generation efficiency with respect to the high frequency (RF) is very good.
The second crucible has a bottom (bottomed) and a side wall that rises upward from the periphery of the bottom.

The height of the upper end of the second crucible (the uppermost portion of the side wall) is set so as not to be higher than the upper end of the first crucible so that carbon gas or carbon particles generated when the graphite is heated does not enter the melt. Is done. In the example shown in FIG. 1, the upper ends of both are in a flush state.
The inside of the second crucible preferably has an outer diameter and an inner diameter appropriately set so that the entire outer surface of the first crucible and the entire inner surface of the second crucible are in contact with each other. Also at the bottom, it is preferable that the inner surface of the bottom of the second crucible be shaped so that the first crucible can be slid into the second crucible 19 in contact with the outer surface of the bottom of the first crucible.
If the inner surface of the second crucible and the outer surface of the first crucible are mirror finished, the first crucible can be easily slid into the second crucible and stored.
Although FIG. 1 shows an example in which the first crucible and the second crucible are arranged in contact with each other, the side wall of the first crucible and the side wall of the second crucible may be arranged separately. Good.
In the present embodiment, the upper end of the second crucible 19 is not higher than the upper end of the first crucible.

(Carbon felt material)
In the example shown in FIG. 1, the heating chamber 15 is composed of a zirconia refractory.
When zirconia (ZrO ₂ ) reaches a high temperature (1800 ° C. or higher), it undergoes an oxidation / reduction reaction, and oxygen is released as shown in the following formula (1) to oxidize molybdenum of the crucible material. When Mo is oxidized, black-blue smoke is generated, and this smoke is mixed into the surface of the sapphire raw material or the sapphire melt to cause coloring and a decrease in purity. The same applies to the case where tungsten is used as the crucible material. Moreover, even if it is refractories other than a zirconia, reaction of Formula (1) will arise, although there is a difference in temperature.
2ZrO ₂ ⇔ 2ZrO + O ₂ (1)
Therefore, in this embodiment, the carbon felt material 16 is provided around the outer wall of the second crucible 19. Since the carbon felt 16 prevents radiation from the second crucible 19 to the refractory 15, the temperature of the refractory 16 is prevented from rising to a temperature at which an oxidation / reduction reaction occurs. Therefore, it becomes easier to use a crucible made of Mo or W as a crucible.

(Single crystal material)
The single crystal in the present invention may be any material, and single crystals of semiconductor materials, compound semiconductor materials, oxides and other materials can be grown.
In particular, it is effective when applied to an oxide material, and more effective than when applied to sapphire and ScAlMgO4.
Further, the size of the single crystal to be grown is not limited, and a single crystal having any size can be grown. However, conventionally, when the outer diameter of the single crystal is 6 inches or more, the temperature distribution of the melt in the crucible becomes large, and the quality of the grown single crystal is deteriorated.
When the method according to the present invention is employed, the temperature gradient becomes gentle and the convection is stabilized, so that the shape of the solid-liquid interface that affects the quality of the crystal is induced from the downward convex shape to the flat shape. It becomes flatter as it gets bigger. The flatter the crystal quality becomes. Therefore, in the present invention, even if it is 6 inches or more, it is possible to maintain the same quality as a single crystal of less than 6 inches. Therefore, the effect of applying to a single crystal of 6 inches or more remarkably appears. The same applies to 8 inches or more.
(Other components)
Although not shown in FIG. 1, the single crystal pulling apparatus includes a vacuum pump, an oscillator for high frequency induction heating, control of the oscillator, computer control of the single crystal pulling growth furnace, temperature control, drive system control, growth A control device and other devices for controlling the crystal diameter and the like are provided.

[Second form of training apparatus]
FIG. 2 shows another form.
In this embodiment, a bottomed third crucible 17 made of molybdenum is placed inside the first crucible 18 with the side walls spaced apart and a spacer 21 made of tungsten on the bottom.
In this embodiment, the crucible has a triple structure. The inner surface of the first crucible 18 is tungsten, and the third crucible 17 is heated by radiation from the surface. The temperature gradient in the melt 300 in the third crucible 17 is further reduced, and a single crystal with less distortion is obtained.

  When the heater crucible is small (when 8 inches d are full), the melt heating side wall (heater crucible) is relatively uniformly heated, and the natural convection of the melt is maintained. However, when the heater crucible becomes large (over 8 inches), the density of the high-frequency magnetic flux generated in the coil becomes weaker as it becomes the center of the heater crucible, creating a hot area where a part of the outer wall of the crucible is particularly heated, resulting in a temperature gradient. It becomes tight. FIG. 7 shows the magnetic field around the circular coil.

In order to weaken this phenomenon, the crucible that is not directly heated by the cushion is arranged inside rather than directly heating the melt by the heater crucible, so that the heating from the side is relatively weakened and the temperature distribution of the melt is reduced. The variation becomes mild and the temperature gradient does not become steep. When the temperature gradient of the melt is relaxed, natural convection is stabilized and the effect of suppressing crystal defects and strains is produced.
In addition, when a triple structure is used, the life of each crucible can be increased.

A tungsten spacer 21 is disposed on the bottom inner wall of the first crucible, and the third crucible is placed on the spacer 21. In other words, heat is provided by radiation at the side walls while being separated, but heat is provided by heat conduction at the bottom wall without separation. Thereby, a temperature gradient can be decreased more.

[Third embodiment of the training apparatus]
FIG. 4 shows a growing apparatus according to the third embodiment.
A heating chamber formed of a heat insulating material 15 provided in the chamber 11; a crucible provided in the heating chamber; and a heating coil 20 disposed on the outer periphery of the heating chamber; and heating the crucible In the single crystal growth apparatus for bringing the seed crystal 210 into contact with the obtained raw material melt 300 and then growing the single crystal 200 by pulling up the seed crystal 210.
The crucible includes a bottomed first crucible 17 and a bottomed second crucible 19 made of graphite disposed outside the first crucible 17, and the outer periphery of the first crucible 17 and the A tungsten carbide powder 350 is charged into a space formed by the inner periphery of the second crucible 19.

The training apparatus according to the present embodiment is created by the following procedure, for example.
(1) After the graphite crucible 19 as the second crucible is placed on the base in the heating chamber, the tungsten carbide powder 350 is spread on the bottom surface inside the graphite crucible 19 to a thickness of about 1 to 5 mm.
(2) In this example, the first crucible 17 is a tungsten crucible, and the tungsten crucible 17 is placed on the tungsten carbide powder 350 so that the centers of the crucibles 17 and 19 coincide.
(3) The outer shape of the tungsten crucible 17 is, for example, about 10 mm smaller than the inner diameter of the graphite crucible 19. If it does so, the clearance gap between the graphite crucible 19 and the tungsten crucible 17 will be 5 mm.

(4) Tungsten carbide powder is injected into the gap.
According to this embodiment, the following various effects are achieved.
Crystal growth is much cheaper and easier than coating with tungsten carbide. The tungsten carbide coating is worried about cracking and deterioration when the number of uses increases due to the difference in thermal expansion coefficient, but in the case of powder, it can absorb the difference in thermal expansion.
In addition, since the heat transfer amount and transfer speed from the first crucible to the second crucible can be controlled by controlling the packing density, the optimum transfer amount and transfer speed can be set so that no temperature gradient occurs. Easy to do.

[Growth method]
<Preparation process>
In the preparation step, a seed crystal is prepared and attached to the holding member 13 of the pulling rod 12. Subsequently, a tungsten crucible 18 having carbide on the skin is arranged on the inner side, and a tungsten plate 21 is placed on the bottom of the double structure integrated crucible in which a graphite crucible 19 is arranged on the outer side. A molybdenum crucible 17 is placed thereon. Providing a triple crucible. Further, the raw material powder is filled, and the carbon felt material 16 and the zirconia refractory 15 are assembled as a heat insulating container so as to surround the crucible in the chamber 11. Furthermore, a quartz tube 14 is disposed between the heating coil 20 and the heat insulating container 15. After the preparatory work is completed, the gas supply unit 22 is not supplied with a gas, and the inside of the chamber is decompressed using the exhaust unit 23.

Thereafter, argon gas is supplied from the gas supply unit 22 to bring the inside of the chamber 11 to normal pressure in an inert gas atmosphere. When supplying the gas, it is preferable to supply the gas so that the gas flows upward from below. Thereby, it can reduce that an impurity etc. mix in the melt 300. FIG.
<Melting process>
In the melting step, argon gas is supplied from the gas supply unit 22 to the chamber 11. The coil power supply supplies a high-frequency current to the heating coil 20, magnetic flux is generated in the heating coil 20, and eddy current is generated in the graphite crucible 19 that is a heating element.

Since the melting point of the graphite crucible 19 is 3000 ° C., it is possible to heat the graphite crucible 19 to 2500 ° C. or higher, and the working efficiency increases when heated to 2500 ° C. or higher. However, the heating of the graphite crucible 19 is preferably 2500 ° C. or less, and more preferably 2300 ° C. or less. By limiting the heating temperature of the graphite crucible 19 in this way, the life of the crucible becomes much longer.

Then, the tungsten crucible 18 is heated by heat conduction from the graphite crucible 19 which is a heating element, and the molybdenum crucible 17 is heated by heat radiation or heat conduction from the tungsten crucible 18. In this way, the bottom and the wall of the molybdenum crucible 17 are heated, and when the aluminum oxide accommodated in the molybdenum crucible 17 is heated to exceed its melting point (2054 ° C.), alumina in the molybdenum crucible 17 is obtained. The raw material, that is, aluminum oxide is melted to form the alumina melt 300.

<Seeding process>
In the seeding step, the gas supply unit 22 supplies argon gas into the chamber 23. The pulling drive unit lowers the pulling rod 12 to a position where the lower end of the seed crystal 200 attached to the holding member 13 comes into contact with the alumina melt 300 in the molybdenum crucible 17 to stop. In this state, the coil power supply adjusts the current value of the high-frequency current supplied to the heating coil 20 based on the weight signal from the weight detector.

<Shoulder formation process>
In the shoulder forming step, after the high frequency current supplied from the coil power supply to the heating coil 20 is adjusted, the temperature is kept for a while until the temperature of the alumina melt 300 is stabilized, and then the pulling rod 12 is moved at the first rotational speed. Pull up at the first pulling speed while rotating. Then, the seed crystal 210 is pulled up while being rotated in a state where its lower end is immersed in the alumina melt 300, and a shoulder 220 that expands directly below the lead circle is formed at the lower end of the seed crystal 210. Will be formed. When the diameter of the shoulder 220 becomes several mm larger than the desired diameter of the substrate, the shoulder formation process is completed.

<Straight body part formation process>
In the straight body forming step, the gas supply unit 22 supplies argon gas into the chamber 11. The coil power supply continues to supply high-frequency current to the heating coil 20 to heat the alumina melt 300 via the molybdenum crucible 17. The pulling drive unit pulls the pulling rod 12 at the second pulling speed. Here, the second pulling speed is a speed different from the first pulling speed in the shoulder forming step. Further, the rotation drive unit rotates the pulling rod 12 at the second rotation speed.

Here, the second rotation speed is a speed different from the first rotation speed in the shoulder portion forming step. Since the shoulder 220 integrated with the seed crystal 210 is pulled up while being rotated with its lower end immersed in the alumina melt 300, a cylindrical straight body portion is provided at the lower end of the shoulder 220. 230 is formed. The diameter of the straight body 230 may be several mm larger than the desired diameter of the substrate.

<Tail formation process>
In the tail formation step, the gas supply unit 22 supplies argon gas into the chamber 11. Further, the coil power supply continues to supply a high frequency current to the heating coil 20 to heat the alumina melt 300 via the molybdenum crucible 17. Further, the pulling drive unit pulls the pulling rod 12 at the third pulling speed. Here, the third pulling speed is a speed different from the first pulling speed in the shoulder forming process or the second pulling speed in the straight body forming process.

Furthermore, the rotation drive unit rotates the pulling rod 12 at the third rotation speed. Here, the third rotation speed is a speed different from the first rotation speed in the shoulder portion forming step or the second rotation speed in the straight body portion forming step. Note that the lower end of the tail portion 240 is kept in contact with the alumina melt 300 in the early stage of the tail portion forming step.
Then, at the end of the tail forming process after a predetermined time has elapsed, the pulling drive unit increases the pulling speed of the pulling rod 12 to raise the pulling rod 12 further upward, so that the lower end of the tail 240 is fused with alumina. Pull away from liquid 300. Thereby, the sapphire ingot 200 shown in FIG. 2 is obtained.

<Cooling process>
In the cooling process, the gas supply unit 22 supplies argon gas into the chamber 11. Further, the coil power supply stops the supply of the high frequency current to the heating coil 20 and stops the heating of the alumina melt 300 via the crucible 17. Further, the pulling drive unit stops the pulling of the pulling rod 12, and the rotation driving unit stops the rotation of the pulling rod 12. 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 17. For this reason, with the stop of heating, the alumina melt 300 in the crucible 17 is gradually cooled and solidifies in the crucible 17 after being lower than the melting point of aluminum oxide, and becomes a solid of aluminum oxide. Then, the sapphire ingot 200 is taken out from the chamber 11 in a state where the inside of the chamber 11 is sufficiently cooled.

As described above, in the present embodiment, the crucible 17 is indirectly heated without directly heating the wall portion of the crucible 17 by the heating coil 20. For this reason, compared with the case where the wall part of the crucible 17 is directly heated with the heating coil 20, the temperature gradient of the melt in the crucible 17 can be relieved. Therefore, distortion generated in the single crystal grown by the rapid temperature gradient can be suppressed.

Example 1
In this example, a high-frequency induction heating type Czochralski furnace equipped with a high-frequency heating coil having a chamber inner diameter of 1000φ was used. 4N (99.99%) as a starting material for an integrated double crucible in which a graphite crucible is closely placed on the outside of a crucible coated with tungsten carbide having a thickness of 0.5 mm on the outer wall of a tungsten crucible with an inner diameter of 295 mm 52 kg of the aluminum oxide raw material was charged. The crucible charged with the raw material was charged into the heating chamber of the growth furnace. A heat insulating structure was provided on the outer periphery of the integrated double crucible with carbon felt material and zirconia, a high-frequency heating coil was disposed on the outermost periphery of the heating chamber, and a quartz tube was disposed on the inner side. In order to circulate the atmosphere gas in the heating chamber by introducing argon gas from the lower part of the furnace after evacuating the furnace, flowing at a flow rate of 1.0 L / min, providing an exhaust port above the apparatus, and circulating the atmospheric gas in the heating chamber, Arranged to seal the gas.

When the inside of the furnace became atmospheric pressure, the crucible was started to be heated gradually over 12 hours until reaching the melting point of aluminum oxide. After melting, an aluminum oxide single crystal was used as a seed crystal, and the seed crystal was lowered to near the melt. The seed crystal is gradually lowered while rotating at a speed of 2 revolutions per minute, and the seed crystal is lowered at a pulling speed of 2 mm / h while gradually lowering the temperature by bringing the tip of the seed crystal into contact with the melt. The crystal was grown by raising.

  As a result, a single crystal having a diameter of 205 mm and a length of the straight body portion of 150 mm was obtained. When this single crystal was observed, minute bubbles were not observed. Further, when the wafer was cut and polished into a wafer and the inside was observed with polarized light, no generation of subgrains was observed.

(Example 2)
In this example, a high-frequency induction heating type Czochralski furnace equipped with a high-frequency heating coil having a chamber inner diameter of 1000 mmφ was used. A molybdenum crucible with an inner diameter of 230 mm is placed inside an integrated double crucible in which a graphite crucible is placed in close contact with the outside of a crucible coated with tungsten carbide having a thickness of 0.5 mm on the outer wall of a tungsten crucible with an inner diameter of φ295 mm. The molybdenum crucible is disposed in a tungsten crucible having an inner wall coated with tungsten carbide via a tungsten spacer.

As a starting material, 22 kg of 4N (99.99%) aluminum oxide material was charged into a molybdenum crucible. The crucible charged with the raw material was charged into the heating chamber of the growth furnace. A heat insulating structure was provided on the outer periphery of the integrated double crucible with carbon felt material and zirconia, a high-frequency heating coil was disposed on the outermost periphery of the heating chamber, and a quartz tube was disposed on the inner side. In order to circulate the atmosphere gas in the heating chamber by introducing argon gas from the lower part of the furnace after evacuating the furnace, flowing at a flow rate of 1.0 L / min, providing an exhaust port above the apparatus, and circulating the atmospheric gas in the heating chamber, Arranged to seal the gas. When the inside of the furnace became atmospheric pressure, the crucible was started to be heated gradually over 12 hours until reaching the melting point of aluminum oxide. After melting, an aluminum oxide single crystal was used as a seed crystal, and the seed crystal was lowered to near the melt. The seed crystal is gradually lowered while rotating at a speed of 10 revolutions per minute, and the seed crystal is pulled at a pulling speed of 2 mm / h while gradually lowering the temperature by bringing the tip of the seed crystal into contact with the melt. The crystal was grown by raising.

As a result, a single crystal having a diameter of 155 mm and a length of the straight body portion of 150 mm was obtained. When this single crystal was observed, minute bubbles were not observed. Further, when the wafer was cut and polished into a wafer and the inside was observed with polarized light, no generation of subgrains was observed.
(Example 3)
In this example, a single crystal is grown using an apparatus in which tungsten carbide powder is inserted between a first crucible and a second crucible.
All the single crystals produced in Examples 1 to 3 had lower hardness than the conventional ones. The reason why the single crystal according to this example has lower hardness than the conventional single crystal is presumed as follows.
Conventionally, in the conventional breeding apparatus, iridium is used for the crucible, and the thermal insulation chamber is formed from zirconia. Therefore, in the conventional growth apparatus, it is estimated that oxygen was generated in the furnace and the generated oxygen increased the hardness of the single crystal. In contrast, in this example, the inside of the furnace was purged with argon gas and oxygen was excluded from the inside of the furnace, so the single crystal was softer and easier to process than the sapphire crystal grown with the conventional growth equipment. It is presumed that Note that it is preferable to use a gas having an oxygen and moisture content of 100 ppb or less (more preferably 100 ppt or less) as the argon gas.

11 Chamber 12 Lifting rod 13 Holding member 14 Quartz tube 15 Heating chamber 16 Carbon felt 17 Third crucible 18 First crucible 19 Second crucible 20 Heating coil 22 Gas supply section 23 Gas exhaust section 200 Ingot 210 Seed crystal 220 Shoulder Part 230 Straight body part 240 Tail part 300 Raw material melt 350 Tungsten carbide powder

Claims (14)

A heating chamber formed of a heat insulating material provided in the chamber, a crucible provided inside the heating chamber, and a heating coil arranged on the outer periphery of the heating chamber, and obtained by heating the crucible In a single crystal growing apparatus for raising a seed crystal by bringing the seed crystal into contact with the raw material melt,
The crucible, it from a first crucible having a bottom with a carbide tungsten bottom outer surface on the surface of the tungsten, the second crucible with a bottom made of graphite is disposed outside the first crucible Ri, said first crucible of the bottom outer surface of said carbide and said second crucible single crystal growing apparatus that Do and bottom contacting the inner surface of. 2. The single crystal growing apparatus according to claim 1, wherein the bottomed third crucible made of molybdenum is arranged inside the first crucible via a spacer made of tungsten. The single crystal growing apparatus according to claim 1, wherein the single crystal is an oxide single crystal. 4. The single crystal growing apparatus according to claim 1, wherein the oxide is sapphire (Al ₂ O ₃ ) or ScAlMgO ₄ . The single crystal growing apparatus according to any one of claims 1 to 4, wherein the first crucible is arranged in contact with or apart from the second crucible. The single crystal growing apparatus according to any one of claims 1 to 5, wherein a carbon felt is disposed on an outer periphery of the second crucible. 7. The sapphire single crystal growing apparatus according to claim 1, wherein the tungsten carbide has a thickness of 0.2 mm to 5 mm. The single-crystal growth apparatus according to any one of claims 1 to 7, wherein the tungsten carbide is formed by thermal spraying, sputtering, or CVD. A heating chamber formed of a heat insulating material provided in the chamber, a crucible provided inside the heating chamber, and a heating coil arranged on the outer periphery of the heating chamber, and obtained by heating the crucible In a single crystal growing apparatus for raising a seed crystal by bringing the seed crystal into contact with the raw material melt,
The crucible includes a bottomed first crucible and a bottomed second crucible made of graphite disposed outside the first crucible, and an outer periphery of the first crucible and the second crucible. A single crystal growth apparatus in which tungsten carbide powder is charged in a space formed by the inner periphery of the steel. The single crystal growing apparatus according to any one of claims 1 to 9, wherein the single crystal is a single crystal having a diameter of 6 inches or more. A method for growing a single crystal using the single crystal growing apparatus according to any one of claims 1 to 10,
The raw material powder is charged into the first crucible, the pressure in the heating chamber is subsequently reduced, and the second crucible is heated to a high temperature by supplying a high-frequency current to the heating coil, and the first crucible is heated by the heat. A method for growing a single crystal, in which a raw material inside is melted, a seed crystal is brought into contact with the molten melt, and the seed crystal is pulled up while rotating to grow a single crystal. The single crystal growth method according to claim 11, wherein the single crystal is a sapphire single crystal, and the growth is performed while introducing an argon gas into the apparatus. The single crystal growth apparatus according to claim 12, wherein the argon gas is introduced from below the apparatus. The method for growing a single crystal according to claim 12 or 13, wherein the second crucible is heated to 2300 ° C or lower.

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