JP7412276B2 - Filling method for raw silicon - Google Patents

Description

The present invention relates to a method for filling raw material silicon for pulling a silicon single crystal using the Czochralski method.

The Czochralski method (CZ method) is known as a method for manufacturing silicon single crystals. In the CZ method, granular polycrystalline silicon as a raw material is put into a crucible, and a heater surrounding the crucible heats and melts the polycrystalline silicon. When the silicon melt is formed in the crucible, the seed crystal held on the crucible is lowered while rotating the crucible in a fixed direction and brought into contact with the surface of the silicon melt in the crucible. By raising the seed crystal while rotating it in a predetermined direction, a cylindrical silicon single crystal is grown below the seed crystal.

In growing a silicon single crystal using such a CZ method, the amount of silicon melt in the crucible decreases as the silicon single crystal is pulled. Generally, crucibles used during crystal growth by the CZ method are disposable, and conventionally a single-pull operation was performed in which one silicon single crystal was pulled in one operation. However, in recent years, so-called multi-pull operations have been carried out because replenishing the reduced silicon melt and pulling a plurality of silicon single crystals leads to cost reduction. Continuous multi-pulling operations also lead to improved productivity.

In the so-called recharge method, which replenishes the lost amount of silicon melt and secures the necessary amount of melt, a raw material supply device that feeds granular polycrystalline silicon, which is the raw material, is placed above the center of the crucible in the pulling device. However, it is important to drop polycrystalline silicon evenly in the circumferential direction of the silicon melt in the crucible. This can cause damage to the crucible when replenishing polycrystalline silicon, or splashes of silicon melt can attach to parts such as the radiation shield in the pulling equipment, causing them to deteriorate. This is to avoid problems such as adverse effects on the growth of single crystals.

If parts inside the pulling device are damaged or deteriorated during recharging, dislocations are likely to occur in the silicon single crystal being pulled. Patent Document 1 describes an invention of a cylindrical recharge tube in a raw material supply device for recharging or additionally charging polycrystalline silicon to a silicon melt in a crucible. The recharge tube of Patent Document 1 has a plurality of divided tubes that are divided in the axial direction when filling the solid raw material, and a connecting portion that connects the divided tubes vertically when filling the crucible with the solid raw material, In the divided tube, the inner diameter of the upper end of the lower divided tube is designed to be equal to the inner diameter of the lower end of the upper divided tube, or larger than the inner diameter of the lower end of the upper divided tube. As a result, when filling raw materials, polycrystalline silicon is charged without directly hitting the upper end of the lower dividing tube, and scratches, cracks, or chips do not occur near the upper end of the lower dividing tube. In other words, in Patent Document 1, since it is possible to prevent the generation of impurities due to damage to the recharge tube during filling of raw materials, it is possible to prevent deterioration of characteristics such as formation of dislocations in the silicon single crystal, and by recharging, the crucible can be It is stated that the number of single crystals pulled per single crystal can be increased.

On the other hand, in the silicon single crystal pulling equipment using the CZ method, recharging or additional charging of raw materials can be facilitated by installing a cooler for cooling the single crystal and a heat shield that surrounds the single crystal so that they can be moved within the equipment. A method has also been reported (Patent Document 2). Patent Document 2 states that when recharging or additionally charging solid raw materials, members within the device, especially coolers and heat shields, become obstacles, and that if the cooler is located near the crucible, it may cause problems during charging. Since it is necessary to heat the crucible to an extent that exceeds the cooling effect of the cooler, it is necessary to raise the crucible quickly, preferably at a high speed of 300 mm/min, to keep the cooler and heat shield away from the surface of the silicon melt. Are listed.

JP2019-112238A Japanese Patent Application Publication No. 2001-240492

However, the risk of damage to the quartz crucible due to rapid changes in the thermal environment during recharging work has not been sufficiently avoided.

By raising the position of the radiation shield before introducing solid raw materials through the recharge tube, you can not only secure the field of view when charging, but also prevent the raw materials from coming into contact with each other and the silicon melt from splashing. It is thought that it is possible to prevent the adhesion of droplets caused by On the other hand, the radiation shield also serves as a lid when melting raw materials, and it is known that if the temperature is raised too high, the temperature inside the device will drop. Furthermore, recent quartz crucibles generally have a structure of two or more layers made of natural quartz and synthetic quartz, and sometimes have three or four layers to increase the strength of the crucible. When a multilayer quartz crucible is used in this way, if the temperature at the top of the quartz crucible, which is in a high temperature state near the heater, suddenly decreases by raising the radiation shield, the outer layer of the quartz crucible will Cracks may occur. When cracks occur, silicon melt leaks from the cracks, making subsequent crystal growth difficult and reducing production capacity. Furthermore, if the discovery is delayed and the raw material leaks out even though it is filled with a sufficient amount of raw material melt, the pulling member and equipment will also be damaged and a large amount of costs will be incurred. Therefore, there is a need for a method for supplying raw materials that does not cause such cracks.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for filling raw material silicon without causing adverse effects such as cracks in a quartz crucible due to rapid changes in the thermal environment during a recharge operation.

The present invention consists of the following matters.
The method for filling raw material silicon of the present invention is a silicon single crystal pulling apparatus equipped with a recharge mechanism for supplying raw material silicon and a radiation shield that can be raised and lowered. After raising the shield, the quartz crucible is lowered, and during the subsequent cycle of supplying raw materials, the cooling temperature gradient from the highest temperature at the top of the quartz crucible is set to 14. .0°C/min or less.

When raising the radiation shield, it is preferable that the closest distance between the radiation shield and the member on which the radiation shield is placed is 70 mm or less.
Preferably, the radiation shield is raised all at once without stopping until the quartz crucible reaches its maximum temperature.
When the position where the upper end of the quartz crucible and the upper end of the main heater installed outside the carbon crucible that holds the quartz crucible are at the same height is 0 mm, the upper end of the quartz crucible is +50 to +50 mm from the above position. Preferably, the distance is within the range of −150 mm. Here, the state in which the upper end of the quartz crucible is located above the upper end of the main heater is defined as "+".

If the raw material, granular polycrystalline silicon, is replenished according to the method of the present invention, cracks will not occur in the outer layer of the quartz crucible. Therefore, according to the present invention, a plurality of silicon single crystals can be stably pulled, and cost reduction and productivity improvement can be expected.

FIG. 1 shows a schematic cross-sectional view of a silicon single crystal pulling apparatus used for recharging. FIG. 2(a) shows when the recharging work starts, (b) after the recharging work starts, when the closest distance between the radiation shield and the member on which the radiation shield is placed is 115 mm (R115), and (c) after the recharging work starts, FIG. 2 is a semi-schematic cross-sectional view of a silicon single crystal pulling furnace when the closest distance between a radiation shield and a member on which the radiation shield is mounted is 70 mm (R70). FIG. 3 shows temperature changes in the quartz crucibles of the conventional example and Example 1 when the radiation shield is raised. FIG. 4 compares the temperature changes of the quartz crucibles of Example 1 and the conventional example with the temperature changes of the quartz crucible of Comparative Example 5, which was stopped during the raising of the radiation shield.

Hereinafter, the present invention will be described in detail with reference to the drawings.
A silicon single crystal manufacturing apparatus 100 shown in FIG. 1 is a schematic vertical cross-sectional view of one form of the silicon single crystal manufacturing apparatus used in the present invention, and includes a crucible filled with raw material silicon 22, a main heater 13, and a lower heater 18. , a recharge mechanism for supplying raw material silicon 22, a radiation shield 11 that can be raised and lowered, a member 12 on which the radiation shield is mounted, and the like. Silicon single crystal manufacturing apparatus 100 is divided into two parts, chamber 10 and subchamber 1, via a gate valve (not shown).

In the silicon single crystal production apparatus 100, the crucible includes a quartz crucible 16 that directly accommodates raw silicon 22 and silicon melt 26, and a carbon crucible 17 that supports the quartz crucible 16 on the outside. The quartz crucible 16 and the carbon crucible 17 are supported by a crucible shaft 15 that is attached to the lower part of the silicon single crystal manufacturing apparatus 100 and is rotatably movable up and down by a rotational drive mechanism (not shown).

The recharge mechanism is composed of a raw material container 20 consisting of a straight recharge tube 21 filled with raw material silicon 22, a bottom lid 25, and a ring 27, a wire 23 for suspending the raw material container 20, and a lifting motor 24 for winding up the wire 23. has been done. The wire 23 passes through the center of the raw material container 20 and is fixed at the center of the bottom lid 25 of the raw material container 20. The bottom cover 25 supports the lower end of the recharge tube 21, thereby holding the entire raw material container 20. Then, the raw material container 20 filled with raw material silicon 22 descends toward the quartz crucible 16 . When the ring 27 attached to the raw material container 20 is hooked to the peripheral edge provided on the inner wall of the subchamber 1, only the bottom cover 25 begins to descend, creating a gap that causes the silicon melt in the quartz crucible 16 to leak. Raw material silicon 22 is supplied to 26 . A feature of the present invention is that before supplying the raw material silicon 22, the radiation shield 11 is raised, and then, while the quartz crucible 16 is lowered together with the carbon crucible 17, the cooling temperature gradient from the highest temperature at the upper end of the quartz crucible 16 is maintained. It is to be 14.0°C/min or less.

Here, in the silicon single crystal manufacturing apparatus 100, a main heater 13 and a lower heater 18 are arranged so as to surround the quartz crucible 16 and the carbon crucible 17. A heat insulating member 14 and its cover 19 are provided to prevent heat from being directly radiated into the chamber 10. Then, the radiation shield 11 connects the silicon melt 26, the crucible, and the silicon single crystal so that the heat from the silicon melt 26, the quartz crucible 16, and the carbon crucible 17 does not hinder the cooling of the pulled silicon single crystal. is established between.

The radiation shield 11 is made of a metal such as molybdenum, tungsten, and tantalum, carbon, whose surface is coated with silicon carbide, and a molded heat insulating material provided on the inside thereof, which serves to control radiant heat. It is made of a material that fulfills the following requirements. The heat retaining member 14 is made of a material with excellent heat retaining properties, such as a molded heat insulating material.

Next, the supply of raw materials by recharging after pulling the silicon single crystal will be explained.
First, a silicon single crystal ingot having a predetermined diameter and length is grown, the lid of the subchamber 1 is opened, and the crystal is taken out.

Next, the raw material container 20 filled with the raw material, granular polycrystalline silicon (raw material silicon 22), is suspended from the wire 23 outside the silicon single crystal production apparatus 100, and then the lid is closed again to seal it. . Thereafter, the pressure inside the subchamber 1 is reduced and replaced with an inert gas, and the gate valve is opened to allow the chamber 10 and the subchamber 1 to communicate with each other. After that, the radiation shield 11 is raised. Raising the radiation shield 11 not only ensures visibility while supplying the raw silicon 22, but also prevents interference between the raw silicon 22 and the radiation shield 11, that is, collision of the raw silicon 22 with the radiation shield 11. It is possible to prevent the silicon melt 26 from falling into the quartz crucible 16 by sliding on the slope of the surface of the radiation shield 11, and from adhering to the inner wall of the silicon single crystal manufacturing apparatus 100 due to droplets of the silicon melt 26 caused by the fall. It can be prevented. The radiation shield 11 is raised at a speed of approximately 50 to 150 mm/min, for example, 100 mm/min.

After the radiation shield 11 is raised, the quartz crucible 16 is lowered. By lowering the quartz crucible 16 and bringing it closer to the lower heaters (main heater 13 and lower heater 18), it is possible to suppress the temperature drop that would occur due to the radiation shield 11 being separated from the heater. The quartz crucible 16 is normally lowered at a speed of 50 to 180 mm/min.

Then, while the radiation shield 11 is raised and the quartz crucible 16 is lowered, the cooling temperature gradient from the maximum temperature reached at the upper end of the quartz crucible 16 is set to 14.0° C./min or less, preferably 12° C./min or less. By setting the cooling temperature gradient from the highest temperature at the upper end of the quartz crucible 16 to 14.0°C/min or less and reducing the temperature drop at the upper end of the quartz crucible 16, cracks can be prevented from forming in the quartz crucible 16, especially in its outer layer. It can be suppressed. After that, the raw material container 20 is lowered. When the ring 27 is latched onto the peripheral edge, only the bottom cover 25 is further lowered. Then, a gap is created between the recharge tube 21 and the bottom cover 25, and the raw material silicon 22 is supplied into the quartz crucible 16 by its own weight through this gap. Repeat these several times until the desired charge amount is reached.

When raising the radiation shield 11, it is preferable that the closest distance between the radiation shield 11 and the member 12 on which the radiation shield is placed is 70 mm or less. This is because if the radiation shield 11 is raised too much, a drop in temperature cannot be prevented even if the quartz crucible 16 is lowered to the vicinity of the heater. The closest distance between the radiation shield 11 and the member 12 on which the radiation shield is mounted is more preferably 60 mm or less. Note that the closest distance between the radiation shield 11 and the member 12 on which the radiation shield is placed is a circle centered on the tip of the member 12 on which the radiation shield is placed that is closest to the radiation shield 11 and in contact with the radiation shield 11. It refers to the radius (R) when

It is preferable that the radiation shield 11 be raised all at once without stopping until the quartz crucible 16 reaches its maximum temperature. The reason for this is that since the radiation shield 11 is located directly above the silicon melt 26, the lower part thereof is originally at a high temperature. If the radiation shield 11 is raised in such a high temperature state, the temperature of the quartz crucible 16 will rise as shown in FIG. This is because the temperature of the quartz crucible 16 further increases as shown in FIG. 2, and a sudden temperature difference will be experienced due to the subsequent rise of the radiation shield 11, which may lead to the occurrence of cracks.

When the position where the upper end of the quartz crucible 16 and the upper end of the main heater 13 installed outside the carbon crucible 17 that holds the quartz crucible 16 are at the same height is 0 mm, the upper end of the quartz crucible 16 is It is preferable to locate within a range of +50 to -200 mm from the above position. This is because the closer the quartz crucible 16 is to the heater, the less it is affected by the temperature drop due to the rise of the radiation shield 11.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.
[Example 1]
In a silicon single crystal pulling apparatus in which the outer diameter of the quartz crucible is φ810 mm, the radiation shield is installed so that the closest distance R between the radiation shield and the member on which the radiation shield is mounted is 70 mm, with 50 kg of silicon melt remaining. was raised all at once without stopping in the middle. Next, the quartz crucible and the carbon crucible holding the quartz crucible were lowered. While the radiation shield was raised and the quartz crucible was lowered, the cooling temperature gradient from the highest temperature at the top of the quartz crucible was 11.3° C./min. Furthermore, the position of the crucible when the shield is raised is 0 mm, where the upper end of the quartz crucible is at the same height as the upper end of the heater installed outside the carbon crucible, and the position of the upper end of the quartz crucible is 0 mm. I made it so.
Thereafter, the raw material container 20 was lowered to supply the raw material. After the raw materials had melted to some extent, the quartz crucible was visually observed to see if any cracks had occurred. No cracks were observed in the outer layer of the quartz crucible obtained in Example 1, and the crack occurrence rate was 0.0%.

[Example 2]
In Example 1, granular raw silicon was recharged in the same manner as in Example 1 except that the closest distance R between the radiation shield and the member on which the radiation shield is placed was 60 mm. The cooling temperature gradient from the highest temperature at the top of the quartz crucible was 10.9°C/min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in Example 2 was 0.0%.

[Example 3]
In Example 1, granular raw material silicon was prepared in the same manner as in Example 1 except that the distance from the position where the upper end of the quartz crucible and the upper end of the heater were at the same height to the upper end of the quartz crucible was +50 mm. I did a recharge. The cooling temperature gradient from the highest temperature at the top of the quartz crucible was 13.5° C./min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in Example 3 was 0.0%.

[Example 4]
In Example 1, particles were prepared in the same manner as in Example 1 except that the position of the top of the quartz crucible was set to -50 mm when the position where the top of the quartz crucible and the top of the heater were at the same height was 0 mm. Recharged bulk raw material silicon. The cooling temperature gradient from the highest temperature reached at the top of the quartz crucible was 10.8° C./min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in Example 4 was 0.0%.

[Example 5]
In Example 1, grains were prepared in the same manner as in Example 1, except that when the position where the top end of the quartz crucible and the top end of the heater were at the same height was 0 mm, the position of the top end of the quartz crucible was set to -150 mm. Recharged bulk raw material silicon. The cooling temperature gradient from the highest temperature reached at the top of the quartz crucible was 10.6° C./min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in Example 4 was 0.0%.

[Comparative example 1]
In Example 1, granular raw silicon was recharged in the same manner as in Example 1, except that the closest distance R between the radiation shield and the member on which the radiation shield is placed was 90 mm. The cooling temperature gradient from the highest temperature reached at the top of the quartz crucible was 17.5°C/min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in Comparative Example 1 was 3.2%.

[Comparative example 2]
In Example 1, granular raw material silicon was recharged in the same manner as in Example 1, except that the closest distance R between the radiation shield and the member on which the radiation shield is placed was 80 mm. The cooling temperature gradient from the highest temperature reached at the top of the quartz crucible was 15.8° C./min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in Comparative Example 2 was 0.6%.
In Comparative Examples 1 and 2, since R was large, the upper end of the quartz crucible was cooled rapidly, which is thought to have led to the occurrence of cracks.

[Comparative example 3]
In Example 1, the process was repeated in the same manner as in Example 1, except that when the position where the upper end of the carbon crucible and the upper end of the heater were at the same height was 0 mm, the position of the upper end of the quartz crucible was +100 mm. The raw material silicon was recharged. The cooling temperature gradient from the highest temperature at the top of the quartz crucible was 16.2°C/min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in Comparative Example 3 was 0.5%.
In Comparative Example 3, it is thought that the amount of heat that the quartz crucible received from the heater was not sufficient, which led to the occurrence of cracks in the quartz crucible.

[Comparative example 4]
In Example 3, the granular raw material silicon was recharged in the same manner as in Example 3, except that the radiation shield was stopped twice during the raising. The cooling temperature gradient from the highest temperature at the top of the quartz crucible was 16.2°C/min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in Comparative Example 4 was 0.9%.
In Comparative Example 4, the temperature at the top of the quartz crucible rose further because the radiation shield was stopped twice during the raising process, and the subsequent rise in the radiation shield caused a larger temperature drop, which is thought to have led to the occurrence of cracks. .

[Comparative example 5]
In Example 3, the granular raw material silicon was recharged in the same manner as in Example 3, except that the radiation shield was stopped once during raising. The cooling temperature gradient from the highest temperature at the top of the quartz crucible was 15.1°C/min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in Comparative Example 5 was 0.4%.
In Comparative Example 5, the radiation shield was stopped once during the raising process, so although it was not as great as in Comparative Example 4, which stopped twice, it can be said that the temperature rise at the upper end of the quartz crucible and the subsequent decrease were large.

[Conventional example]
In Example 1, granular raw material silicon was recharged in the same manner as in Example 1, except that the closest distance R between the radiation shield and the member on which the radiation shield is placed was 115 mm. The cooling temperature gradient from the highest temperature at the top of the quartz crucible was 20.1°C/min.
When the presence or absence of cracks generated in the quartz crucible was observed in the same manner as in Example 1, the crack occurrence rate in the conventional example was 4.7%.

Table 1 shows the test conditions and crack occurrence rates of Examples 1 to 5, Comparative Examples 1 to 5, and conventional examples.

1 Sub-chamber 10 Chamber 11 Radiation shield 12 Radiation shield mounting member 13 Main heater 14 Heat-insulating member 15 Crucible shaft 16 Quartz crucible 17 Carbon crucible 18 Lower heater 19 Cover 20 Raw material container 21 Recharge tube 22 Raw material silicon (granular polycrystalline silicon) )
23 wire 24 motor 25 bottom cover 26 silicon melt 27 ring 100 silicon single crystal manufacturing device

Claims (4)

In a silicon single crystal pulling apparatus equipped with a recharge mechanism for supplying raw material silicon and a radiation shield that can be raised and lowered,
Before supplying raw silicon through the recharge mechanism,
A method for filling raw material silicon, which comprises lowering a quartz crucible after raising a radiation shield, and during this period, the cooling temperature gradient from the maximum temperature reached at the upper end of the quartz crucible is set to 14.0° C./min or less. 2. The method of filling raw silicon according to claim 1, wherein when raising the radiation shield, the closest distance between the radiation shield and the member on which the radiation shield is placed is 70 mm or less. 3. The method for filling raw silicon according to claim 1, wherein the radiation shield is raised at once without stopping until the quartz crucible reaches its maximum temperature. When the position where the upper end of the quartz crucible and the upper end of the main heater installed outside the carbon crucible holding the quartz crucible are at the same height is 0 mm,
The method for filling raw silicon according to any one of claims 1 to 3, wherein the upper end of the quartz crucible is located within a range of +50 to -150 mm from the position.

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