Method for supplementing doping by placing cover and preparation method of monocrystalline silicon

Abstract

The invention relates to the technical field of semiconductors, in particular to a cover-placing doping supplementing method and a preparation method of monocrystalline silicon, and the cover-placing doping supplementing method comprises the following steps: after welding, controlling the power of a heater of a crucible to be smaller than the power of the heater during seeding; after seeding for a first set time, placing a cover and lifting the cover again, in the step of lifting the cover, lifting the cover out of a rotary plate valve of the single crystal furnace, and leaving the cover in an auxiliary chamber of the single crystal furnace; adding a doping agent into the cover through a slag taking opening of the auxiliary chamber, descending the cover to a position which is a first set distance away from the lower edge of a water-cooling screen of the single crystal furnace and staying for a second set time, continuing descending the cover to a position which is a second set distance away from the liquid level of the crucible and staying for a third set time, and then the cover descends, and the shoulder cover is immersed in the liquid level. The method for placing the cover to supplement doping can be applied to preparation of monocrystalline silicon, and the method can effectively solve the problem that the cover and the supplement doping agent in the cover are blown away together.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, in particular to a method for supplementary doping by placing a cap and a method for preparing single crystal silicon. Background Art

[0002] The Czochralski method is a commonly used method for preparing single crystal silicon. The process flow of this preparation method includes: placing polycrystalline silicon material in a quartz crucible to melt, then allowing the seed crystal to contact with the melt, allowing the molten silicon at the solid-liquid interface to cool and crystallize along the seed crystal, and grow by slowly pulling out the seed crystal. After the necking is completed, the crystal growth diameter is enlarged by reducing the pulling speed and / or the melt temperature until the target diameter is reached; after the shoulder is released, the crystal growth enters the equal diameter growth stage by controlling the pulling speed and the melt temperature; finally, the diameter of the crystal growth surface is gradually reduced by increasing the pulling speed and raising the melt temperature to form a tail cone, until the crystal finally leaves the melt surface, and the growth of the single crystal silicon rod is completed.

[0003] In the process of preparing single crystal silicon by the direct pulling method, it is often necessary to dope elements such as phosphorus and antimony. Placing a lid is a commonly used method of supplementary doping. The method includes: controlling the liquid surface temperature to reach the critical point of solid-liquid conversion, immersing the seed crystal in the liquid surface, giving a descending speed to make it slowly crystallize to form an inverted umbrella-shaped crystalline silicon wafer, which is the lid. After cooling, the crystalline silicon wafer is slowly taken out, the dopant is placed in the crystalline silicon wafer, and then it and the dopant are lowered into the silicon liquid to dissolve.

[0004] However, the lid placement method provided by the related art is prone to the problem of the lid and the dopant being blown away. Summary of the invention

[0005] The purpose of the present invention is to provide a method for supplementary doping with a lid and a method for preparing single crystal silicon. The method for supplementary doping with a lid of the present invention can be applied to the preparation of single crystal silicon, and the method can effectively improve the problem of the lid and the supplementary doping agent in the lid being blown away together.

[0006] The present invention is achieved in that:

[0007] In a first aspect, the present invention provides a method for adding a cap, comprising:

[0008] After welding, the crucible heater power is controlled to be less than the heater power during seeding;

[0009] After the first set time of seeding, the lid is placed and then lifted. In the step of lifting the lid, the lid is lifted from the rotary valve of the single crystal furnace and the lid is left in the auxiliary chamber of the single crystal furnace.

[0010] Add dopants to the lid through the slag removal port of the auxiliary chamber, then lower the lid to a position a first set distance from the lower edge of the water-cooled screen of the single crystal furnace and stay there for a second set time, then continue to lower the lid to a position a second set distance from the liquid level of the crucible and stay there for a third set time, then lower the lid again and make the liquid level submerge the shoulder cover.

[0011] In an optional embodiment, the first set distance is 10-20 mm; the second set time is 1-2 min.

[0012] In an optional embodiment, the second set distance is 30-40 mm, and the third set time is 1-2 min.

[0013] In an optional embodiment, in the step of lowering the cover and allowing the liquid level to submerge the shoulder cover, the cover lowering speed is 80-120 mm / h.

[0014] In an optional embodiment, in the step of lifting the lid, the crucible is lowered by a third set distance, and the heater is controlled to increase the temperature of the crucible.

[0015] In an optional embodiment, the third set distance is 15-30 mm, and the power of the heater is 80-90 kw.

[0016] In an optional embodiment, the step of lifting the lid includes a first lifting and a second lifting, wherein the speed of the first lifting is lower than the speed of the second lifting; and / or,

[0017] The step of placing the lid includes: a first sub-step and a second sub-step, wherein the pulling speed of the first sub-step is greater than the pulling speed of the second sub-step.

[0018] In an optional embodiment, in the first lifting step, the crystal lifting speed is 240-270 mm / h, and the crystal lifting time is 4-6 min; in the second lifting step, the crystal lifting speed is 360-400 mm / h.

[0019] In an optional embodiment, the pulling speed of the first sub-step is controlled to increase gradually and meet 90-180 mm / h. When the diameter of the cover reaches 80-120 mm, the second sub-step is executed, and the pulling speed of the second sub-step is 50-60 mm / h.

[0020] In a second aspect, the present invention provides a method for preparing single crystal silicon, comprising the cap-doping method of any one of the aforementioned embodiments.

[0021] The beneficial effects of the method for placing a lid and supplementing doping according to the embodiment of the present invention include: in the step of lifting the lid, the lid is lifted out of the rotary plate valve of the single crystal furnace, and the lid is left in the auxiliary chamber of the single crystal furnace, and at the same time, dopants are added to the lid through the slag removal port of the auxiliary chamber, so that there is no need to take the lid out of the auxiliary chamber, that is, the extracted lid is always located in the auxiliary chamber, so as to improve the problem of excessive hot and cold alternation of the lid caused by taking the lid out of the auxiliary chamber, adding supplementary dopants and then putting it back into the auxiliary chamber, so as to improve the structural strength and stability of the lid itself, and improve the problem of the lid being removed from the auxiliary chamber, cooled, and then put back into a high temperature environment, which causes the lid to be To solve the problems of hidden cracks, the cover can be ensured not to explode easily at high temperature when the cover is lowered to the liquid surface; at the same time, when the cover with dopant added is lowered, the cover is first lowered to a position of a first set distance from the lower edge of the water-cooling screen of the single crystal furnace and stays therefor for a second set time, and then the cover is further lowered to a position of a second set distance from the liquid surface of the crucible and stays therefor for a third set time, and finally the cover is lowered again and the liquid surface is made to immerse the shoulder cover. In this way, the cover and the dopant therein can be preheated by lowering the cover in sections, thereby improving the problem that the cover and the dopant are directly immersed in the melt surface of the crucible, resulting in excessive temperature difference and explosion. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0023] The present disclosure provides a method for preparing single crystal silicon, which may refer to a Czochralski method; the method for preparing single crystal silicon performs element doping by a method of placing a cap and supplementary doping.

[0024] The method for placing a lid and supplementing doping comprises: after welding, controlling the power of the heater of the crucible to be less than the power of the heater during seeding; after a first set time of seeding, placing the lid and then lifting the lid, in the step of lifting the lid, lifting the lid from the rotary plate valve of the single crystal furnace and leaving the lid in the auxiliary chamber of the single crystal furnace; adding doping agent to the lid through a slag taking port of the auxiliary chamber, and then lowering the lid to a position at a first set distance from the lower edge of the water cooling screen of the single crystal furnace (that is, lowering the lid to a position above the lower edge of the cold water screen and at a first set distance from the lower edge of the cold water screen), and staying for a second set time, and then continuing to lower the lid to a position at a second set distance from the liquid level of the crucible, and staying for a third set time, and then lowering the lid and making the liquid level immerse the shoulder cover.

[0025] In the lid-placing and doping method, in the lid-lifting step, the lid is lifted from the rotary plate valve of the single crystal furnace and the lid is left in the auxiliary chamber of the single crystal furnace, and at the same time, dopants are added to the lid through the slag taking port of the auxiliary chamber, so that the lid does not need to be taken out of the auxiliary chamber, that is, the extracted lid is always located in the auxiliary chamber, so as to improve the problem of excessive hot and cold alternation of the lid caused by taking the lid out of the auxiliary chamber, adding the supplementary doping agent and then putting it back into the auxiliary chamber, so as to improve the structural strength and stability of the lid itself, improve the problem of hidden cracks on the lid caused by the lid being taken out of the auxiliary chamber, cooled and then put back into a high temperature environment, and then lower the lid to the liquid. At the same time, when lowering the lid with dopants added, first lower the lid to a position at a first set distance from the lower edge of the water-cooled screen of the single crystal furnace and stay there for a second set time, then continue to lower the lid to a position at a second set distance from the liquid surface of the crucible and stay there for a third set time, and finally lower the lid again to immerse the liquid surface in the shoulder cover. In this way, the lid and the dopant therein can be preheated by lowering the lid and the dopant therein in sections, thereby improving the problem that the lid and the dopant are directly immersed in the melt surface of the crucible, resulting in excessive temperature difference and explosion.

[0026] It should be noted that although adding the dopant to the lid in the sub-chamber causes the dopant to enter a high-temperature environment, the dopant (for example, antimony) will react with the silicon component of the lid to release heat. However, since the lid itself is solid and the contact area between the dopant and the lid is small, the reaction is slow and there will be no violent reaction due to the addition of the dopant to the lid, and the structure of the lid will not be damaged. Compared with directly putting the dopant into the crucible, this can improve the problem of violent reaction between the dopant and the melt in the crucible, resulting in boiling over, and the problem of instantaneous release of heat causing the dopant to explode.

[0027] Optionally, in the method of placing a lid and supplementing doping disclosed in the present invention, after the seed crystal is fused, the power is reduced to 10-15kw lower than the seeding power (for example: 10kw, 11kw, 12kw, 13kw, 14kw, 15kw, etc., not specifically limited here), and the seeding is carried out when the aperture where the seed crystal contacts the liquid surface of the melt in the crucible shows 4 saturated points, and the seeding time is controlled at 15-25min (for example: 15min, 18min, 20min, 23min, 25min, etc., not specifically limited here), and then the lid is placed.

[0028] It should be noted that the aperture where the seed crystal contacts the liquid surface of the melt in the crucible shows four saturated points, which can be directly photographed and detected by optical detection equipment such as a camera.

[0029] Optionally, after adding the dopant to the lid in the auxiliary chamber, the slag removal port can be closed and the auxiliary chamber can be purged, for example: an inert gas such as argon is introduced into the auxiliary chamber; after the auxiliary chamber is purified, the rotary valve can be opened to lower the lid and the dopant therein.

[0030] It should be noted that the dopant can be added into the lid located in the sub-chamber using a tungsten gold spoon.

[0031] Optionally, when lifting the lid, when the lid is lifted above the uppermost end of the rotary vane valve by 50-100 mm (for example, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, etc., not specifically limited here), the rotary vane valve can be closed and pressurized to normal pressure using an inert gas such as argon.

[0032] Optionally, the first set distance is 10-20 mm (for example: 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, etc., not specifically limited here); the second set time is 1-2 min (for example: 1 min, 1.2 min, 1.3 min, 1.5 min, 1.8 min, 2 min, etc., not specifically limited here). In this way, the preheating temperature of the lid can be guaranteed, and the problem of hidden cracks on the lid caused by too high temperature in the initial preheating period can be improved.

[0033] Optionally, the second setting distance is 30-40 mm (for example: 30 mm, 32 mm, 34 mm, 36 mm, 38 mm, 40 mm, etc., not specifically limited here), and the third setting time is 1-2 min (for example: 1 min, 1.2 min, 1.3 min, 1.5 min, 1.8 min, 2 min, etc., not specifically limited here). In this way, gradual preheating can be achieved to ensure the effectiveness of preheating, and effectively improve the problem of the lid being finally immersed in the liquid surface and bursting.

[0034] Optionally, in the step of lowering the cover and making the liquid surface immerse the shoulder cover, the speed of the cover lowering is 80-120 mm / h (for example: 80 mm / h, 85 mm / h, 90 mm / h, 95 mm / h, 100 mm / h, 105 mm / h, 110 mm / h, 115 mm / h, 120 mm / h, etc., not specifically limited here). By slowly lowering the cover until the shoulder cover is immersed in the liquid surface, the cover can gradually adapt to the temperature of the melt, effectively improving the problem of the cover and the dopant therein being blown away by the high temperature that is instantly exposed.

[0035] Optionally, in the step of lifting the lid, the crucible is lowered by a third set distance, and the heater is controlled to heat the crucible. In this way, the problem of rapid temperature drop when the lid is lifted can be improved, and the problem of cracks being easily formed can be improved by controlling the cooling speed of the lid, so as to ensure the structural stability and strength of the lid.

[0036] Optionally, the third set distance is 15-30mm (for example: 15mm, 17mm, 20mm, 24mm, 28mm, 30mm, etc., not specifically limited here), and the power of the heater is 80-90kw (for example: 80kw, 83kw, 86kw, 90kw, etc., not specifically limited here).

[0037] It should be noted that, in the step of lifting the lid, the lowering of the crucible and the lifting of the lid can be performed simultaneously to improve efficiency.

[0038] Optionally, the step of lifting the lid includes a first lifting and a second lifting, wherein the speed of the first lifting is lower than the speed of the second lifting. Lifting the lid at a slower speed can improve the problem of the lid's temperature dropping too fast in the initial period of lifting the lid, thereby improving the problem of the lid being prone to cracks, and can effectively improve the problem of the lid and the dopant being blown away when the lid and the dopant therein are subsequently lowered into the melt; and accelerating the lifting during the second lifting can improve efficiency.

[0039] Optionally, in the first lifting step, the crystal lifting speed is 240-270 mm / h (for example: 240 mm / h, 245 mm / h, 250 mm / h, 255 mm / h, 260 mm / h, 265 mm / h, 270 mm / h, etc., not specifically limited herein), and the crystal lifting time is 4-6 min (for example: 4 min, 5 min, 6 min, etc., not specifically limited herein); in the second lifting step, the crystal lifting speed is 360-400 mm / h (for example: 360 mm / h, 370 mm / h, 380 mm / h, 390 mm / h, 400 mm / h, etc., not specifically limited herein).

[0040] Optionally, the step of placing the lid includes: a first sub-step and a second sub-step, wherein the pulling speed of the first sub-step is greater than the pulling speed of the second sub-step. In this way, a lid with an upturned edge can be reliably prepared, so that the dopant can be reliably added to the lid.

[0041] Optionally, the pulling speed of the first sub-step is 90-180mm / h (for example: 90mm / h, 100mm / h, 110mm / h, 120mm / h, 130mm / h, 140mm / h, 150mm / h, 160mm / h, 170mm / h, 180mm / h, etc., not specifically limited herein), and when the diameter of the cover reaches 80-120mm (for example: 80mm, 90mm, 100mm, 110mm, 120mm, etc., not specifically limited herein), the second sub-step is performed, and the pulling speed of the second sub-step is 50-60mm / h (50mm / h, 52mm / h, 55mm / h, 57mm / h, 60mm / h, etc., not specifically limited herein).

[0042] Furthermore, the pulling speed in the first sub-step may be variable, that is, as the diameter of the lid gradually increases, the pulling speed may gradually increase, and in the entire first sub-step, the pulling speed always satisfies 90-180 mm / h. For example, the pulling speed is 90 mm / h when the lid is first placed, and in the process of the lid diameter gradually increasing to 80-120 mm, the pulling speed gradually increases to 180 mm / h. For another example, the pulling speed is 100 mm / h when the lid is first placed, and in the process of the lid diameter gradually increasing to 80-120 mm, the pulling speed gradually increases to 160 mm / h, etc., which is not specifically limited here.

[0043] Optionally, the time of the second sub-step can be controlled within 1-3 minutes, for example: 1 minute, 2 minutes, 3 minutes, etc., which is not specifically limited here.

[0044] It should be noted that after the supplementary doping is completed, other processes such as raising the pot position, adjusting the temperature, seeding, releasing the shoulder, rotating the shoulder, equalizing the diameter, and finishing can be carried out according to the crystal pulling process.

[0045] The present invention is further described in detail below in conjunction with embodiments.

[0046] Example 1

[0047] After the second section of the equal-diameter head is broken, the detected resistance is 1.5Ω, and the target resistance is 1.25Ω. The actual resistance detected exceeds the target resistance and does not meet the difference with the target resistance. Supplementary doping is required. The supplementary doping steps are as follows:

[0048] After taking out the broken wire lifting head, purify the auxiliary chamber (fill with argon), and at the same time control the heater power to 90kw to increase the temperature. After the auxiliary chamber is purified, open the rotary valve to lower the seed crystal for welding. The liquid surface temperature in the crucible reaches 1457℃ and the welding is completed. Reduce the power of the heater to 10kw lower than the seeding power to stabilize the temperature. After 25 minutes, 4 full light spots appear for the seeding process. Put the lid on 25 minutes after seeding. The pulling speed when putting the lid is 90mm / h. As the diameter of the lid increases, the pulling speed gradually increases. When the lid grows to a diameter of 100mm, reduce the pulling speed from 180mm / h to 50mm / h and maintain it for 1min. After the lid is placed, the crucible position is lowered by 30mm, the power of the heater is controlled to 90kw, and the crystal lifting speed is controlled to 270mm / h. Lift for 5 minutes, then control the crystal lifting speed to 360mm / h, lift the lid to 100mm from the uppermost end of the rotary valve, fill with normal pressure, open the slag removal door cover of the auxiliary chamber, use a tungsten gold spoon to put the dopant on the lid, and then close the slag removal door cover to purify the auxiliary chamber. After the purification is completed, open the rotary valve to lower the lid, lower the lid to above the lower edge of the water-cooled screen, and keep it 20mm away from the lower edge of the water-cooled screen, stay for 1 minute, and then continue to lower it to 30mm away from the liquid surface in the crucible and stay for 2 minutes. Finally, after it is lowered to the liquid surface, it slowly immerses the shoulder cover (the descending speed is 80mm / h) to complete the doping. After the lid is completely melted, the crucible is raised to the temperature adjustment, crystal seeding, shoulder placement, shoulder rotation, equal diameter, and finishing processes. After the second crystal rod is produced, the measured resistance value is 1.26Ω, which meets the difference with the target resistance and meets the standard.

[0049] Example 2

[0050] When the third section starts to weld, the resistance of the first rod is measured to be 1.45Ω, and the target resistance is 1.25Ω. The actual resistance detected exceeds the target resistance and does not meet the difference with the target resistance. Supplementary doping is required. The supplementary doping steps are as follows (only the differences from Example 1 are recorded):

[0051] The liquid surface temperature in the crucible reaches 1457℃ and the welding is completed. The power of the heater is reduced to 15kw lower than the seeding power to stabilize the temperature. After 15 minutes, 4 full light spots appear and the seeding process is carried out. The lid is placed 15 minutes after seeding. The pulling speed when placing the lid is 100mm / h. As the diameter of the lid increases, the pulling speed gradually increases. When the lid grows to a diameter of 80mm, the pulling speed is reduced from 180mm / h to 60mm / h and maintained for 2min. After the lid is placed, the crucible position is lowered by 15mm, the power of the heater is controlled to 80kw, and the crystal lifting speed is controlled to 240mm / h for 5 minutes, and then the crystal lifting speed is controlled to 400mm / h to lift the lid. To 50mm from the top of the rotary valve, fill with normal pressure, open the slag removal door cover of the auxiliary chamber, use a tungsten gold spoon to put the dopant on the cover, and then close the slag removal door cover to purify the auxiliary chamber. After the purification is completed, open the rotary valve to lower the cover, and lower the cover to the top of the lower edge of the water-cooled screen and 10mm away from the lower edge of the water-cooled screen, stay for 2min, and then continue to lower it to 40mm away from the liquid surface and stay for 1min. Finally, after it is lowered to the liquid surface, slowly immerse the shoulder cover (the descending speed is 120mm / h) to complete the doping. After the cover is completely melted, the crucible is raised to the position for temperature adjustment, crystal induction, shoulder placement, shoulder rotation, equal diameter, and finishing. After the second crystal rod is produced, the measured resistance value is 1.255Ω, which meets the difference with the target resistance and meets the standard.

[0052] Example 3

[0053] The difference between Example 3 and Example 1 is that:

[0054] During the process of placing the lid, when the diameter of the lid reaches 120mm, the pulling speed is reduced from 180mm / h to 50mm / h and maintained for 3min; after the lid is placed, the crucible position is lowered by 25mm, the power of the heater is controlled to 85kw, and the crystal lifting speed is controlled to 255mm / h at the same time, and it is lifted for 6min, and then the crystal lifting speed is controlled to 380mm / h, so that the lid is lifted to 80mm from the uppermost end of the rotary valve and filled with normal pressure.

[0055] The lowering process of adding the dopant to the lid is as follows: lower the lid to above the lower edge of the water-cooling screen and 15 mm away from the lower edge of the water-cooling screen, stay for 1.5 minutes, then continue to lower it to 35 mm away from the liquid surface in the crucible and stay for 1.5 minutes, and finally lower it to the liquid surface and slowly immerse the shoulder cover (the descending speed is 100 mm / h).

[0056] Comparative Example 1

[0057] The difference between Comparative Example 1 and Example 1 is that (the unrecorded process refers to Example 1): after the dopant is placed in the lid and the sub-chamber is purified, the lid is directly immersed in the liquid surface at a descending speed of 80 mm / h. Some dopants have a volatilization effect, and the resistance value of the second crystal rod obtained after production is measured to be 1.38Ω, which is significantly different from the target resistance.

[0058] Comparative Example 2

[0059] The difference between Comparative Example 2 and Example 1 is that (the unrecorded process refers to Example 1): when the lid is lifted, the lid is removed from the sub-chamber and then the dopant is added; when the lid is immersed in the liquid surface, the lid explodes, and the resistance value of the second crystal rod produced after production is measured to be 1.60Ω, which is significantly different from the target resistance.

[0060] Comparative Example 3

[0061] The difference between Comparative Example 3 and Example 1 is that (the unrecorded process refers to Example 1): when placing the lid, when the lid diameter reaches 100 mm, the pulling speed is not reduced, but maintained at 180 mm / h, and when adding the dopant, part of the dopant falls directly into the melt in the crucible, and the measured resistance value of the second crystal rod obtained after production is 1.45Ω, which is significantly different from the target resistance.

[0062] Comparative Example 4

[0063] The difference between Comparative Example 4 and Example 1 is that (the unrecorded process refers to Example 1): when lifting the lid, it is lifted to 100 mm from the uppermost end of the rotary valve at a crystal lifting speed of 300 mm / h; when the lid is immersed in the liquid surface, the lid cracks, and the resistance value of the second crystal rod obtained after production is measured to be 1.37Ω, which is significantly different from the target resistance.

[0064] In summary, the method of supplementary doping by placing a lid in the present invention can be applied to the preparation of single crystal silicon, and the method can effectively improve the problem of the lid and the supplementary doping agent in the lid being blown away together.

[0065] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for adding a lid, characterized in that: include: After welding, controlling the crucible heater power to be less than the heater power during seeding; After the first set time of seeding, the lid is placed and then lifted. In the step of lifting the lid, the lid is lifted from the rotary valve of the single crystal furnace and the lid is left in the auxiliary chamber of the single crystal furnace. Add dopants to the lid through the slag removal port of the auxiliary chamber, then lower the lid to a position a first set distance from the lower edge of the water-cooled screen of the single crystal furnace and stay there for a second set time, then continue to lower the lid to a position a second set distance from the liquid level of the crucible and stay there for a third set time, then lower the lid and make the liquid level submerge the shoulder cover.

2. The method for adding additional doping by placing a lid according to claim 1, characterized in that: The first setting distance is 10-20 mm; the second setting time is 1-2 min.

3. The method for adding additional doping by placing a lid according to claim 1, characterized in that: The second setting distance is 30-40 mm, and the third setting time is 1-2 min.

4. The method for adding additional doping by placing a lid according to claim 1, characterized in that: In the step of lowering the cover and making the liquid surface submerge the shoulder cover, the speed at which the cover is lowered is 80-120 mm / h.

5. The method for adding additional doping by placing a lid according to claim 1, characterized in that: In the step of lifting the lid, the crucible is lowered by a third set distance, and the heater is controlled to increase the temperature of the crucible.

6. The method for adding additional doping by placing a lid according to claim 5, characterized in that: The third set distance is 15-30 mm, and the power of the heater is 80-90 kw.

7. The method for adding additional doping to a lid according to claim 1, characterized in that: The step of lifting the lid includes a first lifting and a second lifting, wherein the speed of the first lifting is lower than the speed of the second lifting; and / or, The step of placing the lid includes: a first sub-step and a second sub-step, wherein the pulling speed of the first sub-step is greater than the pulling speed of the second sub-step.

8. The method for adding additional doping by placing a lid according to claim 7, characterized in that: In the first lifting step, the crystal lifting speed is 240-270 mm / h, and the crystal lifting time is 4-6 min; in the second lifting step, the crystal lifting speed is 360-400 mm / h.

9. The method for adding additional doping to a lid according to claim 7, characterized in that: The pulling speed of the first sub-step is controlled to increase gradually and meet 90-180 mm / h. When the diameter of the cover reaches 80-120 mm, the second sub-step is executed, and the pulling speed of the second sub-step is 50-60 mm / h.

10. A method for preparing single crystal silicon, characterized in that: The invention comprises the method for adding a cap by placing the cap as described in any one of claims 1 to 9.