A method for single crystal silicon crystal pulling process

Abstract

The present application provides a single crystal silicon crystal pulling process method doped with a volatile dopant. The crystal pulling process method includes maintaining a low furnace pressure of no more than 18 Torr in the single crystal furnace during the isodiameter stage of crystal growth, and keeping the argon gas flow rate introduced into the single crystal furnace within a constant range. The present application realizes isodiameter crystal pulling at a lower furnace pressure. Through the process method of the present application, the axial resistivity attenuation slope of a single crystal doped with a volatile dopant, especially gallium, can be reduced, and its resistivity effective length can be increased.

Description

[0001] This application is a divisional application of a Chinese patent application with the application number 202110984273.4, the publication number CN113652737A, the application date of August 25, 2021, and the invention title of "A Method for Growing Single Crystal Silicon". Technical Field

[0002] This application belongs to the technical field of single crystal silicon growth, and particularly relates to a CZ pulling process method for pulling single crystal silicon doped with dopants (including volatile dopants) with a given target resistivity, and particularly relates to a gallium-doped single crystal silicon pulling process method. In the crystal growth process, the resistivity accuracy of the head of the crystal rod is controlled to improve production efficiency and product yield. Background Art

[0003] With the environmental crisis brought about by global climate change and the energy crisis caused by over-exploitation of fossil energy, people are paying more and more attention to the development of clean energy. As the most representative clean energy, photovoltaic power generation has been increasingly valued globally and has been vigorously developed.

[0004] Currently, the main basic material for photovoltaic power generation is gallium-doped P-type single crystal. Compared with traditional boron-doped single crystal, since it avoids the generation of BO complexes, it effectively reduces the initial light-induced degradation (LID), ensuring that P-type photovoltaic modules can maintain long-term efficient, stable and reliable operation.

[0005] However, the segregation coefficient of gallium is very low, only 0.008. The resistivity of the head and tail of gallium-doped single crystal is generally set to 1.0 and 0.4 respectively. According to the segregation principle, during the growth process of the crystal rod, the resistivity of the crystal rod will gradually decrease as its length increases, limiting the length of the crystal rod within the effective resistivity range. At the same time, the oxygen content increases and the minority carrier lifetime of the crystal rod becomes lower. Summary of the Invention

[0006] This solution aims to solve the problems that the axial resistivity of single crystal doped with dopants (especially volatile dopants such as gallium) decays rapidly, the effective resistivity length range is limited in principle, the oxygen content increases, and the minority carrier lifetime becomes lower.

[0007] The specific technical solution of the present invention is as follows:

[0008] 1. A method for growing single crystal silicon, the crystal growth method includes that the furnace pressure of the single crystal furnace does not exceed 18 Torr during the isodiametric stage of crystal growth, and the argon gas flow rate introduced into the single crystal furnace is maintained within a constant range, and the single crystal silicon is doped with dopants.

[0009] 2. According to the method for growing single crystal silicon described in item 1, during the isodiametric stage of crystal growth, the furnace pressure of the single crystal furnace is gradually reduced as the length of the crystal rod increases.

[0010] 3. The single-crystal silicon crystal pulling process method according to item 2, wherein the furnace pressure of the single-crystal furnace does not exceed 15 Torr during the isodiameter stage of crystal growth; preferably, the furnace pressure of the single-crystal furnace does not exceed 10 Torr.

[0011] 4. The single-crystal silicon crystal pulling process method according to item 2, when the isodiameter length of the single-crystal silicon is any length within the range greater than 0 mm and less than 250 mm, control the furnace pressure of the single-crystal furnace to be U 5a , U 5a takes values within the range of 8 - 15 Torr; when the isodiameter length of the single-crystal silicon is within the range greater than or equal to 250 mm and less than 600 mm, control the furnace pressure of the single-crystal furnace to be U 5b , U 5b takes values within the range of 4 - 12 Torr; when the isodiameter length of the single-crystal silicon is 600 mm or more, control the furnace pressure of the single-crystal furnace to be U 5c , U 5c takes values within the range of 2 - 8 Torr; where U 5c <U 5b <U 5a .

[0012] 5. The single-crystal silicon crystal pulling process method according to item 5, the process of gradually reducing the furnace pressure of the single-crystal furnace includes:

[0013] When the crystal grows to a preset length, obtain the furnace pressure value U of the single-crystal furnace;

[0014] Compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U5, when U > U5, reduce the furnace pressure until U ≤ U5.

[0015] 6. The single-crystal silicon crystal pulling process method according to item 5, the process of gradually reducing the furnace pressure of the single-crystal furnace includes:

[0016] When the crystal grows to a preset length, obtain the furnace pressure value U of the single-crystal furnace;

[0017] Compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U5,

[0018] When U ≤ U5, keep the frequency of the vacuum pump unchanged;

[0019] When U > U5, increase the frequency of the vacuum pump, then detect the furnace pressure U of the single-crystal furnace, and compare the magnitudes of U and U5, when U ≤ U5, keep the frequency of the vacuum pump unchanged.

[0020] 7. The single-crystal silicon crystal pulling process method according to item 5, the process of gradually reducing the furnace pressure of the single-crystal furnace includes:

[0021] When the isodiameter length of the single-crystal silicon grows to any length within the range greater than or equal to 100 mm and less than 350 mm, obtain the furnace pressure value U of the single-crystal furnace; compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U51 When U > U 51 , reduce the furnace pressure until U ≤ U 51 , where U 51 ranges from 6 to 14 Torr, preferably U 51 ranges from 8 to 12 Torr;

[0022] When the isodiametric length of the single crystal silicon grows to any length within the range greater than or equal to 350 mm and less than 600 mm, obtain the furnace pressure value U of the single crystal furnace; compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U 52 When U > U 52 , reduce the furnace pressure until U ≤ U 52 , where U 52 ranges from 4 to 10 Torr, preferably U 52 ranges from 5 to 8 Torr;

[0023] When the isodiametric length of the single crystal silicon grows to any length within the range greater than or equal to 600 mm, obtain the furnace pressure value U of the single crystal furnace; compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U 53 When U > U 53 , reduce the furnace pressure until U ≤ U 53 , where U 53 ranges from 2 to 8 Torr, preferably U 53 ranges from 2 to 6 Torr;

[0024] Where U 53 < U 52 < U 51 .

[0025] 8. According to the single crystal silicon crystal pulling process method described in item 5, the process of gradually reducing the furnace pressure of the single crystal furnace includes:

[0026] When the isodiametric length of the single crystal silicon is any length within the range less than 10% of the total crystal bar length, obtain the furnace pressure value U of the single crystal furnace; compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U 51 When U > U 51 , reduce the furnace pressure until U ≤ U 51 , where U 51 ranges from 4 to 10 Torr;

[0027] When the isodiametric length of the single crystal silicon is any length within the range greater than or equal to 10% of the total crystal bar length and less than 45% of the total crystal bar length, obtain the furnace pressure value U of the single crystal furnace; compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U 52 When U > U 52 , reduce the furnace pressure until U ≤ U 52 , where U 52The value ranges from 2 to 4 Torr;

[0028] When the isodiameter length of single-crystal silicon is any length within the range of being greater than or equal to 45% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace; compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U 53 When U > U 53 Reduce the furnace pressure until U ≤ U 53 where U 53 The value ranges from 0 to 2 Torr;

[0029] where U 53 < U 52 < U 51 .

[0030] 9. The single-crystal silicon crystal pulling process method according to item 5

[0031] When the isodiameter length of single-crystal silicon is any length within the range of being less than 10% of the total crystal bar length, control the furnace pressure of the single-crystal furnace to be U S501 U S501 The value ranges from 1 to 3 Torr;

[0032] When the isodiameter length of single-crystal silicon is any length within the range of being greater than or equal to 10% and less than 45% of the total crystal bar length, control the furnace pressure of the single-crystal furnace to be U S502 U S502 The value ranges from 0.3 to 2 Torr;

[0033] When the isodiameter length of single-crystal silicon is any length within the range of being greater than or equal to 45% of the total crystal bar length, control the furnace pressure of the single-crystal furnace to be U S503 U S503 The value ranges from 0.01 to 0.3 Torr;

[0034] where U S503 < U S502 < U S501 .

[0035] 10. The single-crystal silicon crystal pulling process method according to item 9

[0036] When the isodiameter length of single-crystal silicon is any length within the range of being less than 10% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace, compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U S51 When U > U S51 Reduce the furnace pressure until U ≤ U S51 U S51 The value ranges from 1 to 3 Torr;

[0037] When the isodiametric length of single-crystal silicon is greater than or equal to 10% of the total crystal bar length and less than any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace, and compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U S52 , when U > U S52 , reduce the furnace pressure until U ≤ U S52 , U S52 ranges from 0.3 to 2 Torr;

[0038] When the isodiametric length of single-crystal silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace, and compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U S53 , when U > U S53 , reduce the furnace pressure until U ≤ U S53 , U S53 ranges from 0.01 to 0.3 Torr;

[0039] Where U S53 < U S52 < U S51 .

[0040] 11. According to the single-crystal silicon crystal pulling process method described in item 5,

[0041] When the isodiametric length of single-crystal silicon is less than any length within the range of 10% of the total crystal bar length, control the furnace pressure of the single-crystal furnace to be U S501 , U S501 does not exceed 500 mTorr;

[0042] When the isodiametric length of single-crystal silicon is greater than or equal to 10% of the total crystal bar length and less than any length within the range of 45% of the total crystal bar length, control the furnace pressure of the single-crystal furnace to be U S502 , U S502 does not exceed 300 mTorr;

[0043] When the isodiametric length of single-crystal silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, control the furnace pressure of the single-crystal furnace to be U S503 , U S503 does not exceed 100 mTorr;

[0044] Where U S503 < U S502 < U S501 .

[0045] 12. According to the single-crystal silicon crystal pulling process method described in item 11,

[0046] When the isodiametric length of single-crystal silicon is less than any length within the range of 10% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace, and compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U S51 , when U > US51 When the time comes, reduce the furnace pressure until U ≤ U S51 , U S51 shall not exceed 500 mTorr;

[0047] When the isodiameter length of the single crystal silicon is greater than or equal to 10% of the total crystal bar length and less than any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single crystal furnace, and compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U S52 , when U > U S52 When the time comes, reduce the furnace pressure until U ≤ U S52 , U S52 shall not exceed 300 mTorr;

[0048] When the isodiameter length of the single crystal silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single crystal furnace, and compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U S53 , when U > U S53 When the time comes, reduce the furnace pressure until U ≤ U S53 , U S53 shall not exceed 100 mTorr;

[0049] where U S53 < U S52 < U S51 .

[0050] 13. The single crystal silicon crystal pulling process method according to any one of items 1 - 3, the method further includes controlling the furnace pressure during the melting / feeding stage, seeding stage, shoulder releasing stage, and shoulder turning stage before the isodiameter stage;

[0051] Preferably, during the melting / feeding, seeding, shoulder releasing, and shoulder turning stages, the furnace pressure does not exceed 18 Torr, and more preferably, the furnace pressure does not exceed 2 Torr.

[0052] 14. According to the single crystal silicon crystal pulling process method described in item 1, at least one moment during the isodiameter stage of crystal growth, the following relationship is satisfied among the furnace pressure U of the single crystal furnace, the percentage L of the isodiameter length of the crystal bar, the argon gas flow rate P, and the vacuum pump frequency F:

[0053] U = A * L + B * P + D * F + C,

[0054] where,

[0055] 1 ≤ A ≤ 10, 0.01 ≤ B ≤ 0.02, -0.6 ≤ D ≤ -0.2, 10 ≤ C ≤ 25;

[0056] The unit of the furnace pressure U of the single crystal furnace is Torr, the percentage L of the isodiameter length of the crystal bar is the percentage of the drawn length to the total crystal bar length, the unit of the argon gas flow rate P is slpm, and the unit of the vacuum pump frequency F is HZ.

[0057] 15. The single-crystal silicon crystal pulling process method according to item 14, where the furnace pressure is 0.001 Torr ≤ U ≤ 15 Torr, the argon gas flow rate is 0 slpm < P ≤ 70 slpm; the vacuum pump frequency is 20 HZ ≤ F ≤ 60 HZ.

[0058] 16. The single-crystal silicon crystal pulling process method according to any one of items 1-15, where the dopant is gallium, and the mass percentage content of gallium is preferably 0.01% - 0.03%.

[0059] According to an embodiment of the present invention, in the crystal pulling process method, the vacuum pump is preferably a dry pump.

[0060] In the present invention, Torr is a unit of pressure, 1 Torr is 1 mmHg, and 1 Torr = 1000 mtorr; slpm is the abbreviation of stard liter per minute, that is, the standard liter per minute flow value.

[0061] The technical solution of the present invention has the following technical effects:

[0062] (1) The present invention adopts a low furnace pressure crystal pulling process, which accelerates the volatilization rate of impurity elements including gallium, reduces the impurity elements in the solution, thereby inhibiting the attenuation rate of the resistivity of the crystal bar, increasing the length of the crystal bar within the effective range of resistivity. When the tail resistivity is 0.45, the length of the crystal bar increases significantly, the draw ratio increases, and the minority carrier lifetime is greatly improved, reaching more than 10%, and the improvement effect is obvious.

[0063] (2) Under the low furnace pressure of the present invention, the melting point of silicon decreases, the ambient temperature will drop to a certain extent, the temperature of the crucible wall decreases accordingly, and the dissolution rate of the crucible also decreases, resulting in a decrease in oxygen content, effectively controlling the oxygen content in the crystal, and the oxygen content at the head of the crystal bar decreases significantly, and the oxygen reduction effect is obvious. Description of the Drawings

[0064] Figure 1 - Axial resistivity attenuation trend diagram during crystal pulling at different furnace pressures simulated by the theoretical model in the specific embodiment part of the present invention.

[0065] Figure 2 - Figure 1 Partial enlarged view of the boxed part. Specific Embodiments

[0066] The following description in the specification is a preferred embodiment for implementing the present invention. The description is for the purpose of the general principles of the specification and is not intended to limit the scope of the present invention. The protection scope of the present invention shall be subject to the scope defined by the claims. The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although specific embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein.

[0067] The present invention provides a low furnace pressure single crystal pulling process method.

[0068] The present invention uses the Czochralski method (abbreviated as CZ method) to produce single crystal silicon. In this method, polycrystalline silicon material is placed in a quartz crucible and melted. During the process of directly pulling a single crystal, first, the seed crystal is brought into contact with the melt, and the molten silicon at the solid-liquid interface crystallizes along the seed crystal by cooling, and grows by slowly pulling out the seed crystal. After the seeding is completed, the crystal growth diameter is enlarged until the target diameter is reached by reducing the pulling speed and / or the melt temperature; after the shoulder turning, the crystal growth enters the "constant diameter growth" stage by controlling the pulling speed and the melt temperature; finally, the diameter of the crystal growth surface is gradually reduced to form a tail cone by increasing the pulling speed and raising the melt temperature until the crystal finally leaves the melt surface, that is, the growth of the single crystal rod is completed.

[0069] Specifically, taking the growth of a silicon rod as an example, the crucible is charged with materials, and the silicon material is completely melted to obtain a melt. After the melt is stabilized, it enters the above-mentioned temperature adjustment operation stage. Then, the seed crystal is lowered to a certain distance from the melt surface, and the seed crystal is preheated to reduce the temperature difference between the seed crystal and the melt and inhibit the generation of thermal stress inside the seed crystal when the seed crystal contacts the melt. After the temperature difference between the seed crystal and the melt meets the required temperature range, it enters the seeding stage. In the seeding stage, the seed crystal is inserted into the melt to weld the seed crystal and the melt. After that, usually, the crystal diameter is reduced to the required length range at a high pulling speed to prevent dislocations from occurring in the grown crystal rod. After the seeding stage is completed, the crystal diameter needs to be enlarged to the target diameter. Specifically, when the thin neck grows to a sufficient length and reaches a certain pulling rate, the pulling rate can be appropriately reduced to enter the shoulder broadening stage. When the crystal diameter in the shoulder broadening stage is close to the preset target diameter, in order to make the crystal grown in the shoulder broadening stage smooth and the diameter uniformly transition to the constant diameter stage, a shoulder turning stage is required. After the crystal diameter grows to the preset target diameter, it enters the constant diameter stage. In the constant diameter stage, in order to keep the isothermal surface of the crystal flat, the height of the crucible will change as the crystal rises. After the constant diameter length of the crystal meets the preset target constant diameter length, the finishing stage is carried out. The function of the finishing stage is to prevent the occurrence of dislocation back-extension when the crystal suddenly detaches from the melt surface and ensure that the crystal rod grown in the constant diameter operation stage has good quality. After the finishing stage is completed, according to the actual growth situation, continue to add materials for continuous crystal pulling or enter the furnace shutdown stage to complete the crystal pulling work.

[0070] The present invention provides a method for pulling single crystal silicon. It is characterized in that, in the isodiameter stage of crystal growth, the furnace pressure of the single crystal furnace does not exceed 18 Torr, the flow rate of argon gas introduced into the single crystal furnace is maintained within a constant range, and the single crystal silicon is doped with a dopant.

[0071] In an embodiment of the present invention, the process method may optionally include: a melting / feeding stage, a seed crystal introducing stage, a shoulder releasing stage, a shoulder turning stage, and an isodiameter stage, which are specifically as follows:

[0072] Melting / feeding stage S100: Place silicon blocks into a quartz crucible, introduce argon gas, control the furnace pressure at 0.5 - 15 Torr, the melting power at 60 - 110 Kw, heat and melt the silicon material to form a uniform silicon melt. At the initial stage of melting, control the argon gas flow rate at 10 - 100 SLPM. After the material blocks in the crucible are completely melted into a liquid, the melting stage ends, and then enter the temperature stabilization stage. The thermal field is stabilized to a suitable temperature for introducing the seed crystal to prepare for the fusion of the seed crystal and the silicon melt. In the temperature stabilization stage, control the furnace pressure at 0.5 - 10 Torr and the argon gas flow rate at 10 - 100 SLPM;

[0073] Seed crystal introducing stage S200: The seed crystal is fused with the silicon melt to eliminate dislocations generated during the solid-liquid contact. Control the furnace pressure at 0.5 - 15 Torr, the argon gas flow rate at 10 - 100 SLPM, and the maximum shall not exceed 120 SLPM to provide a stable environment for the fusion process and prevent the seed crystal from shaking during the dissolution process. In order to improve the crystal formation rate, control the upper limit of the fusion diameter at 16.5 mm, the lower limit of the fusion diameter at 13 mm, the minimum diameter value at 10 mm, and adjust the seed crystal introducing gain value to 0.085;

[0074] Shoulder releasing stage S300: Adjust the temperature and pulling speed to enlarge the diameter to the required crystal diameter. The diameter of the single crystal silicon rod is 240 - 310 mm. In the shoulder releasing stage, control the argon gas flow rate at 10 - 100 SLPM and the furnace pressure at 0.5 - 15 Torr;

[0075] Shoulder turning stage S400: After the crystal diameter reaches the specified requirement, adjust the pulling speed and temperature to perform shoulder turning so that the crystal can enter the isodiameter growth stage. In the shoulder turning stage, control the argon gas flow rate at 10 - 100 SLPM and the furnace pressure at 0.5 - 15 Torr;

[0076] Isodiameter stage S500: After the silicon rod reaches the specified diameter, enter the isodiameter stage. Control the single crystal growth process by controlling the pulling speed of the single crystal silicon rod and the temperature of the melt in the furnace. In this stage, the crystal growth tends to be stable. During the process, the furnace pressure is gradually reduced as the length of the crystal rod increases. After 200 mm of isodiameter, keep the furnace pressure not exceeding 2 Torr, and the argon gas flow rate decreases. And synchronously adjust other pulling crystal parameters such as power. The whole isodiameter process is automatically controlled by the system;

[0077] Finishing stage: As the crystal grows, the molten silicon in the crucible continuously decreases. After the remaining material reaches a certain weight, the diameter of the single crystal rod is reduced by changing the pulling speed and temperature, and the dislocation length generated when the crystal detaches from the liquid surface is reduced by reducing the thermal shock. In this stage, the argon gas flow rate can be increased to 40 - 100 SLPM, and the furnace pressure is controlled at 0 - 15 Torr.

[0078] ……

[0079] Repeat the above steps until the furnace is finished.

[0080] In one embodiment of the present invention, the furnace pressure of the single crystal furnace is gradually reduced as the length of the crystal rod increases during the equal - diameter stage of crystal growth.

[0081] In one embodiment of the present invention, the process of gradually reducing the furnace pressure of the single crystal furnace includes:

[0082] When the crystal grows to a preset length, obtain the furnace pressure value U of the single crystal furnace;

[0083] Compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U5. When U > U5, reduce the furnace pressure until U ≤ U5.

[0084] In one embodiment of the present invention, the process of gradually reducing the furnace pressure of the single crystal furnace includes:

[0085] When the crystal grows to a preset length, obtain the furnace pressure value U of the single crystal furnace;

[0086] Compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U5,

[0087] When U ≤ U5, keep the frequency of the vacuum pump unchanged;

[0088] When U > U5, increase the frequency of the vacuum pump, then detect the furnace pressure U of the single crystal furnace, and compare the magnitudes of U and U5. When U ≤ U5, keep the frequency of the vacuum pump unchanged.

[0089] Specifically, when the equal - diameter length of the single crystal is any length within the range less than 10% of the total crystal rod length, obtain the furnace pressure value U of the single crystal furnace, and compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U S51 ,when U > U S51 ,reduce the furnace pressure until U ≤ U S51 ,U S51 takes values within the range of 1 - 3 Torr;

[0090] When the equal - diameter length of the single crystal is greater than or equal to 10% and less than 45% of the total crystal rod length, obtain the furnace pressure value U of the single crystal furnace, and compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U S52 ,when U > US52 When the isodiameter length of the single crystal silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single crystal furnace, and compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U S52 , U S52 takes values within the range of 0.3 - 2 Torr;

[0091] When the isodiameter length of the single crystal silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single crystal furnace, and compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U S53 , when U > U S53 When the isodiameter length of the single crystal silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single crystal furnace, and compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U S53 , U S53 takes values within the range of 0.01 - 0.3 Torr;

[0092] where U S53 < U S52 < U S51 , where, U S51 is less than the preset furnace pressure value at any stage of seeding, shoulder releasing, and shoulder turning.

[0093] In a preferred embodiment of the present invention, when the isodiameter length of the single crystal silicon is less than any length within the range of 10% of the total crystal bar length, control the furnace pressure of the single crystal furnace to be U S501 , U S501 does not exceed 500 mTorr;

[0094] When the isodiameter length of the single crystal silicon is greater than or equal to 10% and less than any length within the range of 45% of the total crystal bar length, control the furnace pressure of the single crystal furnace to be U S502 , U S502 does not exceed 300 mTorr;

[0095] When the isodiameter length of the single crystal silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, control the furnace pressure of the single crystal furnace to be U S503 , U S503 does not exceed 100 mTorr;

[0096] where U S503 < U S502 < U S501 , where U S501 is less than the preset furnace pressure value at any stage of seeding, shoulder releasing, and shoulder turning.

[0097] Specifically, when the isodiameter length of the single crystal silicon is less than any length within the range of 10% of the total crystal bar length, obtain the furnace pressure value U of the single crystal furnace, and compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U S51 , when U > U S51 When the isodiameter length of the single crystal silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single crystal furnace, and compare the obtained furnace pressure value U of the single crystal furnace with the preset furnace pressure value U S51 , U S51 does not exceed 500 mTorr;

[0098] When the equal-diameter length of single-crystalline silicon is greater than or equal to 10% of the total crystal bar length and less than any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace, and compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U S52 , when U > U S52 , reduce the furnace pressure until U ≤ U S52 , U S52 does not exceed 300 mTorr;

[0099] When the equal-diameter length of single-crystalline silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace, and compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U S53 , when U > U S53 , reduce the furnace pressure until U ≤ U S53 , U S53 does not exceed 100 mTorr;

[0100] where U S53 < U S52 < U S51 where U S51 is less than the preset furnace pressure value in any stage of seed crystal drawing, shoulder releasing, and shoulder turning.

[0101] In an embodiment of the present invention, the method further includes controlling the furnace pressure during the melting / feeding stage, seed crystal drawing stage, shoulder releasing stage, and shoulder turning stage before the equal-diameter stage; preferably, during the melting / feeding, seed crystal drawing, shoulder releasing, and shoulder turning stages, the furnace pressure does not exceed 18 Torr, and more preferably, the furnace pressure does not exceed 2 Torr;

[0102] For example, the furnace pressures in the melting / feeding stage, seed crystal drawing stage, shoulder releasing stage, and shoulder turning stage can be 0.001, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18 Torr or any range therebetween.

[0103] In an embodiment of the present invention, at least one moment during the equal-diameter stage of crystal growth satisfies the following among the furnace pressure U of the single-crystal furnace, the percentage L of the equal-diameter length of the crystal bar, the argon gas flow rate P, and the vacuum pump frequency F:

[0104] U = A * L + B * P + D * F + C,

[0105] wherein,

[0106] 1 ≤ A ≤ 10, 0.01 ≤ B ≤ 0.02, -0.6 ≤ D ≤ -0.2, 10 ≤ C ≤ 25;

[0107] The unit of the crystal furnace pressure U of the single crystal furnace is Torr, the percentage L of the equal - diameter length of the crystal bar is the percentage of the drawn length to the total length of the crystal bar, the unit of the argon gas flow rate P is slpm, and the unit of the vacuum pump frequency F is HZ; wherein, 0.001 Torr ≤ U ≤ 15 Torr for the furnace pressure, 0 slpm < P ≤ 70 slpm for the argon gas flow rate; 20 HZ ≤ F ≤ 60 HZ for the vacuum pump frequency.

[0108] In an embodiment of the present invention, the single - crystal silicon is doped with a dopant.

[0109] In a preferred embodiment of the present invention, the dopant is gallium.

[0110] A single - crystal furnace is a device that melts polycrystalline materials such as polysilicon with a graphite heater in an inert gas environment and grows dislocation - free single - crystal silicon by the Czochralski method. During the production of single - crystal silicon using a single - crystal furnace, in order to meet the requirements of cell processing, a dopant is added during the growth of crystalline silicon to meet the requirements of electrical properties. Group - V elements are commonly used as N - type dopants for single - crystal silicon, mainly including phosphorus, arsenic, antimony, etc. Group - III elements are commonly used as P - type dopants for single - crystal silicon, mainly including boron, aluminum, gallium, etc. However, during the actual production of single - crystal silicon using a single - crystal furnace, due to the different diffusion rates of the doping elements of the above - mentioned dopants in the solid - liquid two - phase at the growth interface in the single - crystal silicon, the longitudinal resistivity of the drawn - formed single - crystal silicon crystal is inconsistent, that is, the resistivity of the drawn - formed single - crystal silicon crystal gradually decreases from the head to the tail. Especially for N - type single - crystal silicon, the resistivity difference between the head and the tail of the single - crystal silicon crystal is particularly large. For example, currently, the resistivity of the semiconductor - grade single - crystal silicon produced decays severely from the head to the tail. The resistivity of the head of the semiconductor - grade single - crystal silicon is about 38 Ω·cm, the resistivity of the middle part is about 32 Ω·cm, and the resistivity of the tail is about 20 Ω·cm.

[0111] Among them, because the segregation coefficient of boron in silicon (0.8) is relatively close to 1, the resistivity distribution of the boron - doped silicon crystal prepared is relatively uniform. However, the cell prepared from the boron - doped silicon wafer will show the phenomenon of light - induced degradation after use, reducing the conversion efficiency of the cell. Currently, it is mainly considered to be related to the boron - oxygen complex formed by the doped boron atoms and the oxygen atoms in the crystalline silicon under sunlight irradiation.

[0112] The formation of boron-oxygen complexes can be avoided by doping with gallium, thereby suppressing the phenomenon of light attenuation. However, the segregation coefficient of gallium is small (0.008), resulting in a wide range of resistivity for the obtained crystalline silicon. In particular, the gallium doping concentration in the last-grown part of the crystalline silicon during the crystal growth process (the tail of Czochralski single-crystal silicon, the ingot of directionally solidified polysilicon, or the head of quasi-single-crystalline silicon) is relatively high, and the resistivity is relatively low. The area with resistivity meeting the requirements (1 - 3 Ω·cm) is too small, and the yield of crystalline silicon that can be used to prepare high-efficiency solar cells is only 50% - 60%, which makes the cost of growing crystalline silicon too high.

[0113] In the technical solution of the present invention, a low furnace pressure crystal pulling process is adopted, even reaching the mTorr level. When the furnace pressure approaches the saturated vapor pressure of gallium atoms, 0.01 Torr, the volatilization rate of gallium atoms increases. At this time, the saturated vapor pressures of elements including P, As, Zn, Mg, Ca, Mn, etc. are all > 0.01 Torr, and they will also volatilize rapidly under this condition. Therefore, the impurities in the molten silicon will rapidly decrease under this condition. With the rapid volatilization of gallium atoms, the gallium atoms in the solution rapidly decrease, thereby suppressing the attenuation rate of the resistivity of the crystal rod, increasing the length of the crystal rod within the effective range of resistivity, improving the resistivity uniformity during the crystal pulling process, with the resistivity change range fluctuating slightly, controlled within ±0.1, and the minority carrier lifetime is greatly improved, reaching more than 10%. The resistivity distribution is uniform, achieving good technical effects.

[0114] The term "minority carrier lifetime" refers to the average survival time of non-equilibrium minority carriers, which is called the minority carrier lifetime, abbreviated as minority carrier lifetime. The minority carrier lifetime of a crystalline silicon solar cell is one of the important parameters for evaluating the solar cell, and it has a very close relationship with the integrity of the material and the impurity content. The minority carrier lifetime reflects the recombination rate of photo-generated carriers on the surface and in the substrate of the solar cell, that is, it reflects the utilization degree of photo-generated carriers.

[0115] The "oxygen content" in the term refers to the oxygen concentration in the crystal, which is one of the core parameters of the crystal quality. It mainly comes from the quartz crucible. In the molten state, the molten silicon reacts with the quartz crucible to generate SiO, which melts into the silicon melt. During the crystal pulling process, most of the SiO in the silicon melt volatilizes freely from the melt surface, a part enters the single crystal due to segregation, and a part remains in the silicon melt. Since there is more silicon melt in the crucible at the beginning of the isodiameter process and the contact area with the crucible is the largest, the oxygen content is relatively high at this time. After the oxygen content is higher than a certain level, vacancy oxygen defect rings will be formed, and thermal donors or oxygen precipitates will be formed during the crystal cooling process, ultimately affecting the minority carrier lifetime or resistivity.

[0116] Oxygen content / minority carrier lifetime: A technical parameter characterizing the internal quality of monocrystalline silicon (in the photovoltaic field, generally, the lower the oxygen content, the better, and the higher the minority carrier lifetime, the better).

[0117] Czochralski single crystal silicon: A growth technique for growing single crystal silicon. Different conductivity type single crystal silicon needs to be doped with different elements. For example, doping with boron (B) results in P-type single crystal silicon, and doping with phosphorus (P) results in N-type single crystal silicon.

[0118] The resistivity formula is expressed as ρ = 1 / qpμ (where ρ is the resistivity, q is the unit charge amount, p is the hole concentration in p-type silicon or the electron concentration in n-type silicon, and μ is the majority carrier mobility). In non-compensated silicon, the relationship between μ and p in this formula has been clearly obtained through a large number of previous experiments, and the carrier concentration in the silicon crystal can be directly converted by measuring the resistivity. However, in a silicon crystal with a compensation effect, the total impurity concentration of donors and acceptors and the compensation degree will cause the mobility to deviate from the original μ-p relationship, and this deviation is difficult to measure in advance.

[0119] The term "length of the ingot when the tail resistivity is 0.45" refers to the length of the pulled ingot when the tail resistivity of the ingot is 0.45 Ω·cm.

[0120] The term "pull-out ratio when the tail resistivity is 0.45" refers to the ratio of the weight of the pulled ingot to the initial total charge amount of the crucible when the tail resistivity of the ingot is 0.45 Ω·cm.

[0121] The present invention can be further described in detail through examples. These examples are only used to illustrate the present invention and do not limit the scope of the present invention. The example part of this application consists of "Examples", "Comparative Examples", "Comparison Examples", and "Experimental Examples".

[0122] Specific embodiments of the present invention will be described in detail below. Although specific embodiments of the present invention are shown here, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0123] Example 1

[0124] The growth process of gallium-doped single crystal silicon (CZ method) is as follows:

[0125] During the melt stage, temperature adjustment stage, seeding stage, and shoulder release stage of crystal growth, maintain the furnace pressure of the single crystal furnace at 11 - 15 Torr and the argon gas flow rate at 100 slpm.

[0126] During the constant diameter stage, control the percentage of the constant diameter length of the ingot and the furnace pressure of the single crystal furnace according to Table 1 below, and control the furnace pressure to make them correspond to each other by adjusting the argon gas flow rate and / or the dry pump frequency.

[0127] Table 1

[0128] Equal - diameter length percentage Furnace pressure (Torr) 0％ 10 4％ 7 7％ 5 10％ 4 18％ 3 44％ 2 74％ 2 96％ 2 100％ 2

[0129] Comparative Example 1

[0130] The difference between Comparative Example 1 and Example 1 lies only in the different parameters shown in the following table. The data such as the furnace pressure in Comparative Example 1 are as shown in Comparative Table 1 below:

[0131] Comparative Table 1

[0132]

[0133]

[0134] Example 2

[0135] The growth process (CZ method) of a gallium-doped single-crystalline silicon crystal is as follows:

[0136] During the melt stage, temperature adjustment stage, seeding stage, and shoulder release stage of crystal growth, maintain the furnace pressure of the single-crystal furnace at 11 - 15 Torr and the argon gas flow rate at 100 slpm.

[0137] During the constant-diameter stage, control the percentage of the constant-diameter length of the crystal rod as L, the furnace pressure U of the single-crystal furnace, the argon gas flow rate P, and the dry pump frequency F to correspond to each other as shown in Table 2 below, and always maintain that they satisfy U = A*L + B*P + D*F + C among them,

[0138] where 5 ≤ A ≤ 10, 0.01 ≤ B ≤ 0.02, -0.6 ≤ D ≤ -0.2, 15 ≤ C ≤ 20.

[0139] Among them, the furnace pressure value is in the range of 2 Torr ≤ U ≤ 10 Torr, the argon gas flow rate value is in the range of 50 slpm ≤ P ≤ 70 slpm; the dry pump frequency value is in the range of 20 HZ ≤ F ≤ 60 HZ

[0140] The relevant parameters in this example are as shown in Table 2 below:

[0141] Table 2 Parameters of the constant-diameter stage of crystal growth

[0142]

[0143]

[0144] Comparative Example 1

[0145] The comparison of the resistivity of the head of the 100% single-crystalline silicon crystal rod and the resistivity of the effective tail of the crystal rod obtained in Examples 1 and 2 and Comparative Example 1 is as shown in Comparative Table 1 below:

[0146] Comparative Table 1

[0147] Example 1 Example 2 Comparative Example 1 Resistivity of the head of the ingot 1.01 1.01 1.01 Resistivity of the effective tail of the ingot 0.50 0.49 0.46

[0148] Referring to the above comparison table 1, when the resistivity of the obtained 100% monocrystalline silicon ingot is equal at the head, the resistivity of the effective ingot tail in Example 1 and Example 2 is higher than that in Comparative Example 1.

[0149] Example 3

[0150] The growth process of gallium-doped monocrystalline silicon crystal (CZ method) is as follows:

[0151] During the melt / feed stage, seeding stage, shoulder release stage, and shoulder turning stage of crystal growth, maintain the furnace pressure of the single crystal furnace at 5 - 11 Torr, the argon gas flow rate at 70 slpm, and the dry pump frequency at 20 Hz;

[0152] During the constant diameter stage, control the constant diameter length percentage of the ingot as L, the furnace pressure of the single crystal furnace as U, the argon gas flow rate as P, and the dry pump frequency as F to correspond to each other according to Table 3 below, and always maintain that they satisfy U = A*L + B*P + D*F + C among each other,

[0153] where 1 ≤ A ≤ 10, 0.01 ≤ B ≤ 0.02, -0.6 ≤ D ≤ -0.2, 10 ≤ C ≤ 25.

[0154] Among them, the furnace pressure value ranges from 0.01 Torr ≤ U ≤ 4 Torr, the argon gas flow rate value ranges from 5 slpm ≤ P ≤ 50 slpm; the dry pump frequency value ranges from 20 HZ ≤ F ≤ 60 HZ

[0155] The relevant parameters in this example are shown in Table 3 below:

[0156] Table 3 Parameters of the constant diameter stage of crystal growth

[0157]

[0158]

[0159] Example 4

[0160] The growth process of gallium-doped monocrystalline silicon crystal (CZ method) is as follows:

[0161] During the melt / feed stage, seeding stage, shoulder release stage, and shoulder turning stage of crystal growth, maintain the furnace pressure of the single crystal furnace at 5 - 11 Torr, the argon gas flow rate at 70 slpm, and the dry pump frequency at 20 Hz;

[0162] During the constant diameter stage, control the constant diameter length percentage of the ingot as L, the furnace pressure of the single crystal furnace as U, the argon gas flow rate as P, and the dry pump frequency as F to correspond to each other according to Table 4 below, and always maintain that they satisfy U = A*L + B*P + D*F + C among each other,

[0163] Where 1 ≤ A ≤ 10, 0.01 ≤ B ≤ 0.02, -0.6 ≤ D ≤ -0.2, 10 ≤ C ≤ 25.

[0164] Where the furnace pressure is in the range of 0.01 Torr ≤ U ≤ 1.5 Torr, the argon flow rate is in the range of 5 slpm ≤ P ≤ 35 slpm; the dry pump frequency is in the range of 20 HZ ≤ F ≤ 60 HZ

[0165] The relevant parameters in this embodiment are shown in Table 4 below:

[0166] Table 4 Parameters in the isodiametric stage of crystal growth

[0167]

[0168]

[0169] Example 5

[0170] The growth process of gallium-doped single-crystalline silicon crystals (CZ method) is as follows:

[0171] In the melt / feeding stage, seeding stage, shoulder release stage, and shoulder turning stage of crystal growth, maintain the furnace pressure of the single crystal furnace at 5 - 11 Torr, the argon flow rate at 70 slpm, and the dry pump frequency at 20 Hz;

[0172] In the isodiametric stage, control the isodiametric length percentage of the crystal rod as L, the furnace pressure U of the single crystal furnace, the argon flow rate P, and the dry pump frequency F to correspond to each other as shown in Table 5 below, and always maintain that they satisfy U = A * L + B * P + D * F + C among each other,

[0173] Where 1 ≤ A ≤ 10, 0.01 ≤ B ≤ 0.02, -0.6 ≤ D ≤ -0.2, 10 ≤ C ≤ 25.

[0174] Where the furnace pressure is in the range of 1 mTorr ≤ U ≤ 500 mTorr, the argon flow rate is in the range of 5 slpm ≤ P ≤ 35 slpm; the dry pump frequency is in the range of 20 HZ ≤ F ≤ 60 HZ

[0175] The relevant parameters in this embodiment are shown in Table 5 below:

[0176] Table 5 Parameters in the isodiametric stage of crystal growth

[0177]

[0178] Example 6

[0179] Example 6 is different from Example 4 in that during the melting / feeding stage, seeding stage, shoulder release stage, and shoulder turning stage of crystal growth, the furnace pressure of the single crystal furnace is maintained not to exceed 2 Torr, and the remaining parameters are the same. The parameters in the equal diameter stage are the same as those in Example 4.

[0180] Example 7

[0181] Example 7 is different from Example 5 in that during the melting / feeding stage, seeding stage, shoulder release stage, and shoulder turning stage of crystal growth, the furnace pressure of the single crystal furnace is maintained not to exceed 2 Torr, and the remaining parameters are the same. The parameters in the equal diameter stage are the same as those in Example 5.

[0182] Experimental Example 1

[0183] Comparison conditions: Resistivity requirement: 0.4 - 1.0, thermal field size 26 inches, single furnace charge: 330 kg, furnace pressure 11 Torr, argon flow rate: 80 L / min, round bar size: 228 mm;

[0184] Experimental conditions: Resistivity requirement: 0.4 - 1.0, thermal field size 26 inches, single furnace charge: 330 kg, furnace pressure < 1.5 Torr, argon flow rate: 5 - 70 L / min, round bar size: 228 mm;

[0185] Characterization method: Resistivity: detected by four-probe method; Oxygen content: detected by Fourier transform infrared spectroscopy; Minority carrier lifetime: detected by BCT400 equipment.

[0186] Other experimental conditions are carried out according to the usual experimental conditions in the art

[0187] Comparative Example 3

[0188] The comparison of the resistivity at the head of the 100% single crystal silicon ingot and the resistivity at the effective tail of the ingot obtained in Examples 3 - 7 is as follows in Comparison Table 2:

[0189] Comparison Table 2

[0190]

[0191] It can be seen from Comparison Table 2 that, as can be seen from Examples 3 - 5, during the melting / feeding stage, seeding stage, shoulder release stage, and shoulder turning stage, the furnace pressure of the single crystal furnace is maintained at 5 - 11 Torr. And in the equal diameter stage, the lower the furnace pressure is controlled, the longer the length of the ingot when the tail resistivity is 0.45, and the higher the draw ratio when the tail resistivity is 0.45.

[0192] It can be seen from Example 6 and Example 4, Example 7 and Example 5 that, under the condition of the same furnace pressure in the equal-diameter stage, when the furnace pressure of the single crystal furnace does not exceed 2 Torr during the melting / feeding stage, seeding stage, shoulder release stage, and shoulder turning stage, the longer the length of the crystal bar with a tail resistivity of 0.45, the higher the pulling ratio with a tail resistivity of 0.45, that is, the better the technical effect.

[0193] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A single-crystal silicon crystal pulling process method, characterized in that The crystal pulling process method includes that in the isodiameter stage of crystal growth, the pressure in the single crystal furnace does not exceed 18 Torr, the flow rate of argon gas introduced into the single crystal furnace is maintained within a constant range, and the single crystal silicon is doped with a dopant; In the isodiameter stage of crystal growth, the pressure in the single crystal furnace is gradually reduced as the length of the crystal bar increases; The process of gradually reducing the pressure in the single crystal furnace includes: When the crystal grows to a preset length, obtain the pressure value U of the single crystal furnace; Compare the obtained pressure value U of the single crystal furnace with the preset pressure value U5. When U > U5, reduce the pressure until U ≤ U5; When the isodiametric length of single-crystalline silicon is any length within the range less than 10% of the total crystal bar length, control the furnace pressure of the single-crystal furnace to be U S501 , U S501 shall not exceed 500 mTorr; When the equal-diameter length of single-crystalline silicon is any length within the range greater than or equal to 10% of the total crystal bar length and less than 45% of the total crystal bar length, control the furnace pressure of the single-crystal furnace to be U S502 , U S502 shall not exceed 300 mTorr; When the isodiametric length of single-crystalline silicon is any length within the range where it is greater than or equal to 45% of the total crystal bar length, control the furnace pressure of the single-crystal furnace to be U S503 , U S503 shall not exceed 100 mTorr; Among which U S503 <U S502 <U S501 ; The method further includes controlling the pressure in the furnace during the melting / feeding stage, seeding stage, shoulder releasing stage, and shoulder turning stage before the isodiameter stage; In the melting / feeding, seeding, shoulder releasing, and shoulder turning stages, the furnace pressure does not exceed 2 Torr.

2. The single-crystal silicon crystal pulling process method according to claim 1, wherein The process of gradually reducing the pressure in the single crystal furnace includes: When the crystal grows to a preset length, obtain the pressure value U of the single crystal furnace; Compare the obtained pressure value U of the single crystal furnace with the preset pressure value U5, When U ≤ U5, keep the frequency of the vacuum pump unchanged; When U > U5, increase the frequency of the vacuum pump, then detect the pressure U of the single crystal furnace, and compare the magnitudes of U and U5. When U ≤ U5, keep the frequency of the vacuum pump unchanged.

3. The single crystal silicon crystal pulling process method according to claim 1, wherein When the equal-diameter length of single-crystalline silicon is any length within the range less than 10% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace, and compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U S51 , when U > U S51 , reduce the furnace pressure until U ≤ U S51 , U S51 shall not exceed 500 mTorr; When the equal-diameter length of single-crystalline silicon is greater than or equal to 10% of the total crystal bar length and less than any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace, and compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U S52 , when U > U S52 , reduce the furnace pressure until U ≤ U S52 , U S52 does not exceed 300 mTorr; When the equal-diameter length of single-crystalline silicon is greater than or equal to any length within the range of 45% of the total crystal bar length, obtain the furnace pressure value U of the single-crystal furnace, and compare the obtained furnace pressure value U of the single-crystal furnace with the preset furnace pressure value U S53 , when U > U S53 , reduce the furnace pressure until U ≤ U S53 , U S53 shall not exceed 100 mTorr; Among them, U S53 <U S52 <U S51 。 4. The single-crystal silicon crystal pulling process method according to claim 1, characterized in that The process of gradually reducing the pressure in the single crystal furnace includes: When the isodiameter length of the single crystal silicon is less than or equal to any length within 10% of the total crystal bar length, control the pressure value of the single crystal furnace to be within the range of 0.3 - 0.5 Torr; When the isodiameter length of the single crystal silicon is greater than 10% and less than or equal to any length within 45% of the total crystal bar length, control the pressure value of the single crystal furnace to be within the range of 0.1 - 0.3 Torr; When the isodiameter length of the single crystal silicon is greater than 45% and less than or equal to any length within 85% of the total crystal bar length, control the pressure value of the single crystal furnace to be within the range of 0.01 - 0.1 Torr; When the isodiameter length of the single crystal silicon is greater than 85% of the total crystal bar length, control the pressure value of the single crystal furnace to be within the range of 0.001 - 0.01 Torr.

5. The single-crystal silicon crystal pulling process method according to claim 1, wherein At least at one moment in the isodiameter stage of crystal growth, the following relationship is satisfied among the pressure U of the single crystal furnace, the percentage L of the isodiameter length of the crystal bar, the argon gas flow rate P, and the frequency F of the vacuum pump: U = A * L + B * P + D * F + C, wherein, 1 ≤ A ≤ 10, 0.01 ≤ B ≤ 0.02, -0.6 ≤ D ≤ -0.2, 10 ≤ C ≤ 25; The unit of the pressure U of the single crystal furnace is Torr, the percentage L of the isodiameter length of the crystal bar is the percentage of the drawn length to the total crystal bar length, the unit of the argon gas flow rate P is slpm, and the unit of the frequency F of the vacuum pump is HZ.

6. The single-crystal silicon crystal pulling process method according to claim 5, characterized in that, The furnace pressure is 0.001 Torr ≤ U ≤ 15 Torr, and the argon gas flow rate is 0 slpm < P ≤ 70 slpm; the frequency of the vacuum pump is 20 HZ ≤ F ≤ 60 HZ.

7. The single-crystal silicon crystal pulling process method according to any one of claims 1-6, characterized in that, The dopant is gallium.

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