A method of crystal growth and crystalline silicon

Abstract

The application provides a crystal growth method and a crystal silicon, and relates to the technical field of solar photovoltaics, wherein the method comprises the following steps: after the completion of a melt, temperature adjustment is performed under a first furnace pressure; the first furnace pressure is less than or equal to 3 Torr; after the completion of the temperature adjustment, crystal pulling, shoulder separation and shoulder rotation operations are performed under a second furnace pressure; the second furnace pressure is less than or equal to the first furnace pressure; after the completion of the shoulder rotation, equal-diameter growth is performed, and during the equal-diameter growth stage, the crystal is directly grown by reducing the pulling furnace pressure starting from the second furnace pressure according to the actual equal-diameter growth length of the doped single crystal silicon. The application can reduce the axial concentration distribution difference of the doping elements in the doped single crystal silicon, improve the axial resistivity uniformity of the single crystal silicon, and simultaneously improve the production efficiency.

Description

Technical Field

[0001] This application relates to the field of solar photovoltaic technology, and in particular to a crystal growth method and crystalline silicon. Background Technology

[0002] At present, monocrystalline silicon is widely used in the solar photovoltaic industry.

[0003] In the solar photovoltaic industry, monocrystalline silicon is generally produced using the Czochralski method. The Czochralski method requires a series of processes in a single-crystal furnace, including silicon melting, crystal pulling, shoulder formation, shoulder rotation, constant-diameter growth, and finishing. To alter the energy level structure of silicon and improve its semiconductor performance, doping elements are typically added during the silicon melting process to dope the monocrystalline silicon.

[0004] However, doped single-crystal silicon prepared by the existing Czochralski method is prone to uneven distribution of doping elements during the growth process, resulting in large differences in axial resistivity. As a result, the resistivity of the doped single-crystal silicon obtained in the end cannot meet the requirements of actual photovoltaic products such as solar cells. Summary of the Invention

[0005] This application provides a crystal growth method aimed at improving the uniformity of dopant element distribution in doped single-crystal silicon prepared by the Czochralski method and reducing the difference in axial resistivity.

[0006] In a first aspect, embodiments of this application provide a crystal growth method, wherein the method includes:

[0007] After the material is melted, the temperature is adjusted under the first furnace pressure; the first furnace pressure is less than or equal to 3 Torr.

[0008] After temperature adjustment, crystal pulling, shoulder formation, and shoulder rotation are performed under the second furnace pressure; the second furnace pressure is less than or equal to the first furnace pressure.

[0009] After the shoulder is completed, constant diameter growth is carried out. During the constant diameter growth stage, the crystal pulling furnace pressure is reduced from the second furnace pressure to carry out crystal direct pulling growth based on the actual constant diameter growth length.

[0010] Optionally, in the crystal growth method, based on the actual constant diameter growth length of the single-crystal silicon, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform Czochralski growth, including:

[0011] The furnace pressure during the constant diameter growth stage is controlled at 1 mTorr to 3 Torr, the argon flow rate is 50 to 200 L / min, and the dry pump frequency is 30 to 55 Hz.

[0012] Optionally, in the crystal growth method, based on the actual constant diameter growth length of the single-crystal silicon, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform Czochralski growth, including:

[0013] The crystal rotation speed is 5–11 RPM, and the crucible rotation speed is 4–9 RPM.

[0014] Optionally, in the crystal growth method, based on the actual constant diameter growth length, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform Czochralski growth, including:

[0015] When the actual constant-diameter growth length increases from zero to less than or equal to 5% of the total length of the constant-diameter portion, the furnace pressure is controlled at 0.3–3 torr, the argon flow rate at 15 L / min–50 L / min, and the heating power is reduced by 2.5 kW. Optionally, the furnace pressure can be 0.3 torr, 0.5 torr, 1 torr, 2 torr, etc.

[0016] Optionally, in the crystal growth method, the crystal pulling furnace pressure is reduced from the second furnace pressure to carry out direct crystal pulling growth according to the actual constant diameter growth length, including: pulling speed of 75mm / hr to 120mm / hr and crucible rotation of 5RPM to 6RPM.

[0017] Optionally, the crystal growth method further includes, based on the actual constant diameter growth length, reducing the crystal pulling furnace pressure from the second furnace pressure to perform Czochralski growth, and further includes:

[0018] When the actual constant diameter growth length increases from 5% of the total length of the constant diameter portion to less than or equal to 10% of the total length of the constant diameter portion, the furnace pressure is controlled at 5 mtorr to 0.3 torr and the argon flow rate is controlled at 5 L / min to 15 L / min.

[0019] Optionally, in the crystal growth method, based on the actual constant diameter growth length, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform Czochralski growth, including:

[0020] When the actual constant diameter growth length increases from 10% of the total length of the constant diameter portion to less than or equal to 55% of the total length of the constant diameter portion, the furnace pressure is controlled to be no greater than 5 mtorr and the argon flow rate is controlled to be no less than 5 L / min.

[0021] Optionally, in the crystal growth method, based on the actual constant diameter growth length, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform Czochralski growth, including:

[0022] When the actual constant diameter growth length increases from 55% of the total length of the constant diameter portion to less than or equal to 100% of the total length of the constant diameter portion, the furnace pressure is controlled at 1 mtorr to 5 mtorr, the argon flow rate is 5 L / min, and the dry pump frequency is 55 Hz.

[0023] Optionally, in the crystal growth method, during the process of reducing the crystal pulling furnace pressure from the second furnace pressure to carry out crystal Czochralski growth, the pulling speed increment ΔV and the power increment ΔP satisfy ΔV=-K*ΔP, where K is 0.06~0.11.

[0024] Optionally, in the crystal growth method, the furnace pressure P of the single crystal furnace and the number of dry pumps n, the frequency of the dry pumps f, and the argon flow rate Q satisfy the following relationship:

[0025] P = A / (n*f) - B / Q + C;

[0026] Where A is between 1 and 120, B is between 1 and 100, C is between 0 and 0.05, and Q is ≥ 1 L / min.

[0027] Secondly, embodiments of this application provide a doped single-crystal silicon, wherein the silicon is prepared by the crystal growth method described above, and the oxygen content of the crystalline silicon is less than or equal to 11 ppma.

[0028] In this embodiment of the application, after the melting is completed, the temperature is adjusted under the first furnace pressure, which is less than or equal to 3 Torr; after the temperature is adjusted, the crystal pulling furnace pressure is reduced from the second furnace pressure to less than or equal to the first furnace pressure, and the shoulder forming and shoulder turning operations are performed; after the shoulder turning is completed, constant diameter growth is performed, and during the constant diameter growth stage, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform crystal Czochralski growth based on the actual constant diameter growth length of the doped single crystal silicon. Using a low furnace pressure of less than or equal to 3 Torr during temperature control, crystal pulling, shoulder formation, and shoulder turning operations allows for faster achievement of the low furnace pressure state for constant diameter growth while maintaining stable crystal pulling-shoulder formation quality. Simultaneously, by continuously lowering the crystal pulling furnace pressure as the constant diameter growth length increases, dopant volatilization can be prevented in the early stages of constant diameter growth, ensuring the stability of the doping amount within the furnace. This not only improves the uniformity of resistivity and the accuracy of doping at the head but also increases the head pulling speed. Furthermore, using even lower furnace pressure in the later stages of constant diameter growth promotes dopant volatilization within the furnace, increases the tail resistivity, and increases the crystal's constant diameter length. Therefore, the embodiments of this application can reduce the difference in axial concentration distribution of dopants in doped single-crystal silicon, improve the uniformity of axial resistivity of single-crystal silicon, and simultaneously increase production efficiency. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1A flowchart illustrating the steps of a crystal growth method according to Embodiment 1 of this application is shown;

[0031] Figure 2 A flowchart illustrating the steps of a crystal growth method according to Embodiment 2 of this application is shown;

[0032] Figure 3 A schematic diagram showing the length of the doped single-crystal silicon rod grown in Embodiment 1 of this application and the single-crystal silicon rod prepared by the existing Czochralski method is shown.

[0033] Figure 4 The diagram shows the resistance distribution of the doped single-crystal silicon rod grown in Embodiment 1 of this application and the single-crystal silicon rod prepared by the existing Czochralski method. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] Before providing a detailed description of the embodiments of this application, let's first introduce the application scenarios of these embodiments.

[0036] With the development of new high-efficiency solar cell structures such as PERC, the demand for P-type high-efficiency Czochralski monocrystalline silicon wafers in the crystalline silicon photovoltaic market has increased dramatically.

[0037] Existing Czochralski single crystal manufacturing methods generally employ argon atmosphere depressurization crystal pulling. Argon gas is introduced in combination with the suction force of a vacuum pump to form an argon gas flow depressurization atmosphere of about 10 to 20 Torr, which remains constant throughout the crystal pulling process.

[0038] Under these high fixed furnace pressure conditions, based on the principles of vacuum evaporation purification and fractional condensation, most of the dopants and impurities in the silicon material cannot volatilize. This causes the resistivity at the tail of the crystal rod to decrease with increasing length during crystal pulling, resulting in a significant difference in the axial resistivity of the grown crystal rods and limiting the rod length within the effective resistivity range. Simultaneously, due to the poor resistivity hit rate at the crystal head and the rapid decrease in resistivity at the tail, the effective rod length is short, leading to low single-furnace output and high overall crystal pulling costs.

[0039] Based on the above problems, this application provides a crystal growth method to improve the uniformity of dopant element distribution in doped single crystal silicon prepared by the Czochralski method, reduce the difference in axial resistivity, and avoid the problem that the uneven distribution of dopant elements in the doped single crystal silicon prepared by the Czochralski method during the growth process leads to a large difference in axial resistivity, which makes the resistivity of the finally grown doped single crystal silicon unable to meet the requirements of actual photovoltaic products such as solar cells.

[0040] Example 1

[0041] Reference Figure 1 , Figure 1 A flowchart of a crystal growth method according to Embodiment 1 of this application is shown. The method is applied to the growth process of a doped crystal and may include steps 101 to 103.

[0042] Step 101: After the material is melted, the temperature is adjusted under the first furnace pressure; the first furnace pressure is less than or equal to 3 Torr.

[0043] In this step, by observing the melting rate of the material block in the quartz crucible in the single crystal furnace, after the silicon material and dopants have completely melted, the temperature adjustment operation is completed through seed crystal temperature testing, welding and stabilization, and the furnace pressure is controlled to be less than or equal to 3 Torr during the above process.

[0044] In this embodiment of the application, the furnace pressure of the melting operation can be greater than the first furnace pressure, or it can be less than or equal to the first furnace pressure.

[0045] Optionally, in the method provided in this application, the melting operation is carried out at an argon flow rate of 50–120 L / min and a furnace pressure of less than or equal to 1 Torr. This facilitates the volatilization and removal of impurities in the furnace by using a high argon flow rate and low furnace pressure, thereby improving the purity of the molten silicon. Specifically, the argon flow rate during the melting process can be 50 L / min, 100 L / min, or 120 L / min, and the furnace pressure can be 1 Torr or 0.5 Torr.

[0046] Step 102: After temperature adjustment, crystal pulling, shoulder formation, and shoulder rotation operations are performed under the second furnace pressure; the second furnace pressure is less than or equal to the first furnace pressure.

[0047] In this step, after the temperature is adjusted, the crystal is introduced, the shoulder is formed, and the shoulder is rotated in sequence, and the furnace pressure is controlled to be in the second furnace pressure state in each of the above processes.

[0048] The second furnace pressure is less than or equal to the first furnace pressure, and the first furnace pressure is less than or equal to 3 Torr. That is, the second furnace pressure is also a relatively small furnace pressure value, which can quickly enter the target low furnace pressure state during the constant diameter stage while ensuring the quality of crystal pulling and shoulder formation.

[0049] Optionally, the argon flow rate during temperature control, crystal introduction, shoulder formation, and shoulder rotation operations is 50–200 L / min.

[0050] Step 103: After the shoulder is turned, constant diameter growth is performed. During the constant diameter growth stage, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform crystal Czochralski growth based on the actual constant diameter growth length of the doped single crystal silicon.

[0051] In this step, starting from the point where the doped single-crystal silicon enters the constant diameter growth stage, the constant diameter growth length of the doped single-crystal silicon is continuously monitored and obtained, which is taken as the actual constant diameter growth length mentioned above.

[0052] In this step, as the actual constant diameter growth length increases, the furnace pressure is gradually reduced starting from the second furnace pressure to control the direct pulling growth of the crystal. That is, a lower furnace pressure is used in the early stage of constant diameter growth, while an even lower furnace pressure is used in the middle and later stages of constant diameter growth.

[0053] As impurities accumulate in the melt during silicon crystal growth, the impurity concentration in the molten silicon increases, the impurity concentration at the tail of the crystal also increases, the resistivity decreases, and the smaller the segregation coefficient, the greater the difference in resistivity between the head and tail.

[0054] According to the principle of segregation, blast furnace pressure can suppress the volatilization of dopants under localized high temperatures within the furnace, thereby improving the accuracy and uniformity of resistivity hit rate. Therefore, during crystal pulling, using relatively high furnace pressure for crystal pulling during crystal introduction, shoulder formation, shoulder rotation, and equal-diameter head pulling can improve the accuracy of resistivity hit rate at the crystal head.

[0055] The dopants in Czochralski-grown single-crystal silicon are mainly Group IIIA and VA elements. According to the principle of vacuum evaporation purification, low furnace pressure promotes the volatilization of dopants, effectively reducing the resistivity decay at the crystal tail and improving the overall crystal resistivity. Therefore, during the crystal pulling process, in the later stages of constant diameter growth, using a low furnace pressure atmosphere promotes the volatilization of dopants and other metallic impurities, improving the crystal resistivity distribution and achieving effective narrowing of the resistivity of the single-crystal silicon rod under the same pull ratio. Effective resistivity narrowing helps improve the quality of the single-crystal silicon wafer ends, thereby improving cell conversion efficiency. Simultaneously, due to the narrowing of the axial resistivity of the single-crystal silicon rod, the pulling length of the single-crystal silicon rod can be significantly increased within the same resistivity specification range, helping to improve single-crystal production efficiency and reduce the overall manufacturing cost of single-crystal production.

[0056] The doping elements mentioned above can be phosphorus, arsenic, boron, gallium, etc.

[0057] Optionally, in one embodiment, the above-mentioned reduction of the crystal pulling furnace pressure from the second furnace pressure to perform Czochralski growth based on the actual constant diameter growth length of the doped single-crystal silicon includes:

[0058] The furnace pressure during the constant diameter growth stage is controlled at 1 mTorr to 3 Torr, the argon flow rate is 5 to 200 L / min, and the dry pump frequency is 30 to 55 Hz.

[0059] In this embodiment, by controlling the argon gas flow rate to 5–200 L / min and the dry pump frequency to 30–55 Hz, the furnace pressure for crystal pulling is maintained at 1 mTorr–3 Torr, gradually decreasing from the constant-diameter head. Since the oxygen in the crystal mainly originates from the high-temperature dissolution reaction in the quartz crucible (primarily SiO₂ + Si = 2SiO), some of the generated SiO enters the crystal, causing oxygen formation. According to the principle of vacuum volatilization, lower furnace pressure accelerates the volatilization of SiO and oxygen, effectively reducing the oxygen content in the head of the crystal rod. Theoretically, the lower the furnace pressure, the more significant the oxygen reduction effect.

[0060] In this embodiment, the initial furnace pressure for constant diameter crystal pulling is 3 torr, which effectively reduces the oxygen content in the crystal head while maintaining stable crystal formation efficiency. The actual reduction in oxygen content is >3 ppm. Simultaneously, a high argon flow rate is used at the constant diameter head, which not only improves the accuracy of the head resistance hit rate but also allows for rapid heat removal, thereby significantly increasing the pulling speed by 50% in the first 50% of the constant diameter stage.

[0061] Optionally, in one specific embodiment, the above-mentioned reduction of the crystal pulling furnace pressure from the second furnace pressure to perform Czochralski growth based on the actual constant diameter growth length of the doped single-crystal silicon includes:

[0062] The furnace pressure for the crystal pulling process at the head stage of constant diameter growth is controlled to be 5 mTorr to 3 Torr; the furnace pressure for the tail stage of constant diameter growth is less than or equal to 5 mTorr.

[0063] In this embodiment, a furnace pressure crystal pulling process with a higher pressure of 5mTorr to 3Torr is used in the head stage of constant diameter growth than in the tail stage, which reduces dopant volatilization and improves the accuracy of head resistivity hit rate; while the crystal pulling furnace pressure in the tail stage of constant diameter growth is lower than 5mTorr, which can promote dopant volatilization in the furnace in the middle and later stages of constant diameter growth, increase tail resistivity, and increase the crystal constant diameter length.

[0064] Optionally, in one specific embodiment, the above-mentioned reduction of the crystal pulling furnace pressure from the second furnace pressure to perform Czochralski growth based on the actual constant diameter growth length of the doped single-crystal silicon includes:

[0065] The crystal rotation speed is 5–11 RPM, and the crucible rotation speed is 4–9 RPM.

[0066] In this embodiment, at the constant diameter growth node, the crystal rotation speed is controlled between 5 and 11 RPM and kept stable, for example, 5 RPM, 8 RPM or 11 RPM, while the crucible rotation speed is between 4 and 9 RPM and gradually increases. That is, the head adopts low crucible rotation, which weakens the forced thermal convection effect and increases the thickness of the diffusion boundary layer between the crucible and the melt. This can effectively reduce the entry of oxygen atoms into the melt. On the other hand, it reduces the radial temperature gradient of the melt and lowers the temperature of the quartz crucible wall, thereby reducing the dissolution reaction rate of the quartz crucible and also reducing the oxygen content in the crystal.

[0067] Optionally, in one specific embodiment, the above-mentioned reduction of the crystal pulling furnace pressure from the second furnace pressure to perform Czochralski growth based on the actual constant diameter growth length of the doped single-crystal silicon includes:

[0068] Pulling speed 75mm / hr~120mm / hr, crucible rotation 5RPM~6RPM.

[0069] In this specific embodiment, during the constant diameter growth stage, the control crucible rotation is increased from 5 RPM to 6 RPM, while the pulling speed is between 75 mm / hr and 120 mm / hr, and is first increased and then decreased. This can effectively improve the crystal pulling efficiency while reducing the oxygen content in the crystal and ensuring the crystal quality.

[0070] Optionally, in one specific embodiment, the argon flow rate during the head stage of the constant diameter growth is set to 50–200 L / min; the argon flow rate during the tail stage of the constant diameter growth is less than 5 L / min.

[0071] In this embodiment, the equal-diameter head adopts blast furnace pressure crystal pulling and a large argon flow rate compared to the equal-diameter tail. This not only improves the accuracy of the head resistance hit rate, but also allows the large argon flow rate to quickly remove heat, thereby significantly increasing the pulling speed by 50% in the first 50% of the equal-diameter section.

[0072] Optionally, in one specific embodiment, the equal diameter growth head stage is the equal diameter growth stage corresponding to the equal diameter head, and the equal diameter growth tail stage is the equal diameter growth stage corresponding to the equal diameter tail. The length of the equal diameter head is less than or equal to 10% of the total length of the equal diameter portion, and the length of the equal diameter tail is greater than 85% of the total length of the equal diameter portion.

[0073] Optionally, in one specific embodiment, based on the actual constant diameter growth length, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform Czochralski growth, including:

[0074] When the actual constant diameter growth length increases from zero to less than or equal to 5% of the total length of the constant diameter portion, the furnace pressure is controlled at 0.3 to 3 torr, the argon flow rate is 15 L / min to 50 L / min, and the heating power is reduced by 2.5 kW.

[0075] In the specific embodiments described above, during the growth stage when the length of the crystal rod is within the first 5% of the total crystal rod length, for example, when the crystal rod is stretched from 0 mm to 300 mm, the furnace pressure is controlled to decrease from 3 torr to 0.3 torr, the argon flow rate is reduced from 50 L / min to 15 L / min, and the heating power is reduced by 2.5 kW. Optionally, the furnace pressure can be 0.3 torr, 0.5 torr, 1 torr, 2 torr, etc.

[0076] If the furnace pressure drop is too large, the large fluctuation in furnace pressure can cause uneven temperature gradients in the thermal field, leading to an increase in the frequency of crystal breakage and reduced production efficiency. At the same time, in order to match the increased production efficiency by setting the pulling speed in the early stage of equal diameter growth, the equal diameter power needs to be gradually reduced by 2.5 kW to alleviate the problem that the pulling speed cannot be increased due to the increased heat accumulation in the furnace chamber and the inability to dissipate the latent heat of crystallization at the solid-liquid interface of the growing crystal. If the total cooling of equal diameter growth is too large, the supercooling will increase, and the crystal growth will be prone to excessively fast pulling speed, which can easily cause crystal rod deformation and crystal wire breakage. The cooling range is affected by many factors, such as the thermal field insulation, the size of the thermal field, and the liquid gate distance.

[0077] In addition, because the furnace pressure continues to decrease, the aforementioned argon flow rate and dry pump frequency can quickly bring the furnace pressure to the set value. According to the heat transfer method and the principle of vacuum insulation, the lower the furnace pressure, the lower the convective heat transfer and heat conduction heat dissipation, which can improve the furnace insulation.

[0078] Optionally, in one specific embodiment, based on the actual constant diameter growth length, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform Czochralski growth, including:

[0079] When the actual constant diameter growth length increases from 5% of the total length of the constant diameter portion to less than or equal to 10% of the total length of the constant diameter portion, the furnace pressure is controlled at 5 mtorr to 0.3 torr and the argon flow rate is controlled at 5 L / min to 15 L / min.

[0080] In the specific embodiments described above, during the growth stage when the crystal rod length is 5% to 10% of the total crystal rod length, for example, when the crystal rod length is stretched from 300 mm to approximately 550 mm, the furnace pressure is gradually reduced from 0.3 torr to a minimum furnace pressure of 5 mtorr, and the argon flow rate is reduced from 15 L / min to 5 L / min. This promotes the effective volatilization of dopants in the melt, which can reduce the difference in the axial concentration distribution of dopants in the doped single crystal silicon and improve the uniformity of the axial resistivity of the single crystal silicon. Theoretically, the lower the furnace pressure, the greater the volatilization effect of the dopants. The volatilization of dopants is greater than segregation, resulting in a more concentrated resistivity at the beginning and end of the crystal and a more uniform axial resistivity distribution of the single crystal silicon rod.

[0081] Optionally, in one specific embodiment, based on the actual constant diameter growth length, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform Czochralski growth, including:

[0082] When the actual constant diameter growth length increases from 10% of the total length of the constant diameter portion to less than or equal to 55% of the total length of the constant diameter portion, the furnace pressure is controlled to be no greater than 5 mtorr and the argon flow rate is controlled to be no less than 5 L / min.

[0083] In this specific embodiment, during the growth stage when the length of the crystal rod is 10% to 55% of the total length of the crystal rod, for example, when the length of the crystal rod is stretched from 550mm to 3000mm, the furnace pressure is controlled to be less than or equal to 5mtorr and the argon flow rate is greater than or equal to 5L / min. With moderate furnace pressure and argon flow rate, the middle part of the crystal rod can be stretched quickly, uniformly and stably.

[0084] Optionally, in one specific embodiment, based on the actual constant diameter growth length, the crystal pulling furnace pressure is reduced from the second furnace pressure to perform Czochralski growth, including:

[0085] When the actual constant diameter growth length increases from 55% of the total length of the constant diameter portion to less than or equal to 100% of the total length of the constant diameter portion, the furnace pressure is controlled at 1 mtorr to 5 mtorr, the argon flow rate is 5 L / min, and the dry pump frequency is 55 Hz.

[0086] In this specific embodiment, during the growth stage at the tail of the crystal rod, for example when the length of the crystal rod is stretched from 3000mm to 5500mm, the furnace pressure is controlled at 1mtorr to 5mtorr, the argon flow rate is 5L / min, and the dry pump frequency is 55Hz, which forces the dopant to volatilize further and ensures that the tail of the crystal rod has a high resistivity.

[0087] During the growth stage at the tail of the crystal rod, as the amount of material remaining in the crucible continues to decrease, the heat dissipation area increases, and the position of the crucible continues to rise, the melt moves away from the heating zone of the heater. In order to prevent the melt from crystallizing due to overcooling, a heating process is required. When the length of the crystal rod is stretched from 4200mm to 5500mm, the heating power of the constant diameter needs to be increased by about 5kW.

[0088] In this embodiment of the application, during the process of directly pulling crystals by reducing the crystal pulling furnace pressure starting from the second furnace pressure, the pulling speed is negatively correlated with the heater power. For example, during the growth stage when the length of the crystal pulling rod is 10% to 55% of the total length of the crystal rod, that is, during the process of stretching the crystal rod length from 550mm to 3000mm, the pulling speed is controlled to be increased from 100mm / hr to 120mm / hr, while the heating power is gradually reduced by 1.8kw.

[0089] Optionally, in one embodiment, during the Czochralski growth of crystals by reducing the furnace pressure starting from the second furnace pressure, the pulling speed increment ΔV and the power increment ΔP satisfy ΔV = -K*ΔP, where K is 0.06 to 0.11. Using the above relationship, the pulling speed can be linearly adjusted based on the heater power change to ensure the stability of the crystal rod.

[0090] Optionally, in one embodiment, the single crystal furnace used in the crystal growth method provided in this application includes a vacuum device composed of n parallel dry pumps. The furnace pressure P of the single crystal furnace satisfies the following relationship with the number of dry pumps n, the pump frequency f, and the argon flow rate Q:

[0091] P = A / (n*f) - B / Q + C;

[0092] Where A is between 1 and 120, B is between 1 and 100, C is between 0 and 0.05, and Q is ≥ 1 L / min.

[0093] Among them, the performance parameters of each dry pump are the same, and A, B, C and Q are constants related to the system configuration, which were determined in advance through experiments.

[0094] In this specific embodiment, given a certain argon flow rate, the furnace pressure of the single crystal furnace can be adjusted to the target furnace pressure by controlling the number of dry pumps involved in vacuuming and the frequency of each dry pump.

[0095] Optionally, in one embodiment, step 104 is included before step 101 described above:

[0096] Step 104: After the silicon material is melted, the silicon material and dopant are added a second time under the conditions of argon flow rate of 100-200 L / min and furnace pressure of 10-100 Torr.

[0097] In this step, after the silicon material melts in the quartz crucible, a second feeding is performed. The silicon material and dopant are added through a quartz feeding cylinder or feeding device. The argon flow rate is set to 100–200 L / min, and the furnace pressure is increased to 10–100 Torr. The high furnace pressure prevents effective volatilization of the dopant, ensuring the stability and uniformity of the dopant concentration within the furnace. Insufficient argon flow rate would prevent volatiles from being smoothly expelled from the furnace during the feeding process, potentially causing accumulation of volatiles inside the furnace. Conversely, excessive argon flow rate would prevent the dry pump from adjusting the furnace pressure to 10–100 Torr. Therefore, the argon flow rate is set to 100–200 L / min.

[0098] Optionally, when adding silicon material and dopants a second time, the argon flow rate is set to 100-150 L / min and the furnace pressure to 10-100 Torr.

[0099] The dopants mentioned above can be phosphorus, arsenic, boron, gallium, etc.

[0100] In this embodiment, a low furnace pressure of less than or equal to 3 Torr is used in the temperature control, crystal pulling, shoulder formation, and shoulder turning operations. This allows for a faster attainment of the low furnace pressure state for equal-diameter growth while maintaining stable crystal pulling-shoulder formation quality. Simultaneously, by continuously lowering the crystal pulling furnace pressure as the equal-diameter growth length increases, dopant volatilization can be prevented in the early stages of equal-diameter growth, ensuring the stability of the doping amount within the furnace. This not only improves the uniformity of resistivity and the accuracy of doping at the head but also increases the head pulling speed. Furthermore, using an even lower furnace pressure in the later stages of equal-diameter growth promotes dopant volatilization within the furnace, increases the tail resistivity, and increases the crystal's equal-diameter length. Therefore, this embodiment can reduce the difference in the axial concentration distribution of dopants in doped single-crystal silicon, improve the uniformity of axial resistivity of single-crystal silicon, and simultaneously increase production efficiency.

[0101] In practical applications, the crystal growth method provided in this application has the following specific steps:

[0102] A quartz crucible filled with silicon material is hoisted into a single crystal furnace. After the furnace is closed, the furnace is evacuated to a preset vacuum level and pressure is maintained to confirm the equipment leakage rate and airtightness. Once the leakage rate is confirmed to meet the normal operating leakage rate of the equipment, pressure melting is performed. During the pressure maintenance period, the argon flow rate can be set to 50-200 L / min, and argon can be introduced multiple times to accelerate the evacuation speed inside the furnace.

[0103] During the melting process, the argon flow rate is set to 50-120 L / min, and the furnace pressure is maintained at less than 1 Torr. The silicon material in the quartz crucible is heated and melted through the main heater and the bottom heater.

[0104] After the silicon material melts in the quartz crucible, under the conditions of argon flow rate of 100-200L / min and furnace pressure of 10-100Tor, the silicon material and dopant are added a second time through the quartz feeding cylinder or feeding device.

[0105] By observing the melting rate of the material block inside the quartz crucible, after the silicon material has completely melted, the seed crystal temperature test, welding and temperature stabilization are carried out under the conditions of argon flow rate of 50-200L / min and furnace pressure less than or equal to 3 Torr, so as to complete the temperature adjustment operation.

[0106] After temperature adjustment and reaching the crystal-leading standard, automatic crystal-leading and shoulder formation are carried out under the conditions of argon flow rate of 50-200 L / min and furnace pressure less than or equal to 3 Torr.

[0107] After the crystal pulling and shoulder formation are completed, the constant diameter growth stage begins. In the early stage of constant diameter growth, the furnace pressure is controlled to be less than or equal to 3 Torr, and the argon flow rate is set to 50-200 L / min. This is to take away more heat by utilizing the large argon flow rate, thereby increasing the head pulling speed.

[0108] As the constant diameter growth length increases, the furnace pressure is gradually reduced. After the constant diameter growth length reaches 10% of the total length of the constant diameter section, the furnace pressure is reduced to less than 5 mTorr and the argon flow rate is reduced to less than 5 L / min. This is to use the low furnace pressure to promote the volatilization of dopants in the furnace during the middle and later stages of the constant diameter growth, improve the tail resistivity, and increase the constant diameter length of the crystal.

[0109] After the crystal rod reaches the desired length or weight, the process is completed under conditions where the argon flow rate is less than 5 L / min and the furnace pressure is less than 5 mTorr.

[0110] After the finishing process is completed, the crystal rod extraction step is carried out under the conditions of argon flow rate of 100-200 L / min and furnace pressure of 10-100 Torr.

[0111] In other words, in the embodiments of this application, during the single crystal furnace evacuation and leak detection, feeding, melting, release, equal diameter, and finishing processes, different furnace pressure changes are used to improve the resistivity at the beginning and end of the crystal, so that the resistivity attenuation per 100cm of the crystal rod is reduced by more than 65% compared with the conventional furnace pressure crystal pulling process, thereby achieving the goal of improving production efficiency.

[0112] This application also provides a crystalline silicon, which is prepared by the crystal growth method described above, and the oxygen content of the crystalline silicon is less than or equal to 11 ppma.

[0113] Specifically, when preparing the aforementioned doped single-crystal silicon, temperature control, crystal pulling, shoulder formation, and shoulder rotation are performed at a lower furnace pressure of less than or equal to 3 Torr. This allows for a faster attainment of the low furnace pressure state for constant-diameter growth while maintaining stable crystal pulling-shoulder quality. As the crystal Czochralski growth progresses, further lowering the crystal pulling furnace pressure can prevent dopant volatilization in the early stages of constant-diameter growth, ensuring the stability of the doping amount within the furnace. This not only improves the uniformity of resistivity and the accuracy of doping at the head but also increases the head pulling speed. Furthermore, using an even lower furnace pressure in the later stages of constant-diameter growth can promote doping volatilization within the furnace, increase the tail resistivity, and increase the crystal's constant-diameter length. This reduces the axial concentration distribution difference of dopants in the doped single-crystal silicon, resulting in higher axial resistivity uniformity for the aforementioned doped single-crystal silicon.

[0114] Example 2

[0115] Reference Figure 2 , Figure 2 A flowchart illustrating the steps of a crystal growth method according to Embodiment 2 of this application is shown. The method may include steps 201 to 204:

[0116] Step 201: Determine a first correspondence between the crystal pulling furnace pressure of doped monocrystalline silicon and the constant diameter growth length range; wherein, in the first correspondence, the crystal pulling furnace pressure corresponding to different constant diameter growth length ranges is at least partially different, so that when the crystal is pulled by Czochralski according to the crystal pulling furnace pressure determined by the first correspondence during the constant diameter growth stage, the axial concentration of doped elements in the doped monocrystalline silicon tends to be uniform.

[0117] In this step, based on the law that the dopant element is unevenly distributed in the axial direction of single crystal silicon due to the pressure of the crystal pulling furnace at different constant diameter growth lengths, the crystal pulling furnace pressure that can make the saturated vapor pressure of the dopant element in the doped single crystal silicon in the constant diameter growth stage change continuously with the constant diameter growth of the silicon single crystal, and control the axial concentration of the dopant element to tend to be uniform, is calculated in advance, that is, the above-mentioned first correspondence is determined.

[0118] Specifically, the total length of constant diameter growth can be divided into multiple constant diameter growth length ranges, either uniformly or non-uniformly, and then different crystal pulling furnace pressures can be set for each constant diameter growth length range.

[0119] Optionally, in the first correspondence mentioned above, the furnace pressure for pulling doped single-crystal silicon is negatively correlated with the constant diameter growth length range. That is, in the first relationship mentioned above, the furnace pressure decreases gradually as the constant diameter growth length range increases. This means that when adjusting the furnace pressure according to the first correspondence mentioned above, not only can the axial concentration of the dopant elements be controlled to be more uniform, but the crystal pulling quality can also be further improved.

[0120] Optionally, in the first correspondence mentioned above, the crystal pulling furnace pressure of doped monocrystalline silicon can be linearly negatively correlated with the constant diameter growth length range, or be linearly negatively correlated with the constant diameter growth length range, that is, as the constant diameter growth length range increases, the crystal pulling furnace pressure continuously decreases.

[0121] Step 202: After the melting is completed, a temperature adjustment operation is performed under the first furnace pressure; the first furnace pressure is less than or equal to 3 Torr.

[0122] For details of this step, please refer to step 101 above, which will not be repeated here.

[0123] Step 203: After temperature adjustment, crystal pulling, shoulder formation, and shoulder rotation operations are performed under the second furnace pressure; the second furnace pressure is less than or equal to the first furnace pressure.

[0124] For details of this step, please refer to step 102 above, which will not be repeated here.

[0125] Step 204: After the shoulder is formed, constant diameter growth is performed, and when the doped single crystal silicon is in the constant diameter growth stage, the actual constant diameter growth length of the doped single crystal silicon is obtained.

[0126] In this step, starting from the point where the doped single-crystal silicon enters the constant diameter growth stage, the constant diameter growth length of the doped single-crystal silicon is continuously monitored and obtained, which is taken as the actual constant diameter growth length mentioned above.

[0127] Step 205: Determine the target equal diameter growth length range to which the actual equal diameter growth length belongs.

[0128] In this step, based on the actual equal diameter growth length obtained and the upper limit and lower limit of the equal diameter growth length corresponding to each equal diameter growth length range in the first correspondence, the range of equal diameter growth length including the actual equal diameter growth length is determined as the target equal diameter growth length range.

[0129] Step 206: Determine the target crystal pulling furnace pressure corresponding to the actual constant diameter growth length based on the first correspondence between the crystal pulling furnace pressure of doped single crystal silicon and the constant diameter growth length range.

[0130] In this step, the first correspondence mentioned above specifies the crystal pulling furnace pressure corresponding to different equal diameter growth length ranges. Therefore, after determining the equal diameter growth length range of the actual equal diameter growth length, the corresponding crystal pulling furnace pressure, namely the target crystal pulling furnace pressure, can be determined.

[0131] Step 207: Control the direct crystal growth according to the target crystal pulling furnace pressure.

[0132] In this step, because the saturated vapor pressure of the dopant element in the doped single crystal silicon is constantly changing when the crystal pulling furnace pressure is controlled according to the first correspondence during the constant diameter growth stage, the axial concentration of the dopant element tends to be uniform. Therefore, when the crystal pulling process parameters are controlled according to the above-mentioned target crystal pulling process parameters, the concentration distribution of the dopant element in the single crystal silicon is relatively small, and the axial resistivity of the silicon crystal becomes more uniform.

[0133] Optionally, in one embodiment, step 207 specifically includes step 271:

[0134] Step 271: Adjust the crystal pulling process parameters according to the target crystal pulling furnace pressure. The crystal pulling process parameters include argon flow rate and dry pump frequency.

[0135] In this embodiment, since a high argon flow rate can remove more heat, thereby increasing the crystal pulling rate of monocrystalline silicon, but due to the performance limitations of the dry pump, when it reaches the upper limit of the frequency, it is necessary to reduce the argon flow rate to continue to reduce the crystal pulling furnace pressure. Therefore, by adjusting the argon flow rate and the dry pump frequency, the required crystal pulling furnace pressure can be achieved within the performance range of the dry pump.

[0136] Optionally, in one specific embodiment, step 2710 is included before step 207, and step 271 includes steps 2711 to 2712.

[0137] Step 2710: Determine the second correspondence between the crystal pulling furnace pressure of doped monocrystalline silicon and the argon flow rate and dry pump frequency; wherein, when controlling the crystal Czochralski growth according to the argon flow rate and dry pump frequency determined by the second correspondence, the crystal pulling furnace pressure of the doped monocrystalline silicon is adjusted to the corresponding pressure value, and the crystal pulling rate of the doped monocrystalline silicon tends to a maximum value.

[0138] In this step, a higher argon flow rate can remove more heat, thus increasing the crystal pulling rate. However, with a constant furnace pressure, a higher argon flow rate requires a higher dry pump frequency. Since the dry pump has a frequency limit due to performance limitations, the crystal pulling rate of monocrystalline silicon is determined by both the argon flow rate and the dry pump frequency when the furnace pressure remains constant. Therefore, based on the principle that a higher argon flow rate can remove more heat and increase the crystal pulling rate, and combined with the working performance of the dry pump, the maximum argon flow rate for each crystal pulling furnace pressure within the dry pump's operating frequency range is determined, which is the second correspondence mentioned above.

[0139] Step 2711: Based on the second correspondence between the crystal pulling furnace pressure of doped monocrystalline silicon and the argon flow rate and dry pump frequency, determine the target argon flow rate and target dry pump frequency corresponding to the target crystal pulling furnace pressure.

[0140] In this step, since the argon flow rate and dry pump frequency under each crystal pulling furnace pressure are determined in the second correspondence, when the target crystal pulling furnace pressure is obtained, the corresponding argon flow rate and dry pump frequency can be determined through the above second correspondence, that is, the above target argon flow rate and target dry pump frequency.

[0141] Step 2712: Control the Czochralski growth of the crystal according to the target argon flow rate and the target dry pump frequency.

[0142] In this step, since the second correspondence determines the maximum argon flow rate of each crystal pulling furnace within the operating frequency range of the dry pump, controlling the direct crystal pulling growth under the above-mentioned target argon flow rate and target dry pump frequency can not only achieve the target crystal pulling furnace pressure, but also pull crystals at the maximum value of the crystal pulling rate, thereby improving the overall crystal pulling rate.

[0143] Optionally, in one specific embodiment, in the second correspondence mentioned above, the crystal pulling furnace pressure and the argon gas flow rate are positively correlated. That is, as the crystal pulling furnace pressure decreases, the argon gas flow rate also decreases continuously, thereby effectively improving the crystal pulling rate of the crystal head.

[0144] In the above embodiments, when the doped monocrystalline silicon is in the constant diameter growth stage, the corresponding target crystal pulling furnace pressure is first determined according to the actual constant diameter growth length, and then the corresponding argon flow rate and dry pump frequency are determined according to the target crystal pulling furnace pressure to control the crystal direct pulling growth. This not only reduces the target crystal pulling furnace pressure to alleviate the axial resistivity difference of monocrystalline silicon, but also allows crystal pulling to be performed at the maximum value of the crystal pulling rate, thereby improving the overall crystal pulling rate.

[0145] Optionally, in one embodiment, the above crystal pulling process parameters further include crucible rotation rate, crystal pulling rate and heater power, and step 2720 is included before step 271. Step 271 includes steps 2721 to 2722.

[0146] Step 2720: Determine the third correspondence between the crystal pulling furnace pressure of doped monocrystalline silicon and the argon flow rate, dry pump frequency, crucible rotation rate, crystal pulling rate, and heater power; wherein, when controlling the Czochralski growth of crystal according to the argon flow rate, dry pump frequency, crucible rotation rate, and heater power determined according to the third correspondence, the crystal pulling furnace pressure of the doped monocrystalline silicon is adjusted to the corresponding pressure value, and the crystal pulling rate of the doped monocrystalline silicon tends to a maximum value.

[0147] In this step, a high argon flow rate can remove more heat, thus increasing the crystal pulling rate; while a reduced heater power can decrease heat generation, further increasing the crystal pulling rate; and an increased crucible rotation rate can accelerate cooling, thereby increasing the crystal pulling rate. However, with constant furnace pressure, a higher argon flow rate requires a higher dry pump frequency, but the dry pump has a frequency limit due to performance limitations. Simultaneously, excessively low heater power and excessively fast crucible rotation can affect the molten silicon state and the crystal pulling quality. In other words, with constant furnace pressure, the crystal pulling rate of single-crystal silicon is determined by the argon flow rate, dry pump frequency, heater power, and crucible rotation rate. Therefore, based on the principle that a high argon flow rate removes more heat, and that low heater power and high crucible rotation rate increase the crystal pulling rate, and considering the dry pump's operating performance, the maximum argon flow rate, minimum heater power, and maximum crucible rotation rate for each crystal pulling furnace pressure are determined within the dry pump's operating frequency range—this is the third correspondence mentioned above.

[0148] Step 2721: Based on the third correspondence between the crystal pulling furnace pressure of doped single crystal silicon and the argon flow rate, dry pump frequency, crucible rotation rate, crystal pulling rate and heater power, determine the target argon flow rate, target crucible rotation rate, target crystal pulling rate and target heating power corresponding to the target crystal pulling furnace pressure.

[0149] In this step, since the argon flow rate, dry pump frequency, heater power and crucible rotation rate under each crystal pulling furnace pressure are determined in the third correspondence, when the target crystal pulling furnace pressure is obtained, the corresponding argon flow rate, dry pump frequency, heater power and crucible rotation rate can be determined through the above third correspondence, that is, the above target argon flow rate, target dry pump frequency, target heater power and target crucible rotation rate.

[0150] Step 2722: Control the crystal Czochralski growth according to the target argon flow rate, target dry pump frequency, target heater power, and target crystal pulling rate.

[0151] In this step, since the third correspondence determines the maximum argon flow rate, appropriate heater power, and appropriate crucible rotation within the operating frequency range of the dry pump, controlling the direct crystal growth under the above-mentioned target argon flow rate, target dry pump frequency, target crucible rotation rate, and target heater power can not only achieve the target crystal pulling furnace pressure, but also pull crystals at the maximum value of the crystal pulling rate, thereby improving the overall crystal pulling rate.

[0152] In the above embodiments, when the doped monocrystalline silicon is in the constant diameter growth stage, the corresponding target crystal pulling furnace pressure is first determined according to the actual constant diameter growth length. Then, the corresponding argon flow rate, crucible rotation rate, dry pump frequency, heater power, and crystal pulling rate are determined according to the target crystal pulling furnace pressure. By controlling the direct crystal pulling growth, not only can the target crystal pulling furnace pressure be smoothly reduced to alleviate the axial resistivity difference of monocrystalline silicon, but crystal pulling can also be performed at the maximum value of the crystal pulling rate, thereby improving the overall crystal pulling rate.

[0153] The present application will be described in detail below through embodiments.

[0154] Example 1

[0155] An example is given using a 32-inch hot zone, a maximum rod length of 5500mm, and a constant diameter full-range crystal rotation at 8RPM:

[0156] (1) The quartz crucible filled with silicon material is hoisted into the single crystal furnace, and the single crystal furnace is evacuated after the furnace is closed. After the single crystal furnace is evacuated, pressure is applied and the material is melted. The crucible rotation is set to 1 RPM, the heater power is 250 Kw, the argon flow rate is 50 L / min, the furnace pressure is maintained at 1 Torr, and the dry pump frequency is 45 Hz.

[0157] (2) After the silicon material in the quartz crucible melts, the silicon material and dopant are added a second time through the quartz feeding cylinder or feeding device. The crucible rotation is set to 1 RPM, the heater power is 250 Kw, the argon flow rate is 100 L / min, the furnace pressure is maintained at 15 Torr, and the dry pump frequency is 50 Hz.

[0158] (3) After the silicon material is completely melted, seed crystal temperature test, welding and temperature stabilization are carried out to complete the temperature adjustment operation. The crystal rotation is set to 8 RPM, the crucible rotation is set to 5 RPM, the argon flow rate is 50 L / min, the furnace pressure is maintained at 3 Torr, and the dry pump frequency is 30 Hz.

[0159] (4) After the temperature adjustment is completed and the crystal pulling standard is reached, automatic crystal pulling and shoulder setting is performed. The crystal rotation is set to 8 RPM, the crucible rotation is set to 5 RPM, the argon flow rate is set to 50 L / min, the furnace pressure is maintained at 3 Torr, and the dry pump frequency is set to 30 Hz.

[0160] (5) After the temperature adjustment is completed and the crystal pulling standard is reached, automatic crystal pulling and shoulder setting is performed. The crystal rotation is set to 8 RPM, the crucible rotation is set to 5 RPM, the argon flow rate is set to 50 L / min, the furnace pressure is maintained at 3 Torr, and the dry pump frequency is set to 30 Hz.

[0161] (6) After the crystal pulling and shoulder formation are completed, the constant diameter growth stage is entered. Adjust the crystal pulling process parameters according to Table 1 to obtain doped single crystal silicon.

[0162] Table 1

[0163]

[0164]

[0165] Example 1 uses a low furnace pressure crystal pulling process with a furnace pressure as low as 5 mtorr. The oxygen content in the crystal is reduced by about 3 ppm compared with conventional furnace pressure (>10 torr). Specifically, the oxygen content at the head is reduced by >3 ppm, the middle part of the crystal is reduced by >2 ppm, and the tail part is reduced by >2.5 ppm.

[0166] Example 2

[0167] An example is given using a 32-inch hot zone, a maximum rod length of 5500mm, and a constant diameter full-range crystal rotation at 8RPM:

[0168] (1) The quartz crucible filled with silicon material is hoisted into the single crystal furnace, and the single crystal furnace is evacuated after the furnace is closed. After the single crystal furnace is evacuated, pressure is applied and the material is melted. The crucible rotation is set to 1 RPM, the heater power is 250 Kw, the argon flow rate is 50 L / min, the furnace pressure is maintained at 1 Torr, and the dry pump frequency is 45 Hz.

[0169] (2) After the silicon material in the quartz crucible melts, the silicon material and dopant are added a second time through the quartz feeding cylinder or feeding device. The crucible rotation is set to 1 RPM, the heater power is 250 Kw, the argon flow rate is 100 L / min, the furnace pressure is maintained at 15 Torr, and the dry pump frequency is 50 Hz.

[0170] (3) After the silicon material is completely melted, seed crystal temperature test, welding and temperature stabilization are carried out to complete the temperature adjustment operation. The crystal rotation is set to 8 RPM, the crucible rotation is set to 5 RPM, the argon flow rate is 50 L / min, the furnace pressure is maintained at 3 Torr, and the dry pump frequency is 30 Hz.

[0171] (4) After the temperature adjustment is completed and the crystal pulling standard is reached, automatic crystal pulling and shoulder setting is performed. The crystal rotation is set to 8 RPM, the crucible rotation is set to 5 RPM, the argon flow rate is set to 50 L / min, the furnace pressure is maintained at 3 Torr, and the dry pump frequency is set to 30 Hz.

[0172] (5) After the temperature adjustment is completed and the crystal pulling standard is reached, automatic crystal pulling and shoulder setting is performed. The crystal rotation is set to 8 RPM, the crucible rotation is set to 5 RPM, the argon flow rate is set to 50 L / min, the furnace pressure is maintained at 3 Torr, and the dry pump frequency is set to 30 Hz.

[0173] (6) After the crystal pulling and shoulder formation are completed, the constant diameter growth stage is entered. Adjust the crystal pulling process parameters according to Table 2 to obtain doped single crystal silicon.

[0174] Table 2

[0175]

[0176]

[0177] Example 2 uses a low furnace pressure crystal pulling process with a furnace pressure as low as 1 mtorr. The oxygen content in the crystal is reduced by about 3.5 ppm compared with conventional furnace pressure (>10 torr). Specifically, the oxygen content at the head is reduced by >3.5 ppm, the middle part of the crystal is reduced by >2.5 ppm, and the tail part is reduced by >3 ppm.

[0178] Based on the axial resistivity decay and the required electrical performance parameters of the monocrystalline silicon rods, the lengths of monocrystalline silicon rods A1, A2, and A3 prepared under 26-inch / 32-inch / 33-inch thermal fields using Example 1 of this application were evaluated. The rod lengths of monocrystalline silicon rods B1, B2, and B3 prepared under 26-inch / 32-inch / 33-inch thermal fields using the existing Czochralski method were also evaluated. The results are as follows: Figure 3 .

[0179] pass Figure 3 It can be seen that, according to the same resistivity specification requirements, compared with the existing Czochralski method, the low furnace pressure crystal pulling process provided in this application embodiment, combined with the single crystal silicon rod life decay status, actually increases the 26-inch rod length by 55%, the 32-inch rod length by 25%, and the 33-inch rod length by 23.5%.

[0180] Comparison of the actual resistance distributions of single-crystal silicon rod A1 and single-crystal silicon rod B1: Figure 4 As shown.

[0181] pass Figure 4 It can be seen that, under the same bar length conditions, compared with the existing Czochralski method, the low furnace pressure crystal pulling process provided in this application embodiment increases the actual output bar tail resistivity by more than 65%.

[0182] It should be noted that, for the sake of simplicity, the method embodiments are all described as a series of actions. However, those skilled in the art should understand that the embodiments of this application are not limited to the described order of actions, because according to the embodiments of this application, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also understand that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily essential to the embodiments of this application.

[0183] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0184] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of this application.

[0185] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.

Claims

1. A method of crystal growth, characterized by, The method comprises: After the completion of the melt, temperature adjustment is performed at a first furnace pressure, which is less than or equal to 3 Torr; After the completion of the temperature adjustment, seeding, shoulder formation and shoulder transition are performed at a second furnace pressure, which is less than or equal to the first furnace pressure; After the completion of the shoulder transition, equal-diameter growth is performed, and during the equal-diameter growth, the crystal is grown by reducing the furnace pressure from the second furnace pressure according to the actual equal-diameter growth length. The crystal is grown by reducing the furnace pressure from the second furnace pressure according to the actual equal-diameter growth length, comprising: The crystal rotation speed is gradually increased between 5 RPM and 8 RPM, and the crucible rotation speed is gradually increased between 4 RPM and 6 RPM.

2. The crystal growth method according to claim 1, wherein The crystal is grown by reducing the furnace pressure from the second furnace pressure according to the actual equal-diameter growth length, comprising: The furnace pressure during the equal-diameter growth is controlled to be 1 mTorr to 3 Torr, the argon flow rate is controlled to be 5 L / min to 200 L / min, and the dry pump frequency is controlled to be 30 Hz to 55 Hz.

3. The crystal growth method according to claim 1, wherein The crystal is grown by reducing the furnace pressure from the second furnace pressure according to the actual equal-diameter growth length, comprising: When the actual equal-diameter growth length increases from zero to less than or equal to 5% of the total length of the equal-diameter portion, the furnace pressure is controlled to be 0.3 Torr to 3 Torr, the argon flow rate is controlled to be 15 L / min to 50 L / min, and the heating power is reduced by 2.5 kW.

4. The crystal growth method according to claim 1, wherein The crystal is grown by reducing the furnace pressure from the second furnace pressure according to the actual equal-diameter growth length, comprising: a pulling rate of 75 mm / hr to 120 mm / hr and a crucible rotation speed of 5 RPM to 6 RPM.

5. The crystal growth method according to claim 4, wherein The crystal is grown by reducing the furnace pressure from the second furnace pressure according to the actual equal-diameter growth length, further comprising: When the actual equal-diameter growth length increases from 5% of the total length of the equal-diameter portion to less than or equal to 10% of the total length of the equal-diameter portion, the furnace pressure is controlled to be 5 mTorr to 0.3 Torr, and the argon flow rate is controlled to be 5 L / min to 15 L / min.

6. The crystal growth method according to claim 1, wherein The crystal is grown by reducing the furnace pressure from the second furnace pressure according to the actual equal-diameter growth length, comprising: When the actual equal-diameter growth length increases from 10% of the total length of the equal-diameter portion to less than or equal to 55% of the total length of the equal-diameter portion, the furnace pressure is controlled to be not greater than 5 mTorr, and the argon flow rate is controlled to be not less than 5 L / min.

7. The crystal growth method according to claim 1, wherein The crystal is grown by reducing the furnace pressure from the second furnace pressure according to the actual equal-diameter growth length, comprising: When the actual equal-diameter growth length increases from 55% of the total length of the equal-diameter portion to less than or equal to 100% of the total length of the equal-diameter portion, the furnace pressure is controlled to be 1 mTorr to 5 mTorr, the argon flow rate is controlled to be 5 L / min, and the dry pump frequency is controlled to be 55 Hz.

8. The crystal growth method according to any one of claims 5 to 7, characterized by, During the process of growing the crystal by reducing the furnace pressure from the second furnace pressure, the pulling rate increment ΔV and the power increment ΔP satisfy ΔV = -K*ΔP, wherein K is 0.06 to 0.

11.

9. The crystal growth method according to claim 1, wherein The furnace pressure P of the single crystal furnace, the number n of dry pumps, the dry pump frequency f, and the argon flow rate Q satisfy the following relationship: P = A / (n*f) - B / Q + C wherein A is between 1 and 120, B is between 1 and 100, C is between 0 and 0.05, and Q is greater than or equal to 1 L / min.

10. A crystalline silicon characterized in that, The crystalline silicon is prepared by the method of any one of claims 1 to 9 and has an oxygen content of less than or equal to 11 ppma.

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