Crystal pulling method for reducing internal porosity of large-size MCZ monocrystalline silicon
Through time-dividing material and variable magnetic field crystallization technology, the MCZ single crystal silicon production process is optimized, and the problem of high porosity of single crystal silicon is solved, and the porosity is significantly reduced.
Patent Information
- Application Number
- CN202510588976.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-08
- Publication Date
- 2025-08-01
AI Technical Summary
The porosity of the existing MCZ single crystal silicon is high, and bubbles are difficult to escape, resulting in a large porosity of the internal monocrystalline silicon.
The time-dividing materialization process is adopted to control the power of the main heater and the argon flow rate, and combined with the variable magnetic field crystallization technology, the materialization and stability process are optimized, and bubble dissipation is increased, and bubble generation and diffusion in the melt are reduced.
The porosity inside the single crystal silicon is effectively reduced from 1.19% to 0.53%.
Smart Images
Figure CN120400976A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of single crystal silicon production, and specifically to a crystal pulling method for reducing the internal porosity of large-size MCZ single crystal silicon. Background Art
[0002] MCZ is based on the traditional CZ method. A magnetic field is applied to the silicon melt, and the Lorentz force generated by the magnetic field and the melt is used to suppress the melt convection to achieve the growth of high-quality crystalline silicon. That is, MCZ is a process of crystal pulling using a magnetic field and is the main method for pulling large-size single crystals in the industry. However, although applying a magnetic field suppresses the melt convection and ensures the smoothness of the crystal growth interface, it increases the magnetic viscosity of the melt and slows down the escape of impurities and bubbles inside the melt. Figure 3 and Figure 4 is the transmission path of SiO generated by the reaction of molten silicon and quartz crucible during crystal pulling. The combination of oxygen and vacancy V2O moves along this transport path, and the aggregation of vacancies will cause small pores; after the reaction of molten silicon and quartz crucible, the bubbles inside the quartz crucible overflow or other impurities overflow and gasify at high temperature to form bubbles, and the bubbles will also move along this transport path; after the polysilicon melts, the gas inclusions inside the polysilicon will also overflow into the melt to form bubbles. The bubbles generated in the above process are not easy to escape and remain in the crystal bar during the crystal bar growth process, increasing the porosity of the single crystal silicon. Summary of the Invention
[0003] [[ID=1�]]In order to solve the problem of large porosity of single crystal silicon in the prior art, the present invention provides a crystal pulling method for reducing the internal porosity of large-size MCZ single crystal silicon, which reduces the generation of bubbles in the melt, increases the escape of bubbles at the same time, and reduces the internal porosity of the single crystal silicon.
[0004] To achieve the above object, the specific solution adopted by the present invention is as follows: A crystal pulling method for reducing the internal porosity of large-size MCZ single crystal silicon, including a charging process, a material melting process, a stabilizing process, a seed crystal introducing process, a shoulder releasing process, a shoulder turning process, an equal diameter process and a tailing process. The material melting process is a staged material melting process, including a fixed crucible material melting stage and a moving and rotating material melting stage; during the fixed crucible material melting stage, the crucible position is 120 - 150 mm, the power of the main heater is increased to 85 - 90 kw at a rate of 2 - 3 kw / min, the argon gas flow rate is 80 - 120 slpm, the furnace pressure is 0 - 10 torr, and the power of the bottom heater is adjusted to 10 - 15 kw; during the moving and rotating material melting stage, the crucible starts to move downward at a speed of 20 - 30 mm / h and rotates at a speed of 1 - 2 rpm.
[0005] As an optimization scheme of the crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon mentioned above: after the material melting process is completed, adjust the power of the main heater to the power of the main heater in the seed crystal pulling process ±5 kw, adjust the crucible to rotate at a speed of 8 - 10 rpm, and raise it at a rate of 50 - 60 mm / h for 1.5 h, then raise it at a rate lower than 10 mm / h until the stable crucible position; the thermal shield starts to move downward by 50 mm every 20 - 30 min until it is lowered to the thermal shield 0 position.
[0006] As another optimization scheme of the crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon mentioned above: during the stabilization process, the distance between the liquid surface and the crucible bottom is 15 - 25 mm, and the magnetic field intensity is 1000 GS.
[0007] As another optimization scheme of the crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon mentioned above: during the loading process, use lump materials with a diameter of 45 - 90 mm.
[0008] As another optimization scheme of the crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon mentioned above: during the loading process, the lump materials are in contact with the surface of the crucible, and the diameter of the lump materials at the edge of the crucible is 70 - 90 mm.
[0009] As another optimization scheme of the crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon mentioned above: when pulling 8-inch single-crystalline silicon, the material melting process takes 8 - 9 h.
[0010] As another optimization scheme of the crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon mentioned above: the time used for the crucible positioning and material melting stage is 1 / 4 - 1 / 3 of the time used for the material melting process.
[0011] As another optimization scheme of the crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon mentioned above: during the crucible positioning and material melting stage, the power of the main heater increases to 85 kw at a rate of 2 - 3 kw / min, the argon gas flow rate is 100 - 1 of the time used for the material melting process.
[0012] As another optimization scheme of the crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon mentioned above: during the moving and rotating material melting stage, the crucible first moves downward at a speed of 20 mm / h for 1.5 h, and then moves downward at a speed of 30 mm / h until the material melting is completed.
[0013] As another optimization solution for the crystal pulling method of reducing the porosity inside large-size MCZ single-crystalline silicon: in the seed crystal process, shoulder formation process, shoulder turning process, constant diameter process, and finishing process, during the seed crystal process, shoulder formation process, shoulder turning process, and the head part of the constant diameter process, the magnetic field intensity increases from 1000 GS to 3000 - 4000 GS; during the middle part of the constant diameter process, the tail part of the constant diameter process, and the finishing process, the magnetic field intensity is 3000 - 4000 GS.
[0014] Compared with the prior art, the present invention has the following beneficial effects:
[0015] 1. The present invention provides a crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon. The charge is divided into periods to reduce the generation of bubbles, and the porosity inside the single-crystalline silicon is reduced to 1.19%.
[0016] 2. In the present invention, the bubble dissipation process is added and the stabilization process is adjusted to increase the dissipation of bubbles, and further reduce the porosity inside the single-crystalline silicon to 0.53%. Description of the Drawings
[0017] Figure 1 It is a schematic diagram of the quartz crucible after loading;
[0018] Figure 2 It is a physical diagram after loading;
[0019] Figure 3 It is the oxygen distribution and transmission path in the quartz crucible melt;
[0020] Figure 4 It is the temperature distribution and transmission path in the quartz crucible melt;
[0021] Figure 5 It is the initial treatment of the crucible in the charge melting process;
[0022] Figure 6 It is a schematic diagram of the argon gas flow direction during the crystal pulling process;
[0023] Figure 7 It is a schematic diagram of the argon gas flow direction and pressure distribution during the crystal pulling process. Detailed Embodiments
[0024] The following further elaborates on the technical solutions of the present invention in combination with specific embodiments. For parts not detailedly recorded and disclosed in the following embodiments of the present invention, they should all be understood as the prior art known or should be known to those skilled in the art.
[0025] In the prior art, there is also a method of reducing the porosity in the magnetic-controlled crystal pulling process by increasing the power of the main heater and decreasing the power of the bottom heater. However, this method does not consider the possible "bridging" phenomenon during the material melting process. This phenomenon will increase the duration of the high-temperature molten material. In addition, the sudden collapse of the "bridge" causes the material block to fall, and the falling of the material block will carry the inner wall of the quartz crucible, thereby causing bubbles to enter the melt and increasing the porosity inside the single crystal silicon.
[0026] A crystal pulling method for reducing the porosity inside large-size MCZ single crystal silicon includes a charging process, a material melting process, a stabilizing process, a seed crystal introducing process, a shoulder forming process, a shoulder turning process, an equal diameter process, and a finishing process.
[0027] In the charging process, polycrystalline lump materials with a diameter of 45 - 90 mm are used. The polycrystalline lump materials are in a broken and formed state, with irregular surfaces and edges. If the diameter of the polycrystalline lump materials is too small, their specific surface area is relatively large, and it is easy for the lump materials to adhere to each other, resulting in the problem of material block overlap. During the charging process, first spread the polycrystalline lump materials flat on the bottom of the quartz crucible, and then place the materials layer by layer to provide support for the subsequent polycrystalline lump materials, avoiding bottom sliding caused by subsequent charging, and thus preventing the polycrystalline lump materials from rubbing against the quartz crucible; at the same time, avoid the sharp point contact between the polycrystalline lump materials and the side wall of the quartz crucible, thereby avoiding scratching of the quartz crucible by the sharp points during the material collapse process. When reaching the upper part of the R corner of the quartz crucible, the polycrystalline lump materials are in surface contact with the quartz crucible; in the later stage of the charging process, select polycrystalline lump materials with a diameter of 70 - 90 mm at the edge of the quartz crucible, and it is prohibited to exceed the outer diameter of the upper edge of the quartz crucible to avoid adhesion between the lump materials and the quartz crucible during the material melting process.
[0028] The material melting process is a time-segmented material melting process. The material melting time is set according to a material melting rate of 15 ± 1.5 kg / h. The material melting process includes a fixed crucible material melting stage and a moving and rotating material melting stage. Among them, the time used in the fixed crucible material melting stage is 1 / 4 - 1 / 3 of the time used in the material melting process. During the fixed crucible material melting stage, the bottom of the crucible is located at the center position of the heater, that is, high crucible position material melting is adopted. The crucible position refers to the distance between the upper edge of the graphite crucible and the upper edge of the heater. This place is called the initial material melting position, ensuring that the bottom polycrystalline lump materials are in the high-efficiency heating area at the center of the main heater, so that the bottom polycrystalline lump materials first melt, and then gradually collapse downward; at the same time, maintain a large longitudinal temperature gradient in the quartz crucible, which is beneficial to the escape of bubbles.
[0029] During the fixed crucible material melting stage, the power of the main heater is increased to 85 - 90 kw at a rate of 2 - 3 kw / min. If the power of the main heater increases too fast, it will not only cause the reaction between the polycrystalline lump materials and the quartz crucible to intensify, but also cause uneven heating inside and outside the quartz crucible, resulting in the expansion of bubbles outside the quartz crucible being greater than that of the inner transparent layer, and finally causing the bubbles to diffuse inward. Therefore, control the rate of increase of the power of the main heater to avoid the diffusion of bubbles into the melt, thereby reducing the bubbles in the melt and finally reducing the porosity inside the crystal bar.
[0030] During the crucible melting stage, the argon flow rate is 80 - 120 slpm and the furnace pressure is 0 - 10 torr, which is beneficial to the escape of impurities and bubbles inside the melt, and can quickly carry away the impurities and bubbles volatilized to the melt surface.
[0031] After 1 / 4 - 1 / 3 of the time from the start of melting to the end of melting, the moving and rotating melting stage is carried out. During the moving and rotating melting stage, the crucible starts to move downward at a speed of 20 - 30 mm / h and rotates at a speed of 1 - 2 rpm. The power of the bottom heater is adjusted to 10 - 15 kw to ensure that the bottom of the quartz crucible is not supercooled, so as to generate longitudinal convection to facilitate the transmission of bubbles; at the same time, ensure the temperature stability of the whole melting process to avoid recrystallization after the polycrystalline material block at the bottom melts and react with the bottom of the quartz crucible again to generate bubbles.
[0032] After the melting process is completed, the bubble escape process is carried out. The power of the main heater is adjusted to the power of the main heater in the seeding process ±5 kw. The crucible rotates at a speed of 8 - 10 rpm and quickly rises at a rate of 50 - 60 mm / h for 1.5 h, and then rises at a speed lower than 10 mm / h to the stable crucible position. At the same time, the heat shield starts to move downward by 50 mm every 20 - 30 min until it is lowered to the heat shield 0 position to reach the liquid level distance required for the stable process. This bubble escape process takes 2 - 3 h, the argon flow rate is 80 - 120 slpm, and the furnace pressure is 0 - 10 torr, which is conducive to the volatilization of bubbles and impurities and the removal by the high argon flow rate; the purpose of lowering the heat shield is to facilitate the stability of the melt temperature. At the same time, it reduces the argon channel formed between the heat shield and the melt, and plays a synergistic role with the increase in the crucible rotation speed to increase bubble escape.
[0033] In the stable process, the liquid level distance is 15 - 25 mm, the magnetic field strength is 1000 GS, the argon flow rate is 80 - 120 slpm, and the furnace pressure is 0 - 10 torr, so that the upper part of the melt surface is in a high flow rate and low pressure state, and the Venturi effect is used to carry away more impurity volatiles and bubbles.
[0034] In the seeding process, shoulder forming process, shoulder turning process, equal diameter process and finishing process, variable magnetic field crystal pulling is adopted. Among them, during the seeding process, shoulder forming process, shoulder turning process and the first 150 mm of the equal diameter process, the magnetic field strength gradually increases from 1000 GS to 3000 - 4000 GS. In the middle part of the equal diameter process, the tail part of the equal diameter process and the finishing process, the magnetic field strength is 3000 - 4000 GS; other process parameters are those of the prior art and will not be elaborated here.
[0035] Example 1
[0036] A crystal pulling method for reducing the internal porosity of large-size MCZ single crystal silicon includes the following steps:
[0037] In the charging process, polycrystalline ingots with a diameter of 45 - 90 mm are used, and the charging amount in the crucible is 140 kg. During the charging process, the polycrystalline ingots are first laid flat on the bottom of the quartz crucible, and then stacked layer by layer. When at the upper part of the R corner of the quartz crucible, the polycrystalline ingots are in contact with the surface of the quartz crucible. In the later stage of the charging process, polycrystalline ingots with a diameter of 70 - 90 mm are selected and placed at the edge of the quartz crucible, and it is prohibited to exceed the upper outer edge of the quartz crucible.
[0038] The melting time of the melting process is 8 h. Among them, in the fixed crucible melting stage: the bottom of the crucible is located at the center position of the heater, the crucible position is 120 mm, the power of the main heater increases to 85 kw at a rate of 3 kw / min, the power of the bottom heater is 12 kw, the argon flow rate is 100 - 120 slpm, and the furnace pressure is 8 - 10 torr. The fixed crucible melting stage takes 2.5 h.
[0039] In the moving and rotating melting stage, the crucible first descends at a speed of 20 mm / h for 1.5 h, and then descends at a speed of 30 mm / h until the melting is completed. During the entire moving and rotating melting stage, the crucible rotates at a speed of 1 rpm.
[0040] In the processes of crystal pulling, shoulder releasing, shoulder turning, equal diameter growth, and end finishing, variable magnetic field crystal pulling is adopted. Among them, during the processes of crystal pulling, shoulder releasing, shoulder turning, and the first 150 mm of equal diameter growth, the magnetic field intensity gradually increases from 1000 GS to 4000 GS. In the middle part of equal diameter growth, the tail part of equal diameter growth, and the end finishing process, the magnetic field intensity is 4000 GS; other process parameters are those of the existing technology and will not be elaborated here.
[0041] The internal porosity of the single crystal silicon obtained by the above method is 1.19%.
[0042] Example 2
[0043] A crystal pulling method for reducing the internal porosity of large - size MCZ single crystal silicon, comprising the following steps:
[0044] In the charging process, polycrystalline ingots with a diameter of 45 - 90 mm are used, and the charging amount in the crucible is 140 kg. During the charging process, the polycrystalline ingots are first laid flat on the bottom of the quartz crucible, and then stacked layer by layer. When at the upper part of the R corner of the quartz crucible, the polycrystalline ingots are in contact with the surface of the quartz crucible. In the later stage of the charging process, polycrystalline ingots with a diameter of 70 - 90 mm are selected and placed at the edge of the quartz crucible, and it is prohibited to exceed the upper outer edge of the quartz crucible.
[0045] The melting time of the melting process is 9 h. Among them, in the fixed crucible melting stage: the bottom of the crucible is located at the center position of the heater, the crucible position is 150 mm, the power of the main heater increases to 90 kw at a rate of 2 kw / h, the power of the bottom heater is 15 kw, the argon flow rate is 80 - 100 slpm, and the furnace pressure is 0 - 5 torr. The fixed crucible melting stage takes 2.5 h.
[0046] Move back to the charge melting stage. First, the crucible descends at a speed of 20 mm / h for 1.5 h, and then descends at a speed of 30 mm / h until the charge melting is completed. During the whole moving back and charge melting stage, the crucible rotates at a speed of 2 rpm.
[0047] During the crystal seeding process, shoulder broadening process, shoulder turning process, equal diameter process and ending process, variable magnetic field crystal pulling is adopted. Among them, during the crystal seeding process, shoulder broadening process, shoulder turning process and the first 150 mm of the equal diameter process, the magnetic field intensity gradually increases from 1000 GS to 3000 GS. During the middle part of the equal diameter process, the tail part of the equal diameter process and the ending process, the magnetic field intensity is 3000 GS. Other process parameters are those of the prior art and will not be elaborated here.
[0048] The internal porosity of the single crystal silicon obtained by the above method is 1.20%.
[0049] Example 3
[0050] A crystal pulling method for reducing the internal porosity of large-size MCZ single crystal silicon, comprising the following steps:
[0051] In the loading process, polycrystalline ingots with a diameter of 45 - 90 mm are used, and the loading amount of the crucible is 140 kg. During the loading process, first spread the polycrystalline ingots flat on the bottom of the quartz crucible, and then stack the materials layer by layer. When at the upper part of the R corner of the quartz crucible, the polycrystalline ingots are in contact with the surface of the quartz crucible. In the later stage of the loading process, select polycrystalline ingots with a diameter of 70 - 90 mm at the edge of the quartz crucible, and it is prohibited to exceed the upper outer edge of the quartz crucible.
[0052] The melting time of the charge melting process is 8 h. Among them, in the fixed crucible charge melting stage: the bottom of the crucible is located at the center position of the heater, the crucible position is 130 mm, the power of the main heater increases to 92 kw at a rate of 2.5 kw / h, the power of the bottom heater is 14 kw, the argon flow rate is 100 - 120 slpm, and the furnace pressure is 8 - 10 torr. The fixed crucible charge melting stage takes 2.5 h.
[0053] In the moving back and charge melting stage, the crucible descends at a speed of 25 mm / h until the charge melting is completed. During the whole moving back and charge melting stage, the crucible rotates at a speed of 1.5 rpm.
[0054] During the crystal seeding process, shoulder broadening process, shoulder turning process, equal diameter process and ending process, variable magnetic field crystal pulling is adopted. Among them, during the crystal seeding process, shoulder broadening process, shoulder turning process and the first 150 mm of the equal diameter process, the magnetic field intensity gradually increases from 1000 GS to 4000 GS. During the middle part of the equal diameter process, the tail part of the equal diameter process and the ending process, the magnetic field intensity is 4000 GS. Other process parameters are those of the prior art and will not be elaborated here.
[0055] The internal porosity of the single crystal silicon obtained by the above method is 1.19%.
[0056] Example 4
[0057] A crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon, comprising the following steps:
[0058] In the charging process, polycrystalline lump materials with a diameter of 45 - 90 mm are used, and the charging amount of the crucible is 140 kg. During the charging process, the polycrystalline lump materials are first laid flat on the bottom of the quartz crucible, and then the materials are placed layer by layer. When at the upper part of the R corner of the quartz crucible, the polycrystalline lump materials are in contact with the surface of the quartz crucible; in the later stage of the charging process, polycrystalline lump materials with a diameter of 70 - 90 mm are selected to be located at the edge of the quartz crucible, and it is prohibited to exceed the upper outer edge of the quartz crucible.
[0059] The melting time of the melting process is 8 h. Among them, in the fixed crucible melting stage: the bottom of the crucible is located at the central position of the heater, the crucible position is 120 mm, the power of the main heater is increased to 85 kw at a rate of 2 kw / min, the power of the bottom heater is 10 kw, the argon flow rate is 100 - 120 slpm, the furnace pressure is 8 - 10 torr, and the fixed crucible melting stage takes 2.5 h.
[0060] In the moving and rotating melting stage, the crucible first descends at a speed of 20 mm / h for 1.5 h, and then descends at a speed of 30 mm / h until the melting is completed. During the whole moving and rotating melting stage, the crucible rotates at a speed of 1 rpm.
[0061] After the melting process is completed, a bubble dissipation process is carried out. The power of the main heater is adjusted to 55 kw, the crucible is adjusted to rotate at a speed of 8 rpm, and it rises rapidly at a rate of 50 - 60 mm / h for 1.5 h, and then the rate is reduced to 8 mm / h for slow rising to the stable crucible position. The thermal shield starts to move downward by 50 mm every 30 min until it is lowered to the 0 position of the thermal shield. This bubble dissipation process takes 2 h, the argon flow rate is 100 slpm, and the furnace pressure is 5 - 8 torr.
[0062] In the stabilization process, the distance from the liquid level to the crucible bottom is 15 - 25 mm, the magnetic field strength is 4000 GS, the argon flow rate is 80 - 120 slpm, and the furnace pressure is 0 - 10 torr.
[0063] In the seed crystal pulling process, shoulder releasing process, shoulder turning process, equal diameter process and ending process, variable magnetic field crystal pulling is adopted. Among them, during the seed crystal pulling process, shoulder releasing process, shoulder turning process and the first 150 mm of the equal diameter process, the magnetic field strength gradually increases from 1000 GS to 4000 GS. In the middle part of the equal diameter process, the tail part of the equal diameter process and the ending process, the magnetic field strength is 4000 GS; other process parameters are those of the prior art and will not be elaborated here.
[0064] The porosity inside the single-crystalline silicon obtained by the above method is 0.53%.
[0065] Pull single-crystalline silicon separately using the methods described in the above-mentioned Embodiment 1 and Embodiment 4. The total number of single-crystalline silicon wafers and the number of wafers with pore defects obtained are shown in Table 1.
[0066] Table 1 Total number of wafers Number of wafers with pore defects Porosity Example 1 2093 25 1.19％ Example 2 1833 22 1.20％ Example 3 1345 16 1.19％ Example 4 5459 29 0.53％
[0067] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.
Claims
1. A crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon, comprising a charging process, a material melting process, a stabilization process, a seed crystal introducing process, a shoulder releasing process, a shoulder turning process, an equal diameter process and a finishing process, characterized in that: The material melting process is carried out in time segments, including the fixed crucible material melting stage and the moving and rotating material melting stage; during the fixed crucible material melting stage, the crucible position is 120 - 150 mm, the power of the main heater increases at a rate of 2 - 3 kw / min to 85 - 90 kw, the argon gas flow rate is 80 - 120 slpm, the furnace pressure is 0 - 10 torr, and the power of the bottom heater is adjusted to 10 - 15 kw; during the moving and rotating material melting stage, the crucible starts to move downward at a speed of 20 - 30 mm / h and rotates at a speed of 1 - 2 rpm.
2. The crystal pulling method for reducing the porosity inside large-size MCZ single crystal silicon according to claim 1, characterized in that: After the material melting process is completed, adjust the power of the main heater to the power of the main heater in the crystal pulling process ±5 kw, adjust the crucible to rotate at a speed of 8 - 10 rpm, and raise it at a rate of 50 - 60 mm / h for 1.5 h, and then continue to rise at a rate of less than 10 mm / h to the stable crucible position; the thermal shield starts to move downward by 50 mm every 20 - 30 min until it is lowered to the thermal shield 0 position.
3. The crystal pulling method for reducing the porosity inside large-size MCZ single crystal silicon according to claim 1, characterized in that: During the stabilization process, the distance from the liquid outlet is 15 - 25 mm, and the magnetic field strength is 1000 GS.
4. A crystal pulling method for reducing the porosity inside large-size MCZ single crystal silicon as described in claim 1, characterized in that: During the loading process, lumps with a diameter of 45 - 90 mm are used.
5. The crystal pulling method for reducing the porosity inside large-size MCZ single crystal silicon according to claim 4, characterized in that: During the loading process, the lumps are in contact with the surface of the crucible, and the diameter of the lumps at the edge of the crucible is 70 - 90 mm.
6. The crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon according to claim 1, characterized in that: When pulling 8-inch single crystal silicon, the material melting process takes 8 - 9 h.
7. The crystal pulling method for reducing the porosity inside large-size MCZ single crystal silicon according to claim 1, wherein: The time used in the fixed crucible material melting stage is 1 / 4 - 1 / 3 of the time used in the material melting process.
8. A crystal pulling method for reducing the porosity inside large-size MCZ single crystal silicon as described in claim 1, characterized in that: During the fixed crucible material melting stage, the power of the main heater increases at a rate of 2 - 3 kw / min to 85 kw, the argon gas flow rate is 100 - 120 slpm, and the furnace pressure is 8 - 10 torr.
9. A crystal pulling method for reducing the porosity inside large-size MCZ single-crystalline silicon as described in claim 1, characterized in that: During the moving and rotating material melting stage, the crucible first moves downward at a speed of 20 mm / h for 1.5 h, and then moves downward at a speed of 30 mm / h until the material melting is completed.
10. The crystal pulling method for reducing the porosity inside large-size MCZ single crystal silicon as described in claim 1, characterized in that: During the crystal pulling process, shoulder forming process, shoulder turning process, constant diameter process and end process, during the crystal pulling process, shoulder forming process, shoulder turning process and the head part of the constant diameter process, the magnetic field strength increases from 1000 GS to 3000 - 4000 GS, and during the middle part of the constant diameter process, the tail part of the constant diameter process and the end process, the magnetic field strength is 3000 - 4000 GS.