Crystal pulling method for improving light boron-doped crystal BMD and monocrystalline silicon rod

Abstract

The invention provides a crystal pulling method for improving light boron-doped crystal BMD and a silicon single crystal rod, and belongs to the technical field of silicon single crystal pulling, crystal rod pulling is carried out in a predetermined thermal field to change the temperature gradient in the thermal field and increase the interval length of the BMD nucleation temperature, and in the crystal pulling process, the BMD nucleation temperature is increased. According to the present invention, the crystal rotation, the crucible rotation and the pulling speed are adjusted so as to improve the concentration and the distribution uniformity of the interstitial oxygen and the vacancy in the crystal bar, such that the concentration and the distribution uniformity of the interstitial oxygen and the vacancy in the crystal bar are pre-improved so as to provide sufficient raw materials for BMD nucleation, and then the temperature gradient in the thermal field is changed so as to increase the interval length of the BMD nucleation temperature, interstitial oxygen and vacancies are promoted to generate BMD, and then the BMD defect density in the light boron-doped crystal is remarkably improved through the synergistic effect of a preset thermal field, crystal transition, crucible transition and the pulling speed.

Description

Technical Field

[0001] This invention relates to the field of lightly doped single-crystal silicon crystal pulling technology, and particularly to a crystal pulling method and a single-crystal silicon rod for improving the boron-doped crystal molecular density (BMD). Background Technology

[0002] Bulk microdefects (BMDs) have a critical impact on the performance and reliability of logic chips. While logic chip manufacturing typically uses high-purity silicon substrates, trace amounts of metal contaminants can still be introduced during the process. These impurities can significantly degrade the electrical characteristics and long-term stability of the device. By forming high-density BMDs, metal impurities can be captured and immobilized within the silicon, thereby suppressing their migration within the substrate and mitigating their adverse effects on device performance.

[0003] In advanced process logic chips, the requirements for defect control in the near-surface region of the wafer are extremely stringent. Appropriate introduction of near-surface metal defects (BMDs) helps improve the yield of the final product. In lightly boron-doped substrate logic chips, maintaining a high BMD density is particularly important for improving the overall performance and reliability of the device, as BMDs can effectively adsorb rapidly diffusing metallic impurities on the wafer surface.

[0004] In existing technologies, silicon substrate fabrication companies typically control the formation of boron-doped substrates (BMDs) by optimizing process parameters to meet the requirements of logic chips on lightly boron-doped substrates. However, the control range of BMD formation by optimizing process parameters is limited, making it impossible for BMDs to meet the required range. Therefore, it is necessary to explore a crystal pulling method to improve the density of lightly boron-doped crystal BMDs. Summary of the Invention

[0005] In view of this, and to address the above shortcomings, it is necessary to propose a crystal pulling method for improving lightly boron-doped crystals (BMD) to significantly increase the density of BMD.

[0006] It is also necessary to provide a single-crystal silicon rod.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] On the one hand, the present invention provides a crystal pulling method for improving light boron-doped crystals (BMD). The crystal rod is pulled in a predetermined thermal field, and during the crystal pulling process, the crystal rotation, crucible rotation, and pulling speed are adjusted to increase the concentration and distribution uniformity of interstitial oxygen and vacancies in the crystal rod. At the same time, the length of the temperature range for the formation of BMD nucleation by interstitial oxygen and vacancies is increased, which increases the density of BMD nucleation and makes the BMD nucleation uniformly distributed in the crystal rod.

[0009] The temperature range for BMD nucleation is 700℃-1100℃.

[0010] Preferably, the predetermined hot field includes a quartz crucible, a heating component, a thermal insulation material, and a cooling component. The heating component is located at the bottom and side of the quartz crucible. The heating component located on the side of the quartz crucible is positioned between the quartz crucible and the thermal insulation material. The thermal insulation material is located circumferentially around the quartz crucible. The cooling component is located above the quartz crucible and overlaps the thermal insulation material. The cooling component includes an inner screen, an outer screen, and a thermal insulation material. The inner screen is fitted inside the outer screen. The thermal insulation material fills the lower part of the cavity formed by the inner screen and the outer screen to extend the temperature range of 700℃-1100℃ within the predetermined hot field.

[0011] Preferably, the upper edge of the heat shield insulation material is 5cm-10cm higher than the upper edge of the heating assembly located on the side of the quartz crucible.

[0012] Preferably, the longitudinal section of the heat shield insulation material is stepped, with the upper step located near the heating component located on the side of the quartz crucible. The upper edge of the upper step is 5cm-10cm higher than the upper edge of the heating component located on the side of the quartz crucible, and the width of the upper step is 40mm-60mm.

[0013] Preferably, the height between the upper step and the adjacent lower step is 50mm-70mm.

[0014] Preferably, during the crystal pulling process, the crystal rotation speed is 11-12 rpm, the crucible rotation speed is 1-3 rpm, and during the constant diameter process, the pulling speed is 1.1-1.0 mm / min.

[0015] Preferably, during the crystal pulling process, the crucible rotation remains stable from the initial stage of material preparation to the early stage of equal diameter, gradually increases from the early stage of equal diameter to the later stage of equal diameter, and gradually decreases from the later stage of equal diameter to the end of crystal pulling.

[0016] Preferably, the early stage of equal diameter refers to the stage where the equal diameter length is less than 1 / 5 of the crystal rod length, the later stage of equal diameter refers to the stage where the equal diameter length is greater than 4 / 5 of the crystal rod length, when the crucible rotation is stable, the crucible rotation is 2 rpm, the crucible rotation gradually increases refers to the crucible rotation increasing from 2 rpm to 3 rpm, and the crucible rotation gradually decreases refers to the crucible rotation decreasing from 3 rpm to 1 rpm.

[0017] Preferably, during the crystal pulling process, the crystal pulling parameters also include magnetic field strength, furnace pressure, and argon gas, wherein the magnetic field strength is 2500GS-3500GS, the furnace pressure is 4-5KPa, and the argon gas is 120-150slm.

[0018] On the other hand, the present invention provides a single-crystal silicon rod, which is pulled by the crystal pulling method described above for improving the light boron-doped crystal BMD.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This invention provides a crystal pulling method for improving the BMD (bond-doped metal) density of lightly boron-doped crystals. The method involves pulling a crystal rod in a predetermined thermal field to alter the temperature gradient within the field, increasing the range of BMD nucleation temperatures. During the pulling process, the crystal rotation, crucible rotation, and pulling speed are adjusted to improve the concentration and uniformity of interstitial oxygen and vacancies within the crystal rod. Therefore, this invention pre-increases the concentration and uniformity of interstitial oxygen and vacancies within the crystal rod to provide sufficient raw materials for BMD nucleation. Then, by altering the temperature gradient within the thermal field to increase the range of BMD nucleation temperatures, the method promotes the formation of BMD nuclei from interstitial oxygen and vacancies. Thus, the synergistic effect of the predetermined thermal field and the crystal rotation, crucible rotation, and pulling speed significantly improves the BMD defect density within the lightly boron-doped crystal. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the predetermined thermal field.

[0022] Figure 2 This is a schematic diagram of the thermal field structure in existing technology.

[0023] Figure 3 The image shows the BMD density distribution of the constant diameter portion of the crystal rod obtained in the embodiments, comparative examples 1, 2, and 3 of this invention.

[0024] In the figure: pre-designated hot zone 10, quartz crucible 100, heating component 200, bottom heater 210, side heater 220, thermal insulation material 300, cooling component 400, inner screen 410, outer screen 420, thermal insulation material 430. Detailed Implementation

[0025] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0026] This invention provides a crystal pulling method for improving light boron-doped crystals (BMD). The crystal rod is pulled in a predetermined thermal field 10. During the crystal pulling process, the crystal rotation, crucible rotation, and pulling speed are adjusted to increase the concentration and uniformity of interstitial oxygen and vacancies in the crystal rod. At the same time, the length of the temperature range for BMD nucleation by interstitial oxygen and vacancies is increased, which increases the density of BMD nucleation and makes the BMD nucleation uniformly distributed in the crystal rod.

[0027] The temperature range for BMD nucleation is 700℃-1100℃.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention provides a crystal pulling method for improving the BMD (Boron Defect Density) of lightly boron-doped crystals. The method involves pulling a crystal rod within a predetermined thermal field 10 to alter the temperature gradient within the thermal field, increasing the range of BMD nucleation temperatures. During the crystal pulling process, the crystal rotation, crucible rotation, and pulling speed are adjusted to improve the concentration and uniformity of interstitial oxygen and vacancies within the crystal rod. Therefore, this invention pre-increases the concentration and uniformity of interstitial oxygen and vacancies within the crystal rod to provide sufficient raw materials for BMD nucleation. Then, by altering the temperature gradient within the thermal field and increasing the range of BMD nucleation temperatures, the method promotes the formation of BMD nuclei from interstitial oxygen and vacancies. Consequently, the synergistic effect of the predetermined thermal field 10 and the crystal rotation, crucible rotation, and pulling speed significantly improves the BMD defect density within the lightly boron-doped crystal.

[0030] Please refer to Figure 1 In one optional embodiment, to reduce the temperature of the predetermined hot zone 10 and improve its temperature gradient, the predetermined hot zone 10 includes a quartz crucible 100, a heating component 200, a thermal insulation material 300, and a cooling component 400. The heating component 200 is located at the bottom and side of the quartz crucible 100. The heating component 200 located on the side of the quartz crucible 100 is positioned between the quartz crucible 100 and the thermal insulation material 300, which is circumferentially positioned. The cooling component 400 is located above the quartz crucible 100 and overlaps with the thermal insulation material 300. Above the thermal insulation material 300, the cooling component 400 includes an inner screen 410, an outer screen 420, and a thermal insulation material 430. The inner screen 410 is fitted inside the outer screen 420. The thermal insulation material 430 fills the lower part of the cavity formed by the inner screen 410 and the outer screen 420, so that the upper part of the cavity formed by the inner screen 410 and the outer screen 420 is hollow, reducing the temperature of the upper part of the predetermined hot field 10 of the single crystal furnace, thus extending the temperature range of 700℃-1100℃ in the hot field. During the process of the crystal rod moving upward from the silicon solution interface, the interstitial oxygen and vacancies in the crystal have sufficient time to form BMD nuclei, so that the density of BMD nuclei is significantly increased.

[0031] In one optional embodiment, the heating assembly 200 includes a bottom heater 210 and a side heater 220. The bottom heater 210 is located at the bottom of the quartz crucible 100, and the side heater 220 is located between the quartz crucible 100 and the heat insulation material to heat the quartz crucible 100. Since the inner screen 410 and the outer screen 420 are made of graphite, and the outer screen 420 is close to the side heater 220, in order to prevent the service life of the outer screen 420 from being shortened, the upper edge of the heat insulation material 430 is 5cm-10cm higher than the upper edge of the side heater 220 to insulate and protect the outer screen 420 and the inner screen 410, and to prevent high temperatures from affecting the service life of the outer screen 420 and the inner screen 410.

[0032] In one optional embodiment, in order to protect the service life of the outer screen 420 and the inner screen 410 from being affected, and to reduce the temperature as much as possible and extend the temperature range for forming the BMD core, the longitudinal section of the thermal insulation material 430 is stepped, with the upper step located near the side heater 220. The upper edge of the upper step is 5cm-10cm higher than the upper edge of the side heater 220, and the width of the upper step is 40mm-60mm. Preferably, there are two steps.

[0033] In one optional embodiment, the height between the upper step and the adjacent lower step is 50mm-70mm.

[0034] In one optional embodiment, during the crystal pulling process, to increase the concentration of interstitial oxygen, the crystal rotation is 11-12 rpm and the crucible rotation is 1-3 rpm; to increase the vacancy concentration, during the constant diameter process, the pulling speed is 1.1-1.0 mm / min; specifically, the crystal rotation remains stable, and the pulling speed gradually decreases during the constant diameter process. After crystal pulling is performed using a predetermined hot zone 10, the overall pulling speed is increased, the crystal pulling time is shortened, and the crystal pulling efficiency is improved.

[0035] In one optional embodiment, during the crystal pulling process, the crucible rotation remains stable from the initial stage of material preparation to the early stage of equal diameter, gradually increases from the early stage of equal diameter to the later stage of equal diameter, and gradually decreases from the later stage of equal diameter to the end of crystal pulling.

[0036] In one optional embodiment, the early stage of equal diameter refers to the stage where the equal diameter length is less than 1 / 5 of the crystal rod length, the later stage of equal diameter refers to the stage where the equal diameter length is greater than 4 / 5 of the crystal rod length, the crucible rotation is 2 rpm when the crucible rotation is stable, the crucible rotation gradually increases from 2 rpm to 3 rpm, and the crucible rotation gradually decreases from 3 rpm to 1 rpm.

[0037] In one optional embodiment, the crystal pulling process further includes magnetic field strength, furnace pressure, and argon gas. The magnetic field strength is 2500GS-3500GS, the furnace pressure is 4-5KPa, and the argon gas concentration is 120-150slm. Specifically, the magnetic field is a horizontal magnetic field. Based on the above crystal pulling parameters, the density of BMD is greatly improved, reaching a significant increase to 1.0E+9ea / cm. 3 The above are true, and the axial uniformity is excellent.

[0038] On the other hand, the present invention provides a single-crystal silicon rod, which is pulled by the crystal pulling method described above for improving the light boron-doped crystal BMD.

[0039] To further understand the present invention, the following examples of the method of the present invention and comparative examples of the conventional method demonstrate the pulling process of single crystal silicon and the detection results of BMD defect density formed by BMD nucleus growth after the same heat treatment.

[0040] Example:

[0041] Adopting such Figure 1 The predetermined hot field 10 is applied with a transverse magnetic field. A 12-inch lightly boron-doped single-crystal silicon rod is pulled using the Czochralski method (material preparation - stabilization - crystal pulling - shoulder formation - shoulder rotation - equal diameter - finishing - cooling). In the cooling assembly 400, the longitudinal section of the heat shield 430 is stepped and contains two steps. The width of the upper step is 50mm. The height of the cavity formed by the inner screen 410 and the outer screen 420 is 460mm. The height of the upper step is 180mm, and the height of the lower step is 120mm. The upper edge of the upper step is 5cm higher than the upper edge of the side heater 220. During the crystal pulling process, the magnetic field strength is 3000GS, the crystal rotation speed is 12rpm, and the furnace pressure is 4... The argon flow rate is 120 slm. During the stage from the initial material preparation to the point where the diameter is less than 1 / 5 of the crystal rod length, the crucible rotation speed remains constant at 2 rpm. From the stage where the diameter is 1 / 5 of the crystal rod length to the stage where the diameter is 4 / 5 of the crystal rod length, the crucible rotation speed increases from 2 rpm to 3 rpm. From the stage where the diameter is 4 / 5 of the crystal rod length until the end of crystal pulling, the crucible rotation speed decreases from 3 rpm to 1 rpm. The diameter pulling speed is 1.1-1.0 mm / min. After pulling the crystal rod using the above parameters, a boron-doped crystal rod is obtained. The boron-doped crystal rod is then subjected to roller milling, cutting, slicing, and heat treatment. The number of BMD defects on each silicon wafer is detected, and the BMD density distribution of the diameter portion of the boron-doped crystal rod is statistically analyzed and calculated. Figure 3 As shown.

[0042] Comparative Example 1:

[0043] Adopting such Figure 2The predetermined hot field 10, as shown, applies a transverse magnetic field, and a 12-inch lightly boron-doped single crystal silicon rod is pulled using the Czochralski method (material preparation - stabilization - crystal pulling - shoulder formation - shoulder rotation - equal diameter - finishing - cooling). In the cooling assembly 400, the heat shield insulation material 430 fills the cavity formed by the inner screen 410 and the outer screen 420. During the crystal pulling process, the magnetic field strength is 3000 GS, the crystal rotation speed is 8-9 rpm, the furnace pressure is 4 kPa, the argon gas flow rate is 120 slm, and the length from the material preparation to the equal diameter is... During the stage where the length is less than 1 / 5 of the crystal ingot, the crucible rotation speed remains stable at 0.5 rpm. From the stage where the constant diameter length is 1 / 5 of the crystal ingot length until the end of crystal pulling, the crucible rotation speed increases from 0.5 rpm to 1 rpm, and the constant diameter pulling speed is 0.9-0.7 mm / min. After pulling the crystal ingot using the above parameters, a boron-doped crystal ingot is obtained. The boron-doped crystal ingot is then subjected to roller milling, cutting, slicing, and heat treatment. The number of BMD defects on each silicon wafer is detected, and the BMD density distribution of the constant diameter portion of the boron-doped crystal ingot is statistically analyzed and calculated. Figure 3 As shown.

[0044] Comparative Example 2:

[0045] Adopting such Figure 2 The predetermined hot field 10, as shown, applies a transverse magnetic field, and a 12-inch lightly boron-doped single crystal silicon rod is pulled using the Czochralski method (material preparation - stabilization - crystal pulling - shoulder formation - shoulder rotation - equal diameter - finishing - cooling). In the cooling assembly 400, the heat shield insulation material 430 fills the cavity formed by the inner screen 410 and the outer screen 420. During the crystal pulling process, the magnetic field strength is 3000 GS, the crystal rotation is 12 rpm, the furnace pressure is 4 kPa, and the argon gas flow rate is 120 slm. During the stage from material preparation to the equal diameter stage where the length is less than 1 / 5 of the crystal rod length, the crucible rotation is maintained for 2 seconds. The pm remains constant. From the stage where the constant diameter length is 1 / 5 of the crystal rod length to the stage where the constant diameter length is 4 / 5 of the crystal rod length, the crucible rotation speed increases from 2 rpm to 3 rpm. From the stage where the constant diameter length is 4 / 5 of the crystal rod length until the end of crystal pulling, the crucible rotation speed decreases from 3 rpm to 1 rpm. The constant diameter pulling speed is 0.9-0.7 mm / min. After pulling the crystal rod using the above parameters, a boron-doped crystal rod is obtained. The boron-doped crystal rod is then subjected to roller milling, cutting, slicing, and heat treatment. The number of BMD defects on each silicon wafer is detected, and the BMD density distribution of the constant diameter portion of the boron-doped crystal rod is statistically analyzed and calculated. Figure 3 As shown.

[0046] Comparative Example 3:

[0047] Adopting such Figure 2The predetermined hot field 10, as shown, applies a transverse magnetic field, and a 12-inch lightly boron-doped single crystal silicon rod is pulled using the Czochralski method (material preparation - stabilization - crystal pulling - shoulder formation - shoulder rotation - equal diameter - finishing - cooling). In the cooling assembly 400, the heat shield insulation material 430 fills the cavity formed by the inner screen 410 and the outer screen 420. During the crystal pulling process, the magnetic field strength is 3000 GS, the crystal rotation is 12 rpm, the furnace pressure is 4 kPa, and the argon gas flow rate is 120 slm. During the stage from material preparation to the equal diameter stage where the length is less than 1 / 5 of the crystal rod length, the crucible rotation is maintained for 2 seconds. The pm remains constant. From the stage where the constant diameter length is 1 / 5 of the crystal rod length to the stage where the constant diameter length is 4 / 5 of the crystal rod length, the crucible rotation speed increases from 2 rpm to 3 rpm. From the stage where the constant diameter length is 4 / 5 of the crystal rod length until the end of crystal pulling, the crucible rotation speed decreases from 3 rpm to 1 rpm. The constant diameter pulling speed is 1.1-1.0 mm / min. After pulling the crystal rod using the above parameters, a boron-doped crystal rod is obtained. The boron-doped crystal rod is then subjected to roller milling, cutting, slicing, and heat treatment. The number of BMD defects on each silicon wafer is detected, and the BMD density distribution of the constant diameter portion of the boron-doped crystal rod is statistically analyzed and calculated. Figure 3 As shown.

[0048] Depend on Figure 3 It can be seen that the effect of BMD improvement in crystal is better in Example 1 of the present invention than in Comparative Example 3 (only adjusting crucible rotation, crystal rotation, and pulling speed), and the effect of Comparative Example 3 is better than in Comparative Example 2 (only adjusting crystal rotation and crucible rotation), and the effect of Comparative Example 2 is better than in Comparative Example 1 (traditional crystal pulling). As illustrated by Comparative Examples 1-3, adjusting crystal rotation, crucible rotation, and pulling speed can increase the density of BMD defects, but the increase is limited, and the uniformity of BMD defect density is not well improved. However, by improving the structure of the heat shield insulation material 430 and adjusting crystal rotation, crucible rotation, and pulling speed, the raw materials for BMD nucleation are increased while providing a longer time range for BMD nucleation temperature. As a result, the raw materials and nucleation driving force for BMD nucleation are sufficient, and the defect density of BMD is significantly improved.

[0049] The above comparisons fully demonstrate that the method of this application can not only increase the BMD defect density in lightly boron-doped single crystal silicon, but also improve the uniformity of its axial distribution. The high density and uniformity of BMD defects can effectively adsorb the rapidly diffusing metal impurities on the wafer surface, thereby providing a reliable guarantee for improving the performance and yield of the final device.

[0050] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A crystal pulling method for improving the boron density (BMD) of lightly boron-doped crystals, characterized in that, The crystal rod is pulled in a predetermined hot field. During the crystal pulling process, the crystal rotation, crucible rotation, and pulling speed are adjusted to increase the concentration and distribution uniformity of interstitial oxygen and vacancies in the crystal rod. At the same time, the length of the temperature range for BMD nucleation by interstitial oxygen and vacancies increases, which increases the density of BMD nucleation and makes the BMD nucleation uniformly distributed in the crystal rod. The temperature range for BMD nucleation is 700℃-1100℃.

2. The crystal pulling method for improving the boron-doped crystal (BMD) as described in claim 1, characterized in that, The predetermined hot field includes a quartz crucible, a heating component, a thermal insulation material, and a cooling component. The heating component is located at the bottom and side of the quartz crucible. The heating component located on the side of the quartz crucible is positioned between the quartz crucible and the thermal insulation material. The thermal insulation material is located circumferentially around the quartz crucible. The cooling component is located above the quartz crucible and overlaps the thermal insulation material. The cooling component includes an inner screen, an outer screen, and a thermal insulation material. The inner screen is fitted inside the outer screen. The thermal insulation material fills the lower part of the cavity formed by the inner screen and the outer screen to extend the temperature range of 700℃-1100℃ within the predetermined hot field.

3. The crystal pulling method for improving the BMD of lightly boron-doped crystals as described in claim 2, characterized in that, The upper edge of the heat shield insulation material is 5cm-10cm higher than the upper edge of the heating assembly located on the side of the quartz crucible.

4. The crystal pulling method for improving the BMD of lightly boron-doped crystals as described in claim 3, characterized in that, The longitudinal section of the heat shield insulation material is stepped, with the upper step located near the heating component located on the side of the quartz crucible. The upper edge of the upper step is 5cm-10cm higher than the upper edge of the heating component located on the side of the quartz crucible, and the width of the upper step is 40mm-60mm.

5. The crystal pulling method for improving the BMD of lightly boron-doped crystals as described in claim 4, characterized in that, The height between the upper step and the adjacent lower step is 50mm-70mm.

6. The crystal pulling method for improving the BMD of lightly boron-doped crystals as described in claim 1 or 2, characterized in that, During the crystal pulling process, the crystal rotation speed is 11-12 rpm, the crucible rotation speed is 1-3 rpm, and during the constant diameter process, the pulling speed is 1.1-1.0 mm / min.

7. The crystal pulling method for improving the boron-doped crystal (BMD) as described in claim 6, characterized in that, During the crystal pulling process, the crucible rotation remains stable from the initial stage of material preparation to the early stage of equal diameter. From the early stage of equal diameter to the later stage of equal diameter, the crucible rotation gradually increases. From the later stage of equal diameter to the end of crystal pulling, the crucible rotation gradually decreases.

8. The crystal pulling method for improving the boron-doped crystal (BMD) as described in claim 7, characterized in that, The term "early stage of equal diameter" refers to the stage where the equal diameter length is less than 1 / 5 of the crystal rod length, and the term "late stage of equal diameter" refers to the stage where the equal diameter length is greater than 4 / 5 of the crystal rod length. When the crucible rotation is stable, the crucible rotation is 2 rpm. The term "gradually increasing crucible rotation" refers to the crucible rotation increasing from 2 rpm to 3 rpm, and the term "gradually decreasing crucible rotation" refers to the crucible rotation decreasing from 3 rpm to 1 rpm.

9. The crystal pulling method for improving the BMD of lightly boron-doped crystals as described in claim 6, characterized in that, During the crystal pulling process, the crystal pulling parameters also include magnetic field strength, furnace pressure, and argon gas. The magnetic field strength is 2500GS-3500GS, the furnace pressure is 4-5KPa, and the argon gas is 120-150slm.

10. A single-crystal silicon rod, characterized in that, It is produced by crystal pulling method as described in any one of claims 1-9 for improving lightly boron-doped crystals (BMD).

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