Crystal pulling method to improve the in-plane VF value uniformity of 111 crystal orientation devices

Abstract

A crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices includes: when pulling a heavily doped single-crystal silicon rod, when the rod enters the constant diameter stage, adjusting the Gap value according to a first predetermined constant diameter length; the first predetermined constant diameter length includes a first predetermined length, a first second predetermined length, and a first third predetermined length; within the first predetermined length, keeping the first Gap value constant; within the first second predetermined length, decreasing the first Gap value to a second Gap value at a linear rate; within the first third predetermined length, keeping the second Gap value constant; the first Gap value is 25-30 mm; and the second Gap value is 20 mm.

Description

Technical Field

[0001] This invention relates to the field of monocrystalline silicon manufacturing technology, and in particular to a crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices. Background Technology

[0002] The crystal orientation of a crystal affects its physical properties; different crystal orientations result in different carrier mobilities. Since the hole mobility is typically higher in the 111 crystal orientation, 111-oriented single-crystal silicon is preferred as the substrate material for devices whose conduction mechanism relies on hole movement, such as fast recovery diodes, thyristors, and tunneling field-effect transistors. In these 111-oriented semiconductor devices, the forward voltage (VF) is a key performance indicator in the on-state, playing a decisive role in the device's conduction losses and heat generation. If the VF value distribution within a single device plane is non-uniform, then when a large current flows through, the current density in the region with the lower VF value will be higher. The higher current density causes the local junction temperature in that region to rise more quickly, and the increased temperature further reduces the VF value, thereby attracting more current to that region. This process forms a positive feedback loop of "hot spot" or "current accumulation." Consequently, the temperature in the region with the lower VF value may far exceed the device's stable temperature, ultimately leading to the following consequences: 1. Local overheating accelerates aging; 2. Local high temperature causes a surge in intrinsic carrier concentration, which may reduce the breakdown voltage in that region, making it more prone to local breakdown when subjected to high voltage during turn-off; 3. In the most extreme case, the positive feedback cannot be stopped, causing the device to melt in that region. Therefore, the uniformity of the VF value within the plane of a 111 crystal orientation semiconductor device is crucial to its performance, reliability, and safety.

[0003] The factors affecting the in-plane VF value uniformity of 111-oriented semiconductor devices mainly come from three aspects: the quality of the substrate ingot, the thickness and doping uniformity of the epitaxial layer during device manufacturing, and the symmetry of packaging stress and heat dissipation during the packaging stage. Among these, since the substrate ingot is the foundation of device manufacturing and packaging, its quality is key to improving the in-plane VF value uniformity of 111-oriented devices. During the pulling process of the 111-oriented ingot, the stability of the thermal field has a crucial impact on the ingot's growth process and final quality. In the existing technology, on the one hand, the gap value during the equal diameter process, that is, the distance from the thermal shield opening to the solid-liquid interface, varies greatly from the beginning to the end of the equal diameter process. On the other hand, the equal diameter temperature compensation value during the equal diameter process is larger in the early stage and the duration of the compensation is longer, that is, the period when the equal diameter temperature compensation value is less than 0℃ lasts for a long time. In the later stage, the equal diameter temperature compensation value is greater than 0℃, and the total equal diameter temperature compensation value is larger throughout the entire equal diameter process. These factors all affect the stability of the thermal field, and thus affect the quality of the 111 crystal orientation crystal rod. Summary of the Invention

[0004] In view of this, it is necessary to provide a crystal pulling method to improve the in-plane VF value uniformity of 111 crystal orientation devices, so as to solve one of the above-mentioned deficiencies, thereby improving the thermal field stability during the pulling process of 111 crystal orientation ingots, improving the in-plane VF value uniformity of 111 crystal orientation devices, and improving the performance, reliability and safety of 111 crystal orientation devices.

[0005] A crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices includes: when pulling a heavily doped single crystal silicon rod, adjusting the Gap value according to a first predetermined equal diameter length when the rod enters the equal diameter stage;

[0006] The first predetermined equal diameter length includes a first predetermined length, a first second predetermined length, and a first third predetermined length; within the first predetermined length, the first gap value is kept constant; within the first second predetermined length, the first gap value decreases to the second gap value at a linear rate; within the first third predetermined length, the second gap value is kept constant; the first gap value is 25-30 mm; the second gap value is 20 mm.

[0007] Preferably, it further includes: when the crystal rod enters the constant diameter stage, adjusting the constant diameter temperature compensation value according to the second predetermined constant diameter length.

[0008] Preferably, the first predetermined length is 10% of the length from the crystal rod equal diameter to the overall equal diameter.

[0009] Preferably, the first and second predetermined lengths start from 10% of the length from the crystal rod equal diameter to the overall equal diameter and end at 90% of the length from the crystal rod equal diameter to the overall equal diameter.

[0010] Preferably, the first and third predetermined lengths begin from 90% of the length of the crystal rod equal in diameter to the overall equal in diameter length and end at the crystal rod equal in diameter.

[0011] Preferably, the second predetermined constant diameter length includes a second first predetermined length, a second second predetermined length, and a second third predetermined length; within the second first predetermined length, the constant diameter temperature compensation value is negative and gradually increases to 0℃; within the second second predetermined length, the constant diameter temperature compensation value is constant at 0℃; within the second third predetermined length, the constant diameter temperature compensation value is positive and gradually increases from 0℃; within the second first predetermined length, the sum of the constant diameter temperature compensation values ​​ranges from -8 to -10℃; within the second third predetermined length, the sum of the constant diameter temperature compensation values ​​is 46 to 48℃.

[0012] Preferably, the sum of the constant diameter temperature compensation values ​​within the second predetermined length, the second predetermined length, and the third predetermined length is 30-41℃.

[0013] Preferably, the second predetermined length is 5%-6% of the length from the start of the crystal rod's equal diameter to the overall equal diameter.

[0014] Preferably, the second predetermined length is 10%-11% of the length from the end of the second predetermined length to the length from the crystal rod to the overall equal diameter.

[0015] Preferably, the second and third predetermined lengths start from the end of the second and second predetermined lengths and end at the end of the equal diameter.

[0016] The aforementioned crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices adjusts the Gap value according to a first predetermined equal-diameter length during the equal-diameter stage, causing the Gap value to change with the equal-diameter length during the equal-diameter process. Within the first predetermined length, the first Gap value remains constant; within the first second predetermined length, the first Gap value decreases to a second Gap value at a linear rate; within the first third predetermined length, the second Gap value remains constant; the first Gap value is 25-30 mm; the second Gap value is 20 mm. Compared with existing technologies, reducing the first Gap value results in a smaller longitudinal space of the thermal field in the crystal growth region during crystal pulling, bringing the crystal closer to the cooling region at the top of the thermal field. The resulting effect is: on the one hand, the radial temperature and axial temperature of the crystal growth region are reduced. The more uniform temperature distribution in the 111 crystal orientation makes the thermal field in the crystal growth region more stable, suppressing the "small facets" during the growth process. The axial temperature gradient of the entire thermal field increases, and the supercooling of the solid-liquid interface increases. Under the combined influence of radial and axial temperature changes, the solid-liquid interface of the crystal growth is flatter. On the other hand, the solid-liquid interface closer to the top of the thermal field makes the melt convection more stable, and the impurity segregation in the small facet region and the non-small facet region is more consistent. The combination of these two aspects makes the radial resistivity change rate RRG smaller during the 111 crystal orientation growth process, improving the quality of the 111 crystal orientation ingot, thereby improving the uniformity of the in-plane VF value of the 111 crystal orientation device, and improving the performance, reliability and safety of the 111 crystal orientation device. Attached Figure Description

[0017] Figure 1 This is the VF value distribution within the surface of the device in Comparative Example 1 of this invention.

[0018] Figure 2 This is the distribution of VF values ​​within the device plane in Embodiment 1 of the present invention.

[0019] Figure 3 This is the distribution of VF values ​​within the device plane in Embodiment 2 of the present invention.

[0020] Figure 4 This is the VF value distribution within the device plane in Embodiment 3 of the present invention.

[0021] Figure 5This is the VF value distribution within the surface of the device in Comparative Example 2 of this invention.

[0022] Figure 6 This is the distribution of VF values ​​within the device plane in Embodiment 4 of the present invention. Detailed Implementation

[0023] The technical solutions and effects of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0024] A crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices includes: when pulling a heavily doped single crystal silicon rod, adjusting the Gap value according to a first predetermined equal diameter length when the rod enters the equal diameter stage;

[0025] The first predetermined equal diameter length includes a first predetermined length, a first second predetermined length, and a first third predetermined length; within the first predetermined length, the first gap value is kept constant; within the first second predetermined length, the first gap value decreases to the second gap value at a linear rate; within the first third predetermined length, the second gap value is kept constant; the first gap value is 25-30 mm; the second gap value is 20 mm.

[0026] The solid-liquid interface during the growth of a 111 crystal is often curved due to the constraint of the melt isotherms in the crucible. During growth, a small, flat plane appears at the solid-liquid interface, called a facet. The impurity concentration in the facet region differs significantly from that in the non-facet region. This abnormal distribution of impurities in the facet region is called facet effect. The facet effect leads to the formation of localized high-density regions during crystal growth. These regions have different resistivity compared to other regions, thus increasing the radial resistivity change rate (RRG) of the crystal. This results in inhomogeneous in-plane resistivity (VF) values ​​when the crystal is fabricated into a device.

[0027] Therefore, in this embodiment, compared with the prior art, the first gap value is reduced, which reduces the longitudinal space of the thermal field in the crystal growth region during crystal pulling, and the crystal is closer to the cooling region at the top of the thermal field. The effects are as follows: on the one hand, the radial and axial temperature distribution in the crystal growth region is more uniform, the thermal field is more stable, and the "small facet" is suppressed during the growth of the 111 crystal orientation rod. Meanwhile, the axial temperature gradient of the entire thermal field increases, the supercooling of the solid-liquid interface increases, and under the combined influence of radial and axial temperature changes, the solid-liquid interface of the crystal growth is flatter. On the other hand, the closer the crystal is to the solid-liquid interface, the more stable the melt convection becomes, and the more consistent the impurity segregation in the small facet region and the non-small facet region becomes. The combination of these two aspects reduces the radial resistivity change rate RRG during the growth of the 111 crystal orientation rod, improves the quality of the 111 crystal orientation rod, and thus improves the uniformity of the in-plane VF value of the 111 crystal orientation device, as well as the performance, reliability and safety of the 111 crystal orientation device.

[0028] Furthermore, in order to further stabilize the thermal field during the equal diameter process and thereby improve the quality of the 111 crystal orientation ingot, the method also includes: when the ingot enters the equal diameter stage, adjusting the equal diameter temperature compensation value according to the second predetermined equal diameter length.

[0029] In this embodiment, as the constant diameter process proceeds, the temperature of the thermal field will change accordingly. In order to make the thermal field more stable, the constant diameter temperature compensation value is adjusted synchronously, so that it works in conjunction with the technique of adjusting the gap value to reduce the gap value, together providing a more favorable thermal field environment for the growth of 111 crystal rods, thereby improving the quality of 111 crystal rods.

[0030] Furthermore, the first predetermined length is 10% of the length from the crystal rod equal diameter to the overall equal diameter.

[0031] By setting the above, the gap value remains unchanged in the first stage starting with equal diameter, which facilitates the initial stable formation of the 111 crystal rod.

[0032] Furthermore, the first and second predetermined lengths begin from 10% of the length from the crystal rod's equal diameter to the overall equal diameter and end at 90% of the length from the crystal rod's equal diameter to the overall equal diameter.

[0033] Furthermore, the first and third predetermined lengths begin from 90% of the length of the crystal rod equal in diameter to the overall equal in diameter length and end at the crystal rod equal in diameter.

[0034] Furthermore, the second predetermined constant diameter length includes a second first predetermined length, a second second predetermined length, and a second third predetermined length; within the second first predetermined length, the constant diameter temperature compensation value is negative and gradually increases to 0; within the second second predetermined length, the constant diameter temperature compensation value is constant at 0℃; within the second third predetermined length, the constant diameter temperature compensation value is positive and gradually increases from 0℃; within the second first predetermined length, the sum of the constant diameter temperature compensation values ​​ranges from -8 to -10℃; within the second third predetermined length, the sum of the constant diameter temperature compensation values ​​is 46 to 48℃.

[0035] In this embodiment, by setting the equal-diameter temperature compensation value to a negative value within the second predetermined length (i.e., temperature reduction), the excess heat accumulated during the shoulder-growing stage can be consumed, achieving a smooth transition from shoulder-growing to stable equal-diameter growth. Simultaneously, since in the prior art, the sum of the equal-diameter temperature compensation values ​​within the second predetermined length is typically -13 to -15°C, and the sum of the equal-diameter temperature compensation values ​​within the second and third predetermined lengths is typically 52 to 59.5°C, this embodiment uses a negative sum of the equal-diameter temperature compensation values ​​within the second predetermined length. The temperature is set to -8 to -10℃, and the sum of the equal-diameter temperature compensation values ​​within the second and third predetermined lengths is set to 46 to 48℃. Compared with the prior art, this reduces the total temperature reduction within the second predetermined length, thereby reducing the temperature change of the thermal field in both the second and third predetermined lengths. This technique, combined with the technique of adjusting the Gap value to be smaller, makes the thermal field more stable, providing a more favorable thermal field environment for the growth of 111 crystal orientation ingots, and thus improving the quality of 111 crystal orientation ingots.

[0036] Furthermore, the sum of the constant-diameter temperature compensation values ​​within the second predetermined length, the second predetermined length, and the third predetermined length is 30-41℃.

[0037] In this embodiment, the above-mentioned settings reduce the overall temperature change during the constant diameter process compared to the prior art. This technique, combined with the technique of adjusting the Gap value to be smaller, makes the thermal field more stable, providing a more favorable thermal environment for the growth of 111 crystal rods, thereby improving the quality of 111 crystal rods.

[0038] Furthermore, the second predetermined length is 5%-6% of the length from the start of the crystal rod's equal diameter to the overall equal diameter length.

[0039] In the prior art, the second predetermined length is usually 7.5% of the length from the start of the crystal rod equal diameter to the overall equal diameter length. Therefore, in this embodiment, by setting it as described above, compared with the prior art, the time for temperature reduction after the start of equal diameter is reduced, thereby reducing the change time of the thermal field during the temperature reduction stage. This technical means, combined with the technical means of reducing the total amount of temperature reduction within the second predetermined length, reduces the amount and duration of change of the thermal field in the initial stage of equal diameter, making the thermal field more stable and providing a more favorable thermal field environment for the growth of 111 crystal orientation crystal rods, thereby improving the quality of 111 crystal orientation crystal rods.

[0040] Furthermore, the second predetermined length is 10%-11% of the length from the end of the second predetermined length to the length from the crystal rod to the overall equal diameter.

[0041] In the prior art, the stage where the constant diameter temperature is 0°C is set from the end of the second predetermined length to 10%-11% of the length from the crystal rod to the overall constant diameter. However, since the second predetermined length ends at 7.5% of the length from the crystal rod to the overall constant diameter in the prior art, in this embodiment, the above setting extends the duration of the stage where the constant diameter temperature is 0°C compared to the prior art, making the thermal field more stable and providing a more favorable thermal environment for the growth of 111 crystal rods, thereby improving the quality of 111 crystal rods.

[0042] Furthermore, the second and third predetermined lengths are from the end of the second and second predetermined lengths to the end of the equal diameter.

[0043] In the prior art, the second and third predetermined lengths are from the end of the second and second predetermined lengths to the end of the equal diameter. However, in the prior art, the sum of the equal diameter temperature compensation values ​​within the second and third predetermined lengths is greater than the sum of the equal diameter temperature compensation values ​​in this application. Therefore, in this embodiment, compared with the prior art, although the duration is the same within the second and third predetermined lengths, the amount of temperature change is reduced. As a result, the thermal field provided by this application is more stable, providing a more favorable thermal field environment for the growth of 111 crystal orientation rods, thereby improving the quality of 111 crystal orientation rods.

[0044] The beneficial effects of the present invention will be described below with reference to specific comparative examples and embodiments.

[0045] In Comparative Examples 1 to 3, the crystal pulling parameters that were not explicitly stated were all the same; in Comparative Examples 2 to 4, the crystal pulling parameters that were not explicitly stated were all the same.

[0046] Comparative Example 1

[0047] First, an 8-inch 111-oriented heavily arsenic-doped single-crystal silicon rod was pulled, with an overall constant diameter length of 2000 mm. The first gap value was 45 mm, and the second gap value was 35 mm. The first predetermined constant diameter length started from the constant diameter and continued until the rod reached a constant diameter of 200 mm. The first and second predetermined constant diameter lengths started from the constant diameter of 200 mm and continued until the rod reached a constant diameter of 1800 mm. The first and third predetermined constant diameter lengths started from the constant diameter of 1800 mm and continued until the constant diameter ended. After the crystal pulling was completed, the rod was removed, and the radial resistivity change rate (RRG) of the rod was tested for every 100 mm increase in constant diameter length, from 100 mm to 2000 mm. Then, after slicing, polishing, and epitaxy, wafers were fabricated, and the VF value of the wafer at a constant diameter length of 1000 mm was tested. The test results are shown in Table 1 and... Figure 1 As shown.

[0048] Example 1

[0049] First, an 8-inch 111-oriented heavily arsenic-doped single-crystal silicon rod was pulled, with an overall constant diameter length of 2000 mm. The first gap value was 30 mm, and the second gap value was 25 mm. The first predetermined constant diameter length started from the constant diameter and continued until the rod reached a constant diameter of 200 mm. The first and second predetermined constant diameter lengths started from the constant diameter of 200 mm and continued until the rod reached a constant diameter of 1800 mm. The first and third predetermined constant diameter lengths started from the constant diameter of 1800 mm and continued until the constant diameter ended. After the crystal pulling was completed, the rod was removed, and the radial resistivity change rate (RRG) of the rod was tested for every 100 mm increase in constant diameter length, from 100 mm to 2000 mm. Then, after slicing, polishing, and epitaxy, wafers were fabricated, and the VF value of the wafer at a constant diameter length of 1000 mm was tested. The test results are shown in Table 1 and... Figure 2 As shown.

[0050] Example 2

[0051] First, an 8-inch 111-oriented heavily arsenic-doped single-crystal silicon rod was pulled, with an overall constant diameter length of 2000 mm. The first gap value was 25 mm, and the second gap value was 20 mm. The first predetermined constant diameter length started from the constant diameter and continued until the rod reached a constant diameter of 200 mm. The first and second predetermined constant diameter lengths started from the constant diameter of 200 mm and continued until the rod reached a constant diameter of 1800 mm. The first and third predetermined constant diameter lengths started from the constant diameter of 1800 mm and continued until the constant diameter ended. After the crystal pulling was completed, the rod was removed, and the radial resistivity change rate (RRG) of the rod was tested for every 100 mm increase in constant diameter length, from 100 mm to 2000 mm. Then, after slicing, polishing, and epitaxy, wafers were fabricated, and the VF value of the wafer at a constant diameter length of 1000 mm was tested. The test results are shown in Table 1 and... Figure 3 As shown.

[0052] Example 3

[0053] First, an 8-inch 111-oriented heavily arsenic-doped single-crystal silicon rod was pulled, with an overall constant diameter length of 2000 mm. The first gap value was 27 mm, and the second gap value was 22 mm. The first predetermined constant diameter length started from the constant diameter and continued until the rod reached a constant diameter of 200 mm. The first and second predetermined constant diameter lengths started from the constant diameter of 200 mm and continued until the rod reached a constant diameter of 1800 mm. The first and third predetermined constant diameter lengths started from the constant diameter of 1800 mm and continued until the constant diameter ended. After the crystal pulling was completed, the rod was removed, and the radial resistivity change rate (RRG) of the rod was tested for every 100 mm increase in constant diameter length, from 100 mm to 2000 mm. Then, after slicing, polishing, and epitaxy, wafers were fabricated, and the VF value of the wafer at a constant diameter length of 1000 mm was tested. The test results are shown in Table 1 and... Figure 4 As shown.

[0054] Comparative Example 2

[0055] First, an 8-inch 111-oriented heavily arsenic-doped single-crystal silicon rod is drawn, with an overall constant diameter length of 2000mm. The first gap value is 45mm, and the second gap value is 35mm. The first predetermined constant diameter length starts from the constant diameter and ends when the rod reaches a constant diameter of 200mm. The first and second predetermined constant diameter lengths start from the constant diameter of 200mm and end when the rod reaches a constant diameter of 1800mm. The first and third predetermined constant diameter lengths start from the constant diameter of 1800mm and end when the constant diameter ends.

[0056] The second predetermined length is from the beginning of the equal diameter to the crystal rod reaching a diameter of 150 mm; the second predetermined length is from the beginning of the crystal rod reaching a diameter of 150 mm to the beginning of the crystal rod reaching a diameter of 200 mm; the second predetermined length is from the beginning of the crystal rod reaching a diameter of 200 mm to the end of the equal diameter period.

[0057] Within the second predetermined length, the sum of the constant diameter temperature compensation values ​​is -13℃; within the second and third predetermined lengths, the sum of the constant diameter temperature compensation values ​​is 52℃; the total sum of the constant diameter temperature compensation values ​​within the second predetermined length, the second predetermined length, and the third predetermined length is 39℃.

[0058] After crystal pulling, the crystal ingot is removed. Starting from a constant diameter length of 100mm and ending at 2000mm, the radial resistivity variation rate (RRG) of the crystal ingot is tested for every 100mm increase. Then, after slicing, polishing, and epitaxy, wafers are fabricated, and the VF value of the wafer at a constant diameter length of 1000mm is tested. The test results are shown in Table 1 and... Figure 5 As shown.

[0059] Example 4

[0060] First, an 8-inch 111-oriented heavily arsenic-doped single-crystal silicon rod is drawn, with an overall constant diameter length of 2000mm. The first gap value is 27mm, and the second gap value is 22mm. The first predetermined constant diameter length starts from the constant diameter and extends to 200mm. The first and second predetermined constant diameter lengths start from 200mm and extend to 1800mm. The first and third predetermined constant diameter lengths start from 1800mm and extend to the end of the constant diameter period.

[0061] The second predetermined length is from the beginning of the equal diameter to the crystal rod reaching 100mm; the second predetermined length is from the beginning of the crystal rod reaching 100mm to the beginning of the crystal rod reaching 200mm; the second predetermined length is from the beginning of the crystal rod reaching 200mm to the end of the equal diameter.

[0062] Within the second predetermined length, the sum of the constant diameter temperature compensation values ​​is -10℃; within the second and third predetermined lengths, the sum of the constant diameter temperature compensation values ​​is 48℃; the total sum of the constant diameter temperature compensation values ​​within the second predetermined length, the second predetermined length, and the third predetermined length is 38℃.

[0063] After crystal pulling, the crystal ingot is removed. Starting from a constant diameter length of 100mm and ending at 2000mm, the radial resistivity variation rate (RRG) of the crystal ingot is tested for every 100mm increase. Then, after slicing, polishing, and epitaxy, wafers are fabricated, and the VF value of the wafer at a constant diameter length of 1000mm is tested. The test results are shown in Table 1 and... Figure 4 As shown;

[0064] exist Figure 1-6 In the diagram, the numbers corresponding to the color markers on the right represent the VF values ​​for that color. The highest number represents the maximum VF value (VFmax), and the lowest number represents the minimum VF value (VFmin). The uniformity of VF within the device plane is determined by the difference between VFmax and VFmin, ΔVF. Figures 1-6 The ΔVF of Comparative Example 1, Comparative Example 2 and Examples 1-4 were obtained, as shown in Table 2.

[0065] Table 1

[0066]

[0067] Table 2

[0068]

[0069] As shown in Table 1, compared with Comparative Example 1, except for the three locations with equal diameter lengths of 300mm, 1400mm, and 1700mm where the RRG of the crystal rod in Example 1 did not decrease, the RRG of the crystal rod in Example 1 decreased at all other equal diameter lengths, indicating that the RRG of the crystal rod in Example 1 generally shows a decreasing trend compared with Comparative Example 1. Furthermore, compared with Comparative Example 1, the RRG of the crystal rods in Examples 2-3 also decreased. Table 2 shows that compared with Comparative Example 1, the uniformity of the VF value of the wafers in Examples 1-3 was greatly improved. Therefore, compared with the prior art, by reducing the first and second Gap values ​​during the pulling process of 111-oriented heavily arsenic-doped single crystal silicon rods, the longitudinal space of the thermal field in the crystal growth region is reduced during the crystal pulling process, and the crystal is closer to the cooling region at the top of the thermal field. The resulting effects are: on the one hand, the radial and axial temperature distributions in the crystal growth region are more uniform, making the thermal field in the crystal growth region more stable, and reducing the formation of "small facets" during the 111-oriented growth process. The axial temperature gradient of the entire thermal field increases, the supercooling of the solid-liquid interface increases, and under the combined influence of radial and axial temperature changes, the solid-liquid interface of the crystal growth becomes flatter. On the other hand, the closer the crystal is to the solid-liquid interface, the more stable the melt convection becomes, and the more consistent the impurity segregation between the small planar region and the non-small planar region becomes. The combination of these two aspects results in a smaller radial resistivity change rate RRG during the growth of 111 crystal rods, which improves the quality of 111 crystal rods and thus improves the uniformity of VF values ​​in the 111 crystal device plane.

[0070] As shown in Table 1, compared with Comparative Example 2, the RRG of the crystal rod in Example 4 is smaller. As shown in Table 2, compared with Comparative Example 2, the VF value uniformity of the wafer in Example 4 is greatly improved. Therefore, compared with the prior art, by reducing the duration of the second predetermined length and the total amount of temperature compensation within the second predetermined length, while increasing the duration of the second predetermined length and maintaining the duration of the second predetermined length, the total amount of temperature compensation within the second predetermined length is reduced. This reduces the amount and duration of change of the thermal field in the initial stage of constant diameter, extends the duration of the constant diameter temperature at 0°C, and reduces the amount of temperature change within the second and third predetermined lengths. As a result, the thermal field provided by this application is more stable, providing a more favorable thermal field environment for the growth of 111 crystal rods. This reduces the radial resistivity change rate RRG during the growth of 111 crystal rods, improves the quality of 111 crystal rods, and thus improves the uniformity of the VF value in the 111 crystal device plane.

[0071] 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 in-plane VF value uniformity of 111 crystal orientation devices, characterized in that, include: When pulling a heavily doped single-crystal silicon rod, the gap value is adjusted according to the first predetermined equal diameter length when the rod enters the constant diameter stage. The first predetermined equal diameter length includes a first predetermined length, a first second predetermined length, and a first third predetermined length; within the first predetermined length, the first gap value is kept constant; within the first second predetermined length, the first gap value decreases to the second gap value at a linear rate; within the first third predetermined length, the second gap value is kept constant; the first gap value is 25-30 mm; the second gap value is 20 mm. The first predetermined length starts from the crystal rod equal diameter and extends to 10% of the length from the crystal rod equal diameter to the overall equal diameter; the first and second predetermined lengths start from 10% of the length from the crystal rod equal diameter to the overall equal diameter and end at 90% of the length from the crystal rod equal diameter to the overall equal diameter; the first and third predetermined lengths start from 90% of the length from the crystal rod equal diameter to the overall equal diameter and end at the crystal rod equal diameter.

2. The crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices as described in claim 1, characterized in that, Also includes: When the crystal rod enters the constant diameter stage, the constant diameter temperature compensation value is adjusted according to the second predetermined constant diameter length.

3. The crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices as described in claim 2, characterized in that: The second predetermined equal diameter length includes a second first predetermined length, a second second predetermined length, and a second third predetermined length; within the second first predetermined length, the equal diameter temperature compensation value is negative and gradually increases to 0℃; within the second second predetermined length, the equal diameter temperature compensation value is constant at 0℃; within the second third predetermined length, the equal diameter temperature compensation value is positive and gradually increases from 0℃; within the second first predetermined length, the sum of the equal diameter temperature compensation values ​​ranges from -8 to -10℃; within the second third predetermined length, the sum of the equal diameter temperature compensation values ​​ranges from 46 to 48℃.

4. The crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices as described in claim 3, characterized in that: The sum of the constant-diameter temperature compensation values ​​within the second predetermined length, the second predetermined length, and the third predetermined length is 30-41℃.

5. The crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices as described in claim 3, characterized in that: The second predetermined length is 5%-6% of the length from the start of the crystal rod's equal diameter to the overall equal diameter length.

6. The crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices as described in claim 3, characterized in that: The second predetermined length is 10%-11% of the length from the end of the second predetermined length to the length from the end of the crystal rod to the end of the overall equal diameter.

7. The crystal pulling method for improving the in-plane VF value uniformity of 111 crystal orientation devices as described in claim 3, characterized in that: The second and third predetermined lengths begin from the end of the second and second predetermined lengths and end at the equal diameter.

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