Method for improving resistivity uniformity of heavily doped red phosphorus czochralski silicon single crystal

Abstract

The application provides a preparation method for improving the resistivity uniformity of heavy-doped red phosphorus direct-drawn silicon single crystal, belongs to the technical field of heavy-doped red phosphorus preparation, and performs crystal bar drawing in a hot field, wherein a predetermined slow-release doping device is arranged on the hot field, doping is performed through the predetermined slow-release doping device, a "continuous slow-release" dopant is pre-doped, the effective doping time window of red phosphorus is effectively prolonged, the doping efficiency is improved, the drawing speed of the crystal bar and the axial temperature gradient at the solid-liquid interface are controlled during the constant-diameter process, and the occurrence of component supercooling is effectively inhibited, meanwhile, the drawing speed is gradually reduced to adapt to the continuous increase of the phosphorus concentration in the melt, so that the V / G ratio is always maintained below the critical value of component supercooling; meanwhile, the tail impurity volatilization effect is amplified, so that the resistivity of the constant-diameter tail part is appropriately increased, thereby compensating for the problem of low tail resistivity caused by the segregation effect, and improving the axial resistivity uniformity of the 12-inch heavy-doped red phosphorus crystal bar.

Description

Technical Field

[0001] This invention relates to the field of heavy red phosphorus preparation technology, specifically to a preparation method for improving the resistivity uniformity of Czochralski silicon single crystals with heavy red phosphorus. Background Technology

[0002] With the rapid development of power semiconductor devices, the demand for low-resistivity silicon substrate materials is becoming increasingly urgent for power devices such as insulated-gate bipolar transistors (IGBTs) and metal-oxide-semiconductor field-effect transistors (MOSFETs). Heavily doped red phosphorus Czochralski silicon single crystals, due to their extremely low resistivity, have become one of the preferred materials for power device substrates. 12-inch heavily doped red phosphorus polished wafers can be widely used in the manufacture of semiconductor devices such as sensors, analog chips, discrete / power devices, and RF front-end chips.

[0003] In existing techniques for preparing heavily doped silicon single crystals, red phosphorus has a high solid solubility in the silicon lattice (up to 1.3 × 10⁻⁶). 21 atoms / cm 3 Red phosphorus is advantageous for achieving low substrate resistance, thus becoming the primary dopant choice for heavily doped N-type single-crystal silicon rods. However, heavy doping with red phosphorus faces three major technical challenges:

[0004] I. The high volatility of red phosphorus leads to low doping efficiency. Red phosphorus sublimates at only 41°C under normal pressure, while the melt temperature during silicon single-crystal pulling is above 1420°C and is carried out under negative pressure. Red phosphorus is highly volatile, making it difficult to incorporate into the silicon melt at high concentrations. A large amount of dopant is lost with the argon gas, making it difficult to accurately control the actual doping amount. Consequently, the actual resistivity of the crystal rod often fails to meet the target resistivity requirements.

[0005] II. High-concentration doping induces supercooling, disrupting dislocation-free single-crystal growth. When the solute concentration in the melt is very high, supercooling easily occurs at the solid-liquid interface, leading to instability of the crystal growth interface and causing crystal defects such as dislocations. In heavily doped N-type (phosphorus, arsenic, antimony) silicon wafers, oxygen precipitation is suppressed, and the low oxygen precipitation density induces stacking faults, further deteriorating crystal quality.

[0006] Third, the segregation coefficient of phosphorus is only 0.35, which is much less than 1. As the silicon single crystal ingot is pulled, the concentration of phosphorus in the molten silicon in the crucible gradually increases, which makes the axial resistivity distribution of the pulled silicon single crystal ingot extremely uneven, and the resistivity of the whole crystal rod varies greatly.

[0007] In the existing technology, such as Chinese invention application number 201210382987.9, a method for improving the axial resistivity uniformity of Czochralski single-crystal silicon and the obtained single-crystal silicon are disclosed. The specific steps include: (1) melting polycrystalline silicon raw materials and solid dopants in an argon atmosphere to obtain stable molten silicon; (2) introducing seed crystals into the stable molten silicon, and the crystal growth goes through a necking and shouldering process to enter the constant diameter growth stage; (3) in the constant diameter growth stage, introducing a doping gas with the opposite conductivity type to the solid dopant until the Czochralski single-crystal silicon growth is completed. In this invention, the type and amount of doping gas in the method for improving the axial resistivity uniformity of Czochralski single-crystal silicon are easy to control, and various desired impurity concentration distributions can be obtained; the utilization rate of Czochralski single-crystal silicon is improved; and the resistivity uniformity of Czochralski single-crystal silicon is significantly improved. However, in the above scheme, the dopant still enters the melt through volatilization. Red phosphorus is very easy to volatilize under negative pressure, resulting in low doping efficiency and poor resistivity uniformity. Summary of the Invention

[0008] In view of this, the present invention provides a method for improving the resistivity uniformity of heavily doped red phosphorus Czochralski silicon single crystals to improve doping efficiency and resistivity uniformity.

[0009] The technical solution adopted by this invention to solve its technical problem is:

[0010] A method for improving the resistivity uniformity of heavily red phosphorus-doped Czochralski silicon single crystals involves pulling a crystal rod in a thermal field. A predetermined slow-release doping device is set on the thermal field, and doping is performed through the predetermined slow-release doping device to pre-dopact the dopant in a continuous slow-release manner, thereby improving the doping efficiency. At the same time, the pulling speed of the crystal rod and the axial temperature gradient at the solid-liquid interface are controlled during the constant diameter process to effectively suppress the occurrence of component supercooling and improve the uniformity of the axial resistivity of the 12-inch heavily red phosphorus-doped crystal rod.

[0011] The axial temperature gradient at the solid-liquid interface is 1.5-3.5 K / mm, and the axial temperature gradient at the solid-liquid interface gradually decreases with the increase of the constant diameter length.

[0012] The pulling speed is 0.2 mm / min to 1.20 mm / min, and the pulling speed gradually decreases as the diameter length increases.

[0013] Preferably, the predetermined slow-release doping device includes an isolation feed component, a driving component, and a slow-release component. The isolation feed component and the driving component are installed outside the thermal field, and the slow-release component is installed inside the thermal field. The isolation feed component is connected to the slow-release component. The driving component is connected to both the isolation feed component and the slow-release component. The driving component drives the isolation feed component to open and close, so that the dopant enters the slow-release component through the isolation feed component. The driving component drives the slow-release component to rise and fall, so that the lower part of the slow-release component is located at a predetermined distance within the silicon solution for slow release of the dopant.

[0014] Preferably, the slow-release component includes a telescopic part and a slow-release part located within the thermal field. One end of the telescopic part is connected to the isolation feeding component, and the other end of the telescopic part is connected to the slow-release part. The telescopic end of the telescopic part is also connected to the driving component.

[0015] Preferably, the slow-release unit includes a coaxial cylindrical body and a guide graphite tube. The upper part of the cylindrical body is open, and the side wall of the cylindrical body has evaporation holes. The interior of the guide graphite tube is a hollow cylindrical body, and the diameter of the cylindrical body is smaller than the diameter of the hollow cylindrical body of the guide graphite tube. The cylindrical body is located inside the hollow cylindrical body of the guide graphite tube. The upper part of the cylindrical body is connected to the upper part of the guide graphite tube to form a first evaporation chamber outside the cylindrical body and inside the guide graphite tube. The outer wall of the guide graphite tube is provided with external threads, and the guide graphite tube is threadedly connected to the free end of the telescopic part so that the upper opening of the cylindrical body is aligned with the lower outlet of the telescopic part. The lower part of the guide graphite tube can enter the silicon solution a predetermined distance. The inner layer of the guide graphite tube is hollow and communicates with the bottom to form a second evaporation chamber. The inner wall of the guide graphite tube is made of a high-temperature resistant porous material so that the dopant enters the first evaporation chamber and the second evaporation chamber sequentially from the cylindrical body into the silicon solution.

[0016] Preferably, the upper part of the guide graphite tube is cylindrical and the lower part is an inverted frustum, with the inverted frustum of the guide graphite tube located within the silicon melt.

[0017] Preferably, the lower part of the guide graphite tube can enter the silicon solution by a predetermined distance of 50mm-150mm.

[0018] Preferably, the telescopic part includes a fixed quartz tube and a telescopic quartz tube located within the thermal field. One end of the fixed quartz tube is connected to the lower part of the isolation feeding assembly, and the other end of the fixed quartz tube is movably connected to one end of the telescopic quartz tube. The other end of the telescopic quartz tube is connected to the upper end of the guide graphite tube. The driving assembly includes a driving cylinder, a first connecting rod, a traction rod, and a second connecting rod. The driving cylinder is parallel to the traction rod and perpendicular to the first connecting rod. The driving cylinder and the first connecting rod are located outside the thermal field. The telescopic end of the driving cylinder is connected to one end of the first connecting rod, and the other end of the first connecting rod is connected to one end of the traction rod. The other end of the traction rod is connected to one end of the second connecting rod, and the other end of the second connecting rod is connected to the outer wall of the telescopic quartz tube, thereby driving the telescopic quartz tube to move up and down along the fixed quartz tube.

[0019] Preferably, the isolation feeding assembly includes a feeding pipe, a tilting shaft, and two tilting plates arranged sequentially from top to bottom along the feeding pipe. There are two tilting shafts, one end of which is fixedly provided with a tilting rod, and the other end of which is provided with a gravity hammer. The driving assembly includes a driving motor and a driving plate. The feeding pipe is connected to the top of the fixed quartz tube. The tilting shaft is arranged along the height direction of the feeding pipe. One side of the tilting plate is connected to the tilting shaft. The driving shaft of the driving motor is connected to one end of the driving plate. The other end of the driving plate can contact one of the tilting rods under the rotation of the driving motor to drive the corresponding tilting plate to tilt.

[0020] Preferably, controlling the pulling speed of the crystal rod and the axial temperature gradient at the solid-liquid interface during the constant diameter process specifically includes the following steps:

[0021] In the first stage of constant diameter, the pulling speed is 1-1.2 mm / min, and the axial temperature gradient at the solid-liquid interface is 2.5-3.5 K / mm.

[0022] In the second stage of constant diameter, the pulling speed starts from the pulling speed at the end of the first stage and decreases linearly at a rate of 0.015-0.025 mm / (min·100 mm), and the axial temperature gradient at the solid-liquid interface is 2.0-3.0 K / mm.

[0023] In the third stage of constant diameter, the pulling speed starts from the pulling speed at the end of the second stage and decreases linearly at a rate of 0.03-0.05 mm / (min·100mm), and the axial temperature gradient at the solid-liquid interface is 1.5-2.5 K / mm.

[0024] The first, second, and third stages of equal diameter are continuous equal diameter processes. The first stage of equal diameter refers to the process from the start of equal diameter to 200mm, the second stage of equal diameter refers to the process from 200mm to 700mm, and the third stage of equal diameter refers to the process from 700mm to the end of equal diameter.

[0025] Preferably, in the first stage of equal diameter, the power ratio of the side heaters in the thermal field is 60%-70%, and the power ratio of the bottom heaters is 30%-40%; in the second stage of equal diameter, the power ratio of the side heaters in the thermal field is 55%-65%, and the power ratio of the bottom heaters is 35%-45%; in the third stage of equal diameter, the power ratio of the side heaters in the thermal field is 50%-60%, and the power ratio of the bottom heaters is 40%-50%.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention provides a method for improving the resistivity uniformity of heavily red phosphorus-doped Czochralski silicon single crystals. The method involves pulling a crystal rod within a thermal field, where a predetermined slow-release doping device is installed. Doping is performed through this device to pre-dopact the dopant in a continuous, slow-release manner, effectively extending the effective doping time window for red phosphorus and improving doping efficiency. Simultaneously, the pulling speed and axial temperature gradient at the solid-liquid interface are controlled during the constant-diameter process to match the changing trend of the axial temperature gradient at the solid-liquid interface with the melt impurity concentration, thereby effectively suppressing compositional undercooling. Furthermore, by gradually reducing the pulling speed to accommodate the continuously increasing phosphorus concentration in the melt, the V / G ratio is maintained below the critical value for compositional undercooling. The method also amplifies the tail-end impurity volatilization effect, resulting in an appropriate increase in the resistivity at the tail end during constant-diameter production, thus compensating for the low tail resistivity caused by segregation effects and improving the uniformity of the axial resistivity of the 12-inch heavily red phosphorus-doped crystal rod. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the predetermined slow-release doping device.

[0029] Figure 2 for Figure 1 Enlarged view of part A in the middle.

[0030] Figure 3 This is a first cross-sectional view of the predetermined slow-release doping device.

[0031] Figure 4 This is a second cross-sectional view of the predetermined slow-release doping device.

[0032] Figure 5 This is a third cross-sectional view of the predetermined slow-release doping device.

[0033] Figure 6 The resistivity measurement diagram is shown in the example.

[0034] Figure 7 This is a comparative resistivity measurement graph.

[0035] Figure 8 The diagram shows the axial resistivity uniformity test results for this embodiment.

[0036] Figure 9 This is a comparative diagram showing the axial resistivity uniformity test results.

[0037] Figure 10 The carbon content detection graphs are for the examples and comparative examples.

[0038] In the figure: hot zone 10, predetermined slow-release doping device 20, isolation feeding assembly 100, feeding pipe 110, flipping shaft 120, flipping plate 130, flipping rod 140, gravity hammer 150, drive assembly 200, drive cylinder 210, first connecting rod 220, traction rod 230, second connecting rod 240, drive motor 250, drive plate 260, slow-release assembly 300, telescopic part 310, fixed quartz tube 311, telescopic quartz tube 312, slow-release part 320, cylinder 321, evaporation hole 3211, guide graphite tube 322. Detailed Implementation

[0039] To facilitate understanding of this application, a more comprehensive description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are also given. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and complete understanding of the disclosure of this application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0041] Please refer to Figure 1 A method for improving the resistivity uniformity of heavily red phosphorus-doped Czochralski silicon single crystals involves pulling a crystal rod within a thermal field 10. A predetermined slow-release doping device 20 is installed on the thermal field 10, and doping is performed through the predetermined slow-release doping device 20 to pre-dopact the dopant in a continuous slow-release manner, thereby improving the doping efficiency. At the same time, the pulling speed of the crystal rod and the axial temperature gradient at the solid-liquid interface are controlled during the constant diameter process to effectively suppress the occurrence of component undercooling and improve the uniformity of the axial resistivity of the 12-inch heavily red phosphorus-doped crystal rod.

[0042] The axial temperature gradient at the solid-liquid interface is 1.5-3.5 K / mm, and the axial temperature gradient at the solid-liquid interface gradually decreases with the increase of the constant diameter length.

[0043] The pulling speed is 0.2 mm / min to 1.20 mm / min, and the pulling speed gradually decreases as the diameter length increases.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] This invention provides a method for improving the resistivity uniformity of heavily red phosphorus-doped Czochralski silicon single crystals. The method involves pulling a crystal rod within a thermal field 10, where a predetermined slow-release doping device 20 is installed. Doping is performed through this device, allowing for continuous, slow-release doping of the dopant, effectively extending the effective doping time window for red phosphorus and improving doping efficiency. Simultaneously, the pulling speed and axial temperature gradient at the solid-liquid interface are controlled during the constant-diameter process to match the changing trend of the axial temperature gradient at the solid-liquid interface with the concentration of impurities in the melt, thereby effectively suppressing compositional undercooling. Furthermore, by gradually reducing the pulling speed to accommodate the continuously increasing phosphorus concentration in the melt, the V / G ratio is maintained below the critical value for compositional undercooling. Simultaneously, the tail-end impurity volatilization effect is amplified, resulting in an appropriate increase in the resistivity at the tail end during the constant-diameter process, thus compensating for the low tail resistivity caused by segregation effects and improving the uniformity of the axial resistivity of the 12-inch heavily red phosphorus-doped crystal rod.

[0046] Therefore, this invention addresses the doping efficiency issue by using a predetermined slow-release doping device 20, providing a controllable impurity concentration background for the dynamic thermal field 10. Then, during the constant diameter process, the dynamic thermal field 10 provides a temperature gradient condition matching the impurity concentration, preventing component overcooling. Simultaneously, staged pulling speed matching further optimizes the V / G ratio and impurity distribution, jointly solving the problems of component overcooling and axial uniformity. These three dimensions are interconnected, forming a self-consistent closed-loop process control system.

[0047] Furthermore, the predetermined slow-release doping device 20 includes an isolation feed assembly 100 (which may be an isolation valve), a drive assembly 200, and a slow-release assembly 300. The isolation feed assembly 100 and the drive assembly 200 are installed outside the thermal field 10, and the slow-release assembly 300 is installed inside the thermal field 10. The isolation feed assembly 100 is connected to the slow-release assembly 300. The drive assembly 200 is connected to both the isolation feed assembly 100 and the slow-release assembly 300. The drive assembly 200 drives the isolation feed assembly 100 to open and close, allowing the dopant to enter the slow-release assembly 300 through the isolation feed assembly 100. The drive assembly 200 also drives the slow-release assembly 300 to rise and fall, causing the lower part of the slow-release assembly 300 to... Dopant is released gradually at a predetermined distance within the silicon molten silicon. When dopant needs to be added, the drive component 200 activates the isolation feed component 100, establishing an entry channel for the dopant. Under gravity, the dopant passes through the isolation feed component 100 into the slow-release component 300 installed inside the hot zone 10. After feeding is complete, the drive component 200 deactivates the isolation feed component 100 and lowers the slow-release component 300, immersing its lower part into the silicon molten silicon at a predetermined distance. The dopant in the slow-release component 300 is gradually released under the influence of the high-temperature silicon molten silicon. Due to the structural limitations of the slow-release component 300 (such as the size of the lower opening and porosity) and the control of the immersion depth, the dopant continuously enters the silicon molten silicon at a slow and controllable rate. This slow-release method effectively avoids the violent vaporization and "dopant explosion" phenomenon caused by a large-scale one-time dopant injection. Therefore, by controlling the structural rate limit and immersion depth of the slow-release component 300, the dopant is released into the silicon melt in a slow and continuous manner. Compared to a one-time injection method, slow-release doping significantly reduces the amount of dopant lost due to vaporization and volatilization caused by sudden heating. Simultaneously, the dopant vapor is directly introduced into the silicon melt volume, allowing more dopant to actually enter the melt and participate in doping, thereby improving dopant utilization and reducing dopant usage costs. Furthermore, slow-release doping allows the dopant to continuously enter the melt at a relatively stable rate, which is beneficial for the uniform diffusion and distribution of the dopant in the silicon melt. The steady increase in dopant concentration avoids abrupt concentration changes, which is conducive to growing silicon crystals with better resistivity uniformity.

[0048] Furthermore, once the dopant dose has been released or the predetermined doping time has been reached, the driving component 200 can drive the slow-release component 300 to rise and reset, exiting the silicon melt. Alternatively, it can remain in the silicon melt; if it exits the melt, the slow-release component 300 is raised to the same position as the liquid outlet distance to facilitate redoping.

[0049] Furthermore, the slow-release component 300 includes a telescopic portion 310 and a slow-release portion 320 located within the thermal field 10. One end of the telescopic portion 310 is connected to the isolation feeding component 100, and the other end of the telescopic portion 310 is connected to the slow-release portion 320. The telescopic end of the telescopic portion 310 is also connected to the driving component 200, so that, according to the actual situation, it can be selected whether the slow-release portion 320 continuously enters the silicon solution or whether the slow-release portion 320 is lifted and removed from the silicon solution after doping is completed.

[0050] Furthermore, the slow-release unit 320 includes a coaxial cylindrical body 321 and a guide graphite tube 322. The upper part of the cylindrical body 321 is open, and evaporation holes 3211 are formed on the side wall of the cylindrical body 321. The interior of the guide graphite tube 322 is a hollow cylinder. The diameter of the cylindrical body 321 is smaller than the diameter of the hollow cylinder of the guide graphite tube 322. The cylindrical body 321 is located inside the hollow cylinder of the guide graphite tube 322. The upper part of the cylindrical body 321 is connected to the upper part of the guide graphite tube 322 to form a first evaporation chamber outside the cylindrical body 321 and inside the guide graphite tube 322. The outer wall of the guide graphite tube 322 is provided with external threads. The guide graphite tube 322 is threadedly connected to the free end of the telescopic part 310 so that the upper opening of the cylindrical body 321 is connected to the lower opening of the telescopic part 310. With the openings aligned, the lower part of the guide graphite tube 322 can enter the silicon solution a predetermined distance. The inner layer of the guide graphite tube 322 is hollow and connected to the bottom to form a second evaporation chamber. The inner wall of the guide graphite tube 322 is made of a high-temperature resistant porous material so that the dopant enters the first evaporation chamber and the second evaporation chamber sequentially from the cylinder 321 into the silicon solution. Therefore, through the double-layer structure of "cylinder 321 storage - guide graphite tube 322 slow release", a concentration gradient and time gradient for red phosphorus release are constructed: after the red phosphorus in the storage chamber of cylinder 321 sublimates, the gaseous red phosphorus molecules will not directly rush into the silicon melt in large quantities, but will enter the porous graphite sleeve of the guide graphite tube 322 through the evaporation holes 3211 spirally arranged on the side wall of the storage chamber of cylinder 321, and then slowly diffuse into the silicon melt through the physical barrier effect of the graphite pores. This design transforms the traditional "instantaneous burst" doping into "continuous slow-release" doping, effectively extending the effective doping time window of red phosphorus and significantly improving doping efficiency.

[0051] Furthermore, the diameter of the evaporation pores 3211 is 0.5-1.5 mm, the axial spacing between adjacent evaporation pores 3211 is 3-8 mm, the total open area of ​​the evaporation pores 3211 is 3%-8% of the surface area of ​​the storage cavity of the cylinder 321, the inner wall of the guide graphite tube 322 is made of porous high-purity graphite material with a porosity of 25%-45% and a wall thickness of 3-8 mm, and the average particle size of the graphite particles in the inner wall of the guide graphite tube 322 is 50-200 μm, and the average pore size is 10-50 μm, so as to allow gaseous red phosphorus molecules to diffuse slowly and be fully released.

[0052] Furthermore, the upper part of the guide graphite tube 322 is cylindrical, and the lower part is an inverted frustum. The inverted frustum of the guide graphite tube 322 is located in the silicon melt, and the cone angle of the inverted frustum of the guide graphite tube 322 is 60°-90°, which facilitates immersion in the silicon melt.

[0053] Furthermore, the lower part of the guide graphite tube 322 can enter the silicon solution by a predetermined distance of 50mm-150mm, and the immersion speed of the guide graphite tube 322 is 1-3mm / min. During this process, the red phosphorus in the inner storage chamber is heated and gradually sublimates. The gaseous red phosphorus molecules enter the first volatilization chamber through the volatilization holes 3211 on the side wall of the cylinder 321, and then slowly diffuse into the second volatilization chamber through the pores of the porous guide graphite tube. Finally, they enter the silicon melt through the cone of the guide graphite tube 322, thus avoiding the large amount of red phosphorus volatilization caused by traditional bell jar doping, which leads to low doping efficiency.

[0054] Furthermore, the telescopic part 310 includes a fixed quartz tube 311 and a telescopic quartz tube 312 located within the thermal field 10. One end of the fixed quartz tube 311 is connected to the lower part of the isolation feeding assembly 100, and the other end of the fixed quartz tube 311 is movably connected to one end of the telescopic quartz tube 312. The other end of the telescopic quartz tube 312 is connected to the upper end of the guide graphite tube 322. The driving assembly 200 includes a driving cylinder 210, a first connecting rod 220, a traction rod 230, and a second connecting rod 240. The driving cylinder 210 is parallel to the traction rod 230. The driving cylinder 210 is perpendicular to the first connecting rod 220. The driving cylinder 210 and the first connecting rod 220 are located outside the hot field 10. The telescopic end of the driving cylinder 210 is connected to one end of the first connecting rod 220, and the other end of the first connecting rod 220 is connected to one end of the traction rod 230. The other end of the traction rod 230 passes through the housing of the hot field 10 and is connected to one end of the second connecting rod 240. The other end of the second connecting rod 240 is connected to the outer wall of the telescopic quartz tube 312 to drive the telescopic quartz tube 312 to move up and down along the fixed quartz tube 311.

[0055] Furthermore, the isolation feeding assembly 100 includes a feeding pipe 110, a flipping shaft 120, and two flipping plates 130 arranged sequentially from top to bottom along the feeding pipe 110. There are two flipping shafts 120. One end of the flipping shaft 120 is fixedly provided with a flipping rod 140, and the other end of the flipping shaft 120 is provided with a gravity hammer 150. The driving assembly 200 includes a driving motor 250 and a driving plate 260. The feeding pipe 110 is connected to the top of the fixed quartz tube 311. The flipping shaft 120 is arranged along the height direction of the feeding pipe 110. One side of the flipping plate 130 is connected to the flipping shaft 120. The driving shaft of the driving motor 250 is connected to one end of the driving plate 260. The other end of the driving plate 260 can contact one of the flipping rods 140 under the rotation of the driving motor 250 to drive the corresponding flipping plate 130 to flip, so as to ensure that at least one flipping plate 130 is closed and to ensure sealing.

[0056] Furthermore, controlling the pulling speed of the crystal rod and the axial temperature gradient at the solid-liquid interface during the constant diameter process specifically includes the following steps:

[0057] In the first stage of constant diameter, the pulling speed is 1-1.2 mm / min, and the axial temperature gradient at the solid-liquid interface is 2.5-3.5 K / mm.

[0058] In the second stage of constant diameter, the pulling speed starts from the pulling speed at the end of the first stage and decreases linearly at a rate of 0.015-0.025 mm / (min·100 mm), and the axial temperature gradient at the solid-liquid interface is 2.0-3.0 K / mm.

[0059] In the third stage of constant diameter, the pulling speed starts from the pulling speed at the end of the second stage and decreases linearly at a rate of 0.03-0.05 mm / (min·100mm), and the axial temperature gradient at the solid-liquid interface is 1.5-2.5 K / mm.

[0060] The first, second, and third stages of equal diameter are continuous equal diameter processes. The first stage of equal diameter refers to the process from the start of equal diameter to 200mm, the second stage of equal diameter refers to the process from 200mm to 700mm, and the third stage of equal diameter refers to the process from 700mm to the end of equal diameter.

[0061] In the initial stage of constant diameter, due to the low phosphorus concentration in the melt, the risk of component undercooling is small. Therefore, a large axial temperature gradient of 2.5-3.5 K / mm at the solid-liquid interface is set, which is beneficial to the formation of a stable solid-liquid interface convex to the melt and promotes dislocation-free growth. As the constant diameter length increases, the phosphorus concentration in the melt gradually increases due to the segregation effect, and the risk of component undercooling increases. At this time, the axial temperature gradient at the solid-liquid interface is reduced in stages to effectively suppress the occurrence of component undercooling. This is to match the axial temperature gradient at the solid-liquid interface with the changing trend of the melt impurity concentration. At the same time, the drawing speed is gradually reduced to adapt to the continuous increase of phosphorus concentration in the melt, so that the V / G ratio is always maintained below the critical value of component undercooling. On the other hand, the larger drawing speed reduction rate in the third stage (0.03-0.05 mm / (min·100 mm)) further amplifies the tail impurity volatilization effect, so that the resistivity of the constant diameter tail is appropriately increased, thereby compensating for the problem of low tail resistivity caused by the segregation effect and achieving further uniformity of axial resistivity.

[0062] Furthermore, in the first stage of equal diameter measurement, the crystal rotation speed is 11-13 rpm, the crucible rotation speed is 0.5-4 rpm, the argon flow rate is 130-140 slpm, and the furnace pressure is 12-16 kPa. In the second stage of equal diameter measurement, the crystal rotation speed is 10-12 rpm, the crucible rotation speed is 0.5-4 rpm, the argon flow rate is 140-160 slpm, and the furnace pressure is 16-25 kPa. In the third stage of equal diameter measurement, the crystal rotation speed is 8-12 rpm, the crucible rotation speed is 0.5-4 rpm, the argon flow rate is 120-140 slpm, and the furnace pressure is 25-20 kPa. Maintaining a crystal rotation speed higher than the crucible rotation speed in each stage promotes a more uniform radial distribution of phosphorus impurities at the solid-liquid interface, effectively improving radial resistivity uniformity.

[0063] Furthermore, in the first stage of equal diameter, the power ratio of the side heaters in the thermal field 10 is 60%-70%, and the power ratio of the bottom heaters is 30%-40%. In the second stage of equal diameter, the power ratio of the side heaters in the thermal field 10 is 55%-65%, and the power ratio of the bottom heaters is 35%-45%. In the third stage of equal diameter, the power ratio of the side heaters in the thermal field 10 is 50%-60%, and the power ratio of the bottom heaters is 40%-50%.

[0064] Example:

[0065] Adopting such Figure 1-5 The apparatus shown is used for doping. High-purity red phosphorus (purity ≥99.9999%) is filled into the storage chamber 321 of the cylinder. The filling amount is 1.5-2.5 times the theoretical doping amount calculated based on the target resistivity. It is located above the quartz crucible and parallel to the seed crystal.

[0066] The polycrystalline silicon raw material was placed into a quartz crucible and evacuated to a vacuum of 1.0 × 10⁻⁶. -3 Below Pa, high-purity argon gas is introduced, the furnace pressure is 10-16 kPa, and the heater is started to heat the polycrystalline silicon until it is completely melted. The temperature of the silicon melt is stabilized at 1420-1450℃.

[0067] After the silicon melt temperature stabilizes, the guide graphite tube 322 is slowly immersed into the silicon melt through the telescopic quartz tube and the drive cylinder 210 at an immersion speed of 1-3 mm / min, with the immersion depth of the guide graphite tube 322 being 100 mm below the surface of the silicon melt. During this process, the red phosphorus in the inner storage chamber gradually sublimates upon heating, and the gaseous red phosphorus molecules enter the first volatilization chamber and the second volatilization chamber through the volatilization holes 3211 on the side wall of the storage chamber, entering the silicon solution. After doping is completed, the drive cylinder 210 drives the tube upward, causing the guide graphite tube 322 to detach from the silicon solution and be positioned above the quartz crucible.

[0068] The crystal pulling operation is performed using conventional methods, with a pulling speed of 2.5-4.0 mm / min, a crystal rotation speed of 8-16 rpm, and a crucible rotation speed of 0.5-4 rpm. After crystal pulling, a shoulder-forming operation is performed to gradually increase the crystal diameter to the target diameter.

[0069] Once the crystal diameter reaches the target size, it enters the constant diameter growth stage.

[0070] Starting from a constant diameter and gradually increasing to a constant diameter of 200 mm, the pulling speed is reduced from 1.2 mm / min to 1 mm / min, and the axial temperature gradient at the solid-liquid interface is 2.5-3.5 K / mm. In the thermal field 10, the side heater accounts for 60% of the power, the bottom heater accounts for 40%, the crystal rod rotation speed is 12 rpm, the crucible rotation speed is 0.5 rpm, the furnace pressure is 16 kPa, and the argon flow rate is 130 slm.

[0071] The crystal rod is drawn from a diameter of 200 mm to a diameter of 700 mm. The drawing speed is linearly reduced at a rate of 0.015-0.025 mm / (min·100 mm), starting from the drawing speed at the end of the first stage. The axial temperature gradient at the solid-liquid interface is 2.0-3.0 K / mm. The side heater in the thermal field 10 accounts for 55% of the power, the bottom heater accounts for 45% of the power, the crystal rod rotates at 10 rpm, the crucible rotates at 1 rpm, the furnace pressure gradually increases from 16 kPa to 25 kPa as the diameter length increases, and the argon flow rate gradually increases to 150 slm.

[0072] From the initial drawing length of 700 mm to the end of the drawing process, the drawing speed decreases linearly at a rate of 0.03-0.05 mm / (min·100 mm), starting from the drawing speed at the end of the second stage. The axial temperature gradient at the solid-liquid interface is 1.5-2.5 K / mm. The power ratio of the side heater in the thermal field 10 is 50%, and the power ratio of the bottom heater is 40%. The crystal rod rotation speed is 9 rpm, the crucible rotation speed is 2 rpm, the furnace pressure gradually increases from 25 kPa to 20 kPa as the length of the drawing length increases, and the argon flow rate gradually decreases to 130 slm.

[0073] Once the ingot reaches the target length, the pulling speed is increased at a rate of 0.2-0.4 mm / min for the finishing operation, gradually reducing the ingot diameter until it detaches from the molten silicon surface. After finishing, the ingot is slowly cooled to room temperature at a cooling rate of 3-8 °C / min.

[0074] Comparative Example

[0075] The process is the same as in the examples, using a conventional bell jar for doping.

[0076] The experiments were conducted three times according to the schemes of the examples and comparative examples. The resistivity, axial resistivity uniformity, and carbon content of the obtained crystal rods were measured respectively, and the results are as follows. Figure 6-10 As shown.

[0077] Depend on Figure 6 , 7 As shown, the resistivity of the crystal rods prepared by the method in the embodiments is relatively stable and has good reproducibility. The resistivity of the crystal rods pulled in the comparative example is unstable and too high, indicating that the doping using the device of the present invention can continuously dope and directly dope into the silicon melt to achieve low resistance and ensure resistivity stability.

[0078] Depend on Figure 8 , 9 As shown, the resistivity uniformity of the crystal rod prepared by the method of the embodiment is greatly improved compared with that of the comparative method, and the uniformity is excellent.

[0079] Because the predetermined slow-release doping device 20 of the present invention uses porous graphite material, the carbon content at the tail of the single crystal is monitored. Figure 10 As shown, the carbon content of the crystal rod prepared by the method of the embodiment is the same as that of the comparative example. Therefore, the porous graphite material used in the predetermined slow-release doping device 20 of the present invention will not have a significant impact on the carbon content (it can be controlled below 0.4 ppma).

[0080] 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 method for improving the resistivity uniformity of heavily phosphorus-doped Czochralski silicon single crystals, characterized in that, In a thermal field, a pre-set slow-release doping device is set on the thermal field. Doping is carried out through the pre-set slow-release doping device to pre-dope the dopant in a continuous slow-release manner, thereby improving the doping efficiency. At the same time, the pulling speed of the ingot and the axial temperature gradient at the solid-liquid interface are controlled during the constant diameter process to effectively suppress the occurrence of component undercooling and improve the uniformity of the axial resistivity of the 12-inch heavily doped red phosphorus ingot. The axial temperature gradient at the solid-liquid interface is 1.5-3.5 K / mm, and the axial temperature gradient at the solid-liquid interface gradually decreases with the increase of the constant diameter length. The pulling speed is 0.2 mm / min to 1.20 mm / min, and the pulling speed gradually decreases as the diameter length increases.

2. The preparation method for improving the resistivity uniformity of heavily phosphorus-doped Czochralski silicon single crystals as described in claim 1, characterized in that, The predetermined slow-release doping device includes an isolation feed assembly, a driving assembly, and a slow-release assembly. The isolation feed assembly and the driving assembly are installed outside the thermal field, and the slow-release assembly is installed inside the thermal field. The isolation feed assembly is connected to the slow-release assembly. The driving assembly is connected to both the isolation feed assembly and the slow-release assembly. The driving assembly drives the isolation feed assembly to open and close, allowing the dopant to enter the slow-release assembly through the isolation feed assembly. The driving assembly drives the slow-release assembly to rise and fall, so that the lower part of the slow-release assembly is located at a predetermined distance within the silicon solution for slow release of the dopant.

3. The preparation method for improving the resistivity uniformity of heavily doped red phosphorus Czochralski silicon single crystal as described in claim 2, characterized in that, The slow-release component includes a telescopic part and a slow-release part located within the thermal field. One end of the telescopic part is connected to the isolation feeding component, and the other end of the telescopic part is connected to the slow-release part. The telescopic end of the telescopic part is also connected to the driving component.

4. The preparation method for improving the resistivity uniformity of heavily phosphorus-doped Czochralski silicon single crystals as described in claim 3, characterized in that, The slow-release unit includes a coaxial cylindrical body and a guide graphite tube. The upper part of the cylindrical body is open, and the side wall of the cylindrical body has volatilization holes. The interior of the guide graphite tube is a hollow cylindrical body, and the diameter of the cylindrical body is smaller than the diameter of the hollow cylindrical body of the guide graphite tube. The cylindrical body is located inside the hollow cylindrical body of the guide graphite tube. The upper part of the cylindrical body is connected to the upper part of the guide graphite tube to form a first volatilization chamber outside the cylindrical body and inside the guide graphite tube. The outer wall of the guide graphite tube is provided with external threads, and the guide graphite tube is threadedly connected to the free end of the telescopic part so that the upper opening of the cylindrical body is aligned with the lower outlet of the telescopic part. The lower part of the guide graphite tube can enter the silicon solution a predetermined distance. The inner layer of the guide graphite tube is hollow and communicates with the bottom to form a second volatilization chamber. The inner wall of the guide graphite tube is made of a high-temperature resistant porous material so that the dopant enters the first volatilization chamber and the second volatilization chamber sequentially from the cylindrical body into the silicon solution.

5. The preparation method for improving the resistivity uniformity of heavily phosphorus-doped Czochralski silicon single crystals as described in claim 4, characterized in that, The upper part of the guide graphite tube is cylindrical, and the lower part is an inverted frustum-shaped cone. The inverted frustum-shaped guide graphite tube is located within the silicon melt.

6. The preparation method for improving the resistivity uniformity of heavily doped red phosphorus Czochralski silicon single crystal as described in claim 5, characterized in that, The lower part of the guide graphite tube can enter the silicon solution by a predetermined distance of 50mm-150mm.

7. The preparation method for improving the resistivity uniformity of heavily doped red phosphorus Czochralski silicon single crystal as described in claim 4, characterized in that, The telescopic part includes a fixed quartz tube and a telescopic quartz tube located within the thermal field. One end of the fixed quartz tube is connected to the lower part of the isolation feeding assembly, and the other end of the fixed quartz tube is movably connected to one end of the telescopic quartz tube. The other end of the telescopic quartz tube is connected to the upper end of the guide graphite tube. The driving assembly includes a driving cylinder, a first connecting rod, a traction rod, and a second connecting rod. The driving cylinder is parallel to the traction rod and perpendicular to the first connecting rod. The driving cylinder and the first connecting rod are located outside the thermal field. The telescopic end of the driving cylinder is connected to one end of the first connecting rod, and the other end of the first connecting rod is connected to one end of the traction rod. The other end of the traction rod is connected to one end of the second connecting rod, and the other end of the second connecting rod is connected to the outer wall of the telescopic quartz tube, thereby driving the telescopic quartz tube to move up and down along the fixed quartz tube.

8. The preparation method for improving the resistivity uniformity of heavily doped red phosphorus Czochralski silicon single crystal as described in claim 7, characterized in that, The isolation feeding assembly includes a feeding pipe, a tilting shaft, and two tilting plates arranged sequentially from top to bottom along the feeding pipe. There are two tilting shafts, one end of which is fixedly equipped with a tilting rod, and the other end of which is equipped with a gravity hammer. The driving assembly includes a driving motor and a driving plate. The feeding pipe is connected to the top of the fixed quartz tube. The tilting shaft is arranged along the height direction of the feeding pipe. One side of the tilting plate is connected to the tilting shaft. The driving shaft of the driving motor is connected to one end of the driving plate. The other end of the driving plate can contact one of the tilting rods under the rotation of the driving motor to drive the corresponding tilting plate to tilt.

9. The preparation method for improving the resistivity uniformity of heavily doped red phosphorus Czochralski silicon single crystal as described in claim 1, characterized in that, Controlling the pulling speed of the crystal rod and the axial temperature gradient at the solid-liquid interface during the constant diameter process specifically includes the following steps: In the first stage of constant diameter, the pulling speed is 1-1.2 mm / min, and the axial temperature gradient at the solid-liquid interface is 2.5-3.5 K / mm. In the second stage of constant diameter, the pulling speed starts from the pulling speed at the end of the first stage and decreases linearly at a rate of 0.015-0.025 mm / (min·100 mm), and the axial temperature gradient at the solid-liquid interface is 2.0-3.0 K / mm. In the third stage of constant diameter, the pulling speed starts from the pulling speed at the end of the second stage and decreases linearly at a rate of 0.03-0.05 mm / (min·100mm), and the axial temperature gradient at the solid-liquid interface is 1.5-2.5 K / mm. The first, second, and third stages of equal diameter are continuous equal diameter processes. The first stage of equal diameter refers to the process from the start of equal diameter to 200mm, the second stage of equal diameter refers to the process from 200mm to 700mm, and the third stage of equal diameter refers to the process from 700mm to the end of equal diameter.

10. The preparation method for improving the resistivity uniformity of heavily doped red phosphorus Czochralski silicon single crystal as described in claim 9, characterized in that, In the first stage of equal diameter, the power of the side heaters in the thermal field accounts for 60%-70%, and the power of the bottom heater accounts for 30%-40%. In the second stage of equal diameter, the power of the side heaters in the thermal field accounts for 55%-65%, and the power of the bottom heater accounts for 35%-45%. In the third stage of equal diameter, the power of the side heaters in the thermal field accounts for 50%-60%, and the power of the bottom heater accounts for 40%-50%.

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