A method for pulling low-phosphorus-doped single crystal silicon in a low-pressure environment

Abstract

The present application relates to the technical field of semiconductor single crystal silicon preparation, in particular to a drawing method of low-doped phosphorus single crystal silicon under low furnace pressure environment, the present application controls the whole process of low furnace pressure section by precise control of melting material, crystal pulling, shoulder, constant diameter and tailing, which can effectively inhibit the mixing of oxygen and carbon impurities in the single crystal furnace, reduce the internal defect density of the crystal bar, accurately control the uniformity of the doping concentration of the low-doped phosphorus system, solve the problem of excessive evaporation of phosphorus element under low furnace pressure, greatly reduce the axial and radial resistivity deviation of the crystal bar, improve the overall quality and yield of the crystal bar, and the process has strong stability and wide adaptability, can be used to prepare high-uniformity, low-impurity and low-defect low-doped phosphorus n-type single crystal silicon bar on a large scale, and is suitable for the preparation of high-end semiconductor devices, photovoltaic high-efficiency cells and integrated circuit substrate materials.

Description

Technical Field

[0001] This invention relates to the field of semiconductor single-crystal silicon preparation technology, specifically a method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure. Background Technology

[0002] With the development of the semiconductor market, monocrystalline silicon is playing an increasingly important role. Due to its excellent conductivity and uniform crystal structure, it has become a key material for modern integrated circuit manufacturing. The Czochralski growth process is the gradual crystallization of molten polycrystalline silicon into solid monocrystalline silicon. Intrinsic monocrystalline silicon without impurities has a very high resistivity and is almost non-conductive, making it unsuitable for market applications. Therefore, dopants are added to introduce impurities and change the resistivity of monocrystalline silicon. Generally, phosphorus is used as the dopant for lightly doped N-type monocrystalline silicon.

[0003] For example, Chinese patent CN1201387482A discloses a crystal pulling method to reduce OISF in large-size lightly phosphorus-doped monocrystalline silicon rods. In this technical solution, the raw materials and dopant (phosphorus master alloy) are placed together in a crucible for melting during the material preparation stage. Although the rapid volatilization of phosphorus can be suppressed to some extent in the blast furnace pressure process, the argon convection rate in the single crystal furnace is slow under the blast furnace pressure environment. Oxygen and carbon impurities in the furnace cannot be discharged in time, which can easily lead to excessive oxygen and carbon content in the crystal rod, causing defects such as dislocations, vacancies, and micropores inside the crystal rod, seriously affecting the electrical properties and service life of the monocrystalline silicon. At the same time, the traditional constant furnace pressure process cannot adapt to the doping characteristics of the lightly phosphorus-doped system. The light phosphorus concentration range is narrow and the sensitivity is high. Under blast furnace pressure, the diffusion of melt doping is uneven, which can easily cause large deviations in axial and radial resistivity of the crystal rod, severe head resistance warping, poor stability in mass production, and low yield of finished products. Summary of the Invention

[0004] To address the problems existing in current technology, the purpose of this invention is to provide a method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure. This method employs a staged gradient low furnace pressure control process, coupled with appropriately matched argon flow rate, crystal rotation, crucible rotation, temperature compensation, and doping compensation processes. Furthermore, the phosphorus in the introduced dopant is not easily volatilized.

[0005] Complete the Czochralski growth of lightly phosphorus-doped single crystal silicon

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure, characterized by comprising the following steps:

[0008] S1. After cleaning and drying the high-purity polycrystalline silicon raw material, it is placed into the quartz crucible of the single crystal furnace. The phosphorus dopant is evenly spread on the surface and interlayer of the polycrystalline silicon raw material. The single crystal furnace is sealed, and a vacuum is continuously drawn and high-purity argon is introduced as a protective gas. The temperature is controlled in stages and the furnace pressure is controlled in stages until the polycrystalline silicon raw material is completely melted into a uniform silicon melt.

[0009] S2. After the material is melted, stabilize the silicon melt surface and maintain the furnace pressure at 60-80 Pa. Control the crystal rotation speed at 20-22 r / min and the crucible rotation speed at 4-6 r / min. Using the conventional necking crystal pulling process, drive the seed crystal rod to slowly descend, bringing the silicon seed crystal close to the silicon melt surface. Hover the seed crystal at a position 20-30 mm away from the melt surface for 3-5 minutes to preheat and eliminate cold shock. Then slowly lower the seed crystal to lightly touch the silicon melt surface. After the seed crystal contacts the melt, hold it for 10-20 seconds to allow the seed crystal surface to slightly melt. Slightly reduce the furnace temperature by 2-5℃ and instantly increase the pulling speed to quickly pull out a thin-diameter crystal neck with a necking diameter of 3-5 mm and a necking length of 15-25 mm. After the necking is formed, briefly maintain the pulling speed, temperature, and furnace pressure unchanged for 30-40 seconds to confirm that the necking is complete, without dislocations or cracks. The crystal pulling process is then complete.

[0010] S3. After crystal pulling is completed, the shoulder formation stage begins. The furnace pressure is maintained at 50-60 Pa. The temperature is slowly reduced to expand the shoulder, and the shoulder formation rate is controlled at 0.8-1.2 mm / min. After the shoulder reaches the target crystal rod diameter, the furnace pressure is kept constant. The crystal rotation speed is gradually increased to the preset constant diameter speed at an increase rate of 0.3-0.4 r / min. Then, the crucible rotation speed is slightly increased at an increase rate of 0.2-0.3 r / min. The entire adjustment time is controlled at 60-90 s. Simultaneously, the crystal pulling rate is slightly increased and the furnace temperature is finely adjusted to offset the interface supercooling. The crystal is smoothly switched from the conical shoulder growth state to the cylindrical constant diameter growth state. There are no parameter changes or liquid surface disturbances throughout the process. This avoids melt sloshing, local segregation of phosphorus doping, and growth dislocations in the crystal rod under low pressure. The furnace pressure is kept constant during the shoulder formation stage, and there is no pressure fluctuation.

[0011] S4. After the shoulder is completed, the constant diameter growth stage begins. The entire process uses an ultra-low and stable furnace pressure of 30-50 Pa. The argon flow rate and heating power are dynamically adjusted according to the growth length of the crystal rod to compensate for the loss of phosphorus volatilization under low furnace pressure. The constant diameter growth rate is controlled at 1.0-1.5 mm / min. The crystal rotation and crucible rotation are dynamically adjusted simultaneously to ensure the uniformity of radial and axial doping of the crystal rod.

[0012] S5. After the crystal rod grows to the target length, gradually increase the furnace pressure to 100-120Pa, slowly increase the heating power, reduce the temperature difference between the crystal rod and the melt, use a slow-ending process to separate the crystal rod and the silicon melt, then cool down in sections, pressurize and repressurize, and take out the crystal rod after it cools naturally to room temperature in the furnace to complete the pulling process.

[0013] Furthermore, in step S1, the high-purity polycrystalline silicon has a purity ≥ 99.9999999%;

[0014] The phosphorus doping concentration in the silicon melt is 1×10⁻⁶. 15 -5×10 15 cm -3 (10 to the power of 15 phosphorus atoms are added to every cubic centimeter of silicon).

[0015] The flow rate of the argon gas is controlled at 80-120 L / min.

[0016] Furthermore, in step S1, the segmented heating and segmented furnace pressure control are specifically operated as follows: the furnace pressure is 150-200 Pa in the initial stage of melting and maintained for 30-40 min, the heating rate is 4-6℃ / min, and the temperature is raised to 1400-1450℃; in the middle stage of melting, the furnace pressure is reduced to 100-150 Pa and maintained for 50-80 min, and the temperature is continuously raised to 1460-1470℃; in the final stage of melting, the furnace pressure is stabilized at 80-100 Pa, and the temperature is maintained and the material is stabilized for 25-30 min.

[0017] Furthermore, in step S4, during the constant diameter growth stage, the argon flow rate is finely adjusted by 2-5 L / min and the heating power by 0.5-1.5 KW for every 100 mm increase in crystal rod growth, to compensate for phosphorus volatilization loss under low furnace pressure and ensure that the axial resistivity deviation of the crystal rod is ≤3%.

[0018] During the constant diameter growth stage, the crystal rotation speed is 20-24 r / min, the crucible rotation speed is 5-7 r / min, and the crystal rotation and crucible rotation are kept in opposite directions.

[0019] Furthermore, in step S5, the heating rate during the final stage is 2-3℃ / min, the furnace pressure recovery rate is 5-7Pa / min, and the crystal rods are cooled in stages after separation, with a cooling rate of 1-2℃ / min, to avoid thermal stress defects in the crystal rods.

[0020] As a further preferred embodiment of the present invention, the phosphorus-based dopant is prepared by the following method:

[0021] 1) After cleaning and drying the high-purity silicon, spread it evenly in the graphite crucible of the vacuum activation furnace. The thickness of the spread material is controlled at 40-50mm. After sealing, it is treated at a constant temperature in a vacuum environment for 2-3 hours and then cooled to room temperature.

[0022] 2) In a room temperature and light-protected environment, static weak etching is performed using electronic-grade high-purity hydrofluoric acid. The etching time is controlled at 8-12 minutes. Then, it is repeatedly rinsed with ultrapure water and dried at 120-130℃ to obtain pretreated high-purity silicon.

[0023] 3) Using the silicon sandwich phosphorus layering method, the bottom layer is pretreated high-purity silicon, the middle layer is uniformly spread with high-purity red phosphorus powder, and the top layer is covered with pretreated high-purity silicon. Then the whole thing is placed in a quartz crucible in a vacuum melting furnace, vacuumed to 30-60Pa, held for 5-10 minutes, and then heated to 1250-1300℃ and kept at a constant temperature for 1-2 hours.

[0024] 4) After the processing is completed, first cool down to 1000-1050℃, then let it cool naturally to room temperature with the furnace. After polishing the obtained silicon-phosphorus alloy material, wash it with ultrapure water, lightly acid wash it with dilute nitric acid, and rinse it with ultrapure water in sequence to remove impurities. Then dry it for 2-3 hours to obtain granular phosphorus dopant.

[0025] Furthermore, in step 1), the cleaning process involves ultrasonic cleaning with deionized water and electronic-grade anhydrous ethanol for 15-20 minutes.

[0026] The constant temperature treatment is performed at a temperature of 800-900℃ and a pressure of 50-80Pa.

[0027] Furthermore, in step 2), the concentration of the electronic-grade high-purity hydrofluoric acid is 4-5 wt%.

[0028] Furthermore, in step 3), the heating rate is 3-5°C / min.

[0029] Furthermore, in step 4), the cooling rate is 2-3℃ / min;

[0030] The drying process takes place at a temperature of 110-120℃.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] This invention achieves precise segmented control of the entire process—from melting and crystal pulling to shoulder formation, equal diameter setting, and finishing—with low furnace pressure. This effectively suppresses the incorporation of oxygen and carbon impurities in the single crystal furnace, reducing the internal defect density of the crystal rod. It also precisely controls the uniformity of the doping concentration in the lightly phosphorus-doped system, solving the problem of excessive phosphorus volatilization under low furnace pressure. This significantly reduces the axial and radial resistivity deviation of the crystal rod, improving the overall quality of the crystal rod and the yield of the finished product. Furthermore, the process exhibits strong stability and wide adaptability, enabling the large-scale preparation of highly uniform, low-impurity, and low-defect lightly phosphorus-doped n-type single crystal silicon rods. It is suitable for the preparation of high-end semiconductor devices, high-efficiency photovoltaic cells, and integrated circuit substrate materials.

[0033] Meanwhile, to further reduce phosphorus volatilization under high temperature and low furnace pressure, and to avoid problems such as phosphorus concentration drift, uneven resistivity at the head and tail of the crystal rod, and head resistance reversal, this invention uses a novel process to prepare phosphorus-based dopants. First, high-purity silicon is cleaned and dried, then placed in a vacuum activation furnace for treatment. The low-temperature vacuum environment can precisely destroy the original dense and complete crystal lattice structure of the silicon raw material, inducing the generation of uniformly distributed lattice vacancies and micro-dislocation defects inside the silicon matrix. At the same time, a loose microcrystalline structure is initially formed, providing basic active sites for subsequent pore formation and phosphorus embedding. Hydrofluoric acid is used for etching, which can precisely etch the dense oxide passivation layer on the surface of the silicon material, while also corroding silicon atoms at lattice defects, constructing a three-dimensional interconnected microporous network structure inside the silicon matrix, thereby obtaining highly active, porous, defect-enriched pretreated high-purity silicon. Then, a silicon-intercalated phosphorus-laying method is used: the bottom layer is pretreated high-purity silicon, the middle layer is uniformly sprinkled with high-purity red phosphorus powder, and the top layer is covered with pretreated high-purity silicon, avoiding direct exposure and high-temperature volatilization of red phosphorus. To ensure uniform phosphorus source penetration, under the high-temperature environment of a vacuum melting furnace (temperature below the melting point of silicon and above the melting point of phosphorus), molecular diffusion under high temperature and low pressure is utilized to allow the liquid phosphorus phase to fully penetrate into the micropores, lattice vacancies, and dislocation defects of the silicon matrix, achieving in-situ embedding of phosphorus atoms. Simultaneously, slow cooling allows the phosphorus atoms embedded in the micropores and lattice defects to achieve a stable arrangement, gradually replacing silicon atoms to form stable Si-P covalent bonds, completing atomic-level solidification. This achieves a dual effect of physical adsorption and chemical bonding to lock in the phosphorus component, greatly inhibiting the release of free phosphorus. Furthermore, polishing removes trace amounts of free phosphorus and unbonded residual phosphorus components adhering to the alloy surface, retaining only the stable phosphorus component anchored by lattice bonds and micropores within the matrix. This eliminates the high-temperature volatilization loss of free phosphorus from the source, thereby inhibiting the migration and diffusion of phosphorus atoms to the melt surface and preventing large-scale volatilization of phosphorus on the melt surface. This completely solves the core problems of rapid phosphorus loss and head resistance warping in the early stage of crystal pulling under low furnace pressure. Detailed Implementation

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

[0035] Example 1

[0036] A method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure conditions, specifically including the following steps:

[0037] S1. After cleaning and drying the high-purity polycrystalline silicon raw material with a purity of 99.9999999%, it is placed into a quartz crucible in a single-crystal furnace. Phosphorus dopant is evenly spread on the surface and interlayer of the polycrystalline silicon raw material, with a phosphorus doping concentration of 1×10⁻⁶.15 cm -3 The single crystal furnace was sealed, and a vacuum was continuously drawn while high-purity argon gas with a purity of 99.9999% was introduced as a protective gas. The argon gas flow rate was controlled at 80L / min throughout the process. The furnace pressure was 150Pa in the initial stage of melting and maintained for 30min. The heating rate was 4℃ / min, and the temperature was raised to 1400℃. In the middle stage of melting, the furnace pressure was reduced to 100Pa and maintained for 50min. The temperature was then continuously raised to 1460℃. In the final stage of melting, the furnace pressure was stabilized at 80Pa. The furnace was held at the temperature for 25min to stabilize the material. The polycrystalline silicon raw material was completely melted into a uniform silicon melt.

[0038] S2. After the melting is completed, stabilize the state of the silicon melt surface, maintain the furnace pressure at 60Pa, control the crystal rotation speed at 20r / min and the crucible rotation speed at 4r / min, and use the conventional necking crystal pulling process to quickly pull out a thin-diameter crystal neck with a necking diameter of 3mm and a necking length of 15mm. After the necking is formed, keep the pulling speed, temperature and furnace pressure unchanged for a short time and stabilize for 30s. Confirm that the necking is complete, without dislocations or cracks, and the crystal pulling process is completed.

[0039] S3. After the crystal pulling is completed, the shoulder expansion stage begins. The furnace pressure is maintained at 50Pa. The temperature is slowly reduced to expand the shoulder. The shoulder expansion rate is controlled at 0.8mm / min. After the shoulder reaches the target crystal rod diameter, the rotation speed parameters are smoothly adjusted to complete the shoulder rotation, ensuring that there are no sudden changes in air pressure or temperature during the shoulder rotation process.

[0040] S4. After the shoulder is completed, the constant diameter growth stage begins. The entire process uses an ultra-low and stable furnace pressure of 30 Pa. During the constant diameter growth stage, the argon flow rate is finely adjusted to 2 L / min and the heating power to 0.5 KW for every 100 mm of crystal growth to compensate for the loss of phosphorus volatilization under low furnace pressure, ensuring that the axial resistivity deviation of the crystal rod is ≤3%. The constant diameter growth rate is controlled at 1.0 mm / min, the crystal rotation speed is 20 r / min, and the crucible rotation speed is 5 r / min. The crystal rotation and crucible rotation are kept in opposite directions to ensure the uniformity of radial and axial doping of the crystal rod.

[0041] S5. After the crystal rod grows to the target length, gradually increase the furnace pressure to 100Pa, slowly increase the heating power at a heating rate of 2℃ / min, and increase the furnace pressure at a rate of 5Pa / min to reduce the temperature difference between the crystal rod and the melt. Use a slow-ending process to separate the crystal rod from the silicon melt. After the crystal rod is separated, cool it in stages at a rate of 1℃ / min. After the furnace is naturally cooled to room temperature, take out the crystal rod to complete the pulling process.

[0042] The preparation method of phosphorus-based dopants is as follows:

[0043] 1) Clean the high-purity silicon with deionized water and electronic-grade anhydrous ethanol by ultrasonic cleaning for 15 minutes and then dry it. Then spread it evenly in the graphite crucible of the vacuum activation furnace, with the thickness of the material controlled at 40 mm. After sealing, treat it at 800℃ and 50 Pa vacuum for 2 hours and then cool it to room temperature.

[0044] 2) In a room temperature and light-protected environment, static weak etching was performed using 4wt% electronic-grade high-purity hydrofluoric acid. The etching time was controlled at 8 minutes. Then, the silicon was repeatedly rinsed with ultrapure water and dried at 120°C to obtain pretreated high-purity silicon.

[0045] 3) Using the method of silicon material sandwiching phosphorus, the bottom layer is pretreated high-purity silicon, the middle layer is uniformly spread with high-purity red phosphorus powder, the top layer is covered with pretreated high-purity silicon, and then the whole thing is placed in a quartz crucible of a vacuum melting furnace, vacuumed to 30Pa, held for 5min, and then heated to 1250℃ at a rate of 3℃ / min and kept at a constant temperature for 1h.

[0046] 4) After the processing is completed, the temperature is first reduced to 1000℃ at a rate of 2℃ / min, and then naturally cooled to room temperature with the furnace. After polishing the obtained silicon-phosphorus alloy material, it is washed with ultrapure water, lightly acid-washed with dilute nitric acid, and rinsed with ultrapure water in sequence to remove impurities. After drying at 110℃ for 2 hours, granular phosphorus dopant can be obtained.

[0047] Example 2

[0048] A method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure conditions, specifically including the following steps:

[0049] S1. After cleaning and drying the high-purity polycrystalline silicon raw material with a purity of 99.9999999%, it is placed into a quartz crucible in a single-crystal furnace. Phosphorus dopant is then evenly spread on the surface and interlayer of the polycrystalline silicon raw material, with a phosphorus doping concentration of 3 × 10⁻⁶. 15 cm -3 The single crystal furnace was sealed, and a vacuum was continuously drawn while high-purity argon gas with a purity of 99.9999% was introduced as a protective gas. The argon gas flow rate was controlled at 100L / min throughout the process. The furnace pressure was 170Pa in the initial stage of melting and maintained for 35min. The heating rate was 5℃ / min, and the temperature was raised to 1420℃. In the middle stage of melting, the furnace pressure was reduced to 120Pa and maintained for 7min. The temperature was then continuously raised to 1470℃. In the final stage of melting, the furnace pressure was stabilized at 90Pa. The temperature was held and the material was stabilized for 25min, and the polycrystalline silicon raw material was completely melted into a uniform silicon melt.

[0050] S2. After the melting is completed, stabilize the state of the silicon melt surface, maintain the furnace pressure at 70Pa, control the crystal rotation speed at 21r / min and the crucible rotation speed at 5r / min, and use the conventional necking crystal pulling process to quickly pull out a small diameter crystal neck with a necking diameter of 4mm and a necking length of 20mm. After the necking is formed, keep the pulling speed, temperature and furnace pressure unchanged for a short time, stabilize for 35s, and confirm that the necking is complete, without dislocations or cracks. The crystal pulling process is then completed.

[0051] S3. After the crystal pulling is completed, the shoulder expansion stage begins. The furnace pressure is maintained at 55Pa. The temperature is slowly reduced to expand the shoulder. The shoulder expansion rate is controlled at 1mm / min. After the shoulder reaches the target crystal rod diameter, the rotation speed parameters are adjusted smoothly to complete the shoulder expansion. Ensure that there are no sudden changes in air pressure or temperature during the shoulder expansion process.

[0052] S4. After the shoulder is formed, the constant diameter growth stage begins. The entire process is carried out under an ultra-low and stable furnace pressure of 40 Pa. During the constant diameter growth stage, the argon flow rate is finely adjusted to 3 L / min and the heating power is adjusted to 1 KW for every 100 mm of crystal growth to compensate for the loss of phosphorus volatilization under low furnace pressure. This ensures that the axial resistivity deviation of the crystal rod is ≤3%. The constant diameter growth rate is controlled at 1.2 mm / min, the crystal rotation speed is 22 r / min, and the crucible rotation speed is 6 r / min. The crystal rotation and crucible rotation are kept in opposite directions to ensure the uniformity of radial and axial doping of the crystal rod.

[0053] S5. After the crystal rod grows to the target length, gradually increase the furnace pressure to 110 Pa, slowly increase the heating power at a heating rate of 2.5℃ / min, and increase the furnace pressure at a rate of 7 Pa / min to reduce the temperature difference between the crystal rod and the melt. Use a slow-ending process to separate the crystal rod from the silicon melt. After the crystal rod is separated, cool it in sections at a rate of 1.5℃ / min. After the furnace is naturally cooled to room temperature, remove the crystal rod to complete the pulling process.

[0054] The preparation method of phosphorus-based dopants is as follows:

[0055] 1) High-purity silicon was ultrasonically cleaned with deionized water and electronic-grade anhydrous ethanol for 20 minutes and then dried. It was then evenly spread in the graphite crucible of the vacuum activation furnace, with the thickness of the spread material controlled at 45 mm. After sealing, it was constant temperature treated at 850℃ and 70 Pa vacuum for 2.5 h and then cooled to room temperature.

[0056] 2) In a room temperature and light-protected environment, static weak etching was performed using electronic-grade high-purity hydrofluoric acid with a concentration of 4.5wt%. The etching time was controlled at 10 min. Then, the silicon was repeatedly rinsed with ultrapure water and dried at 125℃ to obtain pretreated high-purity silicon.

[0057] 3) Using the method of silicon material sandwiching phosphorus, the bottom layer is pretreated high-purity silicon, the middle layer is uniformly spread with high-purity red phosphorus powder, the top layer is covered with pretreated high-purity silicon, and then the whole thing is placed in a quartz crucible of a vacuum melting furnace, vacuumed to 50Pa, held for 8min, and then heated to 1280℃ at a rate of 4℃ / min, and kept at a constant temperature for 1.5h.

[0058] 4) After the processing is completed, the temperature is first reduced to 1020℃ at a rate of 2.5℃ / min, and then naturally cooled to room temperature with the furnace. After polishing the obtained silicon-phosphorus alloy material, it is washed with ultrapure water, lightly acid-washed with dilute nitric acid, and rinsed with ultrapure water in sequence to remove impurities. After drying at 115℃ for 2.5h, granular phosphorus dopant can be obtained.

[0059] Example 3

[0060] A method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure conditions, specifically including the following steps:

[0061] S1. After cleaning and drying the high-purity polycrystalline silicon raw material with a purity of 99.9999999%, it is placed into a quartz crucible in a single-crystal furnace. Phosphorus dopant is then evenly spread on the surface and interlayer of the polycrystalline silicon raw material, with a phosphorus doping concentration of 5 × 10⁻⁶. 15 cm -3 The single crystal furnace was sealed, and a vacuum was continuously drawn while high-purity argon gas with a purity of 99.9999% was introduced as a protective gas. The argon gas flow rate was controlled at 120L / min throughout the process. The furnace pressure was 200Pa in the initial stage of melting and maintained for 40min. The heating rate was 6℃ / min, and the temperature was raised to 1450℃. In the middle stage of melting, the furnace pressure was reduced to 150Pa and maintained for 80min. The temperature was then continuously raised to 1470℃. In the final stage of melting, the furnace pressure was stabilized at 100Pa. The temperature was held and the material was stabilized for 30min, and the polycrystalline silicon raw material was completely melted into a uniform silicon melt.

[0062] S2. After the melting is completed, stabilize the state of the silicon melt surface, maintain the furnace pressure at 80Pa, control the crystal rotation speed at 22r / min and the crucible rotation speed at 6r / min, and use the conventional necking crystal pulling process to quickly pull out a thin-diameter crystal neck with a necking diameter of 5mm and a necking length of 25mm. After the necking is formed, keep the pulling speed, temperature and furnace pressure unchanged for a short time and stabilize for 40s. Confirm that the necking is complete, without dislocations or cracks, and the crystal pulling process is completed.

[0063] S3. After the crystal pulling is completed, the shoulder expansion stage begins. The furnace pressure is maintained at 60Pa. The temperature is slowly reduced to expand the shoulder. The shoulder expansion rate is controlled at 1.2mm / min. After the shoulder reaches the target crystal rod diameter, the rotation speed parameters are smoothly adjusted to complete the shoulder rotation, ensuring that there are no sudden changes in air pressure or temperature during the shoulder rotation process.

[0064] S4. After the shoulder is formed, the constant diameter growth stage begins. The entire process is carried out under an ultra-low and stable furnace pressure of 50 Pa. During the constant diameter growth stage, the argon flow rate is finely adjusted to 5 L / min and the heating power to 1.5 KW for every 100 mm of crystal growth. This compensates for the loss of phosphorus due to volatilization under low furnace pressure, ensuring that the axial resistivity deviation of the crystal rod is ≤3%. The constant diameter growth rate is controlled at 1.5 mm / min, the crystal rotation speed is 24 r / min, and the crucible rotation speed is 7 r / min. The crystal rotation and crucible rotation are kept in opposite directions to ensure the uniformity of radial and axial doping of the crystal rod.

[0065] S5. After the crystal rod grows to the target length, gradually increase the furnace pressure to 120 Pa, slowly increase the heating power, with a heating rate of 3℃ / min and a furnace pressure recovery rate of 8 Pa / min to reduce the temperature difference between the crystal rod and the melt. Use a slow finishing process to separate the crystal rod from the silicon melt. After the crystal rod is separated, cool it in stages at a rate of 2℃ / min. After the furnace is naturally cooled to room temperature, take out the crystal rod to complete the pulling process.

[0066] The preparation method of phosphorus-based dopants is as follows:

[0067] 1) After ultrasonically cleaning the high-purity silicon with deionized water and electronic-grade anhydrous ethanol for 20 minutes and drying it, it is then evenly spread in the graphite crucible of the vacuum activation furnace. The thickness of the spread material is controlled at 50 mm. After sealing, it is treated at a constant temperature of 900℃ and 80Pa vacuum for 3 hours and then cooled to room temperature.

[0068] 2) In a room temperature and light-protected environment, static weak etching was performed using 5wt% electronic-grade high-purity hydrofluoric acid. The etching time was controlled at 12 min. Then, the silicon was repeatedly rinsed with ultrapure water and dried at 130℃ to obtain pretreated high-purity silicon.

[0069] 3) Using the method of silicon material sandwiching phosphorus, the bottom layer is pretreated high-purity silicon, the middle layer is uniformly spread with high-purity red phosphorus powder, the top layer is covered with pretreated high-purity silicon, and then the whole thing is placed in a quartz crucible of a vacuum melting furnace, vacuumed to 60Pa, held for 10min, and then heated to 1300℃ at a rate of 5℃ / min and kept at a constant temperature for 2h.

[0070] 4) After the processing is completed, the temperature is first reduced to 1050℃ at a rate of 3℃ / min, and then naturally cooled to room temperature with the furnace. After polishing the obtained silicon-phosphorus alloy material, it is washed with ultrapure water, lightly acid-washed with dilute nitric acid, and rinsed with ultrapure water in sequence to remove impurities. After drying at 120℃ for 3 hours, granular phosphorus dopant can be obtained.

[0071] Comparative Example 1: This comparative example is basically the same as Example 1, except that the phosphorus dopant used is a commercially available ordinary dense silicon-phosphorus master alloy, and it is fed in small pieces in a conventional manner.

[0072] Comparative Example 2: This comparative example is basically the same as Example 1, except that step 1 is omitted in the preparation of the phosphorus dopant.

[0073] Comparative Example 3: This comparative example is basically the same as Example 1, except that step 2 is omitted in the preparation of the phosphorus dopant.

[0074] Comparative Example 4: This comparative example is basically the same as Example 1, except that in the preparation of the phosphorus dopant, the method of removing the silicon material interlayer and laying phosphorus in step 3) is to directly mix silicon and phosphorus together.

[0075] Comparative Example 5: This comparative example is basically the same as Example 1, except that in the preparation of phosphorus dopant, the slow cooling in step 4) is removed, and natural cooling with the furnace is directly adopted.

[0076] Test experiment:

[0077] Single-crystal silicon rod samples (1000 samples in each group) were obtained by pulling using the methods provided in Examples 1-3 and Comparative Examples 1-5, respectively. The yield was recorded (the proportion of whole rods without broken crystals, polycrystalline structures, or large cracks that could be sliced ​​and used). Ten finished samples were randomly selected from each group, and the number of dislocations per unit area in the same region of the rod sample was counted using a microscope. At the same time, the overall phosphorus volatilization loss rate was calculated on average. Loss rate % = (theoretical total phosphorus mass - measured total phosphorus mass of the rod) ÷ theoretical phosphorus mass × 100%. The experimental results are shown in Table 1.

[0078] Table 1

[0079] Example 1 Example 2 Example 3 Comparative Example 1 Crystal dislocation defects No visible dislocation No visible dislocation No visible dislocation There is obvious dislocation Finished Product Rate % 98.5 99.2 98.8 85.5 Overall phosphorus volatilization loss rate % 2.3 2.0 2.1 15.3 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Crystal dislocation defects A small number of dislocations exist A small number of dislocations exist A small number of dislocations exist A small number of dislocations exist Finished Product Rate % 89.3 91.2 92.7 95.2 Overall phosphorus volatilization loss rate % 12.3 9.6 7.1 5.4

[0080] As shown in Table 1, the pulling method for lightly phosphorus-doped monocrystalline silicon provided by the present invention significantly reduces phosphorus volatilization loss, resulting in monocrystalline silicon rods with very few lattice defects and a high yield. It is suitable for the preparation of high-end semiconductor devices, high-efficiency photovoltaic cells, and integrated circuit substrate materials.

[0081] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure, characterized in that, Specifically, the steps include the following: S1. After cleaning and drying the high-purity polycrystalline silicon raw material, it is placed into the quartz crucible of the single crystal furnace. The phosphorus dopant is evenly spread on the surface and interlayer of the polycrystalline silicon raw material. The single crystal furnace is sealed, and a vacuum is continuously drawn while high-purity argon is introduced. The temperature is controlled in stages and the furnace pressure is controlled in stages until the polycrystalline silicon raw material is completely melted into a uniform silicon melt. S2. After the melting is completed, stabilize the silicon melt surface state, maintain the furnace pressure at 60-80Pa, control the crystal rotation speed at 20-22r / min and the crucible rotation speed at 4-6r / min, and complete the single crystal pulling process using the conventional necking crystal pulling process; S3. After crystal pulling is completed, the shoulder formation stage begins. The furnace pressure is maintained at 50-60 Pa. The temperature is slowly reduced to expand the shoulder. The shoulder formation rate is controlled at 0.8-1.2 mm / min. After the shoulder reaches the target crystal rod diameter, the crystal rotation and crucible rotation parameters are smoothly adjusted to complete the shoulder transition. S4. After the shoulder is completed, the constant diameter growth stage begins. The entire process uses an ultra-low and stable furnace pressure of 30-50 Pa. The argon flow rate and heating power are dynamically adjusted according to the growth length of the crystal rod to compensate for the loss of phosphorus volatilization under low furnace pressure. The constant diameter growth rate is controlled at 1.0-1.5 mm / min. The crystal rotation and crucible rotation are dynamically adjusted simultaneously to ensure the uniformity of radial and axial doping of the crystal rod. S5. After the crystal rod grows to the target length, gradually increase the furnace pressure to 100-120Pa, slowly increase the heating power, reduce the temperature difference between the crystal rod and the melt, use a slow-ending process to separate the crystal rod and the silicon melt, then cool down in sections, pressurize and repressurize, and take out the crystal rod after it cools naturally to room temperature in the furnace to complete the pulling process.

2. The method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure according to claim 1, characterized in that, In step S1, the high-purity polycrystalline silicon has a purity ≥ 99.9999999%; The phosphorus doping concentration in the silicon melt is 1×10⁻⁶. 15 -5×10 15 cm -3 ; The flow rate of the argon gas is controlled at 80-120 L / min.

3. The method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure according to claim 1, characterized in that, In step S1, the segmented heating and segmented furnace pressure control are specifically operated as follows: the furnace pressure is 150-200 Pa in the initial stage of melting and maintained for 30-40 min, the heating rate is 4-6℃ / min, and the temperature is raised to 1400-1450℃; in the middle stage of melting, the furnace pressure is reduced to 100-150 Pa and maintained for 50-80 min, and the temperature is continuously raised to 1460-1470℃; in the final stage of melting, the furnace pressure is stabilized at 80-100 Pa, and the temperature is maintained for 25-30 min.

4. The method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure according to claim 1, characterized in that, In step S4, during the constant diameter growth stage, the argon flow rate is finely adjusted by 2-5 L / min and the heating power by 0.5-1.5 KW for every 100 mm increase in crystal rod growth, to compensate for phosphorus volatilization loss under low furnace pressure and ensure that the axial resistivity deviation of the crystal rod is ≤3%. During the constant diameter growth stage, the crystal rotation speed is 20-24 r / min, the crucible rotation speed is 5-7 r / min, and the crystal rotation and crucible rotation are kept in opposite directions.

5. The method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure according to claim 1, characterized in that, In step S5, the heating rate in the final stage is 2-3℃ / min, the furnace pressure recovery rate is 5-7Pa / min, and the crystal rods are cooled in stages after separation, with a cooling rate of 1-2℃ / min, to avoid thermal stress defects in the crystal rods.

6. The method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure according to claim 1, characterized in that, The phosphorus-based dopant is prepared as follows: 1) After cleaning and drying the high-purity silicon, spread it evenly in the graphite crucible of the vacuum activation furnace. The thickness of the spread material is controlled at 40-50mm. After sealing, it is treated at a constant temperature in a vacuum environment for 2-3 hours and then cooled to room temperature. 2) In a room temperature and light-protected environment, static weak etching is performed using electronic-grade high-purity hydrofluoric acid. The etching time is controlled at 8-12 minutes. Then, it is repeatedly rinsed with ultrapure water and dried at 120-130℃ to obtain pretreated high-purity silicon. 3) Using the silicon sandwich phosphorus layering method, the bottom layer is pretreated high-purity silicon, the middle layer is uniformly spread with high-purity red phosphorus powder, and the top layer is covered with pretreated high-purity silicon. Then the whole thing is placed in a quartz crucible in a vacuum melting furnace, vacuumed to 30-60Pa, held for 5-10 minutes, and then heated to 1250-1300℃ and kept at a constant temperature for 1-2 hours. 4) After the processing is completed, first cool down to 1000-1050℃, then let it cool naturally to room temperature with the furnace. After polishing the obtained silicon-phosphorus alloy material, wash it with ultrapure water, lightly acid wash it with dilute nitric acid, and rinse it with ultrapure water in sequence to remove impurities. Then dry it for 2-3 hours to obtain granular phosphorus dopant.

7. The method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure according to claim 6, characterized in that, In step 1), the cleaning process involves ultrasonic cleaning with deionized water and electronic-grade anhydrous ethanol for 15-20 minutes. The constant temperature treatment is performed at a temperature of 800-900℃ and a pressure of 50-80Pa.

8. The method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure according to claim 6, characterized in that, In step 2), the electronic-grade high-purity hydrofluoric acid has a concentration of 4-5 wt%.

9. The method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure according to claim 6, characterized in that, In step 3), the heating rate is 3-5℃ / min.

10. The method for pulling lightly phosphorus-doped single-crystal silicon under low furnace pressure according to claim 6, characterized in that, In step 4), the cooling rate is 2-3℃ / min; The drying process takes place at a temperature of 110-120℃.