Polysilicon rod for cutting silicon ingots and method of making same

Abstract

The application discloses a polycrystalline silicon rod for cutting silicon cores and a preparation method thereof. The polycrystalline silicon rod comprises, from inside to outside along a radial direction thereof, an original silicon core region and at least three layers of dense deposition regions, a buffer deposition region being formed between two adjacent dense deposition regions, and a density of the buffer deposition region being less than that of the dense deposition regions adjacent to the buffer deposition region. The silicon core product obtained by cutting the polycrystalline silicon rod has high quality and low production cost, and has a high yield.

Description

Technical Field

[0001] This invention belongs to the field of polycrystalline silicon, and more specifically, relates to polycrystalline silicon rods for cutting silicon cores and methods for preparing the same. Background Technology

[0002] Silicon cores are key materials for producing polycrystalline silicon rods using the improved Siemens process. They serve as the initial carrier for chemical vapor deposition (CVD). After deposition, the silicon cores are crushed along with the silicon rods. Current silicon core production processes mainly employ the direct silicon core pulling method and the monocrystalline silicon ingot cutting method. The direct silicon core pulling method requires a dedicated silicon core furnace and polycrystalline rods, resulting in high production costs and difficulty in controlling the impurity content of the silicon cores. The monocrystalline silicon ingot cutting method involves pulling silicon blocks to form monocrystalline silicon rods, which are then cut and acid-washed to produce silicon cores. This method requires high-temperature conditions to promote monocrystalline growth, making product quality difficult to control and resulting in high production costs. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a polycrystalline silicon rod for dicing silicon cores and a method for preparing the same. The silicon core products obtained by dicing this polycrystalline silicon rod are not only of high quality and have low production costs, but also have a high yield.

[0004] In one aspect of the invention, a polycrystalline silicon rod for cutting silicon cores is provided. According to an embodiment of the invention, the polycrystalline silicon rod comprises, from the inside to the outside, a raw silicon core region and at least three densely deposited regions along its radial direction. A buffer deposition region is formed between two adjacent densely deposited regions, the density of which is less than that of the adjacent densely deposited regions. The inventors have found that during the cutting of polycrystalline silicon rods, radial and axial cutting are required. During the cutting process, the silicon rod is subjected to cutting forces in two directions. Compared with existing polycrystalline silicon rods, the present invention, by forming at least three densely deposited regions with higher density along the radial direction of the polycrystalline silicon rod, enables the polycrystalline silicon rod to have good overall density. Simultaneously, by forming buffer deposition regions with lower density alternating with the densely deposited regions, a certain cutting and compression resistance can be provided during the cutting of the silicon rod. Furthermore, by making the outermost layer of the polycrystalline silicon rod a densely deposited region, lower mechanical stress can be provided, reducing the risk of cracking or breakage of the silicon rod during the cutting process. In summary, using polycrystalline silicon rods with the aforementioned multi-layered structure to cut and prepare silicon cores is not only a simple process with low silicon core production costs, but also yields high-quality silicon cores and is suitable for the preparation of electronic-grade silicon cores.

[0005] In addition, the polycrystalline silicon rod for cutting silicon cores according to the above embodiments of the present invention may also have the following additional technical features:

[0006] In some embodiments of the present invention, the density of the dense deposition region located on the outermost layer of the polycrystalline silicon rod is greater than the density of the dense deposition region located on the inner layer.

[0007] In some embodiments of the present invention, the deposition rate of the dense deposition zone is less than that of the adjacent buffer deposition zone.

[0008] In some embodiments of the present invention, the deposition rate of each dense deposition zone is independently 0.3 to 0.6 mm / h, and the deposition rate of each buffer deposition zone is independently 0.4 to 0.7 mm / h.

[0009] In some embodiments of the present invention, the deposition thickness of the single-layer buffer deposition zone is 5 to 10 mm.

[0010] In some embodiments of the present invention, the diameter of the polycrystalline silicon rod is not less than 150 mm.

[0011] In some embodiments of the present invention, the polycrystalline silicon rod is obtained by chemical vapor deposition, and the reaction temperature for forming each layer of the dense deposition region is independently 970-1080°C, and the reaction temperature for forming each layer of the buffer deposition region is independently 1030-1100°C, wherein the reaction temperature for forming the buffer deposition region is higher than the reaction temperature of the dense deposition region adjacent to it.

[0012] In some embodiments of the present invention, the reaction temperature for forming the dense deposition region in each layer of the inner layer of the polycrystalline silicon rod is independently 990 to 1080°C, and the reaction temperature for forming the dense deposition region in the outermost layer of the polycrystalline silicon rod is 970 to 1030°C.

[0013] In some embodiments of the present invention, the reaction temperature for forming each layer of the dense deposition region decreases layer by layer in the direction from the inside to the outside along the radial direction of the polycrystalline silicon rod.

[0014] In another aspect of the invention, a method for preparing the aforementioned polycrystalline silicon rod is provided. According to an embodiment of the invention, the method includes: placing a silicon core in a reduction furnace, introducing a mixture of trichlorosilane and hydrogen into the reduction furnace, and using chemical vapor deposition (CVD) to form a multilayer deposition structure with alternating dense deposition regions and buffer deposition regions on the outer surface of the silicon core, thereby obtaining the polycrystalline silicon rod. Compared with the prior art, this method is not only simple in process, highly efficient, and low in production cost, but also facilitates the control of impurity content, resulting in polycrystalline silicon rods with higher purity, stable quality, easily controllable density, and lower residual stress. Furthermore, it allows for effective control of the distribution of the multilayer deposition structure and the relative density of each layer by adjusting parameter changes during the deposition process. This enables the prepared polycrystalline silicon rod to utilize the buffer deposition region to provide a certain cutting and extrusion resistance when cutting to obtain silicon cores, and ensures that the outer dense deposition region has lower mechanical stress during cutting, thereby reducing the risk of cracking or breakage of the silicon rod during cutting, improving yield, and obtaining higher quality silicon cores. This method is suitable for the production of electronic-grade polycrystalline silicon rods and silicon cores.

[0015] In addition, the method for preparing the polycrystalline silicon rod according to the above embodiments of the present invention may also have the following additional technical features:

[0016] In some embodiments of the present invention, the reaction temperature is adjusted by applying a current to the silicon core.

[0017] In some embodiments of the present invention, the polycrystalline silicon rod comprises, from the inside to the outside, the following in a radial direction: a silicon core region, a first dense deposition region, a first buffer deposition region, a second dense deposition region, a second buffer deposition region, and a third dense deposition region.

[0018] In some embodiments of the present invention, the reaction temperature controlled to form the first dense deposition zone is 990–1080°C, the volume percentage of trichlorosilane in the mixed gas is 20–30%, and the deposition rate is 0.3–0.6 mm / h.

[0019] The reaction temperature controlled to form the first buffer deposition zone is 1030-1100℃, the volume percentage of trichlorosilane in the mixed gas is 25-40%, and the deposition rate is 0.4-0.7 mm / h.

[0020] The reaction temperature controlled to form the second dense deposition zone is 990–1050°C, the volume percentage of trichlorosilane in the mixed gas is 25–30%, and the deposition rate is 0.3–0.6 mm / h.

[0021] The reaction temperature controlled to form the second buffer deposition zone is 1030-1100℃, the volume percentage of trichlorosilane in the mixed gas is 25-40%, and the deposition rate is 0.4-0.7 mm / h;

[0022] The reaction temperature controlled to form the third dense deposition zone is 970–1030°C, the volume percentage of trichlorosilane in the mixed gas is 30–55%, and the deposition rate is 0.3–0.6 mm / h.

[0023] In some embodiments of the present invention, the reaction temperature controlled to form the first dense deposition zone is 1030-1060°C, the volume percentage of trichlorosilane in the mixed gas is 20-30%, and the deposition rate is 0.4-0.6 mm / h;

[0024] The reaction temperature controlled to form the first buffer deposition zone is 1050-1070℃, the volume percentage of trichlorosilane in the mixed gas is 25-40%, and the deposition rate is 0.5-0.7 mm / h.

[0025] The reaction temperature controlled to form the second dense deposition zone is 1000-1030℃, the volume percentage of trichlorosilane in the mixed gas is 25-30%, and the deposition rate is 0.4-0.55 mm / h;

[0026] The reaction temperature controlled to form the second buffer deposition zone is 1040–1060 °C, the volume percentage of trichlorosilane in the mixed gas is 25–40%, and the deposition rate is 0.5–0.7 mm / h.

[0027] The reaction temperature controlled to form the third dense deposition zone is 970–1000°C, the volume percentage of trichlorosilane in the mixed gas is 30–55%, and the deposition rate is 0.3–0.45 mm / h.

[0028] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0030] Figure 1 This is a schematic cross-sectional view of a polycrystalline silicon rod along its radial direction according to an embodiment of the present invention. Detailed Implementation

[0031] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0032] In this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0033] In one aspect of the invention, a polycrystalline silicon rod for dicing silicon cores is provided. According to embodiments of the invention, combined with... Figure 1 Understanding is that the polycrystalline silicon rod comprises, from the inside out, a pristine silicon core region 10 and at least three densely deposited regions 20 along its radial direction (wherein, reference...). Figure 1 Understandably, the at least three dense deposition regions along the radial direction of the polycrystalline silicon rod can be labeled as 21, 22, 23, ... respectively (from the inside to the outside), and a buffer deposition region 30 is formed between two adjacent dense deposition regions 20 (wherein, reference...). Figure 1 It is understood that the buffer deposition region 30, from the inside to the outside along the radial direction of the polycrystalline silicon rod, can be labeled 31, 32, ..., respectively. The density of the buffer deposition region 30 is less than that of the adjacent dense deposition region 20. The inventors discovered that during the cutting process of polycrystalline silicon rods, radial and axial cutting are required. During the cutting process, the silicon rod is subjected to cutting forces in two directions. Compared with existing polycrystalline silicon rods, this invention forms at least three layers of dense deposition regions with high density along the radial direction of the polycrystalline silicon rod, which enables the polycrystalline silicon rod to have good overall density. At the same time, by forming buffer deposition regions with lower density that are alternately distributed with the dense deposition regions, a certain cutting and extrusion resistance can be provided during the cutting of the silicon rod. In addition, by making the outermost layer of the polycrystalline silicon rod a dense deposition region, lower mechanical stress can be provided to reduce the risk of cracking or breaking of the silicon rod during the cutting process. In summary, using polycrystalline silicon rods with the aforementioned multi-layered structure to cut and prepare silicon cores is not only a simple process with low silicon core production costs, but also yields high-quality silicon cores and is suitable for the preparation of electronic-grade silicon cores.

[0034] According to an embodiment of the present invention, the dense deposition region located on the outermost layer of the polycrystalline silicon rod (as shown in the reference) Figure 1 To understand, taking a three-layered dense sedimentary zone as an example, the density of the outermost dense sedimentary zone (23) can be greater than that of the dense sedimentary zones located in the inner layers. Specifically, combining... Figure 1It is understood that when the polycrystalline silicon rod has three dense deposition regions, the density of the outermost dense deposition region 23 can be greater than that of the inner dense deposition regions (21, 22). By controlling the density of the outermost dense deposition region to be relatively large, and combining it with the structural design of alternating distribution of buffer deposition regions and dense deposition regions, the risk of cracks or fractures caused by stress during the cutting process of the silicon rod can be effectively reduced. It should also be noted that the density of each dense deposition region in the inner layer of the polycrystalline silicon rod is higher than that of the adjacent buffer deposition region. In order to ensure that each region of the silicon rod can meet the requirements for silicon core use and improve the utilization rate of the polycrystalline silicon rod, it is also possible to optimize (by controlling the production process conditions) so that the density of the buffer deposition region is not lower than the requirements of the silicon core to be obtained. This is more conducive to obtaining a polycrystalline silicon rod with higher overall density and complete morphology. Therefore, when the silicon rod is cut and silicon core is prepared, the utilization rate of the silicon rod can be improved, and a silicon core with a higher yield and better quality can be obtained.

[0035] According to an embodiment of the present invention, the deposition rate of the dense deposition region 20 can be lower than that of the adjacent buffer deposition region 30. By controlling the deposition rate of the dense deposition region 20 to be smaller, the density of the dense deposition region 20 can be effectively improved. By controlling the deposition rate of the buffer deposition region 30 to be larger, its density can be relatively lower. By arranging the deposition region and the buffer deposition region alternately, the polycrystalline silicon rod can have good density while having a certain cutting and extrusion resistance. When cutting the polycrystalline silicon rod, the occurrence of cracks and fractures can be reduced, resulting in silicon cores with high yield and high quality, such as electronic-grade silicon cores.

[0036] According to embodiments of the present invention, the deposition rate of each dense deposition zone (such as 21, 22, 23) can be independently 0.3 to 0.6 mm / h, for example, 0.35 mm / h, 0.4 mm / h, 0.5 mm / h, or 0.55 mm / h; the deposition rate of each buffer deposition zone (such as 31, 32, 23) can be independently 0.4 to 0.7 mm / h, for example, 0.45 mm / h, 0.5 mm / h, 0.6 mm / h, 0.65 mm / h. The inventors discovered that if the deposition rate of the dense deposition region 20 is too low, although it is beneficial to improve density, the process is more difficult and the production cost is too high. If the deposition rate of the dense deposition region 20 is too high, it is not conducive to achieving a high degree of density and is prone to increasing structural defects. Furthermore, if the deposition rate of the buffer deposition region 30 is too low, the density of this region is relatively high, making it difficult to form an effective density difference between the buffer deposition region and the dense deposition region, thus making it difficult to provide sufficient compression resistance during the cutting process. If the deposition rate of the buffer deposition region 30 is too high, structural defects or popcorn effect are likely to occur. This invention, by controlling the deposition rates of the dense deposition region and the buffer deposition region within the above-mentioned range, is beneficial to achieve a high overall density of the polycrystalline silicon rod, meeting the requirements of electronic-grade polycrystalline silicon, etc. It also enables an effective density difference between the buffer deposition region and the dense deposition region, avoiding the generation of too many structural defects and excessive production costs. As a result, when cutting polycrystalline silicon rods to obtain silicon cores, the utilization rate of silicon rods, the yield of silicon cores, and the quality of silicon cores can be improved.

[0037] According to embodiments of the present invention, the deposition thickness of the single-layer buffer deposition region 30 can be 5-10 mm, for example, 6 mm, 7 mm, 8 mm, or 9 mm. The inventors have found that if the deposition thickness of the single-layer buffer deposition region is too large, it may lead to insufficient overall density or uneven crystal distribution of the polycrystalline silicon rod, which can easily cause structural defects during cutting and affect the performance of the silicon core. If the deposition thickness of the single-layer buffer deposition region is too small, it is difficult to provide sufficient cutting and extrusion resistance. The present invention, by controlling the deposition thickness of the single-layer deposition region within the above-mentioned range, helps to promote good overall density and internal stress distribution in the polycrystalline silicon rod, thereby improving the yield and obtaining higher-quality silicon cores during cutting. Furthermore, the diameter of the polycrystalline silicon rod can be not less than 150 mm, which not only ensures the density of the silicon rod and reduces the impurity content, but also effectively controls production costs.

[0038] According to embodiments of the present invention, polycrystalline silicon rods can be obtained by chemical vapor deposition (CVD). Using trichlorosilane (TCS) as the gas source and hydrogen as the carrier gas, polycrystalline silicon rods are prepared via CVD. For example, after installing silicon cores and completing relevant preparations in a CVD reduction furnace, the furnace can be started. A mixture of trichlorosilane (TCS) and hydrogen is introduced into the furnace. By setting the current in the silicon rod, the surface temperature of the silicon rod is controlled within a certain range. When the diameter of the silicon rod reaches the expected value, deposition is stopped, completing the production of the corresponding batch. This method not only has a simple production process, high production efficiency, and low production cost, but also facilitates the control of impurity content, resulting in polycrystalline silicon rods with higher purity, stable quality, easily controllable density, and low residual stress. Furthermore, it allows for effective control of the distribution of the multilayer deposition structure and the density of each layer by adjusting parameter changes during the deposition process.

[0039] According to some specific embodiments of the present invention, the reaction temperature for forming each dense deposition zone can be independently 970-1080°C, for example 980°C, 1000°C, 1020°C or 1050°C, etc., and the reaction temperature for forming each buffer deposition zone can be independently 1030-1100°C, for example 1050°C, 1070°C, 1080°C or 1090°C, etc., wherein the reaction temperature for forming the buffer deposition zone 30 is higher than the reaction temperature of the adjacent dense deposition zone 20. The inventors discovered that the deposition rate can be controlled by adjusting temperature conditions, thereby controlling the density of each deposition layer. If the reaction temperature for forming a dense deposition zone is too low, it affects the decomposition of trichlorosilane, resulting in a slower rate of Si formation, lower production efficiency, and higher production costs. Conversely, if the reaction temperature is too high, the deposition rate is too fast, leading to a lower Si packing density and potentially insufficient density and an increase in defect structures within the dense deposition zone. If the reaction temperature for forming a buffer deposition zone is too low, the deposition rate is too slow, resulting in a denser deposition zone that cannot provide sufficient cutting and extrusion resistance. Conversely, if the reaction temperature is too high, the deposition rate is too fast, potentially leading to insufficient density in the buffer deposition zone, resulting in significant differences in density within the silicon rod and numerous structural defects, affecting the quality and yield of the silicon cores obtained from cutting. This invention, by controlling the above deposition conditions, allows the silicon rod to achieve both good overall density and low internal stress, which is beneficial for obtaining high-yield and high-quality silicon cores from the silicon rod through cutting.

[0040] According to an embodiment of the present invention, in combination Figure 1Understanding this concept, the outermost layer of a polycrystalline silicon rod is a dense deposition region, while the deposition regions outside this outermost dense deposition region are the inner layers of dense deposition regions. The reaction temperatures for forming these inner layers can be independently set between 990 and 1080°C, for example, 995°C, 1000°C, 1030°C, or 1050°C. The reaction temperature for forming the outermost dense deposition region is between 970 and 1030°C, for example, 980°C, 990°C, 1000°C, or 1200°C. This approach yields a dense outermost deposition region, effectively reducing or preventing cracks or fractures caused by stress during the cutting process. Simultaneously, the inner layers of dense deposition regions also exhibit high density, resulting in a polycrystalline silicon rod with high overall density and a complete morphology. Consequently, cutting this rod yields silicon cores with higher yield and better quality. Furthermore, the reaction temperature for forming each dense deposition region 20 in the radial direction of the polycrystalline silicon rod from the inside to the outside can be gradually reduced. This is more conducive to increasing the density of each dense deposition region in the radial direction of the polycrystalline silicon rod from the inside to the outside. This can further enable the silicon rod to have good overall density and low mechanical stress, which is more conducive to improving the yield, production efficiency and product quality when preparing silicon cores by the cutting method.

[0041] In another aspect of the invention, a method for preparing the aforementioned polycrystalline silicon rod is provided. According to an embodiment of the invention, the method includes: placing a silicon core in a reduction furnace, introducing a mixture of trichlorosilane and hydrogen into the reduction furnace, and using chemical vapor deposition (CVD) to form a multilayer deposition structure with alternating dense deposition zones and buffer deposition zones on the outer surface of the silicon core by adjusting the reaction temperature and reaction atmosphere, thereby obtaining a polycrystalline silicon rod. Compared with the prior art, this method is not only simple in process, highly efficient, and low in production cost, but also facilitates the control of impurity content, resulting in polycrystalline silicon rods with higher purity, stable quality, easily controllable density, and lower residual stress. Furthermore, it allows for effective control of the distribution of the multilayer deposition structure and the relative density of each layer by adjusting parameter changes during the deposition process. This enables the prepared polycrystalline silicon rod to utilize the buffer deposition zone to provide a certain cutting and extrusion resistance when cutting to obtain silicon cores, and ensures that the outer dense deposition zone has lower mechanical stress during cutting, thereby reducing the risk of cracking or breakage of the silicon rod during cutting, improving the yield, and obtaining higher quality silicon cores. This method is suitable for the production of electronic-grade polycrystalline silicon rods and silicon cores. It should be noted that the features and effects described above for cutting polycrystalline silicon rods for silicon cores are applicable to the method for preparing polycrystalline silicon rods, and will not be repeated here.

[0042] According to embodiments of the present invention, the reaction temperature can be adjusted by applying a current to the silicon core. It should be noted that the magnitude of the current flowing through the silicon rod affects the heat generation, and consequently, the surface temperature of the silicon rod. Under otherwise identical reaction conditions, a higher applied current results in a higher silicon rod temperature. Furthermore, there are no particular limitations on the method for controlling the magnitude of the applied current; those skilled in the art can adjust it flexibly according to actual conditions.

[0043] According to an embodiment of the present invention, in combination Figure 1 It is understood that a polycrystalline silicon rod, from the inside to the outside along its radial direction, can sequentially include: a silicon core region 10, a first dense deposition region 21, a first buffer deposition region 31, a second dense deposition region 22, a second buffer deposition region 32, and a third dense deposition region 23. The density of the third dense deposition region 23 can be made greater than that of the first and second dense deposition regions 21 and 22 by controlling the fabrication process conditions, and the density of each dense deposition region should not be less than that of its adjacent buffer deposition region. This effectively avoids cracks or fractures in the silicon rod due to stress during the cutting process. Furthermore, it should be noted that the density of the first dense deposition region 21, the second dense deposition region 22, the third dense deposition region 23, the first buffer deposition region 31, and the second buffer deposition region 32 can all meet the quality and usage requirements of the silicon core by controlling the fabrication process conditions. Furthermore, the density of the first dense deposition region, the second dense deposition region, and the third dense deposition region can be increased sequentially. This is more conducive to giving the silicon rod good density and deposition structure distribution, as well as low mechanical stress. This can improve the yield and quality of silicon cores when cutting them to obtain silicon cores, and reduce the risk of cracks and fractures during cutting.

[0044] According to an embodiment of the present invention, taking a polycrystalline silicon rod comprising three dense deposition regions as an example, the reaction temperature controlled for forming the first dense deposition region 21 can be 990–1080°C, the volume percentage of trichlorosilane in the mixed gas can be 20–30%, and the deposition rate can be 0.3–0.6 mm / h; the reaction temperature controlled for forming the first buffer deposition region 31 can be 1030–1100°C, the volume percentage of trichlorosilane in the mixed gas can be 25–40%, and the deposition rate can be 0.4–0.7 mm / h; the reaction temperature controlled for forming the second dense deposition region 22 can be 990–1080°C. The reaction temperature for forming the second buffer deposition zone 32 can be controlled at 0–1050℃, the volume percentage of trichlorosilane in the mixed gas can be 25–30%, and the deposition rate can be 0.3–0.6 mm / h; the reaction temperature for forming the third dense deposition zone 23 can be controlled at 970–1030℃, the volume percentage of trichlorosilane in the mixed gas can be 30–55%, and the deposition rate can be 0.3–0.6 mm / h. This facilitates the acquisition of polycrystalline silicon rods with the aforementioned desired structure, and ensures an effective relative difference in density between the dense deposition region and the buffer deposition region, both of which meet the usage and quality requirements of the silicon core. In the aforementioned method for preparing the polycrystalline silicon rod, a first dense deposition region 21, a first buffer deposition region 31, a second dense deposition region 22, a second buffer deposition region 32, and a third dense deposition region 23 are sequentially deposited on the silicon core region 10 using chemical vapor deposition. As the deposition reaction proceeds, the diameter of the silicon rod increases. With the increase in the diameter of the silicon rod, if the reaction conditions remain unchanged, the deposition temperature difference along the radial direction from the inside to the outside of the silicon rod increases, affecting the uniformity and stability of the density of the dense deposition region. In this invention, by controlling the volume percentage of trichlorosilane in the mixed gas to the aforementioned range, the mixture used to form each layer of dense deposition region can be mixed along the radial direction of the polycrystalline silicon rod from the inside to the outside. The proportion of trichlorosilane in the gas increases layer by layer, thereby reducing the content of the carrier gas (i.e., hydrogen) and avoiding excessive heat loss due to excessive carrier gas, which would affect the reaction temperature, deposition rate, and deposition density. In addition, the inventors found that the reaction temperature and deposition rate are positively correlated. By controlling the reaction temperature and deposition rate of each deposition zone of the silicon rod within the above range, a multilayer structure with alternating dense deposition zones and buffer deposition zones can be obtained, so that the silicon rod has both good density and certain cutting and extrusion resistance. Furthermore, the reaction temperature for forming the first, second, and third dense deposition zones can be decreased layer by layer, which is more conducive to the gradual increase of the density of each dense deposition zone in the radial direction from the inside to the outside of the polycrystalline silicon rod, further giving the silicon rod good density and deposition structure distribution, as well as low mechanical stress.

[0045] According to an embodiment of the present invention, taking a polycrystalline silicon rod comprising three dense deposition regions as an example, the reaction conditions controlled for forming the first dense deposition region 21 are preferably: a temperature of 990–1080°C, a volume percentage of trichlorosilane in the mixed gas of 20–30%, and a deposition rate of 0.3–0.6 mm / h; the reaction conditions controlled for forming the first buffer deposition region 31 are preferably: a temperature of 1030–1100°C, a volume percentage of trichlorosilane in the mixed gas of 25–40%, and a deposition rate of 0.4–0.7 mm / h; the reaction conditions controlled for forming the second dense deposition region 22 are preferably: The preferred reaction conditions for forming the second buffer deposition zone 32 are: a temperature of 990–1050℃, a volume percentage of trichlorosilane in the mixed gas of 25–30%, and a deposition rate of 0.3–0.6 mm / h; and a temperature of 1030–1100℃, a volume percentage of trichlorosilane in the mixed gas of 25–40%, and a deposition rate of 0.4–0.7 mm / h. The preferred reaction conditions for forming the third dense deposition zone 23 are: a temperature of 970–1030℃, a volume percentage of trichlorosilane in the mixed gas of 30–55%, and a deposition rate of 0.3–0.6 mm / h. This not only makes it easier to obtain polycrystalline silicon rods with the above-mentioned expected structure, and ensures that the density of the dense deposition region and the buffer deposition region has an effective relative difference, both of which can meet the usage and quality requirements of silicon cores, but also makes it easier to control the size and difference of each deposition region, resulting in polycrystalline silicon rods with good density and deposition structure distribution, as well as low mechanical stress. When cutting polycrystalline silicon rods to obtain silicon cores, the quality and yield of silicon cores can be improved.

[0046] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0047] Example 1

[0048] The silicon core is placed in a reduction furnace, and a mixture of trichlorosilane and hydrogen is introduced into the furnace. Chemical vapor deposition (CVD) is used, with the reaction temperature adjusted to 1030°C, the volume percentage of trichlorosilane in the mixture to be 20%, and the deposition rate to be 0.42 mm / h, forming a first dense deposition zone. When the silicon rod diameter reaches 40 mm, the deposition conditions are adjusted: the reaction temperature to 1050°C, the volume percentage of trichlorosilane in the mixture to be 25%, and the deposition rate to be 0.5 mm / h, forming a first buffer deposition zone. When the silicon rod diameter reaches 45 mm, the deposition conditions are adjusted: the reaction temperature to 1000°C, the volume percentage of trichlorosilane in the mixture to be 25%, and the deposition rate to be 0.5 mm / h, forming a first buffer deposition zone. With a volume fraction of 25% and a deposition rate of 0.4 mm / h, a second dense deposition zone is formed. When the silicon rod diameter reaches 120 mm, the deposition conditions are adjusted: the reaction temperature is 1040℃, the volume fraction of trichlorosilane in the mixed gas is 25%, and the deposition rate is 0.62 mm / h, forming a second buffer deposition zone. When the silicon rod diameter reaches 125 mm, the deposition conditions are adjusted: the reaction temperature is 970℃, the volume fraction of trichlorosilane in the mixed gas is 30%, and the deposition rate is 0.4 mm / h, forming a third dense deposition zone, resulting in a polycrystalline silicon rod with a diameter of 160 mm. This polycrystalline silicon rod is then cut to obtain a native square silicon core.

[0049] Example 2

[0050] The differences from Example 1 are shown in Table 1.

[0051] Table 1. Reaction parameters of each sedimentary zone in Example 2.

[0052]

[0053]

[0054] Example 3

[0055] The differences from Example 1 are shown in Table 2.

[0056] Table 2. Reaction parameters of each sedimentary zone in Example 3.

[0057]

[0058] Example 4

[0059] The differences from Example 1 are shown in Table 5.

[0060] Table 3. Reaction parameters of each sedimentary zone in Example 4.

[0061]

[0062] Currently, the main methods for producing silicon cores include the Czochralski method and the monocrystalline silicon ingot cutting method. The Czochralski method uses a specialized silicon core furnace to locally heat and melt polycrystalline silicon rods, then directly pulls them from seed crystals to produce silicon cores. The monocrystalline silicon ingot cutting method uses a single-crystal furnace to produce large-diameter monocrystalline silicon, which is then cut into silicon cores using cutting equipment. The Czochralski method has a long production process, high costs, and low production efficiency. Silicon cores produced using the monocrystalline silicon ingot cutting method have a higher impurity content and cannot be used for the production of high-purity electronic-grade polycrystalline silicon.

[0063] Comparative Example 1

[0064] The silicon core is placed in a reduction furnace, and a mixture of trichlorosilane and hydrogen is introduced into the reduction furnace. Chemical vapor deposition is used, and the reaction temperature is adjusted to 1030°C, the volume ratio of trichlorosilane in the mixture is 30%, and the deposition rate is 0.6 mm / h to obtain a polycrystalline silicon rod with a diameter of 160 mm. The polycrystalline silicon rod is then cut to obtain the silicon core.

[0065] The differences from Example 1 are shown in Table 4.

[0066] Table 4 shows the reaction parameters of the sedimentary zone in Comparative Example 1.

[0067]

[0068]

[0069] Comparative Example 2

[0070] The differences from Example 1 are shown in Table 5.

[0071] Table 5. Response parameters of each sedimentary zone in Comparative Example 2.

[0072]

[0073] Comparative Example 3

[0074] The differences from Example 1 are shown in Table 6.

[0075] Table 6. Response parameters of each sedimentary zone in Comparative Example 3.

[0076]

[0077] Comparative Example 4

[0078] The difference from Example 1 is that the deposition thickness of the first buffer deposition zone is 3 mm and the deposition thickness of the second buffer deposition zone is 3 mm.

[0079] Performance evaluation:

[0080] The yield of silicon cores prepared in Examples 1-4 and Comparative Examples 1-4 was tested under the same conditions, and the test results are shown in Table 7.

[0081] Table 7 Test results of Examples 1-4 and Comparative Examples 1-4

[0082]

[0083]

[0084] Results and Discussion:

[0085] Based on the test results of Examples 1-4 and Comparative Examples 1-4, it can be seen that Examples 1-4, by controlling the deposition temperature of the polycrystalline silicon rod, the volume ratio of trichlorosilane in the mixed gas, and the deposition rate, obtained polycrystalline silicon rods with three dense deposition regions and a buffer deposition region formed between adjacent dense deposition regions. The yield of silicon cores prepared by cutting was 50% or higher. However, Comparative Example 1 did not form a polycrystalline silicon rod with a buffer deposition region, resulting in a lower yield. In Comparative Example 2, the deposition temperature and deposition rate for preparing the buffer deposition region were both high, resulting in an excessively low density of the buffer deposition region. In Comparative Example 3, the deposition temperature and deposition rate for preparing the buffer deposition region were both low, resulting in an excessively high density of the buffer deposition region. Both of these factors led to a decrease in the yield of silicon cores prepared by cutting. In Comparative Example 4, the excessively small deposition thickness of the buffer deposition region also resulted in a decrease in the yield of silicon cores prepared by cutting.

[0086] In summary, the polycrystalline silicon rods used for cutting silicon cores according to the above embodiments of the present invention, by setting three dense deposition regions and forming a buffer deposition region between adjacent dense deposition regions, not only have lower production costs but also improve the yield of cut silicon cores.

[0087] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0088] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A polycrystalline silicon rod for cutting and producing electronic-grade silicon cores, characterized in that, The polycrystalline silicon rod comprises, from the inside to the outside, the following in its radial direction: a raw silicon core region and at least three dense deposition regions, wherein a buffer deposition region is formed between two adjacent dense deposition regions, and the density of the buffer deposition region is less than that of the dense deposition region adjacent to it. The deposition rate of the dense deposition zone is lower than that of the adjacent buffer deposition zone; The deposition rate of each dense depositional zone is independently 0.3~0.6 mm / h, and the deposition rate of each buffer depositional zone is independently 0.4~0.7 mm / h. The deposition thickness of a single-layer buffer deposition zone is 5~10 mm; The density of the dense deposition region located on the outermost layer of the polycrystalline silicon rod is greater than the density of the dense deposition region located on the inner layer; The reaction temperatures for forming the buffer deposition zones in each layer are independently 1030~1100℃.

2. The polycrystalline silicon rod according to claim 1, characterized in that, The diameter of the polycrystalline silicon rod is not less than 150 mm.

3. The polycrystalline silicon rod according to claim 1, characterized in that, At least one of the following conditions must be met: The polycrystalline silicon rod is obtained by chemical vapor deposition. The reaction temperature for forming each layer of the dense deposition region is independently 970~1080℃, wherein the reaction temperature for forming the buffer deposition region is higher than the reaction temperature of the adjacent dense deposition region. The reaction temperature for forming the dense deposition region in each layer of the inner layer of the polycrystalline silicon rod is independently 990~1080℃, and the reaction temperature for forming the dense deposition region in the outermost layer of the polycrystalline silicon rod is 970~1030℃. In the direction from the inside to the outside along the radial direction of the polycrystalline silicon rod, the reaction temperature for forming each layer of the dense deposition zone decreases layer by layer.

4. A method for preparing a polycrystalline silicon rod according to any one of claims 1 to 3, characterized in that, include: The silicon core is placed in a reduction furnace, and a mixture of trichlorosilane and hydrogen is introduced into the reduction furnace. A multilayer deposition structure with alternating dense deposition zones and buffer deposition zones is formed on the surface of the silicon core by chemical vapor deposition and by adjusting the reaction temperature and reaction atmosphere, so as to obtain the polycrystalline silicon rod.

5. The method according to claim 4, characterized in that, The reaction temperature is adjusted by applying a current to the silicon core; and / or The polycrystalline silicon rod comprises, from the inside to the outside along its radial direction, a silicon core region, a first dense deposition region, a first buffer deposition region, a second dense deposition region, a second buffer deposition region, and a third dense deposition region.

6. The method according to claim 5, characterized in that, The reaction temperature controlled to form the first dense deposition zone is 990~1080℃, the volume percentage of trichlorosilane in the mixed gas is 20~30%, and the deposition rate is 0.3~0.6mm / h; The reaction temperature controlled to form the first buffer deposition zone is 1030~1100℃, the volume percentage of trichlorosilane in the mixed gas is 25~40%, and the deposition rate is 0.4~0.7mm / h; The reaction temperature controlled to form the second dense deposition zone is 990~1050℃, the volume percentage of trichlorosilane in the mixed gas is 25~30%, and the deposition rate is 0.3~0.6mm / h; The reaction temperature controlled to form the second buffer deposition zone is 1030~1100℃, the volume percentage of trichlorosilane in the mixed gas is 25~40%, and the deposition rate is 0.4~0.7mm / h; The reaction temperature controlled to form the third dense deposition zone is 970~1030℃, the volume percentage of trichlorosilane in the mixed gas is 30~55%, and the deposition rate is 0.3~0.6mm / h.

7. The method according to claim 5, characterized in that, The reaction temperature controlled to form the first dense deposition zone is 1030~1060℃, the volume percentage of trichlorosilane in the mixed gas is 20~30%, and the deposition rate is 0.4~0.6mm / h; The reaction temperature controlled to form the first buffer deposition zone is 1050~1070℃, the volume percentage of trichlorosilane in the mixed gas is 25~40%, and the deposition rate is 0.5~0.7mm / h; The reaction temperature controlled to form the second dense deposition zone is 1000~1030℃, the volume percentage of trichlorosilane in the mixed gas is 25~30%, and the deposition rate is 0.4~0.55mm / h; The reaction temperature controlled to form the second buffer deposition zone is 1040~1060℃, the volume percentage of trichlorosilane in the mixed gas is 25~40%, and the deposition rate is 0.5~0.7mm / h; The reaction temperature controlled to form the third dense deposition zone is 970~1000℃, the volume percentage of trichlorosilane in the mixed gas is 30~55%, and the deposition rate is 0.3~0.45mm / h.

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