Single crystal furnace and method for producing single crystal silicon

Abstract

The application relates to a single crystal furnace and a preparation method of single crystal silicon. The single crystal furnace comprises a furnace body, a crucible arranged in the furnace body and a heater, and further comprises: an ionization device arranged above a silicon solution in the crucible, used for generating an electric field along a first direction; a first electric field device arranged on one side of the crucible, used for generating an electric field along a second direction; and a second electric field device arranged above the silicon solution, used for generating an electric field along the second direction; the first direction intersects the second direction, and the first direction is an axial direction of the crucible. The electric field along the first direction generated by the ionization device ionizes SiO into SiO + ions, and the electric field along the second direction intersecting the first direction generated by the first electric field device and the second electric field device drives the ions to be extracted after being separated from the liquid surface and combined, so that oxygen is removed, the oxygen content of a crystal rod is reduced under high furnace pressure, the crystal breaking rate during crystal pulling is reduced, the crystal defects are reduced, and the single crystal quality is improved.

Description

Technical Field

[0001] This application relates to the field of monocrystalline silicon preparation technology, and in particular to monocrystalline furnaces and methods for preparing monocrystalline silicon. Background Technology

[0002] With the rapid development of the semiconductor and photovoltaic industries, higher demands are being placed on the quality and production efficiency of monocrystalline silicon. During the Czochralski single crystal growth process, silicon monoxide (SiO), generated by the reaction of the quartz crucible and silicon melt at high temperatures, is the main source of oxygen impurities in the crystal rod. The industry commonly employs a process of reducing the pressure inside the single crystal furnace. By increasing the saturated vapor pressure difference of SiO, it promotes its volatilization from the melt surface, thereby reducing the oxygen content of the crystal rod.

[0003] However, the aforementioned low-furnace-pressure oxygen reduction method relies on a vacuum dry pump system, which requires the dry pump to maintain high-frequency operation during the later stages of crystal pulling, leading to increased equipment energy consumption and higher maintenance costs and failure risks for the dry pump. Under low furnace pressure conditions, increased volatilization on the melt surface may affect liquid surface stability, increasing the probability of crystal pulling wire breakage and reducing production efficiency and yield. Summary of the Invention

[0004] Therefore, it is necessary to provide a single crystal furnace and a method for preparing single crystal silicon to address the problems of oxygen impurities affecting crystal rod quality and production efficiency in the current single crystal growth process.

[0005] A single crystal furnace includes a furnace body, a crucible disposed within the furnace body, and a heater, and further includes:

[0006] An ionization device is positioned above the silicon solution inside the crucible to generate an electric field along a first direction;

[0007] A first electric field device is disposed on one side of the crucible to generate an electric field along the second direction;

[0008] The second electric field device is positioned above the silicon solution to generate an electric field along the second direction;

[0009] The first direction intersects with the second direction, and the first direction is the axial direction of the crucible.

[0010] In one embodiment, the ionization device includes a tip discharge structure that extends along a first direction and points toward the liquid surface of the silicon solution.

[0011] In one embodiment, a flow guide tube is also included, with the tip discharge structure disposed around the outer periphery of the flow guide tube along a first direction.

[0012] In one embodiment, the tip discharge structure is coaxially arranged with the guide tube, and the tip discharge structure includes multiple turns of electrode structure arranged at intervals along a first direction.

[0013] In one embodiment, the electrode structure of the tip discharge structure has 1-4 turns; each turn of the electrode structure includes 2-30 electrode units arranged circumferentially along the guide tube.

[0014] In one embodiment, a first electric field device is disposed on the top of the crucible and surrounding the outer periphery of the guide tube; a gap exists between the first electric field device and the silicon solution.

[0015] In one embodiment, the second electric field device is a ring structure, and the second electric field device is disposed around the outer periphery of the crucible along a second direction perpendicular to the first direction.

[0016] The aforementioned single crystal furnace ionizes SiO into SiO2 using an electric field generated along a first direction by an ionization device. + Ions are driven to rapidly detach from the liquid surface and recombine with an electric field generated by the first and second electric field devices along a second direction intersecting the first direction. This process removes oxygen, thereby reducing the oxygen content of the crystal rod under higher furnace pressure, alleviating the energy consumption and maintenance pressure of the dry pump, reducing the crystal pulling breakage rate, reducing crystal defects, and improving the quality of single crystals.

[0017] According to another objective of the present invention, a method for preparing single-crystal silicon is also provided, comprising:

[0018] During the melting stage, silicon material is loaded into a crucible and heated until it is completely melted to form a silicon solution, and a voltage is applied to the ionization device to generate an electric field along the first direction;

[0019] During the temperature adjustment stage, the crystal seeding stage, and the constant diameter stage, the temperature of the silicon solution is adjusted, and the contact between the seed crystal and the liquid surface of the silicon solution is lowered to start crystal growth and shoulder formation. A voltage is applied to the first electric field device and / or the second electric field device to generate an electric field along a second direction intersecting the first direction.

[0020] During the final stage to the cooling stage, after the crystal growth is completed, the crystal rod is lifted out of the liquid and cooled, and the ionization device, the first electric field device and the second electric field device are turned off.

[0021] In one embodiment, the equal diameter stage includes a first equal diameter stage, which is the stage from the start of crystal growth to the crystal rod diameter reaching 100 mm.

[0022] During the temperature adjustment phase to the first equal diameter phase, only the first electric field device and the second electric field device are subjected to the first voltage, and the ionization device is turned off.

[0023] In one embodiment, during the first equal-diameter stage to the closing stage, a first voltage is applied to the first electric field device and the second electric field device, while a second voltage is applied to the ionization device, wherein the first voltage is less than the second voltage.

[0024] The above-described method for preparing single-crystal silicon involves ionizing the volatilized SiO into SiO2 using an electric field along a first direction. + Ions, and SiO2 driven by an electric field along the second direction. + The lateral movement of ions causes them to recombine and then be extracted, thus achieving deoxygenation, reducing the breakage rate during crystal pulling, reducing crystal defects, and improving the quality of single crystals. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a single crystal furnace.

[0026] Figure 2 for Figure 1 A cross-sectional view at point AA along the middle.

[0027] Figure 3 This is a schematic diagram of the first and second electric field devices.

[0028] Figure 4 This is a schematic diagram of the ionization device.

[0029] Figure 5 Flowchart of a method for preparing single-crystal silicon Figure 1 .

[0030] Figure 6 Flowchart of a method for preparing single-crystal silicon Figure 2 .

[0031] In the figure: 10, furnace body; 11, flow guide tube; 12, shell; 20, crucible; 30, ionization device; 31, electrode structure; 41, first electric field device; 42, second electric field device. Detailed Implementation

[0032] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0033] In the description of this application, it should be understood that if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0034] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0035] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0036] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0037] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.

[0038] See Figure 1 , Figure 2 , Figure 1 A schematic diagram of the structure of a single crystal furnace according to an embodiment of this application is shown. Figure 2 An embodiment of this application is shown. Figure 1 A cross-sectional view at point AA along the middle.

[0039] An embodiment of this application provides a single crystal furnace, including a furnace body 10, a crucible 20 disposed within the furnace body 10, and a heater for heating silicon material in the crucible 20.

[0040] The single crystal furnace also includes an ionization device 30, a first electric field device 41, and a second electric field device 42. The ionization device 30 is disposed above the silicon solution in the crucible 20 to generate an electric field along a first direction. The first electric field device 41 is disposed on one side of the crucible 20 to generate an electric field along a second direction. The second electric field device 42 is disposed above the silicon solution to generate an electric field along a second direction. The first and second directions intersect, and the first direction is the axial direction of the crucible 20.

[0041] In this embodiment, the crucible 20 can be a quartz crucible 20, and the interior of the crucible 20 is used to contain molten silicon solution. A heater is arranged around the periphery of the crucible 20, and the heater can be a graphite heater, which melts the silicon material inside the crucible 20 through radiation heating.

[0042] The ionization device 30 is positioned above the silicon solution inside the crucible 20. Specifically, the ionization device 30 can be fixed to one side of the guide tube 11 at the top of the furnace body 10 or fixed to the guide tube 11, with the end of the ionization device 30 pointing towards the surface of the silicon solution.

[0043] In some embodiments, the ionization device 30 may employ a tip discharge structure, which may be a needle-shaped electrode made of a high-temperature resistant metal, such as tungsten or molybdenum, or high-purity graphite. The tip of the tip discharge structure has a small radius of curvature. The ionization device 30 is electrically connected to an external high-voltage DC power supply via a high-voltage cable to generate an electric field along a first direction.

[0044] In this embodiment, the first direction is the axial direction of the crucible 20, that is, the direction along the central axis of the furnace body 10 from the top of the furnace to the bottom of the furnace or towards the crucible 20. When a voltage is applied, a strong electric field is formed near the tip discharge structure, causing corona discharge in the surrounding gas, thereby ionizing the silicon monoxide (SiO) gas molecules volatilized from the silicon solution into positively charged SiO under the protection of the inert gas. + Ions. Simultaneously, the electric field generated by the ionization device 30 along the axial direction of the crucible 20 affects the ionized SiO₂. + Ions exert an electric field force along the axial direction.

[0045] In some embodiments, the number of ionization devices 30 can be one or more. When the number of ionization devices 30 is multiple, the multiple tip discharge structures can be evenly distributed circumferentially to improve ionization uniformity.

[0046] The first electric field device 41 is disposed on one side of the crucible 20. In this embodiment, the first electric field device 41 is a ring electrode, which is disposed around the outer periphery of the crucible 20. Specifically, the first electric field device 41 is fixed to the inner wall of the furnace body 10 or supported by an insulating bracket. The first electric field device 41 is electrically connected to a DC power supply via a wire, which can be an adjustable voltage power supply.

[0047] The first electric field device 41 is used to generate an electric field along a second direction, which in this embodiment is the radial direction of the crucible 20. That is, when the first electric field device 41 is energized, the direction of the electric field formed in the space surrounding the crucible 20 is approximately along the radial direction of the crucible 20. Specifically, this electric field direction can point radially outward from the central axis of the crucible 20, or it can point radially outward from the central axis. The selection of the electric field direction can be set according to the charge polarity of the ions to be driven. For example, when it is necessary to drive positively charged SiO₂... + When ions are driven away from the center region of crucible 20 to the edge, the electric field direction of the first electric field device can be set along the radial direction of crucible 20 from its center outward.

[0048] In some embodiments, the annular structure of the first electric field device 41 can be a complete circular ring or it can be composed of multiple arc-shaped electrode units. When a segmented structure is used, each electrode unit can be controlled independently to adjust the local electric field strength. The number of electrode units can be selected according to the size of the thermal field; for example, 2 to 30 electrode units can be set per ring. The number of ring electrodes can be 1 to 4 rings, with each ring of ring electrodes arranged at intervals along the axial or radial direction.

[0049] The second electric field device 42 is disposed above the silicon solution. In this embodiment, the second electric field device 42 may be a ring electrode, which is disposed around the outer periphery of the guide tube 11, or directly fixed to the inner wall of the top of the furnace body 10, and located at a certain height above the surface of the silicon solution. Specifically, the second electric field device 42 is electrically connected to another DC power supply through another set of wires, which may also be an adjustable voltage power supply.

[0050] The second electric field device 42 is used to generate an electric field along a second direction, that is, along the radial direction of the crucible 20. The radial electric field generated by the second electric field device 42 may be the same as or different from the radial electric field generated by the first electric field device 41. In this embodiment, the electric fields generated by the first electric field device 41 and the second electric field device 42 are in the same direction, both pointing to the radially outer side of the crucible 20.

[0051] In some embodiments, the annular structure of the second electric field device 42 can also be one or more complete circular rings, or it can be composed of multiple arc-shaped electrode units spliced ​​together. The number of electrode units and the number of rings can be adjusted according to the size of the thermal field; for example, 2 to 30 electrode units can be set per ring, and the number of rings can be 1 to 4. The second electric field device 42 is independent of the first electric field device 41, and each has its own independent power supply and control system to ensure independent switching on, off, and voltage amplitude adjustment. This allows the electric field strength and direction to be adjusted at different crystal pulling stages to meet process requirements.

[0052] The first direction and the second direction intersect each other. The electric field generated by the ionization device 30 along the axial direction of the crucible 20 and the electric fields generated by the first electric field device 41 and the second electric field device 42 along the radial direction of the radius or diameter of the crucible 20 are spatially intersected.

[0053] In actual operation, the ionization device 30, the first electric field device 41, and the second electric field device 42 work together. After the silicon material is completely melted, the ionization device 30 is activated, causing corona discharge at its tip. This ionizes the SiO gas molecules volatilized from the surface of the silicon solution into positively charged SiO2 molecules under the protection of argon gas. + The ionization device 30 simultaneously exerts an axial electric force on the ion through an axial electric field generated along its axis. Meanwhile, the radial electric field generated by the first electric field device 41 and the second electric field device can decompose SiO₂. + Ions are driven outward from the crystal growth interface, altering their migration path and guiding them to accelerate their escape from the liquid surface, when SiO + When ions come into contact with negatively charged ions or free electrons, they recombine to form neutral SiO molecules, thus no longer being affected by the electric field force and escaping from the tip discharge region. They are eventually drawn away by the dry pump, thus removing SiO, improving removal efficiency, reducing the oxygen content in the crystal rod, reducing crystal defects, and improving crystal quality.

[0054] Since the electric field actively drives the furnace instead of relying on natural volatilization with low pressure difference, the furnace pressure can be adjusted according to process requirements. There is no need to maintain a low furnace pressure, which alleviates the energy consumption and maintenance pressure of the dry pump under high-frequency operation, and avoids the increase in crystal pulling breakage rate caused by low furnace pressure.

[0055] In this embodiment, the single crystal furnace also includes a crucible 20 shaft and its driving mechanism that support the crucible 20 and drive it to rise, fall and rotate; a seed crystal pulling mechanism that clamps the seed crystal and realizes pulling and rotating; a graphite crucible 20 and a heat insulation layer disposed around the crucible 20; and a vacuum dry pump, an argon gas inlet system and a pressure control system connected to the furnace body 10.

[0056] Combination Figure 3 , Figure 4 As shown, Figure 3 This is a schematic diagram of the structure of the first electric field device 41 and the second electric field device 42 provided in one embodiment of this application. Figure 4 This is a schematic diagram of the structure of an ionization device 30 provided in one embodiment of this application. In one embodiment, the ionization device 30 includes a tip discharge structure that extends along a first direction and points toward the liquid surface of the silicon solution.

[0057] The first direction is the axial direction of the crucible 20, that is, the direction from the top of the furnace to the inside of the crucible 20. In this embodiment, the tip discharge structure can be a needle-shaped electrode that extends axially, with the tip of the tip discharge structure pointing downwards axially towards the surface of the silicon solution.

[0058] When a sufficiently high voltage is applied, the tip discharge structure generates corona discharge under an argon (Ar) protective atmosphere. Under the influence of a strong electric field, silicon monoxide (SiO) gas molecules volatilized from the silicon melt are ionized into positively charged SiO₂ molecules. + Ions. Because the tip of the tip discharge structure faces the liquid surface axially, the ionization region is concentrated above the liquid surface, which is beneficial for the ionized SiO₂. + Ions enter other electric fields. SiO + Ions gain kinetic energy in a radial electric field. When they come into contact with negatively charged ions or free electrons, they recombine to form neutral SiO molecules, thus no longer being affected by the electric field force. They then leave the tip discharge region and are eventually removed by the dry pump.

[0059] By pointing the tip discharge structure axially toward the surface of the silicon solution, the ionization region is more concentrated, thereby improving the ionization efficiency.

[0060] Combination Figure 4 As shown, Figure 4 This is a schematic diagram of the ionization device 30 provided in one embodiment of the present application. In one embodiment, it also includes a guide tube 11, with a tip discharge structure disposed around the outer periphery of the guide tube 11 along a first direction.

[0061] The single crystal furnace also includes a flow guide tube 11, which is positioned above the crucible 20 to guide airflow and create a temperature gradient. A tip discharge structure is arranged around the outer periphery of the flow guide tube 11 along a first direction. That is, the tip discharge structure is annular in shape, arranged around the outer wall of the flow guide tube 11, and extends along the first direction, i.e., along the axial direction of the flow guide tube 11 or the crucible 20. This arrangement of the tip discharge structure allows the ionization region to cover the entire outer periphery of the flow guide tube 11, improving the uniformity of ionization.

[0062] In one embodiment, the tip discharge structure is coaxially arranged with the guide tube 11, and the tip discharge structure includes multiple turns of electrode structure 31 arranged at intervals along a first direction.

[0063] The tip discharge structure is coaxially arranged with the guide tube 11, meaning the central axis of the tip discharge structure coincides with the central axis of the guide tube 11. In some embodiments, the tip discharge structure includes multiple rings of electrode structures 31 spaced apart along a first direction. That is, multiple independent ring electrodes are distributed along the axial direction of the guide tube 11, with gaps between each ring, forming a multi-layer ionization structure. This multi-layer design increases the spatial range of ionization, ensuring that SiO gas evaporating from the silicon solution surface can be effectively ionized at different heights.

[0064] In one embodiment, the electrode structure 31 of the tip discharge structure has 1-4 turns; each turn of the electrode structure 31 includes 2-30 electrode units arranged circumferentially along the guide tube 11.

[0065] The electrode structure 31 of the tip discharge structure has 1 to 4 turns. Further, the electrode structure 31 of the tip discharge structure can have one of 1, 2, 3, or 4 turns. Specifically, the number of electrode turns can be selected according to the size of the thermal field; for example, one turn can be used for a smaller thermal field, while three or four turns can be used for a larger thermal field.

[0066] Each ring of electrode structure 31 includes 2-30 electrode units arranged circumferentially along the guide tube 11. Further, the number of electrode units arranged circumferentially along the guide tube 11 in each ring of electrode structure 31 is one of 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or 30. Specifically, the number of electrode units in each ring can be adjusted according to the thermal field size and ionization requirements. For example, 8, 16, or 24 electrode units can be set in each ring, with adjacent electrode units evenly spaced circumferentially to ensure uniform circumferential ionization.

[0067] By arranging the tip discharge structure around the guide tube 11 and coaxially, effective ionization coverage of the entire annular area above the silicon solution surface is achieved.

[0068] Combination Figure 4 As shown, Figure 4 This is a schematic diagram of the ionization device 30 provided in one embodiment of the present application. In one embodiment, a first electric field device 41 is disposed on the top of the crucible 20 and surrounds the outer periphery of the guide tube 11; there is a gap between the first electric field device 41 and the silicon solution.

[0069] The guide tube 11 has a cylindrical structure and is positioned above the crucible 20. In some embodiments, the first electric field device 41 is a ring electrode, which is mounted around the outer periphery of the shell 12 of the guide tube 11 via an insulating support to ensure the circumferential uniformity of the electric field it generates. The first electric field device 41 is located in the top region of the crucible 20, but it maintains a certain vertical distance from the surface of the silicon solution and does not contact the liquid surface. This distance can be adjusted according to process requirements, for example, from 50mm to 200mm, to avoid thermal radiation damage to the electrode from the high-temperature liquid surface, while ensuring that the electric field can effectively act on the space above the silicon solution.

[0070] In some embodiments, the first electric field device 41 may be a circular ring structure, electrically connected to an adjustable DC power supply via wires. The ring electrode of the first electric field device 41 may be made of high-purity graphite or high-temperature resistant metals, such as molybdenum or tungsten, and its cross-sectional shape may be circular.

[0071] In this embodiment, the first electric field device 41 is used to generate an electric field along the second direction, i.e., along the radial direction of the crucible 20. Since the first electric field device 41 is disposed around the outer periphery of the shell 12 of the guide tube 11 and maintains a distance from the liquid surface of the silicon solution, the radial electric field generated by the first electric field device 41 covers the annular region between the guide tube 11 and the crucible 20, effectively acting on the SiO₂ that evaporates from the liquid surface and rises to this region. + Ions, driven to move radially, enhance the effect on SiO2. + Ion driving efficiency.

[0072] In one embodiment, the second electric field device 42 is a ring structure, and the second electric field device 42 is arranged around the outer periphery of the crucible 20 along a second direction perpendicular to the first direction.

[0073] The first direction is the axial direction of the crucible 20, and the second direction is the radial direction of the crucible 20. That is to say, the second electric field device 42 is ring-shaped as a whole, its circumferential axis coincides with the central axis of the crucible 20, and the plane in which the ring structure is located is approximately perpendicular to the axial direction, that is, it unfolds in the radial direction.

[0074] In some embodiments, the second electric field device 42 is fixedly mounted on the outer periphery of the crucible 20 by an insulating support. Specifically, the second electric field device 42 can be one or more coaxially arranged annular electrodes, with a circumferential diameter larger than the outer diameter of the crucible 20, thereby surrounding the crucible 20. In this embodiment, the annular electrode can be made of high-purity graphite or high-temperature resistant metals such as molybdenum or tungsten, and its cross-sectional shape can be circular, rectangular, or other shapes. The second electric field device 42 is electrically connected to an adjustable DC power supply via a wire to generate an electric field in the radial direction. When energized, the direction of the electric field generated by the second electric field device 42 is approximately along the radial direction of the crucible 20 and perpendicular to the first direction.

[0075] In this embodiment, the second electric field device 42 and the first electric field device 41 are independent of each other and can be controlled to turn on, off, and adjust their voltage amplitudes separately. The second electric field device 42 is positioned on the outer periphery of the crucible 20, so that the radial electric field it generates can effectively cover the annular region between the edge of the crucible 20 and the inner wall of the furnace body 10, thereby affecting the SiO2 that migrates to this region. + Ions exert a radial driving force.

[0076] Combination Figure 5 As shown, Figure 5 This is a flowchart illustrating a method for preparing single-crystal silicon provided in one embodiment of this application. Figure 1 In one embodiment, a method for preparing monocrystalline silicon is applied in the aforementioned monocrystalline furnace, utilizing the ionization device 30, the first electric field device 41, and the second electric field device 42 in the monocrystalline furnace to achieve efficient removal of oxygen impurities from the silicon melt.

[0077] In this embodiment, the method for preparing single-crystal silicon includes the following steps:

[0078] Step S1: In the melting stage, silicon material is loaded into a crucible and heated until it is completely melted to form a silicon solution, and a voltage is applied to the ionization device 30 to generate an electric field along the first direction;

[0079] Step S2: In the temperature adjustment stage, crystal seeding stage and constant diameter stage, adjust the temperature of the silicon solution and lower the contact between the seed crystal and the liquid surface of the silicon solution to start crystal growth and shoulder formation, and apply voltage to the first electric field device 41 and / or the second electric field device 42 to generate an electric field along the second direction intersecting the first direction.

[0080] Step S3: In the final stage to the cooling stage, after the crystal growth is completed, the crystal rod is lifted out of the liquid and cooled, and the ionization device 30, the first electric field device 41 and the second electric field device 42 are turned off.

[0081] In step S1, during the melting stage, polycrystalline silicon material is loaded into crucible 20, furnace body 10 is sealed, and inert gas, such as argon, is introduced. The furnace pressure is set to 6 torr-7 torr, and the silicon material is heated to a molten state by a heater, with the heating power controlled at 100kW-150kW and the crucible rotation speed at 2rpm-3rpm. After the silicon material has completely melted into a silicon solution and before the start of the temperature adjustment stage, a voltage of 300V-600V is applied to the tip discharge structure of the ionization device 30 to generate corona discharge near its tip, forming an electric field along the first direction. During this stage, neither the first electric field device 41 nor the second electric field device 42 is subjected to voltage.

[0082] In this embodiment, the first direction is the axial direction of the crucible 20, that is, from the top of the furnace towards the surface of the silicon solution or the opposite direction. Under the action of a strong electric field, silicon monoxide (SiO) gas molecules volatilized from the surface of the silicon solution are ionized into positively charged SiO2. + ion.

[0083] In step S2, during the temperature adjustment stage, the seed crystal stage, and the constant diameter stage, the temperature of the silicon solution is adjusted to lower the contact between the seed crystal and the surface of the silicon solution, initiating crystal growth and shoulder formation. During this process, a voltage is applied to the first electric field device 41 and / or the second electric field device 42 to generate an electric field along a second direction intersecting the first direction.

[0084] In this embodiment, the second direction is the direction intersecting the first direction, and the second direction is either the radial direction of the crucible 20 or a direction perpendicular to the axial direction of the crucible 20. Specifically, the first electric field device 41 is disposed on the outer periphery of the crucible 20, and the second electric field device 42 is disposed above the silicon solution and on the outer periphery of the shell 12 of the guide tube 11. Depending on the different stages of the crystal pulling process, voltage is applied to the first electric field device 41 or the second electric field device 42, or voltage is applied to both the first electric field device 41 and the second electric field device 42 simultaneously to generate a radial electric field.

[0085] In one embodiment, only the first electric field device 41 is subjected to a voltage of 400V-500V, while the second electric field device 42 is not subjected to a voltage.

[0086] In another embodiment, only the second electric field device 42 is subjected to a voltage of 100V-200V, while the first electric field device 41 is not subjected to a voltage.

[0087] In another embodiment, voltages are applied to the first electric field device 41 and the second electric field device 42 simultaneously, with the first electric field device 41 applying a voltage of 400V-500V and the second electric field device 42 applying a voltage of 100V-200V.

[0088] This embodiment illustrates the simultaneous operation of two electric field devices, but those skilled in the art can choose either method according to actual needs. During the temperature control and crystal growth stages, the furnace pressure is 6-7 torr, the heating power is 45kW-55kW, the crucible rotation is 3-5 rpm, the crystal rotation is 6-10 rpm, and the ionization device 30 remains off. In this stage, the transverse electric field drives the existing SiO₂ in the furnace... + Ions move toward the edge of the crucible and recombine.

[0089] In step S3, from the finishing stage to the cooling stage, after the crystal growth is completed, the crystal rod is lifted out of the liquid surface and cooled, and the ionization device 30, the first electric field device 41 and the second electric field device 42 are turned off.

[0090] Once the constant diameter length reaches the target value, the final stage begins. The furnace pressure is restored to 6-7 torr, the crucible rotation is 2-3 rpm, and the crystal rotation is 6-10 rpm. The ionization device 30, the first electric field device 41, and the second electric field device 42 are turned off to conserve energy. The crystal rod is then removed from the liquid surface and cooled in the auxiliary chamber, with all electric field devices remaining off during the cooling stage.

[0091] In this embodiment, the simultaneous activation of the first electric field device 41 and the second electric field device 42 is taken as an example. The radial electric field generated by the first electric field device 41 and the second electric field device 42 drives SiO2. + The ions move radially, for example, driven away from the center to the edge of crucible 20. During this movement, SiO... + Ions collide and recombine with free electrons or other negatively charged particles, transforming into neutral SiO gas, which is then extracted by a vacuum dry pump along the conventional silicon vapor path.

[0092] By applying voltages to the ionization device 30, the first electric field device 41, and the second electric field device 42 at different crystal pulling stages, an electric field is formed along the first direction or along the second direction, thereby accelerating the crystal pulling process of SiO2. + Lateral ion removal from the crystal growth interface helps reduce the oxygen content at the crystal rod tip. Simultaneously, it enables the formation of SiO₂... + Ions are rapidly extracted from the liquid surface area. This ensures effective ion aggregation in the lateral direction and high-speed migration in the vertical direction, improving the removal efficiency of SiO. This method allows operation under relatively high furnace pressure conditions, reduces the energy consumption and line breakage risk of dry pumps, resolves the contradiction between oxygen reduction and single-unit yield in traditional processes, achieves higher oxygen content in crystal rods under higher furnace pressure, and improves the quality of monocrystalline silicon.

[0093] Combination Figure 6 As shown, Figure 6 This is a flowchart illustrating a method for preparing single-crystal silicon provided in one embodiment of this application. Figure 2In one embodiment, the equal diameter stage includes a first equal diameter stage, which is the stage from the start of crystal growth to the crystal rod diameter reaching 100 mm; step S2 includes step S21, from the temperature adjustment stage to the first equal diameter stage, applying a first voltage only to the first electric field device 41 and the second electric field device 42, and turning off the ionization device 30.

[0094] In this embodiment, the first equal-diameter stage refers to the initial stage of equal-diameter growth of the single-crystal silicon rod, for example, the stage where the diameter of the crystal rod grows from the beginning of equal-diameter growth to reach a preset value, such as 100mm. In this stage, only the first electric field device 41 and the second electric field device 42 are turned on to generate a transverse electric field along the second direction, that is, along the radial direction, while the ionization device 30 remains in the off state and does not generate an axial electric field.

[0095] After the silicon material has completely melted but before the temperature adjustment stage, the ionization device 30 has already been turned on to ionize the silicon monoxide (SiO) gas volatilized from the surface of the silicon solution into positively charged SiO₂. + Ions. At this time, a certain concentration of SiO2 exists within the furnace body 10. + ion.

[0096] After entering the temperature adjustment stage, the ionization device 30 is turned off, and no longer an axial electric field is generated. Then, during the entire stage from the temperature adjustment stage to the first equal-diameter stage, for example, before the crystal rod diameter reaches 100 mm, only the first electric field device 41 and the second electric field device 42 are applied to generate a transverse electric field along the second direction. In this embodiment, the first voltage applied to the first electric field device 41 and the second electric field device 42 can be the same or different. For example, a voltage of 400V-500V is applied to the first electric field device 41 and a voltage of 100V-200V is applied to the second electric field device 42, or both are applied.

[0097] At this time, SiO + Under the influence of a transverse electric field, ions are driven by Coulomb forces and move horizontally towards the negative electrode, for example, migrating from the center to the edge of crucible 20. During this movement, SiO... + Ions collide and recombine with free electrons or other negatively charged particles, transforming into neutral SiO gas, which is then pumped away by a vacuum dry pump along the same path as conventional silicon vapor. Simultaneously, the radial electric field also exerts a driving force on other intrinsically charged impurity ions that may exist in the silicon melt, such as metal ions and dopant ions, causing them to move horizontally and further reducing the concentration of these impurities near the crystal growth interface.

[0098] During this stage, the furnace pressure is controlled at 6 torr-7 torr, the heating power is 35kW-45kW, the crucible rotation is 4rpm-6rpm, the crystal rotation is 6rpm-10rpm, and the pulling speed is 1.0mm / min-1.5mm / min.

[0099] Furthermore, the furnace pressure can be any one of 6 torr, 6.2 torr, 6.4 torr, 6.8 torr, or 7 torr.

[0100] Furthermore, the heating power can be any one of 35kW, 37kW, 40kW, 42kW, or 45kW.

[0101] Furthermore, the crucible rotation speed can be any one of the following values: 4 rpm, 4.2 rpm, 4.5 rpm, 4.7 rpm, 5 rpm, 5.5 rpm, and 6 rpm.

[0102] Furthermore, the crystal rotation speed can be any one of 6 rpm, 7 rpm, 8 rpm, 9 rpm, or 10 rpm.

[0103] Furthermore, the pulling speed can be any one of the following values: 1 mm / min, 1.1 mm / min, 1.2 mm / min, 1.3 mm / min, 1.4 mm / min, and 1.5 mm / min. Alternatively, the pulling speed can be any other value greater than 1.5 mm / min.

[0104] By shutting off the ionization device 30 and turning on only the two radial electric fields during the first isodiameter stage, interference from ionization discharge on the thermal field and liquid surface stability is avoided in the initial stage of crystal growth, ensuring the smooth progress of crystal seeding and shoulder formation. On the other hand, the radial electric fields can actively drive away existing intrinsically charged impurity ions in the melt, reducing their concentration at the solid-liquid interface, thereby reducing impurity defects at the crystal rod head and improving crystal quality. At the same time, the shutdown of the ionization device 30 also saves energy consumption in this stage, optimizing the overall energy distribution.

[0105] In one embodiment, step S3 includes step S31, from the first equal diameter stage to the closing stage, applying a first voltage to the first electric field device 41 and the second electric field device 42, while applying a second voltage to the ionization device 30, wherein the first voltage is less than the second voltage.

[0106] In this embodiment, during the process from when the crystal rod diameter reaches 100 mm until the crystal rod is completely removed from the liquid surface, a first voltage is applied to the first electric field device 41 and the second electric field device 42 to generate a transverse electric field along the second direction; at the same time, a second voltage is applied to the ionization device 30 to generate a longitudinal electric field along the first direction, and the first voltage is controlled to be less than the second voltage, that is, the intensity of the transverse electric field is less than the intensity of the longitudinal electric field.

[0107] In this embodiment, the ionization device 30 applies a second voltage of 400V-600V, the first electric field device 41 applies a first voltage of 100V-200V, and the second electric field device 42 applies a first voltage of 100V-200V. The furnace pressure is controlled at 6 torr-8 torr, the heating power is 35kW-45kW, the crucible rotation is 4-6 rpm, the crystal rotation is 6 rpm-10 rpm, and the pulling speed is 1.3mm / min-1.7mm / min.

[0108] Furthermore, the second voltage can be any value among 400V, 450V, 500V, 550V, and 600V.

[0109] Furthermore, the first voltage can be any value among 100V, 120V, 140V, 160V, 180V, and 200V.

[0110] At this point, the transverse electric field provides a transverse force that pulls the SiO above the silicon solution. + Ions are guided to the region of influence of the longitudinal electric field. The longitudinal electric field affects SiO₂. + Ions exert an axial driving force, causing them to move upwards. Under the combined effect of a strong axial electric field and a weak radial electric field, SiO₂... + Ions are rapidly carried away from the surface region of the silicon solution. During this movement, SiO₂... + The ions gain electrons, recombine to form neutral SiO gas, and are eventually pumped away by a vacuum dry pump.

[0111] By increasing the axial electric field generated by the ionization device 30 from the first equal diameter stage to the final stage, ions are rapidly drawn upwards, avoiding excessive transverse electric field that could cause ion retention and improving the removal efficiency of SiO.

[0112] In this embodiment, as shown in Table 1, Table 1 describes the preparation method of single crystal silicon using the present application, as well as the specific process parameters of the present application in the embodiments.

[0113] Table 1

[0114]

[0115] As shown in Table 2, Table 2 presents comparative examples of single-crystal silicon preparation methods that do not use the present application and those that use the specific process parameters of the present application.

[0116] Table 2

[0117]

[0118] Therefore, in the first equal-diameter stage, i.e., when the crystal rod diameter is less than or equal to 100 mm, only the first and second electric field devices are activated in this embodiment, while the ionization device is turned off. The SiO is driven by the transverse electric field. + Ions move towards the edge of the crucible and recombine, resulting in an oxygen content of 7 ppma; in the comparative example, without any electric field, the oxygen content is 9 ppma. The comparison shows that using only a transverse electric field can reduce the oxygen content by approximately 2 ppma, demonstrating the effectiveness of the transverse electric field in removing oxygen impurities during the early stages of crystal pulling.

[0119] In the second equal-diameter stage, i.e., when the crystal rod diameter is 100mm-600mm, the ionization device, the first electric field device, and the second electric field device are simultaneously activated in this embodiment. The voltage of the longitudinal ionization device is higher than the voltage of the transverse electric field device, creating a synergistic effect of transverse guidance and longitudinal extraction, reducing the oxygen content to 5 ppma. In the comparative example, no electric field is used, and the oxygen content is 8 ppma. The comparison shows that the introduction of the longitudinal electric field further reduces the oxygen content by approximately 3 ppma, improving the oxygen reduction effect.

[0120] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0121] The embodiments described above are merely examples of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A single crystal furnace, comprising a furnace body, a crucible disposed within the furnace body, and a heater, characterized in that, Also includes: An ionization device is disposed above the silicon solution in the crucible to generate an electric field along a first direction; A first electric field device is disposed on one side of the crucible to generate an electric field along a second direction; A second electric field device is disposed above the silicon solution to generate an electric field along a second direction; The first direction intersects the second direction, and the first direction is the axial direction of the crucible.

2. The single crystal furnace according to claim 1, characterized in that, The ionization device includes a tip discharge structure that extends along the first direction and points toward the liquid surface of the silicon solution.

3. The single crystal furnace according to claim 2, characterized in that, It also includes a flow guide tube, and the tip discharge structure is disposed around the outer periphery of the flow guide tube along a first direction.

4. The single crystal furnace according to claim 3, characterized in that, The tip discharge structure is coaxially arranged with the guide tube, and the tip discharge structure includes multiple electrode structures arranged at intervals along a first direction.

5. The single crystal furnace according to claim 4, characterized in that, The electrode structure of the tip discharge structure has 1-4 turns; each turn of the electrode structure includes 2-30 electrode units arranged circumferentially along the guide tube.

6. The single crystal furnace according to any one of claims 3-5, characterized in that, The first electric field device is disposed on the top of the crucible and surrounds the outer periphery of the guide tube; there is a gap between the first electric field device and the silicon solution.

7. The single crystal furnace according to any one of claims 1-5, characterized in that, The second electric field device is a ring structure, and the second electric field device is arranged around the outer periphery of the crucible along a second direction perpendicular to the first direction.

8. A method for preparing single-crystal silicon, characterized in that, include: During the melting stage, silicon material is loaded into a crucible and heated until it is completely melted to form a silicon solution, and a voltage is applied to the ionization device to generate an electric field along the first direction; During the temperature adjustment stage, the crystal seeding stage, and the constant diameter stage, the temperature of the silicon solution is adjusted, and the contact between the seed crystal and the liquid surface of the silicon solution is lowered to start crystal growth and shoulder formation. A voltage is applied to the first electric field device and / or the second electric field device to generate an electric field along a second direction intersecting the first direction. During the final stage to the cooling stage, after the crystal growth is completed, the crystal rod is lifted out of the liquid and cooled, and the ionization device, the first electric field device and the second electric field device are turned off.

9. The method for preparing single-crystal silicon according to claim 8, characterized in that, The equal diameter stage includes a first equal diameter stage, which is the stage from the start of crystal growth to the crystal rod diameter reaching 100 mm. During the temperature adjustment phase to the first equal diameter phase, only the first electric field device and the second electric field device are subjected to the first voltage, and the ionization device is turned off.

10. The method for preparing single-crystal silicon according to claim 9, characterized in that, During the first equal-diameter stage to the final stage, a first voltage is applied to the first electric field device and the second electric field device, while a second voltage is applied to the ionization device, wherein the first voltage is less than the second voltage.

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