Single crystal furnace thermal field capable of improving crystal pulling rate

Abstract

The present application relates to the technical field of single crystal silicon, in particular to a single crystal furnace heat field capable of improving the crystal pulling rate. The single crystal furnace heat field comprises an upper furnace body and a lower furnace body, an outer pipe body and an inner pipe body are arranged in the upper furnace body, a wind cavity is formed between the outer pipe body and the inner pipe body, a gas inlet is tangentially arranged on one side of the top of the outer pipe body, a gas outlet is arranged above the top of the inner pipe body, helical blades are arranged on the outer side wall of the inner pipe body, a gap is arranged between the helical blades and the inner side wall of the outer pipe body, the inner pipe body has a diameter expansion part and a diameter reduction part, the diameter expansion part and the diameter reduction part are arranged alternately, a flow guide device is arranged below the inner pipe body, the flow guide device comprises a straight cylinder part and an inverted cone part outside the helical blades, the diameter of the outer pipe body gradually increases at the corresponding position of the upper end of the straight cylinder part and cooperates with a sealing head to form a dust collection chamber. The present application is more helpful for the control of temperature gradient, improves the crystal pulling rate, and is helpful for improving the dust removal efficiency and reducing the energy consumption.

Description

Technical Field

[0001] This invention relates to the field of monocrystalline silicon technology, and more specifically to a hot zone for a monocrystalline furnace that can improve the crystal pulling rate. Background Technology

[0002] The temperature field in single crystal growth refers to the spatial distribution of temperature within the single crystal furnace, also known as the thermal field. During calcination, the temperature distribution within the thermal system is relatively stable, known as the static thermal field. During single crystal growth, the thermal field changes, and is called the dynamic thermal field.

[0003] Crystals grow from the solid-liquid interface. During the growth of single-crystal silicon, there are two states in the thermal field: solid and melt. There are also two types of temperature gradients: the longitudinal and radial temperature gradients in the crystal and the longitudinal and radial temperature gradients in the melt. These are two completely different temperature distributions, but the temperature gradient at the solid-liquid interface has the greatest influence on the crystallization state.

[0004] A sufficiently large longitudinal temperature gradient at the crystallization interface is necessary to create the required supercooling, providing sufficient growth momentum for the single crystal. However, it cannot be too large, otherwise structural defects will occur. Conversely, the radial temperature gradient should be as small as possible to make the crystallization interface flat. The control of the longitudinal temperature gradient at the crystallization interface has a significant impact on the crystallization rate. Traditionally, the temperature gradient is controlled at 10–30 °C / cm, but to ensure product quality, it is often not controlled too high, which results in a reduction in the crystal pulling speed.

[0005] Therefore, this invention optimizes the thermal field in the single crystal furnace, making the control of the temperature gradient more accurate. As a result, a higher crystal pulling speed can be achieved under a higher temperature gradient, thereby improving production efficiency. Summary of the Invention

[0006] The purpose of this invention is to provide a single crystal furnace thermal field that can improve the crystal pulling rate, thereby solving the problem that the temperature gradient control of existing single crystal furnaces is difficult and affects the crystal pulling speed.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a single crystal furnace hot zone that can improve the crystal pulling rate, comprising an upper furnace body and a lower furnace body, the upper furnace body comprising an outer tube body, a cap provided below the outer tube body, the cap body being sealed and detachably fitted with the lower furnace body, characterized in that: the upper furnace body further comprises an inner tube body, and an air cavity is formed between the inner tube body and the outer tube body;

[0008] An air inlet is tangentially provided on one side of the top of the outer tube body, and the air inlet is connected to the air cavity. An air outlet is provided on the top of the upper furnace body, and the air outlet is connected to the inner tube body.

[0009] Inert gas enters the air cavity through the air inlet. The inert gas flows at different speeds in the air cavity. Vent holes are provided on the side wall of the inner tube where the flow rate is faster. The inner tube is connected to the air cavity through the vent holes.

[0010] A flow guiding device is installed below the inner tube body. The flow guiding device is sealed and connected to the end cap. The diameter of the outer tube body gradually increases at the position corresponding to the upper end of the flow guiding device and is connected to the end cap. The dust collection chamber is formed by the outer tube body, the end cap, and the flow guiding device.

[0011] Furthermore, the inner tube body is provided with helical blades on the outer wall. The diameter and spacing of the helical blades remain unchanged and are arranged from top to bottom. A gap is formed between the helical blades and the inner wall of the outer tube body. The inner tube body includes an enlarged diameter section and a reduced diameter section, which are arranged alternately. The vent is arranged on the enlarged diameter section.

[0012] Furthermore, the flow guiding device is wrapped around the spiral blades on the outer wall of the end of the inner tube. The flow guiding device includes a straight cylindrical section and an inverted conical section. The lower end of the inner tube is located in the straight cylindrical section, and there is no diameter expansion section in the straight cylindrical section.

[0013] Furthermore, a dust door is provided on one side of the dust collection chamber, and the dust door is sealed to the dust collection chamber.

[0014] Furthermore, the air outlet is connected to the dust collector. After the inert gas is discharged from the air outlet, it exchanges heat with the inlet gas, and then returns to the air inlet for recycling after being cleaned by the dust collector.

[0015] Furthermore, a seed crystal pulling head is provided above the upper furnace body, and the seed crystal pulling head pulls the crystal rod to grow upward in the inner tube.

[0016] Furthermore, one side of the upper furnace body is connected to the lid opening mechanism, a furnace chamber is provided in the furnace body, a crucible support is in the furnace chamber, and the crucible support is rotatably and sealedly connected to the lower furnace body; the lower part of the crucible support is connected to the crucible lifting and rotating mechanism.

[0017] Furthermore, a crucible tray is provided on the crucible support, a graphite crucible is provided on the crucible tray, a quartz crucible is placed in the graphite crucible, a heater is provided around the outer periphery of the graphite crucible, and a heat insulation layer is provided on the inner sidewall of the lower furnace body and the end cap.

[0018] Furthermore, the end cap is provided with a feed inlet and an observation port.

[0019] The beneficial effects of this invention are:

[0020] 1. The present invention sets up an air cavity and sets the flow rate of inert gas in the air cavity to alternate between fast and slow. This allows some of the high-temperature airflow returning from the inner tube to enter the air cavity during the airflow process, thereby heating the inert gas. This process makes it easier to control the temperature gradient, allowing for a larger temperature gradient and thus a larger pulling speed.

[0021] 2. During the airflow recirculation process in the inner tube, the present invention can separate and collect dust in the recirculating airflow in the dust collection chamber through the action of rotation and centrifugation. On the one hand, it improves the dust removal efficiency, and on the other hand, it reduces the processing load of the downstream dust removal equipment. The airflow recirculation and dust removal play a positive role in reducing system energy consumption.

[0022] 3. The present invention uses a flow guiding device to give the airflow a greater speed after passing through the flow guiding device. At a higher speed, the airflow diffuses and can carry away the dust generated in the furnace. At the same time, since the airflow is discharged upward through the inner tube, the range of action of the inert gas is more concentrated. On the one hand, it reduces unnecessary energy loss, and on the other hand, it is equivalent to isolating the crystal rod from the internal space of the furnace, making the growth environment of the crystal rod more stable, which also helps to improve the speed and quality. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the single crystal furnace structure of the present invention;

[0024] Figure 2 This is the present invention. Figure 1 A magnified view of part A in the middle;

[0025] Figure 3 This is a schematic diagram of the structure of the inner tube body in the furnace body of the present invention;

[0026] Figure 4 This is a schematic diagram illustrating the principle of airflow within the air cavity in this invention;

[0027] Figure 5 This is a schematic cross-sectional view of the connection between the lower furnace body and the upper furnace body of the present invention;

[0028] Figure 6 This is the present invention. Figure 4 A schematic diagram of the cross-sectional structure of section B.

[0029] The names corresponding to each mark in the diagram:

[0030] 1. Lower furnace body; 11. Furnace chamber; 12. Crucible support; 13. Crucible tray; 14. Graphite crucible; 15. Quartz crucible; 16. Heater; 17. Insulation layer; 2. Upper furnace body; 21. Air inlet; 22. Air outlet; 23. Opening mechanism connection part; 24. End cap; 241. Feed inlet; 242. Observation port; 25. Outer tube; 26. Inner tube; 261. Reduction section; 262. Expansion section; 2621. Vent hole; 27. Spiral blade; 28. Flow guide device; 281. Straight cylinder section; 282. Inverted cone section; 3. Seed crystal pulling head; 4. Dust collection chamber; 41. Ash door; 5. Air cavity; 51. Air duct; 52. Gap; 6. Crystal rod. Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0032] like Figure 1-6 As shown, the hot zone of the single crystal furnace of the present invention includes an upper furnace body 2 and a lower furnace body 1. The lower furnace body 1 includes a furnace chamber 11. A crucible support 12 is provided in the furnace chamber 11. The crucible support 12 is connected to a crucible lifting and rotating mechanism at its lower part. The crucible lifting and rotating mechanism is movably sealed to the furnace chamber 11. A crucible tray 13 is provided above the crucible support 12. A graphite crucible 14 is provided on the crucible tray 13. A quartz crucible 15 is placed in the graphite crucible 14.

[0033] A heater 16 is provided around the outside of the graphite crucible 14. In this embodiment, the heater 16 is a graphite heater 16 with an upper limit of heating temperature of about 1500°C. The two sides of the heater 16 are electrodes and are fixed in the lower furnace body 1. A heat insulation layer 17 is provided around the furnace chamber 11.

[0034] The upper furnace body 2 includes an outer tube 25, an inner tube 26, and a head 24. The outer tube 25 is connected to the head 24. The head 24 has a feed inlet 241 and an observation port 242. A wind chamber 5 is formed between the outer tube 25 and the inner tube 26. An air inlet 21 is located above the outer tube 25 and communicates with the wind chamber 5. An air outlet 22 is also located above the outer tube 25 and communicates with the interior of the inner tube 26. Spiral blades 27 are provided on the inner tube 26. The pitch of the spiral blades 27 and... The diameter remains constant, and an air duct 51 is formed between the inner tube 26 and the outer tube 25. A gap 52 is formed between the spiral blade 27 and the outer tube 25. Simultaneously, the inner tube 26 is a variable diameter tube, comprising an expanding section 262 and a reducing section 261. The expanding section 262 and the reducing section 261 are arranged alternately on the inner tube 26, and both are located between the spiral blades 27. A vent 2621 is provided on the expanding section 262, and the vent 2621 connects the ventilation cavity 5 to the interior of the inner tube 26. The specific implementation is as follows: Figure 4 As shown, during the spiral motion of the gas, the diameter of the inner tube 26 gradually increases and then gradually decreases in the direction of airflow, and is alternately arranged. It should be noted that in the accompanying drawings of this invention, a reduced diameter section 261 and an expanded diameter section 262 are alternately arranged. According to actual production needs, multiple reduced diameter sections 261 and one expanded diameter section 262 can also be alternately arranged.

[0035] A seed crystal lifting head 3 is provided above the outer tube body 25. A cap opening mechanism connecting part 23 is provided on one side above the outer tube body 25. The cap opening mechanism connecting part 23 is connected to the cap opening mechanism and is used for the transfer and removal of the crystal rod 6 after crystal pulling is completed. At the contact point between the outer tube body 25 and the end cap 24, the diameter of the outer tube body 25 gradually increases and is fixedly connected to the end cap 24. At the position where the diameter of the lower end of the outer tube body 25 begins to increase, a flow guiding device 28 is provided on the inner tube body 26. The flow guiding device 28 includes a straight cylinder 281. The spiral blade 27 is included in the straight cylinder 281. The straight cylinder 281 is sealed and fixedly connected to the end cap 24. A dust collection chamber 4 is formed between the straight cylinder 281 and the expanded diameter section at the lower end of the inner tube body 26. A dust door 41 is provided on the dust collection chamber 4.

[0036] The flow guiding device 28 also includes an inverted cone portion 282, which is connected to the straight cylinder portion 281. The inner tube 26 is not provided with an expansion portion 262 inside the flow guiding device 28. The crystal rod 6 grown on the surface of the molten quartz crucible 15 is pulled into the inner tube 26 by the crystal rod 6 lifting head. After the inert circulating gas (argon) in the single crystal furnace is disturbed in the furnace chamber 11, it carries dust through the inner tube 26 and then is discharged through the gas outlet 22.

[0037] The principle of this invention is as follows:

[0038] In the process of using this invention, high-purity polycrystalline silicon (99.9999%) is placed into a quartz crucible 15 through the feed port 241. Then, a vacuum is drawn and an inert gas (argon) is introduced. At this time, the heater 16 is started to heat and melt the polycrystalline silicon. The heating temperature during the process is about 1420°C.

[0039] After the polycrystalline silicon has melted, the seed crystal is lowered onto the surface of the melt through the pulling head and the crystal is pulled. During the process, the temperature gradient (10-30℃ / cm) is controlled. The melt begins to crystallize at the end of the seed crystal. The rotation speed of the seed crystal and the melt is controlled (opposite directions, rotation speed of 5-20 rpm). The pulling speed is controlled to neck the crystal, and then the pulling speed is reduced and the shoulder is formed to the required diameter. Then, the crystal is grown at the same diameter and the end is finished.

[0040] In this invention, during the growth of the crystal rod 6, the inert gas is introduced from the top and rotates downwards, passing through the expansion section 262 and the contraction section 261. As a result, when passing through the expansion section 262, the cross-sectional area of ​​the gas flow decreases, thus increasing the gas velocity and decreasing the pressure. This draws some of the high-temperature gas in the inner tube 26 back into the air chamber 5. On the one hand, this separates the dust carried in the high-temperature gas in the inner tube 26 (the dust is thrown onto the inner wall of the outer tube 25 under the action of centrifugal force and then falls into the dust collection chamber 4). On the other hand, the high-temperature gas mixes with the inlet gas and heats the inert gas. This process helps to reduce energy consumption and control the temperature gradient, and also plays a positive role in increasing the crystal pulling speed.

[0041] The heated gas passes through the flow guide device 28 and is then ejected from the inverted cone portion 282 of the flow guide device 28. During the process, the diameter of the inverted cone portion 282 is reduced, which increases the gas flow rate. When the gas flow is ejected from the inverted cone portion 282, it diffuses outward due to its own centrifugal force. In this process, the dust (SiO) generated under high temperature conditions can be cleaned. At the same time, the inert gas is discharged through the inner tube 26 through the surface of the crystal rod 6, which is equivalent to isolating the crystal rod 6 from other spaces in the furnace chamber 11. This helps to ensure the quality of the product. Furthermore, the heating of the gas helps to control the temperature gradient. Under a stable temperature gradient, a more efficient crystal pulling process can be achieved.

[0042] During the process of airflow being discharged through the inner tube 26, part of the gas is drawn into the air chamber 5, and the other part of the gas is discharged and exchanges heat with the intake air to preheat the intake air. After being treated by the dust removal device, it is recycled. In the process, some dust is removed, which helps to reduce the energy consumption of the downstream dust removal device, making it more energy-efficient and convenient for production use.

[0043] After crystal pulling is completed, the capping mechanism lifts the cap 24 and rotates it to one side. Then, the produced crystal rod 6 can be lowered and transferred through the seed crystal lifting head 3, thereby realizing the entire production process. The capping mechanism, lifting head, and crucible lifting and rotating mechanism involved in the process are existing mature technical solutions, and this invention does not improve them, so they will not be described in detail. In addition, although the conventional settings in existing single crystal furnaces such as water-cooled screens are not described in detail in this invention, conventional settings based on these by those skilled in the art should be within the protection scope of this invention.

[0044] Example 1

[0045] In this embodiment, a traditional single-crystal furnace is compared with the single-crystal furnace of the present invention.

[0046] The single crystal furnace has a furnace chamber diameter of 1000mm and is used to prepare crystal rods with a diameter of 300mm. The crystal pulling speed of a traditional single crystal furnace is 1.5mm / min.

[0047] In this embodiment, the diameter of the inner tube's expanding section is 500 mm, the diameter of the contracting section is 350 mm, the pitch of the spiral blades is 100 mm, the outlet diameter of the inverted cone section is 200 mm, the argon flow rate is controlled at 60-80 L / min, the inlet temperature is controlled at 300 °C, and the inner tube is divided into three equal sections: upper, middle, and lower. The opening rates of the vent holes relative to the expanding section in the upper, middle, and lower sections are 18% (6 mm diameter), 12% (4 mm diameter), and 7% (2.5 mm diameter), respectively. Measurements show that the wind speed in the air cavity is 2-4 m / s, the outlet wind speed of the flow guiding device is 10-15 m / s, and the outlet temperature is 800-900 °C.

[0048] During operation, the heater temperature is controlled at 1420-1450℃, the seed crystal rotation speed is 15-20 rpm (counterclockwise), and the crucible rotation speed is 10-15 rpm. Measurements show that the longitudinal temperature gradient at the crystallization interface can be stably controlled at 20-25℃ / cm, with gradient fluctuation less than ±2℃ / cm, radial temperature difference <3℃, crystal pulling speed can reach 2.5mm / min, and the oxygen content of the crystal rod is <15ppma, resulting in a crystal pulling efficiency improvement of over 60%.

[0049] During the operation of this invention, effective dust removal was achieved, resulting in good energy-saving effects. The removal rate of SiO dust reached over 90%, while reducing system energy consumption by over 20%, significantly promoting industrial production.

[0050] This invention is not limited to the preferred embodiments described above. Anyone can derive other forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A single crystal furnace thermal field capable of improving crystal pulling rate, comprising an upper furnace body (2) and a lower furnace body (1), the upper furnace body (2) comprising an outer tube body (25), a cap (24) disposed below the outer tube body (25), the cap (24) and the lower furnace body (1) being sealed and detachably fitted, characterized in that: The upper furnace body (2) also includes an inner tube body (26), and an air cavity (5) is formed between the inner tube body (26) and the outer tube body (25); An air inlet (21) is provided tangentially on one side of the top of the outer tube (25), and the air inlet (21) is connected to the air cavity (5). An air outlet (22) is provided on the top of the upper furnace body (2), and the air outlet (22) is connected to the inner tube (26). Inert gas enters the air chamber (5) through the air inlet (21). The inert gas flows at different speeds in the air chamber (5). When the flow rate is faster, a vent (2621) is provided on the side wall of the inner tube (26). The inner tube (26) is connected to the air chamber (5) through the vent (2621). A flow guiding device (28) is provided below the inner tube (26). The flow guiding device (28) is sealed to the end cap (24). The outer tube (25) gradually increases in diameter at the position corresponding to the upper end of the flow guiding device (28) and is connected to the end cap (24). The dust collection chamber (4) is formed by the outer tube (25), the end cap (24) and the flow guiding device (28). The inner tube (26) is provided with a spiral blade (27) on the outer side wall. The diameter and spacing of the spiral blade (27) remain unchanged and are arranged from top to bottom. A gap (52) is formed between the spiral blade (27) and the inner side wall of the outer tube (25). The inner tube (26) includes an enlarged diameter section (262) and a reduced diameter section (261). The enlarged diameter section (262) and the reduced diameter section (261) are arranged alternately. A vent (2621) is arranged on the enlarged diameter section (262).

2. The single crystal furnace hot zone for improving crystal pulling rate according to claim 1, characterized in that: The flow guiding device (28) is wrapped around the spiral blade (27) on the outer side wall of the end of the inner tube (26). The flow guiding device (28) includes a straight cylindrical part (281) and an inverted conical part (282). The lower end of the inner tube (26) is located in the straight cylindrical part (281), and there is no enlarged diameter part (262) in the straight cylindrical part (281).

3. The single crystal furnace hot zone for improving crystal pulling rate according to claim 1, characterized in that: A dust door (41) is provided on one side of the dust collection chamber (4), and the dust door (41) is sealed to the dust collection chamber (4).

4. The single crystal furnace hot zone for improving crystal pulling rate according to claim 1, characterized in that: The outlet (22) is connected to the dust collector. After the inert gas is discharged from the outlet (22), it exchanges heat with the inlet gas and then returns to the inlet (21) for recycling after being cleaned by the dust collector.

5. The single crystal furnace hot zone for improving crystal pulling rate according to claim 1, characterized in that: A seed crystal pulling head (3) is provided above the upper furnace body (2), and the seed crystal pulling head (3) pulls the crystal rod (6) to grow upward in the inner tube body (26).

6. The single crystal furnace hot zone for improving crystal pulling rate according to claim 1, characterized in that: One side of the upper furnace body (2) is connected to the lid opening mechanism. A furnace chamber (11) is provided in the furnace body. A crucible support (12) is in the furnace chamber (11). The crucible support (12) is rotatably and sealedly connected to the lower furnace body (1). The crucible support (12) is connected to the crucible lifting and rotating mechanism at its bottom.

7. The single crystal furnace thermal field according to claim 6, characterized in that: The crucible support (12) is provided with a crucible tray (13), a graphite crucible (14) is provided on the crucible tray (13), a quartz crucible (15) is placed in the graphite crucible (14), a heater (16) is provided around the outside of the graphite crucible (14), and a heat insulation layer (17) is provided on the inner sidewall of the lower furnace body (1) and the end cap (24).

8. The single crystal furnace hot zone for improving crystal pulling rate according to claim 1, characterized in that: The end cap (24) is provided with a feed inlet (241) and an observation port (242).

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