Exhaust device for pulling single crystal silicon and single crystal furnace

Abstract

The present invention relates to the technical field of exhaust for single-crystal silicon crystal pulling, and provides an exhaust device and a single-crystal furnace for single-crystal silicon crystal pulling, including a gas guiding cylinder body, characterized in that: the inner cavity of the gas guiding cylinder body forms a gradually expanding structure along the gas flow direction, the inner cavity radius continuously increases from the air inlet end to the air outlet end, and the expansion angle α of the gas guiding cylinder body satisfies 2° ≤ α ≤ 12°, wherein the expansion angle is the angle between the axis of the gas guiding cylinder body and the tangent line of the inner wall; the inner wall surface of the gas guiding cylinder body forms a continuous flow channel without step mutation. The exhaust device and the single-crystal furnace of the present invention can synchronously solve the problems of oxide deposition, furnace pressure fluctuation and oxygen content out of control without external intervention.

Description

Technical Field

[0001] The present invention relates to the technical field of single crystal silicon pulling production, and in particular to an exhaust device for single crystal silicon pulling and a single crystal furnace. Background Art

[0002] In the growth process of the Czochralski method for growing single crystal silicon, the inner cavity of the single crystal furnace needs to maintain a high-purity environment to ensure the quality of the single crystal silicon. During this process, oxide-containing gases (such as , CO, etc.) volatilized from the high-temperature melt (above about 1420 °C) need to be quickly discharged through the exhaust device to avoid silicon melt contamination or crystal defects caused by gas retention.

[0003] Figure 1 The figure shows a schematic structural diagram of a traditional exhaust device, which adopts a vertical equal-diameter air guide cylinder structure to connect the inner cavity of the single crystal furnace and the external exhaust pipeline. However, there are significant oxide deposition problems in practical applications. Specifically, the structural characteristics of the traditional equal-diameter air guide cylinder provide a stable attachment interface for the deposits: the precipitated oxide particles gather towards the lower part of the cylinder under the action of gravity, and the equal-diameter structure makes the particles more likely to collide and deposit in the flow channel, forming a self-thickening annular scale layer. When the oxygen-containing gas flows through the equal-diameter air guide cylinder, the friction between the gas and the cylinder wall causes the boundary layer turbulence to intensify, especially in the middle and lower parts of the cylinder (the area where the temperature gradient drops from 1000 °C to 600 °C), and the gas flow rate decreases significantly. At this time, gaseous oxides such as SiO2 reach supersaturation due to the temperature drop, and a large number of solid SiO2 particles precipitate and adhere to the cylinder wall; as the deposition layer thickens, the effective flow cross-sectional area of the air guide cylinder gradually shrinks, and the local pressure loss rises sharply (the measured pressure loss increase can reach 40% - 70%). This phenomenon directly leads to: (1) Out-of-control furnace pressure: The increase in exhaust resistance causes the furnace chamber pressure to deviate from the set value (usually required to be maintained in the range of 1 - 10 Pa). The increase in pressure will inhibit the oxygen volatilization efficiency in the silicon melt and instead increase the melt oxygen content; (2) Oxygen content rebound: The decrease in exhaust efficiency results in the inability to discharge volatile oxides in time. Some gases react secondarily in the furnace to generate oxygen impurities, and finally the crystal oxygen content exceeds the standard (>15 ppm), resulting in uneven resistivity of the silicon ingot or even dislocation defects. Summary of the Invention

[0004] Therefore, the purpose of the present invention is to overcome the problems of exhaust blockage, furnace pressure fluctuation, and oxygen content out-of-control caused by the equal-diameter exhaust cylinder in the prior art, and provide an exhaust device for single crystal silicon pulling and a single crystal furnace, which can synchronously solve the problems of oxide deposition, furnace pressure fluctuation, and oxygen content out-of-control without external intervention.

[0005] In a first aspect, to solve the above technical problems, the present invention provides an exhaust device for pulling single crystal silicon, which includes a gas guiding cylinder body. The inner cavity of the gas guiding cylinder body forms a gradually expanding structure along the gas flow direction. The inner cavity radius continuously increases from the air inlet end to the air outlet end, and the expansion angle α of the gas guiding cylinder body satisfies 2° ≤ α ≤ 12°. Wherein, the expansion angle is the angle between the axis of the gas guiding cylinder body and the tangent line of the inner wall; the inner wall surface of the gas guiding cylinder body forms a continuous flow channel without step mutation.

[0006] In an embodiment of the present invention, the expansion angle α of the gas guiding cylinder body satisfies 5° ≤ α ≤ 8°.

[0007] In an embodiment of the present invention, the expansion curve of the gradually expanding structure satisfies a logarithmic spiral;

[0008] Wherein, the polar coordinate equation of the logarithmic spiral is expressed as ;

[0009] r represents the polar radius; θ represents the polar angle; a represents the initial radius scale factor, which is a constant and satisfies a ∈ [50, 150] mm; e represents the base of the natural logarithm; b represents the curvature control factor, which is a constant and satisfies b ∈ [0.02, 0.15].

[0010] In an embodiment of the present invention, the gas guiding cylinder body includes at least two functional sections, which are, in sequence along the gas flow direction,

[0011] A gradually expanding transition section, whose length accounts for 60% - 70% of the total length of the gas guiding cylinder body, and its expansion angle α satisfies α = 5° ± 0.5°;

[0012] A pressure stabilizing and separating section, whose length accounts for 15% - 30% of the total length of the gas guiding cylinder body, and its expansion angle α satisfies α = 12° ± 1°.

[0013] In an embodiment of the present invention, the inner wall surface of the gradually expanding transition section is provided with a three - level wettability gradient coating, and the three - level wettability gradient coating includes,

[0014] A hydrophobic coating area, which is configured as a composite coating of carbon fluoride nanotubes and polytetrafluoroethylene;

[0015] A transition coating area, which is configured as a plasma - sprayed Al2O3 - TiO2 duplex ceramic layer;

[0016] A hydrophilic coating area, which is configured as a hydroxyapatite - based hydrophilic coating;

[0017] Wherein, the hydrophobic coating area, the transition coating area and the hydrophilic coating area are arranged in sequence along the gas flow direction.

[0018] In one embodiment of the present invention, the connecting regions of the hydrophobic coating region, the transition coating region and the hydrophilic coating region form a metallurgical bonding transition zone based on laser remelting.

[0019] In one embodiment of the present invention, it further includes a temperature control module, which is arranged on the outer wall of the air guide cylinder; wherein, the temperature control module includes multiple groups of refrigeration components, the multiple groups of refrigeration components are evenly distributed along the circumferential direction, and the refrigeration power of each group of refrigeration components decreases in a gradient along the air flow direction, and the refrigeration power gradient is positively correlated with the temperature gradient of the inner wall of the air guide cylinder.

[0020] In one embodiment of the present invention, the refrigeration component is configured as a thermoelectric cooler, whose cold end is attached to the outer wall of the air guide cylinder, and the hot end is connected to a heat sink fin;

[0021] Wherein, the distance between adjacent thermoelectric coolers is 1 / 12 to 1 / 8 of the perimeter of the air inlet end of the air guide cylinder body; and the refrigeration power gradient satisfies:

[0022] ;

[0023] P0 is the maximum power at the air inlet end of the air guide cylinder body, L is the total length of the air guide cylinder body, n is the attenuation index, and 1.2 ≤ n ≤ 1.8; x represents the coordinate along the air flow direction, and x ∈ [0, L]; P(x) represents the refrigeration power at position x.

[0024] In one embodiment of the present invention, it further includes an air flow monitoring module, which includes,

[0025] An optical fiber sensor, which is embedded in the inner wall of the air guide cylinder for real-time monitoring of the exhaust gas flow rate and particle concentration;

[0026] A controller, which is connected to the optical fiber sensor and the refrigeration component, and is used to adjust the refrigeration power of the refrigeration component according to the monitoring data of the optical fiber sensor.

[0027] In a second aspect, to solve the above technical problems, the present invention provides a single crystal furnace, including the exhaust device for single crystal silicon crystal pulling described above.

[0028] The above technical solutions of the present invention have the following beneficial effects compared with the prior art:

[0029] The exhaust device for single crystal silicon crystal pulling of the present invention solves the problem of oxide deposition without external intervention.

[0030] Specifically, the inner cavity radius of the gas guide cylinder continuously increases along the gas flow direction to form a smoothly expanding flow channel. According to the principle of fluid mechanics, when gas flows in a gradually expanding flow channel, the flow velocity gradually decreases as the cross-sectional area of the flow channel increases, and the change in the flow velocity gradient is gentle. Compared with the sudden expansion cross-section of an equal-diameter structure, the shear stress between the gas and the wall is significantly reduced, thereby reducing the turbulence intensity and suppressing the generation of boundary layer turbulence. The reduction in turbulence intensity directly reduces the collision frequency between oxide particles (such as SiO2) and the cylinder wall, thereby reducing the deposition of substances on the wall of the gas guide cylinder and solving the exhaust blockage problem caused by deposition. At the same time, the gradually expanding structure causes the particles to disperse as the flow channel cross-sectional area expands when moving downward with the gas flow, further reducing the particle concentration per unit area and avoiding local accumulation.

[0031] Among them, the expansion angle α of the gradually expanding structure satisfies 2° ≤ α ≤ 12°, which is determined by multi-scale coupling optimization of fluid dynamics and thermodynamics and is the optimal design based on the gas flow characteristics and deposition suppression requirements in the single-crystal silicon crystal pulling process. 2° ≤ α ≤ 12° makes the gas expansion rate match the boundary layer adhesion ability, which can not only avoid flow separation but also ensure that the residence time of the gas in the sensitive temperature zone is shortened.

[0032] In addition, the gradually expanding structure has a "self-cleaning" effect: in the lower part of the gas guide cylinder (the oxide precipitation sensitive zone where the temperature drops to 600 - 800 °C), the increase in the cross-sectional area of the gradually expanding flow channel further reduces the gas flow velocity to below the critical deposition velocity. At this time, the already precipitated solid particles move downward due to gravity, but the gradually expanding structure does not provide the narrow attachment surface of an equal-diameter cylinder. The particles continue to move towards the exhaust channel under the action of the low-speed gas flow and are finally discharged from the system.

[0033] In addition, there are no step mutations on the inner wall surface of the gas guide cylinder, avoiding the vortex regions (such as flange connections) caused by structural mutations in traditional gas guide cylinders. The elimination of the vortex regions can prevent oxide particles from staying locally and forming initial deposition nuclei, thereby further solving the exhaust blockage problem caused by material deposition.

[0034] The single-crystal furnace described in the present invention, based on the use of an exhaust device with an innovative structure, synchronously solves the problems of furnace pressure fluctuation and out-of-control oxygen content without external intervention. Specifically, the gradually expanding flow channel reduces the gas flow resistance (pressure loss) compared with the equal-diameter structure by reducing the flow velocity and turbulence intensity. More importantly, the gradually expanding design avoids the non-linear increase in pressure loss caused by deposition thickening in traditional gas guide cylinders (i.e., the clogging-pressure loss vicious cycle), thereby maintaining the stability of the exhaust flux; the stable exhaust flux ensures that the oxygen-containing gas volatilized from the silicon melt is continuously discharged, and the oxygen partial pressure in the furnace is always lower than the oxygen solubility threshold of the silicon melt. Description of the Drawings

[0035] In order to make the content of the present invention easier to be clearly understood, the present invention will be further described in detail below with reference to the specific embodiments of the present invention and the accompanying drawings.

[0036] Figure 1 It is a schematic structural diagram of an air guide cylinder body in the prior art;

[0037] Figure 2 It is a schematic structural diagram of an exhaust device for single crystal silicon crystal pulling in a preferred embodiment of the present invention;

[0038] Figure 3 It is a schematic cross-sectional view of the air inlet end of the air guide cylinder body in a preferred embodiment of the present invention;

[0039] Figure 4 It is Figure 2 a partial enlarged schematic view of area A in

[0040] Explanation of reference numerals in the drawings of the specification:

[0041] Air guide cylinder body, 21 - gradually expanding transition section, 211 - hydrophobic coating area, 212 - transition coating area, 213 - hydrophilic coating area; 22 - pressure stabilizing and separating section;

[0042] 4 - Temperature control module, 41 - Refrigeration component;

[0043] 6 - Airflow monitoring module, 61 - Optical fiber sensor, 62 - Controller. Specific embodiments

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited do not limit the present invention. Embodiment 1

[0045] Referring to Figure 2 and Figure 4 shown, an embodiment of the present invention discloses an exhaust device for single crystal silicon crystal pulling, including an air guide cylinder body 2. The inner cavity of the air guide cylinder body 2 forms a gradually expanding structure along the air flow direction, and its inner cavity radius continuously increases from the air inlet end to the air outlet end. Moreover, the expansion angle α of the air guide cylinder body satisfies 2° ≤ α ≤ 12°, where the expansion angle is the angle between the axis of the air guide cylinder body and the tangent line of the inner wall; the inner wall surface of the air guide cylinder body forms a continuous flow channel without step mutation.

[0046] The exhaust device is applied in a single crystal furnace for Czochralski single crystal production. The gas discharged from the single crystal furnace is guided to the exhaust pipe at the rear through the air guide cylinder body 2. One end of the air guide cylinder body 2 connected to the single crystal furnace is the air inlet end, and one end connected to the exhaust pipe is the air outlet end. The air flow direction is from the air inlet end to the air outlet end.

[0047] The expansion angle α is defined as the angle between the axis of the gas guiding cylinder body and the tangent line of the inner wall, which characterizes the expansion rate of the flow channel cross-sectional area along the flow direction. Its geometric relationship satisfies:

[0048] ;

[0049] D0 represents the initial inner diameter at the air inlet end; D(z) represents the inner diameter at the axial position z; L represents the axial length of the gradually expanding section.

[0050] Specifically, the inner cavity radius of the gas guiding cylinder body 2 continuously increases along the gas flow direction to form a smoothly expanding flow channel. According to the principle of fluid mechanics, when gas flows in the gradually expanding flow channel, the flow velocity gradually decreases as the cross-sectional area of the flow channel increases, and the change of the flow velocity gradient is gentle. Compared with the sudden expansion section of the equal-diameter structure, the shear stress between the gas and the wall surface is significantly reduced, thereby reducing the turbulence intensity and suppressing the generation of boundary layer turbulence. The reduction of the turbulence intensity directly reduces the collision frequency between oxide particles (such as SiO2) and the cylinder wall, thereby reducing the deposition of substances on the wall of the gas guiding cylinder body and solving the problem of exhaust blockage caused by deposition. At the same time, the gradually expanding structure enables the particles to disperse as the flow channel cross-sectional area expands when moving downward with the gas flow, further reducing the particle concentration per unit area and avoiding local accumulation.

[0051] In addition, the gradually expanding structure has a "self-cleaning" effect: in the lower part of the gas guiding cylinder body 2 (the oxide precipitation sensitive area where the temperature drops to 600 - 800 °C), the increase in the cross-sectional area of the gradually expanding flow channel further reduces the gas flow velocity below the critical deposition velocity. At this time, the solid particles that have already precipitated move downward due to gravity, but the gradually expanding structure does not provide a narrow attachment surface of an equal-diameter cylinder body. The particles continue to move towards the exhaust channel under the carrying of the low-speed gas flow and are finally discharged from the system.

[0052] Refer to Figure 2 and Figure 4 As shown, the expansion angle α of the gas guiding cylinder body satisfies 2° ≤ α ≤ 12°. It is determined by the multi-scale coupling optimization of fluid dynamics and thermodynamics and is the optimal design based on the gas flow characteristics and deposition inhibition requirements in the single-crystal silicon crystal pulling process. 2° ≤ α ≤ 12° makes the gas expansion rate match the boundary layer attachment ability, which can not only avoid flow separation but also ensure the shortening of the gas residence time in the sensitive temperature zone.

[0053] Specifically, when the expansion angle α < 2°, the gradually expanding flow channel is too long (the cross-sectional area change rate is too low under the same length), and the gas flow velocity drops too gently. Although it can reduce the turbulence intensity, it will lead to: the residence time of the gas in the sensitive temperature zone (600 - 800 °C) is prolonged, and there is still sufficient time for oxides to precipitate and deposit; the axial dimension of the gas guiding cylinder body 2 is too large, conflicting with the compact space layout of the single-crystal furnace and increasing the manufacturing cost.

[0054] When the expansion angle α > 12°, the expansion rate of the flow channel cross-sectional area is too fast, and boundary layer separation (FlowSeparation) is likely to occur in gas flow, forming a local eddy current area. Experiments show that when α = 15°, the length ratio of the eddy current area reaches 30%, resulting in: the particle collision probability in the eddy current area increases by 2 - 3 times, and the deposition rate rebounds; the pressure loss increases by 15% - 20% due to the eddy current disturbance, weakening the structural advantage.

[0055] Specifically, in the upper high-temperature area (above 1000 °C) of the conductor cylinder, a smaller expansion angle such as α = 3° maintains a higher flow rate, enabling gaseous oxides to pass through quickly before reaching the precipitation temperature and inhibiting premature phase change; in the lower low-temperature area (600 - 800 °C) of the gas guiding cylinder, a larger expansion angle such as α = 10° rapidly expands the cross-sectional area of the flow channel, and the gas flow velocity drops to 1 - 2 m / s (lower than the critical deposition velocity of SiO2 particles, 1.5 m / s). At this time: the precipitated particles sink due to gravity, but the gradually expanding structure has no narrow attachment surface like an equal-diameter cylinder, and the particles continue to move towards the exhaust pipe under the drag force of the low-speed gas flow; the expansion of the flow channel cross-sectional area dilutes the particle concentration, and the deposition amount per unit area decreases by 70% - 85%.

[0056] In particular, considering the balance between flow stability and turbulence suppression, the expansion angle α of the gas guiding cylinder satisfies 5° ≤ α ≤ 8°.

[0057] Specifically, when α ≥ 9°, the expansion rate of the flow channel is too fast and is likely to trigger boundary layer separation (simulation shows that when α = 10°, the separation critical Reynolds number drops to ), resulting in an expansion of the local eddy current area (occupancy ratio > 20%). When α ≤ 8°, the expansion rate of the flow channel matches the gas viscous dissipation rate, completely suppressing flow separation (experimental verification shows that when α = 8°, the separation critical Reynolds number > ), and the turbulence intensity drops to 15% - 20% of the initial value. In the range of 5° - 8°, the residence time of the gas in the oxide precipitation sensitive temperature zone (600 - 800 °C) is shortened to 2.5 - 3.8 seconds (6 - 8 seconds for the traditional equal-diameter structure), enabling SiO2 particles to be carried out of the system before reaching the critical deposition size and reducing the deposition probability.

[0058] Specifically, when 5° ≤ α ≤ 6°, the cross-sectional area of the upper part of the gas guiding cylinder expands gently, maintaining a gas flow velocity > 5 m / s (higher than the critical vaporization velocity of SiO2, 4.2 m / s), ensuring that gaseous oxides do not undergo phase change precipitation in the high-temperature area. In the lower flow channel where 7° ≤ α ≤ 8°, the expansion rate of the cross-sectional area accelerates, and the gas flow velocity drops to 1.2 - 1.8 m / s (lower than the critical deposition velocity of SiO2 particles, 1.5 m / s). At this time: the precipitated particles sink due to gravity, but the gradually expanding flow channel has no narrow attachment surface like an equal-diameter structure, and the particles continue to move towards the exhaust pipe under the drag force of the low-speed gas flow; the expansion of the flow channel cross-sectional area dilutes the particle concentration, and the deposition amount per unit area decreases.

[0059] In addition, an expansion angle of 5° - 8° can be formed by single - pass numerical control spinning (while the traditional multi - segment welding structure requires 3 - 5 processes), and the cost of the gas guide cylinder is controllable. At the same time, the stress concentration problem caused by the sudden change of the flow channel when α > 10° is avoided, and the service life of the gas guide cylinder is extended.

[0060] Specifically, the expansion curve of the gradually expanding structure satisfies a logarithmic spiral.

[0061] Among them, the polar coordinate equation of the logarithmic spiral is expressed as ;

[0062] r represents the polar radius; θ represents the polar angle; a represents the initial radius scale factor, which is a constant and satisfies a ∈ [50, 150] mm; e represents the base of the natural logarithm, also known as the natural constant or Euler's number, e ≈ 2.71828; b represents the curvature control factor, which is a constant and satisfies b ∈ [0.02, 0.15].

[0063] Specifically, the radius of curvature of the logarithmic spiral changes continuously, which is a non - linear expansion, avoiding the local curvature mutation of the traditional linear gradually expanding structure, promoting the reduction of the risk of boundary layer separation, increasing the attenuation rate of turbulent kinetic energy, and reducing the particle collision frequency.

[0064] As a further improvement of the embodiment of the present invention, referring to Figure 3 As shown, the gas guide cylinder 2 at least includes two functional segments, which are, in the gas flow direction, a gradually expanding transition segment 21 and a pressure - stabilizing separation segment 22 in sequence; among them, the length of the gradually expanding transition segment 21 accounts for 60% - 70% of the total length of the gas guide cylinder, and its expansion angle α satisfies α = 5° ± 0.5°; the length of the pressure - stabilizing separation segment 22 accounts for 15% - 30% of the total length of the gas guide cylinder, and its expansion angle α satisfies α = 12° ± 1°.

[0065] Specifically, in the embodiment solution of the present invention, the gas guide cylinder 2 is divided into a dual - function collaborative structure of a gradually expanding transition segment 21 and a pressure - stabilizing separation segment 22. The gradually expanding transition segment 21 maintains the laminar flow state of the gas flow in the high - temperature area through small - angle gradual expansion, inhibits the premature phase change of gaseous SiO2 to solid SiO2, and reduces the precipitation amount. The length ratio of the gradually expanding transition segment 21 is 60% - 70%, which matches the high - temperature area of the single - crystal furnace thermal field, ensuring that the residence time of gaseous oxides in the high - temperature section is less than or equal to 2 s (the traditional structure is greater than or equal to 4 s), and avoiding deposition in the sensitive temperature area. The pressure - stabilizing separation segment 22 matches the steep - expansion design in the low - temperature area, the cross - sectional area of the flow channel accelerates to expand, the gas flow velocity drops suddenly, forming a "low - speed escape area", and the precipitated SiO2 particles sink under the action of gravity, but due to the sudden expansion of the cross - sectional area of the flow channel, the particles cannot adhere to it and are continuously discharged from the system under the drag of the low - speed gas flow.

[0066] Furthermore, referring to Figure 2As shown, the inner wall surface of the gradually expanding transition section 21 is provided with a three-stage wettability gradient coating. The three-stage wettability gradient coating includes a hydrophobic coating area 211, a transition coating area 212, and a hydrophilic coating area 213 arranged in sequence along the air flow direction. Among them, the hydrophobic coating area 211 is configured as a composite coating of fluorinated carbon nanotubes and polytetrafluoroethylene; the transition coating area 212 is configured as a plasma-sprayed Al2O3-TiO2 duplex ceramic layer; the hydrophilic coating area 213 is configured as a hydroxyapatite-based hydrophilic coating.

[0067] In the present invention, by setting a three-stage wettability gradient coating (hydrophobic → transition → hydrophilic) on the inner wall of the gradually expanding transition section 21, the wettability gradient generates a directional capillary migration effect, combined with the air flow direction and temperature gradient changes, to achieve a synergistic mechanism of "dynamic repulsion - transition buffer - directional removal" of oxide particles, which is specifically described as follows:

[0068] The hydrophobic surface of the hydrophobic coating area 211 in the high-temperature section inhibits the adhesion of molten silicon volatiles (such as SiO2 particles and metal vapors) through the low surface energy characteristic, so that SiO2 gaseous molecules cannot wet the wall surface due to the hydrophobic effect in the high-temperature section, reducing the particle adhesion force. More than 90% of the particles pass through in gaseous form, reducing the initial nucleation probability; among them, the chemical inertness of fluorinated carbon nanotubes F-CNTs inhibits the high-temperature cracking and carbon deposition of hydrocarbons, avoiding the co-deposition with SiO2 to form a hard sintered layer.

[0069] In the middle-temperature section, the wettability of the transition coating area 212 transitions, inhibiting the particle retention caused by the sudden change in wettability and dissipating the remaining particle kinetic energy to avoid impact and breakage; in the low-temperature section, the hydrophilic coating area 213 forms a liquid film scouring effect through water film migration and chemical bonding blocking, and directionally removes 95% of the escaped particles.

[0070] Among them, the surface energy of fluorinated carbon nanotubes (F-CNTs) ≤ 15 mN / m (close to the superhydrophobic threshold), and it has high thermal conductivity, which can quickly conduct local heat and reduce the risk of coating spalling caused by thermal stress; the nanotube array forms a micro-nano composite structure; the polytetrafluoroethylene (PTFE) substrate has a heat resistance of up to 400 degrees Celsius, a friction coefficient of less than 0.05, and resists high-temperature particle erosion and wear.

[0071] Al2O3 (thermal expansion coefficient 8.6×10 -6 / °C) is matched with TiO2 (thermal expansion coefficient 8.4×10 -6 / °C), alleviating the thermal expansion difference between the hydrophobic area (PTFE thermal expansion coefficient ~ 100×10 -6 / °C) and the hydrophilic area (hydroxyapatite ~ 10×10 -6 / °C), and preventing interface cracking.

[0072] Hydroxyapatite (HA)-based coating: chemical formula , with a surface energy > 72 mN / m (contact angle < 30°), at high temperature (600 °C), partial dehydration of hydroxyl groups forms a microporous structure (pore size 50 - 200 nm). HA forms a monolayer of adsorbed water in trace amounts of water vapor in the process gas (dew point - 40 °C), and the hydrophilic surface adsorbs trace water molecules in argon (below dew point - 40 °C). Through capillary action, sub - micron - sized particles (such as 0.1 - 1 μm SiO2) aggregate into larger particles, accelerating gravitational sedimentation. At the same time, the wettability of the hydrophilic coating area reduces the tendency of the airflow boundary layer separation, avoiding the generation of vortices in the constant - pressure separation section due to the adverse pressure gradient.

[0073] The explanation of chemical - bond blocking is as follows: The Ca of HA 2+ undergoes ion exchange with the groups on the SiO2 surface to form a CaSiO3 transition layer, reducing the binding energy between the particles and the wall surface, making the sediment easily stripped by the airflow.

[0074] Furthermore, the connection area between the hydrophobic coating area 211, the transition coating area 212, and the hydrophilic coating area 213 forms a metallurgical - bonding transition zone based on laser remelting. The laser - remelted transition zone forms a micron - level interpenetrating structure, ensuring that the bonding strength between the coatings ≥ 50 MPa.

[0075] As a further improvement of the embodiment of the present invention, referring to Figure 2 and 3 shown, the exhaust device further includes a temperature control module 4, and the temperature control module 4 is arranged on the outer wall of the air - guiding cylinder body 2; wherein, the temperature control module includes multiple groups of refrigeration components 41, the multiple groups of refrigeration components 41 are evenly distributed in the circumferential direction, the refrigeration power of each group of refrigeration components 41 decreases in a gradient along the airflow direction, and the refrigeration - power gradient is positively correlated with the temperature gradient of the inner wall of the air - guiding cylinder.

[0076] In a specific application scenario, a group of refrigeration components 41 reduces the temperature of the outer wall of the air - guiding cylinder body 2, forming a temperature gradient with the inside being hot and the outside being cold, reducing the thermal expansion effect of the gas near the wall surface, thereby further reducing the gas viscosity, suppressing turbulent pulsation, and enhancing the viscous - dominated characteristic of the flow, causing the Reynolds number to decrease and delaying the transition from laminar flow to turbulent flow. The multiple groups of refrigeration components are evenly distributed in the circumferential direction, eliminating the temperature asymmetry caused by single - side cooling, avoiding lateral secondary flow, and maintaining an axisymmetric flow field. Through gradient refrigeration (high refrigeration power at the inlet end - low at the outlet end), the wall - surface temperature gradient is controlled, so that the thermophoretic force of large particles is weak and mainly dominated by inertia, and they are carried out by the high - speed airflow; the thermophoretic force of sub - micron particles is significant, but through forced refrigeration at the inlet end, they are adsorbed onto the hydrophobic coating area in advance, reducing the deposition at the rear end.

[0077] In an embodiment of the present invention, the refrigeration component is configured as a thermoelectric cooler, whose cold end is attached to the outer wall of the air - guiding cylinder, and the hot end is connected to a heat - dissipating fin;

[0078] Among them, the distance between adjacent semiconductor refrigeration chips is 1 / 12 to 1 / 8 of the perimeter of the air inlet end of the air guide cylinder; and the refrigeration power gradient satisfies:

[0079] ;

[0080] P0 is the maximum power at the air inlet end of the air guide cylinder, L is the total length of the air guide cylinder, n is the attenuation index, and 1.2 ≤ n ≤ 1.8; x represents the coordinate along the air flow direction, and x ∈ [0, L]; P(x) represents the refrigeration power at position x.

[0081] In specific application scenarios, the semiconductor refrigeration chip can precisely control the temperature, and the refrigeration power decreases along the air flow direction (n = 1.5 to 2.5), so that the gas cooling rate is synchronized with the decrease in the flow rate, maintaining the Reynolds number less than 2 × 10 4 , reducing the boundary layer thickness and the probability of particle collision.

[0082] As a further improvement of the embodiment of the present invention, the exhaust device further includes an air flow monitoring module 6. The air flow monitoring module 6 includes an optical fiber sensor 61 and a controller 62. The optical fiber sensor 61 is embedded in the inner wall of the air guide cylinder 2 for real-time monitoring of the exhaust gas flow rate and particle concentration; the controller 62 is connected to the optical fiber sensor 61 and the refrigeration component 41 for adjusting the refrigeration power of the refrigeration component 41 according to the monitoring data of the optical fiber sensor 61.

[0083] Specifically, the optical fiber sensor is based on the Doppler frequency shift principle to measure the air flow velocity in real time and dynamically identify the area where the flow rate decreases. Based on the change in the intensity of the backscattered Rayleigh light, the concentration of SiO2 particles is monitored online to predict the deposition risk in advance; when the particle concentration exceeds the threshold, the controller increases the refrigeration power in real time, causing the local temperature to drop suddenly and suppressing the precipitation of oxides. The controller predicts the change trend of the pressure loss based on the PID algorithm by the real-time feedback of the flow velocity distribution of the optical fiber sensor and adjusts the refrigeration power gradient in advance. Embodiment 2

[0084] The present invention discloses a single crystal furnace, including the exhaust device for pulling single crystal silicon.

[0085] The single crystal furnace of the present invention, based on the use of an exhaust device with an innovative structure, synchronously solves the problems of furnace pressure fluctuation and out-of-control oxygen content without external intervention. Specifically, the gradually expanding flow channel reduces the gas flow resistance (pressure loss) compared with the equal-diameter structure by reducing the flow rate and turbulence intensity. More importantly, the gradually expanding design avoids the non-linear increase in pressure loss caused by deposition thickening in the traditional air guide cylinder (i.e., the clogging-pressure loss vicious cycle), thereby maintaining the stability of the exhaust flux; the stable exhaust flux ensures that the oxygen-containing gas volatilized from the silicon melt is continuously discharged, and the oxygen partial pressure in the furnace is always lower than the oxygen solubility threshold of the silicon melt.

[0086] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or alterations derived therefrom are still within the protection scope of the present invention.

Claims

1. An exhaust device for single crystal silicon pulling, comprising an air guide cylinder, characterized in that: The inner cavity of the air guide cylinder forms a gradually expanding structure along the air flow direction, and the inner cavity radius thereof increases continuously from the air inlet end to the air outlet end, and the expansion angle α of the air guide cylinder satisfies 2°≤α≤12°, wherein the expansion angle is the angle between the axis of the air guide cylinder and the tangent of the inner wall; the inner wall surface of the air guide cylinder forms a continuous flow channel without step mutation; The expansion curve of the gradually expanding structure satisfies a logarithmic spiral; The polar coordinate equation of the logarithmic spiral is expressed as ; r represents the polar diameter; θ represents the polar angle; a represents the initial radius scale factor, which is a constant and satisfies a∈[50, 150] mm; e represents the base of the natural logarithm; b represents the curvature control factor, which is a constant and satisfies b∈[0.02, 0.15]; The air guide cylinder body comprises at least two functional sections, which are, in order, A gradually expanding transition section, the length of which accounts for 60%-70% of the total length of the gas guide cylinder, and the expansion angle α satisfies α=5°±0.5°; The pressure stabilizing separation section has a length that accounts for 15%-30% of the total length of the gas guide cylinder body, and its expansion angle α satisfies α=12°±1°.

2. The exhaust device for pulling single crystal silicon according to claim 1, characterized in that: The expansion angle α of the air guide cylinder satisfies 5°≤α≤8°.

3. The exhaust device for pulling single crystal silicon according to claim 1, characterized in that: The inner wall surface of the gradually expanding transition section is provided with a three-level wettability gradient coating, and the three-level wettability gradient coating comprises: a hydrophobic coating region, which is configured as a composite coating of fluorinated carbon nanotubes and polytetrafluoroethylene; a transition coating zone configured as a plasma-sprayed Al2O3-TiO2 dual-phase ceramic layer; a hydrophilic coating region configured as a hydroxyapatite-based hydrophilic coating; Wherein, the hydrophobic coating area, the transition coating area and the hydrophilic coating area are arranged in sequence along the air flow direction.

4. The exhaust device for pulling single crystal silicon according to claim 3, characterized in that: The connection area of ​​the hydrophobic coating area, the transition coating area and the hydrophilic coating area forms a metallurgical bonding transition zone based on laser remelting.

5. The exhaust device for pulling single crystal silicon according to claim 1, characterized in that: It also includes a temperature control module, which is arranged on the inner wall of the air guide cylinder; wherein, the temperature control module includes multiple groups of refrigeration components, and the multiple groups of refrigeration components are evenly distributed along the circumferential direction, and the refrigeration power of each group of refrigeration components decreases gradually along the air flow direction, and the refrigeration power gradient is positively correlated with the temperature gradient of the inner wall of the air guide cylinder.

6. The exhaust device for single crystal silicon pulling according to claim 5, characterized in that: The refrigeration component is configured as a semiconductor refrigeration sheet, the cold end of which is attached to the outer wall of the air guide cylinder, and the hot end is connected to the heat dissipation fins; The spacing between adjacent semiconductor cooling sheets is 1 / 12 to 1 / 8 of the circumference of the air inlet end of the air guide cylinder; and the cooling power gradient satisfies: ； P0 is the maximum power at the air inlet end of the air guide cylinder, L is the total length of the air guide cylinder, n is the attenuation index, and satisfies 1.2≤n≤1.8; x represents the coordinate along the air flow direction, and satisfies x∈[0,L]; P(x) represents the cooling power at position x.

7. The exhaust device for pulling single crystal silicon according to claim 5, characterized in that: It also includes an airflow monitoring module, the airflow monitoring module includes: An optical fiber sensor is embedded in the inner wall of the gas guide cylinder and is used to monitor the exhaust flow rate and particle concentration in real time; A controller is connected to the optical fiber sensor and the refrigeration component, and is used to adjust the refrigeration power of the refrigeration component according to the monitoring data of the optical fiber sensor.

8. A single crystal furnace, characterized in that: An exhaust device for single crystal silicon pulling comprising the exhaust device described in any one of claims 1-7.

Images