Low-pressure vertical diffusion furnace and working method thereof

Abstract

The invention provides a low-pressure vertical diffusion furnace and a working method thereof, relates to the field of low-pressure vertical diffusion furnaces, and adopts the scheme that the low-pressure vertical diffusion furnace comprises a wafer boat and a stand column, and further comprises a lifting seat, the lifting seat is arranged on the stand column in a lifting manner, a lifting driving assembly is arranged on the stand column, and the lifting driving assembly is connected with the lifting seat; the rotating seat is rotationally arranged on the lifting seat, the lifting seat is connected with a rotating driving assembly, and the wafer boat is arranged on the rotating seat; and the furnace door is arranged on the lifting seat, and the furnace door is arranged at the upper part of the rotating seat. The wafer heating device can rotate during heating, it is guaranteed that wafers are evenly heated, and the quality is improved.

Description

Technical Field

[0001] This invention relates to the field of low-pressure vertical diffusion furnaces, and more particularly to a low-pressure vertical diffusion furnace and its operating method. Background Technology

[0002] In the semiconductor manufacturing industry, low-pressure diffusion furnaces are mainly used for high-temperature heat treatment processes in a controlled low-pressure environment, such as doping diffusion, oxidation, annealing, and low-pressure chemical vapor deposition (LPCVD). Their core function is to achieve uniform diffusion of impurity atoms (such as boron and phosphorus) in silicon wafers or batch deposition of high-quality thin films (such as polycrystalline silicon, silicon nitride, and silicon dioxide) by precisely controlling temperature, atmosphere, and pressure.

[0003] The furnace tubes and external heating components of the vertical low-pressure diffusion furnace adopt a coaxial symmetrical multi-layer nested structure. The core furnace tube is a high-purity quartz tube, and multiple sets of silicon carbide or silicon molybdenum heating elements are tightly surrounded on the outside of the furnace tube. These heating elements are arranged independently in zones, and each zone is equipped with a dedicated temperature control module and platinum-rhodium thermocouple, which can achieve precise zone temperature regulation. A high-density alumina fiber insulation layer is filled between the heating elements and the furnace tube. This insulation layer can effectively reduce heat loss and weaken the radial temperature gradient of the furnace body. In addition, the outermost layer of the heating components is a metal sealed shell, which not only provides structural support but also isolates external environmental interference. The upper and lower ends of the furnace tube are connected to the gas distribution system and the crystal boat transmission mechanism through high-temperature resistant seals, respectively, to ensure the sealing of the low-pressure environment inside the furnace and the uniform flow of process gas.

[0004] However, the above technical solutions still suffer from uneven wafer heating, manufacturing tolerances in the surrounding heating elements, and oxidation aging at different rates after long-term high-temperature operation, resulting in inconsistent heating power in different zones. In addition, the limited number of thermocouple monitoring points makes it difficult to provide real-time feedback on the temperature distribution throughout the furnace, and the temperature control system has a lag in adjustment. Summary of the Invention

[0005] To address the issue of uneven heating in existing vertical diffusion furnaces, this invention provides a low-pressure vertical diffusion furnace and its operating method, which enables the wafer boat to rotate within the furnace, ensuring uniform heating of the wafer and improving its quality.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a low-pressure vertical diffusion furnace, comprising a crystal boat and a column, further comprising: a lifting seat, wherein the lifting seat is movably disposed on the column, and a lifting drive assembly is disposed on the column, the lifting drive assembly being connected to the lifting seat; a rotating seat, wherein the rotating seat is rotatably disposed on the lifting seat, the lifting seat being connected to a rotating drive assembly, and the crystal boat being disposed on the rotating seat; and a furnace door, wherein the furnace door is disposed on the lifting seat, the furnace door is disposed on the upper part of the rotating seat, and the furnace door is capable of abutting against the furnace body.

[0007] This invention uses a rotating base and a rotating drive assembly to drive the crystal boat to rotate, allowing the wafer to sweep across different temperature regions in the circumferential direction. This achieves time-averaged heat exposure, improves temperature field uniformity, and simultaneously, the rotation of the crystal boat can fully stir the atmosphere inside the furnace, disturb the boundary layer, and promote uniform contact of the reactive gas with each silicon wafer. This ensures that each silicon wafer is periodically in different gas flow positions within the furnace tube, averaging the temperature and concentration gradient, significantly improving diffusion uniformity, and reducing local overdoping or underdoping.

[0008] Furthermore, the rotary drive assembly includes a rotary motor, which is mounted on the lifting seat. The rotary motor includes a motor shaft that passes through the lifting seat and the furnace door and is connected to the rotary seat. A magnetic fluid seal is provided between the motor shaft and the furnace door. The rotary motor is equipped with an encoder and is connected to the lower end of the magnetic fluid seal.

[0009] This invention reliably isolates the corrosive atmosphere inside the furnace from the external atmosphere through a magnetic fluid seal, and can also support the long-term stable rotation of the crystal boat, significantly improving process consistency and equipment reliability. By setting an encoder, the rotation speed of the rotary motor can be accurately controlled.

[0010] Furthermore, a positioning pin is provided between the crystal boat and the rotating base.

[0011] This invention uses a positioning pin to ensure the connection strength between the crystal boat and the rotating base, preventing the crystal boat from shaking.

[0012] Furthermore, the lifting drive assembly includes a lifting motor, which is mounted on the top of the column. The lifting motor is connected to a lead screw, which is rotatably mounted on the lifting seat. A lead screw nut is mounted on the lead screw and connected to the lifting seat.

[0013] Furthermore, a distance sensor is installed on the column, which can measure the position of the lifting seat.

[0014] This invention can accurately control the position of the lifting platform, i.e., the furnace door, by setting a distance measuring sensor.

[0015] Furthermore, a sealing ring is provided on the sealing surface of the furnace door.

[0016] Furthermore, an active sealing compensation component is provided between the furnace door and the lifting seat. When the sealing ring fails, the active sealing compensation component can adjust the position of the furnace door before the lifting drive component.

[0017] This invention can compensate for the loss of sealing ring compression by setting an active sealing compensation component, and intervene in the early stage of the decline in sealing performance to avoid leakage and ensure process stability.

[0018] Furthermore, the active sealing compensation assembly includes multiple springs arranged circumferentially on the end face of the lifting seat. The two ends of each spring abut against the lifting seat and the furnace door, respectively. A guide rod is provided on the furnace door, extending into the guide hole of the lifting seat. The guide rod is movable along the guide hole, and a limit nut is provided at the end of the guide rod. There is a gap between the limit nut and the lower surface of the lifting seat.

[0019] This invention utilizes a spring for active compensation, offering advantages such as sensitive response and precise adjustment, enabling seamless compensation.

[0020] Furthermore, the lifting platform is equipped with a fiber optic displacement sensor, which can detect the distance between the furnace door and the lifting platform.

[0021] This invention uses a fiber optic displacement sensor to detect spring failures in a timely manner, ensuring a good seal.

[0022] Secondly, the present invention also provides a method for operating a low-pressure vertical diffusion furnace, which employs the aforementioned low-pressure vertical diffusion furnace and includes the following steps: S01: Place the wafer on the wafer boat and send it into the furnace by the lifting platform; S02: The lifting platform continues to move until it reaches the set height; S03: The rotary seat rotates at a set speed; S04: When the sealing force of the sealing ring decreases, the spring automatically extends to compensate for the loss of sealing compression. S05: When the fiber optic displacement sensor detects a decrease in the distance between the furnace door and the lifting seat, the lifting drive assembly drives the lifting seat to move until the distance between the furnace door and the lifting seat reaches the set threshold.

[0023] This invention constructs a dual adaptive compensation mechanism by combining the elastic elongation of the spring with the active adjustment of the lifting drive component triggered by the fiber optic displacement sensor. When the sealing force decreases due to high-temperature aging or compression relaxation of the sealing ring, the system can first automatically compensate for the compression loss by the spring, and then monitor the furnace door position in real time through the fiber optic displacement sensor. When the distance between the furnace door and the lifting seat decreases, the lifting drive component is driven to press the furnace door tightly, thereby realizing online closed-loop control of sealing performance, effectively resisting the effects of thermal deformation and material creep, and improving process stability, equipment reliability and wafer yield while ensuring high airtightness.

[0024] As can be seen from the above technical solutions, the present invention has the following advantages: This invention provides a low-pressure vertical diffusion furnace and its operating method. A rotating base and a rotation drive assembly drive the crystal boat to rotate, allowing the wafer to sweep across different temperature regions circumferentially. This achieves time-averaged heat exposure, improving temperature field uniformity. Simultaneously, the crystal boat rotation effectively stirs the furnace atmosphere, disturbs the boundary layer, and promotes uniform contact of reactant gases with each silicon wafer. This periodically positions each silicon wafer at different gas flow positions within the furnace tube, averaging the temperature and concentration gradient, significantly improving diffusion uniformity and reducing localized overdoping or underdoping. A magnetic fluid seal reliably isolates the corrosive atmosphere inside the furnace from the external atmosphere and supports long-term stable rotation of the crystal boat, significantly improving process consistency and equipment reliability. A distance sensor accurately controls the position of the lifting base (furnace door). An active sealing compensation component compensates for seal compression loss, preventing early degradation of sealing performance. Intervention is implemented to prevent leakage and ensure process stability. Active compensation using springs offers advantages such as sensitive response and precise adjustment, enabling seamless compensation. Fiber optic displacement sensors can promptly detect spring failures, ensuring sealing performance. A dual adaptive compensation mechanism is constructed by combining the elastic elongation of the springs with the active adjustment of the lifting drive assembly triggered by the fiber optic displacement sensor. When the sealing force decreases due to high-temperature aging or compression relaxation of the sealing ring, the system first automatically compensates for the compression loss with the springs. Then, the fiber optic displacement sensor monitors the furnace door position in real time and drives the lifting drive assembly to press the furnace door shut when the distance between the furnace door and the lifting seat decreases. This achieves online closed-loop control of sealing performance, effectively resisting the effects of thermal deformation and material creep, improving process stability, equipment reliability, and wafer yield while ensuring high airtightness. Attached Figure Description

[0025] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention.

[0027] Figure 2 This is a schematic diagram of the assembly structure of the crystal boat, rotating seat, and lifting seat in Embodiment 1 of the present invention.

[0028] In the diagram, 1. Lifting motor; 2. Column; 3. Lifting seat; 4. Rotary motor; 5. Support flange; 6. Furnace door; 7. Furnace body; 8. Crystal boat; 9. Rotary seat; 10. Positioning pin; 11. Motor shaft; 12. Magnetohydrodynamic seal; 13. Sealing ring; 14. Rotary drive assembly; 15. Spring; 16. Fiber optic displacement sensor; 17. Distance sensor; 18. Lead screw; 19. Lifting drive assembly; 20. Guide rod; 21. Limit nut. Detailed Implementation

[0029] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the specific embodiments. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this patent, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this patent.

[0030] Example 1 like Figure 1 and Figure 2 As shown, this embodiment provides a low-pressure vertical diffusion furnace, including a furnace body 7, a furnace door 6, a crystal boat 8, a column 2, a lifting seat 3, and a rotating seat 9. The lifting seat 3 is movably mounted on the column 2, and a lifting drive assembly 19 is provided on the column 2. The lifting drive assembly 19 is connected to the lifting seat 3, and the lifting seat 3 can drive the crystal boat 8 to extend into the furnace body 7. The rotating seat 9 is rotatably mounted on the lifting seat 3, and a rotating drive assembly 14 is connected to the lifting seat 3. The crystal boat 8 is mounted on the rotating seat 9, and the rotating seat 9 can drive the crystal boat 8 to rotate. The furnace door 6 is located on the lifting seat 3 and on the upper part of the rotating seat 9, and the furnace door 6 can abut against the furnace body 7. In this embodiment, a support flange 5 is provided on the lifting seat 3, and the furnace door 6 is located on the support flange 5.

[0031] In this embodiment, the rotating seat 9 and the rotating drive assembly 14 drive the crystal boat 8 to rotate, so that the wafer sweeps across different temperature regions in the circumferential direction, realizing time-averaged heat exposure and improving temperature field uniformity. At the same time, the rotation of the crystal boat 8 can fully stir the atmosphere in the furnace, disturb the boundary layer, and promote the uniform contact of the reactive gas with each silicon wafer, so that each silicon wafer is periodically in different airflow positions in the furnace tube, averaging the temperature and concentration gradient, significantly improving diffusion uniformity, and reducing local overdoping or underdoping.

[0032] To improve transmission efficiency, such as Figure 2 As shown, in this embodiment, the rotary drive assembly 14 includes a rotary motor 4, which includes a motor body and a reducer. The rotary motor 4 includes a motor shaft 11, which passes through the lifting seat 3 and the furnace door 6 and is connected to the rotating seat 9. Since the motor shaft 11 rotates relative to the furnace door 6, it needs to be sealed to avoid leakage and ensure the vacuum level inside the furnace body 7. For this purpose, a magnetic fluid seal 12 is provided between the motor shaft 11 and the furnace door 6. The magnetic fluid seal 12 can reliably isolate the corrosive atmosphere inside the furnace body 7 from the external atmosphere and can also support the long-term stable rotation of the crystal boat 8, significantly improving process consistency and equipment reliability. In this embodiment, the magnetic fluid seal 12 is a commercially available finished product and belongs to the prior art, so it will not be described in detail here. The upper end of the magnetic fluid seal 12 is connected to the furnace door 6, and the lower end of the magnetic fluid seal 12 is connected to the rotary motor 4.

[0033] In this embodiment, the rotary motor 4 drives the rotating base 9 to rotate at a low speed, ranging from 0.2 rpm to 0.5 rpm. This speed range effectively averages the temperature and gas concentration distribution within the furnace through slow rotation, significantly improving doping uniformity. It also avoids silicon wafer slippage, fragmentation, or process instability caused by centrifugal force, vibration, or airflow disturbance. To accurately control the rotation speed, the rotary motor 4 is equipped with an encoder, i.e., an encoder built into the motor body. The encoder enables closed-loop control of the motor body's rotation speed, improving the accuracy of the rotation speed control of the crystal boat 8. Figure 2 As shown, in this embodiment, a positioning pin 10 is provided between the crystal boat 8 and the rotating seat 9. A pin hole is provided at the lower part of the crystal boat 8 and the corresponding position of the rotating seat 9. The positioning pin 10 passes through the pin hole, which effectively prevents the crystal boat 8 from shaking, improves the stability of the crystal boat 8's movement, and avoids damage to the wafer due to force.

[0034] like Figure 1 As shown, in this embodiment, the lifting drive assembly 19 can adopt the following specific structure: the lifting drive assembly 19 includes a lifting motor 1, the lifting motor 1 is disposed on the top of the column 2, the lifting motor 1 is connected to a lead screw 18, the lead screw 18 is rotatably disposed on the lifting seat 3, the lead screw 18 is provided with a lead screw nut, the lead screw nut is connected to the lifting seat 3; in order to accurately determine the position of the lifting seat 3, a distance sensor 17 is disposed on the column 2, the distance sensor 17 can measure the position of the lifting seat 3. In this embodiment, the distance sensor 17 is a laser distance sensor 17, the receiving end of the laser distance sensor 17 is disposed on the top of the column 2, and the transmitting end is disposed on the lifting seat 3.

[0035] like Figure 2As shown, to ensure sealing, a sealing ring 13 is provided on the sealing surface of the furnace door 6. Because the sealing ring 13 is subjected to harsh conditions such as high temperature, repeated temperature changes, corrosive atmosphere, and mechanical compression for extended periods, it is prone to thermal aging and hardening, leading to a decrease in sealing force and leakage of the furnace body 7. To address this issue, in this embodiment, an active sealing compensation component is provided between the furnace door 6 and the lifting seat 3. When the sealing ring 13 fails, the active sealing compensation component can adjust the position of the furnace door 6 before the lifting drive component 19. The active sealing compensation component can compensate for the compression loss of the sealing ring 13, intervening in the early stages of sealing performance degradation to prevent leakage and ensure process stability. Furthermore, the active sealing compensation component includes multiple springs 15, which are circumferentially arranged on the end face of the lifting seat 3. The two ends of each spring 15 abut against the lifting seat 3 and the furnace door 6, respectively. A guide rod 2 is provided on the furnace door 6. 0. The guide rod 20 extends into the guide hole of the lifting seat 3. The guide rod 20 can move along the guide hole. The end of the guide rod 20 is provided with a limit nut 21. There is a gap between the limit nut 21 and the lower surface of the lifting seat 3. Active compensation is achieved by using a spring 15, which has the technical advantages of sensitive response and fine adjustment, and can achieve sensorless compensation. Since the spring 15 will fail due to fatigue after long-term use and cannot compensate for the sealing loss, the lifting seat 3 is provided with an optical fiber displacement sensor 16. The optical fiber displacement sensor 16 can detect the distance between the furnace door 6 and the lifting seat 3. When the optical fiber displacement sensor 16 detects that the distance between the furnace door 6 and the lifting seat 3 has decreased, it indicates that the spring 15 has undergone plastic deformation and cannot provide the elastic force required by the design. At this time, the initial positioning force of the lifting drive assembly 19 alone may not be enough to maintain the sealing compression. Therefore, the lifting drive assembly 19 needs to drive the lifting group to lift and press the furnace body 7.

[0036] Example 2 This embodiment provides a method for operating a low-pressure vertical diffusion furnace, which employs the aforementioned low-pressure vertical diffusion furnace and includes the following steps: S01: Place the wafer on the crystal boat 8 and send it into the furnace by the lifting platform 3; S02: The lifting platform 3 continues to move until it reaches the set height; S03: Rotary seat 9 rotates at a set speed; S04: When the sealing force of the sealing ring 13 decreases, the spring 15 automatically extends to compensate for the loss of sealing compression. S05: When the fiber optic displacement sensor 16 detects that the distance between the furnace door 6 and the lifting seat 3 has decreased, the lifting drive assembly 19 drives the lifting seat 3 to move until the distance between the furnace door 6 and the lifting seat 3 reaches the set threshold.

[0037] This embodiment combines the elastic elongation of spring 15 with the active adjustment of lifting drive assembly 19 triggered by fiber optic displacement sensor 16 to construct a dual adaptive compensation mechanism. When the sealing force of sealing ring 13 decreases due to high temperature aging or compression relaxation, the system can first automatically compensate for the compression loss by spring 15, and then monitor the position of furnace door 6 in real time by fiber optic displacement sensor 16. When the distance between furnace door 6 and lifting seat 3 decreases, the lifting drive assembly 19 is driven to press furnace door 6, thereby realizing online closed-loop control of sealing performance, effectively resisting the effects of thermal deformation and material creep, and improving process stability, equipment reliability and wafer yield while ensuring high airtightness.

[0038] In S04, when the sealing ring 13 fails and a gap exists, the spring 15 always provides a pressing force towards the furnace body 7 to the furnace door 6. When the compression of the sealing ring 13 is lost, the spring 15 pushes the furnace door 6 to move upward to make up for the gap, and the distance between the furnace door 6 and the lifting seat 3 increases. Through the active compensation action of the spring 15, it has the advantages of sensitive response and fine adjustment, and there is no need for the lifting motor 1 to work repeatedly for adjustment.

[0039] In S05, when the spring 15 plastically deforms, the elastic force it can provide decreases. Under the reaction force of the furnace body 7, the furnace door 6 moves downward, and the distance between the furnace door 6 and the lifting seat 3 decreases. At this time, the fiber optic displacement sensor sends a signal to the controller, and the controller controls the lifting motor 1 to rotate, driving the lifting seat 3 to move until the distance between the lifting seat 3 and the furnace door 6 reaches the set threshold. This set threshold is less than the distance between the sealing ring 13 and the spring 15 under normal conditions, ensuring that the furnace door 6 is pressed tightly against the furnace body 7 to avoid leakage.

[0040] As can be seen from the above specific embodiments, the present invention has the following beneficial effects: 1. The rotating seat 9 and the rotating drive assembly 14 drive the crystal boat 8 to rotate, so that the wafer sweeps across different temperature regions in the circumferential direction, realizing time-averaged heat exposure and improving temperature field uniformity. At the same time, the rotation of the crystal boat 8 can fully stir the atmosphere in the furnace, disturb the boundary layer, promote the uniform contact of the reactive gas with each silicon wafer, and make each silicon wafer periodically in different airflow positions in the furnace tube, averaging the temperature and concentration gradient, significantly improving diffusion uniformity, and reducing local overdoping or underdoping. 2. The magnetic fluid seal 12 reliably isolates the corrosive atmosphere inside the furnace body 7 from the external atmosphere, and can also support the long-term stable rotation of the crystal boat 8, significantly improving process consistency and equipment reliability; 3. By setting the distance sensor 17, the position of the lifting seat 3, i.e., the furnace door 6, can be accurately controlled; 4. By setting up an active sealing compensation component, the compression loss of sealing ring 13 can be compensated, and intervention can be carried out in the early stage of sealing performance decline to avoid leakage and ensure process stability. 5. By using spring 15 for active compensation, it has the technical advantages of sensitive response and fine adjustment, and can achieve seamless compensation; 6. The fiber optic displacement sensor can detect the failure of spring 15 in a timely manner, ensuring the sealing effect; 7. By combining the elastic elongation of spring 15 with the active adjustment of lifting drive assembly 19 triggered by fiber optic displacement sensor 16, a dual adaptive compensation mechanism is constructed. When the sealing force of sealing ring 13 decreases due to high temperature aging or compression relaxation, the system can first automatically compensate for the compression loss by spring 15, and then monitor the position of furnace door 6 in real time by fiber optic displacement sensor 16. When the distance between furnace door 6 and lifting seat 3 decreases, the lifting drive assembly 19 is driven to press furnace door 6, thereby realizing online closed-loop control of sealing performance, effectively resisting the effects of thermal deformation and material creep, and improving process stability, equipment reliability and wafer yield while ensuring high airtightness.

[0041] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A low-pressure vertical diffusion furnace, comprising a furnace body (7), a crystal boat (8), and a column (2), characterized in that, Also includes: Lifting seat (3), the lifting seat (3) is lifted and lowered on the column (2), the column (2) is provided with a lifting drive assembly (19), the lifting drive assembly (19) is connected to the lifting seat (3); A rotating seat (9) is rotatably mounted on the lifting seat (3). The lifting seat (3) is connected to a rotation drive assembly (14). The crystal boat (8) is mounted on the rotating seat (9). Furnace door (6), the furnace door (6) is located on the lifting seat (3), the furnace door (6) is located on the upper part of the rotating seat (9), and the furnace door (6) can abut against the furnace body (7).

2. The low-pressure vertical diffusion furnace as described in claim 1, characterized in that, The rotary drive assembly (14) includes a rotary motor (4), which includes a motor shaft (11). The motor shaft (11) passes through the lifting seat (3) and the furnace door (6) and is connected to the rotary seat (9). A magnetic fluid seal (12) is provided between the motor shaft (11) and the furnace door (6). The rotary motor (4) is equipped with an encoder and is connected to the lower end of the magnetic fluid seal (12).

3. The low-pressure vertical diffusion furnace as described in claim 2, characterized in that, A positioning pin (10) is provided between the crystal boat (8) and the rotating seat (9).

4. The low-pressure vertical diffusion furnace as described in claim 3, characterized in that, The lifting drive assembly (19) includes a lifting motor (1), which is located on the top of the column (2). The lifting motor (1) is connected to a lead screw (18), which is rotatably mounted on the lifting seat (3). A lead screw nut is provided on the lead screw (18), and the lead screw nut is connected to the lifting seat (3).

5. The low-pressure vertical diffusion furnace as described in claim 4, characterized in that, A distance sensor (17) is installed on the column (2), and the distance sensor (17) can measure the position of the lifting seat (3).

6. The low-pressure vertical diffusion furnace as described in any one of claims 1-5, characterized in that, A sealing ring (13) is provided on the sealing surface of the furnace door (6).

7. The low-pressure vertical diffusion furnace as described in claim 6, characterized in that, An active sealing compensation component is provided between the furnace door (6) and the lifting seat (3). When the sealing ring (13) fails, the active sealing compensation component can adjust the position of the furnace door (6) before the lifting drive component (19).

8. The low-pressure vertical diffusion furnace as described in claim 7, characterized in that, The sealing active compensation component includes multiple springs (15), which are arranged circumferentially on the end face of the lifting seat (3). The two ends of the springs (15) abut against the lifting seat (3) and the furnace door (6) respectively. A guide rod (20) is provided on the furnace door (6). The guide rod (20) extends into the guide hole of the lifting seat (3) and can move along the guide hole. A limit nut (21) is provided at the end of the guide rod (20). There is a gap between the limit nut (21) and the lower surface of the lifting seat (3).

9. The low-pressure vertical diffusion furnace as described in claim 8, characterized in that, The lifting seat (3) is equipped with an optical fiber displacement sensor (16), which can detect the distance between the furnace door (6) and the lifting seat (3).

10. A method for operating a low-pressure vertical diffusion furnace, characterized in that, The low-pressure vertical diffusion furnace as described in claim 9 includes the following steps: S01: Place the wafer on the wafer boat (8) and send it into the furnace by the lifting seat (3); S02: The lifting seat (3) continues to move until it reaches the set height; S03: Rotary seat (9) rotates at a set speed; S04: When the sealing force of the sealing ring (13) decreases, the spring (15) automatically extends to compensate for the loss of sealing compression. S05: When the fiber optic displacement sensor (16) detects that the distance between the furnace door (6) and the lifting seat (3) has decreased, the lifting drive assembly (19) drives the lifting seat (3) to move until the distance between the furnace door (6) and the lifting seat (3) reaches the set threshold.

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