A tube-type oxidation diffusion furnace

Abstract

The present invention discloses a tubular oxidation diffusion furnace, which relates to the technical field of oxidation diffusion furnaces and includes a heat preservation layer. A heating component is arranged inside the heat preservation layer, and an outer furnace tube is fixedly installed inside the heat preservation layer. An inner furnace tube is slidably installed inside the outer furnace tube; a circular groove is formed at the inner end of the inner furnace tube, and an end cover is installed at the outer end of the inner furnace tube. Air inlet holes and air outlet holes are formed on the inner furnace tube, and an air inlet groove and an air outlet groove are formed on the outer furnace tube; an air inlet channel and an air outlet channel are formed on the heat preservation layer; a sealing plate is slidably installed on the heat preservation layer, and a through groove is formed on the sealing plate. In the present invention, the inner furnace tube can translate relative to the outer furnace tube. When an operator opens the end cover to take out the quartz boat, the air overflowing from the inner furnace tube has a relatively low temperature and will not pose a hidden danger to the personal safety of the operator. During the process of pushing the inner furnace tube inward to reset by an external force, the hot air inside the outer furnace tube returns to the inner furnace tube through the circular groove, and less heat is required for preheating before the next oxidation operation, reducing the energy consumption of the equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of oxidation diffusion furnaces, and particularly to a tube-type oxidation diffusion furnace. Background Art

[0002] A tube-type oxidation diffusion furnace is a key device used in semiconductor manufacturing and microelectronics processes, mainly for performing high-temperature oxidation, doping, or annealing processes on the surface of silicon wafers (wafers). Its core function is to form an oxide layer on the silicon wafer surface or diffuse impurity atoms into the silicon material by precisely controlling temperature, gas environment, and time, thereby changing the electrical properties of the material. In terms of structure, a tube-type oxidation diffusion furnace mainly consists of a high-temperature-resistant furnace tube, a multi-point arranged resistance wire heating element, a precise atmosphere control system, and a temperature control system. The furnace tube design needs to adapt to different wafer specifications, the heating element ensures uniform temperature distribution inside the furnace, the atmosphere control system precisely regulates the flow of the oxidation atmosphere, and the temperature control system ensures the accuracy of the process temperature through real-time monitoring and regulation.

[0003] For example, a tube-type diffusion furnace disclosed in the Chinese utility model patent with the publication number CN207353273U includes a diffusion furnace tube and a heating module. Among them, the heating module heats the diffusion furnace tube so that the temperature inside the diffusion furnace tube increases along the direction in which the process gas is filled into the diffusion furnace tube. If the temperature inside the diffusion furnace tube increases along the direction in which the process gas is filled into the diffusion furnace tube, then during the diffusion process, it can be realized that the temperature inside the diffusion furnace tube increases along the gas filling direction of the diffusion furnace tube, so that the temperature at the position with a higher process gas concentration inside the diffusion furnace tube is lower, and the temperature at the position with a lower process gas concentration is higher.

[0004] Another example is a vertical diffusion furnace nozzle disclosed in the Chinese utility model patent with the publication number CN220265945U, which includes a first nozzle and a second nozzle. One end of each of the first nozzle and the second nozzle is provided with an air inlet part. The first nozzle is longer than the second nozzle, and spray holes are formed on the side walls of both the first nozzle and the second nozzle; the spray holes on the second nozzle are arranged along the side wall of the second nozzle, and the spray holes on the first nozzle are arranged along the side wall of the first nozzle that is longer than the second nozzle, and the spray holes are used to spray air currents towards both sides of the first nozzle and the second nozzle.

[0005] During actual use, after oxidation is completed, it is necessary to discharge the high-temperature residual gas in the furnace to prevent the high-temperature gas in the furnace from quickly overflowing from the furnace mouth when the operator opens the furnace cover, which poses a potential safety hazard to the operator's personal safety. However, after the high-temperature gas overflows, the temperature inside the furnace decreases, and the furnace body needs to be preheated during the next oxidation operation, resulting in high energy consumption of the equipment. Summary of the Invention

[0006] The purpose of the present invention is to provide a tube-type oxidation diffusion furnace to solve the above-mentioned deficiencies in the prior art.

[0007] To achieve the above object, the present invention provides the following technical solution: a tubular oxidation diffusion furnace, including a heat insulation layer, a heating component is arranged inside the heat insulation layer, an outer furnace tube which is fixedly installed and fits with the heat insulation layer is also arranged inside the heat insulation layer, and an inner furnace tube is slidably installed along its length direction inside the outer furnace tube; a circular groove is opened at the inner end of the inner furnace tube, and an end cover is installed at the outer end of the inner furnace tube;

[0008] An air inlet hole and an air outlet hole are opened on the inner furnace tube, an air inlet groove which cooperates with the air inlet hole and an air outlet groove which cooperates with the air outlet hole are opened on the outer furnace tube; an air inlet passage which cooperates with the air inlet groove and an air outlet passage which cooperates with the air outlet groove are opened on the heat insulation layer; a sealing plate which cooperates with the air outlet passage is slidably installed on the heat insulation layer, and a through groove is opened on the sealing plate.

[0009] As a preferred technical solution of the present invention, a first rack is fixedly installed at one end of the sealing plate, a sliding rod which penetrates through the heat insulation layer and the outer furnace tube is slidably installed at a position corresponding to the inner furnace tube on the heat insulation layer, a second rack is fixedly installed on the sliding rod, and a gear is rotatably installed outside the heat insulation layer through a bracket, and both the first rack and the second rack are engaged with the gear.

[0010] As a preferred technical solution of the present invention, a torsion spring is installed between the end of the gear and the bracket.

[0011] As a preferred technical solution of the present invention, when the outer end face of the inner furnace tube is in contact with the inner end face of the outer furnace tube, the positions of the air outlet hole, the air outlet passage and the through groove correspond; when the positions of the air outlet hole and the air outlet passage do not correspond, the positions of the through groove and the air outlet passage also do not correspond.

[0012] As a preferred technical solution of the present invention, a circular mesh structure is installed at a position corresponding to the circular groove on the inner furnace tube; a graphene plate is installed at a position corresponding to the circular groove on the inner end face of the outer furnace tube; a first inclined groove corresponding to the bottom end of the graphene plate is opened on the outer furnace tube, and a second inclined groove communicating with the first inclined groove is opened on the heat insulation layer.

[0013] As a preferred technical solution of the present invention, the diameter of the mesh structure is the same as the diameter of the circular groove, a vertical rotating shaft is installed at the top of the mesh structure, and a strip-shaped groove which cooperates with the top of the rotating shaft is opened on the inner circumferential surface of the outer furnace tube, and the strip-shaped groove is parallel to the axis of the outer furnace tube.

[0014] As a preferred technical solution of the present invention, a toothed ring located in the strip-shaped groove is fixedly sleeved on the rotating shaft, a receiving groove is opened in the strip-shaped groove, an inclined guiding groove is opened in the receiving groove, and a third rack which cooperates with the guiding groove is installed in the receiving groove; one end of the third rack is connected with the end face of the strip-shaped groove by a telescopic spring.

[0015] As a preferred technical solution of the present invention, a ball which rolls and cooperates with the guiding groove is installed on the third rack.

[0016] In the above technical solution, a tube-type oxidation diffusion furnace provided by the present invention has an inner furnace tube that can translate relative to the outer furnace tube. After the oxidation diffusion treatment is completed, during the process of pulling the inner furnace tube outward by an external force, the hot air in the inner furnace tube will enter the outer furnace tube through the circular groove, and the air with a lower temperature outside will enter the inner furnace tube. When the operator opens the end cover to take out the quartz boat, the air overflowing from the inner furnace tube has a lower temperature and will not pose a hidden danger to the personal safety of the operator. During the process of pushing the inner furnace tube inward by an external force to reset, the hot air in the outer furnace tube returns to the inner furnace tube through the circular groove. In this way, less heat is required for preheating before the next oxidation operation, reducing the energy consumption of the equipment.

[0017] In addition, during the wet oxidation process, when the hot air passes through the mesh structure in the circular groove, water vapor will adhere to the mesh structure to form water droplets; when the inner furnace tube reciprocates once, the water vapor will pass through the mesh structure twice, and the impurities in the water vapor will adhere to the mesh structure together with the water vapor and be adsorbed by the graphene plate, and finally discharged from the inner furnace tube, avoiding the contamination of the wafer. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0019] Figure 1 Schematic diagram of the first state inside the tube-type oxidation diffusion furnace in the embodiment;

[0020] Figure 2 For Figure 1 Enlarged schematic diagram of part A in

[0021] Figure 3 Schematic diagram of the second state inside the tube-type oxidation diffusion furnace in the embodiment;

[0022] Figure 4 For Figure 3 Enlarged schematic diagram of part B in

[0023] Figure 5 For Figure 3 Enlarged schematic diagram of part C in

[0024] Figure 6 Schematic diagram of the three-dimensional structure of the inner furnace tube in the embodiment.

[0025] Description of the reference numerals:

[0026] 1. Thermal insulation layer; 101. Intake duct; 102. Exhaust duct; 103. Second inclined chute; 2. Heating assembly; 3. Outer furnace tube; 301. Intake groove; 302. Exhaust groove; 303. First inclined chute; 304. Strip groove; 305. Accommodating groove; 306. Guide groove; 4. Inner furnace tube; 401. Circular groove; 402. Intake hole; 403. Exhaust hole; 5. End cover; 6. Sealing plate; 601. Through groove; 7. First rack; 8. Sliding rod; 9. Second rack; 10. Bracket; 11. Gear; 12. Mesh structure; 13. Graphene plate; 14. Rotating shaft; 15. Ring gear; 16. Third rack; 17. Telescopic spring. Detailed implementation manners

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further introduced in detail below in conjunction with the accompanying drawings.

[0028] As Figure 1 shown, this embodiment provides a tube-type oxidation diffusion furnace, including a thermal insulation layer 1, and the thermal insulation layer 1 plays a heat insulation role. A heating assembly 2 is arranged inside the thermal insulation layer 1, and the heating assembly 2 is a prior art, specifically, it can be a resistance coil; an outer furnace tube 3 that is fixedly installed and fits with the thermal insulation layer 1 is also arranged inside the thermal insulation layer 1, and an inner furnace tube 4 is slidably installed along the length direction inside the outer furnace tube 3; after the heating assembly 2 is powered on, it generates heat to increase the temperatures of the outer furnace tube 3 and the inner furnace tube 4; a circular groove 401 coaxial with it is opened on the inner end surface of the inner furnace tube 4, and an end cover 5 is installed at the outer end of the inner furnace tube 4, and the end cover 5 and the inner furnace tube 4 are connected by threads or other commonly used methods in the prior art.

[0029] Specifically, a quartz boat for carrying wafers is placed inside the inner furnace tube 4, and a support frame (not shown in the figure) for supporting the quartz boat is arranged inside the inner furnace tube 4; in the working state, the heating assembly 2 heats the inner furnace tube 4, so that the air temperature inside the inner furnace tube 4 rises, and oxidation diffusion is performed on the wafers on the quartz boat; after the oxidation is completed, the inner furnace tube 4 is pulled outwards by an external force, and then the end cover 5 is opened to take out the quartz boat and unload the wafers on the quartz boat.

[0030] As Figure 1 、 Figure 3 and Figure 5As shown, intake holes 402 and outlet holes 403 are formed in the inner furnace tube 4, an intake groove 301 mating with the intake holes 402 and an outlet groove 302 mating with the outlet holes 403 are formed in the outer furnace tube 3; an intake channel 101 mating with the intake groove 301 and an outlet channel 102 mating with the outlet groove 302 are formed in the heat insulation layer 1; a sealing plate 6 mating with the outlet channel 102 is slidably mounted on the heat insulation layer 1, and a through groove 601 is formed in the sealing plate 6. When the outer end face of the inner furnace tube 4 is in contact with the inner end face of the outer furnace tube 3, the positions of the outlet holes 403, the outlet channel 102 and the through groove 601 correspond; when the positions of the outlet holes 403 and the outlet channel 102 do not correspond, the positions of the through groove 601 and the outlet channel 102 do not correspond either.

[0031] Figure 1 In this state, external oxygen passes through pure water and then enters the interior of the inner furnace tube 4 through the intake channel 101, the intake groove 301 and the intake holes 402, and the residual gas inside the inner furnace tube 4 is discharged through the outlet groove 302, the outlet channel 102 and the through groove 601; after the gas filling is completed, the position of the sealing plate 6 is adjusted by an external force so that the positions of the through groove 601 and the outlet channel 102 are staggered, so as to ensure that no internal gas overflows from the through groove 601 when the inner furnace tube 4 is in a high temperature and high pressure state; after the heating assembly 2 is powered on, it generates heat to increase the temperature inside the inner furnace tube 4, so that the inside of the inner furnace tube 4 is in a high temperature and high pressure state, thereby performing oxidation diffusion on the wafers on the quartz boat. After the oxidation is completed, the position of the sealing plate 6 is adjusted by an external force so that the through groove 601 returns to a position corresponding to the outlet channel 102, so that part of the high-pressure gas inside the inner furnace tube 4 can be discharged from the inner furnace tube 4. Then, the inner furnace tube 4 is pulled to the right by an external force to enter Figure 3 the state shown; during this process, the sealing plate 6 closes the outlet channel 102, the high-temperature gas inside the inner furnace tube 4 enters the outer furnace tube 3 through the circular groove 401, and external air enters the inner furnace tube 4 through the intake holes 402; after the inner furnace tube 4 is pulled to the predetermined position, the operator opens the end cover 5 to take out the quartz boat. Since the high-temperature gas inside the inner furnace tube 4 has entered the outer furnace tube 3, the gas overflowing from the inner furnace tube 4 has a lower temperature and will not pose a safety hazard to the operator. After the operator removes the oxidized wafers, new wafers are placed on the quartz boat, and the quartz boat is placed inside the inner furnace tube 4, then the end cover 5 is installed, and then the inner furnace tube 4 is pushed back to the left to Figure 1 the state shown; during this process, the high-temperature gas inside the outer furnace tube 3 returns to the inner furnace tube 4 through the circular groove 401, and the air inside the inner furnace tube 4 is discharged through the intake holes 402; in summary, the outer furnace tube 3 plays a role in temporarily storing the high-temperature gas in the inner furnace tube 4 during the whole process, that is, during the material taking process, the high-temperature gas in the inner furnace tube 4 enters the outer furnace tube 3, and during the feeding process, the high-temperature gas returns to the inner furnace tube 4. In this way, it can not only avoid the safety hazard caused by high-temperature gas to the operator, but also reduce the heat required for preheating during the next oxidation, thus reducing the energy consumption.

[0032] As Figure 1 and Figure 3 shown, a first rack 7 is fixedly installed at one end of the sealing plate 6, a sliding rod 8 penetrating through the heat insulation layer 1 and the outer furnace tube 3 is slidably installed at a position corresponding to the inner furnace tube 4 on the heat insulation layer 1, a second rack 9 is fixedly installed on the sliding rod 8, a gear 11 is rotatably installed outside the heat insulation layer 1 through a bracket 10, and both the first rack 7 and the second rack 9 are engaged with the gear 11; a torsion spring is installed between the end of the gear 11 and the bracket 10.

[0033] Specifically, in the Figure 1 state, the end face of the inner furnace tube 4 is in contact with the outer furnace tube 3, the right end of the sealing plate 6 is in contact with the end face of the inner furnace tube 4, the torsion spring between the gear 11 and the bracket 10 is in a deformed state, and the gear 11 has a tendency to rotate clockwise. However, due to the blocking of the inner furnace tube 4 on the sealing plate 6, the gear 11, the first rack 7, and the sealing plate 6 all remain in a stable static state; when the inner furnace tube 4 moves to the right under an external force, the gear 11 will move clockwise under the action of the torsion spring, and drive the first rack 7 and the sealing plate 6 to move to the left, thereby automatically adjusting the through slot 601.

[0034] During the actual wet oxidation process, the high-temperature and high-pressure water vapor in the inner furnace tube 4 will vaporize the impurities remaining in the inner furnace tube 4. The water vapor mixed with impurities will have an adverse effect on the quality of subsequent wafer oxidation, and these impurities will adhere to the inner wall of the inner furnace tube 4 at room temperature and are difficult to clean; in view of this problem, the present embodiment also makes the following design.

[0035] As Figure 1 , Figure 2 , Figure 3 and Figure 4As shown in the figure, a circular mesh structure 12 is installed at the position corresponding to the circular groove 401 on the inner furnace tube 4. The mesh structure 12 is 200 mesh, and the thickness of the mesh structure 12 does not exceed 1 cm. A graphene plate 13 is installed at the position corresponding to the circular groove 401 on the inner end face of the outer furnace tube 3. The graphene plate 13 is heat-resistant and has water absorption. A first inclined groove 303 corresponding to the bottom end of the graphene plate 13 is opened on the outer furnace tube 3, and a second inclined groove 103 communicating with the first inclined groove 303 is opened on the heat insulation layer 1. The diameter of the mesh structure 12 is the same as that of the circular groove 401. A vertical rotating shaft 14 is installed at the top of the mesh structure 12. A strip-shaped groove 304 matching with the top of the rotating shaft 14 is opened on the inner circumferential surface of the outer furnace tube 3. The strip-shaped groove 304 is parallel to the axis of the outer furnace tube 3. A gear ring 15 located in the strip-shaped groove 304 is fixedly sleeved on the rotating shaft 14. An accommodating groove 305 is opened in the strip-shaped groove 304. An inclined guiding groove 306 is opened in the accommodating groove 305. A third rack 16 matching with the guiding groove 306 is installed in the accommodating groove 305. A ball rolling with the guiding groove 306 is installed on the third rack 16. One end of the third rack 16 is connected with a telescopic spring 17 between the end face of the strip-shaped groove 304.

[0036] Specifically, when the inner furnace tube 4 moves to the right from the Figure 1 state, the high-temperature water vapor in the inner furnace tube 4 passes through the mesh structure 12 from right to left. After the water vapor contacts the mesh structure 12, part of the water vapor forms water droplets on the right side surface of the mesh structure 12, and part of the impurities in the water vapor are also mixed in the water droplets and attached to the mesh structure 12. As the inner furnace tube 4 continues to move to the right, the gear ring 15 and the third rack 16 enter the meshing state. Since the third rack 16 cannot move to the right under the supporting action of the telescopic spring 17, the gear ring 15 will rotate under the reaction force of the third rack 16. Specifically, when the inner furnace tube 4 moves to the predetermined position to the right, the gear ring 15 drives the rotating shaft 14 and the mesh structure 12 to rotate 180°. It should be noted that there is a certain damping between the rotating shaft 14 and the inner furnace tube 4, so only an external force exceeding a certain value can drive the gear ring 15 and the rotating shaft 14 to rotate. When the inner furnace tube 4 moves horizontally to the left from the rightmost position, the gear ring 15 will drive the third rack 16 meshing with it to move to the left, and the telescopic spring 17 is stretched. During the process of the third rack 16 moving to the left, it moves downward relative to the gear ring 15 under the guiding action of the guiding groove 306 until it is completely separated from the gear ring 15. After being separated from the gear ring 15, the third rack 16 returns to the Figure 2The state shown; during the process of the inner furnace tube 4 moving leftward, the high-temperature water vapor in the outer furnace tube 3 passes through the mesh structure 12 from left to right. After the water vapor contacts the mesh structure 12, part of the water vapor forms water droplets on the left side surface of the mesh structure 12. Thus, during the reciprocating translation of the inner furnace tube 4, water droplets are formed on the same side surface, and this side surface will be in contact with the graphene plate 13. The graphene plate 13 adsorbs the water droplets on the mesh structure 12, and the water in the graphene plate 13 will gather downward under the action of gravity and be discharged through the first inclined groove 303 and the second inclined groove 103. To sum up, in this embodiment, through the flow of water vapor during the reciprocating translation of the inner furnace tube 4, the water vapor is liquefied, so that part of the impurities adhere to the mesh structure 12 and are discharged along with the liquefied water vapor; during the process of the inner furnace tube 4 changing the direction of movement, the mesh structure 12 will also automatically rotate 180°, so that only one side surface of the mesh structure 12 has liquefied water vapor, which is convenient for the graphene plate 13 to adsorb the water droplets. Thus, the impurity content in the inner furnace tube 4 can be reduced, and the oxidation quality of the wafer can be improved.

[0037] Only some exemplary embodiments of the present invention have been described by way of illustration above. Undoubtedly, for those of ordinary skill in the art, without departing from the spirit and scope of the present invention, the described embodiments can be modified in various different ways. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the protection scope of the claims of the present invention.

Claims

1. A tubular oxidation diffusion furnace, comprising a heat-insulating layer (1), wherein a heating assembly (2) is arranged in the heat-insulating layer (1), characterized in that: An outer furnace tube (3) is fixedly installed in the thermal insulation layer (1) and is fitted therewith. An inner furnace tube (4) is slidably installed in the outer furnace tube (3) along its length direction. A circular groove (401) is provided at the inner end of the inner furnace tube (4), and an end cover (5) is installed at the outer end of the inner furnace tube (4). When the inner furnace tube (4) is pulled out, the high-temperature gas in the inner furnace tube (4) enters the outer furnace tube (3) through the circular groove (401); when the inner furnace tube (4) is pushed back, the high-temperature gas in the outer furnace tube (3) returns to the inner furnace tube (4) through the circular groove (401). The inner furnace tube (4) is provided with an air inlet hole (402) and an air outlet hole (403); the outer furnace tube (3) is provided with an air inlet groove (301) cooperating with the air inlet hole (402) and an air outlet groove (302) cooperating with the air outlet hole (403); the thermal insulation layer (1) is provided with an air inlet passage (101) cooperating with the air inlet groove (301) and an air outlet passage (102) cooperating with the air outlet groove (302); A sealing plate (6) cooperating with the air outlet (102) is slidably mounted on the thermal insulation layer (1), and a through groove (601) is provided on the sealing plate (6).

2. A tubular oxidation diffusion furnace according to claim 1, characterized in that: A first rack (7) is fixedly mounted on one end of the sealing plate (6); a sliding rod (8) penetrating the thermal insulation layer (1) and the outer furnace tube (3) is slidably mounted on the thermal insulation layer (1) at a position corresponding to the inner furnace tube (4); a second rack (9) is fixedly mounted on the sliding rod (8); a gear (11) is rotatably mounted on the outside of the thermal insulation layer (1) via a bracket (10); and both the first rack (7) and the second rack (9) are meshed with the gear (11).

3. A tubular oxidation diffusion furnace according to claim 2, characterized in that: A torsion spring is installed between the end of the gear (11) and the bracket (10).

4. A tubular oxidation diffusion furnace according to claim 3, characterized in that: When the outer end surface of the inner furnace tube (4) is in contact with the inner end surface of the outer furnace tube (3), the positions of the air outlet hole (403), the air outlet passage (102) and the through groove (601) correspond; when the positions of the air outlet hole (403) and the air outlet passage (102) do not correspond, the positions of the through groove (601) and the air outlet passage (102) do not correspond either.

5. The tubular oxidation diffusion furnace according to claim 4, characterized in that: A circular mesh structure (12) is installed at a position corresponding to the circular groove (401) on the inner furnace tube (4); a graphene plate (13) is installed at a position corresponding to the circular groove (401) on the inner end surface of the outer furnace tube (3); a first inclined groove (303) corresponding to the bottom end of the graphene plate (13) is provided on the outer furnace tube (3), and a second inclined groove (103) connected to the first inclined groove (303) is provided on the thermal insulation layer (1).

6. The tubular oxidation diffusion furnace according to claim 5, characterized in that: The diameter of the mesh structure (12) is consistent with the diameter of the circular groove (401), a vertical rotating shaft (14) is installed on the top of the mesh structure (12), and a strip groove (304) matching the top of the rotating shaft (14) is opened on the inner circumferential surface of the outer furnace tube (3), and the strip groove (304) is parallel to the axis of the outer furnace tube (3).

7. The tubular oxidation diffusion furnace according to claim 6, characterized in that: A gear ring (15) is fixedly sleeved on the rotating shaft (14) and is located in the strip groove (304); a receiving groove (305) is provided in the strip groove (304); an inclined guide groove (306) is provided in the receiving groove (305); a third rack (16) matched with the guide groove (306) is installed in the receiving groove (305); and a telescopic spring (17) is connected between one end of the third rack (16) and the end surface of the strip groove (304).

8. The tubular oxidation diffusion furnace according to claim 7, characterized in that: The third rack (16) is provided with a ball that rolls in cooperation with the guide groove (306).

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