Diffusion furnace with uniform flow plate set

Abstract

The utility model relates to diffusion furnace equipment technical field, aims at solving the technical problem that the existing diffusion furnace gas distribution uneven leads to silicon wafer yield decline. For this, the utility model provides a kind of diffusion furnace with uniform flow plate group, including furnace tube, quartz boat for placing silicon wafer is equipped in furnace tube, quartz boat is equipped with uniform flow plate group respectively along length direction two sides, uniform flow plate group includes at least two each other parallel and along the interval setting of furnace tube axis direction uniform flow plate, multiple uniform flow hole groups are equipped on each uniform flow plate, each uniform flow hole group includes multiple radial interval arrangement uniform flow hole, multiple uniform flow hole groups are with the axis of corresponding uniform flow plate as center rotation distribution, and the projection of at least part uniform flow hole on the adjacent uniform flow plate in the direction perpendicular to uniform flow plate does not coincide. The utility model is designed by above-mentioned uniform flow plate group, continues to optimize along furnace tube axis airflow, effectively eliminates vortex and flow uneven, realizes the significant improvement of quartz boat head and tail area silicon wafer diffusion uniformity.

Description

Technical Field

[0001] This utility model relates to the field of diffusion furnace equipment technology, specifically providing a diffusion furnace with a flow equalization plate assembly. Background Technology

[0002] In the high-temperature diffusion (such as boron diffusion) and oxidation processes of photovoltaic crystalline silicon wafer manufacturing, the high-temperature tube diffusion furnace is a core piece of equipment. In traditional designs, silicon wafers are typically loaded vertically into a quartz boat and then placed into the furnace tube for processing. This vertical loading method limits the number of silicon wafers that can be loaded into a single tube (or furnace chamber). While the vertical structure facilitates the longitudinal flow of process gases between the wafers to some extent, its wafer processing capacity per unit time has limitations, making it difficult to meet the ever-increasing demands for high-efficiency mass production.

[0003] To significantly improve single-machine capacity and hourly output efficiency, the main technological improvement direction in the industry at present is to change the silicon wafer loading method from vertical insertion to horizontal placement. This horizontal structure allows more silicon wafers to be stacked in a single tube, almost doubling the capacity. However, in actual large-scale production applications, it has been found that this high-density horizontal loading method brings new challenges: the diffusion uniformity (i.e., the consistency of doping concentration or oxide thickness in different areas of the same silicon wafer) of the two small boats of silicon wafers located at the beginning and end of the furnace tube fluctuates significantly, seriously affecting the process yield and cell performance uniformity of the silicon wafers at this location. Analysis confirmed that the main root cause of this problem is the uneven distribution of the process gas flow field in the furnace tube. Under the high-load horizontal structure, the gas is prone to eddies, stagnation, or uneven flow velocity distribution at the furnace tube inlet, outlet, and densely loaded wafer areas of the quartz boats, resulting in the silicon wafer surface in the areas where the quartz boats are located not obtaining uniform and stable reactive gas coverage and heat exchange conditions.

[0004] Therefore, there is a need in the art for a new diffusion furnace accessory to solve the above problems. Utility Model Content

[0005] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problem of uneven gas distribution in existing diffusion furnaces leading to a decrease in silicon wafer yield.

[0006] To address this, the present invention provides a diffusion furnace with a flow equalization plate assembly. The diffusion furnace includes a furnace tube, and a quartz boat for placing silicon wafers is disposed inside the furnace tube. Flow equalization plate assemblies are respectively disposed on both sides of the quartz boat along its length. Each flow equalization plate assembly includes at least two parallel flow equalization plates spaced apart along the axial direction of the furnace tube. Each flow equalization plate is provided with multiple flow equalization hole groups. Each flow equalization hole group includes multiple flow equalization holes arranged radially spaced along the flow equalization plate. The multiple flow equalization hole groups are rotated and distributed around the axis of the corresponding flow equalization plate, and at least some of the flow equalization holes on adjacent flow equalization plates do not overlap in the direction perpendicular to the flow equalization plate.

[0007] In some feasible embodiments of the diffusion furnace with flow equalization plate groups described above, the included angle between each adjacent flow equalization hole group is the same.

[0008] In some feasible embodiments of the diffusion furnace with uniform flow plates described above, if the number of uniform flow plates is N and the included angle between adjacent uniform flow hole groups is α, then in the installed state, the circumferential deflection angle of adjacent uniform flow plates is α / N.

[0009] In some feasible embodiments of the diffusion furnace with flow equalization plate groups described above, the number of flow equalization hole groups is greater than or equal to 3.

[0010] In some feasible embodiments of the diffusion furnace with flow equalization plate group described above, each flow equalization plate in the flow equalization plate group has the same structure and the number is greater than or equal to 3.

[0011] In some feasible embodiments of the diffusion furnace with flow equalizers described above, the spacing between adjacent flow equalizers is the same.

[0012] In some feasible embodiments of the diffusion furnace with flow equalization plate group described above, the plate spacing between adjacent flow equalization plates is 10mm-200mm.

[0013] In some feasible embodiments of the diffusion furnace with flow equalization plate assembly described above, the flow equalization plate is sealed to the inner wall of the diffusion furnace when the installation is complete.

[0014] In some feasible embodiments of the diffusion furnace with flow equalization plates described above, the diameter of each flow equalization hole on the flow equalization plate gradually increases along the airflow direction to form a flow guide taper.

[0015] In some feasible embodiments of the diffusion furnace with uniform flow plate group described above, the diffusion furnace is a horizontally placed diffusion furnace.

[0016] The diffusion furnace provided by this invention features flow equalization plate assemblies on both sides of a quartz boat. Each flow equalization plate assembly includes at least two parallel flow equalization plates spaced apart along the furnace tube axis. The radial arrangement and rotational distribution of flow equalization holes on the plates, along with a design where at least some holes on adjacent plates do not overlap vertically, prevents direct airflow penetration and the formation of localized high-speed zones while ensuring sufficient open area ratio for efficient gas flow. This design continuously optimizes airflow along the furnace tube axis, effectively eliminating eddies and velocity unevenness within the furnace tube, and significantly improving the diffusion uniformity of the silicon wafers at both ends of the quartz boat.

[0017] Furthermore, the included angles between each flow-equalizing orifice group are the same, ensuring a uniform distribution of the orifice groups in the circumferential direction. This design ensures that the gas flow rate remains consistent in the circumferential direction of the furnace tube, avoiding local gas supply deviations caused by uneven orifice distribution, thereby reducing the difference in process gas concentration in the circumferential position of the silicon wafer and further improving the uniformity of the flow field.

[0018] Furthermore, the circumferential deflection angle of adjacent flow equalizers is α / N. Through this stepped circumferential deflection design, the holes of the multi-stage flow equalizers form a continuous coverage in the circumferential direction, which can effectively eliminate areas of concentrated airflow, make the gas distribution in the circumferential direction more fine and uniform, enhance the overall uniformity of the flow field, and ensure that the silicon wafer surface can obtain a more uniform gas coverage.

[0019] Furthermore, having three or more flow-equalizing aperture groups increases the circumferential coverage density. Compared to fewer aperture groups, three or more aperture groups can reduce the circumferential spacing, allowing gas to flow through more angles, reducing "blind spots" in airflow distribution, avoiding local airflow stagnation, and making the gas supply between the silicon wafer edge and center more balanced, thus improving the uniformity of airflow.

[0020] Furthermore, identical flow equalizers facilitate uniform deflection angles and achieve synergistic effects. Three or more flow equalizers mean that the airflow undergoes multiple corrections, with each stage adjusting the airflow deviation of the previous stage. This multi-stage synergistic flow equalization method can gradually eliminate eddies and velocity fluctuations in the airflow, forming a stable and uniform flow field. It is particularly suitable for the complex flow field environment of high-density horizontal wafer placement, improving the overall diffusion consistency of the silicon wafer.

[0021] Furthermore, the uniform spacing between each flow equalizer provides a uniform adjustment space for the airflow. This design ensures that the adjustment effect of each flow equalizer on the airflow is stable and consistent, avoiding over-correction or under-correction of local airflow caused by uneven spacing. It also ensures the uniformity of airflow along the furnace tube axis (i.e., the length direction of the quartz boat), so that the silicon wafers at the beginning, middle and end of the quartz boat are in the same airflow environment.

[0022] Furthermore, the spacing between adjacent flow equalization plates is limited to 10mm-200mm, with the specific spacing value determined based on different furnace tube lengths and isothermal zone lengths. This spacing design effectively balances the flow equalization effect and flow efficiency. Too small a spacing leads to excessive airflow resistance and turbulence; too large a spacing diminishes the effect of the previous flow equalization stage, causing the airflow to become uneven again. A spacing of 10mm-200mm ensures that the airflow after the previous flow equalization stage remains stable when reaching the next stage, without excessively increasing system resistance, making it suitable for the process gas flow requirements of photovoltaic diffusion furnaces.

[0023] Furthermore, by sealing each flow equalizer plate with the inner wall of the furnace tube, the gap between the flow equalizer plate and the furnace tube is eliminated, preventing gas from bypassing the flow equalizer hole and flowing directly through. This forces all gas to pass through the flow equalizer hole, ensuring that the flow equalizer plate's guiding and equalizing effects are fully effective, and avoiding interference of the gap airflow with the flow field around the quartz boat.

[0024] Furthermore, by gradually increasing the diameter of each flow-equalizing orifice along the airflow direction to form a guiding taper, this gradually expanding orifice design guides the gas to flow smoothly through the orifice, reducing orifice eddies and airflow separation, and avoiding abrupt changes in gas flow direction caused by straight orifices. Simultaneously, it reduces airflow resistance, allowing the gas to enter the quartz boat region more stably, which is beneficial for the uniform adsorption and diffusion of reactant gases on the silicon wafer surface, thus improving the stability of the flow field. Attached Figure Description

[0025] The preferred embodiments of this utility model are described below with reference to the accompanying drawings, in which:

[0026] Figure 1 This is a schematic diagram of the structure of a diffusion furnace provided in an embodiment of the present utility model, which only shows the flow equalization plate group arranged on the side of the quartz boat away from the air inlet;

[0027] Figure 2 This is a schematic diagram of the flow uniform plate assembly provided in an embodiment of the present invention.

[0028] List of reference numerals in the attached diagram:

[0029] 1. Furnace tube; 2. Quartz boat support; 3. Silicon wafer; 4. Air inlet; 5. Exhaust outlet; 6. Furnace door; 7. Flow equalization plate assembly; 71. Flow equalization plate; 711. Flow equalization hole assembly; 7111. Flow equalization hole. Detailed Implementation

[0030] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0031] To better illustrate this invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this invention can be implemented even without certain specific details.

[0032] In the description of this utility model, terms such as "upper," "lower," "inner," "outer," "front," "rear," "left," and "right," which indicate direction or positional relationships, are based on the illustrated directions or positional relationships. This is merely for ease of description and does not indicate or imply that the device to be protected must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the orientations in the following embodiments should not be construed as limitations on this utility model. Furthermore, ordinal numbers such as "first" and "second" are only for ease of explanation and are not used to indicate or imply relative importance.

[0033] Furthermore, it should be noted that, in the description of this utility model, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0034] The structure of the diffusion furnace with flow equalization plate assembly provided in the embodiments of this utility model will be described in detail below with reference to the accompanying drawings. It should be noted that the drawings are all in a simplified form and use non-precise proportions, and are only used to facilitate and clearly assist in explaining the embodiments of this utility model, and are not intended to limit the protection scope of this utility model.

[0035] like Figure 1As shown, the diffusion furnace in this embodiment mainly consists of a furnace tube 1, a quartz boat support 2, and a quartz boat (not shown), which is used to support silicon wafers 3. The furnace tube 1 is equipped with an air inlet 4, an exhaust outlet 5, and a furnace door 6. Two sets of flow equalization plates 7 are installed inside the furnace tube 1. The furnace tube 1 is a quartz tube, forming a sealed space for the diffusion process. In actual production, its length is usually selected from several meters to over ten meters depending on specific capacity requirements and equipment design. The tube diameter is also determined based on factors such as the size of the quartz boat and the loading density, with common diameters ranging from tens of centimeters to about one meter. The quartz boat support 2 is installed inside the furnace tube 1 and is used to support the quartz boat (not shown) on which the silicon wafers 3 are placed. Its material is usually selected as high-temperature resistant and chemically stable quartz material to ensure long-term stable operation in high-temperature, corrosive process gas environments. The silicon wafers 3 are placed horizontally inside the quartz boat. This horizontal wafer placement method greatly increases the silicon wafer loading capacity of a single tube, thereby significantly improving the single-machine capacity. For ease of control, in this embodiment, the air inlet 4 and exhaust outlet 5 are located at one end of the furnace tube 1. The process gas flows in through the air inlet 4 and, after reacting with the silicon wafer 3, exits through the exhaust outlet 5. The furnace door 6 is used to open and close the furnace tube 1 during wafer loading and unloading to ensure the equipment's airtightness during operation. It is understood that the air inlet 4 and exhaust outlet 5 can also be located at opposite ends of the furnace tube 1.

[0036] The flow equalization plate group 7 is the key structure of this utility model. In this embodiment, two flow equalization plate groups 7 are provided, which are respectively installed on both sides of the quartz boat support 2 along the length direction (only one side is shown in the figure, and the other side is not shown).

[0037] The following is based on Figure 1 Taking one side as an example, the structural features of the flow uniform plate group 7 are explained in detail.

[0038] like Figure 1 and Figure 2 As shown, the flow equalizer group 7 includes at least two flow equalizers 71 that are parallel to each other and spaced apart along the axis of the furnace tube 1. In this embodiment, the number of flow equalizers 71 is selected as three, which is a relatively optimized number determined after extensive experiments and actual production verification. In practical applications, the number of flow equalizers can be flexibly adjusted within a range of three or more, depending on parameters such as the specific length, diameter, and process gas flow rate of the furnace tube. For example, for longer furnace tubes, the number of flow equalizers can be appropriately increased to four or five to better optimize the airflow along the furnace tube axis.

[0039] like Figure 2As shown, the flow equalization plate 71 in this embodiment is a circular plate structure, the diameter of which precisely matches the inner diameter of the approximately circular furnace tube 1 of the diffusion furnace. When installed, the flow equalization plate 71 fits tightly against the inner wall of the diffusion furnace to form a sealed connection. This installation method effectively eliminates gaps between the flow equalization plate 71 and the furnace tube, preventing gas from bypassing the flow equalization holes and flowing directly through. In actual installation, sealing rings can be placed on the edge of the flow equalization plate 71 to further enhance the sealing effect, ensuring that all gas must pass through the flow equalization holes, thus allowing the flow equalization and guiding effects of the flow equalization plate 71 to be fully effective, avoiding interference from gap airflow to the flow field around the quartz boat. If there is a large gap between the flow equalization plate and the furnace tube, a large amount of gas will flow through the gap, causing the flow equalization plate to lose its gas rectification effect, resulting in turbulent flow field inside the furnace tube and severely affecting the diffusion uniformity of the silicon wafer. Alternatively, the flow equalization plate 71 can also be configured in other suitable shapes, as long as it can match the furnace tube 1.

[0040] Each flow equalizer plate 71 is provided with multiple flow equalizer hole groups 711, and each flow equalizer hole group 711 contains multiple flow equalizer holes 7111 arranged radially at intervals along the flow equalizer plate 71. In this embodiment, the number of flow equalizer hole groups 711 is set to 3, which can effectively increase the circumferential coverage density. Compared with fewer hole groups, 3 hole groups can reduce the circumferential interval, allowing gas to have flow channels at more angles and reducing the "blind spots" of airflow distribution. In practical applications, the number of flow equalizer hole groups can be appropriately adjusted according to the diameter of the furnace tube. For furnace tubes with larger diameters, the number of flow equalizer hole groups can be increased to 4 or 5 to further improve the uniformity of circumferential airflow. The included angle between each flow equalizer hole group 711 is the same; in this embodiment, the included angle α is set to 120°. This uniform angle design ensures consistent gas flow around the furnace tube, avoiding localized gas supply deviations caused by uneven orifice distribution. This reduces process gas concentration differences around the silicon wafer, further improving the circumferential uniformity of the flow field. In different application scenarios, the angle α can be adjusted within a certain range based on the characteristics and flow rate of the process gas, as well as the simulation results of the flow field within the furnace tube, to achieve the optimal uniform flow effect.

[0041] The flow equalization hole group 711 is distributed in a rotating manner around the axis of the flow equalization plate 71, and at least some of the flow equalization holes 7111 on adjacent flow equalization plates 71 do not overlap in the direction perpendicular to the flow equalization plate 71. If the number of flow equalization plates 71 is N (N=3 in this embodiment), and the included angle between adjacent flow equalization hole groups is α (α=120° in this embodiment), then in the installed state, the circumferential deflection angle (deflection in the same direction) of adjacent flow equalization plates 71 is α / N, which is 40° in this embodiment. Through this stepped circumferential deflection design, the holes of the multi-stage flow equalization plates form a continuous coverage in the circumferential direction, which can effectively eliminate the area of ​​concentrated airflow, make the gas distribution in the circumferential direction more fine and uniform, enhance the overall uniformity of the flow field, and ensure that the silicon wafer surface can obtain a more uniform gas coverage. In the actual manufacturing process, the flow equalization hole group can be accurately processed on the flow equalization plate through precision machining technology, and the circumferential deflection angle of the flow equalization plate can be precisely controlled by positioning fixtures during installation to ensure the realization of design requirements.

[0042] Furthermore, the diameter of each flow equalization orifice 7111 gradually increases along the airflow direction to form a guiding taper. For example, in this embodiment, the inlet diameter of the flow equalization orifice 7111 is 5 mm, and the outlet diameter is 8 mm. This gradually expanding orifice design guides the gas to flow smoothly through the flow equalization orifice, reducing orifice eddies and airflow separation, and avoiding abrupt changes in gas flow direction caused by straight orifices. Simultaneously, it reduces airflow resistance, allowing the gas to enter the quartz boat region more stably, which is beneficial for the uniform adsorption and diffusion of the reactant gas on the silicon wafer surface, improving the stability of the flow field. In different diffusion processes, the taper and specific orifice diameter of the flow equalization orifice can be adjusted according to the type and flow rate of the process gas and the required gas velocity. For example, for process gases with high viscosity, the taper can be appropriately increased to better guide gas flow; for processes with high gas velocity requirements, the inlet diameter can be appropriately reduced to increase the gas velocity through the flow equalization orifice.

[0043] Preferably, the spacing between each flow equalizer 71 is the same. For example, the spacing between adjacent flow equalizers 71 can be set to 50mm. It should be noted that this specific value of the spacing was determined through extensive experiments and simulations based on different furnace tube lengths and constant temperature zone lengths. This spacing can effectively balance the flow equalization effect and flow efficiency. An appropriate spacing allows the airflow after the previous stage of equalization to remain stable when it reaches the next stage, without excessively increasing the system resistance, which is suitable for the process gas flow requirements of photovoltaic diffusion furnaces. In practical applications, for diffusion furnaces of different specifications, the plate spacing can be reasonably adjusted within the range of 10mm-200mm according to parameters such as furnace tube length, tube diameter, and process gas flow rate. For example, for shorter furnace tubes and smaller process gas flow rates, the plate spacing can be appropriately reduced to 30mm; for longer furnace tubes and larger process gas flow rates, the plate spacing can be appropriately increased to 80mm.

[0044] In practical use of the diffusion furnace of this invention, after the process gas flows into the furnace tube from the inlet 4, it first impacts the flow equalization plate group located on the right side of the quartz boat near the inlet. Due to the radial arrangement and rotational distribution of the flow equalization holes 711 on the flow equalization plate 71 around the axis, and the design that at least some of the flow equalization holes 7111 on adjacent flow equalization plates 71 do not overlap in vertical projection, the gas cannot directly penetrate to form a local high-speed zone, but is uniformly dispersed into each flow equalization hole 7111. As the gas passes through each level of flow equalization plate 71 in sequence, each level of flow equalization plate adjusts the airflow deviation of the previous level, gradually eliminating eddies and velocity fluctuations in the airflow, and finally forming a stable and uniform flow field. This provides uniform and stable reactive gas coverage and heat exchange conditions for the silicon wafers 3 inside the quartz boat, significantly improving the diffusion uniformity of the silicon wafers in the head and tail areas of the quartz boat.

[0045] In addition, the flow equalization plate group located on the left side of the quartz boat mainly serves to assist in flow equalization. Specifically, the airflow in contact with the flow equalization plate group on the left side is the airflow after the reaction with the silicon wafer has been completed. This part of the airflow, through the flow equalization effect of the left-side flow equalization plate group, can maintain the stability of the airflow in the outlet area, and prevent unreacted gas residue or eddy current generation caused by outlet pressure fluctuations or airflow turbulence. This ensures that the exhaust gas can be discharged from the furnace tube evenly and smoothly, further guaranteeing the stability of the flow field inside the entire furnace tube and the uniformity of the silicon wafer process.

[0046] In summary, this utility model, through careful design and optimization of the structure of the flow equalization plate group 7, effectively solves the problem of uneven gas distribution in existing diffusion furnaces leading to a decrease in silicon wafer yield, improves the stability of photovoltaic diffusion process and product quality, and has significant economic benefits and practical value.

[0047] The technical solution of this utility model has been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the protection scope of this utility model is obviously not limited to these specific embodiments. Without departing from the principle of this utility model, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of this utility model.

Claims

1. A diffusion furnace with a flow equalization plate assembly, characterized in that, The diffusion furnace includes a furnace tube (1), and a quartz boat for placing silicon wafers (3) is provided inside the furnace tube (1). A flow equalization plate group (7) is provided on both sides of the quartz boat along its length direction. The flow equalization plate group (7) includes at least two flow equalization plates (71) that are parallel to each other and spaced apart along the axial direction of the furnace tube (1). Each flow equalization plate (71) is provided with a plurality of flow equalization hole groups (711). Each flow equalization hole group (711) includes a plurality of flow equalization holes (7111) arranged radially spaced along the flow equalization plate (71). The plurality of flow equalization hole groups (711) are rotated and distributed around the axis of the corresponding flow equalization plate (71), and at least some of the flow equalization holes (7111) on adjacent flow equalization plates (71) do not overlap in the direction perpendicular to the flow equalization plate (71).

2. The diffusion furnace with flow equalization plate assembly according to claim 1, characterized in that, The included angle between each adjacent flow uniform hole group (711) is the same.

3. The diffusion furnace with flow equalization plate assembly according to claim 2, characterized in that, If the number of the flow equalizers (71) is N and the included angle between adjacent flow equalizer groups (711) is α, then in the installed state, the circumferential deflection angle of adjacent flow equalizers (71) is α / N.

4. The diffusion furnace with flow equalization plate assembly according to claim 3, characterized in that, The number of the uniform flow orifice group (711) is greater than or equal to 3.

5. The diffusion furnace with a flow equalization plate assembly according to claim 2, characterized in that, Each of the flow equalizers (71) in the flow equalizer group (7) has the same structure and the number is greater than or equal to 3.

6. The diffusion furnace with a flow equalization plate assembly according to claim 5, characterized in that, The spacing between adjacent flow equalizers (71) is the same.

7. The diffusion furnace with a flow equalization plate assembly according to claim 6, characterized in that, The spacing between adjacent flow equalization plates (71) is 10mm-200mm.

8. The diffusion furnace with a flow equalization plate assembly according to claim 1, characterized in that, When installed, the flow equalization plate (71) is sealed to the inner wall of the diffusion furnace.

9. The diffusion furnace with a flow equalization plate assembly according to claim 1, characterized in that, Along the airflow direction, the diameter of each of the flow equalization holes (7111) on the flow equalization plate (71) gradually increases to form a flow guide taper.

10. The diffusion furnace according to any one of claims 1-9, characterized in that, The diffusion furnace is a horizontally placed diffusion furnace.

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