JP3753476B2 - heater - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heater, and can be used as a heating means for a heat treatment furnace that performs diffusion of impurities, formation of an oxide film, and the like in a manufacturing process of a semiconductor device, a liquid crystal display substrate, and the like.
[0002]
[Prior art and problems to be solved by the invention]
A conventional heater 101 shown in FIG. 7 is used in a heat treatment furnace such as a diffusion furnace or an oxidation furnace, and includes a heat insulating material having a cylindrical peripheral wall 102 and a heating element provided on the inner peripheral side of the peripheral wall 102. 103 and a single cylindrical shell 104 covering the outer peripheral side of the peripheral wall 102, diffusion of impurities, formation of an oxide film, and the like are performed in a heating space surrounded by the heat insulating material.
[0003]
In the heat treatment using the conventional heater 101, a thermal change outside the heater may affect the internal temperature. In the future, it is expected that semiconductor devices will be made finer and more uniform, and it is necessary to suppress the above effects as much as possible.
[0004]
The influence of such a thermal disturbance can be reduced by increasing the heat capacity of the entire heater by increasing the heat insulating effect by increasing the thickness of the heat insulating material. However, the rate of change of the internal temperature is reduced, and it takes a long time to change the internal temperature to the desired temperature, so that the responsiveness when changing the internal temperature is deteriorated.
[0005]
Therefore, in the conventional heat treatment furnace, the influence of the thermal disturbance has been corrected by providing a boat rotation drive mechanism for holding the heat treatment object. However, such a rotational drive mechanism is expensive and the structure is complicated.
[0006]
An object of this invention is to provide the heater which can solve the said problem.
[0007]
[Means for Solving the Problems]
The heater of the present invention includes a heat insulating material having a cylindrical peripheral wall, a heating element provided on the inner peripheral side of the peripheral wall, a cylindrical first shell covering the outer peripheral side of the peripheral wall, and an outer periphery of the first shell And a second shell having a cylindrical shape covering the side, and the shells are arranged with a radial interval therebetween.
[0008]
According to the configuration of the present invention, since the first shell and the second shell are arranged at a radial interval from each other, a thermally stable space can be formed between both shells as compared with the outside of the heater. Thereby, the influence of the thermal disturbance with respect to the temperature in the internal space surrounded by a heat insulating material can be made small, without thickening a heat insulating material and enlarging a heat capacity compared with the heater covered with the conventional single shell.
[0009]
In the heater of the present invention, it is provided with means for forcibly flowing the gas in the axial direction in a laminar flow state in the space between both shells, the gas flow rate can be adjusted, and the gas introduced into the space between both shells is It is discharged from the space without reaching the heating space covered with the heat insulating material .
Natural convection occurs in the space between the two shells based on the internal and external temperature differences, but the gas is forced to flow in the axial direction of the shell in a laminar flow state, and the gas flow rate is not affected by natural convection. By making it large, the space can be made into a thermally stable space so as not to be affected by natural convection.
[0010]
In the heater of the present invention, the inner and outer circumferences of each shell are arranged on a concentric cylindrical surface, an annular dispersion member concentric with the cylinder is arranged between both shells, and a plurality of gas flow holes are uniformly formed in the dispersion member. Preferably, the gas is fed into the space between the shells through the gas flow holes.
Thereby, the gas flow in the space between both shells can be made uniform, and the space can be made more uniform thermally.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
A heat treatment furnace 1 shown in FIG. 1 holds a heater 2, a furnace core tube 3 arranged in a heating space covered by the heater 2, and a processing object 4 such as a semiconductor substrate in the furnace core pipe 3. A boat 5 and an elevating device 6 for taking the boat 5 into and out of the furnace are provided.
[0012]
The heater 2 includes a heat insulating material 11, a heating element 12, a first shell 13, and a second shell 14. The heat insulating material 11 is constituted by a peripheral wall 21 having a cylindrical shape with a vertical axis and an upper wall 22 covering the upper portion of the peripheral wall 21, and the inside of the peripheral wall 21 is the heating space. The lower end of the peripheral wall 21 and the furnace core tube 3 are closed by an annular heater support base 23, and the lower part of the furnace core tube 3 is closed by an elevating device 6.
[0013]
The heating element 12 includes a plurality of resistance heating wires 12 a provided on the inner peripheral side of the peripheral wall 21. That is, as shown in FIG. 2, a plurality of grooves 21a extending in the vertical direction are formed on the inner periphery of the peripheral wall 21 at regular intervals in the circumferential direction. Each resistance heating wire 12a is formed into a shape having a straight portion and a curved portion arranged in parallel vertically by bending the wire in a meandering manner. In each of the upper portion, the lower portion, and the upper and lower intermediate portions in each groove 21a, the resistance heating wire 12a has a straight portion exposed and a curved portion embedded in the heat insulating material 11. Each resistance heating wire 12a can be controlled to generate heat independently.
[0014]
The first shell 13 and the second shell 14 are made of metal and have a cylindrical shape with a longitudinal axis. The outer peripheral side of the peripheral wall 21 is covered by the first shell 13, and the first shell 13 is covered by the second shell 14. The outer peripheral side of is covered. That is, the outer diameter of the first shell 13 is made smaller than the inner diameter of the second shell 14, and the inner and outer peripheries of the shells 13 and 14 are arranged on a concentric cylindrical surface so that the shells 13 and 14 are mutually connected. Arranged at intervals in the radial direction. The first shell 13 has an inner diameter substantially equal to the outer diameter of the peripheral wall 21 and is fixed to the peripheral wall 21. The lower ends of the shells 13 and 14 are fixed to an annular metal lower cover 24, and the upper ends are fixed to an annular metal upper cover 25. Thereby, the heater 2 has a double shell structure.
[0015]
In the space 31 between the first shell 13 and the second shell 14, there is provided means for forcibly flowing the gas in the axial direction of the shells 13 and 14 in a laminar flow state. That is, a high-pressure gas from a gas supply source (not shown) is introduced into the space 31 through an air supply pipe 32 connected to a gas introduction port 24a formed in the lower cover 24, and the upper cover The gas introduced through the exhaust pipe 33 connected to the gas discharge port 25a formed in 25 is discharged. As the gas, for example, an inert gas such as nitrogen gas or air can be used. A flow meter 35 is provided in the middle of the air supply pipe 32, and an exhaust pressure control valve 36 is provided in the middle of the exhaust pipe 33. By controlling the exhaust pressure, the gas flow rate in the space 31 can be adjusted. Has been. Opening / closing valves 38 and 39 are provided on the downstream side of the flow meter 35 and the upstream side of the exhaust pressure control valve 36 to stop the gas flow. The number of gas inlets 24a and gas outlets 25a is not particularly limited.
[0016]
By adjusting the gas flow rate, the gas is forced to flow from the lower side to the upper side in the axial direction in the laminar state in the space 31, and the gas flow rate is made sufficiently large so as not to be affected by natural convection. can do.
In addition, the specific value of the gas flow rate can be set with reference to theoretical calculation. For example, assuming that the outer peripheral surface of the first shell 13 and the inner peripheral surface of the second shell 14 are flat plates, the y coordinate and the radial outward direction are upward from the outer peripheral surface of the first shell 13 at the lower end of the space 31. Taking the x coordinate, the outer peripheral surface temperature of the first shell 13 is Tw, the inner peripheral surface temperature of the second shell 14 is T∞, the Prandtl number of the fluid is Pr, the Grashof number at the x coordinate is Grx, and the gravitational acceleration is In the case of g, the gas flow velocity Vx due to natural convection in the xy coordinates in the space 31 is (y / x) × (Grx / 4) ^1/4 and [Vx / { 2 × (g × x) ^1/2 }] × {T∞ / (Tw−T∞)} ^1/2 . The gas flow rate by forced flow is set to a sufficiently large value (for example, about 20 times or more) within the range where the laminar flow can be maintained with respect to the gas flow rate Vx by natural convection. Here, the outer diameter of the first shell 13 is 0.5 m, the inner diameter of the second shell 14 is 0.6 m, the axial length of the space 31 is 0.7 m, Tw is 670 ° K, and T∞ is 418 °. When K, x = 0.025 m, y = 0.35 m, and the fluid is nitrogen, according to the theoretical calculation, the gas flow velocity Vx by natural convection is about 0.0098 m / sec. Moreover, the upper limit gas flow rate which can maintain a laminar flow is 0.76 m / sec, and the gas flow rate in this case is 4100 liters / min. Therefore, if the gas flow rate is 100 liters / min, the gas flow rate can be set to a sufficient size without being influenced by natural convection by about 0.019 m / sec.
[0017]
A dispersion member 41 having an annular shape concentric with the inner and outer peripheries of the shells 13 and 14 is disposed at a lower portion between the first shell 13 and the second shell 14. As shown in FIG. 3, the dispersion member 41 is formed so that a large number of gas flow holes 41a having a smaller diameter than the gas introduction ports 24a are uniformly distributed, and the above-described space 31 is introduced into the space 31 through the gas flow holes 41a. Gas is sent in.
[0018]
According to the heater 2, since the first shell 13 and the second shell 14 are arranged at a radial interval from each other, a space that is more thermally stable than the outside of the heater 2 between the shells 13 and 14. 31 can be formed. Thereby, compared with the heater covered with the single shell like the past, the influence of the thermal disturbance with respect to the temperature in the internal space enclosed by the heat insulating material 11 can be made small, without thickening a heat insulating material and enlarging a heat capacity. .
In addition, natural convection occurs in the space 31 between the shells 13 and 14 based on the internal and external temperature difference. In the space 31, gas is forced to flow in the axial direction in a laminar flow state, and the gas flow velocity is influenced by the natural convection. By making it large enough not to be received, the space 31 can be made a more thermally stable space that is not affected by natural convection.
Furthermore, since the gas is fed into the space 31 through the gas distribution holes 41a that are uniformly distributed in the dispersion member 41, the gas flow in the space 31 can be made uniform, and the space 31 can be made more uniform thermally. Can do.
Thereby, for example, the film thickness distribution of the oxide film formed on the surface to be processed in the heat treatment furnace 1 can be made uniform, and the responsiveness when changing the internal temperature of the heater 2 is not lowered. .
[0019]
FIG. 4 shows a second embodiment of the present invention. The difference from the first embodiment is that the dispersion member 41 is arranged in the upper part of the space 31 between the first shell 13 and the second shell 14, the gas inlet 25 b is formed in the upper cover 25, and the lower cover 24 is A gas discharge port 24b is formed, and the gas is introduced into the space 31 between the shells 13 and 14 from the upper side and exhausted from the lower side. Others are the same as in the first embodiment, and the same parts are denoted by the same reference numerals.
FIG. 5 shows a third embodiment of the present invention. The difference from the first embodiment is that the dispersion member 41 is arranged in the upper part of the space 31 between the first shell 13 and the second shell 14, the gas inlet 25 b is formed in the upper cover 25, and the upper cover 25 Insertion ports 25 c and 41 b of the exhaust pipe 33 are formed in the dispersion member 41, and an end opening of the exhaust pipe 33 is arranged in the lower part of the space 31 to serve as a gas exhaust port 33 a, and the gas flows upward into the space 31. It is in the point which introduce | transduces from above and exhausts from the upper side. Others are the same as in the first embodiment, and the same parts are denoted by the same reference numerals.
FIG. 6 shows a fourth embodiment of the present invention. The difference from the first embodiment is that the insertion holes 24 c and 41 b of the exhaust pipe 33 are formed in the lower cover 24 and the dispersion member 41, and the end opening of the exhaust pipe 33 is arranged in the upper part of the space 31. The gas discharge port 33a is used to introduce gas into the space 31 from the lower side and exhaust from the lower side. Others are the same as in the first embodiment, and the same parts are denoted by the same reference numerals.
[0020]
In addition, this invention is not limited to the said embodiment. For example, another shell that covers the outer peripheral side of the second shell may be provided to form a triple or more shell structure. Moreover, in the said embodiment, although the outer peripheral side of the heat insulating material was directly covered with the 1st shell, it is good also as a shell structure more than triple by providing another shell interposed between a 1st shell and a heat insulating material. . In short, it is only necessary to include a first shell that covers the outer peripheral side of the heat insulating material and a second shell that covers the outer peripheral side of the first shell with a radial interval. Moreover, the structure of a heat generating body is not specifically limited, For example, what is provided helically in the inner periphery of a heat insulating material may be used.
[0021]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the temperature in the space enclosed with a heat insulating material can be stabilized, and the heater which does not reduce the responsiveness at the time of changing the temperature can be provided.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a heat treatment furnace equipped with a heater according to the first embodiment of the present invention. FIG. 2 is a partial perspective view of the heater according to the first embodiment of the present invention. Fig. 4 is a plan sectional view of the heater. Fig. 4 is a diagram illustrating the configuration of a heat treatment furnace including the heater according to the second embodiment of the present invention. Fig. 5 is a diagram illustrating the configuration of a heat treatment furnace including the heater according to the third embodiment of the present invention. FIG. 7 is a structural explanatory view of a heat treatment furnace equipped with a heater according to a fourth embodiment of the present invention. FIG. 7 is a cross-sectional view of a heat treatment furnace equipped with a conventional heater.
DESCRIPTION OF SYMBOLS 11 Heat insulating material 12 Heat generating body 13 and 14 Shell 21 Perimeter wall 31 Space 32 Supply pipe 33 Exhaust pipe 41 Dispersing member 41a Gas distribution hole

Claims (2)

A heat insulating material having a cylindrical peripheral wall;
A heating element provided on the inner peripheral side of the peripheral wall;
A cylindrical first shell covering the outer peripheral side of the peripheral wall;
A cylindrical second shell covering the outer peripheral side of the first shell,
Each shell is arranged at a radial distance from each other ,
A means for forcibly flowing the gas in the axial direction in a laminar flow state in the space between both shells, the gas flow rate is adjustable,
A heater in which the gas introduced into the space between the two shells is discharged from the space without reaching the heating space covered with the heat insulating material . The inner and outer peripheries of each shell are arranged on a concentric cylindrical surface, and an annular dispersion member concentric with the cylindrical surface is arranged between both shells so that a plurality of gas flow holes are uniformly distributed in the dispersion member. The heater according to claim 1 , wherein the gas is fed into a space between both shells through the gas flow holes .

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