Heating – Heating apparatus element having protective cooling structure – Wall – floor or roof element
Reexamination Certificate
1999-09-13
2001-12-11
Lu, Jiping (Department: 3749)
Heating
Heating apparatus element having protective cooling structure
Wall, floor or roof element
C432S004000, C432S077000, C432S197000, C432S199000, C432S200000
Reexamination Certificate
active
06328561
ABSTRACT:
The present invention relates to a method for cooling a furnace and a furnace.
BACKGROUND OF THE INVENTION
A method of this kind is known from American U.S. Pat. No. 4,925,388, which describes a furnace in which, for cooling purposes, a gas is guided through the furnace either from above or from below. The direction of flow of the gas alternates, and this alternating movement is controlled by a number of valves. The gas moves in the space between the heating element and the core tube and in the space between the heating element and the insulation arranged at a distance therefrom. The air or other gas which is used as cooling medium is discharged via a fan.
It has been found that the discharge of such gases into a discharge system of a relatively large installation is accompanied by major drawbacks, since by definition these gases are hot and consequently can damage a discharge system of this kind, in particular if it is composed of plastic components. Moreover, harmful substances may be present in the gases.
The object of the present invention is to avoid this drawback and to provide a method which, on the one hand, allows rapid and uniform cooling and, on the other hand, does not subject the gas-discharge system to further loading.
An aspect of the invention involves a method for cooling a furnace having a core tube that has an elongate boundary wall and is configured to accommodate wafers for processing the wafers in a treatment atmosphere. The furnace includes a cooling chamber defined between the elongate boundary wall and an outer casing of the furnace, wherein the outer casing includes a heating element and has first lateral, circumferentially spaced openings in proximity of a first end of the outer casing and second lateral, circumferentially spaced openings in proximity of a second end of the outer casing. Cooling gas is supplied through one of the first and second lateral, circumferentially spaced openings to a region of one end of the cooling chamber and provides for a cooling atmosphere. The cooling gas is guided along the cooling chamber with a uniform distribution of flow and discharged through one of the first and second lateral, circumferentially spaced openings from a region of an opposite end of the cooling chamber. A direction of flow of the cooling gas is periodically reversed during cooling, wherein the cooling gas is guided along an essentially closed circuit so that the cooling gas is preserved and so that the cooling atmosphere is separated from the treatment atmosphere. A liquid-gas heat exchanger cools the cooling gas.
SUMMARY OF THE INVENTION
In principle, it would be possible to discharge the gas solely via the heat exchanger and to guide it into the gas-discharge system without using a closed circuit. However, the drawback of this is that it is constantly necessary to introduce additional gas and, in the case of air, this will generally emanate from the clean room, i.e., it will have been purified extensively. As a result, a particularly large installation for cleaning air is required, with all the associated costs. Moreover, it is undesirable to periodically withdraw air from or introduce air into a clean room.
If, in accordance with the invention, the gas is guided in a closed circuit with a heat exchanger, it is not necessary to constantly supply fresh gas, such as air. Moreover, it is possible as a result to make use of a gas having more specific properties, such as nitrogen. This is because basically there is no loss of gas, with the result that the extra costs of nitrogen or some other gas can be justified. The method according to the invention makes it possible to treat a greater number of wafers per hour, and the thermal loading to which each wafer is subjected will be reduced. Moreover, the treatment of the various wafers is more uniform.
It has been found that alternating the direction of flow of the cooling gas at a certain frequency enables the temperature gradient across the furnace to be limited as far as possible. It will be understood that the hottest part will now be situated in the centre of the furnace. Moreover, it has been found that the cooling rate can be increased considerably by comparison with designs in accordance with the prior art.
According to an advantageous embodiment of the invention, the reversal frequency of the flow of gas lies between 2 and 600 seconds, and more particularly between 5 and 60 seconds. Advantageously, the reversal frequency lies between 10 and 20 seconds. The above-described design makes it possible to achieve a cooling rate in the region of the wafers of approximately 50° C. per minute.
Another aspect of the invention involves a furnace assembly, comprising a furnace which is provided with a cooling device for using gas to cool the boundary wall of said furnace, a cooling chamber for gas being present in the region of said boundary wall, which chamber opens out on both sides into a line which is provided with valves, which valves comprise diverter valves, in order to move the gas alternately in one direction along said boundary wall and then in the opposite direction along said boundary wall, in which said diverter valves are connected to a closed circuit in which a liquid-gas heat exchanger is arranged.
According to an advantageous embodiment of the invention, the supply/discharge of gas is arranged in the outer casing of the furnace assembly, i.e. is effected via the wall and not via the end closures, such as the base or cover. This allows a more uniform distribution of flow to be achieved. This is because the movement of the gas in the gap between heating element and core tube is particularly difficult to control. However, this control is important if sufficient uniformity is to be ensured. This distribution of flow can be promoted further by introducing and discharging the gas via a number of openings which are arranged in a ring or other regular curve along the circumference of the furnace wall. These openings form a restriction to the gas flow and in fact locally determine the metering of the gas flow. By distributing these openings regularly along the wall, it is possible to ensure an even distribution of the gas flow, and hence an even dissipation of heat.
REFERENCES:
patent: 2257229 (1941-09-01), Drake
patent: 2397810 (1946-04-01), Roof
patent: 3035824 (1962-05-01), Weaver
patent: 3622135 (1971-11-01), Roth et al.
patent: 3918890 (1975-11-01), Blaine
patent: 4348174 (1982-09-01), Spigarelli
patent: 4351805 (1982-09-01), Reisman et al.
patent: 4430055 (1984-02-01), Sugiyama
patent: 4457705 (1984-07-01), Ramesohl et al.
patent: 4560348 (1985-12-01), Moller et al.
patent: 4925388 (1990-05-01), Iseki et al.
Hasper Albert
Huussen Frank
Oosterlaken Theodorus Gerardus Maria
Van Putten Jack Herman
ASM International N.V.
Knobbe Martens Olson & Bear LLP
Lu Jiping
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