STATIC PRESSURE STABILIZER FOR LOCAL EXHAUST
An exhaust system is provided for a plurality of machines, each machine having an exhaust stream connected to a local branch of the system. The system includes a stabilizer connected to an exhaust line in parallel to the exhaust stream of a machine. The stabilizer controls an exhaust pressure in the exhaust stream by opening and closing in response to variations in the exhaust pressure; the stabilizer opens to admit gas flow into the exhaust line when the exhaust pressure is less than a predetermined value, and closes when the exhaust pressure is greater than that predetermined value. The stabilizer unit thus provides a constant static exhaust pressure. The stabilizer provides relief flow in the exhaust stream, causing the gas flow into the exhaust line to increase when an exhaust flow in the exhaust stream decreases.
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This invention relates to building exhaust systems in integrated circuit manufacturing facilities (“IC fabs”). More particularly, this invention relates to control of local static pressure in such systems.
BACKGROUND OF THE INVENTION A modern IC fab has numerous sophisticated machines for performing manufacturing processes on semiconductor materials. These machines are referred to in the industry as “production tools” or simply “tools.” In general, each production tool is connected to a building-wide exhaust system for removing air or spent process gases from the interior of the tool. A typical building exhaust system is shown schematically in
Optimum operation of the production tools requires that the exhaust be as stable as possible. Even though a stable exhaust is provided at the fan manifold/header level (so that the overall system is stable), there are often fluctuations in the exhaust where a local branch connects to a set of tools (so that a particular zone of the system is not stable). A given tool will typically not have a constant exhaust; for example, a tool exhaust flow may vary due to the process being performed. The adjacent tools in the tool set will then be subjected to variations in the exhaust static pressure. This has a negative effect on the performance of those tools. For example, as shown in
One method of solving this problem is to provide a local barometric damper which opens at a set static pressure. However, a barometric damper does not hold a constant static pressure as the flow varies. Another approach is to bleed air into the exhaust system. This can reduce the overall variation in local static pressure, but increases the load on the system and therefore makes the system more expensive to operate.
There is a need for a device and method for maintaining a constant static pressure at the local exhaust of a tool, even when the exhaust flow fluctuates.
SUMMARY OF THE INVENTIONThe present invention addresses the above-described need by providing a static pressure stabilizer unit which, when connected in parallel with the exhaust stream of a production tool, maintains a constant static exhaust pressure at that tool.
According to a first aspect of the invention, an exhaust system is provided for a plurality of machines, each machine having an exhaust stream connected to a local branch of the system. The system includes a stabilizer connected to an exhaust line in parallel to the exhaust stream of a machine. The stabilizer controls an exhaust pressure in the exhaust stream by opening and closing in response to variations in the exhaust pressure; the stabilizer opens to admit gas flow into the exhaust line when the exhaust pressure is less than a predetermined value, and closes when the exhaust pressure is greater than that predetermined value. The stabilizer unit thus provides a constant static exhaust pressure. The stabilizer provides relief flow in the exhaust stream, causing the gas flow into the exhaust line to increase when an exhaust flow in the exhaust stream decreases.
The gas flow may be a flow of ambient air.
According to another aspect of the invention, a static pressure stabilizer is provided for a local exhaust stream of a machine connected to an exhaust system. The static pressure stabilizer includes a first pipe, a second pipe and a float inside the second pipe. One end of the first pipe is connected to the exhaust system while the other end has a first opening therein to admit gas flow. The second pipe is set in the first opening and has a wall with a second opening therein. The float is capable of movement along an axis of the second pipe; in a first position of the float the first opening is closed, thereby preventing gas flow into the first pipe, and in a second position the second opening communicates with the first opening, thereby permitting gas flow into the first pipe. The gas flow may be a flow of ambient air. When the stabilizer is connected to the exhaust system in parallel to the local exhaust stream, the stabilizer is effective to maintain a constant static exhaust pressure for the machine. The weight of the float may be adjusted in accordance with a desired value of the static exhaust pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
Details of stabilizer 30 are shown in
Stabilizer 30 has been constructed from PVC pipe material, with pipes 31 and 32 having diameters of 10 inches (25.4 cm) and 6 inches (15 cm) respectively. Float 33 may be made from any convenient chemically stable material, sized to move smoothly inside pipe 32. A typical weight for float 33 is 1 pound (0.454 kg). Float 33 also need not be a solid cylinder, provided that the same circular area is presented on the top and bottom ends.
The stabilizer may be calibrated by adjusting the weight of the float 33 in accordance with the desired static pressure.
The operation of the stabilizer 30 may be contrasted with that of a conventional barometric damper 60 with a hinged opening flap 61, shown in
A static pressure stabilizer such as described above may advantageously be installed at each production tool. This assures that the building exhaust system is stable both generally and locally, thereby contributing to reliable and effective tool operation.
While the invention has been described in terms of specific embodiments, it is evident in view of the foregoing description that numerous alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the invention is intended to encompass all such alternatives, modifications and variations which fall within the scope and spirit of the invention and the following claims.
Claims
1. An exhaust system for providing exhaust to a plurality of machines, each machine having an exhaust stream connected to a local branch of the system, comprising:
- a stabilizer connected to an exhaust line in parallel to the exhaust stream of a machine, wherein said stabilizer controls an exhaust pressure in said exhaust stream by opening and closing in response to variations in said exhaust pressure, the stabilizer opening to admit gas flow into the exhaust line when said exhaust pressure is less than a predetermined value, and closing when said exhaust pressure is greater than said predetermined value.
2. An exhaust system according to claim 1, wherein the gas flow is a flow of ambient air.
3. A system according to claim 1, comprising a plurality of stabilizers, wherein each machine connected to the local branch has a stabilizer connected in parallel thereto.
4. A system according to claim 1, wherein said exhaust pressure is characterized as a static exhaust pressure for the machine, and the stabilizer associated with the machine maintains a constant static exhaust pressure for that machine.
5. A system according to claim 3, wherein said exhaust pressure is characterized as a static exhaust pressure for each machine, and the stabilizer associated with a given machine maintains a constant static exhaust pressure for that machine.
6. A system according to claim 1, wherein said stabilizer causes the gas flow into the exhaust line to increase when an exhaust flow in the exhaust stream decreases.
7. A static pressure stabilizer for a local exhaust stream of a machine connected to an exhaust system, the static pressure stabilizer comprising:
- a first pipe having a first end and a second end, the first end connected to the exhaust system and the second end having a first opening therein to admit gas flow;
- a second pipe set in the first opening and having a wall with a second opening therein; and
- a float inside said second pipe and capable of movement along an axis thereof, so that in a first position of said float the first opening is closed, thereby preventing gas flow into said first pipe, and in a second position of said float the second opening communicates with the first opening, thereby permitting gas flow into said first pipe.
8. A static pressure stabilizer according to claim 7, wherein the gas flow is a flow of ambient air.
9. A static pressure stabilizer according to claim 7, wherein said stabilizer is connected to the exhaust system in parallel to the local exhaust stream, so that said stabilizer is effective to maintain a constant static exhaust pressure for the machine.
10. A static pressure stabilizer according to claim 9, wherein a weight of said float is adjusted in accordance with a desired value of the static exhaust pressure.
11. A static pressure stabilizer according to claim 9, wherein the constant static exhaust pressure has a predetermined value, and said float is given a force in a direction from the first position toward the second position when the static exhaust pressure is less than said value.
12. A static pressure stabilizer according to claim 9, wherein the constant static exhaust pressure has a predetermined value, and said float is given a force in a direction from the second position toward the first position when the static exhaust pressure is greater than said value.
13. A static pressure stabilizer according to claim 7, wherein said float has an end surface, the first opening defines a plane, and an angle of the end surface with respect to said plane remains constant during movement of said float.
14. A static pressure stabilizer according to claim 8, wherein flow of ambient air is permitted into the first pipe in response to a decrease in exhaust flow in the local exhaust stream.
Type: Application
Filed: Jan 6, 2005
Publication Date: Jul 13, 2006
Applicant: INTERNATIONAL BUSINESS MACHINES CORPORATION (Armonk, NY)
Inventors: Roy Johnson (Wappingers Falls, NY), Joseph D'Angelo (Newburgh, NY)
Application Number: 10/905,479
International Classification: F24F 7/06 (20060101);