U.S. patent application number 10/905479 was filed with the patent office on 2006-07-13 for static pressure stabilizer for local exhaust.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Joseph J. D'Angelo, Roy P. Johnson.
Application Number | 20060154595 10/905479 |
Document ID | / |
Family ID | 36653892 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060154595 |
Kind Code |
A1 |
Johnson; Roy P. ; et
al. |
July 13, 2006 |
STATIC PRESSURE STABILIZER FOR LOCAL EXHAUST
Abstract
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.
Inventors: |
Johnson; Roy P.; (Wappingers
Falls, NY) ; D'Angelo; Joseph J.; (Newburgh,
NY) |
Correspondence
Address: |
INTERNATIONAL BUSINESS MACHINES CORPORATION;DEPT. 18G
BLDG. 300-482
2070 ROUTE 52
HOPEWELL JUNCTION
NY
12533
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
New Orchard Road
Armonk
NY
|
Family ID: |
36653892 |
Appl. No.: |
10/905479 |
Filed: |
January 6, 2005 |
Current U.S.
Class: |
454/251 |
Current CPC
Class: |
F24F 2007/001 20130101;
F24F 7/06 20130101; B08B 15/002 20130101 |
Class at
Publication: |
454/251 |
International
Class: |
F24F 7/06 20060101
F24F007/06 |
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.
Description
FIELD OF THE INVENTION
[0001] 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
[0002] 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 FIG. 1. Multiple
fans and/or scrubbers 1 are connected in a manifold 2 to provide
controlled, stable exhaust at header point 3. From this point a
distribution system branches out in different directions throughout
the building, with branches 4, sub-branches 5, and local branches 6
connecting to each of the tools (not shown).
[0003] 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 FIG. 2, a
variation in exhaust flow at tool 11 will change the local lateral
static pressure in local branch 6, affecting the other tools in
tool set 10. Process monitoring or safety requirements may force
shutdown of a tool if the static pressure variation is too great
(for example, a -20% or +40% departure from normal). Besides the
loss of tool uptime, any degradation in performance of the
production tools may be detrimental to the product yield.
Accordingly, static pressure variations at each local tool exhaust
(e.g. local exhaust 12 of tool 11) must be minimized.
[0004] 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.
[0005] 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 INVENTION
[0006] The 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.
[0007] 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.
[0008] The gas flow may be a flow of ambient air.
[0009] 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
[0010] FIG. 1 schematically illustrates a typical building exhaust
system, showing a distribution of branches to which production
tools are connected.
[0011] FIG. 2 shows a typical production tool set, in which an
exhaust flow variation in one tool impacts the performance of
adjacent tools.
[0012] FIG. 3 shows the tool set of FIG. 2 with a static pressure
stabilizer installed, in accordance with an embodiment of the
present invention.
[0013] FIG. 4A shows construction of a static pressure stabilizer
according to an embodiment of the invention.
[0014] FIG. 4B illustrates operation of the static pressure
stabilizer of FIG. 4A.
[0015] FIGS. 5A and 5B show how the static pressure stabilizer
provides a constant static pressure according to the present
invention.
[0016] FIGS. 6A and 6B show operation of a conventional barometric
damper, in contrast to the operation of the static pressure
stabilizer of FIGS. 5A and 5B respectively.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0017] FIG. 3 illustrates an embodiment of the invention, in which
a static pressure stabilizer device 30 is installed at local tool
11 in the tool set 10 of FIG. 2. Stabilizer 30 is connected to an
exhaust line 13 in parallel to the exhaust stream 12 of tool 11.
Stabilizer 30 opens (admitting a flow of room air 100) and closes
as the local static pressure at tool 11 changes, due to the process
being run in tool 11 or possibly some other factor. The result is
that static pressure variations in the local exhaust are
minimized.
[0018] Details of stabilizer 30 are shown in FIG. 4A. An outer pipe
31, connected to the exhaust system, has a capped end 31a with an
opening in which is set an inner concentric pipe 32. One or more
slots 32a are provided in the wall of pipe 32. A cylindrical float
33 fits inside pipe 32 and is able to move up and down along the
axis thereof. In its resting position float 33 closes off the
bottom opening of pipe 32; this is the closed state of stabilizer
30. An annular cap 34 prevents float 33 from falling out of the
opening. If the static pressure decreases due to a fluctuation in
the exhaust flow, ambient pressure forces the float upwards (see
FIG. 4B). Air flow 100 enters the stabilizer through the slots 32a,
providing a relief flow which compensates for the reduced exhaust
flow from the tool. This has the effect of increasing the static
pressure, which in turn increases the downward force on the float
and causes the float to return to its resting position.
[0019] 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.
[0020] The stabilizer may be calibrated by adjusting the weight of
the float 33 in accordance with the desired static pressure. FIG.
5A illustrates the situation where the float is in its resting
position, and the upward and downward forces on the float are
balanced. If the float is just at the point of lifting up, the
upward force due to room air pressure is balanced by the downward
force of the static exhaust pressure combined with the weight of
the float. The downward force is given by F.sub.1=W+SP1*A, where W
is the weight of the float, A the area of each end of the float,
and SP1 is the static exhaust pressure. The upward force is given
by RP*A, where RP is the room air pressure. Thus, when the
stabilizer is about to open, SP1=RP-(W/A). Any decrease in the
static pressure will cause the float to lift inside pipe 32 and
permit air to flow into the exhaust stream (FIG. 5B). If the static
pressure rises above SP1, the downward force on the float will
exceed the upward force, and the float will move back down to its
resting position. The stabilizer 30 therefore maintains the static
pressure at a value of SP1. It is noteworthy that as float 33 moves
up and down inside pipe 32, surface 33a on the exposed end of float
33 maintains the same angle with respect to the opening in end cap
31a (in this case, surface 33a is parallel to the opening).
[0021] 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 FIGS. 6A and 6B. FIG. 6A illustrates a situation
similar to FIG. 5A, where the upward and downward forces on the
flap 61 are balanced, so that the damper is at the point of
opening. The downward force is given by F2=W+SP2*A, where W and A
are the weight and area of the flap respectively; the upward force
is RP*A. The static pressure at this point is therefore
SP2=RP-(W/A). The angle of the flap with respect to the opening is
clearly not constant. If the flap opens by an angle .quadrature.
and forces on the flap are balanced (FIG. 6B), force F.sub.3 is
balanced by the force due to room air pressure RP*A. However, force
F.sub.3 is now given by F.sub.3=W*cos .quadrature.+SP3*A. Thus
SP3=RP-(W/A) cos .quadrature.. Since SP3>SP2 whenever the damper
is open, the barometric damper will attempt to maintain a new
pressure greater than SP2. Furthermore, since SP3 depends on the
opening angle .quadrature., this new pressure will fluctuate as the
flap 61 moves (SP3=SP2 at .quadrature.=0.degree.; SP3=RP at
.quadrature.=90.degree.). Accordingly, the barometric damper cannot
assure a constant static pressure.
[0022] 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.
[0023] 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.
* * * * *