Measuring and testing – With fluid pressure – Clamp – plug – or sealing feature
Reexamination Certificate
2000-02-22
2002-06-04
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Clamp, plug, or sealing feature
C073S04050R, C073S040000, C251S163000
Reexamination Certificate
active
06397664
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and an apparatus for detecting leakage in a flow control valve and more particularly, relates to a method and an apparatus for detachably mounting a leakage detection device to a bellow-type flow control valve for detecting leakage of a facility gas into a high purity process gas that is controlled by the flow control valve.
BACKGROUND OF THE INVENTION
In the semiconductor process industry, a large variety of different ultra pure gases are used in the fabrication plants. These gases include bulk gases such as N
2
, O
2
, H
2
and Ar which are normally used in very large quantities, and specialty gases such as He, A
S
H
3
, PH
3
, SiH
4
, NH
3
and NF
3
which are used only in small quantities. In general, the bulk gases are used for purging of chambers, oxidation and cleaning of wafers, while the specialty gases are used as reactant or etching gases.
The bulk gases are normally stored in large storage facilities, for instance, N
2
can be supplied from a liquified-nitrogen storage tank located in the gas yard or delivered from a pipeline from a remote air-separation plant; O
2
and Ar can be supplied from liquified gas storage tanks; while H
2
can be delivered from either a liquified-gas storage tank or a bank of high-pressure gas cylinders. The bulk gases are normally passed through purifiers and gas filters for removing impurities and contaminating particles before allowed to enter a gas-distribution piping system installed inside a cleanroom. On the other hand, the speciality gases are normally stored in small quantities in gas cylinders and are sent directly to the process tools from cylinders stored inside gas cabinets in the cleanroom. The gas cabinets are exhausted safety enclosures that contain the gas cylinders and the necessary gas handling equipment. The gas cabinets serves a major function of allowing purging and safe exchange of the speciality gas cylinders. The gas handling equipment, which includes gas panels incorporating all components for the control and monitoring of high purity gases. In most semiconductor fabrication facilities, the gas cabinet contains at least two process cylinders to allow easy switch-over when one cylinder is empty. In addition, another cylinder of inert gas such as nitrogen is provided for purging the piping line.
In most fabrication processes, the supply pressure for the bulk and the speciality gases is kept at under 10 Kg/cm
2
. A few exceptions exist such as chlorine and dichlorosilane. At each point of use, the pressure of the bulk or speciality gas has to be independently and locally controlled by a series of flow control valves, pressure regulators, pressure sensors and particle filters located inside a gas manifold box. The precise pressure required for each bulk or speciality gases to be delivered to a specific process tool is determined by the process requirement. In most semiconductor cleanroom facility, one or more gas manifold boxes are installed nearby to each process tool to facilitate gas distribution and control.
A frequently used tool for gas distribution or control is a bellow-type flow control valve for controlling the flow of high purity process gases. One of such commercially available valves is a Nupro valve. Due to the large number of different process gases used in a single process machine, i.e. in a chemical vapor deposition chamber, a large number of bellow-type flow control valves are required for controlling fluid conduits in which process gases pass through.
An illustration of a typical bellow-type flow control valve
10
and its application in controlling a high purity process gas are shown in FIG.
1
. To operate the bellow-type flow control valve
10
, a facility gas such as a facility nitrogen is normally required. The facility gas is normally controlled by a shut-off valve
14
for controlling its flow. A suitable shut-off valve may be one that is an electromagnetic valve shown in
FIG. 1
of a normal-closed type. When a high pressure facility gas, such as nitrogen, is applied to the normal-closed valve
14
, the valve
14
opens to let the facility gas to flow therethrough into a fluid conduit
16
. The facility gas then enters the bellow-type flow control valve
10
to compress a bellow to open a flow passageway therein allowing a high purity process gas to pass through conduit
12
for feeding to a process chamber (not shown). When the high purity process gas is no longer needed, the bellow-type flow control valve
10
is closed by closing the shut-off valve
14
and thus stopping the flow of the facility gas.
The bellow-type flow control valves have been widely used in gas flow control in the industry, and particularly, in the semiconductor fabrication industry. Problems occur when bellow-type flow control valves have been used for a length of time which frequently leads to a malfunction of the bellow inside the valve control mechanism. When the problem is serious, proper performance of the flow control valve can be affected to render the valve ineffective. One of the frequently observed problems is the leakage of facility gas into a high purity process gas flow due to a leakage existed in the bellow inside the flow control valve. Since a facility gas such as nitrogen frequently contains various impurities of oxygen, hydrogen, water vapor or other impurities, a severe contamination of the high purity process gas occurs which leads to serious fabrication problems. Since a large number of bellow-type flow control valves are normally utilized on a single process machine, it is an insurmountable task to identify a specific flow control valve that is responsible for a leakage. Conventionally, the only way to find a defective valve is by a trial and error method, i.e. by replacing one valve at a time until the contamination problem is solved. This turns out to be an extremely time and labor consuming task resulting in a significant loss in fabrication yield.
It is therefore an object of the present invention to provide a method for detecting leakage in a flow control valve that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for detecting leakage in a bellow-type flow control valve by connecting a leakage detection apparatus in-between a shut-off valve and the flow control valve.
It is a further object of the present invention to provide a method for detecting leakage in a bellow-type flow control valve by a leakage detection apparatus which includes a mass flow controller and a recording means for connecting between a shut-off valve and the flow control valve.
It is still another object of the present invention to provide a method for detecting leakage in a bellow-type flow control valve by temporarily connecting a leakage detection apparatus in-between a facility gas source and the flow control valve.
It is another further object of the present invention to provide a method for detecting leakage in a bellow-type flow control valve wherein a leakage detection apparatus is connected in-between a shut-off valve and the flow control valve by quick disconnect means.
It is yet another object of the present invention to provide a leakage detection apparatus which includes a mass flow controller and a recording means for detecting leakage through a bellow-type flow control valve.
It is still another further object of the present invention to provide a flow control apparatus that is equipped with a built-in leakage detection device including a shut-off valve, a fluid conduit, a leakage detection device and a bellow-type flow control valve.
It is yet another further object of the present invention to provide a flow control apparatus that is equipped with a built-in leakage detection device which is connected to the flow control apparatus by quick disconnect valves.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and an apparatus for detecting leakage in a flow control valve are provided.
In a preferred embodiment, a me
Chien Hung-Ju
Lee Chin-Chung
Taiwan Semiconductor Manufacturing Company Ltd
Tung & Associates
Wiggins David J.
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