Gas separation – With inflow gas control or distribution
Reexamination Certificate
2001-07-13
2003-10-14
Hopkins, Robert A. (Department: 1724)
Gas separation
With inflow gas control or distribution
C055S482000, C055SDIG002, C220S088200, C048S192000
Reexamination Certificate
active
06632261
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
None
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OF DEVELOPMENT
Not applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and apparatus for suppressing explosions in gas lines, including natural gas lines and the like but specifically relating to gas lines carrying pyrophoric gases such as silane (SiH
4
).
2. Description of the Related Art
Silane (SiH
4
) is a pyrophoric gas used extensively in semiconductor manufacturing. When silane is exposed to even very small amounts of oxygen, the silane will burn extremely quickly, leaving behind a white powdery residue of “sand-like” material (i.e., SiO
2
). In the normal course of semiconductor operations, silane lines are sometimes compromised through small leaks or cracks and exposed to oxygen. When this occurs, the resulting reaction burns through the silane line in both directions, leaving behind the powdery residue and rendering the line unusable. All lines and exposed equipment where this occurs require replacement, often at quite significant cost and effort. This occurs frequently enough that some facilities are known to install duplicate silane lines during construction for just these events. The present invention constitutes a method and apparatus intended to stop any such explosive reaction as soon as it encounters the apparatus, thus protecting all equipment on the side of the apparatus opposite the origin of the explosion.
The present invention provides a method and apparatus for first detecting and then terminating the occurrence of an explosion in a gas line, particularly as to an explosion of silane gas within a pipe line in the course of semiconductor chip fabrication. Silane (SiH
4
) is a pyrophoric gas, and must be contained within a pipe line that isolates the silane from the atmosphere. Upon any leakage of air into that pipe line, the silane can explode to yield disastrous results both to the particular operation and to the facilities as a whole, especially with respect to the wafer fabrication chambers within which the wafer is to be fabricated in part through use of the silane gas. The invention does not prevent an explosion, but rather limits the extent of damage that an explosion produces, and in particular “downstream” damage towards those fabrication chambers. The method and apparatus can also be used for the handling of other gases under similar circumstances.
Operation of the invention rests on event detection, on the immediate reduction of heat within an explosion by use of a filter medium, and then upon application of the initial pressure surge of the explosion to a multi-port diaphragm that both inhibits re-initiation of the explosion and protects the downstream portion of the gas line. The latter step is of particular importance in semiconductor fabrication, since that work requires an ultimately clean environment, and if contaminated by a silane explosion, a gas line becomes useless for that purpose and must be replaced.
The prior art in this field has been concerned with the suppression or limitation of damage of (a) explosions in enclosed spaces and (b) the prevention of flashback along a pipeline from an intended combustion source back to a source of combustible fuel. As will be shown below, none of the prior art of which the inventors are aware has considered downstream damage effects of pipeline explosions, or in particular the suppression of explosions of pyrophoric gases in a pipeline. Filter type media have been used to control small explosions such as exists in auto air bags. High purity diaphragm valves are used throughout the semiconductor business, but none in the manner of the present invention. Prior devices have been simply on/off devices manually or air actuated.
The control of fire has as long a human history as perhaps any other activity other than stone tool-making. In modern times, such activities center largely on apparatus, most often operated electrically, that first detect the presence of a fire and then release a fire suppressant in response thereto. Typical of such endeavors is the apparatus disclosed in U.S. Pat. No. 5,718,294 issued Feb. 17, 1998, to Billiard et al., together with U.S. Pat. No. 5,816,330 issued Oct. 6, 1998, to the same inventors, which treat a manually operated handle that initiates either an electrically responsive initiator or a gas-generating cartridge activator, these then acting to generate, e.g., the firing of a blasting cap, so as to rupture a disc to release fire suppressant to the area. Another device that employs such a rupture disc is found in U.S. Pat. No. 6,006,842 issued Dec. 28, 1999, to Stilwell et al.
Somewhat different types of fire detection and suppression apparatus are found in U.S. Pat. No. 5,826,664 issued Oct. 27, 1998, to Richardson, which discloses such a device mounted externally to a tank within which a fire or explosion is to be suppressed by injection of suppressant medium into the tank, and in U.S. Pat. No. 6,012,532 issued Jan. 11, 2000, to Kiefer et al., which discloses a flexible bladder containing an inert gas that upon rupture of the bladder will help suppress a fire or explosion.
U.S. Pat. No. 6,104,301 issued Aug. 15, 2000, to Golden, discloses a fire detection and suppression device that operates through an electronic processor to detect and respond also to other types of hazard, e.g., as an intrusion detector. A more extensive electronically operated fire detector and suppressor which employs several detection means and provides multi-level responses is described in U.S. Pat. No. 6,057,549 issued May 2, 2000, to Castleman. Although this '549 patent to Castleman mentions the clean room environment as an example of one in which fires can occur, none of the aforementioned patents address fires or explosions that actually occur within a pipeline.
Further elaboration of the specific features that appear in these patents are found in U.S. Pat. No. 4,173,140 issued Nov. 6, 1979, to Liebman et al., which discloses a trigger device including a pressure sensor and at least two flame sensors, and which serves to erect an explosion barrier in front of an explosion to limit its extent; U.S. Pat. No. 5,225,622 issued Jul. 6, 1993, which discloses an acoustic shock wave attenuating assembly; U.S. Pat. No. 4,505,180 issued Mar. 19, 1985, to Hinrichs, which discloses a rupture disc assembly that does not burst under high pressure from one direction but bursts at a relatively low pressure from the opposite direction and is useable in the context of hand-held firearms; U.S. Pat. No. 4,579,315 issued Apr. 1, 1986 to Kowalski, which discloses a quick-opening valve for release of fire suppressant after having been activated by an electrical signal; U.S. Pat. No. 6,031,462 issued Feb. 29, 2000, to Van den Schoor et al., which discloses a rate-of-rise detector that monitors the pressure within a protected area and generates a signal to release fire suppressant when that pressure increases at more than a predetermined threshold rate; and U.S. Pat. No. 5,122,628 issued Jun. 16, 1992 to McClelland et al., which discloses a pressure increase detector for the like purpose.
Another body of patents specifically treats the occurrence of explosions in gas-containing pipe lines, but none of such patents of which the inventors are aware addresses the particular problem of pyrophoric materials. Thus, U.S. Pat. No. 5,103,916 issued Apr. 14, 1992, to McClelland, discloses a differential fire and explosion protection system for protection against explosions in pneumatic transport systems, often used with process equipment, that convey potentially combustible particulate materials such as dust. Two thermocouples, one fast-responding and the other slow-responding, are disposed within an air outlet duct, and the occurrence of a temperature differential between the two thermocouples, arising from an explosion, causes shut-down of the blower operating the transport system, and the resultant pressure drop, along with subsequent release of fire suppressant material, ac
Browning Roy
Gardner Brian
Hamilton Mark
Hopkins Robert A.
Lovell William S
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