Gas separation: processes – With control responsive to sensed condition – Concentration sensed
Reexamination Certificate
2002-01-24
2003-03-25
Simmons, David A. (Department: 1724)
Gas separation: processes
With control responsive to sensed condition
Concentration sensed
C095S901000, C096S111000, C096S417000, C073S031030, C422S082020
Reexamination Certificate
active
06537347
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATION
This application claims all benefits accruing 35 U.S.C. 119 from the Japanese Patent Application No. 2001-18953, filed on Jan. 26, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for deciding on the timing of replacing a chemical filter for cleaning air used for clean rooms, semiconductor manufacturing apparatuses, etc.; a filer life detection sensor for detecting the timing of replacing the chemical filter; a chemical filter unit provided with a filter life detection sensor; and a semiconductor manufacturing apparatus provided with the chemical filter unit.
2. Description of the Related Art
In recent years, as the degree of integration of semiconductor devices increases, a problem of chemical contamination inside clean rooms or semiconductor manufacturing apparatus chambers has arisen. In order to cope with the chemical contamination, chemical filters of an activated charcoal fiber type or an ion-exchange type, which are capable of removing gaseous contaminants (chemical substances), are widely used.
Conventionally, the life of such chemical filters (replacement timing) would be determined as follows.
(1) Measure amounts of adsorbed chemical substances which were contained in the air in front and at the back of the chemical filter, respectively, take the difference between the two measurements, and use the difference in assessing the change of adsorption capability for chemical substances (the change of the state of activation) of the chemical filter. If the difference in the amounts of adsorbed chemical substances between in front and at the back of the chemical filter reaches a predetermined value or less, then it would be interpreted as a sign indicating an end of filter's life and the filter would be replaced.
(2) Remove the chemical filter and measure its weight. If the increase in weight reaches a predetermined value and beyond, then it would be interpreted as a sign indicating an end of filter's life and the filter would be replaced.
However, since these conventional method for determining filter's life does not allow continuous monitoring for filter's condition and, therefore, the timing of replacing the filter cannot appropriately be determined, it would be quite possible for the filter to be used beyond the end of its life.
The present invention was made to resolve this problem, and its objectives are to provide a method for deciding on the timing of replacing a chemical filter, a filter life detection sensor, a chemical filter unit, and a semiconductor manufacturing apparatus, where an adsorption state of chemical substances can continuously be monitored while the filter is in service, thereby making it possible to replace the filter without missing the end of its life.
SUMMARY OF THE INVENTION
In order to resolve the above-mentioned problem, a method for deciding on the timing of replacing a chemical filter placed in a ventilation path for removing contaminants from air according to the present invention includes: providing sensors constituted of the same material as the chemical filter; and taking a measurement of an impedance of the material as the chemical filter; where: an adsorption state detection sensor through which air containing contaminants flows and a reference sensor to which a flow of air is blocked serve as the sensors; the measurement of the impedance of the material constituting the adsorption state detection sensor is corrected with the measurement of the impedance of the material constituting the reference sensor, thereby obtaining a corrected measurement; and the timing of replacing the chemical filter is decided based upon the corrected measurement.
The impedance of the material of the chemical filter varies with parameters such as temperature and humidity as well as the amount of adsorbed contaminants. If the change in impedance due to factors other than the amount of adsorbed contaminants can be detected based on results obtained by the reference sensor and the measurement by the adsorption state detection sensor is corrected, then the amount of adsorbed contaminants can be obtained with great accuracy, and the timing of replacing the chemical filter can accurately be determined.
Incidentally, the impedance can be measured by using an oscillation circuit including the sensor as a part of the oscillating conditions, where the measurement is taken based on an oscillation frequency or an oscillation amplitude thereof.
By having the above-mentioned construction, changes in impedance can precisely be detected, and the timing of replacing the chemical filter can accurately be determined.
A filter life detection sensor according to the present invention is constituted of the same material as a chemical filter placed in a ventilation path for removing contaminants from air and includes: an adsorption state detection sensor through which air containing contaminants flows; and a reference sensor to which a flow of air is blocked.
Since the filter life detection sensor according to the present invention is constituted of the same material as the chemical filter placed in the ventilation path, the timing of replacing the chemical filter can be determined by taking a measurement of an impedance of the adsorption state detection sensor. Furthermore, if changes in impedance due to factors other than the amount of adsorption of contaminants is detected by the reference sensor and the measurement taken by the adsorption state detection sensor is corrected accordingly, then the amount of adsorption of contaminants can be obtained with great accuracy. This makes it possible to accurately decide on the timing of replacing the chemical filter.
Furthermore, since a filter life detection sensor according to the present invention includes an air cleaning reference sensor or an adsorption state detection sensor in front of a reference sensor, by taking a deviation of an impedance of the reference sensor from an impedance of the adsorption state detection sensor, a chemical filter's life can be detected without being affected by not only temperature and humidity but also the air passing therethrough.
Since a chemical filter unit according to the present invention include a chemical filter and sensors, the chemical filter's life can individually be decided independent of other chemical filter units. Furthermore, even in the case of a plurality of stages of chemical filter units, the chemical filter's life can individually be decided independent of other chemical filter units.
By providing the chemical filter unit according to the present invention in a ventilation path of a semiconductor manufacturing apparatus, the adsorption state of chemical substances can continuously be monitored while the semiconductor manufacturing apparatus is still in service, and the timing of replacing the chemical filter can accurately be decided.
Incidentally, a chemical filter used in the present invention may be of an activated charcoal fiber type, which is expected to improve the capability of the filter to adsorb chemical substances passing therethrough.
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Hayashi Teruyuki
Hirao Iichi
Motouji Satoshi
Saito Misako
Foley & Lardner
Lawrence Frank M.
Omron Corporation
Simmons David A.
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