Measuring and testing – Sampler – sample handling – etc. – Plural parallel systems
Reexamination Certificate
1999-06-29
2002-10-29
Noland, Thomas P. (Department: 2856)
Measuring and testing
Sampler, sample handling, etc.
Plural parallel systems
C073S023360, C073S023410, C422S088000, C422S089000, C422S093000, C436S050000, C436S178000, C436S181000
Reexamination Certificate
active
06470760
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for automatically analyzing a trace substance, and more Particularly, to a method and an apparatus for automatically analyzing a desired gaseous substance or substances existing in an atmosphere, which are preferably applied to monitoring gaseous contaminants existing in a clean room used in the field of semiconductor device fabrication.
2. Description of the Prior Art
A trace of gaseous contaminant remaining in a clean room atmosphere tends to increasingly cause failures or defects in next-generation semiconductor devices during their fabrication process steps. To stabilize the prosecution of the mass-production processes of the next-generation semiconductor devices, usually, suitable dust/chemical filters are used for removing dusts and chemicals existing in the air in the clean room. However, there is a possibility that contamination accidents occur due to supplied source materials for fabrication processes and that the dust/chemical filters may be damaged or broken due to contaminants. Thus, it is required to automatically and continuously measure and monitor contaminants existing in the air in a clean room.
In a prior-art multi-point measuring method for measuring trace contaminants at different positions in a clean room, desired gaseous contaminants are sampled from the air and then, concentrated to specific concentrations corresponding to the lower limit of an analytical apparatus or instrument by using the impinger method while taking a lot of time, thereby analyzing and quantitative analyzing the concentrated contaminants. However, there is a problem that the measuring interval of time is too long and the total amount of the contaminants at the measuring positions is unable to be determined, and that an outbreak of a high-concentration contaminant is unable to be well-treated.
On the other hand, there is a known prior-art multi-point analyzing method for automatically analyzing ammonia existing in a clean room atmosphere using a diffusion scrubber.
FIGS. 1 and 2
show prior-art multi-point ammonia analytical apparatuses that perform this analyzing method, which are disclosed in the Japanese Non-Examined Patent Publication No. 8-54380 published in June 1994 and its corresponding U.S. Pat. No. 5,714,676 issued on Feb. 3, 1998.
In
FIG. 1
, the prior-art multi-point ammonia analytical apparatus is comprised of a sampler
1100
, a concentrator
1200
, and an analyzer
1300
. The sampler
1100
has a switch valve
601
with ten inlets connected respectively with ten sampling points P
1
to P
10
located in the clean room, and a diffusion scrubber
602
connected to an outlet of the valve
601
. The concentrator
1200
includes a concentration column
604
of an ion chromatograph
603
. The analyzer
1300
includes a separation column
605
, a suppressor
606
, and an electrical conductivity meter
607
of the ion chromatograph
603
. A controller
608
controls the whole operation of the sampler
1100
, the concentrator
1200
, and the analyzer
1300
.
With the prior-art analytical apparatus of
FIG. 1
, the total measuring time T
total
for all the sampling points P
1
to P
10
is expressed as the following equation (1), where n is the number of the sampling points, and T
pt
, T
r
, T
s
, and T
sa
are the times for the pre-treatment operation, the rinsing operation, the sampling operation, and the separation/analyzing operation, respectively.
T
total
=n
×(T
pt
+T
r
+T
s
+T
sa
) (1)
The schedule of the individual operations for the sampling points P
1
to P
10
is shown in FIG.
2
. Specifically, at first, the pre-treatment and sampling operations are successively carried out for the sampling point P
1
and then, the rinsing and separation/analysis operations for the same point P
1
are successively carried out. Next, the same time schedule is successively repeated for each of the points P
2
to P
10
.
In the prior-art analytical apparatus of
FIG. 1
, the switch valve
601
of the sampler
1100
assigns alternately one of the sampling points P
1
to P
10
to the diffusion scrubber
602
. Thus, there is a problem that the total measuring time T
total
for all the sampling points P
1
to P
10
is very long.
For example, if the time T
pt
for the pre-treatment operation is 25 minutes, the time T
r
for the rinsing operation is 0.5 minute, the time T
s
for the sampling operation is 7.5 minutes, and the time T
sa
for the separating/analyzing operation is 8 minutes, the total time T
total
is 410 minutes.
The prior-art multi-point ammonia analytical apparatus shown in
FIG. 3
is comprised of a sampler
2100
, a concentrator
2200
, and an analyzer
2300
.
The sampler
2100
has a switch valve
701
a
having five inlets connected respectively with five sampling points P
1
to P
5
, a diffusion scrubber
702
a
connected to an outlet of the valve
701
a
, a switch valve
701
b
having five inlets connected respectively with five sampling points P
6
to P
10
, and a diffusion scrubber
702
b
connected to an outlet of the valve
701
b.
The concentrator
2200
is comprised of a concentration column
704
of an ion chromatograph
703
. The analyzer
2300
is comprised of a separation column
705
, a suppressor
706
, and an electrical conductivity meter
707
of the ion chromatograph
703
.
A controller
708
controls the whole operation of the sampler
2100
, the concentrator
2200
, and the analyzer
2300
.
With the prior-art analytical apparatus of
FIG. 3
, the controller
708
controls so that one of the valves
701
a
and
701
b
is used for the pre-treatment operation while the other of the valves
701
a
and
701
b
is used for the rinsing, sampling, and separation/analysis operations. The schedule of the individual operations for the sampling points P
1
to P
10
is shown in FIG.
4
.
Thus, the total measuring time T
total
for all the sampling points P
1
to P
10
is expressed as the following equation (2) under the condition that the following inequality (3) is established.
T
total
=n
×(T
r
+T
s
+T
sa
) (2)
T
pt
≧T
r
+T
s
+T
sa
(3)
The inequality (3) means that the time T
pt
for the pre-treatment operation is equal to or greater than the sum of the times for the rinsing, sampling, and separation/analysis operations, i.e., (T
r
+T
s
+T
sa
).
In the prior-art analytical apparatus of
FIG. 3
, for example, if the time T
pt
for the pre-treatment operation is 25 minutes, the time T
r
for the rinsing operation is 0.5 minute, the time T
s
for the sampling operation is 7.5 minutes, and the time T
sa
for the separating/analyzing operation is 8 minutes, the total time T
total
is 185 minutes. Thus, there is a same problem that the total time measuring time T
total
for all the sampling points P
1
to P
10
is still long.
Moreover, gaseous ammonia tends to remain in the sampler
1100
or
2100
and the concentrator
1200
or
2200
after a sampled air with high-concentration ammonia is measured. The remaining ammonia or residue in a prior measuring step affects badly a subsequent measuring step. This is called the “memory effect” of the residue.
In particular, when an organic substance such as monoethanolamine is analyzed and measured in the above-described prior-art apparatuses of
FIGS. 1 and 3
, the organic substance is extremely easy to remain in the inside of the apparatuses. Thus, correct measurement is unable or very difficult to be carried out.
SUMMARY OF THE INVENTION
Accordingly, a general object of the present invention to provide a method and an apparatus for automatically analyzing a trace substance capable of automatic analysis of a trace substance in a short time with high accuracy.
A specific object of the present invention to provide a method and an apparatus for automatically analyzing a trace substance that decreases the time for each cycle of measurement or analysis.
Another specific object of the present invention to provide a method
Satou Yuuichi
Shimobayashi Masaru
Shinozaki Tsutomu
NEC Corporation
Noland Thomas P.
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