Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
1999-08-05
2001-01-30
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S487500
Reexamination Certificate
active
06178995
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement of an apparatus for feeding various kinds of fluids such as gas for use in the manufacture of semiconductors, chemicals, precision machine parts, and the like. More particularly, this invention relates to a fluid feeding apparatus which permits high precision control of the flow rate of fluid at the times of starting to feed a fluid and of switching fluids from one kind to another.
2. Description of the Prior Art
Fluid feeding apparatuses requiring control with high precision of the flow rate are used in semiconductor manufacturing facilities and chemical production plants. Most of those apparatuses are equipped with so-called mass flow controllers.
FIG. 8
shows an apparatus for feeding fluid (gas) for use in a high purity moisture generator in semiconductor manufacturing facilities. It is designed so that H
2
and O
2
are fed to a reactor
51
from a gas feeding apparatus
50
at specific flow rates and are radicalized with a platinum catalyst and allowed to react with each other in a non-combustion state to generate moisture gas (water vapor). The moisture gas thus generated in the reactor
51
is then supplied to an oxidizing furnace
52
.
In
FIG. 8
, the reference numeral
54
designates a circuit for measuring moisture generation responsiveness of the reactor
51
, and includes a suction rate regulating valve
55
, a quadrupole mass spectrometer (Q-mass spectrometer)
56
, a turbo molecular pump
57
, and a vacuum pump
58
.
The Q-mass spectrometer
56
is for measuring ion concentrations of H
2
O, H
2
, O
2
, and N
2
. A quadrupole mass analyzer MSQ-150A (ULVAC Corporation, Japan) is used for the purpose. The aforesaid gas feeding apparatus
50
is formed from three mass flow controllers MFC
1
, MFC
2
, and MFC
3
, changeover valves V
1
, V
2
, and V
3
, gas storage containers (not shown), and pressure regulators (not shown). The changeover valves V
1
, V
2
, and V
3
in this example are of the electric metal diaphragm type.
From the respective gas storage containers (not shown), H
2
at a gauge pressure of 2 kgf/cm
2
, O
2
at a gauge pressure of 2 kgf/cm
2
, and N
2
at a gauge pressure of 6 kgf/cm
2
are supplied to the primary sides of the three mass flow controllers MFC
1
, MFC
2
, and MFC
3
.
To generate moisture in the reactor
51
, in the meantime, the flow rates and other conditions of the three mass flow controllers MFC
1
, MFC
2
, and MFC
3
in the gas feeding apparatus
50
are set, and then the system is purged with N
2
, V
1
and V
2
being closed and V
3
being opened. Then V
3
is closed and V
2
, is opened to supply O
2
, and at the same time that O
2
is supplied, or about
3
seconds after the O
2
supply, V
1
is opened to supply H
2
. Thus, moisture gas (water vapor) starts to be generated in the reactor
51
.
Part of the moisture gas or the like from the reactor
51
is sucked into the measurement circuit
54
for a specific time by operating the suction-regulating valve
55
, where the concentrations of H
2
, O
2
, H
2
O, and N
2
in the generated moisture are measured by the Q-mass spectrometer
56
.
FIGS. 9
to
11
illustrate the concentrations of H
2
, O
2
, N
2
, and H
2
O measured by the Q-mass spectrometer
56
in the moistures produced in a moisture-generating testing arrangement. The testing arrangement was provided with a gas feeding apparatus
50
equipped with the mass flow controllers as shown in FIG.
8
. And the measurements were taken under the following conditions (1), (2), and (3). The gauge pressure of H
2
, O
2
, and N
2
on the primary sides of the mass flow controllers in the gas feeding apparatus
50
were 2 kgf/cm
2,
2 kgf/cm
2
, and
6
kgf/cm
2
, respectively.
(1) Pressure on the secondary side of the mass flow controllers: 1 kg/cm
2
abs
H
2
: 50 sccm+O
2
: 1000 sccm
N
2
: 1000 sccm
H
2
starts to be fed 3 seconds after O
2
supply.
(2) Pressure on the secondary side of the mass flow controllers:0.5 kg/cm
2
abs
H
2
: 50 sccm +O
2
: 1000 sccm
N
2
: 1000 sccm
H
2
starts to be fed 3 seconds after O
2
supply.
(3) Pressure on the secondary side of the mass flow controllers: 0.2 kg/cm
2
abs
H
2
: 50 sccm+O
2
: 1000 sccm
N
2
: 1000 sccm
H
2
starts to be fed 3 second after O
2
supply.
It is to be understood that “sccm” is a unit indicating the flow rate/minute in volume (cm
3
) of H
2
, O
2
, N
2
, etc. in the standard state. As is evident from
FIGS. 9
to
11
, the concentration of H
2
rises and peaks at a peak P
H2
at the start of the gas feeding as the pressure decreases on the secondary side of the mass flow controllers MFC's (pressure reduction) in the moisture generation testing arrangement provided with the gas feeding apparatus
50
equipped with mass flow controllers. Along with that, there appears a peak P
H2
O in the concentration of H
2
O.
H
2
and H
2
O peak at P
H2
and P
H2O
in the initial stage of the gas feeding. That means it is impossible to precisely effect H
2
concentration control (flow rate control). The mass flow controller cannot meet the demand for high precision control of the flow rate of H
2
.
It should also be noted that if the peak P
H2
of the concentration of H
2
rises to several percent, there will arise a possibility of hydrogen exploding in the downstream oxidizing furnace
52
, raising a safety problem.
On the other hand,
FIGS. 12
to
13
also show the concentrations of H
2
, O
2
, N
2
, and H
2
O measured by the Q-mass spectrometer
56
in the moistures produced in a moisture-generating testing arrangement. The testing arrangement was provided with a gas feeding apparatus
50
equipped with the mass flow controllers as shown in FIG.
8
. And the measurements were taken under the following conditions (1) and (2). The supply pressures (gauge pressures) of H
2
, O
2
, and N
2
on the primary sides of the mass flow controllers were 2 kgf/cm
2
, 2 kgf/cm
2
, and 6 kgf/cm
2
, respectively.
(1) Pressure on the secondary side of the mass flow controllers: 0.5 kg/cm
2
abs
H
2
: 100 sccm+O
2
: 50 sccm (H
2
:O
2
=2:1)
N
2
: 1000 sccm
H
2
and O
2
started to be fed simultaneously and were cut off at the same time.
(2) Pressure on the secondary side of the mass flow controllers: 0.5 kg/cm
2
abs
H
2
: 100 sccm+O
2
: 50 sccm (H
2
:O
2
=2:1)
N
2
: 1000 sccm
H
2
started to be fed 3 seconds after O
2
supply and the feeding of H
2
was cut off three minutes earlier than O
2
cut-off.
As is clear from
FIG. 12
, the concentration peak P
H2
of H
2
in the initial stage of gas feeding rises to some 10 percent if H
2
and O
2
are fed simultaneously in the gas feeding apparatus
50
equipped with the prior art mass flow controller and there arises a safety question.
Furthermore, the concentration P
O2
of O
2
suddenly falls in the region where a peak P
H2
of H
2
is observed because O
2
is consumed in its reaction with H
2
. As a result, it will be impossible to generate an intended quantity of moisture.
Also, as is shown in
FIG. 13
, the concentration peak P
H2
of H
2
increases to more than some 50 percent at the beginning of gas feeding in the gas feeding apparatus
50
using the prior art mass flow controller, further increasing the danger.
In addition, a large quantity of O
2
is consumed at the aforesaid peak P
H2
of H
2
, resulting in a substantial fall in the concentration O
2
. That makes it difficult to produce a required amount of moisture.
As set forth above, the gas feeding apparatus
50
equipped with the prior art mass flow controllers has a problem that the flow rate of H
2
and O
2
is impossible to control with high precision, because H
2
and O
2
flow in excessively in what is called an overshooting in the initial stage of the gas feeding or suspension.
In generating moisture in the gas feeding apparatus
50
with the mass flow controllers, it is natural that the amount of moisture generated deviates greatly from the set level, because of the overshooting of H
2
and O
2
, and it is difficult to control the generation of
Dohi Ryousuke
Ikeda Nobukazu
Kagazume Tetu
Kawata Kouji
Minami Yukio
Fujikin Incorporated
Griffin & Szipl, P.C.
Michalsky Gerald A.
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