Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
1999-11-12
2003-01-21
Buiz, Michael Powell (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S487500, C251S335200, C251S900000
Reexamination Certificate
active
06508268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vacuum pressure control apparatus for controlling vacuum pressure in a vacuum vessel to a predetermined value, the vacuum vessel being used in semiconductor producing processes, and particularly to a vacuum pressure control apparatus for accurately and promptly controlling vacuum pressure in a vacuum vessel to a predetermined value in a low vacuum region near atmospheric pressure.
2. Description of Related Art
One of vacuum pressure control systems which have conventionally been used in semiconductor producing processes is described in U.S. Patent application No. 08/580,358 filed by applicant of the present invention. This vacuum pressure control system uses a vacuum proportional opening and closing valve which is disposed between a vacuum chamber and a vacuum pump and regulates the quantity of gas flow to be sucked by the vacuum pump to regulate the internal pressure value of the vacuum chamber into a predetermined vacuum pressure. The vacuum proportional opening and closing valve is provided with a poppet valve as a main element. Referring to
FIG. 8
, the structure of this poppet valve is described.
FIG. 8
shows a part of the vacuum proportional opening and closing valve in a closed state.
FIG. 9
shows the same in an open state to provide a medium vacuum region in the vacuum chamber.
A poppet valve
133
has a valve member
133
a
connected to a piston rod not shown, an annular groove
133
b
which fixedly holds an O-ring
135
, and a connection portion
133
c
to which a valve element
134
made from stainless steel is assembled. The O-ring
135
will be depressed against the upper surface of a valve seat
136
constructed of a cylindrical inner surface formed in a lower center of a valve body
145
of the vacuum proportional opening and closing valve when a tapered surface
134
a
formed on the outer periphery of the stainless valve element
134
of the poppet valve
133
is fully inserted in the valve seat
136
. Accordingly, the O-ring
135
serves to prevent leakage of fluid through a flow passage defined by the valve seat
136
of the valve body
145
having a port
139
formed below the valve seat
136
and connected to the vacuum chamber. The inclination angle &thgr; of the tapered surface
134
a
of the stainless valve element
134
is set to 3 degrees in the U.S. Patent application No. 08/580,358. The stainless valve element
134
has also a straight surface
134
b
above the tapered surface
134
a.
As shown in
FIG. 9
, when the stainless valve element
134
with the tapered surface
134
a
is moved along the center line (in a vertical direction in figure) of the valve seat
136
, an annular clearance between the tapered surface
134
a
and the valve seat
136
changes in sectional area. In response to the clearance area, the opening degree of the vacuum proportional opening and closing valve is changed. As shown in
FIG. 8
, when the poppet valve
133
comes into contact with the upper surface of the valve seat
136
, pressing the O-ring
135
against the upper surface of the valve seat
136
, the O-ring
135
completely blocks the flow passage to prevent a leakage flow of fluid.
However, the above conventional vacuum pressure control system and control apparatus have the following problems.
Specifically, the clearance area between the tapered surface
134
a
and the valve seat
136
is changed to regulate the quantity of fluid flow sucked by the vacuum pump. This can relatively facilitate the provision of the flow quantity corresponding to high vacuum pressure near high vacuum or medium vacuum pressure.
The clearance area between the tapered surface
134
a
and the valve seat
136
is relatively large, however, and it is difficult to regulate the quantity of fluid flow so as to maintain the pressure in the vacuum chamber in a low vacuum region near atmospheric pressure, in particular, extremely close to atmospheric pressure. Such the regulation of the flow quantity to very-low-vacuum pressure is much more difficult when the O-ring made of rubber is used because it is prone to come into intimate contact with the flat upper surface of the valve seat
136
. When process gas precipitates on the inside of the valve body
145
and others, the contact degree of the O-ring
135
to the valve seat
136
increases, and the poppet valve
133
will quickly change its moving distance due to the change in the friction coefficient which shifts to dynamical friction from static friction in association with the movement of the poppet valve
133
, causing the O-ring
135
to instantaneously separate from the flat upper surface of the valve seat
136
. This disables the control to accurately provide a very small clearance between the tapered surface
134
a
and the valve seat
136
.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a vacuum pressure control apparatus capable of accurately controlling the internal pressure in a vacuum vessel in a low vacuum region near atmospheric pressure.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a vacuum pressure control apparatus for controlling vacuum pressure in a vacuum vessel from which gas is sucked by means of a vacuum pump, the apparatus including a vacuum proportional opening and closing valve which is disposed between the vacuum pump and the vacuum vessel and changes its opening for controlling the vacuum pressure in the vacuum vessel, the vacuum proportional opening and closing valve including a valve seat having a central flow passage through which the gas is sucked from the vacuum vessel to the vacuum pump, and a valve member that is movable to come into contact with the valve seat and to separate from the same, the valve member being provided with an elastic sealing member on a surface that comes into contact with the valve seat, and the vacuum pressure control apparatus controlling a change in an elastic deformation amount of the elastic sealing member which is in contact with the valve seat to regulate the quantity of gas leakage between the elastic sealing member and the valve seat and to provide a predetermined vacuum pressure in the vacuum vessel.
In the vacuum pressure control apparatus, preferably, a force applied to the elastic sealing member which is in contact with the valve seat through the valve member is controlled to change the elastic deformation amount of the elastic sealing member.
For instance, the vacuum proportional opening and closing valve may include a pilot cylinder for moving the valve member, and the vacuum pressure control apparatus controls a change in air pressure to be supplied to the pilot cylinder to thereby control the force applied to the elastic sealing member which is in contact with the valve seat through the valve member and change the elastic deformation amount of the elastic sealing member.
Next, operation of the vacuum pressure control apparatus configured in the above manner is described below.
The vacuum pump connected to the vacuum vessel makes a constant suction of gas from the vacuum vessel. By changing the opening degree of the vacuum proportional opening and closing valve disposed between the vacuum vessel and the vacuum pump, the quantity of gas flow sucked into the vacuum pump from the vacuum vessel is regulated, thus changing vacuum pressure in the vacuum vessel.
In order to regulate the pressure in the vacuum vessel to high or medium vacuum pressure, the opening degree of the vacuum proportional and opening valve is adjusted in the manner that the valve element is moved by the pilot cylind
Buiz Michael Powell
CKD Corporation
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Krishnamurthy Ramesh
LandOfFree
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