Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
2000-02-02
2001-03-20
Rivell, John (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C251S121000, C137S492500
Reexamination Certificate
active
06202681
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vacuum pressure control system capable of controlling vacuum pressure in vacuum vessels at a prescribed value, the vacuum vessels being usually used in semiconductor producing processes.
2. Description of Related Art
In a conventional vacuum pressure control system, which is shown in
FIG. 16
, usually a vacuum chamber
11
serving as a vacuum vessel is provided with an inlet
13
and an outlet
14
, in which wafers
15
to be processed are placed in tires. The inlet
13
is connected with a source of process gas and a source of nitrogen gas which is used for purging the inside
12
of the vacuum chamber
11
. The outlet
14
is connected to an inlet port of a pilot type opening and closing valve
20
which consists of a bellows poppet valve. An outlet port of the pilot valve
20
is connected via an opening proportional valve
23
to a vacuum pump
19
. The opening proportional valve
23
consists of a butterfly type of opening adjustment valve.
The proportional valve
23
is formed of a circular plate arranged within a pipe extending between the pilot valve
20
and the vacuum pump
19
which has an approximately same diameter as the inner diameter of the pipe and is rotatably about a support shaft provided along the center line of the circular plate. The support shaft is rotated and stopped by a step motor. The opening degree of the proportional valve
23
is dependent on the stop position of the step motor. Usually, measurement of the vacuum pressure inside of the vacuum chamber
11
is made by a pressure sensor
17
and its measured values are fed back to control the stop position of the step motor of the opening proportional valve
23
so as to equalize a vacuum pressure to be measured with a prescribed value of vacuum pressure.
During a producing process, the vacuum chamber
11
is supplied with process gas. In the conventional vacuum pressure control system, the proportional valve
23
is controlled to increase its opening degree when the vacuum pressure value become higher toward the atmospheric pressure than a desired value, thereby allowing the vacuum pump
19
to suck a larger amount of flow of the gas. The proportional valve
23
is, to the contrary, controlled to decrease its opening when the vacuum pressure value become lower toward the absolute value than the desired value, thereby allowing the vacuum pump
19
to suck a lesser amount of flow of the gas.
The butterfly type proportional valve like the aforesaid opening proportional valve
23
can not effect a complete shutoff due to its construction. In trying to completely shut off the pipe with the butterfly type proportional valve, the butterfly valve is usually equipped with an O-ring and the like around the valve to contact with the inner wall of the pipe. In semiconductor producing apparatuses, however, products produced from process gas would be deposited on the surface of the O-ring and make it impossible for the butterfly valve to fully shut off the pipe. It is also impossible to apply a torque load sufficient to the O-ring in order to effect the complete shutoff. The conventional vacuum pressure control system therefore needs an emergent shutoff valve like the pilot type opening and closing valve
20
to be connected to the proportional valve
23
in series.
The shutoff valve needs to have, in addition to the full vacuum shutoff function, an emergency shutoff function to shut off flow of gas as soon as power to the apparatus is cut off. A cylinder type pilot valve is used for the pilot valve
20
accordingly.
In creating a vacuum in the vacuum chamber
11
, if the opening of the proportional valve
23
is set larger while a large amount of process gas remains in the vacuum chamber
11
, a great volume of the process gas is sucked from the vacuum chamber
11
for a short time, inducing gas current inside thereof and thereby causing a problem of flying up particles which have adhered to the inner wall of the vacuum chamber
11
.
Suction of all the particles flied up can not easily be effected. When a large amount of process gas remains in the vacuum chamber
11
, usually, control of the suction amount of process gas is effected by increasing little by little at first the opening of the proportional valve
23
. To enable this, the proportional valve
23
must be kept stable in a small opening.
However, within a small opening range, the butterfly type proportional valve would largely change its opening by a slight rotation angle due to its construction. It is therefore difficult to set the proportional valve
23
stable with its opening small and slowly outgas from the vacuum chamber
11
by means of the vacuum pump
19
.
To solve the problem, in the conventional system, a bypass valve
22
and a shutoff valve
21
are connected in a line. The bypass valve
22
is formed to have a small opening. Closing the pilot valve
20
, opening the proportional valve
23
and then opening the shutoff valve
21
, the vacuum chamber
11
can be connected to the vacuum pump
19
through a small opening to make it possible to suck slowly the process gas remaining in the vacuum chamber
11
.
The control of the suction is effected by a vacuum control device (not illustrated) based on the outputs measured by the pressure sensor
17
to measure the vacuum pressure of the outlet
14
. A shutoff valve
16
used for the maintenance of the pressure sensor
17
is further disposed between the outlet port
14
and the pressure sensor
17
.
The conventional vacuum pressure control system, however, has the following problems.
(1) A combination of the opening proportional valve
23
consisting of a butterfly type proportional valve and the bypass valve
22
can not effect the precise control of vacuum pressure in a wide range from a low vacuum region including the vacuum pressure near the atmospheric pressure (ex. several Torr), a medium region, to a high region (ex. several mmTorr). In particular, the butterfly valve can not allow a little amount of flow of gas to pass therethrough. The conventional system, even if using the bypass valve, can not cope with the necessity of slight variations in vacuum pressure because the amount of flow of gas is kept constant by the bypass valve.
(2) Besides the proportional valve
23
, it needs the pilot valve
20
, the bypass valve
22
and the shutoff valve
21
, having many joints in a pipe line. This may cause the mixture of particles and others from the joints into the pipe line. The combination of the valves makes the size of a whole apparatus larger and also its using process more complex. This is a problem for the equipment to be used in the semiconductor producing process which requires compactness to each equipment. In addition, there is an issue of cost up in the above equipment.
(3) It is conceivable to utilize a poppet valve for a means of resolving the above problems. This means is that a step motor or a servo motor controls the position of a flat valve to come into contact with and separate from a seat valve. This realizes an integrated component of the proportional valve
23
, the bypass valve
22
and the shutoff valve
21
. It is however difficult to provide the emergent shutoff function to the poppet valve to be driven by the step motor or the servo motor. Because the step motor or the servo motor stops at the time of interruption of electric service and thus can not close the poppet valve in an emergency. When the valve needs to be closed at a high speed, there is also a problem of it taking about ten seconds for the valve to fully close since the rotation of a step motor can not be speeded up due to the necessity of generating the torque to drive the poppet valve.
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 system capable of controlling precisely vacuum pressure in a wide range from a low vacuum region to a high, and comprising an emergent shutoff fun
Kouketsu Masayuki
Nitta Shinichi
Takehara Hiroshi
Watanabe Masayuki
CDK Corporation
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Rivell John
LandOfFree
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