U.S. patent application number 10/066659 was filed with the patent office on 2002-07-18 for flow control of process gas in semiconductor manufacturing.
Invention is credited to Ollivier, Louis A..
Application Number | 20020092564 10/066659 |
Document ID | / |
Family ID | 24135599 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020092564 |
Kind Code |
A1 |
Ollivier, Louis A. |
July 18, 2002 |
Flow control of process gas in semiconductor manufacturing
Abstract
A flow control system and method for controlling batchwise
delivery of process gas for semiconductor manufacturing are
disclosed, wherein the flow control system is operable in a flow
mode for delivery of a batch of process gas in a delivery period of
time and, alternately, in a no-flow mode. After the start of the
delivering, the pressure drop of the gas in a reference capacity of
the system is measured for a measurement period of time while
interrupting the flow of process gas from a source of the process
gas to the reference capacity and continuing to deliver process gas
from the system to a semiconductor manufacturing apparatus at a
controlled flow rate. The rate of pressure drop in the reference
capacity during the measurement period of time is used as a measure
of the actual flow rate. Where the actual flow rate does not agree
with a specified flow rate for delivering, the controlled flow rate
for a subsequent delivery period of time in which another batch of
process gas is delivered, is adjusted. Components of the flow
control system are arranged along a gas manifold in the form of an
elongated delivery stick having a width of less than 1.5 inches,
saving important space in a group of the flow control systems that
may comprise up to 20 units.
Inventors: |
Ollivier, Louis A.; (Palo
Alto, CA) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
24135599 |
Appl. No.: |
10/066659 |
Filed: |
February 6, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10066659 |
Feb 6, 2002 |
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09535750 |
Mar 27, 2000 |
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60133295 |
May 10, 1999 |
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Current U.S.
Class: |
137/487.5 |
Current CPC
Class: |
Y10T 137/86397 20150401;
G05D 16/0661 20130101; Y10T 137/7761 20150401; Y10T 137/776
20150401; Y10T 137/7759 20150401; G05D 7/0647 20130101; Y10T
137/0324 20150401 |
Class at
Publication: |
137/487.5 |
International
Class: |
F16K 031/12 |
Claims
I claim:
1. A method of controlling the batchwise delivery of process gas
for semiconductor manufacturing using a flow control system
operable in a flow mode for delivery of a batch of process gas and,
alternately, in a no-flow mode, said method comprising: delivering
a batch of process gas from a source of pressurized process gas
through a flow line of said flow control system to a semiconductor
manufacturing apparatus at a controlled flow rate for a delivery
period of time, said line of the flow control system including a
pressure regulator for establishing a regulated pressure of said
process gas in said line, an on/off valve downstream of said
pressure regulator to start and stop said flow mode during which
said process gas is delivered to said apparatus for said delivery
period of time and, upstream in said line from said pressure
regulator, a reference capacity used to measure the actual flow
rate of said delivering, after the start of said delivering of said
batch of process gas, measuring for a measurement period of time
the pressure drop of said process gas in said reference capacity
while interrupting the flow of process gas through said line to
said reference capacity and continuing to deliver process gas from
said line of said flow control system to said semiconductor
manufacturing apparatus at said controlled flow rate, determining
from said measuring the rate of pressure drop in said reference
capacity during said measurement period and the actual flow rate of
said batch of process gas being delivered and, in case said actual
flow rate does not agree with a specified flow rate for said
delivering, adjusting said controlled flow rate in the direction of
said specified flow rate from said actual flow rate for a
subsequent delivery period of time in which another batch of
process gas is delivered.
2. The method according to claim 1, wherein said flow control
system further comprises a mass flow control valve downstream of
said pressure regulator, and wherein said adjusting of said
controlled flow rate includes adjusting a set point value of said
mass flow control valve.
3. The method according to claim 1, wherein said flow control
system further comprises a fixed orifice in said flow line
downstream of said pressure regulator, and wherein said adjusting
of said controlled flow rate includes adjusting a pressure setting
of said pressure regulator.
4. The method according to claim 3, wherein said pressure regulator
is a dome loaded pressure regulator whose pressure setting is
established by a fluid pressure applied to the dome of the pressure
regulator, and said method including at the end of said delivery
period of time removing the pressure signal applied to the dome of
the pressure regulator to prevent creep at the outlet of the
pressure regulator in a no-flow mode.
5. The method according to claim 1, wherein said flow control
system can be adjustably set to establish said controlled flow rate
of gas delivery within a range of possible controlled flow rates
depending upon the setting of said flow control system, and said
method further including establishing a mathematical relationship
between the actual flow rate and the flow rate setting of said flow
control system and in case said determined actual flow rate of said
batch of process gas being delivered does not agree with said
specified flow rate for said delivery, referring to said
mathematical relationship in determining the size of said adjusting
of said controlled flow rate.
6. The method according to claim 5, including storing said
mathematical relationship in a reference memory of said control
system for said reference thereto.
7. The method according to claim 5, wherein said flow control
system includes a mass flow control valve having a range of
possible controlled flow rate settings which extends to 100% of its
full scale with an effective rangeability of 10:1.
8. The method according to claim 1, wherein said measurement period
of time has a duration of less than or equal to 20 seconds.
9. The method according to claim 1, wherein said measurement period
of time continues for a predetermined maximum duration or is
terminated sooner when the pressure in the measurement capacity
reaches a predetermined minimum pressure.
10. The method according to claim 1, further comprising at the end
of said measurement period of time ceasing said interrupting of the
flow of process gas through said line to said reference capacity to
return the pressure in said reference capacity to a pressure level
of the process gas supplied from said source of pressurized
gas.
11. The method according to claim 1, wherein said pressure
regulator has an inlet coupled in fluid communication with said
source of pressurized process gas, an outlet, a valve element which
is actuable to close said regulator to the flow of process gas and,
alternately, to throttle the flow of said process gas through said
regulator, said valve element being actuated by a diaphragm coupled
in force transmitting communication therewith and disposed in fluid
communication with said process gas to be responsive to a fluid
pressure force thereof, and said regulator further including an
adjustable main pressure setting assembly for applying a select
pressure setting force on said diaphragm, and wherein said method
further comprises: adjusting the main pressure setting assembly of
said regulator such that the flow of said process gas therefrom is
regulated at an outlet pressure which is less than a desired outlet
pressure for delivering said process gas at said controlled flow
rate; applying at about the start of said delivery period of time a
differential force on said diaphragm independent of said pressure
setting force such that the flow of said process gas therefrom in
said delivery period of time is regulated at an outlet pressure
which is about said desired outlet pressure; and terminating the
application of said differential force at about the end of said
delivery period of time.
12. The method according to claim 1, including repeating said
method to deliver another, discrete batch of process gas for
semiconductor manufacturing during a subsequent delivery period of
time.
13. The method according to claim 1, wherein said controlled flow
rate is maintained uniform at least during said measurement period
of time.
14. The method according to claim 1, wherein said controlled flow
rate is maintained uniform throughout said delivery period of
time.
15. The method according to claim 1, wherein said flow control
system is adjustable for delivering process gas at a range of
controlled flow rates, and said method further comprising using
said actual flow rate to calibrate said flow control system over
said range for delivering additional batches of said process
gas.
16. The method according to claim 1, further comprising arranging
components of said flow control system along a gas manifold in the
form of an elongated delivery stick having a width less than 1.5
inches.
17. The method according to claim 1, further comprising measuring
the temperature of said process gas being delivered and using the
measured temperature to express said actual flow rate determined at
standard conditions.
18. A flow control system for use within a fluid circuit having a
source of pressurized gas to be delivered batchwise at a controlled
flow rate to a destination by said flow control system, said flow
control system being operable in a flow mode for delivering a batch
of gas and, alternately, in a no-flow mode, said flow control
system comprising: a flow line through which gas from said source
of pressurized gas can be delivered, a pressure regulator in said
flow line to establish a regulated gas pressure in said line, an
on/off valve in said line downstream of said pressure regulator to
start and stop said flow mode during which said gas is delivered
for a delivery period of time, a reference capacity in said flow
line upstream of said pressure regulator for use in measuring the
actual flow rate of gas being delivered by said flow control
system, a pressure sensor to measure a pressure drop of said gas in
said reference capacity during a measurement period of time
commencing after the start of a delivery period of time, means in
said line upstream of said reference capacity for interrupting the
flow of gas from said source of pressurized gas to said reference
capacity during delivery of said gas by said flow control system,
and p1 a controller for determining from said measured pressure
drop and the rate of pressure drop in said reference capacity
during said measurement period, the actual flow rate of a batch of
process gas being delivered and, in case said actual flow rate does
not agree with a specified flow rate for said delivering, adjusting
said controlled flow rate in the direction of said specified flow
rate from said actual flow rate for a subsequent delivery period of
time in which another batch of process gas is delivered.
19. The flow control system according to claim 18, further
comprising a mass flow control valve in said line downstream of
said pressure regulator, said controller adjusting a set point
value of said mass flow control valve for adjusting said controlled
flow rate.
20. The flow control system according to claim 19, wherein said
mass flow control valve has a range of possible controlled flow
rate settings which extends to 100% of its full scale with an
effective rangeability of 10:1.
21. The flow control system according to claim 19, wherein said
controller includes a reference memory storing a mathematical
relationship between the actual flow rate and the flow rate setting
of said mass flow control valve for reference in determining the
size of said adjusting of said controlled flow rate.
22. The flow control system according to claim 18, further
comprising a gas manifold in the form of an elongated delivery
stick having a width less than 1.5 inches, components of said flow
control system being arranged along said gas manifold.
23. The flow control system according to claim 18, further
comprising a fixed orifice in said flow line downstream of said
pressure regulator, said pressure regulator having an adjustable
pressure setting for adjusting said controlled flow rate.
24. The flow control system according to claim 23, wherein said
pressure regulator is a dome loaded pressure regulator whose
pressure setting is established by a fluid pressure applied to the
dome of the pressure regulator, and wherein said controller at the
end of a delivery period of time removing the pressure signal
applied to the dome of the pressure regulator to prevent pressure
creep at the outlet of the pressure regulator in the no-flow mode
of said system.
25. The flow control system according to claim 18, wherein said
pressure regulator has an inlet coupled in fluid communication with
said source of pressurized gas, an outlet, a valve element which is
actuable to close said regulator to the flow of gas and,
alternately, to throttle the flow of said gas through said
regulator, said valve element being actuated by a diaphragm coupled
in force transmitting communication therewith and disposed in fluid
communication with said gas to be responsive to a fluid pressure
force thereof, and said regulator further including an adjustable
main pressure setting assembly for applying a select pressure
setting force on said diaphragm such that the flow of gas from the
regulator is regulated at an outlet pressure which is less than a
desired outlet pressure for delivering said gas at said controlled
flow rate, and a differential pressure setting assembly actuable to
apply a differential force on said diaphragm independent of said
pressure setting force such that together said forces provide a
regulated outlet pressure of said gas which is about said desired
outlet pressure, and wherein said controller operates said
differential pressure setting assembly at about the start of said
delivery period of time to apply said differential force during
said delivery period of time, and terminates the application of
said differential force on said diaphragm at about the end of said
delivery period of time.
26. The flow control system according to claim 18, wherein said
means for interrupting is an on/off valve.
27. An apparatus for semiconductor manufacturing requiring the
delivery of a process gas batchwise at a controlled flow rate
during said manufacturing, said apparatus comprising, in
combination, a source of pressurized process gas, a semiconductor
manufacturing apparatus, and a flow control system operable in a
flow mode for delivery of a batch of process gas from said source
of pressurized process gas to said semiconductor manufacturing
apparatus and, alternately, in a no-flow mode, said flow control
system comprising: a flow line through which process gas from said
source of pressurized process gas can be delivered, a pressure
regulator in said flow line to establish a regulated process gas
pressure in said line, an on/off valve in said line downstream of
said pressure regulator to start and stop said flow mode during
which said gas is delivered for a delivery period of time, a
reference capacity in said flow line upstream of said pressure
regulator for use in measuring the actual flow rate of gas being
delivered by said flow control system, a pressure sensor to measure
a pressure drop of said gas in said reference capacity during a
measurement period of time commencing after the start of a delivery
period of time, means in said line for interrupting the flow of
process gas from said source of pressurized process gas to said
reference capacity during delivery of said process gas by said flow
control system, and a controller for determining from said measured
pressure drop the rate of pressure drop in said reference capacity
during said measurement period of time the actual flow rate of a
batch of process gas being delivered and, in case said actual flow
rate does not agree with a specified flow rate for said delivering,
adjusting said controlled flow rate in the direction of said
specified flow rate from said actual flow rate for a subsequent
delivery period of time in which another batch of process gas is
delivered.
Description
RELATED APPLICATION
[0001] Reference is made to commonly owned Provisional Application
Ser. No. 60/133,295, filed May 10, 1999, for "Fluid Pressure
Regulator with Differential Pressure Setting Control", the
disclosure of which is incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a flow control system and
method for controlling the batchwise delivery of process gas to a
semiconductor manufacturing tool. Functional components of the
system are assembled on a gas manifold in the form of a narrow
delivery "stick".
BACKGROUND
[0003] The semiconductor manufacturing process includes a phase in
which the process gas is delivered to the tool according to a
program that specifies a flow for a period of time. The flow rate
is established by a mass flow controller, which is supplied with
process gas at a regulated pressure. The output of the mass flow
controller is delivered to the manufacturing tool through a
pneumatically operated on/off shut-off valve. The delivery is
started by actuating the shut-off valve to open and energizing the
mass flow controller to deliver a flow at a preset value. The
delivery is stopped by actuating the shut-off valve to close and
de-energizing the set point of the mass flow controller.
[0004] An important consideration is the accuracy with which the
flow is delivered during the process phase. To that effect, it is
recommended to set the mass flow controller at a value between 40
and 100% of its full scale. In other words, a given mass flow
controller has a rangeability of 2.5 to 1. Also, the mass flow
controller must be calibrated for the specific gas to which it is
applied. This means that in order to cover a range of flows from 5
to 1000 standard cubic centimeters per minute (sccm), as many as
six mass flow controllers for any given gas may be required. The
accuracy consideration also requires that the mass flow controller
retain its calibration for some period of time, preferably as long
as possible.
[0005] A dynamic gas flow controller is disclosed in U.S. Pat. No.
5,865,205 to Wilmer, for controlling the delivery of a gas from a
reservoir to a semiconductor process chamber. The method and
apparatus disclosed therein involve determining an initial mass of
the gas residing within the reservoir prior to a delivery operation
and the final mass of gas residing in the reservoir when the flow
of gas to the process chamber is terminated. The initial mass and
final mass of gas values are compared to determine the actual mass
of gas released from the reservoir during the recipe step. This
value serves as an input to a calibration servo loop to update the
system calibration constant for a subsequent gas delivery recipe
step. The execution of the calibration servo loop serves as a
continuous self calibration of a dynamic servo loop, wherein the
flow of gas to the process chamber is metered by a variable flow
valve upstream of an orifice. The gas pressure created ahead of the
orifice during delivery is sensed to measure the gas flow rate.
[0006] In the patent to Wilmer, the concept of flow control applies
to a gas flowing out of a reservoir instead of a gas flowing in a
line. The control signal which operates the variable flow valve is
determined by a circuit in which an input signal (representing the
desired flow) is integrated over the duration of the delivery step
to define the desired volume/mass. The desired volume is compared
to the actual volume taken out of the reservoir. A control signal
is generated as a function of that comparison and applied as a set
point to the control circuit. In the dynamic control circuit, the
set point is compared to the pressure signal sensing the flow and a
control signal is applied to the variable flow valve to create the
desired pressure/flow. That is, in Wilmer, the flow signal is
integrated over time and compared to the actual volume. The control
signal is applied to the flow control, which consists of the
variable flow valve creating a pressure ahead of the orifice.
[0007] The patent to Kennedy, U.S. Pat. No. 4,285,245, discloses a
method and apparatus for measuring and controlling volumetric flow
rate of gases in a line. The patent is of interest for its
disclosure of a method of determining the flow rate of gas flowing
in a line by imposing a uniform flow rate at a point downstream of
a flow measurement chamber in the line, restricting temporarily the
flow at a point upstream of the chamber and measuring the pressure
decrease in the chamber between the upstream and the downstream
points during part of the duration of the restricted flow, the rate
of the pressure decrease being substantially proportional to the
volumetric flow rate. The patent to Kennedy does not relate to the
batchwise delivery of process gas for semiconductor manufacturing
or a flow control system therefor operable in a flow mode for the
accurate delivery of a batch of process gas and, alternately, in a
no-flow mode.
[0008] There is a need for an improved method and flow control
system for controlling the batchwise delivery of process gas for
semiconductor manufacturing, which can complement a conventional
delivery stick by the addition of only a few components, and which
will allow verification of the accuracy of the flow delivered in an
active phase. There is also a need for an improved method and flow
control system for controlling the batchwise delivery of process
gas for semiconductor manufacturing which increase the effective
range of the mass flow controller, ensure long-term stability of
the calibration and eliminate the need to pre-calibrate for
specific gases.
SUMMARY
[0009] The method of the invention for controlling the batchwise
delivery of process gas for semiconductor manufacturing using a
flow control system of the invention operable in a flow mode for
delivery of a batch of process gas and, alternately, in a no-flow
mode, comprises delivering a batch of process gas from a source of
pressurized process gas through a flow line of the flow control
system to a semiconductor manufacturing apparatus at a controlled
flow rate for a delivery period of time. The line of the flow
control system includes a pressure regulator for establishing a
regulated pressure of the process gas in the line, an on/off valve
downstream of the pressure regulator to start and stop the flow
mode during which the process gas is delivered to the apparatus for
the delivery period of time and, upstream in the line from the
pressure regulator, a reference capacity used to measure the actual
flow rate of the delivery.
[0010] The method further comprises, after the start of the
delivering of the batch of process gas, measuring for a measurement
period of time the pressure drop of the process gas in the
reference capacity while interrupting the flow of process gas
through the line to the referenced capacity and continuing to
deliver process gas from the line of the flow control system to the
semiconductor manufacturing apparatus at the controlled flow rate.
The rate of pressure drop in the reference capacity during the
measurement period and the actual flow rate of the batch of process
gas being delivered are determined from the measuring. In case the
actual flow rate does not agree with a specified flow rate for the
delivering, the controlled flow rate is adjusted in the direction
of the specified flow rate from the actual flow rate for a
subsequent delivery period of time in which another batch of
process gas is delivered.
[0011] A flow control system according to the invention is for use
within a fluid circuit having a source of pressurized gas to be
delivered batchwise at a controlled flow rate to a destination by
the flow control system. The flow control system is operable in a
flow mode for delivering a batch of gas and, alternately, in a
no-flow mode. The flow control system comprises a flow line through
which gas from the source of pressurized gas can be delivered, a
pressure regulator in the flow line to establish a regulated gas
pressure in the line, an on/off valve in the line downstream of the
pressure regulator to start and stop the flow mode during which the
gas is delivered for a delivery period of time, a reference
capacity in the flow line upstream of the pressure regulator for
use in measuring the actual flow rate of gas being delivered by the
flow control system, a pressure sensor to measure a pressure drop
of the gas in the reference capacity during a measurement period of
time commencing after the start of a delivery period of time, means
in the line upstream of the reference capacity for interrupting the
flow of the gas from the source of pressurized gas to the reference
capacity during delivery of the gas by the flow control system, and
a controller for determining from the measured pressure drop the
rate of pressure drop in the reference capacity during the
measurement period the actual flow rate of a batch of process gas
being delivered and, in case the actual flow rate does not agree
with a specified flow rate for the delivering, adjusting the
controlled flow rate in the direction of the specified flow rate
from the actual flow rate for a subsequent delivery period of time
in which another batch of process gas is delivered.
[0012] In one embodiment of the invention, the flow control
arrangement of the system comprises a mass flow control valve in
the line downstream of the pressure regulator. The controller of
the system adjusts a set point value of the mass flow control valve
for adjusting the controlled flow rate. Advantageously, the mass
flow control valve has a range of possible controlled flow rate
settings which extends to 100% of its full scale with an effective
rangeability of 10:1.
[0013] According to another form of the invention, the flow control
arrangement of the system comprises a fixed orifice in the flow
line downstream of the pressure regulator. The pressure regulator
has an adjustable pressure setting for adjusting the controlled
flow rate.
[0014] The flow control system of the invention uses functional
components compatible with a 1 1/8 inch width manifold. The
assembly features surface mounting on a modular base. A significant
benefit is to reduce the length of the delivery stick and to make
it possible to place the parallel manifolds side-by-side at a
distance of 1.2 inches between center lines instead of the current
1.6 inches. In the flow control system employing a mass flow
control valve, increasing the effective rangeability of the
controller from 2.5 to 1 up to 10 to 1, makes it possible to cover
flows from 5 to 1000 sccm with only three ranges: 1000, 200 and 50
sccm. The long term stability of calibration is also ensured
through automatic calibration during each active phase and the need
to calibrate for each specific gas is eliminated.
[0015] These and other features and advantages of the present
invention will become more apparent from the following detailed
description of several embodiments of the present invention taken
with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1A is a schematic illustration of a flow control system
for batchwise delivery of process gas in semiconductor
manufacturing according to one embodiment of the invention.
[0017] FIG. 1B is an enlarged schematic drawing of a portion of the
flow control system of FIG. 1A along a narrow elongated manifold or
delivery "stick" of the system having components of the system
mounted thereon.
[0018] FIG. 2A is a schematic illustration of a flow control system
for batchwise delivery of a process gas in semiconductor
manufacturing according to a second embodiment of the
invention.
[0019] FIG. 2B is an enlarged, schematic drawing of a portion of
the flow control system of FIG. 1B along a narrow, elongated
manifold or delivery stick supporting components of the system.
[0020] FIG. 3 illustrates a flow chart of one embodiment of the
invention.
[0021] FIG. 4 is a cross-sectional view of a diaphragm-type
pressure regulator which can be used in the flow control system of
the invention, the regulator including a manually adjustable main
pressure setting assembly, and a pneumatically controllable
differential pressure setting assembly which is actuable to apply a
differential force on the regulator diaphragm independent of the
main pressure setting force.
[0022] FIG. 5 is a magnified view of the regulator of FIG. 4
showing the manual main pressure setting adjustment thereof in
enforced detailed.
[0023] FIG. 6 is a representative pressure response of a the
regulator of FIGS. 4 and 5 with a controlled differential pressure
setting, the response being shown as the regulator outlet pressure
traced as a cyclic function of time and as compared to the response
of a regulator which is conventionally operated at a constant
pressure.
[0024] FIGS. 7A and 7B are front and back views, respectively, of
the controller of the flow control systems of FIGS. 1A and 1B and
FIGS. 2A and 2B.
[0025] FIG. 8 is an electrical-pneumatic diagram of the flow
control system of FIGS. 1A and 1B.
[0026] FIG. 9 is an electrical-pneumatic diagram of the flow
control system of FIGS. 2A and 2B.
DETAILED DESCRIPTION
[0027] The semiconductor industry utilizes the batchwise delivery
of process gases in the manufacture of integrated circuit (IC)
chips or dies. In the general mass production of semiconductor
devices, hundreds of identical "integrated" circuit (IC) trace
patterns are photolithographically imaged over several layers on a
single semiconductor wafer which, in turn, is cut into hundreds of
identical dies or chips. Within each of the die layers, the circuit
traces are deposited from a metallizing process gas such as
tungsten hexafluoride (WF.sub.6), and are isolated from the next
layer by an insulating material deposited from another process gas.
The process gases typically are delivered in discrete flow cycles
or "batches" from pressurized supplies, thereby requiring delivery
systems of a type which may be operated in alternate flow and
no-flow modes.
[0028] An improved flow control system 10 according to the
invention for this purpose is shown in the schematic of FIG. 1.
Referring to FIG. 1, the system 10 may be seen to comprise a flow
line 1 through which gas from a pressurized process gas supply 12
can be delivered batchwise to a semiconductor manufacturing tool 2.
The system 10 is operable in a flow mode for delivering a batch of
gas and, alternately, in a no-flow mode, by means of controller 3,
for example, a suitably programmed computer.
[0029] The flow control system 10 further comprises a pressure
regulator 16 in the flow line 1 to establish a regulated gas
pressure in the line. An on/off valve 24 in the line 1 downstream
of the pressure regulator 16 is actuated by the controller 3 to
start and stop the flow mode during which the gas is delivered for
a delivery period of time. The valve 24 is a pneumatically operated
valve in the disclosed embodiment, see the schematic
pneumatic-electrical diagram of FIG. 8.
[0030] A reference capacity 5 is provided in the flow line 1
upstream of the pressure regulator 16 for use in measuring the
actual flow rate of gas being delivered by the flow control system
as discussed below. A pressure sensor 6 in the form of a pressure
transducer is located in the line 1 adjacent the reference capacity
5 to measure a pressure drop of the gas in the reference capacity
during a measurement period of time commencing after the start of a
delivery period of time.
[0031] The reference capacity 5 incorporates a temperature sensing
element to measure the temperature of the gas inside the capacity.
The temperature value is used by the controller, in conjunction
with the rate of pressure decrease, to determine the actual flow
expressed for standard conditions [14.7 psia and 20.degree. C.
(293.degree. K. )]. The flow for standard conditions is: 1 Qsccm @
20 .degree. C . = V 14.7 .times. P t .times. 293 T
[0032] V is the volume of the capacity in cc 2 P t
[0033] is the rate of pressure change in psi/min
[0034] T is the temperature in .degree.K.
[0035] A means 14, a pneumatically operated valve in the
illustrated embodiment, in the line 1 upstream of the reference
capacity 5 can be set in an off position by the controller 3 for
interrupting the flow of process gas from the source 12 to the
reference capacity 5 during delivery of the gas to the tool 2 by
the flow control system.
[0036] According to the method of controlling the batchwise
delivery of process gas for semiconductor manufacturing using the
flow control system 10 of the invention, a batch of process gas is
delivered from a source of pressurized process gas through the flow
line 1 of the flow control system 10 to the semiconductor
manufacturing apparatus 2 at a controlled flow rate for a delivery
period of time. After the start of the delivering of the batch of
process gas, the pressure drop of the process gas in the reference
capacity is measured for a measurement period of time while
interrupting the flow of process gas through the line to the
reference capacity with the valve 14 and continuing to deliver
process gas from the line of the flow control system to the
semiconductor manufacturing apparatus 2 at the controlled flow
rate.
[0037] From the measured pressure drop of the process gas in the
reference capacity for the measurement period of time, the rate of
pressure drop in the reference capacity and, in turn, the actual
flow rate of the batch of process gas being delivered, are
determined. In case the actual flow rate does not agree with a
specified, desired flow rate for the delivering, the controlled
flow rate of delivery by the system is adjusted in the direction of
the specified flow rate from the actual flow rate for a subsequent
delivery period of time in which another batch of process gas is
delivered. In the disclosed embodiment of FIGS. 1A and 1B, this
determining and adjusting is performed by controller 3, a
programmed computer. The controller 3 adjusts a set point value of
the mass flow control valve 22 by a signal sent by the controller
for adjusting the controlled flow rate for a subsequent delivery
period of time in which another batch of process gas is delivered.
For this purpose, the controller 3 includes a reference memory 28
storing a mathematical relationship between the actual flow rate
and the flow rate setting of the mass flow control valve for
reference in determining the size of the adjusting of the
controlled flow rate so that the difference between the two values
is reduced to zero in the subsequent delivery period of time.
[0038] The flow control system 10 further comprises a gas manifold
7 in the form of an elongated delivery stick having a width less
than 1.5 inches. Components of the flow control system are arranged
along the gas manifold in communication with the flow line 1 which
extends through the manifold and to each of the components mounted
on the upper surface of the manifold. Thus, the gas manifold 7
serves as a mounting base for these components. The mounting base
has a width of 1.125 inches in the disclosed embodiment. This
allows placing a plurality of the flow control systems side-by-side
at a distance of 1.20 inches between the parallel center lines,
thus saving important space in a group that may comprise up to 20
units. The pneumatically operated valve 8 can be selectively opened
to allow a purge gas to be passed through the flow line of the flow
control system.
[0039] The flow control system to be used in conjunction with a
conventional mass flow control valve 22, offers a significant
improvement by increasing the effective rangeability of the mass
flow control valve from 2.5 to 1 up to 10 to 1, making it possible
to cover flows from 5 to 1000 sccm with only three ranges: 1000,
200 and 50 sccm. The flow control system also eliminates the need
to calibrate the system for each specific gas and ensures the long
term stability of the calibration through automatic recalibration
during each delivery phase for the next phase.
[0040] The method of controlling the batchwise delivery of process
gas for semiconductor manufacturing using the flow control system
involves setting the desired flow value as a percent of full scale
by setting the desired flow setting of the flow controller 3 for
making delivery of process gas. The actual flow during the delivery
phase is measured and the command to the mass flow control valve is
adjusted so that the actual flow is kept equal to the set point
value in the following delivery phase(s). This operation may be
repeated at each delivery phase or after a desired number of
delivery phases. The actual flow rate determined by measuring the
pressure change in the reference capacity 5 is expressed in
standard units and applies essentially to any gas. The actual value
is compared to the desired set point value. If there is any
difference between the two values, the flow control system modifies
the command signal sent to the mass flow control valve 22 so that
the difference (error signal) is reduced to zero.
[0041] A digital display 40 in FIGS. 7A and 8, on the controller
allows the operator to read, alternately, by switching switch 41,
the set point flow value and the actual flow value. The set point
value may be adjusted by actuating up and down pushbuttons 42 and
43. A second switch 44 allows to start and stop delivery of the
process gas. Typically, the pressure regulator 16 is set to supply
the mass flow control valve 22 at a regulated pressure of 10-15
psi. The small reference capacity 5 used to measure the actual flow
is mounted directly upstream of the pressure regulator. The
pressure transducer 6 measures the pressure in the capacity. The
pneumatically operated on/off valve 14 is mounted upstream of the
capacity. When the valve 14 is open, it supplies the capacity with
process gas from the supply line at a typical pressure of 40-50
psi. It is not required to regulate precisely the supply pressure
to the system 10. It can be anywhere between 45 and 60 psi, for
example.
[0042] Prior to the start of a delivery phase, the supply on/off
valve 14 is opened and the reference capacity 5 is filled at the
supply pressure. The pressure regulator 16 maintains a constant
pressure at the inlet of the mass flow control valve 22. At the
start of a given delivery operation, which lasts typically from
20-40 seconds, the on/off valve 24 downstream of the mass flow
control valve 22 is actuated to open and the mass flow control
valve is energized to deliver flow at the set point value. The
measurement period begins after the start of the delivery, e.g., 1
second after the start of the delivery. With continued delivery of
the process gas, the pressure in the reference capacity 5 decreases
progressively. The measurement period continues for a maximum
duration of 20 seconds or is terminated when the pressure in the
measurement capacity reaches a predetermined value such as 20 psi.
At the end of the measurement period, the flow indication displayed
at display 40 on the controller 3 is updated to agree with the
measured exact value and, if necessary, any correction factor is
determined to be applied to the next delivery phase. The change in
pressure at the inlet of the pressure regulator, which occurs at
the end of the measurement period, does not affect the regulated
outlet pressure, which is typically set at 10-15 psi as noted
above. Thus, the pressure in the reference capacity 5 is allowed to
go from a nominal value of 50 psi down to a limited value of 20
psi. The measurement period will be limited to the maximum of 20
seconds at lower flow values. At higher flow values, the 20 psi
limit may occur before the 20 second limit.
[0043] At the beginning of the delivery phase, the flow indicator
40 on the controller will display the flow value of the previous
delivery. Then it will change to an indication of the current flow
when the measurement period is completed. As the measurement period
is terminated, the on/off valve 14 at the supply side is actuated
to open and the pressure in the reference capacity 5 returns to the
supply level. This does not affect the regulated pressure applied
to the inlet of the mass flow control valve.
[0044] The flow control system 10' in the embodiment of FIGS. 2A
and 2B eliminates the need of the mass flow control valve 22 and
its attendant shut-off valve. The flow control is provided by a
pressure regulator 16' and an orifice 36 incorporated in the seat
of on/off valve 20. For a given orifice, the flow is proportional
to the absolute pressure applied to it by the pressure regulator
16'. In this application, the set point of the pressure regulator
is established by a pressure signal applied to the dome of the
pressure regulator. The pressure signal is created by an
electric/pneumatic convertor 38, see FIGS. 2A and 9, which
generates a pressure proportional to the input voltage from the
controller (analogous to the signal applied to the mass flow
control valve). Any difference (error signal) between the set point
and the measured flow is used to correct the pressure signal
applied to the dome of the pressure regulator as in the operation
of the flow control system of FIGS. 1A and 1B. At the end of the
delivery phase, the on/off valve 20 downstream of the orifice 36 is
actuated to close and the pressure signal is removed from the dome
of the pressure regulator 16'. This keeps the pressure upstream of
the orifice 36 at the set point value and prevents the creep that
would normally occur at the outlet of the pressure regulator in a
no-flow condition. The given orifice may be used to deliver flow
with a rangeability of 10:1, making it possible to cover flows from
5-1000 sccm with only three orifice sizes corresponding to 1000,
200 and 50 sccm.
[0045] The operating sequence of a program for a flow control
system according to the invention, particularly the flow control
system of FIGS. 1A and 1B, is shown in the flow chart of FIG. 3.
With reference to a functional demonstration of the control system,
it is noted that the mass flow control valve 22 of the system in
the disclosed embodiment has a range of 200 sccm. The pressure
regulator is set at a nominal 10 psi (25 psia). The nominal volume
of the reference capacity is 20 cc. The pressure transducer 6 has a
range of 0-100 psia. The supply to the reference capacity 5 is at a
nominal value of 50 psi (65 psia). It does not have to be very
precise (.+-.2 psi) as indicated above.
[0046] A first operation as referred to in FIG. 3 is to establish
the calibration factor for the flow control system at mass flow
control valve setting of 100%. To accomplish this, the flow check
switch 45 on the controller is set to "yes" and a delivery run of
process gas is made with the setting of the controller 3 at 100%
and the actual flow being delivered is read with a calibrated flow
meter. This establishes the relationship between the flow indicated
by the digital display 40 (in %) on the controller 3 and the actual
flow. The calibration factor is then created in the controller
which makes 100% indication correspond to the desired full scale of
200 sccm. Example: the calibration run delivers 220 sccm and the
flow indication is 120%. The calibration factor to obtain 100% and
200 sccm will be 100/120.times.200/220=0.75. With the controller
switch 44 at "stop" and the display switch 41 at "setting" so as to
display the calibration factor on digital display 40, the new
factor is set by using the up and down buttons 42 and 43 on the
controller 3. Another delivery run is then made to verify that the
flow is 200 sccm and the indication is 100%. The procedure can be
repeated if necessary.
[0047] The next step in the process is to establish a mathematical
relationship between the actual flow and flow setting over the
range of the mass flow control valve flow settings. This is
obtained by making a delivery run at 100% setting, followed by a
delivery run at 10% setting and determining the actual flow
(measured by the controller) in each run. That transfer function is
established within the controller where it is used to calculate the
control signal to be sent to mass flow control valve so that the
flow remains equal to the setting. The following sequence creates
the calibration runs: set the display switch 41 to "setting" and
the flow operation switch 44 to "stop"; push the two buttons 42 and
43 and hold until the calibration factor is displayed; and then set
display switch 41 to "flow". This initiates the two successive
delivery runs.
[0048] The next step is to set a desired flow setting of the flow
controller 22 for making a delivery of process gas, for example,
80%. This is done by adjusting with the up and down push buttons 42
and 43 on the controller 3 while the display switch 41 is set to
"setting". The flow check switch 45 on the controller is set to
"yes". Delivery is started by switching flow switch 44 to "start".
The display switch 41 is set to "flow" and the indication of flow
is watched on digital display 40 during the delivery. At the end of
the measurement period, the flow indication on the display will be
updated. The start of the updated value will be flashed briefly
(1-2 seconds). The delivery is stopped by switching flow switch 44
to "stop". In the case the flow check switch 45 on the controller 3
were set to "no", the flow indication on the display 40 would
remain unchanged for the length of the delivery. This mode of
operation may be selected if it is felt that the flow controller 3
needs calibration verification only periodically.
[0049] The setting is then changed to 50%, the flow check is set to
"yes" and another delivery is started and the flow indication on
the display is watched. Initially, the flow indication will be
close to 50%. At the end of the measurement period, the actual flow
value will be shown. If it is not 50%, a correction will be
calculated, to be applied to the next delivery. It may take two or
three runs to establish the flow value at 50.+-.0.1%. The setting
can then be changed to 20% and the procedure repeated. Likewise,
the setting is changed to 10% and the procedure repeated.
[0050] A functional demonstration of the flow control 10' of the
embodiment of FIGS. 2A and 2B involved the use of an on/off valve
20 which incorporated an orifice 36 having a diameter of 0.004 inch
in its seat. This provides a flow of 10 to 150 sccm as the
regulated pressure is controlled from 2.5 to 25 psia. To establish
a calibration factor, the aforementioned procedure is used to
obtain an operating condition of 150 sccm at 100% indication. Next
a calibration run is made to establish the transfer function or
mathematical relationship. Practice delivery runs can then be made
at 80, 50, 20 and 10% as in the previous functional
demonstration.
[0051] In both functional demonstrations, the flow control system
10.sup.1 is used to provide a flow setting, read the actual value
of the flow delivered, start and stop a delivery phase and select
flow verification at each delivery or periodically, as desired. In
the ultimate configuration, the functions displayed and
incorporated within the flow control system are implemented in the
central computer of the machine as will be understood by the
skilled artisan from a reading of applicant's disclosure.
[0052] According to a further feature of the present invention, the
conventional pressure regulators 16 and 16' of the embodiments of
FIGS. 1A, 1B and 2A, 2B can be replaced with the pressure regulator
50 shown in FIGS. 4 and 5 for mitigating the effect of pressure
creep and, when the flow control systems are operated in the
alternate flow and no-flow modes, allowing faster pressure response
and steady-state operation for improved process gas utilization or
other system economy. This pressure regulator is disclosed in
commonly owned Provisional Application Ser. No. 60/133,295, filed
May 10, 1999.
[0053] In basic construction, the regulator 50 includes a housing,
referenced at 52, which may comprise a generally annular, upper cap
portion, 54, and a lower body portion, 56. An associated nut, 58,
may be received over a flanged lower end, 60, of the cap 54 for a
threaded connection with an externally-threaded upper end, 62, of
body 56. Cap and body portions 54 and 56 thereby may be engaged to
define an internal chamber, 63, within housing 52. Upper and lower
support plates, 64 and 65, respectively, are clamped between the
cap and body portions 54 and 56 for supporting other regulator
components. Each of plates 64 and 65 are formed as having a central
opening, 66 and 67, respectively. Plate 65 further is formed as
having a plurality of axially-extending through bores or channels,
one of which is referenced at 68, and is made to compressively
engage a raised annular surface, 69, of body 56 to effect a back-up
seal against leakage of the gas or other fluid flowing through the
regulator 50.
[0054] Body portion 56 of housing 52 itself is formed as having an
internal fluid passageway, 70, which may be divided into generally
L-shaped upstream and downstream portions 71a and 71b, each
extending from an axial surface, 72, of body 56, to an upper radial
surface, 73, thereof. Fluid passageway 70 itself extends between an
inlet, 74, and an outlet, 75, of the regulator for the flow of
fluid therethrough in the direction referenced by arrows 76. Within
the fluid circuit in the control systems 10 and 10' of FIGS. 1A, 1B
and 2A, 2B, a high pressure flow of gas is supplied to regulator
inlet 74 from supply 127 and a regulated, lower pressure flow is
delivered to mass flow control valve 22 from regulator outlet 75.
In this regard, regulator inlet 74 may be coupled in fluid
communication with supply via valve 14, with outlet 75 being
coupled in fluid communication with mass flow control valve 22 via
valve 20. Each of inlet 74 and outlet 75 accordingly may be
configured, as is shown, as flanged tubing extensions, 76a-b,
respectively, which may be joined to body portion 56. For
connection within the fluid system 10, extension 76a is shown as
having an associated female fitting connector, 78, with extension
76b being shown as having an associated male connector, 80.
[0055] For controlling the flow of fluid through passageway 70,
chamber 63 houses a valving assembly including a poppet, 82, and an
associated valve seat, 84, defined within passageway 70 such as by
a disc which is supported over the upstream portion 71a of
passageway 70 and clamped between the central opening 67 of lower
support plate 56 and the opening of passageway portion 71a into the
upper radial surface 73 body portion 56. Valve seat 84, is oriented
relative to the flow direction 76 as having an upstream side, 86,
and a downstream side, 88, and includes an aperture, 90, for
admitting fluid pressure into a lower plenum, 92, of chamber 63,
which plenum is defined partially by lower support plate 65. Flow
out of plenum 92 and into the downstream portion 71b of passageway
70 is accommodated via plate channels 68. The disc for valve seat
disc 84 preferably is formed of a plastic or other polymeric
material, and most preferably of a fluoropolymer such as Kel-F.RTM.
(3M, St. Paul, Minn.).
[0056] Poppet 82 is movable along a central longitudinal axis, 94,
of the regulator 50 between a first position (shown in FIG. 4)
closing passageway 70 to fluid flow for the operation of fluid
system (FIG. 1A) in its no-flow mode, and a variable second
position throttling the fluid flow through passageway 70 for the
operation of system in its flow mode. For cooperation with valve
seat 84, poppet 82 is provided to extend along axis 94 from a lower
head portion, 96, disposed opposite the upstream side 86 of valve
seat 84, to an upper, elongate stem portion, 98, which, in turn,
extends through aperture 90 and lower plate opening 67 along axis
94 from a lower proximal end, 100, connected to head portion 96, to
an upper distal end, 102. Poppet head portion 96 is configured,
such as the general conic shape shown, to annularly vary the
relative size of aperture 90 and, accordingly, the flow rate
through the regulator, when moved toward or away from valve seat 84
in the variable second poppet position.
[0057] For controlling the movement of poppet 82 along axis 94, a
diaphragm, 110, is received within chamber 63 as disposed in fluid
communication with passageway 70 to define a flexible upper wall of
plenum 92, and as coupled in force transmitting contact with poppet
82. Diaphragm 110 is of a conventional single or multiple piece
construction, and includes a circumferentially extending, generally
flexible "membrane" portion 112. Membrane portion 112 extends
radially outwardly to an outer margin which defines the outer
periphery of the diaphragm 110, and which is clamped between the
upper and lower plates 64 and 65 for the mounting of diaphragm 110
within chamber 63. In a two-piece construction of diaphragm 110,
membrane portion 110 is welded, bonded or otherwise attached to a
backup portion, 114, which supports the membrane portion 112, and
which extends axially therefrom through the opening 66 of plate 64
in defining a cylindrical extension, 115, including an internal
central passage, 116, and an external shoulder, 118. Passage 116 is
configured to receive the distal end 102 of poppet stem 98, and may
be internally threaded for engagement with an externally threaded
portion, 120, of stem 98. So received in chamber 63, diaphragm 110
is provided to be responsive to a fluid pressure force, which is
proportional to the inlet pressure (P.sub.i) and outlet fluid
pressure (P.sub.o) of the fluid flow to regulator 50 and is applied
to the direction referenced at 122 to urge poppet 82 toward its
first position closing passageway 70 to fluid flow. Atmospheric
pressure (P.sub.a) is admitted in chamber 63 on the upper side of
diaphragm 110 via port 124 through cap 54.
[0058] A main pressure setting assembly, reference generally at
127, is actuable to applying a balancing force on diaphragm 110 in
the direction referenced at 128 for opposing the fluid pressure
force 122 and urging poppet 82 toward its second position opening
passageway 70 to fluid flow. Such force 128 is developed at least
in part by the adjustable compression of a main coil spring, shown
in phantom at 130, or other resilient member received within
chamber 63. In the illustrated embodiment of FIG. 4, spring 130 is
disposed coaxially with axis 94 for compression intermediate
diaphragm 110 and a manually-adjustable knob, 132, which is
translatable along axis 94. For a compact design of regulator 50,
knob 132 is externally-threaded as at 134, and is housed within cap
54 as threadably rotatably engaged with an internally threaded
portion, 136, thereof. As may be seen best with momentary reference
to the magnified frontal view of main pressure setting assembly 127
shown in FIG. 5, cap 54 is provided as having a window, 140 (also
shown in phantom in FIG. 4), through which a knurled portion, 142,
of knob 132 is provided to be hand accessible.
[0059] Returning to the cross-sectional view of FIG. 4, spring 130
may be seen to be received within chamber 63 as disposed
intermediate an upper retainer, 150, and a lower retainer, 152.
Upper spring retainer 150 is generally disc-shaped, and is disposed
in abutting, force-transmitting contact with a thrust portion, 154,
of knob 132. Lower spring retainer 152 is generally
cylindrically-shaped, and is received coaxially over diaphragm
back-up extension 115 as threadably engaged in force transmitting
contact with an externally threaded portion 156, thereof. Retainer
152 is fastened onto extension 115 with a nut, 160, which may have
an associated O-ring 162, over which the lower end of spring 130
may be friction fit for assisting the coaxial alignment of the
spring with axis 94. A compression ring, 164, or other spacer may
be received with retainer 152 over extension 115 for delimiting the
travel of the retainer over the extension.
[0060] For applying an additional force on diaphragm 110 in the
direction of arrow 122, a wave spring or other compressible member,
shown in phantom at 170, is received coaxially over retainer 152.
Spring 170 is supported on upper support plate 64 for compression
therebetween and a radially-outwardly extending flange portion,
172, of retainer 152. Such compression of spring 170 provides a
biasing force for further urging poppet 82 toward its first
position such that fluid passageway 70 is normally closed in the
absence of a pressure setting force 128. The movement of poppet 82
between its first and second positions may be damped with a
compressible foam washer, 174, which is received coaxially over
diaphragm extension 115 for compression intermediate retainer 152
and plate 64. The displacement of poppet 82 in its second position
by the application of pressure setting force 128 is delimited by
the abutting engagement of a lower stop surface, 176, of retainer
152 with plate 64.
[0061] Regulator 50 further includes a differential pressure
setting assembly, referenced generally at 180. In accordance with
the precepts of the present invention, differential pressure
setting assembly 180 is provided to be actuable independently of
the main pressure setting assembly 127 to apply a differential
force, such as via the compression of a second coil spring member,
181, on diaphragm 110 in the direction of arrow 128 further urging
poppet 82 toward the second position opening passageway 70 to fluid
flow. In the illustrated embodiment of FIG. 4, differential
pressure setting assembly 180 is actuable responsive to a pneumatic
on/off control signal of a given input pressure (P.sub.s) which,
preferably, may be between about 50-60 psig to be at the same level
which is conventionally employed in operating the pneumatic valves
14 and 24 of fluid system of FIG. 1. The signal to assembly 180, as
well as valves 14 and 24 of system 10, may be provided under the
common control of, for example, of a pneumatic 3-way valve (not
shown).
[0062] The pressure control signal may be admitted to regulator 50
via a tubing or other fitting connection, 182, having, for example,
a female end, 184, configured for a tubing or other connection to
the above mentioned 3-way valve or other control signal source, and
male end, 186, configured for a threaded connection with an
adapter, 190, of regulator housing 52. Adapter 190, in turn, has a
male end, 192, configured for a threaded connection with an
internally threaded upper end, 194, of cap 54, and a female end,
196, which, depending upon the sizing of fitting end 186, may be
coupled thereto via a bushing or other reducer, 198. The female end
196 of adapter 190 further is configured as having a recess which
extends to internal end wall, 200, that defines a second chamber,
202, within housing 52. The adapter male end 192 further is
configured as having an elongate guide portion, 204, which is
fitted within a generally cylindrical counter bore, 206, of knob
132 to assist in guiding the knob along axis 94.
[0063] For controlling the compression of second spring member 181,
a piston, 210, having an associated O-ring or other seal or packing
ring, 211,is received within chamber 202 as displaceable
intermediate lower end wall 200 and an upper end wall, 212, of
chamber 202. Upper end wall 212 is defined, such as by a
radially-inwardly extending internal shoulder portion of reducer
198, about a common opening, 214, of adapter 190 and reducer 198,
which opening 214 functions as a port for the admission of the
signal fluid pressure into chamber 202.
[0064] Piston 210 is operably coupled to spring 181 via an elongate
force transmitting member, 220. Such member 220 extends along axis
94, as received coaxially through a central bore, 222, formed
through each of adapter 190, knob 132, and spring retainer 150,
from an upper end, 224, disposed in abutting contact with piston
220, to a lower end, 226, disposed in abutting contact with spring
181. spring 181 itself is disposed coaxially within main pressure
setting spring 130 as mounted over diaphragm extension 115 for
compression between the shoulder portion 118 thereof, and an
inverted U-shaped retainer, 228, interposed between spring 181 and
the lower end 226 of elongate member 220.
[0065] Within chamber 202, piston 210 is actuable responsive to the
control pressure signal as admitted through opening 214 and applied
to an upper surface, 230, of the piston. That is, piston 210 is
displaceable along axis 94 from a normally-biased upper position to
the lower position shown in FIG. 4. For biasing piston in its upper
position, a compressible spring coil, 232, may be received within a
recess, 234, formed within a lower surface, 236, of the piston for
compression against adapter lower end wall 200. In its lower
position, piston 210 depresses elongate member 220 which, in turn,
effects the compression of spring 181 to apply a differential
force, which may be between about 3-4 psig, on a diaphragm 110. In
this way, a controlled application of the differential force may be
achieved independent of the application of the main pressure
setting force.
[0066] The force applied by spring 181 is "differential" in that it
may be applied as a step function to effect a proportionate change
in the regulator outlet pressure without changing the main pressure
setting. for example, with the main pressure setting assembly 127
of regulator 50 being adjusted within a range of between about 0-30
psi, differential pressure setting assembly 180 is actuable by the
control signal to increase the effective regulator setting by a
nominal 3 psi. If desired, the pressure of the control signal may
be adjusted to effect a generally proportional increase or decrease
in the differential force.
[0067] Considering the next operation of regulator 50 of the
invention as employed in the fluid circuit of the batchwise gas
delivery circuit of FIG. 1 (with regulator 50 of the invention
being substituted therein for regulator 16), reference may be had
additionally to FIG. 6 wherein a typically response of regulator 50
within such circuit is graphically portrayed at 250 as plot of
outlet pressure (P.sub.o) versus time (t). For a given inlet fluid
pressure, which may be between about 50-60 psi, and a specified
outlet pressure set point of about 15 psi, the system is operated
prior to time t.sub.o in a flow mode, In such mode, gas is
delivered through regulator 50 at a steady-state flow rate of, for
example, 200 sccm and a regulated outlet pressure of about 14.8
psi. Such pressure is effected under the control of the main
pressure setting of the regulator 50 which is adjusted to a nominal
pressure of 12 psi, and with signal pressure being supplied to the
regulator to apply a differential pressure which is normally 3 psi.
Both the main and the differential pressure settings may be set at
a lower flow rate of, for example, 50 sccm. In this regard, it may
be noted that the actual regulator outlet pressure at steady flow
is about 0.2 psi less than the set point due to the effect of
"droop" as the flow rate is increased from low flow to its
steady-state value.
[0068] At about time t.sub.o, corresponding to the termination of
the flow mode, the mass flow control valve 22 (FIG. 1) is commanded
"off". Shortly thereafter, i.e., 0.5 sec or less, pneumatic on/off
valve 24 is actuated to close such that fluid flow decreases from
the steady-state rate to zero. Generally simultaneously with the
actuation of valve 24, signal pressure is discontinued to regulator
50 to remove the differential pressure setting. In this regard, the
operation of valve 24 and regulator 50 advantageously may be
synchronized under the control of a common signal pressure.
[0069] With the differential pressure setting being removed, the
setting of regulator 50 effective is reduced to 12 psi. Inasmuch as
the outlet pressure remains at the operating pressure of 14.8 psi,
the regulator closes such that the outlet pressure is maintained
substantially at 14.8 psi. Depending upon the length of the no-flow
period and/or on the internal, typically about 0.5 sec, between
when the no-flow mode is initiated and when the control pressure
signal is removed to effect the closing of the regulator, the
outlet pressure may increase slightly, to perhaps 15 psi, over the
period .DELTA.t.sub.o. It will be appreciated, however, that by
virtue of the controlled differential pressure setting, no
appreciable creep effect is evident even when the system is
operated with very long internals, i.e., 1 hour or more, between
the flow modes. continuing then along trace 250, at time t.sub.1,
corresponding to the initiation of the next flow mode, the pressure
signal is resumed to open valve 24 and to re-apply the differential
force on the regulator. Shortly thereafter, the mass flow control
valve 22 is commanded to again control flow. In such operation,
flow may be increased from zero to a steady-state value before any
appreciable increase in the outlet pressure as a result of creep
induced from the effective change in the regulator setting from 12
psi to 15 psi. Thus, as the flow rate increase, the outlet pressure
decreases only about 0.2 psi to settle quickly at the operating
pressure within a very short period .DELTA.t.sub.1 of about 0.5
sec. or less. Importantly, as no overshoot or other oscillatory
effects are observed, the transition from zero to steady-state flow
is able to be established within 1 sec or less.
[0070] For purposes of comparison, the pressure trace of a
regulator conventionally operated at a constant pressure setting of
15 psi is shown at 250'. At time t.sub.o and continuing over the
period .DELTA.t.sub.o' which may be 100 sec or more, the outlet
pressure of trace 250' may be noticed to increase by about 2 psi
from the operating pressure. As compared to the 0.2 psi increase
for valve 50 of the invention, such increase is significant, as is
the period .DELTA.t.sub.1' which may be 1.5 sec or more with some
overshoot or other oscillatory effects being evident.
[0071] Thus, in the disclosed flow control system and method, this
unique and efficient fluid pressure regulator construction and
method of operation mitigate the effect of pressure creep and, when
the flow control systems are operated in alternate flow and no-flow
modes, allow faster pressure response and steady-state operation
for improved process gas utilization or other system economy.
[0072] Unless otherwise specified, materials of construction are to
be considered conventional for the uses involved. Such materials
generally will be corrosion resistant and otherwise selected for
compatibility with the fluid being transferred or for desired
mechanical properties.
[0073] As it is anticipated that certain changes may be made in the
present invention without departing from the precepts herein
involved, it is intended that all matter contained in the foregoing
description shall be interpreted in an illustrative rather in a
limiting sense.
* * * * *