U.S. patent application number 09/900829 was filed with the patent office on 2002-01-10 for fluid mass flow control valve and method of operation.
This patent application is currently assigned to FuGasity Corporation. Invention is credited to Mudd, Daniel T..
Application Number | 20020002996 09/900829 |
Document ID | / |
Family ID | 22809021 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020002996 |
Kind Code |
A1 |
Mudd, Daniel T. |
January 10, 2002 |
Fluid mass flow control valve and method of operation
Abstract
A fluid mass flow control apparatus, particularly adapted for
use in controlling fluid flow to semiconductor fabrication
processes, comprises a tubular body part having inlet and outlet
fittings and a bore extending therethrough and supporting a valve
seat in the bore. A closure member is connected to an arm which
extends laterally through a tubular spigot portion of the body
part. The body part has a reduced thickness wall at the spigot
portion to allow elastic deflection of the wall and movement of the
arm to control the position of the closure member. An elongated
tube or rod actuator on which a resistance heating coil is
supported is operably connected to a control system for heating the
actuator to move the arm to control flow of fluid through the
apparatus. A flow restrictor is mounted upstream of the valve seat
and a mass flow sensor is in communication with the passage to
provide a mass flow rate signal to the control system.
Inventors: |
Mudd, Daniel T.; (St.
Charles, MO) |
Correspondence
Address: |
RANDALL C BROWN
AKIN GUMP STRAUSS HAUER & FELD
P O BOX 688
DALLAS
TX
75313
|
Assignee: |
FuGasity Corporation
Sparks
NV
|
Family ID: |
22809021 |
Appl. No.: |
09/900829 |
Filed: |
July 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60216928 |
Jul 8, 2000 |
|
|
|
Current U.S.
Class: |
137/487.5 |
Current CPC
Class: |
Y10T 137/0324 20150401;
G05D 7/0635 20130101; G01F 1/6842 20130101; Y10T 137/87354
20150401; Y10T 137/0368 20150401; G01F 1/6847 20130101; Y10T
137/7761 20150401; G01F 5/00 20130101; Y10T 137/7759 20150401 |
Class at
Publication: |
137/487.5 |
International
Class: |
G01D 007/00 |
Claims
What is claimed is:
1. A fluid flow control apparatus comprising: a body part including
an inlet port, an outlet port and a flow passage extending
therethrough between said ports; a valve seat disposed in said flow
passage; a closure member operable to be engaged with said valve
seat; an arm engageable with said closure member and connected to
said body part in fluid-tight sealed relationship therewith; and an
actuator operably connected to said arm and operable to move said
arm to affect movement of said closure member to control flow of
fluid through said apparatus.
2. The apparatus set forth in claim 1 wherein: said body part
comprises a generally cylindrical tube having a reduced thickness
wall portion adjacent a point of connection of said arm to said
body part and elastically deflectable in response to operation of
said actuator to allow said arm to move said closure member.
3. The apparatus set forth in claim 2 wherein: said arm projects
through a bore formed by a spigot portion of said body part
adjacent said reduced thickness wall portion.
4. The apparatus set forth in claim 3 wherein: said arm is secured
to said spigot portion by one of welding and brazing.
5. The apparatus set forth in claim 1 wherein: said actuator
comprises a thermal type actuator.
6. The apparatus set forth in claim 5 wherein: said actuator
comprises an elongated member formed of a material responsive to
temperature change to elongate and contract.
7. The apparatus set forth in claim 6 wherein: said actuator
includes a heating element in operable engagement with said
elongated member to affect a change in temperature of said
elongated member to move said arm to change the position of said
closure member.
8. The apparatus set forth in claim 6 wherein: said elongated
member comprises one of a rod and tube extending generally parallel
to a longitudinal axis of said body part, said elongated member is
fixed at one end with respect to said body part and is connected at
another end to said arm.
9. The apparatus set forth in claim 1 including: a flow restrictor
interposed said closure member and said inlet port.
10. The apparatus set forth in claim 1 including: a fluid mass flow
sensor in fluid flow communication with said flow passage for
sensing mass flow of fluid through said apparatus.
11. The apparatus set forth in claim 1 including: a control system
operably connected to said actuator for effecting movement of said
closure member to control the flow of fluid through said
apparatus.
12. The apparatus set forth in claim 11 including: a fluid shut off
valve operably connected to said control system and in fluid flow
communication with said apparatus and operable to shut off flow of
fluid through said apparatus.
13. The apparatus set forth in claim 1 wherein: said arm includes a
portion thereof forming a recess for engagement with said closure
member and said closure member comprises a spherical ball
disposable in said recess and engageable with said valve seat.
14. The apparatus set forth in claim 1 wherein: said arm includes a
planar surface formed thereon and said closure member includes a
cooperating planar surface engageable with said planar surface on
said arm and moveable relative to said arm to align said closure
member with said valve seat.
15. The apparatus set forth in claim 14 wherein: said planar
surface on said arm is formed by a recess on said arm for receiving
at least a portion of said closure member.
16. A fluid mass flow control apparatus comprising: a body part
including an inlet port, an outlet port, a flow passage extending
therethrough between said ports, said body part being formed of a
tube having an elastically deflectable wall portion; a valve seat
in said flow passage; a closure member operable to be engaged with
said valve seat; an arm engageable with said closure member and
connected to said body part in fluid-tight sealed relationship
therewith, said arm projecting through a bore formed by a portion
of said body part adjacent said wall portion; and an actuator
operably engaged with said arm for moving said arm to control
movement of said closure member with respect to said valve
seat.
17. The apparatus set forth in claim 16 wherein: said actuator
comprises an elongated member formed of a material responsive to
temperature change to elongate and contract; and said apparatus
includes a heating element in operable engagement with said
elongated member to affect a change in temperature of said
elongated member to move said arm to change the position of said
closure member.
18. The apparatus set forth in claim 17 wherein: said elongated
member comprises one of a rod and tube extending generally parallel
to a longitudinal axis of said body part, said elongated member is
fixed at one end with respect to said body part and is connected at
another end to said arm.
19. The apparatus set forth in claim 16 wherein: said arm includes
a portion thereof forming a recess for engagement with said closure
member and said closure member comprises a spherical ball
disposable in said recess and engageable with said valve seat.
20. The apparatus set forth in claim 16 wherein: said arm includes
a planar surface formed thereon and said closure member includes a
cooperating planar surface engageable with said planar surface on
said arm and moveable relative to said arm to align said closure
member with said valve seat.
21. The apparatus set forth in claim 20 wherein: said planar
surface on said arm is formed by a recess on said arm for receiving
at least a portion of said closure member.
22. A method for controlling fluid mass flow to a process
comprising the steps of: providing a fluid mass flow control
apparatus including a control system, an actuator for a fluid mass
flow control valve, a sensor for sensing mass flow of fluid through
said apparatus, and a shutoff valve operably connected to said
apparatus for controlling flow of fluid thereto; closing said
shutoff valve; changing a set point command of said control system
from zero to a desired fluid mass flow rate through said apparatus
at a predetermined time sufficient to ensure that said actuator has
sufficient time to achieve a steady state position of said flow
control valve prior to the time when actual fluid mass flow is
desired at said process; causing said actuator to position said
flow control valve to effect control of fluid flow through said
apparatus in accordance with said desired fluid mass flow rate;
opening said shutoff valve and allowing fluid to flow to said
apparatus; and causing fluid to flow through said apparatus at a
rate which is nominally said desired fluid mass flow rate as
determined by prepositioning of said actuator.
23. The method set forth in claim 22 including the step of:
maintaining said fluid mass flow rate through said apparatus until
a predetermined time has passed for said sensor to accurately
measure fluid mass flow through said apparatus.
24. The method set forth in claim 22 including the steps of:
causing said control system to maintain a desired fluid flow rate
through said apparatus based on a signal received from said sensor;
and causing said shutoff valve to close when fluid flow at said
desired fluid flow rate is complete.
25. The method set forth in claim 22 including the step of: causing
said control system to record signals related to the condition of
said actuator which maintained said desired fluid flow rate during
said process.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This Application claims the priority of U.S. Provisional
Patent Application Serial No. 60/216,928 filed Jul. 8, 2000.
BACKGROUND OF THE INVENTION
[0002] Typical fluid mass flow control valves or so called mass
flow controllers of the type useful in the semiconductor
manufacturing industry are required to be relatively precise
instruments. Known types of fluid mass flow controllers are
typically constructed by machining the valve body from a solid
block of corrosion resistant dense metal. This type of fabrication
results in the significant removal of material to generate the flow
passages and mounting details for the valve seat and actuator and
seals required to isolate the valve components from the gas flow
stream. After the significant amount of machining required in prior
art fluid mass flow controllers, the machine finished parts are
required to be mechanically and electro polished to improve surface
finish and corrosion resistance.
[0003] Still further, certain known types of fluid mass flow
controllers utilize so called thermal actuators which are adapted
to effect movement of a valve closure member by flexing a
mechanical diaphragm connected to a branch tee or similar conduit
part of the valve body. However, this type of construction is
relatively expensive, complicated and produces uniform elastic
deflection of a link connected to the closure member in all
directions. Moreover, certain prior art types of fluid mass flow
controllers utilize a thermal actuator comprising a hollow tube
sealed at both ends and placed in the fluid flow stream. This
arrangement complicates the control function since the temperature
of the actuator tube is influenced by the flow of fluid (gas) which
it is controlling. These arrangements typically result in slow
response time required to reach a steady state flow for the
controller. Still further, with prior art fluid mass flow
controllers, the maximum displacement of the actuator is
significantly affected by the specific gas that is being controlled
by the controller. However, the present invention provides a fluid
mass flow control valve and method of operation which overcomes
several disadvantages of prior art fluid mass flow controllers.
BRIEF SUMMARY OF THE INVENTION
[0004] The present invention provides an improved fluid mass flow
control valve or so-called controller and method of operation. In
particular, the invention provides a fluid mass flow control valve
of a type useful in controlling fluid mass flow in applications in
the semiconductor processing industry.
[0005] In accordance with one important aspect of the present
invention a fluid mass flow control apparatus is provided which
utilizes a section of commercially available cylindrical tubing as
a valve body and which is subject to relatively minor machining
operations to provide a flexible wall portion of the valve body
creating a pivot point at which a valve actuator arm is attached
and is operable to move a valve closure member for controlling mass
flow through the apparatus. The flexible wall portion is configured
in such a way that elastic deflection is uniform in the desired
directions of movement of the valve actuator arm but the flexible
wall portion exhibits greater stiffness to resist deflection in
unwanted directions.
[0006] In accordance with another aspect of the present invention
and improved fluid mass flow control apparatus is provided which
comprises a unique actuator for moving a pivoting control arm
operably engaged with a closure member. The fluid mass flow control
apparatus utilizes relatively uncomplicated and inexpensive
components for construction of the valve body, provides simplified
fabrication required to construct the mass flow control apparatus
and is adaptable to utilize different types of actuators for moving
the actuator control arm. Although a thermal actuator is one
preferred type, other types of valve actuators may also be used.
Moreover, the actuator is not susceptible to heating or cooling
effects of the fluid flowing through the flow control
apparatus.
[0007] The fluid mass flow control apparatus of the invention also
improves the response time for changing the mass flow rate of fluid
being controlled by the apparatus. The present invention also
provides a method of operation of a fluid mass flow control
apparatus which provides more rapid and accurate responses to
required fluid mass flow changes.
[0008] Those skilled in the art will further appreciate the
advantages and superior features of the invention upon reading the
detailed description which follows in conjunction with the
drawing.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0009] FIG. 1 is a top plan view of an improved fluid mass flow
control apparatus in accordance with the invention;
[0010] FIG. 2 is a longitudinal central section view and schematic
diagram of the fluid mass flow control apparatus shown in FIG. 1
and taken generally along the line 2-2 of FIG. 1;
[0011] FIG. 3 is a section view taken generally along the line 3-3
of FIG. 2;
[0012] FIG. 4 is a detail view taken generally along the same line
as the view of FIG. 2 on a larger scale and showing details of the
controller closure member and actuator control arm;
[0013] FIG. 5 is a section view taken generally along the line 5-5
of FIG. 3; and
[0014] FIG. 6 is a detail section view of an alternate embodiment
of an actuator control arm and closure member.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] In the description which follows like elements are marked
throughout the specification and drawing with the same reference
numerals, respectively. The drawing figures are not necessarily to
scale and certain elements and features may be shown in generalized
or somewhat schematic form in the interest of clarity and
conciseness.
[0016] Referring to FIGS. 1 and 2, there is illustrated a fluid
mass flow control device or apparatus in accordance with the
invention and generally designated by the numeral 10. The apparatus
10 is characterized by an elongated cylindrical tubular body part
12 having a longitudinal central cylindrical bore 14, FIG. 2,
extending therethrough. Tubular body part 12 is, in one preferred
embodiment, secured to opposed externally threaded tubular coupling
members 16 and 18 at opposite ends of the body part by
circumferential gastight welds 20 and 22, FIG. 2. Coupling members
16 and 18 include respective ports or flow passages 15 and 17
formed therein and in fluid flow communication with bore 14, as
shown.
[0017] As shown in FIGS. 2 and 3, body part 12 is provided with a
transversely extending recess 25, FIG. 2, to reduce the wall
thickness of the body part. Recess 25 is configured so as to form,
in particular, longitudinally extending thin wall portions 25a and
25b, FIG. 4, connected to a generally cylindrical thin walled
radially outwardly projecting tubular spigot portion 28. Spigot
portion 28 defines a cylindrical radially extending bore 30 which
intersects the bore 14, see FIGS. 4 and 6, in particular. Recess 25
may be formed by machining away the outer wall portion of body part
12 circumferentially about the spigot 28 to form a planar surface
defining in part the thin wall portions 25a and 25b, as shown in
FIGS. 1, 4 and 6. The integral tubular spigot portion 28 is
dimensioned to receive an elongated generally cylindrical actuator
control arm member 32, FIGS. 1 through 4, which projects radially
outwardly from the spigot portion and is secured thereto by a gas
tight circumferential braze or weld 34, FIGS. 3 and 4. In the
embodiment shown in FIG. 4, the arm 32 includes a notch 33, see
FIG. 2 also, forming a flat surface in which an arcuate recess 36,
FIG. 4, is formed for supporting a spherical ball closure member
38.
[0018] As shown in FIGS. 2, 3 and 4, closure member 38 is engaged
with a generally cylindrical valve seat member 40 having a
cylindrical passage 41, FIG. 4, extending therethrough. Valve seat
40 is mounted in a cylindrical tubular support member 44 which, in
turn, is supported in a collar 46 suitably fixed in the bore 14 of
the body part 12. Member 44 and collar 46 may be formed as an
integral part. Accordingly, closure member 38 is operable to move
with respect to valve seat 40 in response to pivotal movement of
the arm 32, generally about a pivot point located at the spigot 28,
which pivot point is allowed by the relatively thin walled portions
25a and 25b of the body part 12 and which are formed at the recess
25. The elastically deflectable thin walls 25a and 25b formed by
the recess 25 provide a suitable support for the arm 32 while
allowing movement of the arm to allow suitable displacement of the
closure member 38 with respect to the valve seat 40.
[0019] Actuator control arm 32 is operable to be moved by an
elongated actuator tube or rod member 50, FIGS. 1 through 4, which
is suitably secured to the arm 32 adjacent an end portion 32a
opposite an end portion 32b wherein end portion 32b includes notch
33 and the recess 36 for supporting the closure member 38. Actuator
member 50 is suitably secured to the arm 32 by conventional means,
such as an integral collar 50a, FIG. 4, and a threaded portion
engaged with a hex nut 53, for example. As shown in FIGS. 1 and 2,
the opposite end 50b of actuator tube or rod 50 is anchored to a
projection 56 which is suitably secured to the body part 12 at a
position spaced substantially from the spigot 28. Actuator member
50 is operable to be heated to cause it to elongate generally in
the direction of central axis 11 of the apparatus 10 thereby
tending to pivot the arm 32 in a clockwise direction, viewing FIGS.
2 and 4, and to force the closure member 38 tightly against the
valve seat 40. Conversely, by reducing the temperature of the
actuator member 50, its axial length tends to decrease to pivot the
arm 32 in a counterclockwise direction, viewing FIG. 4, to relax
forcible engagement with the closure member 38 whereby fluid
flowing through the bore 14 and the tubular member 44 will unseat
the ball-type closure member a selected amount in accordance with
the position of the arm 32. Actuator member 50 is preferably formed
as a rod and more preferably formed as a tube so as to respond to
rapid changes in heating effort. Actuator member 50 may be
selectively heated by a heater comprising a wire coil conductor 60
wrapped around the actuator member 50, as shown, and operably
connected to a source of electrical power included in a control
system 62, FIG. 2. Accordingly, by selective controlled heating of
the actuator member 50, the arm 32 may be moved to control flow of
fluid through the bore 14 and the passage 41, depending on the
force tending to keep the closure member 38 seated tightly against
the valve seat 40. Those skilled in the art will recognize that
comprising the actuator member 50 and wire coil 60 may be replaced
by other types of actuator mechanisms such as a solenoid actuator
or a piezo-electric type actuator, for example.
[0020] The configuration of the recess 25 and the resulting thin
wall portions 25a and 25b arranged as shown in FIGS. 3, 4 and 6
provides for elastic deflection of the control arm 32 and a
longitudinal direction, that is, generally in the direction of the
access 11 at a desired stiffness. Conversely, deflection of the
control arm and the spigot portion 28 in a direction generally
normal to the axis 11 is at a different and higher spring rate, for
example. Accordingly, the forces required to deflect the control
arm 32 and the closure member 38 to control flow through the
apparatus 10 are relatively moderate while the control arm 32
resists deflection in other directions to thereby maintain suitable
control over the position of the closure member 38.
[0021] Referring briefly to FIG. 6, an alternate and preferred
embodiment of an actuator control arm and closure member
arrangement in accordance with the invention is illustrated. In
FIG. 6, a control arm 32c is shown in place of control arm 32
having a first and 32d in which a notch 33a is formed and a second
and 32e which is attached to the actuator member 50 in the same
manner as the arrangement shown in FIG. 4. However, control arm 32c
supports a modified closure member 38a which is of a substantially
hemispherical shape and includes a substantially planar surface 38b
thereon which is in sliding engagement with a planar surface 33b of
control arm 32c. Control arm 32c is preferably provided with a
generally cylindrical recess 33c, as shown, of a larger diameter
than the diameter of the closure member 38a, and defining the
surface 33b. In this way, the closure member 38a is free to slide
on surface 33b over a limited distance provided by the recess 33c
so as to provide for substantially centering the closure member 38a
against valve seat 40. Accordingly, dimensional tolerances
associated with the normal position of the control arm 32c relative
to the body 12 and the position of the valve seat 40 relative to
the body 12 may be accommodated by the ability of the closure
member 38a to move at least slightly with respect to the arm 32c to
accommodate any misalignment while maintaining a proper position
with respect to the valve seat surface 40a, see FIG. 6.
[0022] Referring further to FIGS. 2 and 4, the fluid mass flow
control apparatus 10 is further characterized by a fluid flow
restrictor 66 disposed in the bore 14 between the valve closure
member 38 and inlet port 15 of the fitting 16. The flow restrictor
66 may be one of several types including, for example, a porous
sintered metal plug, or a body with plural, parallel tubular
passages or orifices formed therein. The flow restrictor 66 is
suitably fixed within the bore 14, generally in the position shown
in the drawing figures.
[0023] Referring further to FIGS. 2 and 5, the fluid mass flow
control apparatus 10 is further characterized by fluid mass flow
sensor means including, as shown in FIG. 5, spaced apart bores 69
and 70 formed in body part 12 and intersecting bore 14 on opposite
sides of the flow restrictor 66. An elongated open ended sensor
tube 72, FIG. 5, includes spaced apart transverse legs 73 and 75
which extend through bores 69 and 70, respectively and are secured
therein by brazing to form gas tight connections to the body 12.
Sensor tube 72 provides for conducting a bypass flow of fluid
flowing through the bore 14 around the flow restrictor 66. A
removable cover 12a encloses the sensor tube 72, as shown in FIG.
5. The fluid mass flow sensor formed by the sensor tube 72 includes
spaced apart upstream and downstream temperature sensitive
resistance wire coils 80 and 82 which are suitably electrically
connected to the control system 62, FIG. 2. For example, a bridge
type electrical circuit, not shown, is operable to be connected to
the upstream coil 80 and the downstream coil 82 as circuit elements
therein and operable to provide voltages representative of the
fluid mass flow rate through the apparatus 10. Further description
of the mass flow sensor may be obtained from my U.S. Pat. No.
5,660,207, issued Aug. 26, 1997, the entirety of which is
incorporated herein by reference. The mass flow sensor for the
apparatus 10 is not believed to require further description. Other
forms of mass flow sensors may be used in conjunction with the
apparatus 10 and the novel features thereof.
[0024] Accordingly, the control system 62 may be operated to
control fluid mass flow rates through the apparatus 10 in
accordance with a setpoint required by a semiconductor
manufacturing process, for example. By sensing the actual fluid
mass flow rate across the flow restrictor 66 by the mass flow
sensor herein described and shown, the control system 62 may adjust
the flow rate through the passage 41 by actuating the thermal
actuator comprising the rod or tube 50 and the resistance wire coil
60 to cause the actuator control arms 32 or 32c to move the closure
members 38 or 38a in such a way as to throttle the flow of fluid
through the passage 41 and to the outlet port 17 at the fitting 18,
FIG. 2.
[0025] The fluid mass flow control apparatus 10 enjoys several
advantages in the art of fluid mass flow controllers. The
configuration of the arms 32 and 32c and the body part 12 are such
that controlled movement of the arms in a direction parallel with
the axis 11 is obtained. The protrusion of the actuator control or
pivot arms 32 or 32c into the bore 14 form a clean flow path for
fluid flowing through the bore due to the absence of any dead
volume in a vertical leg or tee structure, such as with prior art
apparatus. The clean flow path provided by the apparatus 10 also
reduces purging and drying times required in semiconductor
processing gas delivery systems, for example.
[0026] The manufacturing cost of the apparatus 10 is reduced as
compared with prior art fluid mass flow controllers. The body part
12, for example, may be fabricated from commercially available
tubing which has been mechanically and electro polished and is of a
type typically used in semiconductor process gas delivery
applications. One-half inch diameter tubing available from the
Valex Corporation, for example, may be used. The valve seat and
closure member may also be of types commercially available. The
seat 40 may be a sapphire seat and the closure member 38 may be
formed of ruby, for example. The fittings 16 and 18 may be of types
commercially available. As mentioned previously solenoid actuators
or piezo-electric type actuators may be substituted for the thermal
actuator comprising the rod or tube 50 and the resistance type
heating coil 60. However, the thermal actuator disclosed herein is
also advantageous in that it is independent of the flow of fluid
through the apparatus 10. The arrangement of the wire coil 60 wound
around the outside of the actuator tube or rod 50 to act as a
heating coil in intimate contact with the tube or rod 50 is
advantageous. The actuator is thus disposed outside and not
influenced by the fluid flowing through the apparatus 10 and is not
subject to any cooling effect of the fluid flowing through the
apparatus. The wire coil 60 may be of a type commercially available
such as Evenohm brand alloy wire which is a type wherein resistance
characteristics do not change with temperature over a range of
normal operation of the actuator described herein. Alternatively,
the wire 60 may be of a type available from California Fine Wire
Company, Grover Beach, Calif., as their alloy no. 120, for example.
Such wire has a high temperature coefficient of resistance allowing
the temperature of the coil to be actively sensed in real time,
thus providing additional control benefits. Moreover, the thermal
actuator provided by the rod or tube 50 and the wire coil 60 also
provides improved response time of the actuator to changes in mass
flow rate commanded by the control system 62. In this regard the
member 50 is preferably a thin walled tube providing a high surface
to mass ratio and more rapid response.
[0027] In a typical application of the fluid mass flow control
apparatus 10, as illustrated in FIG. 2, a fast acting shutoff valve
99 is preferably interposed the apparatus 10 and a controllable
pressure regulator 100. Regulator 100 is connected to a suitable
source of gas to be controlled, not shown, and connected to conduit
102. A pressure transducer 101 is in communication with conduit 102
between regulator 100 and valve 99 and is connected to control
system 62 for sending signals thereto. Valve 99 may be disposed
downstream of apparatus 10 also.
[0028] Typically, a fluid mass flow controller of the type used in
process gas flow control in semiconductor manufacturing is used to
step the flow rate to the process from near zero to a desired flow
rate at a desired point in time. A typical sequence used to achieve
flow changes requires opening the shutoff valve 99, for example, a
few seconds before the desired flow change is required so as to
pressurize the upstream side of the fluid mass flow control
apparatus 10. This step is carried out, particularly, when the
valve 99 is located as shown in FIG. 2. During this time the flow
command given to the fluid mass flow control apparatus 10 is zero
to minimize any flow through the flow control valve such as
provided by the closure member 38 or 38a, the seat 40 and the
actuator for the closure member comprising the arm 32 or 32c. When
the desired flow change is commanded, the set point command given
to the mass flow control apparatus 10 is typically changed from
zero to the desired value and the actuator for the arm 32 or 32c is
adjusted based on a feedback signal provided by the mass flow
sensor until the desired flow is actually achieved and maintained.
The sequence of events can be modified to utilize the mass flow
control apparatus 10 equipped with a thermal type actuator to
achieve nearly instantaneous flow change. The control system 62 may
be utilized to maintain and update a table of actuator excitation
voltages, currents or temperatures which correspond to a particular
flow rate through the apparatus 10.
[0029] Accordingly, prior to initiating fluid flow, the shutoff
valve 99 is maintained in a closed position and, at a predetermined
point in time prior to the point at which actual flow change is
desired, a set point command is changed from zero to the desired
flow value by the control system 62. This predetermined time is
fixed and is sufficient to ensure that the actuator of apparatus 10
has sufficient time to achieve a steady state position prior to the
time when the actual flow change is desired. The control system 62
is then operable to cause the actuator formed by the rod or tube 50
and the wire coil 60 to be powered at a voltage, current or
temperature that corresponds to the desired flow and the excitation
of the actuator during this time is independent of any feedback
signal from the mass flow sensor. When the desired time for the
flow change arrives and the shut off valve 99 is opened to allow
gas to pressurize the apparatus 10 flow through the apparatus is at
a rate that is nominally at a desired flow due to pre-positioning
of the arm 32 or 32c. The control system 62 is operable to maintain
the voltage, current or temperature of the actuator until an
adequate time has passed for the mass flow sensor to accurately
measure the flow through the mass flow control apparatus 10 and/or
the sensed flow reading through the apparatus has stabilized. This
predetermined period of time may be actively sensed by the
indicated flow rate from the apparatus 10. After this period of
time has elapsed the control system 62 converts to relying on a
flow feedback signal from the flow sensor to correct and maintain
the desired flow.
[0030] When the portion of the process where the fluid flow is
required at a desired level is complete, a flow command given by
the control system 62 to the apparatus 10 may be set to zero. The
control system 62 then notes the voltage, current or temperature of
the actuator for the apparatus 10 which maintained the desired flow
during the process and updates internal tabulated values to be used
during the next process cycle.
[0031] The construction and operation of the apparatus 10 is
believed to be within the purview of one skilled in the art based
on the foregoing description. Materials used in constructing the
apparatus 10 may be as indicated herein and otherwise in accordance
with materials known to those skilled in the art of fluid mass flow
controllers for fluids used in the semiconductor manufacturing
process industry. Still further, those skilled in the art will
recognize that the flow of fluid through the apparatus 10 may be in
the opposite direction to that described above while the control
valve formed by the actuator arm 32 or 32c and closure member 38 or
38a are still operable to control flow. Also, the mass flow sensor
described for the apparatus 10 may be located where described or
placed upstream of the valve seat 40 when the flow is in the
opposite direction to that shown and described herein above.
[0032] Although preferred embodiments of the invention have been
described in detail, those skilled in the art will also recognize
that various substitutions and modifications may be made without
departing from the scope and spirit of the appended claims.
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