U.S. patent application number 10/749949 was filed with the patent office on 2004-08-12 for chemical delivery systems and methods of delivery.
Invention is credited to Forshey, Randy, Soberanis, David.
Application Number | 20040155057 10/749949 |
Document ID | / |
Family ID | 26916346 |
Filed Date | 2004-08-12 |
United States Patent
Application |
20040155057 |
Kind Code |
A1 |
Soberanis, David ; et
al. |
August 12, 2004 |
Chemical delivery systems and methods of delivery
Abstract
The present invention relates to chemical delivery systems and
methods for delivery of liquid chemicals. In one embodiment, the
present invention relates to systems having multi-reservoir load
cell assemblies for delivering chemicals used in the semiconductor
industry. In one embodiment, the present invention provides a
multi-reservoir load cell assembly, including a controller, a
buffer reservoir, a main reservoir, one or more load cells, coupled
to the assembly and to the controller, operable to weigh the liquid
in the reservoir(s), a plurality of supply lines, each supply line
having a valve and connecting one of the supply containers to the
main reservoir, and a gas and vacuum sources for withdrawing the
liquid from the assembly when demanded by the controller and for
refilling the assembly from the supply containers.
Inventors: |
Soberanis, David; (Tracy,
CA) ; Forshey, Randy; (Discovery Bay, CA) |
Correspondence
Address: |
Ira Lee Zebrak
The BOC Group, Inc.
Legal Services - Intellectual Property
100 Mountain Ave.
Murray Hill
NJ
07974
US
|
Family ID: |
26916346 |
Appl. No.: |
10/749949 |
Filed: |
December 31, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10749949 |
Dec 31, 2003 |
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09968566 |
Sep 29, 2001 |
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6675987 |
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09968566 |
Sep 29, 2001 |
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09870227 |
May 30, 2001 |
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6340098 |
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09870227 |
May 30, 2001 |
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09568926 |
May 11, 2000 |
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6269975 |
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09568926 |
May 11, 2000 |
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09224607 |
Dec 31, 1998 |
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6098843 |
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09224607 |
Dec 31, 1998 |
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09222003 |
Dec 30, 1998 |
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Current U.S.
Class: |
222/56 |
Current CPC
Class: |
B01F 2101/58 20220101;
B01F 35/7543 20220101; B01F 35/881 20220101; B01F 2101/2204
20220101; B67D 7/0283 20130101; B67D 7/0272 20130101; B67D 7/74
20130101; B01F 35/75 20220101; C30B 25/14 20130101; B67D 7/0238
20130101 |
Class at
Publication: |
222/056 |
International
Class: |
B67D 005/08 |
Claims
What is claimed:
1. A liquid chemical delivery system for use with a plurality of
supply containers, comprising: a controller; a multi-reservoir load
cell assembly, including, a buffer reservoir with a chemical
output, a main reservoir, a reservoir valve connecting the buffer
reservoir to the main reservoir, and a load cell, coupled to the
assembly and to the controller, operable to weigh the liquid in the
reservoir assembly; a plurality of supply lines, each having a
valve coupled to the controller and to one of the supply containers
to the main reservoir; and means for withdrawing the liquid from
the chemical output, opening and closing the reservoir valve, and
refilling the main reservoir from the supply containers when
demanded by the controller based on signals from the load cell.
2. The system of claim 1, wherein the means for withdrawing the
liquid from the output and for refilling the main reservoir from
the supply containers, includes a gas line connected to the main
reservoir, a gas source connected to the gas line, a vacuum source,
a vacuum line connecting the vacuum source to the gas line, a gas
valve connecting the gas line, the gas source, and the vacuum
source, wherein the controller opens the gas valve to permit gas to
flow from the gas source to the main reservoir when liquid is
withdrawn from the reservoir and to generate a vacuum in the main
reservoir when the reservoir is refilled from the supply
containers.
3. The system of claim 1, wherein the controller closes the buffer
reservoir from the main reservoir when the reservoir is refilled
and liquid is withdrawn such that the buffer reservoir undergoes no
negative pressure from the vacuum in the main reservoir.
Description
BACKGROUND
[0001] The present invention relates generally to systems and
methods for delivering of liquid chemicals, and more particularly,
to systems and methods for delivery of liquid chemicals in precise
amounts using logic devices and multi-reservoir load cell
assemblies.
[0002] The present invention has many applications, but may be best
explained by considering the problem of how to deliver photoresist
to silicon wafers for exposure of the photoresist in the process of
photolithography. To form the precise images required, the
photoresist must be delivered in precise amounts on demand, be free
of bubbles, and be of precise uniform thickness on the usable part
of the wafer. The conventional systems have problems as discussed
below.
[0003] As shown in FIG. 1, a representative conventional
photoresist delivery system includes supply containers 100, 102,
typically bottles, which supply photoresist to a single-reservoir
104 by line 117, which is connected to supply lines 106, 108
monitored by bubble sensors 110, 112 and controlled by valves V1
and V2. The bottom of the reservoir is connected to a photoresist
output line 114 to a track tool (not shown) which dispenses
photoresist on the wafer. The space above the photoresist in the
reservoir 104 is connected to a gas line 118 which, based on
position of a three-way valve V3, either supplies nitrogen gas to
the reservoir 104 from a nitrogen manifold line 126, regulated by
needle valve 1, or produces a vacuum in the reservoir 104. To sense
the level of the photoresist in the reservoir 104, the system
employs an array of capacitive sensors 122 arranged vertically on
the walls of the reservoir 104. A two-way valve V4, located between
the nitrogen gas manifold and the inlet of a vacuum ejector 124,
supplies or cuts off flow of nitrogen to the vacuum ejector
124.
[0004] The photoresist delivery system must be "on-line" at all
times so the track tool can dispense the photoresist as required.
Many of the photoresist delivery systems attempt to use the
reservoir to provide an on-line supply of photoresist to the track
tool, but the photoresist delivery system must still refill the
reservoir on a regular basis which is dependent on timely
replacement of empty supply containers. Otherwise, the track tool
will still fail to deliver the photoresist when demanded.
[0005] During dispense mode, when photoresist is withdrawn by the
track tool from the reservoir 104, the valve V3 permits the
nitrogen to flow from the nitrogen manifold to the reservoir 104 to
produce a nitrogen blanket over the photoresist to reduce
contamination and to prevent a vacuum from forming as the
photoresist level drops in the reservoir. Once the photoresist in
the reservoir 104 reaches a sufficiently low level the system
controller (not shown) initiates refill mode, where a set of
problems arise.
[0006] During refill mode, the valve V4 is activated so that
nitrogen flows from the manifold line 126 to the vacuum ejector 124
which produces a low pressure line 170 thereby producing a low
pressure space above the photoresist in the reservoir 104. The
bubble sensors 110, 112 monitor for bubbles in the supply lines
106, 108, presumed to develop when the supply containers 100, 102,
become empty. If, for example, the bubble sensor 110 detects a
bubble, the controller turns off the valve V1 to supply container
100 and the valve V2 opens to supply container 102 to continue
refilling the reservoir 104. However, bubbles in the supply line
106 may not mean supply container 100 is empty. Thus, not all of
the photoresist in supply container 100 may be used before the
system switches to the supply container 102 for photoresist. Thus,
although the conventional system is intended to allow multiple
supply containers to replenish the reservoir when needed, the
system may indicate that a supply container is empty and needs to
be replaced before necessary.
[0007] If the supply container 100 becomes empty and the operator
fails to replace it and the system continues to operate until the
supply container 102 also becomes empty, the reservoir 104 will
reach a critical low level condition. If this continues, bubbles
may be arise due to photoresist's high susceptibility to bubbles;
if a bubble, however minute, enters the photoresist delivered to
the wafer, an imperfect image may be formed in the photolithography
process.
[0008] Further, if the pump of the track tool, connected downstream
of the chemical output line 114, turns on when the reservoir is
refilling, the pump will experience negative pressure from the
vacuum in the single-reservoir pulling against the pump. Several
things can happen if this persists: the lack of photoresist
delivered to the track tool may send a false signal that the supply
containers are empty, the pump can fail to deliver photoresist to
its own internal chambers, lose its prime and ability to adequately
dispense photoresist, and the pump can even overheat and burn out.
The result of each scenario will be the track tool receives
insufficient or even no photoresist, known as a "missed shot,"
which impacts the yield of the track tool.
[0009] The present invention addresses these problems as well as
avoids waste of expensive photoresist, provides a friendly user
interface depicting the amount of photoresist remaining in the
supply containers, and reduces system capital and operating costs.
If, for example, the amount of photoresist in the supply containers
cannot be seen, the present invention permits the interface to be
provided at a distance by conventional computer network
capabilities and the electronics provided.
SUMMARY OF THE INVENTION
[0010] The present invention relates to systems using controllers
or logic devices and multi-reservoir load cell assemblies for
precision delivery of liquid chemicals. It also relates to methods
of delivering liquid chemicals from supply sources to processes
such that the present invention accurately accounts and adjusts for
the dynamic supply and use of the liquid chemical to meet process
requirements. Finally, the present invention provides
multi-reservoir load cell assemblies for monitoring, regulating,
and analyzing the liquid supply available to a process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 illustrates a chemical delivery system using a
single-reservoir and bubble sensors on the supply lines leading to
the single-reservoir.
[0012] FIG. 2A is a front cross-section of a first embodiment of
the multi-reservoir load cell assembly of the present
invention.
[0013] FIG. 2B is a top view of the first embodiment of the
multi-reservoir load cell assembly.
[0014] FIG. 3, a piping and instrument diagram, illustrates
embodiments of the chemical delivery system including the
multi-reservoir load cell assemblies of FIGS. 2A-2B or 4A-4B.
[0015] FIG. 4A is a front cross-section of a second embodiment of
the multi-reservoir load cell assembly.
[0016] FIG. 4B is a side cross-section of the second embodiment of
the multi-reservoir load cell assembly.
[0017] FIG. 5A is a front cross-section of a third and sixth
embodiment of the multi-reservoir load cell assembly.
[0018] FIG. 5B is a side cross-section of the third and sixth
embodiment of the multi-reservoir load cell assembly.
[0019] FIG. 6, a piping and instrument diagram, illustrates
embodiments of the chemical delivery system including the
multi-reservoir load cell assemblies of FIGS. 5A-5B or 11A-11B.
[0020] FIG. 7A is a front cross-section of a fourth embodiment of
the multi-reservoir load cell assembly.
[0021] FIG. 7B is a side cross-section of the fourth embodiment of
the multi-reservoir load cell assembly.
[0022] FIG. 8, a piping and instrument diagram, illustrates an
embodiment of the chemical delivery system including the
multi-reservoir load cell assembly of FIGS. 7A-7B.
[0023] FIG. 9A is a front cross-section of a fifth embodiment of
the multi-reservoir load cell assembly.
[0024] FIG. 9B is a side cross-section of the fifth embodiment of
the multi-reservoir load cell assembly.
[0025] FIG. 10, a piping and instrument diagram, illustrates an
embodiment of the chemical delivery system including the
multi-reservoir load cell assembly of FIGS. 9A-9B.
[0026] FIG. 11A is a front cross-section of a seventh embodiment of
the multi-reservoir load cell assembly.
[0027] FIG. 11B is a side cross-section of the seventh embodiment
of the multi-reservoir load cell assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] In the first embodiment, the present invention includes a
multi-reservoir load cell assembly 200 as shown in FIGS. 2A-2B. The
assembly 200 can be part of the system shown in FIG. 3, and can
replace the problematic single-reservoir 104 and bubble sensors
110, 112 of FIG. 1.
[0029] In this embodiment, the assembly 200, constructed of Teflon,
SST or any chemical compatible material, includes an upper
compartment 202, a main reservoir 206, and a buffer reservoir 208,
all in an outer housing 212. The buffer reservoir 208 is sealed
from the main reservoir 206 by a separator 209, and an o-ring seal
211 seals the perimeter of the separator 209 to the outer housing
212. The separator 209 uses a center conical hole 250 that allows
an internal sealing shaft 204 to form a liquid and gas-tight seal
with the separator 209. The separator 209 forms a liquid and
gas-tight seal to the pneumatic tube 215 with an o-ring seal 210.
The main reservoir 206 contains a middle sleeve 214 that forms a
rigid separation between the separator 209 and the reservoir cap
205. The perimeter of reservoir cap 205 seals against the internal
surface of the outer housing 212 with the use of an o-ring 203. The
reservoir cap 205 seals against the internal sealing shaft 204, the
chemical input tube 217, and the pneumatic tubes 215 and 218 with a
set of o-ring seals 207, 220, 222, and 224 (hidden, but location
shown in FIG. 2B), respectively. Mounted to the reservoir cap 205
is a spacer 244 which also mounts to the pneumatic cylinder 226.
The reservoir cap 205 is held in position by the upper sleeve 233
and the middle sleeve 214. The outer Teflon reservoir top 201 is
bolted to the outer housing 212 and forms a mechanical hard stop
for the upper sleeve 233 and the pneumatic cylinder 226. Pneumatic
air lines for the pneumatic cylinder 226 penetrate the outer Teflon
reservoir top 201 through the clearance hole 260.
[0030] It should be clear that the present invention is not limited
to the delivery of photoresist on silicon wafers. For example,
although the invention shows advantages over the conventional
system in this environment, the systems of the present invention
can deliver other liquid chemicals for other types of processes,
such as the delivery of developer or chemical mechanical polishing
slurries. Because the novelty of the present invention extends
beyond the nature of the chemical being delivered, the following
description refers to the delivery of chemicals to avoid a
misunderstanding regarding the scope of the invention.
[0031] As shown in FIG. 3, the multi-reservoir load cell assembly
200 shown in FIGS. 2A-2B is suspended on and weighed by a load cell
412, preferably such as a Scaime load cell model no.
[0032] F60X10C610E and a programmable logic controller (PLC) 330,
preferably such as the Mitsubishi FX2N, a computer, or another
conventional logic device determines the volume of the chemical in
the assembly 200 from the load cell weight and the specific gravity
of the chemical. As chemical from line 217 is drawn into the main
reservoir 206, the load cell 412 outputs a small mV analog signal
324 proportional to the weight on the load cell 412. In one
embodiment, an ATX-1000 signal amplifier 326 boosts the small
signal 324 to the 4-20 millivolt range and sends it to an
analog-to-digital converter 328, such as the Mitsubishi FX2N4-AD,
and the output digital signal 332 is sent to the PLC 330. The PLC
330 can be rapidly programmed by conventional ladder logic. During
withdrawal of the chemical, the weight of the assembly 200
decreases until the software set point of the PLC 330 is
reached.
[0033] As further shown in FIG. 3, the PLC 330 may control valves
V1-V5 using 24 DC Volt solenoid actuated valves, and activate them
by an output card such as the Mitsubishi FX2N. Each solenoid valve,
when opened, allows pressurized gas from regulator 2 such as a
VeriFlow self-relieving regulator, to the pneumatically operated
valves V1-V5 to open or close the valves. The sequence of operation
of the first embodiment is programmed in the PLC 330 so the
components shown in FIGS. 2A-2B and 3 work as described below.
[0034] Once the chemical drops to a certain level, the PLC 330
triggers the system shown in FIG. 3 to begin an automatic refill
sequence using the multi-reservoir load cell assembly 200 of FIGS.
2A-2B as follows:
[0035] a) A blanket of preferably low pressure, e.g., one psi inert
gas is continuously supplied by the regulator 1, such as a Veriflow
self-relieving regulator, to the main reservoir 206 by the
pneumatic tube 218.
[0036] b) The internal sealing shaft 204 is lifted by the pneumatic
cylinder 226, thereby sealing the buffer reservoir 208 from the
main reservoir 206.
[0037] c) Once the buffer reservoir 208 is sealed, the main
reservoir 206 is evacuated to a vacuum of approximately 28 inches
of mercury. As shown in FIGS. 2A-2B, the pneumatic tube 218 from
the main reservoir 206 connects to the output side of a three-way
valve V4. Valve V4 is actuated so that the tube 218 communicates
with the line 316 connected to the vacuum ejector 324 as shown in
FIG. 3. The vacuum ejector 324 is powered by compressed gas which
is directed to it by the two-way valve V5. Once valve V5 is on, it
allows compressed gas to pass through and the vacuum ejector 324
develops about 28 inches of mercury (vacuum) through the line 316
communicating with the main reservoir 206.
[0038] d) The vacuum is isolated from the buffer reservoir 208
which has an inert gas slight blanket above it and continues to
supply chemical to the process or tool without exposing the
chemical being delivered to the tool to negative pressure or a
difference in pressure.
[0039] e) The vacuum generated in the main reservoir 206 creates a
low pressure chemical line that is connected to the valves V1 and
V2. Assuming that valve V2 opens, the low pressure line 217 causes
chemical from the supply container 102 to flow into the main
reservoir 206. During this period of time the main reservoir 206
refills with chemical until a determined full level is
achieved.
[0040] f) The full level is determined by use of the load cell 412
and weight calculations performed by the PLC 330. For example, one
preferred embodiment uses a buffer reservoir 208 with a volume
capacity of 439 cubic centimeters (cc) and a main reservoir 206
with a capacity of 695 cc. Using the specific gravity of the
chemical, the PLC 330 calculates the volume that the chemical
occupies. The PLC 330 then begins a refill sequence once the
chemical volume reaches or falls below 439 cc. The refill stops
once the chemical volume reaches 695 cc. This sequence allows
nearly all of the 439 cc of the chemical in the buffer reservoir
208 to be consumed while refilling the main reservoir 206 with the
695 cc of chemical and prevents overflow of the main reservoir 206
or complete evacuation of chemical from the buffer reservoir
208.
[0041] g) Once the main reservoir 206 has refilled, the valve V5 is
turned off, thereby stopping gas flow to and vacuum generation by
the vacuum ejector 324. The three-way valve V4 is then switched so
that the inert gas line 218 communicates with the main reservoir
206 and an inert gas blanket is again formed over the chemical in
the main reservoir 206 at the same pressure as the buffer reservoir
208, since both lines 218, 215 receive gas from the same inert gas
manifold 318 (see FIG. 3). Also, the valve V2 is closed which now
isolates the supply container 102 from the main reservoir 206.
[0042] After the main reservoir 206 is full of chemical with an
inert gas blanket above, the internal sealing shaft 204 is lowered
and allows chemical from the main reservoir 206 to flow into the
buffer reservoir 208. Eventually, the buffer reservoir 208
completely fills along with a majority of the main reservoir 206.
The pneumatic tube 215 connecting the buffer reservoir 208 fills
with chemical until the chemical in the tube 215 reaches the same
level as the main reservoir 206, because the pressures in both
reservoirs are identical. The internal sealing shaft 204 remains
open until it is determined, to once again, refill the main
reservoir 206.
[0043] Because the first embodiment uses load cells instead of
bubble sensors for determining the amount of chemical in the supply
containers, the present invention provides a number of very useful
features. One can accurately determine in real-time the chemical
remaining in the supply containers. If the supply containers are
full when connected to the system, the PLC can easily calculate the
chemical removed (and added to the multi-reservoir load cell
assembly) and how much chemical remains in the supply containers.
This information can be used to provide a graphical representation
of the remaining amount of chemical in the containers. A second
feature is that the PLC can determine precisely when a supply
container is completely empty by monitoring the weight gain within
the system. If the weight of the reservoir does not increase during
a refill sequence then the supply container is inferred to be
empty. This causes the valve for the supply container to be closed
and the next supply container to be brought on line. A related
third feature is the load cell technology provides the ability to
accurately forecast and identify the trends in chemical usage.
Since the exact amount of chemical is measured coming into the
reservoir the information can be easily electronically stored and
manipulated and transmitted.
[0044] A second embodiment of the multi-reservoir load cell
assembly 400 shown in FIGS. 4A-4B, includes a buffer reservoir 408,
fastened and sealed by the O-rings 411 to the bottom cap 410. The
output chemical flows through tube connection 401. Connected to the
buffer reservoir 408 are a pneumatic tube 415, a chemical valve
407, a load cell separator 413, and the load cell 412. The load
cell 412 is securely bolted to the buffer reservoir 408 and the
other side is securely bolted to a rigid member (not shown) not
part of the multi-reservoir load cell assembly 400. The outer
sleeve 404 slips around the buffer reservoir 408 and rests against
the bottom cap 410. The outer sleeve 404 is machined to allow the
load cell 412 to pass through it unencumbered. End 405 of the valve
407 connects to the main reservoir 406 and the other end 409
connects to buffer reservoir 408. The main reservoir 406 is
encapsulated and sealed, by O-rings in the upper cap 403. The upper
cap 403 incorporates a stepped edge along its periphery to secure
the outer sleeve 404 to it. Pneumatic line 418 and chemical input
line 417 are secured to the upper cap 403. The outer sleeve 404
provides the mechanical strength for the separate reservoirs 406
and 408.
[0045] The multi-reservoir load cell assembly shown in FIGS. 4A-4B,
and used in the system of FIG. 3, is similar to the first
embodiment with the following notable differences:
[0046] a) Valve 407 provides control of the fluid path between the
main reservoir 406 and the buffer reservoir 408.
[0047] b) The outer sleeve 404 provides the mechanical support to
form the rigid assembly that supports the main reservoir 406 as
well as the buffer reservoir 408.
[0048] A third embodiment of the multi-reservoir load cell assembly
shown in FIGS. 5A-5B, employs two reservoirs 506, 508 spaced apart
from each other but connected by a flexible fluid line 516.
[0049] The third embodiment uses many of the previous components
shown in FIGS. 4A-4B, except: (i) it does not use an outer sleeve
404; (ii) the buffer reservoir 508 is not mechanically suspended
from the main reservoir 506; and (iii) the load cell spacer 513 and
the load cell 512 are fastened to the bottom of the main reservoir
506.
[0050] The third embodiment operates like the second embodiment
except the load cell 512 only measures the volume of chemical in
the main reservoir tank 506 as shown in FIGS. 5A-5B and 6. The
advantage of the third embodiment is the precise amount of chemical
brought into the main reservoir 506 is always known and the PLC
does not have to infer the amount of chemical that was removed from
the buffer reservoir 508 during a refill operation. The third
embodiment can be used in the system of FIG. 6 with the control
system (i.e., PLC, A/D, signal amplifier, etc.) of FIG. 3. Note, in
the application, the lead digit of the part numbers generally
indicates which drawing shows the details of the part, while the
trailing digits indicate that the part is like other parts with the
same trailing digits. Thus, the buffer reservoir 206 and the buffer
reservoir 306 are similar in function, and found in FIG. 2A and
FIG. 3A, respectively.
[0051] A fourth embodiment of the multi-reservoir load cell
assembly 700 shown in FIGS. 7A-7B, employs the same components as
the third embodiment, however, a second load cell 722 is attached
to the buffer reservoir 708. The assembly 700 is preferably used
with the system of FIG. 8 with the control system of FIG. 3 with
additional components for the second load cell.
[0052] The fourth embodiment of the multi-reservoir load cell
assembly 700 shown in FIGS. 7A-7B, operates much like the second
embodiment except that the load cell 712 only measures the chemical
in the main reservoir 706 and the load cell 722 only measures the
chemical in the buffer reservoir 708. The advantage here is the
buffer reservoir 708 is constantly monitored so if the downstream
process or tool suddenly consumes large amounts of chemical during
a refill cycle, the system can stop the refill cycle short to bring
chemical into the buffer reservoir 708 from the main reservoir 706
to prevent the complete evacuation of chemical from the buffer
reservoir 708.
[0053] A fifth embodiment of the multi-reservoir load cell assembly
900 shown in FIGS. 9A-9B uses the same components as the third
embodiment, except the load cell 912 is attached to the buffer
reservoir 908 instead of the main reservoir 906. The fifth
embodiment is preferably used in the system depicted in FIG. 10
with the control system (i.e., PLC, A/D, signal amplifier, etc.)
shown in FIG. 3.
[0054] Functionally, the fifth embodiment of the multi-reservoir
load cell assembly 900 operates the same as the second embodiment,
the only difference is the load cell 912 only weighs the chemical
in the buffer reservoir 908.
[0055] As the process or tool consumes the chemical, the weight of
the buffer reservoir 908 remains constant until the main reservoir
906 also becomes empty. Then the weight in the buffer reservoir 908
will start to decrease, indicating that the main reservoir 906
needs to be refilled. At this point the main reservoir 906 is
refilled for a calculated period of time. During this sequence the
buffer reservoir 908 decreases until the main reservoir 906 has
been refilled and the valve 907 has been reopened between the two
reservoirs 906, 908.
[0056] A sixth embodiment uses the same components of third
embodiment shown in FIG. 5A-5B. The only notable difference is that
the inert gas blanket (see FIG. 6) of approximately one psi is
increased to approximately 80 psi (more or less depending on the
type of chemical). The increased inert gas pressure enables the
sixth embodiment to pressure dispense the chemical at a constant
output pressure which remains unaffected even during the refill
cycle. This method would allow very precise non-pulsed output flow
of the chemical. This may be a highly critical feature in an ultra
high purity application that pumps the chemical through a filter
bank. Any pulsation of the chemical can cause particles to be
dislodged from the filter bank into the ultra-pure chemical output
flow.
[0057] A seventh embodiment uses the same components as the third
embodiment with additional components shown in FIGS. 11A-11B,
including a main reservoir 1106, a buffer reservoir 1108, a second
chemical input line 1119 added to the main reservoir 1106 through
the valve 1122, a valve 1123 added to the chemical input line 1117,
and a stir motor 1120 and an impeller assembly 1121.
[0058] Functionally, the seventh embodiment operates the same as
the third embodiment with the added capability of mixing two
chemicals in precise proportions before transferring the mixture to
the buffer reservoir 1108. The chemical can be drawn into the main
reservoir 1106 through open valve 1123 and the chemical input line
1117 and weighed by the load cell 1112. When the proper amount has
been drawn into the main reservoir 1106, the valve 1123 is closed
and the valve 1122 is opened to allow the second chemical to enter
the main reservoir 1106. When the proper amount has been drawn into
the main reservoir 1106, the valve 1122 is closed and the chemicals
are blended via the stir motor 1120 and impeller assembly 1121. The
stirring of the chemicals can be initiated at any time during the
above sequence. Once the mixing is complete, the valve 1107 opens
to allow the chemical to transfer to the buffer reservoir 1108,
which is also connected to gas line 1115. This is an ideal way to
mix time sensitive chemistries and maintain a constant, non-pulsed
output of the blended chemicals.
[0059] In review, the present invention provides at least the
following benefits. The output chemical can be maintained at a
constant pressure. A track tool never experiences a low pressure
chemical line that could prevent a dispense sequence from
occurring, therefore the yield of the track tool is increased. A
multitude of containers and sizes can be connected to the reservoir
system as chemical supply containers. If the fluid volume of the
supply containers are known before they are connected, the computer
can calculate very accurately the amount of chemical that has been
removed from the container and therefore present the information to
a display for a visual, real time indication of the remaining
amount of chemical. The graphical interface communicates to the
operator at a "glance" the condition of the supply containers. The
load cells can determine when the supply container is completely
empty since there will not be a continued weight increase during a
refill sequence. This indicates the supply container is empty and
that another container should be brought on line. In one
embodiment, data logging of chemical usage can be provided since
the chemical in the reservoir(s) is continuously and accurately
weighed by load cell(s) which give an input signal to the PLC or
other logic device which outputs real time, accurate information as
to the amount of chemical available in the reservoir. The load cell
is an inherently safe sensing device since failure is indicated by
an abnormally large reading or an immediate zero reading, both of
which cause the PLC or other logic device to trigger an alarm. The
invention can also prevent bubbles that occur during a supply
container switching operation from passing through to the output
chemical line, can provide constant, non-varying pressure dispense
with multiple supply containers, can refill itself by vacuum or by
pumping liquid to refill the reservoir or refill with different
chemicals at precise ratios and mix them before transferring the
mixture to the buffer reservoir, which may be important for time
dependent, very reactive chemistries.
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