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| United States Patent | 5490611 |
| Link to this page | http://www.wikipatents.com/5490611.html |
| Inventor(s) | Bernosky; Eugene W. (Hollister, CA);
Geatz; J. Tobin (Durham, NC);
Ferrie, Jr.; Edward T. (Gilroy, CA);
Roberson, Jr.; Glenn A. (Hollister, CA) |
| Abstract | Apparatus and method for accurate measuring and mixing of chemicals is
disclosed. The apparatus includes one or more metered vessels having a
container of predetermined volume and at least one constricted vent tube
therein. By mounting a sensor on the constricted vent tube, a greatly
amplified measurement of the precise chemical volume in the metered vessel
is provided. The apparatus and method of the present invention readily
lends itself to a variety of applications and can be adapted to handle
virtually any form of chemical mixing, diluting, or generating process. |
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Title Information  |
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Drawing from US Patent 5490611 |
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Process for precise volumetrio diluting/mixing of chemicals |
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| Publication Date |
February 13, 1996 |
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| Filing Date |
December 5, 1994 |
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| Parent Case |
The present application is a division of U.S. patent application Ser. No.
035,252 filed Mar. 22, 1993 now U.S. Pat. No. 5,370,269 , which was a
continuation-in-part of U.S. patent application Ser. No. 948,392, filed
Sep. 21, 1992 now Pat. No. 5,330,072, which was a continuation-in-part of
U.S. patent application Ser. No. 583,826, filed Sep. 17, 1990, and issued
as U.S. Pat. No. 5,148,945 on Sep. 22, 1992. |
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Title Information |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus and method for mixing/diluting,
generating, and/or transferring of process chemicals. More particularly,
the present invention provides improved process and apparatus for the
precise mixing/diluting all forms of chemicals and, especially, ultra-high
purity chemicals for use in a variety of industries, such as in the
manufacture of semiconductor wafers and similar products.
2. Description of the Prior Art
The inventions of the parent applications are directed to process and
apparatus for the transfer and delivery of high-purity chemicals from a
bulk source to one or more end-use stations. As is explained therein, in
many applications in industry today it is extremely important to maintain
process chemicals free of virtually all contaminants. For instance, in the
semiccnductor industry the purity of chemicals, such as sulfuric acid,
hydrogen peroxide, and ammonium hydroxide, used in semiconductor wafer
production must be pure on level of approximately 25 (or fewer) particles
per milliliter with a particle size of less than a fraction of a micron.
As a result of these purity standards, many conventional methods of
chemical transfer and delivery, such as paddled pumps and similar devices,
have proven completely unsatisfactory.
Of further concern in these industries is that many of the chemicals
employed are toxic, chemically aggressive, and/or require special conduit
material, and must be carefully handled. In order to assure adequate
purity and worker safety, it is extremely important that such chemicals be
transferred, stored, and dispensed in a closed system, with minimal
contact with the environment or workers.
Prior to the inventions of the parent applications, generally one of two
methods were employed to effectuate high-purity chemical transfer. The
first method is a "pumped delivery." In this method a positive
displacement pump, usually an air powered double diaphragm type, is
employed to provide both lift at a suction inlet from a bulk source of the
chemicals and simultaneous pressure at the output to the end-user. The
chemical is lifted from a chemical drum, driven through a pump, and pushed
out to the point of use.
Although the pumped delivery system is widely employed, it is far from
satisfactory. This system is capable of producing only minimal lift from
the chemical bulk source--usually on the order of only a few pounds per
square inch. Moreover, the system is replete with contamination problems:
the rapidly expanding and contracting of the pump diaphragm material (e.g.
TEFLON.RTM.) causes mechanical degradation, with the degradation
by-products (many of which being too small to filter with state-of-the-art
filtration equipment) entering the chemical process stream; further, the
rapid action of the pump (usually greater than 60 cycles per minute)
creates massive impulses in the system with a resulting pulsed flow which
forces particles through filters--thus rendering the filters far less
effective. Finally, the mechanical shock and vibration inherent in this
system creates constant maintenance problems, such as leaks.
The other system which is generally used addressed only some of these
problems. In a "pump/pressure delivery" system, a positive displacement
pump is again employed to provide lift from the bulk source of chemicals.
However, the chemicals are delivered to an intermediate vessel from which
inert gas pressure is used to motivate chemical to the use areas.
Although the pump/pressure system is better controlled and is more
conducive to use of filters to assure chemical purity, it still has
serious drawbacks in a sub-micron chemical environment. Again, lift
provided by a double diaphragm pump is restricted. Further, such pumps are
prone to degradation--with the by-products entering the chemical stream.
Finally, the use of a single pressure vessel for delivery results in
non-continuous delivery--constraining the volume of each delivery to
"batch" sizes based on the size of the pressure vessel. If demand exceeds
the volume of the pressure vessel, further delivery must be "queued" while
the pump refills the pressure vessel. Alternatively, pressure from the
pump that is equal to or greater than the pressure of the delivery vessel
must be applied to the delivery vessel to supplement or refill it during
demand; this further compounds filtration and maintenance problems.
The inventions disclosed in the parent applications solve all these
problems. In those inventions, a combination of vacuum and pressure is
used to transfer chemical smoothly from a bulk source, through one or more
intermediate pressure/vacuum vessels ("PVV"), and to one or more end-use
stations. First, a vacuum pump is used to establish a vacuum in one of the
PVVs to draw chemicals into the PVV. Once a PVV is filled, the vessel is
then pressurized to motivate chemical to an end-use station, to another
PW, or for recirculation back to the bulk source. The elimination of pumps
from all chemical conduits in the system avoids the problems of
degradation and contamination.
As is explained in the parent applications, the advantages of this improved
transfer and delivery apparatus include: even (i.e. non-pulsed) flow
through the system, reducing maintenance problems and allowing far more
efficient use of filters; built-in redundancy to assure constant chemical
supply and fail-safe operation; and electronic controls to monitor and
maintain all aspects of system operation automatically.
In light of these substantial advantages of a vacuum/pressure transfer and
delivery system, applicants believe that similar advantages can be
achieved in a vacuum/pressure system for taking chemicals from multiple
bulk sources and automatically mixing them (e.g. combining two or more
process chemicals or diluting one or more process chemicals with water or
other chemical) prior to delivery to the end-user.
Although liquid mixing systems are known, none addresses the contamination
concerns of a high-purity environment. Most existing systems employ
conventional fluid transfer means (e.g. pumps or water line pressure) to
fill two or more metered vessels. From these vessels, the liquids to be
mixed are then transferred, usually by pumps, to a mixing vessel and then
to a storage facility or user. Examples of such existing systems are
illustrated in U.S. Pat. Nos. 3,960,295, issued Jun. 1, 1976, to Horak,
4,019,528, issued Apr. 26, 1977, to Tyrrell, 4,215,719, issued Aug. 5,
1980, to Laar et al., and 4,823,987, issued Apr. 25, 1989, to Switall.
None of these teaches means to assure that high purity chemicals will not
be contaminated on a sub-micron level by the mixing apparatus itself.
Additionally, none of the existing mixing systems provides a simple yet
effective method of accurately mixing chemicals in precise volumes.
Although it is common to employ multiple metered vessels to measure the
amount of each chemical to be mixed, with sensors typically used to cease
the flow of liquid to the metered vessel once it is filled, none of these
systems provides means to amplify the sensors' accuracy in order to assure
very precise measurement of the volume of each vessel. The use of other
metering methods, such as highly accurate flow meters or similar devices,
may address some of these concerns, but are generally undesirable due to
their expense, fragile nature, and/or possible contamination risks. As a
result, none of the existing diluting/mixing systems is considered fully
satisfactory in providing accurate mixing of high purity chemicals
required by many industries.
Accordingly, it is a primary object of the present invention to provide
improved apparatus and method for accurate mixing of chemicals from two or
more bulk sources. It is a further object of the present invention to
provide an apparatus and method that includes, or readily interfaces with,
means to transfer and deliver chemical from the bulk sources to end-use
stations.
It is another object of the present invention to provide an apparatus and
method that includes means to transfer and mix high-purity process
chemicals from bulk sources and deliver them reliably and without
contamination to end-use stations.
It is yet another object of the present invention to provide an apparatus
and method that includes a simple and relatively inexpensive means to
yield extremely precise volumetric measurement of chemicals.
It is an additional object of the present invention to provide an apparatus
and method that employs a vacuum-pressure transfer and delivery system so
as to generate even flow and negligible mechanical shock in the system.
These and other objects of the present invention will become evident from
review of the following specification.
SUMMARY OF THE INVENTION
The present invention provides an improved apparatus and method for
extremely accurate mixing of chemicals from two or more chemical bulk
sources.
In operation the invention employs one or more metered vessels of
predetermined volume in communication with the bulk source of chemical via
an intake line and in communication with a downstream facility via a
dispense line. Each of the metered vessels includes one or more
constricted vent tubes therein. Chemical is transferred from each of the
bulk sources to the metered vessel until a set capacity is attained. At
that point, chemical flow proceeds up the vent tube until a sensor is
reached. A valve is provided on the intake line to cease fluid flow to the
metered vessel in response to a signal from the sensor. By employing a
constricted vent tube, the signal from the sensor can be greatly amplified
to provide for more accurate filling of the metered vessel and more
accurate mixing of chemicals. By including adjustable valve means on the
intake lines and multiple sensors on the vent tubes, the rate of flow into
the metered vessel can be carefully adjusted to provide extremely accurate
chemical mixing proportions.
For improved motivation of chemicals through the apparatus of the present
invention, a vacuum system and a pressure system are provided. Chemical
can be smoothly drawn from the bulk source by decompressing (i.e. to a
negative pressure) the metered vessel via the vacuum system. Once the
metered vessel is filled, the metered vessel can then be pressurized using
compressed gas in the pressure system to drive chemical through the
dispense line to an intermediate or end-use station. The pressure system
may also be used to perform other functions in the apparatus of the
present invention, such as activating pneumatic valves or pressurizing
sealed bulk sources and/or intermediate storage vessels to assist in
motivation of chemical.
For many applications it is desirable to provide a separate mix tank where
the measured proportions of chemicals can be thoroughly combined. As is
disclosed, the mix tank may include a variety of means to improve the
mixing process, such as heat exchange apparatus to adjust temperature of
the chemicals or a gas sparger system or similar apparatus for producing
turbulence to aid in the mixing process. This apparatus may also be
included on the metered vessels themselves, which is particularly
beneficial in instances where mixing of chemicals occurs in the metered
vessels.
In addition to chemical mixing/diluting of virtually any form of chemical
solution, the present invention encompasses other useful applications,
such as serving as a chemical generator, or as a low-volume chemical
transfer/dispense apparatus.
DESCRIPTION OF THE DRAWINGS
The operation of the present invention should become apparent from the
following description when considered in conjunction with the accompanying
drawings, in which:
FIG. 1 is a schematic representation of the diluter/mixer apparatus of the
present invention.
FIG. 2 is an enlarged schematic representation of one embodiment of a
metered vessel of the present invention.
FIG. 3 is an enlarged schematic diagram illustrating the theory of
operation of the constricted vent tubes of the present invention.
FIG. 4 is a schematic representation of another embodiment of the
diluter/mixer apparatus of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an improved apparatus and method for
precisely mixing chemicals from two or more bulk sources and delivering
the mixture to a variety of possible downstream destinations, including
end use stations, intermediate storage vessels, and/or independent
chemical transfer or dispense apparatus.
Illustrated in FIG. 1 is one embodiment of a diluter/mixer 10 of the
present invention. The diluter/mixer 10 includes two metered vessels 12a,
12b. The first metered vessel 12a receives chemical from a bulk source 16
through a first chemical inlet 18 and a first intake line 20. The second
metered vessel 12b receives chemical from a bulk source 22 through a
second chemical inlet 24 and a second intake line 26.
In the embodiment shown, chemical exits each of the metered vessels 12a,
12b through a dispense line 28, 30 to a mix tank 32 where the chemicals
are combined in the manner described below. Once mixing is completed,
chemical can then be transferred through a continuation of the dispense
line 31 to variety of destinations, such as: intermediate storage vessels
34, 36; chemical transfer/delivery apparatus 38, such as the apparatus
disclosed in applicant's U.S. Pat. No. 5,148,945; or one or more
point-of-use stations 40.
It should be understood that under certain conditions the mix tank 32 may
be eliminated without diminishing the utility of the present invention.
Examples of such circumstances are: where intermediate storage vessels or
similar receptacles are employed and complete mixing of chemical can occur
in the intermediate tanks themselves; and a single vessel diluter/mixer
apparatus, such as that shown in FIG. 4 and described below, wherein
mixing occurs in the metered vessel.
To accomplish extremely accurate mixing of chemicals, the metered vessels
12 of the present invention are provided with means to amplify the precise
fluid level within the vessels as they approach filled capacity. As is
shown in FIGS. 1 and 2, each of the metered vessels 12a, 12b, 12c of the
present invention comprises a sealed main container 42a, 42b, 42c and a
constricted vent tube 44a, 44b, 44c. Once the chemical content of the
container 42 reaches the vent tube 44, the pressure of the trapped air in
the top of the sealed container 42 will cause chemical to cease filling
the container 42 and to begin filling only the tube 44. As is explained
below, the greatly constricted capacity of the tube 44 provides a
significantly amplified accuracy of measurement of chemical in the metered
vessel and permits more accurate cessation of chemical flow into the
vessel 12.
The theory of operation of the constricted vent tubes of the present
invention can be better understood with reference to FIG. 3. As is
illustrated, a reliable yet relatively low cost sensor 46a, 46b might have
an effective "bandwidth" of about 1/2 inch. Mounting such a sensor on a
container 48 having a volume of V.sub.v, the range of error of the sensor
46a would comprise the volume V.sub.w (i.e. the volume occupied by a 1/2"
of chemical across the entire diameter of container 48).
In contrast, by employing the same type of sensor 46b, with the exact same
1/2" bandwidth, on a vent tube 50, the range of error is greatly reduced.
In this instance, the range of error is only the volume V.sub.n (i.e. the
volume occupied by a 1/2" of chemical across the much smaller diameter of
the vent tube 50). Since the volume V.sub.n is insignificant relative to
the volume V.sub.v, this simple modification of the metered vessel
provides vastly improved accuracy to the process of filling the vessel
without the need of introducing more expensive (and generally less
reliable) sensors having narrower bandwidths.
To improve the accuracy of filling the metered vessels 12 further, in the
preferred embodiments shown in FIGS. 1 and 2, two sensors 52, 54 are
provided to monitor the presence of chemical in the metered vessels 42 and
vent tubes 44. The first sensor 52a, 52b, 52c (shown in FIG. 2 mounted on
the container 42c near the level of the base of the vent tube 44c, and
shown in FIG. 1 mounted on the vent tube 44a, 44b itself) provides a
signal when chemical approaches or initially enters the vent tube 44a,
44b, 44c. The second sensor 54a, 54b, 54c is mounted on the vent tube 44a,
44b, 44c and provides a signal when chemical reaches the desired
predetermined capacity of each vessel 12a, 12b, 12c. As is explained
below, t | | |
