Agitating – Having interrelated feed and discharge means – Including means to monitor or control operation
Reexamination Certificate
1998-07-07
2001-05-01
Walker, W. L. (Department: 1723)
Agitating
Having interrelated feed and discharge means
Including means to monitor or control operation
C366S131000, C366S136000, C366S152100, C366S348000
Reexamination Certificate
active
06224252
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
Many industrial applications of chemicals require high purities and minimal storage of such high purity chemicals. Some chemicals are desired in mixtures of commonly commercially available chemicals. Diluted forms of such chemicals are desired such as the semiconductor industry's need for diluted ammonium hydroxide in 28 to 30 wt. % in deionized water. Such chemical mixtures require blending of ammonia gas and deionized water in a precise manner. Alternatively, mixtures of ammonium hydroxide and hydrogen fluoride or hydrogen chloride are desired.
To facilitate ease and economy of use, operators have begun to generate or blend chemicals at or near the point of use, which can be referred to as on-site generation. When gaseous ammonia and deionized water are blended to make aqueous ammonium hydroxide, the process is sometimes referred to as gas to chemical generation. Attempts to generate chemical blends at or near the point of use have been made in the prior art, but purity problems continue to exist, such as when blending is not precise or when blended chemical picks up impurities during transit to storage or during extended storage prior to use.
U.S. Pat. No. 5,522,660 discloses a process and apparatus for mixing deionized water and a chemical in which the blended chemical is sensed for compositional properties downstream of the mixing and storage tank and additional chemical is added to the extent the sensed values do not meet predetermined values. Chemical is mixed with the deionized water only by recycle to the mixing and storage tank after the blended chemical has been sensed. This is an awkward manner in which to blend chemical, in which the blending initially occurs in a process line downstream of the mixing and storage tank. Continuous recycle is not envisioned and blending and storage is performed in one vessel.
International Patent Appln. No. WO 96/39651 describes a process and apparatus for mixing ultra high purity chemicals for semiconductor usage on-site. Various chemicals can be blended in a blend tank and delivered to a finished product storage tank. Blended chemical from the blend tank can be sensed prior to delivery to the finished product storage tank and the blend adjusted based upon such sensing. A process line connects the blend tank to the chemical line downstream of the sensor, but recycle is not specifically addressed and chemical delivered to the finished product storage tank cannot be recycled for reblending or repurification.
Other prior art of interest includes: U.S. Pat. No. 5,148,945; U.S. Pat. No. 5,242,468; U.S. Pat. No. 5,330,072; U.S. Pat. No. 5,370,269; U.S. Pat. No. 5,496,778; U.S. Pat. No. 5,426,944; U.S. Pat. No. 5,539,998; U.S. Pat. No. 5,644,921; International Appln. No. WO 96/39265; International Appln. No. WO 96/39237; International Appln. No. WO 96/39263; International Appln. No. WO 96/39264; International Appln. No. WO 96/39266; International Appln. No. WO 96/41687; Peters, Laura, “Point of Use Generation: The Ultimate Solution for Chemical Purity”, Semiconductor International, Jan. 1994, pp 62-66; and “Products in Action; Gas-to-Chemical Generation System Reduces ProcessChemical Costs”, Microcontamination, June 1994, pp. 79-80.
The prior art has proposed various on-site gas to chemical and chemical to chemical generators and mixers to provide high purity chemical at an industrial use site, such as a semiconductor fab; however the prior art has failed to provide adequate methods and apparatus to repeatedly or continuously purify or filter and monitor compositional properties of chemical that is generated, as well as chemical that is in storage awaiting use after generation. The present invention overcomes the drawbacks of the prior art by providing repeated or continuous purification or filtering and monitoring of not only just-generated blended chemicals, but also chemical which is in storage awaiting use, so as to maintain the purity and compositional properties of the produced chemical at all times, including during periods of low utilization or no utilization, which capabilities will be set forth in greater detail below.
BRIEF SUMMARY OF THE INVENTION
The present invention is an apparatus for blending high purity chemicals to produce a high purity chemical mixture with circulation, purification and sensing of the chemical mixture between a blending vessel and a chemical mixture storage vessel, comprising:
a) a blending vessel having a first inlet for receiving a first high purity chemical, a second inlet for receiving a second high purity chemical and a first outlet for dispensing a high purity chemical mixture of the first and second high purity chemicals;
b) a first source of the first high purity chemical connected to the first inlet of the blending vessel, the first source having a first valve to control the introduction of the first high purity chemical from the first source to the blending vessel;
c) a second source of a second high purity chemical connected to the second inlet of the blending vessel, the second source having a second valve to control the introduction of the second high purity chemical from the second source to the blending vessel;
d) a chemical mixture storage vessel having a third inlet for receiving the chemical mixture from the blending vessel, a second outlet for dispensing the chemical mixture to a point of use and a third outlet for recycling the chemical mixture;
e) a delivery line connected to the first outlet of the blending vessel and the third inlet of the chemical mixture storage vessel, a means to purify the chemical mixture passing from the blending vessel to the chemical mixture storage vessel through the delivery line and means for sensing the composition of the chemical mixture in the delivery line;
f) a recycle line connected to the third outlet of the chemical mixture storage vessel and connected to the delivery line between the blending vessel and the means to purify the chemical mixture to recycle the chemical mixture from the chemical mixture storage vessel to the delivery line for further passage through the means to purify and the means for sensing and having pumping means to recycle the chemical mixture through the recycle line; and
g) an automatic control means connected to the means for sensing and connected to the first valve and the second valve, containing means capable of receiving a signal from the means for sensing representative of the sensed composition of the high purity chemical mixture, comparing it to a predetermined composition value for the high purity chemical mixture and if the sensed composition does not match the predetermined composition value, initiating a signal to the first valve and/or the second valve to adjust the flow of the first high purity chemical and/or the second high purity chemical through the first valve and/or the second valve to return the sensed composition to the predetermined composition value.
Preferably, the blending vessel is two parallel blending vessels each having a valved connection to the first and second sources of chemical and to the delivery line.
Preferably, the means for purification is a filter.
Preferably, the pumping means is a diaphragm pump.
Preferably, the blending vessel has a source of high pressure inert gas to assist to dispense the high purity chemical mixture from the blending vessel.
The present invention is also a process for blending high purity chemicals to produce a high purity chemical mixture with circulation, purification and sensing of the chemical mixture between blending of the high purity chemicals and storage of the high purity chemicals for use, comprising the steps of:
a) providing a source of a first high purity chemical and a source of a second high purity chemical;
b) blending the first high purity chemical and the second high purity chemical in a blending zone in a predetermined ratio to result in a high purity chemical mixture hav
Greenawald Bruce Herman
Munroe James Platt
Samsal Richard Linton
Air Products and Chemicals Inc.
Chase Geoffrey L.
Ocampo Marianne S.
Walker W. L.
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