Agitating – Having specified feed means – Responsive to condition sensor
Reexamination Certificate
1999-12-20
2004-10-05
Sorkin, David (Department: 1723)
Agitating
Having specified feed means
Responsive to condition sensor
C366S152100, C137S003000, C137S005000
Reexamination Certificate
active
06799883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to novel methods and apparatus for continuously blending a chemical solution for use in semiconductor processing and, more particularly, to their on-site use at a semiconductor manufacturing facility.
2. Description of the Related Art
In the semiconductor manufacturing industry, extensive use is made of liquid chemicals, for example, in wafer cleaning and etching processes. Accurate mixing of reagents at desired ratios is particularly important because variations in concentration of the chemicals introduce uncertainty in etch rates and, hence, are a source of process variation.
Conventionally used chemicals in the semiconductor manufacturing industry which are formed by mixing together two or more chemicals include, for example, hydrofluoric acid (HF), ammonium fluoride (NH
4
F), hydrochloric acid (HCl), ammonium hydroxide (NH
4
OH) and nitric acid (HNO
3
) On-site preparation of such chemicals in ultrapure form is described, for example, in U.S. Pat. Nos. 5,785,820, 5,722,442, 5,846,387, 5,755,934 and in International Publication No. WO 96/39263, the contents of which documents are herein incorporated by reference.
Conventionally, the blending of chemicals is performed by chemical suppliers off-site from the semiconductor manufacturing facility. The chemicals are typically blended through the use of load cells and mixing tanks, with analytical verification. The use of load cells, however, is undesirable for various reasons. For example, piping, which is attached to the weighed mixing vessel, exerts an unpredictable force. This can lead to inaccuracies in measuring the weight of the fluid in the vessel resulting in chemical blends of imprecise formulation.
In addition, expensive electronic equipment is typically required for such known blending processes. The exposure of this equipment to corrosive chemical environments often leads to corrosion and premature failure thereof. Moreover, load cells require the use of additional laboratory instrumentation to determine incoming chemical assay as well as program adjustments to compensate for assay variability.
Upon obtaining a desired chemical formulation, the chemicals are conventionally packaged in totes or drums for shipment to the semiconductor manufacturing facilities. Packaging and storage of the chemicals in this manner is undesirable in that the process of packaging the chemicals and the containers themselves are sources of contamination.
Furthermore, the cost per unit volume of transporting ultrapure chemicals is high. This cost can be especially prohibitive if chemicals of all requisite concentrations are to be shipped. In this regard, the conventionally used chemicals, such as hydrofluoric acid, are often employed at various dilutions in the semiconductor manufacturing process. Chemical shipment is particularly inefficient with very dilute acids.
Once at the semiconductor manufacturing site, the chemicals are stored until used. Such storage, however, is not particularly desirable, as considerable space is required and costs are incurred due to storage and management of the totes in the manufacturing facility.
In addition, the chemicals are often unstable and therefore have limited shelf lives. High purity water (“deionized” or “DI” water), typically employed in the manufacture of chemicals, exhibits organic growth after short periods of time. Hence, it is not uncommon for the shelf life of a chemical to expire prior to use. The unused chemical must therefore be disposed of, resulting in economic loss as well as environmental issues associated with waste disposal.
To address the problems associated with the processing of chemicals off-site from the point-of-use, on-site blending methods and apparatus have been proposed for semiconductor applications. An on-site blending method is described, for example, in International Publication No. WO 96/39651, the contents of which are incorporated herein by reference. An exemplified embodiment of that document involves a batch-type process, with mixing of the components taking place in a single blender tank. After mixing two chemicals in the blender tank to a desired endpoint, those chemicals are shut off. A third chemical is next introduced into the tank to a desired endpoint.
One of the disadvantages associated with such a batch-type process is that it is difficult to achieve steady state conditions and the desired chemical formulation in a small amount of time. In addition, it is necessary with the batch-type process that a supply of the blended chemical be stored in a tank or other container to avoid production down time if the chemical should become depleted. The use of a storage container, however, is undesirable at least due to its space and management requirements.
To meet the requirements of the semiconductor manufacturing industry and to overcome the disadvantages of the related art, it is an object of the present invention to provide novel methods for continuously blending a chemical solution. The invention allows for real time, precise control of chemical formulations by continuous monitoring and flowrate adjustment of the chemicals employed. The desired formulations can be achieved in a fast and facile manner from startup based on calibration data stored in one or more controllers.
Furthermore, total cost associated with the chemicals can be significantly reduced since only concentrated acids, and not dilute solutions, need be shipped to the end user's site. This renders unnecessary the need to inventory and handle large volumes of dilute chemicals. In addition, the costs and time associated with laboratory analytical verification can be avoided or minimized, since the process is calibrated to analytical analysis at the time the process is set up and only periodically thereafter to ensure continued calibration accuracy.
It is a further object of the invention to provide methods of continuously blending a chemical solution on-site at a semiconductor manufacturing facility.
A further object of the present invention is to provide a novel apparatus for continuously blending a chemical solution.
It is a further object of the invention to provide an apparatus for continuously blending a chemical solution on-site at a semiconductor manufacturing facility.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art on a review of the specification, drawings and claims appended hereto.
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Hoffman Joe G.
Thompson John B.
Urquhart Karl J.
Air Liquide America L.P.
Haynes Elwood L.
Russell Linda K.
Sorkin David
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