Chemistry: analytical and immunological testing – Including sample preparation – Digestion or removing interfering materials
Reexamination Certificate
1998-11-12
2001-01-23
Carrillo, Sharidan (Department: 1746)
Chemistry: analytical and immunological testing
Including sample preparation
Digestion or removing interfering materials
C436S073000, C436S100000, C436S101000, C436S102000, C436S103000, C436S106000, C436S110000, C436S119000, C436S124000, C436S125000, C134S002000, C134S003000, C134S021000, C134S026000, C134S032000, C134S034000, C134S036000, C073S863210, C073S863830, C073S863840
Reexamination Certificate
active
06177279
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to silicon wafer cleaning, and in particular to an apparatus and method for determining inorganic ionic contamination on a single surface of a wafer.
A substantial concern in the manufacture of silicon wafers for semiconductor chips is surface contamination. Impurities degrade wafer surfaces allowing a haze to form on the surfaces, and can cause corrosion of metallic components of semiconductor devices. Among the contaminants that have a detrimental impact on the quality and reliability of integrated circuit devices are inorganic anions such as chloride, sulfate, nitrate, and fluoride.
Accurate measurement of silicon wafer surface anion contamination is crucial to maintain quality control of the manufacturing process. Contamination levels must be monitored to ensure that products are of a quality necessary for production of integrated circuit devices. Typically, a small percentage of production wafers are randomly sampled for testing. If anion concentration exceeds an allowable level, wafer production may be halted until the contamination source(s) can be identified and eliminated.
Previous measurement methods have not allowed testing a single side of a silicon wafer. Single-side data is of primary importance since integrated circuit devices are typically mounted only on one side of the wafer, and only on that side is contamination a concern. One technique established in the art for detection of inorganic ionic contaminants on all surfaces of the wafer is to perform a water extraction, in which the wafer is immersed in pure water for a period of time to cause a transfer of anions (which are water-soluble) from the wafer surface to the water. The water is subsequently analyzed using an ultra trace analysis method such as ion chromatography (IC) or capillary electrophoresis (CE) to determine anion concentrations. This technique provides the average contamination level of the entire wafer, including both sides, but precludes measuring contamination on a single surface.
Further, previous measurement methods are subject to inaccuracy and non-reproducibility. Sampled wafers are exposed to contamination not only during the manufacturing process but also during the contamination measurement process. Airborne gas phase species in any open environment circulate past deionized water used in an extraction and contaminate it. Even class 1 cleanrooms contain airborne molecular species contaminants. When IC or CE test results indicate high levels of contamination, uncertainty arises as to whether the impurities originate in the manufacturing process or in the measurement process.
SUMMARY OF THE INVENTION
Among the several objects and features of the present invention may be noted the provision of a process and apparatus to extract inorganic ionic contaminants from a single side of a silicon wafer; the provision of such a process and apparatus which provides an accurate sample of ionic inorganic contaminants on a single side of the wafer; the provision of such a process and apparatus that minimizes contamination from airborne sources; and the provision of such a process and apparatus which is economical to use.
Briefly, a process of the present invention for extracting inorganic ionic contaminants from a front surface of a silicon wafer for chemical analysis comprises placing the wafer upon a mount that supports the wafer in a generally level orientation with the front surface of the wafer facing upwardly. The wafer is isolated to inhibit air circulation over the front surface and a layer of extraction fluid is deposited upon the front surface of the wafer. The layer of extraction fluid is held on the front surface of the wafer for a period of time so that contaminants on the front surface are extracted into the layer of fluid, and a portion of the layer of fluid from the front surface is collected for subsequent analysis.
In another aspect, apparatus of the present invention extracts inorganic ionic contaminants from a front surface of a silicon wafer. The apparatus comprises a container adapted to receive the wafer, and a sampling device for taking a sample from the layer of extraction fluid on the front surface of the wafer. The container has a support for holding the wafer in a generally level orientation with the front surface of the wafer facing upwardly. The container is further adapted to inhibit air circulation over the front surface of the wafer. The container has an inlet orifice for introducing the layer of extraction fluid to the front surface of the wafer.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.
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Article entitled “Demonstrating a contamination-free wafer surface extraction system for usewith CE and IC”, Micromagazine, Apr., 1999, p. 41 XP002132594; Peng Sun, et al.
Anal. Chemical, “Determination of Boron and Phosphorus in Borophosphosilicate Thin Films on Silicon Substrates by Capillary Electrophoresis”, by R. A. Carpio, et al., vol. 64, Issue 18, pp. 2123-2129, Sep., 1992.
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Adams Marty
Sun Peng
Carrillo Sharidan
MEMC Electronic Materials , Inc.
Senniger Powers Leavitt & Roedel
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