Semiconductor device manufacturing: process – With measuring or testing
Reexamination Certificate
1999-05-28
2001-05-01
Chaudhari, Chandra (Department: 2813)
Semiconductor device manufacturing: process
With measuring or testing
Reexamination Certificate
active
06225135
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to a sensor for real time monitoring of chemical baths used in the fabrication of semiconductor devices and, more specifically, to an electrolytic cell having channel electrodes coupled thereto that are capable of monitoring the presence of transition metals in chemical baths used in the fabrication of semiconductor devices and a method of use therefore.
BACKGROUND OF THE INVENTION
The manufacturing of semiconductors regularly employs the use of chemical solvent baths, i.e., acids, bases and organic solvents, for both cleaning the semiconductor wafer and removing unneeded portions of layers, e.g., photolithographic masks, formed during an intermediate process. Especially in acids or strong bases, certain transition metals, such as copper (Cu), iron (Fe), and zinc (Zn) may be soluble as ions in the solvents used. Unfortunately, traces of these metals in an acid etch or solvent cleaning solution can precipitate onto critical areas of the semiconductor wafer during processing, resulting in failure of the integrated circuit. As the concentration of a particular metal ion increases in the solvent, the likelihood of contamination of the wafer increases. Heretofore, the only available method of monitoring metal ion concentration in the solvent has been by sampling the solvent and analyzing the sample ex situ, while the processing of semiconductor wafers continues. The major problem with this procedure is that the wafers processed while the solvent testing is being performed are at risk of contamination and failure.
Historically, copper has not been a major problem in it semiconductor manufacturing. Aluminum (Al) has been the metal of choice in the formation of interconnectivity traces in the semiconductor back-end. It was only recently that the problems associated with using copper in semiconductor manufacturing were solved. However, with the recent advances in copper technology, the movement in the industry will certainly be toward greater use of copper because of its superior conductive properties over aluminum. Therefore, any metal ion monitoring method must address the introduction of copper to semiconductor manufacture.
Accordingly, what is needed in the art is an in situ, real time, monitoring system for transition metals in semiconductor processing chemical baths.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides an electrolytic cell for use in a process for real time monitoring of a chemical bath used in the fabrication of a semiconductor wafer and having different metal ions therein. In one embodiment, the electrolytic cell comprises a fluid chamber having an inlet, an outlet and chamber walls, and channel electrodes coupled to the chamber walls. The inlet and outlet permit a throughflow of at least of a portion of the chemical bath. Each of the channel electrodes corresponds to one of the different metal ions. Each channel electrode is energized to a detection potential selected to provide electrical conduction when the corresponding different metal ion reaches a prescribed concentration.
In an alternative embodiment, at least one of the channel electrodes further comprises an ion-selective film formed on the channel electrode; the ion-selective film being capable of capturing the metal ion from the chemical bath. In such embodiments, the ion-selective film may further comprise a receptor molecule formed on a surface of the channel electrode. In a one particular embodiment, the receptor molecule may be a derivative of 2,2′-trichorosilane-bisalkyl acetoacetonate having the general formula: Cl
3
Si[CH
2
(CH
2
)
n
—O—C(O)CH
2
C(O)CH
3
]
2
. The receptor molecule, in a more specific embodiment, may be 2,2′trichlorosilane-bisethyl acetoacetonate or 2,2′-silobisethyl acetoacetonate. It is believed that the receptor molecule captures the metal ion by way of dative bonding.
In another embodiment, the ion-selective film further comprises a surface sealing component. For example, the surface sealing component may be an organic fatty acid having the general formula of C
n
H
2n+1
COOH, where n is equal to or greater than 4, or an n-alkyl trichlorosilane having the general formula C
n
H
2n+1
SiCl
3
.
The metal ion, may be an M
2+
or M
3+
metal ion. In a particular embodiment, the metal ion is an M
2+
metal ion selected from the group consisting of Cu
2+
, Zn
2+
, or Cd
2+
. In another embodiment, the metal ion may be an M
3+
metal ion selected from the group consisting of Fe
3+
or Ce
3+
.
In an alternative embodiment, the channel electrode is an inert electrode selected from the group consisting of: platinum, glassy carbon, or n-type silicon. In yet another embodiment, the electrolytic cell further comprises electrical connectors that connect each of the channel electrodes to an analyzer capable of determining a concentration of at least one of the metal ions in the chemical bath as a function of the current.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 5364510 (1994-11-01), Carpio
G. Compton and P.R. Unwin; “The Dissolution of Calcite in Aqueous Solution pH<4: Kinetics and Mechanism”; Phil. Trans. R. Soc. Lond. vol. 330; 1990; pp. 1-45.
R. G. Compton & A. Hamnett; “The Use of Channel Electrodes in the Investigation of Interfacial Reaction Mechanisms”; vol. 29—New Techniquest for the Study of Electrodes and Their Reactions; 1989; pp. 173-296.
Frank Aaron L.
Obeng Jennifer S.
Obeng Yaw S.
Chaudhari Chandra
Lucent Technologies - Inc.
Thompson Craig
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