Processes for the preparation of organoluthenium compounds...

Details Processes for the preparation of organoluthenium compounds... Processes for the preparation of organoluthenium compounds...

2001-07-19

2002-11-05

Nazario-Gonzalez, Porfirio (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heavy metal containing

C427S248100

Reexamination Certificate

active

06476247

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a national stage application filed under 35 U.S.C. 371 of International Application No. PCT/JP00/08596, filed Dec. 05, 2000.
1. Technical Field
The present invention relates to a method of producing an organic ruthenium compound for use in forming, through chemical vapor deposition, ruthenium thin film or ruthenium compound thin film.
2. Background Art
In recent years, thin film formed of a precious metal such as ruthenium, platinum, or iridium or thin film formed of an oxide thereof has been used as a material for forming an electrode in a capacitor included in ICs and LSIs. The reason for employment of these precious metals is that a thin film electrode produced from these precious metals is endowed with excellent electrode characteristics. Particularly, ruthenium and ruthenium compounds have become of interest in that these ruthenium species are expected to serve as main-stream materials for producing thin film electrodes.
Generally, ruthenium thin films and ruthenium compound thin films are produced through chemical vapor deposition (hereinafter referred to as CVD), because CVD facilitates production of thin film of uniform thickness and attains excellent step coverage (step covering performance). Therefore, CVD is expected to be a predominant process for producing a thin film electrode in the future, because CVD meets a demand of recent years for higher packaging density of circuits and electronic parts.
As source substances used in CVD, among metallic compounds, organometallic compounds are used in view of low melting point and ease of handling. Particularly, as an organic ruthenium compound, bis(cyclopentadienyl)ruthenium (ruthenocene) represented by Formula 1:
has conventionally been used.
Bis(cyclopentadienyl)ruthenium, having high stability in air and no toxicity, is a suitable source for CVD. However, this compound is in solid form at ambient temperature and has a melting point as high as approximately 199-201° C. Thus, a relatively large amount of energy is required for vaporizing the source.
In view of higher efficiency of thin film production, a variety of studies have been carried out on a ruthenium compound having a lower vaporization energy and lower melting point.
In order to lower the melting point of an organic ruthenium compound, there has been employed a method in which a functional group is added to at least one cyclopentadiene ring of bis(cyclopentadienyl)ruthenium, to thereby form a bis(cyclopentadienyl)ruthenium derivative.
Among such organic ruthenium compounds in which a functional group is added to a cyclopentadiene ring of bis(cyclopentadienyl)ruthenium, one promising candidate for a CVD source at present is bis(ethylcyclopentadienyl)ruthenium (also called 1,1′-diethylruthenocene), represented by Formula 2:
in which the functional group is added to each cyclopentadiene ring.
Bis(ethylcyclopentadienyl)ruthenium is in liquid form at ambient temperature and has a relatively low melting point, to thereby provide sufficient vapor pressure. Thus, this compound is regarded a suitable CVD source substance endowed with essential characteristics.
In addition, an organometallic compound, represented by Formula 3:
(wherein R
2
represents a linear or branched alkyl group) in which a functional group is introduced into only one cyclopentadiene ring of bis(cyclopentadienyl)ruthenium also shows promise as a CVD source.
For example, (ethylcyclopentadienyl)cyclopentadienylruthenium—R
2
is an ethyl group—has a melting point of approximately 12° C., which is remarkably lower than that of bis(cyclopentadienyl)ruthenium. Thus, this ethyl-substituted compound is considered to serve as an excellent CVD source in a source vaporization step and a step of transferring the formed gas source.
As methods of producing these bis(cyclopentadienyl)ruthenium derivatives, the following methods are known.
(1) Conventional Methods of Producing Bis(cyclopentadienyl)ruthenium
The following three methods for introducing an ethyl group into each cyclopentadiene ring of bis(cyclopentadienyl)ruthenium; i.e., methods for producing bis(ethylcyclopentadienyl)ruthenium, are known.
The first method is drawn to a method of producing bis(ethylcyclopentadienyl)ruthenium by reducing bis(acetylcyclopentadienyl)ruthenium by sodium borhydride (NaBH
4
) (for detailed description of this production method, see G. B. Shul'pin,
Zh. Obshch. Khim
., vol. 51, 2152 (1981)).
The second method is drawn to a method of producing bis(ethylcyclopentadienyl)ruthenium through ligand-exchange reaction between bis(ethylcyclopentadienyl)iron ((C
2
H
5
C
5
H
4
)
2
Fe) and ruthenium trichloride (RuCl
3
) (for detailed description of this production method, see G. J. Gauthier,
Chem. Commun
., 690 (1969)).
The third method is drawn to a method of producing bis(ethylcyclopentadienyl) ruthenium by reacting ethylcyclopentadiene (C
2
H
5
C
5
H
4
) and ruthenium trichloride (RuCl
3
) in an alcoholic solvent in the presence of zinc powder (for detailed description of this production method, see Japanese Patent Application Laid-Open (Kokai) No. 11-35589).
(2) Conventional Methods of Producing Alkylcyclopentadienyl(cyclopentadifenyl)ruthenium
Taking a method of producing (ethylcyclopentadienyl)cyclopentadienylruthenium as an example, a method of producing alkylcyclopentadienyl(cyclopentadienyl)ruthenium in which a functional group has been introduced into only one cyclopentadiene ring of bis(cyclopentadienyl)ruthenium is described next. In one known method, bis(cyclopentadienyl)ruthenium and acetic anhydride are reacted in the presence of aluminum chloride serving as a catalyst, to thereby form (acetylcyclopentadienyl)cyclopentadienylruthenium represented by the following Formula:
(wherein R
1
represents a linear or branched alkyl group) in which one hydrogen atom of bis(cyclopentadienyl)ruthenium is substituted by an acetyl group, and the thus-formed (acetylcyclopentadienyl)cyclopentadienylruthenium is reduced by aluminum chloride and lithium aluminum hydride (LiAlH
4
), to thereby form (ethylcyclopentadienyl)cyclopentadienylruthenium (for detailed description of this technique, see M. D. Rausch et al.,
J. Am. Chem. Soc
., vol. 82, p76 (1960) and V. Mark et al.,
Inorg. Chem
., vol. 3, No. 7, p1067 (1964)).
However, when a functional group is introduced into a cyclopentadiene ring of bis(cyclopentadienyl)ruthenium through any of these conventional methods, to thereby produce a derivative thereof, the below-described problems arise. (3) Problems Involved in Conventional Methods of Producing Bis(ethylcyclopentadienyl)ruthenium.
Problems in connection with the aforementioned three conventional methods of producing bis(ethylcyclopentadienyl)ruthenium is described. In the first method, sodium—a component of sodium borohydride serving as a reducing agent—is intermingled as an impurity into produced bis(ethylcyclopentadienyl)ruthenium. As a result, sodium is also incorporated into the thin film prepared from this compound. Since an alkali metal such as sodium is an impurity which greatly affects electrical properties of the thin film, the bis(ethylcyclopentadienyl)ruthenium produced through the first method is not preferred as a CVD source substance.
The second method also involves a similar problem. Into bis(ethylcyclopentadienyl)ruthenium produced through the second method, an iron compound (ferrocene) having properties similar to those of bis(alkylcyclopentadienyl)ruthenium is intermingled. In addition, the iron compound is difficult to remove. Thus, when the bis(ethylcyclopentadienyl)ruthenium produced through the second method is used, a CVD apparatus and the thin film produced through CVD are also contaminated by the compound.
In terms of the purity of the product, the third method is more excellent that the other two methods. However, ethylcyclopentadiene which serves as a starting substance in this method is produced through pyrolysis of bis(ethylcyclopentadiene), which is generally difficult to obtain and is an expensive material. Thus, the produced

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