Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2002-09-09
2003-08-12
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C427S248100, C427S587000, C427S593000
Reexamination Certificate
active
06605735
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to organometallic ruthenium complexes which are useful for forming a ruthenium-containing thin film by the chemical vapor deposition method (hereinafter referred to as the CVD method), the coating heat decomposition method and so on, a process for producing the same and a process for producing a ruthenium-containing thin film to be used in electronics devices such as semiconductor memories.
BACKGROUND OF THE INVENTION
With the progress of fine processing in memory cells in association with the recent tendency toward highly integrated semiconductor memory devices, attempts have been made to use ferroelectric thin films such as (Ba,Sr)TiO
3
as insulating films in capacitors. In capacitors provided with ferroelectric thin films, use is made of noble metals such as Pt, Ru and Ir as electrodes. Among these metals, Ru is expected as the most useful electrode material, since its oxide has a conductivity and excellent fine processing properties. Thus, examinations have been made on electrodes made of an Ru thin film or an RuO
2
thin film. To form such ruthenium-containing thin films in highly integrated memory devices, the CVD method is the most suitable since it is excellent in step coverage and composition controlling.
It is considered that organometallic compounds, which have low melting point and can be easily handled among metal compounds, are adequate as precursors for forming thin films by this CVD method. As organometallic compounds for the deposition of ruthenium or ruthenium oxide thin films, it has been a practice to use ruthenocene or tris(dipivaloylmethanato)ruthenium (hereinafter referred to as Ru(DPM)
3
) [Japanese Patent Laid-Open No. 283438/1994]] or tris(octane-2,4-dionato)ruthenium (hereinafter referred to as Ru(OD)
3
) [Japanese Patent Laid-Open No. 2000-212744]. Ruthenocence has a sandwich structure carrying ruthenium sandwiched between two cyclopentadienyl rings each consisting exclusively of carbon and hydrogen. Because of being highly stable in the atmosphere and having no toxicity, ruthenocene is suitable as a CVD precursor. However, it suffers from difficulties in the vaporization of the precursor and transportation onto substrates somewhat, since it is in the state of a solid at ordinary temperature and has a relatively high melting point of about 200° C.
Accordingly, studies have been vigorously made in recent years on ruthenium compounds having lower melting point. The melting point of a ruthenium-containing organometallic compound can be lowered by converting it into a ruthenocene derivative in which at least one of the hydrogen atoms in the cyclopentadienyl rings of ruthenocene is substituted by an alkyl group such as a methyl or ethyl group. For example, Japanese Patent Laid-Open No. 35589/1999 discloses bis(alkylcyclopentadienyl)ruthenium typified by bis(ethylcyclopentadienyl)ruthenium (hereinafter referred to as Ru(EtCp)
2
) and bis(isopropylcyclopentadienyl)ruthenium as a ruthenocene derivative. Further, Japanese Patent Laid-Open No. 2000-281694 discloses use of alkyl-substituted ruthenocenes as CVD precursors. It is stated that each of these organometallic compounds is in the state of a liquid at ordinary temperature and has a lower melting point than ruthenocene, i.e., having characteristics required as precursors suitable for the CVD method. However, these bis(alkylcyclopentadienyl)rutheniums fundamentally have the ruthenocene structure. Since this structure has an extremely high stability, these complexes have high decomposition points. Therefore, it is essentially needed to elevate the substrate temperature to a high level in the step of film-formation, which results in a problem of worsening in the step coverage.
On the other hand, R. Gleiter et al. (Organometallics, 8, 298 (1989)) reported (cyclopentadienyl)(2,4-dimethylpentadienyl)ruthenium as an example of the synthesis of a half-sandwich complex having a cyclopentadienyl group as a ligand. However, this complex cannot be considered as suitable as a CVD precursor, since it has a melting point of 136 to 137° C. and occurs as a solid at ordinary temperature. There has been reported no case of synthesizing a half-sandwich ruthenium complex which is in the state of a liquid at room temperature and shows excellent vaporization properties.
To synthesize a half-sandwich ruthenocene, it has been a common practice to add a pentadiene derivative, a cyclopentadiene derivative, zinc and halogenated ruthenium hydrate to an appropriate solvent at once and then reacting under appropriate reaction conditions. However, this method is not practically usable since only an extremely low yield can be achieved thereby. As the post-treatment following the reaction, it has been also a practice that the liquid reaction mixture is concentrated to give a pasty mixture and the target product is extracted from the pasty mixture with the use of an appropriate solvent followed by purification by filtration through celite or column chromatography using an alumina column to thereby give the target product. However, this method involves industrially unfavorable steps such as the extraction from the pasty mixture obtained by concentration after the completion of the reaction and the celite-filtration or the column chromatography. To make half-sandwich organometallic ruthenium compounds industrially advantageous, therefore, it has been urgently required to establish a production process whereby a target product can be obtained in a stable state at a high yield.
On the other hand, film-formation by the coating heat decomposition method has been applied to the production of elements having a relatively low integration level. Since precursors to be used in the coating heat decomposition method are dissolved in organic solvents before using to thereby control the film thickness, it is favorable that these precursors are soluble in organic solvents and decompose at low temperature. However, there have been few ruthenium compounds having the above characteristics.
There has been known no carbonylbis(diene)ruthenium complex other than carbonylbis(1,3-butadiene)ruthenium (D. Minniti and P. L. Timms, J. Organomet. Chem., 258, C12(1983)), carbonylbis(2,3-dimethyl-1,3-butadiene)ruthenium and carbonylbis(1,3-cyclohexadiene)ruthenium (D. N. Cox and R. Roulet, Helv. Chim. Acta, 67, 1365 (1984)). These complexes are produced by a process with a need for a reaction at a low temperature, i.e., reacting Ru with a diene at −196° C. and then adding CO.
In the CVD method, a complex employed as a thin film precursor should be supplied as a gas. Among the complexes employed hitherto, Ru(DPM)
3
is to be vaporized by sublimation because of its high melting point of 168° C. In the vaporization by sublimation, there arises a problem that the precursor gas concentration varies depending on changes in the surface area of the solid and thus the precursor gas cannot be stably supplied. To overcome this problem, Japanese Patent Laid-Open No. 132776/1993 proposes a method wherein a complex is dissolved in an organic solvent before using. However, the precursor can be not always supplied stably by this method too, since there arise some problems that the solvent alone is vaporized or the solid is deposited due to a difference in vaporization properties between the solvent and the complex. On the other hand, Ru(OD)
3
and Ru(EtCp)
2
suffer from no problem in the stable supply of the precursors, since they each occurs as a liquid at room temperature and has a relatively high vapor pressure. In these complexes, however, Ru is stably bonded to the respective organic ligands. Thus, these complexes are hardly decomposed and should be treated at a high temperature for the film-formation.
SUMMARY OF THE INVENTION
The present invention aims at providing ruthenium complexes which can be subjected to the film-formation by the CVD method at a low temperature compared with the complexes as described above and can suitably supply a precursor thereof, a process for producing the same and a proc
Furukawa Taishi
Kawano Kazuhisa
Kumagai Shuji
Oshima Noriaki
Sekimoto Kenichi
Nazario-Gonzalez Porfirio
Tosoh Corporation
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