Synthesis of substituted ruthenocene complexes

Details Synthesis of substituted ruthenocene complexes Synthesis of substituted ruthenocene complexes

2001-09-27

2003-02-18

Nazario-Gonzalez, Porfirio (Department: 1621)

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

Organic compounds

Heavy metal containing

C427S252000, C427S255280

Reexamination Certificate

active

06521772

ABSTRACT:

FIELD OF THE INVENTION
This invention is related to a method of synthesizing organometallic materials. More specifically, this invention is directed to the synthesis of substituted ruthenocene complexes.
BACKGROUND OF THE INVENTION
Ruthenium (Ru) and ruthenium oxide (RuO
2
) are materials that may be used as electrodes in future semiconductor devices (e.g. DRAM and Logic chips). These materials possess attractive physical properties, such as low electrical resistance, high work functions, inter-layer chemical diffusion resistance and thermal and oxidative stability. In addition, Ru and RuO
2
thin films have lattice parameters and thermal expansion coefficients that are compatible with many dielectric materials under consideration for future semiconductor devices.
Chemical vapor deposition (CVD) is a technique that is widely utilized in the fabrication of semiconductor devices to produce the layers of materials that make the devices. In CVD, chemical compounds (referred to as precursors) are transported in the vapor phase to or near a surface where they decompose by some means (e.g. thermal, chemical or plasma activation) to produce a solid film of a desired material composition. The use of CVD techniques to produce both ruthenium and ruthenium oxide thin films for semiconductor devices is known. See, WO 00/12766. Ruthenium compounds suitable for use as CVD precursors to ruthenium and ruthenium oxide thin films will be required if these materials are incorporated into commercial semiconductor devices using the CVD technique.
One class of compounds that appears to have suitable derivatives for CVD precursors are substituted cyclopentadienyl ruthenium complexes (SCRs) of the general formula (C
5
H
4
R)Ru(C
5
H
4
R′) [R,R′=H, alkyl, silyl, etc.]. Selected derivatives of this class of compounds meet several criteria desirable for their use as CVD precursors. They exist as liquids in the pure state at or near room temperature, possess moderate volatility, air stability, and most importantly have been demonstrated to produce Ru and RuO
2
films under appropriate CVD conditions. For example, the liquid derivative bis(ethylcyclopentadienyl) ruthenium has been reported to be a suitable CVD precursor for deposition of both Ru and RuO
2
films (See, e.g., Kim et. al., J. Electrochem Soc., 2000, 147 (3), pp. 1161-1167).
U.S. Pat. No. 6,002,036 discloses a method for the synthesis of a subclass of the substituted cyclopentadienyl ruthenium complexes, specifically bis(ethylcyclopentadienyl) ruthenium and bis(isopropylcyclopentadienyl) ruthenium (R =CH
2
CH
3
, CH(CH
3
)
2
respectively). These compounds are reported to be liquids of moderate volatility at 25° C., which make them potentially attractive as Ru/RuO
2
CVD precursors. The '036 patent discloses a one step synthesis to produce bis(ethylcyclopentadienyl) ruthenium from ruthenium trichloride hydrate in 70% yield). This report is reasonably substantiated by an earlier report in the chemical literature for producing bis(cyclopentadienyl) ruthenium, (a ruthenocene) (R=H) using near identical reaction conditions (See, Pertici, P., Inorg. Synth., 1983, 22, p. 180). In these reactions ruthenium trichloride hydrate is reacted with cyclopentadiene or a substituted-cyclopentadiene and a reducing agent (such as zinc) in the presence of a solvent (such as alcohol) to produce SCRs.
Several alternate synthetic routes to alkyl-substituted cyclopentadienyl ruthenium compounds employing ruthenocene as a starting material are known. The production of monoethylcyclopentadienyl ruthenium (R=CH
2
CH
3
, R′=H) through a multi-step reaction sequence has been disclosed (See, Rausch, M. et al.,
J. Org. Chem
., 1964, 3, 7 pp. 1067-1069). In this synthesis Friedel-Crafts acylation is employed to produce an acetyl substituted cyclopentadienyl ruthenium complex. The acyl group is then reduced to an alkyl group by using lithium aluminum hydride.
The use of Li-TMEDA to prepare metallated intermediates for nucleophilic substitution reactions has previously been reported for production of iodine substituted ruthenocene derivatives (See, Neuse E., J. Organomet. Chem., 1979, 168 p. C8-C12).
Finally, ruthenocene and bis(ethylcyclopenta-dienyl) ruthenium have also been prepared by the ligand exchange reaction between ruthenium trichloride and ferrocene or bis(ethylcyclopentadienyl) iron respectively in low yield. (See, Gauthier, G. J. Chem Soc. D, 1969 p. 690).
In order to successfully incorporate ruthenium CVD precursors into mainstream semiconductor fabrication processes, a suitable industrial process for their manufacture must be developed. The process must repeatedly produce material that meets the semiconductor industry's purity specifications. Due to the high cost of ruthenium (a platinum group metal) development of a high yield, low cost process is required to competitively produce these materials.
Kadokura disclosed that it produced bis(ethylcyclopentadienyl) ruthenium in a single step from ruthenium trichloride hydrate with a yield of 70%. To produce bis(ethylcyclopentadienyl) ruthenium using the invention described herein starting from ruthenium chloride, a two step synthesis is employed with an overall yield of at least about 65%. While the overall yield of the present invention is lower, it has several advantages. The most important advantage is that the present synthetic procedure permits the production of a greater variety of chemical derivatives; both mono-, bis- and tri-substituted products can be obtained by varying the stoichiometric amount of reactants employed. This is an advantage because the structure of the precursor effects its physical properties. Mono-substituted ruthenocene derivatives are expected to be desirably more volatile than similar bis-substituted compounds. In low-pressure CVD processes the surface chemistry ultimately determines film properties. For example, the sticking coefficient and surface lifetimes of the precursors will determine the process efficiency, while the surface mobility will effect the conformality of the deposited material. Thus, having a synthetic platform that provides access to a variety of similar derivatives is preferential to allow a comparative determination of which precursor structures lead to the desired film characteristics.
Additionally, the reagents employed in the invention reported here are commercially available, whereas the alkyl substituted cyclopentadienes are not. Thus, while the method of Kadokura can produce bis-alkyl substituted products in higher yield, an economic advantage is achieved only if the cost of the alkylcyclopentadiene is less than the cost of extra reagents used in this process. Again it should be stressed that Kadokura's method is clearly limited in its exclusive production of bis-substituted products.
The method disclosed by Rausch et. al. (Scheme 3) produces alkyl-substituted material starting from ruthenocene, uses commercially available reagents of similar cost to the invention described here, and is reported to produce alkyl-substituted ruthenocenes in similar yield. However, Rausch's route is not flexible since reduction chemistry on the acyl intermediate must be employed. Additionally the process steps are more labor intensive than those employed herein.
The ligand exchange process reported by Gauthier suffers the disadvantage of producing material in the poorest yield of all the processes discussed above. An additional disadvantage is the necessity of producing the alkyl-substituted cyclopentadienyl iron complex (and presumably employing one of the synthetic routes described here to do so) as a starting material. Finally iron is a key impurity in the final ruthenium products, so its inclusion in the synthetic route is not desirable.
The advantages of the present synthesis process includes the ability to synthesize a variety of different substituted cyclopentadienyl ruthenocene complexes in a manner that allows mono-, bis- or multiple substitution in a novel manner.
SUMMARY OF THE INVE

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