Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Patent
1995-02-27
1995-12-05
Nazario-Gonzales, Porfirio
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
568 7, 427585, 427586, 427593, C07F 500, C07F 502, C07F 506
Patent
active
054730902
DESCRIPTION:
BRIEF SUMMARY
This application is a request for U.S. examination under 35 U.S.C. 371 of International application No. PCT/EP93/01770, filed on Jul. 1, 1993.
The present invention relates to the preparation of trialkyl compounds of Group 3a metals. These organometallic compounds find increasing use in the semiconductor industry. In this industry a Group 3a metal compound is deposited onto suitable substrates, generally together with one or more compounds of a Group 5 element, such as arsenic or phosphorus. The deposition of such compounds can be carried out via the decomposition of organometallic compounds from the vapor phase. Such decomposition is known as Metal Organic Chemical Vapor Deposition (MOCVD). When epitaxial layers are grown from such decomposition the technique is better known as Metal Organic Vapor Phase Epitaxy (MOVPE).
A convenient route for the preparation of such trialkyl compounds is via the reaction of Group 3a metal chlorides with either a Grignard reagent, viz. an alkylmagnesium halide, or an alkyllithium compound. A disadvantage of these methods resides in the use of the Group 3a metal chlorides, which are difficult to obtain in the high purity that is required for further use in the semiconductor industry. High purity metals are available commercially and represent therefore a suitable starting material for the preparation of trialkyl compounds of such Group 3a metals.
In the preparation of alkyl compounds of Group 3a metal frequent use is made of elemental Group 3a metal in combination with magnesium.
In Japanese application No. 01/301,684 the preparation of alkyl gallium and alkyl indium compounds is described using a gallium-magnesium or an indium-magnesium alloy, respectively.
In UK patent specification No. 2,123,423 a process for the preparation of trimethylgallium or triethylgallium is described in which an alloy Ga.sub.2 Mg.sub.5 is reacted with methyl iodide in the presence of an ether. The ether may be a relatively volatile ether, such as diethyl ether, or an ether with a relatively high boiling point, e.g. di-isopentyl ether or diphenyl ether.
The use of magnesium has the drawback that commercially pure magnesium still contains minor amounts of zinc and silicon. Because unintentional zinc and silicon doping in the MOCVD or MOVPE of trialkyl compounds of Group 3a metals needs to be avoided, it would be desirable if different metals or alloys could be used in combination with Group 3a elements.
Accordingly, the present invention provides a process for the preparation of trialkyl compounds of Group 3a metals, in which a Group 3a metal is contacted with an alkyl halide in the presence of an alkali metal to obtain the trialkyl compound of the Group 3a metal and alkali-metal halide.
The advantage of the invention vis-a-vis the above processes is the use of alkali metal which in commercially pure form does not contain zinc in detectable amounts.
The halogen moiety of the alkyl halide can be selected from chlorine, bromine, iodine or mixtures thereof. Especially alkyl bromides and/or alkyl iodides are advantageously used in the present process.
The alkyl groups in the trialkyl compounds may be normal or branched. Although the present process can be carried out with a wide variety of alkyl halides, including those having long chain alkyl groups, the use of alkyl groups with more than 6 carbon atoms is not practical, since the trialkyl Group 3a metal compounds thus obtained have a decreasing thermal stability. Therefore, the alkyl group in the alkyl halide has preferably from 1 to 5 carbon atoms. More preferably, the alkyl moieties are methyl or ethyl groups or mixtures thereof.
The reaction may be carried out under very mild conditions. The pressure may be atmospheric, but also subatmospheric or superatmospheric pressures are feasible. Generally, the pressure is from 0.1 to 10 bar. Since it is most convenient to operate at atmospheric pressure the process is preferably carried out at such pressure. The trialkyl compound is prepared under an inert atmosphere, e.g. under nitrogen, argon or helium.
REFERENCES:
patent: 2863894 (1958-12-01), Smith
Purification of Group III Metal Alkyls Using Nitrogen Donor Ligands., Foster, et al. Chemtronics, 1988, vol. 3, Mar., pp. 38-43.
Chemical Abstracts, vol. 11, 1990, p. 728.
Smit Cornellis J.
Van Der Lee Aart J.
Van Eijden Gerbrand J. M.
Air Products and Chemicals Inc.
Chase Geoffrey L.
Marsh William F.
Nazario-Gonzales Porfirio
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