Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Patent
1990-07-31
1992-05-26
Shaver, Paul F.
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
562899, C07F 308, C07C39100
Patent
active
051170213
DESCRIPTION:
BRIEF SUMMARY
This invention relates to methods for the purification of tellurium and selenium alkyls, particularly the dialkyls of these metals.
Tellurium and selenium alkyls are important compounds used in the semiconductor industry, for example in the preparation of cadmium mercury telluride (CMT) used in opto-electronic applications. In many such uses the alkyls are decomposed, usually thermally to form the element, which may itself be deposited on a substrate, or combined with other elements in compounds. It is a very important requirement of such alkyls that they be extremely pure, as the presence of even minute quantities of impurities eg on a ppm level can have a detrimental effect on the properties of the semiconductor.
Present methods of purification of tellurium and selenium alkyls generally involve fractional distillation and are unable to easily reach the abovementioned levels of purity. Another known method of purifying metal alkyls involves the formation of an adduct that has properties which allow it to be decomposed in such a way that the pure alkyl is formed as a decomposition product.
The use of adducts in this way to purify tellurium and selenium alkyls is as yet unknown, although some work has been done to investigate various adducts of these alkyls. For example G E Coates, J Chem Soc (1951) pp 2003-2013, Challenger & North, J Chem Soc (1934) 1 pp 68-71, Carr & Pearson, J Chem Soc (1938) p 282, and Ferguson & Loh, Austral. J Chem (1973) 26 pp 2615-22 all mention that these adducts dissociate with relative ease, but none have been previously known to dissociate in such a way as to yield the pure alkyls.
The present invention seeks to overcome the problems of prior art methods of purification of tellurium and selenium alkyls by novel routes using adducts, some of which are themselves novel.
According to the present invention, there is provided a method of purification of a tellurium or selenium alkyl, which is characterised by forming an adduct of the alkyl with at least one compound of a Group IB or IIB metal (Cu, Ag, Au, Zn, Cd, Hg) and thermally dissociating the said adduct to yield the alkyl. Preferably the at least one compound of a group 11 or 12 metal is an inorganic compound.
The method is suitable for the purification of all tellurium and selenium alkyls, but is particularly suitable for the metal dialkyls. The alkyl group may be straight or branched chain, and is preferably a lower alkyl eg containing up to 4 carbon atoms. These lower alkyls are most useful for semiconductor production.
Preferred Group 11 or 12 metals are cadmium, mercury and copper. The compound is preferably a halide or nitrate, most preferably halides, these being bromides, chlorides and iodides. The most preferred compounds are therefore: CuI, CdI.sub.2, CdBr.sub.2, HgCl.sub.2, Cu.sub.2 I.sub.2, HgI.sub.2.
Preferably the method is carried out in the following way:
(i) A solution of the alkyl in a suitable solvent is prepared, and this is added to a solution of the metal compound in a suitable solvent, preferably an organic solvent.
Preferred solvents in both cases are polar aliphatic organic solvents containing 1 to 10 carbon atoms, preferably 1 to 5. It is desirable to use a solvent for the alkyl that is also capable of dissolving the metal compound.
Suitable solvents for the alkyl include ethers, such as THF but especially diethyl ether; alcohols, especially ethanol; and nitriles especially acetonitrile. These solvents are also suitable for the metal compound.
Typically the alkyl is dissolved in an ether and is added at an appropriate rate to a solution of the metal compound in an alcohol. Preferably the amount of alkyl and metal compound used are in approximately stoichiometric ratios.
(ii) When reaction appears to be complete, excess solvents may be separated by filtration from any precipitated product, or alternately or additionally the bulk of the solvent may be removed by evaporation.
(iii) The solid adduct product is washed with an appropriate solvent, eg the ether used in the reaction, and excess volatiles remov
REFERENCES:
patent: 4946994 (1990-08-01), Higa
Cole-Hamilton David J.
Mullin John B.
Shenai-Khatkhate Deodatta V.
Webb Paul
Shaver Paul F.
The Secretary of State for Defense in Her Britannic Majesty's Go
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