Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2002-04-06
2003-12-09
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C427S248100, C427S588000, C428S001100, C257S049000
Reexamination Certificate
active
06660874
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of organometallic compounds. In particular, the present invention relates to trialkyl Group VA metal compounds which are suitable for use as precursors for chemical vapor deposition.
Metal films may be deposited on surfaces, such as non-conductive surfaces, by a variety of means such as chemical vapor deposition (“CVD”), physical vapor deposition (“PVD”), and other epitaxial techniques such as liquid phase epitaxy (“LPE”), molecular beam epitaxy (“MBE”), and chemical beam epitaxy (“CBE”). Chemical vapor deposition processes, such as metalorganic chemical vapor deposition (“MOCVD”), deposit a metal layer by decomposing organometallic precursor compounds at elevated temperatures, i.e. above room temperature, either at atmospheric pressure or at reduced pressures.
A wide variety of metals may be deposited using such CVD or MOCVD processes. See, for example, Stringfellow,
Organometallic Vapor Phase Epitaxy: Theory and Practice
, Academic Press, 2
nd
Edition, 1999, for an overview of such processes. Organometallic compounds of arsenic, antimony, and bismuth are used to deposit epitaxial films in the semiconductor and related electronic industries. Epitaxial films such as gallium arsenide find applications in optoelectronic devices such as detectors, solar cells, light-emitting diodes (“LED's”), lasers and electronic switching devices such as field effect transistors (“FET's”) and high electron mobility FET's (“HEMT's”). Ternary arsenic alloys also exist such as gallium indium arsenide (“GaInAs”) and aluminum indium arsenide (“AlInAs”), which are more attractive than GaAs or aluminum gallium arsenide (“AlGaAs”) for the most powerful fiber optic systems operating in the 1.3 to 1.55 micron wavelength range. Gallium arsenide phosphide (“GaAsP”) is suitable for visible LED's and fiber optic emitters/detectors. Trimethylarsine in particular has been used as a precursor for carbon doping. Antimony and antimony alloy films are useful in fiber optics communication systems, particularly in the 1.3 and 1.55-micron regions. Antimony-containing semiconductor materials also have commercial applications including detection for seeker, night vision and surveillance devices (infrared detectors) and sources (LED's or lasers). A variety of binary, ternary and quaternary Group III/V semiconductor systems containing antimony have been evaluated for applications in infrared emitters and detectors operating in the 3 to 5 micron and 8 to 12 micron spectral ranges. These wavelength ranges are important since they are natural windows in the atmosphere for infrared transmission. Epitaxial antimony-based Group III/V semiconductors have potential applications in long wavelength detectors and high-speed electronic devices.
For such semiconductor and electronic device applications, these Group VA metal alkyls must be highly pure and be substantially free of detectable levels of both metallic impurities, such as silicon and zinc, as well as oxygenated impurities. Oxygenated impurities are typically present from the solvents used to prepare such organometallic compounds, and are also present from other adventitious sources of moisture or oxygen.
The most common method of preparing Group VA metal alkyl compounds consists of reacting Group VA metal trihalides with Grignard reagents in an ethereal solvent, such as alkyl ethers, glymes or tetrahydrofuran. Aluminum alkyls can also be used instead of Grignard reagents in the preparation of Group VA metal alkyl compounds. For example, Zakharkin et al.,
Bull. Acad. Sci. USSR
, 1959, p1853, discloses a method of producing trialkyl compounds of antimony and bismuth, as shown in equation (I), where R is ethyl, n-propyl or iso-butyl and X is chloride or fluoride.
MX
3
+R
3
Al+diethylether→MR
3
+AlX
3
(I)
Trace amounts of ethereal solvent invariably remain in the target organometallic compound obtained using conventional techniques. Such residual ethereal solvent contributes oxygen as a deleterious impurity in metal films deposited from such precursor compounds.
Attempts have been made to synthesize Group VA organometallics in non-ethereal solvents. For example, Takashi et al.,
J. Organometal. Chem.,
8, pp 209-223, 1967, disclose the reaction of antimony trichloride with triethylaluminum in hexane. Such reaction was found to produce triethylstibine in extremely low yields (only about 10%), the remainder being about 42% metallic antimony and about 46% of an antimony-aluminum complex, (SbEt
4
)(Al
2
Et
5
Cl
2
). This article does not teach how to obtain triethylstibines free of antimony-aluminum complexes.
U.S. Pat. No. 4,906,762 (Sawara et al.) discloses a method of producing pure trialkylarsines from aluminum alkyls and diarsenic trioxide using alkali metal halides as complexing agents in hydrocarbon solvents. The method constitutes a two-step synthesis, both stages being heterogeneous reactions with final yields not more than 65%, and rendering highly reactive/pyrophoric reaction residues. Tertiary amines are not disclosed in this patent.
There is thus a need for methods for preparing Group VA metal alkyls in high yields with less reactive reaction residues and for Group VA metal compounds substantially free of both metallic and oxygenated impurities for use as precursor compounds for CVD.
SUMMARY OF THE INVENTION
It has been found that Group VA metal alkyls can be prepared in high yield and in high purity by reacting Group VA trihalides and Group IIIA alkyls in the presence of tertiary amines in hydrocarbon solvents. Group VA alkyl compounds produced by this method are extremely pure and substantially free of oxygenated impurities.
In one aspect, the present invention provides a method for preparing trialkyl Group VA metal compounds including the step of reacting a Group VA metal trihalide with a Group IIIA compound of the formula R
n
M
1
X
3−n
in the presence of a tertiary amine in an organic solvent that is free of oxygen substitution, wherein each R is independently selected from (C
1
-C
6
)alkyl; M
1
is a Group IIIA metal; X is halogen and n is an integer from 1-3.
In a second aspect, the present invention provides a method for depositing a film of a Group VA metal on a substrate including the steps of: a) conveying a Group VA metal source compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the Group VA metal source compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the Group VA metal source compound is prepared by the method including the step of reacting a Group VA metal trihalide with a Group IIIA compound of the formula R
n
M
1
X
3−n
in the presence of a tertiary amine in an organic solvent that is free of oxygen substitution, wherein each R is independently selected from (C
1
-C
6
)alkyl; M
1
is a Group IIIA metal; X is halogen and n is an integer from 1-3.
In a third aspect, the present invention provides a method for manufacturing an electronic device including the step of depositing a film of a Group VA metal on an electronic device substrate including the steps of: a) conveying a Group VA metal compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the Group VA metal compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the Group VA metal compound is prepared by the method including the step of reacting a Group VA metal trihalide with a trialkyl Group IIIA compound of the formula R
n
M
1
X
3−n
in the presence of a tertiary amine in an organic solvent that is free of oxygen substitution, wherein each R is independently selected from (C
1
-C
6
)alkyl; M
1
is a Group IIIA metal; X is halogen and n is an integer from 1-3.
In another aspect, the present invention provides trialkylantimony compounds substantially free of ethereal solvents. In still another aspect, the present invention provides trialkylbi
Amamchyan Artashes
Power Michael B.
Shenai-Khatkhate Deodatta V.
Cairns S. Matthew
Nazario-Gonzalez Porfirio
Shipley Company L.L.C.
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