Process for preparing a limo2 type heterometallic oxide film

Details Process for preparing a limo2 type heterometallic oxide film Process for preparing a limo2 type heterometallic oxide film

2000-06-01

2002-06-25

Utech, Benjamin L. (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Forming from vapor or gaseous state

With decomposition of a precursor

C117S944000, C117S950000, C427S255320, C427S255340

Reexamination Certificate

active

06409830

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for preparing a heterometallic oxide film of the LIMO
2
type, wherein M is a Group 13 element such as Al or Ga, using a volatile organometallic compound of formula LiOR′.(R′O)MR
2
wherein R is a C
1-10
alkyl group; and R′ is a C
2-10
alkyl group.
DESCRIPTION OF THE PRIOR ART
Theoretical and experimental studies have projected that a heterometallic oxide of the LiMO
2
type, e.g., LiAlO
2
and LiGaO
2
would be useful in a process for depositing a blue luminescent GaN film thereon because its lattice constant (a-axis) is almost identical with that of GaN (Nicholls, J. F. H. et al., “Growth and optical properties of GaN grown by MBE on novel lattice-matched oxide substrates” in
Gallium Nitride and Related Materials;
and Ponce, F. A. et al., eds. Materials Research Society Symposium Proceedings, 395, pp. 535-539 (Materials Research Society, Pittsburgh, Pa., USA, 1990)).
From these studies, it is thought that films of LiO
2
type grown on Si wafers should be useful as buffer layer for the deposition of GaN films.
Despite such anticipated usefulness, a LiMO
2
film has not been successfully prepared in the past due mainly to the lack of suitable organometallic precursor compounds that can be used in the chemical vapor deposition (CVD) process for preparing a LiMO
2
type oxide.
Accordingly, there has existed a need to develop a scheme for the preparation of such precursor compounds.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a process for preparing a heterometallic oxide film of the LiMO
2
type, wherein M is a Group 13 element.
In accordance with one aspect of the present invention, there is provided a process for preparing said film which comprises contacting the vapor of a volatile organometallic compound of formula LiOR′.(R′O)MR
2
with a substrate heated to a temperature above 300° C., wherein M is a Group 13 element; R is a C
1-10
alkyl group; and R′ is a C
2-10
alkyl group.
DETAILED DESCRIPTION OF THE INVENTION
The organometallic compound which may be used in the present invention is a highly volatile compound of formula LiOR′.(R′O)MR
2
which has a Li:M:O atomic ratio of 1:1:2. It can be, therefore, advantageously used in a CVD process for depositing a LiMO
2
type heterometallic oxide film on a substrate. In the organometallic compound of formula LiOR′.(R′O)MR
2
, M is a Group 13 element such as Al or Ga; R is a C
1-10
alkyl group; and R′ is a C
2-10
alkyl group. The preferred compounds in practicing the present invention are lithium dimethylaluminum isopropoxide, LiOPr
i
.(Pr
i
O)AlMe
2
; lithium dimethylaluminum tert-butoxide, LiOBu
t
.(Bu
t
O)AlMe
2
; and lithium dimethylgallium isopropoxide, LiOPr
i
.(Pr
i
O)GaMe
2
.
The organometallic compound may be prepared according to the process described in WO 97/29112 or in U.S. Pat. No. 6,063,951. That is, a dialkylmetal alkoxide((R′O)MR
2
) may be directly reacted with a lithium alkoxide(Li(OR′)) in a molar ratio of 1:1 to obtain the desired product, as shown below:
LiOR′+(R′O)MR
2
→LiOR′.(R′O)MR
2
wherein M, R and R′ have the same meanings as defined above.
The organometallic compound thus obtained may be preferably vaporized at a temperature ranging from room temperature to 100° C.
A heterometallic oxide film of the LiMO
2
type may be deposited on a substrate by bringing the vapor of the organometallic compound thus obtained into contact with the surface of the substrate preheated to a temperature above 300° C., preferably from 300° C. to 600° C. under a pressure of from 7.5×10
−6
to 1.5×10
−2
Torr., preferably under a pressure ranging from 5×10
−3
to 1.2×10
−2
Torr.
The substrate which may be used in practicing the present invention is any inorganic solid which is stable at or above the film deposition temperature, and examples thereof include: glass, quartz, silicon, gallium arsenide, sapphire, alkali metal niobate, alkaline earth metal titanate, gallium nitride, niobium nitride and the like. Among those, single crystals of silicon, gallium arsenide and sapphire are preferred when the coated substrate is intended for use in electronic applications.
The following Preparation Examples and Examples are provided only for the purpose of illustrating certain aspects of the present invention; and they are not to be construed as limiting the scope of the present invention in any way.
In each of Examples, the coated substrate obtained after treatment with an organometallic compound was immediately transferred to an X-ray photoelectron spectroscope in order to minimize its exposure to air.


REFERENCES:
patent: 4880492 (1989-11-01), Erdmann et al.
patent: 6063951 (2000-05-01), Kim et al.
patent: 404294063 (1992-10-01), None

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