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PURPOSEFUL CHEMICAL DESIGN OF MOCVD PRECURSORS FOR SILICON-BASED SYSTEMS

BERNARD J. AYLETT Department of Chemistry, Queen Mary College,

London El 4NS,

U.K.

ABSTRACT It is shown that volatile molecular compounds with silicon-metal bonds can act as effective MOCVD precursors to metal silicides, which are deposited as thin films under relatively mild conditions. Strategies for the design and synthesis of such "prevenient" precursors are explored, and possible extensions of this approach are considered.

INTRODUCTION Chemical vapour deposition (CVD) techniques offer an extremely attractive route to microelectronics device structures. Thickness and composition of the deposited films can be readily altered, sharp horizontal interfaces between different phases can be achieved, adequate purity can usually be maintained, and epitaxial deposition is often possible. Most importantly, the experimental arrangements are far more conducive to routine large-scale production than alternative techniques such as molecular beam epitaxy. Variants such as photo-assisted or plasma-enhanced CVD can often provide significant advantages or new features. This approach has been particularly successful in relation to III/V systems; organometallic precursors have been widely used, in reactions developed from the original work of Manasevit and Simpson El]: GaMe3 + AsH3 - GaAs + 3CH () to produce many binary, ternary, and quaternary phases such as Ga xAl1x As yP 1y This metallo-organic chemical vapour deposition (MOCVD) approach has led to a range of sophisticated device architectures, electronic and optoelectronic applications.

with wide

It would clearly be of great significance if a similar variety of silicon-based device structures were available, especially if they could be produced relatively cheaply by MOCVD techniques. The huge amount of existing expertise in silicon-based systems could then be built on and enhanced.

PRESENT-DAY SILICON DEVICE MATERIALS Existing CVD procedures in this area are chiefly directed towards deposition of polycrystalline or amorphous silicon and insulating/dielectric layers of silicon oxide, nitride, and oxynitride, e.g.: SinH2n+

2 -nSi

+ (n + l)H2

(2a)

(n = 1,2....) SiHCl3 + H -

Si + 3HCI

Mat. Res. Soc. Symp. Proc. Vol. 131. 1989 Materials Research Society

(2b)

384

Si(OEt)

4

- SiO2 . .....

(3a)

SiH4 + N2 0 - Si02 + N2 . .....

(3b)

3SiH4 + 4NH3 - Si3N4 + 12H2

(4)

Some work has also been reported [2] on the deposition of metal silicides by reactions such as: H2

WCl5 + SiC14

-

WSi2 etc.

(5)

WSi2 etc.

(6)

900K WF6 + SiH4

plasma

570K It appears that silicide films made in this way usually contain halide as contaminant, although this need not always be the case [3]. Metal silicides for electronic devices are not made commercially in this way; normally a thin metal layer is deposited by sputtering or by evaporation on the silicon substrate, then heated. Mutual interdiffusion occurs, producing one or more silicide phases [4]. Annealing at temperatures up to 1150K may be required. These