Page 424 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

P1: FMX Final Pages
Encyclopedia of Physical Science and Technology EN009J-427 July 6, 2001 20:25

Metalorganic Chemical Vapor Deposition 509

to grow IVA–VIA compounds by MOCVD in 1975. Since Another important class of oxides that have been grown
this time, the MOCVD process has been used to grow thin by MOCVD are the ferroelectrics, including PbTiO 3 ,
films of many of these alloys. The precursors employed are BaTiO 3 , PbLaZrTiO 3 , and PbZr 1−x Ti x O 3 . This work is
typically tetraethyllead (TEPb), TESn, and H 2 Te. How- still in its infancy, however, promising results have been
ever, most work in this area has been halted since these achieved. Further studies of the relationship between film
materials are somewhat unstable and other semiconductor properties, the mechanism of deposition, growth parame-
compounds can cover the same spectral region. ters, and the choice of precursors are necessary to discover
an optimized MOCVD process for this class of impor-
tant ferroelectrics thin films which will be of great use
B. II–VI Semiconductor Compounds
in the next generation of deep-submicron Si device design
The semiconductors composed of elements in Columns and manufacture. Another dielectric material that has been
IIB and VIA consist of materials covering the “wide- grown by MOCVD is ZnO.
bandgap” region and the “narrow-bandgap” compound
semiconductors. The wide-bandgap materials are those
D. Deposition of Metals by MOCVD
in the ZnMgSSe/ZnCdSSe systems. The wide-bandgap
II–VI compounds in the Zn x Cd 1−x S y Se 1−y /Zn x Mg 1−x S y An important new application for MOCVD is the deposi-
Se 1−y system have been grown by MOCVD. The tion of pure metal films for semiconductor integrated cir-
commonly used sources are DEZn, dimethylsele- cuit applications. Important metals deposited by MOCVD
nium (DMSe), ditertiarybutylselenide (DTBSe), DMCd, include Al, Cu, CuAl alloys, and W films using pre-
bismethyl-cyclopendadienyl-magnesium [(MeCp) 2 Mg], cursors listed in Table I. It is expected that this ap-
diethyl sulfide (DES), and H 2 S. These materials are use- plication area for MOCVD will expand rapidly in the
ful for visible LEDs and laser diodes. However, to date, next few years as the demand increases for high-density
difficulties in the MOCVD growth of high-conductivity metal interconnects for Si integrated circuit technology.
p-type materials in this system has prevented the demon- High-purity Al metal films have also been grown by
stration of LEDs with characteristics comparable to those MOCVD.
fabricated from MBE-grown materials.
The most important IIB–VIA narrow-gap materials
are in the HgCdZnTe quaternary system, with the ternary V. OTHER DEVELOPMENTS IN MOCVD
Hg x Cd 1−x Te (MCT) being the most commonly used for
photodetectors in the 8–12 µm regime. The narrow-gap The limitations of space and the specific subject of this ar-
materials can be grown by MOCVD using elemental ticle have prevented me from describing many of the other
Hg, dimethylmercury (DMHg), diethyltelluride (DETe), importantdevelopmentsleadingtothebreadthandsuccess
methylallyltelluride (MATe), diisopropyltelluride of the current MOCVD technology. An important devel-
(DIPTe), dimethylcadmium (DMCd), and dimethylz- opment mentioned above is the use of advanced chemi-
inc (DMZn). These semiconductors are all low- cal kinetics, surface kinetics, and hydrodynamics models
melting-point materials and are typically grown in the that can provide for full three-dimensional solutions to
350 C ≤ T g ≤ 450 C range. Recently, the RDR multiple- the multifaceted boundary conditions occurring in a CVD
◦
◦
wafer reactor geometry has been adapted to provide system. The Sandia National Laboratories (USA) CVD
for large-area growth of uniform layers in the HgCdTe Sciences Group, particularly M. E. Coltrin, has provided
system. tools for the detailed analysis of MOCVD systems, and
they have contributed greatly to the understanding of the
large-area commerical MOCVD reactors in common use
C. Growth of Oxides by MOCVD
today. These chemical process models have become com-
A variety of oxides have been grown by MOCVD, in- mercially available and are now offered by several compa-
cluding the important class of high-temperature supercon- nies. Using these models, important modifications to re-
ducting Cu oxides. Particular attention has been given to actor designs have been made that greatly improve growth
the BiSrCaCuO and YBaCuO systems. Superconducting efficiencies, material uniformity, interface abruptness, and
metal oxide films grown by MOCVD have been limited in materials quality. This is especially important for the
performance largely by the relatively primitive state of the design and optimization of very large-scale MOCVD re-
novel precursors used for these materials, and by the need actors, e.g., systems with capacities for seven 6.0 in. diam-
to develop reactor designs compatible with the low vapor eter wafers as shown in Figs. 6 and 7. In fact, these large-
pressures of these materials, and the oxidizing nature of scale reactors are difficult and expensive to build, even
the growth ambient. in prototype form. Evaluating reactor designs through