(204a) Molecular Layer Deposition of Nanoscale Organic Films

Atomic layer deposition (ALD) has
gained attention by allowing for nanoscale control of inorganic films via a
sequence of self-limiting surface reactions.  In an analogous technique,
nanoscale organic thin films are deposited by molecular layer deposition (MLD),
utilizing a series of self-limiting reactions of organic molecules.  In this
study, 1,4-phenylene diisocyanate (PDIC) and ethylenediamine (ED) are employed
to deposit polyurea films on a silicon substrate.  3-aminopropyltriethoxysilane
is vapor deposited on the hydroxylated SiO₂ surface to yield an
amine-terminated surface, as confirmed by ellipsometry and XPS.  Following
amine termination, PDIC and ED are dosed in a binary cycle, and this cycling is
repeated to yield the desired thickness of organic film.  Ellipsometry and SEM
indicate a linear growth rate of 6.7 Å/cycle, with each of the reactants demonstrating
saturation behavior with increasing exposure time.  The urea coupling moiety is
confirmed by FT-IR, and films are shown to have stoichiometric composition by
XPS.  Temperature dependent measurements show that the films have good thermal
stability.  Density function theory is used to elucidate the reaction pathway
and predicts an estimated growth rate of 6.4 Å/cycle.   Experimental and
theoretical studies of related MLD systems, including combinations of
diisocyanates and diisothiocyanates with diols, dithiols, and diamines, will
also be presented.