Appl. Phys. Lett., Vol. 84, No. 20, 17 May 2004
Chen et al.
4019
more, the density of the HfO2 on the loosely packed SAM
sample varies spatially along the interface. These results are
consistent with the model of deposition beginning at discrete
nucleation sites, where these sites likely correspond to de-
fects ͑pinholes͒ in the SAM where unreacted hydroxyl
groups at the surface are exposed to the ALD precursors.
Considering these factors, formation of a high-quality SAM
is extremely important for application of these monolayers as
resist materials in area selective ALD.16
In summary, closely packed ODTS self-assembled
monolayers have been demonstrated to be a promising can-
didate for a monolayer ALD resist which blocks the surface
functional groups that are necessary for nucleation and
growth during subsequent atomic layer deposition. Obtaining
well-packed SAMs is important for achieving the deactiva-
tion of the substrate surface with respect to HfO2 and ZrO2
ALD. Self-assembled monolayers can be integrated into the
patterning of high and other films by the ALD process.
This may make processing routes such as area selective
deposition feasible for future device fabrication.
FIG. 3. Time dependence of ODTS film formation. ͑water contact angle and
ellipsometry analysis͒ and its ALD blocking effect.
HfO2 (ZrO2) ALD process by blocking reactive groups such
as hydroxyl species on the oxidized silicon surface. Even
small amounts of uncovered surface can result in a signifi-
cant amount of HfO2 deposition. To explore this effect fur-
ther, AFM measurements were carried out. The AFM images
shown in Fig. 4 compare the condensed ODTS film ͑formed
after 2880 min of exposure͒ with a more porous ODTS film
͑formed after 1200 min͒. A significant number of nanometer
scale pinholes can be found in the porous film, while the
densely packed film demonstrates an ultrasmooth surface
with ϳ1 Å surface roughness. The pinhole regions shown in
the AFM images in Fig. 4 may be the initial sites for precur-
sors to permeate through the organic film and reach uncov-
ered hydroxyl groups on the substrate. HfCl4 (ZrCl4) precur-
sors can form stable chemical bonds to these sites, and films
can nucleate at these sites through subsequent ALD cycles.
To further probe the mechanism of the ALD film growth
on the loosely packed ODTS substrate, cross-sectional TEM
was used to visualize the interface ͑Fig. 2͒. It is clear that
there are some HfO2 regions ͑dark contrast͒ on the loosely
packed ODTS substrate ͓Fig. 2͑b͔͒, whereas there is no HfO2
deposition evident on the well-packed sample ͓Fig. 2͑c͔͒.
However, the density of the HfO2 film in Fig. 2͑b͒ is much
lower than that of the films directly deposited onto the
chemical oxide passivated Si substrate ͓Fig. 2͑a͔͒. Futher-
This work was supported in part by the NSF/SRC Center
for Environmentally Benign Semiconductor Manufacturing,
NSF Grant No. EEC9528813, and by a Mayfield Fellowship
͑H.K.͒.
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FIG. 4. AFM sectional analysis of ͑a͒ closely packed ODTS film; ͑b͒
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On: Wed, 14 May 2014 21:54:39