A New Type of Cross-Linked Resist for Small
Pattern Roughness
Toru Yamaguchi, Masao Nagase, Kenji Yamazaki,
and Hideo Namatsu
Device Physics Laboratory
In the fabrication of high-performance nanodevices,
such as single electron transistors, even
nanometer-order roughness produces large
variations in device characteristics because
device sizes are less than 10 nm. We have
clarified that roughness is due to polymer
aggregates 20-30 nm in size, which are contained
in resist materials [1]. In resist films
containing these aggregates, the polymers
surrounding aggregates dissolve faster and
the aggregates can be extracted from the
resist surface one by one since the polymer
density is higher inside the aggregates (the
aggregate extraction development [2]). As
a result, many aggregates remain embedded
on the pattern sidewall and they are responsible
for pattern roughness [Fig. 1(a)].
To reduce roughness, aggregate extraction
development must be suppressed. To achieve
this, we have developed SAGEX (suppressed
aggregate extraction development) resist
[3]. In SAGEX resist, the polymer aggregates
are thermally cross-linked with each other
before electron-beam exposure. In the exposed
regions, the resist dissolves uniformly over
the whole surface since cross-linking slows
down the dissolution rate of the surrounding
polymers to the point where it is the same
as that of the aggregates themselves. As
a result, the aggregate extraction development
is suppressed and the resulting patterns
have smaller roughness.
Figure 2 shows surface roughness on the exposed
region observed by an atomic force microscope
(AFM). In conventional resists, the surface
becomes rougher because of the appearance
of the aggregates on the surface. In contrast,
in SAGEX resists, no aggregates can be observed
and the surface roughness is drastically
reduced to less than one-third compared to
that with conventional resist film. This
proves that the aggregate extraction development
is actually suppressed in SAGEX resist. These
results show that SAGEX resist is very effective
for nanodevice fabrication.
[1] T. Yamaguchi et al., Appl. Phys. Lett.
71 (1997) 2388.
[2] T. Yamaguchi et al., Proc. SPIE 3333 (1998) 830.
[3] T. Yamaguchi et al., Jpn. J. Appl. Phys.
38 (1999) 7114.
Fig. 1. Formation process of resist patterns.
Fig. 2. AFM images of the exposed resist.
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