EVG FinalDr 1/3/10 12:35 Page 17
Nanoimprint Lithography
cassette handling of Si substrates, polymers and
working stamps.
This article does not report any specific data
on the achieved alignment accuracy as this work
is in progress and statistically evaluable data are
not available yet. However, first data have
proven that alignment accuracies of better than
10 µm are achievable for the aligned imprint
processes. These results are in-line with the
requirements for micro fluidic devices. More
details concerning alignment results will be
published later.
Issue I 2010
In contrast to established hot embossing
square4
applications, the process we are reporting here
.com
on the EVG 750 system employs soft working
stamps materials which exhibit manifold benefits
over hard stamp materials like Si or Ni: (1) soft Figure 5: Influence of the imprint temperature on the pattern fidelity
working stamps can be fabricated at low cost
from expensive e-beam written masters, (2) soft
working stamp can be used for multiple imprints,
(3) the use of soft working stamps does not
oasiasemiconductor
require compliant layers as they already exhibit
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this trait and (4) these stamps are fully
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compatible with optical alignment to a
structured Si substrate or to a second working
17
stamp for double side imprinting.
Fully automated de-embossing
A method for automated de-embossing by
mechanically fixing of a Si stamp on a top chuck
and separating the substrate by an “air knife”
using a mechanical frame to hold the substrate
in place has been proposed by a different
group
[5]
. Another suggested way is the fixation Figure 6: Influence of the imprint force on the pattern fidelity
of the substrate by utilizing the high adhesion
force of a Si wafer to a polydimethylsiloxane embossing arm moves out of the imprinted
(PDMS) layer described in the same paper. press and the substrate is transferred to a robot
In the current work the de-embossing end-effector. Substrates are unloaded to the
process was realized in the following way. The receive cassette.
backplane of the working stamp is fixed by
vacuum on its respective chuck surface and the Polymer imprints
Si substrate with spin-on layer is vacuum fixed Soft working stamps were fabricated from Ni
on the counterpart chuck surface. Polymer masters or directly from resist masters after
substrates are transferred via a small centre pin optical lithography. In figure 4 the basic process
through the working stamp backplane to the top flow of the soft working stamp fabrication
chuck after hot embossing. For all four processes process is demonstrated. The liquid pre-cursor
described in figure 1 a de-embossing arm moves of the polymer is dispensed onto the master and
into the imprinting module in between top and squeezed between the master and a glass
bottom chuck and removes either the polymer backplane. Curing of the polymer is achieved by
substrate transferred to the top chuck or the UV-exposure. The soft working stamp attached
wafer with imprinted spin–on polymer layer. For to the glass backplane is released from the
spin-on layers the imprinted substrate is released master and represents the reversible image of
from the bottom chuck during the opening of the master design. The resist master was treated
the press and transferred to the top chuck with an anti-sticking layer (fluorinated chemical)
together with the working stamp. The de- in order to ensure a residual free separation of
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