EVG FinalDr 1/3/10 12:35 Page 18
Nanoimprint Lithography
the polymer from the master. Ni masters were depth of features than the nominal stamp
not treated as they exhibit good release feature depth of 200 µm. A process temperature
properties from the master. of 160°C results in very good agreement of the
The influence of the imprint temperature imprint depth and the stamp feature depth.
and the imprinting pressure on the result was The influence of the piston pressure on the
evaluated by imprinting in cyclo-olefine pattern fidelity is shown in figure 6. Contact
copolymer (COC). COC is a widely used polymer forces of 5 kN and 10 kN lead to the targeted
Figure 7: Optical for micro fluidic applications due to its superior imprint depth of 200 µm. All further experiments
microscope picture of properties like the chemical resistance and its were performed with 5 kN contact force in order
working stamp, optical transparency
[6]
. Those replicated to minimize mechanical stress on the soft
channel width is structures are used directly as functional devices working stamp material.
200 µm deployed in microfluidic devices. The glass An evidence of the achieved good pattern
transition temperature of the used COC was fidelity can be depicted from optical microscope
139°C. A soft working stamp was created from a images of figures 8 and 9.
150 mm master containing smallest feature sizes
of 200 µm and a depth of 200 µm defined in the Spin-on polymer imprints
negative tone resist SU-8 3025. The soft working stamps were fabricated from an
Another master used for the imprinting tests e-beam written 100 mm Si master with feature
showed features from 30 µm to 300 µm and an sizes down to 50 nm and a feature height of 100
imprint depth of 20 µm. While the diameter of nm with the process described in figure 4. The
Figure 8: Optical the first working stamp was 150 mm, the second
microscope picture working stamp was 3” in diameter, both
of corresponding attached on a 150 mm glass backplanes. The
18
imprint in COC from embossing temperature was varied between
working stamp shown 140°C and 160°C, while an imprint pressure of 5
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in figure 7 kN and 10 kN was applied for the first master
.eur (200 µm imprint depth). In figure 5 the
oasiasemiconductor
dependence of the imprint temperature on the
pattern fidelity – the agreement of the stamp
and imprint features - is demonstrated.
Temperatures lower than 160°C lead to lower
.com
Figure 10: Large area SEM image of 300 nm hot
embossed crossbar structures (100 nm in height)
square4
Issue I 2010
utilizing working stamps
Figure 11: SEM image of 200 nm hot embossed
left: Figure 9: AFM picture of imprinted features with resolutions of 300 nm meander structures (100 nm in height) utilizing
and imprint depths of 100 nm working stamps
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