Multiple replication of hierarchical structures frompolymer masters with anisotropy
A. Mayer, J. Rond, J. Staabs, M. Leifels, H.-C. Scheer
Microstructure Engineering, University of Wuppertal, Germany
J. Zajadacz, M. Erhardt, P. Lorenz, K. Zimmer
Leibniz Institute for Surface Modification, Leipzig, Germany
E-mail: amayer@uni-wuppertal.de

Hierarchical structures find a lot of applications ranging from tribology to optics1. Whenthese structures, in addition, feature anisotropy, this specific quality renders directionality tothe interaction properties induced by these structures. Here we address the realization of adirection-dependent adhesion.
Typically the preparation of hierarchical structures may be complex. Applications hence ask
for a replication of such structures to multiply the number of samples on hand; there arematerials available that have specifically been developed for the purpose of replication, as
e.g. OrmoStamp2. However, often a situation is met where the original exists as a polymeric
template only; Fig. 1 exemplifies this by hierarchical structures obtained by opticallithography with subsequent laser treatment. Then the question arises whether standard
replication procedures work with such delicate polymeric templates, in particular when
multiple replication is employed to obtain a large number of samples from a single template
which, at worst, may be lost. This is the focus of our work.
This investigation relies on two replication materials, OrmoStamp and SU-8. SU-8 layers on
Si are also used to characterize all replication results, as these samples can easily be cleaved
for cross-sectional inspection. Fig. 2 illustrates the experience gained when the template isalready from OrmoStamp. Only the copy into a different material (here SU-8) is successful,whereas the copy into the same material (OrmoStamp) fails. When OrmoStamp and SU-8 areused alternately, the number of replication steps can be chosen almost at will.
We will investigate the multiple replication process according to Fig. 2 with the polymeric
templates shown in Fig. 1. Characteristic issues in this context are the limited adhesion andthe limited chemical inertness of the photoresist. Feature distortion is also an issue, as anumber of subsequent replications is required to end up with the target tone
(positive/negative) and the target material.

12M. Tormen at al, Nanotechnology 18 (2007) 385301.
M. Mühlberger et al, Microel. Engin. 86 (2009) 691; H. Schift et al, JVST B27 (2009) 2846.

50

shear force / mN

20 mbaracross

40

along

30
20
100
0

102030displacement a.u.

Figure 1: Hierarchical polymeric template.
Preparation in photoresist by lithography andsubsequent laser treatment resulting in selfordered LIPSS (laser-induced periodic surfacestructures).

Figure 3: Adhesion withanisotropic hierarchicalstructures (here 1 µm widelines on 20 µm square posts).

copy 1(OrmoStamp)

200 nmpolymeric
template(OrmoStamp)

copy 1copy 2(SU 8)(OrmoStamp)

200 nm1 µm

200 nmFigure 2: Multiple replication of polymeric templates in OrmoStamp and SU-8.
Successful repeated replication advises alternating the replication materials.
Feature distortion is critical when a specific tone of the structures in a specificmaterial is aimed, as it asks for repeating this replication cycle several times.