Complex 3D structures via double imprint of hybrid structures and sacrificial mould techniques

- Combination of micro- and nanostructures without laborious writing techniques
- Limitation of a surface-hardened SU-8 layer with high aspect ratio structures
- Successful replication of complex 3D structures in UV-PDMS

The preparation of transparent complex 3D structures over large areas at low cost paves the way for numerous optical applications. We prepared nanostructures on the surface of microstructures in a negative tone photoresist by a double imprint process combined with VUV-induced surface hardening. Successful preparation of the aforementioned structures asks for a compromise between the surface hardening of the nanostructures and the replication fidelity of the microstructures. Our results show that a VUV treatment time of at least 3 s is required so that the cross-linked layer does not break-up. Adequate process parameters as well as their limiting values were identified by using high aspect ratio microstructures. The complex 3D structures were successfully replicated in UV-PDMS to provide long-term stable templates. To ensure effective separation despite of the undercuts a sacrificial mould technique is applied.

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