3D-microfabrication by two-photon polymerization of an integrated sacrificial stencil mask

This work aims at developing a new and unconventional Sacrificial Stencil Mask (SSM) technology by exploiting Two-Photon Polymerization (2PP) in an IP-L/SU-8 double layer resist system. The process consists of the sequential deposition of two different resists, such as SU-8 and IPL, onto the same glass substrate, followed by 2PP lithography and distinct development processes. The 2PP writing process was used to polymerize structures inside the top and bottom resist layers to form, in one single exposure process, both SSM and a permanent polymeric structure, in our case a plain pedestal. The top IPL resist was developed using Isopropyl Alcohol (IPA), which does not affect either exposed or un-exposed SU-8 regions. In this way, structures written into the bottom layer remained latent, while exposed areas of the top IPL resist, including the stencil mask, were developed. The realization of 3D stencil masks, designed to be anchored inside the un-exposed bottom layer, was combined with metal evaporation to demonstrate the deposition of a plain metal line through the stencil mask. The final development of the bottom layer led to the lift off of the sacrificial stencil mask, uncovering the underlying, permanent polymer-metal structure. The combination of sacrificial polymer structures with permanent ones opens new possibilities in 3D MEMS design, enabling the integration of distributed electronic transducers in flexible polymeric structures. © 2019 The Authors