Two-photon direct laser writing with metrologically traceable positioning

The extension of nanopositioning and nanomeasuring machines (NPM-machines) to fabrication machines by using a femtosecond laser for the implementation of direct laser writing by means of two-photon absorption (2PA) is a promising approach for cross-scale metrological fabrication in the field of lithographic techniques [23]. To this end, a concept for integrating two-photon technology into an NPM machine was first developed and implemented. This was followed by a characterization of the system and targeted investigations to provide evidence for the synergy of the two techniques. On this basis, a new approach to high-throughput micro- and nano-fabrication was developed and investigated, demonstrating new possibilities in cross-scale, high-precision manufacturing [5]. This mix-and-match approach is based on a combination of 2PA laser writing with field emission lithography to fabricate masters for subsequent nanoimprint lithography. Not only the advantages of the large positioning range of the NMM-1 could be highlighted, but also the advantages resulting from the highly accurate positioning. A systematic reduction of the distance between two adjacent lines resulted in a minimum photoresist width of less than 30 nm [15], which can be classified among the smallest distances between two laser-written lines described in the literature [3, 9, 19]. The center-to-center distance of the lines of about 1.695 µm at a numerical aperture of 0.16 and a wavelength of 801 nm is only about 56 % of the Rayleigh diffraction limit extended for the two-photon process. Thus, for the first time, a resist width far below the diffraction limit could be realized with conventional two-photon laser writing in positive photoresist. © 2021 De Gruyter Oldenbourg. All rights reserved.