Microfabrication system based on two-photon lithography

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A device is requested that will enable the fabrication of three-dimensional (3D) structures down to submicron structure sizes. The microfabrication system should allow the fabrication of the broadest possible class of 3D geometries, particularly structures with high aspect ratios, undercuts, structures with complex topologies, and structures that cannot be described as a projection onto a plane. The system should be able to structure volumes down to the order of one cubic centimeter. Multiscale capability is desired, i.e. different structuring modes are to be used depending on the desired structure size, whereby coarse structures can be produced faster than fine ones. In this way, it will be possible to structure even relatively large volumes with moderate time expenditure. Other important requirements are the biocompatibility of the materials used and low surface roughness, which comes into play for applications in optics, for example. One of the most important areas of application for the microfabrication system will be in microfluidics. In the corresponding projects, microfluidic supply networks, structures for lab-on-a-chip systems or optofluidic components will be required, for example. Research into the devices available on the market has shown that, on the whole, these requirements are only met by systems based on two-photon lithography (2PL). Here, a solution of photopolymers that polymerize under UV light serves as the starting material. The wavelength of the irradiated light is chosen such that the absorption of two photons is necessary to initiate polymerization. Thus, the polymerization process depends nonlinearly on the light intensity. As a result, a very small spatial region is obtained in the laser focus where the intensity is sufficient to initiate polymerization. This results in the possibility to fabricate very fine structures with sizes in the submicrometer range. In practical implementation, a laser beam scans the photopolymer solution, which hardens locally in the process. The non-polymerized solution can then be removed so that the volumes scanned by the laser beam finally form the 3D structure.