By Karlsruhe Nano Micro Facility (KNMF)
KNMFi Laboratory for Micro- and Nanostructuring 3D Direct Laser Writing is a tool to fabricate 3D freeform structures down sub µm. It is based on Two-Photon Lithography but beyond that 2D and 2.5D structures with nano dimensions are also possible. This system uses a nonlinear two-photon absorption process to modify, e.g. polymerize, a photosensitive medium at a specific point in the resist. By scanning the photoresist with a stage over this point a 3D-structure with dimensions in the submicron scale or greater can be written. Equipment - Nanoscribe Photonic Professional GT - Several sample holders - Galvoscan unit - Hybrid stage for large accurate travel distances - Critical point dryer (supercritical CO 2) - Coming soon: UV flood exposure (shell writing mode for large structures) Features - Resolution: 3D:200 nm lateral, 750 nm normal 2D: 180 nm - Feature Structure size: max. 600 x 600 x 3700 µm³ depending on filling factor - Writing modes: piezo (100x DIP), galvoscan (63x GT, 25x GT) - Corresponding writing fields: 300 x 300 x 300 µm³; 140 x 140 µm²; 280 x 280 µm² - Writing times: piezo slow, galvoscan fast - Larger areas have to be stitched - Accessible writing area: 100 x 100 mm² where structures could be placed Limitations/constraints - The realizable structure size depends on the structural stability of the design - The best results can be reached by using the IP-resists Materials Resists - Negative Resists: IP-L, IP-G, IP-Dip, IP-S, and similar resists that are photosensitive at a wavelength of 380nm - Positive Resist: AZ9260 (in preparation) - Experimental Resists are possible, but only the Air mode objective or oil-immersion Objective are applied. Dip-in techniques can only be used with proven compatibility. Substrates - 25 x 25 x 0.7 mm Glass, glass covered with ITO, cover slides 22 x 22 x 0.17 mm - Si-wafer 4’’ (100 mm) - Si/SiO2-wafer 4’’ (100 mm - Metallized Si-Wafer (Cr/Au) - Other substrates have to be provided by the user. Writing principle Sketch of the writing of a line in 3D-space inside a resist layer. The inset shows the modification in the voxel (blue) at the focal position. Only in the voxel two-photon absorption occurs. Data - Stl-format - CAD data can be exported in stl-format: - Sometimes CAD programs export erroneous stl-files. Solid works and similar programs used in mechanical engineering produce correct stl.files. - To avoid errors within stl-files the following rules can help: - Use correct units during contruction (µm), otherwise resolution could be bad - Use volumes, no areas, these objects have to be closed - Avoid Boolean operations - Avoid duplexes (use snaps) - Think about plane orientation. Normals are used to define interior or exterior. Therefore contruct plane consistently. - Avoid additional structures not necessary (not written) to your part. Correction of the stl-file is nearly impossible - In case of periodic structures a single unit cell is sufficient.
