Fabrication of three-dimensional stamps for embossing techniques by lithographically controlled isotropic wet etching
Example of a process for the fabrication of complex 3D structures. A masking layer (e.g., chromium) is deposited on quartz (a) and patterned by standard lithographic techniques (e.g., by e-beam lithography) (b). The quartz substrate with the patterned masking layer is introduced in the etching solution (c). The openings in the mask represent the origin of the etching front. The etching front is represented by (the convolution of) hemispherical surfaces growing linearly in time. The quartz is removed from the etching solution and rinsed. New openings in the mask are fabricated in a second lithographic step (d), followed by a second step of etching (e). Then the masking layer is stripped (f). Holes are directly fabricated in quartz by FIB (g) followed by a final step of etching (h). The template is used in nanoimprinting or hot embossing processes (i).
Variety of different high quality 3D structures is fabricated in quartz. Compared to other 3D micro- and nanostructuring methods, in which a hard material is directly “sculptured” by energetic beams, the present technique requires a much less intensive use of lithographic equipments, for comparable volumes of structured material. The reason is that in the present method the lithographic tools (EB and FIB) are employed only for defining the initial boundary conditions of the surface or modifying the intermediate ones before and between isotropic wet etching steps.
tapping mode AFM image of a quartz sample after 50 min of etching in hydrofluoric acid 39.5 wt %. The rms roughness of the sampled area is 0.9 nm.
Evolution of the surface roughness of quartz as a function of the etching time in HF 39.5 wt % (the etching rate was ). AFM measurements were taken in tapping mode over a sampling area.
3D structures hot embossed in different polymers (ZEONEX and PMMA). The technique allows us to fabricate a structure similar to those of the compound eyes of the insects (the inset shows part of an ant’s head).
Two different kinds of defects observed in 3D patterning of polymer material caused by trapping of air.
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