Figure 5.

Grayscale photolithography combined with backside UV exposure enables control over microstructure height. (A) Digital 8-bit grayscale photomask designs that were used for the grayscale photolithography experiments, using the PRIMO setup and a 5X objective. (i) Linear grayscale gradient to generate SU-8 height gradient. (ii) Staircase-like pattern with various grayscale values to generate multi-level SU-8 structures. (iii) Circles with a radial grayscale gradient to generate cone-like SU-8 structures. (B) SU-8 ramp fabricated using linear grayscale gradient as measured by optical profilometry. (i) Structure increases in height from 0 µm to 50 µm. (ii) Near linear gray-height response with a laser dose of 2 mJ/mm². Laser doses that are too high (3 mJ/mm² and 6 mJ/mm²) lead to an early plateauing of SU-8 structures. (C) Multi-level SU-8 structures can be obtained using grayscale photolithography. (i) SEM image of multi-level SU-8 structure, generated using staircase-like grayscale pattern. (ii) Optical profilometric 3D scan of the multi-level structure. (D) Cone-like structures can be fabricated using circles with a radial grayscale gradient. (i) SEM image of cone-like SU-8 structures. (ii) Optical profilometric 3D scan of cone-like SU-8 structures.