Grayscale photolithography

Unrivalled performances

• Easy and local control of the UV dose on grayscale resist
• Creation of complex structures such as ramps, stairs, furrows, etc.
• Microfabrication in grayscale using standard SU-8

Easy and local control of the UV dose

By the simple use of the grayscale images, the PRIMO system enables resist to respond quantitatively to the UV dose, resulting in a modulation of the polymerization height.

In the example down below, one can see the different heights of the microstructures measured on the resist molds which enables the observation of the effects of the UV dose and the development time.

Creation of complex structures such as ramps, stairs, furrows, etc.

As the PRIMO system allows an easy control of the local dose, it makes it possible to prototype substrates with structures like ramps, stairs, concave throughs, convex humps or furrow within a few seconds. It is then possible to micropattern cells on the surface to recreate in vivo like environments for your experiments.

In the following example, we present some structures obtained with PRIMO, these are ramps separated by walls, concave microwells that are very smooth thanks to the reflow process and a large ramp.

Microfabrication in grayscale using SU-8

It is also possible to do grayscale photolithography with regular SU-8 using the PRIMO system.

In the following example, they spincoated SU-8 onto a glass coverslip. After projection with UV patterns through the glass, the local UV dose reticulated the SU-8 on greater or lesser depth. After development, the resulting structures were of different height.

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 conelike 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. Kasi et al., Micromachines, 2021.

(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. Kasi et al., Micromachines, 2021.