Resist of the month of October 2019: Medusa 82 UV – excellently suited for grayscale lithography

Medusa 82 UV was already chosen as resist of the month in January 2019. Back then, we highly appreciated the first results for a use as photoresist. Shown are now results with respect to an application in grayscale lithography which were also presented at the MNE 2019 in Greece.

At the Leibniz Institute of Photonic Technology (Leibniz IPHT, Jena), Dr. med. U. Hübner and P. Voigt conducted investigations on the production of diffractive optical elements (DOEs) by e-beam lithography. When evaluating the dose scale (Figure 1), the scientists noticed that the surface of Medusa 82 UV structures turned out to be very smooth. Since the resist mainly consists of SiO₂ after cross-linking, structures are very similar to glass. This offered good perspectives for a use of the structures in optical applications.

Fig.1 Dose scale of Medusa 82 UV

Subsequent experiments indeed demonstrated that a writing DOE was comparably easily possible. Fig. 2 describes the principle of grayscale lithography: Structures with different dose strengths are written in a Medusa layer and developed, which results in the desired topologies. While the general standard process for the production of DOEs consists of five substeps, only one step is required if grayscale-lithography with Medusa 82 UV is performed. According to Dr. Hübner, process times are thus reduced by approx. 80 %.

Fig. 2 Principle of grayscale lithography

Fig. 3 SEM image of a 3-level DOE pixel produced in 800 nm Medusa 82 UV

This was reason enough for us to choose Medusa 82 UV for the second time as resist of the month.