After initial investigations, we presented Medusa 84 as the resist of the month In October 2023, full of hope based on the promising first results. Now we are able to show reliable results that even exceed our expectations. Through a targeted synthesis which precisely separates the stable and sensitive molecular fraction of the HSQ polymer, and through complex cleaning procedures, it is possible to offer a significantly more stable resist. After 6 months of unopened refrigerator storage (8-12 °C), the application properties remain unchanged, an expensive refrigerated transport thus is not necessary. The process control in electron beam lithography can also be interrupted for a few days without making further processing impossible. The stability is achieved by an optional addition of stabilizers which neutralize the water and amines from the ambient air, thereby suppressing the “natural” aging of the HSQ.

The comparison between Medusa 84 and HSQ demonstrates similar behaviour of both resists, with Medusa 84 exhibiting slightly higher sensitivity. The developer in each case was 6.5 % TMAH.

Fig. 1: Contrast curves of Medusa 84 and a commercial HSQ

In the following, further application examples are shown:

Fig. 2: Single line structures of Medusa 84 SiH on GaA, written at 30 kV. An experimental TMAH-NaCl developer was used to improve contrast while maintaining good adhesion properties. (© E. Maggiolini, JKU Linz)

Fig. 3: Circular 100 nm line/space structures written at 1000 µC/cm² at 100 kV on silicon and developed with AR 300-73 (6.5 % TMAH solution). (© J. Hohmann, KIT-IMT, Karlsruhe)

Fig. 4: Square pillars with 22 nm edge length and 50 nm height on GaAs, written at 30 kV and developed with AR 300-44 (2.38 % TMAH). (© E. Maggiolini, JKU Linz)

As the icing on the cake it can be mentioned that a special Electra 92 has been developed for Medusa 84, which is therefore also suitable for HSQ.

Fig. 5: Siemens star written on quartz with the new conductive layer Electra 92 (AR-PC 5092.02/1), which was spun on to prevent charging. This variant of Electra 92, specially developed for HSQ, is characterised by excellent coating and adhesion properties. (© B. Drent, AMOLF, Nanolab Amsterdam)

We presented Medusa 84 at the EIPBN 2024 (Triple Beam) in San Diego. The interest of the congress participants was overwhelming, and many wanted to try out the new resist quickly. Sales of samples have now started, and the regular market launch is planned in a few weeks.

This success has prompted us to make Medusa 84 the resist of the month.