Resist of the Month October 2021:

Many companies meanwhile use the conductivity of Electra layers for their processes and technologies. Since its introduction on the market in 2018, synthesis and processing of Electra have continuously been improved. The conductivity of this resist could for example be increased by a factor of five between 2018 and 2020. An unwanted side effect was however that the long-term stability of certain batches fell below the guaranteed storage stime of six months, resulting in defects during coating. We have now solved this problem with an innovative manufacturing technology.

At first, synthesis process parameters were subjected to thorough tests by applying a sophisticated temperature regime during which a defined pH value was set at all times. This increased the yield by 33 %, whereby the optimal spectroscopic extinction values ensuring the high quality were also met.

During these tests it became evident that the drying step after dialysis which had been carried out so far caused the reduced long-term stability of the polymers with the highest conductivity. Searching for alternative solutions, we came across Tangential Flow Filtration (TFF). The company Satorius subsequently adapted a SARTOFLOW device specifically to our requirements (see also AR NEWS April 2021).

Tangential Flow Filtration with SARTOFLOW

First test runs conducted in spring turned out to be quite successful and the TFF device was, as is tradition at Allresist, given a catchy name – “Tiffy”. The working time per approach is reduced to 1/30 as compared to the old technology, and in addition 80 % of the required DI water can be saved. Yielding a very high quality, the entire Electra production via Tiffi is now progressing much faster and considerably more environmentally compatible.

Our investigations have also shown that an addition of ethanol instead of isopropanol improves both coating behavior and long-term stability. If we should change the recipe accordingly in future, we will inform our customers in time.

These successful investigations were the reason why we selected Electra 92 as resist of the month of October.

Oliver Schirmer (right) and Eric Röschke (left) exchanging filters at “Tiffy”