2023 Volume 36 Issue 5 Pages 411-416
Metal impurities in lithography chemicals is critical to wafer fabrication processes. Since these trace amount of metal impurities is difficult to detect by existing in-line inspection systems, they should be removed as much as possible before wafer processing begins. Metal reduction media implemented as a filter is one strong candidate to remove metals. Ion-exchange type media is typical for metal reduction with the metal reduction mechanism of ion-exchange type media utilizing a strong acid function group such as a sulfonic group. However, lithography chemicals are very sensitive to acidic conditions. For instance, the reaction mechanism of chemically amplified resists utilizes acid catalysis and ester solvent such as PGMEA, which is very widely used as casting solvent for photo resists and underlayer coating materials may be decomposed under acid coexistence. The potential impact of acid presence in ion-exchange type media is a concern. For this reason, we have developed a new metal purifier called “Nylonpolar” to process lithography chemicals in advanced semiconductor applications. Nylonpolar consists of a nylon based membrane and carboxylic group for metal reduction. We were able to confirm that Nylonpolar doesn’t decompose PGMEA solvent, while ion-exchange type media did. Also it was confirmed that Nylonpolar can remove a wide range of metal impurities. This data indicates that Nylonpolar is better metal purifier, especially for lithography process chemicals. Additionally, we have developed another different kind of metal purifier called “MGS2M”. The membrane structure of this metal purifier consists of an ion-exchange type media and acid capture membrane. The acid that was released from the ion-exchange media can be captured by the second acid capture membrane. It was confirmed that MGS2M doesn’t leach the acid, while a more typical ion-exchange type media did. And also, this MGS2M can remove more kinds of metal impurities than typical ion-exchange type media.
