TMAH, tetra-methyl ammonium hydroxide, aqueous solution is widely used as a photoresist developer. The resist development process is the final process of the resist patterning process, just before an etching process, therefore we have to pay attention to the cleanliness of the TMAH developer, especially metal contamination. The reason metal contamination is most concerning is that metal impurities typically can’t be detected by general pattern defect inspection tools. Additionally, metal impurities inside the resist and underlayer films can become etch stoppers because of the lower etching rate of the metal. This makes reducing metal impurities from TMAH aqueous solution critical. One of the convenient and promising devices to reduce metal impurities from chemicals are metal purifiers in form of the filter devices. Strong cation type ion-exchange media is widely used for metal reduction in various industries. When we applied this type of metal purifier to a TMAH solution, metal removal efficiency was low. We decided to develop new purifier media to reduce metal impurities in TMAH solutions. Using surface modified polyethylene (PE) media as the basic purifier media, we found that chelating modified PE showed the better metal removal performance. We also noticed a difference between non-woven PE and PE membrane on the metal removal performance. Finally, we were able to improve the metal removal efficiency by optimization of the functional group and membrane structure.
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