Novel Negative-Tone Dry Film Resist and Process for Fine Pitch Copper Wiring with L/S = 1.5/1.5 μm on Build-up Substrate

Currently, higher density interconnects are required to improve electronic performance, and solutions such as 2.xD packages with fine redistribution layer (RDL) have been widely developed. Regarding photoresist materials for forming RDL, liquid resists are currently mainstream due to their high resolution, while dry film resists are not mainly used for RDL formation due to their lower resolution capability despite other good features such as panel compatibility, lower cost, and easy handling. To address this issue, we have developed a new negative-tone dry film resist with high resolution of 1 μm (aspect ratio 6.0) on wafers and 1.5 μm (aspect ratio 4.0) on ABF substrates panel. We also demonstrated fine pitch copper wiring with the new dry film resist by optimizing the process conditions; copper wiring with L/S=1/1 μm on wafer (aspect ratio 4.0) and L/S=1.5/1.5 μm (aspect ratio 3.3) on ABF substrates panel. It was also found that when it comes to producing fine copper wiring less than 2 μm, traditional wet-cleaning is challenging and it may be necessary to develop new wet-cleaning process that provides high cleaning performance while minimizing the risk of resist swelling. Otherwise the plasma cleaning may be needed instead of wet-cleaning.