Development of fluoro-free surfactant rinse solutions for EUV photoresists

In the photolithographic process of semiconductor manufacture, a photoresist is exposed to light and then developed to create a pattern on the photoresist surface. After development, a rinse step is necessary to prevent pattern collapse and to remove polymer residues that linger after development. Surfactants are essential in these rinse solutions and help mobilize polymer residues while also minimizing capillary forces that are responsible for pattern collapse. An ideal surfactant system interacts with the polymer surface enough to mobilize debris particles, but not enough to cause swelling and shift the critical dimension; while at the same time creating a surface tension and contact angle to prevent pattern collapse. In this work, we investigated various non-fluorinated surfactants and their interaction with EUV photoresists by measuring surface tension, contact angle, and photoresist swelling. Although the difference of solubility parameters (DSP) between surfactants and photoresists were shown to correlate to photoresist swelling. No correlation between resist swelling and the difference of solubility parameters was found in the study. Through this work, we identified that ideal surfactant rinse properties can be achieved in a fluoro-free surfactant formulation. Ideal fluoro-free EUV surfactant rinse formulations achieve no pattern collapse, low CD-shift, and good residue clean performance for an EUV photolithographic process.