Unravelling the effect of fluorinated ligands in hybrid EUV photoresists by X-ray spectroscopy

Organic-inorganic hybrid compounds are arising as promising resist materials for extreme-ultraviolet (EUV) lithography, a new technique introduced in the semiconductor industry for the fabrication of integrated circuits of sub-10 nm feature size. In this work, we show that the sensitivity to EUV radiation of zirconium oxo clusters with methacrylate ligands is substantially enhanced when a small fraction of the ligands are replaced by trifluoromethylacrylates. We studied the details of the chemical changes that occur in thin films of the precursor and the partially fluorinated materials using scanning transmission X-ray microscopy (STXM) and X-ray photoelectron spectroscopy (XPS). Evidence is presented for radical chain polymerization as a mechanism for the solubility switch. Yet, XPS results also indicate that Zr-F bonds are formed during the exposure to EUV light in the fluorinated material, dissociative electron attachment being likely involved. Our observations show that, while fluorinated ligands enhance EUV absorption, their effect on the reactivity of the material might be more critical, thereby contributing to an increase in the sensitivity of the resist in both ways.