Organic-inorganic hybrid materials with high refractive index have attracted considerable attention for many optoelectronic applications, including spin-on-type hardmask for ArF lithography (193 nm). In this study, we demonstrate the synthesis of a C-60-embedded organosilicon hybrid polymer, C-60-embedded poly-xylene-hexamethyltrisiloxane hybrid (C-60-PXS), of tunable optical properties. C-60 was covalently bonded to the PXS backbone through Pt-catalyzed hydrosilylation, in which the PXS was formed possibly by unexpected transition metal-catalyzed benzylic C-H silylation and oxygenation of the o-xylene. The C-60-PXS thin films fabricated using a spin-coating method showed much higher refractive index by 5 -22% according to the curing temperatures, than the PXS thin films containing no C-60. In particular, the C-60-PXS thin film cured at 350 degrees C showed the refractive index (n) and extinction coefficient (k) at 193 nm to be 1.61 and 0.29 that are very close to the optimum values for the Si-hardmask. This implies the high applicability of the C-60-embedded organosilicon hybrid polymer, C-60-PXS, for the spin-on Si-hardmask in ArF lithography. (C) 2016 Elsevier B.V. All rights reserved.