Photoresist Absorption Measurement at Extreme Ultraviolet (EUV) Wavelength by Thin Film Transmission Method

A methodology to measure photoresist absorption under soft X-ray radiation is presented in this work. The high photoresist sensitivity required for the extreme-ultraviolet lithography (EUVL) technology can be achieved by increasing the EUV photon absorption of photoresist material, hence high extinction coefficient is preferred. To determine the extinction coefficient of a photoresist, a small-scale manufacturing process has been developed to obtain free standing thin silicon nitride (SiN) membranes and use it as sample holder for photoresist thin film characterization. The SiN membrane has been characterized in terms of film thickness, composition and density. Transmission measurements through the thin films of SiN and photoresist have been carried out in the energy range between 90.6 eV and 92.6 eV by using X-ray Absorption Spectroscopy (XAS) at the BEAR beamline Elettra synchrotron research facility, in Italy. The method permits an experimental measurement of the absorption coefficient of thin films, with an accuracy of 3 ×10−4, providing a tool helpful for EUV photoresist research and development.