Extreme UV and selective inner-shell fragmentation studies of novel polymeric resist materials

Full text: Two key concepts are important in extreme ultraviolet lithography (EUVL) to be the candidate for mass production of future integrated circuits: the polymer formulation and the photo-fragmentation process. We present here a detailed study of EUV and carbon inner-shell excitation of homopolymers and copolymers that have in their structures sulfonium and triflate groups as EUV absorption-enhancing units. The goal is to achieve sub-20 nm line patterns having low line edge roughness (LER) of < 2.0 nm and high sensitivity. The present work demonstrates the lithographic performance of several photoresists, MAPDST homopolymer and MAPDST-MMA copolymer, and the correlation with the photodynamic fragmentation processes. The dependence of the photodynamic processes on the excitation energy was studied by scanning the synchrotron energy. Particular excitations were selected which finally led to selective fragmentation of the polymers. The unique properties of the synchrotron radiation, highly monochromatic and intense, allowed to obtain detailed information about the photodegradation process in the new resists. The SGM (spherical grating monochromator) and the Planar Grating Monochromator (PGM) beamlines for VUV and soft X-ray spectroscopy were use in the present study. NEXAFS, XPS and QMS techniques were employed as analytical tools. The polymers were found to be sensitive to EUV irradiation at 103.5 eV showing that the triflate and the ester group were the weakest part of the MAPDST homopolymer with important desorption of SO²⁺ , SO⁺ and CF³⁺ fragments during irradiation. The presence of a metacrilate group (MMA) led to a lower gas desorption rate and higher resistant to irradiation than the homopolymer. When a new MANTMS homopolymer and co-polymer (having a biphenyl group) were irradiated at selected carbon inner-shell excitation energies it was found a highly selective process of bond breaking mainly under the π*C=C excitation of the phenyl functional groups. The defluorination and loss of sulfonated groups with the increase in the irradiation time for the MANTMS homopolymer was evident when the excitation energy was tuned to excite the π*C=C transition. On the contrary, C1s → π*C=O and C1s → σ*C–F excitations did not produce important changes in the polymer surface region. This methodical investigation will provide guidance in designing new resist materials with improved efficiency for EUVL through polymer microstructure engineering. (author)