First-row transitional-metal oxalate resists for EUV

We have developed inorganic oxalate compounds [PPh3(CH2Ph)][M(2,2′-bipyridine)n(oxalate)(3-n)] (n=1, 2, 3; M = Co, Fe, Cr) capable of acting as negative-tone extreme ultraviolet (EUV) resists. Two important trends are observed: (1) sensitivity increases with the number of oxalate ligands; (2) Cobalt and iron complexes exhibit greater sensitivity than analogous chromium complexes. Lithographic studies of the most successful compound, [PPh3(CH2Ph)][Co(2,2′-bipyridine)(oxalate)2], show that it can consistently achieve 20 nm h/p lines at doses approaching 30 mJ/cm2. Infrared, paramagnetic nuclear magnetic resonance, and cyclic voltammetric studies of this compound show that the reaction products of the EUV photochemistry are Co(II)(2,2′-bipyridine)(oxalate) and [PPh3(CH2Ph)]2(oxalate) formed from the decomposition of one of the oxalate ligands into two equivalents each of carbon dioxide and electrons.