Low-LER Tin Carboxylate Photoresists using EUV

Pure thin films of organotin compounds have been lithographically evaluated using extreme ultraviolet lithography (EUVL, 13.5 nm). Twenty-one compounds of the type R2Sn(O2CR')(2) were spin-coated from solutions in toluene, exposed to EUV light, and developed in organic solvents. Exposures produced negative-tone contrast curves and dense-line patterns using interference lithography. Contrast-curve studies indicated that the E-max values were linearly related to molecular weight when plotted separately depending upon the hydrocarbon group bound directly to tin (R = butyl, phenyl and benzyl). Additionally, E-max was found to be linearly related to free radical stability of the hydrocarbon group bound directly to tin. Dense-line patterning capabilities varied, but two resists in particular show exceptionally good line edge roughness (LER). A resist composed of an amorphous film of (C6H5CH2)(2)Sn(O2CC(CH3)(3))(2) (13) achieved 1.4 nm LER at 22 nm half-pitch patterning and a resist composed of (C6H5CH2)(2)Sn(O2CC6H5)(2) (14) achieved 1.1 nm LER at 35 nm half-pitch at high exposure doses (600 mJ/cm(2)). Two photoresists that use olefin-based carboxylates, (C6H5CH2)(2)Sn(O2CCH=CH2)(2) (11) and (C6H5CH2)(2)Sn(O2CC(CH3)=CH2)(2) (12), demonstrated much improved photospeeds (5 mJ/cm(2) and 27 mJ/cm(2)) but with worse LER.