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 R 2 Sn(O 2 CR’) 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 (C 6 H 5 CH 2 ) 2 Sn(O 2 CC(CH 3 ) 3 ) 2 (13) achieved 1.4 nm LER at 22 nm half-pitch patterning and a resist composed of (C 6 H 5 CH 2 ) 2 Sn(O 2 CC 6 H 5 ) 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, (C 6 H 5 CH 2 ) 2 Sn(O 2 CCH=CH 2 ) 2 (11) and (C 6 H 5 CH 2 ) 2 Sn(O 2 CC(CH 3 )=CH 2 ) 2 (12), demonstrated much improved photospeeds (5 mJ/ cm 2 and 27 mJ/cm 2 ) but with worse LER.