Nonchemically-amplified Resists Based on Photosensitive Oxime Ester Functionalized Polystyrene
Two styrene derivatives 2,2,2-trifluoro-1-(4'-vinyl-[1,1'-biphenyl]-4-yl)ethan-1-one-O-(3-methylbenzoyl)oxime(OXE-P)and 2,2,2-trifluoro-1-(4'-vinyl-[1,1'-biphenyl]-4-yl)ethan-1-one-O-thiophene-2-carbonyl oxime,OXE-S)modified by photosensitive oxime ester group were synthesized.They were characterized by 1H nuclear magnetic resonance(1H-NMR)spectroscopy and high-resolution mass spectrometry(HRMS).New polymers(POXE-P and POXE-S)were prepared by the reversible addition-fragmentation transfer(RAFT)polymerization,and were further characterized by gel permeation chromatography(GPC),giving molecular weights(Mw)of 8.3 kDa and 7.2 kDa,and polydispersites(Ð)of 1.1.Both polymers possess good solubility,thermal stability and film-forming capability,which meet the requirements of resist materials.The polymers were dissolved separately in the propylene glycol methyl ether acetate(PGMEA)to form nonchemically-amplified resists(n-CARs).The lithographic performance of the POXE-P resist was examined by e-beam lithography,giving a 50 nm HP(half-pitch)lithographic pattern.The mechanism of POXE-P resist during exposure was investigated by Fourier transform infrared spectrometer(FTIR)and in situ outgassing analysis.It showed that the oxime ester group decomposed during exposure to form carbonyl compounds,CO2,and other small molecules.The cleavage of side chains and the possible crosslinking led to the solubility switch of the polymer,resulting in negative lithographic patterns.
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