Fluorination enhanced lithographic performance of sulfonium-based molecular nonchemically-amplified resist

BackgroundNonchemically amplified resists (n-CARs) have emerged as a promising candidate for the next-generation of resists. Sulfonium-based n-CARs exhibit the capability of forming patterns with high resolution and low LER. However, their practical application is severely hindered by the low sensitivity.AimIt is expected to improve the sensitivity of sulfonium-based n-CARs by enhancing the absorption of extreme ultraviolet (EUV) or electron irradiation, thereby increasing the yield of secondary electrons and promoting the subsequent chemical reactions.ApproachFluorine has a higher EUV absorption cross-section than that of carbon and oxygen elements. Introduction of F-C bonds to resist matrix will boost the EUV photons or electrons absorption and induce the occurrence of new photochemical reactions. We synthesized a multisulfonium-based molecular glass (MG) functionalized with pentafluorobenzylphenylmethylsulfonium (AD-4PF), together with the nonfluorinated MG of AD-4Ph. The lithographic performances of both resists were evaluated by electron beam lithography (EBL) and extreme ultraviolet lithography (EUVL).ResultsThe sensitivity of AD-4PF resist (2487 μC cm−2) was 30% higher than that of AD-4Ph model resist (3559 μC cm−2) in EBL, achieving well-defined 20 nm line/space (L/S) patterns at a dose of 2900 μC cm−2. A similar sensitivity improvement (112 versus 172 mJ cm−2) was observed in EUVL. Photochemical reaction confirmed that the solubility switch of both MG resist films originated from the cleavage of the bond of benzylic S+−CH2PF to form nonpolar methyl thioether.ConclusionsThe fluorinated AD-4PF molecular resist demonstrates high resolution and improved sensitivity, which has been confirmed by EBL and EUVL. The difference in sensitivity between the AD-4PF and AD-4Ph resists is mainly attributed to the significantly enhanced absorption cross-section, the reduced bond energy, and the additional possible dissociative electron attachment (DEA) process by fluorine incorporation.