Ferrocene bearing non-ionic poly-aryl tosylates: Synthesis, characterization and electron beam lithography applications

Abstract

The development of new organic-inorganic hybrid photoresists with optimal lithographic performances is an extremely important but challenging task. In this regard, we have synthesized a new family of homo- and hybrid-polymer resists based on 4-(tosyloxy)phenyl methacrylate (TPMA) and ferrocene methacrylate (FEMA) monomers for micro-/nano-lithography applications. The homo polymer resist, poly(TPMA), was synthesized by a free radical polymerization of TPMA monomer in ACN/THF (2:1, v/v) solvent system using azobisisobutyronitrile (AIBN) as the radical initiator. The hybrid copolymer resists, 2.0%-&4.0%-poly(FEMA-co-TPMA), containing 2.0 and 4.0 weight percentages of FEMA respectively, were synthesized by reacting FEMA (10 and 20% initial feed ratios respectively) and TPMA (90 and 80% initial feed ratios respectively) under similar reaction conditions. The ferrocene contents of the hybrid copolymers were calculated by proton NMR analysis. The potential of these polymer resists to pattern microand nano-features were tested under deep ultraviolet (DUV) and electron beam (e-beam) lithography tools respectively. The thin films formed by 4.0%-poly(FEMA-co-TPMA) exhibited high surface roughness in comparison to those of poly(TPMA) and 2.0%-poly(FEMA-co-TPMA) resists, probably due to the high ferrocene content of the former. The scanning electron microscopy (SEM) analysis of the e-beam exposed (dose 950 µC/cm 2 ) thin films of poly(TPMA) revealed patterning of 40 nm (L/10S to L/4S), 30 nm (L/10S & L/5S) and 22 nm (L/10S) line features. Similarly, 2.0%-poly(FEMA-co-TPMA) patterned 40 nm (L/5S to L/S), 30 (L/5S to L/S) and 20 nm (L/5S & L/4S) line features under the e-beam exposure (dose 500 µC/cm 2 ). The sensitivity and contrast values were calculated from the normalized remaining thickness (NRT) curve analysis as 270 µC/cm 2 ; 5.2 and 153 µC/cm 2 ; 1.98 respectively for poly(TPMA) and 2.0%-poly(FEMA-co-TPMA) resists. The present study therefore reveals that the incorporation of small amounts of ferrocene into the poly-aryl tosylate based resist formulations helps to enhance its sensitivity and resolution.