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 micro- and 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/cm2) 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/cm2). The sensitivity and contrast values were calculated from the normalized remaining thickness (NRT) curve analysis as 270 µC/cm2; 5.2 and 153 µC/cm2; 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.
