Aliphatic platforms for the design of 157-nm chemically amplified resists

Abstract

ABSTRACT Our primary platform for 157 nm positive resists is built on a copolymer of t-butyl 2-trifluoromethylacrylate (TBTFMA) andnorbornene bearing hexafluoroisopropanol (NBHFA) as an acid group, which is prepared by radical copolymerization. Theradical copolymerization of 2-trifluoromethylacrylic monomers with norbornene derivatives has been found throughreactivity ratio determination and in situ 1 H NMR analysis of kinetics to deviate from the terminal model but to follow thepenultimate model. These copolymers typically contain >50 mol% TBTFMA, are lipophilic, and fail to provide goodimaging due to poor wettability. Blending a homopolymer of NBHFA (optical density (OD)=1.7/ m at 157 nm) into thecopolymers (OD=2.5-2.7/ m) increases the hydrophilicity and reduces OD to 2.2-2.0/ m, providing high resolution images.Another platform we have identified is a copolymer of TBTFMA with vinyl ethers, which can be prepared by using acommon radical initiator. Some of the vinyl ether copolymers are also homogeneously miscible with the NBHFAhomopolymer and thus their OD and aqueous base development can be improved by blending.Keywords: 2-trifluoromethylacrylate, hexafluoroisopropanol, radical copolymerization, reactivity ratios, copolymerizationkinetics, terminal model, penultimate model, dissolution kinetics, quartz crystal microbalance, chemical amplification, 157nm lithography