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

Abstract

Our primary platform for 157 nm positive resists is built on a copolymer of t-butyl 2-trifluoromethylacrylate (TBTFMA) and norbornene bearing hexafluoroisopropanol (NBHFA) as an acid group, which is prepared by radical copolymerization. The radical copolymerization of 2-trifluoromethylacrylic monomers with norbornene derivatives has been found through reactivity ratio determination and in situ <SUP>1</SUP>H NMR analysis of kinetics to deviate from the terminal model but to follow the penultimate model. These copolymers typically contain &gt;50 mol% TBTFMA, are lipophilic, and fail to provide good imaging due to poor wettability. Blending a homopolymer of NBHFA (optical density (OD)=1.7/micrometers at 157 nm) into the copolymers (OD=2.5-2.7/micrometers ) increases the hydrophilicity and reduces OD to 2.2-2.0/micrometers , providing high resolution images. Another platform we have identified is a copolymer of TBTFMA with vinyl ethers, which can be prepared by using a common radical initiator. Some of the vinyl ether copolymers are also homogeneously miscible with the NBHFA homopolymer and thus their OD and aqueous base development can be improved by blending.