Fluoropolymers for 157/193 nm lithography: Chemistry, new platform, formulation strategy, and lithographic evaluation

A copolymer of t-butyl 2-trifluoromethylacrylate (TBTFMA) and norbornene bearing hexafluoroisopropanol (NBHFA) as an acid group, which is prepared by radical copolymerization, is employed in our 157 nm resist. The radical copolymerization of 2-trifluoromethylacrylic monomers with norbornene derivatives has been shown to follow the penultimate model much better than the commonly employed terminal model. These copolymers (containing >50 mol% TBTFMA) are too lipophilic to provide good imaging. Blending a NBHFA homopolymer with an optical density (OD) of 1.7/mum at 157 nm into the copolymers (OD=2.5-2.7/mum) results in increased hydrophilicity and reduced OD (2.2-2.0/mum) and provides high resolution images. A copolymer of TBTFMA with vinyl ethers has been identified as a new platform, which can be prepared facilely by common radical polymerization. Certain vinyl ether copolymers are also compatible with the NBHFA homopolymer and thus blending improves their OD and aqueous base development. Because these fluoropolymers are highly transparent at 193 nm as well, they are evaluated as 157/193 dual wavelength resists.