Fluoropolymer resists: Progress and properties

Various new fluoropolymers have been prepared for use in 157 nm lithography in the last few years. While several different backbone structures are available, what is common to all these 157 nm polymers is the exclusive use of hexafluoroisopropanol (HFA) as an acid group. The major effort has been placed on reduction of the absorption at 157 nm. In addition, we focused our attention on the hydrophobicity-hydrophilicity balance and understanding of the interaction of the HFA moiety with other functional groups and the dissolution behavior of the HFA polymers. Initially, we developed four platforms; a) all-acrylic, b) all-norbomene, 3) aliphatic, and 4) aromatic systems. The all-acrylic system based on 2-trifluoromethylacrylic monomers was meant to be for tool-testing and the all-norbornene system based on norbornene with pendant HFA (NBHFA) has been primarily 2 engineered for 193 nm application (COBRA 5000). Since the aromatic system (PF2-ESCAP) based on a copolymer of t-butyl 2-trifluoeomethylacrylate (TBTFMA) with styrene bearing HFA (STHFA) has a rather high absorption of 3.2/mum, our major development effort has been directed to the aliphatic system based on a copolymer of TBTFMA and NBHFA or vinyl ether. New copolymers have been prepared by radical copolymerization of TBTFMA with vinyl ethers bearing HFA, resulting in lower absorption and lower/controllable glass transition temperatures. In addition to the new copolymers with polar vinyl ethers, the dissolution behavior and hydrogen bonding interaction of HFA polymers are described.