In the past several years, ArF immersion lithography has been developed rapidly for practical applications. ArF
immersion lithography is now researched actively and developed for the purpose of implementing the 45-nm technology
node. For the device designs involved immersion lithography, line width roughness (LWR) and film wettability are very
important criteria to control in the point of high resolution and defectivity.
Free radical polymerization in the presence of thiocarbonylthio compounds of general structure Z-C(=S)S-R provides
living polymers of predetermined molecular weight and narrow molecular weight distribution by a process of reversible
addition-fragmentation chain transfer (RAFT). A rationale for selecting the most appropriate thiocarbonylthio
compounds for a particular monomer type is presented with reference to the polymerization of methacrylates, styrenes,
acrylates, acrylamides, and vinyl acetate.
In this study, resist polymers with narrow polydispersity (PD) and controlled molecular structure were prepared using
controlled radical polymerization techniques, such as RAFT polymerization. PD index of polymers showed between
about 1.2 to 1.4 and in some instances, between about 1.1 to 1.2 or less. Additionally, each polymer chain has a RAFT
end group. That is the resulting polymer contains a chain transfer agent (CTA) moiety at each terminal end of polymer
backbone. It is possible that hydrophobic CTAs can be used to decrease the hydrophilicity of resist film.