(549a) Image Formation In Thin Films of Chemically-Amplified Photoresists

Next-generation
nanofabrication requires economical lithographic processes that achieve sub-22
nm resolution. Current manufacturing practices are based on projection
lithography with chemically-amplified (CA) photoresists.
CA resists are comprised of a polymer resin (reactant) blended with a photoacid generator (catalyst); a coupled
reaction-diffusion mechanism drives image formation, where resolution is
controlled by slow diffusion of the acid catalyst. Extending the lifetime of CA
resists requires a comprehensive understanding of the physical and chemical
variables that control image formation in ultrathin films. Challenges
associated with thin films include surface segregation of acid catalyst,
adsorption of airborne contaminants, and changes in polymer mobility due to
thin film confinement. Currently, there are no methods that offer spatially
resolved feedback for the reaction-diffusion mechanism. In this talk, we
demonstrate that image formation in CA resists can be accurately measured
through the film thickness with small-angle X-ray diffraction. Proof-of-concept
experiments are based on poly(4-hydroxystyrene-co-tertbutylacrylate) resin loaded with 6.5
wt% triphenylsulfonium sulfonate
photoacid generator. The CA resist is cast in 80 nm
films on silicon/silicon nitride substrates, and the spatial distribution of
acid catalyst is generated with electron-beam patterning.  Image formation is completed at temperatures
in the range of 130-140⁰C, which are near the glass
transition temperature of the reactant. Preliminary results demonstrate that
spatial extent-of-reaction can vary through the film thickness, and
measurements of the thin film glass transition suggest that enhanced dynamics
at the free surface are responsible for this behavior.