24 July 2002 Acid mobility in chemically amplified photoresists
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In a chemically amplified resist the exposure energy is used to generate a catalytic species, which promotes a solubility-switching reaction during a post exposure processing step. Using an absorbed photon to generate a catalyst, instead of using it to directly cause a solubility-switching photochemical reaction, allows for much lower exposure doses to be used for patterning since the catalytic species can eventually promote multiple solubility-switching events instead of just one. Some level of catalyst mobility is necessary to achieve the amplification effect as the catalyst must move from reaction site to reaction site, but any catalyst mobility creates the possibility of movement from exposed regions into unexposed regions causing image blur or line width spreading. As the catalyst diffuses in the resist, it promotes chemical reactions; these chemical reactions complicate analyses of catalyst diffusion by changing the chemical environment of the diffusant. Thus, the material properties of the surrounding resin are changing, sometimes drastically, as the catalyst diffuses. In addition to simple changes in material type, the chemical reaction also generates a transient material state as reaction by-products either remain in the resist film or desorb. The variation in lifetime of this transient state is another factor that must be considered in a full analysis. This work reports a method to separate reaction effects from catalyst diffusion effects. Acid diffusion in polymers which are close structural analogues to poly(4-t-butyloxycarbonyloxystrene) (TBOCST), while being unreactive to diffusing acidic molecules, was studied. Specifically, the diffusion properties of photogenerated perfluorobutanesulfonic acid in the unreactive TBOCST analogues poly(4-isopropyloxycarbonyloxystyrene) and poly(4-neopentyloxycarbonyloxysytrene) are reported. Measuring and understanding diffusion in these analogue polymers provides insight into the more complicated, and more important, reaction-diffusion processes of TBOCST.
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Michael D. Stewart, Darren J. Becker, Timothy B. Stachowiak, Gerard M. Schmid, Timothy B. Michaelson, Hoang Vi Tran, C. Grant Willson, "Acid mobility in chemically amplified photoresists", Proc. SPIE 4690, Advances in Resist Technology and Processing XIX, (24 July 2002); doi: 10.1117/12.474168; https://doi.org/10.1117/12.474168

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