Measurements of water distribution in thin lithographic films

Neutron and x-ray reflectivity measurements quantify the non-uniform distribution of water within poly(4- tert -butoxycarbonyloxystyrene) (PBOCSt) and poly(4-hydroxystyrene) (PHOSt) thin films on silicon wafer substrates. Two contrasting surface treatments were examined, silicon oxide, representing a hydrophilic interface and a trimethylsilane primed surface, representing a hydrophobic interface. The distribution of water in the films was sensitive to the surface preparation and photoresist relative hydrophilicity. Depending upon the water contact angle of the substrate in comparison to the polymer film, an excess of water near the interface occurs when the substrate is more hydrophilic than the photoresist. Likewise, interfacial depletion results when the photoresist is more hydrophilic than the substrate. These non-uniform water distributions occurs within (50 ± 10)a of the photoresist/substrate interface. The water concentration in this interfacial region appears to be independent of the photoresist properties, but is strongly dependent upon the substrate surface energy.