Equilibrium water uptake and diffusion behavior in model polynorbornene photoresist polymers

As 193 nm immersion lithography continues to evolve, the need to understand the effect of the immersing liquid on the resulting photoresist properties continues to grow. With this in mind, the sorption of water (using both liquid and vapor environments) in two model photoresist polymer resins based on functionalized poly(norbornene) was examined using quartz crystal microbalance techniques. Similar to the results presented by Berger and coworkers, it was found that the water uptake in bis-trifluoromethyl carbinol substituted polynorbornene (HFAPNB) increases as the polymer molecular weight increases, while the diffusion coefficient of water in these materials remains relatively constant over the same range in molecular weight.(1) In contrast, trifluorosulphonamide-substituted polynorbornene displays a relatively constant level of water uptake as a function of polymer molecular weight, while the diffusion coefficient decreases by more than an order of magnitude over the same molecular weight range. Sorption experiments performed as a function of temperature have shown that the water diffusion in these polynorbornene polymers can be described using an Arrhenius relationship. The activation energy of water diffusion was compared in both HFAPNB and poly(hydroxystyrene). The activation energy for diffusion of water in HFAPNB is substantially larger than in the case of poly(hydroxystyrene). This is consistent with the view that polynorbornenes possess relatively stiff and rigid backbones as compared to more flexible polymers such as poly(hydroxystyrene). The activation energy for water diffusion in HFAPNB was found to be a strong, function of polymer molecular weight, with the activation energy decreasing with increasing molecular weight.