Water absorption in thin photoresist films
Bryan D. Vogt, Christopher L. Soles, Ronald L. Jones, Vivek M. Prabhu, Wen-li Wu, Eric K. Lin
In this work, we quantify deviations in the moisture absorption into model photoresist films upon changing thickness. Both the thermodynamics and kinetics of the absorption process are examined. Water in the resist films has been shown to have a significant influence on the photoacid reaction-diffusion process. Additionally understanding the diffusion processes in these films is of paramount importance in chemically amplified photoresists, affecting processes diverse as deprotection trhough the mobility of the photoacids and dissolution through diffusivity of the aqueous developer into the resist film. The diffusivity of the water is decreased by orders of magnitude when the photoresist thickness approaches the molecular dimensions of the polymer chain. The dissolution rate of a photoresist film also decreases in thin films. Thus, the dynamics of other species appear to follow the transport properties of water in these photoresists. The equilibrium swelling also deviates in the thin films. In this case, the change can be attributed to a non uniform water distribution, namely adsorption or repulsion of water at the polymer / substrate interface. The water distribution was directly observed using isotopic substitution and neutron reflectivity. The amount of water at this buried interface can be controlled by changing the surface chemistry.
Bryan D Vogt
Polymers Division, Electronics Applications Group
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