Characterization of thin and ultrathin polymer and resist films

The need for a better understanding of the physicochemical properties of radiation-sensitive thin polymer coatings for lithographic applications is driven by the trend of ever-shrinking pattern dimensions and film thickness, imposed by the semiconductor industry. In this work, we address the issue of film uniformity and moisture absorption for thin and ultrathin films (250 nm to 50 run) of poly 4-hydroxystyrene (PHS). Using high resolution x-ray reflectivity, the roughness and density of spin coated films was found to remain constant within experimental error for the thickness range examined. Also, water uptake on PHS films was studied by neutron and x-ray reflectivity. Exposure of the polymer film to a controlled humidity level is shown to swell the polymer and be absorbed uniformly throughout the film. No preferential absorption of water at the interface was noticed, regardless of the hydrophilic or hydrophobic nature of the substrate surface. Overall density changes in the polymer matrix due to the moisture-induced increase in the film thickness are also discussed.