EUV-induced physico-chemical changes in near-surface layers of polymers

In this work a laser-plasma EUV source based on a gas puff target was used for micro- and nanostructuring of polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and poly-oxydiphenylene-pyromellitimide (Kapton HN) foils. The plasma radiation was focused using a gold-plated grazing incidence ellipsoidal collector. The collector allowed for effective focusing of Kr plasma radiation from the wavelength range λ = 9-70 nm. The polymer foils were irradiated in the focal plane or at some distance downstream the focal plane of the EUV collector. The surface morphology of the irradiated polymer samples was investigated using a scanning electron microscope (SEM) and the chemical changes by X-ray photoelectron spectroscopy (XPS). Different kinds of micro- and nanostructures created in near-surface layers of the polymers were obtained. The form of the structures depends on the type of polymer and the EUV exposure. In case of PEN even a single shot was sufficient to obtain visible changes in surface morphology. In case of Kapton clearly visible surface modification requires tens of EUV pulses. To investigate the changes in the chemical structure XPS spectra, corresponding to the valence band of the polymer samples, were measured. Significant differences were revealed in the XPS spectra of irradiated and not-irradiated polymers showing decrease of functional groups containing oxygen was indicated.