Characterization of submicrometer periodic structures produced on polymer surfaces with low-fluence ultraviolet laser radiation

Abstract

Periodic ripples and dot patterns with spacing smaller than 200 nm have been produced on various highly absorbing polymers [poly(ethylene terephthalate), poly(butylene terephthalate), polystyrene, polycarbonate, etc.] using a polarized beam of an ArF and KrF excimer laser. The period of the structures increases with the wavelength used and with the angle of incidence of the beam, whereas the ripple direction is parallel to the polarization direction. The fluence interval in which the pattern can be produced is far below the ablation threshold of the polymer but probably allows a local melting or photolysis of the surface. For polystyrene, a strong influence of the presence of oxygen was observed, which leads to the conclusion that photooxidative processes play a major role in the structure growing mechanisms. Due to the small size (0.1 μm) of the structure scattering techniques using visible light (0.4–0.8 μm) could not be used in this study and scanning electron microscopy and transmission electron microscopy were found adequate techniques. However, as alternative means of characterization a method called sample rotation ellipsometry has been successfully developed.