Laser-induced periodic surface structures on different poly-carbonate films

Laser-induced periodic surface structures (LIPSS) were generated on oriente d and amorphous thick, as well as on spin-coated thin, poly-carbonate films by polarized ArF excimer laser light. The influence of the film structure and thickness on the LIPSS formation was demonstrated. Below a critical thi ckness of the spin-coated films the line-shaped structures transformed into droplets. This droplet formation was explained by the laser-induced meltin g across the whole film thickness and subsequent de-wetting on the substrat e. The thickness of the layer melted by laser illumination was computed by a heat-conduction model. Very good agreement with the critical thickness fo r spin-coated films was found. The original polymer film structure influenc es the index of refraction of the thin upper layer modified by the laser tr eatment, as was proven by the dependence of the structure's period on the a ngle of incidence both for 's'- and 'p'-polarized beams. The effect of the original surface roughness - grains in thick films or holes in thin films - was studied using atomic force microscopy. It was shown that the oblique i ncidence of 's'-polarized beams results in an intensity confinement in the direction of the forward scattering and in asymmetrical interference patter n formation around these irregularities. A new, two-dimensional grating-lik e structure was generated on spin-coated films. These gratings might be use d as a special kind of mask.