Interactions of excimer lasers with polymers

Interaction of high photon energy (> 5-eV) radiation from excimer lasers with polymeric materials has drawn much interest because of its potential importance in material processing such as etching and patterning which have found use over a number of diversified fields such as medicine, polymer science, and microelectronics. The laser etching process is noncontact, maskless, selective, and offers a high spatial resolution. Although the topic has been the subject of numerous recent studies, basic parameters for understanding interactions between polymers and high energy photons are not well understood. In this paper we present the results of a recent study on VUV optical properties of several polymeric materials including polymethyl methacrylate (PMMA), polystyrene (PS), polyvinylacetate (PVA), polyimide (PI), and polycarbonate (PC) and review parameters that are critical for understanding the interaction of polymers with excimer laser radiation. Results of a study of the surface compostions using small area x-ray photoelectron spectroscopy of two kinds of polymer, PMMA and PS, irradiated with an ArF laser at a photon energy of 6.4 eV are discussed. A simple model is then presented to show how various parameters including optical constants, photon energy, laser fluence, and polymer structures affect characteristics of photon etching observed in these polymers.