Laser Lithography of Thin Polymer Films

Abstract

Laser lithography has been implemented in many ways to pattern polymeric materials. By using a tightly focused laser beam we can induce sharp thermal gradients, exceeding 1,500,000 °C/cm, onto the surface of a thin polymer film. The temperature dependence of the surface tension in such a thermal field gives rise to a flow of material away from the center of the beam focus driven by the Marangoni or thermocapillary effect. The evolution of a film irradiated by a focused laser can be, in a general sense, predicted by a presented hydrodynamic model, which is based on simple fluid mechanics. However, the details of the individual evolution profiles show a more complicated behaviour. It has been shown that this complex behaviour can be explained by considering the optical interference effects of the thin polymer coating. An optical feedback control routine has been developed to compensate for the interference effect by monitoring and maintaining a constant absorbed laser power. This ensures that the temperature gradient that drives the lithography process is consistent during operation. Additional studies involving high laser power effects, different material systems and other thin film phenomena have revealed an interesting assortment of novel behaviours. The extension of these behaviours to the lithography process lead towards the development of applications in microfabriation and microfluidic devices.