Direct and subdiffraction-limit laser nanofabrication in silicon

We propose a method for nanofabrication at a resolution much below the diffraction limit for projection optical lithography using a backside-irradiation method. Feature sizes below lambda/260 have been achieved in silicon. An infrared laser (CO2, lambda=10.6 mum) was used to illuminate the backside of a Si substrate with Au particles on its polished surface. The morphologies of created features were characterized by atomic force microscope and field emission scanning electron microscope. The formation mechanisms of these nanofeatures have been discussed and associated with localized optical excitations in Au colloid aggregates with a fractal structure. This backside-irradiation laser-assisted nanofabrication method may also be extended to various metals, particle shapes, particle sizes, substrates, and other lasers. It can be used to investigate optical excitations and near fields in these systems. (C) 2003 American Institute of Physics.