Laser-assisted nanoimprinting using self-assembled nanoparticles

A new approach to fabricating hemispherical-cavity arrays on silicon substrates using laser-assisted nanoimprinting of self-assembled particles has been developed. Monolayers of silica or polystyrene particles, with different diameters ranging from 160 nm to 5 /spl mu/m, were deposited on silicon substrates by self-assembly. A quartz plate, which is transparent to the laser wavelength of 248 nm, was tightly placed on the surface of each sample, which has been preheated. A KrF excimer laser beam with a wavelength of 248 nm was vertically irradiated on the quartz / nanoparticle / silicon structure. The silica particles were imprinted into silicon substrates by the quartz due to the transient Si surface melting during the laser irradiation. Ultrasonic cleaning and hydrofluoric-acid (HF) solution were then used to remove the silica particles. Hemispherical cavities on the silicon substrate were formed on the substrate surface. The effects of silica particle size, different laser fluence, laser pulse number and substrate temperature will be discussed in detail. It was found that polystyrene particles could not be used for the laser-assisted imprinting due to their low melting point. Raman spectroscopy will be used to analyze the material properties in the fabricated structures. Periodical multiple-layer structures (3-D structures) will also be made on silicon substrates.