Sub-micron parallel laser direct-write

We have developed a modified laser induced forward transfer (LIFT) technique which allows for the parallel deposition of hundreds of sub-micron features. The approach utilizes a self-assembled monolayer of monodisperse polystyrene microspheres as the focusing element. A monolayer of close-packed microspheres is formed on top of an ultra-thin quartz support (25 μm thick), and a metallic thin film is then deposited on the underside of the quartz. This approach is different from previous parallel microsphere-assisted LIFT experiments that required the deposition of metal directly onto the surface of the periodic microsphere structure. For this study, an 800 nm, 130 fs laser pulse was directed toward the microsphere layer to focus the incident laser beam through the thin quartz layer to the quartz–metal interface. At this interface, a portion of the thin metal film was ablated directly below each microsphere, resulting in an array of holes in the thin metal film. The metal removed from the film was patterned onto a receiving substrate to form an array of discrete deposits. In some cases, a two layer thin film was utilized resulting in the forward transfer of bilayer metal features. The holes and deposited features were characterized using scanning electron microscopy, atomic force microscopy, and scanning Auger electron spectroscopy. The diameter of the holes (0.5–5 μm) as well as the diameter (0.9–5 μm) and quality of the deposited metallic features were modulated by varying the sphere size, incident laser energy, and material composition.