Nanometer-scale machining with extreme ultraviolet lasers

Abstract

This thesis demonstrates the feasibility of direct machining in the nanometer scale using Extreme Ultraviolet (EUV) laser radiation. Laser machining of materials has been widely used for the development of micromechanical components and devices. Advances in technology further motivate the extension of laser machining of microstructures to smaller dimensions. The advent of high repetition rate table top EUV lasers has opened the possibility of extending laser machining to the nanometer-scale. It has been previously demonstrated that single laser shots from a 46.9 nm wavelength capillary discharge laser can ablate very clean holes with a diameter as small as 82 nm on polymethyl methacrylate (PMMA) photoresist. This thesis extends previous work by demonstrating nanometer-scale machining of polymers with a focused EUV laser beam. Sub-200 nm wide trenches several micrometers in length were machined on PMMA. These are,to our knowledge, the smallest ablated trenches machined with a focused laser beam. This work also discusses the study of warm plasmas created by EUV laser irradiation of solid targets in which single-photon photoionization is the dominant energy absorption mechanisms. Low-absorption (silicon, Z=14) and high-absorption (chromium, Z=24, and silver, Z=47) targets were heated by ~ 1 ns duration pulses from a 46.9 nm wavelength EUV laser. The spectra obtained agree with 1 1/2 dimension simulations in showing that the Si plasmas are significantly colder and less ionized, confirming that in contrast to plasmas created by optical lasers the plasma properties are largely determined by the absorption coefficient of the target material.