Lithography of poly(methyl methacrylate) through the simultaneous excitation of inner- and outer-shell electrons

We demonstrated soft X-ray lithography at a wavelength of 3.37 nm using a laser-plasma source and a multi-layer mirror, where the resist was poly(methyl methacrylate) and the developer was ethanol. A nickel mesh was used as a contact mask. The results of lithography showed that the poly(methyl methacrylate) could be etched highly efficiently using X-ray pulses with an intensity of 6.5 μJ/cm2, where the dose required for an etching depth of 0.1 μm was 5.3 mJ/cm2. Additionally, in a proof-of-principle study of the concept that more efficient X-ray lithography can be achieved through the simultaneous excitation of inner- and outer-shell electrons, lithography through double-beam irradiation was tested. The etching efficiency was increased by a factor of 2 using an ultraviolet lamp and a factor of 1.7 using a CO2 infrared laser, relative to the use of X-ray irradiation alone. It is expected that the adoption of the concept will be effective in X-ray micromachining.