Nanopatterning of Au absorber films on Mo/Si EUV multilayer mirrors by STM lithography in self-assembled monolayers

We report on the fabrication and characterization of artificial nanostructures in alkanethiol-type self-assembled monolayers (SAMs) and subsequent pattern transfer into the underlying Au film by wet etching. A gold-covered Mo/Si multilayer was immersed in a solution of hexadecanthiol molecules [CH3(CH2)15SH], thus forming a self-assembled monolayer spontaneously on top of the Au surface. Afterwards, the SAM films were patterned by STM lithography in ultra-high-vacuum ambient with 1 V bias voltage and 1 nA tunnel current. The patterns were transferred, by a wet etching process using a solution of 0.1 M KCN and 1 M KOH, into the underlying gold layer followed by a characterization by means of atomic force microscopy and scanning electron microscopy. The patterned Au films act as an efficient EUV absorber layer on top of the underlying EUV multilayer mirror, thus providing an amplitude-modulated EUV multilayer structure.