Effect of substrate and beam diameter on direct laser patterning of ruthenium thin films

Recently, a method was introduced to produce ruthenium/ruthenium-oxide electrically conductive islands through laser-induced oxidation of ruthenium thin films, followed by subsequent removal of the un-oxidized ruthenium using a NaClO solution. In this paper, we provide additional insight intp the patterning process by measuring the effect of Ru film thickness and substrate material on the pattern formation. In particular, understanding the role of the substrate, which affects the island formation mainly through the Ru film-substrate interfacial thermal conductance, is crucial. Experimental results and numerical heat diffusion calculations are used for comparing the island formation process when using a 2 µm exposure beam diameter and a 0.8 µm one. It is shown that in-plane heat diffusion results in a faster decay of the surface lattice temperature of the film after exposure to the 0.8 µm beam diameter. Although exposing the samples to a smaller beam diameter could, in principle, enable obtaining patterns with smaller features, in-plane heat diffusion may be the limiting factor for the smallest features achievable using this method.