Breaking symmetry: programmable free-form laser nanolithography of silicon

Ultrafast and nanosecond laser writing deep inside silicon enables “in-chip” photonic devices. The emerging platform has already enabled integrated waveguides, lenses, holograms and stress-engineered waveplates. Here we show that, when combined with advanced beam shaping, if further provides a route to large-area free-form surface nanolithography. In our subsurface-seeded surface nanolithography approach, a ~250 nm-thick planar modification written ~50 µm beneath the surface [1] is translated toward the interface, where nonlinear energy deposition reorganizes the uppermost layers. The process yields nano-line arrays with widths of 150–800 nm, pitches tunable between 700 nm and 2 µm, and peak-to-valley relief of ~80 nm. By tailoring beam polarization, scan trajectories and holographic projection, we further realize curved, circular and braided patterns over mm-to-cm scales. Thus, the approach overcomes the symmetry constraints of laser-induced periodic surface structures (LIPSS) and interference lithography, opening a pathway to programmable free-form laser nanostructuring of semiconductors. [1] R. A. Sabet, A. Ishraq, A. Saltik, M. Bütün, O. Tokel, Nature Commun.,15, 5786, (2024).