Electrochemical nanoimprinting of silicon: A direct patterning approach

Soft-lithography and nanoimprinting lithography have been critical in manufacturing 3D features with sub-20 nm resolution onto polymeric materials which have often been employed for producing micro and nanoscale optical materials and surfaces. However, methods for transferring 3D polymeric patterns (i.e. mask) into silicon have relied upon the etch selectivity of the mask pattern during reactive etching, which in turn limits resolution, aspect-ratio and surface roughness. This paper demonstrates an electrochemical nanoimprinting process for single-crystal semiconductors for directly etching 3D features into silicon wafers. It is shown that stamps made of porous catalysts play a critical role in enabling diffusion of chemical species during imprinting which, in turn, allows for morphology control of imprinted silicon features with sub-20 nm resolution in 3D. This process delivers mirror surface finish (RMS < 5 nm), low-defect density, and large-area patterning (>1 cm²) in a single imprinting operation. Further, it outperforms the resolution and scalability of leading serial (e.g. FIB, electron beam) and parallel (e.g. gray-scale lithography) methods altogether, allowing for fast replication of patterns onto hard materials from a soft mold. This technique bypasses the need for dry etching and is potentially compatible with roll-to-roll platforms, amorphous and poly silicon and III-V semiconductors. In turn, it may pave the way for mold replication onto hard molds and the manufacturing of complex objects for infrared optics.