Direct Imprinting of Liquid Silicon.

A polymeric precursor solution for semiconducting silicon called "liquid silicon" was synthesized and directly imprinted to form well-defined and fine amorphous silicon patterns. The spin-coated film was cured and imprinted followed by annealing at 380 °C to complete the polymer-to-silicon conversion. A pattern with dimensions of several hundreds of nanometers or less was obtained on a substrate. We demonstrated that the curing step before imprinting is particularly important in the imprinting process. A curing temperature of 140-180 °C was found to be optimal in terms of the film's deformability and molding properties. Fourier transform infrared spectroscopy and thermal analysis clarified that the cross-linking of the polymer due to the 1,2-hydrogen shift reaction was induced exponentially with the release of a large amount of SiH4/H2 gases at temperatures between 140 and 220 °C, leading to the solidification of the film. Consequently, the film completely lost its deformability at higher temperatures. Despite a volume shrinkage as large as 53-56% during the polymer-to-silicon conversion, well-defined angular patterns were preserved. Fine silicon patterns were formed via the direct imprinting of liquid silicon with high resolution and high throughput, demonstrating the usefulness of this technique for the future manufacturing of silicon electronics.