The current nanofabrication techniques including electron beam lithography provide fabrication resolution in the nanometer range. The major limitation of these techniques is their incapability of arbitrary three-dimensional nanofabrication. This has stimulated the rapid development of far-field three-dimensional optical beam lithography where a laser beam is focused for maskless direct writing. However, the diffraction nature of light is a barrier for achieving nanometer feature and resolution in optical beam lithography. Here we report on three-dimensional optical beam lithography with 9 nm feature size and 52 nm two-line resolution in a newly developed two-photon absorption resin with high mechanical strength. The revealed dependence of the feature size and the two-line resolution confirms that they can reach deep sub-diffraction scale but are limited by the mechanical strength of the new resin. Our result has paved the way towards portable three-dimensional maskless laser direct writing with resolution fully comparable to electron beam lithography.
Compared with single-beam OBL, two-beam OBL utilizes a doughnut-shaped inhibition beam to inhibit the photopolymerization triggered by the writing beam at the doughnut ring, leading to reduced feature size and improved resolution. Although both focused writing and inhibition beams result in the spot size limited by diffraction, the fabricated feature size and resolution by two-beam OBL can break the limit defined by the diffraction spot size of the two focused beams. In fact, the smallest feature size and the highest resolution are limited by the mechanical strength of the solidified material, which can be far beyond the diffraction limit provided that an appropriate photoresin with high mechanical strength can be developed. But this breakthrough has not yet been achieved. Here, we demonstrate 3D deep sub-diffraction OBL with 9 nm (λ/42 for the wavelength of the inhibition beam) feature size and 52 nm (λ/7) two-line resolution in a resin that can efficiently harness two-photon polymerization (2PP) and single-photon inhibition.