The adoption of a novel method for producing fine features by 1 nm proximity x-ray lithography would solve all of the current technical limitations to its extensibility. These limitations include the fabrication of fine features on masks and the maintenance of narrow mask-wafer gaps. Previously, with demagnification by bias, we described line features of 43 nm width produced with comparatively large clear mask features and large mask-wafer gaps. The method is generally applicable and has been shown to be extensible to beyond 25 nm printed features sizes on the wafer. The demagnification, ×1-×6, is a result of Fresnel diffraction and occurs without lenses or mirrors. The method takes advantage of the modern control of resist processing and has good exposure stability. We now expand on the optimization of the process by defining and explaining the critical condition and by demonstrating the consistency of various types of simulation. The simulations demonstrate the effects of the gap width, non-symmetric rectangular masks, spectral bandwidth, outriggers, T junctions, blur, etc. In two-dimensional images, the spectral bandwidth allows sharp features due to interference and effectively eliminates ripple parallel to the longer dimension. Demagnification by exposure near the critical condition extends the most mature of the next generation lithographies which we define generically-following actual current lithographic practice-in terms of the departure from the classical requirement for fidelity in the reproduction of masks. Specifically, for 1 nm proximity lithography, demagnification of critical features greatly facilitates the printing of fine features.

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We report on the process parameters of nanoimprint lithography for the fabrication of two-dimensional (2D) photonic crystals. The nickel mold with 2D photonic crystal patterns covering an area up to 20 mm2 is produced by electron-beam lithography and electroplating. Periodic pillars as high as 200 nm to 250 nm are produced on the mold with the diameters ranging from 180 nm to 500 nm. Optimization of process parameters is essential to generate high-quality nanoscale patterns and control the residual stress in the mold. The mold is employed for nanoimprinting on the poly-methyl-methacrylate (PMMA) layer spin-coated on the silicon substrate. Periodic air holes are formed in PMMA above its glass-transition temperature and the patterns on the mold are well transferred. This process can be utilized for commercial applications of photonic crystal devices.

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