Abstract
By using the near field in proximity x-ray lithography (PXL), a technique is demonstrated that extends beyond a resolution of 25 nm print feature size for dense lines. 'Demagnification by bias' of clear mask features is positively used in Fresnel diffraction together with multiple exposures of sharp peaks. Exposures are performed without lenses or mirrors between the mask and wafer, and 'demagnification' is achieved in a selectable range, 1 × –9 ×. The pitch is kept small by multiple stepped exposures of sharp, intense image peaks followed by single development. Low pitch nested lines are demonstrated. The optical field is kept compact at the mask. Since the mask–wafer gap scales as the square of the mask feature size, the mask feature sizes and mask–wafer gaps are comparatively large. Because the features are themselves larger, the masks are more easily manufactured. Meanwhile, exposure times for development levels high on sharp peaks are short, and there are further benefits including defect reduction, virtual elimination of sidebands, etc. A critical condition (CC) has been identified that is typically used for the highest resolution. Many devices, including batches of microprocessors, have been demonstrated previously by traditional 1 × PXL, which is the only next generation lithography developed and which is now further extended. For two-dimensional near field patterning, temporal and spatial incoherence at the CC have been used to show not only that peculiarities in the aerial pattern, such as 'ripple' and 'bright spots', can be virtually eliminated but also that there is an optimum demagnification, around 3 ×, in the Fresnel diffraction, where the contrast and, therefore, critical dimension control are highest. In the simulation of a bridge pattern, 'ripple' is likewise controlled. Blur and run-out are compared for various sources. Magnification corrections can be applied by various means. Extension to 15 nm printed features is predicted.
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