Fabrication of Fresnel zone plates by holography in the extreme ultraviolet region
Schematic of the holographic technique. Spherical wave created by pinhole diffraction interferes with the attenuated plane wave partially transmitted through the pinhole mask to produce FZP pattern on the exposure plane at a distance .
(A)–(D) Schematic of the pinhole mask fabrication. Starting with a Cr coated membrane on Si substrate, EBL exposure is done on PMMA layer on the membrane (A). After development the Cr is etched with plasma (B), and subsequently is etched through (C) and additional Au is deposited (D). (E) shows scanning electron micrograph of a pinhole with diameter.
(A)–(D) Schematic of the FZP processing technique. Starting with a Cr coated membrane on Si substrate, the holographic intensity pattern is recorded on the EUV resist coated membrane (A) and after development Cr is etched to transfer the ZP pattern (B). is etched partially (C) and finally a photolithography is done in order to cover the rest of the membrane (D). (E) shows a scanning electron microscopic image of the FZP produced with the pinhole shown in Fig. 2(e).
Zone radius measured from the SEM image (squared) is plotted with zone number (green circles). The straight line fit shows a focal length of . The inset shows the zone placement deviation normalized to the local zone width.
Knife edge scan profile of the zone plate focal spot. The (black) dotted line represents the measured profile, while the (blue) solid line represents the calculated theoretical behavior.
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