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Multilayer phase-only diffraction gratings: Fabrication and application to extreme ultraviolet optics
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View: Figures


Image of FIG. 1.
FIG. 1.

SEM micrograph of multilayer deposited with dc magnetron sputtering on top of binary gratings. Sputter plasma having nonuniform radial angular distribution propagates topography along the average direction of incident flux denoted here by the angle. Also notice the smoothing effect of multilayer as features propagate throughout the multilayer volume.

Image of FIG. 2.
FIG. 2.

SEM micrographs of an etched multilayer grating with period. Etch depth is set to approximately , yielding a phase shift on reflection (round trip). Embedded Cr etch-stop layer fabricated to exactly one multilayer period ensures suppression of the zeroth order and highest possible performance.

Image of FIG. 3.
FIG. 3.

[(a) and (b)] Idealized model for the efficiency of square wave gratings and the relationship between the zeroth and the first orders.

Image of FIG. 4.
FIG. 4.

Theoretical model for the performance of a multilayer with embedded Cr buried 16 layers below the surface.

Image of FIG. 5.
FIG. 5.

(a) Schematic of trilayer cross section used to calibrate Cr deposition parameters. (b) Schematic of multilayer system, with embedded Cr etch-stop layer and Cr hard mask, ready for lithography and pattern transfer.

Image of FIG. 6.
FIG. 6.

Simplified three-step lithography process for pattern transfer. (a) KRS-XE e-beam resist used to define features with e-beam lithography. (b) Resist development, plus chemistry to etch through Cr hard mask, and chemistry to etch through multilayer. (c) Removal of residual hydrocarbons using descum, and Cr wet etchant to remove Cr hard mask.

Image of FIG. 7.
FIG. 7.

Results. (a) Measured grating efficiency, better than 88% with respect to the ideal. (b) Measured multilayer reflectivity, before and after processing, showing the result of increased surface roughness.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Multilayer phase-only diffraction gratings: Fabrication and application to extreme ultraviolet optics