Extreme ultraviolet binary phase gratings: Fabrication and application to diffractive optics

Abstract

Diffractive optics play an important role in a variety of fields such as astronomy, microscopy, and lithography. In the extreme ultraviolet region of the spectrum they have been difficult to make due to the extremely precise control required of their surface structure. We have developed a robust fabrication technique that achieves the required topographic control through the deposition of a thin film of Si on a Cr etch stop. We have fabricated binary phase gratings using this approach that have an efficiency of 80% of the theoretical maximum. This technique could be applicable to similar binary phase structures requiring precise topography control.

5000 groove/mm multilayer-coated blazed grating with 33% efficiency in the 3rd order in the EUV wavelength range

“…Here we took into account the fact that the topography translates along the average direction of an incident atomic flux that was observed in Ref. 14 for binary phase multilayer gratings.…”

Holographic optical elements for the extreme-ultraviolet regime

“…Detailed description of this measurement can be found in Ref. [13]. We choose the carrier period of the null hologram to be 200-nm, nearly half the size of the carrier used for the HOE presented here.…”

“…Reflection HOEs can themselves take on several forms, including a patterned relief substrate overcoated with a multilayer reflector [8], an etched multilayer relying on the difference in index of refraction between vacuum and the multilayer [9], as well as a patterned Mo coating on top of the multilayer. In this case the Mo coating, the layer need only be 43-nm thick owing to the round trip propagation through the material.…”

“…The first EUV hologram we fabricated used the relief substrate architecture and was fabricated using a hardmask method previously described [13]. The HOE was characterized at the calibration and standards bend-magnet beamline 6.3.2 at the Advanced Light Source located at Lawrence Berkeley National Laboratory [14].…”

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

“…In the past, patterned relief methods providing high efficiency binary gratings have been demonstrated. 1 These methods suffer from resolution limitations because the deposited multilayer on top of the relief structures cannot grow perfectly conformal to the surface. Inherent rounding effects near feature edges and other deposition-related phenomena 2 (see Figure 1) make it nearly impossible to precisely translate topography throughout the multilayer stack.…”