Modification and Polishing of the Holographic Diffraction Grating Grooves by a Neutralized Ar Ion Beam
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ICS OF NANOSTRUCTURES
Modification and Polishing of the Holographic Diffraction Grating Grooves by a Neutralized Ar Ion Beam S. A. Garakhina,*, M. V. Zorinaa, S. Yu. Zueva, M. S. Mikhailenkoa, A. E. Pestova, R. S. Pleshkova, V. N. Polkovnikova, N. N. Salashchenkoa, and N. I. Chkhaloa aInstitute
for Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod, 607680 Russia *e-mail: [email protected] Received April 13, 2020; revised April 13, 2020; accepted April 13, 2020
Abstract—We describe the method for increasing the efficiency of holographic diffraction gratings (HDGs) intended for operation in the X-ray wavelength range. We describe the procedure of processing of HDG surface for reducing the amplitude and roughness of grooves. For reducing the groove amplitude, we have used Xe ions with an energy of 600 eV, while ion polishing was performed with Ar ions having an energy of 800 eV. It is shown that, after ion polishing, the diffraction efficiency of the grating at a wavelength of 4.47 nm increases by almost four times. DOI: 10.1134/S1063784220110110
INTRODUCTION The perfecting the technology of preparation of optical elements for extreme ultraviolet and soft X-ray ranges requires the data of monitoring of X-ray optical properties (spectral, angular, and polarization dependences of the reflection/transmission coefficients, scattering indicatrix, etc.) of synthesized samples at the working wavelengths. The use of synchrotrons alone strongly restricts the opportunities of researchers. Experience shows that the fabrication of highquality multilayer structures requires operating data on their properties for analysis and optimization of synthesis without breaking the technological sequence; for this reason, multifunctional laboratory reflectometers have been developed in recent years [1–6]. For such purposes, based on a Czerny–Turner spectrometer–monochromator with two collimating mirrors and a planar diffraction grating [7], we developed the reflectometer described in [8]. For diffraction gratings, we used holographic gratings fabricated at the State Institute of Applied Optics (Kazan) and intended for operating in the wavelength with a shortwavelength boundary of 50 nm [9]. Therefore, additional investigations are required for effective application of holographic diffraction gratings (HDGs) in a wavelength range shorter than 50 nm. In this study, we analyze the roughness and profiles of grooves, which most strongly affect the diffraction properties of the gratings in the grazing geometry used in the soft X-ray range. We demonstrate the possibility of a noticeable influence of ion beam etching on the
roughness and shape of grooves, which improves their X-ray characteristics. 1. FORMULATION OF THE PROBLEM In this study, we tested two HDGs with geometrical sizes of 10 × 60 × 75 mm (Fig. 1). The grooves were patterned parallel to height (60 mm). The periods of the grating D were 1.111 and 3.333 μm or 900 and 300 lines/mm, respectively. The basic equations for the Czerny–Turner scheme, which establish
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