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Anisotropic wet etching of vicinal monocrystalline Si(111)4° wafers was used to obtain blazed gratings that are highly efficient in the soft X-ray (SXR) and extreme ultraviolet (EUV) applications. An improved experimental technology for the fabrication of triangular-grooved Si gratings, both medium-frequency (250 and 500 mm–1) and high-frequency (2500 mm–1) ones, is presented. The stages of forming a Cr-mask for grooves etching, removing Si nubs in order to smooth the profile, and polishing the surface to reduce nanoroughness have been optimized. This paper describes the way of simultaneously (in one process) obtaining a smoothed triangular profile of the Si grating and a polished surface of facets by wet etching. [ABSTRACT FROM AUTHOR]

Using direct laser lithography and wet etching of polished vicinal Si(111) wafers, a technology was developed and diffraction gratings 500 grooves/mm with a blaze angle of 4° were fabricated. The manufacturing process of a reflective Si-grating with the triangular profile (sawtooth) can be divided into four main steps: (1) obtaining a pattern of a protective mask for grooves etching; (2) anisotropic etching of grooves in KOH solution; (3) etching to smooth the grating profile and polish the surface of working facets; (4) coating to increase reflectivity. The samples obtained were characterized using scanning electron microscopy and atomic force microscopy methods to determine the shape of the groove profile and roughness: the shape turned out to be close to the ideal triangular, and the RMS roughness was less than 0.3 nm. Using PCGrateTM software and taking into account the measured real groove profile, the diffraction efficiency of gratings operating in classical and conical mounts in soft-X-ray and extreme ultraviolet radiation has been simulated. The obtained efficiency values are close to the record ones for the corresponding spectral range and the Au-coating of the grating. [ABSTRACT FROM AUTHOR]

The effect of the groove profile shape and random roughness of the reflecting facet of five silicon diffraction gratings (1°–4° blaze angle, period 0.4, 1.4, 2, and 4 μm, various coatings) operating in the soft X-ray and extreme ultraviolet radiation ranges on the outflow of the diffraction efficiency from working orders is studied. Diffraction gratings were fabricated by wet etching of Si(111) vicinal wafers and characterized by atomic force microscopy to determine the shape of the groove profile and roughness. The diffraction efficiency of gratings operating in classical and conical diffraction mounts was calculated based on realistic groove profiles by computer simulation using the PCGrateTM code and taking into account the scattering intensity using Nevot–Croce or Debye–Waller corrections or using the Monte Carlo method (rigorously). The effect ofthe groove profile shape and roughness on the diffraction efficiency of the fabricated Si gratings is shown. [ABSTRACT FROM AUTHOR]

The influence of the reflective facet parameters, primarily its camber, on the diffraction efficiency of perfect silicon gratings with blaze angles of 3°–4° and a groove density of 500 and 250 mm–1, which are intended for operation in soft X-ray and extreme UV radiation, is studied. The investigated diffraction gratings are fabricated by the wet etching of Si (111) vicinal wafers and characterized by atomic-force microscopy to determine the relief of the grooves. For one of the considered gratings with a Mo/Si multilayer coating, a record-breaking absolute efficiency of ~40% at a wavelength of 13.5 nm in the –8th order of unpolarized radiation was obtained recently. The possibility of achieving high efficiencies of high diffraction orders, with a number of ~10 and more is considered; this means the possibility of unique X-ray echelle fabrication. An estimate of the influence of the introduced camber parameter of the reflected facet on the maximum achievable order number of highly efficient diffraction is obtained. The absolute and relative (grating) efficiencies are determined by simulation using the PCGrate™ code based on the method of boundary integral equations and groove profiles measured using atomic-force microscopy. [ABSTRACT FROM AUTHOR]

Blazed and low-roughness 500 lines/mm diffraction gratings, designed for operation in high orders in the soft X-ray and extreme UV (EUV) radiation ranges and having Au and multilayer Mo/Si coatings, have been fabricated by wet anisotropic etching of Si(111)4° vicinal wafers and investigated by atomic force and scanning electron microscopy. The diffraction efficiency of the gratings was determined both using a laboratory reflectometer and by modeling based on a rigorous method of boundary integral equations in the PCGrate™ code, taking into account realistic groove profiles. The diffraction efficiency values measured in unpolarized light with wavelengths of 13.5 and 4.47 nm and the calculated values, found with allowance for random roughness, are almost the same. The absolute efficiency of the grating with a multilayer (five Mo/Si bilayers) coating with a period of 20 nm is ~40% in the –8th diffraction order at an angle of incidence of 70.5°, which is a record value for a high-order mid-frequency grating. [ABSTRACT FROM AUTHOR]

The results of studies of photochemical etching processes, which were carried out without applying external voltage, for structures with Ga- and N-polar GaN layers synthesized by molecular-beam epitaxy with the plasma activation of nitrogen are reported. It is shown that the etching rates of layers with different polarities are markedly different. At the same time, the use of gold-based masks instead of titanium-based ones for the etching of GaN layers also provides a means for increasing the rate of layer etching. [ABSTRACT FROM AUTHOR]

The results obtained in a study of the synthesis of n+-GaN layers by plasma-assisted molecular-beam epitaxy on GaN/c-Al2O3 templates are reported. In particular, a method is developed for the pre-epitaxial cleaning of the GaN surfaces of templates to remove foreign atoms. It is shown that, to form GaN layers of comparatively good quality, including those doped with silicon up to ~4.6 × 1019 cm–3, GaN template surfaces should be pre-epitaxially cleaned in a flow of activated nitrogen particles, with the substrate temperature increased from TS = 400 to 600°C and the substrate surface subsequently exposed to a flow of activated nitrogen at a fixed value of TS = 600°C for 1 h. After that the substrate temperature should be raised to TS = 700°C and the GaN surface finally cleaned by means of a procedure for gallium deposition/desorption. [ABSTRACT FROM AUTHOR]

Abstract: Two different approaches for the etching of the gallium nitride epitaxial layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy have been elaborated. It is demonstrated that anisotropic etch profiles can be achieved by both photoenhanced wet chemical etching and reactive plasma-chemical etching methods. Moreover, it is shown, that the photoenhanced wet chemical etching allows to remove GaN layer without damaging silicon substrate. [ABSTRACT FROM AUTHOR]