Off-plane grazing-incidence blazed grating with radial grooves as an efficient spectral purity filter for EUV lithography

It was found that the high-blaze-angle reflective diffraction grating operating in the off-plane grazing-incidence configuration allows the separation and focusing of a 2% wavelength band in the vicinity of 13.5 nm. A model of a cooled multiple grating with a fan-groove geometry was used to separate the desired spectral range and to achieve a record efficiency and stigmatic focusing of images at high dispersion of adjacent orders. The highest relative efficiency in the range of 0.96–0.99 and reflectances from 0.71 to 0.96 can be achieved for an off-plane fine-pitch grating irradiated at angles of 70°–85° with a converging unpolarized light beam from a EUV collector. Such efficiency is higher than that of the corresponding in-plane configuration. The absolute efficiency of 0.72 was achieved in the minus-first order of a Mo-coated test Si grating with 5000 grooves/mm in unpolarized light using the PCGrate^®-SX? code and the AFM-measured groove profile.     

Determining angles of incidence and heights of quantum dot faces by analyzing X-ray diffuse and specular scattering

Scattering of X rays by structures with multilayer ensembles of quantum dots MBE-grown in the In(Ga)As-GaAs system is studied by high-resolution grazing X-ray reflectometry. The peaks of the diffuse scattering intensity are discovered for the first time in structures with both vertically uncorrelated and vertically correlated quantum dots. It is shown that the position of the peak is totally determined by angle of inclination of the quantum dot pyramidal faces (the so-called blaze condition for diffraction gratings), which was theoretically predicted earlier. Comparison with the results of scattering simulation carried out by the technique of boundary integral equations indicates that a simple geometrical condition allows one to exactly determine the value of from the position of the intensity peak, the shape of which depends on many parameters. As follows from the theory and experiment, the width and height of the peaks for samples with vertically correlated quantum dots are larger than for those with uncorrelated dots. The roughness and interdiffusion of interfaces and the height of quantum dots are found from the position and amplitude of Bragg peaks. Thus, the conventional application of high-resolution grazing X-ray reflectometry is extended in this work to determination of the quantum dot geometry.     

Development of the Design of Super-Multiperiod Structures Grown by Molecular-Beam Epitaxy and Emitting in the Terahertz Range

Journal of Experimental and Theoretical Physics - A design of terahertz (THz) radiation source has been developed based on an AlGaAs/GaAs superlattice grown by molecular-beam epitaxy. The gain and...     

Diffraction gratings for short-wave radiation: Modern requirements and achievements

Recent achievements in the field of making and certifying gratings for the soft X-ray and extreme ultraviolet regions are described, including those intended for space flights and having new or record characteristics of diffraction efficiency. The diffraction efficiency of gratings is investigated both by computation using the electromagnetic PCGrate® code with realistic data for layers, and by measurements using synchrotron radiation.     

Grazing incidence off-plane lamellar grating as a beam splitter for a 1-Å free electron laser

A beam splitter based on the diffraction grating working in the grazing incidence conical diffraction is proposed for x-ray free-electron laser (XFEL) experiments with coherent beams in plasma and atomic physics. Such a beam splitter can provide undistorted wavefronts, high-power radiation scattering, and split beams with equal intensities, which propagate with delay along different paths to the target chamber of the XFEL end station. Using the PCGrate software based on rigorous electromagnetic theory and developed for the short-wavelength range, it is shown that the plane grating with lamellar groove profile of a certain depth, operating in grazing conical incidence mount (grooves are parallel to the incident beam), separates three beams in the ?1, 0, and +1 orders with close diffraction efficiency. Numerical simulation predicts 23–27% absolute efficiency for 0.1-nm incident radiation in each separated order of a bulk or multilayer grating, taking into account the atomic level roughnesses and interdiffusion. When using a multilayer coating based on Ru/C or Ru/B₄C pairs, the optimum grazing angle providing approximately equal efficiencies is ～1.038° which is four times higher than for the Pt-coated grating. Such optimization of radiation geometry, groove profile shape, and multilayer coating parameters can be performed for various XFEL wavelengths. The proposed grating, in addition to diffraction, technological, and design advantages over the beam splitter based on a set of perfect crystals, can be fabricated and tested using currently available methods.     

Nonlinear continual growth model of nonuniformly scaled reliefs as applied to the rigorous analysis of the X-ray scattering intensity of multilayer mirrors and gratings

It is revealed that certain terms entering into the nonlinear continual equation describing thin-film growth enable its application to the simulation of the surfaces of multilayer mirrors and gratings with a large height and/or jumps of boundary-profile gradients. The proposed model characterizes both variations in the power spectral-density function of the surface of Al/Zr multilayer mirrors and the smoothing and shift of the boundaries of Mo/Si and Al/Zr gratings grown on Si substrates with triangular groove profiles by means of magnetron and ion-beam deposition. Rigorous calculations indicate that the intensities of diffuse X-ray scattering by Au mirrors, which have similar boundary profiles with Gaussian and exponential autocorrelation functions, differ substantially from each other. Computer simulation of the growth of Mo/Si and Al/Zr multilayer gratings is performed. On the basis of the calculated boundary profiles, the absolute diffraction efficiencies of the Mo/Si and Al/Zr gratings are found via the integral equation method in the extreme UV region. It is demonstrated that the proposed comprehensive approach to calculations of the boundary profiles and the intensities of short-wavelength scattering from multilayer mirrors and gratings makes it possible to carry out studies comparable in accuracy to measurements based on synchrotron radiation.