Vecheslav Yunkin

X-ray refractive planar lens with minimized absorption

Silicon refractive planar parabolic lenses with minimized absorption were fabricated by a combination of photolithography and dry-etching techniques. Focusing and spectral properties of the lenses were studied with synchrotron radiation in the energy range 8–25 keV at the European Synchrotron Radiation Facility. A focal spot of 1.8 μm with a gain of 18.5 and transmission of more then 80% was measured at 15.6 keV. The spectral characteristics were analyzed taking into account material dispersion and photon-energy attenuation in the hard x-ray range.

Highly anisotropic selective reactive ion etching of deep trenches in silicon

Abstract Reactive ion etching (RIE) of single crystal silicon using a gas mixture of SF 6 and C 2 Cl 3 F 3 in parallel plate electrode reactor was investigated. A detailed study of etching characteristics as functions of gas composition, rf power, pressure, self-bias voltage was performed. The results were explored in order to optimize deep trench RIE process. The optimized process resulted in a high etch rate, a good selectivity silicon-to-photoresist, a high anisotropy, a nearly vertical etch profile, and smooth surface morphology. This process was successfully used to fabricate silicon preforms for a replication technology of polymer-based devices.

X-ray focusing by planar parabolic refractive lenses made of silicon

Abstract First refractive planar parabolic lenses are realized in Si. They comprise a set of parabolic profiles (planar parabolic lenses) or parabolic segments (planar parabolic lenses with minimized absorption) with symmetry axis lying in Si wafer surface plane. The relief depth achieved by dry etching processes is 100 μm. Experimental testing of lenses has been carried out on an RU-200 rotating anode generator with CuKα radiation (8.05 keV). The focal length, estimated and confirmed by experiment, is F=18 cm for planar parabolic lenses. The lenses with minimized absorption have shorter focal length F=16.8 cm, showing a 5 μm recorded source image. The calculated transmission for these lenses reaches T=37%, approaching values of transmission for compound refractive lenses made of low Z materials.

X-ray standing wave microscopy: Chemical microanalysis with atomic resolution

We introduce a microprobe technique based on the x-ray standing wave method (XSW) demonstrating that structural analysis can be achieved with chemical sensitivity on a microscopic scale. We apply this XSW microscopy technique to study an epitaxially grown GaAs/Al0.1Ga0.9As/GaAs(001) heterostructure in cross section. We focus the x-ray beam by a refractive lens onto the cleaved sample and analyze the constituent elements within the 4 μm thick Al0.1Ga0.9As layer resolving the substitutional location of Al. The new micro-XSW technique will permit microscopic examinations of the structure of integrated semiconductor devices or microscopic crystalline grains with chemical sensitivity and structural resolution on the pm scale.

Silicon planar parabolic lenses

Silicon planar parabolic refractive lenses with relief depth of 100 micrometer are realized by microfabrication technique. A set of 5 planar lenses with simple parabolic profiles and equal apertures and equal focal distances is realized. This set consists of different number (from 1 to 8) of individual lenses. Lenses with minimized absorption as a set of parabolic segments are fabricated too. Focusing and spectral properties of silicon planar parabolic lenses were studied with synchrotron radiation in the x-ray energy range 8 - 25 keV at the ESRF. Linear focus spots of 1.5 micrometer width were recorded for the parabolic lenses and 1.8 micrometer for the lenses with minimized absorption. The intensity transmission of the lens with minimized absorption is two times greater than this value of simple parabolic lenses at 8 keV and in the x-ray energy range over 15 keV overcomes 90%. Spectral properties of the lenses with minimized absorption are discussed in details. Heatload properties of the silicon planar lenses are analyzed and compared with the lenses made of diamond.

X-ray lens with kinoform refractive profile created by x-ray lithography

X-ray kinoform lenses were proposed earlier as focusing devices with refractive and diffractive properties. Deep X-ray lithography technique was applied to realize kinoform lenses in thick resist layers PMMA. Created lens has rather short focal distance 20 cm at base energy 17.5 keV and full aperture 1.5mm with outermost segments 2 μm in width. Predicted performance of created lens is compared with simple parabolic lenses. Applications of kinoform lenses are considered and potentials of X-ray lithography for creation new versions of refractive focusing devices are discussed.

Planar parabolic lenses for focusing high-energy x-rays

Microelectronics technology involving photolithography and highly anisotropic plasma etching techniques was applied to fabricate planar parabolic refractive lenses. A set of Si planar parabolic lenses with apertures from 0.5 to 1.8 mm and 200 microns deep has been fabricated especially for high energy X-rays (E > 50 keV). Focusing properties in terms of the spot size and the efficiency in the energy range from 50 to 100 keV have been studied at the ESRF ID15 beamline. Linear focusing by single lens and by two-lens system as well as two-dimensional focusing by two lenses in cross geometry has been realized. Features of refractive collimator based on a set of planar lenses have been investigated and a technique for evaluation of the beam divergence in a micro radian range has been proposed. Future applications of proposed planar lenses are discussed.

Experimental study of anisotropy mechanisms during reactive ion etching of silicon in a SF6/C2Cl3F3 plasma

Abstract The experimental results of the investigations of the mechanisms of anisotropy of silicon RIE, using a SF6/C2Cl3F3 plasma, are presented and discussed.

Refractive and diffractive X-ray optical elements.

The planar microelectronics technology, involving lithography and highly anisotropic plasma etching techniques, allows manufacturing high quality refractive and diffractive lenses, which may be used in hard X-ray microprobe and microscopy applications. These silicon lenses are mechanically robust and can withstand high beat load of the white X-ray beam at third generation synchrotron radiation sources. For the first time we designed and manufactured a new type of lenses: kinoform lenses and parabolic lenses with scaled reduction of curvature radii. The theoretical background for such type of lens features is presented. Focusing properties in the terms of focus spot and efficiency of all these lenses were tested at the ESRF beamlines. Magnified imaging with planar lense was realized. Some future developments are discussed.

Experimental study and computer simulation of aspect ratio dependent effects observed in silicon reactive ion etching

Abstract The aspect ratio dependent etching of deep trenches in silicon is investigated as a function of polymer deposition rate which, in turn, depends on the C 2 Cl 3 F 3 content in a SF 6 C 2 Cl 3 F 3 gas mixture. The experimental results are compared to computer simulations. A model which takes into account simultaneous ion-enhanced etching and polymer deposition is developed to explain the observed two-dimensional effects such as feature size dependent profile evolution, RIE lag, and inverse RIE lag. Computer program includes different transport mechanisms of ions, reactive neutrals, polymer precursors and some parameters, namely, the angular distributions of species, sticking coefficients, and re-emission functions. The influence of these parameters on aspect ratio dependent etching is considered.